Nazare Canyon Research Articles

Measuring Vulnerability of Marine and Coastal Habitats’ Potential to Deliver Ecosystem Services: Complex Atlantic Region as Case Study

The main objective of this work is to promote Ecosystem Based Management (EBM) using a complex Atlantic region to demonstrate how InVEST model tool and associated methods can be applied to calculate benthic habitats cumulative risk and create a vulnerability index of the potential of these habitats to deliver ecosystem services (ES). The study area, in the Western-Atlantic coast of Portugal, includes the Nazare Canyon (> 3000m depth within the study region), Obidos Lagoon (transitional waters), Sao Martinho do Porto bay (marine inlet), and Berlengas Archipelago (UNESCO world biosphere reserve). The ES delivered by this complex coastal region support the main regional/local socio-economic activities (e.g. fisheries and tourism activities). The approach combined the InVEST habitat risk assessment tool with the identified ES to create a proxy for the habitats’ vulnerability to deliver ES. Within the region twenty eight marine benthic habitats were identified and combined with twelve classes of ES (Common International Classification of ES), and two prospective scenarios were analysed (a potential socio-economic scenario for 2025 and a climate change scenario for the end of the century). The results show that the applied vulnerability approach enables the combination of information from different sources, including local knowledge, and the translation of the generated information into 2D spatial explicit maps that can support management strategic options, namely in the context of maritime spatial planning and ‘Blue Growth’. The interpretation of the habitat vulnerability approach requires taking into account data spatial resolution, its quality and the impact of associated pressures. However, despite the limitations and assumptions (e.g. all ES classes are equally important), models such asthis have opened new avenues contributing to improve EBM, by combining spatial explicit GIS tools with supply and demand of marine ES, human activities and their related positive and negative impacts.

Eustatic sea-level controls on the flushing of a shelf-incising submarine canyon

Turbidity currents are the principal processes responsible for carving submarine canyons and maintaining them over geological time scales. The turbidity currents that maintain or “flush” submarine canyons are some of the most voluminous sediment transport events on Earth. Long-term controls on the frequency and triggers of canyon-flushing events are poorly understood in most canyon systems due to a paucity of long sedimentary records. Here, we analyzed a 160-m-long Ocean Drilling Program (ODP) core to determine the recurrence intervals of canyon-flushing events in the Nazare Canyon over the last 1.8 m.y. We then investigated the role of global eustatic sea level in controlling the frequency and magnitude of these canyon-flushing events. Canyon-flushing turbidity currents that reach the Iberian Abyssal Plain had an average recurrence interval of 2770 yr over the last 1.8 m.y. Previous research has documented no effect of global eustatic sea level on the recurrence rate of canyon flushing. However, we find that sharp changes in global eustatic sea level during the mid-Pleistocene transition (1.2–0.9 Ma) were associated with more frequent canyon-flushing events. The change into high-amplitude, long-periodicity sea-level variability during the mid-Pleistocene transition may have remobilized large volumes of shelf sediment via subaerial weathering, and temporarily increased the frequency and magnitude of canyon-flushing turbidity currents. Turbidite recurrence intervals in the Iberian Abyssal Plain have a lognormal distribution, which is fundamentally different from the exponential distribution of recurrence intervals observed in other basin turbidite records. The lognormal distribution of turbidite recurrence intervals seen in the Iberian Abyssal Plain is demonstrated to result from the variable runout distance of turbidity currents, such that distal records are less complete, with possible influence from diverse sources or triggering mechanisms. The changing form of turbidite recurrence intervals at different locations down the depositional system is important because it ultimately determines the probability of turbidity current–related geohazards.

