Development and demise of the Maldives carbonate platform, Oxygen Minimum Zone and monsoon in the northern Indian Ocean: IODP expedition 359

马尔代夫碳酸盐台地、最低氧区和北印度洋季风的发展和消亡：IODP 探险 359

• 批准号: NE/N012739/1
• 负责人: Dick Kroon
• 金额: $ 4.57万
• 依托单位: University of Edinburgh
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2015
• 资助国家: 英国
• 起止时间: 2015 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FN012739%2F1
• 关键词: Development; demise; Maldives; carbonate; platform

Carbonate platforms are shallow water areas in the oceans where large amounts of carbonate are produced by organisms such as algae, bryozoans, foraminifera and corals. Carbonate platforms are important hotspots of biodiversity. Examples of modern carbonate platforms are the Bahamas, Great Barrier Reef and Maldives. There are also numerous fossil carbonate platforms in the geological record. These were diverse ecosystems that eventually ceased forming when they were uplifted out of the seawater, or drowned as carbonate production was unable to keep up with (relatively) rising waters. These drowning processes are poorly understood. Previous work has mentioned subsidence, sea level, various environmental conditions such as acidification of the ocean, sea surface temperature, and the coupled oxygen-nutrient state of the ocean as various reasons why carbonate platforms drown. Complex scenarios with multiple causes of drowning are likely. This is currently a pressing issue, because understanding how platforms drown is critical to implementing conservation policies for modern ones, where sea level rise is accompanied by multiple environmental changes. Fossil drowning events can be portrayed as warning signs for how modern carbonate platforms may behave in the future.The Maldives archipelago offers the unique opportunity to study a relatively modern platform. The Maldives archipelago in the central equatorial Indian Ocean is an isolated tropical carbonate platform. A north-south-oriented double row of atolls encloses the Inner Sea of the Maldives. Seismic profiles indicate that the atolls reside on a partially drowned platform, and that the Inner Sea is partly filled with sediments. IODP excursion 359 is designed to drill bore holes in the sedimentary cover and partly sunk platform, and bore holes in the sedimentary drift deposit in the Inner Sea between the atolls. The scientists on this team will reconstruct why this specific platform partly disappeared beneath the waves in the Miocene. It is this partial nature of the drowning that is critical to enable the environmental factors of platform demise to be investigated, as subsidence and sea level rise cannot explain the phenomenon of partial drowning. Adverse local environmental conditions of the platform ecosystem and continued subsidence are key in understanding why the platform partially drowned.The so-called Oxygen Minimum Zone (OMZ) is a very important environmental feature in the subsurface waters unique to the northern Indian Ocean. The OMZ is characterized by low oxygen and high nutrient content and originates in the western Arabian Sea under the influence of the summer monsoon. It extends as a tongue to the Maldives area and further south. Local upwelling, forced by monsoonal winds, of the coupled low oxygen-high nutrient subsurface waters is unfavourable to the carbonate platform ecosystem. It is poorly known when the OMZ expanded to dominate the northern Indian Ocean but it is widely regarded that this likely happened in the Miocene. Therefore, the partial drowning of the platform may be related to the onset of the OMZ.This Moratorium proposal offers two projects. In the first project, I propose to precisely date the sedimentary sequences recovered during IODP expedition 359 in order to constrain timing of changes in the architecture of the Maldives carbonate platform, using foraminiferal biostratigraphy. There is insufficient time on board to perform dating with a high temporal resolution. Here, I propose to increase the resolution to precisely date certain key intervals (samples will be taken from the core store at Kochi, Japan). In the second project, I propose to examine the geochemistry and microfossil content of the drift sediments in the Inner Sea, I will establish the timing of the onset of the OMZ, and its evolution through time, specifically with respect to the timing of the carbonate platform demise.

