The influence of seasonal sea ice on the physics of the coastal waters : Gulf of Finland

The Gulf of Finland is located in the seasonal sea ice zone (SSIZ), were sea ice forms in the wintertime and melts in late spring. This seasonality entitles this sea as a key area regarding the impact of climatic changes. When the basin of interest is located at the climatological edge of the SSIZ, there is also high inter-annual variability in the ice conditions. The aim of this study was to examine the influence of the sea ice on the physics of the coastal waters in the Gulf of Finland. Three sites were chosen, two located at each side of Hanko Peninsula, northwest entrance of the Gulf, and one at the estuaries of River Kymijoki, northeast side of the Gulf. Long-term hydrographic and sea ice data were examined in order to study the inter-annual variability and trends of the hydrographic characteristics, heat content, freezing and break-up days and ice thickness during the last century in the coastal zone of the Gulf of Finland. The influence of the seasonal sea ice on the physics of the water body hydrography, circulation, atmosphere-ocean interaction was evaluated. The results showed significant decrease of the ice season length by almost 30 days in the last century. The maximum annual sea ice thickness decreased by 8 cm in the last 40 years. In the last 85 years, surface water temperature increased by 1 ˚C and surface salinity increased by 0.5 PSU. The water body stratification in the coastal zone was strongly affected by the limited wind mixing in the wintertime. The circulation under ice became weaker by almost 1 cm s-1. The ice cover was a good control measure of the net surface heat exchange. Solar radiation had a strong seasonal cycle with monthly maximum at 160 W m-2 and minimum below 10 W m-2. Terrestrial radiation was mostly between 40 and 60 W m-2. Latent heat exchange was much more important than sensible heat exchange, similar to the net terrestrial radiation values in summer and autumn

Interannual variability and trends in winter weather and snow conditions in Finnish Lapland

The interannual variability of the air temperature, precipitation and snow conditions were examined in the Finnish Arctic region based on data from the period 1946-2012. The purpose of this work was to describe the climatology of the region and to examine long-term variations in the climatic parameters. This information is essential for both environmental and socioeconomic aspects of the Finnish Arctic region. The air temperature, precipitation and snow depth records from nine weather stations were analysed in order to study the evolution of the winter duration (sub-zero temperature days), precipitation, snow cover duration and snow depth. The climatological description was based on the most recent 30-year period record available (1982-2011). Since 1946, air temperature has increased significantly by 0.4 degrees C/decade. Significant precipitation trends reached up to 35 mm/decade. For the most part there were no significant trends in snow depth and snow cover duration.Peer reviewe

Seasonal and annual heat budgets offshore the Hanko Peninsula, Gulf of Finland

Peer reviewe

Simulation and Seasonal Characteristics of the Intra-Annual Heat Exchange Process in a Shallow Ice-Covered Lake

The intra-annual heat exchange process has a considerable influence on the energy circulation, material metabolism, and ecological succession of lakes. The input and output of heat in an ice-covered lake provide the basic dynamic force driving changes in the biochemical state of the lake. Based on the heat balance between the lake surface and the atmosphere, we established a thermodynamic model for calculating the thermodynamic factors of shallow inland lakes during the ice and open seasons. The data of the Ulansuhai Lake, Inner Mongolia, from two years (2012 and 2013) are used to analyze the seasonal characteristics and associated influences of the heat budget on the ecosystem. The results indicated that the monthly mean lake temperature over the past 10 years was 1.7–2.2 °C lower than in the previous 50 years. The absorbed solar radiation reached up to 210 W/m2 in 2012 and 179 W/m2 in 2013, and there were clear differences in the heat budget between the ice-covered and open seasons. The mean net heat fluxes in the ice season were −33.8 and −38.5 W/m2 in 2012 and 2013, respectively; while in the open season water, these fluxes were 62.5 and 19.1 W/m2. In the simulations, the wind was an important factor for intensive evaporation in summer and the main driver of the ice cover formation patterns in winter, involving the transmission and diffusion of material and energy in the lake. The results provide a theoretical foundation for simulating ice cover growth and ablation processes in shallow lakes. They also present data on the ecological evolution in these lacustrine environments

Influence of landfast ice on the hydrography and circulation of the Baltic Sea coastal zone

