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Ship-based time-series observations provide crucial data for understanding marine ecosystems, improving decision making in ocean and coastal management. However, only a few time series survive for more than a decade. RADIALES is one of the longest multidisciplinary programs in operation in the northern and northwestern coast of Spain. In the last 30Â years, this program collected monthly data on physical, chemical and plankton observations in an array of five sections of stations representative of upwelling and stratified dynamics. Here, the main achievements, including key contributions to ecosystem conservation policies, are summarized. The development of this program, in line with similar initiatives in other countries, included phases focused on the study of seasonality, on comparative analysis, and lately on the analysis of decadal variability and regime shifts. Furthermore, in recent years there was a substantial improvement in the identification of plankton species by genomics. Among the main findings of RADIALES are the quantification of ocean warming at subsurface layers, the determination of climatologies in thermohaline, biogeochemical and biological variables, the inventory of plankton species (from bacteria to zooplankton) and the identification of regionally coherent regime shifts. Baselines defined by RADIALES series were instrumental for the assessment of environmental impacts (e.g. oil spills) and for the support of environmental policies (e.g. Marine Strategy Framework Directive). By contributing to international databases, data from programs as RADIALES combined with new instrumental observations will help to develop a more coherent and comprehensive understanding of the ocean ecosystems, enhancing our ability to detect and forecast risks., IEO, GAIN (Xunta de Galicia), 3,269

Piñeiro, S., González-Pola, C., Fernández-Díaz, J. M., Naveira-Garabato, A. C., Sánchez-Leal, R., Puig, P., et al. (2021). Persistent, depth-intensified mixing during the Western Mediterranean Transition's initial stages. Journal of Geophysical Research: Oceans, 126, e2020JC016535. https://doi.org/10.1029/2020JC016535. © 2020. American Geophysical Union. All Rights Reserved., © 2020. American Geophysical Union. All Rights Reserved. Major deep-convection activity in the northwestern Mediterranean during winter 2005 triggered the formation of a complex anomalous deep-water structure that substantially modified the properties of the Western Mediterranean deep layers. Since then, evolution of this thermohaline structure, the so-called Western Mediterranean Transition (WMT), has been traced through a regularly sampled hydrographic deep station located on the outer continental slope of Minorca Island. A rapid erosion of the WMT's near-bottom thermohaline signal was observed during 2005–2007. The plausible interpretation of this as local bottom-intensified mixing motivates this study. Here, the evolution of the WMT structure through 2005–2007 is reproduced by means of a one-dimensional diffusion model including double-diffusive mixing that allows vertical variation of the background mixing coefficient and includes a source term to represent the lateral advection of deep-water injections from the convection area. Using an optimization algorithm, a best guess for the depth-dependent background mixing coefficient is obtained for the study period. WMT evolution during its initial stages is satisfactorily reproduced using this simple conceptual model, indicating that strong depth-intensified mixing (K ∞ (z) ≈ 22 × 10−4 m2 s−1; z ⪆ 1,400 dbar) is a valid explanation for the observations. Extensive hydrographic and current observations gathered over the continental slope of Minorca during winter 2018, the first deep-convective winter intensively sampled in the region, provide evidence of topographically localized enhanced mixing concurrent with newly formed dense waters flowing along-slope toward the Algerian sub-basin. This transport-related boundary mixing mechanism is suggested to be a plausible source of the water-mass transformations observed during the initial stages of the WMT off Minorca., CTM2014-54374-R. BES-2015-074316., Estudio de la anomalía termohalina en las aguas profundas del Mediterráneo Occidental y su relación con las oscilaciones climáticas, ATHAPOC, SI

Ocean surface warming is commonly associated with a more stratified, less productive, and less oxygenated ocean. Such an assertion is mainly based on consistent projections of increased near‐surface stratification and shallower mixed layers under global warming scenarios. However, while the observed sea surface temperature (SST) is rising at midlatitudes, the concurrent ocean record shows that stratification is not unequivocally increasing nor is MLD shoaling. We find that while SST increases at three study areas at midlatitudes, stratification both increases and decreases, and MLD deepens with enhanced deepening of winter MLDs at rates over 10 m decade−1. These results rely on the estimation of several MLD and stratification indexes of different complexity on hydrographic profiles from long‐term hydrographic time‐series, ocean reanalysis, and Argo floats. Combining this information with estimated MLDs from buoyancy fluxes and the enhanced deepening/attenuation of the winter MLD trends due to changes in the Ekman pumping, MLD variability involves a subtle interplay between circulation and atmospheric forcing at midlatitudes. Besides, it is highlighted that the density difference between the surface and 200 m, the most widely used stratification index, should not be expected to reliably inform about changes in the vertical extent of mixing., Key Points Ocean observations show that surface warming is not definitively linked to a more stratified and less mixed oceanSubtle interplay between changes in circulation and atmospheric forcing contribute to find warmer and deeper MLDsHow our findings reconcile with the observation of a less productive and oxygenated ocean is discussed

