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The European Slope Current (SC) is a major section of the warm poleward flow from the Atlantic to the Arctic, which also moderates the exchange of heat, salt, nutrients and carbon between the deep ocean and the European shelf seas. The mean structure of the geostrophic flow, seasonality, interannual variability and long-term trend of SC are appraised with an unprecedented continuous 20-year satellite altimeter dataset. Comparisons with long term in situ data showed a maximum correlation of r2 = 0.51 between altimeter and Acoustic Doppler Current Profilers (ADCP), with similar results for drogued buoy data. Mean geostrophic currents were appraised more comprehensively than previous attempts, and the paths of 4 branches of the North Atlantic Current (NAC) and positions of 5 eddies in the region were derived quantitatively. A consistent seasonal cycle in the flow of the SC was found at all 8 sections along the European shelf slope, with maximum poleward flow in the winter and minimum in the summer. The seasonal difference in the altimetry current speed amounted to ~ 8–10 cm s− 1 at the northern sections, but only ~ 5 cm s− 1 on the Bay of Biscay slopes. This extended altimeter dataset indicates significant regional and seasonal variations, and has revealed new insights into the interannual variability of the SC. It is shown that there is a peak poleward flow at most positions along a ~ 2000 km stretch of the continental slope from Portugal to Scotland during 1995–1997, but this did not clearly relate to the extreme negative North Atlantic Oscillation (NAO) in the winter of 1995–1996. The speed of the SC exhibited a long term decreasing trend of ~ 1% per year. By contrast the NAC showed no significant trend over the 20-year period. Major changes in the NAC occurred three times, and these changes followed decreases in the NAO index.

The flow of upper-layer surface water and circulation for the Bay of Biscay, continental slope and in the wider region of the NE Atlantic is presented, as well as the seasonality of flow and internal tides. The marine plankton environments of Biscay Ocean, Biscay Eddies, Biscay Slope and Biscay Shelf are defined. The Shelf region (Armorican and Celtic) is further divided into Stratified Shelf, Frontal and Tidally Mixed. Seasonal distributions of chlorophyll a are given for all environment from in situ measurements and remote sensing data. Mixing and stabilisation of surface water in the euphotic layer for the start of the spring bloom using in situ profiling measurements is examined. Some regional responses for the slope current, dinoflagellate blooms and interannual variations in spring diatom numbers with respect to weather and climate in the Bay of Biscay and around the British Isles are suggested and discussed. An example of the Eastern European Ocean Margin continental slope response to winter weather (sea level atmospheric pressure forcing) resulting in warm winter water in the southern Bay of Biscay (Navidad, with eddy production) and off the Shetland continental slopes (the warm-water supply route to the Arctic) is given from the slope climate observation series.

Some results of the Bay of Biscay regional oceanography presented at ISOBAY are summarized including contributions to physical oceanography, chemical and biological oceanography, marine geology, deep water ecology, marine pollution, fisheries research and cetacean studies. A long-term analysis of the spring bloom of phytoplankton in the area during the last 17 years (1997–2014) is presented as an example of Bay of Biscay climate research. The Spring Bloom presents cycles of 4–6 years reflecting probably the availability of nutrients from the previous winter and has increased in peak intensity during the last decades.

