Download Rationale: Atmospheric carbon dioxide concentrations have

ME2109 Developing a Trial Monitoring Strategy for pH in UK
Marine Waters
A Report to Defra
Plymouth Marine Laboratory
Prospect Place
West Hoe
Plymouth PL1 3DH
ME2109 Developing a Trial Monitoring Strategy for pH in UK Marine Waters
Contents
page
List of contributors and project management……………………………………….3
Executive summary…………………………………………………………………4
List of abbreviations………………………………………………………………...6
Proposal for a Trial Monitoring Strategy for pH in UK Marine Waters………7
Introduction to reviews and proposal development…………………………………12
Section 1 A review of data sets in which pH has been measured directly
or can be calculated from other carbonate system measurements...14
Section 2 A formal validation of existing model performance against data
mined for this project ………………………………………………22
Section 3 A review ranking the biogeochemical and physical processes likely
to determine the acidity of seawater in different shelf regions……28
Section 4 A review of where our shelf seas are most vulnerable to pH changes…...33
Section 5 Development of an observational programme……………………………43
5a A critical review of existing and developing technologies for
measuring the variability and change of pH………………………...43
5b Development of an observing plan……………………………………….65
5c Quality control……………………………………………………………70
Appendices
1. Original Proposal for ME2109……………………………………………………76
2. Strawman monitoring proposal for consultation with MARG……………………82
3. Outline summary of feedback from MARG………………………………………87
4. Written feedback from MARG……………………………………………………89
5. Factors limiting additional UK sampling capability for pH………………………93
6. Costings for a UK pH monitoring scheme as proposed…………………..……....95
2
ME2109 Contributing authors and project management
Plymouth Marine Laboratory:
Prospect Place
West Hoe
Plymouth, PL1 3DH
Dr Carol Turley*
Dr Anthony Bale
Mr Jerry Blackford
Dr Nicholas Hardman-Mountford
Ms Nancy Jones
telephone 01752 633100
* [email protected]
National Oceanography Centre:
Dr David Hydes*
Dr Boris Kelly-Gerreyn
Dr Eric Achterberg
Dr Cedric Floquet
Dr Toby Tyrrell
Dr Matt Mowlem
University of Southampton
Waterfront Campus
European Way
Southampton, SO14 3ZH
telephone 023 8059 6547
switchboard 023 8059 6666
*[email protected]
University of East Anglia:
School of Environmental Sciences
Norwich, NR4 7TJ
Prof. Andrew Watson
Dr. Dorothea Bakker*
Dr. Ute Schuster
telephone 01603 592648
Switchboard 01603 592542
* [email protected]
_____________________________________________________________________
ME2109 Defra Project Management
Project Officer
Dr Beth Greenaway
Management Group
Dr. Andrea Leedale
Dr. Paul Leonard
Dr. Andy Greaves
Dr. Steve Malcolm
Dr. Christoph Heinze
Defra
Defra
Defra
CEFAS
CARBOOCEAN
Stakeholder Consultation
MARG
3
ME2109 Developing a Trial Monitoring Strategy for pH in UK Marine Waters
Executive Summary
Background

Concentrations of CO2 are increasing in the atmosphere. About 7x109 tonnes of
CO2 enter the oceans each year.

Calculations based upon the IPCC "Business as Usual" scenario show that by the
mid-21st century the additional CO2 will cause the acid content of the ocean's
surface to double (equivalent to a decrease* of 0.3 in the measured pH). The
probability of this occurring is high.
(* NB the pH scale decreases with increasing acidity)

Baseline measurements of pH against which changes in UK waters can be judged
are not available.
Existing Data

There are almost no high quality, directly-measured data on pH for UK marine
waters.

pH can be calculated from other measurements. Good quality time series data is
becoming available in some areas. Data for the Atlantic waters that are the source
waters for UK shelf seas are available from 2002 onwards but funding for these
time series is uncertain after 2007/8.
Modelling of pH (ERSEM-POLCOM-HALTAFALL model)

It is unlikely that we can gain a comprehensive view of the spatial distribution of
vulnerabilities from observational data alone. An alternative approach is to use
existing data to validate deterministic simulation models as developed under
ME2107 and use these to perform the desired analysis.

Little data exists against which to validate models. The model captures the
essential bulk properties of the carbonate system when compared with available
data and can be considered as fit for purpose. Improved treatment of coastal
processes: river loads, optical properties and parameterisation of alkalinity, are the
key model refinements required.

The present variability of pH in marine water due to seasonal temperature and
biological activity, away from estuary plume effects, is about 0.4. The model
simulations suggest that North Sea pH will be 0.2 pH units lower than preindustrial by 2050.
Processes influencing the acidity of seawater in different shelf regions.

The acidity of UK waters is determined by the biogeochemical cycle of growth
and decay, exchange of waters with the Atlantic and of CO2 with the atmosphere.
4

Processes are intensified in estuary plumes (annual ranges greater than 1 pH unit
are predicted).
Which areas of UK shelf seas are most vulnerable to pH changes?

All UK waters will experience declining pH.

The current state of knowledge on the impacts of ocean acidification is not yet
sufficient to distinguish areas more or less vulnerable to changing shelf sea pH.
Existing capability and developing technology

Detection of change of pH at the predicted annual rate of 0.003 (pH units)
requires measurements at the limit of what is now possible. Presently pH must be
calculated from measurements of other carbonate system parameters.

The UK has excellent capacity for measuring the partial pressure of CO2, (pCO2)
in seawater on voluntary observing ships (VOS) and research vessels.

To calculate pH from pCO2, additional measurements of alkalinity and total CO2
have to be made on water samples in the laboratory using time consuming and
therefore expensive methods.

Analytical equipment using pH electrodes could be developed relatively quickly
(6 months) to deliver measurements of the required precision, exploiting previous
work for the EA.

Development of a system based on colorimetry offers the possibility of systems
which are robust enough for autonomous use (promising resolution of current
undersampling in space and time), with levels of precision better than can be
achieved by other means (~0.001pH). The cost of such development would be
(~£200k) which must be balanced against savings in recurrent measurement cost.
Proposed work

Requirements (i) best technologies and methods be used to get a precision and
accuracy (±0.003 pH) equal to projected annual change (ii) annual range of pH in
key hydrographic and biogeochemical process areas be defined (iii) regular data
be collected appropriate for development and validation of prognostic models (iv)
data be made rapidly available for use in models and indicators of eco-system
change.

TASK 1 Collection of data documenting the change in pH through two years in
waters representing the range of conditions found in UK waters from eutrophic to
waters of recent ocean origin. The data sets would include the necessary
hydrodynamic and biogeochemical data needed for the better development of
numerical models. This will be possible using existing observational efforts,
which collect both data sufficiently frequently during the year for the annual
changes to be precisely defined and where the ancillary data are already collected.
To be based on POL, PML and, given sufficient resources, FRS Aberdeen
Observatories and NOC (FerryBox) high frequency Portsmouth-Bilbao sampling.
5

TASK 2 Sustained monitoring is required of ocean waters as these are the source
waters to the UK shelf. Rates of change being observed in the North Atlantic
disagree with those currently predicted by numerical models.

TASK 3 Data will need to be quality controlled and archived along with meta
data that fully describes how the data were collected and how pH values were
obtained and calibrated. Data will be available through BODC, MDIP and
MERMAN.

TASK 4 Investment should be put into instrument development so that
measurement of pH can be done autonomously at high accuracy and precision.
Both the pH electrode and the colorimetric approach should be followed.

TASK 5 Modelling and statistical methods should be used to evaluate the
baseline data collected in Tasks 1 & 2 so that an efficient long term monitoring
programme can be established as part of the UK’s Clean Safe Seas Environmental
Monitoring Programme (CSEMP).
List abbreviations that are not defined in the text
BODC
British Oceanographic Data Centre
FRS
Fisheries Research Services
MDIP
Marine Data and Information Partnership
NOC
National Oceanography Centre
PML
Plymouth Marine Laboratory
POL
Proudman Oceanographic Laboratory
TA
Total Alkalinity
UEA
University of East Anglia
VOS
Voluntary Observing Ship
6
ME2109: Proposal for a trial Monitoring Strategy for pH in UK Marine Waters
The “baseline study”
Purpose of study
Requirements
Resources constraints
Resources
Present Status
Measurement summary & Standardisation
Definition of tasks
The “baseline study”
Before a long term monitoring programme can be established, high-resolution
“baseline” data on the current levels of acidity (pH) are needed. The work would
precisely determine both pH and its variability across the range of marine waters
around the UK coast. The baseline study and the parallel refinement of protocols for
sampling and analyses would enable a monitoring programme to be established which
would provide statistically robust data for UK waters and adjacent ocean waters.
Definition:“Baseline” measurements are carried out using the most appropriate
available technology and recording both the data and methods used. Consequently
any measurements made at a future time can be referenced back to these
measurements and changed, or reassessed, with a known degree of certainty.
Purpose of study

To define the range and variability in pH over a two year period in key water
types that represent the range of conditions in UK waters and the ocean waters which
are the source waters to UK shelf seas.

To provide reference points for the detection of long term changes against a
background of natural variation.

To provide validation of the procedures that will be adopted in a future
programme that provides long term monitoring of pH.

To provide a data set which will assist the development and validation of
numerical models that will enable better understanding of ocean acidification and
likely future rates of change.

