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Coastal and shelf seas provide a diverse range of ecosystem services, which are often mediated by seasonal density stratification through its control on biogeochemical cycles. These seas are highly vulnerable to climate change and downscaling studies consistently project an increase in seasonal stratification over the next century, but without a clear explanation. Here we revisit a well-established theory of coastal ocean mixing and demonstrate with a new ensemble of downscaled simulations for the Northwest European continental shelf seas to 2100 that the increase of expansivity with temperature is sufficient to consistently increase the seasonal stratification. Where there is a closed balance between buoyancy input and mixing, small changes in expansivity are amplified to a large relative change in stratification. This simple link between global heating and stratification substantially reduces uncertainty in projections of this key parameter in seas around the world.

Strong interannual variability in pre-spring nitrate concentrations have been observed in shelf seas. These variations contribute to interannual variability in net primary production during the following spring and summer and thus also regulate the biological uptake of atmospheric carbon dioxide. Most of the nitrate required by shelf seas to maintain their high productivity is supplied from the open ocean. In this study, we investigate for the first time the importance of variability in the depth of winter mixing along the shelf edge and subsequent wind-driven across-shelf Ekman transport in setting the pre-spring nitrate concentrations across the NW European shelf. Monthly EN4 temperature data is used to identify the maximum depth of winter mixing along the NW European shelf edge between 2000 and 2016 and monthly climatologies of nitrate from the World Ocean Atlas are used to estimate the resulting concentration of surface water nitrate. The wind-driven across-shelf nitrate transport for each sector of the shelf during late winter is then derived using wind velocities from ERA5. The deepest winter mixing close to the shelf edge occurs in the Rockall Trough. However, the largest interannual variations in winter mixed layer depth occur in the Bay of Biscay and Porcupine Sea Bight. The smallest variations are seen in the Faroe-Shetland channel. The estimated nitrate concentration near the shelf edge after winter mixing (i.e., recharge of surface water nitrate concentrations) shows strong interannual variability in the Bay of Biscay and Porcupine Sea Bight (interannual differences of 1- 2.5 mmol/m3), comparable to variability that has been observed on the shelf in this region. Further north, despite deeper winter mixing, there are much smaller interannual differences in surface water nitrate concentrations at the end of winter. This is because the vertical gradients in nitrate concentration within the range of maximum winter mixed layer depths are much weaker. Over the northern sectors of the NW European Shelf large interannual differences in wind-driven Ekman transport drive between 1 and 6 mmol N m-1 s-1 on-shelf during the winter. Further south wind-driven nitrate transport during the winter is typically off-shelf, weaker (typically 1 mmol N m-1 s-1), and much less variable between years.

The balance of physical and biological processes governing phytoplankton growth rates and the accumulation of biomass is widely debated in the literature, notably during the winter–spring transition. Here we show, in a temperate shelf sea that variability in the depth of the actively mixing surface layer is the leading order control. During a 2-week period preceding the peak of the spring bloom we observe two distinct regimes; first, growth within the euphotic zone during the day and re-distribution of new biomass to the seasonal pycnocline at night by convective mixing; then, more rapid biomass accumulation trapped within a shallower, wind-driven actively mixing layer that was decoupled from the pycnocline below. Our observations of the bloom in the Celtic Sea, Northwest European Shelf, were made using ocean gliders and include measurements of the dissipation of turbulent kinetic energy. A 1-D phytoplankton growth model driven by our measurements of dissipation and incident irradiance replicates the observed bloom and reinforces the conclusion that physical processes that mediate light availability were key. Day-to-day variability in cloud cover and the ability of phytoplankton to acclimate to their light environment were also important factors in determining growth rates, and the timing of the biomass peak. Our results emphasize the need for accurate turbulent mixing parameterizations in coupled hydrodynamic-ecosystem models. Our findings are applicable to any region where wind-driven mixing can modify nutrient and light availability, especially across subpolar shelves in the northern hemisphere where light rather than nutrients is typically the limiting factor on phytoplankton growth.

Unprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre., Warming ocean water plays a significant role in accelerating Arctic sea ice melt. Here the authors present detailed observations of warm water of Pacific origin entering and diving beneath the Arctic ocean surface, and explore the dynamical processes governing its evolution.

