Download Document

Early history of Earth in 1 slide
HallidayNature
409,2001
Impact hypothesis of Moon origin
1 hour
5 hours
•Moon contains no volatile elements H,C,N
•Moon has much less iron, object impacted differentiated Earth
1000 years
•Oxygen isotope relative abundance same for Earth and Moon
4.1 Ga-oldest rocks on Moon, stabilized by by 3 Ga
What about the origin of the oceans? Likely DEGASSED, with some
Addition from chondrites and comets. :Website that discusses both.
http://www.oceansonline.com/ocean_form.htm
Paleoclimate Overview
Longest instrumental climate record: Central England
Air Temp From 1659 to the present
Peter_Almasi/Spring_2003/Orals_Study_Group
Climate history of the Earth
•Solar output has decreased as CO2 increased
•Temperature has remained suitable for liquid water over most of
Earth history
Climate: Tertiary to Present
Magnitudes of Climate Variability
History of Pleistocene Study
Observations of: climatically displaced faunas
Sedimentary processes no longer occurring
Moraines,
DILUVIALISTS: Biblical Noachian deluge. Poles flooded icebergs
rafted boulders "CATASTROPHIST" abrupt, unique event "DRIFT”
implies water transport for sediments: till, erratics
GLACIALISTS: Glacial Expansion. Emphasis on Uniformitarianism
(James Hutton). Called on existing natural processes.
Louis Agassiz - Swiss zoologist-paleontologist July 24, 1837
Presidential address, Swiss Society of Natural Science.
European Environmental Sequence
Penck and Brueckner, 1909
North American Environmental Sequence
Pollen diagrams
Function of Production, Dispersion, Preservation, Identification
Surface samples provide calibration of pollen-climate relationship
Southwestern US
Ocean Sediment Cores
Cores at Deep Sea Sample Repository at Lamont
Ocean Sediment Cores2
•Accumulation rate ranges from 0.21 to 40 cm/ka in open ocean
•Low sed rate in deep Pacific, high in Atlantic and on margins
•1872 H.M.S Challenger: first oceanographic expedition
•1950s Maurice Ewing at Lamont: “A core a day.”
•Composed of clays (~95%), biogenic tests, volcanic ash, dust
and ice-rafted debris (IRD)
Methods of Dating Marine Records
•Radiocarbon 0-~45,000 years, calibrated by 14C in tree rings (to 13ka)
and U-Th in annually-banded corals
•d18O correlation with ice cores GISP2 or GRIP (very common)
•Tuning a d18O record assuming periodic orbital forcing of climate
(Milankovitch cyclicity). SPECMAP chronology of Doug Martinson
et al. (1987) of Lamont-Doherty
•Paleomagnetic reversal chronology: Bruhnes-Matuyama at 730 ka
•Volcanic Ash Layers (Vedde Ash in North Atlantic at 9.8 ka (14C)
Oxygen isotopes in foraminifera
99.7% 16O
(18O/16O) sample - (18O/16O) SMOW
del 18O =
\--------------------------------------------x 1000‰
0.2% 18O
(18O/16O) SMOW
17
0.04% O
Controlled by Temperature, Salinity, and Global ice volume
•Temperature control on fractionation during calcite precipitation
d18O increases 0.22 ‰ per degree C cooling
•d18O of ocean water increased 1.2 per mil during glaciations due to
16O sequestration in continental ice sheets
•Formation of sea ice only mildly fractionates oxygen isotopes,
but does increase Salinity of water, so d18O/Salinity varies
T=16.9-4.30(d18Oc-d18Ow)
d18O-Salinity relationship is variable
What if it also
varies with
time?
Schmidt,
GRL 2002
Oxygen isotope stratigraphy
I,II,III Glacial terminations
1-9 Marine isotope stages (MIS) and a-d (substages)
Emiliani, 1955 Classic Paper
Doug Martinson at Lamont, Quaternary Research (1987)
Insolation at 65 degrees N
Insolation 65 deg. North
560
540
520
In so lation (W/m2)
500
480
460
440
420
400
0
25000
50000
75000
100000
125000
Years BP
Constructed using the calculations of Laskar, 1993
150000
175000
200000
225000
250000
Onset of glaciation 2.57 Ma
Cooling begins at 3 Ma, but ice-rafted debris appears in North Atlantic
by 2.57 Ma.
