[1] Monitoring seawater CO 2 for a full year with seasonal observations of community metabolism in Ishigaki Island, Japan, revealed seasonal variation and anomalous values owing to the bleaching event in 1998. The daily average pCO 2 showed a seasonal pattern on an annual scale, 280 to 320 matm in winter and 360 to 400 matm in summer, which was determined primarily by the seasonal change in seawater temperature. By contrast, the range in the diel variation in pCO 2 , 400 to 500 matm in summer 200 to 300 matm in winter, was attributed to the seasonal variation in community metabolism: Gross primary production (P g ) and respiration (R) were high in summer and low in winter. During the 1998 bleaching event, although P g and R increased, community excess organic production (E) decreased by three quarters compared with the same month in 1999, when the coral community showed high recovery. This change in metabolism led to large diel range and increased average value of pCO 2 levels in the seawater on the reef flat. The decrease in the range and increase in the average value of pCO 2 were observed by monitoring the Palau barrier reef flat, where overall mortality of corals occurred after the bleaching. All the metabolic parameters, P g , R, E and calcification (G) were reduced by half after the bleaching, which increased the average pCO 2 value by 10 matm and decreased its diel range from 200-400 matm to 100-200 matm. Bleaching and resultant mortality of coral reefs led to degradation of their metabolic performance, and thus resulted in the loss of their active interaction with the carbon cycle.

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We studied the seawater carbon dioxide (CO 2 ) system in the Palau coral reef by measuring total alkalinity (TA) and total dissolved inorganic carbon (DIC). Variation in the CO 2 system on the reef flat and in the lagoon was analyzed by TA-DIC diagrams, taking into accounts the differing residence times of seawater. CO 2 in the offshore water was relatively stable in space and time, but on the reef flat it was subject to rapid (about 3 h) and substantial changes due to photosynthesis and calcification during the day and due to respiration and calcification at night. Water flowed into the lagoon where decomposition of organic matter and continuing calcification occurred over relatively long residence times (,30 d). Despite the spatial and temporal variations, the center of the lagoon had relatively constant TA and DIC values similar to the mean values for the entire lagoon. A long-term 30-40% decrease in reef productivity and calcification has occurred over the last decade, primarily a result of degradation of the reef environment following a major coral reef bleaching event in 1998. This is reflected in decreases in the differences in TA and DIC between offshore lagoon waters and those in center of the lagoon.

[1] We measured the gas-transfer velocity (k) and analyzed factors regulating k at coral reefs and an estuary at Ishigaki Island, Japan, using the floating-chamber method and the measured energy-dissipation rate (e) to represent turbulence in a small-eddy model. We confirmed the validity of the floating-chamber method quantitatively for the first time by the comparing e values inside and outside the chamber device. We also compared k to e and empirical parameters such as wind and current speeds. Measured k had a low correlation with the empirical parameters and a high correlation with e, as indicated by the small-eddy model. The high e values may have been regulated by topographic conditions, e.g., corals or seagrasses that generate wakes, and complex coastlines or large-scale (on the order of kilometers) topographic factors that generate horizontal current shear. Our measurements indicate that coastal k is regulated by e and cannot be accurately determined using wind or current speeds. Topographic conditions in coastal regions are important factors that regulate e; thus, a quantitative analysis of the effects of these conditions is necessary to accurately determine coastal air-water gas flux.Citation: Tokoro, T