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Ocean Acidification Monitoring Network: Oʻahu, Hawaiʻi

Principal Investigator: Eric DeCarlo

Graduate Student: Gerarda Terlouw

Human emissions of carbon dioxide and partial uptake of this gas by the oceans increase the acidity of the oceans and affects adversely the ability of organisms to make calcium carbonate shells and skeletons. How this occurs, however, remains incompletely understood. Computer simulations suggest a future corrosive marine environment where dissolution of existing carbonate sediments will exceed production and corals will have difficulty accreting at current rates. Much research to date on this topic has focused on the open-ocean and “model” environments, but tropical estuaries and coral reefs are understudied. These areas represent a significant fraction of the global system and play a critical role in the global carbon cycle. For these reasons time series data in different reef settings in Hawaiʻi are critical to quantify contributions of reefs to air-sea exchange of CO2. We propose to continue and enhance our highly successful CRIMP-CO2 project to studies of air-sea exchange of CO2 and carbonate mineral stability in barrier and fringing reef settings.  We plan to collect high temporal frequency data at four buoys, whose locations differ in a variety of ways that will help us to constrain better how physical forces and biological processes interact to affect carbon system parameters. We will follow protocols used in our ongoing SeaGrant funded and PacIOOS studies, and continue a close and successful collaboration with our colleagues at NOAA/PMEL. Our work will quantify the direction and magnitude of the air-sea exchange of carbon dioxide in different coral reef settings representative of a substantial portion of the subtropical coastal ocean. It will also quantify calcification and carbonate mineral dissolution in the water column and sediments of coral reef ecosystems, and provide improved understanding of these processes under representative in situ conditions necessary to develop both regional and global estimates of their magnitude.  For the past five years, we have built upon the successful approach employed in earlier work to obtain high-frequency time-series records at multiple sites and have established critical understanding of how physical processes act in concert with biological activity and impact air-sea exchange of carbon dioxide. Our work has shown coastal reefs of Oahu are net annual sources of CO2 to the atmosphere, but the strength of the signal is seasonal and evidence exists suggesting fringing reef sites are slowly changing to become sinks of this greenhouse gas. Our research has resulted in several MS graduates, two of whom are now working in closely related technical fields and another is pursuing a PhD in our group. Multiple journal articles, book chapters, and conference presentations have described our results to date.