Martinho Marta-Almeida

Surface circulation in the Gulf of Cadiz: 2. Inflow-outflow coupling and the Gulf of Cadiz slope current

[1] A study of the upper slope circulation in the Gulf of Cadiz is presented. Observations, both original and revisited, and realistic numerical modeling are used together to describe the structure and variability of the slope current system above the Mediterranean outflow. It is shown that the Mediterranean inflow-outflow coupling plays a stronger role than that of the atmospheric forcing in driving the upper slope currents. The Mediteranean outflow forces a surface open ocean current toward the Strait of Gibraltar. Part of it is entrained into the outflow and the remaining flows into the Mediterranean. This latter component does not suffice for the observed transport of the Atlantic inflow into the Mediterranean. A secondary contribution to the inflow is therefore needed to complement the transport. This contribution comes from a persistent equatorward current along the upper slope between Cape St. Vincent and the Strait of Gibraltar. The jet is 20–30 km wide and significant in the upper 200 m attaining subinertial maxima as much as 0.3–0.4 m/s and monthly means in the order of 0.1–0.15 m/s. This current shows a strong variability at time scales in the order of 2–8 days, and displays a significant vertical shear. The response of the upper slope current to synoptic and seasonal atmospheric variability is analyzed. Very low correlation was detected at synoptic scales and the response of the system to seasonal forcing is unclear. A cycle of intensification in June–July and a decrease in winter is apparent in the measurements, but is weak in the model results. It is speculated that the cycle in the observed currents is associated with variability in the inflow/outflow coupling system, rather than driven by seasonally changing wind forcing.

Fundão Dam collapse: oceanic dispersion of River Doce after the greatest Brazilian environmental accident

On 5 November 2015, the Fundão tailings dam collapsed and its content first reached River Doce and then the Atlantic Ocean by 22 November. This study focuses on the oceanic time and space patterns of river discharge dispersion. By using an ocean model together with nLw(555) and RGB images from MODIS sensors, the river plume was followed for 2months after the arrival of the tailings at the ocean. The results show the huge effect of this accident and reveal that riverine waters may have dispersed hundreds of kilometres, reaching regions as far as the shelf in front of the city of Rio de Janeiro. The movement of the freshwater was essentially to the south in accordance with the seasonal wind regime. Episodic frontal systems, leading to wind reversion, and oceanic mesoscale features contribute to the offshore dispersion of the plume. The region more often in contact with the riverine waters was located at the inner shelf between the river mouth and the city of Vitória, turning to the outer shelf and shelf break at lower latitudes.

Towards Operational Modeling and Forecasting of the Iberian Shelves Ecosystem

There is a growing interest on physical and biogeochemical oceanic hindcasts and forecasts from a wide range of users and businesses. In this contribution we present an operational biogeochemical forecast system for the Portuguese and Galician oceanographic regions, where atmospheric, hydrodynamic and biogeochemical variables are integrated. The ocean model ROMS, with a horizontal resolution of 3 km, is forced by the atmospheric model WRF and includes a Nutrients-Phytoplankton-Zooplankton-Detritus biogeochemical module (NPZD). In addition to oceanographic variables, the system predicts the concentration of nitrate, phytoplankton, zooplankton and detritus (mmol N m−3). Model results are compared against radar currents and remote sensed SST and chlorophyll. Quantitative skill assessment during a summer upwelling period shows that our modelling system adequately represents the surface circulation over the shelf including the observed spatial variability and trends of temperature and chlorophyll concentration. Additionally, the skill assessment also shows some deficiencies like the overestimation of upwelling circulation and consequently, of the duration and intensity of the phytoplankton blooms. These and other departures from the observations are discussed, their origins identified and future improvements suggested. The forecast system is the first of its kind in the region and provides free online distribution of model input and output, as well as comparisons of model results with satellite imagery for qualitative operational assessment of model skill.

Characterization of the structure and cross‐shore transport properties of a coastal upwelling filament using three‐dimensional finite‐size Lyapunov exponents

The three dimensional structure, dynamics and dispersion characteristics of a simulated upwelling filament in the Iberian upwelling system are analyzed using Lagrangian tools. We used a realistic regional simulation of the western Iberian shelf which is concomitant with an in-situ oceanographic campaign that surveyed the area. We compute 3d fields of finite--size Lyapunov exponents (FSLE) from 3d velocity fields and extract the fields ridges to study the spatial distribution and temporal evolution of the Lagrangian Coherent Structures (LCSs) evolving around the filament. We find that the most intense curtain-like LCSs delimit the boundaries of the whole filamentary structure whose general properties match well the observations. The filament interior is characterized by small dispersion of fluid elements. Furthermore, we identify a weak LCS separating the filament into a warmer vein and a colder filament associated with the interaction of a mesoscale eddy with the upwelling front. The cold upwelled water parcels move along the filament conserving their density. The filament itself is characterized by small dispersion of fluid elements in its interior. The comparison of LCSs with potential temperature and salinity gradient fields shows that the outer limits of the filament coincide with regions of large hydrographic gradients, similar to those observed, explaining the isolation of the interior of the filament with the surrounding waters. We conclude that the Lagrangian analysis used in this work is useful in explaining the dynamics of cross-shore exchanges of materials between coastal regions and the open ocean due to mesoscale processes.

