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| Titel |
Seaglider Observations of the Seasonal Evolution of the Upper Ocean in the Northeast Atlantic |
| VerfasserIn |
Gillian Damerell, Karen Heywood, Andrew Thompson |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250095906
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| Publikation (Nr.) |
 EGU/EGU2014-11382.pdf |
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| Zusammenfassung |
| As part of the Ocean Surface Mixing Ocean Submesoscale Interaction Study (OSMOSIS), a
year-long Seaglider deployment was undertaken at 48.7°N, 16.2°W, in the subpolar
Northeast Atlantic 41 km south-east of the Porcupine Abyssal Plain sustained observatory.
Two Seagliders at a time were deployed with turnarounds at roughly three month intervals,
collecting a total of 8138 profiles to 1000 m of temperature, salinity and biogeochemical
variables, plus an estimate of the average current over each dive cycle. The region sampled
was approximately 15 km by 15 km. This unique data set has a vertical resolution between
0.5 and 1 m, and an average time interval between profiles of 2.1 hours. Here we present the
highlights of the physical observations.
The surface mixed layer reached its maximum depth of 390 m in early February 2013,
and the mixed layer depth is highly variable during the winter on timescales of hours to
weeks. In July and early August 2013, more than half the profiles show no mixed layer up to
the minimum depth reliably observed by the glider (2-3 m). The mixed layer depth is very
stable in the summer, then deepens and increases in variability in the autumn. The mixed
layer has a significant seasonal cycle in temperature, with a marked warm layer and seasonal
thermocline during the summer and early autumn. However, the mixed layer shows less
short-term (hours to weeks) temporal variability than the water layers beneath.
The temporal variability in temperature generally increases with depth, except that
during September and October 2012, a layer of water from just below the mixed
layer to approximately 100 m shows increased variability in temperature compared
with all other times and depths. In late August to early September 2013, the same
increased variability layer seems to be developing, suggesting that this is a seasonal
feature.
There is no obvious seasonal cycle in salinity, although there is some evidence of
increased temporal variability in summer/autumn compared with winter/spring down to
approximately 200 m. This is similar to the increased variability in temperature beneath the
mixed layer in summer/autumn, but the signal is weaker in salinity and covers a greater depth
range. Below 400 m, the variability in salinity increases with depth, and below approximately
800 m, this is linked to the intermittent appearance of patches of high salinity Mediterranean
Water.
The dive-average currents reach a maximum of 38 cm s-1. Currents with speeds >20 cm
s-1 include flow to the south-east in September and early October 2012, north-eastward
veering to south-eastward through late January to mid-February, and north-eastward in
August 2013. In late April through May 2013, there is a reversal, with south-westward flow
with speeds > 20 cm s-1. At other times, the currents are weaker ( |
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