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History and Future of Snow and Sea Ice in the Baltic Sea  

Matti Leppäranta

The physics of the ice season in the Baltic Sea is presented for its research history and present state of understanding. Knowledge has been accumulated since the 1800s, first in connection of operational ice charting; deeper physics came into the picture in the 1960s along with sea ice structure and pressure ridges. Then the drift of ice and ice forecasting formed the leading line for 20 years, and over to the present century, ice climate modeling and satellite remote sensing have been the primary research topics. The physics of the Baltic Sea ice season is quite well understood, and toward future ice conditions realistic scenarios can be constructed from hypothetical regional climate scenarios. The key factor in climate scenarios is the air temperature in the Baltic Sea region. The local freezing and breakup dates show sensitivity of 5–8 days’ change to climate warming by 1 °C, while this sensitivity of sea ice thickness is 5–10 cm. However, sea ice thickness and breakup date show sensitivity also to snow accumulation: More snow gives later breakup, but the thickness of ice may decrease due to better insulation or increase due to more snow-ice. The annual probability of freezing decreases with climate warming, and the sensitivity of maximum annual ice extent is 35,000–40,000 km2 (8.3%–9.5% of the Baltic Sea area) for 1 °C climate warming. Due to the large sensitivity to air temperature, the severity of the Baltic Sea ice season is closely related to the North Atlantic Oscillation.

Article

Climate Change and Coastal Processes in the Baltic Sea  

Tarmo Soomere

Various manifestations of climate change have led to complicated patterns of reactions of the Baltic Sea shores to varying hydrodynamic drivers. The northern and western bedrock and limestone coasts of this young water body experience postglacial uplift that is faster than the global sea-level rise. These coastal segments are thus insensitive with respect to changes in hydrodynamic forcing. Sedimentary and easily erodible coasts of the westernmost, southern, and eastern shores of this water body evolve under the impact of relative sea-level rise, changing wave properties and gradual loss of sea ice in conditions of chronic deficit of fine sediment. Several classic features of coastal processes, such as the cut-and-fill cycle of beaches, are substantially modified in many coastal sections. Waves approaching the shore systematically at large angles drive massive alongshore sediment transport in many coastal segments. This transport has led to the development of large sand spits and many relict lakes separated from the sea by coastal barriers. The concept of closure depth is reinterpreted because of frequent synchronization of strong waves and elevated water levels. The gradual loss of sea ice cover endangers most seriously coastal systems around the latitudes of the Gulf of Finland (about 60°N). The combined influence of climatically controlled sea-level rise and intense wave action leads to a gradual increase in eroding sections and the acceleration of coastal retreat on the southern downlifting shores of Poland and Germany. The bidirectional wind forcing has created a delicate balance of sediment on the shores of Latvia and Lithuania. This balance is vulnerable with respect to changes in strong wind directions. The sedimentary shores of Estonia host a number of small beaches that are geometrically protected against typical strong wind directions but are sensitive with respect to storms from unusual directions. Numerical analysis of sediment transport patterns along the eastern shores of the Baltic Sea has identified major changes in the wave directions in the Baltic Proper that can be attributed to manifestations of climate change.