Eugene G. Morozov

Semidiurnal internal wave global field

Abstract Estimates were made for semidiurnal internal wave generation over subsurface ridges based on Baines ( Deep-Sea Research , 29 , 307–338, 1982) linear model of internal wave generation. Flux was estimated from current measurements and numerical models of the global barotropic tidal field. Energy fluxes from the underwater ridges greatly exceed the fluxes from the continental slopes because the dominating part of tidal flow is directed parallel to the coast line. They account for about one-fourth of the total energy loss from the barotropic tides. The subsurface ridges, if normal to the tidal flow, form an obstacle that can cause the generation of large internal waves. The generated semidiurnal internal waves may be extreme when the depths of the ridge crest are comparatively small with respect to the surrounding depths. Energy fluxes from most subsurface ridges were estimated. The decay of the internal tide during propagation was estimated from measurements with buoy arrays located normal to the ridges. Measurements were made on clusters and arrays of moored buoys in more than 30 areas of the ocean. Combined calculations and measurements result in a map of the global internal wave energy distribution and their amplitudes. Extreme amplitudes are registered near the Mascaren ridge in the Indian Ocean and the Great Meteor bank in Atlantic.

Abyssal Channels in the Atlantic Ocean: Water Structure and Flows

Foreword. Preface. Acknowledgements. 1. Geological and geophysical characteristics of the transform fault zones. 1.1 General description. 1.2 Charlie Gibbs Fracture Zone. 1.3 Vema Fracture Zone. 1.4 Romanche Fracture Zone. 1.5 Chain Fracture Zone. 1.6 Vema Channel. 2. Deep water masses of the South and North Atlantic. 2.1 General description. 2.2 Antarctic Intermediate Water. 2.3 Upper Circumpolar Water and Upper Circumpolar Deep Water. 2.4 North Atlantic Deep Water. 2.5 Lower Circumpolar Water and Lower Circumpolar Deep Water, Circumpolar Bottom Water, Southeast Pacific Deep Water, and Warm Deep Water. 2.6 Antarctic Bottom Water. 3. Source Regions, Abyssal Pathways, and Bottom Flow Channels (for waters of the Antarctic origin). 3.1 General description. 3.2 Weddell Sea and Weddell Gyre. 3.3 Agulhas and Cape basins. 3.4 Drake Passage, Scotia Sea, and Georgia Basin. 3.5 Antarctic Bottom Water in the Argentine Basin. 4. Exchange between the Argentine and Brazil basins Abyssal pathways and bottom flow channels (for waters of the Antarctic origin). 4.1 General description. 4.2 Vema Channel. 4.3 Santos Plateau. 4.4 Hunter Channel. 5. Further propagation of Antarctic Bottom Water from the Brazil Basin. 5.1 Brazil Basin. 5.2 Flow in the Guiana Basin and westward equatorial channels. 5.3 North American Basin. 5.4 Eastward Equatorial Channels. The Romanche and Chain Fracture Zones. 5.5 Vema Fracture Zone. 5.6 Eastern Basin Pathways and further propagation of Antarctic Bottom Water in the East Atlantic. 5.7 Kane Gap. 5.8 Angola Basin. 6. Flows through the Mid-Atlantic Ridge in the northern channels. Charlie Gibbs Fracture Zone and other fracture zones. Integrated conclusions. References. Index.

Decadal warming of the coldest Antarctic Bottom Water flow through the Vema Channel

A decadal warming trend of Antarctic Bottom Water flowing through the Vema Channel is reanalyzed. Our data base consists of 94 high precision, full depth stations from 19 visits to the Vema Sill plus twelve stopovers at two additional key locations. Originally a long-term temperature increase in the near-bottom jet was noted from 1992 onward, after a period of rather constant abyssal temperatures since 1972. From todays perspective the apparent stagnant temperature level until 1991 can be interpreted as a period of feeble rising in comparison with a perspicuous warming trend of 2.8 mK yr(-1) in the following 15 years. However, the clearly manifested temperature rise is superimposed with fluctuations. For the first time the available time series appears long enough to indicate an associated slight freshening of the bottom water. An attempt is made to trace the observed variability back to its source region in the Weddell Sea.

Internal Tides in the Strait of Gibraltar

Abstract Analysis of moored current measurements in the Strait of Gibraltar is provided here. The vertical internal displacements (double amplitudes) with a semidiurnal frequency are extremely large and sometimes exceed 200 m. It is found that these displacements are associated with forced tidal internal waves over Camarinal Sill, which crosses the strait. The separation of tidal components showed that the amplitude of internal tide with M2 frequency is 69 m, while the amplitudes of other components of the internal tide (S2, K1, O1) are 3–5 times smaller. The amplitudes of the waves decrease with the distance from the sill and, at a distance of 50 km from the sill, the amplitudes are 3 times smaller than over the sill. The energy of internal tides is transferred to internal bore and turbulent mixing. The wavelength of the internal tide was estimated on the basis of moored measurements. The wavelength of the east-propagated wave is 90 km, while the west-propagated wave is 60 km. Numerical modeling demonstr...

