Total Organic Carbon and Total Nitrogen Contents in Lake Sediment as a Proxies of Paleoclimate

Recent researches on total organic carbon(TOC) and total nitrogen (TN) contents in lake sediment are overviewed. TOC and TN originate from autochthonous organic products in the lake and external products derived from the land area ; the former are dominant in oligotrophic lakes. It has been recognized recently that the TOC content in modern sediments from AD 1983 to 1999 has a good relationship with annual chlorophyl a amounts and average winter temperatures (from December to March) in Lake Kizaki. This result means that temperature controls the TOC content and also flux in sediment via productivity in lake water. The TOC, TN, and C/N amounts measured in a sediment core from Lake Nojiri show an excellent example of climate variability during the past 45ka, which may correspond well with δ¹⁸O change revealed in the ice core (GRIP) from Greenland. The study of lake sediments in Lake Nojiri also confirmed that the sequential changes of TOC and TN contents correspond well with the changes in pollen composition controlled by climate. These facts suggest that contents of TOC and TN, and C/N ratio in lake sediment may be a powerful tool to clarify climate change.