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（marine isotope stages）11和12（对应约36万~47万年前）所代表的时间间隔，可能记录了晚更新世（Late Pleistocene）最为极端的冰期与间冰期气候状态。有研究提出，冰期阶段12结束时海平面上升幅度约达160米，这比末次冰盛期后的海平面上升量高出30%。由于缺乏高质量的深海岩芯样品，针对阶段11至12期间独特气候环境的详细研究较为匮乏。大洋钻探计划（Ocean Drilling Project）第172航次在西北大西洋沉积物漂移区采集的高沉积速率岩芯，解决了这一研究难题。研究人员利用采集于约4600米至1800米水深的岩芯中的底栖有孔虫碳同位素（δ¹³C）数据，重建了该冰期-间冰期旋回内特定时段深层与中层水团属性的水深梯度。在冰期阶段12期间，西北大西洋深层海域被营养盐含量高于现代南极底层水（Antarctic Bottom Water）的水团所占据；而在2000米以浅海域，当时则存在营养盐含量更低的水团。这类中层水团在更近的冰期也曾被观测到，推测其形成于北大西洋更邻近的区域。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，存在与现代北大西洋深层水（North Atlantic Deep Water）类似的贫营养盐水团（δ¹³C值为0.75‰~1.0‰），其下方则分布着δ¹³C值更低（<0.75‰）的水团，该水团大概率源自南半球。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，我们估算出从阶段12到阶段11的全球平均碳同位素（δ¹³C）变化幅度为0.95‰，这一数值是末次冰盛期至全新世过渡期间全球海洋整体碳同位素变化量的两倍。