Reduction of a population of Canterbury mudfish,Neochanna burrowsius (Galaxiidae), by drovight

A population of Canterbury mudfish Neochanna burrowsius (Phillipps), estimated to exceed 3000 adults in July‐December 1975, and its habitat at Clearwell in mid Canterbury, are described. A 7 month drought nearly extinguished the population; this and the subsequent return migration (in August 1976) of survivors from a stockwater race are recorded.     

Genetic variation and population structure in the New Zealand snapper

Fifteen proteins encoded by 23 gene loci were electrophoretically surveyed in two samples of snapper Chrysophrys auratus (Forster) from Wellington Harbour and the Hauraki Gulf. Between 17% and 26% of the loci examined were found to be polymorphic and the proportion of heterozygous loci per individual was 7.9% to 8.4%. Using Rogers’ genetic distance coefficient an overall similarity of 0.98 was calculated between the two samples.

Three polymorphic loci Est‐4, Gpi‐1, and Idh were examined in an additional 10 samples from around New Zealand. Two genetically distinct stocks were apparent: one along the west coast, the other along the east coast of the North Island. There was an indication of stock mixing at Ninety Mile Beach and in the Bay of Plenty and East Cape. The distribution of alleles at the Est‐4 locus revealed a third stock in Hawke Bay that is genetically more similar to the west coast than the east coast stock. Hydrological conditions in Hawke Bay are more similar to those of the west coast than to those of the north east coast of the North Island. Thus it is possible that Est‐4 alleles are selectively maintained in response to an environmental factor.     

Invertebrate recolonisation of previously dry channels in the Rakaia River

Recolonisation of previously dry channels by stream invertebrates was studied in the Rakaia River during winter 1981 and summer 1982. The winter experiment continued for 42 days, with stable low flows, whereas the summer experiment was characterised by fluctuating large flows which caused it to be abandoned after 27 days. The fauna was dominated numerically by Chironomidae, a leptophlebiid mayfly (Deleatidium), and oligochaetes during the winter, and by Deleatidium alone during the summer. Recolonisation was considered complete after 33 days in winter and 15 days in summer. Flow fluctuations were the main factor affecting colonisation rates, and it was assumed that drift was the main source of colonising animals. Small freshes during low‐flow periods in winter resulted in a rapid increase in total density of invertebrates and number of taxa present and also affected the population structure of Deleatidium larvae in colonisation baskets. Before these freshes numbers had increased steadily over a 27 day period. In summer large floods during high flow periods initially decreased benthic invertebrate numbers in samples but numbers increased rapidly once the flood had passed. This appears to be the first study of its kind on a large unstable river system.     

Small-scale, high-precision and high-accuracy determination of Poisson’s ratios in cohesive marine sediments

Poisson’s ratio (static) appears as a parameter in models of soft-sediment geomechanical processes such as gas bubble formation and bioturbation, and in a number of practical applications, including acoustic imaging, but is rarely measured in soft near-surface (upper 20 cm) marine sediments. A new uniaxial apparatus was developed to assess Poisson’s ratios of cylindrical samples of soft cohesive sediments under finite-strain, unconfined, undrained conditions. No constraining membrane around the sample is necessary in the instrument. By monitoring the fluid level in a capillary, changes in sample volume can be determined to high precision (reproducibility). Measurements on reference materials, i.e., gelatine and polyurethane, also indicate high accuracy (veracity). For natural sediments from Nova Scotia, Canada, Poisson’s ratios range from 0.4951 to 0.5 with no indication of anisotropy; therefore, such sediments act as incompressible solids to short-term/small-magnitude stresses, as occur during bubble formation and infaunal movement.     

Authigenic carbonate mineral formation in the Pagassitikos palaeolake during the latest Pleistocene, central Greece

The Pagassitikos Gulf in Greece is a semi-enclosed bay with a maximum depth of 102 m. According to the present-day bathymetric configuration and the sea level during the latest Pleistocene, the gulf would have been isolated from the open sea, forming a palaeolake since ~32 cal. ka b.p. Sediment core B-4 was recovered from the deepest sector of the gulf and revealed evidence of a totally different depositional environment in the lowest part of the core: this contained light grey-coloured sediments, contrasting strongly with overlying olive grey muds. Multi-proxy analyses showed the predominance of carbonate minerals (aragonite, dolomite and calcite) and gypsum in the lowest part of the core. Carbonate mineral deposition can be attributed to autochthonous precipitation that took place in a saline palaeolake with high evaporation rates during the last glacial–early deglacial period; the lowest core sample to be AMS ¹⁴C dated provided an age of 19.53 cal. ka b.p. The palaeolake was presumably reconnected to the open sea at ~13.2 cal. ka b.p. during the last sea-level rise, marking the commencement of marine sedimentation characterised by the predominance of terrigenous aluminosilicates and fairly constant depositional conditions lasting up to the present day.     

