Reference
Carbotte, S.M., Bell, R.E., Ryan, W.B.F., McHugh, C., Slagle, A., Nitsche, F., Rubenstone, J. 2004. Environmental change and oyster colonization within the Hudson River estuary linked to Holocene climate. Geo-Marine Letters 24: 212-224.
Description
The authors located fossil oyster beds within the Tappan Zee area of the Hudson River estuary, New York, USA (~ 41.13°N, 73.90°W), via chirp sub-bottom and side-scan sonar surveys, after which they retrieved sediment cores from the sites that provided shells for radiocarbon dating. Results of their analyses indicated that "oysters flourished during the mid-Holocene warm period," when "summertime temperatures were 2-4°C warmer than today." Thereafter, the oysters "disappeared with the onset of cooler climate at 4,000-5,000 cal. years BP," but "returned during warmer conditions of the late Holocene," which they specifically identified as the Roman and Medieval Warm Periods as delineated by Keigwin (1996) and McDermott et al. (2001), explicitly stating that "these warmer periods coincide with the return of oysters in the Tappan Zee." They further report that their shell dates suggest a final "major demise at ~500-900 years BP," which timing they describe as being "consistent with the onset of the Little Ice Age." Because the oyster beds of Tappan Zee have not been reestablished during the Current Warm Period, we conclude that temperatures in this region today are not as warm as they were during the MWP (~ AD 600-1250).
References
Keigwin, L.D. 1996. The Little Ice Age and Medieval Warm Period in the Sargasso Sea. Science 274: 1504-1508.
McDermott, F., Mattey, D.P. and Hawkesworth, C. 2001. Centennial-scale Holocene climate variability revealed by a high-resolution speleothem δ18O record from SW Ireland. Science 294: 1328-1331.