Sedimentological investigations and age model on sediment core PS2561-2

Benthic d13C values (F. wuellerstorfi), kaolinite/chlorite ratios and sortable silt median grain sizes in sediments of a core from the abyssal Agulhas Basin record the varying impact of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) during the last 200 ka. The data indicate that NADW influence decreased during glacials and increased during interglacials, in concert with the global climatic changes of the late Quaternary. In contrast, AABW displays a much more complex behaviour. Two independent modes of deep-water formation contributed to the AABW production in the Weddell Sea: 1) brine rejection during sea ice formation in polynyas and in the sea ice zone (Polynya Mode) and 2) super-cooling of Ice Shelf Water (ISW) beneath the Antarctic ice shelves (Ice Shelf Mode). Varying contributions of the two modes lead to a high millennial-scale variability of AABW production and export to the Agulhas Basin. Highest rates of AABW production occur during early glacials when increased sea ice formation and an active ISW production formed substantial amounts of deep water. Once full glacial conditions were reached and the Antarctic ice sheet grounded on the shelf, ISW production shut down and only brine rejection generated moderate amounts of deep water. AABW production rates dropped to an absolute minimum during Terminations I and II and the Marine Isotope Transition (MIS) 4/3 transition. Reduced sea ice formation concurrent with an enhanced fresh water influx from melting ice lowered the density of the surface water in the Weddell Sea, thus further reducing deep water formation via brine rejection, while the ISW formation was not yet operating again. During interglacials and the moderate interglacial MIS 3 both brine formation and ISW production were operating, contributing various amounts to AABW formation in the Weddell Sea.

本数据集涵盖采自阿加勒斯海盆深海岩芯沉积物中的底栖碳同位素δ¹³C值（F. wuellerstorfi）、高岭石/绿石比值以及可分选粉砂中值粒径，其记录了过去20万年以来北大西洋深层水（North Atlantic Deep Water, NADW）与南极底层水（Antarctic Bottom Water, AABW）的影响演化。数据显示，北大西洋深层水的影响强度在冰期减弱、间冰期增强，与晚第四纪全球气候变化趋势一致。与之相对，南极底层水的变化模式更为复杂。威德尔海的南极底层水形成受到两种独立的深水生成机制调控：其一为冰间湖及海冰区形成海冰过程中的盐析作用（冰间湖模式），其二为南极冰架下方冰架水（Ice Shelf Water, ISW）的过冷却过程（冰架模式）。两种机制的贡献比例变化使得南极底层水的生成及向阿加勒斯海盆的输运呈现显著的千年尺度波动。在冰期早期，海冰形成作用增强且冰架水生成活跃，由此形成了大量深层水，此时南极底层水的生成速率达到峰值。当进入盛冰期且南极冰盖陆架搁浅后，冰架水生成过程完全停止，仅通过盐析作用生成少量深层水。在冰消期I、冰消期II以及海洋同位素阶段（Marine Isotope Stage, MIS）4/3转换期，南极底层水的生成速率降至绝对最低值。此时，融冰带来的淡水输入增强与海冰形成减少共同降低了威德尔海表层水密度，进一步削弱了盐析作用驱动的深水生成过程，而冰架水生成尚未恢复。在间冰期以及温和的间冰期MIS 3阶段，盐析作用与冰架水生成过程均处于活跃状态，二者以不同贡献比例参与威德尔海的南极底层水形成。