Use of GO-SHIP data to quantify DOC production and export from the surface and subsequent DOC oxidation along circulation paths within the dark ocean

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UC San Diego
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Craig Carlson
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I propose to identify influences on three global DOC products using existing data collected from GO-SHIP cruise lines extending into the Atlantic, Indian, Pacific and Southern Oceans:

(1) DOC:NCP ratios (depths from surface to ~500m) are estimated using paired profiles of DOC to nitrate or DIC and calculating the difference from either deep water or the redistribution of substrate based on maximum mixing events, which could be estimated using ARGO float density data.

(2) DOC contributions to export (depths from ~200-1000m) are estimated either using water mass changes in DOC concentration and ventilation rate or integrating DOC profiles to the maximum mixed layer depth (again estimated from ARGO floats). The removal rates of DOC can be estimated using water mass ages, which can be modeled in the upper mesopelagic zone using CFCs and are commonly available with the GO-SHIP datasets. δ14C-DIC data could also regressed against DOC to infer removal rates of the longer-lived DOC reservoir in the deeper ocean (e.g., Hansell et al., 2012).

(3) DOC contributions to AOU (depths from ~500-5000m) are estimated using simultaneous changes in DOC and AOU (in C equivalents) as a function of distance within a known water mass (based on physical characteristics of the water). AOU is typically converted to carbon units using the canonical Anderson Δ02:ΔCO2 of 1.4, and is likely a good starting place when comparing across large spatial and temporal scales. Potential departures in Δ02:ΔCO2 perhaps could be tested over meridional transects using estimates of ΔDIC:ΔAOU after accounting for carbonate dissolution using alkalinity (data available through GO-SHIP), among other methods.
The emphasis in the current proposal will be to identify potential influences on DOC products, where hypotheses related to the proposed data products include:
        1. Across the ocean basins, DOC:NCP is largely influenced by local stratification, which will also influence DOC removal rates and the magnitude of DOC export.
        2. DOC contributions to deep ocean organic matter oxidation will decrease moving along the conveyor belt from the North Atlantic to the oldest waters of the deep Pacific.