Browsing by Author "Relvas, Paulo"
Now showing 1 - 10 of 27
Results Per Page
Sort Options
- A 60-year time series analyses of the upwelling along the Portuguese CoastPublication . Leitão, Francisco; Baptista, Vânia; Vieira, Vasco; Laginha Silva, Patrícia; Relvas, Paulo; Teodosio, M ACoastal upwelling has a significant local impact on marine coastal environment and on marine biology, namely fisheries. This study aims to evaluate climate and environmental changes in upwelling trends between 1950 and 2010. Annual, seasonal and monthly upwelling trends were studied in three different oceanographic areas of the Portuguese coast (northwestern-NW, southwestern-SW, and south-S). Two sea surface temperature datasets, remote sensing (RS: 1985-2009) and International Comprehensive Ocean-Atmosphere Data Set (ICOADS: 1950-2010), were used to estimate an upwelling index (UPWI) based on the difference between offshore and coastal sea surface temperature. Time series analyses reveal similar yearly and monthly trends between datasets A decrease of the UPWI was observed, extending longer than 20 years in the NW (1956-1979) and SW (1956-1994), and 30 years in the S (1956-1994). Analyses of sudden shifts reveal long term weakening and intensification periods of up to 30 years. This means that in the past 60 years a normal climate UPWI occurred along the Portuguese coast. An intensification of UPWI was recorded in recent decades regardless of the areas (RS: 1985-2009). Such an intensification rate (linear increase in UPWI) is only significant in S in recent decades (increase rate: ICOADS = 0.02 degrees C decade-1; RS = 0.11 degrees C decade-1) while in NW and SW the increase rate is meaningless. In NW more stable UPWI conditions were recorded, however average UPWI values increased in autumn and winter in NW in recently decades (RS: 1985-2009). An intensification rate of UPWI was recorded during summer (July, August and September) in SW and S in latter decades (RS: 1985-2009). The average UPWI values increased in recent decades in autumn in S. Marked phenological changes were observed in S in summer (before downwelling conditions prevail whilst recently when UPWI regimes prevail) with UPWI seasonal regime in S in recent decades becoming similar to those found in SW and NW. Results of this work can contribute to a better understanding of how upwelling dynamics affect/are correlated with biological data.
- Acoustic inversion of the cold water filaments off the Southwest coast of PortugalPublication . Felisberto, P.; Jesus, S. M.; Relvas, PauloCold water filaments have important implications in the biological and chemical exchanges between the coastal and offshore ocean. The Cape São Vicente area in the Southwest coast of Portugal is a well know region where such phenomenon is observed. In October 2004, the multidisciplinary project ATOMS, involving oceanographers and acousticians, was conducted with the objective to complement the sea surface temperature (SST) satellite observation with a full water column characterization. Due to weather and technical conditions during the project sea trial, only CTD measurements in upper layers of the water column were performed. These at sea collected data together with archival data from the NODC database, allowed to establish realistic scenario of the 3D temperature distribution in the area, including deeper water layers. Archival data of temperature profiles suggest the occurrence of other important oceanic phenomena such as the subduction of warm Mediterrenean water, that should also influence the acoustic propagation. With the help of forward acoustic modelling the significance and signature of the individual oceanographic phenomena on the acoustic propagation, regarding different sampling strategies of the area by acoustic means is investigated. These investigations allowed to develop strategies to settle the main problem addressed by this work: invert the cold water filament structure by acoustic means in a complex environment where acoustic propagation is affected also by other important oceanic and bathymetric features. Since, the objective of this work, is to evaluate the ability to perform a 3D characterization of vertical structure of the ocean, a minimal transmit-receive acquisition composed of a suspended source from a ship and a drifting vertical array, is assumed. The spatial structure is obtained by a combination of inversions for ”mean” sound speed/temperature perturbations obtained for source-array cross-sections covering the area of interest. Matched-field and ray tracing based tomography techniques are used in the inversion for the ”mean” perturbations. The planned sampling strategies and necessary acoustic equipment to resolve such oceanic features is discussed having in mind future sea trials.
