新仙女木时期东亚夏季风降水不稳定的证据

通过位于沙漠 /黄土边界带的杨桃峁剖面AMS14 C年代和磁化率、粒度、有机质总量等气候代用指标的测定分析 ,认为新仙女木 (Youngerdryas)气候事件在该区存在夏季风降水波动和不稳定性 ,反映了东亚季风区和极地高纬地区Youngerdryas时期的气候差异 ,其原因可能是南北半球大气相互作用以及赤道太平洋地区气压异常 (ENSO)所致 .     

Carbon dioxide release from the North Pacific abyss during the last deglaciation

Atmospheric carbon dioxide concentrations were significantly lower during glacial periods than during intervening interglacial periods, but the mechanisms responsible for this difference remain uncertain. Many recent explanations call on greater carbon storage in a poorly ventilated deep ocean during glacial periods, but direct evidence regarding the ventilation and respired carbon content of the glacial deep ocean is sparse and often equivocal. Here we present sedimentary geochemical records from sites spanning the deep subarctic Pacific that--together with previously published results--show that a poorly ventilated water mass containing a high concentration of respired carbon dioxide occupied the North Pacific abyss during the Last Glacial Maximum. Despite an inferred increase in deep Southern Ocean ventilation during the first step of the deglaciation (18,000-15,000 years ago), we find no evidence for improved ventilation in the abyssal subarctic Pacific until a rapid transition approximately 14,600 years ago: this change was accompanied by an acceleration of export production from the surface waters above but only a small increase in atmospheric carbon dioxide concentration. We speculate that these changes were mechanistically linked to a roughly coeval increase in deep water formation in the North Atlantic, which flushed respired carbon dioxide from northern abyssal waters, but also increased the supply of nutrients to the upper ocean, leading to greater carbon dioxide sequestration at mid-depths and stalling the rise of atmospheric carbon dioxide concentrations. Our findings are qualitatively consistent with hypotheses invoking a deglacial flushing of respired carbon dioxide from an isolated, deep ocean reservoir, but suggest that the reservoir may have been released in stages, as vigorous deep water ventilation switched between North Atlantic and Southern Ocean source regions.