The evolution and distribution of temperature and salinity in the
harbour were studied with the weekly CTD surveys during the winter
and summer period. The first analysis was on the seasonal evolution of
the thermal and haline distribution (see Fig. 2 for a representative
example of the variety of results obtained during the campaigns). In
winter, waters are usually well mixed in the vertical with increments
of only 0.3 °C from surface to bottom while, in summer, a marked
stratification is established with vertical gradients of 3 °C. Furthermore,
additional interesting information is obtained from these data.
Despite being a relatively small domain, the harbour shows significant
spatial variations in temperature and salinity. This spatial variability
can be linked to different processes. During the winter period, a fresh
and cold tongue of water is sometimes detected near the south harbour
mouth (see Fig. 2.b). These waters are probably coming from the
Llobregat river (located few Km to the south) provided that there is no
local wastewater discharge in that area. Also, a core of fresh water is
observed in the inner harbour, probably related to the water discharge
draining rain water from the city. In summer, the data suggest the
entrance of shelf waters (saltier and colder) through the southern
mouth near the bottom (see Fig. 2.d) while the inner northern regions,
being more sheltered and isolated from the shelf waters, are warmer.
Aside from the spatial variations, intraseasonal temperature variability
and salinity fields are not at all negligible. Significant changes were
observed at temporal scales of only a few days. In winter, the time
variability seems to be linked to rain episodes through the increase of
water in the Llobregat River and discharges of runoff waste water. The
analysis of the Llobregat river time series (data not shown) shows a
mean runoff of 19 m3
/s but with sudden peaks of up to 100 m3
/s over
24 h, especially in autumn or spring. In summer, however, that variability
is linked to heat fluxes (general warming in the whole harbour
domain) and maybe to variations in shelf water characteristics (see the
change of the near-bottom water characteristics near the southern
mouth in Fig. 2.d).