Insights into the coupling of upper ocean-benthic carbon dynamics in the western Arctic Ocean from an isotopic (13C, 234Th) perspective

The coupling of upper ocean-benthic carbon dynamics in the ice-free western Arctic Ocean (the Chukchi Sea and the Canada Basin) was evaluated during the late July-early September 2003 using natural stable (13C) and radioactive (238U-234Th) isotope tracers. POC export flux estimated from 234Th/238U disequilibria and dissolved CO2 concentration ([CO2(aq)]) pointed out that the strengthened biological pump in the Chukchi Shelf have significantly lowered [CO2(aq)] and altered the magnitude of isotopic (12C/13C) fractionation during carbon fixation in the surface ocean. Further, δ 13C signatures of surface sediments (δ 13Csed) are positively correlated to those of weighted δ 13CPOC in upper ocean (δ 13Csed =13.64+1.56×δ 13CPOC, r 2=0.73, p<0.01), suggesting that the POC isotopic signals from upper ocean have been recorded in the sediments, partly due to the rapid export of particles as evidenced by low residence times of the highly particle-reactive 234Th from the upper water column. It is suggested that there probably exists an upper ocean-benthic coupling of carbon dynamics, which likely assures the sedimentary δ 13C record an indicator of paleo-CO2 in the western Arctic Ocean.