Book 2.indb - US Climate Change Science Program

The U.S. Climate Change Science Program Chapter 4Figure 4.14. Comparison of simulated changes in response to the weakening of the AMOC using the Geophysical Fluid Dynamics Laboratory(GFDL) coupled model (CM2.0) with paleorecords. Upper left (from Zhang and Delworth, 2005; used with permission, copyright 2005,American Meterological Society): Simulated summer precipitation change (color shading, units are m yr –1 ) and surface wind change (black vectors)over the Indian and eastern China regions. Upper right (Zhang and Delworth, 2005): Simulated annual mean precipitation change (colorshading, units are m yr –1 ) and sea-level pressure change (contour, units are hPa). Negative values correspond to a reduction of precipitation.Lower left (Altabet et al., 2002): The δ 15 N records for denitrification from sediment cores from the Oman margin in the Arabian Sea weresynchronous with D-O oscillations recorded in Greenland ice cores (GISP2) during the last glacial period, i.e., the reduced denitrification,indicating weakened Indian summer monsoon upwelling, occurred during cold Greenland stadials. Lower right (Wang et al., 2004): Comparisonof the growth patterns of speleothems from northeastern Brazil (d) with (a) δ 18 O values of Greenland ice cores (GISP2), (b) Reflectance ofthe Cariaco basin sediments from ODP Hole 1002C (Peterson et al., 2000), (c) δ 18 O values of Hulu cave stalagmites (Wang et al., 2001; usedwith permission from Science). The modeled global response to the weakening of the AMOC (Zhang and Delworth, 2005) is consistent withall these synchronous abrupt climate changes found from the Oman margin, Hulu Cave, Cariaco basin, and northeastern Brazil during coldGreenland stadials, i.e., drying at the Cariaco basin, weakening of the Indian and Asian summer monsoon, and wetting in northeastern Brazil(red arrows). Abbreviations: %, percent; ‰, per mil; SMOW, Standard Mean Ocean Water; kyr, thousand years ago; H1, H4, H5, H6, Heinrichevents; W m –2 , watts per square meter; nm, nanometer; m yr –1 , meters per year; hPa, hectoPascals.152