Maximum Depth Range Research Articles

Seasonal, Oceanographic and Atmospheric Drivers of Diving Behaviour in a Temperate Seal Species Living in the High Arctic.

The harbour seal (Phoca vitulina) population in Svalbard marks the northernmost limit of the species’ range. This small population experiences environmental extremes in sea and air temperatures, sea ice cover and also in light regime for this normally temperate species. This study deployed Conductivity Temperature Depth Satellite Relay Data Loggers (CTD-SRDLs) on 30 adult and juvenile harbour seals in 2009 and 2010 to study their foraging behaviour across multiple seasons. A total of 189,104 dives and 16,640 CTD casts (mean depth 72 m ± 59) were recorded. Individuals dove to a mean depth of 41 m ± 24 with a maximum dive depth range of 24 – 403 m. Dives lasted on average 204 sec ± 120 with maximum durations ranging between 240 – 2,220 sec. Average daily depth and duration of dives, number of dives, time spent diving and dive time/surface time were influenced by date, while sex, age, sea-ice concentration and their interactions were not particularly influential. Dives were deeper (~150 m), longer (~480 sec), less numerous (~250 dives/day) and more pelagic during the winter/early spring compared to the fall and animals spent proportionally less time at the bottom of their dives during the winter. Influxes of warm saline water, corresponding to Atlantic Water characteristics, were observed intermittently at depths ~100 m during both winters in this study. The seasonal changes in diving behaviour were linked to average weekly wind stresses from the north or north-east, which induced upwelling events onto the shelf through offshore Ekman transport. During these events the shelf became flooded with AW from the West Spitsbergen Current, which presumably brought Atlantic fish species close to shore and within the seals’ foraging depth-range. Predicted increased in the influx of AW in this region are likely going to favour the growth and geographic expansion of this harbour seal population in the future.

Assessment of the CMD Mini‐Explorer, a New Low‐frequency Multi‐coil Electromagnetic Device, for Archaeological Investigations

ABSTRACTIn this article we assess the abilities of a new electromagnetic (EM) system, the CMD Mini‐Explorer, for prospecting of archaeological features in Ireland and the UK. The Mini‐Explorer is an EM probe which is primarily aimed at the environmental/geological prospecting market for the detection of pipes and geology. It has long been evident from the use of other EM devices that such an instrument might be suitable for shallow soil studies and applicable for archaeological prospecting. Of particular interest for the archaeological surveyor is the fact that the Mini‐Explorer simultaneously obtains both quadrature (‘conductivity’) and in‐phase (relative to ‘magnetic susceptibility’) data from three depth levels. As the maximum depth range is probably about 1.5 m, a comprehensive analysis of the subsoil within that range is possible. As with all EM devices the measurements require no contact with the ground, thereby negating the problem of high contact resistance that often besets earth resistance data during dry spells. The use of the CMD Mini‐Explorer at a number of sites has demonstrated that it has the potential to detect a range of archaeological features and produces high‐quality data that are comparable in quality to those obtained from standard earth resistance and magnetometer techniques. In theory the ability to measure two phenomena at three depths suggests that this type of instrument could reduce the number of poor outcomes that are the result of single measurement surveys. The high success rate reported here in the identification of buried archaeology using a multi‐depth device that responds to the two most commonly mapped geophysical phenomena has implications for evaluation style surveys. © 2013 The Authors.Archaeological Prospectionpublished by John Wiley & Sons Ltd.

Application of Surface Geophysical Measurements to Groundwater Investigation

In this research work, the schlumberger array was adopted. The investigation was carried out in two loca- tions; Ambrose Alli University sports ground and Ujemen village area (Ekpoma environs) in the central part of Edo state, Nigeria. The interpretation of the data showed a resolution of six geoelectric layers. Analyzing the curves, the interpretation gave a total depth of 334.90m (1115.22ft) and 362.60m (1207.46ft) from both VES. Since the dropping of the resistivity in the VES curves indicates an aquifer layer, the depth zone corresponds to the existing saturated aquifer in the study area. These values are found to be in close correlation with the hydrogeological profile of the Ishan plateau. A maximum drill depth range of 320m (1065.6ft) to 350m (1165.5ft) in the study area is suggested.

