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

苏禄海的通风史：热带西太平洋温跃层突变的记录

• 批准号: 1736602
• 负责人: Braddock Linsley
• 金额: $ 28万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-08-15 至 2021-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1736602&HistoricalAwards=false
• 关键词: Ventilation; History; Sulu; Sea; Record

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.

在接下来的几个世纪中，快速高纬度冰层融化对海平面和海洋循环的潜在影响引起了人们的关注。有证据表明，最后一次冰川最大的冰块没有以均匀的速度融化，而是在一个或两个突然的熔融步骤中崩解最快，称为融合脉冲1A（MWP-1A； 〜14,600-13,500年bp））和1B（MWP-1B； 〜11,450至11，000年bp）。 MWP-1A已在多个位置进行了记录，但是关于冰流MWP-1B是否存在以及在该时间间隔内有多少海平面上升的争议。来自苏鲁海盆的初步数据表明，在MWP-1B的几个世纪中，地下海洋迅速变暖和新鲜。这些结果表明，西太平洋地区广泛的海洋学变化，但尚不清楚这种变化是否与融化或海洋气候系统的其他一些变化驱动的海平面上升有关。这项研究将利用苏鲁海中的沉积物档案，进一步了解与MWP-1B事件相关的海洋变化的起源，并记录过去39.5，000年中是否发生过类似事件，这是跨越三个冰川中间冰期周期的时期。该产品将是苏鲁海和海平面相关的通风历史中热跃层条件的新的独特重建。更好地了解西方热带太平洋热线的通风历史以及与高纬度冰盖熔化事件的关系将有助于对未来变化的更准确的预测。该项目的更广泛影响包括对博士学位的支持。学生，将结果纳入教学，并继续进行公共外展活动。该项目将使用深层住宅的浮游生物和底栖有孔虫的地球化学测量来重建西部热带太平洋苏鲁海热层和深层通风事件的时机。在过去的39.5，000年中，苏鲁海浅水有孔虫的较早地球化学工作提供了千禧一代地面海洋变化的详细记录。来自苏鲁海洋沉积物核心的MWP-1B间隔中的热跃层居住有孔虫球肌的初步氧同位素数据表明，与先前测量的表面住宅物种相比，三角洲-18O的降低更大。这种意外的结果提出了以下问题：（1）与MWP-1B同时，这种冰川融合水流到热带太平洋热级或亚洲季风相关信号的证据是否是？ （2）如果这是冰盖融化的信号，为什么热跃层中的响应比表面更大？ （3）在MWP-1B时，热跃层特性的这种变化是与快速海平面上升的脉冲或西部边界当前水流和热阶级水流向西太平洋的变化有关的变化吗？为了解决这些和其他问题，该项目将在高分辨率的G. tumida上分析Delta-18o（钙化〜160-200 m）。 bp），跨冰期间 - 冰川过渡至〜395,000年bp。这些数据将与选定间隔中的MG/CA测量配对，以隔离水温对有孔虫三角洲-18O的测量变化的贡献。该项目还将利用浮游有孔虫的分析，该浮游有孔虫的球形crassaformis在〜700m和底栖有孔虫的umbonatus中钙化，以评估苏鲁海中更深层通风事件的时间。