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，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。同时有证据表明，酸化对碳酸钙的生产和保存产生了负面影响，这加剧了人们对其对珊瑚礁的潜在后果的关切。虽然总体上没有观察到珊瑚礁环境的长期酸化，但据发现，2007-2012年期间百慕大珊瑚礁平台上的海水酸化速度是附近近海开阔海洋时间序列站观测到的长期(1983-2012年)酸化速度的三倍。该项目的研究人员认为，他们现在了解了这种情况是如何发生的，并设计了一项研究来证实或驳斥他们的想法。具体地说，他们认为，2007-2012年观察到的变化可归因于最近珊瑚礁新陈代谢过程的转变，这与珊瑚礁净钙化和异养增加有关。他们掌握的证据表明，这些变化是由于近海初级生产力的增加而导致对珊瑚礁的食物供应增加，这似乎与北大西洋涛动(NAO)的状态有关，NAO是亚极地和亚热带北大西洋之间大气压力差的周期性来回转移。在这个项目中，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，他们将探索这一想法。该项目的主要科学影响和更广泛的社会影响将是它与促进目前对海洋酸化对珊瑚礁的影响的了解有关。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小组成员的研究生和本科生的教育和研究活动，并通过圣地亚哥的海洋探索研究所和百慕大的海洋学院促进社区教育宣传，以吸引代表人数不足的少数群体的学生。这项研究的中心假设是，在冬季NAO为负的年份，强化的混合和增加的营养物质供应增加了近海生产，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，该团队将每月测量一次百慕大珊瑚礁近岸海水的生物地球化学性质(温度、盐度、溶解无机碳、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)，并对其进行表征。这些数据将与作为百慕大-大西洋时间序列和S水电站方案的一部分以及沿近岸-近海截面图收集的数据一起进行评估。预计这一办法将进一步了解百慕大珊瑚礁的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变化，并查明造成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和气候强迫相联系，如NAO。它还讨论了珊瑚礁生物地球化学过程如何缓解或加剧海洋酸化，以及在光照、营养物质和食物可获得性等其他因素的背景下，这些变化对珊瑚礁新陈代谢是否重要。

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.