Gabriel Navarro

Atlantic forcing of the Mediterranean oligotrophy

[1]xa0The Mediterranean Sea shows a peculiar anomaly in its nutrient pattern compared to the global ocean, as there is decrease in nutrient concentration from west to east. This feature has been attributed to the antiestuarine circulation at the Strait of Gibraltar, where an eastward flow of Atlantic nutrient-poor surface waters is compensated by a westward countercurrent of Mediterranean nutrient-rich deep waters. This water exchange has been suggested as the ultimate cause for the oligotrophy of the Mediterranean basin, even though only a few studies have accurately examined the magnitude of the nutrient flux through the Strait of Gibraltar. In this work, data from the Gibraltar Fixed Time series (GIFT) between 2005 and 2008 were used to assess nutrient distributions. Applying a two-layer model of water mass exchange and using the Mediterranean outflow recorded in situ, the net export of nutrients from the Mediterranean to the Atlantic was calculated as 139 and 4.8 Gmol yr−1 of nitrate and phosphate, respectively. The results also demonstrated that the Atlantic inflow is not nutrient depleted and in particular contains significant levels of phosphate, which is the limiting factor for biological productivity in the eastern Mediterranean. The distribution of the quasi-conservative parameter N* in the western and eastern basins indicated that nitrate-deficient surface waters are transformed into phosphate-deficient bottom waters by internal cycling processes. Therefore, phosphate depletion in the Mediterranean does not have its origin in the entry of a phosphorus-impoverished Atlantic inflow through the Strait of Gibraltar.

Environmental Control of Phase Transition and Polyp Survival of a Massive-Outbreaker Jellyfish

A number of causes have been proposed to account for the occurrence of gelatinous zooplankton (both jellyfish and ctenophore) blooms. Jellyfish species have a complex life history involving a benthic asexual phase (polyp) and a pelagic sexual phase (medusa). Strong environmental control of jellyfish life cycles is suspected, but not fully understood. This study presents a comprehensive analysis on the physicochemical conditions that control the survival and phase transition of Cotylorhiza tuberculata; a scyphozoan that generates large outbreaks in the Mediterranean Sea. Laboratory experiments indicated that the influence of temperature on strobilation and polyp survival was the critical factor controlling the capacity of this species to proliferate. Early life stages were less sensitive to other factors such as salinity variations or the competitive advantage provided by zooxanthellae in a context of coastal eutrophication. Coherently with laboratory results, the presence/absence of outbreaks of this jellyfish in a particular year seems to be driven by temperature. This is the first time the environmental forcing of the mechanism driving the life cycle of a jellyfish has been disentangled via laboratory experimentation. Projecting this understanding to a field population under climatological variability results in a pattern coherent with in situ records.

Use of a Real-Time Remote Monitoring Network (RTRM) to Characterize the Guadalquivir Estuary (Spain)

The temporal variability of hydrological variables in the Guadalquivir estuary was examined during three years through a real-time remote monitoring network (RTRM). The network was developed with the aim of studying the influence of hydrodynamical and hydrological features within the estuary on the functioning of the pelagic ecosystem. Completing this data-gathering network, monthly cruises were performed in order to measure biogeochemical variables that are indicative of the trophic status of the aquatic environment. The results showed that several sources of physical forcing, such as wind, tide-associated currents and river discharge were responsible for the spatio-temporal patterns of dissolved oxygen, salinity and turbidity in the estuary. The analysis was conducted under tidal and flood regime, which allowed us to identify river discharge as the main forcing agent of the hydrology inside the estuary. In particular, episodes of elevated turbidity detected by the network, together with episodes of low salinity and dissolved oxygen were closely related to the increase in water supply from a dam located upstream. The network installed provided accurate data that can be rapidly used for research or educational applications and by policy-makers or agencies in charge of the management of the coastal area.

