352
DYNAMICAL OCEANOGRAPHY
The continental geometry of the Arctic basin is substantially different
from that in the Southern Ocean. Whereas the Southern Ocean is unblocked over a range of latitudes, the Arctic basin is quite isolated having
only a few connections with the other ocean basins. Together with the fact
that a large part of the Arctic is ice covered during most of the year, this
gives rise to a peculiar Arctic Ocean circulation. In this chapter, several
characteristics of the Arctic circulation will be mentioned in section 15.1.
Next we will focus on two questions: (i) why are the surface velocities
closely following bottom topographic features and (ii) why are the deep
velocities relatively large? To answer these questions, the occurrence of
closed geostrophic contours is important and introductory dynamical theory is presented in section 15.2. An idealized model that is used to tackle
both questions above is presented in section 15.3 and its application to the
Arctic Ocean and Nordic Seas appears in section 15.4.
Note: All equations in this chapter are dimensional and we will therefore omit
the star subscript.
15.1. Characteristics
As bottom topography is one of the foremost important factors for the circulation in the Arctic Ocean, we start by showing a map of the bathymetry in
Fig. 15.1. The Arctic basin north of Svalbard is comprised of several subbasins
(Canada basin, Makarov basin, Amundsen basin, Nansen basin) of about 30004000 m depth which are separated by ridges (e.g., Alpha-Mendeleyev ridge and
Lomonosov ridge) with depths of only 1000-1500m. The major connection between the Arctic and the surrounding oceans is through Fram Strait (to the Atlantic) and the Bering Strait (to the Pacific). The Bering Strait is only 45 m deep
and 85 km wide. There are some small connections to the Atlantic through the
Canadian Archipelago (e.g., Lancaster Sound) but these are of minor importance
compared to Fram Strait (between Greenland and Svalbard). South of Svalbard,
the area is usually referred to as the Nordic Seas including the Greenland basin
and Norwegian basin.
A large part of the Arctic is ice covered during most of the year. The sea ice
concentration (this quantity is 1 in a particular grid box if the area is totally covered and 0 if there is no sea ice) over the Arctic basin in Winter and Summer
(both averaged over the years 1985-1995) is plotted in Fig. 15.2. What can be
seen directly from Fig. 15.2a is that the sea ice extends much more southward in
the Canadian area than in the Nordic Seas. Harbours in northern Norway are ice
free during most of the winter. This is due to the inflow of warm water through
the Norwegian Current (an extension of the Gulf Stream) which has a mean
DYNAMICAL OCEANOGRAPHY
The continental geometry of the Arctic basin is substantially different
from that in the Southern Ocean. Whereas the Southern Ocean is unblocked over a range of latitudes, the Arctic basin is quite isolated having
only a few connections with the other ocean basins. Together with the fact
that a large part of the Arctic is ice covered during most of the year, this
gives rise to a peculiar Arctic Ocean circulation. In this chapter, several
characteristics of the Arctic circulation will be mentioned in section 15.1.
Next we will focus on two questions: (i) why are the surface velocities
closely following bottom topographic features and (ii) why are the deep
velocities relatively large? To answer these questions, the occurrence of
closed geostrophic contours is important and introductory dynamical theory is presented in section 15.2. An idealized model that is used to tackle
both questions above is presented in section 15.3 and its application to the
Arctic Ocean and Nordic Seas appears in section 15.4.
Note: All equations in this chapter are dimensional and we will therefore omit
the star subscript.
15.1. Characteristics
As bottom topography is one of the foremost important factors for the circulation in the Arctic Ocean, we start by showing a map of the bathymetry in
Fig. 15.1. The Arctic basin north of Svalbard is comprised of several subbasins
(Canada basin, Makarov basin, Amundsen basin, Nansen basin) of about 30004000 m depth which are separated by ridges (e.g., Alpha-Mendeleyev ridge and
Lomonosov ridge) with depths of only 1000-1500m. The major connection between the Arctic and the surrounding oceans is through Fram Strait (to the Atlantic) and the Bering Strait (to the Pacific). The Bering Strait is only 45 m deep
and 85 km wide. There are some small connections to the Atlantic through the
Canadian Archipelago (e.g., Lancaster Sound) but these are of minor importance
compared to Fram Strait (between Greenland and Svalbard). South of Svalbard,
the area is usually referred to as the Nordic Seas including the Greenland basin
and Norwegian basin.
A large part of the Arctic is ice covered during most of the year. The sea ice
concentration (this quantity is 1 in a particular grid box if the area is totally covered and 0 if there is no sea ice) over the Arctic basin in Winter and Summer
(both averaged over the years 1985-1995) is plotted in Fig. 15.2. What can be
seen directly from Fig. 15.2a is that the sea ice extends much more southward in
the Canadian area than in the Nordic Seas. Harbours in northern Norway are ice
free during most of the winter. This is due to the inflow of warm water through
the Norwegian Current (an extension of the Gulf Stream) which has a mean