Ice Algal Communities Research Articles

Carbon flows through the microbial food web of first-year ice in resolute passage (Canadian High Arctic)

Abstract Ice algal communities are host to thriving populations of microheterotrophs whose trophic role remains poorly understood. We report here an inverse modelling analysis of the microbial food web associated with the spring bloom of ice algae at Resolute Passage in the High Arctic. Carbon flows among microbial components (ice algae, autotrophic and heterotrophic nanoflagellates, microflagellates and ciliates) and their exchanges with particulate and dissolved organic carbon (POC and DOC) were inferred from the observed changes in standing stocks of these compartments between 13 April and 22 May 1992. Calculations were made for three phases of the bloom's development and for two sites under thin and thick snow cover. Observed DOC accumulations within the bottom ice originated largely from the ice algae. However, calculated production rates were too high to result strictly from normal physiological exudation. Mechanical or physiological stresses that disrupt the integrity of the cells and grazing by zooplankton at the ice-water interface may well be involved in this process. Inverse modelling confirmed field and experimental evidence that nanoflagellates may directly assimilate DOC to support their growth. Patterns in trophic flows between sites with thin and thick snow cover were similar. In contrast, trophic interactions changed as the bloom progressed: production of DOC and detritus from the ice algae were the only significant carbon flows during the early phase; bacterivory developed and peaked during the middle phase and was superseded by DOC utilization and herbivory by flagellates and ciliates during the late phase. Only ca. 20% of the DOC produced was utilized by the microheterotrophs. Direct links from DOC and ice algae to protists potentially increase the efficiency of C transfers within the ice-associated microbial food web; on the other hand, low recovery efficiency limits the role of the microbial loop in recycling DOC.

The influence of major inorganic nutrients on the growth and physiology of high arctic ice algae

Abstract A long-term nutrient enrichment bioassay was used to test the hypothesis that silicon is the potential limiting nutrient for growth of bottom ice algae in the Canadian High Arctic and to determine the physiological response of the algae to nutrient deprivation. All measures of algal response (chlorophyll a , particulate organic carbon, cell concentration and carbon allocation) indicated that nitrogen rather than silicon was the principal potential limiting nutrient. Silicon was not present in great excess, however, and significantly influenced the growth of most of the dominant species. Algal growth slowed and ultimately stopped in all treatments except for the combined (P, δi and N) addition. Carbon allocation shifted toward lipid and away from protein as growth was slowed by nutrient depletion, with neutral lipids increasing while membrane-associated lipids declined. There was no evidence of carbon storage in polysaccharides. The biosynthetic response of the algae thus confirmed that nutrient limitation can cause lipid accumulation in ice algal communities.

New measurements of phytoplankton and ice algal production in the Arctic Ocean

During the Canada/U.S. 1994 Arctic Ocean Section, algal biomass (Chlorophyll a) and primary production were measured in the water column, at the ice-water interface and in the bottom 2–4 cm of the sea ice along a transect from the Chukchi Sea to the Nansen Basin via the North Pole. Algal biomass and primary production were determined for 0.7–5 μm and > 5 μm size fractions. The algal release rate of DO14C during incubation was also measured. In the Chukchi Sea and in leads of the Makarov and Nansen Basins, total maximum particulate phytoplankton production rates were 2570, 73 and 521 mg C m−2 day −1, respectively. At these stations, where ice cover varied from 55 to 90%, large phytoplankton (> 5 μm) represented 61–98% of the total algal biomass. At stations with higher ice coverage (>90%), the total phytoplankton production decreased to 9–57 mg C m−2 day −1. At these stations, small phytoplankton (0.7–5 μm) accounted for 59–88% of the total biomass and more than 64% of the total production. Along the transect, the percentage of the total phytoplankton production released as extracellular carbon was generally less than 20%, except in the Canadian Basin where it ranged from 31 to 65%. Total particulate ice algal production ranged from 0.5 to 310 mg C mt-2 day−1 and showed maximum rates in the central Arctic Ocean. Large cells (> 5 μm) generally dominated the ice algal community, representing 50–100% of the total biomass and more than 50% of the total production. Ice algae released on average 34% of total carbon fixed during the 4–12 h incubation. Ice algae contributed on average 57% of the entire primary production (water column + sea ice) in the central Arctic and 3% in the surrounding regions. Total primary productivity in the central Arctic Ocean is estimated at 15 g C m−2 year−1, a value at least 10 times higher than previously reported. The difference between estimates is due in part to the previously unmeasured contribution of the particulate production by ice algae and the release of DOC by both ice and pelagic algae.

