Micropaleontological and geochemical evidence for late Miocene to Pliocene warming in the high-latitude North Atlantic (IODP Site U1562).

The late Miocene and Pliocene were periods characterized by warmer-than-present climatic conditions and are therefore commonly used to investigate the possible effects of ongoing global warming. The Atlantic meridional overturning circulation (AMOC) is a crucial component of the climate system, since it involves oceanic currents and controls the redistribution of heat around the globe. Specifically, warm and saline water from the low-latitudes reaches the high-latitude North Atlantic, where it loses heat and sinks to form deep-water masses. This sinking generates strong bottom currents, which flow southwards, powering what is known as the global ocean conveyor belt. Understanding the generation and evolution of these water masses during past warm periods provides valuable insights into their potential response to ongoing increases in ocean temperatures. Recently, International Ocean Discovery Program (IODP) expeditions 395 and 395C made such investigations possible by recovering deep sea sedimentary sequences spanning the late Miocene and Pliocene in the high latitude North Atlantic region (60°N; Parnell-Turner et al., 2025). In this study, we investigate sediment samples from IODP Site U1562 (60°06.3006′N, 26°30.1044′W; ~2003m water depth), located at the edge of a sediment body deposited under the influence of deep-water currents (Björn Drift). This site exhibits continuous sedimentation and excellent microfossil preservation during the latest Miocene to Pliocene (~6.5–3.6 Ma). For our investigation, we use a combination of micropaleontological and geochemical proxies, including X-Ray fluorescence (XRF) core scanning, isotopic analysis of foraminiferal shells, and microfossil species identification and morphometrics. Combining these proxies allows for reconstructing the evolution of temperature, primary productivity, and ocean circulation in the region. Pronounced cyclic variations in calcium carbonate (CaCO₃) preservation indicate a highly dynamic depositional environment, likely controlled by changes in export production and bottom ocean dissolution related to deep-sea currents. These cycles are accompanied by distinct isotopic signatures, with intervals of high CaCO₃ content broadly corresponding to lighter δ¹⁸O values, and vice versa. The occurrence of planktonic foraminifera Orbulina universa, as well as calcareous nannofossils belonging to the genus Discoaster reveal periodically warmer conditions, driven by an overall increase in upper-ocean temperature or enhanced influence of warm currents associated with stronger AMOC. Further analyses will aim to better characterize these cyclic changes, link them to orbital cycles, and combine them with other sedimentological observations to reconstruct the evolution of AMOC during past warm intervals of the late Neogene.

References

Parnell-Turner, R.E., Briais, A., LeVay, L.J., and the Expedition 395 Scientists, 2025. Reykjanes Mantle Convection and Climate. Proceedings of the International Ocean Discovery Program, 395: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.395.2025