Orbital suppression of wind‐driven upwelling in the California Current at 6 ka

Abstract

Marine records clearly show activity in the California Current (CC) system to have been altered during the mid‐Holocene. However, the specific nature of CC activity during this period remains ambiguous, as proxies that suggest cooler than present sea surface temperatures co‐occur in mid‐Holocene marine sediments with multiple proxies that suggest decreased coastal upwelling. To test the sensitivity of wind‐driven upwelling in the CC to mid‐Holocene orbital forcing, we have employed a high‐resolution regional climate model (RCM). The seasonality of modern CC wind‐driven coastal upwelling simulated by the RCM is in strong agreement with observational data. Further, we show that changes in the seasonality of solar insolation induced by mid‐Holocene Milankovitch forcing decrease early and peak season coastal upwelling in the CC, along with increasing late season coastal upwelling. These results are in agreement with several marine and terrestrial proxies, suggesting that, relative to present, CC activity during the mid‐Holocene was characterized by a longer and less vigorous upwelling season with decreased seasonal contrast.