We describe estimates of overall transport across three contrasted sectors of the north-west European shelf edge: the Celtic Sea south-west of Britain, the Malin-Hebrides shelf west of Scotland and the West Shetland shelf north of Scotland. The estimates derive from a variety of measurements in the project FASTNEt (Fluxes across sloping topography of the North East Atlantic): drifters and moored current meters, effective “diffusivity” from drifter dispersion and salinity surveys, other estimates of velocity variance contributing to exchange. Process contributions include transport by along-slope flow, internal waves and their Stokes drift, tidal pumping, eddies and Ekman transports, in a wind-driven surface layer and in a bottom boundary layer. Estimated overall exchange across the shelf edge is several m2/s (Sverdrups per 1000 km) and thereby large compared with many other locations, large compared with oceanic transports if extrapolated globally and potentially important to the shelf-sea and adjacent oceanic budgets. However, the large majority of this is in tides and other motion with periods of order one day or less; such exchange is only effective for water properties that evolve on time-scales of a day or less. Nevertheless, cross-slope fluxes, and exchange due to motion with periods exceeding two days, are large by global standards and also very variable. Flux values nearest the shelf break were in the range 0.3 – 3 m2/s, and exchanges were 0.8 – 4 m2/s. Deeper longer-term moorings and drifters crossing the 500 m depth contour gave much larger fluxes and exchanges up to 20 m2/s. Significance of these transports depends on distinctive properties of the water, or its contents, and on internal shelf-sea circulation affecting the further progress of these transports. For the NW European shelf, transports across the shelf edge enable its disproportionately strong CO2 “pump”.The small scales of numerous processes enabling cross-slope transports, and the complex context, imply a need for models. Measurements remain limited in extent and duration, but a wide variety of contexts, particular conditions, events and behaviours is now available for model validation, especially around the north-west European continental shelf edge. Variability continues to render observations insufficient for stable estimates of transports and exchanges, especially if partitioned by sector and season; indeed, there may be significant inter-annual differences. Validated fine-resolution models give the best prospect of coverage and of estimating shelf-sea sensitivities to the adjacent ocean.

While the entire Arctic Ocean is warming rapidly, the Barents Sea in particular is experiencing significant warming and sea ice retreat. An increase in ocean heat transport from the Atlantic is causing the Barents Sea to be transformed from a cold, salinity-stratified system into a warmer, less-stratified Atlantic-dominated climate regime. Productivity in the Barents Sea shelf is fuelled by waters of Atlantic origin (AW) which are ultimately exported to the Arctic Basin. The consequences of this current regime shift on the nutrient characteristics of the Barents Sea are poorly defined. Here we use the stable isotopic ratios of nitrate (δ15N-NO3, δ18O-NO3) to determine the uptake and modification of AW nutrients in the Barents Sea. In summer months, phytoplankton consume nitrate, surface waters become nitrate depleted, and particulate nitrogen (δ15N-PN) reflects the AW nitrate source. The ammonification of organic matter in shallow sediments resupplies N to the water column and replenishes the nitrate inventory for the following season. Low δ18O-NO3 in the northern Barents Sea reveals that the nitrate in lower-temperature Arctic waters is > 80 % regenerated through seasonal nitrification. During on-shelf nutrient uptake and regeneration, there is no significant change to δ15N-NO3 or N*, suggesting that benthic denitrification does not impart an isotopic imprint on pelagic nitrate. Our results demonstrate that the Barents Sea is distinct from other Arctic shelves where benthic denitrification enriches δ15N-NO3 and decreases N*. As nutrients are efficiently recycled in the Barents Sea and there is no significant loss of N through benthic denitrification, changes to Barents Sea productivity are unlikely to alter N availability on shelf or the magnitude of N advected to the central Arctic Basin. However, we suggest that the AW nutrient source ultimately determines Barents Sea productivity and that changes to AW delivery have the potential to alter Barents Sea primary production and subsequent nutrient supply to the central Arctic Ocean.

While the entire Arctic Ocean is warming rapidly, the Barents Sea in particular is experiencing significant warming and sea ice retreat. An increase in ocean heat transport from the Atlantic is causing the Barents Sea to be transformed from a cold, salinity stratified system into a warmer, less-stratified Atlantic-dominated climate regime. Productivity in the Barents Sea shelf is fuelled by waters of Atlantic origin (AW), which are ultimately exported to the Arctic basin. The consequences of this current regime shift on the nutrient characteristics of the Barents Sea are poorly defined. Here we use the stable isotopic ratios of nitrate (δ15N-NO3, δ18O-NO3), to determine the uptake and modification of AW nutrients in the Barents Sea. In summer months, phytoplankton consume nitrate, surface waters become nitrate depleted, and particulate nitrogen (δ15N-PN) reflects the AW nitrate source. The ammonification of organic matter in shallow sediments resupplies N to the water column through the season. Low δ18O-NO3 in the northern Barents Sea reveals that the nitrate in lower temperature Arctic Waters is > 80 % regenerated through seasonal nitrification. During on shelf nutrient uptake and regeneration, there is no significant change to δ15N-NO3 or N*, suggesting benthic denitrification does not impart an isotopic imprint on pelagic nitrate. Our results demonstrate that the Barents Sea is distinct from other Arctic shelves, where coupled partial nitrification-denitrification enriches δ15N-NO3 and decreases N*. Our results suggest that any current or future changes to productivity on the Barents Sea shelf are unlikely to alter the magnitude or isotopic signature of nutrient supply exported to the central Arctic basin. However, we suggest that the AW nutrient source ultimately determines Barents Sea productivity and changes to this supply may alter Barents Sea primary production and subsequent nutrient supply to the central Arctic Ocean.

