Spring time production of bottom ice algae in the landfast sea ice zone at Barrow, Alaska

The primary production of bottom ice algae is an important food source for sympagic, pelagic and benthic organisms in the Arctic Ocean as well as Antarctic Ocean. Using ¹³C-¹⁵N isotope tracers, the recent ice algal production at Barrow during the spring season was lower in 2003 than three decades ago, although the maximum chlorophyll-a concentration for the bottom ice algae was similar to the values from previous studies. Estimated recent new and total production rates of the ice algae were 0.8 g C m^- 2 yr^- 1 and 2.0 g C m^- 2 yr^- 1 respectively, while the rates of water column phytoplankton were 0.2 g C m^- 2 yr^- 1 and 0.7 g C m^- 2 yr^- 1 for the spring sampling period in 2003. The ice algae contributed 74% of the pelagic primary production under the landfast sea ice at Barrow before the phytoplankton spring bloom. At the end of the season in 2003, a high carbon allocation of lipids in the ice algae was found. Three possible explanations- nutrient depletion, increasing light, and/or changes in species composition- were suggested for the high carbon incorporation into lipids. This high lipid synthesis of the bottom ice algae might be significant to zooplankton and benthic fauna grazers because lipids are the most energy dense biomolecules.     

Timing of blooms,algal food quality and Calanus glacialis reproduction and growth in a changing Arctic

The Arctic bloom consists of two distinct categories of primary producers, ice algae growing within and on the underside of the sea ice, and phytoplankton growing in open waters. Long chain omega‐3 fatty acids, a subgroup of polyunsaturated fatty acids (PUFAs) produced exclusively by these algae, are essential to all marine organisms for successful reproduction, growth, and development. During an extensive field study in the Arctic shelf seas, we followed the seasonal biomass development of ice algae and phytoplankton and their food quality in terms of their relative PUFA content. The first PUFA‐peak occurred in late April during solid ice cover at the onset of the ice algal bloom, and the second PUFA‐peak occurred in early July just after the ice break‐up at the onset of the phytoplankton bloom. The reproduction and growth of the key Arctic grazer Calanus glacialis perfectly coincided with these two bloom events. Females of C. glacialis utilized the high‐quality ice algal bloom to fuel early maturation and reproduction, whereas the resulting offspring had access to ample high‐quality food during the phytoplankton bloom 2 months later. Reduction in sea ice thickness and coverage area will alter the current primary production regime due to earlier ice break‐up and onset of the phytoplankton bloom. A potential mismatch between the two primary production peaks of high‐quality food and the reproductive cycle of key Arctic grazers may have negative consequences for the entire lipid‐driven Arctic marine ecosystem.     

Comparing Springtime Ice-Algal Chlorophyll a and Physical Properties of Multi-Year and First-Year Sea Ice from the Lincoln Sea

With near-complete replacement of Arctic multi-year ice (MYI) by first-year ice (FYI) predicted to occur within this century, it remains uncertain how the loss of MYI will impact the abundance and distribution of sea ice associated algae. In this study we compare the chlorophyll a (chl a) concentrations and physical properties of MYI and FYI from the Lincoln Sea during 3 spring seasons (2010-2012). Cores were analysed for texture, salinity, and chl a. We identified annual growth layers for 7 of 11 MYI cores and found no significant differences in chl a concentration between the bottom first-year-ice portions of MYI, upper old-ice portions of MYI, and FYI cores. Overall, the maximum chl a concentrations were observed at the bottom of young FYI. However, there were no significant differences in chl a concentrations between MYI and FYI. This suggests little or no change in algal biomass with a shift from MYI to FYI and that the spatial extent and regional variability of refrozen leads and younger FYI will likely be key factors governing future changes in Arctic sea ice algal biomass. Bottom-integrated chl a concentrations showed negative logistic relationships with snow depth and bulk (snow plus ice) integrated extinction coefficients; indicating a strong influence of snow cover in controlling bottom ice algal biomass. The maximum bottom MYI chl a concentration was observed in a hummock, representing the thickest ice with lowest snow depth of this study. Hence, in this and other studies MYI chl a biomass may be under-estimated due to an under-representation of thick MYI (e.g., hummocks), which typically have a relatively thin snowpack allowing for increased light transmission. Therefore, we suggest the on-going loss of MYI in the Arctic Ocean may have a larger impact on ice–associated production than generally assumed.     

