The variability of the East Sakhalin Current induced by winds over the continental shelf and slope

Long-term current measurements of the East Sakhalin Current (ESC) in the Sea of Okhotsk are analyzed using the technique of empirical orthogonal functions (EOFs) in the frequency domain. The first and second EOFs at subtidal frequencies represent motions over the continental shelf and slope, respectively, corresponding to the variability of the two cores of the intense ESC. The first EOF can be explained by the first-mode coastal trapped wave (CTW). The structure of the second EOF is similar to that of the second-mode CTW to the first approximation. According to the distribution of the cross-spectra between EOFs and the wind stress over the whole area of the Sea of Okhotsk, the first EOF is correlated with the alongshore component of the wind stress over the northern and western shelves. The distribution of the phase of the wind stress, which is correlated with the first EOF, indicates that a resonance between the CTW and wind stress drives the motion represented by the first EOF at lower frequencies. At higher frequencies the phase of the wind stress correlated with the first EOF is almost uniform in space, being consistent with the greater speed of phase propagation of the EOF compared with that for the free CTW at these frequencies. The second EOF is correlated with the wind stress curl in the central part of the Sea of Okhotsk. The motion by the second EOF is confined over the slope at lower frequencies and becomes large over the shelf at higher frequencies. This change in the structure of the second EOF is consistent with the results of the numerical experiment of the flow induced by the offshore forcing by Chapman and Brink (1987). The phase of the wind stress curl which is correlated with the second EOF changes clearly in space at some frequencies, suggesting that the motion represented by the second EOF propagates along the isobath with the coast to the right. The wind stress curl contains the wavenumber resonant with the lowest two or three modes of CTWs

Seasonal variations in water structure under fast ice near Syowa Station, Antarctica, in 1976

Formation of homogeneous water was observed in the surface layer above a depth of 400m in the Ongul Strait in early September of 1976 when fast ice had the maximum thickness. This water was produced from stratified water as a result of haline convection induced by the exclusion of brine during the growth of fast ice from 1m in thickness in May to about 2m in early September. The salinity of surface water in this strait also increased from 33.93‰ to 34.10‰ by the convection process during the ice growth. Meanwhile in the Hovdebukta, water with the maximum salinity of 35.03‰ was observed at 300m. The formation of the saline water is probably due to the exclusion of brine by the rapid freezing of sea water in cracks as well as by the gradual growth of fast ice. With the beginning of the spring a marked decrease was seen in salinity of bottom water in the Ongul Strait and of intermediate and bottom waters in the Hovdebukta despite a rather increasing salinity of surface water in both areas. It can be explained only by the advection of less saline water into the deeper layers in both areas. The saline water produced by the exclusion of brine was expected to remain near the bottom of glacial troughs until summer, but it was not observed there in summer. An interpretation is given that the saline water disappeared as a result of the advection of less saline water off the Soya Coast and/or the inflow of fresh water produced in the coast of the continent, probably from the bottom of glaciers from spring onward

A preliminary study on Geosat altimeter observation in the Southern Ocean

The Geosat sea-level anomaly in the Southern Ocean south of 30°S in the period from November 1986 to December 1987 is calculated by pplying the collinear method to retrieve sea-level from the Geosat altimeter data. The Geosat sea-level data are used to investigate the variation and time-dependancy in sea-level anomaly in the Southern Ocean.Regions with high variability in sea-level anomaly correspond to the confluence zones of subtropical and subantarctic water and to the Antarctic Circumpolar Current(ACC). Two regions with higher variability exist in the ACC. High variability south of New Zealand is closely irelated to the bottom topography. The sea-level anomaly in this region does not show a clear propagation ignal, while the strong anomaly generated in Drake Passage propagates down stream at a speed of 4.5 cm/s. In the southern regions of the ACC we were not able to find any significant variation of the Geosat sea-level data. time-dependency of sea-level variation along a latitude of 40°S suggests that the Agulhas eddies are generated near 30°S and move westward at a speed of 10-15 cm/s

Characteristics of mid-depth water in summer off Queen Maud-Enderby Lands, Antarctica

Summer oceanographic conditions off Queen Maud-Enderby Lands are examined using temperature, salinity and dissolved-oxygen data from 177 hydrographic stations. The most characteristic feature of the area covered is the presence of a mid-depth water. It is composed of three distinct water masses : less saline, oxygen-rich water at a nearly freezing temperature; warm, saline, oxygen-poor water; and a third water which has properties between the above two. Finally, the regional distribution of the characteristic water masses and their sources are discussed

Convective mixing and sea ice formation in the Weddell-Enderby Basin in 1974 and 1975

The formation of sea ice in the Weddell-Enderby Basin is examined using a one-dimensional convective mixing model. Oceanographic data obtained in late summer of 1974 and 1975 aboard the icebreaker FUJI are used as the initial conditions in the model. The results by the present model indicate that no sea ice forms in the Weddell Polynya region in 1974 and 1975. The major oceanographic criterion for sea ice formation in the winter is salinity of water in a mixed layer in the preceding summer; high salinity gives no sea-ice formation, which is due to an upward heat flux from deep water by deep convection