Ventilation History of the Sulu Sea: Record of Abrupt Changes in the Tropical Western Pacific Thermocline

未来几个世纪，高纬度冰盖快速融化对海平面和海洋环流的潜在影响越来越令人担忧。有证据表明，最后一次冰川盛期的大冰盖并没有以统一的速度融化，而是在一个或两个被称为融水脉冲1A(MWP-1A；约14,600-13,500年BP)和1B(MWP-1B；约11,450-11,000年BP)的突然融化步骤中以最快的速度融化。MWP-1A已经在几个地点被记录下来，但对于是否存在消冰期MWP-1B以及在这段时间间隔内海平面上升了多少，仍然存在争议。来自苏鲁海盆地的初步数据表明，在MWP-1B的几个世纪期间，次表层海洋迅速变暖和变新。这些结果表明西太平洋发生了广泛的海洋变化，但尚不清楚这种变化是否与冰川融化或海洋气候系统的其他变化导致的海平面上升有关。这项研究将利用苏鲁海的沉积物档案进一步了解与MWP-1B事件有关的海洋变化的起源，并记录过去395,000年来是否发生过类似的事件，这段时间跨越了三个冰川-间冰期周期。该产品将是一个新的和独特的苏鲁海温跃层条件和海平面相关的通风历史的重建。更好地了解西太平洋热带温跃层的通风历史及其与高纬度冰盖融化事件的关系，将有助于更准确地预测未来的变化。该项目的更广泛影响包括支持一名博士生，将成果纳入教学，以及继续开展公共宣传活动。该项目将利用对深海浮游动物和底栖有孔虫的地球化学测量，重建西热带太平洋苏鲁海温跃层和深盆通风事件的时间。早些时候对苏鲁海浅水居住有孔虫的地球化学工作提供了过去395,000年来千年尺度的表层海洋变化的详细记录。苏鲁海沉积岩芯MWP-1B段温跃层栖息的有孔虫Globorotalia umida的初步氧同位素数据表明，三角洲-18O的降幅比之前测量的表层生物物种的降幅更大。这一意想不到的结果提出了以下问题：(1)这是冰川融水流入热带太平洋温跃层的证据，还是与MWP-1B同时存在的与亚洲季风有关的信号？(2)如果这是一个冰盖融水信号，为什么温跃层的响应比地面更大？(3)MWP-1B时温跃层性质的变化是与海平面迅速上升的脉冲有关，还是与西太平洋表层和温跃层水的西部边界平流的变化有关？为了解决这些和其他问题，该项目将在苏鲁海沉积岩芯MD97-2141的样品中高分辨率地分析Gumida上的Delta-18O(钙化~160-200m)，跨越全新世到海洋同位素第六阶段(~130000年BP)，并跨越至~395,000年前的冰川-间冰期过渡期。这些数据将与选定间隔的镁/钙测量配对，以分离水温对测量到的有孔虫三角洲-18O变化的贡献。该项目还将利用对海拔约700米处钙化的浮游有孔虫Globorotalia crosa formis和底栖有孔虫Oridorsalis umbonatus的分析，以评估苏鲁海发生更深层次通风事件的时间。

The potential impacts of rapid high-latitude ice sheet melting on sea level and oceanographic circulation in the coming several centuries are of increasing concern. There is evidence that the great ice sheets of the last glacial maximum did not melt at a uniform rate, but instead disintegrated most rapidly in one or two abrupt melting steps known as Meltwater Pulses 1A (MWP-1A; ~14,600-13,500 years BP) and 1B (MWP-1B; ~11,450 to 11,000 years BP). MWP-1A has been documented in several locations, but there remains controversy over whether deglacial MWP-1B existed and how much sea level rose across that time interval. Preliminary data from the Sulu Sea basin indicate that the subsurface ocean rapidly warmed and freshened during the several centuries of MWP-1B. These results suggest wide-spread oceanographic changes in the western Pacific but it is not known whether this change is related to sea level rise driven by melting ice or some other change in the ocean-climate system. This research will utilize the sediment archive in the Sulu Sea to further understand the origin of the ocean changes tied to the MWP-1B event and document whether similar events have occurred over the last 395,000 years, a period spanning three glacial-interglacial cycles. The product will be a new and unique reconstruction of thermocline conditions in Sulu Sea and sea level related ventilation history. Developing a better understanding of the ventilation history of the western tropical Pacific thermocline and the relationship to high-latitude ice sheet melting events will facilitate more accurate predictions about future changes. Broader impacts of the project include support for a Ph.D. student, incorporation of results into teaching, and continued practice of public outreach activities.This project will reconstruct the timing of thermocline and deep basin ventilation events in the Sulu Sea in the western tropical Pacific using geochemical measurements of deep dwelling planktonic and benthic foraminifera. Earlier geochemical work on shallow dwelling foraminifera in the Sulu Sea has provided detailed records of millennial-scale surface ocean change over the last 395,000 years. Preliminary oxygen isotope data from the thermocline dwelling foraminifer Globorotalia tumida across the MWP-1B interval in a Sulu Sea sediment core indicates a larger decrease in delta-18O than in the surface dwelling species previously measured. This unexpected result raises the following questions: (1) is this evidence of glacial meltwater influx into the tropical Pacific thermocline or an Asian monsoon related signal at the same time as MWP-1B? (2) if this is an ice sheet meltwater signal, why is the response larger in the thermocline than at the surface? (3) is this change in thermocline properties at the time of MWP-1B related to pulses of rapid sea level rise or to changes in the western boundary current advection of surface and thermocline waters into the western Pacific? To address these and other questions this project will analyze delta-18O on G. tumida (calcifies ~160-200 m) at high resolution in samples from Sulu Sea sediment core MD97-2141 spanning the Holocene to Marine Isotope Stage 6 (~130,000 years BP), and across glacial-interglacial transitions back to ~395,000 years BP. These data will be paired with Mg/Ca measurements on selected intervals to isolate the water temperature contribution to measured changes in foraminifera delta-18O. The project will also utilize analyses of the planktonic foraminifera Globorotalia crassaformis that calcifies at ~700m and the benthic foraminifera Oridorsalis umbonatus to assess the timing of deeper ventilation events in the Sulu Sea.