| 摘要: | 末次冰消期之（距今 (BP) 之前的 9 至 21000 年 (kyr)）氣候演變是了解氣候驅動力與反饋作用如何影響地球氣候的最佳時間。 南大洋通過湧升流與海洋表層水交換養分和富含碳的深海海水，並將表層海水的有機碳與無機碳帶入深水循環，上述過程在冰期氣候系統中發揮著重要作用. 然而，對推動南大洋湧升流的物理機制的理解仍在發展中. 本論文采用海氣耦合地球系統氣候模式, 在海盆尺度上研究了南大洋末次冰消期海洋-大氣-海冰-陸地表面的氣候演化時間序列. 此外, 本研究的重點是通過一系列的單一強迫力敏感實驗了解冰川變化在軌道日照、溫室氣體、大陸冰蓋和海洋淡水注入強迫力中對經向翻轉環流和南大洋洋流動力學的作用.
這項研究表明, 從南半球近地表西風帶、風切和南極海冰覆蓋範圍看來，從末次冰盛期 (19 至 20 kyr BP) 到海因里希事件 1（Heinrich I 14.7 至17.6 kyr BP）至 Younger Dryas（11.5 至 12.5 kyr BP事件，南大洋上升流主要是由風應力驅動的。然而, 在全新世開始期間(9 到 10 kyr BP), 結果顯示南大洋上升流增加而風切卻下降, 這表明尚有其它替代機制調節南大洋之湧升流強度。
本研究的特別之處在於強調南極海冰融化和海水鹽度分層反饋的變化調節了區域海水密度並對南大洋的密度和浮力通量做出了改變, 並影響了南大洋的洋流動力.這項研究表明：解釋全新世開始期間湧生流強度的增加.
單一強迫力敏感性實驗顯示, 軌道日照的變化對南大洋末次冰消期間的湧升流強度為主控因素。北半球融冰造成的淡水注入通量在經向翻轉環流變化的上下分支中起主導作用.
本論文的主旨在於了解南半球西風帶、海洋和南極海冰在南大洋緯度的動態聯繫，並指出最後一次冰消期間南大洋湧生流的變化是共同受控於風切應力與海水浮力通量的變化.;The last deglacial (9 to 21 thousand years (kyr) Before Present (BP)) climate evolution represents the vital role of feedbacks in the Earth′s climate system. The Southern Ocean plays a fundamental role in the deglacial climate system by exchanging nutrients and carbon-rich deep ocean water with the surface. However, understanding the physical mechanisms that drive the Southern Ocean upwelling dynamics is still developing. This thesis investigates the last deglacial ocean-atmosphere-sea ice-land surface transient evolution in the Southern Ocean on a basin-scale employing a fully coupled Earth system model. Additionally, this study focuses on understanding the roles of the deglacial changes in orbital insolation, greenhouse gasses, continental ice sheet, and meltwater forcing to the Meridional Overturning Circulation and the Southern Ocean dynamics using single-forcing sensitivity experiments.
This study shows the deglacial decrease in Southern Ocean upwelling following the weakening of the Southern Hemisphere near-surface westerlies, wind stress, and Antarctic sea ice coverage from the Last Glacial Maximum (19 to 20 kyr BP) to the Heinrich Stadial 1 (14.7 to 17.6 kyr BP) and the Younger Dryas (11.5 to 12.5 kyr BP). The results support that the Southern Ocean upwelling is primarily driven by wind stress. However, during the onset of the Holocene (9 to 10 kyr BP), results indicate increased Southern Ocean upwelling while wind stress decreased, suggestive of alternative mechanisms regulating the Southern Ocean upwelling.
This study highlights that the changes in Antarctic sea ice melting and formation feedback regulate the salt and freshwater discharge. As a result, it contributed to the Southern Ocean density and buoyancy flux and influenced the Southern Ocean dynamics. Finally, this study indicates increased surface freshwater discharge and meridional density gradient from Antarctic sea ice melting and formation support the increase in Southern Ocean upwelling. Thus, the Antarctic sea ice melt-induced freshwater discharge feedback at the Antarctic sea ice-ocean boundary explains the increased upwelling during the onset of the Holocene.
The single-forcing sensitivity experiments suggest changes in orbital insolation influenced the last deglacial Southern Ocean upwelling. The results also indicate a dominant role of Northern Hemisphere meltwater flux in the upper and lower branch of the Meridional Overturning Circulation changes. Moreover, this study shows an orbital control on the Antarctic sea ice extent (weaker sea ice retreat) and Northern Hemisphere meltwater flux control on Antarctic sea ice retreat (stronger sea ice retreat) during the Heinrich 1 and the Younger Dryas events following the bipolar seesaw.
This thesis highlights the dynamic linkage of the Southern Hemisphere westerlies, ocean, and Antarctic sea ice in the latitudes of the Southern Ocean. Furthermore, it emphasizes that zonal wind stress and buoyancy forcing regulated by Antarctic sea ice explain the change in the Southern Ocean upwelling during the last deglaciation. |
