Interannual and Orbital-Scale Climate Variability in the Early Miocene: Physical, Chemical and Biological Investigations of the Foulden Maar Diatomite

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Interannual and Orbital-Scale Climate Variability in the Early Miocene: Physical, Chemical and Biological Investigations of the Foulden Maar DiatomitebyWilliam D'Andrea, Columbia University, EAR-1349659ABSTRACT(The Antarctic Earth Sciences Program (PLR) co-funded the grant with the Seimentary Geology and Paleobiology Program (EAR).Accurate climate projections for the future require a fundamental understanding of Earth's climate system and its behavior during past warm periods. Sediments that have accumulated in lakes and ocean basins are our only source for observational data to examine changes in Earth's climate in the deep past. Sediment records that accumulated over long periods of time, have annual layering and which contain natural recorders of past climate are extremely rare, but are needed to investigate inter-annual climate variability (for example, the El Niño-Southern Oscillation (ENSO)) under warmer global temperature, as well as the response of the climate system to periodic variations in Earth's orbit. Using a combination of physical and chemical sedimentological techniques, the investigators will take advantage of an exceptional sedimentary record to achieve the following goals:1) Determine the drivers of early Miocene temperature and hydrologic change at suborbital timescales using organic geochemical and stable isotopic techniques. The research will test the hypothesis that natural changes in solar energy at the equator cause variations in mid-latitude climate with a pacing of approximately 11,000 years. 2) Document the nature of ENSO variability under different orbital configurations within the warm background state of the early Miocene by developing records of annual sediment layer thickness across fourteen different 1,000-yr periods. This will test the hypothesis that ENSO transitions to a permanent El Niño-like state during periods of global warmth and will help determine how the climate system behaves in a warmer world and how orbital forcing modulates ENSO. 3) Produce a record of atmospheric CO2 concentrations (pCO2) across an extreme Antarctic glaciation event in the early Miocene using stomatal density of fossil leaves. This will provide important data to examine the role (or lack thereof) of atmospheric pCO2 in driving major climate changes during this time period. The Foulden Maar Diatomite in Otago, New Zealand is an annually layered lake-sediment sequence that was deposited during a 100,000-year period, 23 million years ago. This time period is interesting because although the planet was warmer than present, Antarctic Ice Sheets grew larger than their present size, even though there were no Northern Hemisphere Ice Sheets. Furthermore, data suggest that atmospheric pCO2 levels were similar to today. The investigators will use fossil leaves in the sediments to estimate pCO2 across this enigmatic period of Earth's past, a time when the behavior of ice sheets and global temperature is at odds with the existing pCO2 data. The thickness of the annual sediment layers is related to the productivity of algae in the lake, a parameter controlled by climate. The thickness of these layers can therefore be measured and used to examine how inter-annual climate variability (specifically, ENSO) behaved during this time period and whether it changed due to the natural changes in Earth's orbit. The researchers will determine how temperature and moisture changed over this time period using organic molecules in the sediments and will test the hypothesis that natural changes in solar energy at the equator cause variations in mid-latitude climate with an 11,000-year cycle. The results will contribute to a better understanding of the natural forcing mechanisms that impact ENSO dynamics and its influence on mid-latitude climate. The outcomes of the proposed work will contribute to the fundamental understanding of Earth's climate system, interactions among different climatic processes, and the resulting impacts on global climate.