Spatiotemporal Assessment of CO2–Carbonic Acid System Dynamics in a Pristine Coral Reef Ecosystem, French Frigate Shoals, Northwestern Hawaiian Islands

Abstract

Observations of surface seawater fugacity of carbon dioxide (fCO 2 ) and pH were collected over a period of several days at French Frigate Shoals (FFS) in the Northwestern Hawaiian Islands (NWHI) in order to gain an understanding of the natural spatiotemporal variability of the marine inorganic carbon system in a pristine coral reef ecosystem. These data show clear island-to-open ocean gradients in fCO 2 and total alkalinity that can be measured 10-20 km offshore, indicating that metabolic processes influence the CO 2 -carbonic acid system over large areas of ocean surrounding FFS and by implication the islands and atolls of the NWHI. The magnitude and extent of this spatial gradient may be driven by a combination of physical and biogeochemical processes including reef water residence time, hydrodynamic forcing of currents and tidal flow, and metabolic processes that occur both on the reef and within the lagoon.

Seawater DIC analysis: The effects of blanks and long‐term storage on measurements of concentration and stable isotope composition

“…Changes to DIC and δ 13 C at the surface agree closely with prior reports in which components of the inorganic carbon system exhibit strong diel dynamics at our site (Wootton et al ) and at other coastal sites in the California Current (Frieder et al ; Kapsenberg and Hofmann ). This study joins other, recent studies of the carbon cycle in coastal ecosystems that have demonstrated relatively dynamic patterns (Feely et al ; Hofmann et al ; Wootton and Pfister ; Andersson et al 2014; Kealoha et al ) and the potential for increasing variability (Schulz and Riebesell ), indicating that increased analyses of carbon system parameters are needed.…”

A space-time mosaic of seawater carbonate chemistry conditions in the north-shore Moorea coral reef system

“…It is well understood by earlier studies that the interaction of reef metabolism and the circulation over the reefs leads to large biogeochemical variations, especially on diel scales (Suzuki and Kawahata, 1999;Bates, 2002;Suzuki and Kawahata, 2003;Manzello, 2010;Anthony et al, 2011;Kleypas et al, 2011;Gray et al, 2012;Falter et al, 2013;Teneva et al, 2013;Andersson et al, 2014;Albright et al, 2015;Kealoha et al, 2017;Takeshita et al, 2018;Yan et al, 2018). But our work provides new insights about the nature of this variability.…”

“…The local environmental conditions coral reefs experience can deviate substantially from those of the open ocean, especially for the seawater's carbonate system parameters, such as dissolved inorganic carbon (DIC), total alkalinity (TA), pH (-log([H + ])), the partial pressure of CO 2 (pCO 2 ), or the saturation state with respect to the mineral CaCO 3 aragonite, W a (Manzello, 2010;Gray et al, 2012;Kealoha et al, 2017;Takeshita et al, 2018;Yan et al, 2018). This is a consequence of the interplay between coral metabolism altering the seawater chemistry in the overlying waters and the transport and mixing of the water across the reef (Anthony et al, 2011;Kleypas et al, 2011).…”