Collaborative Research Ocean Acidification: Establishing the links between offshore biogeochemistry, coral reef metabolism and acidification

来自大西洋和太平洋的时间序列观测显示，由于人类从大气中吸收二氧化碳，公海表面海水长期酸化的证据无可争辩。同时有证据表明，酸化对碳酸钙的生产和保存有负面影响，这加剧了人们对珊瑚礁潜在后果的担忧。虽然总体上没有观察到珊瑚礁环境的长期酸化，但2007-2012年间百慕大珊瑚礁平台上的海水酸化速度比附近一个近海公海时间序列站观测到的长期（1983-2012）酸化速度快三倍。该项目的研究人员相信，他们现在明白了这是如何发生的，并设计了一项研究来证实或反驳他们的观点。具体来说，他们认为2007-2012年观察到的变化可归因于最近与净珊瑚礁钙化和异养增加相关的珊瑚礁代谢过程的转变。他们手头的证据表明，这些变化是由珊瑚礁食物供应的增加所推动的，这是由于近海初级生产的增加，似乎与北大西洋涛动（NAO）的状态有关，北大西洋涛动是北大西洋亚极地和亚热带之间大气压力差的周期性来回变化。在这个项目中，他们将通过收集从百慕大珊瑚礁平台到近海开放水域时间序列站的大量物理、化学和生物数据，来探索这一想法。该项目的主要科学和更广泛的社会影响将是它对推进目前对海洋酸化对珊瑚礁影响的理解的相关性。对这一生态系统未来影响的可靠预测需要了解珊瑚礁生物地球化学过程和当地海水酸化的主要驱动因素。其次，该项目将支持作为研究团队成员的研究生和本科生的教育和研究活动，并通过圣地亚哥海洋发现研究所和百慕大海洋学院促进社区教育外展，以吸引来自代表性不足的少数民族的学生。本研究的中心假设是，在负冬季NAO年份，混合加剧和营养供应增加，近海生产增加，导致珊瑚礁钙化和珊瑚礁异养，从而加剧了珊瑚礁局部海水酸化。为了验证这一假设，研究小组将测量和描述近海海水的生物地球化学特性（温度、盐度、溶解的无机碳、总碱度、钙、二氧化碳分压、无机营养物、颗粒有机碳和氮、总有机碳和氮、浮游植物色素和细菌丰度），每个月间隔一次，横跨百慕大珊瑚礁。这些数据将与作为百慕大-大西洋时间序列和水文站S计划的一部分以及沿近海样带收集的数据一起进行评估。预计该方法将进一步了解百慕大珊瑚礁的海水生物地球化学性质（包括海水碳酸盐化学）如何随时间和空间变化，并确定这些变化的主要驱动因素。它将具体讨论近海和近岸生物地球化学过程之间的耦合，以及它们如何与更大规模的海洋学和气候强迫（如NAO）联系起来。它还讨论了珊瑚礁生物地球化学过程如何减轻或加剧海洋酸化，以及这些变化是否对其他强迫（如光、营养和食物供应）背景下的珊瑚礁代谢重要。

Time-series observations from the Atlantic and Pacific Oceans have revealed indisputable evidence of long-term acidification of open-ocean surface seawater due to uptake of anthropogenic carbon dioxide from the atmosphere. Concurrent evidence of negative effects of acidification on the production and preservation of calcium carbonate have fueled concern about the potential consequences to coral reefs. Although long-term acidification in coral reef environments in general has not been observed, seawater acidification rates on the Bermuda coral reef platform between 2007-2012 have been found to be three times faster than the long-term (1983-2012) acidification rate observed at a nearby offshore open-ocean time-series station. The investigators on this project believe that they now understand how this happens and have designed a study to confirm or refute their ideas. Specifically they believe that the observed changes in 2007-2012 are attributable to a recent shift in reef metabolic processes associated with an increase in net reef calcification and heterotrophy. The evidence they have in-hand suggests that these changes have been fueled by an increase in food supply to the reef as a result of increased offshore primary production seemingly linked to the state of the North Atlantic Oscillation (NAO), a periodic back-and-forth shifting of atmospheric pressure differences between the subpolar and the subtropical North Atlantic. In this project, by collecting an extensive set of physical, chemical, and biological data extending from the reef platform at Bermuda to the offshore open-water time-series station, they will explore this idea. The primary scientific and societal broader impacts of this project will be its relevance to advancing current understanding of the effects of ocean acidification on coral reefs. Robust prediction of future effects on this ecosystem requires knowledge of the main drivers of reef biogeochemical processes and of local seawater acidification. Secondly, the project will support the education and research activities of both graduate and undergraduate students working as members of the research team, and foster community educational outreach through the Ocean Discovery Institute in San Diego and the Ocean Academy in Bermuda to engage students from underrepresented minorities. The central hypothesis of this research is that during years of negative winter NAO, intensified mixing and increased nutrient supply enhance offshore production leading to coral reef calcification and reef heterotrophy, thus intensifying the local seawater acidification on the reef. To address this hypothesis, the team will measure and characterize inshore seawater biogeochemical properties (temperature, salinity, dissolved inorganic carbon, total alkalinity, calcium, partial pressure of carbon dioxide, inorganic nutrients, particulate organic carbon and nitrogen, total organic carbon and nitrogen, phytoplankton pigments, and bacterial abundance) on a monthly interval across the Bermuda coral reef. These data will be evaluated in concert with data collected as part of the Bermuda-Atlantic Time-Series and Hydrostation S programs and along inshore-offshore transects. It is expected that this approach will further the understanding of how seawater biogeochemical properties, including seawater carbonate chemistry, vary over time and space on the Bermuda coral reef, and identify the main drivers of these variations. It will specifically address the coupling between offshore and inshore biogeochemical processes and how they are linked to larger-scale oceanographic and climatic forcings, such as the NAO. It also addresses how reef biogeochemical processes may alleviate or exacerbate ocean acidification, and whether these changes are important to reef metabolism in the context of other forcings such as light, nutrients, and food availability.