Response of California Current forcing to mid-Holocene insolation and sea surface temperatures

We find that mid-Holocene insolation causes systematic changes in wind forcing of the California Current System, suppressing wind stress in the spring and enhancing wind stress in the summer and autumn. Both large- and regional-scale processes play an important role in the insolation-enhancement of wind stress, with elevated summer insolation magnifying both large-scale sea level pressure gradients and regional-scale land- sea thermal contrast. We find that prescribed changes in large-scale sea surface temperatures (SSTs) amplify the response of nearshore wind stress to mid-Holocene insolation, with SST-magnification of changes in large- scale sea level pressure gradients overcoming SST-muting of changes in regional-scale land-sea thermal contrast. The climate model simulations are supported by proxy-inferred cooler-than-present sea surface temperatures in the northern California Current System, as well as by high nitrogen isotope values in the southern California Current System. Our results highlight the importance of multi-scale dynamical interactions in regulating the response of regional environments to global-scale changes in radiative forcing.