Browsing by Author "Gomes, A.I."
Now showing 1 - 8 of 8
Results Per Page
Sort Options
- Diatomáceas como potencial ferramenta para reconstituições paleoecológicasPublication . Gomes, A.I.; Boski, T.; Moura, DelmindaAs diatomáceas são algas unicelulares que abundam tanto em águas doces como salgadas. Este trabalho mostra que as associações de diatomáceas presentes ao longo de um perfil de sapal, junto à foz do rio Guadiana, são sensíveis a vários parâmetros ambientais. Desta forma, confirma‑se o seu potencial como indicador para reconstruções paleoecológicas em estuários, especialmente no que diz respeito a variações do nível médio do mar, como as ocorridas desde a última transgressão posglacial.
- Integrated assessment of bioerosion, biocover and downwearing rates of carbonate rock shore platforms in southern PortugalPublication . Moura, Delminda; Gabriel, Selma; Gamito, Sofia; Santos, Rui; Zugasti, Estibaliz; Gomes, A.I.; Tavares, Ana Mafalda; Martins, Ana LuísaBioerosion on rocky shores has been frequently reported as an important mechanism in coastal evolution, with less attention focussed on determining the bioprotective role organisms may have in mediating coastal erosion. This work aims, for the first time, to provide an integrated assessment of both traversing microerosion meter (TMEM) downwearing rates and activity of intertidal organisms on two carbonate shore platforms in southern Portugal. Paired substations positioned on the same substrate but differing in biological cover (one with bare rock and the other with algal cover colonised between the first and final readings) were monitored for eighteen months using a TMEM. At each station, the volume of burrows produced by macro borers was measured. Downwearing rates were lower in the surfaces protected by algal turf except in the station that experienced the longest time of exposure to subaerial conditions. In contrast, TMEM downwearing rates were higher in the areas containing the higher volume of burrows. Both downwearing rates and burrow volumes were negatively correlated with the mechanical strength of the substrate as measured by Schmidt Hammer rebound.
- Mean sea level and coastline: Late QuaternaryPublication . Moura, Delminda; Gomes, A.I.; Gabriel, Selma; Horta, JoãoCoastal zones modified along the geological time forced by tectonic activity, climatic and mean sea level changes and thereby can preserve relevant information concerning past climatic and oceanographic conditions. During lowstands derived by glacial conditions, the coastline migrated seaward and, wide portions of the continental shelves where exposed to sub aerial evolution, the drainage net extended far away in the shelf and dune fields overspread favoured by dry cold conditions and vegetation scarcity. In contrast, during deglatiations, the mean sea level rose forcing the landward migration of the coastline leading to the landscapes submersion. The preservation of morphological features such as beaches, dunes and spit bars depended on several environmental variables and processes, such as, erosion, remobilization by currents, waves and mass movements and sedimentary burial. The relationship between the coastline and the mean sea level evolution along the Quaternary, as well as the environmental variables on the landscape preservation and remobilization are under discussion in this work.
- Moving sands along a headland-embayed beach system (Algarve, Southern Portugal)Publication . Oliveira, Sónia; Horta, João; Nascimento, Ana; Gomes, A.I.; Veiga-Pires, C.; Moura, DelmindaResilience of embayed and pocket beaches located at the southernmost coast of Portugal is currently a major question to coastal management of this region. In fact, several among those beaches have been artificially fed aiming to increase the width of the beach allowing people to maintain a safe distance to the unstable rocky cliffs.
- Sea-level rise and anthropogenic activities recorded in the late Pleistocene/Holocene sedimentary infill of the Guadiana Estuary (SW Iberia)Publication . Delgado, J.; Boski, T.; Nieto, J. M.; Pereira, L.; Moura, Delminda; Gomes, A.I.; Mendes da Silva de Sousa, Carlos A; García-Tenorio, R.This study reviews data on sea-level rise during the last 13000 yr cal. BP (13 kyr) as recorded in the estuarine sediments of the Guadiana River (SE Portugal, SW Spain). We combined new data from a 63 m-long borehole, drilled through the entire postglacial sedimentary sequence, with information on five previously studied cores. By integrating sedimentological, geochemical and palaeontological proxies, we were able to make a palaeoenvironmental reconstruction of the Guadiana terminal palaeovalley during the last 13 kyr and propose a curve of sea-level rise for the SW Iberian Atlantic margin. Our foraminifera-based palaeoecological reconstruction, anchored to a 14C age model, reveals rapid sea-level rise from 13 kyr, interrupted during the Younger Dryas and resuming ca 11.5 kyr. The pace of marine transgression slackened ca. 7.5 kyr and since then has progressed upwards at a rate of 1.2 mm yr 1. HoloceneeAnthropocene sediments from two boreholes were also analysed to assess the timing, levels and sources of trace metals produced by acid mine drainage from the Iberian Pyrite Belt. Study of metal/aluminium ratios through the profiles allowed background metal concentrations to be estimated from lithostratigraphic units older than ca. 5 kyr (i.e. unaffected by anthropogenic activities). Human activities are especially evident from 4.5 kyr (the beginning of the Copper Age), with anthropogenic sources of metal fluxes prevailing over natural sources (especially Pb, Co, Ni, and Mn, and, to a lesser extent, Zn, Cu, and Ni). Mining activities became particularly intensive between the late Bronze Age and the Roman period (3e1.5 kyr), when the highest metal enrichment factors were recorded: EFPb z 2, EFCd > 10, EFCr z 2, EFCu z 3, EFZn ¼ 1.4.This study reveals the utility of postglacial sedimentary records for reconstructing historical changes in regional water-sediment quality and separating natural and anthropogenic sources of geochemical contaminants.
