Investigation of mechanism driving glacial/interglacial variability in stratification/mixing and biological productivity of the Pacific Southern Ocean and potential implications on air-sea CO2-exchange: synthesis of climate and ocean biogeochemical modeli

在最近的气候周期中，大气CO2浓度呈现出逐渐下降和快速上升的重复模式，与温度和海平面变化密切相关。在末次盛冰期（LGM; 23-19 kyr BP），当海平面约。在目前的120米以下，海洋必须额外储存约750 Gt的碳。人们一致认为，南大洋是控制过去和现在二氧化碳变化的一个关键区域。后者不仅具有高度的科学意义，而且也具有社会经济和政治意义，因为南大洋有可能成为有效的人为碳汇。然而，这种碳汇对气候变化引起的风型、海洋环流、分层、海冰范围和生物生产重组的敏感性仍在争论之中。模型尚不能再现所涉及的必要机制，可能是由于缺乏大气和海洋环流的动态表示/分辨率以及缺少碳循环。关于过去南大洋水文地理和生产力的数据主要来自大西洋部分，因此没有充分记录太平洋部分的情况。这一部分不仅是南大洋最大的部分，而且也是以海洋为基础的西南极冰盖（WAIS）的主要流域。在拟议中的研究中，我们的目标是生成古数据集与新建立的代理方法从沉积物芯断面横跨南太平洋。这将加强对南大洋在碳循环中的作用的理解和建模的基线，即海洋/大气CO2交换和碳封存。它还将允许洞察WAIS对过去比现在更温暖的条件的反应。将对纯化的硅藻和放射虫进行成对同位素测量（氧、硅），以描述地表和地下水深度物理和营养特性的冰川/间冰期对比。这将被用来测试（一）尚未考虑的尘埃携带的微量营养素沉积对南太平洋冰川的初级生产力，硅吸收率和碳出口的变化，（二）的影响“硅酸渗漏”假说（SALH）和（三）地表水分层的形成和程度。硅藻和放射虫的氧同位素将提供信息的时间表海洋盐度异常所造成的WAIS融水。气候模式模拟使用复杂的耦合大气海洋环流模式（AOGCM）结合一个复杂的海洋地球化学模型，包括硅同位素将用于与古记录进行比较。分析将涵盖南大洋水文地理、营养循环和海气二氧化碳交换的空间和时间变异模式。在气候模型的帮助下，我们的目标是更好地分离和统计分析海洋环流和生物生产对海气CO2交换的个别影响。

Atmospheric CO2 concentrations present a repetitive pattern of gradual decline and rapid increase during the last climate cycles, closely related to temperature and sea level change. During the Last Glacial Maximum (LGM; 23-19 kyr BP), when sea level was ca. 120 m below present, the ocean must have stored additionally about 750 Gt carbon. There is consensus that the Southern Ocean represents a key area governing past and present CO2 change. The latter is not only of high scientific but also of socio-economic and political concern since the Southern Ocean provides the potential for an efficient sink of anthropogenic carbon. However, the sensitivity of this carbon sink to climate-change induced reorganizations in wind patterns, ocean circulation, stratification, sea ice extent and biological production remains under debate. Models were not yet able to reproduce the necessary mechanisms involved, potentially due to a lack of the dynamic representation/resolution of atmospheric and oceanic circulation as well as missing carbon cycling. Data on past Southern Ocean hydrography and productivity are mainly from the Atlantic sector, thus do not adequately document conditions in the 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). In the proposed study we aim to generate paleo-data sets with a newly established proxy method from sediment core transects across the Pacific Southern Ocean. This will enhance the baselines for the understanding and modeling of the Southern Ocean´s role in carbon cyling, i.e. ocean/atmosphere CO2 exchange and carbon sequestration. It will also allow insight into the response of the WAIS to past warmer than present conditions. Paired isotope measurements (oxygen, silicon) will be made on purified diatoms and radiolarians to describe glacial/interglacial contrasts in physical and nutrient properties at surface and subsurface water depth. This will be used to test (i) the impact of yet unconsidered dust-borne micronutrient deposition on the glacial South Pacific on shifts of primary productivity, Si-uptake rates and carbon export, (ii) the “silicic-acid leakage” hypothesis (SALH) and (iii) the formation and extent of surface water stratification. Diatom and radiolarian oxygen isotopes will provide information on the timing of surface ocean salinity anomalies resulting from WAIS melt water. Climate model simulations using a complex coupled atmosphere ocean general circulation model (AOGCM) in combination with a sophisticated ocean biogeochemical model including Si-isotopes will be used for comparison with the paleo records. The analysis will cover spatial as well as temporal variability patterns of Southern Ocean hydrography, nutrient cycling and air-sea CO2-exchange. With the help of the climate model we aim to better separate and statistically analyse the individual impacts of ocean circulation and biological production on the air-sea CO2-exchange.