Top PDF Seamount physiography and biology in the north-east Atlantic and Mediterranean Sea

Seamount physiography and biology in the north-east Atlantic and Mediterranean Sea

Seamount physiography and biology in the north-east Atlantic and Mediterranean Sea

The south-western top of Coral Patch Seamount is dom- inated by exposed hard substrate, whereas soft sediment is just a minor substrate component (Wienberg et al., 2012). Although exposed hardgrounds are dominant, and thus, of- fer suitable habitat for settlement by benthic organisms, the megafauna shows rather scarce occurrence except for cidarid echinoids and crinoids which were frequently ob- served. Overall, the megafauna on Coral Patch Seamount comprises benthic to epibenthic living organisms with a clear dominance of suspension-feeders, which were observed as live occurrences as well as their skeletal remnants (e.g. shell hash, coral debris). Scleractinian deep-water corals, from which the seamount derived its name, are rare and just com- prise isolated small-sized (< 20 cm in diameter) live occur- rences of the species Lophelia pertusa and Madrepora ocu- lata. In contrast, dead coral framework and coral rubble are more frequent, pointing to a higher abundance of corals on Coral Patch during the recent past (Wienberg et al., 2012). Dead but relatively fresh-looking coral framework was often observed to be entangled in lost longlines. Overall, longlines and various species of commercially important fish were fre- quently observed, emphasising the potential of Coral Patch Seamount as an important target for fisheries that may have impacted the entire benthic community (Wienberg et al., 2012).
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Study of the reproductive biology and chemical communication of sea cucumbers (Holothuria arguinensis and H. mammata)

Study of the reproductive biology and chemical communication of sea cucumbers (Holothuria arguinensis and H. mammata)

New sea cucumber fisheries are emerging in the Mediterranean Sea and Atlantic Ocean in response to a strong Chinese market demand. However, little is known about the biology of the new target species, hindering decisions on their management. The main objective of the present thesis was to study the reproductive biology and the role played by chemical communication and chemosensory systems in Holothuria arguinensis and Holothuria mammata. The different populations sampled in a narrow range along the Iberian Peninsula varied in size/weight, gonadal production, and maturity profile within each species, suggesting the influence of singular features of each location. However, they had all the same general reproductive pattern with a summer-autumn spawning. These results, essential to manage populations, were also useful to determine when to develop bioassays to test whether and how these species communicate during reproduction. Male sea cucumbers, but not females, release chemicals that attract and induce spawning in both sexes. A preliminary analysis of the male spawning water suggests a pheromone with multiple components, among them possibly phosphatidylcholine derivatives. Histology, histochemistry and immunohistochemistry of the potential chemosensory structures involved in the detection of these cues – tentacles, papillae and tube feet – show no obvious differences between them. However, the disc was the most specialized area, with a specific nerve arrangement, rich in nitric oxide synthase and containing numerous cells some of which are likely sensory neurons. The analysis of tissue transcriptomes revealed the presence of at least 591 G-protein-coupled receptors among them at least seven putative odorant receptors distributed mainly in the tentacles, oral cavity, calcareous ring and, papillae and tegument. Overall, this thesis gives valuable insights for sea cucumber fisheries management in the region and a better understanding of how sea cucumbers communicate during reproduction.
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Characteristics of the mesophotic megabenthic assemblages of the vercelli seamount (north tyrrhenian sea).

Characteristics of the mesophotic megabenthic assemblages of the vercelli seamount (north tyrrhenian sea).

Recent studies have indicated that seamounts may not show high endemism rates [5,51], as previously suggested [52–54], but they may host a variety of communities or species that are rarely encountered, or are represented by a very low density on slope habitats [6,55–57]. This is the case of Vercelli Seamount where some species were encountered with a remarkably high abundance respect to Tyrrhenian coastal areas. The Atlantic brown alga L. rodriguezii, known only for some localities of the Mediterranean Sea, is adapted to mesophotic areas, with temperatures less than 15 uC [58]. A well known canopy of this algae has been reported only for the rocky summit (around 40 m depth) of Apollo’s Bank (Ustica Island, Sicily) [59]. Such rocky habitats are important since the records of L. rodriguezii for the rhodolith beds [60] have suffered more the trawling impact [50]. This kelp shows strong seasonal variations of biomass with rapid growth in spring and sorus formation in summer to autumn [61]. The summer growth of L. rodriguezii is visible also on the seamount (Fig. 3a–b), as the algal sheets cover encrusting sponges or small living octocorals visible underneath. In autumn, the decaying of the distal part of the phylloids produces a relevant supply of organic biomass for several organisms such as sea urchins (Echinus melo, Cidaris cidaris) living on the detritic bottoms surrounding the pinnacle. The trophic contribution of kelp debris to deep communities has been well studied in several coastal environments [e.g. 62], but no information is present for shallow seamount ecosystems. Kelp debris processed by heterotrophic prokaryotes is typically enriched in nitrogen [62] thus representing a high-energy source of food for benthic consumers in coastal environments [63,64,65]. Since deep-sea ecosystems depend largely upon the organic matter sinking from the upper water column layers, the sinking of kelps thalli might represent an important fuel also for the seamount’s deep food chains dominated by grazers, such as sea urchins [66], gastropods [62], and detritivorous organisms such as amphipods [62] or bivalves [67].
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An overview of chemosynthetic symbioses in bivalves from the North Atlantic and Mediterranean Sea

