Miocene Evolution of North Atlantic Sea Surface Temperature

We reconstruct sea surface temperatures (SSTs) at Deep Sea Drilling Project Site 608 (42.836 degrees N, 23.087 degrees), north of the Azores Front, and Ocean Drilling Program Site 982 (57.516 degrees N, 15.866 degrees), under the North Atlantic Current, in order to track Miocene (23.1-5.3 Ma) development of North Atlantic surface waters. Mean annual SSTs from TEX86 and U-37(K ') proxy estimates at both sites were 10-15 degrees C higher than modern through the Miocene Climatic Optimum (17-14.5 Ma). During the global cooling of the Middle Miocene Climate Transition (similar to 14.5-12.5 Ma), SSTs at midlatitude Site 608 cooled by similar to 6 degrees C, whereas high-latitude Site 982 cooled by only similar to 2 degrees C, resulting in an similar to 4 Myr collapse of the SST gradient between the two sites. This regional pattern is inconsistent with an increased latitudinal surface temperature gradient, as generally associated with global cooling episodes linked to decreasing pCO(2) levels. Instead, the pattern is best explained by enhanced ocean heat transport into the high-latitude North Atlantic superimposed on the global cooling trend, probably due to enhanced Atlantic meridional overturning circulation and/or a stronger North Atlantic Current. During global late Miocene cooling (similar to 8-7 Ma), surface waters cooled by similar to 6 degrees C at Site 982 while minimal change occurred at Site 608, reestablishing the North Atlantic SST gradient. The collapse and reemergence of the SST gradient between the middle- and high-latitude North Atlantic suggests that interaction between changes in regional ocean circulation and the global response to changes in greenhouse gas concentration was important in Miocene climate evolution.