Long term simulations of potential oil spills around Cuba

Simulations over eight years of continuous surface oil spills around Cuba are carried out to identify the most likely stranding (beaching) locations. The open source Lagrangian oil drift model OpenOil is applied with high resolution hydrodynamic forcing. The actual fraction of the released oil mass reaching different regions is calculated, revealing small differences between a light and a heavy crude oil type. Similar stranding rates for the two oil types are found. Another important conclusion is that, due to the high temporal variability in stranding rates, short term simulations of a few weeks are not suitable to assess environmental risk. The highest stranding rates are simulated in winter in Northern Cuba. It is also found that oil could reach Northern Cuba, Yucatan or Florida in about 3–5 days after a spill.publishedVersio

Influence of the Caribbean Sea eddy field on Loop Current predictions

Previous studies have shown how the passage of eddies from the Caribbean Sea (CS) to the Gulf of Mexico (GoM) can impact the Loop Current (LC) system, in particular the detachments of LC Eddies (LCEs). Here we used numerical modeling to investigate the impact of the eddy field in the CS on LC predictions. We used a HYCOM ocean model configuration of the North Atlantic at 1/12° resolution to perform two data-assimilative experiments: one in which all available observations were assimilated (Ref), and one in which all available observations were assimilated except in the CS, where climatological altimetry values were assimilated instead of actual observations, leading to dampening the mesoscale activity there (NoCarib). These experiments took place in 2015, when the LC was very active with several LCE detachments, re-attachments, and separations. Each of these experiments was used to initialize 28 60-day forecast simulations every 10 days. In terms of model Sea Surface Height (SSH), the forecasts initialized with the Ref experiment had, on average, lower errors than the forecasts initialized with the NoCarib experiment in the southeastern part of the GoM, with a peak during the 31-40 day forecast period. More importantly, the errors in predicting the date of the next LCE detachment or separation were smaller in the forecasts initialized from the more realistic Ref experiment. Finally, the forecasts initialized by the NoCarib experiment showed a much higher level of false negatives predictions, meaning that no LCE detachment was predicted whereas a detachment actually happened. Overall, 68% of LCE detachments were predicted with an error smaller than 15 days in the forecasts initialized from the more realistic Ref experiment, but only 32% in the forecasts initialized from the NoCarib experiment, stressing the importance of the CS eddy field for predicting the LC evolution. These findings have implications on the GoM predictability, highlighting the need to either run data-assimilative models covering both the GoM and the CS, or pay particular attention to accurate boundary conditions for limited-area GoM models

Potential Impacts of PCBs on Sediment Microbiomes in a Tropical Marine Environment

Within the tropical marine study site of Guánica Bay, Puerto Rico, polychlorinated biphenyls (PCBs) are subjected to coastal and oceanic currents coupled with marine microbial and geochemical processes. To evaluate these processes a hydrodynamic model was developed to simulate the transport of PCBs within nearshore and offshore marine areas of Guánica Bay. Material transport and circulation information from the model were matched with measurements from samples collected from within the bay. These samples, consisting of both intertidal and submerged sediments, were analyzed for physical characteristics (organic carbon, grain size, and mineralogy), microbial characteristics (target bacteria levels and microbial community analyses), presence of PCBs, and PCB-degrading enzymes. Results show that the bay geometry and bathymetry limit the mixing of the extremely high levels of PCBs observed in the eastern portion of the bay. Bay bottom sediments showed the highest levels of PCBs and these sediments were characterized by high organic carbon content and finer grain size. Detectable levels of PCBs were also observed within sediments found along the shore. Microbes from the bay bottom sediments showed a greater relative abundance of microbes from the Chloroflexi, phylum with close phylogenetic associations with known anaerobic PCB-degrading organisms. Based on quantitative PCR measurement of the biphenyl dioxygenase gene, the intertidal sediments showed the greatest potential for aerobic PCB degradation. These results elucidate particular mechanisms of PCB’s fate and transport in coastal, tropical marine environments

Process studies on the Po River plume, North Adriatic Sea

The coastal processes in the Adriatic Sea and in particular the development and evolution of the Po River plume are studied with a three‐dimensional, primitive equation model. Experiments are performed to examine the buoyancy‐driven flow and the interaction with topography, wind stress, and ambient stratification. The pathways of particles released from the Po are computed to simulate the transport of land‐drained materials. In the absence of wind forcing, the Po River plume consists of an offshore bulge that occupies most of the north part of the basin and a southward coastal current that is confined within the narrow coastal region along the Italian peninsula. When all Adriatic rivers are included, basinwide, buoyancy‐driven, cyclonic coastal flow is established that diminishes the seaward removal of Po waters and promotes their southward advection through the coastal current. Wind stress modifies the above. Winds that are downwelling‐favorable for the Po discharge site (like Bora) restrict offshore plume development, enhance the southward coastal current, and confine the plume within the narrow western Adriatic shelf. Conversely, upwelling‐favorable winds (like Scirocco) eliminate the baroclinic coastal current and advect low‐salinity Po waters toward the shallow parts of the Northern Adriatic. When preexisting stratification of basin waters is described, the density field is influenced by both temperature and salinity. During winter, when the coastal waters tend to be colder and fresher than offshore waters, the cyclonic circulation is sustained owing to input from rivers and particularly the Po. The intense spatial and temporal variability of wind stress and river runoff and the resulting variability in the circulation of the coastal Adriatic Sea are elaborated through a realistic simulation during January 1994

River plume development in semi-enclosed Mediterranean regions: North Adriatic Sea and Northwestern Aegean Sea

