RESEARCH ARTICLE

Spring phytoplankton onset after the ice break-up and sea-ice signature (Adélie Land, East Antarctica)

Catherine Riaux-Gobin,^1,2 Michel Poulin,³ Gerhard Dieckmann,⁴ Céline Labrune,² & Gilles Vétion,²

¹USR 3278 Centre National de la Recherche Scientifique, École Pratique des Hautes Études, Centre de Recherches Insulaires et Observatoire de l’Environnement, Université de Perpignan, FR-66860 Perpignan, France ²UMR 7621 Centre National de la Recherche Scientifique, Université Pierre et Marie Curie-Paris 6, FR-66650 Banyuls-sur-Mer, France ³Research Division, Canadian Museum of Nature, PO Box 3443, Station D, Ottawa ON K1P 6P4, Canada ⁴Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, GE-27570 Bremerhaven, Germany

Abstract

The phytoplankton onset following the spring ice break-up in Adélie Land, East Antarctica, was studied along a short transect, from 400 m off the continent to 5 km offshore, during the austral summer of 2002. Eight days after the ice break-up, some large colonial and solitary diatom cells, known to be associated with land-fast ice and present in downward fluxes, were unable to adapt in ice-free waters, while some other solitary and short-colony forming taxa (e.g., Fragilariopsis curta, F. cylindrus) did develop. Pelagic species were becoming more abundant offshore, replacing the typical sympagic (ice-associated) taxa. Archaeomonad cysts, usually associated with sea ice, were recorded in the surface waters nearshore. Rough weather restricted the data set, but we were able to confirm that some microalgae may be reliable sea-ice indicators and that seeding by sea ice only concerns a few taxa in this coastal area of East Antarctica.

Keywords
Ice break-up; phytoplankton; sea-ice signature; East Antarctica.

Correspondence
Catherine Riaux-Gobin, USR 3278 Centre National de la Recherche Scientifique, École Pratique des Hautes Études, Centre de Recherches Insulaires et Observatoire de l’Environnement, Université de Perpignan, FR-66860 Perpignan, France. E-mail: catherine.gobin@univ-perp.fr Email: catherine.gobin@univ-perp.fr

Published: 10 January 2011

Citation: Polar Research 2011, 30, 5910, doi: 10.3402/polar.v30i0.5910

Polar Research 2011. © 2011 Catherine Riaux-Gobin et al. This is an open-access article distributed under the terms of the Creative Commons Attribution-Noncommercial 3.0 Unported License (http://creativecommons.org/licenses/by-nc/3.0/), permitting all non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

The onset of the spring phytoplankton bloom, following the ice break-up in Antarctica, has received more attention for the pack ice edge than in coastal circumpolar regions. The edge of the marginal ice zone was considered an ideal environment for phytoplankton blooms (e.g., Sullivan et al. 1988; Fonda Umani et al. 2005; Garrity et al. 2005). However, a large part of the Antarctic shelf and seasonal ice zone remains poorly investigated due to logistical and technical constraints. Predictive models are currently developed based on sea-ice and ice-edge blooms to assess carbon export in seasonally ice-covered regions (e.g., Rodriguez y Baena et al. 2008), but in situ work still remains essential for validating such models, especially in poorly surveyed regions. While differences are noticed in the position and composition of the productive layers in pack and land-fast ice (Palmisano & Garrison 1993), the phytoplankton community also differs in composition, origin and development between coastal and offshore sites (Leventer 2003).

In the land-fast ice off Adélie Land, several surveys have provided an overview of the bottom-ice protist communities, which are composed of diatoms among other organisms (Riaux-Gobin et al. 2000; Riaux-Gobin et al. 2003; Fiala et al. 2006; Poulin et al. 2006). Land-fast ice forms annually in March and is relatively thin along the Adélie Land coast. In spring, the sympagic (ice-associated) community is restricted to a thin layer at the proximate part of the bottom ice and showed a taxonomic composition similar to other sea-ice communities reported from other Antarctic coastal regions (e.g., Cota & Sullivan 1990; Watanabe et al. 1990; Ackley & Sullivan 1994; Günther & Dieckmann 2001). Increasing irradiance and air temperature in springtime, along with ice melting processes, contribute to flush out the protist cells from the bottom ice layer, which are then scattered in the under-ice water column and eventually contribute to the vertical sinking flux of particulate organic material to deep waters and benthic communities (Leventer 2003).

The coastal phytoplankton off Adélie Land following the ice break-up is less documented than the bottom land-fast ice communities (e.g., Beans et al. 2008), but the spatial distribution of the phytoplankton biomass has previously been described (Fiala & Delille 1992). However, the taxonomic composition is only briefly reported in the latter paper, with the presence of large diatom taxa at coastal stations such as Corethron criophilum, Chaetoceros dichaeta and Fragilariopsis kerguelensis, while they observed a reduction in the phytoplankton biomass and a shift in the taxonomic composition with small-sized flagellate cells at offshore stations.

