(Table 1) Chlorophyll a content and microalgae abundance and biovolume in pack ice in the Bellingshausen Sea

Pack ice in the Bellingshausen Sea contained moderate to high stocks of microalgal biomass (3-10 mg Chl a/m**2) spanning the range of general sea-ice microalgal microhabitats (e.g., bottom, interior and surface) during the International Polar Year (IPY) Sea Ice Mass Balance in the Antarctic (SIMBA) studies. Measurements of irradiance above and beneath the ice as well as optical properties of the microalgae therein demonstrated that absorption of photosynthetically active radiation (PAR) by particulates (microalgae and detritus) had a substantial influence on attenuation of PAR and irradiance transmission in areas with moderate snow covers (0.2-0.3 m) and more moderate effects in areas with low snow cover. Particulates contributed an estimated 25 to 90% of the attenuation coefficients for the first-year sea ice at wavelengths less than 500 nm. Strong ultraviolet radiation (UVR) absorption by particulates was prevalent in the ice habitats where solar radiation was highest - with absorption coefficients by ice algae often being as large as that of the sea ice. Strong UVR-absorption features were associated with an abundance of dinoflagellates and a general lack of diatoms - perhaps suggesting UVR may be influencing the structure of some parts of the sea-ice microbial communities in the pack ice during spring. We also evaluated the time-varying changes in the spectra of under-ice irradiances in the austral spring and showed dynamics associated with changes that could be attributed to coupled changes in the ice thickness (mass balance) and microalgal biomass. All results are indicative of radiation-induced changes in the absorption properties of the pack ice and highlight the non-linear, time-varying, biophysical interactions operating within the Antarctic pack ice ecosystem.

Biological and chemical oceanographic profiles from the equatorial Atlantic

The volume presents planktological and chemical data collected during cruise No. 51 of RV "Meteor" to the equatorial Atlantic (FGGE '79) from February to June 1979. A standard section along the meridian 22° W across the equator was sampled ten times between 2° S and 3° N. Together with a temperature and salinity profile, concentrations of oxygen, nutrients and chlorophyll a were analyzed in water samples down to a depth of 250 m. Solar radiation and light depths were measured for determination of primary productivity of the euphotic zone according to the simulated in situ method. Zooplankton biomass was estimated in 5 depth intervals down to 300 m by means of a multiple opening and closing net equipped with a mesh size of 100 µm.

Vertical microalgae fluxes at the mooring station LOMO-2 over the Lomonosov Ridge in the period from September 15, 1995 till August 16, 1996

The first studies of microalgae fluxes over the Lomonosov Ridge in the northern Laptev Sea were carried out with a sediment trap at the year-long mooring station LOMO-2, installed at 150 m depth from September 15, 1995 to August 16, 1996. These studies demonstrated essential seasonal variations of vertical microalgae flux. It was shown that in summer diverse flora (composed mainly of cryophylic diatoms) growed intensively beneath the permanent ice cover. Strongly pronounced seasonal variations of microalgae growth correlate closely with solar radiation. Exactly during the maximum insolation period, from the middle of July until the end of September, the microalgae flux was hundreds of times higher than that in the rest of the year. Summer values of the microalgae flux over the Lomonosov Ridge in the northern Laptev Sea were similar to those in the Weddell Sea (Antarctic) and exceeded summer flux values in the Norwegian and Greenland Seas and in the St. Anna Trough (northwestern Kara Sea).

Primary production of phytoplankton and chlorophyll a in the southeast Barents Sea in August-September 1998

A study was performed from August 11 to September 3, 1998 in the Pechora Sea, which covered the shallow-water southeastern Barents Sea. Chlorophyll a concentration in the surface layer (C_chls) ranged from 0.08 to 1.15 mg/m**3, while primary production in the water column (C_phs) Varied from 17 to 170 mg C/m**2/day, aver. 75 mg C/m**2/day. Transition from central deep-water (60-190 m) parts of the sea to coastal shallow-water (15-30 m) parts was accompanied by increase of average C_chls values 2.4 times (from 0.21 to 0.51 mg/m**3) and decrease in average C_phs 1.6 times (from 95 to 58 mg C/m**2/day); the latter, in turn, resulted from decrease in thickness of the photosynthetic layer (H_ph) from 55 to 12 m and its relative transparency (H) from 17 to 4 m. This sharp change in H value and absence of a positive feedback between C_chls and C_phs were most probably related to rapid increase in the role of yellow substance and suspended matter in absorption of solar radiation in coastal waters. In sea areas with depths greater than 30 m a deep chlorophyll maximum was observed; at most of stations it located in the 20-35 m deep layer during illumination in photosynthetic active radiation range comprising 0.8-1.5% of its surface value. Parameters of photosynthetic light curves in these regions indicate participation of shade-adapted flora in formation of the deep chlorophyll maximum. In coastal waters characterized by a relatively uniform chlorophyll distribution over the water column no light adaptation of phytoplankton to efficient utilization of low irradiation for photosynthesis was encountered. Thus, a conclusion was made that combination of extremely low values of C_phs and H_ph makes the pelagic ecosystem of the Pechora Sea coastal regions very sensitive to anthropogenic impacts that may increase water turbidity.