Absence of a strong, deep-reaching Antarctic Circumpolar Current zonal flow across the Tasmanian gateway during the Oligocene to early Miocene
Absence of a strong, deep-reaching Antarctic Circumpolar Current zonal flow across the Tasmanian gateway during the Oligocene to early Miocene
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DOI：
10.1016/j.gloplacha.2021.103718
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发表时间：
2021-12-07
影响因子：
3.9
通讯作者：
Salabarnada, Ariadna
中科院分区：
文献类型：
--
作者：
Evangelinos, Dimitris;Escutia, Carlota;Salabarnada, Ariadna
南极绕极流（ACC）的强劲东向流动连接着所有主要的海洋盆地，在地球仪的热量、碳和营养物质的输送中发挥着重要作用。然而，建立一个深刻的绕极流，类似于今天的ACC，仍然存在争议，从而模糊了我们的气候影响的理解。破译ACC内的环极深水（CDW）的化学成分可以提供有关其发展和演变的重要见解。在这里，我们提出了新的化石鱼牙齿/骨碎片钕同位素（Nd）记录从深海钻探项目（DSDP）网站278和274在西南太平洋，目的是跟踪变化的深水质量在塔斯马尼亚网关早渐新世和早中新世（类似于33-22马）之间。274号站点提供了第一个渐新世（33.5-23.4 Ma）罗斯海附近的Nd同位素记录。其Nd同位素组成分别在33.5Ma和23.8Ma时偏离到非常放射成因的Nd（Nd（t）=）-3.1和Nd（t）=）-3.7，这是对南极冰盖扩张的主要步骤的响应。在29.7和29.1 Ma之间，向更低、更无放射性的Nd（t）值的转变与该地点原始CDW上涌的影响增加有关。相比之下，Emerald盆地南部278站的Nd同位素记录在渐新世和早中新世（30.9-21.8 Ma）期间变化很小，Nd（t）= -6.0 ~-6.7。与ACC路径以北的已发表数据进行比较，表明在ACC推断开始之前，南太平洋存在两个深水团（33-30 Ma），一个位于大约2500到3000米之间的深度（Nd（t））= -3 ~-5）和深/底层水团（> 3000 m），其Nd同位素组成（Nd（t）=）更接近于-6）。位于原极锋（proto-PF）附近的278号站点表明，在推断的ACC开始之后，与南大西洋和印度洋的原极锋沿着的站点相比，西南太平洋中沐浴在Emerald盆地南部的沃茨仍然更具放射性（Nd（t）=），类似于-8.1）。这表明，沿沿着原PF横跨塔斯马尼亚门户的深沃茨的Nd同位素组成的省性。我们的数据是不兼容的存在现代一样的均匀（横向和纵向）的Nd同位素组成的CDW沿着的主要流动路径的ACC在所有的海洋盆地在渐新世至早中新世。我们属性不同的Nd同位素组成的深沃茨在塔斯马尼亚门户，以反映一个较低的深度达到和较弱的ACC（原ACC）比今天。我们的研究结果表明，现代强大的和深远的ACC流必须在晚第三纪发展。
The vigorous eastward flow of the Antarctic Circumpolar Current (ACC) connects all major ocean basins and plays a prominent role in the transport of heat, carbon and nutrients around the globe. However, the establishment of a deep circumpolar flow, similar to the present-day ACC, remains controversial thereby obscuring our understanding of its climatic impact. Deciphering the chemical composition of Circumpolar Deep Water (CDW) within the ACC can provide critical insights about its development and evolution. Here we present new fossil fish teeth/bone debris neodymium isotope (epsilon(Nd)) records from Deep Sea Drilling Project (DSDP) Sites 278 and 274 in the southwest Pacific Ocean, with the aim to trace changes in deep water masses across the Tasmanian Gateway between the early Oligocene and early Miocene (similar to 33-22 Ma). Site 274 provides the first Nd isotope record proximal to the Ross Sea during the Oligocene (33.5-23.4 Ma). Its Nd isotope composition shows excursions to very radiogenic values, epsilon(Nd(t)=) -3.1 and epsilon(Nd(t)=) - 3.7, at 33.5 Ma and 23.8 Ma, respectively, in response to major steps in Antarctic ice sheet expansion. A shift to lower, more unradiogenic epsilon(Nd)((t)) values between 29.7 and 29.1 Ma is linked to an increased influence of proto-CDW upwelling at the site. In contrast, the Nd isotope record from Site 278 in the southern Emerald Basin shows little variability epsilon(Nd)((t)) = -6.0 to -6.7) throughout the Oligocene and early Miocene (30.9-21.8 Ma). Comparison with published data north of the ACC path, demonstrates the presence of two deep water masses in the South Pacific prior to the inferred onset of the ACC (33-30 Ma), one occupying depths between similar to 2500 and 3000 m (epsilon(Nd(t)) = -3 to -5) and a deep/bottom water mass (> 3000 m) with a more unradiogenic Nd isotope composition (epsilon(Nd(t)=) similar to -6). Site 278 located close to the proto-polar front (proto-PF) indicates that following the inferred onset of the ACC, deep waters bathing the southern Emerald Basin remained more radiogenic in the Southwest Pacific compared to sites along the proto-PF in the South Atlantic and Indian Ocean (epsilon(Nd(t)()=) similar to -8.1). This indicates a provinciality in Nd isotope compositions of deep waters along the proto-PF across the Tasmanian Gateway. Our data are incompatible with the existence of a modern-like homogenous (lateral and vertical) Nd isotope composition of CDW along the main flow path of the ACC in all oceanic basins in the Oligocene to early Miocene. We attribute distinct Nd isotope compositions of deep waters across the Tasmanian Gateway to reflect a less deep reaching and weaker ACC (proto-ACC) than today. Our findings suggest that the modern strong and deep-reaching ACC flow must have been developed at a later point in the Neogene.