The export and fate of organic matter in the ocean: New constraints from combining satellite and oceanographic tracer observations

Abstract

The ocean's biological pump transfers carbon from the surface euphotic zone into the deep ocean, reducing the atmospheric CO2 concentration. Despite its climatic importance, there are large uncertainties in basic metrics of the biological pump. Previous estimates of the strength of the biological pump, as measured by the amount of organic carbon exported from the euphotic zone, range from about 4 to 12 Pg C yr−1. The fate of exported carbon, in terms of how efficiently it is transferred into the deep ocean, is even more uncertain. Here we present a new model of the biological pump that assimilates satellite and oceanographic tracer observations to constrain rates and patterns of organic matter production, export, and remineralization in the ocean. The data‐assimilated model predicts a global particulate organic carbon (POC) flux out of the euphotic zone of ∼9 Pg C yr−1. The particle export ratio (the ratio of POC export to net primary production) is highest at high latitudes and lowest at low latitudes, but low‐latitude export is greater than predicted by previous models, in better agreement with observed patterns of long‐term carbon export. Particle transfer efficiency (Teff) through the mesopelagic zone is controlled by temperature and oxygen, with highest Teff for high‐latitude regions and oxygen minimum zones. In contrast, Teff in the deep ocean (below 1000 m) is controlled by particle sinking speed, with highest deep ocean Teff below the subtropical gyres. These results emphasize the utility of both remote sensing and oceanographic tracer observations for constraining the operation of the biological pump.

Origin, Transformation, and Fate: The Three‐Dimensional Biological Pump in the California Current System

“…Besides that, the spatial pattern and seasonal cycle of net primary production (NPP) in the CalCS are generally captured well. The associated carbon export in the CalCS estimated from the model, and in particular, its pronounced cross‐shore gradient seems to be well supported by both data‐assimilative model estimates (DeVries & Weber, ; Figures e–g) and in situ measurements from the Southern California Bight (Berelson & Stott, ; Munro et al, ; see supporting information). Also, the burial efficiency of the organic matter lies within the range of observational estimates (e.g., Berelson & Stott, ; Jahnke, ).…”

The Role of Particle Size, Ballast, Temperature, and Oxygen in the Sinking Flux to the Deep Sea

“…The oxygen sensitivity of respiration rates has the potential to affect particle remineralization rates in water columns that include oxygen minimum zones (OMZs), where [O 2 ] may become low enough to slow aerobic particle degradation rates. Across a range of K O2 values suggested in previous studies (5–30 μM; DeVries & Weber, ; Kalvelage et al, ; Keil et al, ; Laufkötter et al, ; Ploug, ), our model predicts that T EFF is 1.6–1.7 times greater in OMZs compared to oxygenated water columns (Figure d). However, given that OMZs only occupy a small fraction of the ocean, oxygen likely exerts much weaker influence on larger‐scale variations of T EFF than it does within the OMZ (see section 4.4).…”

Mesoscale Effects on Carbon Export: A Global Perspective

“…The distribution of EP and e‐ratio in CESM is similar to satellite‐based models (Figure ; DeVries & Weber, ; Siegel et al, ), and the difference between satellite‐based estimates is comparable to the difference between the model integrations and the satellite‐based models. For example, relative to Siegel et al (), export in CESM is higher in the coastal North Pacific, more similar to DeVries and Weber (). Satellite‐based export is higher near the Amazonian outflow and across many coastal regions; in both CESM simulations, riverine nutrient inputs are not included and coastal upwelling circulation is not well simulated, even at 0.1° resolution (Small et al, ; Wang et al, ).…”

“…Results from the satellite‐based food web models of DeVries and Weber [DeVries and Weber ()] (left column) and Siegel et al [Siegel et al ()] (right column). Shown are net primary productivity (NPP) (top row), export production (EP) (center row), and e‐ratio (bottom row).…”