Quantification and mapping of urban fluxes under climate change: Application of WRF-SUEWS model to Greater Porto area (Portugal)

&NA; Climate change and the growth of urban populations are two of the main challenges facing Europe today. These issues are linked as climate change results in serious challenges for cities. Recent attention has focused on how urban surface‐atmosphere exchanges of heat and water will be affected by climate change and the implications for urban planning and sustainability. In this study energy fluxes for Greater Porto area, Portugal, were estimated and the influence of the projected climate change evaluated. To accomplish this, the Weather Research and Forecasting Model (WRF) and the Surface Urban Energy and Water Balance Scheme (SUEWS) were applied for two climatological scenarios: a present (or reference, 1986–2005) scenario and a future scenario (2046–2065), in this case the Representative Concentration Pathway RCP8.5, which reflects the worst set of expectations (with the most onerous impacts). The results show that for the future climate conditions, the incoming shortwave radiation will increase by around 10%, the sensible heat flux around 40% and the net storage heat flux around 35%. In contrast, the latent heat flux will decrease about 20%. The changes in the magnitude of the different fluxes result in an increase of the net all‐wave radiation by 15%. The implications of the changes of the energy balance on the meteorological variables are discussed, particularly in terms of temperature and precipitation. Graphical abstract: Figure. No caption available. HighlightsAssessment of energy fluxes behaviour under past period and medium‐term climate change projection.Evaluation of climate change at urban scale.Meteorological variables alters the partitioning of the energy fluxes.Changes in the partition of the annual energy balance are found between the two analysed periods.Increase in the magnitude of sensible and storage heat fluxes.

The behaviour of the Doce river sediment plume, Brazil, prior and after an ore dam accident: observational and modelled data results