Drained thaw lake basin recovery on the western Arctic Coastal Plain of Alaska using high-resolution digital elevation models and remote sensing imagery

The landscape on the Arctic Coastal Plain (ACP) of Alaska is dominated by thousands of thaw (thermokarst) lakes and associated drained thaw lake basins (DTLBs). Knowledge of the DTLBs benefits our understanding of thaw lake dynamics, carbon cycles, and paleo-climatic change on the ACP since the end of the Late Glacial. This study initializes the application of high-resolution digital elevation models (DEMs) into a systematic reconstruction of DTLBs on the western ACP and adjacent northern Arctic Foothills. The method combines a machine-based detection algorithm automating the delineation of basin paleoshorelines on IfSAR DEM data and a posterior quality control with the aid of high-resolution aerial photograph and Landsat-5 TM imagery. A total of ~3590km2 of thaw lakes and ~10130km2 of DTLBs were mapped, with an overall accuracy of 99.2% and a Kappa coefficient of 0.988. The delineated DTLB extents are conservative, as validated from eleven field-sampled paleoshorelines. A variety of topologic patterns such as merging, nesting, and overtopping are presented in the reconstructed DTLBs. Basin paleoshoreline levels are subject to average uncertainties of 0.4–0.7 m. The combined area of thaw lakes and DTLBs accounts for 57.1% of the western ACP and 23.2% of the northern Arctic Foothills in the study site. Regional analysis of several spatial and topographic characteristics demonstrates a distinct heterogeneity among the younger Outer Coastal Plain (YOCP), Outer Coastal Plain (OCP), Inner Coastal Plain (ICP), and the Arctic Foothills. Generally, the areal density of DTLBs decreases progressively on higher and older surfaces. The ICP has a lake–DTLB area ratio (0.37) greater than that in the other regions. DTLB bathymetry presents a positive correlation with surface elevation: basin maximum depths range from ~2.0m on the YOCP to ~ 8.0m on the Arctic Foothills. Given the reconstructed DTLBs, a total of 31.9 (±4.9) gigatons of net water drainage were estimated for the entire study area.

Residency time, migration route and survival of Atlantic salmon Salmo salar smolts in a Canadian fjord

Atlantic salmon Salmo salar smolts (n = 181) from two rivers were surgically implanted with acoustic transmitters and released to determine migration route, residency time and survival in a 50 km long estuarine fjord located on the south coast of Newfoundland, Canada. Data obtained from automated receivers placed throughout the Bay d'Espoir fjord indicated that migrating smolts used different routes to reach the outer areas of the fjord. The duration of time that smolts spent in the immediate estuary zone also differed between the two localities (7 and 17 days) although the total time smolts were resident in the fjord was similar and extensive (40 days). Many smolts were resident for periods of 4-8 weeks moving back and forth in the outer part of the fjord where maximum water depths range from 300 to 700 m. Survival in the estuary zone was greater for smolts with prolonged residency in estuarine habitat. Overall smolt survival to the fjord exit was moderately high (54-85%), indicating that the initial phase of migration did not coincide with a period of unusually high mortality.

Three-dimensional active imaging with maximum depth range

In traditional three-dimensional (3D) active imaging methods, the detection depth range is observed to increase linearly with the detection time, and the intensity information was not fully utilized. However, by encoding the relative values into pseudovalues, the intensity information was fully utilized, and we found the maximum detection depth range increases exponentially with the detection time. Furthermore, we present a 3D imaging system capable of exponentially expanding the detection depth range. A 3D scene reconstruction was undertaken with the targets placed at a distance of 600-1100 m. Experimental results indicate that the method expands the detection depth range exponentially without distance resolution loss as compared with the conventional method.

