[1] Recent independent lines of evidence suggest that the dissolution of calcium carbonate (CaCO 3 ) particles is substantial in the upper ocean above the calcite 100% saturation horizon. This shallow-water dissolution of carbonate particles is in contrast with the current paradigm of the conservative nature of pelagic CaCO 3 at shallow water depths. Here we use more than 20,000 sets of carbon measurements in conjunction with CFC and 14 C data from the WOCE/JGOFS/OACES global CO 2 survey to estimate in situ dissolution rates of CaCO 3 in the Atlantic Ocean. A dissolution rate is estimated from changes in alkalinity as a parcel of water ages along an isopycnal surface. The in situ CaCO 3 dissolution increases rapidly at the aragonite 100% saturation horizon. Estimated dissolution rates north of 40 o N are generally higher than the rates to the south, which is partly attributable to the production of exported CaCO 3 being higher in the North Atlantic than in the South Atlantic. As more CaCO 3 particles move down the water column, more particles are available for in situ dissolution. The total water column CaCO 3 dissolution rate in the Atlantic Ocean is determined on an annual basis by integrating estimated dissolution rates throughout the entire water column and correcting for alkalinity input of approximately 5.6 Â 10 12 mol C yr À1 from CaCO 3 -rich sediments. The resulting water column dissolution rate of CaCO 3 for the Atlantic Ocean is approximately 11.1 Â 10 12 mol C yr À1 . This corresponds to about 31% of a recent estimate (35.8 Â 10 12 mol C yr À1 ) of net CaCO 3 production by Lee [2001] for the same area. Our calculation using a large amount of high-quality water column alkalinity data provides the first basin-scale estimate of the CaCO 3 budget for the Atlantic Ocean.
The dissolution of aragonite particles in the ocean primarily depends on the degree of undersaturation of seawater with respect to that mineral. Most of the upper Atlantic Ocean, particularly north of 30ЊS and at depths of less than 2000 m, is supersaturated with respect to aragonite, whereas much of the deep Atlantic is undersaturated. Here we report, for the first time, shallow layers of aragonite-undersaturated water between 20ЊS and 15ЊN in the eastern tropical Atlantic. These layers are centered at 800 m and are surrounded by aragonite-supersaturated water above and below. This feature most likely results from a combination of chemical and biological processes including the uptake of anthropogenic CO 2 and the oxidation of organic matter falling from the highly productive overlying surface water. Reaction with protons resulting from these processes decreases the carbonate ion concentration and consequently the saturation state of the waters with respect to aragonite. The oceanic uptake of anthropogenic CO 2 during the industrial era has caused a significant increase in the size of the undersaturated layers. Future expansion will likely occur laterally to the west and south, where the degree of supersaturation is low compared to waters to the north. This expansion of the undersaturated layers is a prime example of how human activity during the industrial era has altered the upper ocean chemistry by injecting fossil fuel CO 2 into the ocean.The saturation state of seawater with respect to aragonite (⍀ A ) under in situ conditions of temperature, salinity, and pressure is defined as
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.