The sea surface temperature (SST) variability of the Bay of Biscay and adjacent regions (1854–2010) has been examined in relation to the evolution of the Atlantic Multidecadal Oscillation (AMO), a major climate mode. The AMO index explains ~25% of the interannual variability of the annual SST during the last 150 years, while different indices of the North Atlantic Oscillation (NAO) explain ≤1% of the long-term record. NAO is a high frequency climate mode while AMO can modulate low frequency changes. Sixty per cent of the AMO variability is contained in periods longer than a decade. The basin-scale influence of NAO on SST over specific years (1995 to 1998) is presented and the SST anomalies explained. The period analysed represents an abrupt change in NAO and the North Atlantic circulation state as shown with altimetry and SST data. Additional atmospheric climate data over a shorter ~60 year period (1950–2008) show the influence on the Bay of Biscay SST of the East Atlantic (EA) pattern and the Scandinavia (SCA) pattern. These atmospheric teleconnections explain respectively ~25% and ~20% of the SST variability. The winter SST in the shelf-break/slope or poleward current region is analysed in relation to AMO. The poleward current shows a trend towards increasing SSTs during the last three decades as a result of the combined positive phase of AMO and global warming. The seasonality of this winter warm flow in the Iberian region is related to the autumn/winter seasonality of south-westerly (SW) winds. The SW winds are strengthened along the European shelf-break by the development of low pressure conditions in the region to the north of the Azores and therefore a negative NAO. AMO overall modulates multidecadal changes (~60% of the AMO variance). The long-term time-series of SST and SST anomalies in the Bay of Biscay show AMO-like cycles with maxima near 1870 and 1950 and minima near 1900 and 1980 indicating a period of 60–80 years during the last century and a half. Similar AMO-like variability is found in the Russell cycle of the Western English Channel (1924–1972). AMO relates at least to four mesozooplankton components of the Russell cycle: the abundance of the chaetognaths Parasagitta elegans and Parasagitta setosa (AMO −), the amount of the species Calanus helgolandicus (AMO −), the amount of the larvae of decapod crustaceans (AMO −) and the number of pilchard eggs (Sardine pilchardus; AMO +). In addition to AMO, the decadal to multidecadal (D2M) variability in the number of sunspots is analysed for the last 300 years. Several periodicities and a multi-secular linear increase are presented. There are secular minima near 1710, 1810, 1910 and 2010. The long term variability (>11 years) of the solar sunspot activity explains ~50% of the variance of the SST of the Bay of Biscay with periods longer than 11 years. AMO is finally compared with the Pacific Decadal Oscillation, the leading principal component of North Pacific SST anomalies.

The analysis of remotely sensed altimeter data and in situ measurements shows that ERS 2 radar can monitor the ocean permanent thermocline from space. The remotely sensed sea level anomaly data account for ∼2/3 of the temperature variance or vertical displacement of isotherms at a depth of ∼550 m in the Subtropical North Atlantic Ocean near 32·5°N. This depth corresponds closely to the region of maximum temperature gradient in the permanent thermocline where near semi-annual internal vertical displacements reach 200 to 300 m. The gradient of the altimeter sea level anomaly data correlates well with measured ocean currents to a depth of 750 m. It is shown that observations from space can account for ∼3/4 of the variance of ocean currents measured in situ in the permanent thermocline over a 2-y period. The magnification of the permanent thermocline displacement with respect to the displacement of the sea surface was determined as −×650 and gives a measure of the ratio of barotropic to baroclinic decay scale of geostrophic current with depth. The overall results are used to interpret an eight year altimeter data time series in the Subtropical North Atlantic at 32·5°N which shows a dominant wave or eddy period near 200 days, rather than semi-annual and increases in energy propagating westward in 1995 (west of 25°W). The effects of rapid North Atlantic Oscillation climate change on ocean circulation are discussed. The altimeter data for the Atlantic were Fourier analysed. It is shown how the annual and semi-annual components relate to the seasonal maximum cholorophyll-a SeaWiFS signal in tropical and equatorial regions due to the lifting of the thermocline caused by seasonally varying ocean currents forced by wind stress.

Changes in the net heat flux (NHF) into the ocean have profound impacts on global climate. We analyse a long-term plankton time-series and show that the NHF is a critical indicator of ecosystem dynamics. We show that phytoplankton abundance and diversity patterns are tightly bounded by the switches between negative and positive NHF over an annual cycle. Zooplankton increase before the transition to positive NHF in the spring but are constrained by the negative NHF switch in autumn. By contrast bacterial diversity is decoupled from either NHF switch, but is inversely correlated (r =20.920) with the magnitude of the NHF. We show that the NHF is a robust mechanistic tool for predicting climate change indicators such as spring phytoplankton bloom timing and length of the growing season.