An overview of chemosynthetic symbioses in bivalves from the North Atlantic and Mediterranean Sea

opment or after larval settlement. The larval shell (Fig. 3f) suggests planktotrophic larvae with some dispersal capabili- ties (Gaudron et al., 2012). Idas modiolaeformis is the sister species of Idas macdonaldi known from the Gulf of Mex- ico and possibly diverged around 1.84 Mya. This amphi- Atlantic distribution led to the prediction that populations of mussels branching within the I. modiolaeformis/I. mac- donaldi clade should occur at locations in between the east- ern Mediterranean and the Gulf of Mexico. Recently, small Idas-like mussels were indeed recovered from the northeast Atlantic on organic substrates at mud volcanoes in the Gulf of Cadiz (Darwin and Mekn`es MVs) and in the Gorringe Bank (Gettysburg Seamount) (Rodrigues et al., 2013). The studied specimens display COI sequences identical (Gor- ringe) or almost identical (Mekn`es, Darwin MVs) to the specimens from the eastern Mediterranean, suggesting they belong to the same species. Possible settlement is also re- ported on wood block colonization experiments deployed in the western Mediterranean canyons at 500 m deep (personal observation, N. Le Bris, personal communication, 2012). In- terestingly, molecular and microscopic data suggest the ab- sence of methane-oxidizing symbionts. Furthermore, speci- mens from the Mekn`es and Gorringe sites do not seem to have sulfur-oxidizers either. Identified bacteria either belong to the “Gammaproteobacteria G” group, present in I. modi- olaeformis, or to a clade unrelated to any known symbiont (clone G-4), or to the Bacteroidetes. Overall, symbioses in the I. macdonaldi/I. modiolaeformis clade appear unexpect- edly variable. This could be linked with the wide range of habitats colonized, which include alfalfa and wood coloniza- tion devices, natural wood falls, carbonates close to reduced sediment, and siboglinid tubes. The plasticity of the I. mac- donaldi/I. modiolaeformis clade makes it a very good model to study at which stage of the life cycle (spawned oocytes, veliger stages, post-larvae, aposymbiotic juveniles or adult stages) and how symbionts establish, transmit and evolve over a relatively short evolutionary time scale. Other Idas species have been associated with reduced environments. In the Mediterranean, for example, I. simpsoni and I. cylindri- cus have been associated with organic falls (Pastorelli et al., 1999; Pelorce and Poutiers 2009). Another unidentified Idas was found on organic cargo in the wrecked ship Franc¸ois Vieljeux (Dando et al., 1992).
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Phytoplankton biomass, composition, and productivity along a temperature and stratification gradient in the Northeast Atlantic Ocean

Phytoplankton biomass, composition, and productivity along a temperature and stratification gradient in the Northeast Atlantic Ocean

due to a longer growth season) in the North Atlantic. However, our data showed highest depth integrated Chl a at higher latitude non-stratified stations in spring, suggesting that phytoplankton blooms can start under minimal stratification. This indicated that possible earlier onset of stratification (and surface blooming) would not necessarily result in a longer and more productive season. In contrast, delayed stratification may prolong the

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Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

Changes in atmospheric variability in a glacial climate and the impacts on proxy data: a model intercomparison

