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日益令人关切。有证据表明，最后一次盛冰期的大冰盖并不是以均匀的速度融化的，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）的突然融化步骤中最迅速地解体。MWP-1A已经在几个地方被记录下来，但对于冰消期MWP-1B是否存在以及在这段时间内海平面上升了多少仍然存在争议。来自苏禄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淡。这些结果表明，西太平洋的海洋学变化范围很广，但目前还不知道这种变化是否与冰融化或海洋气候系统的其他变化引起的海平面上升有关。这项研究将利用苏禄海的沉积物档案，进一步了解与MWP-1B事件相关的海洋变化的起源，并记录在过去395，000年中是否发生过类似事件，这一时期跨越了三个冰川-间冰期循环。该产品将是苏禄海温跃层条件和海平面相关的通风历史的一个新的和独特的重建。更好地了解热带西太平洋温跃层的通风历史以及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。该项目更广泛的影响包括支持博士学位。该项目将利用对深居浮游有孔虫和底栖有孔虫的地球化学测量，重建热带西太平洋苏禄海温跃层和深盆通风事件的时间。早期对苏禄海浅栖有孔虫的地球化学研究提供了过去395，000年来千年尺度海洋表面变化的详细记录。初步的氧同位素数据从温跃层居住有孔虫Globorotalia膨胀横跨MWP-1B间隔在苏禄海沉积物芯表明一个更大的减少三角洲-18 O比以前测量的表面居住的物种。这一意外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同时出现的亚洲季风相关信号？(2)如果这是一个冰盖融水信号，为什么在温跃层的响应比在表面更大？(3)在MWP-1B时温跃层特性的这种变化是否与海平面快速上升的脉冲有关，或者与表层和温跃层沃茨进入西太平洋的西边界流平流的变化有关？为了解决这些问题和其他问题，本项目将分析G上的delta-18 O。从苏禄海沉积物岩芯MD 97 -2141的样品中，高分辨率的膨胀（钙化约160-200米），跨越全新世到海洋同位素阶段6（约130，000年BP），并跨越冰川-间冰期过渡回到约395，000年BP。这些数据将与选定间隔的Mg/Ca测量值配对，以分离水温对有孔虫δ-18 O测量变化的贡献。该项目还将利用对约700米处钙化的浮游有孔虫Globorotalia crassaformis和底栖有孔虫Oridorsalis umbonatus的分析，以评估苏禄海更深层通风事件的时间。

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.