Nitrogen isotopic composition in South China Sea sediments

The d15N of surface and down-core sediments spanning the last 20-200 kyr from the entire South China Sea (SCS) ranges only from ~3.0 to ~6.5 per mil, with no correlation with discernible paleoclimatic/oceanographic changes. Detailed profiles of the uppermost sediment column, including fluff samples, indicate a minor diagenetic overprint of 0.3-1.2 per mil at the sediment-water interface. The absence of any correlation with reconstructed (glacial-interglacial) changes in primary production, terrigenous input, and/or sea level related basin configuration is attributed to a complete consumption of nitrate during primary production in this marginal basin during at least the last 140,000 years. This, in turn, implies that the d15N of the nitrate used during primary production remained approximately constant during the last climatic cycle. […]

在过去20至200千年的整个南海（SCS）表层及柱状沉积物中，δ15N值仅在约3.0至6.5‰的范围内波动，与可辨识的古气候/海洋学变化无显著相关性。对最上层沉积柱的详细分析，包括绒毛样品，表明在沉积物-水界面上存在0.3-1.2‰的轻微成岩改造。与重建的（冰川-间冰期）初级生产、陆源输入以及或与海平面相关盆地构型变化的无相关性，归因于在此边缘盆地中至少在过去14万年里硝酸盐的完全消耗。这进而表明，在上一气候周期中，用于初级生产的硝酸盐的δ15N值大致保持恒定。