Long-term mesoscale variability of modelled sea-ice primary production in the northern Baltic Sea

• Published in: Elementa: Science of the Anthropocene
• Main Authors: Letizia Tedesco, Elina Miettunen, Byoung W. An, Jari Haapala, Hermanni Kaartokallio
• Format: Article in Journal/Newspaper
• Language: English
• Published: BioOne 2017
• Subjects: sea-ice biogeochemistry; biogeochemical models; Baltic Sea; sea-ice algae; geo; envir; ice algae; Sea ice
• Online Access: https://doi.org/10.1525/elementa.223; https://doaj.org/article/0ee43edc08f74603b74c410b27ed019e

We describe a new ocean-sea ice-biogeochemical model, apply it to the Bothnian Bay in the northern Baltic Sea for the time period 1991–2007 and provide the first long-term mesoscale estimates of modelled sea-ice primary production in the northern Baltic Sea. After comparing the available physical and biogeochemical observations within the study area and the time period investigated with the model results, we show the modelled spatial, intra- and interannual variability in sea-ice physical and biogeochemical properties and consider the main factors limiting ice algal primary production. Sea-ice permeability in the studied area was low compared with the polar oceans, which appeared to be a major reason for the generally low primary production rates. Although the sea ice was less saline in the northernmost parts of the basin, these parts were characterized by sea ice with a larger amount of habitable space, higher levels of photosynthetically active radiation and increased macronutrient availability near the coast, which favoured higher algal growth rates. Other parts of the southern central basin were mostly co-limited by less favourable light conditions (i.e., earlier ice breakups associated with fewer sunlight hours) and lower seawater macronutrient concentrations than in the coastal zones. Although a change towards milder winters (i.e., reduced ice cover, thickness and length of the ice season) was previously detected on a half-century timescale and could partly be seen here, analysis of the temporal evolution of sea-ice biogeochemical properties showed no significant trends over time, though these properties were characterized by large interannual variability.