Wireless Communications for Marine Sensor Networks

Peer Reviewe

Biogeochemical patterns in the Atlantic Inflow through the Strait of Gibraltar

The effects of tidal forcing on the biogeochemical patterns of surface water masses flowing through the Strait of Gibraltar are studied by monitoring the Atlantic Inflow (AI) during both spring and neap tides. Three main phenomena are defined depending on the strength of the outflowing phase predicted over the Camarinal Sill: non-wave events (a very frequent phenomenon during the whole year); type I Internal wave events (a very energetic event, occurring during spring tides); and type II Internal wave events (less intense, occurring during neap tides). During neap tides, a non-wave event comprising oligotrophic open-ocean water from the Gulf of Cádiz is the most frequent and clearly dominant flow through the Strait. In this tidal condition, the inflow of North Atlantic Central Water (NACW) provides the main nutrient input to the surface layer of the Alboran Sea, supplying almost 70% of total annual nitrate transport to the Mediterranean basin. A low percentage of active and large phytoplankton cells and low average concentrations of chlorophyll (0.3–0.4 mg m−3) are found in this tidal phase. Around 50% of total annual phytoplankton biomass transport into the Mediterranean Sea through the Strait presents these oligotrophic characteristics. In contrast, during spring tides, patches of water with high chlorophyll levels (0.7–1 mg m−3) arrive intermittently, and these are recorded concurrently with the passage of internal waves coming from the Camarinal Sill (type I internal wave events). When large internal waves are arrested over the Camarinal Sill this implies strong interfacial mixing and the probable concurrent injection of coastal waters into the main channel of the Strait. These processes result in a mixed water column in the AI and can account for around 30% of total annual nitrate transport into the Mediterranean basin. Associated with type I internal wave events there is a regular inflow of large and active phytoplankton cells, transported in waters with relatively high nutrient concentrations, which constitutes a significant supply of planktonic resources to the pelagic ecosystem of the Alboran Sea (almost 30% of total annual phytoplankton biomass transport)

Baroclinic M2 circulation in Algeciras Bay and its implications for the water exchange with the Strait of Gibraltar: Observational and 3-D model results

The M2 tidal circulation in Algeciras Bay (Strait of Gibraltar) is analyzed using a 3-D, nonlinear, baroclinic, hydrodynamic model, in conjunction with observed data series. Results show the influence of the density stratification on the vertical structure of the M2 currents in Algeciras Bay, although its tidal dynamics shows major differences with respect to the Strait of Gibraltar. Whereas the M2 currents in the Strait present mainly barotropic behavior, the baroclinic effects prevail in Algeciras Bay. A notable finding is the presence of a tidal M2 counter-current system between the upper Atlantic and the lower Mediterranean water layers within the Bay, with amplitudes of up to 25 cm s−1. The interface between the two layers oscillates in antiphase relation with respect to the free-surface elevation, with amplitudes of almost 20 m. The presence of the submarine Algeciras Canyon was found to be determinant in the three-dimensional structure of tidal currents within the Bay, strengthening the baroclinic tidal regime of currents. This situation has quantitative consequences for the flow-exchange processes between Algeciras Bay and the outer Strait, with rates 20 times higher than those obtained when considering only the barotropic behavior, as well as inflow/outflow lateral recirculation volumes during half a tidal cycle that account for more than 20% of the net accumulated volume. This flow-exchange system was found to be affected by the nonlinear interaction processes between the first baroclinic period of resonance of Algeciras Bay and the M2 tide

Seasonal variability of intermediate water masses in the Gulf of Cádiz: implications of the Antarctic and subarctic seesaw

Global circulation of intermediate water masses has been extensively studied; however, its regional and local circulation along continental margins and variability and implications on sea floor morphologies are still not well known. In this study the intermediate water mass variability in the Gulf of Cádiz (GoC) and adjacent areas has been analysed and its implications discussed. Remarkable seasonal variations of the Antarctic Intermediate Water (AAIW) and the Subarctic Intermediate Water (SAIW) are determined. During autumn a greater presence of the AAIW seems to be related to a reduction in the presence of SAIW and Eastern North Atlantic Central Water (ENACW). This interaction also affects the Mediterranean Water (MW), which is pushed by the AAIW toward the upper continental slope. In the rest of the seasons, the SAIW is the predominant water mass reducing the presence of the AAIW. This seasonal variability for the predominance of these intermediate water masses is explained in terms of the concatenation of several wind-driven processes acting during the different seasons. Our finding is important for a better understanding of regional intermediate water mass variability with implications in the Atlantic Meridional Overturning Circulation (AMOC), but further research is needed in order to decode their changes during the geological past and their role, especially related to the AAIW, in controlling both the morphology and the sedimentation along the continental slopes

The Use of Sentinel-3 Altimetry Data to Assess Wind Speed from the Weather Research and Forecasting (WRF) Model: Application over the Gulf of Cadiz

This work presents the quality performance and the capabilities of altimetry derived wind speed (WS) retrievals from the altimeters on-board Copernicus satellites Sentinel-3A/B (S3A/B) for the spatial assessment of WS outputs from the weather research and forecasting (WRF) model over the complex area of the Gulf of Cádiz (GoC), Spain. In order to assess the applicability of the altimetry data for this purpose, comparisons between three different WS data sources over the area were evaluated: in situ measurements, S3A/B 20 Hz altimetry data, and WRF model outputs. Sentinel- 3A/B WS data were compared against two different moored buoys to guarantee the quality of the data over the GoC, resulting in satisfying scores (average results: RMSE = 1.21 m/s, r = 0.93 for S3A and RMSE = 1.36 m/s, r = 0.89 for S3B). Second, the WRF model was validated with in situ data from four different stations to ensure the correct performance over the area. Finally, the spatial variability of the WS derived from the WRF model was compared with the along-track altimetry-derived WS. The analysis was carried out under different wind synoptic conditions. Qualitative and quantitative results (average RMSE < 1.0 m/s) show agreement between both data sets under low/high wind regimes, proving that the spatial coverage of satellite altimetry enables the spatial assessment of high-resolution numerical weather prediction models in complex water-covered zones

