Enhanced Carbonate Dissolution Associated With Deglacial Dysoxic Events in the Subpolar North Pacific
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AbstractHere we use volume density (V) measurements as a metric of sizenormalized weights for Neogloboquadrina pachyderma, a planktonic foraminifer, from upper OMZ and abyssal depth sites in the Gulf of Alaska over the past 20,000years to test for covariation between carbonate preservation and OMZ intensity. We find that dissolution of N. pachyderma is most intense at the upper OMZ site where oxygenation is generally lower than at the abyssal site. We also examine Uvigerina peregrina, a benthic foraminifer, at the upper OMZ site and find that the lowest V measurements in both taxa occur during deglacial and early Holocene dysoxic events. We use computed tomography images to confirm that changes in V are related to shell thickness, observe dissolution features, and test for growth influences on V. Further, we use stepwise selection of multiple regression models in which coregistered environmental proxies are potential predictors of V and find that the best supported models retain negative associations between V and the concentration of redoxsensitive metals and the relative abundance of dysoxiatolerant and opportunistic benthic foraminifera, indicating that low V is associated with lowoxygen conditions and pulsed availability of organic matter at the seafloor. Taken together, our results suggest the primary driver of carbonate dissolution here is related to organic carbon respiration at the seafloor. This highlights the importance of metabolic dissolution in understanding the inorganic carbon cycle and the role regions with highorganic carbon export, such as OMZs, can have as CO2 sources as metabolic dissolution intensifies.
