Paleo-precipitation and water isotopes 10/14/10

Archives of interest:1) ice cores2) deep-sea sediments3) lake sediments4) corals5) speleothems6) groundwaters7) 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 Seaare both semi-enclosed, evaporative basins

growing glaciersdeep-seaforaminifera

Water isotopes in deep-sea cores

The “Ice Volume” effect-Light isotope removed from ocean, locked intolarge ice sheets. Ocean δ18O shift (+1.5‰) recordedin marine carbonates that grew during glacial.

SPECMAP – standard benthic δ18O record,used to date marine sediments of unknown age

Ex: EPICA – a new LONG Antarctic ice core

Augustin, L. et al

Water isotopes in ice cores

Also applied to:Greenland δ18O – GISP, Jouzel et al.,

Andes δ18O, Lonnie Thompson

Alaska δ18O,Ken Moore

and others

Pore fluids – glacial ocean water δ18O

glacialenrichment

advectiondrives waterout of compacting sediments

diffusion works toerase pulsesignal

&

Need to modelpore fluid profilesbecause:

Goal: to quantify the glacial-interglacial change in seawater δ18O; Result = +0.7-0.8‰

Red Sea δ18O – high-resolution sea level history

Theory: when sea level is high, Red Sea well-mixed with light ocean waterwhen sea level is low, Red Sea dominated by evaporation, heavy δ18O

Siddall et al., Nature, 2003red and black = Red Sea benthic foraminfera δ18Ogreen = corals from ocean islands (Cutler et al., 2003)blue = Chappell (2002) scaling deep-sea benthic foram δ18O to sea level

Coral records of paleo-precipitation

Theory: 1) more rain = lighter δ18O“amount” effect2) surface seawater δ18O will become lighter3) coral δ18O lighter

Cole and Fairbanks, 1990

Water isotopes in speleothems (cave stalagmites)

Theory: 1) δ18O of speleothem = δ18O of precipitation2) δ18O 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

temperatetree ring

tropicaltree ring

Theory: δ18O of cellulosewill track the seasonal cyclefrom dry to wet seasons (monsoon)

Water isotopes in tree rings: promising but still potential

seasonal signal

ENSO signal

Evans et al., 2005

and White, 1989

Water isotopes in ecology

Goal: to use isotopes to understandhow water is cycled through abiotic system

Ex: δD 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

For more information see:Stable Isotopes in Ecological Systems, ed. by P. Rundel, J.R. Ehleringer and K.A. Nagy, Springer-Verlag, 1989

Bender, 1994

Water isotopes in ecology

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 enrichmentsover large tropicalcontinents

TES retrievals of q and δD: obs versus modeled

blue = Raleighdistillationorange = pureevaporation

black = vapor in equil w/ ocean water

red = clear sky (dry)blue = cloudy sky (wet)

key results:1)tropical oceanscharacterized by recycled moisture(high q, low δD)

2) tropical continentscharacterized bymore enrichedmoisture (evapotrans?)