Annual and spatial variations of chemical and physical properties in the Ross Sea surface waters (Antarctica)

Temperature, salinity, meltwater percentage, water column stability, dissolved oxygen and nutrients were measured in seawater samples collected at three fixed depths (0, 20, 100 m) in 104 stations located in three different areas of the Ross Sea (Antarctica), during four Italian Antarctic surveys carried out between 1998 and 2006. Nutrient data were used to quantify the nutrient removal, which appears particularly high in 2006, especially in polynya area. The N:P and Si:N disappearance ratios were studied to estimate the dominant phytoplanktonic community. No significant differences in the nutrient drawdown ratio were observed, in fact the N:P ratio was always below the Redfield standard ratio. The principal component analysis (PCA), a multivariate statistical technique, was applied to the measured physical and chemical properties and chlorophyll concentrations. The dataset was split to consider separately surface, 20 and 100 m samples, since the effect of depth resulted much greater than the effect of sampling area and sampling year. For each subset two principal components were extracted, explaining 47-60% of the data variance. The surface samples exhibit higher variability than 20 and 100 m ones, being more influenced by sea-ice-atmosphere exchange and pack-ice melting. The effect of annual variability, particularly on water column stability, temperature and nutrients, was consistent with different pack-ice coverages. In this regard, austral summer 2003, with a massive sea-ice coverage and megaberg presence, exhibited more atypical features (such as low water column stability and scarce nutrient removal) with respect to a normal year (i.e. 2006) than austral summer 1998, when pack-ice extension was conditioned by climate anomaly (El Nino event). (C) 2009 Elsevier Ltd. All rights reserved.