Efficient burial of carbon in a submarine canyon

Burial of organic carbon (OC) in marine sediments moderates atmospheric CO2 levels on geological time scales, but uncertainties remain about how much OC is buried and about the efficiency of OC burial, particularly in heterogeneous seafloor environments such as ocean margins. Here we describe OC burial in Nazare submarine canyon and the adjacent continental slope off Portugal, an area within which sedimentation rates vary by three orders of magnitude. Using a nested series of observations at different scales, ranging from regional bathymetry to sediment cores, we estimate the annual sediment and OC deposited in the canyon at 620,000 t and 12,500 t, respectively. Nazare Canyon is thus a significant sink of both sediment and OC. Canyon sediments typically contain ~2% OC, both in surface sediments and at depth, and there is a limited correlation between sedimentation rate and OC content. The likely explanation is that the OC has already survived a lengthy period of degradation prior to deposition in the canyon, such that additional exposure to oxygenated water has minimal effect. Burial efficiency is difficult to calculate because of extensive resuspension and reworking of OC in the upper canyon, but probably exceeds 30% in areas of high sedimentation. These areas are shown to be 30 times more effective in burying OC than adjacent areas of the continental slope, indicating that Nazare Canyon is a hitherto overlooked sink of OC on a continental margin where OC burial is otherwise low.

Trace metal enrichments in Portuguese submarine canyons and open slope: Anthropogenic impact and links to sedimentary dynamics

In order to evaluate the role of submarine canyons as transport routes for the particulate matter, including anthropogenic trace metals, from coastal areas to the deep sea, we analysed contents of Ca, Al, Fe, Mn, Zn, Cr, Pb, Ni and Cu, organic carbon and calcium carbonate in surface sediments and sediment trap particulate material from canyon and open slope areas of the central Portuguese continental margin. The contribution of trace metals from anthropogenic sources was assessed by comparing present-day concentrations and average elemental concentrations for the industrial period (last ∼ 150 years) with pre-industrial baseline values. Baseline elemental concentrations are very similar for the Lisbon–Setubal and Nazare canyons, but varying degrees of anthropogenic trace metal enrichments are recorded in more recent sediments. The upper Lisbon and Cascais canyons appear the most affected by anthropogenic trace metal deposition; excess Pb, Zn and Cu amount ∼ 55%, ∼ 57% and ∼ 21%, respectively, of total inventories over the last 150 years. The upper Nazare canyon follows with 42%, 21% and 17%, respectively. Lower contributions of anthropogenic trace metals were found for the lower reaches of the canyons and adjacent open slopes, indicating that the upper-canyon areas act as trace metal depocentres, whereas dispersal to deeper canyon and slope areas is limited. The Tagus and to a lesser extent the Sado river appear the main sources of Pb, Zn and Cu to the canyons, but atmospheric dispersal of Pb seems also important, especially in the southern area. Anthropogenic enrichment of Pb and Zn in the Cascais and Lisbon canyons is comparable to values published for canyons in the NW Mediterranean and off Taiwan located in close proximity to industrialized areas. Different from Pb and Zn, present-day Cu enrichment appears to increase toward deeper water where pelagic sedimentation is predominant, suggesting that dispersal of this trace metal is at least partly linked with surface water plankton production.

The "mica sandwich", a remarkable new genus of Foraminifera (Protista, Rhizaria) from the Nazare Canyon (Portuguese margin, NE Atlantic)

Based on morphological and molecular characteristics, we describe a new genus and species of monothalamous agglutinated foraminifera, Capsammina patelliformis, that occurs mainly at bathyal (1000-3400m) water depths in the Nazare Canyon off Portugal. The test is strongly flattened, up to 500µm or more in maximum dimension, and 30-80µm thick. It lacks obvious apertures, and is typically composed of 2-3 large, plate-like grains of mica that form the upper and lower surface of the test; these are separated by fine-grained, white agglutinated material ("mortar") forming a ring around the cell body. The cytoplasm, visible through the mica plates, is whitish in colour with few obvious inclusions. Analysis of a fragment of the SSUrDNA gene indicates that C. patelliformis belongs in a clade branching with Crithionina delacai, C. granum and an undetermined crithioninid species. However, the divergences between the new species and these Crithionina species range from 20% to 21%, and are therefore too high to classify it in the same genus. We also transfer a previously described species, Psammosphaera bowmanni Heron-Allen and Earland 1912, to Capsammina based on its use of mica flakes in test construction. Other monothalamous agglutinated foraminifera, including Psammosphera spp., are phylogenetically distant from Capsammina. The new species occupies a shallow infaunal microhabitat, living mainly in the top 0.5cm of sediment.

