Nutrient status of Baltic Sea ice: Evidence for control by snow‐ice formation, ice permeability, and ice algae

Abstract

[1] Samples of land-fast sea ice collected along the Finnish coast of the Baltic Sea, between latitudes 60.2°N and 65.7°N, in January to April 2000 were analyzed for physical, biological, and chemical parameters. Both spatial and temporal variability were investigated. Snow-ice contributed in average a third of the total ice thickness, while the snow fraction (by mass) of the ice was 20% on average. Snow-ice formation increased the nitrogen concentrations substantially, mainly in the upper parts of the ice cover. Phosphorus on the other hand was controlled by biological uptake, with distinct maxima in the bottommost parts of the ice cover. The chlorophyll-a concentrations were dependent on the physical properties of the ice to some extent. In more saline waters the chlorophyll-a concentrations in the ice were variable (1-17 mg l À1 ). However, in the less saline waters of the Bothnian Bay the concentrations were generally considerably lower (<1 mg l À1 ) than elsewhere. This is presumably caused by formation of ice of low salinity, due to the low ambient salinity in the area and the under-ice flow of river waters, and formation of ice that has no habitable space for ice algae. Atmospheric nutrients possibly enhance the magnitude of the ice algae bloom, through downward flushing of surface deposited nutrients during periods when the ice was permeable. We surmise that atmospheric supply of nutrients plays an important role in biological productivity within the Baltic Sea ice sheet and potentially also in under-ice waters.INDEX TERMS: 4845 Oceanography: Biological and Chemical: Nutrients and nutrient cycling; 4805 Oceanography: Biological and Chemical: Biogeochemical cycles (1615); 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; 4504 Oceanography: Physical: Air/ sea interactions (0312); KEYWORDS: sea ice, nutrient dynamics, atmospheric nutrient deposition, deposition, sea ice algae, Baltic Sea Citation: Granskog, M. A., H. Kaartokallio, and K. Shirasawa, Nutrient status of Baltic Sea ice: Evidence for control by snow-ice formation, ice permeability, and ice algae,

Food web components, and physical and chemical properties of Baltic Sea ice

“…Winter 2000 was milder than the average winters in the study area, air temperature remaining above zero for several days during the first half of January, in mid-February, in early March and again in mid-March (present Fig. 2 and Granskog et al 2003). Warm weather caused ice-sheet warming (Fig.…”

“…New ice formed in the middle of the bay in late January, and the sampling point was moved; at the first mid-bay sampling (25 January) ice thickness was 13 cm, increasing to a maximum of 27 cm in late February. Ice deterioration began in late March and the Granskog et al 2003) ice disappeared in mid-April. During the entire study period, the ice was only occasionally covered with a thin snow layer.…”

“…After a major drop in ice salinity on 22 February salinity in the lower ice increased again from 8 to 14 March. The effect of weather conditions on the physical properties of ice is discussed in detail in Granskog et al (2003).…”

“…In addition, temperature-dependent changes in brine-channel morphology and brine transport processes may be crucial factors shaping the ice-organism community structure and functioning (Gradinger et al 1992, Krembs et al 2000. Reported measured brine salinity values from Baltic sea ice range between 6 and 30 psu (Ikävalko & Thomsen 1997, Mock et al 1997, Kaartokallio 2001) and brine salinity can fluctuate rapidly (Granskog et al 2003) as ice temperature changes. Brine salinity is lower than in polar seas; the reported median value for calculated brine salinity of Baltic sea ice is 10.1 (Meiners et al 2002) and for measured brine salinity 7.9 psu (recalculated from data presented in Kaartokallio 2001).…”

“…Gradinger et al 1992, Fritsen et al 1994, Hudier & Ingram 1994 and experimental systems (Krembs et al 2000(Krembs et al , 2001 suggest a close coupling between physical and chemical properties of the ice and biological processes occurring in the ice. The temperature in thin ice changes rapidly along with air temperature (Krembs et al 2001, Granskog et al 2003 and variables that are dependent on ice temperature, such as brine salinity, concentrations of dissolved constituents and available surfaces inside the brine-channel system, can fluctuate over short timescales. In addition, temperature-dependent changes in brine-channel morphology and brine transport processes may be crucial factors shaping the ice-organism community structure and functioning (Gradinger et al 1992, Krembs et al 2000.…”