Winter Depth Research Articles

Validation and intercomparison of wet and dry deposition schemes using 210Pb in a global three‐dimensional off‐line chemical transport model

We have used 210Pb, a tracer originating from the radioactive decay of 222Rn emitted from soils, to validate different wet and dry deposition schemes in our global three‐dimensional off‐line chemical transport model, TOMCAT. We have tested two different parameterizations for the dry deposition, one with the turbulent exchange in the boundary layer and one without. When dry deposition is linked to the boundary layer scheme, the model shows the ability to resolve shallow mixing depths in winter with enhanced lifetimes and concentrations of surface aerosol. Three conceptually different wet deposition schemes have been implemented and tested in TOMCAT. In the first, where wet removal is assumed to be proportional to the local gradient of the specific humidity, the model has a global mean bias for the surface concentrations of −40%. Using this scheme, the observed surface concentrations are seriously underpredicted, and most of the aerosol burden is scavenged within the boundary layer. In the second scheme, where scavenging is parameterized proportional to the model‐derived total precipitation rate (large scale and convective), the model exhibits a +26% bias. The concentrations are overpredicted, especially in continental areas as this scheme fails to capture the coupling between vertical transport and rainout. In the third scheme, wet removal is coupled with the vertical transport inside convective clouds. The model then shows the best performance with only a −4% bias for the concentrations. Furthermore, other regional discrepancies between model and observations point to a variability in 222Rn emissions, which was not taken into account with our simple 222Rn emission scenario, and also to anomalies in our model‐derived precipitation rate. The aerosol residence times are realistic only when the wet removal schemes use the precipitation rate rather than the specific humidity. The dry subtropical and polar regions can be captured with lifetimes at 500 hPa of more than 50 days whereas in regions of high precipitation the lifetimes are less than 5 days.

Artemia parthenogenetica in Lake Hayward, Western Australia. I. Interrupted recruitment into adult stages in response to seasonal limnology

Lake Hayward, Western Australia, is a pristine, monomictic coastal lake with a residual brine (depth=1.5 m) of 200 gL−1: stratification in winter (May to October) followed the input of ground water and rain. The epilimnion had temperature ranges of 10–30°C, and salinity from 65–110 g L−1. Maximum depth in winter was 2.4 m. The population structure of the brine shrimpArtemia parthenogenetica, the dominant metazoan grazer in Lake Hayward, was studied from September, 1989, to February, 1991. The L. Hayward population ofA. parthenogenetica is predominantly ovoviviparous with little recruitment into the adult population. Cyst production occurs in summer, and there was evidence for recruitment from cyst hatching in the winters of 1989 and 1990. Nauplii were continuously present throughout the study period. Nevertheless, recruitment through to adult stages as defined by the presence of gravid females occurred only twice: in October–December, 1989 and in December, 1990. Based on limited observations of long-term survival of laboratory cultures, we believe that the major mechanism controlling nauplius survival and recruitment ofArtemia in Lake Hayward is food quality and quantity.

Demersal fish community patterns in two areas of the Aegean Sea, Greece

Trawl samples were collected during two periods, autumn 1995 and winter 1996. A total of 2574 specimens per trawling hour (Nh‐1) composed of 105 species were collected in the Cyclades, while in the Saronikos the 1633 specimens (Nlr‐1) that were captured composed of 40 species. Species richness and the Shannon‐Wiener diversity index were higher values in the Cyclades. Higher diversity was recorded in the winter and in the 150–300 m depth zone in both locations. Similarity of the demersal fish communities in the two study areas were investigated using multivariate analysis. It appeared that the affinity of sampling sites, based on the composition of fish catches, was strongly influenced by depth. Trachurus spp (T. picturatus in shallow waters in autumn, and T. trachurus in deeper locations in autumn and in all depths in winter) dominated the Saronikos catches and contributed mainly to the dissimilarity that was displayed between the composition of the demersal fish communities.

