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Mid-Pliocene upwelling and nutrient (Si, N) conditions in the Benguela upwelling system and their relationship to the Southern Ocean paleoceanography

本格拉上升流系统中上新世上升流和营养物（Si，N）条件及其与南大洋古海洋学的关系

基本信息

批准号：
50418050
负责人：
Professor Dr. Martin Frank
金额：
--
依托单位：
Forschungseinheit Paläo-Ozeanographie
依托单位国家：
德国
项目类别：
Infrastructure Priority Programmes
财政年份：
2007
资助国家：
德国
起止时间：
2006-12-31 至 2010-12-31
项目状态：
已结题

来源：
https://gepris.dfg.de/gepris/projekt/50418050?language=en
关键词：
Mid Pliocene upwelling nutrient Si

项目摘要

The closure of the Panama seaway for surface water exchange between about 4 and 2.6 Ma BP led to a profound reorganisation of the ocean thermohaline circulation, the advanced growth of continental ice-sheets, and probably to a more vigorous atmospheric circulation. Concomitant with these processes an extreme increase in diatom productivity and a dominance of Antarctic diatom species in the Benguela upwelling system occurred. This phenomenon is known as the Matuyama Diatom Maximum (MDM) based on results of ODP Leg 175 drill sites off Namibia, and was inferred to be a result of intensification of coastal upwelling and larger entrainment of subAntarctic mode waters. On the other hand, alkenone SST reconstructions and the δ15N signal of organic matter from these sites strongly imply that during the MDM still well stratified, warm surface waters prevailed and nutrient supply was fostered by local nitrogen fixation. This argues against a strong intensification of coastal upwelling conditions, which would have led to surface ocean cooling and subsurface nutrient supply. To resolve this controversy it is proposed to compare detailed proxy records for changes in sea surface temperatures, plankton productivity, as well as for surface ocean stratification or upwelling intensity with records documenting past changes of silicon and nitrogen supply to the Benguela system. This will allow a better understanding of the major factors leading to very high siliceous plankton productivity in eastern boundary current settings under mean states of warmer and more stratified surface water conditions than those prevailing today. The Pliocene conditions may serve as an analogue for the development of coastal upwelling settings under future global warming conditions.

在大约4到2.6 Ma BP之间，巴拿马海道为交换地表水而关闭，导致了海洋热盐环流的深刻重组，大陆冰盖的提前增长，可能还导致了更有力的大气环流。与这些过程同时发生的是硅藻生产力的急剧增加和南极硅藻物种在本格拉上升流系统中的优势地位。这种现象被称为Matuyama硅藻最大值（MDM），这是基于ODP Leg 175在纳米比亚附近钻探点的结果，并被推断为沿海上升流加剧和亚南极模态水域更大的卷带的结果。另一方面，这些地点的烯烃海表温度重建和有机质的δ15N信号强烈表明，在MDM期间，温暖的地表水占主导地位，局部固氮促进了养分供应。这反驳了沿海上升流条件的强烈加剧，这将导致表面海洋冷却和地下营养供应。为了解决这一争议，我们建议将海洋表面温度、浮游生物生产力以及海洋表面分层或上升流强度的详细替代记录与记录本格拉系统硅和氮供应过去变化的记录进行比较。这将使我们能够更好地了解导致东部边界洋流环境中硅质浮游生物生产力非常高的主要因素，这些环境比目前普遍存在的地表水条件更温暖和更分层的平均状态。上新世条件可以作为未来全球变暖条件下沿海上升流环境发展的模拟。