P2C2: Dry or Wet in East Asia During Heinrich Events? New Perspectives from Multiproxy Cave Records and Coupled Model Simulations

点击翻译按钮获取中文摘要

This project aims to disentangle large-scale Asian monsoon circulation from local hydroclimate variability during North Atlantic cooling events of the last glacial cycle (i.e., Heinrich events) using a suite of speleothems from the middle reaches of the Yangtze River in central-eastern China. The project provides support for a postdoctoral research fellow and extensive undergraduate research experience for students at William Paterson University as a primarily undergraduate teaching university with a diverse student body (Hispanic Serving Institution designated by USDOE), including many first generation to attend college.Coupled General Circulation Model (CGCM) simulations suggest that East Asia is likely to get wetter with climatic warming, yet there is still much uncertainty in these projections due in large part to the lack of agreement among model simulations. Reducing these model biases is one of the more pertinent and challenging aspects of modern climate science as a means to provide strategies to meet the future needs in food, water, energy, and biological diversity.Currently, there is a lack a consistent understanding of precisely how sensitive local rainfall variability in central China is to regional perturbations in the Asian monsoon because knowledge of the monsoon in central East Asia principally relies upon oxygen-isotope records which, according to new research, may not necessarily reflect local hydroclimate. Therefore, this project aims to build a more complete picture of local rainfall variability in central-eastern China by addressing the following questions: (1) Can speleothem proxies, such as trace elements (Magnesium, Strontium, Barium) be used to deconvolve regional atmospheric circulation from local hydrology in East Asia. If so, (2) what do these alterative proxies inform us about local hydroclimate in central-eastern China and what are the mechanisms to explain the proxy-inferred changes. (3) How well do the proxy reconstructions match the paleo-simulations from coupled general circulation models (CGCMs). The main objectives of the project include: (1) reconstruct local hydrology in central-eastern China during Heinrich events 1-6 utilizing speleothem trace elements and isotope ratios from a suite of well-dated speleothems from four caves located in the middle reaches of the Yangtze River; (2) delineate the mechanisms for the hydrologic patterns observed in the proxies using the Community Earth System Model CGCM simulations; and (3) conduct model-proxy syntheses in space and time by directly comparing speleothem pseudoproxy time series--constructed using climate model output coupled with Proxy System Models (PSMs)--with measured isotope profiles.To address the above objectives the researchers aim to test the following hypotheses: (1) Despite a weakened Indian monsoon, central China was wetter during Heinrich events thereby challenging the longstanding paradigm that the East Asian Monsoon (EASM) became weaker during North Atlantic (NA) cooling; (2) The higher rainfall in central-eastern China can best be explained by a seasonally-lagged onset of the mei-yu stage of monsoon evolution. A later onset of mei-yu to midsummer during NA cooling would have resulted in a shorter midsummer stage, leaving south-central China wet at the expense of dry conditions to the north; (3) Vegetation demise and subsequent higher dust emissions from the Sahara/Sahel regions during Heinrich events, affected the position of the ITCZ and thus amplified the response outlined in hypothesis (2); (4) Comparison of speleothem pseudoproxy time series (generated from PSMs) with measured records from East Asia will help to identify the dominant controls on speleothem delta 18-Oxygen. It may also allow a more robust assessment of model skill and help to better evaluate any model-proxy biases through abrupt climate change events.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.