People have been trying to examine this from several directions, including remote sensing to quantify how much CO2 is being generated as these stocks warm (http://above.nasa.gov/about.html?#about). The overview article in Nature that this press release refers to is:

http://www.nature.com/nature/journal/v540/n7631/full/540047a...

and the technical article by Crowther et al. is:

http://www.nature.com/nature/journal/v540/n7631/full/nature2...