碳酸盐台地是海洋中的浅水区，其中大量的碳酸盐是由藻类、苔藓虫、有孔虫和珊瑚等生物产生的。碳酸盐岩台地是生物多样性的重要热点。现代碳酸盐台地的例子有巴哈马群岛、大堡礁和马尔代夫。在地质记录中也有许多化石碳酸盐台地。这些多样的生态系统最终停止形成时，他们被抬出海水，或淹没碳酸盐生产无法跟上（相对）上升的沃茨。人们对这些溺水过程知之甚少。以前的工作已经提到了沉降，海平面，各种环境条件，如海洋酸化，海面温度，以及海洋的耦合氧营养状态，作为碳酸盐岩平台沉没的各种原因。可能会出现多种溺水原因的复杂情况。这是目前一个紧迫的问题，因为了解平台如何淹没对于实施现代平台的保护政策至关重要，因为海平面上升伴随着多种环境变化。化石溺水事件可以被描述为现代碳酸盐岩台地未来可能表现的警告信号。马尔代夫群岛提供了研究相对现代台地的独特机会。位于赤道印度洋中部的马尔代夫群岛是一个孤立的热带碳酸盐台地。马尔代夫的内海由南北走向的两排环礁环绕。地震剖面显示，环礁位于一个部分被淹没的平台上，内海部分充满了沉积物。IODP excursion 359的设计目的是在沉积盖层和部分下沉的平台上钻孔，并在环礁之间的内海沉积漂积物存款上钻孔。这个团队的科学家将重建为什么这个特定的平台在中新世部分消失在海浪之下。正是这种部分溺水的性质对于研究平台消亡的环境因素至关重要，因为下沉和海平面上升不能解释部分溺水现象。台地生态系统的不利局部环境条件和持续的沉降是理解台地部分淹没的关键。所谓的氧气最小区（OMZ）是北方印度洋特有的地下沃茨中一个非常重要的环境特征。OMZ的特点是低氧和高营养含量，在夏季风的影响下起源于阿拉伯海西部。它作为舌头延伸到马尔代夫地区和更南部。在季风作用下，低氧-高营养盐耦合的次表层沃茨的局部上升流对碳酸盐台地生态系统是不利的。关于OMZ何时扩张到控制北方印度洋的时间知之甚少，但人们普遍认为这可能发生在中新世。因此，平台的部分淹没可能与OMZ的开始有关。在第一个项目中，我建议，以精确的日期在IODP考察359期间恢复的沉积序列，以限制在马尔代夫碳酸盐台地的架构变化的时间，使用有孔虫生物地层学。船上没有足够的时间进行高时间分辨率的测年。在这里，我建议提高分辨率，以精确地确定某些关键间隔的日期（样本将从日本高知的核心商店中获取）。在第二个项目中，我建议研究内海漂流沉积物的地球化学和微体化石含量，我将确定OMZ开始的时间，及其随时间的演变，特别是碳酸盐台地消亡的时间。

项目成果

A two million year record of low-latitude aridity linked to continental weathering from the Maldives

• DOI: 10.1186/s40645-018-0238-x
• 发表时间: 2018-12
• 期刊: Progress in Earth and Planetary Science
• 影响因子: 3.9
• 作者: T. Kunkelova;Simon J. A. Jung;Erica S. de Leau;N. Odling;Alexander L. Thomas;C. Betzler;G. Eberli;C. Alvarez‐Zarikian;M. Alonso-García;O. Bialik;C. Blättler;J. Guo;S. Haffen;S. Horozal;A. L. H. Mee;M. Inoue;L. Jovane;L. Lanci;J. Laya;T. Lüdmann;Nagender N. Bejugam;M. Nakakuni;K. Niino;L. Petruny;S. Pratiwi;J. Reijmer;J. Reolid;A. Slagle;C. Sloss;X. Su;P. Swart;J. Wright;Z. Yao;J. Young;S. Lindhorst;S. Stainbank;A. Rueggeberg;S. Spezzaferri;I. Carrasqueira;Siyao M. Yu;D. Kroon