Undertake statistical analysis of the data and review model data that will:
o
aid the design of a long term monitoring programme
o
develop appropriate indicators for describing change of pH in UK
waters
Requirements

Measurements of pH made to a precision and accuracy of ±0.003 pH units
which is equal to the projected annual rate of change.

Measurements made with sufficient frequency that the annual range of pH in
UK waters is defined. Model results suggest this range may be as high as 1.0 pH unit
in eutrophic waters.

Measurements made with sufficient geographical spread that dynamic changes
resulting from both hydrographic and biogeochemical processes can be observed.

Measurements made using the best available technologies and methodologies.
7

Measurements documented in such away that derived values of pH can be
recalculated if and when required by future improvements in the accuracy of our
knowledge of chemical equilibria of the carbonate system in sea water.

Measurements made of sufficient carbonate system parameters that the system
is “over defined” and the results of directly measured and calculated pH can be
compared to assess the accuracy and precision of current methodologies.

Measurements made at defined times and regular locations so that they are
appropriate for use in the development and validation of prognostic models.

Measurements made of carbonate system parameters along side those of
hydrodynamic and biogeochemical state so that both direct understanding and
prognostic modelling expertise is improved by the availability of the new data sets.

The methodologies and calculation used by different laboratories must be
traceable between the laboratories. Best practice should be applied following the
internationally agreed recommendations (currently CDIAC (DOE (1994) Handbook
of methods for the analysis of the various parameters of the carbon dioxide system in
sea water. (Version 2), A. G. Dickson & C. Goyet, eds. ORNL/CDIAC-74. which is
under revision ).
Resource constraints
We propose a baseline study which will be based on four existing UK sustained
observing activities with an option of a fifth scheme at Aberdeen. These schemes
provide the ability to collect samples at the required density without extending
existing activities. The required complimentary data on hydrodynamics and
biogeochemistry are already being made in these programmes. In each sampling
scheme, except Aberdeen, some of the carbonate system measurements are already
being made.
The programmes are in order of distance from shore:

POL Coastal Observatory, Liverpool Bay (RV Prince Madog)

FRS Stonehaven long-term sampling station, Aberdeen*

Western Channel Observatory (L4, E1, RV Plymouth Quest transects)

NOC Pride of Bilbao (VOS) data collection

UEA Transatlantic (VOS) data collection
*Inclusion of this sampling scheme is geographically and scientifically attractive
but at present has resource implications in that the samples generated would
exceed the analytical capacity at NOC.
Resources
POL Coastal Observatory, Liverpool Bay:- provides detailed coverage of a region
of strong fresh water influence in a eutrophic system. A key question in this region
is:- is the pH determined more by the respiration of organic matter supplied by the
river or by the production of organic matter which is enhanced by the nutrient input in
the rivers ?
FRS Stonehaven long-term sampling station:- regular weekly sampling for
nutrients, hydrographic information and phyto- and zooplankton data. Extra sampling
is practical to obtain discrete sample for analysis of TA & TCO2 at NOC (given
additional capacity). There are no additional carbonate measurements undertaken at
present.
8
PML Western Channel Observatory:- the RV Plymouth Quest visits the L4 Station
weekly and E1 monthly and is instrumented for pCO2 with the autonomous
PML/Dartcom system - providing detailed information between Plymouth and the
seasonally stratified waters at the E1 site, 22 miles offshore. The waters at the 2
sampling sites are stratified in summer enabling the influence of benthic processes on
pH to be determined.
NOC Pride of Bilbao (VOS) data collection:- provides high time resolution data
allowing detailed recording of changes in pH in relation to biogeochemical activity in
a range of environments from eutrophic harbours to the temperate Atlantic Ocean on
the route between Portsmouth and Bilbao. It provides key information on the
differences in behaviour between shelf seawaters and the ocean waters that are the
source for those shelf sea waters.
UEA Transatlantic (VOS) data collection:- provides data from the longest running
UK data set of marine carbon data. It is critical that we can assess the variability in the
ocean uptake of CO2 and the extent of the consequent year to year fluctuations in pH.
Present Status:
Carbonate system
pCO2 is currently measured automatically and at high resolution at four of the five
sites. Systems are presently operational on the MV Santa Maria, MV Pride of Bilbao,
RV Prince Madog and RV Plymouth Quest.
pH can now be measured to almost the degree of precision required for this work
using a flowing liquid-junction, electrode-cell system (developed at PML for the EA)
in an underway system to provide high resolution data . This system has a precision
of typically ~0.005 pH and a quoted accuracy of 0.01 pH. However experience with
this system in terms of maintaining that precision is lacking. This is currently being
evaluated by NOC and a similar system will be tested at PML.
TA and TCO2 can only be measured to the required degree of accuracy and precision
on discrete samples. We propose to over-determine the system by collection and
measurement of samples in each of the survey schemes except on the MV Santa
Maria (i.e. POL, PML and PoB, and at Aberdeen, if funds allow). These are key
measurements and an internationally-accepted, certified reference material will be
used to control the accuracy of these analyses.
Other biogeochemical system determinands.
By basing the work on 4 existing monitoring programmes we can support this
work within an existing frame work that is collecting high quality data.
Salinity data is available from all areas and calibration is based on well-established
procedures and traced back to use of IAPSO standard sea water.
Temperature data are commonly available but for carbonate system work data must
be accurate and precise to better than 0.1oK. A protocol for the required traceability of
temperature is being developed at NOC by Charlene Bargeron in consultation with
Andrew Dickson as part of a current revision of DoE CDIAC (DOE (1994) Handbook
of methods for the analysis of the various parameters of the carbon dioxide system in
sea water. (Version 2), A. G. Dickson & C. Goyet, eds. ORNL/CDIAC-74.)
Nutrients are currently measured throughout the year at POL, PML and PoB
measured by NOC and PML and at Stonehaven measured by FRS at Aberdeen.
9
Measurement summary & standardisation
All the systems will provide records of hydrographic conditions and changes in
concentrations of nutrients tracking the inputs of land based influences, over turn of
the water and the intensity of the annual production/respiration cycle in the different
areas. All areas, except Aberdeen, will provide data from autonomous pCO2 systems
and water samples will be collected for the determination of total alkalinity and total
CO2 so that the carbonate system can be over-determined in each area.
POL Coastal Observatory, Liverpool Bay:

8 times per year using the RV Prince Madog. Autonomous continuous pCO2
will be made on these survey cruises.

Surface waters samples for the determination of TCO2 and TA will be
collected on each survey at each site (36) and sent to NOC for analysis along with
nutrient samples collected at each station. (288 samples/year).
FRS, Aberdeen Stonehaven Station.

Weekly sampling at 4 depths, 3km offshore and uninfluenced by river runoff.

Parallel sampling for hydrographic variables, nutrients and biological data

Samples will be collected at 4 depths (4 * 50 = 200 samples/year).
Western Channel Observatory (L4, E1, RV Plymouth Quest transects)

Weekly section to L4 and monthly section to E1

Continuous pCO2 and potentially pH in due course (EA system) surface
records

Samples will be collected at 4 depths: (4*50 + 4*12 = 250 samples/year).
NOC Pride of Bilbao (VOS) data collection

Continuous observation of pCO2 330 days per year

36 samples for TA and TCO2 collected on each of 8 manned crossings per
year = 288 samples measured at NOC

pH electrode system measurements made with flowing liquid junction capable
of resolving pH to 0.002 will be implemented to run continuously along side the
pCO2 system.
UEA Transatlantic (VOS) data collection

Continuous observation of pCO2 >120 days per year
Equipment All the analytical and sampling equipment used in this work will be
traceable through the meta data provided alongside the reported data.
Methods The analytical methods used will follow current best practice as described in
the DoE CDIAC Handbook.
Calculations When reporting data derived from calculations, data will be
accompanied by statements of which carbonate system parameterisation have been
used.
10
Definition of tasks:
TASK 1: Two year programme of sample collection to establish “baseline”
condition in UK water types. (Lead NOC with PML)
Carryout a programme of sampling and measurement along side existing UK
sampling programmes:

POL Coastal Observatory, Liverpool Bay

Western Channel Observatory (L4, E1)