The present study focuses on a restricted data set of the phytoplankton off Adélie Land, one week after the spring break-up of 2002. The objective was to compare the taxonomic phytoplankton composition along an offshore gradient in parallel with a survey of some biogeochemical parameters. Sea-ice signature species and possible seeding processes of the phytoplankton are discussed.

Material and methods

Study site and sampling

Due to rough weather, water sampling was only conducted once, on 18 January 2002, eight days after the ice break-up off the Adélie Land, East Antarctica. Water samples were collected with a 4-L Niskin bottle at 0, 5, 10 and 20 m along an offshore transect at four stations Fig. 1 from A (66°39.22′ S, 140°00.14′ E) to D (66°36.81' S, 139°59.56' E) to determine the following variables: chlorophyll (Chl) a, b and phaeopigments (Phaeo) a, b; nitrite (NO₂); nitrate+nitrite (NO₃+NO₂); phosphate (PO₄) and silicic acid (Si[OH]₄); and the identification and enumeration of phytoplankton cells.

Fig. 1.   Map of Adélie Land in Dumont d'Urville Sea, East Antarctica, showing the location of the four stations (A – D) along an offshore transect.

Unfortunately, conductivity–temperature–depth instruments and current meters were not available for us to use along the prospected transect, which limited our understanding of hydrographic parameters. Nevertheless, we studied the under-ice current regime and the Lagrangian north-western drift (mainly governed by the tidal regime and in favour of an offshore export of particles) before the ice break-up on the same area, during the same campaign (Riaux-Gobin et al. in press).

Analytical methods

Biogeochemistry

Samples for nutrient determination were frozen immediately at −20°C prior to be analysed in Banyuls-sur-Mer, France, using an AutoAnalyzer III (Technicon Corporation, New York, NY, USA; Tréguer & Le Corre 1975). Water samples for pigment analysis were filtered through 47-mm GF/F grade filters (Whatman, Maidstone, Kent, UK) and kept frozen at −20°C prior to being analysed in Banyuls-sur-Mer. Following a 3-hour extraction in 5.4 mL of 100% acetone at 4 to 7°C in the dark, the concentrations of Chl a, b and Phaeo a, b were determined with an LS 55 Flourescence Spectrometer (PerkinElmer, Wellesley, MA, USA; Neveux & Lantoine 1993).

Identification and cell enumeration

Samples for the identification and enumeration of phytoplankton cells were preserved with acidic Lugol's solution. Cells were identified to the lowest possible taxonomic rank and enumerated under an inverted microscope (Wild, Heerbrugg, Switzerland) operating with phase contrast optics (Lund et al. 1958). Empty diatom cells were recorded separately as centric or pennate forms. The main taxonomic references used to identify the phytoplankton were Manguin (1957, 1960), Priddle & Fryxell (1985), Medlin & Priddle (1990), Hasle et al. (1994) and Hasle & Syvertsen (1997).

Statistical analysis

A covariance-based principal component analysis (PCA), using Statistica® software, was applied to the set of log-transformed data (log [x+1]) corresponding to abundance data at each of the four sampling sites and at each of the four sampled depths (excluding unidentified taxa and morphological groups; see Table 1). This analysis tentatively discriminates taxonomic communities along axes and illustrates their relationship with the sampling sites.

Results

Biogeochemistry

The photosynthetic pigment biomasses and nutrient concentrations measured at four depths along the offshore transect Fig. 1 were relatively homogeneous throughout the water column Table 2. Phosphate concentrations were slightly higher nearshore in the surface water at station A, while remaining relatively homogeneous elsewhere. Nitrite, nitrate and silicic acid concentrations were homogeneous. Chlorophyll a concentrations were generally low but slightly higher in surface waters averaging at 2.22 µg L⁻¹, with no offshore spatial gradient, while Chl b showed low concentrations everywhere averaging at 0.12 µg L⁻¹, but with the lowest concentrations nearshore (on average 0.09 µg L⁻¹). Phaeopigment a concentrations were low (0.47–0.98 µg L⁻¹) and homogeneous from 0 to 20 m. The Chl a:Phaeo a ratios were high (2.0–2.5) at all depths.

Taxonomic composition

A total of 66 phytoplankton taxa (including two spore groups), representing 49 species in nine algal classes, were recorded for the water column off Adélie Land in mid-January 2002 Table 1. Some taxa, mainly sea-ice indicators, are illustrated in Fig. 2. Several microalgae and morphometric groups Table 1, not ranked to species level, have been recorded and enumerated. The cell abundance concerning the dominant microalgal taxa from the surface samples are listed with a rough ranking following the spatial abundances along the A – D transect Table 3. Three groups are tentatively categorized Table 3: (1) taxa mainly found in nearshore waters, close to ice melt (station A); (2) taxa mostly abundant at station D, close to offshore water masses; and (3) taxa without spatial preference.

