Organic carbon flux and organic carbon to calcite flux ratio recorded in deep‐sea carbonates: Demonstration and a new proxy

Abstract

[1] Theoretical considerations indicate that degree of bottom water calcite saturation, organic carbon flux, and the ratio of that flux to the calcite flux all are reflected in the carbonate preservation record of deep-sea sediments. Separating the influence of these various factors on the record depends first on estimating the percent of the calcite flux which is dissolved at the seabed. We have developed a new proxy for percent dissolved calcite by calibrating a foraminiferal fragmentation index to biogeochemical modelderived data. Application of our proxy, combined with geochemical modeling, to the surface sediments of the Eastern Equatorial Pacific [EEP], demonstrates the need for all three of the variables listed above to account for the observations. Further, we used reverse modeling to map the ratio of the biotic fluxes across the EEP. We observe a coherent regional pattern with highest ratio values, as expected, associated with areas of upwelling, particularly along South America. Our proxy appears to be unaffected by carbonate sediment properties such as percent calcite in samples or the amount of coarse fraction (>63 mm) in the calcareous portion of the sediments; therefore it reflects primarily the geochemical environment rather than characteristics of seabed deposits.

Glacial deep ocean sequestration of CO2 driven by the eastern equatorial Pacific biologic pump

“…Calcite dissolution was estimated in all three cores using the planktonic foraminifer Globorotalia menardii Fragmentation Index (MFI) converted to percent calcite dissolved following the methods of Mekik et al (2002Mekik et al ( , 2010.…”

Quantitative interpretation of pore water O2 and pH distributions in deep-sea sediments

“…Laboratory studies suggest that non-linear rate laws, with n > 1, apply to calcite dissolution in sea water (Keir, 1980;Gehlen et al, 2005). In several modeling studies, however, a linear rate law (n = 1) results in less variability in the dissolution rate constant, k d , when comparing pore water data from multiple locations characterized by variable saturation states of the bottom water (Gehlen et al, 1999;Hales and Emerson, 1997b;Mekik et al, 2002). The majority of previous modeling studies have used a rate order of either 1 or 4.5 with the latter being most dominant (Table 4), whereas Adler et al (2001) tested a range of values from 1 to 4.5.…”

Southern Ocean biogeochemical impact on the tropical ocean: Stable isotope records from the Pacific for the past 25,000 years

“…Elaboration of the biological pump hypothesis recognized that there were two important additional considerations. The productivity of the oceans must be effectively exported to the deep sea for it to impact climate (climate effect depends on export ratio), and the ratio of organic carbon to calcite rain into the deep sea influences oceanic alkalinity (topic review: ; evidence for rain ratio variation in the modern ocean: Deep Sea Research II volume 54 'The Role of Marine Organic Carbon and Calcite Fluxes in Driving Global Climate Change, Past and Future'; Mekik et al, 2002Mekik et al, , 2007; hence separating productivity into its biogenous export components is important (e.g. Dymond and Lyle, 1985;Archer and Maier-Reimer, 1994;Brzezinski et al, 2002;Matsumoto et al, 2002;Sarmiento et al, 2004).…”