17 pages, 11 figures, 1 appendix, The present-day morphology of the Le Danois Bank region has been investigated based on bathymetric and high to ultra-high resolution seismic reflection data. The involved bottom-current processes are associated with the Eastern North Atlantic Central Water, the Atlantic Mediterranean Water and the Labrador Sea Water. Sediments originating from various canyon systems along the Cantabrian Margin and the Asturias continental shelf are transported by downslope and alongslope processes towards the Le Danois intraslope basin. The background flow velocities of bottom currents are all below the threshold (8–10 cm/s) of generating plastered and mounded geometries of contourite drifts. However, bottom currents are locally accelerated (up to 25 cm/s) due to the presence of the Le Danois Bank and the Vizco High, creating a furrow and three moats and generating six plastered drifts, three elongated mounded and separated drifts at different depth intervals. The extension and distribution of the drifts are controlled by slope morphology and/or bottom current velocities. Unlike contourite drifts along other continental slopes, a single contourite drift (the Gijón Drift) with a lateral variation in drift geometry and internal structure indicates the interaction of bottom currents with different flow dynamics. Additionally, scouring of active bottom currents and rapid sedimentation rate of contourite drifts may be at the origin of slope instability events. Besides contourite drifts, internal waves may have induced the formation of sediment waves. In the Le Danois intraslope basin, multiple sedimentary processes work together and shape the present-day seafloor. Bottom currents are focused due to deflection on complex topographical obstacles within a relatively small basin setting, and create a wide variety of sedimentary features, including contourite drifts. The resulting sedimentary features thus have more frequent lateral variations, a feature typical for topographically constrained small basins, This study was carried out within the framework of a Chinese Scholarship Council “CSC Grant” (201506410062). The research was conducted in collaboration with “The Drifters Research Group” of the Royal Holloway University of London (UK) and it is related to the projects CTM 2012-39599-C03, CGL2016-80445-R, and CTM2016-75129-C3-1-R. [...] These research campaigns framed within the ECOMARG (REN2002-00916/MAR) and MARCONI (REN2001-1734 C03-01/M) projects. This study also builds upon achievements of project ESF Euromargins MOUNDFORCE, EC FP5 RTN EURODOM and EC FP6 HERMES (GOCE-CT-2005-511234-1)

The ICES (International Council for the Exploration of the Sea) Working Group on Oceanic Hydrography (WGOH) was established in the late 1970’s with the aim of gathering experts in physical oceanography to provide regular science-based assessments of the North Atlantic hydrographical condition (basically termohaline fields). From the beginning, the WGOH has relied on repeated long-term in-situ sampling at key sites around the North Atlantic, the Nordic Seas and adjacent shelf seas. An annual Report on Ocean Climate (IROC), produced by the WGOH since the late 1990’s, summarizes trends in regional hydrography and identifies patterns linking these changes across the North Atlantic. Regional analyses are prepared by local experts who are directly involved in the monitoring programs responsible for collecting data presented in the report. An interactive webpage created in 2013 allows users to browse and download data that inform the IROC. Within the last two decades the physical oceanography community has evolved quickly incorporating technological advances such as autonomous devices into classical in-situ sampling programs. The WGOH has embraced such technological developments without diverting focus from ongoing in-situ long-term monitoring programs. Having longstanding experience synthesizing data and expertise from a large number of operational programs spanning an extensive international footprint, the WGOH has a unique perspective to offer the global ocean observing community. Here we discuss how we might foster connections with ICES to benefit the GOOS (Global Ocean Observing System) community., Sí

A large production of anomalous dense water in the northwestern Mediterranean Sea during winter 2005 led to a widespread abrupt shift in Western Mediterranean deep waters characteristics. This new configuration, the so-called Western Mediterranean Transition (WMT), involved a complex thermohaline structure that was tracked over time through a deep hydrographic station located NE of Minorca Island, sampled 37 times between 2004 and 2017. In this study, the thermohaline evolution of the WMT signal is analyzed in detail. Using a 1-D diffusion model sensitive to double-diffusive mixing phenomena, the contribution to the heat and salt budgets of the deep Western Mediterranean in terms of ventilation and diffusive transference from the intermediate layers above is disentangled. Results show distinct stages in the evolution of the deep waters, driven by background diffusion and intermittent injections of new waters. The progression of a multilayered structure in the deep ocean is well represented through existing parameterizations of salt fingering and diffusive layering processes and makes it possible to infer an independent estimate of regional background diffusivity consistent with current knowledge. Overall, the deep layers of the Western Mediterranean underwent substantial warming (0.059 °C) and salt increase (0.021) between 2004 and 2017, mostly dominated by injections of dense waters in the 2005–2006 and 2011–2013 periods. Thus, within the WMT period, heat uptake rate in the deep Western Mediterranean was substantially higher than that of the intermediate levels in the global ocean., Sí

The bluntnose sixgill shark, Hexanchus griseus, is a relatively common, wide-spread and deepwater shark that occurs along outer continental shelves and upper slopes. However, very little information exists about its distribution patterns, migrations and behavior. Data on occurrence and behavior of sixgill sharks inhabiting waters north of Spain (Galicia and Cantabrian Sea, NE Atlantic) were obtained from yearly oceanographic trawl surveys, commercial fishing boat records, and a pop-up satellite archival tag that was deployed for 75 days on a juvenile specimen. Most of the specimens were caught in Galician waters, and nearly all of those from surveys were juveniles (length range, 60–121 cm). Catch depth from surveys and commercial vessels ranged from 90 to 800 m and 90 to 1750 m respectively. Combining all data, a moderate relationship was observed between catch depth and size of the sharks (). The sex ratio was 1:1.86 in favor of females. September and February were the months with more catches reported from commercial vessels. Data obtained from one electronic pop-up tag (Mini PAT), provided information about depth and temperature preferences over 75 days. Mean depth obtained during that period was 913 m (depth range 727–1247 m), and the mean temperature was 10.3 °C, (range 8.0–10.8 ° C). Movements up and down in the water column within a single day ranged from 50 to 385 m. No cyclic diel vertical migration was however observed, the shark moved smoothly without a defined pattern. Vertical movements at semidiurnal frequency were intermittently observed. The thereby differences observed in the swimming behavior of H. griseus compared to other areas could be attributed to size, foraging activity or atypical behavior., Sí