For each model’s equilibrium simulation of the LGM and PI climates, 100 years of monthly post-spinup SLP, tempera- ture and precipitation data from 20°–90° N are analyzed. The results presented here are based on monthly anomalies from the seasonal cycle. The variability in the resultant time series is concentrated at interannual time scales and is hereafter re- ferred to as interannual variability. Standard Empirical Or- thogonal Function (EOF)/Principal Component (PC) analy- sis has been used to assess the leading mode of SLP variabil- ity in the North Atlantic. All differences discussed in this study are significant at the 1% confidence level, unless oth- erwise noted. The Atlantic sector is defined as 20°–90° N, 120° W–45° E using the Rocky Mountains and the Urals as boundaries, but the results presented here are not strongly sensitive to the particular definition of the sector.
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New record of Novocrania (Brachiopoda, Craniida) from Madeira, with notes on Recent brachiopod occurrences in the Macaronesian archipelagos

New record of Novocrania (Brachiopoda, Craniida) from Madeira, with notes on Recent brachiopod occurrences in the Macaronesian archipelagos

Two well-preserved dorsal valves of the inarticulated brachiopod Novocrania anomala (Müller) were collected by Swinnen from off Cais do Lazareto, near the port of Funchal, Madeira Island from depths of 150 m and 382 m (exact details on request to Swinnen). This species is known from Sagres (Portugal), Atlantis Seamount (SEAMOUNT 2) and the Firth of Lorne (Scotland), as well as in the Mediterranean sea, while its congener N. turbinata (Poli) is known from the Cape Verde Islands and north-west Africa, as well as several localities mainly in the southern and eastern part of the Mediterranean (Logan & Long 2001). These authors described and illustrated the major differences between the two species, which mainly involve dorsal valve
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Transport of volume, heat, and salt towards the Arctic in the Faroe Current 1993–2013

Transport of volume, heat, and salt towards the Arctic in the Faroe Current 1993–2013

Abstract. The flow of warm and saline water from the At- lantic Ocean, across the Greenland–Scotland Ridge, into the Nordic Seas – the Atlantic inflow – is split into three sepa- rate branches. The most intense of these branches is the in- flow between Iceland and the Faroe Islands (Faroes), which is focused into the Faroe Current, north of the Faroes. The Atlantic inflow is an integral part of the North Atlantic ther- mohaline circulation (THC), which is projected to weaken during the 21st century and might conceivably reduce the oceanic heat and salt transports towards the Arctic. Since the mid-1990s, hydrographic properties and current velocities of the Faroe Current have been monitored along a section ex- tending north from the Faroe shelf. From these in situ obser- vations, time series of volume, heat, and salt transport have previously been reported, but the high variability of the trans- port has made it difficult to establish whether there are trends. Here, we present results from a new analysis of the Faroe Current where the in situ observations have been combined with satellite altimetry. For the period 1993 to 2013, we find the average volume transport of Atlantic water in the Faroe Current to be 3.8 ± 0.5 Sv (1 Sv = 10 6 m 3 s −1 ) with a heat
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Sea-to-air and diapycnal nitrous oxide fluxes in the eastern tropical North Atlantic Ocean

Sea-to-air and diapycnal nitrous oxide fluxes in the eastern tropical North Atlantic Ocean

Acknowledgements. We thank the captains and crews of R/V L’Atalante and R/V Poseidon for their excellent support during the cruises. Also, we thank A. Freing for inspiring discussions about the N 2 O mixed layer source and A. K¨ortzinger, B. Fiedler, T. Tanhua, and M. Glessmer for their support during the field work. We would like to thank two anonymous referees for their constructive comments that helped to improve the manuscript. Financial support for this study was provided by DFG grants DE 1369/1-1 and DE 1369/3-1 (JS and MD) and BMBF grant SOPRAN FKZ 03F0462A (AK). QuikScat data are produced by Remote Sensing Systems and sponsored by the NASA Ocean Vector Winds Science Team. Data are available at www.remss.com.
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The comparison of the structure and microhardness of the tool steel C90 and HS 6-5-2 remelted with the electric arc

The comparison of the structure and microhardness of the tool steel C90 and HS 6-5-2 remelted with the electric arc

The tool steels consistute a very important group of materials used for the production, not only tools, but also machine ele- ments, that need to have the increased strength, for example the high-speed steels are used on the rolling bearing operating in high temperatures [1]. Modern technologies such as: laser treatment, electron treatment, CVD, PVD methods, give the possibility of forming the structure of the surface layer of steels providing the demaded properties. The economic factors direct research in using the plasma of the electric arc for shaping the surface layer of the machine elements and tools. Advantages of that method are the possibilities of receiving wider treated areas with one stream of the heat in comparison with the laser technologies or electron
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Oxygen and hydrogen isotope signatures of Northeast Atlantic water masses

