INTRODUCTION

1. INTRODUCTION The Arctic Ocean Expedition 2001 (AOE-01) aimed for a survey of the role of particle and aerosol release in the cloud formation in the Arctic (Figs. 1. & 2.). One of the sub-tasks of the project was to examine what DMS producing algae are present in sea ice, their abundance, and location in the ice cover during the arctic summer and early fall. MATERIAL AND METHODS Ice cores were drilled along the entire ice-covered cruise track. Cores were processed for analysis of bulk salinity, nutrients (tot-N, tot-P, diss-Si) (Fig. 3.), chl-a (Fig. 4.), and species identification and abundance estimates (Fig. 5.) of ice algae. Vertical temperature profile (Fig. 6.) and ice depth were measured on field. Station drift 4 is chosen as a typical ice habitat in this study. Ice algae and cloud formation in the Arctic in summer-fall 2001 – first resultsJohanna Ikävalko, Finn. Inst. Mar. Res., Finland Tuomo Roine, Univ. of Helsinki, Finland Fig. 1. Particle release from the water column in the Arctic Fig. 2. AOE-01 cruise track RESULTS Ice bulk salinity varied between 0 to 5,5. The growth of sea ice associated algae was obviously limited by low nutrient concentrations. In Fig. 3., calculated N:P –ratios in ice at station”drift 4” are presented. As the ratio was less or very close to 16:1 (M/l, i.e. 7:1 g/l) – and this was the case in 90% of analyzed ice cores - most N and P was in particulate form. Chl-a concentration at drift stations 1-8 (Fig. 4.) ranged from 0 to approximately 13 g/l of melted sea ice. A peak in chl-a concentration and abundance of ice algae was detected in the bottom layers of the ice cover. This is typical for arctic spring and summer ice, and is caused primarily by better temperature conditions (Fig. 6.), and nutrient availability and exchange close to the water column. Fig. 3. Concentrations (g/l) of tot-N, tot-P, and diss-Si at station “drift 4”. Fig. 4. Concentrations (g/l) of chl-a at stations “drift 1-8”. Fig. 5. Abundance and vertical stratification of ice algae at station “drift 4”. Fig. 6. Vertical temperature profiles at stations “drift 1-8”. DISCUSSION DMS producing algae – mainly diatoms – were present in the arctic ice in summer-fall 2001. Their production is limited by inadequate nutrient availability (N, P, Si) and low temperature. In most cases, ice algae were concentrated in the bottom layers of the ice sheet. To the left is a comparison of chl-a values a) in the water column under ice, b) within ice cover and c) in the Marginal Ice Zone (MIZ) along the cruise track. We can conclude that in ice, diatoms are the main DMS producers, while in the MIZ and open water in general, mainly bloom-forming colonial Phaeocystis wouldbe responsible for DMS production. Furthermore, diatoms in the bottom layers of the ice cover are likely to release DMS into the water column, instead of direct release into the atmosphere. Ice can thus be seen as a barrier element inhibiting, or at least strongly dampening, the DMS release and cloud formation in the Arctic. CHL-A (µg/1000 ml ) a) WATER 0.1-0.5 average 3-5 b) ICE 0.1- ~13average 3-5 c) MARGINAL ICE ZONE (MIZ) average ~150 THANKS TO Swedish Polar Secretariat  Swedish Maritime Adm. & crew onboard IB ”Oden”  Nordic Arctic Research Programme (NARP)  Profs. C. Leck & L. Tranvik & P. Wassmann  Tvärminne Zoological Station, Finland  Drs. J. Paatero & Z. Fleming