Wetter Subtropics Lead to Reduced Pliocene Coastal Upwelling

Current global warming scenarios suggest surface temperatures may attain warmth last seen during periods of the early-to mid-Pliocene (5.3-3 Ma). Pliocene proxy reconstructions suggest sea surface temperatures 3-9 degrees C warmer than today along midlatitude coastal upwelling sites. Recent climate modeling efforts focused on the mid-Piacenzian period showed a good model-data fit over midlatitude upwelling regions, but did not attempt to reproduce proxy records of early-Pliocene warmth. Evidence also suggests that subtropical continents were wetter then; we show that warm coastal SSTs can be explained via such wetter land conditions near the upwelling sites. Using a global atmospheric model, we show that introducing idealized wetter conditions over subtropical continents leads to reductions in upwelling-favorable wind events by weakening the land-sea surface pressure gradient. The resulting weaker coastal upwelling of cold deep water can help explain the inferred warm coastal temperatures.