Madeira Research Articles

The role of recycled oceanic crust in the alkaline basalts: Evidence from Zn isotopic compositions of alkaline basalts from the Madeira hotspot (eastern North Atlantic)

Plate tectonic processes introduce oceanic crust (as eclogite) into the sources of oceanic island basalts (OIB). The fate of this recycled material in the deep mantle is still poorly understood. Here we present a systematic study of Zn isotopes on well-characterized alkaline basalts (<5 Ma) from the Madeira Islands in the eastern North Atlantic. Our analyses show that the δ66Zn values of alkaline basalts range from 0.25‰ to 0.34‰, with an average of 0.30 ± 0.05‰ (2SD, N = 15), which is similar to the average of mid-ocean ridge basalts (MORB) (0.28 ± 0.03‰, 2SD), and ∼ 0.14‰ higher than that of the asthenospheric mantle (0.16 ± 0.06‰, 2SD). However, these alkaline basalts have higher Zn/Fe ratios (up to 14.20) than MORB (generally less than 12). Model calculations show that the partial melting of mantle peridotite cannot simultaneously produce the observed MORB-like δ66Zn values and trace element ratios. After excluding the effects of post-eruption alteration, crystal fractionation, and the assimilation of crustal materials during magma upwelling on Zn isotopic compositions of the studied samples, we suggest that the MORB-like δ66Zn values reflect the mixing of peridotite melt and eclogite/pyroxenite-derived melt in the magma source of the Madeira hotspot. This is supported by trace element ratios and radiogenic isotopes, such as high Zn/Fe and Dy/Yb ratios and 206Pb/204Pb values. Our new data provide independent evidence in support of the important role of recycled oceanic crust in the source and generation of alkaline OIBs, and also highlight that such sources are not ubiquitously carbonated.

Collembola of the Cavalum and Landeiro Caves (Madeira, Portugal).

The cave fauna of the Macaronesian archipelagos is rich in endemic species. Unlike the Azores and the Canary Islands, the cave fauna of the Madeira archipelago is little known. The only two cave complexes studied, Machico and São Vicente, lack protection measures. São Vicente is seriously threatened because it is being exploited for touristic purposes, while the Machico complex, the only one in its natural state, is open to the public but without any control. The importance of the conservation of this cave fauna is indisputable. So far, of the 13 cavernicolous species recorded, two of them-genus Centromerus-are critically endangered. Apart from occasional sampling, no monitoring study has ever been carried out. The aim of this work has been to make a species checklist of the cave fauna of the Machico complex, the least studied so far. For this purpose, during 2001-2002, a monitoring study was carried out using traps and manual collections in the lava tubes of Landeiros and Cavalum (I, II, III). Fourteen species of springtails were recorded. Of these, four are new species, Neelus serratus Jordana & Baquero sp. nov., Coecobrya decemsetosa Jordana & Baquero sp. nov., Coecobrya octoseta Jordana & Baquero sp. nov., and Sinella duodecimoculata Jordana & Baquero sp. nov., and one is a new record for the archipelago, Lepidocyrtus curvicollis Bourlet, 1839.

Contourite depositional systems offshore Madeira Island: Decoding the deepwater circulation since the Late Cretaceous to the Quaternary in the NE-Central Atlantic

Contourite depositional systems offshore Madeira Island: Decoding the deepwater circulation since the Late Cretaceous to the Quaternary in the NE-Central Atlantic

IoT, machine learning and photogrammetry in small hydropower towards energy and digital transition: potential energy and viability analyses

