Dynamics of the subpolar gyre and transition zone of the North Atlantic during the last glacial cycle
Dynamics of the subpolar gyre and transition zone of the North Atlantic during the last glacial cycle
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DOI：
10.1016/j.quascirev.2023.108215
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发表时间：
2023-07-17
影响因子：
4
通讯作者：
Wang，Yang
中科院分区：
文献类型：
--
作者：
Zeng，Min;Rashid，Harunur;Wang，Yang
过去对北大西洋海洋沉积物的研究记录了千禧年尺度的海面冷却，这与Dansgaard-Oeschger事件有关，Dansgaard-Oeschger事件影响了末次冰期的海洋锋面和表面水文。大多数研究都集中在利用漂流、单一或多种浮游有孔虫的丰度和地球化学来评估环境变化。然而，北大西洋过渡带（NATZ）和亚极地环流（SPG）完整末次冰期的浮游有孔虫组合的详细资料很少。本文报道了西南SPG （SW SPG）和NATZ Milne海山两个沉积物岩心Hu9007-08和Hu71022-377的浮游有孔虫丰度、氧同位素和浮冰碎屑（IRD）计数。此外，我们利用已发表的浮游有孔虫组合、IRD和SPG东部和西部的同位素数据，提供了极地、北极和亚北极锋面（分别为PF、AF和SAF）的地表水质量变化和动力学的综合重建。尽管在海洋同位素阶段（MIS） 5中，西南SPG（靠近纽芬兰盆地）的整体温度高于东部SPG，但在西南SPG中仍然发现了北大西洋范围的冷却事件C24和C21。此外，EW9303-37JPC岩心的浮游有孔虫丰度（即scarceNeogloboquadrina pachydermaa和abundance globigerinoides inflata）和Hu9007-08岩心的浮游有孔虫丰度与全新世相比显示出相对温暖的MIS 5e。然而，g丰度的下降。inflatas表明，西南SPG在~ 126 ~ ~ 120 ka之间受到季节性的次极水存在的影响，可能受到海洋锋面系统向南移动的影响。在Heinrich漂流事件期间，当融水淹没北大西洋表面时，PF、AF和SAF向南移动，极地/次极地水团短暂侵入SPG和NATZ的西部和东部。在MIS 3前期（60-40 ka），海洋锋面系统从MIS 4的位置向北移动。SPG和NATZ在MIS 3中期（即38 ~ 30 ka）逐渐变暖，次极种球状球虫（globigerina bulloidesin） Hu9007-08、Hu71022-377和CH69-K09增加，表明在洋面系统继续北移的同时，海面持续变暖。这种水文环境在MIS 3-MIS 2晚期（30-19 ka）迅速冷却，在末次盛冰期，PF向南转移到中纬度（~ 45°N）。末次消冰—全新世期间，湖心hu9007—08和湖心hu71022—377区域主要受北大西洋暖流影响，SAF位于两个岩心的北部。为了更好地了解末次冰期北大西洋地表环流的动力学，本研究首次提出了SPG和NATZ的大规模水团运动和锋面变化。
Past studies of marine sediments of the North Atlantic documented millennial-scale sea-surface cooling related to the Dansgaard-Oeschger events that influenced the oceanic fronts and surface hydrology during the last glacial cycle. Most studies have focused on using ice-rafting, single or multiple species of planktonic foraminifers' abundances, and geochemistry to assess environmental changes. However, detailed planktonic foraminiferal assemblage data in the North Atlantic Transition Zone (NATZ) and subpolar gyre (SPG) for the full last glacial cycle are scarce. Here we report planktonic foraminiferal abundances, oxygen isotopes, and ice-rafted detritus (IRD) counts from two sediment cores, Hu9007-08 and Hu71022-377, collected from the Milne seamount of southwestern SPG (SW SPG) and NATZ, respectively. Further, we have used the published planktonic foraminiferal assemblage, IRD, and isotopic data from the eastern and western SPG to provide an integrated reconstruction of changes in the surface water masses and dynamics of the Polar, Arctic, and subarctic fronts (PF, AF, and SAF, respectively). Despite the overall warmth of the SW SPG (near the Newfoundland Basin) compared to the eastern SPG during marine isotope stage (MIS) 5, the North Atlantic-wide cooling events C24 and C21 were still identified in the SW SPG. Further, the planktonic foraminiferal abundances in cores EW9303-37JPC (i.e., scarceNeogloboquadrina pachydermaand abundantGlobigerinoides inflata) and Hu9007-08 reveal a relatively warm MIS 5e compared to the Holocene. However, the decrease in the abundance ofG. inflatasuggests that the SW SPG was influenced by the seasonal presence of subpolar waters and possibly a southward shift in the oceanic frontal systems between ∼126 and ∼120 ka. During the Heinrich ice-rafting events, when meltwater flooded the surface North Atlantic, the PF, AF, and SAF shifted southward, and the polar/subpolar water masses briefly invaded the western and eastern SPG and NATZ. In the early part of MIS 3 (60–40 ka), the oceanic frontal system shifted northward from its position during MIS 4. The SPG and NATZ gradually warmed, and the subpolar speciesGlobigerina bulloidesin cores Hu9007-08, Hu71022-377, and CH69-K09 increased in the middle of MIS 3 (i.e., 38–30 ka), suggesting continuous sea surface warming while the oceanic frontal systems continued to move northward. This hydrological environment rapidly cooled in the late MIS 3-MIS 2 (30–19 ka), with the PF shifted southward to the mid-latitude (∼45°N) during the Last Glacial Maximum. During the last deglaciation-Holocene, the regions of cores Hu9007-08 and Hu71022-377 were mainly influenced by the warm North Atlantic Current, and the SAF was located north of both cores. This study presents the first large-scale water mass movements and frontal changes in the SPG and NATZ to better understand the dynamics of the surface circulation in the North Atlantic during the last glacial cycle.