Download Oceanography Lecture 16

“Only those that intend the absurd,
achieve the impossible”
Escher
Dissolved gases in water
Take a break, Grab a soda…
soda…
Let’s assume we have a clear bottle of soda…
You pop the lid ! gas escapes! (pressure)
You shake it ! more gas escapes! (mixing)
You warm it up ! even more gas escapes!
(temperature)
Does it stop?
!When final gas content of soda is at equilibrium
with temperature and pressure
Oceanography
Lecture 16
a. Dissolved gases
b. The chemistry of Life and Biogeochemical
Cycles
c. Nutrient cycles
d. The carbonate system and the Carbon cycle
e. Coastal hypoxia
Dissolved gases in water
Take a break, Grab a soda…
soda…
The total amount of gas that can be dissolved
eventually reaches an equilibrium concentration
which is proportional to:
- Atmospheric concentration of gas in atmosphere
- Temperature,
- Pressure,
- Salinity of water.
The amount of gas usually " as:
P"
T#
S#
Density structure of the Ocean
Oxygen in the Ocean
CO2(gas) + H2O + Energy $ H12C6O6 (sugar) + O2 (gas)
Photosynthesis possible only in photic zone (0-200 m)
Oxygen minimum (utilization) at pycnocline – O2 Minimum
Dissolved gases in the Ocean
Dissolved gases in the Ocean
Temperature is the most important controlling factor!
The most abundant gases in the atmosphere:
- N2 (78%)
- O2 (21%)
- Argon (0.9%)
- CO2 (0.03%)
The most abundant gases in the Oceans:
- CO2 (94.3%). Much more soluble!
- N2 (3.4%)
- O2 (2%)
- Argon (0.3%)
Difference due to the reactivity of CO2 is seawater leading
to the various carbonate and bicarbonate equilibria
CO2(gas) + H2O + Energy $ H12C6O6 (sugar) + O2 (gas)
Photosynthesis only in possible in photic zone (0-200 m)
Oxygen limitation (utilization) at pycnocline – O2 Minimum
CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32-
Dissolved gases in the Ocean
Dissolved gases in the Ocean
Argon and the other noble gases (He, Ne, Kr, and Ra) and
Nitrogen are essentially unreactive in the Oceans:
Conservative gases
In contrast, CO2 and O2 concentrations are altered by many
biological and chemical processes in the sea.
Non-conservative gases
Photosynthesis/Respiration:
CO2(gas) + H2O + Energy % H12C6O6 (sugar) + O2 (gas)
H12C6O6 (sugar) + O2 (gas) % CO2(gas) + H2O + Energy
Defining the Ecosystem
Biology is not the sole subject of ecosystem studies ! The flow of
energy and materials (i.e. water, chemicals) into and out of biological
communities defines the main theme of ecosystem studies
CO2(gas) + H2O + Energy $ H12C6O6 (sugar) + O2 (gas)
Photosynthesis only possible in photic zone (0-200 m)
Oxygen limitation (utilization) at pycnocline – O2 Minimum
Defining the Ocean Ecosystem
There exists an inseparable relationship between the flow of energy and
the flow of nutrient elements (i.e. N, P, K, Ca, etc)
Biogeochemical Cycles
Chemical Elements (the Periodic Table)
and those essential for life
" Of the 103 elements
in the Periodic Table,
only 24 are required
by organisms
" Macronutrients:
Required in large
amount (“Big Six”
Six”:
C, N, P, S, O, H)
" Micronutrients: small
or moderate amount
Required elt
A simple thing, really…
Chemical Elements - Essential for life
Carbon
" Carbon forms three-dimensional molecules of large size and
complexity in organic (carbon-containing) compounds that form
large molecules (amino acids, sugars, enzymes, DNA), and other
chemicals vital to life on Earth.
Required for some life forms
Toxic elt
Chemistry of Life…
Element
Major Components
Carbon
Oxygen
Hydrogen
Nitrogen
Macronutrients
Phosphorus
Sulfur
Calcium
Silicon
Sodium
Magnesium
Chlorine
Potassium
Iodine
Micronutrients
Iron
Copper
Zinc
Symbol
C
O
H
N
P
S
Ca
Si
Na
Mg
Cl
K
I
Fe
Cu
Zn
Representative Use
>100,000 of every M atoms
All organic molecules
Almost all organic molecules
All organic molecules
Proteins, Nucleic acids
1,000 < per M atoms <100,000
Nucleic acids, teeth/bones/shell
Proteins, cell division
Shell, bone, coral, teeth
Hard parts
Body fluids, osmotic regulation
Osmotic regulation, chlorophyll
ATP formation, nerve discharge
Nerve discharge, osmotic balance
Thyroid hormone
< 1,000 of every M atoms
Electron transport, N assimilation
Electron transport
Nucleic acid replication
Chemical Elements - Essential for life
Nitrogen
" Nitrogen (along with carbon) is the essential element that
allows formation of amino acids (! proteins) and DNA.