Influence of sea ice on the composition of the spring phytoplankton bloom in the northern Baltic Sea

During the late winter and spring of 1994, the influence of sea ice on phytoplankton succession in the water was studied at a coastal station in the northern Baltic Sea. Ice cores were taken together with water samples from the underlying water and analysed for algal composition, chlorophyll a and nutrients. Sediment traps were placed under the ice and near the bottom, and the sedimented material was analysed for algal composition. The highest concentration of ice algae (4.1 mmol C m⁻²) was found shortly before ice break-up in the middle of April, coincidental with the onset of an under-ice phytoplankton bloom. The ice algae were dominated by the diatoms Chaetoceros wighamii Brightwell, Melosira arctica (Ehrenberg) Dickie and Nitzschia frigida Grunow. Under the ice the diatom Achnanthes taeniata Grunow and the dinoflagellate Peridiniella catenata (Levander) Balech were dominant. Calculations of sinking rates and residence times of the dominant ice algal species in the photic water column indicated that only one ice algal species (Chaetoceros wighamii) had a seeding effect on the water column: this diatom dominated the spring phytoplankton bloom in the water together with Achnanthes taeniata and Peridiniella catenata. Received: 9 May 1997 / Accepted: 15 February 1998     

Dynamics of ice algae and phytoplankton in Frobisher Bay

Summary Vertical and seasonal variations of ice algae and phytoplankton were studied in relation to their physico-chemical environments in Frobisher Bay from 1979 to 1986. The biomass, estimated by both chlorophyll a concentrations and cell counts, was greater in the ice algae than in the phytoplankton in the underlying sea-water during winter and spring. Algal distribution in the sea ice varied vertically and seasonally, while in the underlying water column the phytoplankton distribution was much less variable. The ice algal bloom occurred at the bottom of the ice, particularly in the lower 5 cm during late spring, while the phytoplankton bloom took place at depths between 1 and 10 m during early summer after the ice bloom was over. The community structure of the ice algae changed from pennate to centric diatoms as the ice melted. The centrics dominated through the fall, and then decreased as the pennates increased in dominance when the ice formed again in winter. Species diversity and number were greater in the sea ice than in the seawater, but they were similar vertically within each habitat. The evenness of the species distribution did not vary with ice thickness or water depth. Species composition, abundance and dominance of ice algae and phytoplankton continually change both vertically and seasonally. The differential abilities of the species to attain maximal growth rates under various environmental conditions may result in species succession. Evidence is given for the major role of environmental factors regulating the dynamics of ice algae and phytoplankton.     

The Response of Antarctic Sea Ice Algae to Changes in pH and CO2

Ocean acidification substantially alters ocean carbon chemistry and hence pH but the effects on sea ice formation and the CO₂ concentration in the enclosed brine channels are unknown. Microbial communities inhabiting sea ice ecosystems currently contribute 10–50% of the annual primary production of polar seas, supporting overwintering zooplankton species, especially Antarctic krill, and seeding spring phytoplankton blooms. Ocean acidification is occurring in all surface waters but the strongest effects will be experienced in polar ecosystems with significant effects on all trophic levels. Brine algae collected from McMurdo Sound (Antarctica) sea ice was incubated in situ under various carbonate chemistry conditions. The carbon chemistry was manipulated with acid, bicarbonate and bases to produce a pCO₂ and pH range from 238 to 6066 µatm and 7.19 to 8.66, respectively. Elevated pCO₂ positively affected the growth rate of the brine algal community, dominated by the unique ice dinoflagellate, Polarella glacialis. Growth rates were significantly reduced when pH dropped below 7.6. However, when the pH was held constant and the pCO₂ increased, growth rates of the brine algae increased by more than 20% and showed no decline at pCO₂ values more than five times current ambient levels. We suggest that projected increases in seawater pCO₂, associated with OA, will not adversely impact brine algal communities.     

