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
Other literature type, Article
Laurenceau-Cornec , E. C.
Trull , T. W.
Davies , D. M.
Bray , S. G.
Doran , J.
Planchon , F.
Carlotti , F.
Jouandet , M.-P.
Cavagna , A.-J.
Waite , A. M.
Blain , S.
- Publisher: European Geosciences Union
[ SDV.EE ] Life Sciences [q-bio]/Ecology, environment | Ecology | QH540-549.5 | QE1-996.5 | [ SDU.STU.OC ] Sciences of the Universe [physics]/Earth Sciences/Oceanography | QH501-531 | Geology | Life
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<sup>-2</sup> d<sup>-1</sup>, 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 <sup>234</sup>Th
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