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

按照预测的人为碳排放速度，预计到本世纪末，表层海洋的pH将下降0.3个pH单位，到2300年前将下降0.7个pH单位。过去唯一一次海洋可能经历过类似的pH变化是在古新世-始新世最热时期(PETM；56Mya)，这是大规模碳释放的结果，这也使地球变暖。据估计，释放的碳的质量与对未来的预测一样大，但时间跨度为数千年，而不是数百年，因此可以更好地缓冲表层海洋的饱和状态。尽管如此，浮游钙化生物和珊瑚礁的多样性都经历了显著的减少，这可能是由于包括pH值和碳酸盐饱和状态在内的多种因素的综合作用。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碳同位素和碳酸盐沉积物分布等海洋碳酸盐化学变化观测的制约。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，测试受到限制。为了解决这一不足，来自加州大学圣克鲁斯分校、哥伦比亚大学拉蒙特-多尔蒂地球天文台和夏威夷大学的科学家团队正在进行一项为期3年的研究，以量化PETM期间海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B/Ca和B同位素这两种基于硼的替代物来量化酸碱度和可能的碳酸盐离子浓度。该小组将为一些全球分布的地点开发详细的替代记录，目标是确定相对于较长期趋势的表层海洋碳酸盐化学的区域异常。这些数据将用数值模型进行解释，利用基于实验室的现代有孔虫校准研究的信息，并与浮游生物组合记录进行比较。该结果还将提供一种独立的手段来测试碳释放速率和持续时间的模型模拟，以及最终大气CO2的上升。该项目将为研究人为二氧化碳对表层海洋pH和碳酸盐化学的短期和长期影响提供重要的洞察。此外，该项目将整合有关全球变暖和海洋酸化的研究和教育活动，将这些信息直接引入中学和大学课程以及大众期刊。

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.