Stable carbon isotope ratios of Cibicidoides wuellerstorfi of MIS 2 time slices

The interval of time represented by marine isotope stages 11 and 12 (~360–470 ka) contains what may be the most extreme glacial and interglacial climate conditions of the Late Pleistocene. It has been suggested that sea level rose by ~160 m at the termination of glacial stage 12. This is 30% greater than the sea level rise that followed the most recent glacial maximum. There have been few detailed studies of the unique conditions that existed during the stage 11–12 time period because of the lack of high-quality core material. This problem has been addressed by the collection of high deposition rate cores from sediment drifts in the western North Atlantic during Ocean Drilling Project Leg 172. Benthic foraminiferal d13C data from cores collected between ~4600 and 1800 m were used to reconstruct bathymetric gradients in deep and intermediate water properties for selected time slices during this glacial–interglacial cycle. During glacial stage 12, the deep western North Atlantic was filled by a water mass that was more nutrient-enriched than modern Antarctic Bottom Water. Above 2000 m, a more nutrient-depleted water mass existed during this glacial stage. Such an intermediate water mass has been described for more recent glacial periods and presumably forms in a more proximate region of the North Atlantic. Interglacial stage 11 water mass properties closely resemble those of the present-day western North Atlantic. A nutrient-depleted water mass (d13C of 0.75–1.0 per mil), similar to modern North Atlantic Deep Water existed between 3500 and 2000 m. This was underlain by a water mass with lower d13C values (<0.75 per mil) that probably was derived from a southern source. Using Leg 172 data, along with previously published results from the Atlantic and Pacific oceans, we estimate a mean global d13C change of 0.95 per mil from stage 12 to stage 11. This is twice the whole ocean ?13C change reported for the transition from the last glacial maximum to the Holocene.

海洋同位素阶段11与12（marine isotope stages 11 and 12）所代表的时间间隔约为36万至47万年，或许包含了晚更新世（Late Pleistocene）最为极端的冰期与间冰期气候条件。有研究指出，冰期阶段12结束时海平面上升幅度约达160米，较末次冰盛期后的海平面上升量高出30%。由于缺乏高质量岩心样品（high-quality core material），针对该时段独特环境条件的精细研究寥寥无几。大洋钻探计划（Ocean Drilling Project, ODP）第172航次（Leg 172）中，科研人员于西北大西洋沉积漂移区采集了高沉积速率岩心，这一难题由此得以解决。研究人员以采集于约4600米至1800米水深的岩心中的底栖有孔虫（benthic foraminiferal）碳同位素比值（δ¹³C）数据为基础，重建了该冰期-间冰期旋回（glacial–interglacial cycle）中若干关键时段的深层与中层水团属性的水深梯度（bathymetric gradients）。在冰期阶段12期间，西北大西洋深部被一类富营养化程度高于现代南极底层水（Antarctic Bottom Water）的水团占据；而在2000米以浅海域，同期则存在贫营养化水团。这类中层水团曾在更近的冰期被记录到，推测其形成于北大西洋更近的区域。间冰期阶段11的水团属性与现代西北大西洋极为相似：在3500米至2000米水深区间，存在一类与现代北大西洋深层水（North Atlantic Deep Water）类似的贫营养化水团，其δ¹³C值介于0.75‰~1.0‰；该水团下方则分布着δ¹³C值更低（<0.75‰）的水团，其源区大概率位于南半球。结合第172航次的数据与此前大西洋、太平洋海域已发表的研究结果，我们估算出从冰期阶段12到间冰期阶段11的全球平均δ¹³C变化幅度为0.95‰，这一数值是末次冰盛期至全新世（Holocene）过渡期间报道的全大洋δ¹³C变化量的两倍。