Sánchez Leal, Ricardo ... et al.-- 11 pages, 5 figures, supplementary material http://advances.sciencemag.org/cgi/content/full/3/11/eaao0609/DC1, The pathways and transformations of dense water overflows, which depend on small-scale interactions between flow dynamics and erosional-depositional processes, are a central piece in the ocean’s large-scale circulation. A novel, high-resolution current and hydrographic data set highlights the intricate pathway travelled by the saline Mediterranean Overflow as it enters the Atlantic. Interaction with the topography constraints its spreading. Over the initial 200 km west of the Gibraltar gateway, distinct channels separate the initial gravity current into several plunging branches depth-sorted by density. Shallow branches follow the upper slope and eventually detach as buoyant plumes. Deeper branches occupy mid slope channels and coalesce upon reaching a diapiric ridge. A still deeper branch, guided by a lower channel wall marked by transverse furrows, experiences small-scale overflows which travel downslope to settle at mid-depths. The Mediterranean salt flux into the Atlantic has implications for the buoyancy balance in the North Atlantic. Observations on how this flux enters at different depth levels are key to accurately measuring and understanding the role of Mediterranean Outflow in future climate scenarios, We also acknowledge funding and data provided by projects INGRES3 (CTM2010-21229), STOCA (IEO 2009), PESCADIZ (IEO), INDEMARES (LIFE07 NAT/E/000732+), MOC2 (CTM2008-06438-C02-01), MED-OUTFLOW (CTM2008-03422-E/MAR and CTM2010-11488-E), PELCOSAT (IEO), SEMANE (X. Carton), DILEMA (CTM2014-59244-C3-2-R), and INPULSE (CTM2016-75129-C3-1-R) as well as SISMER, PANGEA, IEO, ICES, BODC, and NOAA data centers. Additional funding was provided by the CONTOURIBER (CTM2008-06399-C04-01/MAR) project. Part of the research was conducted in the framework of the “Drifters” Research Group of the Royal Holloway, University of London, UK

Six summer surveys conducted from 2001 to 2005 and in 2012 by the Spanish Institute of Oceanography (IEO) reveal that the hydrographic early summer scenarios around the Balearic Islands are related to the winter atmospheric forcing in the northwestern Mediterranean Sea. The Balearic Islands (western Mediterranean Sea) lie at the transition between the southern, fresher, newly arrived Atlantic Waters (AW) and the northern, saltier, resident AW. The meridional position of the salinity driven oceanic density front separating the new from the resident AW is determined by the presence/absence of Western Intermediate Water (WIW) in the Mallorca and Ibiza channels. When WIW is present in the channels, the oceanic density front is found either at the south of the islands, or along the Emil Boudot escarpment. In contrast, when WIW is absent, new AW progresses northwards crossing the Ibiza channel and/or the Mallorca channel. In this later scenario, the oceanic density front is closer to the Balearic Islands. A good correspondence exists between standardized winter air temperature anomaly in the Gulf ofLions and the presence of WIW in the channels. We discuss the use of a regional climatic index based on these parameters to forecast in a first-order approach the position of the oceanic front, as it is expected to have high impact on the regional marine ecosystem., Sí

A key challenge in oceanography is to capture and quantify processes that happen on short time scales, seasonal changes and inter-annual variations. To address this problem the P&O European Ferries Ltd. Ship MV Pride of Bilbao was fitted with a FerryBox from 2002 to 2010 and data returned to NOC in real time providing near continuous measurements between UK (Portsmouth) and Spain (Bilbao) of temperature, salinity, chlorophyll-fluorescence and oxygen. Additional monthly samples were collected on manned crossings. Over 6000 samples were analysed for nitrate (nitrate and nitrite) concentrations. The timing of nitrate concentration increases (with winter mixing) and decreases (with the spring bloom) are different on and off shelf and in autumn nitrate concentrations remain high on the shelf. Off shelf in the Bay of Biscay, the mixed layer depth assessed using Argo floats, was found to vary from 212 m in relatively mild winters (such as 2007/2008) to 476 m in cold winters (2009/2010). Years with deeper mixing were associated with an increase in nitrate concentrations in the surface waters (~3 µmol l-) and the increased vertical nutrient supply resulted in higher productivity the following spring. Bloom progression could be seen through the increase in oxygen anomaly and decrease in nitrate concentrations off shelf prior to changes further north on the shelf and phytoplankton growth was initiated as shoaling begins. The full dataset demonstrates that ships of opportunity, particularly ferries with consistently repeated routes, can deliver high quality in situ measurements over large time and space scales that currently cannot be delivered in any other way.

Seasonality of hydrographical properties at depth in the western Iberian margin (Eastern North Atlantic) is analysed from a 2003–2010 timeseries of a semi-annual oceanographic section extending ~ 200 nm off Cape Finisterre (43° N). All waters masses down to the whole extent of the permanent thermocline (2000 dbar) show a consistent seasonal signature in their termohaline properties and there is a notable asymmetry between the slope region and the outer ocean (in the surroundings of the Galicia Bank). There is overall cooling and freshening of East North Atlantic Central Waters in summertime, which is larger and deeper-reaching on the slope. In summertime, Mediterranean Water gets tightly attached against the slope and is uplifted, reinforcing its thermohaline signature and diminishing its presence at the outer ocean. In wintertime the situation reverses, MW seems to detach from the slope and spreads out to the open ocean, even developing a secondary branch around the Galicia Bank. Thermohaline seasonality at depth shows values up to 0.4 °C and 0.08 in salinity at the lower MW, of the order of 20 % of the overall interannual variability observed during the whole period. Decomposition of thermohaline changes at isobaric levels to changes along isoneutral surfaces and changes due to vertical displacements helps to analyse the physical processes behind the observed seasonality in terms of (1) the large-scale seasonality of the subtropical gyre in response to the seasonal migration of the subtropical high pressure system and subsequent anomalies in Ekman transport and wind stress curl, (2) the continental slope dynamics, characterized by summer upwelling, winter development of the Iberian Poleward Current and Mediterranean Water spreading and (3) the possible influence of seasonal changes of water mass properties at their formation sources.

