The document summarizes results from the Ross Sea Mesoscale Experiment (RoME) project in the austral summer of 2014. Water samples were collected from 0-200 m depths at 41 stations across four experiments to measure nutrients like NO3-, NO2-, NH4+, PO43- and Si. Nutrient concentrations showed variability over distances of a few kilometers. The highest nutrient removal occurred at stations with high water column stability, as evidenced by oxygen levels above saturation and chlorophyll a maxima. Diatoms, which comprised 90% of the biomass, likely drove high Si removal rates in one experiment. Calculated N:P and N:Si ratios suggested diatom dominance and possible iron limitation across the areas studied. Pron

1. ABSTRACT
Mesoscale variability of nutrients in the surface waters of
the Ross Sea (Antarctica) during the austral summer 2014
Sea water samples (0-200 m) for nutrient (NO3
-
, NO2
-
, NH4
+
, PO4
3-
, Si) determination
were collected in the framework of the Ross Sea Mesoscale Experiment (RoME) Project
in the Ross Sea (Antactica) shelf area during the austral summer 2014. The primary
objective of RoME was to document the mesoscale distribution and spatial-temporal
variability of biogeochemical properties of the upper 200 m layers in the Ross Sea with
a horizontal resolution of 5-10 km. Remote sensing supported both the determination
of the sampling strategy and the placement of in situ stations. Four mesoscale
experiments (RoME 1, RoME 2, RoME 3 and RoME 3.1) were carried out in three
different areas (RoME 1 in the central Ross sea, RoME 2 in a coastal area and 3 + 3.1
in the Southern Ross sea).
Nutrients were measured by colorimetric methods in seawater samples collected at
different depths, according to CTD profiles, at 41 stations. Results showed that there
is a variability of N, P and Si over distances of few kilometres in all experiments, with
significant differences between the stations and between depths.
Nutrient data were used to quantify the nutrient removal. The highest removal
occurred in those stations characterized by a high water column stability, which
favoured the phytoplankton development. This finding is confirmed by dissolved
oxygen concentration above the saturation and by Chl a maxima. In RoME 2, the only
experiment for which data on the taxonomic composition of phytoplankton are
available, the high rates of Si removal have been justified by the presence of diatoms,
which constitute 90% of the biomass in the subsurface layer. The N:P and N:Si ratios
were calculated to estimate the dominant phytoplanktonic community and to
understand whether an iron limitation was occurring in the investigated areas. The N:P
ratios were generally below the Redfield standard value (16), corroborating the
possible presence of diatoms also in the other areas, where no taxonomic data is yet
available. Si:N ratios had values significantly higher of 2, except for the coastal area,
also including NH4
+
, suggesting a condition of iron limitation. By comparison with
previous studies it has been confirmed that there are pronounced annual variations in
the distribution and drawdown of nutrients.