Linear and Nonlinear Responses of Annual Mean Sea Surface Temperature to Orbital Forcing

The response of mean annual sea surface temperature (MASST) to orbital insolation forcing has remained not well understood. Here, we study the MASST response to orbital forcing in a climate model simulation of the last 200,000 years. Our results show that SST responds nearly linearly to insolation across most of the tropics and high latitudes, with the MASST dominated by obliquity variability. In the mid-latitude and the eastern equatorial Pacific, however, SST response is nonlinear such that the MASST is dominated precession variability. The nonlinear MASST response can be biased towards winter or summer SST, caused by the rectification of the seasonal insolation forcing by cloud albedo or mixed layer depth.