Submesoscale, tidally-induced biogeochemical patterns in the Strait of Gibraltar

Tidal forcing and its fortnightly variation are known to be one of the main regulating agents of physical and biogeochemical signatures in the Strait of Gibraltar and surrounding areas. Samples obtained during spring and neap tides in the region were analyzed to determine the influence of this tidal variation on the submesoscale distribution of water masses and biological elements. During spring tides, strong and intermittent mixing processes between Mediterranean and Atlantic waters occur in the vicinity of the Camarinal Sill together with an eastward advection of those mixed waters into the Alboran Sea. Furthermore, the intense suction of surface coastal waters into the main channel of the strait was detected as chlorophyll patches in the Alboran Sea during spring tides. In contrast, the most characteristic phenomenon during neap tides was the arrival of pulses of relatively nutrient-rich North Atlantic Central Waters to the surface regions of the Alboran Sea. In addition, traces of the suction of coastal waters were observed for the first time during neap tides. Therefore, our results show that submesoscale processes are crucial in the dynamics of the Strait of Gibraltar, and they must be considered for the correct description of the biogeochemical features of Alboran Sea, especially during an inactive period of the coastal upwelling

Meteorology for maritime students. Literature search for relevant information on meteorological subject and promotion of teamwork

The Teaching Innovation Project to which we refer below has been focused to pupils of the subject "Meteorology", taught in the third year of the degree in Nautical Sciences and Maritime Transport. Furthermore, the general and specific skills enhanced in the students through this project, are very useful for many other subjects on their degree. The implementation of this project sought the achievement of several learning objectives. First, it was intended to improve the student's preparation in the subject, trying to make more attractive for pupils the usually tedious process of searching and analysis of relevant bibliographic information, not only from an academic point of view, but also from the perspective of the future sailor. Secondly but not least, it has been tried to promote studying and working habits through team activities. Although individual work creates habits of personal reflection, since the student marks his own learning patterns, it carries the risk of leading to subjective interpretations that are little contrast; therefore, is necessary to find a way to properly combine individual and group work. To achieve the aforementioned objectives, this teaching project has enhanced the active work of the student by conducting activities of five members designing thematic posters (chosen from a list of proposed topics), which are later exposed and discussed publicly. Through continuous interaction with fellow students in the preparation of the posters, we have sought to foster critical and self-critical capacity, as well as constructive competition. It promotes creativity and increase the investment of the student in improving their training. A poster is a type of academic communication of great educational interest since, in addition to its obvious importance in the academic field, it provides educational benefits that will be briefly explained below. By having a limited space, the student is forced to develop their ability for synthesize, through the use of graphs, tables, images, etc. This in turn requires applying their capacity for analysis, discerning essential and superfluous concepts. At last, the public exposition and discussion increases the responsibility that falls on the student facing their peers, which positively affects to the quality of the work. This teaching project has been carried out throughout the corresponding semester. With this purpose, a certain number of hours of practical classes were assigned. This affords the student to devote more time for the accomplishment of his work, as well as it allows the teacher a punctual and immediate follow-up of its development. The chosen format (poster size) favoured the attainment of several of the didactic objectives sought, at the same time that it served as an introduction to the student in the methodologies and vehicles of knowledge broadcasting at the academic world

Modeling the biogeochemical seasonal cycle in the Strait of Gibraltar

A physical-biological coupled model was used to estimate the effect of the physical processes at the Strait of Gibraltar over the biogeochemical features of the Atlantic Inflow (AI) towards the Mediterranean Sea. This work was focused on the seasonal variation of the biogeochemical patterns in the AI and the role of the Strait; including primary production and phytoplankton features. As the physical model is 1D (horizontal) and two-layer, different integration methods for the primary production in the Biogeochemical Fluxes Model (BFM) have been evaluated. An approach based on the integration of a production-irradiance function was the chosen method. Using this Plankton Functional Type model (BFM), a simplified phytoplankton seasonal cycle in the AI was simulated. Main results included a principal bloom in spring dominated by nanoflagellates, whereas minimum biomass (mostly picophytoplankton) was simulated during summer. Physical processes occurring in the Strait could trigger primary production and raise phytoplankton biomass (during spring and autumn), mainly due to two combined effects. First, in the Strait a strong interfacial mixing (causing nutrient supply to the upper layer) is produced, and, second, a shoaling of the surface Atlantic layer occurs eastward. Our results show that these phenomena caused an integrated production of 105 g C m− 2 year− 1 in the eastern side of the Strait, and would also modify the proportion of the different phytoplankton groups. Nanoflagellates were favored during spring/autumn while picophytoplankton is more abundant in summer. Finally, AI could represent a relevant source of nutrients and biomass to Alboran Sea, fertilizing the upper layer of this area with 4.95 megatons nitrate year− 1 (79.83 gigamol year− 1) and 0.44 megatons C year− 1. A main advantage of this coupled model is the capability of solving relevant high-resolution processes as the tidal forcing without expensive computing requirements, allowing to assess the effect of these phenomena on the biogeochemical patterns at longer time scales