Temperature- and salinity-balance equations together with a one-dimensional model are used in this work to investigate the governing processes of the surface temperature and salinity variability at low and high frequencies in the southern Bay of Biscay. We found that the temporal evolution of mixed layer temperature is dominated by its seasonal cycle, mostly explained through a vertical balance (80–90%) that is mostly driven by air–sea heat exchange and contributed by entrainment, while horizontal advection plays a secondary role (≤ 12%). A substantial imbalance can be noticed in spring, which surprisingly strongly diminishes from 2003 onward, coinciding with apparent shifts in surface heat flow. The uncertainties of the air–sea heat fluxes and the advective and entrainment terms seem to be responsible for the imbalance of the temperature budget. On the contrary, the interannual variability dominates over the seasonal cycle of mixed layer salinity, and advection accounts for more than 70% of the budget terms, with the sum of vertical processes playing a secondary role. The different contributions of air–sea exchanges on temperature and salinity (heat vs. freshwater) are the ultimate cause of the different patterns observed for both of the parameters.

We investigate the effect of strong meteorological perturbations in early spring on the success of mackerel (Scomber scombrus) recruitment in the N/NW Iberian area (southern Bay of Biscay) for the period 1999–2008. In 2000, the year of the most pronounced recruitment failure on record, two consecutive multidisciplinary surveys sampled hydrographic conditions and mackerel eggs, larvae and post-larvae over the main mackerel spawning grounds of the north and northwest coast of the Iberian Peninsula. Analysis of egg and larval abundance and birthdates based on the otoliths of mackerel juveniles caught between July and October 2000 showed that there were no survivors from the early spring spawns, indicating a massive loss of early spawning effort. Moreover, the abundance of 1-year-old mackerel estimated from an acoustic survey carried out in 2001 was the lowest observed within the 1999–2008 time series. This low or null survival from the early spawns in 2000 could be due to the meteorological and oceanographic conditions of that spring, in particular two storm events in April after a relatively calm March. The first storm event from the north caused strong local wind in the southern Bay of Biscay but a weak oceanographic response. The second storm event from the southwest was mainly felt west of Galicia and caused a notable increase in shelf currents and a shift of the hydrographical structure along the shelf. Detailed analysis of strong wind pulses in early spring within the historical recruitment record suggests that strong local turbulence generated by high wind speeds and advection of larvae caused by the enhancement of shelf currents can contribute to reduced recruitment. Our observations indicate that, in 2000, both mechanisms were present.

Mixed layer depth (MLD) variability from seasonal to decadal time scales in the Bay of Biscay is studied in this work. A hydrographic time series running since 1991 in the study area, a climatology of the upper layer vertical structure based on the topology of this temperature profile time series and a one-dimensional water column model have been used for this purpose. The prevailing factors driving MLD variability have been determined with detail, and agreement with observations is achieved. Tests carried out to investigate climatological profile skill to reproduce the upper layer temporal evolution have demonstrated its ability to simulate variability at seasonal time scales and reproduce the most conspicuous events observed. This has enabled us to carry out a reconstruction of the MLD variability for the last 60 years in the study area. Favourable sequence of intense mixing events explains interannual differences and cases of extraordinary deepening of winter mixed layer. The negative phase of the Eastern Atlantic pattern seems to determine important interannual variability through intense episodes of cooling and mixing as in winter 2005 in the Bay of Biscay. Low-frequency variability is also observed. A very striking and unexpected shallower winter MLD during the 1970s and 1980s than those observed from 1995 has been found. Simulation results support this counter-intuitive outcome of shallower winter mixed layers concurrent with generalized upper water warming trends reported on several occasions for the area. The long-term trends in MLD seem related with decadal variability in the North Atlantic Oscillation, being in phase and opposition with other deepening-shallowing cycles found from subtropical-to-subpolar areas in the North Atlantic., Sí

Special issue The contourite log-book: significance for palaeoceanography, ecosystems and slope instability.-- Hernández-Molina, Francisco J. ... et al.-- 30 pages, 19 figures, 1 table, supplementary data https://dx.doi.org/10.1016/j.margeo.2015.12.008, Our understanding of bottom-currents and associated oceanographic processes (e.g., overflows, barotropic tidal currents) including intermittent processes (e.g., vertical eddies, deep sea storms, horizontal vortices, internal waves and tsunamis) is rapidly evolving. Many deep-water processes remain poorly understood due to limited direct observations, but can generate significant depositional and erosional features on both short and long term time scales. This paper represents a review work, which describes for the first time these oceanographic processes and examines their potential role in the sedimentary features along the Iberian continental margins. This review explores the implications of the studied processes, given their secondary role relative to other factors such as mass-transport and turbiditic processes, and highlights three major results: a) contourite depositional and erosional features are ubiquitous along the margins, indicating that bottom currents and associated oceanographic processes control the physiography and sedimentation; b) the position of interfaces between major water masses and their vertical and spatial variation in time specifically appears to exert primary control in determining major morphologic changes along the slope gradient, including the contourite terraces development; and c) contourites deposits exhibit greater variation than the established facies model suggests. Therefore, a consistent facies model however faces substantial challenges in terms of the wide range of oceanographic processes that can influence in their development. An integrated interpretation of these oceanographic processes requires an understanding of contourites, seafloor features, their spatial and temporal evolution, and the near-bottom flows that form them. This approach will synthesize oceanographic data, seafloor morphology, sediments and seismic images to improve our knowledge of permanent and intermittent processes around Iberia, and evaluate their conceptual and regional role in the margin's sedimentary evolution. Given their complexes, three-dimensional and temporally-variable nature, integration of these processes into sedimentary, oceanographic and climatological frameworks will require a multidisciplinary approach that includes Geology, Physical oceanography, Paleoceanography and Benthic Biology, This contribution is a product of the IGCP-619 and INQUA-1204 projects, and is partially supported through the CTM 2008-06399-C04/MAR (CONTOURIBER); CTM 2012-39599-C03 (MOWER); CTM 2010-21229/MAR projects and MARUM project GALIOMAR, as well as the Continental Margins Research Group (CMRG) at Royal Holloway University of London (UK).

