Sediment dynamics modulated by burrowing crab activities in contrasting SW Atlantic intertidal habitats

Biogenic bottom features, animal burrows and biological activities interact with the hydrodynamics of the sediment–water interface to produce altered patterns of sediment erosion, transport and deposition which have consequences for large-scale geomorphologic features. It has been suggested that depending on the hydrodynamic status of the habitat, the biological activity on the bottom may have a variety of effects. In some cases, different bioturbation activities by the same organism can result in different consequences. The burrowing crab Neohelice granulata is the most important bioturbator at SW Atlantic saltmarshes and tidal plains. Because of the great variety of habitats that this species may inhabit, it is possible to compare its bioturbation effects between zones dominated by different hydrodynamic conditions. Internal marsh microhabitats, tidal creeks bottoms and basins, and open mudflats were selected as contrasting zones for the comparison on a large saltmarsh at Bahía Blanca Estuary (Argentina). Crab burrows act as passive traps of sediment in all zones, because their entrances remain open during inundation periods at high tide. Mounds are generated when crabs remove sediments from the burrows to the surface and become distinctive features in all the zones. Two different mechanisms of sediment transport utilizing mounds as sediment sources were registered. In the first one, parts of fresh mound sediments were transported when exposed to water flow during flooding and ebbing tide, with higher mound erosion where currents were higher as compared to internal marsh habitats and open mudflats. In the second mechanism, mounds exposed to atmospheric influence during low tide became desiccated and cracked forming ellipsoidal blocks, which were then transported by currents in zones of intense water flow in the saltmarsh edge. Sedimentary dynamics varied between zones; crabs were promoting trapping of sediments in the internal saltmarsh (380 g m⁻² day⁻¹) and open mudflats (1.2 kg m⁻² day⁻¹), but were enhancing sediment removal in the saltmarsh edge (between 10 and 500 g m⁻² day⁻¹ in summer). The implication is that biologically mediated sedimentological changes could be different among microhabitats, potentially leading to contrasting geomorphologic effects within a particular ecosystem.     

Assessing multidecadal runoff (1970–2010) using regional hydrological modelling under data and water scarcity conditions in Peruvian Pacific catchments

In a context of water scarcity in Peruvian Pacific catchments as a crucial issue for Peru, added to the paucity of data availability, we propose a methodology that provides new perspectives for freshwater availability estimation as a base reference for unimpaired conditions. Under those considerations, a regional discharge of 709 m³/s to the Pacific Ocean is estimated with a significant increasing trend of about 43 m³/s per decade over the 1970 – 2010 period. To represent the multidecadal behaviour of freshwater runoff along the region, a regional runoff analysis is proposed based on hydrological modelling at annual and monthly time step for unimpaired conditions over the whole 1970 – 2010 period. Differential Split‐Sample Tests are used to assess the hydrological modelling robustness of the GR1A and GR2M conceptual lumped models, showing a satisfactory transposability from dry to wet years inside the thresholds defined for Nash–Sutcliffe and bias criteria. This allowed relating physical catchment characteristics with calibrated and validated model parameters, thus offering a regional perspective for dryland conditions in the study area (e.g., the anticlockwise hysteresis relationship found for seasonal precipitation–runoff relationship) as well as the impacts of climate variability and catchment characteristics.     

3D CFD MODELING OF WATER AND SEDIMENT FLOW IN A HYDROPOWER RESERVOIR

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Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite,Granulitgebirge, Germany

Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re-homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe-rich basalt and the enrichment in LILE and U suggest a subduction-related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene-bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so-called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high-grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T-7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal-derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.     

Interannual variability of wave climate in the Caribbean Sea

Ocean Dynamics - Low-frequency interannual climatic oscillations have been reported to influence the precipitation regimes, river discharges, winds, and sea level in the Caribbean Sea. Here, we...     

A mixed continuous and discrete nonlinear constrained algorithm for optimizing ship hull structural design

A nonlinear search algorithm for optimizing constrained design of ship structures is presented. The decision variables can be continuous or discrete and the constraints can be homogeneous or inequality nonlinear functions of those variables. The algorithm does not use gradients; therefore, it can work with non-systematized functions such as tables or another class of design routine. It was tested in the structural design of a Patrol Boat and has proved to be a powerful tool decreasing the time expended in preliminary design when it is done by the conventional spiral approach.     

