Sources of organic matter and paleo-environmental implications inferred from carbon isotope compositions of lacustrine sediments at Inexpressible Island, Ross Sea, Antarctica

The carbon isotopic composition of organic matter(δ13Corg) was determined in two sediment cores(IIL1 and IIL9) recovered from Inexpressible Island, Ross Sea, Antarctica, and analyzed to identify the sources of that organic matter. The δ13Corgvalues of sediments of IIL9 were found to vary between-14.6‰ and-11.6‰, with a mean of-13.4‰(n=48). These values were significantly higher than those of IIL1 sediments which varied between-23.2‰ and-20.4‰, with a mean of-21.8‰(n=55). The variation in δ13Corgvalues in these two sediment cores indicate different sources of organic matter. The relatively high δ13Corgvalues in IIL9 are in accordance with a source from algae, while the low δ13Corgvalues in IIL1 evince significant influence from penguin guano with algae as the secondary source. Compared with the reference data from other high-latitude lake sediments and plants, the δ13Corgvalues in IIL9 were extremely high, a result likely related to intense competition for CO2assimilation among algal species during the growing season in this relatively shallow pond. These results indicate that sedimentary δ13Corgis a reliable proxy for paleo-primary productivity in ponds at Inexpressible Island.