Description: Improvement/optimization of a sea ice model is of great significance for understanding the sea ice physics and for understanding the Arctic climate system and its linkage to the global climate. For better representation of modeled sea ice properties, we develop a parameter optimization system for a couped ocean-sea ice model. Since the sensitivities of dynamic and thermodynamic parameters of sea ice models are interrelated, the system handles both sets of parameters simultaneously. The system also handles a long assimilation window of 33 years. Such a long time window has never been tested by other algorithms (e.g., adjoint method, EnKF). Since the cost function defined by the model - data misfit may have an ill-shaped structure (multiple local minima), we apply an algorithm, which can find the global minimum of an ill-shaped function. A micro-Genetic Algorithm is one of the possible solutions to optimize sea ice model parameters.

Description: The Fram Strait is the main gateway for water, heat and sea-ice exchanges between the Arctic Ocean and the North Atlantic. The complex physical environment results in a highly variable primary production in space and time. Previous regional studies have defined key bottom-up (ice cover and stratification from melt water controlling the light availability, and wind mixing and water transport affecting the supply of nutrients) and top-down processes (heterotrophic grazing). In this study, in situ field data, remote sensing and modeling techniques were combined to investigate in detail the influence of melting sea-ice and ocean properties on the development of phytoplankton blooms in the Fram Strait region for the years 1998–2009. Satellite-retrieved chlorophyll-a concentrations from temporarily ice-free zones were validated with contextual field data. These were then integrated per month on a grid size of 20 × 20 km, resulting in 10 grids/fields. Factors tested for their influence on spatial and temporal variation of chlorophyll-a were: sea-ice concentration from satellite and sea-ice thickness, ocean stratification, water temperature and salinity time-series simulated by the ice-ocean model NAOSIM. The time series analysis for those ten ice-free fields showed a regional separation according to different physical processes affecting phytoplankton distribution. At the marginal ice zone the melting sea-ice was promoting phytoplankton growth by stratifying the water column and potentially seeding phytoplankton communities. In this zone, the highest mean chlorophyll concentration averaged for the productive season (April–August) of 0.8 mgC/m3 was observed. In the open ocean the phytoplankton variability was correlated highest to stratification formed by solar heating of the upper ocean layers. Coastal zone around Svalbard showed processes associated with the presence of coastal ice were rather suppressing than promoting the phytoplankton growth. During the twelve years of observations, chlorophyll concentrations significantly increased in the southern part of the Fram Strait, associated with an increase in sea surface temperature and a decrease in Svalbard coastal ice.

Description: Observations in the Arctic Ocean have revealed changes in oceanic temperature, salinity and the ice cover of the 1990s in comparison to earlier data. With a numerical model we hindcast the coupled ice-ocean system of the Arctic and sub-Arctic seas for the past two decades to improve the scientific understanding of their modes of response to atmospheric forcing. The model is driven by atmospheric data from the ECMWF reanalysis between 1979 a nd 1993 and from the ECMWF analysis between 1994 and 1999. The focus of the work presented here is on the temperature rise which occurred in the Atlantic layer of the Arctic Ocean in the early 1990s.The model favorably reproduces the development and subsequent propagation of temperature anomalies in the water of Atlantic origin in the Northwest European Shelf area and along the Norwegian coast. These anomalies propagate into the Arctic Ocean via the Barents Sea and the Fram Strait. Two warm anomalies are entering the Arctic Ocean through these passages between 1983 and 1985 and between 1989 and 1994, respectively. While the first smaller anomaly only warms up the western Eurasian Basin, the second large anomaly spreads far into the eastern Eurasian Basin and across the Lomonossov Ridge into the western Arctic basins.Intensified boundary currents during the high NAO state in the first half of the 1990s significantly influence amplitude and speed of the temperature anomalies inside the Arctic Ocean. In contrast to the notion of a continuos warming process during the 1990s our model results suggest the warming of the Atlantic Layer in the Arctic Ocean to happen in the form of events. The event with the largest anomalous heat input during the modeled period entered the Arctic between 1989 and 1994. It delivers an additional heat of about 30 TW to the Arctic Ocean proper compared to most of the 1980s. In the analysis of the model results it is possible to trace back this surplus of heat input to the Arctic to an increased volume inflow via the Faroer-Scotland passage and a reduced heat loss to the atmosphere in the late 1980s and early 1990s.We conclude that apart from the intrusion of anomalously warm water also the strong intensification of the cyclonic circulation in the Nordic Seas and the Eurasian Basin is responsible for the rapid warming of the Arctic boundary current in the early 1990s. After a reduction of warm water inflow into the Arctic Ocean in the second half of the 1990s, the most recent observations and the model results point to a recurrence of a warm anomaly in the inflow from 1999 onwards.