Low‐frequency motions on the Scotian shelf and slope

An examination of current‐meter data gathered in 1967/68 on the continental shelf and slope off Nova Scotia has shown that meteorological forcing is an important source of energy. The response of currents to wind forcing is concentrated in a frequency band of 2.5 to 7 days. Daily mean currents of up to 25 cm/s appear to be associated with wind‐stress events. The highest correlations between wind and current are for the alongshore components of these variables. Wind‐induced currents may have been responsible for an intrusion of slope water onto the shelf which was observed in hydrographic sections from October and December 1968. Long data series (up to 167 days) formed by patching together shorter records demonstrate the existence of distinct low‐frequency variability at periods greater than 10 days. Some aspects of these motions suggest the presence of topographic Rossby waves on the shelf and slope. However, spatial and temporal coverage of data are not sufficient to define the sources of this variability.     

Circulation in the Bras d'Or Lakes

The Bras d'Or Lakes are a system of interconnecting basins open through two narrow channels to the Sydney Bight at the mouth of the Gulf of St Lawrence. Hydrographic surveys between 1972 and 1974 showed that surface waters can warm by more than 10 °C from May to July and that horizontal salinity differences of up to 10 psu can exist between Sydney Bight (30 psu) and the innermost regions of the Lakes. Using the data from May and June 1974 to derive horizontal and vertical exchanges, a simple budget model has been set up consisting of two or three layers in each of nine separate regions. The model has a bottom inflow from Sydney Bight, deep inflow through the narrow channels to other basins and a surface outflow. The exchanges agree reasonably well with estimates derived from available current meter data. The model's predicted temperatures and salinities for July 1974 had rms errors of about 1·5 °C and 0·82 psu, respectively. The dissolved oxygen concentrations in four of the more isolated basins are similar to those calculated from the model, giving support to the derived circulation.     

Mean position and variability of the sea surface temperature front east of the grand banks

Abstract

Three years of weekly sea surface temperature maps were analysed to determine the mean position and standard deviation of the front separating the Mixed Water from the North Atlantic Current water to the east of the Grand Banks between 40–50°N and 40–50°W. The front was found to lie along the path of the North Atlantic Current proposed by Dietrich et al. (1975) and to have a standard deviation ranging from 100 to 200 km. The dominant mode of movement at periods of 6 months and longer consisted of a nearly uniform translation. The trajectories of satellite‐tracked drifting buoys were analysed to create a map of the eddy kinetic energy for the region. The high energy ridge of the map generally corresponded to the mean position of the sea surface temperature front.     

Numerically Controlled Methods of Automatic Plotting and Draughting

Abstract

The equipment available for numerically controlled plotting and draughting is reviewed and certain devices described in some detail. Several systems suited to the digitising of cartographic material exist, while the available plotters may be classified broadly into three categories—those derived from surveying and photogrammetric practice, those associated with computer technology and a group designed substantially for cartographic applications. Finally the various input and output devices associated with cartographic digitising are discussed with special emphasis on their storage capacity, speed of operation and economy.     

Early Tertiary palaeoenvironments and sedimentation in the NE Main Porcupine Basin (well 35/13–1), offshore western Ireland?evidence for global change in the Tertiary

Shell-Agip 35/13–1 well drilled 2445 m of Tertiary sediments in the Main Porcupine Basin situated offshore west of Ireland. Early Tertiary sediments and microfossils indicate a major cycle from deep-sea to marginal marine and terrestrial palaeoenvironments returning to deep water. By means of seismic and lithostratigraphy and petrophysical logs, three deltaic cycles can be distinguished within this major cycle. The microfaunal zonation indicates that these cycles are of late Palaeocene, early Eocene and mid/late Eocene age and, therefore, correlate broadly with the Thanet Cycle, London Clay Cycle and the Bracklesham Cycles of the Anglo-French type sections, although they are up to an order of magnitude thicker due to rapid basin subsidence. Three major unconformities can be distinguished together with a disconformity that becomes an unconformity in the North Porcupine Basin. These surfaces are associated with both local and regional tectonic and igneous events. Detailed microfossil and lithological analyses across the major unconformities allows a reasonable matching with the global sea-level curve and recognition of the major and medium sequence boundaries. Discrepancies during the late Eocene may relate to local faulting. The pattern of sedimentation reflects the restriction of North Atlantic circulation and the tendency to euxinic bottom conditions during the early Palaeogene. In the middle Thanetian these conditions invaded the shelf, an event recorded elsewhere in NW Europe. Discontinuous seismic reflectors indicate ‘chaotic’ sedimentation connected with more vigorous circulation and erosion in the early Oligocene. This was followed by a change to parallel bedded contourites and drifts after the cutting of the early Miocene unconformity. The study reveals the complex interplay of eustatic and oceanographic change with local and regional tectonics in the development of the basin.