Application of frequency-domain helicopter-borne electromagnetics for groundwater exploration in urban areas

Airborne geophysical methods have been used successfully in groundwater exploration over the last decades. Particularly airborne electromagnetics is appropriate for large-scale and efficient groundwater surveying. Due to the dependency of the electrical conductivity on both the clay content of the host material and the mineralisation of the water, airborne electromagnetics is suitable for providing information on groundwater resources, water quality, aquifer conditions and protection levels. Frequency-domain helicopter-borne electromagnetic systems are used to investigate near-surface groundwater occurrences in detail even in rough terrain and populated areas. In order to reveal the subsurface conductivity distribution, the quantities measured, the secondary magnetic fields, are generally inverted into resistivity–depth models. Due to the skin-effect the penetration depths of the electromagnetic fields depend on the system characteristics used: high-frequency data describe the shallower parts of the conducting subsurface and the low-frequency data the deeper parts. Typical maximum investigation depths range from some ten metres (highly conductive saltwater saturated sediments) to several hundred metres (resistive hard rocks). In urban areas there are a number of man-made sources affecting the electromagnetic measurements. These effects on the secondary field values are discussed on the basis of synthetic data as well as uncorrected and corrected field data. The case histories of different hydrogeological setups in Indonesia, The Netherlands and Germany demonstrate that airborne electromagnetics can be applied to groundwater exploration purposes even in urban areas.

Monitoring of active layer dynamics at a permafrost site on Svalbard using multi-channel ground-penetrating radar

Abstract. Multi-channel ground-penetrating radar is used to investigate the late-summer evolution of the thaw depth and the average soil water content of the thawed active layer at a high-arctic continuous permafrost site on Svalbard, Norway. Between mid of August and mid of September 2008, five surveys have been conducted in gravelly soil over transect lengths of 130 and 175 m each. The maximum thaw depths range from 1.6 m to 2.0 m, so that they are among the deepest thaw depths recorded in sediments on Svalbard so far. The thaw depths increase by approximately 0.2 m between mid of August and beginning of September and subsequently remain constant until mid of September. The thaw rates are approximately constant over the entire length of the transects within the measurement accuracy of about 5 to 10 cm. The average volumetric soil water content of the thawed soil varies between 0.18 and 0.27 along the investigated transects. While the measurements do not show significant changes in soil water content over the first four weeks of the study, strong precipitation causes an increase in average soil water content of up to 0.04 during the last week. These values are in good agreement with evapotranspiration and precipitation rates measured in the vicinity of the the study site. While we cannot provide conclusive reasons for the detected spatial variability of the thaw depth at the study site, our measurements show that thaw depth and average soil water content are not directly correlated. The study demonstrates the potential of multi-channel ground-penetrating radar for mapping thaw depth in permafrost areas. The novel non-invasive technique is particularly useful when the thaw depth exceeds 1.5 m, so that it is hardly accessible by manual probing. In addition, multi-channel ground-penetrating radar holds potential for mapping the latent heat content of the active layer and for estimating weekly to monthly averages of the ground heat flux during the thaw period.

Macroecology of live‐bearing in fishes: latitudinal and depth range comparisons with egg‐laying relatives

We examine how fishes with contrasting reproductive modes (egg‐laying versus live‐bearing) differ in geographic range size and distribution. One hypothesis based on dispersal suggests that egg‐laying taxa should occupy a wider range of latitudes than live‐bearing, whereas the opposite prediction has been derived from the idea that enhanced maternal input and a ‘safe harbor’ during development will enable live‐bearers to occupy a wider range of latitudes and depths than egg‐layers. Cross‐species analysis supports the first hypothesis for teleosts, with egg‐layers living in a wider range of latitudes than live‐bearers but at lower latitudes, across a narrower depth range and at shallow depth. However, elasmobranchs show the opposite pattern, live‐bearers having wider latitudinal ranges. Phylogenetic paired comparisons of sister egg‐laying and live‐bearing taxa confirm these contrasting patterns between teleosts and elasmobranchs. However, depth range, maximum latitude and depth do not differ with reproductive mode. Latitudinal range size increases with body size among all taxa. However, only teleosts have a positive relationship between body size and maximum latitude, depth and depth range, but this does not differ between reproductive modes. Egg‐laying elasmobranchs have low dispersal, but live‐bearers have not extended their maximum latitude or depth, despite the benefits of sheltered offspring. The differences in range size between egg‐layers and live‐bearers and the distinction between teleosts and elasmobranchs is consequence of contrasting mechanisms of dispersal and benefits of maternally buffered transport of developing offspring.

