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Research ESRIG - Energy and Sustainability Research Institute Groningen Centre for Isotope Research - CIO Research and project

Carbon Uptake in the Ocean

Steven van Heuven

The atmospheric concentration of the greenhouse gas carbon dioxide is determined by the rates of uptake and release of it by the oceans, land and - since the advent of human civilization - by the release from the deep carbon reservoirs of coal and gas. Although the size of the latter 'anthropogenic' release is small compared to the enormous natural CO2 fluxes, its unidirectionality (as opposed to the seasonal reversal of the natural fluxes) has in the two centuries since the beginning of the industrial revolution lead to a significant increase of the atmospheric concentration of CO2. With it, the heat-trapping potential of the Earth's climate system has also increased. Societal concern over the expected deleterious consequences of the continuing build up of this greenhouse gas has spurred an extensive investigation of the details of Earth's carbon cycle, aimed at obtaining a more fundamental understanding of the changes and consequences to be expected under different future scenarios of societal development, as well as being driven by genuine scientific curiosity about the intriguing processes that keep Earth's climate system in dynamic equilibrium.

One of the many questions yet to be precisely answered about the carbon cycle is how much of the CO2 that has been emitted to the atmosphere by human activities is being transported into the abyssal oceans after having been absorbed by the ocean's surface waters. Several methods of quantifying this more or less permanent oceanic lock-up of carbon are being applied by the extensive scientific community dealing with this question. Various approaches attempt to measure and monitor the uptake process itself, others try to determine its integral - that is, the total amount of carbon taken up so far.

Among the various techniques that aid in this determination is the analysis of the 14C content of the CO2 that is dissolved in seawater. The amount of the radioactive isotope 14C that is present at each particular location in the ocean is governed by a combination of physical, chemical and biological processes. This makes 14C results particularly difficult to interpret in isolation. However, if additional measurements are available, these data are highly valuable for the unraveling of the contributions of these varied processes.

As part of a broad suite of activities at CIO, we measure the 14C content of CO2 in seawater samples. The most recent set of such samples was collected during a pair of four-week-long research cruises of the Dutch R/V Pelagia, carried out between April and July 2010. These cruises sampled the full depth range of a transect in the West-Atlantic Ocean, from the frigid seas near Iceland to the balmy equatorial waters near Brazil (see picture). Together with measurements performed on board, with sample analyses currently being performed in various shore-based labs as well as with 'historical' data collected in the past 3 decades, these new data will provide additional insight into the Atlantic Ocean's pivotal role in the global carbon cycle.

sampling CO2
Sampling in the Atlantic Ocean
Last modified:12 February 2018 10.08 a.m.