Pathways and watermass transformation of Atlantic Water entering the Nordic Seas through Denmark Strait in two high resolution ocean models

(2019) Ypma, S.L. Brüggemann, N., Georgiou, S., Spence, P., Dijkstra, H. A., Pietrzak, J. D., & Katsman, C. A., Deep Sea Research Part I: Oceanographic Research Papers.

Density plot of the particle position in MOM (left panel) and POP (right panel). The inlay shows the pathways near Iceland in more detail (note the different colorscale in the bottom left). The median travel time for the particles to reach the exits of the Nordic Seas is given in years.

The Nordic Seas are seen as the main gateway between the Atlantic and the Arctic Ocean. The Atlantic Ocean is characterized by warm and saline waters, whereas the Arctic Ocean is generally very fresh and cold. These two watermasses meet within the Nordic Seas. Furthermore, the Nordic Seas itself are subject to strong cooling by the atmosphere and freshening from (sea-) ice melt. Therefore, processes in the Nordic Seas play an important role in the formation and spreading of dense watermasses that eventually drive the global overturning circulation.

In this paper, the pathways of the North Icelandic Irminger Current (NIIC) are investigated. The NIIC brings warm and saline Atlantic Water into the Nordic Seas through Denmark Strait. Results from observational studies point towards a connection between this branch and the densest component of the Denmark Strait Overflow Water (DSOW). However, by tracing the watermass in two high resolution ocean models, this study shows that only a fraction of the NIIC is connected to the DSOW. In the model simulations studied, the part of the NIIC watermass that is not connected to the overflows takes many different pathways through the Nordic Seas. How the watermass is mixed and at which depth it enters the Nordic Seas determines which route the NIIC water takes through the Nordic Seas. 

This study further highlights that although these state-of-the-art global ocean models are valuable  tools for detailed analysis, they still have difficulties representing the hydrographic properties of the Nordic Seas correctly. As a result, the NIIC watermass traced takes very different paths through the interior of the Nordic Seas in both models (see Figure).