Surface water mass dynamics at IODP Site U1313 through Principal Component Analysis: Evidence from coccolith assemblages in the ∼25–7 kyr interval

Abstract

Coccolith assemblages from Integrated Ocean Drilling Program Site U1313 (North Atlantic; 41°0′N, 32°57.4′W) are analysed to assess temporal changes in surface water conditions from the Last Glacial Maximum (LGM) to the Middle Holocene (∼25–7 kyr). We perform Principal Component Analysis (PCA), involving both calcareous nannofossil assemblage data and other paleoenvironmental proxies. We reconstruct sea-surface dynamics using calcareous nannofossil assemblage variations and comparison with other previously published proxy data from Site U1313 including C37:4 alkenone, dolomite/calcite and quartz/calcite ratios, Uk’37 SST, as well as the sedimentation rate.We use variations in paleoproductivity proxies, cold and warm water group abundance, and the PCA results to infer North Atlantic Current (NAC) and North Atlantic Transitional Waters (NATW) migration through the studied interval. These proxies are also used to highlight variations in the Subtropical Gyre dynamics. Warming episodes are recorded during the LGM and Heinrich Stadial (HS) 1 as a result of northward expansion of the Subtropical Gyre. High coccolithophore productivity episodes characterize HS 1 and 2, and are concomitant with increasing terrigenous input. Both processes are considered a consequence of iceberg influence, which transport nutrients and ice-rafted debris to the area. A southward shift of the Subpolar Front and NAC favour the expansion of cold water from 25.3 ka to the end of the Younger Dryas, whereas the early Holocene is characterized by NATW influence resulting from northward migration of the NAC and Azores Current.