 |
| Titel |
Description of the biogeochemical features of the subtropical southeastern Atlantic and the Southern Ocean south of South Africa during the austral summer of the International Polar Year |
| VerfasserIn |
F. A. C. Moigne, M. Boye, A. Masson, R. Corvaisier, E. Grossteffan, A. Guéneugues, P. Pondaven |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 10, no. 1 ; Nr. 10, no. 1 (2013-01-18), S.281-295 |
| Datensatznummer |
250017472
|
| Publikation (Nr.) |
 copernicus.org/bg-10-281-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
| Meridional and vertical distributions of several biogeochemical parameters
were studied along a section in the southeastern Atlantic and the Southern
Ocean south of South Africa during the austral summer 2008 of the
International Polar Year to characterize the biogeochemical provinces and to
assess the seasonal net diatom production. Based on analyses of
macro-nutrients, ammonium (NH4), chlorophyll a, (Chl a),
phaeopigments, biogenic silica (BSi), particulate inorganic carbon (PIC), and
particulate organic carbon and nitrogen (POC and PON, respectively), four
biogeochemical domains were distinguished along the section: the subtropical
Atlantic, the confluence zone of the subtropical and subantarctic domains,
the Polar Frontal Zone (PFZ) in the Antarctic Circumpolar Current (ACC), and
the north-eastern branch of the Weddell Gyre. The subtropical region
displayed extremely low nutrient concentrations featuring oligotrophic
conditions, and sub-surface maxima of Chl a and phaeopigments never exceeded
0.5 µg L−1 and 0.25 µg L−1, respectively. The
anticyclonic and cyclonic eddies crossed in the Cape Basin were characterized
by a deepening and a rise, respectively, of the nutrients isoclines. The
confluence zone of the subtropical domain and the northern side of the ACC
within the subantarctic domain displayed remnant nitrate and phosphate
levels, whereas silicate concentrations kept to extremely low levels. In this
area, Chl a level of 0.4–0.5 µg L−1 distributed
homogenously within the mixed layer, and POC and PON accumulated to values up
to 10 µM and 1.5 µM, respectively, indicative of biomass
accumulation along the confluence zone during the late productive period. In
the ACC domain, the Polar Frontal Zone was marked by a post-bloom of diatoms
that extended beyond the Polar Front (PF) during this late summer condition,
as primarily evidenced by the massive depletion of silicic acid in the
surface waters. The accumulation of NH4 to values up to
1.25 µM at 100 m depth centred on the PF and the accumulation of
BSi up to 0.5 µM in the surface waters of the central part of the
PFZ also featured a late stage of the seasonal diatom bloom. The silica daily
net production rate based on the seasonal depletion of silicic acid was
estimated to be 11.9 ± 6.5 mmol m−2 d−1 in the domain of the
vast diatom post-bloom, agreeing well with the previously recorded values in
this province. The Weddell Gyre occasionally displayed relative surface
depletion of silicic acid, suggesting a late stage of a relatively minor
diatom bloom possibly driven by iceberg drifting releases of iron. In this
domain the estimated range of silica daily net production rate (e.g. 21.1
± 8.8 mmol m−2 d−1) is consistent with previous studies, but
was not significantly higher than that in the Polar Front region. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|