Krill and salp faecal pellets contribute equally to the carbon flux at the Antarctic Peninsula

Nora-Charlotte Pauli,Morten H Iversen,Clara M Flintrop,Matteo Bernasconi,Ji-Chang Zhang,Florian Koch,Evgeny A Pakhomov,Steffen Swoboda,Andrew S Brierley,Xin-Liang Wang,Christian Konrad,Bettina Meyer

doi:10.1038/s41467-021-27436-9

Abstract

Krill and salps are important for carbon flux in the Southern Ocean, but the extent of their contribution and the consequences of shifts in dominance from krill to salps remain unclear. We present a direct comparison of the contribution of krill and salp faecal pellets (FP) to vertical carbon flux at the Antarctic Peninsula using a combination of sediment traps, FP production, carbon content, microbial degradation, and krill and salp abundances. Salps produce 4-fold more FP carbon than krill, but the FP from both species contribute equally to the carbon flux at 300 m, accounting for 75% of total carbon. Krill FP are exported to 72% to 300 m, while 80% of salp FP are retained in the mixed layer due to fragmentation. Thus, declining krill abundances could lead to decreased carbon flux, indicating that the Antarctic Peninsula could become a less efficient carbon sink for anthropogenic CO2 in future.

Highlights

Krill and salps are important for carbon flux in the Southern Ocean, but the extent of their contribution and the consequences of shifts in dominance from krill to salps remain unclear
We assess the contribution of krill and salp faecal pellets (FP) to the carbon flux at the Antarctic Peninsula (AP) and present a direct comparison
Krill and salp FP accounted for the majority of the total particulate organic carbon (POC) flux

Summary

Introduction

Krill and salps are important for carbon flux in the Southern Ocean, but the extent of their contribution and the consequences of shifts in dominance from krill to salps remain unclear. The contribution of krill to the carbon flux depends on their abundance, the carbon content and sinking velocity of their FP, as well as on fragmentation and degradation processes of FP during their descend through the water column[11,14,16] This contribution can be disproportionally high when krill form dense, extensive swarms, which produce a rain of FP, possibly exceeding the grazing efficiency of the available detritivores[14,16]. This is evident at the WAP, where krill occur at high abundances[17], and their FP can account for >80% of the sinking particles[18] and for >60% of the organic carbon in sea floor sediments[19]. The warming temperatures have allowed the pelagic tunicate Salpa thompsoni

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Conclusion