This research aims to evaluate and put into practise the design of a small hydropower plant on a stream at São Vicente, in Madeira Island, supported by internet of things (IoT). The photogrammetry technique is also used with a comprehensive digital transformation, in which new concepts, methods and models, such as machine learning (ML), and big data analytics play an important role due to the huge availability time series that have to be exploited in hydropower design studies. Nowadays, digitalization and massive data availability are imposing new ways to address many of the current challenges associated with the energy and digital transition. This research is based on a simple small hydropower design, to present an integrated methodology using new methods assigned by an internet protocol system, which includes the development of different steps and components supported by GIS, photogrammetry and the use of advanced tools, with the support of a drone survey with internet communication (IoT) that allow the generation of experimentally-based estimates in situ characterization, the volumetric flow, the hydrological data treatment, the hydraulic calculations and economic estimations for a real hydro project. Therefore, hydrological variables, hydraulic analysis and topographical survey are carried out in the IoT application platform supported by new tools and methods to optimise the size of hydraulic structures, estimate the performance and potential of the hydropower plant towards the best solution for energy and digital transition. Firstly, the data-base for the all study and posterior sizing of the case study of hydropower plant are defined and then the corresponding analyses and results are presented. Then, the cost estimation for the construction, maintenance and operation of the selected elements that compose the hydropower topology are determined, as well as the respective economic balance, considering the annual energy production. In addition, both economic and environmental return on investment is discussed. Finally, an analysis to equate the cost estimates and the respective benefits of hydropower generation using this new approach applicability is stablished, taking into account some economic indicators to determine the profitability of the project.

Hydraulic Planning in Insular Urban Territories: The Case of Madeira Island—São João Stream, Funchal, Portugal

This study’s primary goal was to conduct an analysis regarding the flood susceptibility of the main watercourse of the São João (Funchal) drainage basin. In addition, if proven necessary, we also aimed to suggest mitigation measures, such as sizing a detention basin and promoting adjustments of the riverbed’s roughness coefficient. This study also resorted to geomorphological data—obtained during the watershed characterization process—that were then utilized in the SIG ArcGIS software, in order to estimate the expected peak flow rate, considering a return period of 100 years using the Gumbel distribution. Finally, the Manning–Strickler equation was utilized to determine the river discharge point’s drainage capacity; the reason for that was to verify whether its drainage capacity was sufficient to drain the entire volume of rainwater associated with an extreme flood event. In summary, the results obtained by this study indicate that the drainage capacity of the river discharge point of the São João watershed (Funchal) is insufficient when considering an extreme flood event, for a return period of 100 years. Hence, it became necessary to explore the two aforementioned mitigation measures: first, regarding the detention basin, its sizing was calculated through both the Dutch method and the simplified triangular hydrograph method; second, aiming to increase the drainage capacity of the river discharge point, it is suggested that the roughness coefficient should also be modified.

Estimation of Productivity and Above-Ground Biomass for Corn (Zea mays) via Vegetation Indices in Madeira Island

The advancement of technology associated with the field, especially the use of unmanned aerial vehicles (UAV) coupled with multispectral cameras, allows us to monitor the condition of crops in real time and contribute to the field of machine learning. The objective of this study was to estimate both productivity and above-ground biomass (AGB) for the corn crop by applying different vegetation indices (VIs) via high-resolution aerial imagery. Among the indices tested, strong correlations were obtained between productivity and the normalized difference vegetation index (NDVI) with a significance level of p &lt; 0.05 (0.719), as well as for the normalized difference red edge (NDRE), or green normalized difference vegetation index (GNDVI) with crop productivity (p &lt; 0.01), respectively 0.809 and 0.859. The AGB results align with those obtained previously; GNDVI and NDRE showed high correlations, but now with a significance level of p &lt; 0.05 (0.758 and 0.695). Both GNDVI and NDRE indices showed coefficients of determination for productivity and AGB estimation with 0.738 and 0.654, and 0.701 and 0.632, respectively. The use of the GNDVI and NDRE indices shows excellent results for estimating productivity as well as AGB for the corn crop, both at the spatial and numerical levels. The possibility of predicting crop productivity is an essential tool for producers, since it allows them to make timely decisions to correct any deficit present in their agricultural plots, and further contributes to AI integration for drone digital optimization.

