Photoadaptation of sea-ice microalgae in springtime: photosynthesis and carboxylating enzymes

The physiological responses of a small unicellular Chaetoceros species, isolated from the Weddell Sea, Antarctica, to changes in temperature, salinity and irradiance simulating those that occur during new-ice formation were investigated. The combination of increased salinity, increased quantum irradiance and decreased temperature significantly reduced growth and photosynthetic rates compared to the control, although cellular metabolism was not inhibited. The cells retained the capacity to photoacclimate, which was observed in the variations in cellular chlorophyll a concentrations and carbon allocation patterns. In terms of photosynthesis, a doubling of quantum irradiance apparently compensated for the adverse effects of increased salinity and lowered temperature. It is thus hypothesized that at least some species of the late season phytoplankton population survive incorporation into ice and continue to photosynthesize and grow under the extreme conditions encountered during sea-ice formation. This potentially prolonges the Antarctic vegetation period well into late austral autumn and winter, enhancing the total primary production available for higher trophic levels.

Section: Cell Counts and Chl A Concentrationssupporting

confidence: 66%

Physiological responses of a small Antarctic diatom (Chaetoceros sp.) to simulated environmental constraints associated with sea-ice formation

Gleitz¹,

Thomas²

1992

“…Cota et al (1988) and Priscu et al (1990), by contrast, did detect a light-dependent response of NO3-and NH4' uptake in antarctic ice algae, although uptake in the dark was significant and saturation light intensities were near ambient as is characteristic of the photosynthetic response of sea ice algae in both polar oceans (e.g. Cota 1985, Palmisano et al 1985, Michel et al 1988.…”

Section: Discussionmentioning

confidence: 97%

“…Most work has focussed on the photoautotrophs (sea-ice algae) and has largely concentrated on their photosynthetic, biochemical and growth response to light (e.g. Cota 1985, Palmisano et al 1985, Smith et al 1987, 1989b, Michel et al 1988) although the effects of other physical and chemical properties of their environment (e.g. temperature, salinity, tidal mixing) have been investigated (e.g.…”

Section: Introductionmentioning

confidence: 99%

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

Harrison¹,

Cota²,

Smith³

1990

Studies of the utilization of inorganic nitrogen (NO3-, NH,+) by sea-ice algal communities were conducted durinq 2 field seasons in Barrow Strait, Northwest Territories (NWTI, Canada. Results showed a significant temporal shift from NO3--dominated metabolism during the early stages of algal biomass accumulat~on under the ice to NHa+-dominated metabolism later on when biomass was in decline. Volume-based uptake rates of both nitrogen compounds were 2 to 3 orders of magnitude higher (1 to 80 pm01 N 1-' h-') than rates typical for coastal plankton populations but so were biomass levels (4 to 18 mg chlorophyll a I-') and interstitial nitrogen concentrations (NO3-:4 to 123 &m01 N I-', NH4+ : 4 to 40 pm01 N 1-'). Ammonium was utilized preferentially as is generally the case in planktonic systems. Despite high concentrations, however, NH4+ apparently had little inhibitory effect on the activity of the NO3-assimilatory enzyme, nitrate reductase (NR), at least during the early stages of ice-algal growth.Complementary physiological experiments camed out during this same period showed (1) concentration-dependent nitrogen uptake kinetics (K,) for these communities were similar to values seen in coastal plankton. (2) no apparent light-dependence of NO3-or NH,+ uptake was evident in short-term experiments. (3) organic nitrogen (urea, amino acids) may represent a significant portion of the sea-ice communities' nitrogen nutrition. (4) an important component of the metabolism of NH,+ and amino acids may be mediated by prokaryotic microorganisms. Our results, along with several other indirect lines of evidence, support the contention that these sea-ice communities are not nitrogen-limited.

“…The main abiotic parameters controlling algal growth rates are irradiance, nutrients, ice temperature and brine salinity (Gosselin et al 1985, Maestrini et al 1986, Grossi et al 1987, Michel et al 1988, Smith et al 1988, Cota & Sullivan 1990). The high photoacclimation potential of polar phytoplankton and sea-ice algal assemblages enables survival and rapid growth under low-light conditions (Rivkin & Putt 1987, Cota & Sullivan 1990, Gleitz & l r s t 1991, Johnsen & Hegseth 1991).…”

Section: Discussionmentioning

confidence: 99%

Determination of Arctic ice algal production with a new in situ incubation technique

Möck¹,

Gradinger²

1999

105

A new in situ incubation technique was developed to measure primary production in sea ice. This method allows fine-scale measurements In 1 cm thick vertical sections throughout the ice column without severe disruption of ice morphology, geochemistry and light field. Easy handling in the field makes this device usable for all scientists working on sea ice biota. Primary production within first-(FYSI) and multi-year sea-ice (MYSI) cores of the Barents and Greenland Seas was determined during the RV 'Polarstern' cruise ARK XIII/l(a+b). In order to measure algal production, 6 slices of 1 cm thickness were cut off at regular intervals along an Ice core and incubated in sealed glass petn dishes. The incubation chambers and a chamber for dark fixation, together with the remaining sections of the ice core, were placed in an an acrylic-glass barrel of 1 m length, and returned to their original positions inside the core hole for in situ rate determinations. Additional ice cores were drilled to determine ice temperature and nutrient and algal pigment concentrations. The incident photosynthetically active radiat~on (PAR) as well as under ice irradiance was measured Steep gradients in primary production were found throughout the ice floes, with maximum values of 7 7 pg C 1-' h-' in the bottom few centimetres corresponding to the highest concentrations of chlorophyll a (84 pg I-'). Nutrient concentrations in brine varied between ice stations and with ice depth: 0-88.4 pm01 I-' for NH4; 2.2-13.6 pm01 1-' for NO3; 0-0.5 pm01 1-' for NOz; 0-12.4 pm01 l-' for PO,; and 0.2-23.5 pm01 1-' for SiO,. Mean integrated production at the 4 stations (0.76-9 67 mg C n1r2 d-') varied with PAR and total dissolved nitrogen. Integrated production of the ice interior community (more than 5 cm from bottom of floe) was in the same range as or sometimes exceeded production in the bottom community (0-5 cm) of FYSI as well as MYSI. Growth rates of the ice algae ranged from 0.01 to 0.5 d-l. As previous primary production methods were restricted to the study of bottom communities only, we assert that algal primary production in Arctic as well as Antarctic sea ice has been severely underestimated.