Variabilidad climática y oceanográfica en el Atlántico Norte subpolar durante el Pleistoceno (1.050.000-403.000 años)

Abstract

[EN] This Thesis is a high resolution micropaleontological study of the IODP Site U1314, recovered during the IODP 306 Expedition, in the Gardar Drift formation (southern Iceland), in the subpolar North Atlantic. The main purpose of this Thesis is the study of climatic variations at different time scales (orbital and suborbital) and the evolution of surface circulation patterns in the North Atlantic through changes in the associations of cocolitophorids that occurred during the interval between 1,050,000 and 400,000 years (MIS 30-11); known as the Middle Pleistocene Transition. The reason for studying the coccolitophorids assemblages’ variations is due to the fact that they conform one of the main components of the phytoplankton in the current oceans. These organisms secrete calcified plaques (cocoliths) that, after sedimentation in the seabed, can be preserved in the fossil record. Coccolithophore abundance and diversity are highly influenced by the environmental conditions that prevailed at time these organisms inhabited the ocean. Hence, the study of coccoliths preserved in the sedimentary record provides useful information to perform paleoenvironmental reconstructions. In this Doctoral Thesis, a record of calcareous nanofossils has been analyzed in the interval from MIS 11 to 30. In addition, statistical and mathematical analyses of the calcareous nanofossils assemblage, especially the spectral analysis and the analysis of delays between different variables (LAG), have been made in order to know the responsetime between two systems (or sites) affected by the same climatic effect. We have also compare our study with site MD03-2699 (southern of site U1314), with the aim of reconstructing how and when the NAC (North Atlantic Current) could vary in the MIS 11-14 interval. The importance of this study, located in the North Atlantic and specifically the subpolar North Atlantic, is related to the sensitivity of the area to climatic and oceanographic changes. The surface oceanographic regime is strongly imprinted by the Subpolar gyre, specifically by the NAC, which feeds the IC (Irminger Current). When the NAC and the IC arrive at high latitudes, they will sink generating deep waters masses. Oceanographic changes at deep waters are important in this area because it is a deepwater formation zone (Labrador Sea and Norwegian Sea-Greenland), which is the motor of the thermohaline circulation and affect the global circulation. The calcareous nanofossils asemblages showed abrupt changes between the warm interval assemblage, where the total abundance of species is greater and dominated by the species associated to the IC and the cold interval assemblage where the total abundance is low and the species associated with waters of the IC abruptly decline. These abrupt changes are due to the latitudinal variation of the NAC waters and the cold waters from farther north, which ultimately determine the position and variation of the IC waters. This variation of the waters throughout the study interval allows us to reconstruct four…