Fig. 2.   Micrographs of some protist taxa, mainly sea-ice indicators, from Adélie Land, in light (e) and scanning electron microscopy (a – d, f – k). (a) Navicula glaciei; (b) Fragilariopsis curta; (c) Nitzschia stellata; (d, g) Amphiprora kufferathii; (e, h) Berkeleya adeliensis; (f) spore of Chaetoceros cf. neglectum; (i – k) Archaeomonadaceae (cysts): (i) Archaeomonas cf. areolata, (j) A. cf. speciosa Deflandre, and (k) Litheusphaerella cf. spectabilis. Scale bars: 3 µm (i – k); 5 µm (b, f, g); 10 µm (a, e, h); 20 µm (c, d).

The PCA was applied on a set of data (concerning all depths sampled) with the 49 species and 16 samples (Fig. 3). Some species, commented in the discussion, are in bold in Fig. 3 (see corresponding full names in Table 1). The first three axes explain 36.0% of the variance in the species data and the first two axes explain 25.6%. Even if these scores are not that high, the PCA allows for the separation of samples or groups of samples (delineated by ellipses/lines in Fig. 3) and the identification of some associated/linked species.

Fig. 3.   Principal component analysis of (a) stations: nearshore and surface samples (stations A and B, with negative scores on axes 1 and 2 are individualized). The analysis also groups the offshore and deeper samples (particularly station D, positive score on axis 1). Principal component analysis of (b) species distribution with a group of sympagic taxa (e.g., BEAD, AMKU and KYCH, negative score on axis 1), a group of typical pelagic taxa (e.g., CHNE, CHDI, POPS, positive scores on axis 1), and an intermediate group of well-adapted taxa to ice-free water conditions (e.g., FRC, FCRU, and PHAN). See Table 1 for abbreviations.

The first PCA axis explains 14.3% of the variance in the microalgal assemblage data set, the coastal sample A5 being the major associated site. The associated species (higher negative scores on axis 1) are the flagellate sp. 2, Navicula sp. 1 and Plagiotropis acuta. The second PCA axis explains 11.4% of the variance in this assemblage. The species with the highest positive score on axis 2 are vegetative cells of the pelagic taxa Chaetoceros cf. neglectum, C. dichaeta and Porosira pseudodenticulata. The species with the highest negative score on axis 2 are the chain-forming diatoms Berkeleya adeliensis (Fig. 2e, h), Amphiprora kufferathii (Fig. 2d, g) and Pseudo-nitzschia sp. 1. The third PCA axis (not illustrated) explains 10.4% of the variance and discriminates pelagic taxa with a positive score such as Odontella weissflogii and centric sp. 1, from the taxon Nitzschia taeniiformis known to be a sympagic taxon. The PCA analysis discriminates relatively clearly the offshore sites D (positive scores on axis 2; Fig. 3) opposite to the more coastal and surface water sites (negative scores on axes 1 and 2).

Discussion

Spatial gradient in biogeochemical parameters

These newly ice-free waters showed no stratification down to 20 m for nutrients (see standard deviations in Table 2), possibly due to rough sea conditions and tidal mixing after the spring ice break-up. The low concentration of phaeopigments and the high Chl a:Phaeo a ratio (Table 2) tend to show a relatively fresh and ungrazed standing stock of microalgal cells. After eight days following the ice break-up, the phytoplankton community is still in a pre-bloom period with very low Chl a biomass in surface waters decreasing at 5 m. However, the Chl a biomass measured at 5 m is higher than the concentrations recorded in the under-ice water the week before (C. Riaux-Gobin, pers. obs.).

NO₃ and Si(OH)₄ concentrations (Table 2, mean 26 and 53 µM, respectively) were very similar to data recorded during the summer of 1995 in the same area, in small polynyas opened before the complete ice break-up at coast (Riaux-Gobin et al. 2000; Table 4; mean 27 and 64 µM, respectively). The Chl a concentrations were lower in 1995 (mean 0.69 µg L⁻¹) than in the present study, possibly due to the fact that the sampling took place before the break-up.

Phytoplankton spatial distribution and origin of sea-ice protist taxa

The ice-free phytoplankton taxonomic composition (Table 2) slightly differed from the one reported from the land-fast ice and the under-ice surface water before the ice break-up in the same area (Riaux-Gobin et al. 2003). Several ice-associated taxa such as Banquisia belgica and Entomoneis kjellmanii were absent in the ice-free conditions, and several microalgae present in the phytoplankton were absent from the sea ice some weeks before (i.e., Membraneis challengeri, Pseudo-nitzschia lineola, Fragilariopsis kerguelensis, most of the centric diatoms, particularly species of Chaetoceros, and several dinoflagellates; M. Poulin, pers. comm.).

