The Arabian Sea (AS) is one of the most productive oceanic regions in the world due to several monsoon-related processes that can increase nutrients contents in the euphotic zone. Previous studies of the imprint of oceanic Primary Productivity (PP) in AS sediments yielded diverse results depending on the studied area and the chosen proxies, with unprecise paleoclimatic interpretations. Here, we provide multi-decennial PP and coastal upwelling dynamic records off northern Oman over the last 23 kyr, based on the analysis of coccoliths from sediment core MD00-2354. Our results have been compared with previous paleoenvironmental records as well as new modelling data to get precise paleoclimatic interpretations. We document higher PP and weaker coastal upwelling during the Last Glacial Maximum relative to the Holocene, and significant millennial-scale variations over the last deglaciation corresponding to the fluctuations of the Atlantic Meridional Overturning Circulation strength. Higher PP and weaker upwelling are found during cold stadials, while lower PP and stronger upwelling during the warm interstadial. We propose that the increases of PP were driven by increased bioavailable nutrient content in surface waters under both stronger winter monsoon conditions that strengthened the convective mixing, and higher aeolian inputs. Over the Holocene, stronger upwelling and slightly lower PP are found during the Early-Mid Holocene, when higher summer insolation triggered stronger summer monsoon. At that time, the lower PP was probably the result of restricted advection of eutrophic summer upwelling seawater under negative wind stress curls and less aeolian inputs.

Key Points

Past primary productivity and upwelling in the NW Arabian Sea are reconstructed by coccolith assemblages from a marine sediment core

Primary productivity was relatively high during the cold periods compared to the warm periods of the last 23 kyr

Primary productivity changes were mainly controlled by winter monsoon through changes in convective mixing and by aeolian inputs

Plain Language Summary

Ocean Primary Productivity is the production rate of organic carbon from inorganic carbon by ocean phytoplankton through photosynthesis, in which nutrients and sunlight are necessary. In the tropical oceans, this rate is usually limited by the availability of nutrients in the sunlit ocean, which is controlled by physical processes such as seawater upward motion, ocean mixing, and dust storms. All these processes play a significant role in the northwestern Arabian Sea today. It is surrounded by arid lands that provide the highest amount of airborne material in the world and it is influenced by the Indian monsoon system that drives seawater upward motion and mixing in summer and winter, respectively. However, not much is known about their impact on Primary Productivity in the past. This work aims to reconstruct changes of Primary Productivity in the northwestern Arabian Sea over the past twenty thousand years and understand by which process(es) they are impacted, based on a model-data comparison approach. We’ve found that Primary Productivity was higher during cold periods than during warm periods. The changes were mainly controlled by both, winter monsoon through changes in convective mixing, and dust storms through changes in nutrient-enrich aeolian inputs.