Proteins contain up to 16% N
Chemical Elements - Essential for life
Carbon:Nitrogen:Phosphorus Ratios
" Organisms actively concentrate certain elements essential for
life: ! Algae concentrate Iron (Fe) 100,000 times vs. its
concentration in the Ocean
• Most organisms keep a rather
constant chemical composition
! Algae and plankton C:N:P
ratio of 106:16:1 (Redfield
Ratio)
! Soil microbes maintain a
relatively constant proportion of
nutrients in their biomass (and
at higher levels than the OM
they decompose)
Chemical Elements - Essential for life
Phosphorus
" Phosphorus is the “energy element”
element” occurring in compounds
called ATP and ADP important for energy transfer processes
and DNA.
Chemical Elements - Essential for life
• Availability of some elements (particularly N & P) is often
limited and the supply of these elements may control the rate
(or type) of primary production in ocean ecosystems.
• External sources of nutrients are varied and depend of
nutrient ! Annual circulation dominates most inputs of limiting
elements (N, P, K)
Biogeochemical cycles in the Ocean
The carbonate system and the Carbon cycle
CO2(gas) dissolves readily in water and forms carbonic acid
(H2CO3). However, at pH of natural waters, carbonic acid
equilibrates as bicarbonate (HCO3-: 80%)
CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32-
CO2(gas) + H2O + Nutrients (N,P) + Energy $ OM + O2 (gas)
The carbonate system and the Carbon cycle
The carbonate system and the Carbon cycle
Ca+ + CO32- $ CaCO3 (solid)
Formation of CaCO3 skeleton parts by micro-organisms as
hard part: ! foraminifers, coccolithophorids, pteropods
to precipitate CaCO3.
CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- + Ca2+$ CaCO3
The carbonate system and the Carbon cycle
Ca+ + CO32- $ CaCO3 (solid)
Ocean surface waters are nearly everywhere
supersaturated with respect to calcium carbonate.
However, no spontaneous precipitation occurs! (inhibition
from Mg2+ in solution)
!Intervention of marine organisms (foraminifers,
coccolithophorids, pteropods) to precipitate CaCO3.
- CaCO3 dissolves readily with decreasing temperature and
increasing pressure. Also,
- Calcite and Aragonite have the same formula but
different crystalline structure. Aragonite is less stable.
The carbonate system and the Carbon cycle
Where should you find carbonate sedimentation?
Where should you not find it?
The carbonate system and the Carbon cycle
As organic matter (OM) “rains”
to the sea floor, it is mostly
degraded (>90% regeneration!)
! production of CO2
! increased formation of acid
! increased dissolution of
carbonates!
CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- $ CaCO3
Where should you find carbonate sedimentation?
Where should you not find it?
The carbonate system and the Carbon cycle
Carbonate Compensation Depth (CCD): the depth at
which all carbonates have dissolved
! The CCD is shallower for Aragonite that for calcite
CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- $ CaCO3
CO2(gas) + H2O $ H2CO3 $ H+ + HCO3- $ H+ + CO32- $ CaCO3
The Carbon cycle
•Different timescales
•Most C in
carbonate rocks
(85%)
•Second largest
reservoir in soil
and sediment OM
(15%)
•Dissolved C in
Oceans (0.08%)
•Fossil fuels
(0.02%)
•Additional less
significant
reservoirs
(Atmosphere,
Biosphere, etc)
• General
equilibrium: 75%!
Dissolved (trace) nutrients in the Ocean
Phosphorus
Nitrogen
Biogeochemical cycles in the Ocean
CO2(gas) + H2O + Nutrients (N,P) + Energy $ OM + O2 (gas)
The silicon cycle
Silicon behaves like a nutrient
! Minor element
! essential for formation of
frustules
! undersaturated in the Oceans
! Micro-organisms (diatoms,
radiolaria) can still use it!
! More soluble in cold waters.
! No Compensation Depth: Slow
dissolution despite
undersaturation!
! General equilibrium: 10%!
CO2(gas) + H2O + Nutrients (N,P) + Energy $ OM + O2 (gas)
Where should you find silicate sedimentation?
Where should you not find it?
Hardness and detergents
Distribution of Ocean Sediments
The hard and soft appellation of waters reflect the fact that doubly charged
Ca2+ and Mg2+ ions can precipitate detergents (molecules with long hydrocarbon
chains and polar head groups)
Detergents are excellent cleanser because of their ability to act as emulsifying
agents (an emulsifier is capable of dispersing one liquid into another immiscible
liquid).
