 |
| Titel |
Early spring mesopelagic carbon remineralization and transfer efficiency in the naturally iron-fertilized Kerguelen area |
| VerfasserIn |
S. H. M. Jacquet, F. Dehairs, D. Lefèvre, A. J. Cavagna, F. Planchon, U. Christaki, L. Monin, L. André, I. Closset, D. Cardinal |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 6 ; Nr. 12, no. 6 (2015-03-17), S.1713-1731 |
| Datensatznummer |
250117864
|
| Publikation (Nr.) |
 copernicus.org/bg-12-1713-2015.pdf |
|
|
|
|
|
| Zusammenfassung |
| We report on the zonal variability of mesopelagic particulate organic carbon
remineralization and deep carbon transfer potential during the Kerguelen
Ocean and Plateau compared Study 2 expedition (KEOPS 2;
October–November 2011) in an area of the polar front supporting recurrent
massive blooms from natural Fe fertilization. Mesopelagic carbon
remineralization (MR) was assessed using the excess, non-lithogenic
particulate barium (Baxs) inventories in mesopelagic waters and
compared with bacterial production (BP), surface primary production (PP) and
export production (EP). Results for this early season study are compared with
the
results obtained during a previous study (2005; KEOPS 1) for the same area at
a later stage of the phytoplankton bloom. Our results reveal the patchiness
of the seasonal advancement and of the establishment of remineralization
processes between the plateau (A3) and polar front sites during KEOPS 2. For the
Kerguelen plateau (A3 site) we observe a similar functioning of the
mesopelagic ecosystem during both seasons (spring and summer), with low and
rather stable remineralization fluxes in the mesopelagic column
(150–400 m). The shallow water column (~500 m), the lateral
advection, the zooplankton grazing pressure and the pulsed nature of the particulate organic carbon
(POC)
transfer at A3 seem to drive the extent of MR processes on the plateau. For
deeper stations (>2000 m) located on the margin, inside a polar front
meander, as well as in the vicinity of the polar front, east of Kerguelen,
remineralization in the upper 400 m in general represents a larger part of
surface carbon export. However, when considering the upper 800 m, in some cases,
the entire flux of exported carbon is remineralized. In the polar front
meander, where successive stations form a time series, two successive events
of particle transfer were evidenced by remineralization rates: a first
mesopelagic and deep transfer from a past bloom before the cruise, and a
second transfer expanding at mesopelagic layers during the cruise. Regarding
the deep carbon transfer efficiency, it appeared that above the plateau (A3
site) the mesopelagic remineralization was not a major barrier to the
transfer of organic matter to the seafloor (close to 500 m). There, the
efficiency of carbon transfer to the bottom waters (>400 m) as assessed
by PP, EP and MR fluxes comparisons reached up to 87% of the carbon
exported from the upper 150 m. In contrast, at the deeper locations,
mesopelagic remineralization clearly limited the transfer of carbon to depths
of >400 m. For sites at the margin of the plateau (station E-4W) and the
polar front (station F-L), mesopelagic remineralization even exceeded upper
150 m export, resulting in a zero transfer efficiency to depths >800 m.
In the polar front meander (time series), the capacity of the meander to
transfer carbon to depth >800 m was highly variable (0 to 73%).
The highest carbon transfer efficiencies in the meander are furthermore
coupled to intense and complete deep (>800 m) remineralization,
resulting again in a near-zero, deep (>2000 m) carbon sequestration
efficiency there. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|