IMPACT OF ULTRAVIOLET‐B RADIATION ON PHOTOSYSTEM II ACTIVITY AND ITS RELATIONSHIP TO THE INHIBITION OF CARBON FIXATION RATES FOR ANTARCTIC ICE ALGAE COMMUNITIES1

ABSTRACT One goal of the Icecolors 1993 study was to determine whether or not photosystem II (PSII) was a major target site for photoinhibition by ultraviolet‐B radiation (QUVB, 280–320 nm) in natural communities. Second, the degree to which QUVBinhibition of PSII could account for QUVBeffects on whole cell rates of carbon fixation in phytoplankton was assessed. On 1 October, 1993, at Palmer Station (Antarctica), dense samples of a frazil ice algal community were collected and maintained outdoors in the presence or a bsence of QUVBand l or ultraviolet‐A (QUVB, 320–400 nm) radiation. Samples were then collected at intervals over the day to track the time course of UV inhibition of primary production. The ice algae were assessed for changes in pigment composition and rates of carbon fixation. The quantum yield of PSII (ØIIc°) was measured by Pulse Amplitude Modulated fluorometry. Over the day, ØIIc° declined due to increasing time‐integrated dose exposure of QUVB. The QUVB‐driven inhibition of ØIIc° increased from 4% in the early morning hours to a maximum of 23% at the end of the day. The QUVB photoinhibition of PSII quantum yield did not recover by 6 h after sunset. In contrast, photoinhibition by QUVA and photosynthetically available radiation (QPAR, 400–700 nm) recovered during the late afternoon. Flourescence‐based estimates of carbon fixation rates were linearly correlated (P =0.002, r2=0.45) with measured carbon fixation. Fluorescence overestimated the observed QUVB inhibition in measured carbon fixation rates by 8% in the morning hours; however, the discrepancy increased during the afternoon. Therefore, researchers should be cautious in using fluorescence measurements to infer ultraviolet inhibition for rates of carbon fixation until there is a greater understanding of the coupling of carbon metabolism to PSII activity for natural populations. Despite these current limitations, fluorescence‐based technologies represent powerful tools for studying the impact of the ozone hole on natural populations on spatial/ temporal scales not possible using conventional productivity techniques.

Nitrogen uptake rates in phytoplankton and ice algae in the Barents Sea

Uptake rates of NH4+, NO3? and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a 15N-technique. NO3? was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in situ NO3? uptake rate in the ice algal communities was light-limited The in situ NO3? and NH4? uptake rates in the subsurface chlorophyll maximum were at times light-limited. It is hypothesised that NH4+ may accumulate in low light in the bottom of the euphotic zone and inhibit the in situ NO3? uptake rate.

RATES OF PHOTOADAPTATION IN SEA ICE DIATOMS FROM MCMURDO SOUND, ANTARCTICA1

ABSTRACTSea ice microalgae are released from their relatively stable light environment to the water column seasonally, and any subsequent growth in a vertically mixed water column may depend, in part, on their photoadaptation rates. In this study we followed the time course of photoadaptation in natural sea ice algal communities from bottom ice and surface ice by measuring their photophysiological response to an artificial shift in the ambient irradiance field. Microalgae from under‐ice habitats, were incubated under full sunlight (LL‐HL) and microalgae from surface ice habitats were incubated under artificial light to mimic under‐ice irradiance (HL‐LL). During 3‐ to 4‐day time course studies, opposite shifts in chlorophyll: carbon, α, PBm, and Ik were observed, depending on the direction of the irradiance change. First‐order rate constants (k) ranged from 0.0067 to 0.29 h−1 for photosynthetic parameters, although PBm did not always show a clear change over time. Rates of photoadaptation for ice algae are comparable to k values reported for temperate phytoplankton, suggesting that sea ice algae may be equally capable of adapting to the light conditions experienced in a vertically mixed water column. This study presents the first evidence that sea ice microalgae are physiologically capable of adapting to a planktonic life and thus could serve as a seed population for polar marine phytoplankton blooms.

