Paleoproductivity and surface water dynamics evolution during the MIS 31 in the Shackleton Site as revealed Coccolithophores

Marine Isotope 31 Stage (MIS-31) records one of the highest high-latitude precession-paced insolation values of the last 5 million years (Laskar et al., 2004). According to this configuration, some studies (e.g. Raymo et al., 2006) predicts a +20 m eustatic sea-level rise for this time interval, reflecting significant retreat of some combination of the West Antarctic Ice Sheet, marginal East Antarctic ice, and the Greenland Ice Sheet, and consequently significant variations in the ocean and climate dynamics at global scale. In this study we show data of variability in the coccolithophore assemblage from IODP Site 1385 (Shackleton Site, IODP 339 and IODP 397) in the interval ca. 1 Ma (close to the Jaramillo event). These sediments are sensitive recorders of North Atlantic Deep Water (NADW) and Antarctic Bottom Water (AABW) oscillations, which makes this site a significant location to test the interhemispheric connection hypotheses. Peaks in abundance of Gephyrocapsa (<3mm), as well as in other Noelarhaddaceae such as Reticulofenestra asanoi and other morphotypes (equivalent with minimum differences at total coccoliths recorded), were interpreted as a signal of paleoproductivity, revealing strong changes during MIS 31. Alternatively, cold water indicators (Coccolithus pelagicus ) or the census of Helicosphaera carteri l(inked to stratification processes) are considered, showing an alternative pattern along the studied interval. After the refinement of the age-model, these data should be compared with other records in close or remote areas (e.g. Flores and Sierro, 2007, Maiorano et al., 2009), to understand the relevance of this interval, particularly sensible in the Antarctic environment, where a potential relevant melting peak was suggested (Scherer et al., 2009). Preliminary results (Jiménez Espejo et al., 2013) reveal a distinct turnover during MIS 31 and different evolution of surface and bottom-waters that could be linked with enhanced circulation of NADW during warm periods. This scenario is consistent with stratification pulses interpreted at the top of MIS 32, where cold and stratified water pulses are influenced by and increase in reworked material coming from proximal regions as a result of eustatic sea-level drops.   Laskar, J., Robutel, P., Joutel, F., Gastineau, M., Correia, A.C.M., & Levrard, B. Astrophys. 428, 261-285 (2004). Raymo, M., Lisiecki, L., Nisancioglu, K. Science. 313, 492-495 (2006). Maiorano, P., Marino, M., Flores, J.A. Mar. Micropaleontol. 71, 166–175 (2009). Flores, J.A., Sierro, F.J. Deep-Sea Res. II 54 (21–22), 2432–2442. (2007) Scherer, R. P., Bohaty, S., Dunbar, R., Esper, O., Flores, J., Gersonde, R., Harwood, D., Roberts, A., and Taviani, M. Geophysical Research Letters. 35, (2009) Jiménez Espejo et al., 11th INTERNATIONAL CONFERENCE ON PALEOCEANOGRAPHY 1-6 September, 2013. Sitges - Barcelona (2013)