The position and structure of the North Atlantic Subtropical Front is studied using Lagrangian flow tracks and remote sensing (AVHRR imagery: TOPEX/POSEIDON altimetry: SeaWiFS) in a broad region (∼31° to ∼36°N) of marked gradient of dynamic height (Azores Current) that extends from the Mid-Atlantic Ridge (MAR), near ∼40°W, to the Eastern Boundary (∼10°W). Drogued Argos buoy and ALACE tracks are superposed on infrared satellite images in the Subtropical Front region. Cold (cyclonic) structures, called ‘Storms’, and warm (anticyclonic) structures of 100–300 km in size can be found on the south side of the Subtropical Front outcrop, which has a temperature contrast of about 1°C that can be followed for ∼2500 km near 35°N. Warmer water adjacent to the outcrop is flowing eastward (Azores Current) but some warm water is returned westward about 300 km to the south (southern Counterflow). Estimates of horizontal diffusion in a Storm (D=2.2×102 m2 s−1) and in the Subtropical Front region near 200 m depth (Dx=1.3×104 m2 s−1, Dy=2.6×103 m2 s−1) are made from the Lagrangian tracks. Altimeter and in situ measurements show that Storms track westwards. Storms are separated by about 510 km and move westward at 2.7 km d−1. Remote sensing reveals that some initial structures start evolving as far east as 23°W but are more organized near 29°W and therefore Storms are about 1 year old when they reach the MAR (having travelled a distance of 1000 km). Structure and seasonality in SeaWiFS data in the region is examined.

Thirteen carefully prepared drogued buoy assemblies have been deployed in the eastern subtropical North Atlantic giving ~20 buoy years of Lagrangian data at a depth of 200 m. The buoy results together with hydrography have revealed the structure of the eastward flowing Azores Current (AC). The main jet had a transport of 26 Sv (near 28°W) with compensating counterflows in March 1992. Jet and counterflows were readily seen in the ADCP current structure and evident in the upper layer temperature (salinity) structure on an isopycnal surface. Buoys and hydrography showed that the adjacent westward flowing counterflows resulted in recirculation both north (anticlockwise circulation) and south (clockwise circulation) of the AC - the Subtropical Recirculations. South-south-west flow (3 cm s−1) occurred in the central region of study west of the Canary Islands. The long-term movement measured in the south or northern North Equatorial Current region was 3·5 cm s−1west-south-west. The mean south displacement per year of the buoys was 2·2° of latitude to the south and most of this displacement occurred in the first half of the year (February-August). The maximum westward displacement rate occurred six months later in October and November. The Subtropical Front/Azores Current region was identified as a zone of increased levels of kinetic energy (>100 cm2s−2) at a latitude near 34°N at the 200 m level, stretching for >2000 km, and as a marked horizontal winter sea surface temperature contrast at a latitude near 36°N. Winter mixing created an outcropping region of water with density in the range 26–40−3along the Subtropical Front near 34°N with a maximum vertical extent of 200 m.

The physical and biological properties of the North Atlantic subtropical region southeast of the Azores were studied during an oceanographic cruise carried out in March 1992. The main patterns of physical variability were defined by the presence of (a) a thermohaline front (subtropical front; STF) located at 34°N–35°N and extending from 15°W to 28°W, which separates warmer more saline Western Atlantic Water from colder and fresher Eastern Atlantic Water, and (b) a strong eastward flow running along the subtropical front (Azores Current; AC) extending down to at least 250 m and showing velocities of 50–70 cm s −1 at the core of the current. Overall a close linkage was observed between the STF-AC physical feature and high levels of chlorophyll a . A high resolution survey showed chlorophyll a fluorescence associated with the southern frontal boundary (consisting of chain forming diatoms and flagellates) and with the AC (made up of cells in the less than 2 μm size-class), respectively. Primary production rates measured in the frontal high-chlorophyll region (> 1 mg C m −3 h −1 ) were much higher than previous measurements carred out in the same area in late spring and summer and about 2 times higher than modelling estimates for the region. The large spatial extension of the biological signature associated with the STF-AC system suggests that carbon fixation within the frontal structure could be significant for regional carbon budgets of the subtropical northeast Atlantic.