Oxygen and hydrogen isotope signatures of Northeast Atlantic water masses

High precision stable isotope (δ 18 O, δD) analyses of fresh and ocean water were first discussed by Epstein and Mayeda (1953) and Friedman (1953). Craig and Gordon (1965) later showed that δ 18 O can be used as a water mass tracer and that the δ 18 O-salinity relationship follows a slope of 0.61 in the surface waters of the high-latitude North Atlantic and thus the North Atlantic Deep Water (NADW) but changes to a slope of 0.22 in the surface waters of the subtropical North Atlantic or even 0.11 in the Atlantic’s equatorial trough. Subsequent studies focused on specific regions (e.g., Fairbanks, 1982; Van Donk and Mathieu, 1969; Weiss et al., 1979) and a global study of seawater stable isotope transects and vertical profiles was made by the GEOSECS program (Östlund et al., 1987). Although the GEOSECS program provided the first global data set, the spatial coverage was limited. In the North Atlantic south of the Greenland-Iceland-Scotland ridge, six vertical stations covered the complete water column, but only Station 115 at 28°N and 26°W was located in the eastern basin. After the GEOSECS program a major gap followed in seawater stable isotope studies. In the last two decades, however, various studies provided new δ 18 O data that focused on high latitude regions and the influence of meltwater in the Atlantic sector (e.g., Azetsu-Scott and Tan, 1997; Bauch et al., 1995; Cox et al., 2010; Mackensen, 2001; Meredith et al., 1999a; Meredith et al., 1999b), the NW African upwelling region off Cape Blanc (Pierre et al., 1994: Fig. 1b) and the Mediterranean Sea (Pierre, 1999). Pierre et al. (1994) proposed a slope of 0.46 for the δ 18 O-salinity mixing line
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Summer and winter living coccolithophores in the Yellow Sea and the East China Sea

Summer and winter living coccolithophores in the Yellow Sea and the East China Sea

In this study, according to Figs. 25 to 28, the distribu- tion of LCs in the Yellow Sea and East China Sea had var- ious connections with temperature and the nutrient concen- tration. In summer, the abundance of coccolith in the surface layer increased from north to south in the survey area, as- sociated with the environment characteristics. In the Yellow Sea, temperature, salinity and the nutrient concentrations are in general low in summer (Liu and Hu, 2009; Zhang, 2009), which limit the survival and growth of the LCs. As for the East China Sea, the temperature and salinity are both sig- nificantly higher (Zou and Xiong, 2001), and the input by the Yangtze River runoff and the Kuroshio waters greatly in- creased the nutrient concentrations in this area (Wang, 2008). The abundance of coccoliths reaches a high value along sec- tion P. The abundance of the coccosphere cells in the survey area presents plaque distribution and is mainly distributed in the Yangtze River diluted water region and the southern part of the East China Sea, resulting from the distribution of temperature, salinity and nutrients in various water masses. Nutrient enrichment is beneficial to the survival and growth of the LCs (Baumann et al., 2005), therefore the maximum abundance of the LCs was found at 20 m depth where the big phytoplankton blooms took place, consistent with what was observed by Jin and Sun (2013).
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New records for the shallow-water chiton fauna (Mollusca, Polyplacophora) of the Azores (NE Atlantic)

New records for the shallow-water chiton fauna (Mollusca, Polyplacophora) of the Azores (NE Atlantic)

Callochiton septemvalvis is based on a single historical observational record by Mor- ton (1967) and no preserved specimens are known from the Azores. Nevertheless, we tentatively accept this record as likely since C. septemvalvis is widely distributed in the North Atlantic but highly cryptic, living in the very low intertidal to 160 m, and at low population densities (Jones and Baxter 1987). Kaas (1985: 580) reported Acanthochi- tona crinita (Pennant, 1777) from the Azores [(it exists) “from (…) Norway, S to the Cape Verde Archipelago”], but the same author unequivocally stated that this species is “not (present) in the Azores” (Kaas, 1991: 95). Notwithstanding recent reports from the area (Segers et al. 2009, Rolán 2011, Moreno and Gofas 2011), which are based solely on bibliographic records, we disregard this species as occurring in the archi- pelago and suggest that it should be eliminated from the Azores shallow-water marine mollusc checklist. Thus, the recorded Azorean shallow-water polyplacophoran fauna consists of seven living species, as no fossil chitons are known from the Azores. Four species (Hanleya hanleyi, Callochiton septemvalvis, Tonicella rubra, and Acanthochitona fascicularis) are common to the north-east Atlantic, but the ubiquitous northern Eu- ropean species Lepidochitona cinerea (Linnaeus, 1878) is absent and replaced by three other warmer-water species of the same genus. The summary presented here includes the first Azorean records of two species: Lepidochitona cf. canariensis and Tonicella ru- bra. The discovery of Tonicella rubra on a shallow, small (~18 ha area of summit) and young seamount (~300 y) leads us to believe that the chitons of the Azores are still poorly known when compared with other molluscan classes.
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Vertical distribution of sub-micron aerosol chemical composition from North-Western Europe and the North-East Atlantic

