Global patterns in efficiency of particulate organic carbon export and transfer to the deep ocean

Abstract

[1] The ocean's biological carbon pump is a key component of the global carbon cycle. Only a small fraction of the carbon fixed by primary production is exported to the deep ocean, yet this flux sets to first order the efficiency with which carbon is sequestered out of further contact with the atmosphere on long time scales. Here we examine global patterns in particle export efficiency (PE eff ), the proportion of primary production that is exported from the surface ocean, and transfer efficiency (T eff ), the fraction of exported organic matter that reaches the deep ocean. Previous studies have found a positive correlation between T eff and deep ocean calcite fluxes recovered from sediment traps, implying that ballasting by calcium carbonate may play an important role in regulating T eff . An alternative explanation is that this correlation is not causative, as regions where the dominant biomineral phase is calcite tend to be subtropical systems, which are hypothesized to produce sinking aggregates highly resistant to degradation. We attempt to distinguish between these alternative hypotheses on the control of T eff by examining the relationship between T eff and biomineral phases exported from the upper ocean, rather than those collected in deep traps. Global scale estimates derived from satellite data show, in keeping with earlier studies, that PE eff is high at high latitudes and low at low latitudes, but that T eff is low at high latitudes and high at low latitudes. However, in contrast to the relationship observed for deep biomineral fluxes in previous studies, we find that T eff is strongly negatively correlated with opal export flux from the upper ocean, but uncorrelated with calcium carbonate export flux. We hypothesize that the underlying factor governing the spatial patterns observed in T eff is ecosystem function, specifically the degree of recycling occurring in the upper ocean, rather than the availability of calcium carbonate for ballasting.Citation: Henson, S. A., R. Sanders, and E. Madsen (2012), Global patterns in efficiency of particulate organic carbon export and transfer to the deep ocean, Global Biogeochem. Cycles, 26, GB1028,

Reconciling fisheries catch and ocean productivity

“…3C). Both of these patterns are supported by past empirical analysis and understanding of the underlying mechanisms (29,40,58,59). However, although the performance of ESM2.6 at the LME scale was encouraging (Table S1), the model still suffers from regional biases and incomplete process resolution.…”

Evaluation of NorESM-OC (versions 1 and 1.2), the ocean carbon-cycle stand-alone configuration of the Norwegian Earth System Model (NorESM1)

“…Note that in the KR02 scheme, living phytoplankton is part of the sinking aggregates (in STD and WLIN phytoplankton does not sink), hence the relatively large export despite the re-tuned ecosystem. The POC flux at 2000 m is significantly smaller than the observed range in STD-slow: 0.16 vs. 0.43 (Honjo et al, 2008) and 0.66 Pg C yr −1 (Henson et al, 2012). It falls within or slightly above this range for the other three runs (0.45, 0.69, and 0.68 Pg C yr −1 for STD-fast, KR02, and WLIN, respectively).…”

“…Figure 23c shows the average POC fluxes at 100 and 2000 m depth, and at the ocean bottom (where water depth is larger than 1000 m) for the four experiments and recent observation-based estimates of these fluxes. The carbon export fluxes (POC flux at 100 m depth) of 4.0 to 5.6 Pg C yr −1 found in the model are at the lower end of observationbased estimates of 4.0 (Henson et al, 2012), 5.7 (Honjo et al, 2008, and 11.2 Pg C yr −1 (Laws et al, 2000). The three runs employing the differently tuned ecosystem show a lower export than the STD-slow configuration.…”

Major impacts of climate change on deep-sea benthic ecosystems

“…Currently, regions with the highest POC export lie at high latitudes, although transfer efficiency (the proportion of POC exported that arrives at the seafloor) is lowest here compared to lower latitudes. At lower latitudes, extensive mineralization takes place in the upper water column leading to less export from the euphotic zone, but transfer efficiency is higher, as most of the exported carbon tends to be refractory (Henson et al, 2012). Enhanced warming of the upper ocean is predicted to enhance stratification, reducing nutrient input to the upper euphotic zone and causing a shift in phytoplankton assemblages from large, fast-sinking diatoms (with low surface area:volume [SA:V] ratios) to slow-sinking picoplankton (with high SA:V ratios; Bopp et al, 2005).…”