Raymo, 1992
Foraminiferal Transfer Functions
Group living fauna into assemblages
A-tropical B-subtropical
C-subpolar
D-polar X-gyre margin assemblage
Multivariate Regression
Tw = 23.6A + 10.4B + 2.7C + 3.7D + 2.0K (K=constant)
CLIMAP and COHMAP
Reconstruction of LGM climate using d 18O and faunal transfer functions
CLIMAP-1970s, 1980s comparison
of LGM and present climate from
COHMAP models climate LGM to
the present and compares with proxy
data
CLIMAP SST data
CLIMAP conclude that tropical cooling during LGM was 0-2 degrees.
This is in conflict with MOST modern proxy reconstructions
Mg/Ca Paleothermometry
Measured in planktic and benthic foraminifera
Provides the planktic or benthicwater temperature to calculate
salinity changes using d 18O
As with d18O, small analytical error
Mg/Ca complications
•Insensitive at low temperatures
•Calcification depth may vary for planktic
forams; also an issue for d18O
•Foram population varies seasonally
•Heterogeneous Mg/Ca within foram test
Post-depositional dissolution DECREASES
Mg/Ca resulting in T too COLD
Mg/Ca calibration
Lab culture or core top calibrations
Elderfield Nature 2000
Paleothermometer comparison
Xfer functions
Nurnberg Paleoceanography, 2000
Alkenone Paleothermometry
Linear realationship between Uk37 and T (Prahl et al. 1988)
Uk37 index based on ratio of certain saturated vs. unsaturated ketones
found in organic matter of coccolithophores. (E. huxleyi)
Alkenones support small cooling of tropics during the glacial.
Issues: Coccoliths are very small (~15-30 µm) and may be transported
If season of their bloom changes, they will record different T.
Thermohaline Circulation
and North Atlantic Deep Water
•North Atlantic climate
experiences such strong
variability relative to other
regions because of variable
ocean heat transport.
•This transport may be affected
within decades, causing abrupt
jumps in Greenland ice and
North Atlantic climate records.
Great Ocean Conveyor
•Thermohaline circulation transports heat and salt to North Atlantic,
warming eastern North America and northern Europe. Gordon (1986)
•Involvement in abrupt climate change recognized by Wallace Broecker
of Lamont-Doherty in the late-eighties (1987,1991)
Benthic 13C distribution as water mass tracer
Charles and Fairbanks, 1992
13C/PO
4
1.5
relationship in forams
 13
C
NADW
as =
0
 13
C
Re
df
ie
as =
0
ld
as =
.5
as =
1
1.
.5
WSBW
Sl
op
e
CDW
0.5
VP
0.0
Bio
lo
gy
Air-Sea Exchange
1 3 C (PDB)
1.0
.
 13
C
 13
C
-0.5
1.0
1.5
AP, SP
 13
C
as =
 13
C
-1
as =
.5
2.0
PO4 (mol kg-1)
2.5
-0
.
5
3.0
Atmospheric d13C is -8.5, so invasion of atmospheric CO2 with a
temperature decrease lowers d13C of water before isotopic equilibrium,
which will eventually raise d13C.
Lynch-Stieglitz et al. 1994
Cd/Ca ratio as a nutrient tracer
Cd/Ca is promising
because it decoupled
from the air-sea effects
which strongly affect 13C
McIntyre GBC 1997
Uncertainties with foram proxies
Paleotemperature: Calcification depth may vary with climate.
Forams calcify while sinking to ocean floor
Paleonutrients: Air-sea exchange high and variable in Nordic Seas affect
d13C.
Cd/Ca is subject to contamination, requiring large
samples and involved sample preparation
Vital effects: Calcification rate can vary with light, nutrients,
salinity and temperature.
This is species and environment specific.
Foraminifera may be transported by fast ocean currents, sea ice
Ice-Rafted Detritus (IRD)
Concentration of IRD in sediment is related to amount of drifting ice.
Generally, MORE IRD in core = COLDER
•Grain size 63 microns and above
•Can trace iceberg or sea ice provenance
•Drifting ice responds to winds and
temperature
•The 1500-year cycle in North Atlantic
defined by specific IRD grain
percentages
Bond et al. (1997)
•Largest down-core variations are in
Heinrich events of the North Atlantic
Terrestrial Climate Records
Ice Cores-paleotemperature and atmospheric gases
Uplifted marine terraces-sea level
Loess-atmospheric response to climate change, vegetation changes
Varves-alluviation, productivity, vegetation changes
Speleothems-cave deposited calcite-paleotemperature
Ice Cores
Records available: d18O (precipitation temperature), CO2, CH4
Sea salt Na (local storminess), non sea-salt K (terrestrial dust),
cosmogenic 36Cl, 10Be (solar magnetic activity)
Caveats:
•Dating is an issue
(layer counts and
flow modeling)
•Gas bubble
inclusion depth
complicates
correlation between
different ice cores
Hemispheric
comparisons in ice
core
records
•GHG positive feedback likely
responsible for climate
connection between the
hemispheres
•Glacial-interglacial climate
changes are synchronous, while
higher frequency events appear
ANTIPHASED. This is the
“bipolar seesaw” idea of
Broecker (1998)
Ice core record of greenhouse gases
Raynaud
QSR 19
2000
GHGs are associated with climate changes. Do they force or respond?
