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中更新世以来南大洋太平洋扇区冰盖稳定性与古海洋演化
王家凯
Subtype博士
Thesis Advisor李铁刚
2022-08-10
Degree Grantor中国科学院大学
Place of Conferral中国科学院海洋研究所
Degree Name理学博士
Keyword南极冰盖 沉积记录 海洋强迫冰盖失稳 古生产力 气候模式
Abstract

更新世以来冰期/间冰期(Glacial/Interglacial, G/IG)旋回中西南极冰盖(West Antarctic Ice Sheet, WAIS)稳定性演化的证据可以为解析大气-海洋过程与冰冻圈环境要素间的相互作用提供重要参照。为探索轨道尺度上南大洋太平洋扇区冰盖-海洋-大气间的相互作用和反馈过程,本文首先以取自南大洋东南太平洋扇区阿蒙森海北部深海平原的重力岩芯ANT34/A2-10为材料,通过对其粘土矿物、冰筏碎屑(Iceberg-rafted Detritus, IRD)和碎屑态Sr-Nd 同位素的分析,并结合东南太平洋扇区已有的历史海洋-大气强迫记录,分析了过去770 ka以来WAIS稳定性与海洋-大气强迫过程的关系。同时我们认为对这一历史海洋-大气强迫过程的理解,也有助于我们厘清晚更新世G/IG旋回中南大洋南极区古生产力变化的机制,并探索它们对大气pCO2 (patm CO2)的影响及响应。一般来说,冰期南大洋“生物泵”的加强会导致冰期patm CO2降低。然而,南极区G/IG旋回中古生产力变化模式的广泛重建却显示了与亚南极地区不一致的结果,近20年来其背后的机制引起了大量的讨论。为此我们继续提供了来自南大洋西南太平洋扇区的重力岩芯ANT31-R23约320 ka以来的高分辨率有机地球化学分析,并通过这些记录与南大洋南太平洋和南大西洋扇区的其他古气候记录以及EPICA-Dome C冰芯记录的对比,阐明了千年时间尺度上南极区古生产力变化模式与海洋-大气强迫过程之间的联系。
ANT34/A2-10岩芯沉积记录与已经发表的南半球高纬度地区海洋和大气强迫记录的对比揭示了自中更新世以来的间冰期WAIS失稳与地球轨道强迫、环极深层水(Circumpolar Deep Water, CDW)和底层水通风与南极绕极流增强以及西风带(Southern Westerly Winds, SWW)增强且极向移密切相关。此外,岩芯碎屑沉积物Sr-Nd 同位素特征表明研究站位物源在 MIS 16期附近发生了显著变化,在MIS 16期之前,扩大的罗斯环流主导了该时期研究区的冰山轨迹,使得冰山搬运的罗斯海来源陆源碎屑沉积成为研究站位附近沉积物的主要贡献者。而在 MIS 16期之后,研究站位整体陆源碎屑的源区呈现多源区混合模式,其反映的冰山输送路径与现代冰山轨迹类似,可能建立自中更新世气候转型结束时由阿蒙森海低压年均中心位置极向跃迁所引起的罗斯环流收缩。此次海洋和大气环流重组可能与随后MIS 13到 15 期间南大洋深部显著的通风状态变化有关。与该状态同步变化的轨道强迫说明该时期(MIS 13到15期)增强的轨道强迫可能对WAIS显著失稳有贡献。与此同时,间冰期WAIS失稳时期,南极干谷冰碛物在南大洋东南太平洋扇区的输入也指示了西南太平洋扇区东南极冰盖(East Antarctic Ice Sheet, EAIS)冰量随着维多利亚地的山地冰川后撤或裂解而发生损失,这一过程与海洋驱动的罗斯冰架支撑力减弱有关。
同时,ANT31-R23岩芯因子得分(F1) 指示陆源碎屑元素变化模式与研究区附近指示G/IG旋回中EAIS动力学变化的记录存在协变关系,进一步验证了研究区的海洋-大气强迫海洋冰盖失稳的正反馈机制,即间冰期SWW极向移动强化了当地海洋基底冰盖受到的海洋热力强迫,引起接地线后退和融水输入,加强了上层水体层化。层化增强后的海洋上层水体更有能力储存通过CDW上涌输送至表层水体的热量,并进一步增强冰盖受到的海洋热力强迫。同时F1与该岩芯古生产力记录同上述系统过程的文献记录之间良好的一致性也说明冰融水注入引起的表层水体层化可能是南大洋近岸区域间冰期生产力升高的必要条件。以上关于海洋-大气强迫太平洋扇区海洋冰盖与古生产力变化的见解可能会改进我们理解南极海洋基底冰盖未来变化的框架。
此外,通过调查现代研究区表层沉积物氧化还原、生产力和营养盐相关指标, 碳酸钙含量以及IPSO25/organic carbon分布模式,我们发现罗斯海和阿蒙森海陆架和近岸冰间湖(表层沉积物沉积年代)生产力和氧化还原环境可能与南极环形模式的正相位变化趋势有关。在该具有长期变化趋势的气候模式下,具有较弱碳酸盐腐蚀性(与高盐陆架水相比)且富营养盐CDW上涌和极地下降风增强/大气与表层海水极向输入的热量减弱,可能促进了研究区沉积物中碳酸钙的保存以及近岸冰间湖中冰藻有关的初级生产力升高,与阿蒙森海近岸冰间湖外缘平均海冰浓度/覆盖面积的显著增加。

