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

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 similar to 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 similar to 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 similar to 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 (similar to 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 similar to 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.

Automated summary

This study reveals significant shifts in monsoon behavior and associated changes in the Oxygen Minimum Zone (OMZ) during the late Pleistocene-Holocene interval off the coast of Goa, eastern Arabian Sea. The analysis of benthic foraminifera, pteropods, and total organic carbon (TOC) provides insights into past environmental changes and their impact on marine life.