Impact of the Geometry of Submarine Landscapes on Deep-Sea Biogeochemistry

浮游植物在海洋表层产生有机碳，然后将其中一些有机碳从海洋表层沉降到底层沉积物中，从大气中提取二氧化碳并将氧气注入大气。据信，在数千年至数亿年的漫长地质时间尺度上，深海沉积物中有机碳沉积量的变化会影响大气的化学组成。因此，深海沉积物中的有机碳埋藏必然是地球上“生命支持系统”的关键过程之一。因此，了解碳从海洋水柱流入底层沉积物和碳在沉积物中埋藏的控制机制至关重要。对这些碳流入深海沉积物的一些可能的控制措施进行了研究。然而，到目前为止，海底地貌几何的影响几乎没有得到任何关注。这是尽管全面和普遍的海底景观的变化，必须发生的结果，在过去的数亿年的大陆和海洋地壳的重新安排。大洋中脊，在某种程度上也包括深海平原，由海底丘陵和山脉构成。这种大规模的海底升高是深海环境变化的一个主要来源。除了它们的存在，海拔与准稳定背景（残差）和潮汐流的相互作用引入了环境的复杂性。这种增加的复杂性预计将影响一系列环境参数和过程，包括深海生物的幼虫扩散、生物多样性（对沉积物地球化学的一个重要的间接控制）、沉积碳埋藏的绝对规模、以及深海沃茨和表层沉积物中有机碳相对于埋藏在更深沉积物中的有机碳的相对比例。该项目将首次阐明大尺度水流/地形相互作用与深海有机碳动力学的三个基本方面之间的联系：（1）海山的存在对有机碳通过水柱的迁移及其在深海沉积物中的归宿的影响。(2)地理纬度的影响：准稳定背景流与海山相互作用，产生的流场形状取决于地球自转的影响，而地球自转又取决于海山的地理纬度。地形控制流场对碳动力学的影响是否存在纬度差异？(3)潮汐的影响：潮流速度在深海的空间上各不相同，在冰河时期的周期中可能也随时间变化，从而在潮汐影响的大小上造成时空变化。不同的潮汐力如何影响在小尺度海底海拔的碳动力学？我们建议通过比较尺度相似但地理纬度和潮汐力不同的海山来阐明这三个问题：在东北大西洋，17 ° N的Senghor海山和35 ° N的Ampere海山具有相似的开阔洋潮汐力，可以在地理纬度的影响方面进行比较;位于北纬35度的安培海山和位于北纬33.5度的东地中海埃拉托色尼海山处于相似的地理纬度，可以在潮汐力方面进行比较，东地中海的潮汐比东北大西洋的潮汐弱得多。这一项目的主要预期成果是对海底几何形状对深海生物地球化学和生物多样性的基本控制有了更深入的了解。

Production of organic carbon by phytoplankton in the surface ocean, followed by transport of some of this organic carbon on sinking particulate matter from the surface ocean into underlying sediments, extracts carbon dioxide from and injects oxygen into the atmosphere. For long geological time scales of thousands up to hundreds of millions of years it is believed that changes in the magnitude of organic-carbon deposition in deep-sea sediments can influence the chemical composition of the atmosphere. Organic-carbon burial in deep-sea sediments must, therefore, be one of the key processes of the 'life-supporting system' on Earth. Consequently, an understanding of the mechanisms controlling the flux of carbon from the oceanic water column into underlying sediments and the burial of carbon in the sediments is of crucial importance. A number of possible controls on these carbon fluxes into deep-sea sediments have been studied. However, to date the impact of submarine landscape geometry has received virtually no attention. This is despite comprehensive and pervasive submarine landscape changes that must have occurred as a result of the rearrangements of continents and oceanic crust during the last hundreds of millions of years. Mid-ocean ridges, but also to some degree abyssal plains, are structured by submarine hills and mountains. Such kilometre-scale seafloor elevations are a major source of environmental variability in the deep sea. In addition to their mere presence, the interaction of the elevations with quasi-steady background (residual) and tidal flow introduces complexity in the environment. This enhanced complexity is expected to influence a range of environmental parameters and processes, including larval dispersal of deep-sea organisms, biodiversity (an important indirect control on sediment biogeochemistry), the absolute magnitude of sedimentary carbon burial, and the relative proportions of organic carbon being remineralised in deep-ocean waters and surface sediments versus organic carbon being buried in deeper sediments. This project will elucidate for the first time the link between three fundamental aspects of kilometre-scale flow/topography interactions and organic-carbon dynamics in the deep ocean: (1) The influence of the PRESENCE OF A SEAMOUNT on the transport of organic carbon through the water column and its fate in deep-sea sediments. (2) The impact of GEOGRAPHICAL LATITUDE: Quasi-steady background flow interacts with the seamount, with the shape of the resulting flow field depending on the impact of the Earth's rotation which, in turn, depends on the geographical latitude of the seamount. Are there latitudinal differences in the impact of topographically controlled flow fields on carbon dynamics? (3) The impact of TIDES: Tidal current velocities vary spatially in the deep sea and may have varied temporally over ice age cycles, thereby introducing spatiotemporal variability in the magnitude of tidal impact. How do different tidal forcings influence carbon dynamics at kilometre-scale seafloor elevations? We propose to elucidate these three problems by comparing seamounts of similar dimensions which differ in terms of their geographical latitude and tidal forcing: In the Northeast Atlantic the Senghor Seamount at 17degN and the Ampere Seamount at 35degN have similar open-ocean tidal forcing and can be compared in terms of the impact of the geographical latitude; the Ampere Seamount at 35degN and the Eratosthenes Seamount in the Eastern Mediterranean at 33.5degN are at similar geographical latitude and can be compared in terms of tidal forcing, with the tides in the Eastern Mediterranean being much weaker than the tides in the Northeast Atlantic. The main anticipated achievement of this project is a much advanced understanding of the fundamental controls of seafloor geometry on deep-sea biogeochemistry and biodiversity.