Other Abstract

Evidence of West Antarctic Ice Sheet (WAIS) instability through Pleistocene glacial/interglacial (G/IG) cycles can provide fundamental constraints on the interactions between the climate system and the cryosphere. In order to explore the interaction and feedback between the ice sheet-ocean-atmosphere in the Pacific Southern Ocean (SO) on the orbital time scale, we analyzed the Iceberg-Rafted Detritus (IRD) and detrital Sr-Nd isotopes from gravity core ANT34/A2-10, which drilled from the northern Amundsen Sea abyssal plain in the Southeast Pacific SO. They are compared with the existed historical ocean-atmospheric forcing records in the Southeast Pacific SO to clarify the relationship and mechanisms between the WAIS stability and historical ocean-atmospheric forcing over the past 770 ka. Meanwhile, we suggest that understanding this past ocean-atmosphere forcing process will help us clarify the mechanism of paleo-productivity changes in the Antarctic Zone of SO during the G/IG cycle since the Late Quaternary and explore their impact and response to the atmospheric pCO2. Generally, atmospheric pCO2 decreases during the glacial period due to the strengthening ‘soft tissue pump’. However, extensive reconstruction of the paleo-productivity pattern during the G/IG cycle from the Antarctic Zone shows inconsistent results from the sub-Antarctic Zone, and their underlying mechanism remains controversial and has led to massive discussion. We, therefore, continue to provide high-resolution organic geochemical analyses of gravity core ANT31-R23 from about 320 ka from the Southwest Pacific Sector of the SO. These records are compared with paleoclimates and paleo-ocean records of the South Pacific and South Atlantic sectors of the SO and records from EPICA-Dome C ice core to clarify the linkage between paleo-productivity changes and ocean-atmosphere forcing processes on the millennial-scale.
Comparing the sedimentology records from core ANT34/A2-10 with other published oceanic and atmospheric forcing records from the region provided evidence that the enhanced IRD abundance-related interglacial WAIS instability since the mid-Pleistocene coincided with increased Circumpolar Deep Water (CDW) ventilation, strengthened Antarctic Circumpolar Current, poleward-shifted Southern Westerly Winds (SWW), and increased orbital forcing. In addition, the Sr-Nd isotope signature of the detrital sediments indicates a shift in provenance at around MIS 16. Before MIS 16, the expanded Ross Gyre dominated the iceberg trajectory in the study area, allowing the transport of Ross Sea-sourced detritus-laden icebergs to become the major contributor to the sediments in site ANT34/A2-10. After MIS 16, the source area of the terrigenous detritus showed a multi-source mixture pattern, reflecting the iceberg transport pathway was similar to the modern-like iceberg trajectory, which may have been established due to the polar shift of the annual mean-median position of Amundsen Sea Low-pressure system that indued Ross Gyre contraction since the end of the mid-Pleistocene transition. This reorganization of the oceanic and atmospheric circulation may relate to the significant changes in deep SO ventilation during the subsequent MIS 13 to 15. Orbital forcing synchronous with this pattern of variation may indicate that the increasing orbital forcing may contribute to the contemporaneous significant WAIS instability. Also, the input of Antarctic dry valley moraines into the South Pacific sector of the SO during the WAIS instability periods indicates the loss of ice mass from the East Antarctic Ice Sheet (EAIS) in the south Pacific sector due to the retreat and breakup of mountain glaciers in Victoria Land, which may cause by ocean-driven buttress loss of Ross Ice Shelf.
Meanwhile, during the G/IG cycle, the factor score (F1) from core ANT31-R23 indicates the pattern of terrigenous elements input that has covariation with EAIS dynamic near the study area. This phenomenon further verifies the positive feedback mechanism of ocean-atmosphere forcing on marine-based ice sheet instability. Specifically, the interglacial poleward-shifted SWW intensified the ocean thermal forcing on local marine-based ice sheets, causing the retreat of the grounding line and the input of meltwater, which enhanced the stratification of the upper water column. This condition is more suitable for storing the heat supplied by the CDW upwelling, further enhancing the thermal forcing on the local marine-based ice sheet. Meanwhile, the good correlation between the F1 and paleo-productivity records of the core ANT31-R23 with reference records of previous systematic processes also indicates that the changes in the paleo-productivity in this region may relate to the locally positive feedback mechanism of ocean-atmosphere forcing on the marine-based ice sheet instability of the Southwest Pacific Sector EAIS. Specifically, the upper water column stratification caused by EAIS-sourced meltwater input could maintain the preformed and regenerated nutrient levels in the surface ocean and is necessary to increase the interglacial paleo-productivity of the Antarctic margin sea. Our study provides insights into the role of ocean-atmosphere forcing on the past behavior of the marine-based ice sheet and paleo-productivity in the South Pacific SO that may help us improve the framework for understanding its future changes.
Furthermore, by investigating the redox, productivity, and nutrient-related indicators, CaCO3 content and Total Organic Carbon normalized the IPSO25 content of the entire surface sediments. We found that the productivity and redox environment of the Ross Sea and Amundsen Sea shelf and coastal polynya regions are also associated with the tendency of the positive phase of the Southern Annular Mode. We suggest that, under this long-term trend climate pattern, the enhanced upwelling of relatively weaker corrosive and eutrophicate CDW (compared to the high salinity shelf water forming in the coastal polynya), enhanced katabatic wind, and decease poleward heat flux, may benefit the preservation of CaCO3 and promote the ice algae-related primary productivity of coastal polynya, and led to the significant increase of sea-ice concentration/coverage at the edge of the coastal polynya.

