Generation of a double Kelvin wave resulting from the reflection of the Rossby wave by the jump layer

This paper considers the evolution of a spatially-localized divergent Rossby wave field near the depth jump. If the jump magnitude is comparable to the depth, Rossby waves are fully reflected and a double Kelvin wave is then generated. The Rossby waves and the double Kelvin wave are described by the first- and zero-approximation fields of the asymptotic expansion, respectively. Over the characteristic Rossby wave period, the level elevation produced by the double Kelvin wave spreads over an extensive area, theraby making up for the change in the total fluid mass of the Rossby waves.Translated by Vladimir A. Puchkin.     

Vertical habitat partitioning by large calanoid copepods in the oceanic subarctic Pacific during Spring

The copepods Neocalanus plumchrus, N. flemingeri, N. cristatus, and Eucalanus bungii dominate the net zooplankton throughout the subarctic Pacific Ocean. All four species have an extensive seasonal ontogenetic vertical migration, completing most or all of their feeding and somatic growth in spring and early summer. We used stratified tows with MOCNESS and BIONESS instrumented net systems to resolve their upper ocean vertical distributions in May and June of 1984, 1987 and 1988. In each year the feeding copepodite stages of all four species were concentrated above the permanent halocline (roughly from 0 to 150m). However, the four species showed strong vertical species zonation and segregation within this layer. We consistently found a near-surface pair (N. plumchrus and N. flemingeri) and a subsurface pair (N. cristatus and E. bungii). The boundary between these groups shifts vertically, but was sharply defined and was very often coincident with a weak and transient thermocline marking the base of the layer actively mixed by surface wind and wave energy. Diel vertical migration was very limited during our sampling periods.The data suggest that the vertical distribution patterns of the copepods could be set by responses to the local intensity of turbulent mixing in the watercolumn. N. plumchrus and N. flemingeri occupied a stratum characterized by strong turbulence. N. cristatus and E. bungii occupied a stratum that was a local minimum in turbulence profiles. The depth of the boundary between the species pairs was deeper when winds and surface energy inputs were strong. The vertical partition pattern may also be determined by a difference in feeding strategy between the species pairs. N. plumchrus and N. flemingeri may feed on the enhanced protozoan population of the mixed layer, while N. cristatus and E. bungii feed on particle aggregates settling from above.     

The impact of mesoscale eddies on plankton dynamics in the upper ocean

A coupled QuasiGeostrophic mixed-layer ECOsystem model (QGECO) is used to investigate the impact of the underlying mesoscale eddy field on the spatial and temporal scales of biological production and on overall rates of primary productivity. The model exhibits temporal trends in the biological and physical fields similar to those observed in the North Atlantic; i.e. the mixed layer shallows in spring causing a rapid increase in phytoplankton concentrations and a corresponding decline in nutrient levels. Heterogeneity is produced in the mixed layer through Ekman pumping velocities resulting from the interaction of windstress and surface currents. This variability impacts on biological production in two ways. Firstly, spatial variations in the depth of the mixed layer affect the photosynthetically active radiation (PAR) availability and hence production rates, and secondly, eddy enhanced exchange between the surface water and those at depth bring additional nutrients into the euphotic zone. These processes result in significant spatial and temporal heterogeneity in the ecosystem distributions.Investigation of the spatial heterogeneity of the biological system finds variability to be significantly greater than that of the mixed layer. The relationship between the eddy field and the ecosystem is investigated. The structure and correlation of the biogeochernical fields change with time. The biological fields are found to have a shorter horizontal scale, but whiter spectrum than the underlying eddy field.Overwinter conditions are found to have a profound effect on the variability, size and timing of the following spring bloom event. Variations in the nitrate levels are primarily responsible for the variability in the biological system in the first year. In subsequent years the variation in the overwintering population is found to be dominant.     

On the vertical structure of temperature anomalies in the North Atlantic

The expansion of the temperature anomaly field in the North Atlantic is considered using natural orthogonal functions of depth. It is shown that the first few components of this expansion describe the field both at the surface and in the upper 1000 m layer accurately enough. The relation between the water temperature anomaly at some levels and the above components is estimated for various regions of the ocean.Translated by Mikhail M. Trufanov.     

Proper movement of a current meter mounted on a suspended drift station

In situ observations of the movement of a current meter attached to a long cable system of a drifting research vessel are discussed. A method is suggested which allows the cable configuration to be restored using measurement data on tangent orientation with respect to the given points. The compiled data indicate that the elements of the cable system shift by dozens of metres with a speed of the order of tens of cm per second. These shifts account for about 90% of the estimated value of current velocity energy pulsations in the frequency band corresponding to the proper frequency oscillations of the current meter and of the vessel's roll and-and-pitch motions.Translated by V. Puchkin.