Observations on the Burrows and Burrowing Behaviour of the Red Band-Fish, Cepola rubescens L.

Abstract. The red band-fish, Cepola rubescens L., lives in burrows in sublittoral muddy sediments. The authors first presented information on the burrows of this species in the 1970s. The present paper presents new information on burrow structure, describes the method of excavation, and comments on the bioturbatory significance of the species. The work derives from field and laboratory studies. A burrow typically consists of a vertical shaft which opens into an expanded terminal chamber. In some cases a side shaft may be added. The paper includes a size analysis of 130 burrows measured in the field and detailed morphological information from a selection of burrows which were cast with polyester resin. The fish burrows are frequently intersected by the burrows of other species and interspecific associations may develop. Burrow size reflects the size of the occupant and may approach 1 m in depth. The biogenic movement of water and particles to this depth is often overlooked in bioturbation studies and is discussed. Burrow distribution is aggregate, which has implications for the bioturbatory impact of the species. Burrows are constructed by mouth excavation and this is described in detail. Fish transport fine material within their mouths and coarse material is grasped in the jaws. Large spoil heaps occur at burrow openings. One obvious effect of this bioturbatory activity at the field site was the redistribution of coarse material (shell gravel) from depth to the sediment surface.     

Nutrient attenuation in a shallow,gravel-bed river. II. Spatial and temporal changes in nitrogen dynamics and community metabolism

ABSTRACT

Instream processes alter the concentration and bioavailability of nutrients as they are transported downstream. By relating primary production and periphyton composition to changes in nutrient concentration in a gravel-bed river this study made inferences about recycling and attenuation. Where dissolved inorganic nitrogen (DIN) was abundant, concentrations decreased linearly with distance but by less than required to meet the nitrogen demand of primary production. Where DIN was barely measurable photosynthesis was reduced but only by 50%. We infer that recycling sustained primary production even when DIN concentrations were negligibly small. One implication is that DIN removal underestimates attenuation. Further experimental research on recycling and improved modelling is required to better quantify the length of streams adversely affected by nutrients.     

In situ experimentation at the water/sediment interface in the deep sea: 1. Submersible experimental instrumentation developed for sampling and incubation

In order to make progress in the study of processes in deep-sea ecosystems, we have developed a strategy for the use of submersibles in conjunction with free vehicles. The BIOCYAN programme, which was conducted by French oceanographers at a permanent station in the Bay of Biscay, involved the use of submersibles for benthic ecological studies. It lead to the development of a variety of equipment for sampling and experimental studies. The submersible Cyana has a limited equipment workload, so the initial step was to develop a free vehicle which could function as a shuttle to act as an independent transport for equipment to be used from the submersible. Two other devices have been developed for sampling with precision the surficial layers of the sediment, one of which can be used in conjunction with an injection module to measure rates of processes in situ by incubations, following injection with labelled substrates. These devices, the free-lift shuttle, tube corers, a blade box corer and the associated injection module are described.     

Scaling analysis of deposition from turbidity currents

Many oil-bearing sedimentary deposits are formed by the settling of particles from turbidity currents. Modeling sedimentary processes that form these turbidites enables the calculation of properties such as extent, depth, porosity and permeability of hydrocarbon-bearing reservoirs. This paper estimates the extent and thickness of turbidites from the initial conditions of the turbidity flow. This is achieved by the application of scaling analysis of the partial differential equations that govern the dynamics of and deposition from turbidity currents. We apply the results of scaling analysis to five modern submarine fans. The predicted and actual values of the dimensions of the fan deposits match well. We then compare the derived results against tabulated sizes of ancient turbidites. The comparisons are good as long as we correctly identify the flow regimes in which the deposition took place. The good agreements observed in the two cases show that the estimates obtained using scaling analysis can provide useful first-guess values for the dimensions of the deposits.     

Geomorphic evolution of the Tongue of the Ocean and the Providence Channels,Bahamas

During their early history the Tongue of the Ocean and the Providence Channels were broad, relatively shallow basins flanked by growing carbonate banks. As the Blake-Bahama platform subsided, sedimentation kept pace with subsidence on the banks, but not in these flat-bottomed troughs, thus increasing the relief. At the outer end of the troughs the Blake-Bahama escarpment, bounding the platform on the east, dropped steeply to the abyssal plain. Sediment gravity flows coursing down this escarpment began to erode a valley headward into the flat-bottom ancestral Northeast Providence Channel. As the relief between the banks and the troughs increased, the flows increased in vigor, and some of them were able to move down the troughs and into the headwardly eroding central valley. The rate of headward erosion thus increased, with the result that still more flows found their way into the valley. The head of this valley is now off central Andros Island, about 225 km from its point of origin, and headward erosion is continuing.Study of bathymetric charts, observations made during sixteen dives in the Tongue of the Ocean using the submersible DSRV “Alvin”, and analogies with subaerial geomorphic processes and their products contributed to the development of this model. The model is consistent with available stratigraphic information.It is emphasized that the morphology of the Tongue of the Ocean and the Providence Channels cannot be explained as the result of a single unidirectional process, such as upbuilding alone or erosion alone. Both have occurred and both are still occurring. Upbuilding predominated early in the history of the Bahamas; it is responsible for the high walls. Erosion began later and has been accelerating through time. It is responsible for the central valley.     