Impact of Lifting Mask Mandates on COVID-19 Incidence and Mortality in Portugal: An Ecological Study

The use of face masks in public was one of several COVID-19 non-pharmaceutical interventions adopted to mitigate the pandemic in Portugal. The aim of this study was to evaluate the impact of lifting the mask mandate on the April 22, 2022 on COVID-19 incidence and mortality in mainland Portugal and in the Azores. As a secondary objective, we aimed to evaluate the evolution of COVID-19 cases in a setting without a mask mandate (Azores islands) and in a setting with a mask mandate (Madeira islands).Surveillance data on laboratory-confirmed COVID-19 cases and COVID-19 deaths were used to conduct an interrupted time series analysis to estimate changes in daily incidence and deaths during a mask mandate period (28th March - 21st April 2022) and during a post-mask mandate period (22nd April - 15th May 2022), in mainland Portugal and the Azores. In a second phase, for each group of islands, we fitted a negative binomial regression model, with daily COVID-19 incident cases as the primary outcome of interest, and relative frequency of Omicron BA.5 lineage as explanatory variable.Significant changes in trends were observed for the overall incidence rate and COVID-19 deaths; increasing trends were observed for COVID-19 incidence and deaths in the post mandate period [5.3% per day; incidence rate ratio (IRR): 1.053; 95% confidence interval (CI): 1.029 - 1.078] and [3.2% per day; mortality rate ratio (MRR): 1.032; 95% CI: 1.003 - 1.062], respectively. For every unit increase in the percentage of Omicron BA.5 lineage there was a 1.5% increase per day (IRR: 1.015; 95% CI: 1.006 - 1.024) in COVID-19 incidence rate in the Azores islands, while for Madeira islands an increase of 0.05% COVID-19 cases per day was observed (IRR: 1.005; 95% CI: 1.000 - 1.010).Lifting the mask mandate in Portugal was associated with an increase in COVID-19 incidence and deaths, thus highlighting the positive effect of face mask policies in preventing respiratory virus transmission and saving lives.

Fecundity, an overlooked life-history trait for coastal management of commercial molluscs?

Gonadal development in limpets is well-known. However, the integration of fecundity data on coastal management actions remains overlooked. Here, we use fecundity of two exploited limpets (Patella ordinaria and P. aspera) to demonstrate its potential as a conservation tool to preserve the harvested populations of both species. From October 2021 to June 2022, 158 females of P. ordinaria and 70 of P. aspera were collected from the coastal rocky shores of the archipelago of Madeira (NE Atlantic Ocean). The fecundity in both species appears to be determinate, and estimated batch fecundity 365,638 ± 204,462 oocytes for P. ordinaria and 73,029 ± 43,496 oocytes for P. aspera. The presence of spawning individuals of both species until May is of significant relevance to their management and conservation. A harvest-ban (November-March) is currently implemented in the coastal governance actions of P. ordinaria and P. aspera. Based on the fecundity results, small adjustments can be made to further improve the conservation of adult individuals, which are important for the continuity of future generations. So far, fecundity data constitute an overlooked life trait of key importance to preserve populations of exploited species, primarily those with limited mobility such as semi-sessile littoral limpets.

Public participation and climate change governance: Between political approach and local actors’ perspective in two Macaronesian territories

