Internal Waves in the Laptev Sea
E.A. Zakharchuk
State Research Center - Arctic and Antarctic Research Institute, 38 Bering St., 199226 St. Petersburg, Russia
Received 3 March 1997 and accepted in revised form 9 February 1998
Abstract - The results of research on internal waves in the northern part of the Laptev Sea
are presented. Significant fluctuations of temperature, salinity and currents with periods
from 2 to 20 minutes within the seasonal pycnocline. These fluctuations are identified as
high-frequency internal gravity waves, the frequency of which is close to the Brunt-VaisaIa
frequency. Current meter data were used to calculate the linear invariant of the spectral
tensor-function of current velocity. Significant spectral density peaks for cycles of 2.0, 2.2,
3.3, 3.6 and 14.8 min were established. It is suggested that the high-frequency internal
gravity waves are generated by destruction of an internal tidal wave in the region of the
continental slope. This supposition is confirmed by temporal variability of the linear
invariant of the variance tensor of current velocity at 10m depth. It is suggested that the
internal waves play an important role in mixing processes and the formation of mesoscale
(tidal) frontal zones close to the continental slope.
Introduction
Internal waves play an important role in a regime of the Arctic Ocean. An increase of the solar
heating, of river runoff and of drift ice melting in the Arctic Ocean in the summer period, leads
to formation of a very sharp seasonal pycnocline which hinders exchange between surface and
deep waters. The shielding influence of sea ice also hinders the wind mixing of the surface
layers. However, observations show that thickness of the top quasi-uniform layer in the Arctic
Ocean can reach 20-30 m (Nikiforov and Shpaikher, 1980) in the summer period. It is unlikely
that such a mixed layer can be formed only by the drift and decay of ice fields. It is possible that
the internal waves could make a significant contribution to the mixing of the upper layer of the
Arctic Ocean in the summer period by generating turbulence through their instability (Turner,
1973). The problem of heat exchange between the surface and Atlantic waters underlaying them
in the Arctic Ocean is poorly investigated. In particular, it is not clear at which space-time scales
there is largest heat exchange between the surface and Atlantic waters, and also what
oceanographic processes are responsible for this exchange. Some researchers consider that their
is a significant contribution to the vertical heat exchange through the destruction of internal
waves (Alekseev et a!., 1974; D' Asaro and Morison, 1992; Muench et aI, 1996; Perkin and
Lewis, 1978; Padman, 1995). Questions of effect of the internal waves on ice deformation and
their contribution to formation of mesoscale frontal zones in the Arctic Ocean remain poorly
investigated. Doubtless, all these problems require deeper and comprehensive research of the
internal waves in the Arctic Ocean both experimental and theoretical level.
Internal wave field in the Arctic Ocean is poorly studied. Most of internal wave observations
were made in the Greenland-Norwegian Sea (e.g. Plueddemann, 1992; Marmorino and Trump,
1991), Fram Strait region (Sandven and Johannessen, 1987; ), Arctic Basin (D' Asaro and
Morison, 1992) and continental slope and deep basin of the Laptev Sea (Muench et a!., 1996).
These works show that internal wave energy was greatest at the shelf break and near rougher
topography (e.g. Nansen-Gakkel Ridge, Yermak Plateau), then decreased rapidly with
increasing water depths reaching of lowest values over the abyssal plains.
However, these studies described mainly the tidal and near-inertial internal waves and
werebased mostly on data from the permanent pycnocline.
In: Kassens. H., H.A. Bauch, I. Dmitrenko, H. Eicken, H.-W. Hubberten, M. Melles, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999, 43-51.
E.A. Zakharchuk
State Research Center - Arctic and Antarctic Research Institute, 38 Bering St., 199226 St. Petersburg, Russia
Received 3 March 1997 and accepted in revised form 9 February 1998
Abstract - The results of research on internal waves in the northern part of the Laptev Sea
are presented. Significant fluctuations of temperature, salinity and currents with periods
from 2 to 20 minutes within the seasonal pycnocline. These fluctuations are identified as
high-frequency internal gravity waves, the frequency of which is close to the Brunt-VaisaIa
frequency. Current meter data were used to calculate the linear invariant of the spectral
tensor-function of current velocity. Significant spectral density peaks for cycles of 2.0, 2.2,
3.3, 3.6 and 14.8 min were established. It is suggested that the high-frequency internal
gravity waves are generated by destruction of an internal tidal wave in the region of the
continental slope. This supposition is confirmed by temporal variability of the linear
invariant of the variance tensor of current velocity at 10m depth. It is suggested that the
internal waves play an important role in mixing processes and the formation of mesoscale
(tidal) frontal zones close to the continental slope.
Introduction
Internal waves play an important role in a regime of the Arctic Ocean. An increase of the solar
heating, of river runoff and of drift ice melting in the Arctic Ocean in the summer period, leads
to formation of a very sharp seasonal pycnocline which hinders exchange between surface and
deep waters. The shielding influence of sea ice also hinders the wind mixing of the surface
layers. However, observations show that thickness of the top quasi-uniform layer in the Arctic
Ocean can reach 20-30 m (Nikiforov and Shpaikher, 1980) in the summer period. It is unlikely
that such a mixed layer can be formed only by the drift and decay of ice fields. It is possible that
the internal waves could make a significant contribution to the mixing of the upper layer of the
Arctic Ocean in the summer period by generating turbulence through their instability (Turner,
1973). The problem of heat exchange between the surface and Atlantic waters underlaying them
in the Arctic Ocean is poorly investigated. In particular, it is not clear at which space-time scales
there is largest heat exchange between the surface and Atlantic waters, and also what
oceanographic processes are responsible for this exchange. Some researchers consider that their
is a significant contribution to the vertical heat exchange through the destruction of internal
waves (Alekseev et a!., 1974; D' Asaro and Morison, 1992; Muench et aI, 1996; Perkin and
Lewis, 1978; Padman, 1995). Questions of effect of the internal waves on ice deformation and
their contribution to formation of mesoscale frontal zones in the Arctic Ocean remain poorly
investigated. Doubtless, all these problems require deeper and comprehensive research of the
internal waves in the Arctic Ocean both experimental and theoretical level.
Internal wave field in the Arctic Ocean is poorly studied. Most of internal wave observations
were made in the Greenland-Norwegian Sea (e.g. Plueddemann, 1992; Marmorino and Trump,
1991), Fram Strait region (Sandven and Johannessen, 1987; ), Arctic Basin (D' Asaro and
Morison, 1992) and continental slope and deep basin of the Laptev Sea (Muench et a!., 1996).
These works show that internal wave energy was greatest at the shelf break and near rougher
topography (e.g. Nansen-Gakkel Ridge, Yermak Plateau), then decreased rapidly with
increasing water depths reaching of lowest values over the abyssal plains.
However, these studies described mainly the tidal and near-inertial internal waves and
werebased mostly on data from the permanent pycnocline.
In: Kassens. H., H.A. Bauch, I. Dmitrenko, H. Eicken, H.-W. Hubberten, M. Melles, J. Thiede and L. Timokhov (eds.)
Land-Ocean Systems in the Siberian Arctic: Dynamics and History. Springer-Verlag, Berlin, 1999, 43-51.