The importance of vertical resolution in sea ice algae production models

• 3 model setups were used to simulate ice algae with variable vertical resolution.
• All setups used the same equations and parameters.
• Results show that vertical resolution influences significantly model outputs.
• Suggestions are made regarding ice-algal modeling and validation data.

In this study an ice-algal mathematical model is used to resolve the vertical fine structure of sea ice with ice algae, and results are compared to simulations with ice algae located only at the bottom ice layer and to those where ice algae are distributed homogeneously across part of the ice column. Ice algae are reported to contribute 4–26% of overall Arctic Ocean primary production and are an important food source for the ice-associated ecosystem. Thus, it is important to estimate the future impacts of global warming on the contribution of ice algae to Arctic primary production. Primary production models, describing the relationships between ice-algal physiology and population dynamics, with environmental forcing and trophic interactions involving bacteria and grazers, can be applied to quantify such impacts. One important aspect in these models is how to represent the vertical distribution of ice algae in sea ice. In most models, only the bottom ice layer is considered where most of the algal biomass tends to be concentrated. However, since ice algae are also present along the entire ice column, this may lead to underestimation of ice-algal production. Some empirical data and model results suggest that ice algae located in the surface and interior layers may be kept at lower concentrations, in spite of high growth rates, due to grazing by micro- and meiofauna. Results obtained in this study show the importance of resolving vertically the distribution of ice algae to avoid bias in primary production estimates, well in line with empirical studies.

Results obtained with model simulations of ice-algal biomass and production using three different setups – zero dimensional (0D), one dimensional vertically resolved (1D) and Biologically Active Layer (BAL) – suggest that vertical resolution of the ice “column” has important implications on model results, in spite of the low standing stocks generally observed in upper layers in the ice column.Figure optionsDownload as PowerPoint slide