A short research cruise was planned to trace the movement of a discrete body of water in the subtropical eastern North Atlantic Ocean. A subtropical ring or deep eddy called STORM was found budding off the Subtropical Front (STF) south-west of the Azores. A physical, chemical and biological survey to depths of 3·5 km was made of this 400 km scale body of water which was spinning cyclonically (anticlockwise). The azimuthal transport or the amount of water swirling in the eddy was 45 Sv. Storm was ‘hooked’ with ten drogued Argos buoys and a further five subsurface Alace floats were deployed. Storm is moving westward at ~3 km a day and is expected to reach the Mid Atlantic Ridge in rather less than a year unless it is destroyed by typography or reabsorbed into the Azores Current. With current technology, Storm's evolution and westward progress can be observed and analysed remotely, at a distance of ~3000 km in the laboratory. Realtime position data means that future sea surveys can be planned.

Swesty is a shallow subtropical subducting westward propagating eddy that was observed to move across the eastern basin of the North Atlantic at a latitude near 25° N. The eddy was first detected by the movement and temperature of a drogued Argos buoy near 23° W, 26° N in February 1993. By December 1993, the drogued buoy had moved 1000 km westward to 33° W and a winter eddy survey was made from RRS Charles Darwin. The eddy was about 100 km in diameter and had a centre water mass core at a depth of 190 m with characteristic temperature 19.9 °C and salinity 37.06 psu, but was best resolved by properties related to vertical gradient structure (e.g. Brunt-Vaisala frequency, temperature perturbation structure). The eddy was particularly flat with a height-to-width aspect ratio of only ca . 0.14% and a vertical decay scale of ca . 250 m for temperature displacements. Maximum azimuthal currents were ca . 16 cm s -1 at a depth of 175 m and the eddy azimuthal transport was only 3 Sv. However, the potential vorticity in the eddy core was 1.5 x 10 -11 rad ms -1 , comparable with other deep anticyclonic lenses and lower than background values by a factor of ten. The eddy appeared slightly elliptical with a detectable sea surface cooling ( ca . 0.2 °C) over its centre. Three Argos buoys with drogues set at a depth of 200 m were deployed near the centre of the eddy and one buoy continued looping westward for a further ca . 800 km. The drogued Argos buoy results showed that the eddy moved westward at ca . 100 km month -1 and about half this westward rate was attributed to self-propagation. During this ca . 1650 km continuously drogued journey, the eddy only slipped southward by about one degree of latitude and so was perhaps resisting the southward component of flow of the Subtropical Gyre. The buoy results suggested that the central rotation rate increased with time but the eddy became smaller. The initial rotation period of the central core was ca . 8 d, giving a corresponding normalized relative vorticity of —0.3. About 400 d later, the period of core rotation was ca . 5 d, with normalized relative vorticity of —0.5. Some of the increase in central rotation rate was attributed to subduction effects. Variance, spectra and filtered components of velocity were derived from the buoy positions. Kinetic energy levels in the eddy ( ca . 73 cm 2 s -2 ) were markedly elevated with respect to background levels ( ca . 29 cm 2 s -2 ). The core properties of the eddy indicated a winter formation near 27° N, 22° W and hydrographic sections showed that the eddy would be sinking at a rate of about 40 m a -1 . By the second year, the subducted water parcel, the eddy core, was sufficiently deep below the surface of the ocean to escape further effects of winter mixing.

This paper reports the results of a hydrographic survey and the successful deliberate deep droguing of a meddy (Pinball) and the seeding of its core with two ALACE floats. The drogued buoy results give important kinematic properties of the eddy core in real timesemicolon the ALACE have allowed the position of the meddy to be tracked for seven months. Pinball was found against the continental slope near Lisbon canyon. The maximum core salinity was 36·564 psu, at a depth of 1260 m, but the maximum rotation rate with period ~2·5 d was in the upper core near 700 m, where temperatures reached 13·2°C. The azimuthal transport to a radius of 50 km was ~13 Sv. Pinball moved from the continental slope near Lisbon to the central Tagus Abyssal Plain, returned towards the continental slope and then moved westwards crossing the central Tagus Abyssal Plain a second time. At times it had a marked remote sensing infra-red sea-surface signature. It moved ~550 km over 204 d and the near real-time data meant that, in principle, this eddy could have been re-surveyed, redrogued or reseeded with floats during this period.