Lagrangian analysis of mixing and transport of water masses in the marine bays

The Lagrangian approach to studying the mixing and transport of a passive admixture in marine bays and gulfs based on the methods of a theory of dynamic systems is developed. This approach is employed to investigate the lateral mixing and transport of waters in the Peter the Great Bay, Japan Sea, using a velocity field of the predictive numerical hydrodynamic circulation model of a synoptic scale. It is shown that the Lagrangian characteristics, such as the maximum accumulated Lyapunov exponent, the time of particle stay in the bay, particle relative displacements, and the number of cyclonic and anticyclonic rotations, allow us to describe the movement of water masses, the character of mixing, and chaos in the Bay. In integrating the advection equations forward and backward in time, maps showing a number of particle arrivals to different regions of the Bay make it possible to establish corridors through which particles leave and enter the Bay.     

Comprehensive studies in the Black Sea and the Sea of Azov in the Summer of 2012

The shelf zones of the Black Sea, Taman Bay, and the Sea of Azov are currently subjected to gross load related to the impact of invasive species, large-scale construction activities near the coast, intensive recreation activity, water pollution in large cities and ports, active navigation, unreasonable coastal arrangement, and dam construction. Another factor substantially affecting the composition of bottom sediments and, thus, the benthos environment is the terrigenous material carried by rivers in the course of catastrophic overflows. An example is the Kubansk flood in 2012, which significantly affected the sea coast near Novorossiysk, Gelendzhik, and Divnomorsk. The intensive onshore dumping results in the delivery of abundant allochthonous material, bottom silting causing changes in the dominants in the benthos associations, a decrease in the photic layer and the death of the phytobenthos, and also debris formation at the bottom. Debris can play the role of artificial reefs contributory for the formation of periphytic biocoenoses.     

Two-dimensional analysis of the semidiurnal tide in some regions of the white sea

An improved method of two-dimensional kinematical structural analysis of tides (the “method of the orbits”) is presented. This method allows us to determine the parameters of the primary tidal waves shaping the observed tidal structure. The construction of the vertical orbits for the individual tidal harmonics is performed along the horizontal coordinate axes; one of them is oriented along the so-called “reactive azimuth,” which coincides with the direction of the tidal current at the instant of the zero tidal level. In this case, the orbit parameters include information on the amplitude-phase relations of the interfering waves and allow us to determine the angle of the waves crossing. The suggested method enables us to quantitatively describe the mechanism of the tidal formation with oblique interference both close to the shore and in the open sea. We tested the new method in two local zones of the White Sea (Morzhovets Island and in the vicinity of the entrance to Kandalaksha Gulf) where the presence of rotating semidiurnal tidal currents evidences the significant role of oblique interference of tidal waves. In these zones, the developed method made it possible to perform a detailed quantitative analysis of the local tide structure caused by the M₂ tidal wave, which plays the dominant role in the White Sea. The result describes the structure of the propagation of the primary tidal waves better than the field of “pure” energy fluxes that was used earlier.     

SAR-imaged spiral eddies in Mutsu Bay and their dynamic and kinematic models

A pattern of slick streaks winding into a spiral, known as a spiral eddy, was identified in 5 images taken by the ERS-1/2 synthetic aperture radar (SAR) in Mutsu Bay (Japan); dynamic and kinematic models of these spiral eddies have been proposed. Common characteristics of the five spiral eddies are: 1) an eddy diameter of about 15 km; 2) their location in the western part of the bay; and 3) their cyclonic direction of rotation. Moreover, the wind conditions over the bay were common: prior to acquiring the images, a strong easterly wind continued blowing for more than one day. The wind field on the bay is known to be orographically steered and has strong windstress vorticity, which generates cyclonic circulation. The diameter and location of the circulation simulated with a numerical ocean model corresponded well to those of the identified spiral eddies. Based on these facts, we propose a dynamic model for the movement of a slick streak, and a kinematic model for the formation of a spiral eddy. We have assumed calm air, a microlayer and seawater with a cyclonic circulation in the dynamic model. The balance of forces is established in the microlayer among the frictional force from the seawater, the frictional force from the calm air, the gravitational force, and the Coriolis force. As a result, the velocity vector of the microlayer deflects slightly towards the center of the cyclonic circulation. We have assumed a point source of the microlayer in the kinematic model. The shapes of a slick streak simulated with the models agree well with the identified patterns in the SAR images.     

Different spreading of Somali and Arabian coastal upwelled waters in the northern Indian Ocean: A case study

The spreading pathways of the Somali and Arabian coastal upwelled waters in the northern Indian Ocean are identified from an ocean re-analysis data set of a single year using numerical passive tracers in a transport model. The Somali and Arabian coastal upwelled waters are found to have entirely different spreading pathways in the northern Indian ocean. The former circulates anticyclonically, is mixed vertically, and is advected to the eastern Indian Ocean along the north equatorial region; while the later intrudes into the northern Arabian Sea, circulates anticyclonically and is advected to the south in the central Arabian Sea and then to the eastern Indian Ocean. The seasonal surface mixing by strong monsoon winds and sheared currents due to dominant eddies of the Somali region are found responsible for mixing 25% of Somali upwelled water with the subsurface and affecting the resultant pathways. The effect of mixing is, however, found negligible in the case of Arabian coastal upwelled water pathways. The seasonal reversal of circulation and eddy dominance during the southwest monsoon cause the Somali upwelled water to spread over the northern Indian Ocean faster than the simultaneously upwelled Arabian coastal water.