Sediment dynamics and geohazards off Uruguay and the de la Plata River region (northern Argentina and Uruguay)

The continental margin off Uruguay and northern Argentina is characterized by high fluvial input by the de la Plata River and a complex oceanographic regime. Here we present first results from RV Meteor Cruise M78/3 of May?CJuly 2009, which overall aimed at investigating sediment transport processes from the coast to the deep sea by means of hydroacoustic and seismic mapping, as well as coring using conventional tools and the new MARUM seafloor drill rig (MeBo). Various mechanisms of sediment instabilities were identified based on geophysical and core data, documenting particularly the continental slope offshore Uruguay to be locus of submarine landsliding. Individual landslides are relatively small with volumes <2km³. Gravitational downslope sediment transport also occurs through the prominent Mar del Plata Canyon and several smaller canyons. The canyons originate at a midslope position, and the absence of buried upslope continuations strongly suggests upslope erosion as main process for canyon evolution. Many other morphological features (e.g., slope-parallel scarps with scour geometries) and abundant contourites in a 35-m-long MeBo core reveal that sediment transport and erosion are controlled predominantly by strong contour currents. Despite numerous landslide events, their geohazard potential is considered to be relatively small, because of their small volumes and their occurrence at relatively deep water depths of more than 1,500?m.     

Stepwise,earthquake-driven coastal subsidence in the Ganges–Brahmaputra Delta (Sundarbans) since the eighth century deduced from submerged in situ kiln and mangrove remnants

Natural Hazards - This study reconstructs the coastal subsidence over the past 1300&nbsp;years in a mangrove region along the coast of the Ganges–Brahmaputra Delta, an area not affected...     

Teasing apart activities of different types of ABC efflux pumps in bivalve gills using the concepts of independent action and concentration addition

Fluorescent dyes and inhibitor compounds are commonly used to detect activity of multixenobiotic resistance (MXR) efflux pumps in marine invertebrates. We here address the question whether compounds acting as specific inhibitors of certain mammalian transporters can be used in dye efflux assays to distinguish different transporter activities in gill tissue from a marine mussel. We quantified effects of PSC833, a specific inhibitor of mammalian P-gp (P-glycoprotein, ABCB1), and MK571, which blocks MRP (Multidrug resistance associated protein, ABCC) type transporters, on calcein-am efflux in gill tissue of Mytilus californianus. Calcein-am acts as a substrate of both P-gp and MRP. Effects of single compounds and mixtures were determined and combined effect models predicting independent action (IA) and concentration addition (CA) of the chemicals were applied. Effect values predicted by IA showed better correspondence with the experimentally obtained data. This indicates that the inhibitor compounds target different mechanisms of calcein-am efflux and points to P-gp and MRP activities in mussel gills. Our approach could be a simple way for identifying the efflux transporter types targeted by chemosensitizers, including environmentally relevant compounds, in native tissues from marine invertebrates.     

Persistent quasi-periodic turbidite activity off Saharan Africa and its comparability to orbital and climate cyclicities

Based on a high-resolution sediment record from a submarine meandering canyon system offshore the present-day hyperarid Saharan Africa, two phases of turbidity-current activity can be distinguished during the past 13,000 years. Frequent, siliciclastic turbidity currents can be related to deglacial sea-level history, whereas rhythmically recurring fine-grained and carbonate-rich turbidity currents with recurrence times of roughly 900 years are inferred for the Holocene. Various trigger mechanisms can be considered to initiate turbidity currents, but only a few can explain a periodic turbidite activity. A comparison of Holocene turbidite recurrence times and basic cycles of 900 and 1,800 years found in various Holocene paleoclimate studies suggests that a previously unrecognized climate-related coupling may be active.     

