A Multi‐Proxy Approach to Unravel Late Pleistocene Sediment Flux and Bottom Water Conditions in the Western South Atlantic Ocean
A Multi‐Proxy Approach to Unravel Late Pleistocene Sediment Flux and Bottom Water Conditions in the Western South Atlantic Ocean
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南大西洋西部晚更新世沉积物通量和底水条件的多代理方法
DOI：
10.1029/2020pa004058
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发表时间：
2021-02
影响因子：
3.5
通讯作者：
G. L. Mathias;S. Roud;C. Chiessi;M. C. Campos;B. Dias;T. Santos;A. Albuquerque;F. Toledo;K. B. Costa;B. Maher
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文献类型：
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作者：
G. L. Mathias;S. Roud;C. Chiessi;M. C. Campos;B. Dias;T. Santos;A. Albuquerque;F. Toledo;K. B. Costa;B. Maher
深海沉积物中的磁性信号有可能通过初级陆源磁性供应的变化来揭示过去的大陆环境变化，但也可以通过原位形成次级磁性矿物来记录过去的海洋环境条件，特别是在由独立代理补充时。通过结合地磁、地球化学和硅质岩粒度数据，我们研究了海洋沉积物岩心GL-1090（24.92°S，42.51°W，2,225 m水深），旨在揭示过去184 ka期间南大西洋西部中层陆源沉积物输入和底层水条件的变化。Al/Si、Fe/κ和硅质矿物粒度数据表明，该岩芯处的陆源沉积物来自南美东南部的普拉塔河。这些物质被巴西沿岸流向北输送，它们输送到我们的核心站点受到海平面振荡的调制。低海平面时期的特点是输入较粗和更丰富的陆源沉积物。环境磁性参数表明，在磁畴状态，我们解释为生物磁铁矿的含量变化后，冰川-间冰期循环显着的downcore变化。磁性颗粒大小和底栖δ 13 C的同时期负偏移表明，单域磁铁矿（可能是趋磁细菌磁铁矿）的浓度随中深水通风而变化。我们认为，减少通风在中深度的西南大西洋底部沃茨在高峰期冰川触发生物磁铁矿的生产减少。反过来，高峰期的冰川作用与北大西洋深水（或其冰川对应物）停留时间的增加有关。
Magnetic signals in deep‐sea sediments have the potential to unravel past continental environmental changes, via changes in primary terrigenous magnetic supply, but also record past marine environmental conditions, via in situ formation of secondary magnetic minerals, particularly when complemented by independent proxies. By combining environmagnetic, geochemical, and siliciclastic grain size data, we investigated marine sediment core GL‐1090 (24.92°S, 42.51°W, 2,225 m water depth) aiming to unravel changes in terrigenous sediment input and bottom water conditions during the last ∼184 ka at the western South Atlantic middepth. The Al/Si, Fe/κ and siliciclastic grain size data show that terrigenous sediments at this core location derived from the Plata River (southeastern South America). This material was transported northwards by the Brazilian Coastal Current and their delivery to our core site was modulated by sea‐level oscillations. Periods of low sea‐level were characterized by the input of coarser and more abundant terrigenous sediments. Environmagnetic parameters indicate significant downcore variations in the magnetic domain state, which we interpret as changes in the content of biogenic magnetite following glacial‐interglacial cycles. Coeval negative excursions in magnetic grain size and benthic δ13C suggests that concentrations of single domain magnetite (possibly magnetotactic bacterial magnetite) vary in response to middepth water ventilation. We suggest that reduced ventilation in the middepth western South Atlantic bottom waters during peak glaciations triggered a decrease in the production of biogenic magnetite. Peak glaciations were, in turn, linked with increases in the residence time of North Atlantic Deep Water (or its glacial counterpart).