A total of nine leafscale gulper sharks Centrophorus squamosus ( Bonnaterre, 1788 ), were tagged with pop-up, satellite, archival, transmitting tags (PSAT) in the Marine Protected Area (MPA) of El Cachucho (Le Danois Bank) located in waters to the north of Spain, (NE Atlantic). Tags provided data on time, pressure and temperature that were used to examine movement patterns and diving behavior. Data collected from Argo floats in the study area have been used to devise a simple geolocation algorithm to infer the probable routes followed by this species. Tag release points revealed that C. squamosus moved both to the west (Galician waters) and to the north (Porcupine Bank) from the tagging area, suggesting well defined preferred pathways. The inferred trajectories indicated that sharks alternate periods constrained to specific geographical regions with quick and prompt movements covering large distances. Two sharks made conspicuous diurnal vertical migrations being at shallower depths around midnight and at maximum depths at midday, while other sharks did not make vertical migrations. Vertical movements were done smoothly and independently of the fish swimming long-distances or resting in the area. Overall results confirm that this species is highly migratory, supporting speeds of 20 nautical miles.day−1 and well capable to swim and make vertical migrations well above the abyssal plain.

A method for characterizing the upper ocean structure is developed. Each temperature (density) profile is fitted by an ideal function based on the assumption that the permanent and seasonal thermoclines can be approximated respectively by steady state and transients of turbulent-diffusive processes and that the mixed layer can advance sharply under external forcing. The ideal profile is composed of two pieces joined at the mixed layer depth (MLD). The upper part is a constant; the part below the MLD is a product of an exponential decay and a Gaussian, representing the seasonal thermocline and decaying asymptotically to a straight line that describes the permanent thermocline. The composition of an exponential decay and a Gaussian accurately fits a wide family of solutions of the diffusion equation and includes the case of a shift of the boundary. The ideal fit for each profile relies on six adjustable parameters including the MLD. As the function is non-linear and non-differentiable, a Differential Evolution optimization algorithm is proposed to make the fitting. The solution gives a good estimate of the MLD based on the topology of the profile. It also provides a measure of the gradient and the shape of each profile, which are intuitive parameters for characterizing the upper ocean structure with direct applicability in ecosystem models. The algorithm is applied to a time series of monthly conductivity–temperature–depth (CTD) profiles from a hydrographical station in the southern Bay of Biscay. The construction of a local climatology of the vertical structure evolution (mixed layer development) is presented as a practical application. Other potential uses of the method are also discussed.

Since its foundation, 100 years ago, the Spanish Institute of Oceanography (IEO) has been observing and measuring the ocean characteristics. Here is a summary of the initiatives of the IEO in the field of the operational oceanography. Some systems like the tide gauges network has been working for more than 70 years. The standard sections began at different moments depending on the local projects, and nowadays there are more than 180 coastal stations and deep-sea ones that are systematically sampled, obtaining physical and biochemical measurements. At this moment, the Observing System includes six permanent moorings equipped with current meters, an open-sea ocean-meteorological buoy offshore Santander and a sea-surface temperature satellite image station. It also supports the Spanish contribution to the Argo international programme with 47 deployed profilers, and continuous monitoring thermosalinometers, meteorological stations and vessel-mounted acoustic Doppler current profilers on the research vessel fleet. The system is completed with the contribution to the Northwest Iberian peninsula and Gibraltar observatories, and the development of regional prediction models. All these systematic measurements allow the IEO to give responses to ocean research activities, official agencies requirements and industrial and main society demands such as navigation, resource management, risks management, recreation, as well as for management development pollution-related economic activities or marine ecosystems. All these networks are linked to international initiatives, framed largely in supranational programmes of Earth observation sponsored by the United Nations or the European Union. The synchronic observation system permits a spatio-temporal description of some events, such as new deep water formation in the Mediterranean Sea and the injection of heat to intermediate waters in the Bay of Biscay after some colder northern storms in winter 2005., SI

The oceanic hydrography of the north-easternmost region of the North Atlantic subtropical gyre has been monitored since 2003 by three sections extending between 100 and 200 nautical miles from the Spanish NW and N coast into the Atlantic and the Bay of Biscay. The sections were occupied twice a year from 2003 to 2010, annually after that, and measure the whole water column (>5000 m). Correlation of series in the vertical and among sections, autocorrelation and estimates of the effect of the noise induced by the mesoscale field, all indicate that observed signatures are robust changes of water masses at the regional scale. The hydrographic time series are not characterized by smooth trends but instead by shifts that persist through consecutive cruises. The most notable features include a shift to more saline central waters around 2005 after which they remained stable, and a decrease in thermohaline properties of the Labrador Sea Water from autumn 2008 to 2010. Years with a strong winter North Atlantic Oscillation (NAO) index are characterized by shifts in thermohaline properties across most of the intermediate levels, with the most notable event being the warming and increasing salinity that followed the large NAO index drop of 2010. The observations are consistent with current understanding of the large-scale functioning of the North Atlantic, which predicts a northeastward expansion of subtropical temperate waters in the eastern boundary as a response to NAO forcing. The observed variability is discussed in relationship to large-scale circulation.

