CO2 fluxes from a coastal transect: a time-series approach

The coastal ocean is a region with highly variable physical processes, and high and variable rates of primary production and organic matter recycling, but very little is known about the effect of these factors on the flux of CO2 into or out of this environment. To address this question, a time-series of geochemical measurements was initiated along a 32 km transect across the inner continental shelf, off New Jersey. Water column measurements of temperature, salinity, total carbon dioxide, total alkalinity, oxygen and nutrients were made approximately monthly at seven stations along the transect. Fluxes (−0.43 to −0.84 mol m−2 yr−1) calculated from local wind speed and the air–sea CO2 difference indicate that this region acts as a small net sink for atmospheric CO2 on a yearly averaged basis. The inner and outer stations varied on different time-scales, but in general, surface waters were a source of CO2 to the atmosphere in the summer and fall, offset by large fluxes into the surface waters during the winter to early spring. The calculated fugacity of surface water carbon dioxide (fCO2) between April 1994 and April 1996 ranged from 211 to 658 μatm. Superimposed on the large spatial and temporal variability typical of the coastal environment, was a clear seasonal trend in fCO2 which was primarily responsible for the observed trend in the flux. The dominant processes responsible for the observed changes in fCO2 are examined in detail. An important finding is that the magnitude of the effect of organic matter cycling on changes in fCO2 generally decreased in the offshore direction.