Investigation of the Distribution of Carbon Dioxide between the Atmosphere and the Sea



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Texas A&M University Department of Oceanography and Meteorology


Measurements of the distribution of CO2 between the atmosphere and the sea are presented with a description of the apparatus used and its calibration. The measurements were made on a series of cruises into the Gulf of Mexico, the Northern Caribbean Sea and the Western North Atlantic Ocean; in the gas phase using a nondispervise double-beam infrared analyzer. Four geographical patterns in the distribution of CO2 between the phases were observed; first, pCO2 of the air over the Southwestern Gulf of Mexico, the Gulf of Campeche and a 40 mile wide strip near shore of the Louisiana Gulf Coast was 303 ppm and pCO2 of the surface waters was 270-290 ppm. The second, bounded by the Bahama Banks, the island of Bermude and the continental United States, has a pCO2 of 311 to 312 ppm in the air and pCO2 of the waters was 290 ppm. A diurnal cycle in pCO2 of the air of 4-8 ppm was observed over this area. The maximum occurred at 1800 hours local time and the minimum between 2400 and 0600. The third, consisting of the Northern Caribbean and Atlantic south of the Bahama Banks, where pCO2 of the air was 316 ppm and pCO2 of the surface waters was between 270 and 300 ppm. A tropical rain squall in this area produced large excursions to 330 ppm of pCO2 in the sea to a depth of 200 feet. The fourth, the Eastern Gulf of Mexico from the straits of Florida to the mouth of the Mississippi River, pCO2 in the air averaged 316 ppm and pCO2 of the sea was above 325 ppm. A diurnal cycle of 70 ppm in the pCO2 of the sea was observed in the Gulf of Batabano, Cube, the maximum was 400 ppm at the time of maximum isolation and the minimum occurred before dawn. The change in pCO2 per degree centrigrage in sea of 19 parts per thousand chlorinity and pH of 8.2 was measured and is a 4.5 ppm. The change in pCO2 with temperature is a function of pH and for the same water is 7.0 ppm per degree at pH of 8.0. The calibration of the analyzer and the system is felt to be accurate to +/- 2 ppm and the precision of a measurement in the field is within +/- 2 ppm for pCO2 of the air and +/- 5 ppm for pCO2 of the water. Water vapor was removed before analysis. In the areas subjected to diurnal variation the pCO2 reported is the arithmetic average and probably represented an error in the positive sense, since no data was available to measure the thickness of the atmospheric layer affected. No vertical gradients in pCO2 of the air were detected, although vertical gradients were present in the sea. The distribution of CO2 between the atmosphere and the sea varies both geographically and temporally in the areas tested. A considerable flux of CO2 appears to be moving between phases in relatively short distances and short time intervals.


131 pages


water chemistry, air chemistry, carbon dioxide concentration, air-surface water exchange, chemical oceanography