SW Iberian Margin 1500 ka (SWIM1500): A benchmark record for comparison with the Beyond EPICA-Oldest Ice (BE-OI) Core

As nearly all the mass, heat capacity, and carbon in the ocean-atmosphere system resides in the deep sea, ice cores must be correlated and integrated with marine sediment cores to provide a comprehensive, dynamic understanding of Earth's past climate. The SW Iberian Margin (SWIM) is a well-known location where sediments accumulate at high rates and can be correlated precisely to the polar ice cores. With new drilling during IODP Expedition 397, we filled a 30-kyr hiatus in the previous record of Site U1385 across the MIS 12/11 transition (Termination V) and extended the record to MIS 53, which we call SWIM1500. For the last 800 kyrs, we demonstrate that CH₄ and δD in the EPICA ice core can be precisely correlated on millennial time scales to the planktic and benthic δ¹⁸O proxies, respectively, using a new Bayesian algorithm for automated synchronization of proxy timeseries (e.g. Muschitiello and Aquino-Lopez, 2024) that factors in prior knowledge on accumulation rates.

We suggest that SWIM1500 can serve as a predictive tool for isotopic and CH₄ variations for the new BE-OI core beyond 800 ka and will aid in evaluating disturbance and/or diffusion in the oldest ice. We focus on the period older than 1.2 Ma because the stratigraphy and chronology of the BE-OI core is less certain in this interval. The unique shapes of the glacial-interglacial cycles (related to the phasing of obliquity and precession) and nested glacial millennial variability offer a template for correlating and interpreting the BE-OI and Site U1385 records. These correlations will be particularly important for evaluating the climate background state in the "41-kyr world" before the beginning of the Middle Pleistocene Transition at 1.2 Ma.

Muschitiello, F. and Aquino-Lopez, M. A.: Continuous synchronization of the Greenland ice-core and U–Th timescales using probabilistic inversion, Clim. Past, 20, 1415–1435, https://doi.org/10.5194/cp-20-1415-2024, 2024.