Desiccation-tolerance of Fagus crenata Blume Seeds from Localities of Different Snowfall Regime in Central Japan

In beech (Fagus crenata Blume) forests on the Pacific Ocean side in Central Japan, snowpack depth is little and xeric conditions may prevail in winter, in contrast to heavy snow in beech forests on the Japan Sea side. The effects of such conditions during winter on the viability of beech seeds were studied at a beech forest on the Pacific Ocean side. Thickness and weight ratio of pericarp of beech seeds were significantly greater in populations on the Pacific Ocean side compared to the Japan Sea side, this apparently being related to snowpack depth in winter. During the initial stage of seed drying, the drying rate of seeds from the Fuji population (the Pacific Ocean side) was less than that from the Sumon population (the Japan Sea side), possibly due to the thicker pericarp. Germination percentage of seeds which dried to a water content as low as 7% d.w. did not decrease for either population, indicating desiccation tolerance of beech seeds. In the beech forest (University Forest at Yamanaka) on the Pacific Ocean side, water content of seeds sown below litter from both populations remained sufficient for viability during winter. Germinating seeds from the populations on the Japan Sea side were more desiccation-sensitive in early spring, compared to those from the Fuji population, partially due possibly to differences in pericarp thickness.

Distribution, Seasonal Occurrence and Vertical Pattern of Tobrilus Gracilis (Bastian, 1865) and T. Medius (Schneider, 1916)

The autecology of Tobrilus gracilis (n = 1705 individuals) and T. medius (n = 298 individuals), two common nematode species of Lake Konigssee, was studied throughout the year 1986. T. gracilis comprised 3.5% of all nematodes in the littoral, 6.3% in the littoriprofundal and 2.7% in the profundal. T. medius comprised 0.3% of all nematodes in the littoral, 1.4% in the littoriprofundal and 3.3% in the profundal. The species contributed to a considerable portion of nematode biomass in Lake Konigssee. Mean yearly biomass of T. gracilis was greatest at 1 m depth (0.52 mg/100 cm 2 ww; 65% of total nematode biomass) and of T. medius at 60 m depth (0.2 mg/100 cm 2 ww; 49% of total nematode biomass). Density of T. gracilis peaked twice a year in 1 m water depth (winter and summer) and once in deeper regions (winter/spring). T. medius peaked once a year in 10 m depth (spring), showed no distinct maximum in 30 m depth and reached higher numbers in 60 m depth in winter. There was considerable water depth- and time-dependent variation in sex ratios of T. gracilis. The main reproductive period seemed to be different for the investigated depths. The proportion of individuals of T. gracilis in the top sediment layer was about 57% and of T. medius about 72%. Juveniles and adults of T. gracilis were partially segregated in the sediment column. Morphometric data of both species revealed sexual dimorphism in size, body shape and weight.

Arnaut Daniel, poesías; traducción, introducción, y notas por M. de R. (review)

