Centennial-millennial scale ocean-climate variability in the northeastern Atlantic across the last three terminations

Changes in Earth's orbital parameters pace the Pleistocene glacial-interglacial cycles, although considerable ambiguity still remains over the interaction of the internal climatic variables, such as ice-sheet instability and ocean circulation that allow transitions into and out of an interglacial. Here, we analyse high-resolution planktic foraminiferal proxies including sea-surface temperature (SST) based on an Artificial Neural Network (ANN) across the last three terminations (TI, TII and TIII) and the subsequent interglacials (Holocene, Marine Isotope Stages (MIS) 5e and 7e) from IODP Site U1385, SW Iberian Margin. To demarcate the stadials and interstadials, we combined the faunal and SST records with existing data at Site U1385 including log (Ca/Ti) and benthic and planktic 818O. The composite records reveal details of the last three terminations in terms of abrupt climatic events occurring during these terminations. Termination I included three well-known climatic events: Heinrich stadial (HS)1, Bolling/Allerod (B/A) complex & Younger Dryas (YD). Termination II was interrupted by only HS11. Termination III included HS8.2 and HS8.1 which show more resemblance to HS2 (a stadial prior to TI) and HS1, suggesting the YD is a unique feature of the last deglaciation. Additionally, TI and TII reveal similar du-rations (-6 kyr) with rates of SST change (-1.5 degrees C/kyr to-2.1 degrees C/kyr), whereas TIII represents a longer process (-10 kyr) with a relatively slow rate of SST change (-0.8 degrees C/kyr). The anatomy of stadials (HS1, HS2, HS11 & HS8.1) reveals a complex history ('W' shaped anatomy) with two or three cold phases sandwiching (a) brief warm event(s). The European ice-sheet melting possibly initiated the stadial cooling at the Iberian Margin fol-lowed by the mid-latitude summertime warming and the intermediate-depth water mass warming that probably induced the Laurentide ice-sheet melting resulting in the complex stadial pattern. Our records further reveal a major reorganization of the surface current system, oceanographic fronts and productivity conditions across these terminations. We also document broad similarities in the climatic evolution of Holocene, MIS 5e and 7e interglacials in terms of SST, surface productivity and current system. The long-term interglacial trends were superimposed by multiple brief cold events interrupting the Holocene (-11.3, 9.9, 8.2, 7.1, 5.5, 2.5 ka), MIS 5e (C28, C27, C27', C27a, C27b, C26, C26', C25), and MIS 7e (-238, 234, 231, 230 ka) interglacials. Integration of our records with benthic foraminiferal 813C records from the Iberian Margin and central North Atlantic suggest fluctuations in the deep water convection process (which in turn were influenced by the conditions in subpolar gyre) possibly resulted in the brief cold events interrupting the interglacials at the Iberian Margin.

Automated summary

Changes in Earth's orbital parameters pace the Pleistocene glacial-interglacial cycles, and this study analyzes high-resolution planktic foraminiferal proxies to explore the last three terminations and subsequent interglacials. The results reveal abrupt climatic events during these terminations and a complex history of stadials with a possible cause being European ice-sheet melting. The study also documents major reorganization of the surface current system, oceanographic fronts, and productivity conditions across these terminations, as well as broad similarities in the climatic evolution of Holocene, MIS 5e, and 7e interglacials.