Europe’s Grand Canyon: Nazaré Submarine Canyon

The Nazare submarine canyon extends similar to 210 km westward from the coast of Portugal, down to a water depth of > 4300 m. The considerable habitat heterogeneity found throughout the canyon is affected by strong currents and high turbidity, especially in the upper parts of the canyon. The canyon morphology comprises steep slopes, scarps, terraces, and overhangs, and a deeply incised thalweg is found in the lower part of the canyon. The seabed within the canyon is composed of varying proportions of rock and sediments that range from sand to fine mud. This great variation in physical environment is reflected by the varied fauna inhabiting the canyon. Diversity tends to decrease with depth, but there is also continual replacement of species with increasing water depth. Certain groups, such as the gorgonians and sea lilies, tend to be found on rocky surfaces, while large protozoans dominate the sediments at 3400-m depth. In addition to describing the fauna of Nazare Canyon, we discuss experiments undertaken as part of the HERMES project to elucidate the ecosystem function processes operating in the deeper parts of the canyon.

Historical trends in Hg, Pb and Zn sedimentation in the central shelf area of Portugal

Temporal records of excess 210Pb, and the determination of major (Al and Ca) and trace elements (Zn, Cr, Ni, Pb, Cu and Hg) in two sediment box-cores, collected in the central area of the Portuguese shelf of North of the Nazare canyon (offshore from the Lis River), allow evaluation of the deposition of various chemical elements normally associated with anthropogenic activities. In order to compensate for the natural sediment variability, heavy metal contents were normalised to Al. Temporal variations of Hg, Pb and Zn (Al-normalised) show an increasing trend since the beginning of the 1920’s, recording the development of industrial activities. Enrichment factors (EF) were calculated to estimate the level of contamination in these sediments. Mercury is the element with the highest average EF values (EF = 3), followed by Pb (EF = 1.5) and Zn (EF = 1.2). The results indicate that since 1991 64% of total Hg, 44% of total Pb and 24% of total Zn are derived from anthropogenic sources. The average anthropogenic fluxes of Hg, Pb and Zn (0.008, 3, 6 μg cm-2yr-1, respectively) for the last 40 years in a ca. 400 km2 deposition area represent a total accumulation of approximately 30, 12000 and 24400 kg per year of Hg, Pb and Zn, respectively. These results indicate that despite the high-energy conditions and the generally sandy nature of the Portuguese shelf sediments, it is possible to identify significant anthropogenic enrichments in some areas of sediment accumulation. These contaminants are not necessarily related to immediate sources but may instead indicate atmospheric and or marine transport from more distant sources.

Distribution of meiobenthos in the Nazaré canyon and adjacent slope (western Iberian Margin) in relation to sedimentary composition

Abundance of metazoan meiofauna and foraminifera, and biomass and community structure of nematodes, were investigated in the benthic zone along the Nazare Canyon and adjacent continental slope in relation to concentration of organic matter and its suitability as a food source for the meiobenthos. The Nazare canyon sediments were richer in organic carbon (Corg), total nitrogen, and phytopigments than the adjacent open slope. In addition, phytodetritus was fresher in the canyon sediment than on the slope (higher chlorophyll a: phaeopigments). Nevertheless, the abundance of polychaetes, copepods, bivalves, nematodes, total metazoans, and nematode biomass were not always higher in the canyon than on the adjacent open slope. Lower densities occurred in the upper and middle canyon, and living benthic foraminifers were significantly more abundant on the adjacent slope. The stations in the upper and middle canyon contained infinitesimal numbers of foraminifers. Reduced diversity and evenness and high K-dominance of the nematode assemblages in the upper part of the canyon indicated environmental stress, perhaps related to high Corg content and sedi- ment disturbance. Non-selective deposit-feeders dominated the nematode assemblages of the upper and middle parts of the canyon, whereas a more diverse trophic structure was found in the deeper parts and the open slope. Conditions in the upper and middle areas of the Nazare canyon are harsh, and only opportunistic organisms can survive there.

Understanding continent‐ocean sediment transfer

Submarine canyons are narrow but deep submarine valleys that extend for hundreds of meters. They represent the most impressive structures that shape the present morphology of passive continental margins. They can occur off the mouth of rivers: the Tagus, Zaire, Amazon, and Orinoco in the Atlantic; the Indus in the Indian Ocean; and the Var, Rhone, and Ebro in the Mediterranean. Some are at times disconnected from any stream mouth such as the Nazare canyon, off Portugal, despite the fact that it is close to the coast. Some were connected to a river mouth during lowstands of sea level, such as the Wilmington canyon in the northwest Atlantic, or the Blackmud canyon in the northeast Atlantic.