Stimulation of phytoplankton photosynthesis by bottom-ice extracts in the Arctic

Chlorophyll-specific photosynthetic rates of marine phytoplankton collected under landfast sea ice in the Canadian Arctic were stimulated by additions of a chelator, ethylenediamine tetra-acetic acid (EDTA), and trace metals. This stimulation was imitated by filtered extracts of bottom ice colonized by sea-ice algae. Compared to controls, the assimilation rates for experimental additions averaged 166%, 184%, and 119% for ETDA, trace metals, and ice extracts, respectively. All experimental treatments displayed similar oscillations consistent with tidal forcing where mixing and photosynthetic performance are enhanced during spring tides. These results suggest that some bioactive soluble material(s) produced within the bottom-ice algal layer acts as a "conditioning" agent that enhances the growth of phytoplankton in arctic waters. The bioactive agent(s) remains unidentified.     

Cumulative solar irradiance and potential large-scale sea ice algae distribution off East Antarctica (30°E–150°E)

We present a computational model of the large-scale cumulative light exposure of sea ice in the Southern Ocean off East Antarctica (30°E–150°E). The model uses remotely sensed or modelled sea ice concentration, snow depth over sea ice, and solar irradiance data, and tracks sea ice motion over the season of interest in order to calculate the cumulative exposure of the ice field to photosynthetically active radiation (PAR). Light is the limiting factor to sea ice algal growth over winter and early spring, and so the results have implications for the estimation of algal biomass in East Antarctica. The model results indicate that highly light-exposed ice is restricted to within a few degrees of the coast in the eastern part of the study region, but extends much further north in the 30°E–100°E sector. The relative influences of sea ice motion, solar flux, and snow depth variations on interannual variations in model predictions were evaluated. The model estimates of cumulative PAR were found to correlate with satellite estimates of subsequent open-water chlorophyll-a concentration, consistent with the notion that sea ice algae can provide inocula for phytoplankton blooms.     

Removal of snow cover inhibits spring growth of Arctic ice algae through physiological and behavioral effects

The snow cover of Arctic sea ice has recently decreased, and climate models forecast that this will continue and even increase in future. We therefore tested the effect of snow cover on the optical properties of sea ice and the biomass, photobiology, and species composition of sea ice algae at Kangerlussuaq, West Greenland, during March 2011, using a snow-clearance experiment. Sea ice algae in areas cleared of snow was compared with control areas, using imaging variable fluorescence of photosystem II in intact, unthawed ice sections. The study coincided with the onset of spring growth of ice algae, mainly an increase in two pennate diatoms (Achnanthes taeniata and Navicula directa), as temperature increased and ice thickness and brine volume stabilized. The increase in biomass was accompanied by an increase in minimum variable fluorescence (F _o) and the maximum quantum yield of PSII (F _v /F _m) and filling of brine channels with fluorescing cells. In contrast, in the minus snow area, PAR transmittance increased sixfold and there was an exponential decrease in chl-a and no increase in F _o, and the area of fluorescing biomass declined to become undetectable. This study suggests that the onset of the spring bloom is predominantly due to temperature effects on brine channel volume, and that the algal decline after snow removal was primarily due to emigration rather than photodamage.     

Pan‐Arctic sea ice‐algal chl a biomass and suitable habitat are largely underestimated for multiyear ice

There is mounting evidence that multiyear ice (MYI) is a unique component of the Arctic Ocean and may play a more important ecological role than previously assumed. This study improves our understanding of the potential of MYI as a suitable habitat for sea ice algae on a pan‐Arctic scale. We sampled sea ice cores from MYI and first‐year sea ice (FYI) within the Lincoln Sea during four consecutive spring seasons. This included four MYI hummocks with a mean chl a biomass of 2.0 mg/m², a value significantly higher than FYI and MYI refrozen ponds. Our results support the hypothesis that MYI hummocks can host substantial ice‐algal biomass and represent a reliable ice‐algal habitat due to the (quasi‐) permanent low‐snow surface of these features. We identified an ice‐algal habitat threshold value for calculated light transmittance of 0.014%. Ice classes and coverage of suitable ice‐algal habitat were determined from snow and ice surveys. These ice classes and associated coverage of suitable habitat were applied to pan‐Arctic CryoSat‐2 snow and ice thickness data products. This habitat classification accounted for the variability of the snow and ice properties and showed an areal coverage of suitable ice‐algal habitat within the MYI‐covered region of 0.54 million km² (8.5% of total ice area). This is 27 times greater than the areal coverage of 0.02 million km² (0.3% of total ice area) determined using the conventional block‐model classification, which assigns single‐parameter values to each grid cell and does not account for subgrid cell variability. This emphasizes the importance of accounting for variable snow and ice conditions in all sea ice studies. Furthermore, our results indicate the loss of MYI will also mean the loss of reliable ice‐algal habitat during spring when food is sparse and many organisms depend on ice‐algae.     

