The data have been obtained using an autonomous instrument measuring the concentration of CO2 in surface water, installed on board the container carrier Nuka Arctica since 2004. The ship crosses the Atlantic between Denmark and Greenland every second week. The data presented in the paper are from 2005, and have been obtained as part of the EU IP CARBOOCEAN.
The North Atlantic is saturated with CO2 during winter
Net global ocean CO2 uptake corresponds to approximately one quarter of the anthropogenic CO2 emissions, and serves to mitigate climate change. Knowing where and why ocean CO2 uptake occurs is important, as changes in the net uptake may affect future climate through its impact on the atmospheric CO2 concentration.
The common view on ocean-atmosphere CO2 exchange has been that CO2 is released to the atmosphere at low latititudes and taken up by the ocean at high, a result of the different water temperatures in these areas and the overturning circulation. The data from Nuka, however, show that the surface waters along 60ºN in the Atlantic are saturated with CO2 during winter. This may be related to the previously reported changes of the North Atlantic CO2 sink (http://www.bjerknes.uib.no/pages.asp?id=933&kat=8〈=1).
But, it is also possible that the waters here have always been saturated, since the North Atlantic Current is rather diffuse and slow moving in this area. This hypothesis will be further explored in the CARBON-HEAT project recently funded by the Research Council of Norway.
The data from Nuka Arctica have also revealed statistically significant relationships between surface CO2 concentrations and concentrations of chlorophyll a, as well as mixed layer depth. These relationships can be used along with remotely sensed and ocean assimilation model data, to predict the CO2 concentration where we lack measurements, thus enabling basin scale estimates of the air-sea CO2 exchange in the area.
The Bjerknes Centre plans to sustain the measurement program on Nuka Arctica in many years to come, providing insight into the year-to-year changes in the behavior of the North Atlantic CO2 sink and its sensitivity to climate change.
Sea-surface CO2 fugacity in the subpolar North Atlantic
A. Olsen, K. R. Brown, M. Chierici, T. Johannessen, and C. Neill
Biogeosciences, 5, 535-547, 2008
Last update: 14.04.2008