Paleo-precipitation and water isotopes
10/14/10
Archives of interest:
1)
2)
3)
4)
5)
6)
7)
ice cores
deep-sea sediments
lake sediments
corals
speleothems
groundwaters
tree rings?
Primary goal:
1) To reconstruct (and hopefully quantify)
environmental changes in the past
Secondary goal:
2) To use isotopes as tracers to study
transport mechanisms and processes
The Eastern Meditteranean and the Red Sea
are both semi-enclosed, evaporative basins
Water isotopes in deep-sea cores
growing glaciers
deep-sea
foraminifera
The “Ice Volume” effectLight isotope removed from ocean, locked into
large ice sheets. Ocean 18O shift (+1.5‰) recorded
in marine carbonates that grew during glacial.
SPECMAP – standard benthic δ18O record,
used to date marine sediments of unknown age
Water isotopes
in ice cores
Ex: EPICA –
a new LONG Antarctic ice core
Augustin, L. et al
Also applied to:
Greenland 18O – GISP,
Jouzel et al.,
Andes 18O,
Lonnie Thompson
Alaska 18O,
Ken Moore
and others
Pore fluids – glacial ocean water 18O
Goal: to quantify the glacial-interglacial change in seawater 18O; Result = +0.7-0.8‰
Need to model
pore fluid profiles
because:
advection
drives water
out of
compacting
sediments
&
diffusion
works to
erase pulse
signal
glacial
enrichment
Red Sea 18O – high-resolution sea level history
Theory: when sea level is high, Red Sea well-mixed with light ocean water
when sea level is low, Red Sea dominated by evaporation, heavy 18O
Siddall et al., Nature, 2003
red and black = Red Sea benthic foraminfera 18O
green = corals from ocean islands (Cutler et al., 2003)
blue = Chappell (2002) scaling deep-sea benthic foram 18O to sea level
Coral records of paleo-precipitation
Theory: 1) more rain = lighter 18O
“amount” effect
2) surface seawater 18O
will become lighter
3) coral 18O lighter
Cole and Fairbanks, 1990
Water isotopes in speleothems (cave stalagmites)
Theory: 1) 18O of speleothem = 18O of precipitation
2) 18O of precipitation fxn of temperature (mid- to high-latitudes)
and/or amount of rainfall (low latitudes)
Wang et al., Science , 2001
Water isotopes in tree rings
temperate
tree ring
tropical
tree ring
Theory: 18O of cellulose
will track the seasonal cycle
from dry to wet seasons (monsoon)
Water isotopes in tree rings: promising but still potential
seasonal signal
Evans et al., 2005
ENSO signal
Water isotopes in ecology
Goal: to use isotopes to understand
how water is cycled through a
biotic system
Ex: D in trees
-photosynthesis occurs in leaf
-leaf experiences evaporative
enrichment
-photosynthetic reactions cause
large depletion in products
-by careful mass balance you can
study the movement of
water through this system
and White, 1989
For more information see:
Stable Isotopes in Ecological Systems,
ed. by P. Rundel, J.R. Ehleringer and K.A. Nagy,
Springer-Verlag, 1989
Water isotopes in ecology
Bender, 1994
The future of water isotopes: satellite retrievals of water vapor
Worden et al, 2007
TES retrievals of water vapor content (q) and isotopes (δD)
key observations:
1) tropics are moist
and enriched
2) largest enrichments
over large tropical
continents
TES retrievals of q and δD: obs versus modeled
black = vapor in
equil w/ ocean water
blue = Raleigh
distillation
orange = pure
evaporation
red = clear sky (dry)
blue = cloudy sky (wet)
key results:
1)tropical oceans
characterized
by recycled moisture
(high q, low δD)
2) tropical continents
characterized by
more enriched
moisture (evapotrans?)