An inverse model study of abrupt climate change during last ice age

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Title: An inverse model study of abrupt climate change during last ice age
Author: Lu, Shaoping
Abstract: Geologic records and climate model simulations suggest that changes in the meridional heat transport in the Atlantic Ocean were involved in the abrupt warming events – the so -called Dansgaard -Oeschger Interstadials (DOIs ) – that punctuated an otherwise cold Greenland climate during the last glacial period . However , the role of Northern Hemisphere (NH ) ice sheets in these events remains a subject of controversy . Here we report on the first attempt to combine quantitatively a paleo -temperature proxy with simplified ocean models , with the specific purpose of extracting information about the changes in mass balance of the NH ice sheets during the last glaciation . A Greenland paleotemperature record is combined with the climate models using Bayesian Stochastic Inversion (BSI ) in order to estimate the changes that would be required to alter the Atlantic Ocean mass and heat transports between ~30 and 39 thousand years ago . The mean sea level changes implied by changes in NH ice sheet mass balance agree in amplitude and timing with reconstructions from the geologic record , which gives some support to the freshwater forcing hypothesis . Our results are unaffected by uncertainties in the representation of vertical buoyancy transport in the tropical ocean , in large part because the global adjustments to high latitude freshening bypass the tropics and affect sinking rate in the opposite pole . However , the solutions are sensitive to assumptions about physical processes at polar latitudes . We find that the inversion reproduces the gradual changes in sea level and Antarctic temperature inferred from the independent evidence provided by proxy records . The Greenland warm event lasting over 3000 years (DOI 8 ) can be explained by sustained growth of NH ice sheet and reduced supply of icebergs to the North Atlantic . Our results indicate a more involved role of the NH ice sheets than previously thought , in which both collapse and subsequent growth would be required to explain the full series of the long ( > 3000 years ) warm events recorded in Greenland ice .
URI: http : / /hdl .handle .net /2152 /ETD -UT -2010 -12 -2041
Date: 2011-02-02

Citation

An inverse model study of abrupt climate change during last ice age. Doctoral dissertation, University of Texas at Austin. Available electronically from http : / /hdl .handle .net /2152 /ETD -UT -2010 -12 -2041 .

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