Structure of Subsurface Sediments in the Scan Basin (Scotia Sea)

The structure of sediments in the Scotia Sea is used as a basis for reconstructing the geological history of its bottom in the Late Quaternary. The Scan Basin is one of the main elements of the topography of the southern Scotia Sea. Its formation played a considerable role in the fragmentation of the continent, which included the Bruce and Discovery banks. The main parameters of the sediment layer in the Scan Basin have been reconstructed by the present time, but its top part has not been studied. In this work, we analyze the first data obtained on the R/V Gesperidas with the use of a TOPAS PS 18/40 high-resolution seismic profilograph in 2012. Three layers in the subsurface sediments on the bottom of the Scan Basin were specified for the first time. The mean periods of their deposition in the Late Quaternary were determined as 115000 years for the first, 76000 years for the second, and 59 000 years for the third layer from the surface of the bottom. The duration of the total accumulation period of the three layers is about 250000 years.     

The infralittoral prograding wedge: a new large-scale progradational sedimentary body in shallow marine environments

A progradational sedimentary body, the infralittoral prograding wedge (IPW), has been developing from the mean fair-weather wave-base level to the storm wave-base level between the onshore (beach) and the offshore (inner continental shelf) depositional zones along the Spanish coast during the Late Holocene. The main sedimentary body is composed of large inclined master beds which prograde seawards parallel to the shoreline, formed by sediments swept offshore by waves from shallow-water littoral environments. The inclined beds downlap onto finer-grained offshore sediments and, in turn, are overlain by shoreface deposits. The IPW is generated by downwelling storm currents and associated seaward transport of sediment. It represents a new depositional model for clastic wave-dominated coasts, and its identification requires a new subdivision of the nearshore environment. Received: 10 June 1999 / Revision accepted: 15 February 2000     

Computer vision techniques for quantifying, tracking, andidentifying bioluminescent plankton

This paper applies computer vision techniques to underwater video images of bioluminescent biota for quantifying, tracking, and identification. Active contour models are adapted for computerized image segmentation, labeling, tracking, and mapping of the bioluminescent plankton recorded by low-light-level video techniques. The system automatically identifies luminous events and extracts features such as duration, size, and coordinates of the point of impact, and uses this information to taxonomically classify the plankton species. This automatic classification can aid oceanographic researchers in characterizing the in situ spatial and temporal relationships of these organisms in their underwater environment. Experiments with real oceanographic data are reported. The results indicate that the approach yields performance comparable to human expert level capability. Furthermore, because the described technique has the potential to rapidly process vast quantities of video data, it may prove valuable for other similar applications     

Biogeochemical implications of the isotopic equilibrium fractionation factor between the oxygen atoms of acetone and water

Carbonyl oxygens of organic molecules undergo isotopic exchange with water during reversible hydration reactions. The equilibrium isotopic fractionation factors between the carbonyl oxygen of acetone and water at 15°, 25°, and 35°C are 1.028, 1.028, and 1.026 respectively. The differences between the δ¹⁸O values of the carbonyl oxygen of acetone and of the water with which it is in equilibrium are similar to the differences that have been observed between the δ¹⁸O values of cellulose and the water used in its synthesis by a variety of aquatic plants and animals. Additionally, the identity of the acetone-water fractionation factors at 15° and 25°C parallels the observation that the difference between the δ¹⁸O values of cellulose and water shows no temperature dependence for individual species of plants grown over the same temperature range. These results are discussed in relation to the proposal that the oxygen isotopic relationship between cellulose and water is established by isotopic exchange occurring during the hydration of carbonyl groups of the intermediates of cellulose synthesis.     

The Gulf of Cadiz: an unstable giant contouritic levee

Recent multibeam bathymetry and acoustic imagery data provide a new understanding of the sedimentary system located in the Gulf of Cadiz which is under the influence of a strong current, the Mediterranean Outflow Water (MOW). When it comes out from the Strait of Gibraltar, the MOW is either channelled along major or secondary channels, or spills over a sedimentary levee. Frequent earthquakes and the constant current shearing generate widespread sediment deformation and instability of contourite deposits. Secondary channels can form by retrogression following an initial failure. At their mouth, sediment accumulates in the form of small sandy contourite lobes. These observations suggest that the Gulf of Cadiz system shares many similarities with channel–levee complexes formed by turbidity current activity. The main difference is that, in the Gulf of Cadiz, the main process is a strongly flowing saline current which locally interacts with gravity processes.     