Most believe it is an ocean carbon cycle positive feedback to
externally-forced climate changes.
YD and ACR
appear
anti-phased
The bi-polar seesaw:
If poleward heat
transport is shut down
in North Atlantic, heat
builds up in tropics,
southern ocean deep
water and thus local
climate are warmed.
Broecker, 1998
Sea Level Reconstructions
BarbadosTerraces, Chappell et al. EPSL (1996)
Huon Pensinsula, New Guinea; Esat et al.,Science (1999)
Chinese Loess (wind transported silt)
Climate Sensitive Parameters
•Maximum Grain Size
•Magnetic Susceptibility
George Kukla of Lamont found glacial-interglacial cycles in Czech
loess in the 1970s Kukla (1970)
Varves
Annually-deposited sediment
MECHANICAL- coarse layers/fine layers
-sediment color
Used in Paleo ENSO reconstructions
BIOLOGICAL- Diatoms and Foraminifera
Bog and Lake
Pollen Records
Oxygen Isotopes in Speleothems
(Cave deposited Calcite)
Timing of interglacial events raised questions of accuracy of ocean core
d 18O and ice core dating methods.
Lichenometry
Lichen grow slowly. Growth
curves are developed with local
calibration.
•Used in surface exposure dating
Dating moraines and flood
deposits
Rhizocarpon geographicum
Tree ring width
Esper et al., Science 2002 used better de-trending techniques to reveal
larger variability for MWP and LIA than before. Solar minima
obvious, especially the Maunder Minimum from 1650-1710 AD.
Red curve is the Mann et al. Nature 1999 reconstruction used by IPCC
Particular Events in Paleoclimate
The Little Ice Age
•Cooling in Europe of
around 1 degree C.
•Marked by large climate
extremes both cold and warm
•Associated with solar minima
Winter market on the Thames, London
Grove, 1988
Dansgaard-Oeschger Events in MIS 3
GRIP members, Nature 1993
Caused by a threshold thermohaline circulation responsein the glacial.
Distinctive ramping structure to a strong cooling, then rapid warming.
(“Bond cycles”)
Climate Impact of Heinrich and D-O events
Broecker and Hemming, 2001
Tropical Climate during LGM
• COHMAP: Climatic change in tropics was minimal: 0 - 2 C
•Current thinking: 3 - 6 oC colder in tropics, 12-16 C at poles
•snow lines 1000 m lower in tropics (Rind & Peteet, 1985)
•tropical glaciers 18O/16O indicate 8 - 12 C colder (Thompson et al., 1995)
•vegetation zones lower in Brasil (Clapperton, 1993)
•ocean coral Sr/Ca ratios indicate 6 C colder (Stiute et al., 1995)
•heat transport by oceans (8.2-4.6 C) colder (Webb et al 1997)
Paleo ENSO reconstructions
Solar influence in the Holocene
Cooling in the North Atlantic is closely associated with proxies of
cosmic ray variability 14C and 10Be.
It is highly unlikely the records of 14C and 10Be are influenced by
climate.
Solar modulation of cosmic ray flux
•Irradiance may vary by up to 0.35% during Holocene millennial cycles.
(Lean et al., 1995; Hoyt and Schatten, 1993)
•Or maybe solar magnetic activity is de-coupled from irradiance.
Lean, GRL (2002)
•The mechanism to amplify this miniscule forcing not known.
Juerg Beer, Spatium 2001
Paleoclimate References
Excellent paleoclimate reviews articles and references
Quaternary Ecology Lecture Notes:
Owen K. Davis at the University of Arizona
The source for many of these figures. Excellent, detailed information
http://www.geo.arizona.edu/palynology/geos462/
Rahmstorf, S. ( 2002). Ocean circulation and climate during the past 120,000 years.
Nature 419, 207-214.
Clark, P. U., Pisias, N. G., Stocker, T. F., and Weaver, A. J. (2002). The role of the
thermohaline circulation in abrupt climate change. Nature 415, 863-869.
Bradley, Raymond 1999. Paleoclimate. Academic Press