How does rising atmospheric CO2 affect marine organisms?

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The Roman Warm Period in Denmark
Rasmussen, P., Petersen, K.S. and Ryves, D.B. 2008. Environmental change in Danish marine waters during the Roman Warm Period inferred from mollusk data. Geological Survey of Denmark and Greenland Bulletin 13: 21-24.

What was done
The authors present "some of the first results from [a] project concerning environmental changes in the Roman Warm Period (c. 2000-1600 years B.P.) as shown by changes in molluscan faunas at two coring sites in Horsens Fjord and Tempelkrog in southern Isefjord," based on analogies with the molluscs' "present-day requirements in relation to salinity, temperature, depth and substrate."

What was learned
Rasmussen et al. report detecting "an increase in mollusk abundance and the appearance of a suite of almost fully marine taxa at various times during the Roman Warm Period," which "testifies to a widespread change to more saline and productive conditions across the inner Danish waters," noting that "the fairly regular presence of Ostrea edulis may also suggest an increase in sea surface temperature during this period." In addition, they write that "large shell middens dated to the centuries around 2000 years B.P., and predominantly composed of Mytilus edulis, Cerastoderma edule, Littorina littorea and to a lesser extent Ostrea edulis, are recorded along several Danish and North German fjords," citing, in this regard, the work of Anger (1973), Harck (1973), Poulsen (1978) and Petersen (1985).

What it means
The three researchers state that "the synchroneity between the inferred changes in the marine environment and the appearance of [the] Iron Age shell middens strongly suggest a causal connection between the two, implying that people responded to the increased productivity in the marine environment by a comprehensive and targeted gathering and processing of shellfish." Hence, there is evidence of both warmer and more productive conditions during the Roman Warm Period in Denmark, as well as evidence for the positive response of the people of that time to those warmer and more productive conditions.

Anger, K. 1973. Untersuchungen an eisenzeitlichen Muschelhaufen an der Flensburger Forde. Offa 30: 55-59.

Harck, O. 1973. Eisenzeitliche Muschelhaufen an der schleswigschen Ost- und Westkuste. Offa 30: 40-54.

Petersen, K.S. 1985. Det sydfynske arkipelag. Dets geologiske udvikling med saerlig hensyntagen til havniveauaendringer og den marine molluskfauna. In: Skaarup, J. (Ed.), Yngre Stenalder pa oerne syd for Fyn, pp. 15-27. Rudkobing: Langelands Museum.

Poulsen, K.L. 1978. Eisenzeitliche Muschelhaufen in Danemark. Offa 35: 64-85.

Reviewed 8 October 2008