REVIEW Martín de Riquer, ed. Arnaut Daniel, poesías; traducción, introducción, y notas por M. de R. Coll. El Festin de Esopo, 5. Barcelona: Quaderne Crema, 1994. Pp. [256J At last, an edition of Arnaut Daniel including all twenty of the extant poems that he definitely or, in the opinion of this reviewer, probably wrote! We have waited almost sixty years since the discovery in 1935 of the fragmentary manuscript Psi (Italian, 14th c. Bibliothèque Nationale ?. acq. fr. 23789), which added two new attributions to the eighteen songs in the canon that had been recognized by Canello (1883) and Lavaud (1910-11). Subsequent editors—Toja (1960), Perugi (1978), and Eusebi (1984)—perpetuated the tradition without seriously considering the new evidence, even though Robert Barroux had edited Psi diplomatically in 194243 . The nineteenth poem, "Entrel taur el doble signe," was edited critically by Marshall in 1969, who concluded in favor of the attribution, and accepted by Wilhelm in his edition (1981); the twentieth, "Moût m'es bel el terns d'estiou," was edited by Paden (1983), who argued in favor ofits acceptance, and again by Zufferey ( 1989), who argued against it. 1 Riquer includes eighteen "Poesías de Arnaut Daniel" and appends the two "Poesías atribuidas," assessing the nineteenth attribution as likely but uncertain, and the twentieth simply as uncertain. Riquer makes no claim to have edited the poems from manuscripts . Rather, following the procedure he employed in his invaluable anthology Los trovadores, he selects the text in an earlier edition and follows it judiciously. Here he adopts the texts of Eusebi for poems 1-18, Marshall's for poem 19, and Zufferey's for poem 20.2 Riquer himself provides literal Castilian translations, a substantial introduction, and notes. He does not give the melodies which are extant for two poems, referring the reader to the general edition ofthe troubadour melodies by van der Werf and Bond. The result is the first edition ofArnaut in Spanish, intended for literary Iberian readers but valuable for any admirer of the "miglior fabbro del parlar materno" (Purgatorio 26.117). As anyone who knows Riquer's work will expect, he is excellent on the historical facts of the poet's activity, which he dates from c. 1169 through the coronation of Philip Augustus in 1179 (not 1180, as has been REVIEW frequently repeated), and down to 1 192-94, when Arnaut appeared in the literary satire by the Monk of Montaudon. Concerning his difficult art, "Se podría decir, exagerando, que Arnaut Daniel no dijo nada nuevo, pero todo lo dijo de un modo nuevo" (22). Under pressure from the demanding formal constraints which he imposed upon himself, he distorted the semantic content ofwords both rare and common, inventing evocative expressions which create a profoundly unreal ambience echoing with unexpected resonances. In this he resembles other "bons poètes que la tyrannie de la rime force à trouver leurs plus grandes beautés" (Proust, Du côté de chez Swann, quoted by Riquer, 29). This reviewer wonders if the Proustian formula betrays an affinity between Arnaut and the Parnassian esthetic ofThéophile Gautier and Théodore de Banville, an aesthetic which played a role in the late nineteenth-century rediscovery of medieval poetry including Canello's editio princeps of Arnaut, not to mention Ezra Pound.3 The elaborate structure of the sestina, says Riquer (following Canettieri), is inspired by the design of gaming dice, cubes with their six faces arranged so that opposite faces produce the sum of seven—six opposite one, and so on; one thinks of Mallarmé, "Un coup de dés." Arnaut says that the love raining into his heart ("l'amor qu'ins el cor mi plueu," poem 9.13) keeps him warm in the depth ofwinter; less boldly, Verlaine reduces the metaphor to a simile in "Il pleure dans mon coeur comme il pleut sur la ville" (37). Among his caras rimas and adynata, however, Arnaut inserts moments of realism which contrast with the cerebral unreality which is his signature. One such moment is his participation in the series of sirventes debating whether the knight of Cornil was right to refuse his lady when she...

Influence of seasonal variation in cloud condensation nuclei, drizzle, and solar radiation, on marine stratocumulus optical depth

A modeling study was performed to investigate the factors that control the seasonal cycle in the optical depth of marine stratocumulus cloud at a Southern Hemisphere site. Cloud optical depth is primarily influenced by cloud depth and cloud droplet concentration, the latter being controlled by more or less known fluctuations in cloud condensation nucleus (CCN) concentration. The study primarily focussed on the factors influencing cloud depth. The results show that there are two important factors controlling cloud depth, namely solar radiation and drizzle. Seasonal variations in insolation act to enhance cloud depth in winter compared to summer, while drizzle acts in the opposite direction. Drizzle intensity is calculated to be higher in winter when the concentration of CCN is low and cloud droplet effective radius is large. Subcloud evaporation of drizzle droplets reduces entrainment rate, while increased. precipitation at the surface depletes cloud water. Thus, because seasonal cycles in cloud depth due to variations in insolation and drizzle are of opposite phase the result is a partial cancelation of their separate influences on cloud optical depth. DOI: 10.1034/j.1600-0889.47.issue5.5.x

A Mechanism for the Recurrence of Wintertime Midlatitude SST Anomalies

Abstract In the early 1970s, Namias and Born speculated that ocean temperature anomalies created over the deep mixed layer in winter could be preserved in the summer thermocline and reappear at the surface in the following fall or winter. This hypothesis is examined using upper-ocean temperature observations and simulations with a mixed layer model. The data were collected at six ocean weather stations in the North Atlantic and North Pacific. Concurrent and lead-lag correlations are used to investigate temperature variations associated with the seasonal cycle in both the observations and the model simulations. Concurrent correlations between the surface and subsurface temperature anomalies in both the data and the model indicate that the penetration of temperature anomalies into the ocean is closely tied to the seasonal cycle in mixed layer depth: high correlations extend to relatively deep (shallow) depths in winter (summer). Lead-lag correlations in both the data and the model, at some of the stations, ...