The large and colonial pennate diatoms, Amphiprora kufferathii and Berkeleya adeliensis, recognized as sympagic taxa (Garrison et al. 1986; Leventer 1998; McMinn 1998; Knox 2006) were only present at the nearshore station A, and Navicula glaciei Fig. 2a) was also rarely recorded in the plankton (it was not recorded at the offshore stations C and D). In contrast, Fragilariopsis cylindrus and F. curta Fig. 2b) were relatively abundant in the pelagic waters, with up to 55×10⁴ cells L⁻¹ at station A (5 m) and 16×10⁴ cells L⁻¹ at station B (10 m), respectively (see discussion of Fragilariopsis cylindrus and F. curta in Leventer 1998). Archaeomonad cysts Fig. 2i – k), also recognized as sea-ice inhabitants (Mitchell & Silver 1982), are not rare on the Adélie Land bottom ice, platelet ice layer and adjacent waters (Riaux-Gobin & Stumm 2006) and were only recorded at the coastal station A.

Pelagic species were abundant offshore throughout the water column, particularly with vegetative cells of Chaetoceros dichaeta and C. cf. neglectum reaching up to 22×10⁴ cells L⁻¹ and 16×10⁵ cells L⁻¹, respectively. These taxa seem to rapidly develop, particularly C. cf. neglectum, while they were absent from the land-fast ice and rare or absent from the under-ice surface water before the ice break-up (Riaux-Gobin et al. 2003). A particular mention can be drawn for the spores of Chaetoceros: during the 1995 campaign in Adélie Land, spores of Chaetoceros were recorded, along with vegetative cells of C. cf. neglectum, only in small adjacent polynyas but apparently not in sea ice (Riaux-Gobin et al. 2003). Before the ice break-up in 2002, spores of Chaetoceros were only recorded at 5-m water depth under the ice sheet, but never in the bottom or platelet ice (M. Poulin, pers. comm.). After the ice break-up (present study), these Chaetoceros spores were surprisingly slightly more abundant at station A than at offshore stations: they may have been overlooked in sea-ice samples (Fig. 2f).

Fragilariopsis kerguelensis, which is reported to be an indicator species of open water conditions with no correlation to sea ice (Pike et al. 2008), was absent at nearshore stations A and B and was present only in the surface waters at offshore stations C and D.

Dinoflagellates and the prymnesiophyte Phaeocystis antarctica, with 11×10⁵ cells L⁻¹, were abundant in the surface waters at coastal stations denoting their relationship with cold waters and ice melting conditions (slightly lower salinity at station A; data not shown), as previously demonstrated by Moisan & Mitchell (1999). In our study, P. antarctica dominated the surface water phytoplankton community representing 16% of the total phytoplankton assemblage.

PCA analysis

As shown from the PCA analysis (Fig. 3) and the rough ranking in Table 3 (only surface samples), one week after the effective ice break-up the water masses, if referred to taxonomy, show a strong gradient from coast to offshore. The coastal stations A and B (0 m) scored negatively on the PCA axes 1 and 2 Fig. 3 and they were characterized by the presence of typical sympagic pennate diatoms such as Amphiprora kufferathii, Berkeleya adeliensis and Nitzschia stellata (Fig. 2c), while these taxa apparently did not survive at offshore ice-free stations. The station A is also characterized by the presence of archaeomonad cysts that were absent from offshore stations.

In contrast, the colonial protist taxa Fragilariopsis cylindrus, F. curta and Phaeocystis antarctica classically present in the bottom layer of the land-fast ice seemed well adapted to open water conditions (central group of taxa in Fig. 3 as previously shown in ice-edge open waters (Hegseth & von Quillfeldt 2002). The same conclusion was recently given for Fragilariopsis cylindrus from a platelet ice community at Terra Nova Bay, which was also well adapted to planktonic conditions (Mangoni et al. 2009). Fragilariopsis curta showed an adaptation to decreasing salinity due to sea-ice melting (Ryan et al. 2004), and both F. cylindrus and F. curta were the most common flourishing microalgae in the marginal ice zone (Leventer 1998), which was also the case for P. antarctica (Fryxell & Kendrick 1988; Kang et al. 2001).

The PCA first and second axes discriminate relatively clearly the origin of the cells: (1) a sympagic coastal origin for several taxa (negative scores of A0, B0 and C0 on axis 2; signature of the land-fast ice present a few days before on the sampling area, particularly in surface coastal waters); in opposition to (2) a pelagic origin for several others taxa (positive scores of all depths at D and deep waters at B on axis 2). The ice break-up was effective at coast only a few days before sampling and drifting ice was still present, implying a strong sympagic component to the coastal diatom community.

