DOWN-CORE SEDIMENT NITROGEN ISOTOPE RATIO AT MM-SCALE RESOLUTION: EXPLORING THE LINKAGE BETWEEN ARABIAN SEA DENITRIFICATION AND MILLENNIAL-SCALE CLIMATE CHANGE

In the Arabian Sea and other regions with intense oxygen minimum zones, sediment nitrogen isotopic ratio can be used as a proxy for water column denitrification intensity, both present and past. Prior studies have shown Arabian Sea denitrification to vary with high fidelity with climate change on orbital to millennial times scales over the late Quaternary. Mechanistic linkages likely involve the strength of the S. Asian monsoon and the oceanic biological production it stimulates via upwelling of nutrient-rich waters. To investigate in detail the relationship between the record for Arabian Sea denitrification and and climate change records, high accumulation rate cores (10 to 20 cm/kyr) from the Oman Margin have been analyzed initially at 1 to 5 cm resolution and subsequently at mm-scale resolution across selected intervals. At the coarser scale, nitrogen isotopic ratio is closely linked to the millennial-scale D-O events recorded in the Greenland ice core record for N. Hemisphere climate change. During warm interstadial D-O events, increased nitrogen isotopic ratio indicates more intense denitrification. Several of these events were analyzed at 2 mm intervals to achieve decadal resolution. For interstadial#11 (~42.5 kyr b.p.), there was a rapid 2 per mil increase in d¹⁵N over 1.6 cm or <100 yr that accounted for most of the rise and dramatically records the rapid alteration of this system during warm interstadial onset. Smaller mm-scale events also occurred throughout the section demonstrating the capability of this core for recording decadal–scale events that may have modern analogues. Sediment chlorin concentration and %N were used as productivity proxies and showed the rise in d¹⁵N to be associated with increased production and presumably increased monsoonal upwelling. Refinements in core chronology have the potential for determining whether D-O events were initiated at low or high latitudes.