Pliocene-Pleistocene orbital cycle transition of summer sea surface temperature in the mid-latitude North Atlantic

The Pliocene-Pleistocene transition marks a significant period in Earth’s climate history. During this period, the climate shifted from the relatively stable and warm unipolar cool-house climate to the bipolar glaciated climate states of the ice-house associated with the gradual development of the Northern Hemisphere Glaciation (NHG) . The onset of the NHG (oNHG) is traced back to approximately 3.6 million years ago (Ma). This was followed by an intensification of the NHG (iNHG) around 2.7 Ma, coinciding with a substantial reorganization of oceanic and atmospheric circulation in the North Atlantic. Despite these shifts, reconstructed alkenone-based sea surface temperature (SST) records from the mid- to high-latitude North Atlantic indicate persistent obliquity-dominated cycles, with a noticeable absence of the precession cycle.

 In this study, we present new high resolution Globigerinoides ruber (white) Mg/Ca-based summer SST records from the early Late Pliocene spanning from 3650 – 3370 thousand years ago (ka) at the IODP Site U1313 (41°N, 33°W, 3412m) in the mid-latitude North Atlantic. Contrary to the previous alkenone-based SST records, our Mg/Ca-based SST records reveal a dominant precession cycle. When compared with early Pleistocene G. ruber Mg/Ca-based SST records, we observed a notable transition in the dominant cycle from precession to obliquity, accompanied by a doubling increase in amplitude. These results indicate a progressively amplified effect on the obliquity cycle, correlated with the progressive growth of the Northern Hemisphere ice sheets.