Biogenic opal isotopes - new tool for evaluation of past nutrient cycling and hydrographic structure in the Pacific Southern Ocean in relation to climate and Antarctic cryosphere evolution

在过去的气候周期中，大气CO2浓度呈现出逐渐下降和快速上升的重复模式，这与气温和全球冰量历史密切相关。人们已经认识到，南大洋是控制过去和现在二氧化碳变化的关键区域。然而，这种碳调节剂对气候变化引起的风型、海洋环流、层化、海冰范围和生物生产重组的敏感性仍然存在争议。关于过去水文和生产力的数据主要来自大西洋地区。为了更全面地了解SO进程，大西洋进程在多大程度上可以转化为研究甚少的太平洋部门，还有待检验。这一区域不仅是南大洋最大的部分，也是以海洋为基础的西南极冰盖的主要流域。这项拟议的研究旨在使用一种新建立的方法，从太平洋上的两个沉积物岩心横断面生成古数据集，其中包括对提纯的硅藻和放射虫进行氧和硅同位素联合测量。选定的沉积物间隔和地点将首次描述不同气候条件下表层和次表层水深度的物理和营养特性的演变，从比现在冷(例如最后一次冰盛期)到比现在热(例如海洋同位素5.5阶段)，以及从极地太平洋东部和西部不同环境环境的演变。这项研究将通过评估(1)太平洋SO生态系统对粉尘微营养素沉积(铁肥)和相关的硅吸收速率的敏感性，(2)表层水层结的形成和程度，以及(3)“硅酸泄漏”假说来检验关于SO‘S在气候系统中的作用的假说，该假说是理解海洋生产力和碳固定的关键。新的指标还将提供关于融水脱落引起的表层海洋盐度异常时间的信息，以获得关于WAIS稳定性的信息，并检验MIS5.5期间WAIS总下沉的假设。获得的古记录将与大气-海洋环流模型和包括正在进行的SPP1158-DFG项目的硅同位素的生物地球化学模型相结合的模拟进行比较(CAU Kiel，Pi B.Schneider)。这将有助于更好地分离海洋环流和生物生产对海-气二氧化碳交换的个别影响，并在统计上得到支持。将与其他国家和国际项目框架内正在进行的研究密切合作，提供关于尘埃和生物沉积速率、海洋物理参数(如海冰、海面温度)和生成适当年龄模型的基本信息。

Atmospheric CO2 concentrations present a repetitive pattern of gradual decline and rapid increase during the past climate cycles, closely related to temperature and global ice volume history. It has been recognized that the Southern Ocean (SO) represents a key area governing past and present CO2 change. However, the sensitivity of this carbon modulator to climate-change induced reorganizations in wind patterns, ocean circulation, stratification, sea ice extent and biological production remains under debate. Data on past SO hydrography and productivity are mainly from the Atlantic sector. To obtain a more comprehensive picture of SO processes it remains to be tested to what extent Atlantic processes can be translated to the yet little studied Pacific sector. This sector is not only the largest part of the Southern Ocean, but it also represents the main drainage area of the marine-based West Antarctic Ice Sheet (WAIS). The proposed study aims to generate paleo-data sets from two sediment core transects across the Pacific SO using a newly-established method, which comprises combined oxygen and silicon isotope measurements of purified diatoms and radiolarians. The selected sediment intervals and sites will allow to describe for the first time the evolution in physical and nutrient properties at surface and subsurface water depth during different climate conditions, from colder than present (e.g. Last Glacial Maximum) to warmer than present (e.g. Marine Isotope Stage 5.5), and from different environmental settings in the eastern and western polar Pacific SO. The study will allow to test hypotheses concerning the SO´s role in the climate system by evaluation of (1) the sensitivity of the Pacific SO ecosystems to dust-borne micronutrient deposition (iron fertilization) and related Si-uptake rates, (2) the formation and extent of surface water stratification and (3) the 'silicic-acid leakage' hypothesis, postulating high-low latitude nutrient exchange critical for understanding productivity and carbon sequestration in the ocean. The new proxies will also provide information on the timing of surface ocean salinity anomalies resulting from meltwater shedding to gain information on WAIS stability and to test the assumption of a total WAIS draw down during MIS 5.5. Obtained paleo-records will be compared with simulations with an atmosphere-ocean general circulation model combined with a biogeochemical model including Si isotopes from an ongoing SPP1158-DFG project (CAU Kiel, PI B. Schneider). This should allow for better separation and statistically supported analysis of the individual impacts of ocean circulation and biological production on the air-sea CO2 exchange. Basic information on dust and biogenic deposition rates, physical ocean parameters (e.g. sea ice, sea surface temperature) and the generation of appropriate age models will be available in close cooperation with ongoing research in the frame of other national and international projects.