Cenozoic/Mesozoic variability of seawater sulfate concentrations

微生物硫酸盐还原（MSR）是连接碳(C)、氧(O)、硫(S)和磷(P)生物地球化学循环的基本过程。海洋沉积物中约85%的沉积有机质由MSR呼吸，因此它是大气氧水平的主要控制因素。MSR也是厌氧甲烷氧化的关键因素，它严格控制甲烷（一种主要的温室气体）在沉积物水界面的通量。MSR依赖于硫酸盐作为电子受体，而硫酸盐浓度的变化以非线性的方式影响这一过程（Wortmann & Chernyavsky, Nature, 2007）。虽然一般认为，随着时间的推移，海洋硫酸盐浓度相当稳定（约为28mmol/l），但我最近发表了一个假设，即在过去130 Ma中，海水硫酸盐浓度在1至30 mmol/l之间波动（Wortmann & Paytan, Science, 2012）。这种程度的硫酸盐浓度变化将以三倍的速度改变有机物再矿化速率（Wortmann & Chernyavsky, 2007），影响微生物的固氮作用，并在很大程度上改变海洋磷酸盐库的大小，这是海洋肥力的主要控制因素。此外，硫酸盐浓度的变化可能会影响硫酸盐气溶胶的浓度，从而改变大气的辐射特性（Wortmann & Paytan, 2012）。考虑到变化的海水硫酸盐浓度的深远影响，理解这一假设的稳健性是很重要的。在这里，我建议使用建模和实地考察相结合的方法来评估其他解释是否与地质记录和我们对海洋化学的理解相一致。这些研究问题处于该领域的前沿，将产生高影响力的出版物，进一步提高加拿大研究能力的国际声誉。本项目将培养数据分析、湿化学实验室方法、稳定同位素分析、计算机编程和国际合作等方面的3名博士和6名硕士生。这些技能为加拿大下一代学术和商业领袖奠定了基础。

Microbial sulfate reduction (MSR) is the fundamental process linking the biogeochemical cycles of carbon (C), oxygen (O), sulfur (S) and phosphorous (P). MSR respires approximately 85% of all sedimentary organic matter in marine sediments, and is thus a major control on atmospheric oxygen levels. MSR is also a key element for anaerobic methane oxidation, which critically controls the flux of methane (a major greenhouse gas) across the sediment water interface. MSR depends on sulfate as an electron acceptor, and variable sulfate concentrations affect this process in a non-linear way (Wortmann & Chernyavsky, Nature, 2007). While it is generally assumed that marine sulfate concentrations have been fairly stable through time (about 28mmol/l), I recently published the hypothesis that seawater sulfate concentrations fluctuated between 1 to 30 mmol/l throughout the last 130 Ma (Wortmann & Paytan, Science, 2012). Sulfate concentration changes of this magnitude will alter organic matter remineralization rates by a factor of three (Wortmann & Chernyavsky, 2007), affect microbial nitrogen fixation, and considerably modify the size of the marine phosphate reservoir, a major control on ocean fertility. Furthermore, it is likely that variable sulfate concentrations will influence the concentration of sulfate aerosols thus altering the radiative properties of the atmosphere (Wortmann & Paytan, 2012). Given the far reaching consequences of variable seawater sulfate concentrations, it is important to understand the robustness of this hypothesis. Here I propose to use a combination of modeling and fieldwork to evaluate whether alternative explanations are consistent with the geologic record and our understanding of ocean chemistry. These research questions are at the leading edge of the field and will result in high impact publications, furthering the international reputation of Canada's research competence. This proposal provides opportunities to train three Ph.D. and six M.Sc. students in data analysis, wet chemical laboratory methods, stable isotope analysis, computer programming, and international collaboration. These skills build the foundations for Canada's next generation of academic and business leaders.