The spectral distribution of light beneath first‐year sea ice in the Arctic Ocean1

Changes in spectral irrad~ance beneath annual sea ice were measured during the development of sea ice microalgal communities in McMurdo Sound, Antarctica. Five different light regimes were initially estabhshed by varying surface snow cover on 10 m X 10 m sea ice quadrats. The presence of ice algae in quadrats w t h 6 5 cm snow cover was indicated by a spectral shift with increased attenuation between 400 and 550 nm and at 671 nm, wavelengths absorbed by diatom pigments. Snow cover had a profound effect on both the rate of community development and community loss by ice ablation. A simple model of factors determining changes in ice algal biomass is described.

Section: Resultsmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 94%

Sea ice microbial communities. VII. Changes in under-ice spectral irradiance during the development of Antarctic sea ice microalgal communities

Palmisano¹,

SooHoo²,

Moe³

et al. 1987

“…The under-ice irradiance (I,) and the chlorophyll a concentrations were determined as described above. Microalgal photosynthetic rates versus irradiance were measured using an incubator described by Lewis & Smith (1983), under the light transmitted through commercial plexiglass, in order to simulate the light conditions prevailing under the ice (light predominantly blue-green : Maykut & Grenfell 1975). Photosynthetic parameters, normalized per unit chlorophyll a, were estimated according to the equations of Platt et al (1980) using a Gauss-Newton algorithm (Jennrich & Sampson 1968).…”

Section: Methodsmentioning

confidence: 99%

Physical control of the horizontal patchiness of sea-ice microalgae

Gosselin¹,

Legendre²,

Therriault³

et al. 1986

149

100

Factors controlling the horizontal distribution of sea-ice microalgae were studied in Southeastern Hudson Bay and adjacent Manitounuk Sound (Canadian Arctic). Both large (-30 km) and small (0.3 to 500m) scales of variability were investigated. Results showed that salinity was the most important factor controlling large scale distribution of the ice-microalgal biomass, through its effect on the structure of the ice (surface available for colonization). Variation in the thickness of the snow-ice cover, which determines irradiance at the bottom of the ice, was the factor controlling distribution of the algal biomass at smaller scale (diameter of patches of microalgal biomass ranging between 20 and 90 m). The relation between ice-algal abundance and snow-ice thickness changed however over the season. At the beginning of the growing season (in April when the bottom-ice irradiance was higher than a minimum critical irradiance), maximum algal biomass was observed under areas covered by the smallest snow depths. Towards the end of the season, when light transmitted through the snow-lce cover increased, maximum algal biomass was observed under areas covered by the deepest snow. This suggests that ice algae have both minimum and maximum critical light levels. The minimum level is the irradiance below which there is no photosynthetic activity (Imi, -7.6 CL Einst m-2 S-') and the maximum level corresponds to the inhibiting light intensity, which may vary during the growth season. The horizontal heterogeneity of the snow-ice cover, whlch is influenced by wind at the air-ice interface, thus provides diversified bottom-ice habitats where irradiance is compatible or not with the physiological limits of the ice microalgals cells. This results in a strong patchiness in distribution of ice-bottom microalgae.

“…Total daily irradiances and oblique sun angle limit both the irradiance and photoperiod within the water column (Kirk 1983, Sakshaug & Holm-Hansen 1984. Ice cover, which is at its seasonal maximum, diminishes wind driven mixing (Carmack 1986), alters the heat flux out of the ocean (Maykut 1986), and has a high albedo that limits available irradiance and alters its spectral quality in the underlying waters (Maykut & Grenfell 1975, Palmisano et al 1987, Arrigo et al 1991. These factors are expected to have a profound seasonal influence on microbial rates and processes both in open-water and in the water column underneath the ice.…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of bacterioplankton biomass and production in the marginal ice-edge zone of the Weddell-Scotia Sea during austral winter

Cw¹,

Dm²,

Cw³

1995

Recent investigations in the marginal ice-edge zone (MIZ) of the western Weddell and Scotia Seas revealed similar distributions of primary and microbial production in spring and autumn. Yet, little is known about the distributions of bacterial biomass and production in winter, and how these distributions may be influenced by local physical oceanographic features or interrelated to other chemical and biological distributions in the M1Z. To help elucidate the ecological and biogeochemical significance of bacterial production in winter, we examined the distributions of bacterial biomass and production in the MIZ of the Weddell-Scotia Sea in austral w~nter 1988 as part of the Antarctic Marine Ecosystem Research at the Ice-edge Zone (AMERIEZ) program. Measurements were made along 3 rapid transects providing a synoptic view of the MIZ. Transects were oriented normal to the ice edge with stations extending up to 100 km into the pack and several hundred km seaward of the ice edge. Winter distributions of bacterial biomass and production were more closely related to local hydrography than to microalgal distributions or the proximity of the ice edge Bacterial characteristics were highest within or in the proximity of warm-core eddies, enrichments which may have resulted from prior ice melt or from advection of more productive waters. Microalgal characteristics and bacterial production were at their seasonal minimum during the winter cruise; however, bacterial biomass was essentially invariant seasonally and was not as greatly influenced by the location of the ice edge as previously demonstrated for phytoplankton. Sirmlar reports for micrograzers suggest that steady-state conditions apply to much of the microbial food web throughout the year. Bacterial production did not dominate ammonium remineralization processes in winter; instead, ammonium maxima under the ice and near the ice edge were attributed to protozooplankton and higher trophic organisms.