Barium distribution across the Southern Ocean frontal system in the Crozet–Kerguelen Basin

We investigated the dissolved and excess particulate Ba distribution (Ba xs, an estimate of biogenic Ba considered to consist mainly of barite [BaSO 4]) across the complex frontal system of the Crozet–Kerguelen Basin (Southern Ocean; 42–47°S, 62–65°E). Ba xs profiles show the characteristic mesopelagic maximum (depth range between 150 and 400 m) reaching up to 1000 pM in the Subantarctic Zone and Subtropical Front, the highest value observed for Southern Ocean mesopelagic waters. Dissolved Ba (concentrations between 38 and 104 nM) correlates with silicate and alkalinity, but the regression is not perfect, reflecting the involvement of different biogenic carriers in the control of the water column distribution of these compounds. Dissolved Ba in the upper 500 m appears strongly influenced by cross-frontal exchanges, involving both northward and southward transport of water masses. In the mesopelagic waters (150–400 m) of the Polar Front Zone, a dissolved Ba depletion faces the Ba xs maximum. This depletion appears mainly maintained by cross-frontal advection of waters containing less Ba and originating north of the Subantarctic Front. Overall, no clear evidence that precipitation of barite reflected by the occurrence of Ba xs maxima does measurably influence the distribution of dissolved Ba was found.

Species range size distributions for some marine taxa in the Atlantic Ocean. Effect of latitude and depth

The range size distributions of 6643 species in ten different fish and invertebrate taxa dwelling in pelagic (latitudinal range sizes) and benthic (latitudinal and depth range sizes) habitats on both sides of the Atlantic Ocean (80 ∞ N - 70 ∞ S) were studied. The objectives were to analyse: (1) the range size distribution patterns for the various taxa and whether they have right/left skewed or lognormal distributions; (2) the geographical species distributions, to ascertain whether the distribution ranges change with latitude (Rapoport’s rule); and (3) the relationship between the depth ranges of benthic species and their maximum depth of occurrence and how depth range size distributions change with latitude. The pelagic taxa exhibited larger range sizes than did the benthic taxa, continental slope/rise species excepted. On the other hand, the boundaries between geographical provinces for both benthic taxa and pelagic taxa tended to occur in association with major oceanographic processes. The shape of the latitudinal range frequency distributions (LRFDs) of the pelagic organisms were distinctly left-skewed, and the LRFDs for most taxa were significantly different from lognormal. There was no common pattern for the distributions of the benthic organisms, which were lognormal in Cephalopoda, Stomatopoda, and Crustacea Decapoda and tended to be left-skewed and significantly different from lognormal in Pisces. The applicability of Rapoport’s rule was not clearly inferable from the results, and the rule appears to be conditioned by the location of biogeographical boundaries and the endemism rate in the different biogeographical provinces. A clear increase in depth range size with maximum depth range was observable for benthic species, confirming previous studies. Species’ depth range distributions displayed a discernible latitudinal pattern, right-skewed at high latitudes and left-skewed at low latitudes. The location of biogeographical boundaries, and endemism rate by biogeographical province were considered to be the factors most useful in explaining species’ distribution patterns and their conformity or nonconformity to Rapoport’s rule. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 437‐455.

