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