Sea-ice proxies

The preservation of phytoplankton and sea-ice diatoms in sediments, particularly in the Southern Ocean and their use for palaeo sea-ice reconstructions (Armand & Leventer 2010), has been commented upon and questioned (Leventer 1998) and remains a topic of current interest (Pike et al. 2008). Pike et al. showed the complexity of studies comparing contemporary and fossil Antarctic diatom communities, but they concluded that the summer community is largely not preserved in the sediments. Tanimura et al. (1990) compared the diatom communities in the water column after the ice break-up with communities from sea ice and the surface sediments in Lützow-Holm Bay, Antarctica. They showed that several weakly silicified diatom taxa that were abundant in the water column and sea-ice (e.g., Berkeleya sp. a, Chaetoceros spp., Cylindrotheca closterium, Navicula glaciei, Nitzschia lecointei, N. stellata, Pleurosigma sp. and Tropidoneis sp.) were not recorded in the sediments. On the other hand, two more strongly silicified species associated with sea ice and the underlying waters, namely Fragilariopsis curta and F. cylindrus, were well-preserved in sediments (see Leventer 1998; Armand et al. 2005). Tanimura et al. (1990) also pointed out that F. kerguelensis in addition to F. obliquecostata (Van Heurck) Heiden, F. separanda Hustedt and F. sublinearis were usually recorded in greater numbers in the sediments than in sea-ice environments, which can be explained by their resistance to corrosion and, for F. kerguelensis, the penetration of open ocean currents under the land-fast ice.

Sympagic land-fast ice pennate diatoms (e.g., Amphiprora kufferathii, Berkeleya adeliensis and Navicula glaciei) that cannot survive in ice-free waters may be considered a land-fast sea-ice signature. However, with respect to diatoms, a reliable signature means that the frustules need to be well preserved in the fossil record, which is not often the case, like for Navicula glaciei (Krebs et al. 1987; Tanimura et al. 1990).

Cysts of Archaeomonas preserved well in sediments (Deflandre 1932; Tynan 1971). In the coastal area of Adélie Land, Archaeomonas cf. areolata Deflandre and Litheusphaerella cf. spectabilis Deflandre were present in sea ice and under-ice waters (Fig. 2i, k) (Riaux-Gobin & Stumm 2006) but preferentially in sea-ice layers. In this study, cysts only occurred in the surface waters at the coastal stations. These observations confirmed the use of these archaeomonad cysts as a signature or a “proxy” of the presence of annual land-fast ice and support previous findings by Mitchell & Silver (1982). The receding ice may seed these organisms in the under-ice water, but as their life cycle is so far unknown this cannot conclusively be inferred.

The presence of Chaetoceros resting spores was interpreted as indicative of high primary production by Leventer (1998) and also as a proxy for spring sea-ice melting (Crosta et al. 2007), but these observations fail to provide details about spore formation in sea ice or adjacent cold waters.

Seeding by sea ice

It is of interest to evaluate the contribution of the land-fast ice to the phytoplankton seeding process. Several environmental variables affect the development of bottom ice protists and their fate following the ice melting events responsible for their release to the water column. It has been demonstrated that sympagic algae may contribute to the pelagic bloom in Ellis Fjord, in eastern Antarctica (McMinn 1996) and also in Terra Nova Bay (Mangoni et al. 2009). However, Ligowski et al. (1992), studying sea-ice diatoms and ice-edge plankton diatoms in the Weddell Sea, stated that sea-ice diatoms in their samples were not in good health and could not be regarded as an inoculum for the phytoplankton diatoms. They concluded the poor physiological state of these ice microalgae may be ascribed to the sampling period (summer) and the sampling region.

Depending on the ice type and history (land-fast ice, pack ice, drifting floes) and the presence/absence of platelet ice, seeding processes are bound to be highly variable. Ichinomiya et al. (2008) investigated the abundance and sinking flux of diatoms under fast ice at Syowa Station in East Antarctica and showed that species released from the ice exhibit differences in their buoyancy control and sinking characteristics.

The study reported here confirms our previous investigations in Adélie Land on small polynyas and leads just before the ice break-up event in the austral summer of 1995, where the under-ice phytoplankton was composed of some sympagic diatoms as well as vegetative cells of Chaetoceros that were not present in the land-fast ice (Riaux-Gobin et al. 2000). Here, the abundance of Fragilariopsis cylindrus and F. curta in ice-free waters indicates a possible seeding by sea-ice for these two taxa, previously demonstrated as successfully exploiting the water column adjacent to the ice as well as the ice itself (Leventer 1998).

The prymnesiophyte Phaeocystis antarctica, an opportunistic taxon (Fryxell & Kendrick 1988), has recently been shown to be capable of surviving in both the ice and the water column (Tang et al. 2009) but with no prevalence of one environment as refuge. During the EPONTA (epontic microalgae) 2001 survey, the communities present in the land-fast ice before the break-up and in the open water immediately after the break-up were investigated in Adélie Land. Before the ice break-up, P. antarctica was shown to grow preferentially in the platelet ice and in the under-ice waters but only during the last 10 days before the ice break-up (M. Poulin, pers. comm.). This observation may possibly imply that sea-ice trapped P. antarctica cells from the underlying water masses, before seeding them back at the ice break-up.

