Evidence for carbon cycling in a large freshwater lake in the Balkans over the last 0.5 million years using the isotopic composition of bulk organic matter

[摘要] In the DEEP core from the Lake Ohrid ICDP drilling project, the carbon isotope composition of bulk organic matter (delta C-13(TOC)) over the last 516 ka shows a negative correlation with total organic carbon (TOC) and total inorganic carbon (TIC). This relationship is marked by periods of lower delta C-13(TOC) values corresponding to higher TIC and TOC. Along with TOC/TN, the correlation between delta C-13(TOC) and delta C-13(TIC) suggests that most of the organic matter in the core is from aquatic primary production within the lake. The combination of TOC, TIC, and delta C-13(TOC) is able to disentangle long-term glacial/interglacial cycles and, to a lesser extent, millennial scale climate variability. Over the longer term, delta C-13(TOC) shows modest variability, indicating that the delta C-13 of the dissolved inorganic carbon (DIC) pool is stabilised by the supply of karst spring water characterised by delta C-13(DIC) influenced by the bedrock delta C-13 value, and the long residence time of the lake water and well mixed upper water column promoting equilibration with atmospheric CO2. However, comparison between arboreal pollen (AP%), TIC and TOC data indicates that the delta C-13(TOC) signal is modulated by the leaching of soil CO2 through runoff and spring discharge, changes in primary productivity, and recycling of organic matter within the lake, all affecting delta C-13(DIC). Exceptionally low delta C-13(TOC) during some interglacial periods (e.g. MIS7 and MIS9) possibly indicate rapid intensification of organic matter recycling and/or increasing stratification and enhanced methanogenesis, even if the latter process is not supported by the sedimentological data. (C) 2018 Elsevier Ltd. All rights reserved.

[发布日期] 2018-12-15

[关键词] Pleistocene;Paleolimnology;Europe;Stable isotopes;Organic matter;Lake Ohrid