Availability of organic carbon in soluble and particle-size fractions from a soil profile

In an agricultural soil profile, the availability of soil organic C for microbial activity decreased from 0 to 100 cm depth in winter, spring and summer. Availability was defined as the ratio of respiration rate to total organic C, or the ratio of microbial biomass C to total organic C. The amount and availability of organic C in various soil fractions was measured. Fractions consisted of aqueous extracts from throughout the profile, and particle-size and density fractions from the 0–20 and 80–100 cm layers. The fractions were incubated with soil inoculum for 24 or 28 days. Availability of organic C in soluble fractions was measured by the decrease in dissolved organic C. Availability of organic C in insoluble fractions was measured by the increase in inorganic C. Availability of organic C in all fractions was similar at each depth, except for the weakly-adsorbed and clay fractions, in which organic C was less available at depth. Availability was least in the silt fractions. Approximately half of the organic C mineralized during incubations originated from the clay fraction in both the 0–10 and 80– 100 cm layers. Of the remainder, at the surface a higher proportion was in the silt and light (>50 μm, d< 2 g cm −3) fractions, due to a larger proportion of total organic C in those fractions. At depth, a higher proportion was in the extracted fractions. The decrease in the availability of total organic C with depth appeared mainly to be due to a decrease in the accessibility of organic C to microorganisms, and a decrease in the availability of clay fraction organic C.

Permafrost, tectonics, and past and future regional climate change, Yukon and adjacent Northwest Territories

Late Tertiary changes in the general circulation of the atmosphere, regionally enhanced by uplift of the Wrangell – Saint: Elias and Coast mountains, were sufficient to promote permafrost development in the western Arctic. Permafrost developed in Yukon Territory and adjacent Northwest Territories during early Pleistocene glacial periods, after continued tectonic activity led to further modification of regional climate, but degraded in the interglacials. Permafrost has been present in northern parts of the region since the Illinoian glaciation, but most ground ice in central Yukon formed in the Late Wisconsinan. The present interglacial is the only one with widespread evidence of permafrost, which is maintained in the valleys of central and southern Yukon by the Saint Elias Mountains blocking continental penetration of maritime air from the Gulf of Alaska. This reduces snow depth in winter, while cold-air drainage in the dissected terrain of the Yukon Plateaus enhances the near-surface inversion, leading to continental minimum temperatures. General circulation models used to simulate climate represent the physiography of northwest Canada crudely. As a result, the simulations are unable to reproduce conditions responsible for the development and preservation of permafrost in the region.

How the food supply harvestable by waders in the Wadden Sea depends on the variation in energy density, body weight, biomass, burying depth and behaviour of tidal-flat invertebrates

For several reasons, waders in the Wadden Sea face a large seasonal and annual variation in their food supply. Observations on a tidal flat in the Dutch Wadden Sea have shown that: 1. - (1) The average energy density of ten invertebrate prey species varies between 21 and 23 kJ·g −1 AFDW. In Scrobicularia plana and Mya arenaria, but not in Macoma balthica, the energy density is 10% lower in winter than in summer. 2. - (2) Depending on the species, body weights of prey of similar size are 30 to 60% lower in winter than in summer. 3. - (3) The year-to-year fluctuation in standing-crop biomass is larger in some species than in others, the difference depending mainly on the frequency of successful recruitment. The overall biomass of the macrobenthos in winter is half of that in summer, but the timing of the peak biomass differs per species. 4. - (4) The burying depth varies per species: Cerastoderma edule live just beneath the surface, while M. balthica, S. plana, M. arenaria, Arenicola marina and Nereis diversicolor bury more deeply and the majority of these prey live out of reach of the bird's bill. In all six species, burying depth increases with size. There is no seasonal variation in depth of C. edule and M. arenaria, but the four other species live at most shallow depth in early summer and most deeply in midwinter. Burying depths in winter vary from year to year, but are unrelated to temperature. Neither has temperature any effect on depth within months. For knot Calidris canutus feeding on M. balthica, the fluctuation in the accessible fraction was the main source of variation in the biomass of prey that is actually harvestable, i.e. the biomass of prey of suitable size that is accessible. Accordingly, the paper reviews the available data on the temporal variations in accessibility, detectability, ingestibility, digestibility and profitability of prey for waders. Only a small part of the prey is harvestable since many accessible prey are ignored because of their low profitability, while many profitable prey are inaccessible. The profitability of prey depends on their size and weight but also on their depth in the mud, since handling time increases with burying depth. A simple biomechanical rule explains why the handling time of small prey increases with bill length and why large, long-billed waders ignore a disproportionately larger part of the small prey. The fraction detectable for visually feeding waders is usually very low, especially when the temperature of the substrate is below 3–6°C. Waders vary their prey choice over the year in response to the changes in the availability and profitability of their different prey species. The food supply harvestable by waders is much lower in winter than in summer. For waders wintering in the Wadden Sea, the food supply may be characterized as unpredictable and usually meagre. Waders wintering in NW Europe are concentrated in coastal sites where the average surface temperature is above 3°C. This probably cannot be explained by a greater burying depth, and only partly by a lower body condition, of prey in colder areas. Yet the harvestable fraction is lower in colder sites, especially for sight-feeding waders, as invertebrates are less active at low temperatures. However, the lower energetic cost of living and reduced chances of the prey being covered by ice may also contribute to the waders' preference for warmer sites.