The accuracy and precision of underwater measurements of length and maximum body depth of southern bluefin tuna ( Thunnus maccoyii) with a stereo–video camera system

The accuracy and precision of in situ stereo–video measurements of the snout to fork length (SNFL) (range 830–1412 mm) and maximum body depth (MBD) (range 228–365 mm) of free-swimming southern bluefin tuna (SBT) ( Thunnus maccoyii) were tested by filming live fish in sea cages immediately prior to harvest. Stereo–video measurements of the SNFL of 54 fish produced an average error of 1.72 mm (relative error of 0.16%), while an average error of 1.37 mm (relative error of 0.51%) was recorded for measurements of MBD from 47 fish. A procedure was developed to maximise the accuracy and precision of measurements of the SNFL and MBD from a single SBT over sequential images to avoid the underestimation of SNFL and overestimation of MBD due to sinusoidal changes in body form associated with fast swimming. The results demonstrate the potential of stereo–video systems to non-destructively make counts and measurements of tuna and other fish in both wild fisheries and mariculture situations, without the need to capture and handle them.

Patterns of diversity, depth range and body size among pelagic fishes along a gradient of depth

AbstractStudies of geographical patterns of diversity have focused largely on compiling and analysing data to evaluate alternative hypotheses for the near‐universal decrease in species richness from the equator to the poles. Valuable insights into the mechanisms that promote diversity can come from studies of other patterns, such as variation in species distributions with elevation in terrestrial systems or with depth in marine systems. To obtain such insights, we analysed and interpreted data on species diversity, depth of occurrence and body size of pelagic fishes along an oceanic depth gradient. We used a database on pelagic marine fishes native to the north‐east Pacific Ocean between 40°N and 50°N. We used data from the Pacific Rim Fisheries Program that were obtained from commercial, management and scientific surveys between 1999 and 2000. Depth of occurrence and maximum body length were used to assess the distributions of 409 species of pelagic fishes along a depth gradient from 0 to 8000 m. A presence–absence matrix was used to classify the depth range of each species into 100‐m intervals. Atmar & Patterson's (1995) software was used to quantify the degree of nestedness of species distributions. Pelagic fish species diversity decreased steeply with increasing depth; diversity peaked at less than 200 m and more than half of the species had mean depths of occurrence between 0 and 300 m. The distribution of species showed a very strong nested subset pattern along the depth gradient. Whereas species with narrow ranges were generally restricted to shallow waters, wide‐ranging species occurred from near the surface to great depths. The relationship between maximum body size and mean depth range differed between teleost and elasmobranch fishes: being positive for teleosts, but negative for elasmobranches. Results support hypotheses that some combination of high productivity and warm temperature promote high species diversity, and reject those that would attribute the pattern of species richness to the mid‐domain effect, habitat area, or environmental constancy. The data provided a clear example of Rapoport's rule, a negative correlation between average depth range and species diversity.

Optical fiber recirculating delay line incorporating a fiber grating array

For a practical optical fiber recirculating delay line the maximum notch depth and tunable free spectral range are difficult to achieve because of fixed coupling coefficient and loop length. We present here an optical fiber recirculating delay line incorporating a fiber grating array. In this work, the effect of insertion loss in the delay loop is investigated and used to maximize the notch depth of the frequency response. The tunable free spectral range is obtained from the wavelength dependent loop length introduced by the fiber grating array.

Shear-wave splitting near Guam

Polarities of shear waves from intermediate-focus events underneath Guam are studied. For records from a group of ten events, shear-wave splitting with faster-arriving E-W components are observed. This event group occurred within, or above, one geographic portion of the Wadati-Benioff zone, with depths ranging between 57 and 148 km. Ray tracing calculations were performed for 3-D and 1-D velocity models constructed for the region to determine expected S-wave polarities and ray patterns, as well as their sensitivities to variations in velocity structure. These were used to infer the probable existence of intrinsic anisotropy at depth and to determine the location and magnitude of anisotropy which can explain the observed shear-wave splitting. The most probable location of the anisotropy is beneath the crust and above, or partially within, the subducting slab. Assuming a maximum depth range of 10–120 km for the location of the anisotropy, its amount is about 1%, which may be viewed as a lower bound. Plausible causes of the anisotropy include mantle flow and thin, sheet-like channels filled with lava, or water vapor migrating upward from the subducting slab.