Krill faecal pellets drive hidden pulses of particulate organic carbon in the marginal ice zone

A Belcher,P Fretwell,S E Thorpe,L Ireland,A Atkinson,G A Tarling,C Manno,S L Hill,S A Henson

doi:10.1038/s41467-019-08847-1

Abstract

The biological carbon pump drives a flux of particulate organic carbon (POC) through the ocean and affects atmospheric levels of carbon dioxide. Short term, episodic flux events are hard to capture with current observational techniques and may thus be underrepresented in POC flux estimates. We model the potential hidden flux of POC originating from Antarctic krill, whose swarming behaviour could result in a major conduit of carbon to depth through their rapid exploitation of phytoplankton blooms and bulk egestion of rapidly sinking faecal pellets (FPs). Our model results suggest a seasonal krill FP export flux of 0.039 GT C across the Southern Ocean marginal ice zone, corresponding to 17–61% (mean 35%) of current satellite-derived export estimates for this zone. The magnitude of our conservatively estimated flux highlights the important role of large, swarming macrozooplankton in POC export and, the need to incorporate such processes more mechanistically to improve model projections.

Highlights

The biological carbon pump drives a flux of particulate organic carbon (POC) through the ocean and affects atmospheric levels of carbon dioxide
According to the KRILLBASE statistical model[27, 28], peak krill densities occur during 24 December–06 January and highest faecal pellets (FPs) export fluxes (104 mg C m−2 d−1 averaged over the entire marginal ice zone (MIZ) area, FP carbon at 100 m (FP100),MIZ) are predicted to occur during this period
Maximum fluxes of cylindrical FPs of 125.5 mg C m−2 d−1 were observed in sediment traps at 170 m depth on the Western Antarctic Peninsula[10] in February

Summary

Introduction

The biological carbon pump drives a flux of particulate organic carbon (POC) through the ocean and affects atmospheric levels of carbon dioxide. Studies of POC flux attenuation struggle to capture episodic, intense, or localised export events because of limited sampling and the patchy nature of such events in time and space. Being one of the largest epipelagic crustaceans, krill produce large faecal pellets (FPs), which sink at speeds of hundreds of metres per day[2, 4], making them important agents in carbon export. In this way, carbon that originated in the atmosphere is transferred to the deep sea where it can be sequestered for periods of centuries or more[7]. Derived models for POC flux that utilise limited in situ snapshot POC flux measurements may not capture episodic fluxes, such as those driven by krill swarms, and likely underestimate the carbon flux in regions of high krill density

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Results

Conclusion