Environmental conditions during phytoplankton blooms in the vicinity of james ross island, east of the antarctic peninsula

Abstract

In waters surrounding James Ross Island (JRI), which is generally inaccessible, high chlorophyll-a concentration [Chla] can often be detected during summer periods by ocean color imagery. The region is influenced by a retreating sea ice edge from Weddell Sea and freshwater runoff from JRI glaciers, factors that probably trigger phytoplankton growth. In this work, we relate phytoplankton composition and biomass [Chla and carbon] with environmental factors in two successive late summer periods, in 2008 (1–3 March) and 2009 (17–20 February). Remote sensing data were used to corroborate the findings during those few sampling days. High surface [Chla] patches were observed through both remote sensing and field data (up to 7.61 mg Chla m-3 in 2009), and associated with a relatively shallow upper mixed layer (UML) (19–109 m in 2008 and 16–74 m in 2009). Sea surface temperatures were lower in 2008 (-1.19 to -0.62 C) than in 2009 (-0.87 to -0.46 C). Sea ice coverage was greater in 2008 than in 2009 summer, implying an earlier sea ice retreat in the latter year, when higher average [Chla] was obtained from field samples (3.3 mg m-3 , compared to 1.5 mg m-3 in 2008). The eastern side of JRI appeared to be relatively sheltered from the dominant pattern of largescale westerly winds. Diatoms dominated the phytoplankton community, with presence of large diatom species (e.g., Odontella weissflogii) typical of an advanced sea ice melt condition. Those blooms were sustained by a shallow UML associated with relative shelter from winds, due to proximity with the island.