Surface Temperatures in the Eastern Caribbean During the 7th Century AD Average up to 4° C Cooler Than Present

We reconstructed the seasonal environmental condition in the eastern Caribbean during the 7th century. In parts of western Europe, the 7th century was a transitional time between the cool 3rd to 5th centuries and the warm 11th century known as the Medieval optimum. Very few reliable quantitative estimates of temperatures during this time period, especially at seasonal scales are available. Isotopic and trace elements proxies were analysed at seasonal resolution from a coral slab, spanning approximately 10 years, retrieved from the skeleton of Montastraea faveolata growing near La Parguera, Puerto Rico in the northeastern Caribbean Sea. The base of the slab was radiometrically dated at AD 680+/-15 yrs by U/Th thermal ionization mass spectrometry (TIMS). The reconstructed values were calculated as anomalies relative to modern conditions. Interpretation of three independent paleoproxies for sea surface temperature (SSTs): oxygen isotopes, Sr/Ca and Mg/Ca ratios gives similar results and showed that mean annual (SSTs) from the 7th century were cooler (2-4° C) than present. The cooling in the Caribbean may have resulted from regional oceanic and atmospheric circulation differences. However, considering that average annual eastern Caribbean SST trends (1900-1998) have a high coherency with the global average annual temperature trend, it is possible that the 7th Century cooling may have been more global in nature.