Water mass mixing and silicate utilization in the Atlantic Ocean

这项拟议研究的中心目标是详细调查溶解钕（Nd），铪（Hf）和硅（Si）的浓度和同位素组成在热带大西洋的水柱的分布。放射性Nd和Hf同位素是强大的地球化学示踪剂的水质量流和混合，以及大陆的输入和风化制度，但有很大的不确定性的输入源，如撒哈拉沙漠的灰尘，河流和交换与陆架沉积物，目前阻止使用这些同位素系统作为定量代理现在和过去的海洋环流的重要性。硅同位素是研究沃茨生物活动对硅利用的一种很有前途的示踪剂，但硅同位素分布也受水体混合的影响。对于所有这些同位素示踪剂，有一个严重缺乏详细的数据，它们的分布在当今的大西洋经向翻转环流（AMOC）在西北和热带大西洋的关键领域，这严重限制了它们作为代理示踪剂的可靠应用。为了消除这一差距，在沿着的Meteor M81/1号考察船的剖面上，以高分辨率并在微量金属清洁条件下对完整的水柱剖面进行了取样（2010年2月/3月，GEOTRACES A11号游轮，加那利群岛-西班牙港，特立尼达和托巴哥）和64 PE 319/321号Pelagia号RV探险期间（GEOTRACES Cruise A02，斯克拉布斯特，苏格兰-福塔莱萨，巴西，2010年4月至7月）在热带和北大西洋西部的考察，将作为拟议研究的材料。的同位素组成和浓度的Nd，Hf和Si的系统测量将首次表征控制其水质量的签名和输入在热带大西洋的因素，并将显着提高其适用性作为代理示踪剂的海洋环流，风化输入，和硅酸盐利用在现在和过去的海洋。

The central goal of this proposed study is a detailed investigation of the distribution of dissolved neodymium (Nd), hafnium (Hf) and silicon (Si) concentrations and isotope compositions in the water column of the tropical Atlantic Ocean. Radiogenic Nd and Hf isotopes are powerful geochemical tracers of water mass flow and mixing, as well as of continental inputs and weathering regimes, but there are significant uncertainties concerning the quantitative importance of input sources such as Saharan dust, rivers and exchange with shelf sediments, which currently prevent the use of these isotope systems as quantitative proxies for present and past ocean circulation. Silicon isotopes are a promising tracer for Si utilization by biological activity the surface waters, but the Si isotope distributions are also influenced by water mass mixing. For all these isotopic tracers there is a severe lack of detailed data on their distribution in critical areas of the present day Atlantic Meridional Overturning Circulation (AMOC) in the northwestern and tropical Atlantic, which severely restricts their reliable application as proxy tracers. To remove this gap, full water column profiles were sampled at high resolution and under trace metal clean conditions along the sections of expedition Meteor M81/1 (GEOTRACES Cruise A11, Canaries – Port of Spain, Trinidad and Tobago in February/March 2010) and during RV Pelagia expedition 64PE319/321 (GEOTRACES Cruise A02, Scrabster, Scotland – Fortaleza, Brasil, April - July 2010) in the tropical and western North Atlantic, which will serve as material for the proposed study. The systematic measurement of the isotope composition and concentration of Nd, Hf, and Si will for the first time characterize the factors controlling their water mass signatures and inputs in the tropical Atlantic Ocean and will significantly improve their applicability as proxy tracers for ocean circulation, weathering inputs, and silicate utilisation in the present and past ocean.