NOC Pride of Bilbao (VOS) data collection

Optionally Stonehaven at FRS, Aberdeen
TASK 2: North Atlantic Data Base (UEA only)
Provide a data set that details the variability of the pH in the North Atlantic waters
that are the source waters for UK shelf seas since the start of observations in 2002,
and continue time series of UEA Transatlantic (VOS) data collection.
TASK 3: UK acid seas monitoring data archive (Lead BODC with partners)
Carryout the necessary formatting and quality control and assembly of meta data
(detailing all the sampling and chemical analysis procedures used and subsequent QC
and calculations applied to the data). Transfer this data to an archive available from
BODC and accessible through MDIP.
TASK 4: Direct measurements of the pH of seawater (Lead PML with CEFAS)
Develop and validate a high precision electrode-based pH measuring device that will
reduce the potential costs of “permanent” monitoring programme and enable
autonomous use on Smart Buoys and in Ferry Boxes.
TASK 5: Design of a statistically robust long term programme for monitoring
change in acidity of marine waters (Lead PML with CEFAS)
Contribute to developing protocols for observational and model data archiving.
Conduct a formal model validation process on a yearly basis incorporating data
gathered under the proposed programme. The resulting error statistics would be used
to drive improvements in the model system (funded under other programs). The
validated model output would be provided to partners to contribute to the fine tuning
of the observational program in subsequent phases.
11
ME2109 Introduction to reviews and proposal development
Rationale: Atmospheric carbon dioxide concentrations have increased substantially
over the last two hundred years through human activities, in particular due to the
burning of fossil fuels. Projections are that CO2 emissions may increase substantially
in the future. It is now widely accepted these increased CO2 emissions have driven
and will drive future changes in the earth’s weather patterns and climate.
Nearly half of this anthropogenic CO2 has been absorbed through the surface of our
oceans and more will be absorbed in the future. Presently ocean uptake of CO2 is
reducing the rate of increase of CO2 in the atmosphere and so slowing the rate of
climate change. However, as CO2 dissolves in seawater the chemical equilibrium of
the carbonate system in the sea is shifted. This is causing the oceans to become
more acidic with the potential to adversely effect the functioning of marine
ecosystems. The potential impacts of acidification in our oceans have been
recognised but we have little evidence of what changes have occurred and are
occurring in waters around the UK. The UK Government and other stakeholders need
this knowledge to determine the implications of acidification of the UK waters.
Approach: To do, this Defra wishes to undertake a programme of measurements
which will:- (i) establish the current status of UK waters with respect to their
carbonate chemistry, and (ii) in combination with experiment work on organism,
biodiversity and process response to higher CO2 and ecosystem modelling, has the
potential to detect future changes and their impact on marine eco-systems, if and
when they occur. The work described here will provide a framework for a future long
term monitoring programme.
Main objectives: The initial phase of the work is an assessment of the available data
sets and ecosystems vulnerable to change, together with a critical review of current
and developing technology for both observations and the throughput of this data into
the marine management cycle. The key outcome of this work will be a set of
recommendations and a plan for a two year trial programme of monitoring. The
design of this programme will be based on the extension of existing marine field work
and, its integration into the developing UK Marine Monitoring and Assessment
Strategy.
Benefits: This effective and costed programme of work will be integrated with
currently operating and developing monitoring programmes. Best practice will be
determined through a review of available measuring technologies, sampling
procedures, data processing and data analysis alongside numerical modelling. This, in
addition to experimental and modelling approaches, will reduce the uncertainty in
assessing the vulnerability to UK marine ecosystems of acidification
Background information: NOC, PML and UEA have measurement systems that are
now providing regular information on the exchange of CO2 between the atmosphere
and the sea in UK waters. These are based on continuous observations using
instruments installed on commercial and research ships and instrumented buoys which
can make measurements autonomously and report the data ashore in real time. These
and other organisation round the UK regularly collect water samples for chemical
analysis, these programmes can be extended to collect samples for the measurement
12
of carbonate chemicals. The numerical ecosystem model ERSEM has reached a level
of maturity where it can contribute to the extrapolation of information into the future
and to areas where in-situ data has not been collected.
Marine Management
Information Needs
Information Use
Monitoring Strategy
Reporting
Network Design
Data Analysis
Sample Collection
Data Processing
Sample Measurement
Schematic outlining the proposed strategy
13
Section 1. A review of existing data sets in which pH has been measured
directly or can be calculated from other carbonate system measurements.
Lead author: Ute Schuster, UEA
This review includes:1. A review of data available in the published literature and elsewhere
and data that may become available at some time in the future from other
sources such as the EU-FP6-project CARBOOCEAN.
2. Data sets under the ownership of project participants (and available to
project partners) to validate existing model systems. The largest is that of
underway pCO2 collected on the UEA trans-Atlantic (Portsmouth Caribbean) Ship of Opportunity. This has been running continuously since
April 2002 with earlier measurements in 1994 and 1995. Additionally there
are data from the PML monitoring stations E1 and L4 in the English
Channel, data collected by the CASIX systems on NERC research ships,
and from NOC on the Portsmouth – Bilbao Ferry box line since September
2005. The best approach for estimating pH from data sets with a single
inorganic carbon parameter (eg. pCO2) will be investigated.
3. A preliminary MCCIP report card will be produced on the basis of the
existing data.
Data available from project partners
MV Santa Maria data, UEA, 2002 to 2006:
SM_Defra_070326.dat
Relevant data (including one carbon parameter and
salinity) are available from the July 2002 onwards,
collected during CAVASSOO (Carbon Variability
Studies by Ships of Opportunity,
http://lgmacweb.env.uea.ac.uk/e072/welcome.htm,
contract number EVK2-CT-2000-00088) and
CarboOcean (Marine carbon sources and sinks
assessment, http://www.carboocean.org/, contract
number 511176-2), on board MV Santa Maria trading between Le Havre, France, or
Portsmouth, UK, and the Caribbean.
PI: Ute Schuster and Andrew Watson, UEA
14
The data file has the following columns
Column
Parameter
1
Year
2
Date
3
Time
4
Decimal day of
year
5
Latitude
6
Longitude
7
SST
8
SSS
9
Sea surface pCO2
10
Alkalinity
11
pH
12
TCO2
13
fCO2
Unit
yyyy
Day since zero
Decimal
Measured/calculated
GPS recording
GPS recording
GPS recording
calculated
[oN]
[oE]
[oC]
[psu]
[μatm]
[μeq/kg]
GPS recording
GPS recording
Measured
Measured
Measured
Calculated Note A
Calculated Note B
Calculated Note B
Calculated Note B
[μmol/kg]
[μatm]
Note A
: Alkalinity was calculated using SST and SSS, south of 30oN according to the
equation given in [Lee, et al., 2006] for the (sub)tropics, and north of 30oN according
to the equation given in [Lee, et al., 2006] for North Atlantic.
Note B
: pH, TCO2, and fCO2 were calculated using CO2sys_macro_PC.xls [Lewis and
Wallace, 1998], using SST, SSS, pCO2, on a seawater pH scale with the dissociation
constants by [Mehrbach, et al., 1973], refitted by [Dickson and Millero, 1987].
Individual data files of each voyage are available under the following file IDs (“SM”
stands for “Santa Maria”, followed by start date of voyage as “yyyymmdd”).
6 5 oN
P&O Pride of Bilbao, NOCS, 2005 and 2006,
PoB_Defra_070326.dat
Pride of Bilbao data 2005 and 2006
6 0 oN
5 5 oN
Data are available from September 2005 to July 2006,
collected during the FerryBox project
(http://www.ferrybox.org/, European Commission contract no:
EVK2-CT-2002-00144), on board Pride of Bilbao sailing
Portsmouth, UK, and Bilbao, Spain.
5 0 oN
4 5 oN
4 0 oN
2 0 oW
1 5 oW
10 oW
5 oW
PI: David Hydes, NOCS
The data file has the following columns
Column
Parameter
1
Year
2
Date
3
Time
4
Decimal day of
year
5
Latitude
6
Longitude
Unit
Day since zero
decimal
[oN]
[oE]
15
Measured/calculated
0
o
o
5 E
o
10 E
o
15 E
7
8
9
10
11
12
13
14
15
SST
Salinity
pCO2
Alkalinity
pH
TCO2
fCO2
Phosphate
Silicate
[oC]
[psu]
[μatm]
[μequ/kg]
[μmol/kg]
[μatm]
[μmol/kg]
[μmol/kg]
Measured
Measured
Calculated Note C
Measured
Calculated Note C
Measured
Calculated Note C
Measured
Measured
Note C
: pH, pCO2, and fCO2 were calculated using CO2sys_macro_PC.xls [Lewis and
Wallace, 1998], using SST, SSS, Total alkalinity, TCO2, phosphate, and silicate, on a
seawater pH scale with the dissociation constants by [Mehrbach, et al., 1973], refitted
by [Dickson and Millero, 1987].
MV Prince of Seas, 1994 to 1995,
PoS_defra_070326.dat
Data are available from 1994 and 1995, collected during UK
DoE contract PECD/7/ 12/143, sailing between the UK and
the Caribbean.
PI: Nathalie Lefevre and Andrew Watson
The data file has the following columns
Column
1
2
3
4
5
6
7
9
Parameter
Year
Date
Time
Decimal day of
year
Latitude
Longitude
SST
Sea surface pCO2
Unit
yyyy
Day since zero
Decimal
Decimal
Measured/calculated
GPS recording
GPS recording
GPS recording
calculated
[oN]
[oE]
[oC]
[μatm]
GPS recording
GPS recording
Measured
Measured
16
PML/Dartcom systems (Carbon-Ops project)
PI: Nick Hardman-Mountford
Ship
Cruise
Discovery
AMT-17
Oct-Nov 2005
N & S Atlantic
D313 (SOLAS DOGEE)
Nov-Dec 2006
NE Atlantic