Understanding the patterns of biological response to physical forcing in the Alborán Sea (western Mediterranean)

[1]xa0A singular value decomposition (SVD) analysis was performed to determine the coupled modes of variability of satellite surface chlorophyll (CHL) and absolute dynamic topography (ADT) data for the Alboran Sea (western Mediterranean) during a 12-year period (1998–2009). From this analysis we have been able to detect features of the Alboran Sea dynamics that had not been recognized in previous research on the primary production of this basin. We have found that the two leading SVD modes represent more than 97% of the total squared covariance. The first mode is associated with the inverse barometer and its impact on chlorophyll distribution, whereas the second physical mode can explain the distribution of eutrophic and oligotrophic waters in the Alboran Sea. The results also confirm that the phytoplankton in the basin is very tightly controlled by meteorological and physical processes, via the advection of properties through the Strait, by the influence of Atlantic Jet intensity, which controls the gyres of the basin, and by the activation of up- or down-welling coastal processes by wind.

Internal waves and short‐scale distribution patterns of chlorophyll in the Strait of Gibraltar and Alborán Sea

[1]xa0A selection of ASAR images have been analyzed, together with instantaneous images of surface chlorophyll recorded with MERIS and MODIS, in order to study the relationship between the physical and biological processes associated with internal waves in the Strait of Gibraltar and Alboran Sea. The images show peak levels of chlorophyll at the coastal edges to the north and south of the Camarinal Sill (CS) during the generation of internal waves, and peak levels of chlorophyll associated with the wave fronts as they travel into the Alboran Sea. The images have been compared with in-situ data. The results seem to indicate that, during the generation of the internal waves, a suction process takes place by which coastal waters rich in chlorophyll are drawn towards the center of the channel and then accompany the internal waves as they move towards the Alboran Sea.

Seasonal and interannual variability of the surface circulation in the eastern Gulf of Cadiz (SW Iberia)

[1]xa0An 11-year (1996–2007) time series of current meter observations representative of the open sea circulation; a 4-year (2001–2005) time series of current meter records over the continental shelf and in situ data during different seasons have been compared in order to study the seasonal and interannual variability of the surface circulation in the eastern Gulf of Cadiz. The open sea velocity observations indicate southeastward flow along the northern continental slope of the Gulf of Cadiz, compatible with anticyclonic circulation, during most of the year and more intense during summer months. Flow reversals (northwestward circulation) at seasonal time scales in late autumn and early winter (preferably December and January) are a rather recurrent feature with variable intensity depending on the year. Anticyclonic circulation is associated with westerlies, whereas flow reversals usually take place under easterly episodes, suggesting wind-driven circulation. Negative North Atlantic Oscillation indices (indicative of southward displacement of the Azores high) are also linked to the reversals. Changes in this mainly wind-driven large-scale surface circulation are echoed by the shelf circulation: the coastal countercurrent that closes the mesoscale cyclonic cell over the eastern shelf in spring-summer (upwelling season) is replaced by and eastward current in autumn and winter.

Recruiting at the Edge: Kinetic Energy Inhibits Anchovy Populations in the Western Mediterranean

The Strait of Gibraltar replenishes the Mediterranean with Atlantic waters through an intense eastward current known as the Atlantic Jet (AJ). The AJ fertilizes the southwestern Mediterranean and is considered to be the ultimate factor responsible for the comparatively high fish production of this region. Here, we perform an analysis of the available historical catches and catch per unit effort (CPUE), together with a long series of surface currents, kinetic energy and chlorophyll concentration. We show that the high kinetic energy of the AJ increases primary production but also negatively impacts the recruitment of anchovy. We contend that anchovy recruitment in the region is inhibited by the advection and dispersion of larvae and post-larvae during periods of strong advection by the AJ. The inhibitory impact of kinetic energy on anchovy landings is not a transient but rather a persistent state of the system. An exceptional combination of events creates an outbreak of this species in the Alboran Sea. These events depend on the Mediterranean-Atlantic exchange of water masses and, therefore, are highly sensitive to climate changes that are projected, though not always negatively, for fish landings.