Sedimentological and paleoenvironmental characterisation of transgressive sediments on the Guadiana Shelf (Northern Gulf of Cadiz, SW Iberia)

During the transgression following the Last Glacial Maximum, four backstepping parasequences were deposited on the northern Gulf of Cádiz shelf (SW Iberia). In contrast to other areas on the shelf, these transgressive deposits are at, or very close to, the surface to the southeast of the Guadiana Estuary mouth. This is particularly true for transgressive parasequence T_C, possibly associated with the Younger Dryas event, and the youngest parasequence T_D, probably linked to a slow-down in sea-level rise at around 8.2 ka BP, both of which form a sandy transgressive bulge on the upper middle shelf.The older and more distal parasequence T_C is characterised on seismic records by convex low-angle sigmoidal clinoforms, and contains high amounts of quartz and bioclasts. In contrast, the younger and more proximal parasequence T_D shows relatively steep concave prograding clinoforms, and contains high amounts of quartz and other terrigenous components, but comparatively low amounts of bioclasts. Furthermore, the difference in age between both parasequences is clearly marked by a difference in the content of glauconite.The results indicate that sediments found in parasequence T_C are associated with deposition related to storm events, with frequent reworking of components, and the more proximal and younger sediments in T_D are the result of rapid sediment accumulation related to floods in the Guadiana River basin, possibly during the transition from a dry cold period to a warmer more humid period, when vegetation cover was lowest and flood frequency increased.Additionally, accumulations of terrigenous components directly associated with the Guadiana River basin found on the outer shelf indicate that, at least during the beginning of the transgression, overflow channels active during large-scale flood events may have spilled material to an area located immediately to the south of the Guadiana Estuary mouth.     

Separating soil and leaf water O isotopic signals in plant stem cellulose

The oxygen-18 signal of soil and leaf water are both recorded in heterotrophically synthesized plant stem cellulose. Presently, these signals can only be teased apart with modeling and assumptions on the nature of the isotopic enrichment of leaf water. A method by which these two signals are chemically separated and analyzed is tested here. Heterotrophically synthesized cellulose from germinating seeds having a mixture of isotopic signals from the reserve carbohydrate (starch) and that of the water during cellulose synthesis was hydrolyzed and the resulting glucose converted to glucose phenylosazone. The analysis of the ¹⁸O/¹⁶O ratios of cellulose and of glucose phenylosazone were used to calculate the oxygen isotope ratio of the oxygen attached to the second carbon of the glucose moieties of the cellulose molecule. The calculated δ¹⁸O value of this oxygen was highly correlated with that of the water available for cellulose synthesis showing a nearly one-to-one relationship (slope = 1.027) and leading to the conclusion that it completely exchanges with water during heterotrophic cellulose synthesis. Once this method is refined so as to increase precision, it will be possible to derive the δ¹⁸O values of soil water available to plants from the oxygen isotope analysis of stem cellulose and its derivative.     

Interactions between rabbits and dung beetles influence the establishment of Erodium praecox

We examine the potential for two species – the wild rabbit Oryctolagus cuniculus and the dung beetle Thorectes valencianus – to affect the establishment of Erodium praecox, an endemic plant of the Iberian Peninsula. Rabbit latrines may be considered potential maternal parent areas of E. praecox. The spatial and temporal stability for nutrients and surface irregularities caused by the activity of rabbits increases bare soil areas. A negative relation between diameter of the basal rosettes of Erodium and the distance to the centroid of latrines was observed. Rabbit latrines were important for E. praecox distribution but their effect was higher when T. valencianus burrows exist. In laboratory conditions, a higher number of seeds buried was observed in latrines with dung beetles, while a lower number of seeds buried was observed in bare soil. T. valencianus activity plays the role of a soil fertilizer, increasing the rate of nutrient cycling and microbial activity which could raise the rate of decomposition of pellets and result in the further release of nutrients. The excavation of the dung beetles increases the soil fertilization and the surface irregularities required for the seeds of E. praecox to be easily self-buried.