Denitrification occurring in the oxygen minimum zone of the Arabian Sea produces nitrous oxide, a powerful greenhouse gas. Therefore, it is important to understand the mechanisms controlling denitrification's intensity and evaluate its influence on the global climate at various timescales. We studied multiple geochemical and isotopic proxies in a sediment core from the southeastern Arabian Sea (SEAS) at a high (centennial-scale) resolution. We find that since the last glacial period, both the ventilation and the productivity caused by the South Asian summer monsoon played a major role in controlling the denitrification variability in SEAS. During the Last Glacial Maximum (LGM) and since the Holocene, denitrification increased in SEAS despite reduced monsoon-induced productivity. During the LGM, weakened thermohaline circulation resulted in reduced ventilation of the intermediate waters of SEAS, causing increased denitrification. During the Holocene, the increase in denitrification is caused by an enhanced inflow of oxygen-depleted Red Sea and Persian Gulf waters into the intermediate depth of SEAS owing to a rising sea level that prohibited ventilation by the Antarctic Intermediate Water. We further find millennial-scale synchronicity between denitrification in SEAS, global monsoons, and the North Atlantic climate, implying systematic linkages via greenhouse gases abundance.

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末次冰期以来阿拉伯海东南部百年尺度反硝化变化成因及气候影响

发生在阿拉伯海氧气最低区的反硝化作用会产生一氧化二氮，这是一种强大的温室气体。因此，了解控制反硝化强度的机制并评估其在不同时间尺度对全球气候的影响非常重要。我们以高（百年尺度）分辨率研究了阿拉伯海东南部 (SEAS) 沉积物核心中的多种地球化学和同位素替代物。我们发现，自末次冰期以来，南亚夏季风引起的通风和生产力在控制 SEAS 反硝化变化方面发挥了重要作用。在末次盛冰期（LGM）和全新世以来，尽管季风引起的生产力降低，但 SEAS 的反硝化作用增加。LGM期间，减弱的温盐循环导致 SEAS 中间水域的通风减少，导致反硝化作用增加。在全新世期间，反硝化作用的增加是由于海平面上升阻碍了南极中间水的通风，导致缺氧的红海和波斯湾水域流入 SEAS 中间深度的增加。我们进一步发现海洋反硝化、全球季风和北大西洋气候之间存在千年尺度的同步性，这意味着通过温室气体丰度的系统联系。反硝化作用的增加是由于海平面上升阻碍了南极中间水的通风，导致缺氧的红海和波斯湾水域流入 SEAS 中间深度的增加。我们进一步发现海洋反硝化、全球季风和北大西洋气候之间存在千年尺度的同步性，这意味着通过温室气体丰度的系统联系。反硝化作用的增加是由于海平面上升阻碍了南极中间水的通风，导致缺氧的红海和波斯湾水域流入 SEAS 中间深度的增加。我们进一步发现海洋反硝化、全球季风和北大西洋气候之间存在千年尺度的同步性，这意味着通过温室气体丰度的系统联系。