The Avilés Canyon System (ACS) is a complex, structurally-controlled canyon and valley system constituted by three main canyons of different morphostructural character. They are, from east to west: La Gaviera Canyon, El Corbiro Canyon and Avilés Canyon. In addition to this ACS, a new canyon has been surveyed: Navia Canyon. We present for the first time a high resolution multibeam map showing with great detail the morphological and structural complexity of this segment of the Cantabrian margin. ACS presents a tectonic imprint marked by NW-SE, NNE-SSW and E-W structures. The morphology of their reaches as well as their single mouth, in addition to some rock dredges in their major valleys, demonstrates active down-slope flushing. The continental shelf shows a flat, uniform slope with local and well defined rock outcrops south of Aviles Canyon head. Sedimentary zones are limited, showing thin unconsolidated sedimentary cover. Strong continental margin water dynamics avoid thicker sediment deposition, being littoral sedimentary dynamics responsible for transport to the canyons heads and conduit to the Biscay Abyssal plain. Biscay Abyssal Plain shows evidence of a strong westward current affecting the surveyed strip of this more than 10 km wide plain. Presence of two parallel deep sea channels, erosive scarps, and erosion of gully divides on the lower slope, may indicate that this is part of the distal fan at the termination of the large turbiditic system fed by Cap Ferret, Capbreton and other large canyons (Santander, Torrelavega, Lastres and Llanes) to the west of ACS., Instituto Español de Oceanografía, SI

Surveys conducted at the complex Aviles Canyon System (southern Bay of Biscay) in order to identify vulnerable habitats and biological communities revealed the presence of noteworthy deep-water coral reefs in one of the tributaries of the system (La Gaviera Canyon). The aim of the present study is to determine why this deep-sea canyon provides suitable environmental conditions for corals to grow. This hanging canyon is characterized by an irregular U-shaped floor with two narrow differentiated flanks. Sand ripples and rocky outcrops structured in diverse W–E directed steps are observed on the canyon floor, suggesting intense hydrodynamic activity. Accordingly, high-frequency near-bottom current and thermal structure profiles showed that there occur strong shifts in currents/hydrography behaving as front-like features at each tidal cycle. These involve the sudden increase of along-axis velocities to over 50 cm/s and vertical velocities of over 5 cm/s in each tidal cycle associated with the passage of sharp thermal fronts and thermal inversions suggesting overturning. A year-long near-bottom current record showed events with near-bottom velocities well over 1 m/s lasting for several days. Three cold-water coral settings were distinguished: a dense coral reef located on stepped rocky bottoms of the eastern and western flanks, carbonate mounds (20–30 m high) located on the canyon floor, and a cluster of shallower water dead coral framework at the head sector of the canyon. Video and still images from a towed sled and ROV verified the presence of dropstones and rippled sand sheets surrounding the mounds and revealed changes in the coral population (alive or dead; total or patchy coverage) in coral reef and carbonate mound areas. The dominant species of the reef are Lophelia pertusa and Madrepora oculata, which considerably increase the habitat′s complexity and biodiversity in relation to other facies described in the canyon. The presence of living cold-water reefs is directly related to a high-energy environment at depths between 700 and 1200 m in the levels between the lower bound of Eastern North Atlantic Central Water (ENACW) and the core of Mediterranean Water (MW). Such level matches the water density range σθ=27.35–27.65 kg m−3 which has been identified as limits for cold-water coral distribution in the North Atlantic.

Le Danois Bank is a seamount-like topographical feature located at the continental shelf in the central Cantabrian Sea (Bay of Biscay), recently declared Marine Protected Area. The bank is partially connected to the shelf by a saddle, topographically bounding an inner valley. Hydrographical cruises and direct current measurements from current meters, vessel-mounted ADCP and subsurface floats are analysed to describe the main circulation patterns in the area. Records are consistent with the presence of anticyclonic flow at the seamount summit. The inner valley seems to support the development of retentive flow structures and the whole system is affected by strong and variable along-slope currents, thus complicating the overall picture. Scaling arguments, based on non-dimensional parameters accounting for the surrounding flow characteristics and the geometry of the seamount, allow an estimate of the dynamical processes that may be active at the bank. Temporary Taylor cap formation by weak impinging flow may occur, although a clear signature of this feature does not emerge from the observed density fields. The strong local amplification of the diurnal tide suggests the presence of resonant seamount trapped waves. The strength of the semidiurnal tide M 2 in the region, in combination with the steepness of the flanks of the bank, points to a significant contribution of tidally rectified flow to the observed residual anticyclonic flow. An observation of an isopycnal vertically repositioned by 50 m within one downcast/upcast period of a CTD profile indicates the importance of high frequency internal wave dynamics.

We examine the trends and variability in temperature of the northwest European shelf seas over the period 1960–2004 using four approaches: a regional model simulation (using the Proudman Oceanographic Laboratory Coastal Ocean Modelling System; POLCOMS), in situ multi-annual timeseries observations, satellite remote sensed (AVHRR) sea surface temperature (SST), and an analysis of data held in an international database at the International Council for the Exploration of the Sea (ICES). We focus on variability for the full period and trends from 1985 to 2004, being limited by the length of model simulation and the availability of satellite data. We find that all data sources give a consistent picture, with both trends and variability being intensified on-shelf and north of ∼48°N. The model and AVHRR SST show statistically significant warming trends in large areas of this region that are clearly distinguishable from both model/observation error and natural variability on these timescales. This ‘signal to noise ratio’ is substantially reduced when near bottom temperatures are considered in the model. The long timeseries at Port Erin (Isle of Man) shows that the variation in trend is well represented by the model and that the warming trend in the period 1985–2004 is substantially larger and of longer duration than previous peaks in 20-year trends since 1914. We find that the SST trends are greater in the model and satellite observations than the air temperature trends in the ERA40 re-analysis used for forcing; the net sea to air heat flux is ∼20% less in 1985–2004 than 1960–1984 (including shortwave, longwave, sensible and latent components). This is partly compensated by a ∼9% reduction in advective warming. The model shows the trends in seasonally stratified regions are greater at the surface than at depth, indicating an increase in this stratification. While this pattern is also seen in the annual trends from the ICES data analysis, the lack of seasonal resolution hampers a quantitative corroboration. The model is seen to have good skill in reproducing both the trends and variability, but tends to underestimate the trends. The modelled variability is overestimated in some coastal and open ocean regions and underestimated elsewhere, while the phase of this variability is generally well represented. Generally the model performance is better on-shelf than in the open ocean.