Conclusion

The sudden increase in irradiance after the ice break-up triggers the growth of the phytoplankton, but the origin of the ice-free protist community is not yet entirely understood. Such uncertainties have also been pointed out in other studies: the seeding attributed to the receding ice edge has been well documented, commented upon and questioned (Lizotte 2001), mostly in pack-ice environments but has never yielded the same conclusions (Leventer 2003). As Ishikawa et al. (2001) also conclude in their study of the origin, evolution and fate of diatom communities under fast ice near Syowa Station during the austral summer, further investigations are needed to clarify the findings. The present set of data is very restricted and only represents a one-time survey concerning Adélie Land. Such samplings have to be replicated several times before giving an accurate and reliable overview of: (1) the taxa present, their origin and relationship with the sea-ice history (having or not experienced winter break-up events); (2) the taxa that immediately sediment (fast vertical flux to the benthos) and do not participate to the pelagic cycle after the ice break-up; (3) the taxa that seed the water column; and finally (4) the taxa that may be good annual sea-ice proxies.

Acknowledgements

We thank the over-wintering team members for their field assistance and fellowship during EPONTA programmes and the Astrolabe polar ship crew. We also thank Louise Oriol (Laboratoire d'Oceanographie Biologique de Banyuls, Banyuls-sur-Mer, France) for providing the nutrient data and Mélanie Simard (Institut des Sciences de la Mer, Université du Québec à Rimouski, Canada) for providing cell enumeration. We acknowledge Dr Leanne Armand and an anonymous reviewer for their valuable suggestions and the journal Antarctic Science for giving approval to reproduce Fig. 2i – k. We thank the Natural Sciences and Engineering Research Council of Canada and the Canadian Museum of Nature for research grants to Michel Poulin. Funds and logistic assistance in the field were supported by the Institut Polaire Français Paul-Émile Victor, Brest, France.

References

Ackley, S.F. & Sullivan, C.W. (1994). Physical controls on the development and characteristics of Antarctic sea ice biological communities—a review and synthesis. Deep-Sea Research Part I, 41, 1583–1604. [Crossref]

Armand, L.K., Crosta, X., Romero, O. & Pichon, J.-J. (2005). The biogeography of major diatom taxa in Southern Ocean sediments: 1. Sea-ice related species. Palaeogeography, Palaeoclimatology, Palaeoecology, 223, 93–126. [Crossref]

Armand L.K. & Leventer A. 2010. Palaeo sea ice distribution and reconstruction derived from the geological records. In D.N. Thomas & G.S. Dieckmann (eds.): Sea ice. 2nd edn. Pp. 469–530. Oxford: Wiley-Blackwell.

Beans, C., Hecq, J.H., Koubbi, P., Vallet, C., Wright, S. & Goffart, A. (2008). A study of the diatom-dominated microplankton summer assemblages in coastal waters from Terre Adélie to the Mertz Glacier, East Antarctica (139°E–145°E). Polar Biology, 31, 1101–1117. [Crossref]

Cota, G.F. & Sullivan, C.W. (1990). Photoadaptation, growth and production of bottom ice algae in the Antarctic. Journal of Phycology, 26, 399–411. [Crossref]

Crosta, X., Denis, D. & Ther, O. (2007). Sea ice seasonality during the Holocene, Adélie Land, East Antarctica. Marine Micropaleontology, 66, 222–232. [Crossref]

Deflandre, G. (1932). Archaeomonadaceae, une famille nouvelle de protistes fossiles marins à loge siliceuse. (Archaeomonadaceae, a new family of marine fossil protists with silicious wall.). Compte Rendu Hebdomadaire des Séances de l’ Académie des Sciences de Paris, 194, 1859–1861.

Fiala, M. & Delille, D. (1992). Variability and interactions of phytoplankton and bacterioplankton in the Antarctic neritic area. Marine Ecology-Progress Series, 89, 135–146. [Crossref]

Fiala, M., Kuosa, H., Kopczyńska, E.E., Oriol, L. & Delille, D. (2006). Spatial and seasonal heterogeneity of sea ice microbial communities in the first-year ice of Terre Adélie area (Antarctica). Aquatic Microbial Ecology, 43, 95–106. [Crossref]

Fonda Umani, S., Monti, M., Bergamasco, A., Cabrini, M., De Vittor, C., Burba, N. & Del Negro, P. (2005). Plankton community structure and dynamics versus physical structure from Terra Nova Bay to Ross Ice Shelf (Antarctica). Journal of Marine Systems, 55, 31–46. [Crossref]

Fryxell, G.A. & Kendrick, G.A. (1988). Austral spring microalgae across the Weddell Sea ice edge: spatial relationships found along a northward transect during AMERIEZ 83. Deep-Sea Research, 35, 1–20. [Crossref]

Garrison, D.L., Sullivan, C.W. & Ackley, S.F. (1986). Sea ice microbial communities in Antarctica. BioScience, 36, 243–250. [Crossref]

