Northern boundary current variability and mesoscale dynamics: a long-term HF RADAR monitoring in the North-Western Mediterranean Sea

Ocean Dynamics - Coastal waters are globally challenging areas to monitor not only because of the high resolution needed to resolve the scales at stake but also because most satellites are not yet...     

Dynamics and transport from the boundary Northern Current toward the Toulon Bay: multi-platform observations and downscaling modelling approaches

Ocean Dynamics - Coastal regions are vulnerable areas with often high population density, as well as tourism and maritime activities that may have negative impact on the environment. From a...     

Distribution and Sources of Carbon,Nitrogen and Their Isotopic Compositions in Tropical Estuarine Sediments of Mtoni,Tanzania

Ocean Science Journal - Elemental (C, N) and isotopic (δ13C, δ15N) signatures were used as proxies to identify seasonal changes in proportions of sedimentary organic matter (OM) in the...     

Abrupt onset of carbonate deposition in Lake Kivu during the 1960s: response to recent environmental changes

This study interprets the recent history of Lake Kivu, a tropical lake in the East African Rift Valley. The current gross sedimentation was characterized from a moored sediment trap array deployed over 2 years. The past net sedimentation was investigated with three short cores from two different basins. Diatom assemblages from cores were interpreted as reflecting changes in mixing depth, surface salinity and nutrient availability. The contemporary sediment trap data indicate seasonal variability, governed by diatom blooms during the annual mixing in the dry season, similar to Lakes Malawi and Tanganyika. The ratio of settling fluxes to net sediment accumulation rates implies mineralization rates of 80–90% at the sediment-water interface. The sediment cores revealed an abrupt change ~40 years ago, when carbonate precipitation started. Since the 1960s, deep-water methane concentrations, nutrient fluxes and soil mineral inputs have increased considerably and diatom assemblages have altered. These modifications probably resulted from a combination of three factors, commonly altering lake systems: the introduction of a non-native fish species, eutrophication, and hydrological changes inducing greater upwelling. Both the fish introduction and increased rainfall occurred at the time when the onset of carbonate precipitation was observed, whereas catchment population growth accompanied by intensified land use increased the flux of soil minerals already since the early twentieth century due to more intense erosion.     

Seasonal changes in zooplanktonic alkaline phosphatase activity in Toulon Bay (France): the role of Cypris larvae

We studied zooplankton contribution to the total particulate phosphatase activity, the kinetics of this activity, the relation to the different taxonomic groups and the role of particle-bound bacteria. The activity of total particulate material collected from a liter of seawater was more elevated in May, June and August than during the rest of the year. These high activities resulted from a high contribution of the >90 microm fraction which account then for more than 60% of the total particulate activity. Two Michaelian processes with high and low V(max) were disclosed on this fraction. The high V(max) component was responsible for the high summer activities. During these periods, high densities of cirriped Cypris were found which were statistically correlated with this high V(max) component as with its specific activity. Moreover, the contribution of attached bacteria to these high activities was low. In return, this contribution was predominant during the periods of low activity. A simple method was developed to characterise this bacterial activity.     

Geomorphology of a modern carbonate slope system and associated sedimentary processes: Example of the giant Great Abaco Canyon,Bahamas

The large acoustic data set acquired during the Carambar cruises is composed of high resolution bathymetry, backscatter data and very‐high resolution seismic lines which allow for an overview of the morphology and sediment transfer processes from the shallow upper slope to the abyssal plain of a modern carbonate system: the north‐eastern slope of the Little Bahama Bank. Surficial distribution of the acoustic facies and echofacies reflects a wide variety of sedimentary processes along and across the slope. The western sector of the Little Bahama Bank is dominated by depositional processes whereas its eastern sector, which is incised in the lower slope by giant canyons, is affected by erosion and bypass processes. Datasets suggest that currents play an important role both in along‐slope sedimentary processes and in the abyssal plain. The Antilles Current appears to affect a large part of the middle and lower slopes. The absence of sizeable present‐day channel/levée complexes or lobes at the mouth of the canyon – revealed by the bathymetric map – indicates that the southward flowing Deep Western Boundary Current influences modern abyssal sediment deposition. Based on depositional processes and indicators of canyon maturity observed in facies distribution, the current study proposes that differential subsidence affects the eastern versus western part of the bank. The morphology of the Great Abaco Canyon and Little Abaco Canyon, which extend parallel to the platform, and the Little Bahama Bank slope appears to be related to the Great Abaco Fracture Zone.     

High-resolution modelling of a coastal harbour in the presence of strong tides and significant river runoff

Ocean Dynamics - In the context of Canada’s Ocean Protection Plan (OPP), improved coastal and near-shore modelling is needed to enhance marine safety and emergency response capacity in the...     

Differences in pathogen indicators between proximal urban and rural karst springs,Central Kentucky,USA

Because of their architecture, karst aquifers are susceptible to contamination by fecal-derived pathogens. Previous studies have examined the behavior of bacterial indicators such as total coliforms (TC) and fecal coliforms (FC) in karst aquifers, but simple techniques for discriminating between human and non-human inputs are still needed. This study examines concentrations of TC, FC, atypical colonies (AC, which grow on the same media as TC), male-specific coliphage virus (MSP, an indicator of human feces), and nitrate at two springs in the Inner Bluegrass region of Kentucky (USA). Blue Hole Spring primarily drains the city of Versailles, whereas spring SP-2 drains pasture. Baseflow was monitored, usually biweekly, from December 2002 to March 2004, while storm flow was monitored in September 2003 and March 2004. At each spring, bacterial concentrations were highest in storm flow and lowest in “normal” baseflow (for which 72-h antecedent precipitation was negligible). Concentrations in baseflow tended to be highest during late spring and summer and lowest during autumn and winter. FC concentrations exceeded regulatory (contact) standards in storm-flow samples. For both storm flow and baseflow, AC concentrations were greater than TC, which in turn were greater than FC. Median AC and TC concentrations were greater in baseflow at Blue Hole than at SP-2. MSP was detected in most samples from Blue Hole but never at SP-2. The AC/TC ratio was typically <15 except for normal baseflow samples at Blue Hole, which is probably impacted by leakage from sanitary sewers, as suggested by MSP and nitrate results. Mobilization of sessile bacteria appears to reduce the AC/TC ratio during storm flow. Consequently, this ratio shows promise as a screening tool to identify sewage inputs in karst groundwater basins under baseflow conditions.     

The effect of density stratification on the prediction of global storm surges

With the long-term goal of developing an operational forecast system for total water level, we conduct a hindcast study of global storm surges for Fall 2014 using a baroclinic ocean model based on the NEMO framework. The model has 19 vertical levels, a horizontal resolution of 1/12°, and is forced by hourly forecasts of atmospheric wind and air pressure. Our first objective is to evaluate the model’s ability to predict hourly sea levels recorded by a global array of 257 tide gauges. It is shown that the model can provide reasonable predictions of surges for the whole test period at tide gauges with relatively large tidal residuals (i.e., gauges where the standard deviation of observed sea level, after removal of the tide, exceeds 5 cm). Our second objective is to quantify the effect of density stratification on the prediction of global surges. It is found that the inclusion of density stratification increases the overall predictive skill at almost all tide gauges. The increase in skill for the instantaneous peak surge is smaller. The location for which the increase in overall skill is largest (east coast of South Africa) is discussed in detail and physical reasons for the improvement are given.