Reconstructing past changes in global thermohaline circulation

全球温盐环流是地球气候系统的关键组成部分，因为它在区域之间传输热量，并控制深海中的二氧化碳储存。重建印度洋表层和深层水团环流的变化将对整个全球温盐环流系统产生重要制约。与其他深水循环的化学指标不同，底层水中的钕（Nd）同位素反映了水团的来源，使其成为“指纹”水团的有用工具。此外，Nd同位素不受生物循环和其他低温过程的影响，因此可以用于重建气候和生物生产力重大转变期间的海洋环流变化。我们计划进一步开发和应用Nd同位素作为海洋环流变化的代理。在深海，高分辨率Nd同位素记录（Piotrowski等人，EPSL，2004; Piotrowski等人，科学，2005年）表明，在最后一个冰川周期的千年时间尺度上，来自北大西洋的沃茨流入南大洋的流量有很大的变化。为了研究这些海洋环流的变化是否在全球传播，我们建议重建深水Nd同位素组成，使用多个地点位于整个印度洋，这是通风与南大西洋沃茨通过南大洋。我们计划确定：1-印度洋深海水团的垂直和横向范围; 2-南大西洋的冰川-间冰期和快速变化是否有效地传递到印度洋; 3-海洋环流如何与碳同位素有关，这是对深海营养物含量敏感的代理。表层海洋环流与当地气候（如厄尔尼诺、墨西哥湾流）有关，可能在触发或放大过去的气候变化方面发挥了重要作用。浮游生物氧同位素和Mg/Ca比值可以作为古温度计来重建海表温度的变化。然而，由于温度是海洋表面水质量的一个属性，它可以在一个特定的海洋位置的变化，无论是在表面水的质量通量，相对于核心站点的横向位置的变化，或在本地或“继承”上游海面温度的变化。实际上，目前使用的海面代用指标反映的是非保守的地表水质量特性，而不是水本身的来源特征。我们计划重建在印度洋的表层海洋环流的强度，通过监测衰减的太平洋衍生的Nd同位素信号从印度尼西亚的洋流（ITF）到达位于沿着南赤道流（SEC）的核心。我们将寻求回答的问题包括：ITF的位置是否在深海环流变化期间发生变化？太平洋暖池温度的变化是否伴随着SEC强度的变化？在南大西洋重建的SST变化是否是由不同数量的Agulhas泄漏或印度洋中部源温度的变化引起的？与ITF相关的太平洋水向印度洋的传播与冰川-间冰期海平面的变化共同变化吗？浮游有孔虫中的放射性同位素（Scrivner等人，2004年;万斯等人，2004年）有可能提供海洋表面电流位置变化的证据。结合海表温度代理，他们将使我们能够重建海表温度变化是否与表面海洋环流，区域热储存，或从上游来源继承的温度变化。

The global thermohaline circulation is a key component of the earth's climate system because it transports heat between regions and controls carbon dioxide storage in the deep ocean. Reconstructing surface and deep water mass circulation changes in the Indian Ocean will place an important constraint on the global thermohaline circulation system as a whole. Unlike other chemical proxies of deep water circulation, neodymium (Nd) isotopes in bottom water reflect water mass provenance, making them a useful tool to 'fingerprint' water masses. Additionally, Nd isotopes are not affected by biological cycling and other low temperature processes, and thus can be used to reconstruct ocean circulation changes during periods of major shifts in climate and biological productivity. We plan to further develop and apply Nd isotopes as a proxy of ocean circulation changes. In the deep ocean, high-resolution Nd isotope records (Piotrowski et al., EPSL, 2004; Piotrowski et al., Science, 2005) show that there was significant variability in the flux of North Atlantic derived waters to the Southern Ocean on millennial timescales during the last glacial cycle. In order to study whether these changes in ocean circulation were propagated globally, we propose to reconstruct deep water Nd isotopic composition using multiple sites located throughout the Indian Ocean, which is ventilated with South Atlantic waters via the Southern Ocean. We plan to determine: 1- the vertical and lateral extent of the deep Indian Ocean water masses; 2- whether glacial-interglacial and rapid variability in the South Atlantic was effectively transmitted to the Indian Ocean; and 3- how ocean circulation relates to carbon isotopes, a proxy sensitive to deep ocean nutrient content. Surface ocean circulation is linked to local climate (e.g. El Nino, Gulf Stream) and likely has played an important role in triggering or amplifying past climate changes. Planktonic oxygen isotopes and Mg/Ca ratio can be used as a palaeothermometer to reconstruct changes in sea surface temperature. However, because temperature is a property of a surface ocean water mass, it can be changed at a particular oceanic location by either changes in surface water mass flux, lateral position relative to core site, or by changes in the local or 'inherited' upstream sea surface temperature. In effect, sea surface proxies currently used reflect non-conservative surface water mass properties rather than the provenance signature of the water itself. We plan to reconstruct the strength of the surface ocean circulation in the Indian Ocean by monitoring the attenuation of the Pacific-derived Nd isotope signal from the Indonesian Throughflow (ITF) reaching cores located along the Southern Equatorial Current (SEC). Questions we will seek to answer include: Does ITF position change during deep ocean circulation variations? Were shifts in Pacific Warm Pool temperature accompanied by changes in SEC strength? Are SST shifts reconstructed in the South Atlantic caused by varying amounts of Agulhas leakage or changing source temperature in the central Indian Ocean? Does ITF-related propagation of Pacific water into the Indian Ocean co-vary with glacial-interglacial sea-level changes? Radiogenic isotopes in planktonic foraminifera (Scrivner et al., 2004; Vance et al., 2004) have the potential to provide evidence of changes in sea surface current positions. In combination with sea surface temperature proxies, they will allow us to reconstruct whether sea surface temperature changes were related to surface ocean circulation, regional heat storage, or temperature changes inherited from upstream sources.