Abstract
The Last Glacial Maximum (LGM; 21 ka BP) was the most recent glacial period when the global ice sheet volume was at a maximum. Therefore, the LGM can be used to investigate atmospheric dynamics under a climate that differed significantly from the present. This study quantitatively compares pollen records of boreal summer (June–July–August) precipitation with the PMIP3 LGM simulations. The data-model comparison shows an overall agreement on a drier than pre-industrial East Asian summer monsoon (EASM) climate. Nevertheless, 17 out of 55 records show a regional precipitation increase that is also simulated over the additional land mass area due to sea level drop. The thermodynamic and dynamic responses are analyzed to explain a drier LGM EASM as a combination of these two antagonistic mechanisms. Relatively low atmospheric moisture content was the main thermodynamic control on the lower LGM (relative to pre-industrial levels) EASM precipitation amounts in both the reconstructions and the models. In contrast, two dynamic processes in relation to stationary eddy activity act to increase EASM precipitation regionally in records and simulations, respectively. Precipitation increase in records is explained by dynamic enhancement of the horizontal moisture transport, while dynamic enhancement of the vertical moisture transport leads to simulated precipitation increase over the specific region where landmass was exposed during LGM along continental coastlines of China due to significant drop in sea level (relative to pre-industrial levels). Overall, the opposing effects of thermodynamic and dynamic processes on precipitation during the LGM provide a means to reconcile the spatial heterogeneity of recorded precipitation changes in sign, although data-model comparison suggests that the simulated dynamic wetting mechanism is too weak relative to the thermodynamic drying mechanism over data-model disagreement regions.
Highlights
The Last Glacial Maximum (~ 21 ka BP, LGM) was the most recent glacial period, when global ice sheets reached a maximum extent and the global sea level was ∼130 m±5 lower than present (Clark and Mix 2002; Clark et al 2009)
To evaluate the consistency of model simulation against proxy data for the LGM East Asian summer monsoon (EASM) region, a data-model comparison over China is displayed in Fig. 1 for annual and seasonal (June–July–August, JJA) precipitation
We will present our diagnostics in terms of thermodynamic and dynamic contributions to variation of precipitation in JJA, which permits us to gain a mechanistic understanding of the precipitation decline in LGM, and to reveal some insights about the regional disagreement of rainfall changes between pollen-based reconstruction and model simulation
Summary
The Last Glacial Maximum (~ 21 ka BP, LGM) was the most recent glacial period, when global ice sheets reached a maximum extent and the global sea level was ∼130 m±5 lower than present (Clark and Mix 2002; Clark et al 2009). Global and regional paleo-datasets documenting the spatial climatic patterns during the LGM have been assembled in recent decades with a specific focus on quantitative paleoclimatic reconstruction (CLIMAP 1976; Farrera et al 1999; MARGO 2009; Bartlein et al 2011; Shakun et al 2012). Such reconstructions are crucial for evaluating changes in the Earth’s climate system on different time scales.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
