(Table 1) Age determimnation of sediment core MD01-2403

Significantly older 14C ages by 2500-7900 years are found for sedimentary total organic carbon (TOC) when compared to ages of codeposited surface-dwelling foraminifera in the southern Okinawa Trough. This age discrepancy increases with rising sea level since the Last Glacial Maximum. A progressive shift in TOC d13C toward more negative values with rising sea level reflects an increasing fractional contribution of terrestrial organics (soil organics, plant debris, and/or fossil organics) to the buried organic pool. Organic matter previously stored on the East China Sea shelf during sea level lowstand and riverine material from Taiwan may be the sources that cause the d13CTOC to shift to more terrestrial values. During the Holocene when sea level is above -40 m, d13CTOC values stabilize within a narrow range (-22.3 to -22.8 per mil) while age discrepancies continue to increase and less chemically weathered sediments are deposited. The increase in age discrepancy between TOC and foraminifera in the Holocene may be due to a wetter climate that drove higher rates of physical weathering on Taiwan and greater transport rates of fossil organic C-bearing lithogenic sediment to the ocean. The climate impact on the relative delivery of fossil and nonfossil TOC in depositional settings influenced by fluvial sources should be considered in interpretations of sedimentary C isotope records.

在冲绳海槽南部，沉积总有机碳（Total Organic Carbon, TOC）的¹⁴C年龄较同期沉积的表栖有孔虫（foraminifera）年龄偏老2500~7900年，二者存在显著年龄差。该年龄差自末次冰盛期（Last Glacial Maximum）以来随海平面上升而逐渐增大。随着海平面上升，TOC的δ¹³C值逐渐向更负方向偏移，这反映出埋藏有机库中陆源有机物（土壤有机物、植物碎屑及/或化石有机物）的占比不断升高。末次冰期低海平面时期储存在东海陆架的有机质，以及源自台湾的河流物质，可能是导致TOC的δ¹³C向更具陆源特征偏移的主要来源。当海平面高于-40米的全新世（Holocene）时期，TOC的δ¹³C值稳定在狭窄区间内（-22.3‰~-22.8‰），而年龄差仍持续增大，同时沉积的沉积物化学风化程度更低。全新世时期TOC与有孔虫之间年龄差的增大，可能源于气候更为湿润，使得台湾地区的物理风化速率提升，且携带化石有机碳的岩源沉积物向海洋的搬运通量增加。在受河流源区影响的沉积环境中，气候对化石与非化石TOC相对输入量的影响，应当在沉积碳同位素记录的解译中予以考虑。