Biogeochemical and Physical Controls on the Inorganic Carbon Chemistry of Coral Reefs, Oahu, Hawaii: A Decade of Continuous Measurements

Chair: James Orr

Eric Heinen De Carlo (1)*, Gerianne Terlouw (1), Patrick S. Drupp (1,2), Fred T. Mackenzie (1), Sylvia Musielewicz (3), Adrienne Sutton (3,4), and Christopher L. Sabine (3)

1 Department of Oceanography, University of Hawaii, Honolulu, HI 96822, USA
2 NOAA Office of Education, 14th St and Constitution Ave NW, HCHB 6857, Washington DC 20230, USA
3NOAA/PMEL, 7800 Sand Point Way NE, Seattle, WA 98115, USA
4 University of Washington, Joint Institute for the Study of the Atmosphere and Ocean, Seattle, WA, 98195, USA

Background and Methods
Beginning in 2005, the NOAA/PMEL and the University of Hawaii established a network of Moored Autonomous pCO2 (MAPCO2) buoys at coastal sites around Oahu, Hawaii. The MAPCO2 buoys measure surface water and atmospheric CO2, along with other parameters at three hour intervals, and were deployed in coral reefs with different physical and biogeochemical characteristics. As part of the GOA-ON, one buoy is designated as a Class III climate site within the National Coral Reef Monitoring Program (NCRMP) and the US Ocean Acidification Program. Buoy measurements are complemented by bottle sampling for laboratory analysis of additional ancillary parameters.

Findings
The data reveal extensive variability in seawater pCO2 reflecting the influence of physical and biogeochemical forcing from winds, waves, temperature, changing atmospheric CO2 concentration, and biogeochemical processes on multiple time scales from hours to years. With an ultimate goal to understand and attribute changes from anthropogenic contributions to ocean acidification, it is critical to understand the natural processes that control short- and long-term CO2 variability on coral reefs. We present a statistical evaluation and interpretation of the longest running high-resolution, coastal CO2 time-series in the world and discuss the variability in seawater pCO2 and air-sea CO2 fluxes at our coral reef sites. Our data are compared to those collected in the open ocean at the WHOTS buoy site, ~100 km north of Oahu, in the North Pacific subtropical gyre.

Conclusions
High temporal resolution monitoring of CO2 has greatly improved our understanding of daily, sub-seasonal, seasonal, and inter-annual CO2 dynamics on coral reefs of Oahu. These data also provide a basis for understanding CO2 dynamics on tropical coral reefs, which is particularly crucial in the face of changing seawater chemistry due to rising atmospheric CO2 concentrations and the concomitant ocean acidification