- Characterisation of coastal counter-currents on the inner shelf of the Gulf of CadizPublication . Garel, Erwan; Laiz, I.; Drago, T.; Relvas, PauloAt the Gulf of Cadiz (GoC), poleward currents leaning along the coast alternate with coastal upwelling jets of opposite direction. Here the patterns of these coastal countercurrents (CCCs) are derived from ADCP data collected during 7 deployments at a single location on the inner shelf. The multiyear (2008–2014) time-series, constituting ~ 18 months of hourly records, are further analysed together with wind data from several sources representing local and basin-scale conditions. During one deployment, temperature sensors were also installed near the mooring site to examine the vertical thermal stratification associated with periods of poleward flow. These observations indicate that the coastal circulation is mainly alongshore and barotropic. However, a baroclinic flow is often observed shortly at the time of flow inversion to poleward. CCCs develop all year-round and exclusively control the occurrence of warm coastal water during the upwelling season. On average, one poleward flow lasting 3 days was observed every week, corresponding to CCCs during ~ 40% of the time without seasonal variability. Thus, the studied region is distinct from typical upwelling systems where equatorward coastal upwelling jets largely predominate. CCCs often start to develop near the bed and are frequently associated with 2-layer cross-shore flows characteristic of downwelling conditions (offshore near the bed). In general, the action of alongshore wind stress alone does not justify the development of CCCs. The coastal circulation is best correlated and shows the highest coherence with south-eastward wind in the basin that proceeds from the rotation of southward wind at the West coast of Portugal, hence suggesting a dominant control of large-scale wind conditions. In agreement, wavelet analyses indicate that CCCs are best correlated with alongshore wind occurring in a band period characteristic of the upwelling system (8–32 days). Furthermore, in the absence of wind coastal currents tend to be poleward during summer. This set of observations supports that CCCs develop in response to the unbalance of an alongshore pressure gradient during the relaxation of (system-scale) upwelling-favourable winds, oriented south-eastward in the basin. The relaxation periods defined based on this wind direction show a good correspondence with the periods of poleward flow.
- Characterisation of coastal counter-currents on the inner shelf of the Gulf of CadizPublication . Garel, Erwan; Laiz, I.; Drago, T.; Relvas, PauloAt the Gulf of Cadiz (GoC), poleward currents leaning along the coast alternate with coastal upwelling jets of opposite direction. Here the patterns of these coastal countercurrents (CCCs) are derived from ADCP data collected during 7 deployments at a single location on the inner shelf. The multiyear (2008-2014) time-series, constituting similar to 18 months of hourly records, are further analysed together with wind data from several sources representing local and basin-scale conditions. During one deployment, temperature sensors were also installed near the mooring site to examine the vertical thermal stratification associated with periods of poleward flow. These observations indicate that the coastal circulation is mainly alongshore and barotropic. However, a baroclinic flow is often observed shortly at the time of flow inversion to poleward. CCCs develop all year-round and exclusively control the occurrence of warm coastal water during the upwelling season. On average, one poleward flow lasting 3 days was observed every week, corresponding to CCCs during-40% of the time without seasonal variability. Thus, the studied region is distinct from typical upwelling systems where equatorward coastal upwelling jets largely predominate. CCCs often start to develop near the bed and are frequently associated with 2-layer cross shore flows characteristic of downwelling conditions (offshore near the bed). In general, the action of alongshore wind stress alone does not justify the development of CCCs. The coastal circulation is best correlated and shows the highest coherence with south-eastward wind in the basin that proceeds from the rotation of southward wind at the West coast of Portugal, hence suggesting a dominant control of large-scale wind conditions. In agreement, wavelet analyses indicate that CCCs are best correlated with alongshore wind occurring in a band period characteristic of the upwelling system (8-32 days). Furthermore, in the absence of wind coastal currents tend to be poleward during summer. This set of observations supports that CCCs develop in response to the unbalance of an alongshore pressure gradient during the relaxation of (system-scale) upwelling-favourable winds, oriented south-eastward in the basin. The relaxation periods defined based on this wind direction show a good correspondence with the periods of poleward flow. (C) 2015 Elsevier B.V. All rights reserved.
