Orbitally driven insolation forcing on Holocene climate trends: Evidence from alkenone data and climate modeling

A global spatial pattern of long‐term sea surface temperature (SST) trends over the last 7000 years is explored using a comparison of alkenone‐derived SST records with transient ensemble climate simulations with a coupled atmosphere‐ocean circulation model under orbitally driven insolation forcing. The spatial trend pattern both in paleo‐SST data and in model results shows pronounced global heterogeneity. Generally, the extratropics cooled while the tropics experienced a warming during the middle to late Holocene. We attribute these divergent Holocene climate trends to seasonally opposing insolation changes. Furthermore, climate mode changes similar to the Arctic/North Atlantic Oscillation are superimposed on the prevalent pattern. It is concluded that nonlinear changes in the entire seasonal cycle of insolation played a dominant role for the temporal evolution of Holocene surface temperatures. For understanding of marine proxy data, apart from the dominance of summer insolation in high latitudes, a notable shift in the maximum insolation of the year in low latitudes has to be taken into account, which may influence timing of phytoplankton production and thus alters the seasonal origin of temperature signals recorded in the proxies.