55 research outputs found
The anomalous warming of summer 2003 in the surface layer of the Central Ligurian Sea (Western Mediterranean)
"Meteorological and sea temperature data from the ODAS Italia 1 buoy (Ligurian Sea, Western Mediterranean) are used to study the anomalous warming of summer 2003 at sea. The event was related to the record heat wave that interested much of Europe from June to September of that year. The data show that the anomalous warming was prevalently confined to within a few meters below the sea surface. On the contrary, the temperatures in the underlying layers were lower than usual. The limited vertical propagation of heat is ascribed to the high temperature difference that arose between the surface and the deeper layers due to protracted calm weather conditions. The degree of penetration of heat deduced from the observations is consistent with that computed on the basis of an energetic argument, wherein the wind constitutes the sole supply of kinetic energy, while the heating is viewed as the source of potential energy that must be ""subtracted"" by mixing. The results support the hypothesis that the scanty energy from the wind is mainly responsible for the development of the temperature anomaly at the sea surface.
Observations of a phytoplankton spring bloom onset triggered by a density front in NW Mediterranean
Phytoplankton blooms in the northwestern Mediterranean Sea are seasonal
events that mainly occur in a specific area comprising the Gulf of Lion and
the Provençal basin, where they are promoted by a general cyclonic
circulation, strong wind-driven mixing and subsequent re-stratification of
the water column. At the southern boundary of this area, a persistent density
front known as the north Balearic front can be found. The front is presumed
to cause an early phytoplankton bloom in its vicinity because (a) it enhances
the transport of nutrients into the euphotic layer and (b) it promotes the
speedy re-stratification of the water column (through frontal instabilities).
In February and March 2013, a glider, equipped with a CTD (conductivity, temperature, and depth device) and a fluorometer, was
deployed on a mission that took it from the Balearic Islands to Sardinia and
back. The frontal zone was crossed twice, once during the outbound leg and
the once on the return leg. The data provided by the glider clearly showed
the onset of a bloom soon after a decrease in wind-driven turbulent
convection and mixing. The in situ observations were supported and confirmed
by satellite imagery. It is shown that frontal dynamics play a key role in
the promotion and acceleration of re-stratification, which is a necessary
pre-conditioning factor for the onset of blooms much like other relevant
processes such as an enhanced biological pump. Swift re-stratification
stimulates new production by inhibiting mixing. Finally, viewing the blooming
phenomenon from a regional perspective, it seems that Sverdrup's critical
depth model applies in the northern well-mixed area whereas, in the south,
front-related re-stratification seems to be the principal cause
Upper layer current variability in the Central Ligurian Sea
Abstract. Long-time series of surface currents and meteorological parameters were analysed to estimate the variability of the upper layer circulation and the response to the local winds. Current meter data were collected by an upward-looking RDI Sentinel 300 kHz ADCP deployed in the Central Ligurian Sea (43°47.77' N; 9°02.85' E) near the meteo-oceanographic buoy ODAS Italia 1 for more than eight months, from 13th of September 2003 to 24th of May 2004. The ADCP sampled the upper 50 m of water column at 8 m vertical resolution and 1 h time interval; surface marine and atmospheric hourly averaged data were provided by the buoy. Currents in the sampled layer were mainly barotropic, directed North-West in accordance with the general circulation of the area, and had a mean velocity of about 18 cm/s and hourly mean peaks up to 80 cm/s. Most of the observed variability in the upper thermocline was determined by inertial currents and mesoscale activity due to the presence of the Ligurian Front. Local wind had a minor role in the near-surface circulation but induced internal waves propagating downward in the water column
Rapid response to climate change in a marginal sea
The Mediterranean Sea is a mid-latitude marginal sea, particularly responsive to climate change as reported by recent studies. The Sicily Channel is a choke point separating the sea in two main basins, the Eastern Mediterranean Sea and the Western Mediterranean Sea. Here, we report and analyse a long-term record (1993–2016) of the thermohaline properties of the Intermediate Water that crosses the Sicily Channel, showing increasing temperature and salinity trends much stronger than those observed at intermediate depths in the global ocean. We investigate the causes of the observed trends and in particular determine the role of a changing climate over the Eastern Mediterranean, where the Intermediate Water is formed. The long-term Sicily record reveals how fast the response to climate change can be in a marginal sea like the Mediterranean Sea compared to the global ocean, and demonstrates the essential role of long time series in the ocean
Zooplankton diel vertical migration in the Corsica Channel (north-western Mediterranean Sea) detected by a moored acoustic Doppler current profiler
Diel vertical migration (DVM) is a survival strategy adopted by zooplankton
that we investigated in the Corsica Channel using acoustic Doppler current profiler (ADCP) data from April 2014
to November 2016. The principal aim of the study is to characterize migration
patterns and biomass temporal evolution of zooplankton along the water
column. The ADCP measured vertical velocity and echo intensity in the water
column range between about 70 and 390 m (the bottom depth is 443 m). During
the investigated period, zooplanktonic biomass had a well-defined daily and
seasonal cycle, with peaks occurring in late winter to spring (2015 and
2016) when the stratification of the water column is weaker. Zooplanktonic
biomass temporal distribution in the whole water column is well correlated
with biomass of primary producers, estimated with satellite data.
Zooplanktonic blooming and non-blooming periods have been identified and
studied separately. During the non-blooming period zooplanktonic biomass was
most abundant in the upper and the deep layers, while during the blooming
period the upper-layer maximum in zooplanktonic biomass disappeared and the
deep layer with high zooplanktonic biomass became thicker. These two layers
are likely to correspond to two different zooplanktonic communities. The
evolution of zooplanktonic biomass is well correlated with chlorophyll, with
phytoplankton biomass peaks preceding the upper-layer secondary production by
a lag of about 3.5Â weeks. Nocturnal DVM appears to be the main
pattern during both periods, but reverse and twilight migration are also
detected. Nocturnal DVM was more evident at mid-water than in the deep and
the upper layers. DVM occurred with different intensities during blooming and
non-blooming periods. One of the main outcomes is that the principal drivers
for DVM are light intensity and stratification, but other factors, like
the moon cycle and primary production, are also taken in consideration.</p
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