The winter of 1989/1990 was a year of marked warm water inflow along the Iberian, Spanish and French continental slopes and three anticyclonic eddies developed in the southern Bay of Biscay. Winter temperatures along the northern Spanish slope were examined in the belief that warm water inflow is related to the production of anticyclonic eddies in the southern Bay of Biscay. The annual cycle of temperature (at ~200 m depth) is most unusual in that the warmest temperatures occur in January, the coldest in the summer. Year-to-year variations are evident with the suggestion of a periodicity, though variable, of about five years.In April 1992, an opportunity presented itself for a late winter eddy survey in the south-eastern corner of the Bay of Biscay from RRS ‘Charles Darwin’. Two Argos buoys were deployed in what was thought to be, or would develop into, an anticyclonic eddy, and one of the buoys was caught in the eddy. This buoy was drogued at a depth of 320 m in a relatively well-mixed part of the water column thought to contain the eddy core. This buoy made ~60 clockwise orbits in the eddy and remained within 15 km of the eddy centre over the 200-d observation period. The normalized relative central vorticity of the eddy had a minimum value of -0·6 and the eddy rotation period experienced by the buoy ranged from 2·5 to 6·5 d. The decay scale for the eddy was estimated at 250 ±100 d. The mean variance of the east-west velocity component was significantly larger than the north-south value, and the buoy's orbit was significantly elliptical towards the end of the period of the observations.

Long-term research in the western English Channel, undertaken by the marine laboratories in Plymouth, is described and details of survey methods, sites, and time series given in this chapter. Major findings are summarized and their limitations outlined. Current research, with recent reestablishment and expansion of many sampling programmes, is presented, and possible future approaches are indicated. These unique long-term data sets provide an environmental baseline for predicting complex ecological responses to local, regional, and global environmental change. Between 1888 and the present, investigations have been carried out into the physical, chemical, and biological components (ranging from plankton and fish to benthic and intertidal assemblages) of the western English Channel ecosystem. The Marine Biological Association of the United Kingdom has performed the main body of these observations. More recent contributions come from the Continuous Plankton Recorder Survey, now the Sir Alister Hardy Foundation for Ocean Science, dating from 1957; the Institute for Marine Environmental Research, from 1974 to 1987; and the Plymouth Marine Laboratory, which was formed by amalgamation of the Institute for Marine Environmental Research and part of the Marine Biological Association, from 1988. Together, these contributions constitute a unique data series-one of the longest and most comprehensive samplings of environmental and marine biological variables in the world. Since the termination of many of these time series in 1987-1988 during a reorganisation of UK marine research, there has been a resurgence of interest in long-term environmental change. Many programmes have been restarted and expanded with support from several agencies. The observations span significant periods of warming (1921-1961; 1985-present) and cooling (1962-1980). During these periods of change, the abundance of key species underwent dramatic shifts. The first period of warming saw changes in zooplankton, pelagic fish, and larval fish, including the collapse of an important herring fishery. During later periods of change, shifts in species abundances have been reflected in other assemblages, such as the intertidal zone and the benthic fauna. Many of these changes appear to be related to climate, manifested as temperature changes, acting directly or indirectly. The hypothesis that climate is a forcing factor is widely supported today and has been reinforced by recent studies that show responses of marine organisms to climatic attributes such as the strength of the North Atlantic Oscillation. The long-term data also yield important insights into the effects of anthropogenic disturbances such as fisheries exploitation and pollution. Comparison of demersal fish hauls over time highlights fisheries effects not only on commercially important species but also on the entire demersal community. The effects of acute ("Torrey Canyon" oil spill) and chronic (tributyltin [TBT] antifoulants) pollution are clearly seen in the intertidal records. Significant advances in diverse scientific disciplines have been generated from research undertaken alongside the long-term data series. Many concepts in marine biological textbooks have originated in part from this work (e.g. the seasonal cycle of plankton, the cycling of nutrients, the pelagic food web trophic interactions, and the influence of hydrography on pelagic communities). Associated projects currently range from studies of marine viruses and bacterial ecology to zooplankton feeding dynamics and validation of ocean colour satellite sensors. Recent advances in technology mean these long-term programmes are more valuable than ever before. New technology collects data on finer temporal and spatial scales and can be used to capture processes that operate on multiple scales and help determine their influence in the marine environment. The MBA has been in the forefront of environmental modelling of shelf seas since the early 1970s. Future directions being pursued include the continued development of coupled physical-ecosystem models using western English Channel time-series data. These models will include both the recent high-resolution data and the long-term time-series information to predict effects of future climate change scenarios. It would be beneficial to provide more spatial and high-resolution temporal context to these data, which are fundamental for capturing processes that operate at multiple scales and understanding how they operate within the marine environment. This is being achieved through employment of technologies such as satellite-derived information and advanced telemetry instruments that provide real-time in situ profile data from the water column.

