Atlantic circulation changes across a stadial-interstadial transition

we combine consistently dated benthic carbon isotopic records distributed over the entire atlantic ocean with numerical simulations performed by a glacial configuration of the norwegian earth system model with active ocean biogeochemistry, in order to interpret the observed cibicides δ13c changes at the stadial-interstadial transition corresponding to the end of heinrich stadial 4 (hs4) in terms of ocean circulation and remineralization changes. we show that the marked increase in cibicides δ13c observed at the end of hs4 between ~2000 and 4200 m in the atlantic can be explained by changes in nutrient concentrations as simulated by the model in response to the halting of freshwater input in the high latitude glacial north atlantic. our model results show that this cibicides δ13c signal is associated with changes in the ratio of southern-sourced (ssw) versus northern-sourced (nsw) water masses at the core sites, whereby ssw is replaced by nsw as a consequence of the resumption of deep water formation in the northern north atlantic and nordic seas after the freshwater input is halted. our results further suggest that the contribution of ocean circulation changes to this signal increases from ~40% at 2000 m to ~80% at 4000 m. below ~4200 m, the model shows little ocean circulation change but an increase in remineralization across the transition marking the end of hs4. the simulated lower remineralization during stadials than interstadials is particularly pronounced in deep subantarctic sites, in agreement with the decrease in the export production of carbon to the deep southern ocean during stadials found in previous studies.

本研究将分布在整个大西洋的、具有一致时间记录的底栖碳同位素数据集与挪威地球系统模型的冰川配置数值模拟相结合，该模拟具有活跃的海洋生物地球化学过程，以对末次盛冰期（HS4）结束时的斯塔季尔-间冰期过渡期间观测到的Cibicides δ13C变化进行解释，该变化与海洋环流和再矿化过程的变化相关。研究表明，在HS4结束时，在大西洋中约2000至4200米深处观测到的Cibicides δ13C的显著增加，可以由模型模拟的营养浓度变化来解释，这是对高纬度冰川北大西洋淡水输入停止的反应。模型结果显示，这种Cibicides δ13C信号与核心站点南部源（SSW）与北部源（NSW）水团比的变化相关，其中SSW被NSW取代，这是由于在淡水输入停止后，北大西洋北部和北欧海域深层水形成的恢复所导致的。进一步的研究结果还表明，海洋环流变化对此信号的贡献从2000米处的约40%增加到4000米处的约80%。在4200米以下，模型显示海洋环流变化不大，但再矿化过程在HS4结束的过渡期间有所增加。与先前研究中发现的在盛冰期碳向深层南大洋的输出减少一致，模型模拟的盛冰期相较于间冰期再矿化较低的现象，在深亚南极海域尤为显著。