Seasonal differences in the current and temperature variability over the northern California Shelf during the Coastal Ocean Dynamics Experiment

A long‐term moored array was maintained over the northern California continental shelf from April 1981 to April 1983 as part of the Coastal Ocean Dynamics Experiment to determine the seasonal differences in the current and water temperature characteristics. The array consisted of two midshelf moorings and one upper slope mooring from April 1981 through July 1982 and one midshelf mooring from August 1982 to April 1983. The two summers were characterized by southeastward mean wind stresses (upwelling favorable), cold water, isotherms sloping upward toward the coast, and a sheared equatorward mean shelf current. The intervening fall and winter were characterized by a weak mean wind stress, relatively warm shelf water, level isotherms, and a more barotropic poleward mean shelf current. In contrast to the differences in the characteristics of the means many of the characteristics of the current and temperature variability are the same for the summer and winter. The vertical structure of the largest current empirical orthogonal functions (EOFs) for each of the shelf moorings, which account for more than 75% of the subtidal variance, do not vary with season. The current is vertically sheared, oriented 15°–20°clockwise relative to local isobaths near the surface and along isobaths near the bottom. Currents at the two shelf moorings (alongshore separation 29–37 km) are correlated with each other and with the local wind stress, and these relationships do not exhibit a seasonal variation. Denser arrays of wind and current sensors during the two summers indicated that there were strong, persistent variations in the wind field over relatively small scales (tens of kilometers) with corresponding variations in the shelf current field during the summer of 1981 but not during the summer of 1982. Over the slope, the largest EOFs account for 56–72% of the current variance and have a vertical structure which is relatively uniform with depth during the summer, fall, and winter of 1981 but is strongly sheared in the upper 100 m during the summer of 1982. Current observations over the slope are not correlated with either the shelf currents or the local wind stress during any season. In contrast, the temperature variability, as described by EOFs, does exhibit a seasonal variation in vertical structure, with the variability concentrated in the upper 20–30 m in summer and more uniform with depth in winter. The near‐surface temperature variability over the slope is correlated with the shelf temperature variability. Estimates of the cross‐shelf heat flux due to the wind‐driven Ekman transport accounts for a large part of the shelf temperature variability. Observations from the midshelf mooring maintained through the fall and winter of 1982–1983 showed evidence of the 1982–1983 El Niño with persistent onshore and poleward currents and water temperatures typically above 12°C.

Distribution and diversity of recurrent groups of demersal fishes in the South China Sea off Viet Nam.

The distribution and diversity of demersal fish communities were described in the South China Sea off Viet Nam from December 1968 to July 1969. The first recurrent group including lizardfish as a principal member was located dispersedly along coastal front from winter to summer. Snapper which was a principal member of the second recurrent group coexisted with largeeyed bream at 40-60m depth in winter. However, snapper coexisted with grunt in the shallow region less than 40m depth in summer. Diversity was relatively high in southeastern area, and was low off the Mekong delta.

