Responses of African livestock and wild herbivores to drought

The ways in which herbivores regulate their energy and water balance under hot, dry conditions are briefly reviewed. Cattle account for about two-thirds of the biomass of domestic stock in Africa, but their Eurasian origin means that their physiology and grazing behaviour are not wholly adapted to the natural pastures and climate of Africa, especially when drought strikes. In general, most herbivores can withstand heat and water shortage quite well, provided conditions do not become extreme. However, malnutrition will inevitably develop as pasture productivity declines under drought and overgrazing. This will affect most seriously animals that cannot range far from water and that depend mainly on drought susceptible grasses rather than on more resistant shrubs and trees.     

Trends in Interdiurnal Temperature Variation for the Central United States, 1945–1985

Temporal variation in the absolute value of interdiurnal variability (AIDV) of January maximum temperatures is examined for the period 1945–1985 in the central United States (90°–105°W). AIDV indicates the magnitude of day-to-day changes in the maximum temperature. Five-year running-mean AIDV values decreased significantly throughout the period. This trend was apparent for the region overall and for the 10 of the 20 study sites analyzed individually. Temporal variation in AIDV values was significantly related to mid-tropospheric flow patterns over the central United States. Meridional circulation was associated with smaller AIDV values in all sites except those in the northwestern and southeastern corners of the study area, whereas zonal flow was linked to larger interdiurnal temperature change. The analysis of selected individual years indicated that mid-tropospheric circulation patterns were more persistent with meridional flow, and surface cyclones and their associated surface fronts tracked through the study area less frequently than in years with zonal flow. Analysis at a daily temporal resolution revealed an added dimension of trends in temperature variability beyond those apparent with a coarser monthly resolution. These results emphasize the importance of finer temporal resolution in the analysis of both past and projected climate change; regionally summarized monthly temperature values mask important variation in temperature trends apparent at shorter temporal and more local spatial scales.     

Factors that influence water exchange in spring-fed tidal canals

Environmental factors that influenced the rates of water exchange in a series of tidal, dead-end canals in Crystal River, Florida, were investigated by measuring the rates of dilution of the fluorescent dye Rhodamine WT. Water temperature regime was the most influential of these factors, with type of tidal cycle (spring or neap) and density of submersed vegetation (dominated byHydrilla verticillata) only affecting dye dilution rates in winter treatments. Dye half-lives were shortest in the summer (12–24 h), longest in the fall and spring (60–120 h), and most sensitive to water temperature patterns in the winter (26–60 h). These data provide useful information relating to the timing of hydrilla management using aquatic herbicides in spring-fed tidal systems. A mechanism is proposed that relates the canal water temperatures to tidal water movement and outputs from the adjacent Three Sisters Springs.     

Winter Oceanographic Conditions in the Southwestern Part of the Okhotsk Sea and Their Relation to Sea Ice

In the southwestern part of the Okhotsk Sea, oceanographic and sea-ice observations on board the icebreaker Soya were carried out in February 1997. A mixed layer of uniform temperature nearly at the freezing point extending down to a depth of about 300 m was observed. This is much deeper than has previously been reported. It is suggested that this deep mixed layer originated from the north (off East Sakhalin), being advected along the shelf slope via the East Sakhalin Current, accompanied with the thick first-year ice (average thickness 0.6 m). This vertically uniform winter water, through mixing with the surrounding water, makes the surface water more saline (losing a characteristic of East Sakhalin Current Water) and the water in the 100–300 m depth zone less saline, colder, and richer in oxygen (a characteristic of the intermediate Okhotsk Sea water). The oceanographic structure and a heat budget analysis suggest that new ice zone, which often appears at ice edges, can be formed through preconditioning of thick ice advection and subsequent cooling by the latent heat release due to its melting. This revised version was published online in August 2006 with corrections to the Cover Date.     

Step-like structure in temperature and salinity profiles,observed near icebergs trapped by fast ice,Antarctica

Step-like thermohaline structure was observed near icebergs trapped by fast ice in Lützow-Holm Bay, Antarctica. The structure was developed within the draft depth of the icebergs. The typical vertical distance between the succeeding step surfaces is 20–30 m, and the temperature and salinity differences across the step surface are about 0.05–0.06 deg and 0.06–0.10 psu, respectively. The structure appears to be generated by a sea-water/iceberg interaction, and is explainable by a simple model in which an ice wall is placed in the ocean linearly stratified by vertical salinity gradient.     

Coastal polynyas off East Queen Maud Land observed from NOAA AVHRR data

Coastal polynyas off East Queen Maud Land in Antarctica are examined using NOAA AVHRR infrared data. From image analyses, two locations of coastal polynyas in this region are identified; one in Breid Bay and the other along the shelf break. The areal coverage of the Breid Bay polynya is significantly related to the strength of katabatic winds, which maintain their strength over the coastal sea due to land topography favoring for their confluence, thereby being capable of removing newly formed ice. Land fast ice in the eastern part of the bay also plays an additional role in the formation mechanism. It is also found that the areal coverage of coastal polynyas in this region fluctuate coherently. Moreover, these fluctuations correspond to the synoptic index, which measures the strength of the offshore wind, with their peaks closely associated with the areal peaks. These facts strongly suggest the influence of synoptic scale weather on the formation and maintenance of polynyas in this region.     

