Ocean Acidification: Collaborative Research: Establishing The Magnitude Of Sea-Surface Acidification During The Paleocene-Eocene Thermal Maximum

按照预计的人为碳排放速率，预计到本世纪末，海洋表面的pH值将下降0.3个pH单位，到2300年将下降0.7个pH单位。过去唯一一次海洋可能经历过类似的pH值变化是在古新世-始新世热极大期（PETM； 56万年），这是大规模碳释放的结果，也使地球变暖。据估计，这次释放的碳量与未来的预测一样大，但这是在数千年而不是几个世纪的时间里发生的，因此可以对表层海洋的饱和状态进行更大的缓冲。尽管如此，浮游钙化物和珊瑚礁的多样性都经历了显著的减少，这可能是对包括pH值和碳酸盐饱和状态在内的多种因素的反应。然而，量化碳酸盐化学变化的努力依赖于间接方法，即碳循环的数值模型受到海洋碳酸盐化学变化（如碳同位素和碳酸盐沉积物分布）观测的限制。在计算碳释放的质量和速率时，这些模型还模拟了海洋pH值和饱和状态的变化。虽然模型估计的范围继续缩小，但由于缺乏关于海洋碳酸盐化学的更直接信息，特别是pH值和/或碳酸盐离子浓度的变化，测试受到了限制。为了解决这一缺陷，来自加州大学圣克鲁斯分校、哥伦比亚大学拉蒙特-多尔蒂地球观测站和夏威夷大学的一组科学家正在进行一项为期3年的研究，以量化PETM期间海洋表面碳酸盐化学的变化。该项目将侧重于应用浮游有孔虫中记录的两种硼基代用品，即B/Ca和B同位素，以量化pH值和可能的碳酸盐离子浓度。该团队将为全球分布的许多地点开发详细的代理记录，目标是建立相对于长期趋势的海洋表面碳酸盐化学的区域异常。这些数据将利用基于实验室的现代有孔虫校准研究的信息，用数值模型进行解释，并与浮游生物组合记录进行比较。这些结果还将提供一种独立的方法来测试碳释放速率和持续时间的模型模拟，以及最终大气中二氧化碳的上升。该项目将为人为二氧化碳对海洋表面pH值和碳酸盐化学的短期和长期影响提供重要见解。此外，该项目将把关于全球变暖和海洋酸化的研究和教育活动结合起来，将这些资料直接纳入中学和大学课程和通俗杂志。

At projected rates of anthropogenic carbon emissions, the pH of the surface ocean is expected to decline by 0.3 pH units by the end of this century, and 0.7 pH units by 2300. The only other time the ocean might have experienced a similar change in pH in the past is during the Paleocene-Eocene Thermal Maximum (PETM; 56 Mya) as a consequence of a massive carbon release, which also warmed the planet. The mass of carbon released is estimated to have been as large as that projected for the future but over thousands of years rather than centuries, thus allowing for greater buffering of the saturation state of the surface ocean. Nonetheless, planktonic calcifiers and coral reefs both experienced significant reductions in diversity, likely in response to a combination of factors, including pH and carbonate saturation state. Efforts to quantify changes in carbonate chemistry, however, have relied on indirect methods, that is with numerical models of the carbon cycle constrained by observations of changes in ocean carbonate chemistry such as carbon isotopes and the distribution of carbonate sediments. In computing the mass and rate of carbon release, the models also simulate changes in ocean pH and saturation state. While the range of model estimates continues to narrow, testing has been limited by the lack of more direct information on ocean carbonate chemistry, specifically changes in the pH and/or carbonate ion concentration. To address this deficiency, a team of scientists from the University of California at Santa Cruz, the Lamont-Doherty Earth Observatory of Columbia University, and the University of Hawaii are conducting a 3-year study to quantify changes in the sea-surface carbonate chemistry during the PETM. The project will focus on the application of two boron-based proxies, B/Ca and B isotopes as recorded in planktonic foraminifera, to quantify pH and possibly carbonate ion concentration. The team will develop detailed proxy records for a number of globally distributed locations, with the goal of establishing regional anomalies in surface ocean carbonate chemistry relative to longer-term trends. The data will be interpreted with numerical models utilizing information from laboratory-based calibration studies of modern foraminifera, and compared with plankton assemblage records. The results will also provide an independent means of testing model simulations of the rate and duration of carbon release, and ultimately the rise in atmospheric CO2.This project will provide important insight into the short- and long-term impacts of anthropogenic CO2 on surface ocean pH and carbonate chemistry. Moreover, the project will integrate research and educational activities on global warming and ocean acidification by introducing this information directly into secondary school and college curricula and popular journals.