Seawater carbonate chemistry and community calcification during a Molokai reef (Hawaii) study 2006

• Main Authors: Yates, Kimberly Kaye, Halley, Roberet B
• Format: Dataset
• Language: English
• Published: PANGAEA 2006
• Subjects: Alkalinity; Gran titration (Gran; 1950); total; Alkalinity anomaly technique (Smith and Key; 1975); Aragonite saturation state; Benthos; Bicarbonate ion; Calcification/Dissolution; Calcification rate of calcium carbonate; Calcite saturation state; Calculated; Calculated using seacarb after Nisumaa et al. (2010); Carbon; inorganic; dissolved; Carbonate ion; Carbonate system computation flag; Carbon dioxide; Coast and continental shelf; DATE/TIME; Entire community; EPOCA; EUR-OCEANS; European network of excellence for Ocean Ecosystems Analysis; European Project on Ocean Acidification; Field observation; Fugacity of carbon dioxide (water) at sea surface temperature (wet air); OCE; Oceanography; Orion Ross conductivity probe; Partial pressure of carbon dioxide (water) at sea surface temperature (wet air); pH; Electrode; Radiation; photosynthetically active; Salinity; Site; Soft-bottom community; Temperature; water; Tropical; YH_06; Ocean acidification
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.721997; https://doi.org/10.1594/PANGAEA.721997

The severity of the impact of elevated atmospheric pCO2 to coral reef ecosystems depends, in part, on how seawater pCO2 affects the balance between calcification and dissolution of carbonate sediments. Presently, there are insufficient published data that relate concentrations of pCO2 and CO3 to in situ rates of reef calcification in natural settings to accurately predict the impact of elevated atmospheric pCO2 on calcification and dissolution processes. Rates of net calcification and dissolution, CO3 concentrations, and pCO2 were measured, in situ, on patch reefs, bare sand, and coral rubble on the Molokai reef flat in Hawaii. Rates of calcification ranged from 0.03 to 2.30 mmol CaCO3 m**-2 h**-1 and dissolution ranged from -0.05 to -3.3 mmol CaCO3 m**-2 h**-1. Calcification and dissolution varied diurnally with net calcification primarily occurring during the day and net dissolution occurring at night. These data were used to calculate threshold values for pCO2 and CO3 at which rates of calcification and dissolution are equivalent. Results indicate that calcification and dissolution are linearly correlated with both CO3 and pCO2. Threshold pCO2 and CO3 values for individual substrate types showed considerable variation. The average pCO2 threshold value for all substrate types was 654±195 µatm and ranged from 467 to 1003 µatm. The average CO3 threshold value was 152±24 µmol/kg, ranging from 113 to 184 µmol/kg. Ambient seawater measurements of pCO2 and CO3 indicate that CO3 and pCO2 threshold values for all substrate types were both exceeded, simultaneously, 13% of the time at present day atmospheric pCO2 concentrations. It is predicted that atmospheric pCO2 will exceed the average pCO2 threshold value for calcification and dissolution on the Molokai reef flat by the year 2100.