From the last 1980s different initiatives have been carried out by the Spanish Institute of Oceanography (IEO) at its Oceanographic Centre of Santander to progressively increase its ocean observing system capabilities. From 1991, shelf and slope waters of the Southern Bay of Biscay are regularly sampled in a monthly hydrographic line north of Santander to a maximum depth of 1500m. In 2003, the Santander section was extended 90 miles offshore in the framework of a larger scale hydrographic and circulation monitoring program (VACLAN/COVACLAN projects, www.vaclan-ieo.es (REN 2003-08193-C03-01/MAR; CTM 2007-64600/MAR)). Measurements from the surface to the more than 5000 meters existing in the basin in deep hydrological standard sections are occupied twice a year including CTDO2, nutrients and currents from vessel-mounted ADCP and LADCP. In order to reinforce its contribution to the ocean surface monitoring, the IEO deployed in June 2007 an oceanic-meteorological buoy (AGL Buoy, 43°50.67' N; 003°46.20' W, and 40 km offshore, www.boya_agl.st.ieo.es/) in the southern Bay of Biscay. Previously, in August 1998 a satellite reception station was mounted at the IEO Santander Centre to receive SST images. Because of technical problems the station stop working in 2007, but a new reception station has been mounted in 2010, with FEDER funds and SST images of the surroundings areas are now available. Recently, a glider experiment has been performed in December 2010 to study the possibilities to repeat the Santander section using the new technology. All those observations are completed with the Santander tide gauge, operated by IEO since 1943. A complete view of oceanic processes is obtained through the combination of this set of monitoring programs, at the same time that the best way to optimize ocean observation is investigated.

Within the framework of the TUNIBAL project that focused on Atlantic bluefin tuna (Thunnus thynnus) larval ecology, ichthyoplankton surveys were conducted from 2001 to 2005 off the Balearic archipelago, which is recognized as one of the main spawning areas of the eastern Atlantic stock of this species. In each survey, a regular sampling grid of about 200 stations, 10 nautical miles apart were sampled. CTD casts and oblique Bongo 60 and surface Bongo 90 plankton tows were carried out. The occurrence frequencies of Atlantic bluefin tuna, albacore tuna (Thunnus alalunga) and bullet tuna (Auxis rochei) larvae in quantitative Bongo 60 samples were 0.14, 0.29 and 0.49 respectively. Mean larval abundances in these positive samples were relatively high: 31 larvae 10 m−2 for Atlantic bluefin tuna, 17 for albacore tuna and 31 for bullet tuna. All species had patchy distributions since more than 90% of the stations showed larval densities under 10 larvae 100 m−3 (70% showed even less than 2 larvae 100 m−3), whereas in some isolated spots, we recorded abundances as high as 867 (Atlantic bluefin) or 872 (bullet tuna) larvae 10 m−2. These results allowed us to relate larval distribution to mesoscale hydrographic features and to characterize the spawning habitat of these species. Single Quotient Parameter analyses were applied to spatial (depth), physical (temperature, salinity, dissolved oxygen and geostrophic current velocities) and biological (mesozooplankton biomass) variables to determine the environmental preferences of each species for spawning. Results showed that the complex hydrodynamic scenarios around the Balearic Islands, due to the interaction between the inflowing surface Atlantic water masses (AW) and Mediterranean surface waters (MW), play a key role in determining the abundance and distribution of tuna larvae in this area, especially in the case of Atlantic bluefin tuna. Spawning of this species seems to take place mainly in offshore mixed waters, as suggested by their preferences for waters with salinities between 36.9 and 37.7, located near frontal areas in the confluence of AW and MW. Atlantic bluefin tuna start to spawn once sea surface temperatures (SST) are over 20.5 °C, and preferentially in the range of 21.5–26.5 °C. Its larval distribution suggests that spawners reach the Balearic Sea in association with the inflowing AW. However, bullet tuna and albacore tuna larvae, species whose Mediterranean stocks stay in this sea year round, had a more widespread distribution and were found both in MW and AW. Bullet tuna starts to spawn in shallower waters near the shelf break once the SST reaches 19 °C, and shows significant preferences for waters over 23.5 °C. Similar to Atlantic bluefin tuna, albacore tuna spawn in offshore waters, but its spawning peak is later than its congeneric species, since it has a significant preference for even warmer waters, over 27 °C., Sí

The extremely cold and dry winter of 2005 in southwestern Europe caused a profound transformation of the upper ocean hydrographic structure of the Bay of Biscay area, making it completely different from the previous decade. The strong local winter cooling resulted in the highest density flux estimated since the 1960s. The extreme buoyancy loss triggered the mixed layer to reach unprecedented depths affecting directly the level of local modal waters that are usually unconnected to air-sea interaction. The water column just below the climatological average mixed layer entered in a process of quick cooling that compensated in 2 years the 0.5°C gained in the period 1994–2004. Enhanced by a pronounced precipitation deficit the event caused concurrently a downward salt injection that made deeper levels of East North Atlantic Central Water begin a process of warming by isopycnal change, something never observed during the 1990s. As an overall result, the stratification of the upper permanent thermocline was dramatically reduced. The observed cold low stratification anomaly had a substantial spatial extent and remained for 2 years below the seasonal thermocline development, constituting a typical case of the reemergence mechanism, but was abruptly interrupted in the warmest winter on record of 2007. In addition to the hydrographic changes, the winter 2005 event had a notable effect on the marine ecosystem., Sí

