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| Titel |
Elephant overflows: Multi-annual variability in Weddell Sea Deep Water driven by surface forcing |
| VerfasserIn |
Andrew Meijers, Michael Meredith, Povl Abrahamsen, Alberto Naviera-Garabato, Miguel Ángel Morales Maqueda, Kurt Polzin |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250106404
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| Publikation (Nr.) |
 EGU/EGU2015-6074.pdf |
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| Zusammenfassung |
| The volume of the deepest and densest water mass in Drake Passage,
Lower Weddell Sea Deep Water (LWSDW), is shown to have been decreasing
over the last 20 years of observations, with an associated reduction
in density driven by freshening. Superimposed on this long term trend
is a multi-annual oscillation with a period of 3-5 years. This
variability only appears in Drake Passage; observations in the east of
the Scotia Sea show a similar long term trend, but with no apparent
multi-annual variability. Clues as to the source of this variability
may be found on the continental slope at approximately 1000 m
immediately north of Elephant Island on the northern tip of the
Antarctic Peninsula. Here there is an intermittent westward flowing
cold/fresh slope current whose volume and properties are strongly
correlated with the LWSDW multi-annual variability, although leading
the LWSDW by around one year. As the slope current and LWSDW are
separated from each other both geographically and in water mass
characteristics, their co-variability implies that they are responding
to a common forcing, while the lag between deep LWSDW and shallow
slope current provides information on the timescale of this response.
A newly available high resolution temperature and salinity multi-year
time series from the Elephant Island slope at 1000 m is compared with
reanalysis and model derived surface fluxes, sea ice extent and wind
stress. We find that there are strong positive relationships between
the surface wind stress and heat flux over the shelf at the tip of the
Antarctic Peninsula and the properties of the slope current at 1000 m
on seasonal to annual timescales. We use tracer release experiments
in the Southern Ocean State Estimate (SOSE) model to investigate the
lag between the slope current and LWSDW timeseries and hypothesise
that the observed multi-annual variability in both water masses is
driven by surface forcing over the shelf and the overflow of modified
water from the slope in the north-west Weddell Sea. The lag observed
between the two time series is due to the difference in water mass
paths to the observation points in Drake Passage. We discuss the role
of atmospheric modes of variability such as ENSO and SAM, as well as
climate trends, on this relationship and their potential impact on
future LWSDW export. |
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