Climate change (CC) is the major current environmental challenge influencing the balance of ecosystems, livelihoods, social organization, public health, and well-being. The Autonomous Region of Madeira and the Autonomous Community of the Canary Islands, considered outermost regions (ORs), form part of continental countries (Portugal and Spain, respectively) and integrate Macaronesia. Due to their location and idiosyncratic characteristics, they are also particularly vulnerable to CC. Regional and local mitigation and adaptation plans and strategies are in force, but policies still do not respond to CC challenges or fully recognize or integrate public participation in their definition and implementation. This article investigates the relevance of public participation in CC policies and how it has been carried out by decision-makers. Thereby, it intends to understand the evolution of CC policies in the archipelagos of Madeira and the Canary Islands, as they have met the interests of relevant scientific, administrative, and economic actors, often underestimating the contributions of other actors, and how public involvement and participation is key to resolve socio-environmental issues in the territories. With this aim in mind, we have conducted a document analysis of the legislation, programs, and strategies on CC, complemented by 20 in-depth interviews, 10 in Madeira and 10 in Las Palmas of Gran Canaria, to a group of local actors, including scientists, technicians, and politicians. Our study shows that despite the efforts leveraged by European and national guidelines, the status quo prevails, with political and institutional arenas systematically keeping their distance from concrete realities of quotidian life. The results show evidence that at international, supranational, and national levels, and at regional/local levels, CC policies often perpetuate domain ties, sectoral and private interests, and are outlined according to narratives not accessible to all actors. Therefore, discourses—political, academic, and corporate—prolong power relations and knowledge that express an institutionalised truth. Thus, we argue that proximity governance is crucial to raise awareness of socio-environmental problems, complement existing knowledge, incite action, and empower local communities. This means that without a collaborative endeavor to boost the required changes, individually and collectively, CC policies might be difficult to implement.

Monitoring marine litter on Funchal beaches (Madeira Island): Insights for litter management

Marine litter is a complex and multi-dimensional problem, with beach litter surveys being an important cost-effective tool for monitoring and assessing marine litter pollution. In Madeira Island (Portugal, NE Atlantic), a region awarded several times as ‘Europe’s Leading Island Destination’ and with a particular orography, there is a scarce understanding of the situation of marine debris. A two-year monitoring (July 2020 to April 2022) of macro-litter was conducted on two beaches in Funchal, the largest city and capital of the island. The abundance, composition, sources, and pathways of the stranded marine litter were assessed following OSPAR guidelines. During the two years, a total of 14,265 items were recorded. The mean litter density was found to be 0.29 items/m2 and the beaches’ clean index ranged between ‘very clean’ and ‘dirty’. Cigarette butts (30.9%) and plastic objects (30.7%) were the most frequent marine litter items, followed by paper/cardboard (9.2%) and metal items (8.3%). The composition of the litter showed that most of the monitored marine debris has a land-based source, with a strong contribution from smoking-related activities and littering in streams. By characterizing the waste and identifying its source, it was possible to propose integrated management actions at a local level. Outreach and raising awareness campaigns, together with actions to limit single-use plastic items and stimulate a circular economy, could contribute to limit marine litter on the studied island but also in other regions with similar profiles.

Shellfish consumption preferences in an oceanic archipelago

A survey on shellfish consumption preferences was conducted in the Eastern Atlantic archipelago of Madeira. A total of 402 valid questionnaires were collected from locals older than 15 years old. Gender, age, highest education level, work status and salary were considered in the sample composition. Participants were inquired about frequency, amount and risks associated with consumption, as well as concerns regarding the freshness of seafood. Shellfish appears to be consumed less than once a week, and 79.1% of these consumers prefer limpets. GLM analysis showed that total salary amount was the demographic variable which most affects seafood consumption. The results indicated that the majority of the respondents consume limpets less than once a week, in an amount that varies between a quarter and a half dose. With regard to health concerns, most respondents are conscious of the importance of products’ freshness and approximately half of them are aware of the existence of risks associated with consumption. In general, the awareness about freshness and possible risks of consumption is dependent on the level of education. Limpets are preferably consumed during summer, both grilled and cooked, respectively. The present study provides preliminary information on shellfish consumption trend in the archipelago of Madeira. Raising the awareness of seafood consumers in line with a health surveillance network in preparation in Macaronesia could be an important tool for spreading information related to the risks associated to its consumption.

