Microalgal community structure and primary production in Arctic and Antarctic sea ice: A synthesis

Abstract

van Leeuwe, MA, et al. 2018 Microalgal community structure and primary production in Arctic and Antarctic sea ice: A synthesis. Elem Sci Anth, 6: 4. DOI: https://doi.org/10.1525/elementa.267 IntroductionSea ice is one of the largest biomes on earth. The area covered by Arctic (15.6 × 10 6 km 2 ) and Antarctic (18.8 × 10 6 km 2 ) sea ice is roughly 4 and 5% of the global ocean surface (361.9 × 10 6 km 2 ) at their respective maximum extents (Meier, 2017;Stammerjohn and Maksym, 2017). Sea ice is a very diverse and potentially very productive habitat, with primary production estimated to amount to 2-24% of total production in sea-ice covered marine areas (Arrigo, 2017). Sea ice is especially productive in spring and summer when, locally, carbon biomass can be ten times higher in the bottom ice than in the seawater, with values greater than 3 mg chlorophyll a) in bottom layers (e.g., Corneau et al., 2013). On some occasions, ice algae may contribute up to 50-60% of total primary production McMinn et al., 2010; Fernandez-Mendez et al., 2015). Sympagic (ice-associated) microalgae (see Horner et al., 1992, for terminology) are REVIEWMicroalgal community structure and primary production in Arctic and Antarctic sea ice: A synthesis Sea ice is one the largest biomes on earth, yet it is poorly described by biogeochemical and climate models. In this paper, published and unpublished data on sympagic (ice-associated) algal biodiversity and productivity have been compiled from more than 300 sea-ice cores and organized into a systematic framework. Significant patterns in microalgal community structure emerged from this framework. Autotrophic flagellates characterize surface communities, interior communities consist of mixed microalgal populations and pennate diatoms dominate bottom communities. There is overlap between landfast and pack-ice communities, which supports the hypothesis that sympagic microalgae originate from the pelagic environment. Distribution in the Arctic is sometimes quite different compared to the Antarctic. This difference may be related to the time of sampling or lack of dedicated studies. Seasonality has a significant impact on species distribution, with a potentially greater role for flagellates and centric diatoms in early spring. The role of sea-ice algae in seeding pelagic blooms remains uncertain. Photosynthesis in sea ice is mainly controlled by environmental factors on a small scale and therefore cannot be linked to specific ice types. Overall, sea-ice communities show a high capacity for photoacclimation but low maximum productivity compared to pelagic phytoplankton. Low carbon assimilation rates probably result from adaptation to extreme conditions of reduced light and temperature in winter. We hypothesize that in the near future, bottom communities will develop earlier in the season and develop more biomass over a shorter period of time as light penetration increases due to the thinning of sea ice. The Arctic is already witnessing changes. The shift forward in time of the algal bloom can resu...

Chlorophyll‐a in Antarctic Landfast Sea Ice: A First Synthesis of Historical Ice Core Data

“…During the ice algal growth season (September to May) total integrated biomass is dominated by bottom ice algal communities. These communities mainly consist of pennate diatom species (van Leeuwe et al, ). We note that the biomass peak in autumn is vertically more uniform than the ice algal accumulation during spring.…”

“…During winter (July to September) the highest ice algal Chl a fraction is found in the sea ice interior. This may be the result of autumnal ice accretion that traps bottom‐ice communities; that is, interior algal biomass peaks are likely to resemble residual autumn ice algal blooms that got incorporated into the ice interior due to ice growth over autumn and winter (Grossi & Sullivan, ; Günther & Dieckmann, ; van Leeuwe et al, ). The presence or absence of interior biomass peaks may be attributed to fast‐ice breakout frequency (McConville & Wetherbee, ).…”

“…While surface algal communities are characteristic for Antarctic pack ice, for example, due to snow loading and subsequent surface flooding (Arrigo, ; Meiners et al, , ), they are less pronounced in landfast sea ice. Sea ice surface algal communities are dominated by flagellate species and generally occur when environmental conditions ameliorate during summer, for example, when ice temperatures increase and brine salinities decrease (van Leeuwe et al, , and references therein). Stoecker et al () described the succession of a halo‐ and cryo‐tolerant flagellate‐dominated community developing into a diatom‐dominated community in snow‐free landfast sea ice in McMurdo Sound.…”

“…The observed vertical zonation of Chl a in AFIAC is consistent with the seasonal dynamics of the major environmental drivers and likely additionally affected by small‐ and medium‐scale sea ice physical features. The algal communities particularly thrive in layers that are spatially or temporally most coupled to the water column, supplying nutrients and providing seed populations of microalgae (Arrigo, ; van Leeuwe et al, ). We note that our description of the drivers of the seasonal and vertical distribution of Chl a is specific for thermodynamically grown landfast sea ice.…”

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

“…Diatoms typically dominate both the phytoplankton and the sea-ice spring blooms, while flagellates, dinoflagellates, and picoeukaryotes usually dominate in late summer (Tremblay et al, 2009;Moran et al, 2012;van Leeuwe et al, 2018). Some diatom species, such as Shionodiscus bioculatus (formerly Thalassiosira bioculata) (Alverson et al, 2006) and Fragilariopsis cylindrus, are sea-ice associated and have been observed both in the water column and in the ice (von Quillfeldt, 2000).…”