Garrity, C., Ramseier, R.O., Peinert, R., Kern, S. & Fischer, G. (2005). Water column particulate organic carbon modeled fluxes in the ice-frequented Southern Ocean. Journal of Marine Systems, 56, 133–149. [Crossref]

Günther, S. & Dieckmann, G. (2001). Vertical zonation and community transition of sea-ice diatoms in fast ice and platelet layer, Weddell Sea, Antarctica. Annals of Glaciology, 33, 287–296. [Crossref]

Hasle, G.R., Medlin, L.K. & Syvertsen, E.E. (1994). Synedropsis gen. nov., a genus of araphid diatoms associated with sea ice. Phycologia, 33, 248–270. [Crossref]

Hasle G.R. & Syvertsen E.E. 1997. Marine diatoms. In C.R. Tomas (ed.): Identifying marine diatoms and dinoflagellates. Pp. 387–584. San Diego, CA: Academic Press.

Hegseth, E.N. & von Quillfeldt, C.H. (2002). Low phytoplankton biomass and ice algal blooms in the Weddell Sea during the ice-filled summer of 1997. Antarctic Science, 14, 231–243. [Crossref]

Ichinomiya, M., Gomi, Y., Nakamachi, M., Honda, M., Fukuchi, M. & Taniguchi, A. (2008). Temporal variations in the abundance and sinking flux of diatoms under fast ice in summer near Syowa Station, East Antarctica. Polar Science, 2, 33–40. [Crossref]

Ishikawa, A., Washiyama, N., Tanimura, A. & Fukuchi, M. (2001). Variation in the diatom community under fast ice near Syowa Station, Antarctica, during the austral summer of 1997/98. Polar Bioscience, 14, 10–23.

Kang, S.-H., Kang, J.-S, Lee, S., Chung, K.H., Him, D. & Park, M.G. (2001). Antarctic phytoplankton assemblages in the marginal ice zone of the northwestern Weddell Sea. Journal of Plankton Research, 23, 333–352. [Crossref]

Knox G.A. 2006. Biology of the Southern Ocean. 2nd edn. Christchurch, New Zealand: CRC Press. [Crossref]

Krebs, W.N., Lipps, J.H. & Burckle, L.H. (1987). Ice diatom floras, Arthur Harbor, Antarctica. Polar Biology, 7, 163–171. [Crossref]

Leventer A. 1998. The fate of Antarctic “sea ice diatoms” and their use as paleoenvironmental indicators. In M.P. Lizotte & K.R. Arrigo (eds.): Antarctic sea ice. Biological processes, interactions and variability. Pp. 121–137. Washington, DC: American Geophysical Union.

Leventer A. 2003. Particulate flux from sea ice in polar waters. In D.N. Thomas & G.S. Dieckmann (eds.): Sea ice. An introduction to its physics, chemistry, biology and geology. Pp. 303–332. Oxford: Blackwell Science.

Ligowski, R., Godlewski, M. & Lukowski, A. (1992). Sea ice diatoms and ice edge planktonic diatoms at the northern limit of the Weddell Sea pack ice. Proceedings of the NIPR Symposium on Polar Biology, 5, 9–20.

Lizotte, M.P. (2001). The contributions of sea ice algae to Antarctic marine primary production. American Zoology, 41, 57–73. [Crossref]

Lund, J.W.G., Kipling, C. & Le Cren, E.D. (1958). The inverted microscope method of estimating algal numbers and the statistical basis of estimations by counting. Hydrobiologia, 11, 143–170. [Crossref]

Mangoni, O., Saggiomo, M., Modigh, M., Catalano, G., Zingone, A. & Saggiomo, V. (2009). The role of platelet ice microalgae in seeding phytoplankton blooms in Terra Nova Bay (Ross Sea, Antarctica): a mesocosm experiment. Polar Biology, 32, 311–323. [Crossref]

Manguin, É. (1957). Premier inventaire des diatomées de la Terre Adélie Antarctique: espèces nouvelles. (First inventory of diatoms from Adélie Land, Antarctica: new species.). Revue Algologique Nouvelle Série, 3, 111–134.

Manguin, É. (1960). Les diatomées de la Terre Adélie, campagne du “Commandant Charcot” 1949–1950. (Adélie Land diatoms, “Commandant Charcot” campaign 1949–1950.). Annales des Sciences Naturelles, Botanique, 1, 223–363.

McMinn, A. (1996). Preliminary investigation on the contribution of fast-ice algae to the spring phytoplankton bloom in Ellis Fjord, eastern Antarctica. Polar Biology, 16, 301–307. [Crossref]

McMinn, A. (1998). Species succession in fast ice algal communities; a response to UV-B radiation?. Korean Journal of Polar Research, 8, 47–52.

Medlin, L.K. & Priddle, J. (1990). Polar marine diatoms. Cambridge: British Antarctic Survey.