D317
Mar-Apr 2007
N Atlantic
D318
Apr-May 2007
N Atlantic
Prince Madog
Dates
MATSIS
Apr 2006
Irish Sea
Hollyhead-Dublin transect x2
Jul 2006
Irish Sea
Autosub
Jul 2006
Irish Sea
MATSIS
Sep 2006
Irish Sea
Sep 2006-Apr 2007
Irish Sea
POL Coastal Observatory (5 to date)
James Clark Ross
Immingham-Stanley
Sep 2006
N & S Atlantic
JR152/159 (Stanley, South Georgia)
Oct 2006
Southern Ocean
JR161 (Stanley, Signy, South Georgia)
Nov 2006
Southern Ocean
Dec 2006-Jan 2007
Southern Ocean
JR163 (Stanley, Rothera, Signy, South Georgia)
Stanley-Montevideo
Jan 2007
JR157 (Stanley, Rothera, Bellingshausen Sea)
Plymouth Quest
SW Atlantic
Jan/Feb 2007
Southern Ocean
JR165/170 (Rothera, Bellinghausen Sea)
Feb/Apr 2007
Southern Ocean
JR168 (Scotia Sea, Weddell Sea)
Apr/May 2007
Southern Ocean
L4/E1 seasonal cycle
L4/E1 weekly/monthly transect
James Cook
Location
None yet (awaiting TSG installation)
17
Mar 2005-Sep 2006
W. English Channel
Apr 2007-Date
W. English Channel
Scheduled Apr 2007
N. Atlantic
Tamar estuary data
File number
File name/date
1
TA-14 SEP 83
2
TA - 16 NOV 83
3
TA- 26 JAN 84
4
TA - 30 MAR 84
5
TA- 15 MAY 84
6
TA - 13 JUN 84
7
TA – 20 JUL 84
8
TA - 23 JUL 84
9
TA - 25 JUL 84
10
TA - 27 JULY 84
11
TA - 29 JULY 84
12
TA- 31 JUL 84
13
TA - 03 AUG 84
14
TA - 05 AUG 84
15
TA - 07 SEP 84
Tamar estuary alkalinity data files:
Number of stations
62
60
44
70
55
37
53
48
51
50
43
48
40
28
45
Number of alkalinity
42
44
29
37
30
18
29
23
21
20
19
20
20
16
18
Data collected between Plymouth Sound and the fresh water of the R. Tamar
.
PI: Tony Bale
Column headings within files:
Column
1
2
3
4
5
6
7
8
Header
Distance
Time
Temperature
Salinity
Oxygen saturation
Suspended solids
pH
alkalinity
Units
Km from Gunnislake weir
local
Celsius
PSU
%
mg per litre
equivalents
These data were all collected between Plymouth Sound and the fresh water of the R.
Tamar.
18
Additional data
Reference
[Frankignoulle,
1988]
Time
1985
[Kempe and
Pegler, 1991]
1985 and 1986
[Hoppema, 1991]
1987
Parameters
pH Measured
pCO2 measured
alk measured
pH: Measured
Alk: measured
TCO2: measured
pCO2: calculated
TCO2: measured
Alk: measured
pH: measured
SSS: measured
pCO2: calculated
[Frankignoulle, et 1992 and 1993
al., 1996]
pH: Measured
Alk: measured
pCO2: calculated
[Borges and
Frankignoulle,
1999]
pH: Measured
pCO2: measured/
calculated
Alk measured
Oxygen:
measured
1995 and 1996
[Frankignoulle, et 1992 to 1997
al., 1998]
pH measured
pCO2 calculated
19
Location
North Sea, Shetland Islands
North
Sea, 3
water
masses:
N.
Atlantic
(enters N
Sea from
the NW),
Skagerra
k (outflow of Baltic), German
Bight (influenced by European
rivers).
Eastern
part of the
Southern
North Sea
Bight
Eng
lish
Cha
nnel
and
Sou
ther
n Bight of the North Sea
Belgian
and
southern
Dutch
coasts
European estuaries
[Frankignoulle
and Borges,
2001]
1993 to 1999
[Bozec, et al.,
2005]
2001
before 1995,
then measured
pH measured
pCO2 calculated
before 1995,
then measured
TCO2: measured
Oxygen:
measured
Nutrients:
measured
Chl a: measured
20
Europea
n
continen
tal shelf
–
Galician
Sea, Bay
of
Biscay,
Armorican Sea, Celtic Sea,
English Channel, North Sea
Nort
h
Sea
References
Borges, A. V., and M. Frankignoulle (1999), Daily and seasonal variations of the
partial pressure of CO2 in surface seawater along Belgian and southern Dutch
coastal areas, J. Mar. Syst., 19, 251-266.
Bozec, Y., et al. (2005), The continental shelf pump for CO2 in the North Sea evidence from summer observation, Marine Chemistry, 93, 131-147.
Dickson, A. G., and F. J. Millero (1987), A comparison of the equilibrium constant
for the dissolution of carbonic acid in seawater media, Deep-Sea Res., 34, 17331743.
Frankignoulle, M. (1988), Field measurements of air-sea CO2 exchange, Limnol
Oceanogr., 33, 313-322.
Frankignoulle, M., et al. (1998), Carbon dioxide emission from European estuaries,
Science, 282, 434-436.
Frankignoulle, M., and A. V. Borges (2001), European continental shelf as a
significant sink for atmospheric carbon dioxide, Global Biogeochem. Cycl., 15,
569-576.
Frankignoulle, M., et al. (1996), Distribution of surface seawater partial CO2 pressure
in the English Channel and in the Southern Bight of the North Sea, Continental
Shelf Research, 16, 381-395.
Hoppema, J. M. J. (1991), The seasonal behavior of carbon dioxide and oxygen in the
coastal North Sea along the Netherlands, Neth. J. Sea Res., 28, 167-179.
Kempe, S., and K. Pegler (1991), Sinks and Sources of CO2 in Coastal Seas - the
North Sea, Tellus, B43, 224-235.
Lee, K., et al. (2006), Global relationships of total alkalinity with salinity and
temperature in surface waters of the world's oceans, Geophysical Research
Letters, 33, L19605, doi:19610.11029/12006GL027207.
Lewis, E., and D. W. R. Wallace (1998), Program Development for CO2 System
Calculations, 26 pp., Carbon Dioxide Information Analysis Center, Oak Ridge
National Laboratory, US Department of Energy, Oak Ridge, Tennessee.
Mehrbach, C., et al. (1973), Measurement of the apparent dissociation constants of
carbonic acid in seawater at atmospheric pressure., Limnol Oceanogr., 18, 897907.
Thomas H. et al. Rapid decline of the CO2 buffering capacity in the
North Sea and implications for the North Atlantic Ocean, Global Biogeochem.
Cycles, accepted (2007).
21
Section 2. A formal validation of existing model performance against data
mined for this project
Authors: Jerry Blackford & Nancy Jones, PML
The numerical ecosystem model ERSEM-POLCOMS has reached a level
of maturity where it can potentially contribute successfully to the
extrapolation of information into the future and estimation of conditions in
areas where in-situ data has not been collected. However the appropriate
use of models depends on their accuracy and an understanding of why and
when models and data deviate. Under ME2107 effort is underway to
validate models; however this project will deliver some new data sets not
currently available. This section reports a formal model validation
exercise incorporating newly available data and quantifies model
accuracy and error, as an input to Section 3.
1. Introduction
Because of the operational limitations of monitoring pH or related variables and the lack of
scientific focus on pH prior to our current concerns about high CO2, it is unlikely that we can
gain a comprehensive or even synoptic view of the spatial distribution of vulnerabilities from
observational data alone. An alternative approach is to use existing data to validate
deterministic simulation models as developed under ME2107 and use these to perform the
desired analysis.
Under ME2107 we have created a UK modelling capacity for exploring the effects of high
CO2 (including lowered pH) on the marine ecosystem of UK shelf waters and made an initial
exploration of marine ecosystem response to elevated CO2. Blackford & Gilbert, (2007)
assesses the annual pH range, its drivers and future predictions for the southern part of the
North Sea (below 56°N). Work has now extended the model domain to the whole of the UK
shelf waters.
The numerical ecosystem model used, (ERSEM-POLCOMS) has reached a level of maturity
where it can potentially contribute successfully to the extrapolation of information into the
future and estimation of conditions in areas where in-situ data has not been collected.
However the appropriate use of models depends on their accuracy and an understanding of
why and when models and data deviate.
2. Model System Synopsis
The model system is a coupling involving three well established model codes, covering the
carbonate system (HALTAFALL; Ingri et al, 1967), the marine ecosystem (ERSEM; Baretta,
1995; Blackford, 2004) and POLCOMS (Holt and James, 2001) giving a 3D hydrodynamic
system. All of these model codes have been used previously in combination (HALTAFALL
and ERSEM (Blackford and Burkill, 2002); ERSEM and POLCOMS (for example Allen et al,
2001; Holt et al 2005).
HALTAFALL provides an iterative method to determine chemical speciation, parameterised
by two of total inorganic carbon (a state variable in the ERSEM ecosystem model), total
alkalinity (TA), pCO2 or pH allowing calculation of the other two variables. We use two
22
regime dependant relationships to derive TA from salinity. For salinity > 34.65 we use the
relationship reported by Bellerby et al (2005) for North Atlantic waters, (TA = 66.96∙S –
36.803); for salinity < 34.65 we approximate from Borges & Frankignoulle (1999) giving TA
= 3887.0 – 46.25∙S. We use the sea water pH scale, with coefficients according to Weiss
(1974), Dickson and Millero (1987), Hansson (1973) and Millero (1979). Air-Sea exchange
of CO2 is calculated using the parameterisation of Nightingale et al (2000) acting on the
derived partial pressure of CO2 in the water and the parameterised atmospheric concentration.
The European Regional Seas Ecosystem Model (ERSEM) is a complex plankton functional
type (PFT) model developed in the context of the North Sea but now finding wider
application (Baretta et al, 1995; Blackford et al, 2004). The POLCOMS hydrodynamic model
is a three dimensional baroclinic circulation model in this case set up for the UK shelf Seas,
taking boundary conditions from wider area versions of the same model. It is described in
detail in Holt and James (2001). Dissolved inorganic carbon (DIC) concentrations for the
main regional rivers are taken from Pätsch & Lenhart (2004). For rivers with no specific data
we use the budget calculations in Thomas et al (2005) to derive a DIC load. For the future
scenarios we assume that riverine DIC is in equilibrium with the prescribed atmospheric
conditions and scaled accordingly. Riverine nutrient and flow rates are taken from various
sources and are assumed not to change in the future scenarios. We prescribe atmospheric CO2
levels according to IPCC (2001) estimates, omitting the small seasonal signal for simplicity
The ERSEM-POLCOMS model demonstrates some skill in reproducing regional observations
(Holt et al., 2005, Allen et al in press, Lewis et al., in press). The carbonate-ERSEM model is
initially validated in Blackford & Gilbert (2007).
3. Data Availability
For this project the model output has been compared against three distinct data sets:
1. Publicly available pH data from the Dutch ‘Waterbase’ database, maintained by
Dutch National Institute for Coastal and Marine Management (RIKZ) and the Dutch
Institute for Inland Water Management and Waste Water treatment (RIZA)
http://www.waterbase.nl/, covering the southern North Sea
2. pCO2 data from the CAVASOO program supplied courtesy of Prof Andy Watson
(UEA), relating to the English Channel.
3. Alkalinity and dissolved organic carbon data supplied by Dr David Hydes from the
NOC Ferrybox program, also relating to the English Channel.
4. Results
4.1 A note on general model validation
Detailed attempts to validate the ERSEM-POLCOMS North Sea simulations against a range
of variables show a generally good representation of the physical environment, skill in
resolving seasonal dynamics but a limited ability to resolve daily variability in harsh like-forlike comparisons with data (Holt et al., 2005; Allen et al., 2005). In stratified and off shore
regions the model generally reproduces the correct partitioning of biomass between functional
units but tends to under-estimate the thermocline depth during summer. In coastal
environments the model does not produce completely the observed draw down in nutrients
during the spring bloom, although chlorophyll levels are broadly correct. It is assumed that
the complex optical properties of the strongly case II waters are not yet well represented in the
model. Despite some specific drawbacks the ERSEM-POLCOMS North Sea models are
generally considered fit-for-purpose and cited as the best validated of all regional modelling
attempts (Moll & Radach, 2003)
23
Figure 2.1. Model (blue line) comparison with Waterbase data (points and error bars); the yaxis on each plot is pH. Each panel represents a distance from the Dutch coast towards the
Dogger Bank (see Blackford and Gilbert, 2007).
24
4.2 Validation against waterbase data.
Figure 2.1 presents a seasonal validation of modelled pH against data available from the
Dutch Waterbase database (www.waterbase.nl) for a transect stretching from the Dutch coast
to the Dogger bank. Because of the high variation, especially in peak timing, between years in
the data and because ERSEM’s skill lies in the seasonal rather than short term prediction, we
have calculated monthly mean, maximum and minimum pH values for the period 1997-2004.
The model reproduces the mean of the data, the spatial trend and the range of the seasonal
signal, although the timing of the main productivity signal in coastal regions is incorrect. This
relates to the poor representation of case II water optical properties, rather than a
misrepresentation of the physiological processes. It is worth noting that there is a considerable
downward trend in pH as recorded in Waterbase, over the period 1997-2004 of about 0.02 pH
units.y-1, about 6 times greater than predicted from increases in atmospheric CO2 over this
period. In our analysis we have de-trended the data around the year 2000 mean, consistent
with our atmospheric CO2 parameterisation.
4.3 Validation against Cavasoo data
Figure 2.2 shows the comparison of model output with ship of opportunity pCO2 data mined
under the CAVASOO project. In this region – the English Channel – the model is producing
more seasonal variability than shown in the data but well represents the mean condition.
Essentially the model over estimates winter levels of pCO2, this could be due to excessive
respiration in the modelled biology, although a range of factors could be contributing.
Without additional data describing concurrent biochemistry it is difficult to be conclusive. A
longitudinally resolved analysis confirms the generally high variability in the model and in
particular identifies a tendency to excessive pCO2 at around 6° west. This probably derives
from over estimation of frontal structures in the region causing excessive production. The
model does reproduce the correct mean and longitudinal trend.
Figure 2.2a. Comparison of model output with CAVASOO data, seasonally resolved. Blue
line represents the model mean, the grey area, model variability.
25
observations
600
model
pCO2w
500
400
300
200
-12
-10
-8
-6
-4
-2
0
longitude
Figure 2.2b. Comparison of model output with CAVASOO data longitudinally resolved
4.4 Validation against Ferrybox data
Although the data is sparse (Fig 2.3) the model is in general agreement with the observations.
Figure 2.3. Model comparison (shaded) with Ferrybox DIC data (circles and range bars).
4.5 Summary
These initial studies identify the improved treatment of coastal processes: river loads, optical
properties and TA parameterisation, as the key model refinements required. However it is
clear that the model captures the essential bulk properties of the carbonate system when
compared with available data and can be considered as fit for purpose.
26
References
Allen, J.I., Blackford, J.C., Ashworth, M.I., Proctor, R., Holt, J.T., Siddorn, J.R., 2001. A
highly spatially resolved ecosystem model for the north-west European continental shelf.
Sarsia. 86, 423-440.
Baretta, J.W., Ebenhöh W. and Ruardij P., 1995. The European regional Seas Ecosystem
Model, a complex marine ecosystem model. Netherlands Journal of Sea Research 33, 233246
Bellerby R.G.J., Olsen A., Furevik T. and Anderson L.A., 2005, Response of the surface
ocean CO2 system in the Nordic Seas and North Atlantic to climate change. In: Climate
Variability in the Nordic Seas, H. Drange, T.M. Dokken, T. Furevik, R. Gerdes, and W.
Berger, Eds., Geophysical Monograph Series, AGU, 189-198
Blackford, J.C., Burkill, P.H., 2002. Planktonic community structure and carbon cycling in
the Arabian Sea as a result of monsoonal forcing: The application of a generic model.
Journal of Marine Systems, 36/3-4, 239-267.
Blackford, J.C., Allen, J.I., Gilbert, F.G., 2004. Ecosystem dynamics at six contrasting sites:
a generic modelling study. Journal of Marine Systems. 52, 191-215.
Blackford, J.C., Gilbert, F.J., 2007. pH variability and CO2 induced acidification in the North
Sea. Journal of Marine Systems. 64, 229-241
Borges, A. V., Frankignoulle, M., 1999. Daily and seasonal variations of the partial pressure
of CO2 in surface seawater along Belgian and southern Dutch coastal areas. Journal of
Marine Systems, 19, 251-266.
Dickson, A. G., Millero, F. J., 1987. A comparison of the equilibrium constants for the
dissociation of carbonic acid in seawater media. Deep Sea Research 34, 1733-1743.
Hansson, I. 1973. A new set of acidity constants for carbonic acid and boric acid in sea water.
Deep Sea Research 20, 461-478.
Holt, J.T., James, I.D., 2001. An s-coordinate model of the North West European Continental
Shelf. Part 1 Model description and density structure. J. Geophys. Res. 106(C7): 1401514034.
Holt, J.T., Allen, J.I., Proctor, R., Gilbert, F.G., 2005. Error quantification of a high
resolution coupled hydrodynamic-ecosystem coastal ocean model: part 1 Model overview
and hydrodynamics. J. Mar. Sys. 57,167-188.
Ingri, N., Kakolowicz, W., Sillén, L.G., Warnqvist, B., 1967. High-speed computers
as a supplement to graphical methods-V. HALTAFALL, a general program for
calculating the composition of equilibrium mixtures. Talanta, 14, 1261.
IPCC, 2001: Climate Change 2001: The Scientific Basis. Contribution of Working Group I to
the Third Assessment Report of the Intergovernmental Panel on Climate Change
[Houghton, J.T.,Y. Ding, D.J. Griggs, M. Noguer, P.J. van der Linden, X. Dai, K. Maskell,
and C.A. Johnson (eds.)]. Cambridge University Press, Cambridge, United Kingdom and
New York, NY, USA, 881pp.
Millero, F. J. 1979. The thermodynamics of the carbonate system in seawater. Geochim.
Cosmochim. Acta 43, 1651-1661.
Nightingale, P. D., Malin, G., Law, C. S., Watson, A. J., Liss, P. S., Liddicoat, M. I., Boutin,
J., Upstill-Goddard, R. C., 2000. In situ evaluation of air-sea gas exchange
parameterizations using novel conservative and volatile tracers. Global Biogeochemical
Cycles 14, 373-388.
Pätsch, J., Lenhart, H. J., 2004. Daily loads of nutrients, total alkalinity, dissolved inorganic
carbon and dissolved organic carbon of the European continental rivers for the years 19772002. Berichte aus dem Zentrum für Meeres- und Klimaforschung, Reihe B:
Ozeanographie.
Thomas, H., Bozec, Y., de Baar, H. J. W., Elkalay, K., Frankignoulle, M., Schiettecatte, L.-S.,
Kattner, G., Borges, A. V., 2005. The carbon budget of the North Sea. Biogeosciences 2,
87-96.
Weiss, R. F., 1974. Carbon dioxide in water and seawater: The solubility of a non-ideal gas.
Marine Chemistry 2, 203-215, 1974.
27
Section 3. A review ranking the biogeochemical and physical processes likely to
determine the acidity of seawater in different shelf regions.
Lead author: Carol Turley, PML
At a particular location the acidity of seawater will vary through the year
because:- (i) seasonal changes in sea surface temperature and mixing
affect surface water pH, (ii) processes of biological growth and decay
influence CO2 in the water, (iii) of external inputs such as rain and rivers,
and (iv) the acidity of the sea water is also determined by reaction with
mineral phases. Based on the existing literature, a ranking has been
made of the processes that are most likely to determine the acidity in
different regions of the UK marine environment at different times of year.
These will be compared with results from the existing ERSEM model
systems.
1. Alkalinity (TA) and Dissolved Inorganic Carbon (DIC): Ocean pH is
controlled by alkalinity and DIC and can be calculated from these two
parameters. Internal variations in DIC and alkalinity are controlled by the ratio
between photosynthesis: respiration (P:R) and between CaCO3 dissolution:
CaCO3 precipitation.
2. Atmospheric CO2 concentration: Increasing CO2 emissions through the
burning of fossil fuels and cement manufacturing have increased atmospheric
CO2 concentrations from 280 ppm in 1800 to 380 ppm at the present day. This
is set to continue to rise if we continue our fossil fuel usage in the same way
(business as usual) with end of century atm CO2 of up to 1000 ppm predicted
(IPCC 2007). However, there are calls for stabilization at 550 ppm (Stern,
2007) and lower. Atm CO2 is the major driver for surface ocean CO2 and