Life History Parameters and Fishing Aspects of the Alien Nimble Spray Crab Percnon gibbesi in a Native Area of the Central-East Atlantic.

Percnon gibbesi is a native crab species characteristic of intertidal and subtidal zones of the Atlantic coast of the European Macaronesian archipelagos (Azores, Madeira, and Canary Islands), and probably also in the neighbouring rocky coasts of northwest Africa. P. gibbesi is considered an invasive alien species in almost all of the Mediterranean, with expanding populations from Spain to Turkey, including Libya; However, its biology and ecology are highly unknown, despite all its range of distribution. In the intertidal zones of Gran Canaria Island, this crab, in the intertidal zones of Gran Canaria Island, shows a carapace length range between 4.1 and 22.7 mm (4.1-22.7 in males and 5.7-22.3 in females), where females showed higher weights and lengths than males on average; However, males predominated in all samples, with a sex ratio of 1:0.57. The L∞ for this crab was estimated to be 27 ± 3 mm (23 ± 4 mm for females and 25 ± 4 mm for males). The growth coefficient (K) was 0.24 year-1, the total mortality (Z) was Z = 1.71 year-1, and the natural mortality (M) was 0.47 year-1. Although females grow faster than males, males are more abundant in the larger length classes. Although the presence of ovigerous females indicated that reproduction takes place twice a year, from March to April and from August to September, the number of cohorts detected by the modal progression analysis showed that reproduction takes place all year.

Phylogenomics of the Olea europaea complex using 15 whole genomes supports recurrent genetic admixture together with differentiation into seven subspecies

BackgroundThe last taxonomic account of Olea recognises six subspecies within Olea europaea L., including the Mediterranean olive tree (subsp. europaea) and five other subspecies (laperrinei, guanchica, maroccana, cerasiformis, and cuspidata) distributed across the Old World, including Macaronesian islands. The evolutionary history of this monophyletic group (O. europaea complex) has revealed a reticulated scenario involving hybridization and polyploidization events, leading to the presence of a polyploid series associated with the subspecies. However, how the polyploids originated, and how the different subspecies contributed to the domestication of the cultivated olive are questions still debated. Tracing the recent evolution and genetic diversification of the species is key for the management and preservation of its genetic resources. To study the recent history of the O. europaea complex, we compared newly sequenced and available genomes for 27 individuals representing the six subspecies.ResultsOur results show discordance between current subspecies distributions and phylogenomic patterns, which support intricate biogeographic patterns. The subspecies guanchica, restricted to the Canary Islands, is closely related to subsp. europaea, and shows a high genetic diversity. The subsp. laperrinei, restricted now to high mountains of the Sahara desert, and the Canarian subsp. guanchica contributed to the formation of the allotetraploid subsp. cerasiformis (Madeira islands) and the allohexaploid subsp. maroccana (western Sahara region). Our phylogenomic data support the recognition of one more taxon (subsp. ferruginea) for the Asian populations, which is clearly segregated from the African subsp. cuspidata.ConclusionsIn sum, the O. europaea complex underwent several processes of hybridization, polyploidy, and geographical isolation resulting in seven independent lineages with certain morphological traits recognised into subspecies.

Regional communication and media analysis of aquaculture in Atlantic islands

The way the media portrays aquaculture-related events can influence how this industry is perceived by the public and affect its success. Since media are an important source of public information, media content analysis has been carried out in several regions of the world. This study aimed to determine which aspects of aquaculture were more exposed and how they were discussed by regional media in the Madeira archipelago, an oceanic group of Portuguese islands. Analysis of aquaculture’s media coverage in the two most-read regional newspapers of Madeira was carried out over a 5-year period (2017 to 2021). For each news article, the assessment focused on the geographic scope, the main topics covered, the stakeholders with access to the debate, and the general tone of the article (risk/benefit framework). A total of 297 articles were analyzed. Results indicate the occurrence of trigger events that contributed to a shift in the amount of news published and in the way media framed aquaculture. In general, political and economic issues dominated the coverage, whereas social, environmental, scientific, and landscape matters received less media attention. The voice of the government was predominant throughout the 5 years in analysis and aquaculture was generally framed with a balanced tone, slightly more negative. Open and transparent communication between the stakeholders and the media is fundamental for the sustainable development of the aquaculture industry.

