Evolution of productivity and monsoonal dynamics in the eastern Arabian Sea during the past 68ka using dinoflagellate cyst records

Abstract

For the first time here we report the dinoflagellate cyst assemblage response to the monsoon variability over the last 68 ka from the Eastern Arabian Sea (EAS). Based on the cyst assemblage, five dinoflagellate cyst zones were established, corresponding to four Marine Isotopic Stages (MIS 1–4). An increased abundance of autotrophic Gonyaulacoid species (especially Spiniferites) during glacials (MIS 2 and 4) and late MIS 3 (~ 41.67 to 25.3 ka) reflects high productivity driven by strong winter convection during the Northeast monsoon. In contrast, their decreased abundance during MIS 1 and early MIS 3 (~ 58.6 to 42.87 ka) reveals decrease in productivity due to strong stratification caused by intense monsoon precipitation induced runoff from the Western Ghats and reduced light penetration driven by cloud cover. The variation in heterotrophic Protoperidinium species abundance could be related to variation in the Oxygen Minimum Zone (OMZ) intensity, with better preservation during intense OMZ in MIS 3 and the late Holocene (~ 3 ka onwards). Therefore, it is proposed here that the abundance of Protoperidinium can be used as an index of OMZ in the EAS.