Organic geochemical and palynological evidence for terrigenous origin of the organic matter in Aegean Sea sapropel S1 |
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| Institution: | 1. Shanghai Engineering Research Center of Hadal Science and Technology, College of Marine Sciences, Shanghai Ocean University, Shanghai 201306, China;2. Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China;3. Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA;4. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266071, China;5. Key Laboratory of Marine Sedimentology and Environmental Geology, First Institute of Oceanography, State Oceanic Administration, Qingdao 266061, China;1. University of Bristol, United Kingdom;2. University of Western Australia, Australia;3. University of York, United Kingdom;4. Pennsylvania State University, United States |
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| Abstract: | Organic geochemistry and micropaleontology are used to determine the origin of sapropel S1 in the Aegean Sea. Low-molecular-weight (C15, C17 and C19) n-alkane data show that net primary productivity (NPP) increased from ～14,000 to 10,000 yr BP at the glacial interglacial transition, but the onset of S1 at 9600 yr BP marks a sharp decline in NPP, which remained low until ～8200 yr BP. The start of sapropel deposition is marked by increased total organic carbon (TOC) and pollen-spore concentrations, together with increased high-molecular-weight (C27, C29, C31 and C33) n-alkanes. Pollen assemblages show large influx of tree pollen from central-northern European forests. Increases in high-molecular-weight n-alkanes suggest greater influx of fresh vascular plant material at the start of S1, although the amount is small compared to other insoluble organic matter. Palynological studies showed that most of this insoluble organic matter are flocks of dark-brown amorphous kerogen, typical of terrigenous humic compounds. From ～8200 yr BP to the top of S1 at ～6400 yr BP, there is a decline in high-molecular-weight n-alkanes and terrigenous kerogen, and an increase in low-molecular-weight n-alkanes, suggesting that NPP recovered during the later deposition of S1 in the Aegean Sea. The increase in low-molecular-weight n-alkanes coincides with the recovery of coccolithophores and dinoflagellates, suggesting that these phytoplankton are primarily responsible for the low-molecular-weight n-alkane variations. These data from the Aegean Sea support the model for sapropel deposition resulting from increased influx of TOC during times of stagnant bottom water, but disagree with Mediterranean models prescribing a large increase in marine productivity. |
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