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Exploring drift simulations from ocean circulation experiments: Application to cod eggs and larval drift

Arne Melsom*, Kristina Øie Kvile, Knut-Frode Dagestad,  Göran Broström, Øystein Langangen

*Corresponding author:

ABSTRACT: Drift models are commonly used to study the transport of early life stages of fish and other marine organisms. Various approaches may be applied for examination of distribution and variability of ocean trajectory pathways. In the present study we compare results using passive Eulerian tracers and Lagrangian float trajectories that are embedded in the numerical models. We supplement this analysis by applying an offline model for drift computations. The contrasts in the results from the various configurations are mainly due to differences in drift depth. Simulations have been performed using horizontal resolutions of 4 km and 0.8 km, respectively. We find that the higher resolution experiment gives somewhat more realistic results for the drift time from Lofoten to the bank Tromsøflaket at the southwestern entrance of the Barents Sea. Furthermore, differences in results between simulation years are much larger than the differences that arise from the choice of model configuration. Climate variability at high latitudes on a multi-decadal time scale is dominated by large interannual variability superimposed on an underlying moderate warming trend. We conclude that a properly configured offline drift model using hourly/two hourly results from a simulation with a horizontal resolution of 1 km or finer is the best approach for investigations of trajectory pathways. The flexibility of an offline drift model is also highly advantageous in biological contexts as it easily allows for a variety of ways in which behavioural characteristics can be parameterized, including descriptions that are defined after the ocean circulation simulation has been executed.