Glacial-Interglacial changes and Holocene variations in Arabian Sea denitrification

摘要: Abstract. At present, the Arabian Sea has a permanent oxygen minimum zone (OMZ) at water depths between about 100 and 1200 m. Active denitrification in the upper part of OMZ is recorded by enhanced δ15 N values the sediments. Sediment cores show increase during middle and late Holocene, which contrary to trend other two regions of water column eastern tropical North South Pacific. We calculated composite sea surface temperature (SST) N ratios time slices 1000 years last 25 kyr better understand the reasons for establishment its response to changes Asian monsoon system. Low of 4–7 ‰ glacial maximum (LGM) stadials (Younger Dryas Heinrich events) suggest that was inactive or weak during Pleistocene cold phases, while warm interstadials (ISs) had elevated N. Fast changes upwelling intensities ventilation from Antarctic were responsible these strong millennial-scale variations glacial. During entire Holocene N values >  6 ‰ indicate relatively stable with enhanced denitrification. The develops parallel strengthening SW monsoon monsoonal after LGM. Despite stable climatic conditions records show regionally different trends Sea. In areas western part basin, are lower mid-Holocene (4.2–8.2 ka BP) compared the late (  4.2 ka BP) due stronger ventilation OMZ during period most intense southwest upwelling. In contrast, northern rose during 8 kyr. displacement core from the region productivity western present position northeast established middle late Holocene. This probably caused (i) reduced longer residence waters (ii) augmented rising consumption due northeast-monsoon-driven biological productivity. This concurs results Kiel Climate Model, an in OMZ volume 9 kyr related increasing age OMZ water mass.