Equivocal evidence for a thermostat and unusually low levels of coral bleaching in the Western Pacific Warm Pool

Abstract

An ocean "thermostat" was recently proposed that limits Western Pacific Warm Pool (WPWP) sea surface temperature (SST) causing anomalously low coral bleaching rates. We analyze WPWP SST trends and bleaching using HadISST data and a coral bleaching database and find no strong evidence for a thermostat or for anomalously low bleaching. A region within the WPWP has a trend of maximum SST near zero, but this signal is not robust - by using different data or periods the signal disappears. We do find a negative correlation between the average warmest month for the years 1950-1969 (average SST max) and the linear trend of maximum monthly temperatures for the years 1950-2006 (linear trend SST max). However this correlation is not unique to the WPWP, it is also observed in a cooler region. Consequently it can not be explained by a thermostat. The observed sparsity of bleaching observations in the WPWP is not in agreement with estimated bleaching likelihood. The sparsity of observations is more likely due to the WPWP's remoteness. Copyright 2009 by the American Geophysical Union.