Mid-Holocene intensification of the oxygen minimum zone in the northeastern Arabian Sea. (15th April 2022) - Azharuddin, Syed
Graphical abstract: Highlights: The Arabian Sea has an intense oxygen minimum zone at intermediate water depths. Lower sea level and weak OMZ conditions in the study area existed during the early Holocene. The rise in sea level and increased surface water productivity intensified OMZ during the middle Holocene. The enhanced sub-surface denitrification in the OMZ increases the nitrous oxide emission. Abstract: The Arabian Sea is characterized by a strong Oxygen Minimum Zone (OMZ) bearing sub-oxic conditions at the intermediate water depth. We analyzed a sediment core near the upper margin of OMZ (174 m water depth) from offshore Saurashtra, northeastern (NE) Arabian Sea to reconstruct multi-proxy biogeochemical response in the area during the Early-Middle Holocene (∼10–4 ka before present). The results indicate lower foraminiferal productivity (both benthic and planktic) and weak sub-surface denitrification causing mild OMZ conditions at the study site during the early Holocene (∼10–8 ka). Subsequently, an increased foraminiferal productivity and sub-surface (both the water column and sediment) denitrification in the area led to intensified OMZ conditions during the mid-Holocene (after ∼8 ka). Our results corroborate other denitrification records from the Arabian Sea, suggesting the large-scale changes in Arabian Sea OMZ during the mid-Holocene. We suggest that the increased nutrient supply with significant freshwater input may have enhanced the primary productivity and further resulted in the intensified OMZ and escalated outgassing of N2 O from the area during the mid-Holocene.