Siphon size and burying depth in deposit- and suspension-feeding benthic bivalves

This paper analyses the significance of siphon investment in the life strategy of benthic bivalves. It describes the relationships between siphon weight, burying depth and shell size in Mya arenaria, Cerastoderma edule. Scrobicularia plana and Macoma balthica. All data were collected on an intertidal flat in the Dutch Wadden Sea during seven successive winter and summer periods. The four species have in common that (1) the increase of depth in relation to size can be described with an S-curve; (2) there is a linear relationship between log siphon weight and log shell size; (3) siphon investment is maximal for the size classes with the greatest increase in their depth; (4) siphon weight, in proportion to total body weight, decreases gradually for the larger size classes whose depth does not increase; (5) burying depth increases with siphon weight if individuals within a same size class are compared, but burying depth levels off above a certain siphon weight. Macoma balthica and Scrobicularia plana live twice as deep in winter as in summer, although siphon weight for both seasons is about the same. In summer both species use a part of the siphon to graze the surface around the burrow, whereas deposit feeding does not occur in winter. This might explain the seasonal variation in burying depth. On the other hand Cerastoderma edule and Mya arenaria, which are both suspension feeders, show hardly any increase of depth in winter as compared to summer. For benthic bivalves the risk of being taken by a predator decreases with depth. The burying depth levels off where individuals reach the depth refuge (though in winter Scrobicularia plana live at greater depth). The conclusion is that siphon size is one of the main factors determining the burying depth of benthic bivalves and thus plays a critical role in their survival.

Modeling of the stratospheric background aerosols from zonally averaged SAGE profiles

The SAGE (Stratospheric Aerosol and Gas Experiment) satellite aerosol extinction profiles at 1.0 and 0.45 μm, averaged over 10° latitude bands, are used to derive a description of the background stratosphere, which is compared to the Standard Radiation Atmosphere model. At middle and high latitudes a small seasonal variation appears, with larger particles and higher optical depths in winter.

The Residual Snow Cover in the Canadian Arctic in July: A Means to Evaluate the Regional Maximum Snow Depth in Winter

This paper examines the residual snow cover in the Canadian Arctic during the month of July in the period 1948-83 inclusive using air photographs. The study area includes the Ungava Peninsula, part of the District of Keewatin and the Arctic Archipelago, except for the mountainous regions to the west of the Labrador Sea, and Baffin Bay, where numerous snow fields and glaciers are present. In spite of the spatial discontinuity of the air photographs taken during the second half of July, the authors were able to study 555,519 sq km or 46%, of the forementioned territory. Within this territory, 1899 sq km are covered by residual snow during summer, or an average of 3336 sq m/sq km. A correlation of r=0.93 was observed between the residual snow cover in the different regions during the second half of July and the maximum snow cover thickness during winter measured by Environment Canada. A model permitting the estimation of the maximum snow cover thickness in regions where meteorological stations do not exist was formulated. The model is applicable at small and medium scales. In addition, the authors propose that the Hudson Strait region is the most susceptible to the formation of glaciers if one hypothesizes that the regions with the thickest residual snow cover are the most susceptible to glaciation. Key words: snow patches, Canadian arctic climate, snowfalls, snow depth, glaciation

The Zooplankton community of Croker Passage, Antarctic Peninsula

Zooplankton species composition, abundance and vertical distribution were investigated in the upper 1000 m of Croker Passage, Antarctic Peninsula during the austral fall (March–April, 1983). 106 species were identified, many being mesopelagic and reported previously from the Southern Ocean. The most numerous species (>1000/100 m3) were the copepodsMetridia gerlachei, Microcalanus pygmaeus, Oncaea antarctica andOncaea curvata. Oncaea curvata alone constituted half the zooplakton population. Zooplankton biomass was dominated by three copepod species,Metridia gerlachei, Calanoides aculus andEuchaeta antarctica,which comprised 74% of the biomass. Size analysis revealed most of the zooplankton numbers were in the >1 mm fraction. The biomass distribution was polymodal with major maxima in the >1 mm and the 4–4.9 mm size classe. The >1 mm peak, exclusive of protozoans, was primarily copepod nauplii and copepodites ofOncaea, Metridia andMicrocalanus. The 4–4.9 mm peak was mostlyCalanoides acutus andMetridia gerlachei. All of the principal species had broad vertical distributions both day and night. There was some suggestion of diel vertial migration byMetridia gerlachei andEuchaeta antarctica, with segments of their populations migrating into the upper 100 m and 200 m, respectively, at night. Most of the dominant and subdominant species were concentrated below 200 m,with only the subdominantOithona similis having its maximum in the epipelagic zone. The occurrence of zooplankton at winter depths appears to have been earlier in Croker Passage in 1983 than has been generally reported for waters south of the Polar Front. Total standing stock of net-caught zooplankton (>15 mm) in the upper 1000 m was estimated at 3.1 gDW/m2, which is somewhat higher than values reported for the West Wind Drift and for open ocean areas of temperate to tropical latitudes.Euphausia superba (17–52 mm) dominated the pelagic biomass, exceeding zooplankton standing stock under a square meter of ocean by a factor of 15. This is in contrast to lower latitudes where zooplankton biomass is usually greater than macrozooplankton-micronekton.