Mitchell, G.J. & Silver, M.W. (1982). Modern archaeomonads indicate sea-ice environments. Nature, 296, 437–439. [Crossref]

Moisan, T.A. & Mitchell, G. (1999). Photophysiological acclimation of Phaeocystis antarctica Karsten under light limitation. Limnology and Oceanography, 44, 247–258. [Crossref]

Neveux, J. & Lantoine, F. (1993). Spectrofluorometric assay of chlorophylls and phaeopigments using the least squares approximation technique. Deep-Sea Research Part I, 40, 1747–1765. [Crossref]

Palmisano A.C. & Garrison D.L. 1993. Microorganisms in Antarctic sea ice. In E.I. Friedmann (ed.): Antarctic microbiology. Pp. 167–218. New York: Wiley-Liss.

Pike, J., Allen, C.S., Leventer, A., Stickley, C.E. & Pudsey, C.J. (2008). Comparison of contemporary and fossil diatom assemblages from the western Antarctic Peninsula. Marine Micropaleontology, 67, 274–287. [Crossref]

Poulin , M., Riaux-Gobin , C., Compère , P. & Simard , M. 2006. Le genre Entomoneis à Terre Adélie, Antarctique. (The genus Entomoneis in Adélie Land, Antarctica.) Symbioses nouvelle série, 14, 51.

Priddle, J. & Fryxell, G. (1985). Handbook of the common plankton diatoms of the Southern Ocean: centrales except the genus Thalassiosira. Cambridge: British Antarctic Survey.

Riaux-Gobin , C., Duchêne , J.-C., Dieckmann , G.S. & Gallois , F. In press. Lagrangian drift under land-fast ice and relationship with tidal regime (Adélie Land, East Antarctica). Oceanology, .

Riaux-Gobin, C., Poulin, M., Prodon, R. & Tréguer, P. (2003). Land-fast ice microalgal and phytoplanktonic communities (Adélie Land, Antarctica) in relation to environmental factors during ice break-up. Antarctic Science, 15, 354–364. [Crossref]

Riaux-Gobin, C. & Stumm, K. (2006). Modern Archaeomonadaceae from the land-fast ice off Adélie Land (Antarctica): a preliminary report. Antarctic Science, 18, 51–60. [Crossref]

Riaux-Gobin, C., Tréguer, P., Poulin, M. & Vétion, G. (2000). Nutrients, algal biomass and communities in land-fast ice and seawater off Adélie Land (Antarctica). Antarctic Science, 12, 160–171. [Crossref]

Rodriguez y Baena, A., Boudjenoun, R., Fowler, S.W., Miquel, J.C., Masqué, P., Sanchez-Cabeza, J.A. & Warnau, M. (2008). ²³⁴Th-based carbon export during an ice-edge bloom: sea-ice algae as a likely bias in data interpretation. Earth and Planetary Science Letters, 269, 596–604. [Crossref]

Ryan, K.G., Ralph, P. & McMinn, A. (2004). Acclimation of Antarctic bottom-ice algal communities to lowered salinities during melting. Polar Biology, 27, 679–686. [Crossref]

Sullivan, C.W., McClain, C.R., Comiso, J.C. & Smith, W.O. (1988). Phytoplankton standing crops within an Antarctic ice edge assessed by satellite remote sensing. Journal of Geophysical Research — Oceans, 93, 12487–12498. [Crossref]

Tang, K.W., Smith, W.O., Elliott, D.T. & Shields, A. (2009). Survival and recovery of Phaeocystis antarctica (Prymnesiophyceae) from prolonged darkness and freezing. Proceedings of the Royal Society of London B, 276, 81–90. [Crossref]

Tanimura, Y., Fukuchi, M., Watanabe, K. & Moriwaki, K. (1990). Diatoms in water column and sea-ice in Lützow-Holm Bay, Antarctica, and their preservation in the underlying sediments. Bulletin of the National Science Museum, Tokyo, C, 16, 15–39.

Tréguer , P. & Le Corre , P. 1975. Manuel d'analyses automatiques des sels nutritifs dans l'eau de mer. Utilisation de l'Auto-Analyzer II Technicon. (Manual of automatic analyses of nutrients in sea water. Use of Autoanalyser II Technicon.) Brest, France: Université Bretagne Occidentale.

Tynan E.J. 1971. Geologic occurrence of the archaeo-monads. In A. Farinacci (ed.): Proceedings of the Second Planktonic Conference, Rome, 1970. Vol. 2. Pp. 1225–1230. Rome: Edizioni Tecnoscienza.

Watanabe K., Satoh H. & Hoshiai T. 1990. Seasonal variation in ice algal assemblages in the fast ice near Syowa Station in 1983/84. In K.R. Kerry & G. Hempel (eds.): Antarctic ecosystems: ecological change and conservation. Pp. 136–142. Berlin: Springer.