Late Quaternary variations in the Oxygen Minimum Zone linked to monsoon shifts as seen in the sediment of the outer continental shelf of the eastern Arabian Sea

Abstract

Multiproxy records of benthic foraminifera, pteropods, and total organic carbon (TOC) are reported from the late Pleistocene-Holocene interval of Core SK291/GC17, located off the coast of Goa (water depth 182 m), eastern Arabian Sea. Findings help unravel significant shifts in monsoon behavior and associated changes in the Oxygen Minimum Zone (OMZ). During the Younger Dryas (11900–11,600 cal yr BP) and ~ 11,600 to 9400 cal yr BP, the coast was closer to the studied core location because of the low eustatic sea level. This interval shows a higher abundance of benthic foraminifera preferring oxic bottom water condition over the suboxic group. At ~8000 cal yr BP, the decreased abundance of pteropod species Limacina trochiformis as well as lower values of TOC suggest the presence of a dry phase of the monsoon. The interval from ~7800 to 6400 cal yr BP was deposited under favorable bottom water conditions, as documented by a higher number of species (S), Information Function (Hs) and species richness of the benthic foraminiferal assemblage. The middle Holocene (~ 6200 to 4200 cal yr BP) interval is marked by a significant increase in the number of epipelagic pteropods caused by higher surface productivity and by a decreasing abundance of mesopelagic pteropods caused by the shoaling and intensification of the OMZ. The oxic group decreased drastically while the dysoxic group of benthic foraminifera increased during this interval due to the intensified OMZ. After ~4200 cal yr BP, the oxic assemblages of benthic foraminifera and pteropods suggest low productivity coinciding with the 4.2 ka dry event observed in the Indian monsoon records. The intervals with oxic assemblages of benthic foraminifera align with Bond events. Further the oxic assemblages show high frequency cycles centered at 692, 440 and 358 yr driven by solar variability, while Uvigerina peregrina , a benthic foraminifer sensitive to OMZ variability, shows high frequency cycles of 403 and 745 yr. • OMZ history of the eastern Arabian Sea during ~13,000 to 3400 cal yr BP • Winter monsoon was relatively stronger during the Younger Dryas cold interval. • The OMZ intensified and shoaled during ~6200 to 4200 cal yr BP. • Pteropod data indicates presence of a dry phase of the monsoon after ~4200 cal yr BP.