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揭示了无可争议的证据，表明由于从大气中吸收人为二氧化碳，公海表层海水长期酸化。酸化对碳酸钙的生产和保存产生负面影响的同时证据引发了人们对珊瑚礁潜在后果的担忧。 尽管总体上尚未观察到珊瑚礁环境的长期酸化，但发现百慕大珊瑚礁平台2007年至2012年期间的海水酸化率比附近近海公海时间序列站观察到的长期（1983年至2012年）酸化率快三倍。 该项目的研究人员相信他们现在了解了这是如何发生的，并设计了一项研究来证实或反驳他们的想法。 具体而言，他们认为 2007 年至 2012 年观察到的变化可归因于最近与净礁石钙化和异养增加相关的珊瑚礁代谢过程的变化。 他们掌握的证据表明，这些变化是由于近海初级生产增加而导致珊瑚礁食物供应增加所推动的，而北大西洋涛动（NAO）状态是副极地和副热带北大西洋之间大气压力差的周期性来回变化。在这个项目中，通过收集从百慕大的珊瑚礁平台到近海开放水域时间序列站的广泛的物理、化学和生物数据，他们将探索这个想法。 该项目的主要科学和更广泛的社会影响将是其与增进当前对海洋酸化对珊瑚礁影响的了解的相关性。对该生态系统未来影响的稳健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探索研究所和百慕大海洋学院促进社区教育外展，吸引来自代表性不足的少数族裔的学生。 这项研究的中心假设是，在冬季NAO负值的年份里，混合加剧和养分供应增加增强了近海生产，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。为了解决这一假设，该团队将每月测量和表征百慕大珊瑚礁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）。 这些数据将与百慕大-大西洋时间序列和 Hydrostation S 计划以及近海-近海横断面收集的数据一起进行评估。 预计这种方法将进一步了解海水生物地球化学特性（包括海水碳酸盐化学）如何随时间和空间在百慕大珊瑚礁上变化，并确定这些变化的主要驱动因素。它将专门解决近海和近海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和气候强迫（例如 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，以及这些变化在光、营养物和食物供应等其他强迫的背景下对珊瑚礁代谢是否重要。

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.