Impact of Remineralization Profile Shape on the Air-Sea Carbon Balance.

Jonathan Maitland Lauderdale,B. B. Cael

doi:10.1029/2020gl091746

Abstract

The ocean's “biological pump” significantly modulates atmospheric carbon dioxide levels. However, the complexity and variability of processes involved introduces uncertainty in interpretation of transient observations and future climate projections. Much research has focused on “parametric uncertainty,” particularly determining the exponent(s) of a power‐law relationship of sinking particle flux with depth. Varying this relationship's functional form introduces additional “structural uncertainty.” We use an ocean biogeochemistry model substituting six alternative remineralization profiles fit to a reference power‐law curve, to systematically characterize structural uncertainty, which, in atmospheric pCO2 terms, is roughly 50% of parametric uncertainty associated with varying the power‐law exponent within its plausible global range, and similar to uncertainty associated with regional variation in power‐law exponents. The substantial contribution of structural uncertainty to total uncertainty highlights the need to improve characterization of biological pump processes, and compare the performance of different profiles within Earth System Models to obtain better constrained climate projections.

Highlights

Carbon and nutrients are consumed by phytoplankton in the surface ocean during primary production, leading to a downward flux of organic matter
We use an ocean biogeochemistry model substituting six alternative remineralization profiles fit to a reference power-law curve, to systematically characterize structural uncertainty, which, in atmospheric pCO2 terms, is roughly 50% of parametric uncertainty associated with varying the power-law exponent within its plausible global range, and similar to uncertainty associated with regional variation in powerlaw exponents
We evaluate structural uncertainty using an ocean biogeochemistry model by systematically substituting six alternative remineralization profiles fit to a reference power-law curve

Summary

Introduction

Carbon and nutrients are consumed by phytoplankton in the surface ocean during primary production, leading to a downward flux of organic matter. This “marine snow” is transformed, respired, and degraded by heterotrophic organisms in deeper waters, releasing those constituents back into dissolved inorganic form. The “biological pump” maintains this vertical gradient in nutrients through uptake, vertical transport, and remineralization of organic matter, storing carbon in the deep ocean that is isolated from the atmosphere on centennial and millennial timescales, lowering atmospheric CO2 levels by hundreds of micro-atmospheres (Ito & Follows, 2005; Volk & Hoffert, 1985). The ubiquitous “Martin Curve” (Martin et al, 1987) is a power-law profile (Equation 1) that assumes slower-sinking and/or labile

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Conclusion