What was done
The authors analyzed diatom data they obtained from core MD992271 (66°30'05"N, 19°30'20"W) on the North Icelandic shelf to derive summer sea surface temperatures (SSTs) for that location based on relative abundances of warm and cold water species, after which they compared the results they obtained with results derived by Jiang et al. (2002, 2005) via similar analyses of nearby cores HM107-03 (66°30'N, 19°04'W) and MD992275 (66°33"N, 17°42'W), as well as results derived from GISP2 δ¹⁸O data and other marine sediment records obtained from still other regions of the North Atlantic.

What was learned
The data from the new sediment core reveal a gradually decreasing temperature trend over the entire expanse of the reconstructed 3000-year SST record, with superimposed centennial- and millennial-scale summer SST fluctuations. In addition, Jiang et al. state that "the Medieval Warm Period and the Little Ice Age are identified in the record," the former of which periods appears to have prevailed between approximately AD 950 and 1250. Unfortunately, the MD992271 record ends in the midst of the Little Ice Age and therefore does not reveal any 19th- or 20th-century warming. The HM107-03 record, on the other hand, extends to within about 50 years of the present; but it too shows no evidence of any warming at its end. Core MD992275 does extend to the nominal present, however; and it suggests that the end of the 20th century was at least three-quarters of a degree Centigrade cooler than the peak temperature of the Medieval Warm Period, which is about the same qualitative and quantitative difference suggested by the GISP2 δ¹⁸O data.

What it means
Jiang et al. state that "comparison of the data from core MD992271 with those from two other cores, HM107-03 and MD992275, on the North Icelandic shelf shows coherent late Holocene changes in reconstructed summer SST values ... reflecting regional [our italics] changes in the summer SSTs on the North Icelandic shelf." In addition, they conclude that "the consistency between changes in the late Holocene summer SSTs on the North Icelandic shelf and in GISP2 δ¹⁸O data, as well as in other marine sediment records from the North Atlantic, further suggests synchronous North Atlantic-wide [our italics] climate fluctuations." And, we would add, the consistency among all of these records and the many similar records from other parts of the world - which we have assembled in our Medieval Warm Period Project database - ultimately suggests the existence of synchronous global climate fluctuations that are beginning to also reveal a warmer-than-present Medieval Warm Period (when there was fully 100 ppm less CO2 in the air than there is today).

References
Jiang, H., Seidenkrantz, M.-S., Knudsen, K.L. and Eiriksson, J. 2002. Late Holocene summer sea-surface temperatures based on a diatom record from the north Icelandic shelf. The Holocene 12: 137-147.

Jiang, H., Eiriksson, J., Schulz, M., Knudsen, K.L. and Seidenkrantz, M.S. 2005. Evidence for solar forcing of sea-surface temperature on the north Icelandic shelf during the late Holocene. Geology 33: 73-76.