MOST Discipline Catalogue理学::海洋科学
Funding ProjectTaishan Scholars Project Funding[ts20190963] ; Strategic Priority Research Program of Chinese Academy of Sciences[XDB42000000] ; Strategic Priority Research Program of Chinese Academy of Sciences[XDB42000000] ; Taishan Scholars Project Funding[ts20190963]
Language中文
Table of Contents

第一章  绪论    1
1.1  引言    1
1.2  西南极冰盖(WAIS)的结构、演变和失稳    7
1.3  南大洋海洋强迫WAIS失稳的反馈机制    12
1.4  极地气候系统和模式与WAIS稳定性的关系    18
1.4.1  南极环形模式(SAM)    19
1.4.2  阿蒙森低压系统(ASL)    21
1.5  南大洋历史海冰重建指标    25
1.5.1  冰芯元素    25
1.5.2  硅藻种属    26
1.5.3  生物标志物    27
1.6  选题依据与研究目标    30
1.7  工作量    33
第二章  区域地质与环境    35
2.1  研究区区域地质概况    35
2.2  研究区水文与气候特征    38
第三章  研究材料与方法    47
3.1  研究材料    47
3.2  研究方法    47
3.2.1  时间序列分析    51
3.2.2  年代地层学    53
3.2.3  沉积矿物学    63
3.2.4  微体古生物学    65
3.2.5  地球化学    66
第四章  ANT34/A2-10岩芯中WAIS失稳信号的识别与解释    75
4.1  ANT34/A2-10岩芯IRD峰值区间的识别    75
4.2  ANT34/A2-10岩芯IRD丰度信号的解释    77
第五章  阿蒙森海沉积物物源及其对极地气候系统演化的响应    87
5.1  IRD峰值区间沉积物不同组分Sr-Nd同位素    87
5.2  ANT34/A2-10岩芯粘土矿物组成    87
5.3  ANT34/A2-10岩芯的物源演化及其控制机制    88
5.3.1  洋流强度驱动的粘土矿物物源变化    92
5.3.2  与高纬度海洋-大气-冰盖过程相关的碎屑态Sr-Nd同位素来源变化    96
5.4  ANT34/A2-10站位物源变化反映中更新世气候转型末期ASL跃变    104
第六章  中更新世以来南大洋太平洋扇区海洋-大气强迫海洋基底冰盖失稳    107
6.1  更新世以来太平洋扇区海洋基底冰盖失稳的研究进展    107
6.2  阿蒙森海海洋-大气强迫冰盖失稳的证据    110
6.2.1  阿蒙森海海洋-大气强迫与WAIS失稳    110
6.2.2  MIS 13和15期东南太平洋扇区WAIS的“崩塌”    117
6.3  罗斯海海洋-大气强迫冰盖失稳的证据    122
6.3.1  罗斯海冰盖动力学与古生产力变化记录    122
6.3.2  罗斯海海洋-大气强迫与EAIS失稳    126
6.4  海洋强迫正反馈过程与大气pCO2变化的联系    130
6.5  小结    133
第七章  南大洋太平洋扇区表层沉积物地球化学特征及其环境意义    135
7.1  表层沉积物生产力与营养盐指标分布特征    136
7.2  表层沉积物TE富集因子分布特征    144
7.3  表层沉积物IPSO25分布特征及其环境意义    149
7.4  小结    156
第八章  结论    159
第九章  更新世WAIS与南大洋古海洋研究展望    163
9.1  罗斯海WAIS历史    164
9.2  阿蒙森海WAIS历史    165
9.3  冰山通道和亚南极海冰与海洋动力学    165
9.4  太平洋扇区ACC动力学    166
参考文献    169
致  谢    216
作者简历及攻读学位期间发表的学术论文与研究成果    219

Document Type学位论文
Identifierhttp://ir.qdio.ac.cn/handle/337002/179700
Collection海洋地质与环境重点实验室
Recommended Citation
GB/T 7714
王家凯. 中更新世以来南大洋太平洋扇区冰盖稳定性与古海洋演化[D]. 中国科学院海洋研究所. 中国科学院大学,2022.
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