TCO2 enrichment and therefore surface ocean pH decline.
3. Ocean uptake: The medium term (decades and centuries) sink for the atm CO2
is the surface of the worlds oceans. Already c. 50% of the CO2 produced (500
Gtons CO2) over the last 200yrs has been taken up by the oceans (Sabine et al.
2004) through air-sea gas exchange and this has resulted in a decline in pH of
0.1 unit. Predictions indicate that the global ocean pH will decline by a further
0.3-0.4 by 2100 and by 0.6 by 2300 in the business as usual scenario (Calderia
& Wickett, 2003). Should changes to air-sea gas exchange (e.g. due to changes
to wind and the balance between photosynthesis and respiration (P:R)) occur
then there could be important small temporal scale variations (hours to weeks).
However, this is unlikely to be important on larger annual time scales.
4. Primary production and respiration: There is a huge natural annual flux of
CO2 between the ocean and the atmosphere of almost 90 Gt C yr-1 that, pre1800, was believed to be almost in balance. There was probably a net flux
from ocean to atmosphere of about 0.6 Gt C yr-1 that balanced the supply of
dissolved inorganic carbon to the oceans via rivers (Sarmiento and Sundquist,
1992). This huge influx and efflux is due to a combination of marine
productivity (the biological pump) and ocean circulation (the solubility pump).
Phytoplankton growth reduces dissolved inorganic carbon (DIC) levels in
28
surface seawater causing an undersaturation of dissolved CO2 and hence CO2
is transferred from the air to the ocean. The re-equilibration time for CO2 is
slow due to the buffering of CO2 in seawater. Respiration processes release
CO2, although some organic and inorganic carbon is transferred to the deeper
oceans via particle sinking. This process is known as the biological pump.
Primary production using photosynthesis results in the removal of CO2 from
the seawater and an increase in pH. Respiration, on the other hand, results in
the production of CO2 and a decrease in pH. The greater the productivity of
the waters the greater the variation in pH due to P:R. so this ratio is important
in UK shelf waters. Both of these are very important controls of the seasonal
variability in pH but are not likely to impact longer time scales unless one of
them changes. Almost all of the anthropogenic CO2 is thought to be taken up
by the solubility pump (IPCC, 2001), as CO2 availability does not normally
limit biological productivity in the world’s oceans. Indeed, a recent modelling
study has indicated that including present biology in oceanic global circulation
models increases the oceanic sink of anthropogenic CO2 by only 4.9% (Orr et
al., 2001).
5. CaCO3 dissolution and CaCO3 precipitation: Calcium carbonate is usually
found in the environment either as calcite or aragonite both of which are
abundant in organisms. However, aragonite is more soluble than calcite.
Calcium carbonate dissolves in seawater as shown below:
CaCO3 = Ca2+ + CO32-
1
Carbonate ions react with carbon dioxide as follows:
CO2 + CO32- + H20 = 2HCO3-
2
Indeed this reaction represents a useful summary of what happens when
anthropogenic carbon dioxide dissolves in seawater. The net effect is removal
of carbonate ions and production of bicarbonate ions and a lowering in pH.
This in turn will encourage the dissolution of more calcium carbonate.
The medium to long-term sink for anthropogenic CO2 is dilution in the oceans
and reaction with carbonate sediments with the long-term (1000-10,000 yrs)
controls on alkalinity and DIC being the weathering (sources) and burial
(sinks) of silicate and carbonate rocks. By 2300 about 70-80% of the
anthropogenic CO2 will be taken up by the oceans, reducing pH by c. 0.7units,
as the oceans turnover the CO2 will react with the deep ocean sediments and
this will buffer ocean pH. This process will take several thousand years
(Archer et al., 1997). Over tens of thousands of years a further buffering will
take place with igneous rocks so that ocean pH will return to around 8.1 and
the effect of the anthropogenic CO2 effectively removed.
Combining equations 1 and 2 gives:
CaCO3 + CO2 + H2O = Ca2+ + 2HCO3-
29
3
The contribution and impact of such buffering in shallow shelf seas is
unknown as are the impacts of erosion and resuspension due to storms, bottom
currents, ice disturbance and anthropogenic activities such as bottom trawling
and aggregate extraction. However, these are only likely to have significant
effects on pH at local and short term time scales.
A common misconception in biogeochemistry is that formation of calcite
removes carbon dioxide. As can clearly be seen above, formation of calcite
(the reverse of equation 3) actually produces CO2. Calcification produces CO2
but CaCO3 shells and liths can act as ballast for the long term removal of C
from the surface oceans (biological pump).
6. Seawater temperature and warming seas: Colder water has greater gas
carrying capacity and can therefore hold more CO2 than warmer water. So this
can have an impact on a seasonal basis. The surface oceans are warming as
well as becoming more acidic (IPCC, 2007). However, a recent paper
indicated that future changes in ocean acidification caused by atmospheric
CO2 emissions are largely independent of the amounts of climate change (Cao
et al. 2007) with a climate sensitivity of 2.5oC the reduction in projected global
mean surface pH is about 0.48 unit rather than 0.47 unit with no consideration
of climate change.
7. Riverine input: Freshwater input from rivers and estuaries is a direct input of
DIC and Alk as well as carbonic acid and can have a significant impact on pH
in estuaries and local coastal waters where there are significant river flows to
the sea (e.g. the Southern North Sea, Eastern Irish Sea). These waters will
experience additional pH variability.
8. Ocean circulation and upwelling of deep water: The controls of alkalinity
and DIC of deep ocean waters are respiration of organic matter and dissolution
of CaCO3. Thus deep water is rich in CO2 and when this upwells carries CO2
to surface waters and therefore reduces pH. Ocean circulation also results in
air-sea exchange of CO2 as the solubility of CO2 is temperature dependent.
9. Nutrients: Nutrient variation can have a small direct impact on pH variation
but this is likely to be seasonal and its significance restricted to areas of high
nutrient input such as estuaries.
10. Other anthropogenic gas emissions to the atmosphere: Fossil-fuel use and
agriculture are dramatically changing the global nitrogen and sulphur budgets,
through the release of large fluxes of nitrogen oxides, ammonia and sulphur
dioxide to the atmosphere. Because of the relatively short life-time (days to
about a week) of reactive nitrogen and sulphur species in the atmosphere, the
majority of the acid deposition occurs on land, in the coastal ocean and in the
open-ocean downwind of the primary source regions. The alterations in
surface water chemistry from anthropogenic nitrogen and sulphur deposition
are a few percent of the acidification and DIC increases due to the oceanic
uptake of anthropogenic CO2. However, the impacts are more substantial in
coastal waters, where the ecosystem responses to ocean acidification could
have the most severe implications for mankind (Doney et al., submitted).
30
11. Rainfall: Rainfall direct to water will have very short term effects on the pH
of the sea that directly interfaces with the air but this will be rapidly diluted
through mixing and is likely to be insignificant on temporal and spatial scales.
12. Vents and seeps: CO2 vents and seeps can impact ocean pH in local waters
where seepage is significant (e.g. Aegean). Although methane seeps occur in
UK shelf waters there are no known CO2 seeps so this is thought to be
insignificant in UK waters.
13. Hypoxic/anoxic waters: waters with low oxygen content experience extreme
fluctuations in pH. Hypoxic or “dead zones” are increasing globally especially
in environments with restricted exchange and high nutrient or organic input
such as enclosed seas (e.g. Baltic Sea, Gulf of Mexico). Increased thermal
stratification due to increased SST may result in their further extension. Some
areas of the southern North Sea are prone to reduced O2 (Wadden Sea).
14. Methane hydrate releases: Increasing global temperatures may result in the
release of methane from melting tundra and sediment bound methane hydrates.
As well as being a strong greenhouse gas, methane is oxidised in the
atmosphere resulting in further increases to atmospheric CO2
concentrations. It is thought that the rapid release of methane hydrates 55 My
ago may have resulted in the ocean acidification event that caused the
extinction of a large proportion of benthic calcifiers (Zachos, 2005).
15. Sediments: Organic-rich sediments experience extreme fluctuations in pH of
an order of 2 pH units – this is due to respiration of microbes as they
decompose organic matter. This has a significant influence on the distribution
of organisms and processes that occur at different depths within the sediment
profile.
References:
Archer, D., H. Kheshgi, and E. Maier-Reimer (1997), Multiple timescales for
neutralization of fossil fuel CO2, Geophys. Res. Lett. 24, 405– 408.
Archer, D., H. Kheshgi, and E. Maier-Reimer (1998), Dynamics of fossil fuel
neutralization by marine CaCO3, Global Biogeochem. Cycles 12, 259– 276.
Caldeira, K. and Wickett, M.E., 2003. Anthropogenic carbon and ocean pH. Nature
425, 365-365.
Cao, L., K. Caldeira, and A. K. Jain (2007), Effects of carbon dioxide and climate
change on ocean acidification and carbonate mineral saturation, Geophys. Res.
Lett. 34, L05607, doi:10.1029/2006GL028605
Doney, S.C., N. Mahowald, I. Lima, R.A. Feely, F.T. Mackenzie, J.-F. Lamarque, and
P.J. Rasch, The impact of anthropogenic atmospheric nitrogen and sulphur
deposition on ocean acidification and the inorganic carbon system, Prod. Nat.
Acad. Sci. USA, submitted.
IPCC (2007) Fischlin A., Midgley G.F., Price J., Leemans R., Gopal B., Turley C.,
Rounsevell M., Dube P., Tarazona J., Velichko A. Intergovernmental Panel for
31
Climate Change Fourth Assessment Report, Working Group II, Chapter 4 –
