The early to mid-Holocene thermal maximum is clearly documented in SST records in the high-latitude North Atlantic-Nordic Seas, with a polar amplification, and an earlier and shorter lasting extension in the areas near the modern sea-ice limit in the Nordic Seas than to the south. Further south, the maximum is most clearly expressed between 8 and 6 ka. In the Irminger Sea the maximum SSTs were delayed, probably due to downwind effects from the remnants of the Laurentide Ice Sheet.

The maximum is expressed by proxy records which sample the uppermost surface layer above the seasonal thermocline. Proxy data from recorders that sample the sub-surface do not document the maximum temperatures. This shows that the SST maximum is mainly forced by the summer insolation maximum and sub-surface proxy data that reflect annual mean or winter-time conditions are not influenced by the summer-time insolation forcing.

The origin of the thermal maximum is primarily from orbital forcing and not advection of SST anomalies from the south. It is difficult to attribute the thermal maximum to long-term persistent atmospheric patterns.

Superimposed on the SST trends is century to millennial scale climate variability. This variability does not occur as a stationary response to specific external forcing, but appears primarily to be induced and later amplified after the thermal maximum by changes in climate system internal dynamics.

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