Balancing the Oceanic Calcium Carbonate Cycle: Consequences of Variable Water Column Ψ

Abstract

The paired chemical reactions, Ca 2? ? 2HCO 3 -$ CaCO 3 ? CO 2 ? H 2 O, overestimate the ratio of CO 2 flux to CaCO 3 flux during the precipitation or dissolution of CaCO 3 in seawater. This ratio, which has been termed w, is about 0.6 in surface seawater at 25°C and at equilibrium with contemporary atmospheric CO 2 and increases towards 1.0 as seawater cools and pCO 2 increases. These conclusions are based on field observations, laboratory experiments, and equilibrium calculations for the seawater carbonate system. Yet global geochemical modeling indicates that small departures of W from 1.0 would cause dramatic, rapid, and unrealistic change in atmospheric CO 2 . W can be meaningfully calculated for a water sample whether or not it is in equilibrium with the atmosphere. The analysis presented here demonstrates that the atmospheric CO 2 balance can be maintained constant with respect to seawater CaCO 3 reactions if one considers the difference between CaCO 3 precipitation and burial and differing values for w (both \1.0) in regions of precipitation and dissolution within the ocean.

The Ecology, Biogeochemistry, and Optical Properties of Coccolithophores

“…There is evidence that the formulation of Equation 1 dates back to the nineteenth century (Berner & Maasch 1996). However, field observations suggest that the ratio of CO 2 produced to CaCO 3 precipitated is not but 1:0.6 (Smith & Gattuso 2011). This 0.6 rule has been discussed extensively in the past (Broecker & Takahashi 1966, Wollast et al 1980.…”

“…This 0.6 rule has been discussed extensively in the past (Broecker & Takahashi 1966, Wollast et al 1980. The parameter has been derived to describe the ratio of CO 2 flux to CaCO 3 flux associated with the dissolution or precipitation of CaCO 3 (Smith & Gattuso 2011). They advocate that Equation 1 be rewritten to include (= CO 2 ↑ /CaCO 3 ↓):…”

Quantitative and mechanistic understanding of the open ocean carbonate pump - perspectives for remote sensing and autonomous in situ observation

“…1) towards CO 2 , thus increasing the partial pressure of CO 2 in seawater, pCO 2 . The amount of CO 2 released per CaCO 3 precipitated, denoted Ψ (mol: mol, Ψ ≤ 1), is controlled by seawater carbonate chemistry, temperature, and salinity (Frankignoulle et al, 1994;Smith and Gattuso, 2011). Contemporary global mean surface values of Ψ are ~0.66 (Smith and Mackenzie, 2016), with values tending towards 1 as seawater cools and pCO 2 increases (Smith and Gattuso, 2011).…”

“…The amount of CO 2 released per CaCO 3 precipitated, denoted Ψ (mol: mol, Ψ ≤ 1), is controlled by seawater carbonate chemistry, temperature, and salinity (Frankignoulle et al, 1994;Smith and Gattuso, 2011). Contemporary global mean surface values of Ψ are ~0.66 (Smith and Mackenzie, 2016), with values tending towards 1 as seawater cools and pCO 2 increases (Smith and Gattuso, 2011). Surface values range from 0.56 to 0.80 from the tropical to the polar oceans (driven by temperature differences) and with depth from 0.66 at the surface to 0.85 at 1000 m (driven mostly by pCO 2 differences) (Smith, 2013;Smith and Gattuso, 2011).…”

Explicit silicate cycling in the Kiel Marine Biogeochemistry Model version 3 (KMBM3) embedded in the UVic ESCM version 2.9

“…aCarr et al (2006),Jin et al (2006).b Smith and Gattuso (2011),Smith and Mackenzie (2016).c Tréguer et al (2021). d Luo et al (2014).…”