Vertical distribution of sub-micron aerosol chemical composition from North-Western Europe and the North-East Atlantic

Ginoux, P., Gong, S., Grini, A., Hendricks, J., Horowitz, L., Huang, P., Isaksen, I., Iversen, I., Kloster, S., Koch, D., Kirkev ˚ag, A., Kristjansson, J. E., Krol, M., Lauer, A., Lamarque, J. F., Liu, X., Montanaro, V., Myhre, G., Penner, J., Pitari, G., Reddy, S., Seland, Ø., Stier, P., Takemura, T., and Tie, X.: Analysis and quantification of the diversities of aerosol life cycles within AeroCom, Atmos. Chem. Phys., 6, 1777–1813, 2006,

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TOPAZ4: an ocean-sea ice data assimilation system for the North Atlantic and Arctic

TOPAZ4: an ocean-sea ice data assimilation system for the North Atlantic and Arctic

For the Canadian mooring the comparison with observations for both the reanalysis and the free run is quite poor. Note, however, that historically TOPAZ has been cali- brated for the North Atlantic and the adjacent Arctic sector rather than for the Canadian basin. Both simulations show a too shallow and too cold Pacific Water, which is likely to be a direct consequence from dis-regarding seasonal variability in the Bering Strait

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First record of the Atlantic blue crab Callinectes sapidus (Crustacea: Brachyura: Portunidae) in the Segura River mouth (Spain, southwestern Mediterranean Sea)

First record of the Atlantic blue crab Callinectes sapidus (Crustacea: Brachyura: Portunidae) in the Segura River mouth (Spain, southwestern Mediterranean Sea)

The introduction of blue crabs can have significant and negative consequences to the ecology of the invaded environments. C. sapidus has been defined as a highly aggressive species and was selected among the 100 worst invasive species in the Mediterranean Sea with impact on both biodiversity and economy (Streftaris and Zenetos, 2006; Castejón and Guerao, 2013). Further studies on this region (SE Spain), monitoring the presence of this invasive species and assessing its potential dispersal, will provide valuable information on population structure and dynamics of the blue crab on the Spanish coast. These data Figure 2. Callinectes sapidus Rathbun, 1896, adult male (A:
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TOPAZ4: an ocean-sea ice data assimilation system for the North Atlantic and Arctic

TOPAZ4: an ocean-sea ice data assimilation system for the North Atlantic and Arctic

Abstract. We present a detailed description of TOPAZ4, the latest version of TOPAZ – a coupled ocean-sea ice data as- similation system for the North Atlantic Ocean and Arctic. It is the only operational, large-scale ocean data assimila- tion system that uses the ensemble Kalman filter. This means that TOPAZ features a time-evolving, state-dependent esti- mate of the state error covariance. Based on results from the pilot MyOcean reanalysis for 2003–2008, we demonstrate that TOPAZ4 produces a realistic estimate of the ocean cir- culation in the North Atlantic and the sea-ice variability in the Arctic. We find that the ensemble spread for tempera- ture and sea-level remains fairly constant throughout the re- analysis demonstrating that the data assimilation system is robust to ensemble collapse. Moreover, the ensemble spread for ice concentration is well correlated with the actual errors. This indicates that the ensemble statistics provide reliable state-dependent error estimates – a feature that is unique to ensemble-based data assimilation systems. We demonstrate that the quality of the reanalysis changes when different sea surface temperature products are assimilated, or when in-situ profiles below the ice in the Arctic Ocean are assimilated. We find that data assimilation improves the match to indepen- dent observations compared to a free model. Improvements are particularly noticeable for ice thickness, salinity in the Arctic, and temperature in the Fram Strait, but not for trans- port estimates or underwater temperature. At the same time, the pilot reanalysis has revealed several flaws in the system that have degraded its performance. Finally, we show that a simple bias estimation scheme can effectively detect the sea- sonal or constant bias in temperature and sea-level.
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Habitat needs of cetaceans in the North-East Atlantic in relation to human pressures and their management