- Connections between upwelling patterns and phytoplankton variability under different coastal regimes in SW Iberia PeninsulaPublication . Krug, Lilian; Silvano, Kathleen M.; Barbosa, Ana B.; Domingues, Rita B.; Galvão, Helena M.; Luis, Joaquim; Platt, Trevor; Relvas, Paulo; Sathyendranath, ShubhaThe region off southwestern Iberia (NE Atlantic) encompasses a wide variety of oceanographic regimes, including differently (geographic) oriented coastal areas impacted by upwelling, riverine inputs and submarine groundwater discharge, submarine canyons and seamounts, and open ocean waters, thereby potentially promoting zone-specific phytoplankton dynamics. Overall, this heterogeneous region is classified as being very sensitive to climate change, and climate-driven alterations (e.g., sea surface warming, changes in upwelling patterns and intensity) have been recently reported for the area. The present study aims to understand the contribution of upwelling to seasonal and interannual variability of coastal phytoplankton, using a remote sensing-based approach. Phytoplankton variability was evaluated using satellite-derived chlorophyll-a (Chl-a), as a proxy for phytoplankton biomass, and primary productivity (PP). Chl-a were obtained from merged SeaWiFS (Seaviewing Wide Field-of-view Sensor), MeRIS (Medium Resolution Imaging Spectrometer) and MODIS-Aqua (Moderate-resolution Imaging Spectroradiometer) sensors at Globcolour portal. PP data at 9.25 km resolution were derived from Eppley’s Vertically Generalized Production Model, based on SeaWiFS and MODIS-Aqua and available at the Ocean Productivity site. Upwelling intensity was estimated using the difference in sea surface temperature (SST) between off and nearshore zones. Advanced Very-High Resolution Radiometer (AVHRR) 4 km SST were obtained from Pathfinder database. Other phytoplankton environmental drivers, such as local (e.g., river flow) and global (e.g., North Atlantic Oscillation - NAO) climate variables, were also analysed. The study area was divided into subareas differently impacted by upwelling and riverine flow, and satellitederived data was averaged for each zone. Seasonal and interannual variability covering a 14-year time series (1998- 2011) for each variable/region were explored. Chl-a at offshelf locations was significantly lower than coastal areas, and exhibited a fairly stable unimodal annual cycle, with maximum during March. Coastal locations displayed more variable annual patterns, with spring and summer Chl-a maxima, reflecting the impact of upwelling events and freshwater inputs. In respect to interannual variability, NAO index and coastal Chl-a were negative and significantly correlated, with 1-month lag. Chl-a interannual trends were also correlated to local climate variables, namely riverine flow for the easternmost coastal zone. The correlation between upwelling intensity and phytoplankton off SW Iberia is region-dependent being less strong within regions dominated by riverine influence.
- Correction to: Northerly wind trends along the Portuguese marine coast since 1950Publication . Leitão, Francisco; Relvas, Paulo; Canovas, Fernando; Baptista, Vânia; Teodósio, M. A.All figure captions are not accurate. Also, there is a repeated error in most figures because the vertical scales incorrectly show Wind Strenght instead of Wind Strength and in Fig. 4 (mid-panel) 2003 instead of 2004.
- Erasmus experience between the University of Cadiz (Spain) and the University of Algarve (Portugal)Publication . Laiz, Irene; Relvas, Paulo; Plomaritis, Theocharis A.; Garel, ErwanA mobility program was carried out during the last two years between the Universities of Cadiz (Spain) and Algarve (Portugal) under the EU funded Erasmus+ Mobility for Teaching. The objective of the mobility was twofold: on one hand, it included the strengthening of the existing scientific cooperation between the University of Cadiz (home institution) and the University of Algarve (host institution) in the field of the Gulf of Cadiz Physical Oceanography; on the other hand, it pretended to improve the teaching quality, focusing on both the lecturers and the students. Both institutions have long ties of cooperation that have recently been intensified under the umbrella of the International Campus of Marine Excellence (CeiMar). Specific objectives oriented towards the lecturers included the exchange of teaching experiences among them as well as the comparison of teaching strategies and methodologies between the host and home institutions at the Master level in order to evaluate and enhance the best teaching practices with the aim of improving the students learning process. Specific objectives oriented towards the students included: (1) to provide local students that cannot afford studying a Master degree abroad with a foreign teacher in the discipline that will offer them different added expectations; (2) to teach students different subjects from those taught at the host institution, thus benefitting from new scientific knowledge and experiences. It must be pointed out that the subject taught by the home institution lecturer represents a competence lacking at the host institution, hence complementing the program of the discipline and providing an added value to the Master degree. Informal questionnaires carried out among students by the host institution revealed that they evaluated having a foreign teacher as a very positive experience. In terms of research, collaboration among both institutions is of great importance because they are both located within the same geographic region and hence, they share common interests. The mobility promoted finishing on-going collaborative publications as well as sharing new research experiences, data and knowledge, hence leading to an improvement of the Physical Oceanography state-of-the-art in the Gulf of Cadiz. In fact, two scientific papers on the Gulf of Cadiz circulation system and two on the storm climate along the Gulf of Cadiz and its relation with coastal hazards have been recently published as a direct result of the mobility program.
