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| Titel |
Autonomous profiling float observations of the high-biomass plume downstream of the Kerguelen Plateau in the Southern Ocean |
| VerfasserIn |
M. Grenier, A. Della Penna, T. W. Trull |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 12, no. 9 ; Nr. 12, no. 9 (2015-05-11), S.2707-2735 |
| Datensatznummer |
250117927
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| Publikation (Nr.) |
 copernicus.org/bg-12-2707-2015.pdf |
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| Zusammenfassung |
| Natural iron fertilisation from Southern Ocean islands results in high
primary production and phytoplankton biomass accumulations readily visible
in satellite ocean colour observations. These images reveal great spatial
complexity with highly varying concentrations of chlorophyll, presumably
reflecting both variations in iron supply and conditions favouring
phytoplankton accumulation. To examine the second aspect, in particular the
influences of variations in temperature and mixed layer depth, we deployed
four autonomous profiling floats in the Antarctic Circumpolar Current near
the Kerguelen Plateau in the Indian sector of the Southern Ocean. Each
"bio-profiler" measured more than 250 profiles of temperature (T), salinity
(S), dissolved oxygen, chlorophyll a (Chl a) fluorescence, and particulate
backscattering (bbp) in the top 300 m of the water column,
sampling up to 5 profiles per day along meandering trajectories extending up
to 1000 km. Comparison of surface Chl a estimates (analogous to values from
satellite images) with total water column inventories revealed largely
linear relationships, suggesting that these images provide credible
information on total and not just surface biomass spatial distributions. However,
they also showed that physical mixed layer depths are often not a reliable guide to
biomass distributions. Regions of
very high Chl a accumulation (1.5–10 μg L−1) were associated
predominantly with a narrow T–S class of surface waters. In contrast, waters
with only moderate Chl a enrichments (0.5–1.5 μg L−1) displayed
no clear correlation with specific water properties, including no dependence
on mixed layer depth or the intensity of stratification. Geostrophic
trajectory analysis suggests that both these observations can be explained
if the main determinant of biomass in a given water parcel is the time since
leaving the Kerguelen Plateau. One float became trapped in a cyclonic eddy,
allowing temporal evaluation of the water column in early autumn. During
this period, decreasing surface Chl a inventories corresponded with
decreases in oxygen inventories on sub-mixed-layer density surfaces,
consistent with significant export of organic matter (~35%) and its respiration and storage as dissolved inorganic carbon in the
ocean interior. These results are encouraging for the expanded use of
autonomous observing platforms to study biogeochemical, carbon cycle, and
ecological problems, although the complex blend of Lagrangian and Eulerian
sampling achieved by the floats suggests that arrays rather than single
floats will often be required, and that frequent profiling offers important
benefits in terms of resolving the role of mesoscale structures on biomass
accumulation. |
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