Development of sea ice microbial communities during autumn ice formation in the Ross Sea

Abstract

Sea ice communities were sampled across the Ross Sea in the austral autumn. The biota in first-year pack ice was assessed by measuring chlorophyll a (chl a), phaeopigments, total particulate carbon and nitrogen (POC and PON, respectively) and collecting samples for identification by microscopy. Physical and chemical parameters were also measured to characterize the environment. Chl a concentrations in ice ranged from 0 to 96.9 µg l -1 in discrete samples and from 0.02 to 20.9 mg m -2 for values integrated throughout floes. Maximum values were similar to those observed in first-year pack ice at other Antarctic locations. Chl a concentrations varied with ice structure and with latitude. POC:chl a and C:N ratios (molar) were high, possibly indicating detritus accumulations. The higher chl a levels north of approximately 72°S were apparently a result of ice forming in the south early in the season with subsequent advection to the north. These dynamics would result in older ice in the mid-or northern pack ice zone that was maintained in a favorable light and temperature regime during the seasonal progression of formation and drift. Chlorophyll levels were low in surface-layer communities. High chlorophyll concentrations were associated with internal communities. Bottom-layer algal populations, while present, did not reach the levels of high biomass reported for autumn blooms in some land-fast ice regions. Apparent nutrient and CO 2 depletion were correlated with biomass parameters but accounted qualitatively for only a fraction of the biomass accumulation measured. Overall, autumn ice-associated production in the Ross Sea may be lower than expected because of the ice drift dynamics, apparently low production in the near-surface layers of first year ice flows, and the absence of rich bottom-layer assemblages.

Algal Hot Spots in a Changing Arctic Ocean: Sea-Ice Ridges and the Snow-Ice Interface

“…In general, the higher light intensities experienced in the snow-ice interface compared to the water column (<1% of incoming irradiance; Assmy et al, 2017), as well as the low salinities at the snowice interface (6.5-21), might have negatively affected part of the P. pouchetii population, while not having as deleterious impact on the diatom portion of the community due to their rigid silica frustules. Similar findings have been observed in ice melt processing studies with respect to flagellate versus diatom species (Buck et al, 1998;Garrison et al, 2003). Pelagic diatoms such as F. oceanica, C. gelidus, and Pseudo-nitzschia sp.…”

“…However, due to the sampling challenges that these complex structures pose, algae have only been sampled sporadically. Snow infiltration communities growing at the snow-ice interface, have been widely described for Antarctic pack ice (Horner et al, 1988;Spindler, 1994;Robinson et al, 1997;Kristiansen et al, 1998;Garrison et al, 2003), where they contribute substantially to sea-ice primary production (Arrigo et al, 1997). In the few observations obtained from the Arctic, the dominant species reported are mostly phytoplankton such as P. pouchetii in pack ice north of Svalbard and Svalbard fjords (McMinn and Hegseth, 2004;von Quillfeldt et al, 2009), and unidentified pennate and centric diatoms in Disco Island, Greenland (Buck et al, 1998).…”

Sea-ice microbial communities in the Ross Sea: autumn and summer biota

“…1). Sea ice was sampled at a number of stations to characterize the ice crystal texture and modes of formation (Jeffries et al 2001), and at many of these stations community biomass parameters such as chl a, and POC and PON were measured , Garrison et al 2003. To provide a more complete description of the biological assemblages in ice, 10 stations from NBP98-3 (autumn) and 13 stations from NBP99-1 (summer) were analyzed using epifluorescence and bright-field light microscopy techniques (see Fig.…”

Sea ice algal biomass and physiology in the Amundsen Sea, Antarctica

“…Surface ponds form either when snowmelt collects in discrete ponds on the surface of relatively flat ice (melt ponds) or when the ice surface is forced below the freeboard level due to ice rafting or snow loading and becomes flooded with seawater (deformation ponds). While melt ponds usually contain relatively little biomass owing to their low nutrient concentrations, deformation ponds can support high algal biomass (Garrison et al, 2003). Internal layers of relatively solid undeformed ice are generally the most inhospitable habitats for microbial life in sea ice.…”

“…Internal layers of relatively solid undeformed ice are generally the most inhospitable habitats for microbial life in sea ice. While these layers often receive ample light, they can be very cold with brine salinities too high for microalgal growth (Arrigo and Sullivan, 1992) and brine volumes too low for adequate nutrient exchange (Golden et al, 1998(Golden et al, , 2007Garrison et al, 2003). When the skeletal layer (the actively growing region at the base of growing sea ice) is present, bottom ice is often the most biologically productive sea ice habitat owing to its ubiquity, proximity to seawater nutrients, and mild temperature and salinity gradients (Grossi et al, 1987).…”