Disadvantages: As salts of weak acids, they are
converted by mineral acids into free fatty acids:
CH3(CH2)16CO2-Na+ + HCl ! CH3(CH2)16CO2H + Na+ + Cl-
Soaps form insoluble salts in hard water, such as water
containing magnesium, calcium, or iron:
2 CH3(CH2)16CO2-Na+ + Mg2+ ! [CH3(CH2)16CO2]2Mg2+ + 2 Na+
Where should you find silicate sedimentation?
Where should you not find it?
Hardness and detergents
Phosphorus Control Measures
A U.S. Case Study
Addition of chelating agents (builder) can bind with cations
through multiple bonds. Particularly effective chelating agents:
The first is a limiting nutrient, the other two biodegrade slowly
(T dependent) and mobilize toxic chemical!
Sodium Tripolyphosphate
(STP)
Nitrilotriactetic acid
(NTA)
EDTA
Source: USGS 1999
•
•
As more States passed detergent-bans legislation, the industry was faced with
maintaining duplicate inventories of detergent around the Nation and ultimately
decided (cost effective) to phase out phosphorus use in domestic detergents
Phosphates are still permitted in dishwashing detergents and industrial cleaning
agents.
Phosphorus Control Measures
A U.S. Case Study
Phosphorus Control Measures
A U.S. Case Study
Source: USGS 1999
Source: USGS 1999
•
•
As more States passed detergent-bans legislation, the industry was faced with
maintaining duplicate inventories of detergent around the Nation and ultimately
decided (cost effective) to phase out phosphorus use in domestic detergents
Phosphates are still permitted in dishwashing detergents and industrial cleaning
agents.
Phosphorus Control Measures: A U.S. Case Study
•
•
Only about 15% of municipal waste-water treatment plants (~40% of total
municipal waste-water discharge) were required to monitor phosphorus
Only 7% have phosphorus limitations (0.5-1.5 mg/L) through tertiary treatment!
Non-Point Sources of Phosphorus
Phosphorus from manure and commercial fertilizers
•
•
Phosphate ban reduced annual loads to Lake Erie (&86%) and Chesapeake Bay (&
(&
55%)
Temporal trend in declining phosphorus levels in surface waters (except Southeast).
However, at least one third of all hydrological units studied showed more than 1/2 of
total phosphorus concentrations exceeding the EPA recommended limit in flowing
waters (0.1 mg/L)
Coastal Hypoxia
Nutrient over-enrichment from anthropogenic sources is one of the major
stresses impacting coastal ecosystems. Generally, excess nutrients lead
to eutrophic conditions and increased algal production which in turn
increases the availability of organic carbon within the aquatic ecosystem.
Gulf Coast Hypoxia
Nitrogen is the most significant nutrient controlling algal growth in coastal
waters, while phosphorus is the most significant nutrient in fresh water
Both the near-coastal hydrodynamics that generate water column
stratification and the nutrients that fuel primary productivity contribute
to the formation of hypoxic zones. Human activities on land can add
excess nutrients to coastal areas or compromise the ability of
ecosystems to remove nutrients either from the landscape or from the
waterways themselves.
(source: USGC)
Coastal Hypoxia
Coastal Hypoxia
Gulf of Mexico: a large area of the Louisiana continental shelf with seasonallydepleted oxygen levels (< 2mg/l). Most aquatic species cannot survive at such low
oxygen levels. The oxygen depletion (hypoxia) begins in late spring, reaches a
maximum in midsummer, and disappears in the fall. After the Mississippi River
flood of 1993, the spatial extent of this zone more than doubled in size, to over
18,000 km2, and has remained about that size each year through midsummer 1997.
The hypoxic zone forms in the middle of the most important commercial and
recreational fisheries in the coterminous United States and could threaten the
economy of this region of the Gulf.
Estimated areal extent of bottom water hypoxia from mid-summer
cruise in the period 1985-1999
20
103 km2
15
10
5
0
(source: Louisiana Universities marine Consortium)
Gulf Coast Hypoxia
Gulf Coast Hypoxia
Long-term record of drainage basin changes:
Nitrogen yields from the Mississippi River Drainage Basin
About 56% of the nitrate transported to the Gulf enters the Mississippi
River above the Ohio River. The Ohio basin subsequently adds another
34% of the nitrate load.
106 metric tons/year
a) annual amount of fertilizer application
106 of acres
b) area artificially drained
1900
1920
1940
1960
1980
2000
Gulf Coast Hypoxia
On average, 61% of the nitrogen load is nitrate; 24% is dissolved organic nitrogen.
The most significant nutrient trend has been nitrate loads, which have almost
tripled from 0.33 million metric tons per year during 1955-70 to 0.95 million
metric tons per year during 1980-96
2.5
30
Streamflow
25
2.0
Organic N
1.5
20
1.0
15
Nitrate
10
0.5
1950
1960
1970
1980
2000
That’s it folks…