Fe redox cycling in Iberian continental margin sediments (NE Atlantic)

In this paper, data are presented on the vertical distribution of pore water Fe 2+ , ferrozine-extractable Fe 2+ and solid phase Fe in sediments along four across-slope transects including the Nazare canyon at the Iberian margin. Sorbed Fe 2+ cannot be measured directly and is operationally defined as the fraction that can be extracted with ferrozine. Our objectives were (1) to investigate the potential role of Fe 2+ sorption in the Fe redox cycle, (2) to quantify Fe redox cycling and (3) to determine its rate limiting factors, with emphasis on differences between stations across the slope and in the canyon. In all sediments pore water Fe 2+ and ferrozine-extractable Fe 2+ concentrations increased simultaneously with depth until a maximum was reached and upon which the pore water Fe 2+ concentration rapidly declined, presumably due to precipitation as iron-sulfide. The ferrozine-extractable Fe 2+ concentration, however, either slowly diminished or remained unchanged when going deeper into the sediment, suggesting ongoing reaction at the sorption surfaces or much slower desorption than adsorption kinetics. Upon Fe reduction, Fe 2+ is released into the pore water where it either directly precipitates and/or adsorbs onto available surfaces of the sediment matrix, including organic matter. Through sorption, authigenic ferrous mineral formation is delayed and Fe 2+ may be transported deeper into the sediment. There, sorbed Fe 2+ can act as a deep source for authigenic ferrous mineral formation. A simple steady-state model was formulated that includes Fe 2+ sorption as a first-order kinetic reaction to estimate Fe reaction rates. Fe oxidation and reduction rates were most intense at the shelf, where organic carbon mineralization rates are high, and decreased with water depth. In the canyon, where deposition fluxes were high, Fe reaction rates increased with water depth until a maximum at the foot of the canyon at 3097 m and decreased again to the abyssal at 4280 m. Turnover times estimated for pore water Fe 2+ , ferrozine-extractable Fe 2+ and solid phase Fe both in the oxidized and reduced layer indicated that sediment mixing was the most important rate limiting factor for Fe cycling at all stations of the Iberian margin. The contribution of Fe reduction to organic matter mineralization was 5% at the 104-m and 113-m stations on the main transect and 6% at the 3097-m station at the foot of the canyon. At the other stations Fe reduction contributed less than 4% to the mineralization of organic matter.

Enhanced short-term sediment deposition within the Nazaré Canyon, North-East Atlantic

Abstract In January and May 1999, interface sediments were sampled within the Nazare Canyon, a large submarine canyon that deeply indents the western Iberian continental margin (NE Atlantic) at around 39°35N. Excess 234Th profiles were established with high resolution to calculate inventories and bioturbation coefficients. A northern transect at 42°N is briefly presented as a reference for the Western Iberian margin. Synthesis of these parameters is used to examine short-term deposition within the Nazare Canyon. 234Thxs was always detected with significant activities on surface in most of the samples. Along the reference transect and in the adjacent area, surface 234Th excesses are about 10–20 dpm g−1. In contrast, 234Thxs reaches very high levels (up to 170 dpm g−1) in the canyon. There is a large range of variability in inventories and bioturbation rates, in relation with depth and location. These results show a preferential deposition in the canyon and focus in the upper and middle part of the canyon. On a monthly time scale the Nazare Canyon appears as a significant locus of sedimentation for the Western Iberian margin.

Diatom assemblages as upwelling indicators in surface sediments off Portugal

Diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the Portuguese margin, an area where seasonal upwelling occurs each year from April to October. Absolute diatom abundance distribution patterns reflect the more intense and/or persistent and more homogeneous upwelling north of the Nazare Canyon, the position of the “inner” upwelling front south of Lisbon, and the eastern continuation of the coastal upwelling jet along the Algarve coast. Distribution patterns of species and of ecologically defined groups, meroplanktonic, oceanic, freshwater and marine benthic, support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system. Small species of the genus Thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and/or higher. Paralia sulcata (Ehr.) Cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases. Resting spores, mainly of Chaetoceros Ehrenberg, record the position of the zone where higher variability occurs, the “inner” upwelling front.