Ecosystems, Their Properties, Goods, and Services.
Sabine, C.L. and 14 others (2004). The oceanic sink for anthropogenic CO2. Science
305, 367-371.
Sarmiento, J.L. and Sundquist, E.T. (1992) Revised budget for the uptake of
anthropogenic carbon-dioxide. Nature 356, 589-953.
Stern, N.H. (2007). The economics of climate change: the Stern review. xix, 692p.,
Cambridge: Cambridge University Press,
Zachos, J.C., Rohl, U., Schellenberg, S.A., Sluijs A, Hodell, D.A., Kelly, D.C.,
Thomas, E., Nicolo, M., Raffi, I., Lourens, L.J., McCarren, H. and Kroon, D.
(2005) Rapid acidification of the ocean during the Paleocene-Eocene thermal
maximum. Science 308, 1611-1615.
32
Section 4 . A review of where our shelf seas are most vulnerable to pH changes.
Lead Author: Carol Turley
We will use modelling and laboratory results from ME2107, current
literature and the output from task 3 to estimate the vulnerability of UK
Shelf Seas to acidification.
In addition to the work planned under
ME2107 we will:1.
Compare, for each part of the model domain, the predicted in-situ pH
range for various future atmospheric CO2 concentrations.
2.
Quantify the distribution of predicted changes relative to natural
seasonal variability in UK waters.
3.
Given the known sensitivities of specific biogeochemical processes to
pH changes we will briefly and qualitatively assess the potential
disruption to the shelf ecosystem.
Introduction
Theoretically, identification of ‘hotspots’ of increased sensitivity to ocean
acidification in UK waters could be beneficial in planning a monitoring programme
for ocean pH. This is because the severity of consequences of ocean acidification may
vary geographically around the UK and may depend on two key factors: (1) the
inherent severity of the pH and associated carbon chemistry changes in each region
and (2) the number of potentially susceptible organisms inhabiting each region. As an
example of the second factor, if a particular area of sea were to be largely barren, then
consequences of acidification are not likely to be important. We discuss here both the
chemical differences and also the distributions of populations of potentially
vulnerable organisms.
There is a distinct shortage of direct pH measurements in UK shelf Sea regions (see
Section 1). In addition we have little knowledge of how pH and/or the CaCO3
saturation state (Ω) vary in near-coastal waters around the coastline of the UK. We
therefore cannot say whether there are differences between the Severn Estuary, the
Humber Estuary and the Moray Firth, for example, or any such detailed comparisons.
Available data sets are summarised in WP1.
Modelled seasonal and depth variation of pH in the North Sea
A more detailed examination of the biologically mediated CO2 fluxes over a seasonal
cycle sheds light on the natural controls of pH variability in the context of a stratified
water column (Figure 4.1).
33
8.18
8.16
8.14
8.12
8.1
8.08
8.06
8.04
8.02
8
7.98
7.96
7.94
Primary Production
-20
Physics
-40
-60
Benthic
Respiration
Modelled pH
-80
0
30
61
91
122
152
183
213
243
274
304
335
160
140
-20
120
100
-40
80
60
40
-60
20
Pelagic Production - Respiration
0
-80
-20
0
30
61
91
122
152
183
213
243
274
304
335
182
213
243
274
304
335
150
Benthic Respiration
100
50
0
0
30
61
91
122
152
365
Figure 4.1. Modelled in-situ temporal and depth variability of pH and interactions
with physical and biological processes over a calendar year (x-axis = days). Pelagic
production units are productivity minus community respiration in mg C m-3 and
benthic respiration is outgassing of CO2 from the benthos also in mg C m-3.
Two broad features, in terms of pH, are apparent. Firstly a pH maximum (up to 0.15
units above background levels), tracks the production maxima from the surface spring
bloom and continuing along the deep chlorophyll layer throughout summer. This
coincides with the distribution of net positive pelagic community production and CO2
uptake. Secondly there is a pronounced pH minima (as much as 0.15 pH units below
background levels) associated with the deeper waters under the thermocline that build
up during the stratified period. Here benthic respiration and the subsequent diffusion
of CO2 into the pelagic are causing elevated CO2 levels that are trapped in the
stratified system. The flux of CO2 across the air-sea interface (not shown) is a net
uptake during April and May, coincident with high primary production. During the
summer months the out-gassing is driven by the net community respiration in the
surface stratified layer. This reduces with the weakening of the thermocline and
resultant increase in surface production during the autumn. A strong out-gassing
signal is seen late in the year as the system finally overturns and the benthic CO2 is
exposed to the atmosphere.
Model predictions of present and future pH variability
Predictive model studies (Blackford & Gilbert, 2007) indicate that in-situ pH ranges
approaching and sometimes exceeding 1 pH unit are associated only with the major
34
river plumes (Figure 4.2), consistent with observations in the region (from the Dutch
Waterbase
Figure 4.2. Modelled current in-situ pH range across the annual cycle. Note that
boundary errors are causing an unrealistic result for the Baltic outflow region.
375ppm
Diff = 0.10
Mean = 8.03
1000ppm
Diff = 0.48
Mean = 7.65
Figure 4.3. Modelled surface pH fields and means for contemporary and one future
atmospheric CO2 scenarios applied to the whole UK shelf. The mean surface value
and the difference from pre-industrial pH is indicated.
35
database) and observations of similar systems (Hinga, 2002). It is suspected that, in
the immediate vicinity of some of the major riverine inputs, the accuracy of the
modelled pH derivation is affected by lack of accurate parameterisation of the riverine
chemistry, particularly the simplification that total alkalinity is solely derived from
salinity. Evidence (Borges & Frankignoulle, 1999; Pätsch & Lenhart, 2004) suggests
that, apart from between river variation, river plumes exhibit significant seasonal
trends. Off shore, away from riverine influence, the annual pH range is much reduced,
generally < 0.4 pH units.
Results from IMCO2 European Region Sea Ecosystem Model (ERSEM) simulations
suggest that North Sea pH will be 0.2 pH units lower than pre-industrial by 2050 and
may decrease by a further 0.13 – 0.28 pH units by 2100, depending on emissions
(Blackford and Gilbert, 2007). All scenarios of atmospheric CO2 result in a consistent
decline in pH across UK shelf waters (Figure 4.3). These estimates are consistent with
modelled global oceanic acidification rates (e.g. Caldeira and Wickett, 2003). The
simulations suggest that by 2050 some areas of the North Sea will be experiencing a
pH range completely distinct from current levels, although the majority of the region
retains some degree of range overlap. By 2100 much of the region will have a distinct
range. Exceptions are restricted to near shore environments which are predominantly
forced by riverine inputs and experience ranges of ~1.0 pH unit. The degree of
overlap in these near river zones is probably exaggerated for two reasons; the riverine
biogeochemistry, particularly the TA loadings are not well represented and the river
loads have been kept constant between each scenario. There is also a tendency for
excessive diffusion and transport of river plumes by the 3D hydrodynamics, arising
from the 7km horizontal resolution.
Acidification and Calcifying Organisms
Ocean acidification is only just emerging as a substantial future threat to marine
organisms and ecosystems – on a par to climate change impacts (Raven et al., 2005;
IPCC, 2007). For this reason, at the present time we have only have a limited
understanding as to which organisms may be impacted by these pH changes, and how
exactly they will be impacted. There is an increasing body of evidence to suggest that
calcifying organisms (those using calcium carbonate to build shells or skeletons) will
be affected but non-calcifiers may be impacted too (see below). The reason that
acidification is observed to affect calcifiers is probably related to the link between
CaCO3 saturation state (Ω, = [CO32-][Ca2+]/Ksp) and pH. The value of Ω has been
found to control inorganic calcification and dissolution in laboratory experiments.
Values of Ω above 1 correspond to the water being more supersaturated with respect
to calcium carbonate. Spontaneous inorganic precipitation (crystallisation) is
increasingly favoured. As Ω decreases to values progressively lower than 1,
dissolution of calcium carbonate becomes more and more likely, or proceeds more
and more rapidly. A value of Ω=1 represents the boundary between supersaturation
and undersaturation.
Given the paucity of data, this assessment can only be extremely rudimentary in
nature, and we are only able to sketch out general principles.
36
From the GLODAP open-ocean dataset it is clear that Ω declines with latitude. This
derives from the effect of temperature on CO2 solubility. Colder waters can hold a
greater concentration of CO2 molecules while still being at equilibrium with the same
overlying atmospheric partial pressure of CO2. For this reason, waters at higher
latitudes tend, on the whole, to have higher TCO2 concentrations, which in turn leads
to lower values of Ω. In line with this general understanding, computer models predict
that the first waters to go undersaturated (Ω<1) will be polar waters (Orr et al., 2005).
In the context of the UK, it is therefore possible that, as pH declines into the future,
more northerly parts of UK waters will experience undersaturation before more
southerly parts.
A second general principle is that deeper waters (below the thermocline) tend to be
more acidic (and as a consequence have lower values of Ω) than surface waters, due
to decomposition of organic matter. Ω also declines with depth because of a pressure
effect, such that waters below several kilometres depth are usually undersaturated;
any calcium carbonate falling onto the seafloor at such greater depths is dissolved.
Waters at depths of only a few hundred metres have intermediate saturation states but
are likely to become undersaturated before surface waters, as long as anthropogenic
