How does rising atmospheric CO2 affect marine organisms?

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Boniface River Area, Northern Québec, Canada
Arseneault, D. and Payette, S. 1997. Reconstruction of millennial forest dynamics from tree remains in a subarctic tree line peatland. Ecology 78: 1873-1883.

The authors obtained tree-ring and growth-form sequences from more than 300 black spruce (Picea mariana) remains buried in a presently treeless peatland located near the tree line in northern Québec (57°44'N, 76°10'W), which they analyzed to produce a proxy record of climate for this region between AD 690 and 1591. Over the course of this 900-year time period, the trees of the region experienced several episodes of suppressed and rapid growth, indicative of both colder and warmer conditions, respectively, than those of the present. The most striking of the warm periods exhibited what they described as "well-defined boundaries" that extended from AD 860 to 1000, which they associated with the Medieval Warm Period (MWP) and which they described as having "exceeded in duration and magnitude" the "20th century warm period." In addition, on the basis of the then-current annual temperatures at their study site and at the northernmost 20th-century location of the forest, which was 130 km south of their study site, they concluded that the Medieval Warm Period was ~1°C warmer than what it was when they conducted their work, which was concluded about the time when 20th-century warming leveled off and reached a plateau from which there has been no further warming over the ensuing years.