A mesocosm study of physical-biological interactions in artificial sea ice: effects of brine channel surface evolution and brine movement on algal biomass

The impact of changing physico-chemical boundary conditions in sea ice on b iological processes was investigated during a 20-day-long simulated freeze- melt cycle in an 180-m(3) mesocosm filled with artificial seawater and addi tion of a mixed Arctic sea-ice community. Ice formation started at T-air of -15 degreesC with a growth rate of 0.7-1.2 mm h(-1) for 10 days. The last 10 days (T-air of= -5 degreesC), ice thickness remained around 20 cm. Ice t emperature gradients inside the ice were linear and determined brine salini ties. Brine was collected by means of centrifugation and its volume ranged from 5 to 30% of total ice volume. Surface areas of interconnected brine ch annels were determined with two similar techniques and maximum values range d between 1.5 and 4.8 m(2) kg(-1)ice. Measurements determined with a modifi ed method varied considerably and differed by a maximal factor of 2.0-6.5. Brine channel surfaces increased during the experiment as a result of the w arming of the ice. The inoculated algal community was dominated by flagella tes < 10 mum. The low diatom biomass increased in the ice after the air tem perature rise with rates comparable to field data (mu =0.2-0.3 day(-1)). Co mparison with brine salinities points towards the hypothesis of vertical br ine stability being a controlling factor for ice algal growth. We infer fro m brine channel surface measurements that persistence of brine channel surf aces during spring might be an important prerequisite for the commencement of net diatom biomass accumulation. Advantages and limitations of mesoscale mesocosms as alternatives in ice biological work are discussed.