Trophic relationships of the sea ice meiofauna in Frobisher Bay,Arctic Canada

Summary A distinct fauna consisting mainly of nematodes, harpacticoid and cyclopoid copepods, rotifers, turbellarians and polychaete larvae, inhabits the lower levels of the sea ice in Frobisher Bay. Similar faunas are found throughout circumpolar regions. Thirteen taxa of the Frobisher Bay ice fauna were entirely herbivorous. Their food consisted of 26 genera of algae dominated by Chlamydomonas, Nitzschia, Navicula and Chaetoceros. There was a clear tendency to feed on the most abundant ice algae, hence little evidence of selective feeding. High algal food concentrations in the ice (estimated at 5000 g C/l) were in sharp contrast with the scant nourishment available from phytoplankton under the ice (8 g C/l) from mid-winter until the start of the summer bloom. Algal stocks and estimated productivity rates indicate that ice meiofaunal food requirements may be met by the ice algae. All the major ice meiofaunal species are well adapted to feeding within the ice. All are small enough to enter brine channels and secure particulate prey from surfaces within confined spaces. The ice meiofaunal species are major consumers of the ice algae and therefore important links in the transfer of energy from the ice to pelagic and benthic predators, including fishes, birds and mammals.     

Aggregation of algae released from melting sea ice: implications for seeding and sedimentation

Summary Factors influencing the fate of ice algae released from melting sea ice were studied during a R V Polarstern cruise (EPOS Leg 2) to the northwestern Weddell Sea. The large-scale phytoplankton distribution patterns across the receding ice edge and small-scale profiling of the water column adjacent to melting ice floes indicated marked patchiness on both scales. The contribution of typical ice algae to the phytoplankton was not significant. In experiments simulating the conditions during sea ice melting, ice algae revealed a strong propensity to form aggregates. Differences in the aggregation potential were found for algal assemblages collected from the ice interior and the infiltration layer. Although all algal species collected from the ice were also found in aggregates, the species composition of dispersed and aggregated algae differed significantly. Aggregates were of a characteristic structure consisting of monospecific microaggregates which are likely to have formed in the minute brine pockets and channels within the ice. Sinking rates of aggregates were three orders of magnitude higher than those of dispersed ice algae. These observations, combined with the negligible seeding effect of ice algae found during this study, suggest that ice algae released from the melting sea ice are subject to rapid sedimentation. High grazing pressure at the ice edge of the investigation area is another factor eliminating ice algae released during melting.Data presented here were collected during the European Polarstern Study (EPOS) sponsored by the European Science Foundation     

The diversity,abundance and fate of ice algae and phytoplankton in the Bering Sea

Despite being an essential part of the marine food web during periods of ice cover, sea ice algae have not been studied in any detail in the Bering Sea. In this study, we investigated the diversity, abundance and ultimate fate of ice algae in the Bering Sea using sea ice, water and sub-ice sediment trap samples collected during two spring periods in 2008 and 2009: ice growth (March–mid-April) and ice melt (mid-April–May). The total ice algal species inventory included 68 species, dominated by typical Arctic ice algal diatom taxa. Only three species were determined from the water samples; we interpret the strong overlap in species as seeding of algal cells from the sea ice. Algal abundances in the ice exceeded 10⁷ cells l^?1 in the bottom 2-cm layer and were on average three orders of magnitude higher than in the water column. The vertical flux of algal cells beneath the ice during the period of ice melt (>10⁸ cells m^?2 day^?1) exceeded export during the ice growth period by one order of magnitude; the vertical flux during both periods can only be sustained by the release of algae from the ice. Differences in the relative species proportions of algae among sample types indicated that the fate of the released ice algae was species specific, with some taxa contributing to seeding in the water column, while other taxa were preferentially exported.     