N chemical markers in the otoliths of temperate and tropical tunas (Thunnus albacares, T. obesus, T. thynnus) were used to investigate their origin and spatial histories at the ocean-basin scale. Here, we provide an overview of the approach and general findings to date for studies conducted in both the Atlantic Ocean and Pacific Ocean. Characterizing the otolith chemistry of youngof-the-year (YOY) tunas is the first step in establishing chemical baselines for each putative nursery (i.e. source), and evaluating the suitability of the approach for investigating trans-ocean movement and homing capabilities. Spatial variation in otolith chemistry of YOY tunas was detected for all species examined and, although elemental ratios and stable isotopes both showed promise for determining an individual’s place of origin, classification success was typically higher for stable isotopes, particularly δ18O. The nursery origin of adolescent and adult T. albacares, T. obesus, and T. thynnus were determined by comparing their otolith core chemistry to YOY baselines, and several interesting patterns were detected. Trans-ocean or trans-boundary movements occurred for all three species examined, suggesting that these tunas are highly migratory with populations connected at the ocean-basin scale. Still, limited movements and high site fidelity were also observed, and this finding indicates that local (versus outside) production may be more important than previously assumed for certain populations of tunas. Given that yields and rebuilding plans are highly sensitive to the movement and mixing of individuals from different production zones, an improved understanding of connectivity is needed to ensure that tuna populations are sustainably managed.During the Cretaceous, the CO2 content of the global atmosphere drastically increased in response to volcanism associated with the disintegration of the former continents. This increase in the global atmospheric CO2 level subsequently led to a considerable rise in global temperatures. The interaction among the high levels of atmospheric CO2, extreme global warmth, and humidity witnessed in the Cretaceous implies extreme environmental conditions, which involved a possibly more acidic and chemically destructive atmosphere than at present; these conditions are believed to have favoured widespread deep weathering at that time. Economically important minerals were reworked from their primary sources during these Cretaceous weathering events. The extreme global warmth witnessed in the Cretaceous also caused the melting of most of the polar ice caps, resulting in the expansion of the volume of Cretaceous seawaters, which subsequently led to a significant rise in the global sea level. Extensive palaeo-seaways played a vital role in transporting and depositing the huge volume of sediments generated during the Cretaceous weathering events, which included economically important minerals (e.g., gold, diamond, and platinum). These mineral deposits are now preserved in Cretaceous sands as placer deposits. Three categories of Cretaceous placer deposits can be distinguished: those occurring in Cretaceous sands resting unconformably on the Precambrian basement, those occurring in Cretaceous sands resting unconformably on the Palaeozoic rocks, and those occurring in Cretaceous sands that unconformably overlay Mesozoic strata.T Doce River (-19.6o; -39.8o), with a watershed of 83.400 km2 and an annual net discharge of 1300m3s-1, represents one of the biggest rivers in Brazil. Along its 853 km there are 228 counties, which are supplied with its waters. The mouth of the Doce River is located at the estuary of Regência, an almost pristine area known by its beaches and where many fishermen get their subsistence. The adjacent continental shelf is narrow (~35km) and is part of one of the most important South Atlantic ecosystems, the archipelago of Abrolhos, which together with the Vitoria-Trindade ridge presents a complex bathymetry, which forces the meandering of the southward Brazilian current and the formation of the Vitoria eddy. Among the Brazilian rivers, the Doce river presents the highest net concentration of suspended particulate matter (SPM, 386,25 mg l-1) and the associated plume extends far north or south depending of the continental shelf preferential flow. The mean shelf circulation is southwards during the spring/summer seasons, presenting a complete reversal during the autumn/winter seasons or during events a cold front passages, becoming northwards. The Brazilian western boundary currents flow at the slope, and to the north of 22oS the circulation between 100-3000 m of the water column is roughly northward. On 5th November 2015 an accident involving a rupture of one of the ore dams of SAMARCO, a Brazilian mining company joint-venture between Vale and the English-Australian BHP Billiton, released 55x106 m3 of toxic-mud into the Doce riverbed. Seventeen days later the mud reached the ocean increasing significantly the SPM concentration of the Doce river plume. Based on a historical (2007-2014) dataset (SPM, currents, tides, waves) collected at numerous stations at the Abrolhos Bank and a realistic numerical simulation performed with the regional ocean modeling system (ROMS) we were able to investigate the seasonal behavior of the plume of the Doce river and infer its influence in the Abrolhos region prior and after the SAMARCO dam accident.The mineral belts of Nigeria include both Pan African structures (N-S, NNE-SSW, ENE-WSW), well preserved in the Western Province of the Nigeria basement complex and the Mesozoic to Early Cenozoic structures (NE-SW and ENE-WSW), less well defined in the Eastern Province of the Nigeria basement. Analyses of these belts revealed that the stress pattern of the Nigerian landmass has changed appreciably from N-S and NNE-SSW trend to NE-SW and ENE-WSW trend over a period of time from Pan African to Early Cenozoic. These changes have led to the growth of intraplate tensional stresses with the resultant development of tensional features such as the Sn-Ta pegmatite belt, the Sn-Nb Younger Granite belt and the Pb-Zn Benue Trough. The mineral belts are connected with deep seated structural features probably extending down to the upper mantle but do not source their metals from this depth except in the case of Cr-serpentinite. The structures serve more as passages for heat/fluid needed to mobilise the metals for redeposition in favourable structures than conduits for transfer of metals from the mantle. The mineral belts source their metals from the adjoining wallrocks, basement rocks and/or sedimentary rocks.W Island is located in Nangroe Aceh Darussalam (NAD) Province, in the city of Sabang, at 95° 12’ 00”-05° 23’ 00” longitude and 05° 46’ 00” 05° 55’ 00” latitude. This is one of the most recent volcanic islands in Sunda orogenic belt which span from Andaman Sea to Banda. This is a type C volcano which means the eruption center of the volcano is unknown but it have fumarole field which is a sign of a past volcanic activity. Based on petrographic and geochemistry analysis show that the type of volcanic rocks found are basalt-andesite. The magma type is tholeiitic and the tectonic environment of volcanic rocks is ”spreading center island”. This result is compatible with tectono-structural of Great Sumatra strike –slip fault which is related to active spreading – arc basin. The structural deformation is a result from Pliosen – Pleistosen tectonic and volcanic activity which is indicated by discovery of the remnant of ancient volcanoes, lineament of volcanic cone, fault scrap, volcanic depression, and lineament of eruption center and also hydrothermal activity as result of past volcanism.Hydrothermal activity discovered in the sea and land of this area. Research about submarine fumarole have been conducted by the Marine Geological Institute of Indonesia (PPPGL) indicate that there is a large amount of submarine fumarole in this area. In the depth 10 meter, the submarine fumarole originated from joints or fissure with a north – south bearing, whereas in the depth of 40 – 50 meter these fumarole mostly formed on top of an undulation which have a similar form as a crater. Based on the location of these fumarole, Semangko strike –slip fault is assumed to have a significant role in the formation and development of it. The fault made joints and fissures on the seabed which make hydrothermal circulation possible.