- High-resolution observations of the ocean upper layer south of Cape St. Vincent, the western northern margin of the Gulf of CádizPublication . Rautenbach, Sarah A.; Mendes da Silva de Sousa, Carlos A; Carapuço, Mafalda; Relvas, PauloThis article presents an Eulerian physical and biogeochemical dataset from the Iberian Margin Cape St. Vincent Ocean observatory (IbMa-CSV), a facility of the European Multidisciplinary Seafloor and water column Observatory European Research Infrastructure Consortium (EMSO-ERIC), located 10 nautical miles south of Cape St. Vincent (Portugal), the southwest tip of the Iberian Peninsula and western limit of the northern margin of the Gulf of Cádiz (GoC). The observatory was installed on the shelf break, and the data time series spans 4 months for most of the variables. The upper 150 m were sampled intensively with a wave-powered vertical profiler at an average rate of 4.5 profiles per hour recording at 2 Hz when ascending at an approximate velocity of 0.2 m s−1 and 10 Hz when descending at a variable velocity. The vertical resolution was always higher than 0.2 m. Measured channels were conductivity, temperature, pressure, chlorophyll a, dissolved O2 concentration, and turbidity. Derived channels are sea pressure, depth, salinity, speed of sound, specific conductivity, dissolved O2 saturation, density anomaly, spiciness, and Brunt–Väisälä frequency. The acquired dataset includes the flow velocity and direction along the water column, taken from an upward-looking 300 kHz acoustic Doppler current profiler (ADCP) recorded every hour for 3 m depth bins extending the same depth range of the vertical profiler. A standard quality-control scheme was applied to the dataset. The dataset is preserved for multiple use and is accessible in the Sea Open Scientific Data Publication (SEANOE) repository via the following address: https://doi.org/10.17882/94769 (Rautenbach et al., 2022).
- High-resolution observations of the ocean upper layer south of Cape St. Vincent, the western northern margin of the Gulf of CádizPublication . Rautenbach, Sarah A.; Mendes da Silva de Sousa, Carlos A; Carapuço, Mafalda; Relvas, PauloThis article presents an Eulerian physical and biogeochemical dataset from the Iberian Margin Cape St. Vincent Ocean observatory (IbMa-CSV), a facility of the European Multidisciplinary Seafloor and water column Observatory European Research Infrastructure Consortium (EMSO-ERIC), located 10 nautical miles south of Cape St. Vincent (Portugal), the southwest tip of the Iberian Peninsula and western limit of the northern margin of the Gulf of C & aacute;diz (GoC). The observatory was installed on the shelf break, and the data time series spans 4 months for most of the variables. The upper 150 m were sampled intensively with a wave-powered vertical profiler at an average rate of 4.5 profiles per hour recording at 2 Hz when ascending at an approximate velocity of 0.2 ms(-1) and 10 Hz when descending at a variable velocity. The vertical resolution was always higher than 0.2 m. Measured channels were conductivity, temperature, pressure, chlorophyll a, dissolved O2 concentration, and turbidity. Derived channels are sea pressure, depth, salinity, speed of sound, specific conductivity, dissolved O2 saturation, density anomaly, spiciness, and Brunt-V & auml;is & auml;l & auml; frequency. The acquired dataset includes the flow velocity and direction along the water column, taken from an upward-looking 300 kHz acoustic Doppler current profiler (ADCP) recorded every hour for 3 m depth bins extending the same depth range of the vertical profiler. A standard quality-control scheme was applied to the dataset. The dataset is preserved for multiple use and is accessible in the Sea Open Scientific Data Publication (SEANOE) repository via the following address: 10.17882/94769 (Rautenbach et al., 2022).
- Importance of the mesoscale in the decadal changes observed in the northern Canary upwelling systemPublication . Relvas, Paulo; Luis, Joaquim; Santos, A. Miguel P.Analysis of sea surface temperature (SST) time series since 1960 from existing data bases shows a generalized warming trend in the northern Canary upwelling system. The field of the satellite-derived SST trends off Western Iberia was built at the pixel scale (4 x 4 km) for the period 1985-2008, revealing significant spatial differences in the warming rates. Weaker warming trends fit to the known upwelling pattern off the southern part of the Western Iberia, pointing out the intensification of this feature since 1985, particularly during the peak summer months. A more regular behavior is found further north suggesting significant decadal changes in the mesoscale patterns of the northern Canary upwelling system. Citation: Relvas, P., J. Luis, and A. M. P. Santos (2009), Importance of the mesoscale in the decadal changes observed in the northern Canary upwelling system, Geophys. Res. Lett., 36, L22601, doi:10.1029/2009GL040504.
- «
- 1 (current)
- 2
- 3
- »