The Mediterranean Sea has many coastal regions with complex topography. The study concentrates on semi-enclosed regions that receive freshwater input from rivers. The development of the river plumes under the influence of the important circulation forcing mechanisms and under the guidance of the topographic controls is examined. The study rivers are the Po (North Adriatic) and the Axios (North Aegean). They both provide important inputs of low-salinity waters and land-drained materials for their respected shelf regimes. The rivers are parameterised as sources of zero salinity in the three-dimensional, primitive equation Princeton Ocean Model (POM). The river plumes are studied in the presence of realistic topography and idealised winds. The influence of the general basin circulation on the plume structure is also examined. The development and evolution of the two river plumes exhibit the following common characteristics. The buoyancy-driven flow is characterised by an anticyclonic bulge seaward of the river mouth and a coastal current south of the discharge site contained within a narrow strip along the coast. The coastal current has a southward direction, as both rivers discharge at the west side of the basin. The “meandering” along this dynamic region is due to a baroclinic instability process. Downwelling-favorable winds enhance the buoyancy-driven coastal current and restrict offshore removal of low-salinity waters, while the opposite holds for upwelling-favorable winds. The circulation is influenced by the presence of three coastal boundaries. Differences in the modeled phenomena for the two study regions arise from (a) interaction with ambient flow, which may substantially influence the behavior of the plumes, and (b) the topography and geometry of each basin. For instance, the presence of strong neighboring rivers influences the Po River plume. On the other hand, the narrowness of the basin near the discharge site of the Axios River allows for offshore expansion of the plume all the way to the east coast and the establishment of anticyclonic flow over a large part of the shelf, regardless of wind conditions

Modeling river plume dynamics with the HYbrid Coordinate Ocean Model

The dynamics of large-scale river plumes are investigated in idealized numerical experiments using the HYbrid Coordinate Ocean Model (HYCOM). The focus of this study is to address how the development and structure of a buoyant plume are affected by the outflow properties, as impacted by processes within the estuary and at the point of discharge to the coastal basin. Changes in the outflow properties involved vertical and horizontal redistribution of the river inflow and enhanced vertical mixing inside an idealized estuary. The development of the buoyant plume was evaluated in a rectangular, f-plane basin with flat and sloping bottom conditions and in the absence of other external forcing. The general behavior of a mid-latitude river plume was reproduced, with the development of a surface anticyclonic bulge off the estuary mouth and a surface along-shore coastal current which flows in the direction of Kelvin wave propagation (“downstream”); the momentum balance was predominantly geostrophic. Conditions within the estuary and the outflow properties at the river mouth (where observed profiles may be available) greatly impacted the fate of riverine waters. In flat bottom conditions, larger mixing at the freshwater source enhanced the estuarine gravitational circulation, promoting larger upward entrainment and stronger outflow velocities. Although the overall geostrophic balance was maintained, estuarine mixing led to an asymmetry of the currents reaching the river mouth and to a sharp anticyclonic veering within the estuary, resulting in reduced upstream flow and enhanced downstream coastal current. These patterns were altered when the plumes evolved in the presence of a bottom slope. The anticyclonic veering of the buoyant outflow was suppressed, the offshore intrusion decreased and the recirculating bulge was displaced upstream. The sloping bottom impacts were accompanied by enhanced transport and increased downstream extent of the coastal current in most cases. No major changes in the general properties and especially the vertical structure of the plumes were observed when the vertical coordinates were changed from cartesian–isopycnal, to sigma or to sigma–isopycnal. The findings offer a benchmark for coastal studies with HYCOM, where plume dynamics should be examined in tandem with additional circulation forcing mechanisms, resulting in transitions of the vertical coordinate system that are dictated by the prevailing dynamics

Connectivity of North Aegean circulation to the Black Sea water budget

The brackish Black Sea Waters (BSW) outflow to the Aegean Sea, through the Dardanelles Strait, affects and determines significantly the physical characteristics of the North Aegean Sea. Continuous monitoring of the Dardanelles outflow physical properties does not exist. Here, we present the development of a novel methodology to extract a 2-year (2002–2003) timeseries of the transport rates and physical characteristics of the exchange at Dardanelles Strait. Specifically, we have developed a two-layer Dardanelles flow mathematical parameterization, based on the Black Sea water budget, in order to calculate the buoyant outflow characteristics. This was applied as time varying input to the high resolution (1/50°), three-dimensional, North Aegean HYCOM model with realistic forcing conditions (boundary, initial, atmospheric). The simulation results revealed a strong correlation between the BSW spreading and the formation of major North Aegean hydrodynamic circulation patterns. The distribution of several physical (salinity, temperature, mixed layer depth) and biological (chlorophyll-a) characteristics, exhibits an intensive horizontal variability, which depends on the combination of four North Aegean factors: the BSW pathways, the meteorological conditions, the major rivers outflow and the mass exchanges with the South Aegean. Validation of the new parameterization approach showed higher correlation between model results and satellite and in situ data, in comparison to previous parameterizations that employed climatogically varying inputs at the Dardanelles. The novel methodology allows, for the first time, the connectivity of the Aegean Sea circulation to the Black Sea water budget through the Dardanelles Strait. ► Connectivity of North Aegean circulation to the Black Sea water budget. ► HYCOM adaptation in the N. Aegean under realistic atmospheric, initial and boundary conditions. ► Parameterization of the Dardanelles 2-layer exchange flow based on the Black Sea water budget. ► Physical parameters spatial and seasonal variability