Towards sustainable fisheries subsidies: Entering a new round of reform under the Common Fisheries Policy

On 22 April 2009 the European Commission published its ‘Green Paper on the Reform of the Common Fisheries Policy’. The Green Paper points out a contradiction in policy, noting on one hand that public financial support to the Community's fisheries sector is substantial, but on the other hand such support is often incompatible with other Common Fisheries Policy (CFP) objectives, particularly the need to reduce overcapacities. Providing an analytical framework to better understand the effects of subsidies as well as an overview of existing funding schemes under the CFP, this article aims at answering some of the questions posed by the European Commission within its Green Paper. Answers are based on two ideas: the exploitation of marine capture resources ultimately depends on the level of available fish stocks and that a large share of subsidies fuels the race to fish by inducing investment incentives for the fisheries sector. Policies that have ignored this tend to encourage inefficient and unsustainable fishing as well as the misallocation of public funds. Although support schemes under the CFP have changed in recent years, some problematic support schemes persist. A future reform will have to continue the course taken towards sustainable and efficient approaches to supporting the fisheries industry.     

Strategic forum: The USA,its Navy and the Pacific

Over one hundred years ago William Seward, then US Secretary of State, remarked, ‘Henceforth, European commerce, European politics and European activity, although becoming actually more intimate, will nevertheless sink in importance, while the Pacific Ocean, its shores, its islands and the vast region beyond, will become the chief theatre of events in the world's great hereafter’. The idea that the Asia/Pacific area is one which the USA will have to take more seriously has clearly attracted increasing support in US policy making circles over the past few years. Since the USA faces the Atlantic and Pacific Oceans, it has naturally been vitally concerned with both over the years and has accorded priority first to one and then to the other. All the signs are that the pendulum is now swinging more in favour of the Pacific than it used to do     

A simple model of seasonal open ocean convection

 Aspects of open ocean deep convection variability are explored with a two-box model. In order to place the model in a region of parameter space relevant to the real ocean, it is fitted to observational data from the Labrador Sea. A systematic fit to OWS Bravo data allows us to determine the model parameters and to locate the position of the Labrador Sea on a stability diagram. The model suggests that the Labrador Sea is in a bistable regime where winter convection can be either “on” or “off ”, with both these possibilities being stable climate states. When shifting the surface buoyancy forcing slightly to warmer or fresher conditions, the only steady solution is one without winter convection.  We then introduce short-term variability by adding a noise term to the surface temperature forcing, turning the box model into a stochastic climate model. The surface forcing anomalies generated in this way induce jumps between the two model states. These state transitions occur on the interannual to decadal time scale. Changing the average surface forcing towards more buoyant conditions lowers the frequency of convection. However, convection becomes more frequent with stronger variability in the surface forcing. As part of the natural variability, there is a non-negligible probability for decadal interruptions of convection. The results highlight the role of surface forcing variability for the persistence of convection in the ocean.     

Sediment recycling and adjustment of deposition during deglacial drowning of a low-accumulation shelf (NW Iberia)

Based on a well-established stratigraphic framework and 47 AMS-¹⁴C dated sediment cores, the distribution of facies types on the NW Iberian margin is analysed in response to the last deglacial sea-level rise, thus providing a case study on the sedimentary evolution of a high-energy, low-accumulation shelf system.     

Evolution of the Galicia Interior Basin over the last 60 ka: sedimentary processes and palaeoceanographic implications

The Galicia Interior Basin (GIB; NW Iberian Peninsula) is located near a critical transition between the subtropical (temperate) and subpolar (cold) gyres of the North Atlantic. It therefore witnesses oceanographic changes driven by global climatic events. This study reports on the recent (latest Pleistocene) sedimentary, palaeoceanographic and palaeoclimatic history of the basin. We integrated analysis of deep‐sea sediment cores retrieved from an E–W transect across the GIB. The analysis indicated three types of sedimentary processes recording glacial (Marine Isotope Stage 2–4) and deglacial events: along‐slope bottom currents (forming contourite deposits), pelagic and hemipelagic sedimentation, and gravitational dislocation. Variation in depositional patterns and sedimentation rates indicate distinctive transport (along‐slope and down‐slope) and depositional processes. These in turn reflect climatic and oceanographic drivers. We interpret changes in sea level from core evidence showing changes in sediment supply. The cores exhibited conspicuous sedimentary evidence of Heinrich events (HEs). The stratigraphic intervals associated with HEs showed significant lateral variation. We suggest that the lateral variation may result from the development of an oceanographic boundary between surface water masses with different temperature and salinity parameters or changes in surface currents which may have introduced relatively warmer water into the GIB during the last glacial period.