ELEVATED MARINE PRODUCTIVITY AND ORGANIC CARBON SINKING FLUXES IN THE EASTERN TROPICAL PANTHALASSIC OCEAN DURING THE LATE PENNSYLVANIAN

Core black shales of Late Pennsylvanian cyclothems of the Midcontinent region of North America exhibit pronounced negative organic-carbon isotope excursions (to ‒31‰) with a minimum that is correlative with a d¹⁵N maximum in each study core (Algeo et al., 2008). Although many factors can influence C-isotope records, the smooth variation in vertical profile of both d¹³C_org and d¹⁵N in these core shales is consistent with a signature inherited from a well-mixed, laterally advected watermass that upwelled onto the Midcontinent Shelf (Algeo and Heckel, 2008). The source of this watermass was the thermocline region of the eastern tropical Panthalassic Ocean (ETPO), in which strong denitrification occurred during Gondwanan deglaciations, probably in response to enhanced upwelling and intensified productivity (see Altman et al. poster, this meeting). In this study, we use an oceanic box model to investigate controls on the marine carbon cycle in ETPO. Specifically, we investigate variations in marine productivity rates and organic matter sinking fluxes as the source of the negative excursion in d¹³C_org in the study units. Our results suggest that a 2 to 4× increase in these fluxes was required at the peak of deglaciations in order to increase the vertical D¹³C_DIC gradient sufficiently to produce the observed ca. ‒4‰ excursions in d¹³C_org, which record the d¹³C_DIC of the thermocline region. These results are consistent with and, therefore, supportive of the results of N-cycle modeling by Altman et al. (poster, this meeting).