Enhanced Carbonate Dissolution Associated With Deglacial Dysoxic Events in the Subpolar North Pacific

Abstract

Introduction Oxygen Minimum and Carbonate Maximum Zones in the PacificOxygen minimum zones (OMZs) are regions at intermediate ocean depths with low dissolved oxygen content, the extent of which vary over time with ocean circulation, nutrient availability, and climate (Deutsch et al., 2011;Helly & Levin, 2004;Keeling et al., 2010). These zones are forecast to expand and intensify with ongoing global climate change driven by rising anthropogenic CO 2 (Keeling et al., 2010;Long et al., 2016;Stramma et al., 2008). OMZs also correspond with maxima in dissolved inorganic carbon (DIC), forming corresponding carbon maximum zones (CMZs), due to high-organic carbon respiration and, potentially, enhanced carbonate dissolution driven by that respiration (Paulmier et al., 2011;Wyrtki, 1962). In addition, prolonged hypoxic to anoxic conditions may amplify the effects of benthic respiration on bottom water pH and carbonate saturation (Ω), further enhancing carbonate dissolution in OMZ sediments as they do in coastal environments (Hu et al., 2017;Wang et al., 2020). As a result of these processes, OMZs are presently the primary carbon reservoir of the subsurface ocean and can be sites of CO 2 transfer from the ocean to the atmosphere with significant consequences for oceanic carbon storage and global climates (Naik et al., 2014;Paulmier et al., 2011). Examining the relationship between past intensification of OMZs and changes in marine calcification and carbonate dissolution is important for parameterizing changes in the inorganic carbon cycle that may occur with climate change.The Pacific Ocean contains the world's largest OMZ (Paulmier & Ruiz-Pino, 2009). Oxygen content has decreased and the upper OMZ boundary has shoaled in this region since at least the 1960s in response to warming-induced declines in solubility, enhanced upper ocean stratification, reduced ventilation, and decreased North Pacific Intermediate Water (NPIW) formation (

Volcanic trigger of ocean deoxygenation during Cordilleran ice sheet retreat

“…Sediment CaCO3 may be affected by dissolution. A previous study found evidence of enhanced dissolution at the intermediate-depth site during the severe deoxygenation intervals but not during the mild deoxygenation intervals 68 . Carbonate dissolution is expected to be stronger at the abyssal site, and thus the increase in calcareous productivity indicated here is likely underestimated.…”