Updated Expressions for Determining Temperatures and Emission Measures from Goes Soft X-Ray Measurements

{We investigate the conversion of the 0.5–4 and 1–8 Å soft X-ray flux measurements made by detectors on the Geostationary Operational Environmental Satellites (GOES) into temperature and emission measures of coronal plasma using modern spectral models and modern understanding of coronal abundances. In particular, the original analysis by Thomas, Starr and Crannell (1985) is updated to take into account the realization that coronal abundances may be quite different from photospheric abundances. An important result of this analysis is that the derived temperatures and emission measures depend strongly on the assumed abundances even at high temperatures where continuum rather than spectral lines dominates the Sun’s X-ray spectrum. This occurs because the higher coronal abundances mean that most of the continuum is due to free–bound emission processes, not free–free emission, and thus is abundance-dependent. We find significant differences between modern calculations of the temperature response of the flux measurements and the versions currently in use: for a typical flare, emission measures may be up to a factor of 4 smaller than the current software suggests. Derived temperatures are similar for both photospheric and coronal abundances for cool flares (e.g., 15 MK), but for hot flares (e.g., 35 MK) coronal abundances can lead to significantly (~25%) lower temperatures being derived.     

Cadmium release caused by the die-back of the saltmarsh cord grass Spartina anglica in Poole Harbour (UK)

As in many other areas, the perennial cord grass Spartina anglica C.E. Hubbard has been extremely successful at colonising the English and Irish south coasts, but it is dying back for reasons that are not completely understood. The present study considers the relationship between die-back and metal concentrations in estuarine sediment. No obvious impact of the metal contamination on the S. anglica growth/die-back could be detected in the study zone, Poole Harbour, although the die-back did seem to have substantially influenced the metal concentrations in the sediments of the estuary. Based on core profiles, the remaining patches of S. anglica still retain elevated concentrations and the overall cadmium concentrations in the sediments have risen since 1925. However, considerable quantities of the cadmium stored in the sediment by S. anglica appear to have been washed out rapidly in the die-back zones. Should serious erosion of the saltmarsh occur, triggered for example by sea-level rise, then sudden and high levels of cadmium release may cause harmful effects to marine biota.     

Magnetic susceptibility of ultrahigh pressure eclogite: The role of retrogression

Retrograde metamorphism played the dominant role in changing the low-field rock magnetic properties and density of 198 specimens of variably retrograded eclogites from the main borehole of the Chinese Continental Scientific Drilling Project (CCSD) and from surface outcrops in the Donghai area in the southern part of the Sulu UHP belt, China. Bulk magnetic susceptibility (κ) of unretrogressed UHP eclogite is controlled by whole-rock chemical composition and ranges from 397 to 2312 μSI with principal magnetic susceptibility carrying minerals paramagnetic garnet, omphacite, rutile and phengite. Partially retrograded eclogites show large variations in magnetic susceptibility between 804 and 24,277 μSI, with high mean magnetic susceptibility values of 4372 ± 4149 μSI caused by appreciable amounts of Fe-Ti oxide minerals such as magnetite, ilmenite and/or titanohematite produced by retrograde metamorphic reactions. Completely retrograded eclogites have lower susceptibilities of 1094 ± 600 μSI and amphibolite facies mineral assemblages lacking high magnetic susceptibility minerals. Jelínek's corrected anisotropy (P_j) of eclogites ranges from 1.001 to 1.540, and shows a positive correlation with low-field magnetic susceptibility (κ). Arithmetic mean bulk density (ρ) shows a steady decrease from 3.54 ± 0.11 g/cm³ (fresh eclogite) to 2.98 ± 0.06 g/cm³ (completely retrograded eclogite). Retrograde metamorphic changes in mineral composition during exhumation appear to be the major factor causing variations in low field magnetic susceptibility and anisotropy. Retrograde processes must be taken into account when interpreting magnetic surveys and geophysical well logs in UHP metamorphic terranes, and petrophysical properties such as density and low-field magnetic susceptibility could provide a means for semi-quantifying the degree of retrogression of eclogite during exhumation.