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Early Cenozoic Asian Monsoons: Mechanisms and Evolution Through Time

Periodic Reporting for period 1 - ECAMMETT (Early Cenozoic Asian Monsoons: Mechanisms and Evolution Through Time)

Reporting period: 2015-09-01 to 2017-08-31

The Asian Monsoon circulation that supplies rainfall to Asia is primarily driven by continent-ocean thermal contrasts, and frequent hydro-meteorological extreme events emphasize that it is affected by recent global climate change in response to increasing atmospheric level of carbon dioxide (pCO2). The medium and longer-timescale effects of circulation changes in the monsoon system control precipitation and aridification in continental Asia and, in the past, shaped Eurasian paleoenvironments and biotic evolution. The Asian monsoons have long been thought to have originated ~23 Million years ago, driven by regional uplift. However, recent studies have shown that the monsoons are millions of years more ancient than previously thought and were possibly regionally similar to today during the high pCO2 Eocene Greenhouse episode. These studies open a vast array of new questions: (1) How did these early monsoons evolve through the Eocene? (2) How did they react to the numerous, short-term hyperthermal and hypothermal pCO2 events that ruled this period? This research project proposes to address these issues by focusing on three key sedimentary records in the Eocene monsoonal realm: in China, Myanmar, and Turkey. After refining the local stratigraphy through U/Pb geochronology of volcanic deposits, the three records will be investigated with respect to different geochemical and mineralogical paleoclimatic proxies. Elemental geochemistry and clay mineralogy will help to understand the evolution of seasonality and precipitation; stable and clumped isotope analyses on pedogenic carbonates and soil organic matter will document past rainfall amount, temperature and pCO2 variations; U/Pb dating on aeolian dust deposits will allow the reconstruction of past monsoonal wind patterns. The resulting findings will document the short- and long-term variations of the Asian monsoons during the Eocene, and in light of modern Global climate Change, are expected to furnish the basis for a substantial advance in our understanding of monsoonal forcing factors in a warmer, high-pCO2 world.
Work Package 1 (China)
All the goals set up for Work Package 1 in the initial working plan have been achieved during the first 6 months of the project. Fieldtrip was accomplished during Month 1, U/Pb results were processed and interpreted during months 2 to 4, and stable and clumped isotope results acquired during month 5 during a secondment at the University of Frankfurt.
Results from the U/Pb approach were submitted and published in two journals: GSA bulletin and Nature Communications. They show that despite a significantly different atmospheric concentration in carbon dioxide during the Eocene, wind patterns and atmospheric pressure systems were very similar to today.
Results from the stable and clumped isotope proxies remain to be exploited and published, but are particularly exciting as they seem to show that central Asian desertification was almost completely achieved by the late Eocene.

Work package 2 (Myanmar)
Fieldwork to Myanmar was achieved during month 6, following the initial work plan. However, due to significant delays to ship the samples back to Germany (samples did not make it until month 9), I had to postpone the initially planned geochemical analyses to year 2, and instead focus on Work package 3.

Work package 3 (Turkey)
Fortunately, I had acquired enough material during a previous fieldtrip to start working on Work package 3 as early as Month 7. U/Pb, elemental, stable and clumped isotope data were acquired between months 5 and 11. Additional fieldwork was carried out earlier than previously planned (on month 9 instead of month 13).
Results were eventually synthesized and submitted to the Journal of Asian Earth Sciences during Month 12. We show that Turkish climate during the Eocene was monsoonal, corroborating the extension of monsoonal ecosystems along the Tethyan domain, but that the area remained biogeographically isolated from Asia.
The results significantly help to understand of how the Asian monsoons react to extreme pCO2 forcing during the past, and how they may respond to global warming in the future where extreme CO2 concentrations are increasingly likely. Work Package 1 results have significant implications for understanding the mechanisms of aridification in central Asia: they suggest that wind patterns will remain the same despite global warming stress; they also suggest the observed northward migration of arid areas in central Asia will not expand for long, as the location of deserts appears to be resilient through time due to synoptic-level atmospheric dynamics. They also have significant implications for our understanding of dust dynamics and of Asian desertification: they show that most of the dust on the Chinese loess plateau is in fact reworked from nearby fluvial deposits and does not travel for long distances from central Asia deserts. It shows the potential impact of irrigation and river management on dust production and regional desertification, and suggests that better management of the Yellow River could have a significant impact on re-greening central China.
Results from Work Package 2 and 3 are not completely acquired yet, so it is hard to make any prediction about their potential impact.
Alexis Licht logging and sampling sediment in Xining, China