Miocene Evolution of North Atlantic Sea Surface Temperature

摘要

We reconstruct sea surface temperatures (SSTs) at Deep Sea Drilling Project Site 608 (42.836°N, 23.087°), north of the Azores Front, and Ocean Drilling Program Site 982 (57.516°N, 15.866°), 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 TEX_(86) and U~(K′)_(37) proxy estimates at both sites were 10-15 °C higher than modern through the Miocene Climatic Optimum (17-14.5 Ma). During the global cooling of the Middle Miocene Climate Transition (~14.5-12.5 Ma), SSTs at midlatitude Site 608 cooled by ~6 °C, whereas high-latitude Site 982 cooled by only ~2 °C, resulting in an ~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 (~8-7 Ma), surface waters cooled by ~6 °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.