Marine ecosystem-based management in the Southern Cone of South America: Stakeholder perceptions and lessons for implementation

Ecosystem-based management (EBM) has recently received considerable attention. However, examples of empirical approaches to marine EBM are scarce. Therefore, empirical information on the presence of EBM elements within existing policies and the way they may provide settings and lessons for EBM implementation is timely. This study analyses stakeholders’ perceptions on the existence of EBM principles in current marine management practices and policies, and how they determine perceptions for success and satisfaction regarding coastal management within selected case studies drawn from four developing countries in the Southern Cone of South America. Patterns of response across study sites show that although EBM principles as such are not explicitly included in management/conservation plans, there are policies (mainly local), which generate conditions for more explicit inclusion of them. These are based on participatory bottom-up planning, place-based management and consensus reaching: all elements included within the theoretical literature on EBM implementation.     

SAR observation and model tracking of an oil spill event in coastal waters

Oil spills are a major contributor to marine pollution. The objective of this work is to simulate the oil spill trajectory of oil released from a pipeline leaking in the Gulf of Mexico with the GNOME (General NOAA Operational Modeling Environment) model. The model was developed by NOAA (National Oceanic and Atmospheric Administration) to investigate the effects of different pollutants and environmental conditions on trajectory results. Also, a Texture-Classifying Neural Network Algorithm (TCNNA) was used to delineate ocean oil slicks from synthetic aperture radar (SAR) observations. During the simulation, ocean currents from NCOM (Navy Coastal Ocean Model) outputs and surface wind data measured by an NDBC (National Data Buoy Center) buoy are used to drive the GNOME model. The results show good agreement between the simulated trajectory of the oil spill and synchronous observations from the European ENVISAT ASAR (Advanced Synthetic Aperture Radar) and the Japanese ALOS (Advanced Land Observing Satellite) PALSAR (Phased Array L-band Synthetic Aperture Radar) images. Based on experience with past marine oil spills, about 63.0% of the oil will float and 18.5% of the oil will evaporate and disperse. In addition, the effects from uncertainty of ocean currents and the diffusion coefficient on the trajectory results are also studied.     

Shifts in an epibenthic trophic web across a marine frontal area in the Southwestern Atlantic (Argentina)

Marine benthic trophic relationships and food web structures may be influenced by benthic–pelagic coupling processes, which could also be intensified by the physical dynamics of marine fronts. In this work, we employed stable isotope (δ¹³C and δ¹⁵N) analysis to investigate the influence of the Southwest (SW) Atlantic shelf-break front (SBF; 38–39°S, 55–56°W; Argentina) on an epibenthic trophic web. Epibenthic organisms were sampled, at depths of ~ 100 m, with a non-selective dredge from a sandy bottom community located in frontal (F) and marginal (M) areas. The SBF position and the chlorophyll-a (chl-a) concentrations were inferred using satellite data of the sea surface temperature (SST) and satellite chl-a concentration, respectively. The most noticeable shifts in stable isotopes between the sampled areas were those of the Patagonian scallop, Zygochlamys patagonica (δ¹³C), and those of the sea urchin, Sterechinus agassizi (δ¹⁵N). Diet analyses inferred from stable isotopes and mixing models demonstrated that the dominant component of this community, Z. patagonica, had variable contributions to higher trophic levels between areas. More importantly, the epibenthic assemblage in F areas showed δ¹³C-enriched and δ¹⁵N-depleted isotopic signatures with respect to the M areas. Collectively, this evidence suggests that frontal dynamics promotes the accumulation of δ¹³C-enriched phytoplankton in the seabed in F areas, while in M areas the more degraded organic matter becomes more important in the trophic web, decreasing the δ¹⁵N isotopic signature of the assemblage. Therefore, the trophic web was sustained by fresher food in F areas than in M areas, demonstrating the role of frontal dynamics in the shaping of these communities.     

Macro benthic community assemblage before and after the 2007 tsunami and earthquake at Paracas Bay,Peru

Macrobenthic soft bottom community assemblages were studied from December 2006 to December 2007 at Paracas Bay (Atenas Beach, 13°45' S, 76°17' W, Peru), including the period of the tsunami of 15 August 2007, providing a unique opportunity to assess the effects of this type of natural disturbance in soft bottom marine ecosystems. The results show that the tsunami affected the soft bottom community assemblage by changing the sediment granulometry, the biomass and abundance of epifaunal species, and by increasing the silt proportion. The event affected all functional groups, resulting in an increased numbers and biomass of filter feeder and grazers that were followed soon after by predators during the post-tsunami period. A similar pattern was observed for biomass and the abundance of infaunal species without changing the functional groups. The slow recovery observed after four months was likely related to the loss of sediment stability. In summary, there were differences in the structure and composition of soft bottom macrofaunal assemblages before and after the earthquake and posterior tsunami disturbance, forcing benthic communities to initiate re-colonisation processes.