Early Detection of Ocean Acidification Effects on Marine Calcification and Deep-Sea Carbonate Dissolution

在过去的200年里，海洋大约吸收了人类排放到大气中的二氧化碳(CO2)的50%。当二氧化碳侵入海洋时，海水变得不那么碱性，pH下降，这一过程被称为海洋酸化。与此同时，海水相对于方解石和文石等碳酸盐矿物的饱和状态下降，这可能在短时间内影响许多钙质生物的钙化速率。在更长的时间尺度上，人为二氧化碳也将影响海底环境，因为很大一部分二氧化碳将与深海沉积物中的碳酸钙反应，并被中和成重碳酸盐离子(化石燃料中和)。海洋酸化的这些后果对海洋生态系统的未来以及天然碳汇的命运至关重要，后者对预测未来的大气二氧化碳水平至关重要。虽然已经在实验室和中微体实验中观察到了对钙化生物的影响，但全球范围内的生态系统反应迄今尚不清楚。深海碳酸盐大规模溶解的速度也存在类似的不确定性。幸运的是，这两个过程都可以通过它们对海洋化学的影响来检测和量化：碳酸钙的产生和溶解改变了海水的总碱度。在这个项目中，夏威夷大学的研究人员将利用模拟和海洋化学数据的综合来解决以下问题：(1)海洋酸化是否导致全球范围内海洋钙化的下降，如果是，下降的幅度和时间尺度是什么？(2)深海沉积物中大规模碳酸盐溶解对化石燃料的中和率是多少？他们将使用三维全球生物地球化学海洋模型HAMOCC(其中包括一个详细的沉积物模块)来预测由于表面钙化和深海碳酸盐溶解速率变化的不同情景而导致的碱度变化。结果将与重复水文测量数据得出的海洋化学变化进行比较。对于给定的情景，他们将计算总碱度的瞬时变化超过自然可变性的位置和时间，并为未来的海洋化学项目确定目标区域，这些区域对于从现场数据计算酸化影响的准确程度至关重要。然后，他们将能够设计一种工具，以早期检测在现场可观察到的海洋酸化的大规模影响，并预测未来数千年深海碳酸盐溶解的未来作用。在更广泛的影响方面，该项目将提供对人为二氧化碳入侵海洋的短期和长期影响的见解。其目的是帮助在不久的将来指导海洋碳循环观测，以便在早期阶段检测海洋钙化和深海碳酸盐溶解对海洋酸化的大规模响应。拟议的工作将包括一个研究生项目，并将为夏威夷大学来自代表性不足群体的本科生提供教育机会。

Over the past 200 years, the ocean has taken up roughly 50% of the carbon dioxide (CO2) released into the atmosphere by mankind. As CO2 invades the ocean, the seawater becomes less alkaline and the pH drops, a process termed ?ocean acidification?. Concurrently, the saturation state of seawater with respect to carbonate minerals such as calcite and aragonite falls, which is likely to impact calcification rates in many calcareous organisms on a short time scale. On longer time scales, anthropogenic CO2 will also impact the benthic environment, as a significant fraction of the CO2 will react with CaCO3 in deep-sea sediments and be neutralized to bicarbonate ions (fossil fuel neutralization). These consequences of ocean acidification are critical for the future of marine ecosystems as well as for the fate of natural carbon sinks, the latter being vital to predicting future atmospheric CO2 levels. While effects on calcifying organisms have been observed in laboratory and mesocosm experiments, the ecosystem response on a global scale is hitherto unknown. Similar uncertainties exist regarding large-scale rates of deep-sea carbonate dissolution. Fortunately, both of these processes can be detected and quantified via their effect on ocean chemistry: production and dissolution of CaCO3 change the total alkalinity of seawater. In this project, researchers at the University of Hawaii will employ a synthesis of modeling and ocean chemistry data in order to address the following questions: (1) Does ocean acidification lead to a decline in marine calcification on a global scale, and if so, what is the magnitude and time scale of the decline? (2) What is the rate of fossil fuel neutralization by large-scale carbonate dissolution in deep-sea sediments? They will use the 3-D global biogeochemical ocean model HAMOCC (which includes a detailed sediment module) to forecast changes in alkalinity due different scenarios of changes in surface calcification and rates of deep-sea carbonate dissolution. The outcome will be compared to changes in ocean chemistry derived from data of repeat hydrographic surveys. For a given scenario, they will calculate the location and time at which transient changes in total alkalinity will exceed the natural variability and identify target regions for future ocean chemistry programs that are critical for computing the exact magnitude of acidification effects from field data. They will then be able to design a tool for early detection of large-scale effects of ocean acidification observable in the field and to project the future role of deep-sea carbonate dissolution during the coming millennia.In terms of broader impacts, this project will provide insights into the short- and long-term effects of invasion of anthropogenic CO2 into the ocean. The aim is to help guide ocean carbon cycle observations in the near future in order to detect the large-scale response of marine calcification and deep-sea carbonate dissolution to ocean acidification at an early stage. The proposed work will include a graduate student project and will provide educational opportunities for undergraduate students from underrepresented groups at the University of Hawaii.