IUGG 2003 Abstract

P03 The Role of Tides, Mesoscale Processes, and Bottom Topography in Energy Transfer and Mixing Tuesday, July 1 PM Location: Site B, Room 19 Presiding Chair:E. Morozov

TIME [ 1420 ] [ P03/01P/B19-002 ]

SEASONAL VARIATIONS OF PERIODIC WATER DYNAMICS ON THE LAPTEV SEA SHELF, SIBERIAN ARCTIC

Igor DMITRENKO(International Arctic Research Center, University of Alaska Fairbanks)

Sergey KIRILLOV(Arctic and Antarctic Research Institute, St.Petersburg, Russia) Jens HölEMANN ( Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany ) Hajo EICKEN ( Geophysical Institute, University of Alaska Fairbanks, USA )

The vast areas of the Siberian Arctic shelf are seasonally ice covered and considerably freshened by intensive river runoff. Being combined with non-uniform bottom topography and high latitude location, the significance of these factors relative to other potential contributors to the water dynamics is not yet known. The seasonal variations of periodic water dynamics on the Laptev Sea shelf was evaluated in 1998-1999 within the frame of the Russian-German project Laptev Sea System 2000. ADCP records (40 and 22 m profiling depths) from two moorings deployed in the eastern Laptev Sea from August 1998 until August 1999 were analyzed. During the wintertime moorings were situated under the land fast ice and at the vicinity of the fast ice edge. Radarsat ScanSAR satellite images taken twice a month for the period of deployment, SSM/I 85 GHz channel passive microwave images for freeze-up 1998 as well as acoustic Doppler echo intensity backscatter signal were examined to evaluate the surface ice conditions. Sea surface wind was derived from NCEP/NCAR reanalysis and has been compared with the nearest meteorological station data and ADCP records from the surface bins. Current spectrum energy associated with the semidiurnal frequency band was found as comparable to the highest-energy regions of the Arctic Ocean and exhibits seasonal variations. The same results were derived from the wavelet transform of current velocity. Horizontal currents energy increase was obtained under the ice cover during the whole winter. The tidal origin of semidiurnal current amplification during winter was confirmed by the results of standard tidal analysis technique. Lunar semidiurnal internal tidal currents amplification from below 7 to as high as 20 cm/s was found out at the depth of pycnocline during most part of the winter in the presence of an ice cover. Baroclinic amplification of lunar internal tide associates with freeze-up. Coastal polynya formation and summer ice melting result in sharp reduction of baroclinic tidal energy, transformation from the baroclinic internal tidal regime into barotropic one, and redistribution of tidal energy to the high frequency band. The general energy increase within high frequency band has been evaluated during open water period of both 1998 and 1999. A clear increase in the high frequency band was observed above the pycnocline following the onset of the wind events. It was also recorded under polynya conditions when the surface wave impact is considerably restricted by limited ice-free area of polynya. It seems that the interaction of barotropic tides with the density stratification and bottom topography generates the background baroclinic tidal internal waves. While their energy appears to be dissipated to higher frequency bands as a result of sea-atmosphere interaction under open-water conditions during summer, the details of this process are not clear.