The sub-ice algal community in the Chukchi sea: large- and small-scale patterns of abundance based on images from a remotely operated vehicle

We examined the sub-ice algal community in the Chukchi Sea during June 1998 using a remotely operated vehicle (ROV). Ice algae were observed on the under-ice surface at all ten stations (from 70°29′N to 72°26′N; 162°00′W to 153°56′W) and varied in abundance and distribution from small aggregations limited to depressions in the ice to nets, curtains and strands of Melosira. There was no relationship between percent cover of sub-ice algae and physical factors at the kilometer scale, but at the scale of individual ice floes the percent cover of sub-ice algae was positively correlated with distance from the floe edge and negatively correlated with snow depth. A significant positive relationship between the concentration of sediment pigments and percent cover of sub-ice could indicate a coupling between ice algal and benthic systems. Pieces of ice algae that appeared to be Melosira were observed on the seafloor to a depth of over 100 m and cells or spores of obligate ice algal taxa were collected from sediments from 44-m to 1,000-m deep. The large biomass of sub-ice algae observed at many stations in the Chukchi Sea and the presence of ice algae on the seafloor indicates that the distribution and abundance of sub-ice algae needs to be understood if we are to evaluate the role of ice algae in the Arctic marine ecosystem.     

Characteristics of two distinct high-light acclimated algal communities during advanced stages of sea ice melt

Biological characteristics of ice-associated algal communities were studied in Darnley Bay (western Canadian Arctic) during a 2-week period in July 2008 when the landfast ice cover had reached an advanced stage of melt. We found two distinct and separate algal communities: (1) an interior ice community confined to brine channel networks beneath white ice covers; and (2) an ice melt water community in the brackish waters of both surface melt ponds and the layer immediately below the ice cover. Both communities reached maximum chlorophyll?a concentrations of about 2.5?mg?m^?3, but with diatoms dominating the interior ice while flagellates dominated the melt water community. The microflora of each community was diverse, containing both unique and shared algal species, the latter suggesting an initial seeding of the ice melt water by the bottom ice community. Absorption characteristics of the algae indicated the presence of mycosporine-like amino acids (MAAs) and carotenoid pigments as a photoprotective strategy against being confined to high-light near-surface layers. Although likely not contributing substantially to total annual primary production, these ice-associated communities may play an important ecological role in the Arctic marine ecosystem, supplying an accessible and stable food source to higher trophic levels during the period of ice melt.     

Life strategy and diet of Calanus glacialis during the winter�Cspring transition in Amundsen Gulf, south-eastern Beaufort Sea

The copepod Calanus glacialis plays a key role in the lipid-based energy flux in Arctic shelf seas. By utilizing both ice algae and phytoplankton, this species is able to extend its growth season considerably in these seasonally ice-covered seas. This study investigated the impacts of the variability in timing and extent of the ice algal bloom on the reproduction and population success of C. glacialis. The vertical distribution, reproduction, amount of storage lipids, stable isotopes, fatty acid and fatty alcohol composition of C. glacialis were assessed during the Circumpolar Flaw Lead System Study. Data were collected in the Amundsen Gulf, south-eastern Beaufort Sea, from January to July 2008 with the core-sampling from March to April. The reduction in sea ice thickness and coverage observed in the Amundsen Gulf in 2007 and 2008 affected the life strategy and reproduction of C. glacialis. Developmental stages CIII and CIV dominated the overwintering population, which resulted in the presence of very few CV and females during spring 2008. Spawning began at the peak of the ice algal bloom that preceded the precocious May ice break-up. Although the main recruitment may have occurred later in the season, low abundance of females combined with a potential mismatch between egg production/development to the first feeding stage and phytoplankton bloom resulted in low recruitment of C. glacialis in the early summer of 2008.     

The Contributions of Sea Ice Algae to Antarctic Marine Primary Production

The seasonally ice-covered regions of the Southern Ocean havedistinctive ecological systems due to the growth of microalgaein sea ice. Although sea ice microalgal production is exceededby phytoplankton production on an annual basis in most offshoreregions of the Southern Ocean, blooms of sea ice algae differconsiderably from the phytoplankton in terms of timing and distribution.Thus sea ice algae provide food resources for higher trophiclevel organisms in seasons and regions where water column biologicalproduction is low or negligible. A flux of biogenic materialfrom sea ice to the water column and benthos follows ice melt,and some of the algal species are known to occur in ensuingphytoplankton blooms. A review of algal species in pack iceand offshore plankton showed that dominance is common for threespecies: Phaeocystis antarctica, Fragilariopsis cylindrus andFragilariopsis curta. The degree to which dominance by thesespecies is a product of successional processes in sea ice communitiescould be an important in determining their biogeochemical contributionto the Southern Ocean and their ability to seed blooms in marginalice zones.     

