How does rising atmospheric CO2 affect marine organisms?

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Victoria Land Coast, Antarctica
Baroni, C. and Orombelli, G. 1994. Abandoned penguin rookeries as Holocene paleoclimatic indicators in Antarctica. Geology 22: 23-26.

Working with data obtained during onsite research carried out by the Italian Antarctic Research Programme (1985-1991) in the Terra Nova Bay area of Victoria Land, plus other data they obtained from the scientific literature, Baroni and Orombelli documented the times and locations of Adelie penguin presence throughout Antarctica during the Holocene. Among other things, this work revealed the historic presence of penguins in "localities not currently occupied by penguins, particularly in the section of coast between Terra Nova Bay and McMurdo Sound." And they specifically state, in this regard, that along the Victoria Land Coast, the Prior Island rookery "was occupied between the eighth and fourteenth centuries AD, an interval comprising the Medieval Warm Period," but that "it was later abandoned."

Therefore, since the two researchers report that (1) Adelie penguins "nest in the ice-free zones of the coastal areas," (2) prior abandonments of such sites have been "attributed to an increase of the sea-ice extension," (3) "a decrease in the population trend of six Ross Sea Adelie penguin rookeries shows correlation with late breaking out of sea ice and with negative December mean temperature anomalies," and (4) an increase of the Adelie penguins in the Ross Sea since 1982 has been attributed to a local "recent warming trend," it can be concluded that the failure of Adelie penguins to return to the section of Victoria Land Coast between Terra Nova Bay and McMurdo Sound implies that that portion of Antarctic coastline has not yet returned to the level of warmth experienced there during the Medieval Warm Period of AD 800-1300.