Oceanographic conditions at the time of the Prestige oil spill (November 2002) and following months are analyzed based on a set of hydrographic cruises. The ship sank off one of the flanks of the Galician Bank, an offshore seamount, and a major oil spill drifted to the N and NW Iberian coast mainly driven by dominant winds. Coastal circulation was characterized by freshwater plumes and the poleward slope current, and could have affected the fate of the oil spill and influenced stranding places. Seasonal evolution of oceanographic conditions in this particular year is compared with the long-term average and reveals specific features that need to be taken into account in studies of the impact of the oil spill on populations. Spring conditions commenced earlier than other years in the Southern Bay of Biscay, contrastingly in western Iberia. The lack of subsurface intrusion of subtropical waters suggests a low intense penetration of the poleward current in Spanish Biscay slopes. In western Iberia, the slope poleward current observed in late autumn weakens and is exported off slope during upwelling pulses in the spring, with no strong intrusion of the poleward current on the slope at the time of the spring bloom. A description of current velocities near the wreck on the Galician Bank is obtained after the analysis of a mooring line.

Ocean hydrological sections provide a very useful mean to study the ocean circulation as well as to determine water mass properties and to estimate fluxes. One basic method for their analysis is the spatial interpolation of data, obtained from a set of predefined stations, into a regular grid for contouring isolines and for further calculations. The shortest length scales that can be solved are limited by the distance between stations. Some of these scales, though resoluble by the sampling design, may be, with respect to time variability, shorter than the time that is needed to complete the section. This situation can produce a lack of synopticity in the obtained data, which is not usually addressed in oceanographic studies because the sequential repetition of oceanographic surveys is not an easy task. Here two samplings are compared—one by CTD- and another by Array for Real-Time Geostrophic Oceanography (Argo)-type profilers—of the same zonal section with a 5-day delay. The integral time scale for the mesoscale field is around 11 days, which implies that the mesoscale signal obtained from consecutive transmissions of the profilers are weakly correlated. The mesoscale field in a transatlantic section, which typically takes 20 days to be carried out, cannot be considered as synoptic.

[1] The properties of the Western Mediterranean Deep Water in a wide area located at the western boundary of the Mediterranean Sea, including the Balearic Sea, have revealed intense changes when observed in summer 2005. Between February and June 2005, a temperature drop of 0.14°C reverted dramatically the progressive warming trend of 0.011°C yr−1 that had been observed since 1996, in the waters below 600 dbar north of the Balearic channels. A similar temperature drop has been observed east of the Minorca Island, below the Levantine Intermediate Water and down to 1500 dbar. In the deepest levels, a complex thermohaline structure, which implies different waters masses as sources, was tracked more than 400 km along the western boundary of the Mediterranean Sea, from Barcelona to the Algerian Basin. It is suggested that the changes may be linked to the severe 2004/2005 winter occurred at the northwestern Mediterranean Sea.

[1] The evolution of the intermediate water masses within the southeastern corner of the Bay of Biscay is studied from the shelf edge and slope stations of a hydrographic standard section northward from Santander (43°30′/43°54′N, 3°47′W). The section was sampled monthly from 1991 to autumn 2003 with some gaps more frequent in the early stages due to weather conditions. Data were systematically collected up to a 1000 m depth (or to the maximum depth at the shallower stations) showing a detailed picture of the variability in water masses below the mixing layer. Eastern North Atlantic Central Water has warmed as a consequence of continuous deepening of the isopycnal levels. Changes in water properties at fixed isopycnal levels are less relevant and highly biased by a 1998 positive peak in temperature and salinity. The warming trend found is 0.032°C per year on average. On the other hand, the Mediterranean Water has been modified along isopycnals (variations 10 times greater than those due to isopycnal displacement) increasing progressively both temperature and salinity for the period 1994–2001. The values found are around 0.020°C per year for temperature and 0.005 for salinity. As a final picture, all water masses below the mixing layer and down to a 1000 m depth in the southern Bay of Biscay have warmed up during the last decade at rates from two to six times greater than the those accepted for the North Atlantic during the last half century.

[1] The ocean section along the 24.5°N has been one of the most frequently sampled of the world's oceans. It has been sampled in 1957, 1981, 1992 and 1998. Previous works showed a progressive warming and salt increase of the thermocline and intermediate waters from around 800 m to 3000 m. The maximum warming rate was 0.009°C/yr at 1100 m. The eastern part of this section was sampled in 2002. The warming of the main thermocline has continued at a higher rate (0.042°/yr at 400 m) in the last 10 years. Salinity has also increased along the thermocline conserving the 1992 θS relationship. From 100 to 1000 db, the warming is mainly due to downward displacement of the isopycnals, though some cooling along isopycnals is also observed in the upper 350 db.

In March 2002, 20 Argo profilers were deployed in the Subtropical North Atlantic, within the European project Gyroscope. In this contribution we compare the θ-distribution on a hydrographical section along the 24.5°N parallel using two different data sets. The first set consists of the first data transmitted by an array of autonomous profilers deployed along the section, and the second set is made up of CTD stations accomplished during the deployment and discusses the representativeness of the field at different scales.

In 2002 a robust minimum maintenance system to measure temperature, conductivity, and chlorophyll fluorescence was installed on a ferry running twice weekly between Portsmouth, UK and Bilbao, Spain. Logged data are transferred from the engine room to an Orbcom satellite communicator on the bridge. On shore data enters an SQL database with access from a public web page. Data from the Iberian margin is linked to monthly surveys by IEO. Target work includes:the structure, transport of and seasonal devel- opment of water masses, and scaling of patchiness of plankton blooms in regions with different hydrographic characteristics.