The influence of landfast ice on hydrography and circulation is examined inSantala Bay, adjacent to the Hanko Peninsula, Gulf of Finland. Three-dimensionalelectromagnetic current meters and conductivity-temperature-depth (CTD) sensorswere deployed in winters 1999-2000 and 2000-2001 during the Finnish-Japanese"Hanko 9012" experiment. In each winter, data collection started one month beforethe initial ice formation and lasted until one month after the ice had meltedcompletely. Temperature and salinity are compared with long-term data from theTvärminne Zoological Station, also located on the Hanko Peninsula. Thewater temperature was 2°C less than the long-term average. Iceformation and melting show up in the salinity evolution of the water body,which makes salinity a good indicator of ice formation and breakup in SantalaBay. The circulation under the ice became weaker by almost 1 cm s^-1

Development of under-ice stratification in Himmerfjärden bay, North-Western Baltic proper, and their effect on the phytoplankton spring bloom

Seasonal sea ice cover reduces wind-driven mixing and allows for under-ice stratification to develop. These under-ice plumes are a common phenomenon in the seasonal sea ice zone. They stabilize stratification and concentrate terrestrial runoff in the top layer, transporting it further offshore than during ice-free seasons. In this study, the effect of sea ice on spring stratification is investigated in Himmerfjärden bay in the NW Baltic Sea. Distinct under-ice plumes were detected during long ice seasons. The preconditions for the development of the under-ice plumes are described as well as the typical spatial and temporal dimensions of the resulting stratification patterns. Furthermore, the effect of the under-ice plume on the timing of the onset and the maximum of the phytoplankton spring bloom were investigated, in terms of chlorophyll-a (Chl-a) concentrations. At the head of the bay, bloom onset was delayed on average by 18 days in the event of an under-ice plume. However, neither the maximum concentration of Chl-a nor the timing of the Chl-a maximum were affected, implying that the growth period was shorter with a higher daily productivity. During this period from spring bloom onset to maximum Chl-a, the diatom biomass was higher and Mesodinium rubrum biomass was lower in years with under-ice plumes compared to years without under-ice plumes. Our results thus suggest that the projected shorter ice seasons in the future will reduce the probability of under-ice plume development, creating more dynamic spring bloom conditions. These dynamic conditions and the earlier onset of the spring bloom seem to favor the M. rubrum rather than diatoms.Peer reviewe

Algal hot spots in a changing Arctic Ocean: Sea-ice ridges and the snow-ice interface

During the N-ICE2015 drift expedition north-west of Svalbard, we observed the establishment and development of algal communities in first-year ice (FYI) ridges and at the snow-ice interface. Despite some indications of being hot spots for biological activity, ridges are under-studied largely because they are complex structures that are difficult to sample. Snow infiltration communities can grow at the snow-ice interface when flooded. They have been commonly observed in the Antarctic, but rarely in the Arctic, where flooding is less common mainly due to a lower snow-to-ice thickness ratio. Combining biomass measurements and algal community analysis with under-ice irradiance and current measurements as well as light modeling, we comprehensively describe these two algal habitats in an Arctic pack ice environment. High biomass accumulation in ridges was facilitated by complex surfaces for algal deposition and attachment, increased light availability, and protection against strong under-ice currents. Notably, specific locations within the ridges were found to host distinct ice algal communities. The pennate diatoms Nitzschia frigida and Navicula species dominated the underside and inclined walls of submerged ice blocks, while the centric diatom Shionodiscus bioculatus dominated the top surfaces of the submerged ice blocks. Higher light levels than those in and below the sea ice, low mesozooplankton grazing, and physical concentration likely contributed to the high algal biomass at the snow-ice interface. These snow infiltration communities were dominated by Phaeocystis pouchetii and chain-forming pelagic diatoms (Fragilariopsis oceanica and Chaetoceros gelidus). Ridges are likely to form more frequently in a thinner and more dynamic ice pack, while the predicted increase in Arctic precipitation in some regions in combination with the thinning Arctic icescape might lead to larger areas of sea ice with negative freeboard and subsequent flooding during the melt season. Therefore, these two habitats are likely to become increasingly important in the new Arctic with implications for carbon export and transfer in the ice-associated ecosystem