The depth of the mixed layer as an indicator of oceanic circulation around New Zealand

Abstract The oceanic circulation around New Zealand is strongly controlled by the bottom topography. One consequence of this control is the influence of the circulation on the depth of the mixed layer, which results from the isopycnals tilting upwards over shallowing bottom topography. The influence is strongest on the winter depth of the mixed layer, which marks the top of the main thermocline. In some regions where the depth of the mixed layer exhibits considerable relief both alongshore and offshore, and the transit time of the water is short compared to that for the horizontal current shear to be cancelled by the vorticity input from the vertical current shear, conservation of vorticity arguments may be applied to the flow of the mixed layer. Where these criteria are met, both near East Cape and on the west coast continental shelf near the head of the Hokitika Canyon, vorticity arguments indicate that the mean current would be expected to increase shorewards.

Management of grassland on the sunny aspect of North Canterbury dry hill country: environment and quantity and quality of herbage

Abstract The climate during the year from April 1979, the soil, and the unimproved vegetation (predominantly Rytidosperma = danthonia/striated clover grassland) of a site in North Canterbury at 500 m altitude, with north-westerly aspect are described. Soil moisture was below wilting point from late November to late February. The block was grazed by 11 hoggets/ha for a week in mid July and with 7.5 ewes/ha plus their lambs from early August to early October. Herbage mass varied throughout the year between 4000 and 1000 kg DM/ha with in vitro digestibility of less than 600/0. Dead herbage was the main component for most of the year and its digestibility of less than 40% depressed herbage quality. Regrowth from quadrats clipped at 3-weekly intervals was 2630 kg DM/ha/a. Although minimum soil temperatures at 20 mm depth in winter exceeded 10°C, herbage regrowth was less than 20 kg DM/ha/day. Differences in herbage regrowth during the moist seasons were related best to seasonal variation in soil temperature at...

Seasonal study of the interrenal function of the European Green frog, in vivo and in vitro

The existence of seasonal changes in the secretory activity of the interrenal glands in European Green frogs has been investigated in vivo, in a natural environment, and in vitro, using a perifusion system technique. In vivo, plasma corticosterone levels have been systematically measured at six different moments during a 24-hr period (03, 07, 11, 15, 19, and 23 hr), for almost all the months, during 2 consecutive years. In this part of the study, corticosterone concentrations were assayed in duplicate, in an average of seven animals at each of the six definite moments of the 24-hr cycle. Significant fluctuations in circulating corticosterone have been recorded: a single peak in late spring (May and June) coinciding with the spawning period; a decrease during summer and autumn; the nadir in the depth of winter (February); and a sharp increase at the emergence from hibernation (end of March). The amplitude of the fluctuations ranged from 0.28 ± 0.07 μg/100 ml in late February to 2.68 ± 0.36 μg/100 ml in late May. No significant difference in plasma corticosterone concentrations was observed between males and females. The in vitro studies consisted of comparing the responses of perifused frog interrenal tissue to increasing doses of homologous pituitary extracts, at various times of the year. According to the date of the experiment, important differences in maximum corticosterone snd aldosterone secretions were recorded. As an example, under submaximum ACTH stimulations, 188 and 193% increases in corticosterone and aldosterone outputs, respectively, were recorded on June 4th, whereas the corresponding figures on October 17th were 38 and 54%. The maximum capacity of interrenal tissue to secrete corticosterone and aldosterone after stimulation by homologous pituitary extract was observed in May and June, whereas the minimum capacity was recorded in winter. These results are in complete agreement with our in vivo data. From the present results, we conclude that corticosterone production undergoes seasonal fluctuations in European Green frog. Since the fluctuations cannot simply originate from variations of ambient temperature ( F. Leboulenger, C. Delarue, M. C. Tonon, S. Jegou, and H. Vaudry, 1978, Gen. Comp. Endocrinol. 36, 327–338), our in vitro results support the view that plasma corticosterone rhythms are due, at least in part, to seasonal variations of interrenal sensitivity to ACTH.