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The relative importance of phytoplankton aggregates and zooplankton fecal pellets to carbon export: insights from free-drifting sediment trap deployments in naturally iron-fertilised waters near the Kerguelen Plateau
Citation
Laurenceau-Cornec, EC and Trull, TW and Davies, DM and Bray, SG and Doran, J and Planchon, F and Carlotti, F and Jouandet, M-P and Cavagna, A-J and Waite, AM and Blain, S, The relative importance of phytoplankton aggregates and zooplankton fecal pellets to carbon export: insights from free-drifting sediment trap deployments in naturally iron-fertilised waters near the Kerguelen Plateau, Biogeosciences, 12, (4) pp. 1007-1027. ISSN 1726-4170 (2015) [Refereed Article]
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Copyright Statement
Copyright 2015 The Author
DOI: doi:10.5194/bg-12-1007-2015
Abstract
The first KErguelen Ocean and Plateau compared Study (KEOPS1), conducted in
the naturally iron-fertilised Kerguelen bloom, demonstrated that fecal
material was the main pathway for exporting carbon to the deep ocean during
summer (January–February 2005), suggesting a limited role of direct export
via phytodetrital aggregates. The KEOPS2 project reinvestigated this issue
during the spring bloom initiation (October–November 2011), when zooplankton
communities may exert limited grazing pressure, and further explored the link
between carbon flux, export efficiency and dominant sinking particles
depending upon surface plankton community structure. Sinking particles were
collected in polyacrylamide gel-filled and standard free-drifting sediment
traps (PPS3/3), deployed at six stations between 100 and 400 m, to examine
flux composition, particle origin and their size distributions. Results
revealed an important contribution of phytodetrital aggregates (49 ± 10
and 45 ± 22% of the total number and volume of particles
respectively, all stations and depths averaged). This high contribution
dropped when converted to carbon content (30 ± 16% of total carbon,
all stations and depths averaged), with cylindrical fecal pellets then
representing the dominant fraction (56 ± 19%).
At 100 and 200 m depth, iron- and biomass-enriched sites exhibited the highest carbon fluxes (maxima of 180 and 84 ± 27 mg C m-2 d-1, based on gel and PPS3/3 trap collection respectively), especially where large fecal pellets dominated over phytodetrital aggregates. Below these depths, carbon fluxes decreased (48 ± 21% decrease on average between 200 and 400 m), and mixed aggregates composed of phytodetritus and fecal matter dominated, suggesting an important role played by physical aggregation in deep carbon export.
Export efficiencies determined from gels, PPS3/3 traps and 234Th disequilibria (200 m carbon flux/net primary productivity) were negatively correlated to net primary productivity with observed decreases from ~ 0.2 at low-iron sites to ~ 0.02 at high-iron sites. Varying phytoplankton communities and grazing pressure appear to explain this negative relationship. Our work emphasises the need to consider detailed plankton communities to accurately identify the controls on carbon export efficiency, which appear to include small spatio-temporal variations in ecosystem structure.
At 100 and 200 m depth, iron- and biomass-enriched sites exhibited the highest carbon fluxes (maxima of 180 and 84 ± 27 mg C m-2 d-1, based on gel and PPS3/3 trap collection respectively), especially where large fecal pellets dominated over phytodetrital aggregates. Below these depths, carbon fluxes decreased (48 ± 21% decrease on average between 200 and 400 m), and mixed aggregates composed of phytodetritus and fecal matter dominated, suggesting an important role played by physical aggregation in deep carbon export.
Export efficiencies determined from gels, PPS3/3 traps and 234Th disequilibria (200 m carbon flux/net primary productivity) were negatively correlated to net primary productivity with observed decreases from ~ 0.2 at low-iron sites to ~ 0.02 at high-iron sites. Varying phytoplankton communities and grazing pressure appear to explain this negative relationship. Our work emphasises the need to consider detailed plankton communities to accurately identify the controls on carbon export efficiency, which appear to include small spatio-temporal variations in ecosystem structure.
Item Details
| Item Type: | Refereed Article |
|---|---|
| Keywords: | phytoplankton aggregates, Kerguelen Plateau, sediment trap deployments |
| Research Division: | Earth Sciences |
| Research Group: | Oceanography |
| Research Field: | Chemical oceanography |
| Objective Division: | Environmental Management |
| Objective Group: | Management of Antarctic and Southern Ocean environments |
| Objective Field: | Antarctic and Southern Ocean oceanic processes |
| UTAS Author: | Laurenceau-Cornec, EC (Mr Emmanuel Laurenceau) |
| UTAS Author: | Trull, TW (Professor Thomas Trull) |
| UTAS Author: | Davies, DM (Ms Diana Davies) |
| UTAS Author: | Bray, SG (Mr Stephen Bray) |
| ID Code: | 100101 |
| Year Published: | 2015 |
| Web of Science® Times Cited: | 76 |
| Deposited By: | CRC-Antarctic Climate & Ecosystems |
| Deposited On: | 2015-05-01 |
| Last Modified: | 2017-10-31 |
| Downloads: | 667 View Download Statistics |
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