Download The possible contribution of CLIMA project to the Victoria Land Project

The possible contribution of CLIMA project to the Victoria Land Project.
Andrea Bergamasco, Serena Fonda Umani, Giancarlo Spezie.
In the framework of the CLIMA project, (1997 – 2001) studies have been carried out at
different scales from basin wide to mesoscale, in order to identify basic mechanisms and relevant
areas. In particular, within the project, the circulation in the Ross Sea (RS) has been investigated by
hydrological and current measurements and by diagnostic models. The flow field within the RS has
proved affected by bottom topography, by the presence of the Ross Ice Shelf (RIS), by the mass
exchange at the continental slope and by localized water mass formation phenomena, which
represent an important component of the Antarctic Bottom Waters (AABW). The smaller scale
processes which determine the physical and biogeochemical dynamics of the RS as well as of
global mechanisms are still to be clarified and assessed.
In the formation processes, a major mechanism takes place, that of water mass ventilation.
Gas transfer coefficients can be estimated on the basis of radon deficit in the upper layers of the
ocean, and that estimate can be extended to the greenhouse gases which are exchanged at the
sea/atmosphere interface. Moreover, many of the projects set in the Southern Ocean have been
designed to assess the flux of CO2 between water and atmosphere. The process is affected by two
factors: the “biological pump” and the dense water formation. The different efficiency of the
biological pump can lead to CO2 release into the atmosphere through respiration or formation of
organic matter, which, trapped in the bottom waters, can be confined in the deep ocean circulation
for decades or centuries.
Particularly during the last two cruises two area were investigated in this respect: the coastal
polynya and the continental slope Polynyas are areas where interactions among air, sea and ice are
the strongest, and they have relevant effects on the formation and spreading of sea ice, on dense
water production and on water ventilation, on biogeochemical fluxes in terms of gas fluxes and on
vertical convection as a mechanism for carbon transport. Earlier activities within the CLIMA
project in the Terranova Bay (TB) area has produced an analysis of the hydrological and
biogeochemical characteristics of the water column on the basis of a three year time series of data
collected by moored instrumentation and on the suveys carried on during the two cruises
On the continental slope the researches was aimed at improving the understanding and
modelling of the outflow processes taking place on the antarctic continental slope, utilizing both
multidisciplinary measurements and phenomenological and numerical models. Earlier studies have
allowed to follow the spreading of those waters up to the slope, where they undergo substantial
modifications due to meso- to small scale processes in the interaction with the front generated by
the presence of the Circumpolar Deep Water (CDW). During the last cruise (2001) we conducted a
mesoscale investigation focussed on the repeated observation of two areas, identified during the
1997-98 cruise, where two analogous phenomena involving two different shelf water masses
(HSSW and ISW) take place. The formation of these waters is characterized by profoundly different
interaction mechanisms at the sea-atmosphere interface. A critical parameter is constituted by the
respective age of the water masses, whose assessment represents therefore on of the main goals of
our research.
During the two cruises (1997-98 and 2001) extended surveys on microbial planktonic
communities were carried out to investigate the carbon partitioning among the different size classes,
and particularly during the 2001 cruise, several dilution experiments were performed from Cape
Hallet to near McMurdo Sound in order to experimental determine the carbon fluxes through the
first steps of the food web.
CLIMA project can usefully interact with the proposed Victoria Land project by studying
the open ocean processes, both from a hydrodinamical point of view as well as from a biological
processes oriented study that can lead to a better understanding of the exchanges of the coastal area
with the open sea and viceversa.