Impact of sea ice on the structure of phytoplankton communities in the northern Antarctic Peninsula

Abstract

The seasonal advance and retreat of sea ice around the northern Antarctic Peninsula can have a significant impact on phytoplankton, mainly due to alterations in the availability of ice-free areas, micro-nutrient inputs by meltwater and variations in water column structure. The aim of this work was to evaluate the effect of sea ice conditions on phytoplankton biomass and community composition in an area off the northern Antarctic Peninsula, a region undergoing important warming processes. In two consecutive summer cruises (2013 and 2014), seawater samples were analysed for nutrients and phytoplankton (through HPLC-CHEMTAX approach), and measurements were made for water column physical structure evaluation. Two contrasting conditions were studied: a strong environmental gradient around the sea ice edge, with a marked meltwater signal (summer 2013) and the same area with little indication of meltwater and no detectable sea ice conditions (summer 2014). In the first year, the phytoplankton communities were massively dominated by nanoflagellates such as cryptophytes, small dinoflagellates and Phaeocystis antarctica, but with differences between stations with less influence of meltwater (dominance of dinoflagellates type B, mainly Gymnodinium spp., mean chlorophyll a = 1.37 mg m −3 ) and stations closer to the sea ice edge (dominance of cryptophytes, mean chlorophyll a = 0.98 mg m −3 ). In the second year, cryptophytes were apparently replaced by diatoms type B (mainly Pseudonitzschia spp., 24% contribution, mean chlorophyll a = 0.93 mg m −3 ), although dinoflagellates were also important. Therefore, there was a clear distinction between the phytoplankton communities under sea ice influence, where mainly cryptophytes were associated with shallow mixed layers and high water column stability in 2013 and an important presence of diatoms in 2014, associated with deeper mixed layers, lower silicic acid concentrations and higher magnitudes of both salinity and temperature, under very little sea ice influence. Gymnodinioid dinoflagellates were an important component in both years, apparently occupying sites/conditions less favourable to cryptophytes. These results support previous suggestions that climate factors leading to shortening of the sea ice season in the region do have an important impact particularly in shaping the dominance of the main phytoplankton functional groups in the region.

Abiotic Changes Driving Microphytoplankton Functional Diversity in Admiralty Bay, King George Island (Antarctica)

“…Sampling under greater influence of meltwater occurred in early summer 2013-2014 (scenario iii) and late summer 2014-2015 (scenario iv), as also observed by Mendes et al (2018) in Weddell-Scotia Confluence Zone in 2013 (sector 7). Despite the high water temperatures recorded in 2010-2011 (average 1.66 • C during late summer) only one station, Botany Point, exhibited an influence from meltwater.…”

“…Lange et al (2014) observed higher salinities during the beginning than at the end of the summer, while Tenenbaum et al (2010) reported reduced salinity for neritic regions, possibly due to the presence of glaciers in the region. In this context, Mendes et al (2018) found lower values for salinity (mean 33.68) in areas near ice-covered regions and higher values (mean 34.14) in regions with little or no influence of ice cover seasonality for sector 7 (Weddel-Scotia Confluence Zone), thus correlating low salinity with water column stability. Additionally, Wasiłowska et al (2015) associated low salinities (<34) with increased water column stability and a shallow (<2 m) mixture layer in sector 1.…”

“…To evaluate possible impacts of sea ice melting on phytoplankton community structure, meltwater percentage (% MW) was calculated from the difference between salinity values at the surface (S surf ) and the bottom (S btm), assuming 6 to be the average salinity value of marine ice (Ackley et al, 1979) (See Equation 1). To classify the environment according to %MW (Mendes et al, 2018), two scenarios were proposed: (i) stations under influence of melting sea ice (>2.25% MW); and (ii) stations not under the influence of melting sea ice (<2.25% MW).…”

“…This, in turn, can be reflected throughout all the trophic levels of the regional trophic web (Moline et al, 2004;Schofield et al, 2010;Lange et al, 2014;Saba et al, 2014). Climate change in WAP (e.g., increase in temperature and environmental variables) has driven modifications in phytoplankton size (Barrera-Alba et al, 2012Lange et al, 2014;Vanzan et al, 2015), composition, biomass and community structure (Kopczyńska, 2008;Montes-Hugo et al, 2009;Piquet et al, 2011;Lange et al, 2014;Tenório et al, 2015;Mendes et al, 2018;Russo et al, 2018).…”

Disentangling Environmental Drivers of Phytoplankton Biomass off Western Iberia

“…Consequently, remote-sensingderived CHL is now considered an essential climate variable by the Global Climate Observing System (GCOS; Bojinski et al, 2014) and a large number of studies on the response of phytoplankton community to environmental changes have been performed, particularly at a global scale (e.g., Behrenfeld et al, 2006;Rost et al, 2008;Beardall et al, 2009;Paerl and Huisman, 2009;Boyce et al, 2010;Hallegraeff, 2010;Litchman et al, 2012). Additionally, coastal studies have already shown responses of phytoplankton biomass and community structure to changes in nutrients, temperature, and salinity (SAL) (e.g., Mendes et al, 2018). However, the phytoplankton communities at a regional scale have complex variations, fluctuating from region to region and there is still much to unravel on community dynamics (e.g., Brotas et al, 2013;Brito et al, 2015).…”