Nitrogen uptake rates in phytoplankton and ice algae in the Barents Sea

Uptake rates of NH4+, NO3? and dissolved organic nitrogen (urea) were measured in phytoplankton and in ice algae in the Barents Sea using a 15N-technique. NO3? was the most important nitrogen source for the ice algae (f-ratio = 0.92). The in situ irradiances in the subsurface chlorophyll maximum and in the ice algal communities were low. The in situ NO3? uptake rate in the ice algal communities was light-limited The in situ NO3? and NH4? uptake rates in the subsurface chlorophyll maximum were at times light-limited. It is hypothesised that NH4+ may accumulate in low light in the bottom of the euphotic zone and inhibit the in situ NO3? uptake rate.

Nitrogen utilization in ice algal communities of Barrow Strait, Northwest Territories, Canada

Nitrogen utilization in ice algal communities of Barrow Strait, Northwest Territories, Canada

PHOTOSYNTHESIS‐IRRADIANCE RELATIONSHIPS IN SEA ICE MICROALGAE FROM McMURDO SOUND, ANTARCTICA1

ABSTRACTSea ice microalgae in McMurdo Sound, Antarctica were examined for photosynthesis‐irradiance relationships and for the extent and time course of their photoadaptation to a reduction in in situ irradiance. Algae were collected from the bottom centimeter of coarse‐grained congelation ice in an area free of natural snow cover. Photosynthetic rate was determined in short term (1 h) incubations at −2° C over a range of irradiance from 0 to 286 μE·m−2·s−1. Assimilation numbers were consistently below 0.1 mg C·mg chl a−1·h−1. The Ik's3 averaged only 7 μE·m−2·s−1, and photosynthesis was inhibited at irradiances above 25 μE·m−2·s−1.Photosynthetic parameters of the ice algal community were examined over a nine day period following the addition of 4 cm of surface snow while a control area remained snow‐free. A reduction of 40% in PmB relative to the control occurred after two days of snow cover; α, β, Ik, and Im were not significantly altered. Low assimilation numbers and constant standing crop size, however, suggested that the algal bloom may have already reached stationary growth phase, possibly minimizing their photoadaptive response.

A physical mechanism for establishing algal populations in frazil ice

In polar regions ice algal communities are not only conspicuous but may also be important production sites and sources of seed populations for pelagic communities1–3. Except for some studies near land-based stations1,4–7, there are few long-term observations of ice algal populations, and few studies have considered how they form and develop. Most researchers suggest that ice algae are derived from sparse water column assemblages that become trapped during ice formation; ice algal populations then develop through in situ growth1. Some previous observations have suggested that ice crystals forming in the water column concentrate algal cells6–8. Dense algal populations in young sea ice may have been recognized as early as the mid-nineteenth century, since Hooker (cited by Alexander2) described discoloured brash and pancake ice (“ …a pale ochreous colour”). But until now, neither the mechanism for this harvesting nor the effects on the composition of the ice community has been clearly demonstrated. In the Weddell Sea, we have sampled young sea ice discoloured by algae, and we present evidence that the algae were concentrated by a physical mechanism. We explain how such a process may accumulate planktonic forms in ice communities.

Standing crop of algae in the sea ice of the Weddell Sea region

Physical and biological measurements were made of sea ice cores taken fron 68° to 78° S in the Weddell Sea. Fluorescence measurements indicated an algal community that was strongly associated with salinity maxima within the ice. Maximum concentrations of chlorophyll a ranged from 0.31 to 4.54 mg m −3. Comparisons with standing crops in the water column indicate that the standing crop within the ice can represent a minor but significant fraction of the total standing crop for the region. The sea ice algal community is apparently distinct from others that have been described for land-fast ice in McMurdo Sound, sea ice in the Arctic, and pack ice off East Antarctica. The highest concentrations of biological material are found in the bottom or top samples from those regions, whereas the Weddell Sea maxima are concentrated at intermediate depths (0.65 to 2.15 m) within the ice. A qualitative model indicating the relationship between thermally induced brine migration and subsequent algal growth is presented. The model indicates that the distribution of algae within the ice depends on the thermal and physical setting for Weddell Sea pack ice where brine drainage is initiated by spring and summer warming but is not carried through so completely as in other regions. It is concluded that the ecological significance of the release of ice algae is greater for the community in the Weddell Sea than elsewhere.