Sea surface-water condition and paleoproductivity reconstructions at Site U1385 (IODP, Exp 339) using the coccolithophore assemblages as proxy within MIS 16-11.

Abstract:

Site U1385 (37°34.285’N, 10°7.562′W, 2578 m water depth) was selected and drilled in the lower slope of the Portuguese margin, during Integrated Ocean Drilling Program (IODP) Expedition 339 (Mediterranean Outflow) to provide a marine reference section of Pleistocene millennial-scale climate variability. Here we present downcore analyses of coccolith assemblages used to assess temporal and spatial changes in surface-water conditions, coccolith production and paleoproductivity during the Marine Isotope Stages (MIS) 16-11. Absolute assemblage counts are used to quantify the CaCO₃ contribution of the coccoliths to the total carbonate accumulation. The Highest Occurrence (HO) of Gephyrocapsa omega within MIS 15, the HO of Pseudoemiliania lacunosa at MIS 12, and the occurrence of Helicosphaera inversa within MIS 11 are considered as biostratigraphic constraints in the examined interval. Total coccolithophore abundance displays considerable changes and highlights an important increase in values from MIS 15 to MIS 11. This variation, is concurrent with a relevant change in the assemblage composition, represented by the beginning of the medium-sized Gephyrocapsa (3-4 μm) dominance interval (mainly Gephyrocapsa caribbeanica) during the mid-Brunhes interval. Small gephyrocapsids (< 3 μm) dominate through MIS 16-15, while G. caribbeanica (> 3 μm) becomes the most important species from MIS 15 to MIS 11. During MIS 13, coccolithophore abundance reaches maximum values and high frequency variability. From MIS 13 to MIS 11 the pattern of coccolithophore production distinctly reflects glacial/interglacial cycles, with higher values during the interglacials. A cumulative curve of warm water taxa was obtained for the studied interval, and it shows high amplitude fluctuations during interglacial periods. The results represent a good coccolithophore dataset for the comprehension of climate and paleoceanographic patterns through the mid Pleistocene and the mid-Brunhes interval.