Hydroclimate footprint of pan-Asian monsoon water isotope during the last deglaciation

Abstract

Oxygen isotope speleothem records exhibit coherent variability over the pan-Asian summer monsoon (AM) region. The hydroclimatic representation of these oxygen isotope records for the AM, however, has remained poorly understood. Here, combining an isotope-enabled Earth system model in transient experiments with proxy records, we show that the widespread AM δ18Oc signal during the last deglaciation (20 to 11 thousand years ago) is accompanied by a continental-scale, coherent hydroclimate footprint, with spatially opposite signs in rainfall. This footprint is generated as a dynamically coherent response of the AM system primarily to meltwater forcing and secondarily to insolation forcing and is further reinforced by atmospheric teleconnection. Hence, widespread δ18Op depletion in the AM region is accompanied by a northward migration of the westerly jet and enhanced southwesterly monsoon wind, as well as increased rainfall from South Asia (India) to northern China but decreased rainfall in southeast China.

Abrupt Heinrich Stadial 1 cooling missing in Greenland oxygen isotopes

“…This apparent lack of  18 O response over Greenland has led to the speculation that Greenland did not cool during HS1, implying a decoupling of the Arctic from hemispheric climate trends (16). Here, combining climate proxies with transient isotopeenabled climate model simulations, we resolve this puzzle and suggest that the HS1 cooling did occur but was not recorded in ice core  18 O.…”

“…We perform a set of four simulations with four realistic forcing factors (Fig. 1A) applied additively: first, ice sheet and bathymetry (ICE), then insolation (ICE+ORB), the greenhouse gases (ICE+ORB+GHG), and, last, meltwater fluxes (ICE+ORB+GHG+MWF) or iTRACE, for the isotope-enabled transient climate experiment (18).…”

“…We decompose the ice core  18 O change approximately into the changes in annual isotopic composition  18 effect with a large temporal slope of ∆ 18 O ann /∆T ~ 1‰ K −1 , characterized by an abrupt isotopic depletion at the HS1 onset and clear BA/YD events. However, precipitation seasonality P S compensates the  18 O ann change such that the total  18 O variability is suppressed relative to  18 O ann over Greenland (Fig. 2A).…”

“…Greenland ice core  18 O of water isotopes is a commonly used proxy for site temperature due to the "temperature effect" (4) and has been considered as a key index that records abrupt climate changes around the Arctic region. However, Greenland  18 O fails to differentiate the DO and Heinrich stadials from similar  18 O levels in Heinrich stadials and regular DO stadials. This contrasts proxies for Atlantic circulation and temperature (5,6) and Asian monsoon (7) that show clearly distinct signatures of the Heinrich stadials.…”

Thermodynamics control precipitation in NE Mexico on orbital to millennial timescales

“…The model tracks stable water isotopes of oxygen and hydrogen through all model components. Previous studies demonstrate that the water isotope tracer components of iCESM1 can accurately simulate the δ 18 O distribution of both present (Nusbaumer et al, 2017) and past climates (He et al, 2021).…”