Habitat needs of cetaceans in the North-East Atlantic in relation to human pressures and their management

Cetaceans are very complex in their biology and ecology, having particular habitat needs that influence their global and local distribution, such as oceanographic features and prey availability. Knowledge on specific habitat needs (essential environmental characteristics for the animals' survival) is of major importance for the definition of effective conservation goals and management measures. These species are vulnerable to pressures from human activities, for instance from whaling, fisheries and navigation, as well as those releasing contaminants or generating oceanic noise. The available information on cetacean habitat preferences and registered human activities' impacts was compiled for North-East Atlantic cetaceans, from primary and secondary references, as presence/absence data matrices. These were analysed descriptively and through Correspondence and Classification Analyses. The habitat needs analyses produced a clear distinction between mysticetes (baleen whales) and odontocetes (toothed whales), and, in a less obvious way, two trends in the dispersion of the odontocetes. The characteristics influencing these distinctions were mainly related to feeding preferences, typical group size, reproductive seasonality and migratory patterns. Similarly, the human activities analysis showed the distinction between mysticetes and odontocetes, and among these, between beaked and sperm whales, and dolphins. Mysticetes were found to be mainly affected by whaling and noise from shipping; beaked and sperm whales by noise from seismic surveys and military activities; and dolphins by by-catch, whale-watching and collisions with ships. Given the increase of human impacts on marine ecosystems, several international, European, regional and local agreements and legislation have been agreed. In general, these aim to reduce and monitor human pressures on biodiversity, and they particularly promote the protection and conservation of cetaceans. Nevertheless, many of these instruments concern only the direct effects, while the indirect ones have been largely overlooked, due to the lack of reliable information from scientific research on both cetacean ecology and the secondary effects of many human activities. In addition, reduced cooperation between the various entities and governments is also a major difficulty. This study aimed to contribute with information on this subject and in the awareness of the urgency of the protection of these charismatic animals.
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Distribution and conservation of three important bird groups of the Atlantic Forest in north-east Brazil

Distribution and conservation of three important bird groups of the Atlantic Forest in north-east Brazil

The Pernambuco Endemism Center in north-east Brazil has the most fragmented forest cover and the largest number of threatened birds of the whole Atlantic Forest. We analyzed the distribution of three groups of bird species: forest-dependent, endemic and/or threatened using the interpolation method of Inverse Distance Weighting. We also checked the concentration of these birds in protected and unprotected areas, suggesting new sites that need to be protected. The richness concentration of forest-dependent, endemic and/or threatened birds in 123 sites were analysed. There was a greater concentration of the three groups in north Alagoas, south and north Pernambuco, and north and west Paraíba. The distribution of the three groups was almost regular in different vegetation types, although a lower concentration was found in the pioneer formation. There was a greater concentration of birds from all three groups between Pernambuco and Alagoas, and this must be due to the presence of more forest fragments with better structure and vegetation heterogeneity. The protected and unprotected areas hosted important records of endemic and/or threatened birds. We suggested some important places for implementation of new protected areas due to the larger concentrations of the target birds and because they are located within the boundaries of the Important Bird Areas.
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Projection of North Atlantic Oscillation and its effect on tracer transport

Projection of North Atlantic Oscillation and its effect on tracer transport

Earth system model simulations with increasing greenhouse-gas (GHG) concentrations can provide pro- jections of the NAO and future trends. Most models have projected a weak positive NAO trend under a global warming climate change scenario. Gillett and Fyfe (2013) found this when considering the mean of 37 CMIP5 models’ merged historical and RCP 4.5 simulations for each season, and Stephenson et al. (2006) obtained similar results to 14 models out of 18 studied. However, some studies found the NAO index in a future scenario only weakly sensitive to the GHG increment, with no significant trends (Fyfe et al., 1999; Dorn et al., 2003; Rauthe et al., 2004; Fischer et al., 2009), or even decreasing trends (Osborn et al., 1997). More recently, Pausata et al. (2015) analysed the impacts due to the aerosol reduction (after air pollution mitigation strategies) and GHG increment on the winter North Atlantic atmospheric circulation and obtained a stronger positive NAO mean state by 2030. The dependency of the results on the model used is still unclear (Gillett et al., 2003; Stephenson et al., 2006). Other research questions are still open, regarding which climate processes govern the NAO variability, how the phenomenon varies in time, and what is the potential for the NAO predictability (Visbeck et al., 2001; Hurrell et al., 2001; Woollings et al., 2015).
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