Histopathological observations on liver,kidney and gonad of plaice (Pleuronectes platessa) taken from the Mersey estuary

The Mersey estuary is the most contaminated estuary in British waters. Detailed studies are underway on the pathology of flounder (Platichthys flesus) from the Mersey and on flounder from the nearby, but less contaminated, Dee estuary. Flounder breed offshore but spend a lot of time in the estuaries, penetrating into freshwater. These flatfish are in close contact with sediments and will be exposed to exenobiotic stored in the sediments. Plaice (Pleuronectes platessa) are flatfish which enter the Mersey with the tidal flow but spend less time in the estuary than flounder and are less likely to show evidence of pollutant exposure. Over 20 plaice were collected from the Mersey. Samples of the liver, kidney and gonad were fixed in 10% formal saline, processed into paraffin wax and 5 microm sections cut and stained with haematoxylin and eosin. Liver changes consisted of variable amounts of glycogen/lipid storage product, minor perivenular and perivascular fibrosis, and helminth parasitisation. No tumours or foci of cellular alteration, necrosis and inflammation were seen. In the gonad only changes consistent with normal gonadal cycling was seen. These studies provide evidence that plaice show little or no evidence of toxic pathological damage resulting from their stay in the estuary.     

Fecundity and spawning of the Atlantic horseshoe crab, Limulus polyphemus, in Pleasant Bay, Cape Cod, Massachusetts, USA

This study provided the first comprehensive analysis of Atlantic horseshoe crab (Limulus polyphemus) fecundity. Limulus appear to be a determinate spawner, maturing all eggs for the breeding season before spawning begins. On average, larger females held a larger number of eggs (63,500) than smaller females (14,500). By the end of the breeding season there was an average of 11,600 mature eggs per female left undeposited, regardless of female size. Larger females laid a higher percentage of the eggs they contained. Thus they not only contain more eggs, but are more effective at laying them as well. Size of spawning females ranged from about 185–300 mm prosomal width, with by far the highest concentration in the mid‐size ranges. Although on an individual basis large females carry and lay the greatest number of eggs, mid‐size crabs as a group contributed more to the horseshoe crab population in Pleasant Bay because they were more plentiful (net fecundity was highest for mid‐size crabs). These results have implications for the management of this important species, which is harvested for bait, scientific, and biomedical uses. Incorporation of these results into models and other management tools can help predict growth rates, effects of size‐selective harvest, reproductive value, and stable stage distribution of populations.     

A towed near-surface optical reflectance meter for measuring ocean colour in support of remote sensing

An underwater optical instrument, the Lighfish, measures near-surface irradiance reflectance in six spectral channels while it is towed from a research vessel at a depth of a few metres. The detectors are configured such that all downward-looking detectors observe the same instrument shadow. Effects of self-shading are negligible for waters and wavelengths having absorption coefficients less than 0.3 m⁻¹. Variance in the derived spectral reflectance ratios is shown to be significantly reduced compared with that in single channel irradiance measurements. The instrument can be used to develop remote sensing algorithms as well as for other oceanographic applications.     

Water mass exchange and diapycnal mixing at Bussol’ Strait revealed by water mass properties

Intensive CTD observations that resolve the mean and tidal components were done with a total of 129 casts in summer of 2001 at Bussol’ Strait. Based on these data and all the available historical data, we have revealed the outflow from Bussol’ Strait to the Pacific and the significant diapycnal mixing in the strait. In the range 27.0−27.3σ _θ , the water property in Bussol’ Strait is almost identical to that of the Kuril Basin Water (KBW). The KBW out of Bussol’ Strait forms a water mass front with the East Kamchatka Current Water (EKCW). This front also corresponds to the front of the Oyashio Current. In the lower part of the intermediate layer (27.3−27.6σ _θ ), part of the water in the strait is characterized by lower temperature, lower salinity, and higher dissolved oxygen than that of KBW and EKCW, which can be explained only by the diapycnal mixing. The strong diapycnal mixing in the strait can also be shown by the density inversion, occurrence frequency of which corresponds well to the amplitude distribution of the diurnal current. In the density range 26.7−26.8σ _θ , the water in Bussol’ Strait has the lowest potential vorticity, suggesting that it is a source region of the low potential vorticity water. Seasonal change of the water can reach up to a density of 26.8σ _θ around Bussol’ Strait. This leads us to propose that the combination of winter convection and local tidal mixing leads to effective ventilation of the intermediate layer.