Interannual Aggregation Behavior of the Endangered SmoothhoundMustelus Mustelusin Madeira Island (Northeast Atlantic)

We describe the first observations of aggregation behavior in the endangered smoothhound, Mustelus mustelus, on Madeira Island (NE Atlantic) across six consecutive years. These observations contribute to the understanding of habitat use by early life stages of this endangered species, with regional implications for conservation efforts.

Genome size variation within Crithmum maritimum: Clues on the colonization of insular environments.

Angiosperms present an astonishing diversity of genome sizes that can vary intra- or interspecifically. The remarkable new cytogenomic data shed some light on our understanding of evolution, but few studies were performed with insular and mainland populations to test possible correlations with dispersal, speciation, and adaptations to insular environments. Here, patterns of cytogenomic diversity were assessed among geographic samples (ca. 114) of Crithmum maritimum (Apiaceae), collected across the Azores and Madeira archipelagos, as well as in adjacent continental areas of Portugal. Using flow cytometry, the results indicated a significant intraspecific genome size variation, spanning from reduced sizes in the insular populations to larger ones in the mainland populations. Moreover, there was a tendency for an increase in genome size along the mainland populations, associated with lower temperatures, higher precipitation, and lower precipitation seasonality. However, this gradient might be the result of historic phylogeographical events associated with previous dispersal and extinction of local populations. Overall, our findings provided evidence that smaller genome sizes might play a critical role in the colonization of islands, corroborating other studies that argue that organisms with smaller genomes use fewer resources, having a selective advantage under insular environments. Although further studies are needed to improve our understanding of the mechanisms underlying genome size evolution on islands, conservation strategies must be promoted to protect the rich cytogenomic diversity found among C. maritimum populations, which occur in coastal areas that are particularly threatened by human activity, pollution, invasive species, and climate changes.

Pollen morphology of the endemic genera of the Madeira archipelago, Portugal

This study presents the first palynological characterisation of the five endemic plant genera of the Madeira archipelago: Chamaemeles Lindl, Melanoselinum Hoffm., Monizia Lowe, Musschia Dumort and Sinapidendron Lowe. Pollen grain morphology of ten endemic species was studied using light and scanning electron microscopy techniques. The size and shape of pollen grains, the polar axis, the equatorial diameter, and the exine ornamentation were measured and described. We found that the pollen grains of the five endemic genera are all medium-size monads. The close relative apiaceous Melanoselinum and Monizia differ in polar (P) and equatorial (E) diameter size and exine ornamentation while Sinapidendron species show differences in P, E, and P/E ratios. The pollen grains of the two Musschia species are very similar to each other, but differ in morphology and ornamentation from the Macaronesian endemic bellflowers Azorina vidalii and Canarina canariensis. This study unveiled differences between the endemic taxa and with their close related species, thus providing support to previous taxonomic findings.

Smart Water Grids and Digital Twin for the Management of System Efficiency in Water Distribution Networks