Air–Water CO2 Fluxes in a Highly Heterotrophic Estuary

Estuaries are hotspots of intense biogeochemical cycling that regulate land–ocean exchanges and support a broad range of ecosystem services. They are a particularly important, still under-resolved, component of the global carbon cycle and often flash points for local socioeconomic conflicts. The mesotidal Guadalquivir estuary is fed by one of the Iberian Peninsula’s largest rivers, has a long history of anthropogenic manipulation, and hosts a surrounding population of over 1.7 million people. Monthly sampling of water biogeochemical properties (pigments, nutrients, alkalinity, pH, dissolved oxygen, and organic matter) was carried out in the estuary at 12 stations along its length between November 2007 and August 2009. pCO2 and dissolved inorganic carbon were calculated from total alkalinity and pH, allowing air–water fluxes (FCO2) and land–ocean transport to be estimated. The spatial distribution of oxygen concentration and suspended materials led to divide the system in three zones, the inner estuary (IE), the middle estuary (ME), and the lower estuary (LE), with a minimum oxygen zone and a maximum turbidity zone being found in the IE and ME, respectively. CO2 exchange pattern defined the estuary as a strong source being the IE the major contributor. Thus, estuarine waters were CO2 oversaturated with respect to the atmosphere during most of the study period, with average annual FCO2 values being 66.9u2009±u200918.6, 29.4u2009±u200920.3, and 3.4u2009±u20098.1xa0mmol C m−2 day−1 in the IE, ME, and LE, respectively. The average annual CO2 flux to the atmosphere was 36.4u2009±u200911.7xa0mol C m−2 year−1. The present study reinforces the heterotrophic status of the estuary in relation to the carbon system variable description.

Contribution of Doñana Wetlands to Carbon Sequestration

Inland and transitional aquatic systems play an important role in global carbon (C) cycling. Yet, the C dynamics of wetlands and floodplains are poorly defined and field data is scarce. Air-water fluxes in the wetlands of Doñana Natural Area (SW Spain) were examined by measuring alkalinity, pH and other physiochemical parameters in a range of water bodies during 2010–2011. Areal fluxes were calculated and, using remote sensing, an estimate of the contribution of aquatic habitats to gaseous transport was derived. Semi-permanent ponds adjacent to the large Guadalquivir estuary acted as mild sinks, whilst temporal wetlands were strong sources of (−0.8 and 36.3 ). Fluxes in semi-permanent streams and ponds changed seasonally; acting as sources in spring-winter and mild sinks in autumn (16.7 and −1.2 ). Overall, Doñanas water bodies were a net annual source of (5.2 ). Up–scaling clarified the overwhelming contribution of seasonal flooding and allochthonous organic matter inputs in determining regional air-water gaseous transport (13.1 ). Nevertheless, this estimate is about 6 times < local marsh net primary production, suggesting the system acts as an annual net sink. Initial indications suggest longer hydroperiods may favour autochthonous C capture by phytoplankton. Direct anthropogenic impacts have reduced the hydroperiod in Doñana and this maybe exacerbated by climate change (less rainfall and more evaporation), suggesting potential for the modification of C sequestration.

Evaluation of forest fire on Madeira Island using Sentinel-2A MSI imagery

Abstract A forest fire started on August 8th, 2016 in several places on Madeira Island causing damage and casualties. As of August 10th the local media had reported the death of three people, over 200 people injured, over 950 habitants evacuated, and 50 houses damaged. This study presents the preliminary results of the assessment of several spectral indices to evaluate the burn severity of Madeira fires during August 2016. These spectral indices were calculated using the new European satellite Sentinel-2A launched in June 2015. The study confirmed the advantages of several spectral indices such as Normalized Difference Vegetation Index (NDVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Burn Ratio (NBR) and Normalized Difference Vegetation Index (NDVIreXn) using red-edge spectral bands to assess the post-fire conditions. Results showed high correlation between NDVI, GNDVI, NBR and NDVIre1n spectral indices and the analysis performed by Copernicus Emergency Management Service (EMSR175), considered as the reference truth. Regarding the red-edge spectral indices, the NDVIre1n (using band B5, 705xa0nm) presented better results compared with B6 (740xa0nm) and B7 (783xa0nm) bands. These preliminary results allow us to assume that Sentinel-2 will be a valuable tool for post-fire monitoring. In the future, the two twin Sentinel-2 satellites will offer global coverage of the Madeira Archipelago every five days, therefore allowing the simultaneous study of the evolution of the burnt area and reforestation information with high spatial (up to 10xa0m) and temporal resolution (5xa0days).