Absolute geostrophic currents in the Drake Passage based on observations in 2003 and 2005

Geostrophic currents in the Drake Passage are studied using the data of two hydrographic sections across the passage occupied in December 2003 and November 2005 along with satellite altimetry data. A conclusion is reached that the altimetry correction of the geostrophic currents has advantages compared to the correction made on the basis of the lowered acoustic Doppler current profiler data. A number of new results about the structure and intensity of the ocean currents in the Drake Passage are obtained; the main one is the distinguishing of several abyssal currents of westward direction confined to deep passages in the bottom topography.

The straits of Gibraltar and Kara Gates: a comparison of internal tides

Moored current measurements, numerical model calculations, and satellite images from the straits of Gibraltar and Kara Gates are compared. The vertical internal displacements (double amplitudes) with a semidiurnal frequency are extremely large in both straits. The displacements are related to internal tidal waves over the sills. The energy of the internal tides is transferred to an internal bore and associated wave packets of short-period internal waves. Their surface manifestation can be seen on the satellite images. Numerical modeling shows that the outflowing current from the Mediterranean Sea to the Atlantic Ocean has a significant influence on internal tides. In the Kara Gates, the flow from the Barents Sea to Kara Sea has a similar influence. The internal tide propagating in the opposite direction to the flows intensifies and breaks down into shorter period waves that are seen on the satellite images in the eastern part of the Strait of Gibraltar and in the southwestern part of the Kara Gates.

Remote sensing of seawater and drifting ice in Svalbard fjords by compact Raman lidar

A compact Raman lidar system for remote sensing of sea and drifting ice was developed at the Wave Research Center at the Prokhorov General Physics Institute of the Russian Academy of Sciences. The developed system is based on a diode-pumped solid-state YVO(4):Nd laser combined with a compact spectrograph equipped with a gated detector. The system exhibits high sensitivity and can be used for mapping or depth profiling of different parameters within many oceanographic problems. Light weight (∼20 kg) and low power consumption (300 W) make it possible to install the device on any vehicle, including unmanned aircraft or submarine systems. The Raman lidar presented was used for study and analysis of the different influence of the open sea and glaciers on water properties in Svalbard fjords. Temperature, phytoplankton, and dissolved organic matter distributions in the seawater were studied in the Ice Fjord, Van Mijen Fjord, and Rinders Fjord. Drifting ice and seawater in the Rinders Fjord were characterized by the Raman spectroscopy and fluorescence. It was found that the Paula Glacier strongly influences the water temperature and chlorophyll distributions in the Van Mijen Fjord and Rinders Fjord. Possible applications of compact lidar systems for express monitoring of seawater in places with high concentrations of floating ice or near cold streams in the Arctic Ocean are discussed.

Convective and shear-induced turbulence in the deep Kane Gap

[1] The boundary layer above a 4569 m deep slope in the near-equatorial N-Atlantic Ocean Kane Gap, a throughflow for Antarctic Bottom Water (AABW), is characterized by two distinct turbulent regimes that differ by an order of magnitude in intensity depending on the direction of throughflow. During southward and downward flow, vertical mixing is vigorous. This is inferred from high-resolution temperature observations between 6 and 132 m above the bottom. For a representative case study of 2 days, average values are found for dissipation rate of e?=?2.1?±?1 × 10-9 W kg-1 and eddy diffusivity of Kz?=?7?±?4 × 10-4 m2 s-1. The mixing is across relatively large vertical overturns. During northward and upward flow, smaller overturns are more horizontal as in stratified shear flow (with representative 2 day mean e?=?6?±?3 × 10-11 W kg-1, Kz?=?4?±?2 × 10-5 m2 s-1). Stratification is approximately the same during both flow directions. Although the different turbulence regimes are partially associated with frictional boundary layers of large-scale flows above sloping topography, but not with those over flat bottoms, and partially with flow across a hill-promontory, internal waves are a dominant process in promoting turbulence. In addition, internal waves are observed to push stratification toward the bottom thereby importantly contributing to the mixing of AABW.

Deep Water Masses of the South and North Atlantic

The Southern Ocean and Antarctic Circumpolar Current isolate the Antarctic continent from other regions of the Earth. Thus, conditions in the study region provide the formation of a special water structure around Antarctica, whereas water structure in the northern regions is determined by interactions between waters of the North Atlantic and those of Arctic origin.

Measurements of sea-ice flexural stiffness by pressure characteristics of flexural-gravity waves

Abstract A method to estimate the flexural stiffness and effective elastic modulus of floating ice is described and analysed. The method is based on the analysis of water pressure records at two or three locations below the bottom of floating ice when flexural-gravity waves propagate through the ice. The relative errors in the calculations of the ice flexural stiffness and the water depth are analysed. The method is tested using data from field measurements in Tempelfjorden, Svalbard, where flexural-gravity waves were excited by an icefall at the front of the outflow glacier Tunabreen in February 2011.