Microfossil-based reconstruction of latitudinal thermal gradients in the Southern Ocean during MIS11c

The Southern Ocean (SO) is a region particularly sensitive to the anthropogenic global warming because of the raising ocean temperatures, leading to latitudinal shifts of oceanographic fronts which govern the position of the South Westerly Winds (SWW) in the SO. Sediments represent a natural climate archive that allows to observe changes in Earth’s systems only affected by natural forcing. In this sense, Marine Isotope Stage (MIS) 11c (∼426–396 ka) is the most similar climate state to the ongoing climate warming that we are facing today, but quantiative climate reconstructions in the SO for this period are scarce. Radiolarians (zooplankton) live in a wide range of depths in the water column and are very abundant in sediments throughout the Neogene in the SO.  Recent radiolarian databases and transfer functions for the SO (Lawler et al. 2021; Civel-Mazens et al. 2022) enable reconstructing quantitatively past climate. For this, three sediment cores, drilled during IODP Expedition 382 and located along latitudinal gradient in the Atlantic sector of the SO (between 53.2°S and 59.4°S), were studied for their fossil radiolarian assemblage composition for the interval corresponding to MIS 11c. Application of the newly developed radiolarian transfer functions to the fossil radiolarian assemblages in these three cores enabled the reconstruction of ocean temperatures and thermal gradients in the SO during MIS 11c. These reconstructions will be used also to infer the position of the oceanographic frontal zones and the position of the SWW in this sector of the SO in the past, which are important for promoting upwelling nutrient rich bottom waters and degassing of deeply sequestered CO₂ during the interglacial maxima.

References:

Civel-Mazens, M., Cortese, G., Crosta, X., Lawler, K. A., Lowe, V., Ikehara, M., & Itaki, T. (2022). New Southern Ocean transfer function for subsurface temperature prediction using radiolarian assemblages. Marine Micropaleontology, 102198.

Lawler, K. A., Cortese, G., Civel-Mazens, M., Bostock, H., Crosta, X., Leventer, A., & Armand, L. K. (2021). The Southern Ocean Radiolarian (SO-RAD) dataset: a new compilation of modern radiolarian census data. Earth System Science Data, 13(11), 5441-5453.