Long-term research in the western English Channel, undertaken by the marine laboratories in Plymouth, is described and details of survey methods, sites, and time series given in this chapter. Major findings are summarized and their limitations outlined. Current research, with recent reestablishment and expansion of many sampling programmes, is presented, and possible future approaches are indicated. These unique long-term data sets provide an environmental baseline,for predicting complex ecological responses to local, regional, and global environmental change. Between 1888 and the present, investigations have been carried out into the physical, chemical, and biological components (ranging from plankton and fish to benthic and intertidal assemblages) of the western English Channel ecosystem. The Marine Biological Association of the United Kingdom has performed the main body of these observations. More recent contributions come from the Continuous Plankton Recorder Survey, now the Sir Alister Hardy Foundation for Ocean Science, dating from 1957; the Institute for Marine Environmental Research, from 1974 to 1987; and the Plymouth Marine Laboratory, which was formed by amalgamation of the Institute for Marine Environmental Research and part of the Marine Biological Association,,from 1988. Together, these contributions constitute a unique data series-one of the longest and most comprehensive samplings of enviromnental and marine biological variables in the world. Since the termination of many of these time series in 1987-1988 during a reorganisation of UK marine research, there has been a resurgence of interest in long-term environmental change. Many programmes have been restarted and expanded with support from several agencies. The observations span significant periods of warming (1921-1961; 1985-present) and cooling (1962-1980). During these periods of change, the abundance of key species underwent dramatic shifts. The first period of warming saw changes in zooplankton, pelagic fish, and larval fish, including the collapse of an important herring fishery. During later periods of change, shifts in species abundances have been reflected in other assemblages, such as the intertidal zone and the benthic fauna. Many of these changes appear to be related to climate, manifested as temperature changes, acting directly or indirectly. The hypothesis that climate is a forcing factor is widely supported today and has been reinforced by recent studies that show, responses of marine organisms to climatic attributes such as the strength of the North Atlantic Oscillation. The long-term data also yield important insights into the effects of anthropogenic disturbances such as fisheries exploitation and pollution. Comparison of demersal fish hauls over time highlights fisheries effects not only on commercially important species but also on the entire demersal community. The effects of acute ("Torrey Canyon" oil spill) and chronic (tributyltin [TBT] antifoulants) pollution are clearly seen in the intertidal records. Significant advances in diverse scientific disciplines have been generated from research undertaken alongside the long-term data series. Many concepts in marine biological textbooks have originated in part from this work (e.g. the seasonal cycle of plankton, the cycling of nutrients, the pelagic food web trophic interactions, and the influence of hydrography on pelagic communities). Associated projects currently range.from studies of marine viruses and bacterial ecology to zooplankton feeding dynamics and validation of ocean colour satellite sensors. Recent advances in technology mean these long-term programmes are more valuable than ever before. New technology collects data on finer temporal and spatial scales and can be used to capture processes that operate on multiple scales and hell) determine their influence in the marine environment. The MBA has been in the forefront of environmental modelling of sheaf seas since the early 1970s. Future directions being pursued include the continued development of coupled physical-ecosystem models using western English Channel time-series data. These models will include both the recent high-resolution data and the long-term time-series information to predict effects of future climate change scenarios. It, would be beneficial to provide more spatial and high-resolution temporal context to these data, which are fundamental for capturing processes that operate at multiple scales and understanding hoiv they operate within the marine environment. This is being achieved through employment of technologies such as sateillite-derived information and advanced telemetry instruments that pro vide real-time in situ profile data from the water column.

The European continental shelf is an area of generally large tide with associated currents frequently exceeding lm sec-. These currents in the relatively shallow water of the shelf seas (Fig. 1) induce high levels of turbulent dissipation.