One of the main factors contributing to water scarcity is water loss in water distribution systems, which mainly arises from a lack of adequate knowledge in the design process, optimization of water availability, and poor maintenance/management of the system. Thus, from the perspective of sustainable and integrated management of water resources, it is essential to enhance system efficiency by monitoring existing system elements and enhancing network maintenance/management practices. The current study establishes a smart water grid (SWG) with a digital twin (DT) for a water infrastructure to improve monitoring, management, and system efficiency. Such a tool allows live monitoring of system components, which can analyze different scenarios and variables, such as pressures, operating devices, regulation of different valves, and head-loss factors. The current study explores a case study in which local constraints amplify significant water losses. It develops and examines the DT model’s application in the Gaula water distribution network (WDN) in Madeira Island, Portugal. The developed methodology resulted in a significant potential reduction in real water losses, which presented a huge value of 434,273 m3 (~80%) and significantly improved system efficiency. The result shows a meaningful economic benefit, with savings of about EUR 165k in water loss volume with limiting pressures above the regulatory maximum of 60 m w.c. after the district metered area (DMA) sectorization and the requalification of the network. Hence, only 40% of the total annual volume, concerning the status quo situation, is necessary to supply the demand. The infrastructure leakage index measures the existing real losses and the reduction potential, reaching a value of 21.15, much higher than the recommended value of 4, revealing the great potential for improving the system efficiency using the proposed methodology.

Plasticrust generation and degeneration in rocky intertidal habitats contribute to microplastic pollution

Plasticrusts are a plastic form that consists of plastic encrusting intertidal rocks. To date, plasticrusts have been reported on Madeira island (Atlantic Ocean), Giglio island (Mediterranean Sea) and in Peru (Pacific Ocean) but information on plasticrust sources, generation, degeneration and fate is largely missing. To address these knowledge gaps, we combined plasticrust field surveys, experiments and monitorings along the Yamaguchi Prefecture (Honshu, Japan) coastline (Sea of Japan) with macro-, micro- and spectroscopic analyses in Koblenz, Germany. Our surveys detected polyethylene (PE) plasticrusts that derived from very common PE containers and polyester (PEST) plasticrusts that resulted from PEST-based paint. We also confirmed that plasticrust abundance, cover and distribution were positively related to wave exposure and tidal amplitude. Our experiments showed that plasticrusts are generated by cobbles scratching across plastic containers, plastic containers being dragged across cobbles during beach clean-ups, and waves abrading plastic containers on intertidal rocks. Our monitorings found that plasticrust abundance and cover decreased over time and the macro- and microscopic examinations indicated that detached plasticrusts contribute to microplastic pollution. The monitorings also suggested that hydrodynamics (wave occurrence, tidal height) and precipitation drive plasticrust degeneration. Finally, floating tests revealed that low density (PE) plasticrusts float whereas high density (PEST) plasticrusts sink suggesting that polymer type floatability influences the fate of plasticrusts. By tracking the entire lifespan of plasticrusts for the first time, our study contributes fundamental knowledge of plasticrust generation and degeneration in the rocky intertidal zone and identified plasticrusts as novel microplastic sources.

A Glider View of the Spreading and Mixing Processes of Antarctic Intermediate Water in the Northeastern Subtropical Atlantic

The Antarctic Intermediate Water (AAIW), one of the most important global intermediate water masses, spreads over the world ocean. Its propagation limit at the Northeast Subtropical Atlantic is characterized by its encounter with the Mediterranean Water (MW), which presents dissimilar thermohaline properties. Previous studies of the AAIW in this region have been based on traditional oceanographic cruise observations, which were later complemented by observations using autonomous systems such as ARGO floats. However, these observations present limitations for the study of processes occurring at mesoscale and smaller scales. In this study, we used high-resolution observations made by cutting edge platforms such as underwater gliders. Specifically, a meridional glider section realized in spring 2016 between the islands of Madeira and Gran Canaria has been used. The temperature, salinity and dissolved oxygen minima have allowed the detection of the AAIW signal north of the Canarian archipelago and significantly westward from its main northward propagation pathway in this region. The results of this work have shown that the encounter of AAIW and MW generates thermohaline intrusions or interleaving layers. It is suggested that double diffusion processes may play a role in the development of these structures, which may be important for water masses mixing and, therefore, in determining the northward spreading boundary of AAIW. The use of the high-resolution glider observations combined with other data products is essential for the study of water masses and dynamics when relevant processes have a wide range of scales.