Sedimentology, age models and stable isotope ratios of sediment cores from the equatorial Pacific

Based on detailed reconstructions of global distribution patterns, both paleoproductivity and the benthic d13C record of CO2, which is dissolved in the deep ocean, strongly differed between the Last Glacial Maximum and the Holocene. With the onset of Termination I about 15,000 years ago, the new (export) production of low- and mid-latitude upwelling cells started to decline by more than 2-4 Gt carbon/year. This reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric CO2 as recorded in ice cores and, with a slight delay of more than 1000 years, to a large-scale gradual CO2 depletion of the deep ocean by about 650 Gt C. This estimate is based on an average increase in benthic d13C by 0.4-0.5 per mil. The decrease in new production also matches a clear 13C depletion of organic matter, possibly recording an end of extreme nutrient utilization in upwelling cells. As shown by Sarnthein et al., [1987], the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades, which in turn was linked via a shrinking extent of sea ice to a massive increase in high-latitude insolation, i.e., to orbital forcing as primary cause.

基于全球分布模式的精细重建研究，深海溶解二氧化碳的底栖碳同位素比值（d13C）记录与古生产力，在末次冰盛期（Last Glacial Maximum）与全新世（Holocene）之间存在显著分异。约15000年前，随着冰消期I（Termination I）的启动，低纬度与中纬度上升流单元的新（输出）生产力开始以每年2~4吉吨碳的速率下降。这一降幅被认为是两大现象的核心驱动因素：其一为冰芯记录中同期大气二氧化碳浓度的上升；其二为滞后约1000余年之后，深海发生的约650吉吨碳的大规模渐进式二氧化碳损耗。该估算基于底栖d13C平均升高0.4‰~0.5‰的观测结果。新生产力的下降同时对应着有机质碳同位素的显著贫化，这可能反映了上升流单元内极端营养盐利用过程的终结。正如Sarnthein等人[1987]的研究所示，生产力的反转现象似乎由经向信风强度的快速减弱触发；而经向信风强度的减弱又通过海冰范围缩减与高纬度日射量的大幅增加相关联，即轨道强迫（orbital forcing）为该现象的根本成因。