How does rising atmospheric CO2 affect marine organisms?

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The Return of Blue Mussels to Svalbard
Berge, J., Johnsen, G., Nilsen, F., Gulliksen, B. and Slagstad, D.  2005.  Ocean temperature oscillations enable reappearance of blue mussels Mytilus edulis in Svalbard after a 1000 year absence.  Marine Ecology Progress Series 303: 167-175.

What was done
The authors describe and discuss the significance of what they refer to as "the first observations of settled blue mussels Mytilus edulis L. in the high Arctic Archipelago of Svalbard for the first time since the Viking Age."

What was learned
The discovery of the established blue mussel colony was made by SCUBA divers in August and September of 2004 at Sagaskjaeret, Isfjorden, Svalbard (7813'N, 14E).  Subsequent analyses by the authors of pertinent regional climatic and oceanographic conditions over the prior few years led them to conclude that "the majority of blue mussels were transported as larvae in unusually warm water by the West Spitsbergen Current from the mainland of Norway to Spitsbergen during the summer of 2002," and that "it is highly probable that the newly established blue mussel population is a direct response to a recent increase in sea surface temperatures."

What it means
Berge et al. note that "distribution patterns of blue mussels Mytilus edulis L. in the high Arctic indicate that this thermophilous mollusk was abundant along the west coast of Svalbard during warm intervals (Salvigsen et al., 1992; Salvigsen, 2002; Lonne and Nemec, 2004) in the Holocene," but that mussels of this species "have not been present at Svalbard for the last 1000 years (Salvigsen, 2002; Lonne and Nemec, 2004)."  In light of these well-documented real-world observations, the fact that blue mussels have only recently begun to reestablish themselves in this part of the world suggests, in their words, that water temperatures there are only beginning to "approach those of the mediaeval warm period."

We agree.  Back in the days of the Vikings, when there was 25% less CO2 in the air than there is currently, it was still warmer than it is today, suggesting there is nothing unusual or unnatural (i.e., anthropogenic-induced) about today's less extreme temperatures, and that the recurrence of whatever caused the greater warmth of that earlier time (the Medieval Warm Period) is likely what is causing temperatures to rise a bit in our day.

Salvigsen, O.  2002.  Radiocarbon dated Mytilus edulis and Modiolus modiolus from northern Svalbard: climatic implications.  Nor. Geograf. Tidskrift 56: 56-61.

Salvigsen, O., Forman, S.L. and Miller, G.H.  1992.  Thermophilous mollusks on Svalbard during the Holocene and their paleoclimatic implications.  Polar Research 11: 1-10.

Sarnthein, M., Van Kreveld, S., Erlenkreuser, H., Grootes, P.M., Kucera, M., Pflaumann, U. and Scholz, M.  2003.  Centennial-to-millennial-scale periodicities of Holocene climate and sediment injections off the western Barents shelf, 75N.  Boreas 32: 447-461.

Reviewed 4 January 2006