Global overturning circulation plays a vital role in atmospheric CO₂ and climate variability during glacial-interglacial (G-I) cycles; however, the exact mechanism remains elusive due to inadequate knowledge on past deep water circulation in the global ocean. Since no deep water is formed in the northern Indian Ocean, it ventilates from the south and acts only as a host for deep water circulation. Absence of any active deep water formation makes the northern Indian Ocean an ideal location to assess the extent of southern source waters and its role on past CO₂ variability during the G-I climate cycles. This study provides the first record of deep water circulation in the Arabian Sea, the northwestern Indian Ocean, during the past 136 ka based on authigenic Nd isotope record (ε_Nd). The Arabian Sea ε_Nd record shows large variability ranging from −8.8 to −6.5 with more radiogenic values during the glacial stages (MIS 2 & 6) and less radiogenic values during the interglacial stages (MIS 1 & 5) indicating changes in water mass sources. The observation of more radiogenic ε_Nd values similar to the glacial Antarctic Bottom Water (AABW) indicates enhanced flow of AABW (95–100%) and substantial reduction and/or almost complete retreat of North Atlantic Deep Water (NADW, 0–5%) during the glacials, whereas less radiogenic values indicate enhanced flow of NADW (∼20–40%) during the interglacials. The Arabian Sea ε_Nd record followed exactly similar pattern to that of the equatorial Indian Ocean (EIO). However, amplitude of their variations differed significantly during the interglacials (MIS 1 & 5); the Arabian Sea ε_Nd values were more radiogenic than the EIO. This suggests that during the interglacials, the Arabian Sea received more fraction of AABW through the western pathway, whereas the EIO received more fraction of NADW through the central pathway. This highlights differences in deep water exports from the Southern Ocean to the Arabian Sea and the EIO during the interglacials whereas export of similar water masses and its uniform distribution up to the northern Indian Ocean during the glacials. Our findings of significant G-I changes in AABW and NADW exports to the Indian Ocean and intra-basinal differences in their distribution have important implications for regional biogeochemical processes, paleo-redox conditions in the water column, carbon sink (organic and inorganic) and atmospheric CO₂ variability during the G-I climate transitions.

在冰川-冰间（GI）循环中，全球翻转循环在大气CO ₂和气候变化中起着至关重要的作用。但是，由于对全球海洋过去的深水循环的了解不足，确切的机制仍然难以捉摸。由于印度洋北部没有深水形成，因此它从南部通风，仅作为深水循环的宿主。由于没有活跃的深水形成，因此北印度洋成为评估南部源水域的范围及其在GI气候周期中对过去CO ₂变异性的作用的理想场所。这项研究基于自生Nd同位素记录（ε_Nd）。阿拉伯海_εNd记录显示出较大的变化范围，从-8.8到-6.5，冰川期（MIS 2和6）的放射源值较高，而冰川间期（MIS 1和5）的放射源值较少，表明水质来源发生了变化。 。更多放射性ε的观察_钕值类似南极冰川底水（AABW）表示增强AABW（95-100％）的流量，并大幅减少和/或北大西洋深层水（NADW几乎完全撤退，0-5％ ）在冰期期间，而较少的放射源值表明在冰期期间NADW流量增加（约20–40％）。阿拉伯海_εNd记录遵循与赤道印度洋（EIO）完全相同的模式。但是，它们之间的变化幅度在冰间期（MIS 1和5）中有很大的不同。阿拉伯海_εNd值比EIO更具有放射源性。这表明在间冰期之间，阿拉伯海通过西部途径获得了更多的AABW，而EIO通过中部途径获得了更多的NADW。这凸显了间冰期期间从南大洋到阿拉伯海和EIO的深水出口的差异，而在冰期期间直到北印度洋的类似水团的出口及其均匀分布。我们对AABW和NADW出口到印度洋的地理标志发生重大变化以及其分布内的基底内差异的发现，对区域生物地球化学过程，水柱中的古氧化还原条件，碳汇（有机和无机）和大气CO具有重要意义。_2个 地理标志气候转变过程中的多变性。