Reconstructing marine productivity of the Cariaco Basin during marine isotope stages 3 and 4 using organic-walled dinoflagellate cysts

摘要

An organic-walled dinoflagellate cyst analysis was carried out on sediment core MD03-2622, retrieved from the Cariaco Basin. The core comprises the 73–30 ka interval. Down core changes in cyst abundance, accumulation rate, and composition of cyst assemblages were used to identify climatic and oceanographic changes at orbital and millennial time scales in this near-equatorial seasonal upwelling area. Throughout the sequence, dinoflagellate cyst assemblages were dominated by heterotrophic dinocysts (mainly Brigantedinium spp.), with the exception of four autotrophic-dominated (mainly Spiniferites ramosus) intervals around 58, 53, 46, and 37 ka. At orbital time scales, changes in the dinoflagellate productivity seem to follow low-latitude insolation, with the highest productivities coinciding with maximum February insolation (47–38 ka). At millennial scales, cyst accumulation rates appeared to coincide with Dansgaard-Oeschger (D-O) variability, with significant increments occurring during warm interstadials. The opposite was true during stadials. Short periods of high nutrient availability and stratified conditions followed Heinrich events H4, H5, H5a, and H6 and concurred with enhanced river runoff. Spectral analyses confirm the existence of these and other higher-frequency periodicities and support the idea of a tightly coupled terrestrial/marine and tropical/high-latitude climate system during the last glacial period.