Effects of snow removal and algal photoacclimation on growth and export of ice algae

Net growth of ice algae in response to changes in overlying snow cover was studied after manipulating snow thickness on land-fast, Arctic sea ice. Parallel laboratory experiments measured the effect of changing irradiance on growth rate of the ice diatom, Nitzschia frigida. After complete removal of thick snow (≥9 cm), in situ ice algae biomass declined (over 7–12 days), while removal of thin snow layers (4–5 cm), or partial snow removal, increased net algal growth. Ice bottom ablation sometimes followed snow removal, but did not always result in net loss of algae. Similarly, in laboratory experiments, small increases in irradiance increased algal growth rate, while greater light shifts suppressed growth for 3–6 days. However, N. frigida could acclimate to relatively high irradiance (110 μmol photons m² s⁻¹). The results suggest that algal loss following removal of a thick snow layer was due to the combination of photoinhibition and bottom ablation. The smaller relative increase in irradiance after removal of thin or partial snow layers allowed algae to maintain high specific-growth rates that compensated for loss from physical mechanisms. Thus, the response of ice algae to snow loss depends both on the amount of change in snow depth and algal photophysiology. The complex response of ice algae growth and export loss to frequently changing snow fields may contribute to horizontal and temporal patchiness of ecologically and biogeochemically important variables in sea ice and should be considered in predictions of how climate change will affect Arctic marine ecosystems.     

Sea ice phenology and timing of primary production pulses in the Arctic Ocean

Arctic organisms are adapted to the strong seasonality of environmental forcing. A small timing mismatch between biological processes and the environment could potentially have significant consequences for the entire food web. Climate warming causes shrinking ice coverage and earlier ice retreat in the Arctic, which is likely to change the timing of primary production. In this study, we test predictions on the interactions among sea ice phenology and production timing of ice algae and pelagic phytoplankton. We do so using the following (1) a synthesis of available satellite observation data; and (2) the application of a coupled ice‐ocean ecosystem model. The data and model results suggest that, over a large portion of the Arctic marginal seas, the timing variability in ice retreat at a specific location has a strong impact on the timing variability in pelagic phytoplankton peaks, but weak or no impact on the timing of ice‐algae peaks in those regions. The model predicts latitudinal and regional differences in the timing of ice algae biomass peak (varying from April to May) and the time lags between ice algae and pelagic phytoplankton peaks (varying from 45 to 90 days). The correlation between the time lag and ice retreat is significant in areas where ice retreat has no significant impact on ice‐algae peak timing, suggesting that changes in pelagic phytoplankton peak timing control the variability in time lags. Phenological variability in primary production is likely to have consequences for higher trophic levels, particularly for the zooplankton grazers, whose main food source is composed of the dually pulsed algae production of the Arctic.     

Integrated abundance and biomass of sympagic meiofauna in Arctic and Antarctic pack ice

The abundance and biomass of sympagic meiofauna were studied during three cruises to the Antarctic and one summer expedition to the central Arctic Ocean. Ice samples were collected by ice coring and algal pigment concentrations and meiofauna abundances were determined for entire cores. Median meiofauna abundances for the expeditions ranged from 4.4 to 139.5 × 10³ organisms m⁻² in Antarctic sea ice and accounted for 40.6 × 10³ organisms m⁻² in Arctic multi-year sea ice. While most taxa (ciliates, foraminifers, turbellarians, crustaceans) were common in both Arctic and Antarctic sea ice, nematodes and rotifers occurred only in the Arctic. Based on the calculated biomass, the potential meiofauna ingestion rates were determined by applying an allometric model. For both hemispheres, daily and yearly potential ingestion rates were below the production values of the ice algal communities, pointing towards non-limited feeding conditions for ice meiofauna year-round. Accepted: 29 March 1999