- The Holocene history of the Guadiana estuary as told by diatoms and chrysophyte cystsPublication . Gomes, A.I.; Boski, T.; Moura, Delminda; Szkornik, Katie; Connor, Simon; Witkowski, AndrzejIn order to tell the history of the Guadiana Estuary since the Last Glacial Maximum, a core collected therein, and spanning more than 13200 cal. years B.P., was studied regarding its diatom and chrysophyte cyst fossil records. Additionally, a diatom-based transfer function was used to reconstruct paleo-salinity and paleo-duration of tidal inundation to better understand the estuary’s evolution in relation to sea-level rise and climate changes. This study identifies some important climatic events, such as the Allerød climatic optimum, the Younger Dryas and three dry and cold events at 10600, 9100 and 7600 cal. years B.P., most of which were not identified by other proxies. Moreover, it also revealed that, prior to 13200 cal. years B.P., there was a mudflat environment in the place where the core was collected, consistent with an estuary slightly confined in the narrow valley under marine/tidal influence. Afterwards, this environment evolved into a salt marsh. The strongest marine influence was inferred to the period between 10000 and 7000 cal. years B.P., embracing a phase of rapid sea-level rise, non compensated by sedimentation, that favored the development of a mudflat. From this period onwards, diatom assemblages seem to indicate an evolution to a more enclosed environment, probably similar to the actual configuration of the area.
- The morphosedimentary behaviour of a headland–beach system: Quantifying sediment transport using fluorescent tracersPublication . Oliveira, Sónia; Moura, Delminda; Horta, João; Nascimento, Ana; Gomes, A.I.; Veiga-Pires, C.Embayed beaches occurring along rocky coasts with headlands controlling hydrosedimentary processes are considered to be constrained sedimentary systems with little longshore sediment transfer between them. Such beaches are likely to narrow under rising sea level and a deficit of fluvial sediment, and because beaches act to dissipate wave energy, cliff erosion is expected to increase. Knowledge of hydrosedimentary processes in fetch-limited environments such as embayed beaches is therefore a fundamental management tool in erosionprone coastal areas such as the Algarve region (southern Portugal). Themain objective of this work is to quantify longshore sediment transport (LST) using a sedimentary tracer and compare the resultswith the ones derived via empirical formulae from several authors. To achieve this, we establish the spatial and temporal patterns of stained sediment, and relate these to marine climate data over six tidal cycles for three adjacent embayed beaches. The values of displaced sand estimated using tracer and scaled to mixed layer depth were compared with the results of five well-known LST formulae to assess the applicability of eachmodel to mesotidal environments. Of the LST formulae used, the CERC (2013) shows to be the most accurate in our study area. This study demonstrates the efficacy of using tracers for tracking and quantifying the sediment transport and as a basis for assessing the viability of different LST formulae for representing transport in these types of environments. Thework also shows the importance of themorphological control of hydrosedimentary processes, including the disruption of longshore drift and the sediment transfer promoted by shore platforms.
- The morphosedimentary behaviour of a headland–beach system: quantifying sediment transport using fluorescent tracersPublication . Oliveira, Sónia; Moura, Delminda; Horta, João; Nascimento, Ana; Gomes, A.I.; Veiga-Pires, C.Embayed beaches occurring along rocky coasts with headlands controlling hydrosedimentary processes are considered to be constrained sedimentary systems with little longshore sediment transfer between them. Such beaches are likely to narrow under rising sea level and a deficit of fluvial sediment, and because beaches act to dissipate wave energy, cliff erosion is expected to increase. Knowledge of hydrosedimentary processes in fetch-limited environments such as embayed beaches is therefore a fundamental management tool in erosionprone coastal areas such as the Algarve region (southern Portugal). The main objective of this work is to quantify longshore sediment transport (LST) using a sedimentary tracer and compare the results with the ones derived via empirical formulae from several authors. To achieve this, we establish the spatial and temporal patterns of stained sediment, and relate these to marine climate data over six tidal cycles for three adjacent embayed beaches. The values of displaced sand estimated using tracer and scaled to mixed layer depth were compared with the results of five well-known LST formulae to assess the applicability of each model to mesotidal environments. Of the LST formulae used, the CERC (2013) shows to be the most accurate in our study area. This study demonstrates the efficacy of using tracers for tracking and quantifying the sediment transport and as a basis for assessing the viability of different LST formulae for representing transport in these types of environments. The work also shows the importance of the morphological control of hydrosedimentary processes, including the disruption of longshore drift and the sediment transfer promoted by shore platforms.