carbon is able to reach them. The invasion of anthropogenic CO2 into surface waters is
translated into an effect on deeper waters in the vicinity of the UK, due to deep water
formation taking place in the Greenland-Iceland-Norwegian Seas, and due to deep
winter mixing in these seas and in the northeastern North Atlantic. Deep water coral
communities, also known as cold water corals, have recently been found along most
of the northwest European shelf break, including the shelf break to the west and
northwest of Scotland at sites such as Mingulay Reef. Models of future aragonite
saturation horizons imply that penetration of anthropogenic CO2 will result in 70% of
such reef sites experiencing undersaturated waters by the end of this century (Guinotte
et al., 2006).
A third general principle is that wintertime values of surface water pH and Ω tend to
be lower than summer values, in temperate locations experiencing seasonal
stratification and strong spring blooms, such as is the case in most waters around the
UK (Figure 4, Merico et al., 2006). Seasonal stratification (and therefore large annual
variations in pH and Ω) occurs in the northern North Sea but not the southern North
Sea. Much of the English Channel is typically well mixed by tides throughout the year,
whereas the Irish Sea has a mixture of well mixed, stratified and transitional waters
(Pingree and Griffiths, 1978). The consequent probable lack of a sustained post-spring
elevation of Ω in the regions that never fully stratify, such as the southern North Sea,
makes it likely that undersaturation in summer will be reached first in these areas.
How the latitudinal and stratification effects will combine is not well understood.
37
Fig 4.4. Model-calculated relationship between phytoplankton seasonal dynamics and
the carbonate system, in the eastern Bering Sea (Merico et al., 2006).
Calcifying phytoplankton (coccolithophores) include bloom-forming species, most
notably Emiliania huxleyi are particularly common in certain parts of the northeastern
North Atlantic and the northwest European Shelf. Due to their high visibility in
satellite images we have a good understanding of where these blooms do and do not
occur around the UK. Blooms occur frequently in the northern North Sea, but not the
southern North Sea. They also occur in the vicinity of the Scilly Isles, in the Celtic
Sea, Normandy Shelf, Bay of Biscay and along the shelf break including to the west
of Ireland. They have not been seen to occur at all, however, in the Irish Sea. Large
blooms also occur in the western English Channel, to the south of Devon and
Cornwall, but blooms have not been observed in the eastern Channel. Bloom
concentrations occur out towards deeper water to the northwest of Scotland.
Less is known about where calcifying zooplankton (foraminifera and pteropods, for
instance) are abundant in the waters around the UK, although the data collected by the
Continuous Plankton Recorder (CPR) should be ideal for this purpose.
Surface-water corals are restricted to lower latitudes and do not occur around the UK.
Recently-discovered deep-water corals occur along the shelf break to the west and
northwest of Scotland at extensive sites, such as Mingulay Reef, but their full
distribution is unknown.
Shellfish also use calcium carbonate as the building material from which to construct
their shells, including mussels, oysters, barnacles, whelks, clams, winkles, cockles and
scallops. Other commercially important calcifiers include lobsters and crabs (Kleypas
et al., 2006). There is accumulating evidence that many of these organisms could be
affected by declining pH and this is of concern to shellfish industries around the UK.
38
Many other benthic animals also produce shells from calcium carbonate, including the
sea urchin and starfish groups. Impacts on egg production and development, pelagic
larvae and juveniles and their settlement and recruitment have been raised as a
particular concern (Turley et al., 2006) and research in this area is just beginning. The
susceptibility of impacts of a future decline in pH and rise in CO2 to organisms and
ecosystems is of concern and has been reviewed for the OSPAR area in Haugan et al.
(2006).
Acidification and Non-Calcifying Organisms
Impacts on calcification have received more research attention than other processes so
it is tempting to focus on calcification and calcifying organisms. However, reviews of
the impact of ocean acidification (Raven et al., 2005; Haugen et al., 2006) conclude
that most organisms and ecosystems are at potential risk either directly or indirectly
from the chemical changes caused by increasing ocean CO2. Indeed, other key
processes besides calcification, such as primary production, nitrification, nutrient
regeneration may also be impacted. For example, the lower pH expected over the next
100 years can theoretically impact the speciation of many chemical elements
(including oxidation states) (Zeebe and Wolf-Gladrow, 2001; Caldeira & Wickett,
2005). These include key nutrients (N, P, Si) and micronutrients (Fe, Co, Mn etc). For
instance, a decrease in pH of 0.3 units could reduce the fraction of NH3 by around
50% (Raven, 1986). Clearly, unravelling the combined impacts of declining pH on
nutrient concentration and speciation, on nutrient uptake by natural phytoplankton
assemblages, their primary production and composition or their nutritional value to
the organisms that feed on them will be a challenge. There is evidence that rates of
nitrification are sensitive to pH, with a reduction of ~ 50% at pH 7 (Huesemann et al.,
2002). While pH is unlikely to fall to these levels, it does indicate the sensitivity of
the process. This may result in a reduction of ammonia oxidation rates, the
accumulation of ammonia instead of nitrate (that is, increasing the NH4:NO3 ratio).
Depending on the nutrient requirements and uptake abilities of different species this
has the potential to impact the growth and biodiversity of phytoplankton and bacteria.
Indeed, animal physiology is also sensitive to rising CO2, investigations in mussels
from the Mediterranean Sea suggest that the effects on calcification as well as
metabolic depression and the shift in energy allocation occur in parallel (Michaelidis
et al., 2005). These effects are drastic, i.e. a growth reduction by more than 50 % was
found in mussels kept under CO2 at pH 7.3, a pH value expected for the year 2300.
Other investigations show a significant reduction of growth and survival in
echinoderms and gastropods from the Pacific at CO2 concentrations just 180 ppm
(µatm) above today's values. In animals, high CO2 (hypercapnia) can cause changes to
metabolic rate, growth rate, reduced reproductive capability and can result in
mortality. Many of these experiments have been carried out at CO2 levels far higher
than what will occur with ocean uptake of atmospheric CO2. However, little is known
about the impact of the relatively low but long term increases in CO2 on animal and
plant physiology. Juveniles of the few species studied are more sensitive than adults
to the effects of increasing CO2 (Kurihara and Shirayama, 2004) if this occurs widely
drastic impact on ecosystems may occur. Most marine phytoplankton are thought to
have mechanisms to actively concentrate CO2, a carbon concentrating mechanism
(CCM). Some investigations have shown that changes in seawater pH and CO2 have
little (<10%) if any direct effect on their growth rate or their elemental composition
(e.g. Beardall and Raven, 2004; Giordano et al., 2005). However, taxon specific
39
differences in CO2 sensitivity have been observed in laboratory culture (Rost et al.,
2003) it is currently unknown whether a reduction of the advantage of possessing
CCM will impact phytoplankton species diversity in the natural environment. This is a
possibility and, should it occur, may impact the contribution of different functional
groups, primary production, food web structure and marine biogeochemical cycles.
Other important changes to the oceans, besides ocean acidification, are predicted to
occur this century which could have synergistic impacts on marine ecosystems
(IPCC2007). Surface water temperature is already increasing and predicted to increase
further, changes in rainfall and land run off will impact salinity and nutrient input to
coastal seas. Increases in temperature will increase the degree of stratification of the
water column (unless currents and wind mixing increase to balance this) and would
reduce the influx of nutrients from below the thermocline that sustains primary
production. The potential risk of hypoxia or anoxia in shelf sea ecosystems could
increase. The combined impact of ocean acidification and other changes could well
influence the relative composition, productivity, timing, location and predominance of
the major functional groups of phytoplankton, zooplankton and benthic dwelling
organisms and thereby impact the rest of the food web (IPCC 2007). Models that
consider the key interactions of these functional groups and their response to a high
CO2 world are key to making predictions of the overall impact on marine
biogeochemical cycles and food webs. Experimentalists will also need to consider
multi-factorial impacts to help provide information to drive or test the models.
Our conclusion from this brief summary of vulnerability to acidification is that
all UK water will experience declining pH with different regions behaving in
different ways that we do not fully understand. A wide variety of processes and
functional groups are potentially vulnerable to reduced pH or increased
seawater CO2 and we do not yet understand the impacts that this will have. For
these reasons, including the scarcity of data, no spatial prioritisation can yet be
made. Further work is needed on the impact of decreasing pH, increasing
temperature etc on important functional groups and further effort is required on
the development of predictive ecosystem models. A future pH monitoring
strategy would sensibly be part of a programme monitoring other important
changes to UK coastal waters.
40
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