5 research outputs found
Anthropogenic carbon distribution in the Ross Sea (Antarctica
The Ross Sea is an area of dense water formation within the Southern Ocean, hence it potentially
plays an important role for anthropogenic CO2 sequestration: In order to estimate the penetration of
anthropogenic carbon in the Ross Sea from total inorganic carbon (TCO2) measurements carried out in
2002\u201303 Antarctic Italian Expedition, we applied two independent models. Anthropogenic carbon was
present throughout the water column. The highest concentrations were associated with the recently
ventilated shelf waters, namely High Salinity Shelf Water (HSSW) and Ice Shelf Water (ISW), due to their
recent contact with the atmosphere. The lowest concentrations were observed for Circumpolar Deep Water
(CDW), due to its relatively older ventilation age. This water mass intrudes onto the shelf in some parts of
the Ross Sea and hence is observed in the sampled section, where it is recognizable for its low O2 and
high TCO2 concentrations. The overflow of the dense High Salinity Shelf Water out of the continental
slope was observed in the area off Cape Adare. Since this recently formed shelf water contributes to the
formation of the Antarctic Bottom Water (AABW), this process represents a pathway for anthropogenic
carbon export down to the deep ocean
Combined effects of hydrographic structure and iron and copper availabilityon the phytoplankton growth in Terra Nova Bay Polynya(Ross Sea, Antarctica)
Surface water (o100 m) samples were collected from the Terra Nova Bay polynya region of the Ross
Sea (Antarctica) in January 2006, with the aim of evaluating the individual and combined effects of
hydrographic structure, iron and copper concentration and availability on the phytoplankton growth.
The measurements were conducted within the framework of the Climatic Long Term Interaction for the
Mass-balance in Antarctica (CLIMA) Project of the Programma Nazionale di Ricerca in Antartide
activities. Dissolved oxygen, nutrients, phytoplankton pigments and concentration and complexation of
dissolved trace metals were determined. Experimental data were elaborated by Principal Component
Analysis (PCA). As a result of solar heating and freshwater inputs from melting sea-ice, the water
column was strongly stratified with an Upper Mixed Layer 4\u201316 m deep. The integrated Chl a in the
layer 0\u2013100 m ranged from 60 mg m2 to 235 mg m2, with a mean value of 138 mg m2.
The pigment analysis showed that diatoms dominated the phytoplankton assemblage. Major nutrients
were generally high, with the lowest concentration at the surface and they were never fully depleted.
The Si:N drawdown ratio was close to the expected value of 1 for Fe-replete diatoms. We evaluated both
the total and the labile dissolved fraction of Fe and Cu. The labile fraction was operationally defined by
employing the chelating resin Chelex-100, which retains free and loosely bound trace metal species. The
total dissolved Fe ranged from 0.48 to 3.02 nM, while the total dissolved Cu from 3.68 to 6.84 nM. The
dissolved labile Fe ranged from below the detection limit (0.15 nM) to 1.22 nM, and the dissolved labile
Cu from 0.31 to 1.59 nM, respectively. The labile fractions measured at 20 m were significantly lower
than values in 40\u2013100 m samples. As two stations were re-sampled 5 days later, we evaluated the shortterm
variability of the physical and biogeochemical properties. In particular, in a re-sampled station at
20 m, the total dissolved Fe increased and the total dissolved Cu decreased, while their labile fraction
was relatively steady. As a result of the increase in total Fe, the percentage of the labile Fe decreased. An
increase of the Si:N, Si:P and Si:FUCO ratios was measured also in the re-sampled station. On this basis,
we speculated that a switch from a Fe-replete to a Fe-deplete condition was occurring