Millennial‐Scale Climate Variability and Dinoflagellate‐Cyst‐Based Seasonality Changes Over the Last ~150 kyrs at “Shackleton Site” U1385

Abstract

During the last glacial period, climate conditions in the North Atlantic region were determinedby the alternation of relatively warm interstadials and relatively cool stadials, with superimposed rapidwarming (Dansgaard‐Oeschger) and cooling (Heinrich) events. So far little is known about the impact ofthese rapid climate shifts on the seasonal variations in sea surface temperature (SST) within the NorthAtlantic region. Here, we present a high‐resolution seasonal SST record for the past 152 kyrs derived fromIntegrated Ocean Drilling Program“Shackleton”Site U1385, offshore Portugal. Assemblage counts ofdinoflagellates cysts (dinocysts) in combination with a modern analog technique (MAT), and regressionanalyses were used for the reconstructions. We compare our records with previously published SST recordsfrom the same location obtained from the application of MAT on planktonic foraminifera. Ourdinocyst‐based reconstructions confirm the impression of the Greenland stadials and interstadials offshorethe Portuguese margin and indicate increased seasonal contrast of temperature during the cold periods ofthe glacial cycle (average 9.0 °C, maximum 12.2 °C) with respect to present day (5.1 °C), due to strong wintercooling by up to 8.3 °C. Our seasonal temperature reconstructions are in line with previously published data,which showed increased seasonality due to strong winter cooling during the Younger Dryas and the LastGlacial Maximum over the European continent and North Atlantic region. In addition, we show that overlonger time scales, increased seasonal contrasts of temperature remained characteristic of the colder phasesof the glacial cycle.