How does rising atmospheric CO2 affect marine organisms?

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The Medieval Warm Period in the Gulf of California
Barron, J.A. and Bukry, D. 2007. Solar forcing of Gulf of California climate during the past 2000 yr suggested by diatoms and silicoflagellates. Marine Micropaleontology 62: 115-139.

What was done
High-resolution records of diatoms and silicoflagellate assemblages spanning the past 2000 years were derived from analyses of sediment cores extracted from three sites on the eastern slope of the Gulf of California, comprising core BAM80 E-17 retrieved at 27.92N, 111.61W; core NH01-21 retrieved at 2617.39'N, 10955.24'W, and core NH01-26 retrieved at 2416.78'N, 10811.65W.

What was learned
In all three of the sediment cores, the relative abundance of Azpeitia nodulifera (a tropical diatom whose presence suggests the occurrence of higher sea surface temperatures), was found to be far greater during the Medieval Warm Period than at any other time over the 2000-year period studied, while during the Modern Warm Period its relative abundance was actually lower than the 2000-year mean, also in all three of the sediment cores. In addition, the first of the cores exhibited elevated A. nodulifera abundances from the start of the record to about AD 350, during the latter part of the Roman Warm Period, as well as between AD 1520 and 1560, during what we have denominated the Little Medieval Warm Period. In addition, by analyzing radiocarbon production data, Barron and Bukry determined that the changes in climate they identified likely were driven by solar forcing.

What it means
The findings of Barron and Bukry add to the growing body of evidence that indicates the Medieval Warm Period was (1) real, (2) global in extent, (3) most likely warmer than the Current Warm Period, and (4) probably solar-induced. See also, in this regard, our Medieval Warm Period Project, which grows ever larger with the results of a different study added each and every week.

Reviewed 16 May 2007