The role of the internal tide in driving tracer transport across the continental slope is examined using simplified layered theory, channel model experiments, and observational diagnostics of near shelf-edge moorings. The effect of the internal tide is interpreted in terms of its Stokes' drift, which is separated into two distinct components: a bolus component, driven by the covariance of layer thickness and the velocity, and a shear component, driven by the velocity following the movement of an interface. For a three-layer ocean, in the model experiments and observations, the onshore propagation of an internal tide drives a Stokes' transport directed onshore in the surface and the bottom layers and directed offshore in the pycnocline. This reversing structure is due to the bolus component dominating near the boundaries, while the shear component dominates at the pycnocline. In the observational diagnostics, the Stokes' transport is not canceled by the Eulerian transport, which is mainly directed along bathymetric contours. The Stokes' drift of the internal tide then provides a systematic on shelf tracer transport if there is a tracer sink on the shelf, carried in the surface or bottom layers. Conversely, the tracer transport is directed offshore if there is a tracer source on the shelf with plumes of shelf tracer expected to be carried offshore along the pycnocline. This tracer transport as a result of the internal tide is diagnosed for heat, salt, and nitrate. The depth-integrated nitrate flux is directed onto the shelf supplying nutrients to the productive shelf seas.

The flow of carbon from atmosphere to sediment fauna and sediments reduces atmospheric CO2, which in turn reduces warming. Here, during the Changing Arctic Ocean Seafloor programme, we use comparable methods to those used in the Antarctic (vertical, calibrated camera drops and trawl-collected specimens) to calculate the standing stock of zoobenthic carbon throughout the Barents Sea. The highest numbers of morphotypes, functional groups and individuals were found in the northernmost sites (80–81.3° N, 29–30° E). Ordination (non-metric multidimensional scaling) suggested a cline of faunal transition from south to north. The functional group dominance differed across all six sites, despite all being apparently similar muds. Of the environmental variables we measured, only water current speed could significantly explain any of our spatial carbon differences. We found no obvious relationship with sea ice loss and thus no evidence of Arctic blue carbon–climate feedback. Blue carbon in the Barents Sea can be comparable with the highest levels in Antarctic shelf sediments.This article is part of the theme issue ‘The changing Arctic Ocean: consequences for biological communities, biogeochemical processes and ecosystem functioning'.

‘The noblest part of a man is his passport’ Ziffel to Kalle in Bertolt Brecht’s Conversations in Exile.1‘What is a refugee?’ and ‘What is a refugee crisis?’ are key questions vexing policy makers, ...

International audience; This study presents a water mass analysis along the JC150 section in the subtropical North Atlantic, based on hydrographic and nutrient data, by combining an extended optimum multiparameter analysis (OMPA) with a Lagrangian particle tracking experiment (LPTE). This combination, which was proposed for the first time, aided in better constraining the OMPA end-member choice and providing information about their trajectories. It also enabled tracing the water mass origins in surface layers, which cannot be achieved with an OMPA. The surface layers were occupied by a shallow type of Eastern South Atlantic Central Water (ESACW) with traces of the Amazon plume in the west. Western North Atlantic Central Water dominates from 100 to 500 m, while the 13 °C-ESACW contribution occurs marginally deeper (500–900 m). At approximately 700 m, Antarctic Intermediate Water (AAIW) dominates the west of the Mid-Atlantic Ridge (MAR), while Mediterranean Water dominates the east with a small but non-negligible contribution down to 3500 m. Below AAIW, Upper Circumpolar Deep Water (UCDW) is observed throughout section (900–1250 m). Labrador Sea Water (LSW) is found centered at 1500 m, where the LPTE highlights an eastern LSW route from the eastern North Atlantic to the eastern subtropical Atlantic, which was not previously reported. North East Atlantic Deep Water (encompassing a contribution of Iceland-Scotland Overflow Water) is centered at ~2500 m, while North West Atlantic Bottom Water (NWABW, encompassing a contribution of Denmark Strait Overflow Water) is principally localized in the west of the MAR in the range of 3500–5000 m. NWABW is also present in significant proportions (>25%) in the east of the MAR, suggesting a crossing of the MAR possibly through the Kane fracture zone. This feature has not been investigated so far. Finally, Antarctic Bottom Water is present in deep waters throughout the section, mainly in the west of the MAR. Source waters have been characterized from GEOTRACES sections, which enables estimations of trace elements and isotope transport within water masses in the subtropical North Atlantic.

We address a long-standing problem of how nutrients are transported from the shelf edge and from rivers to support regular, seasonal primary production in the interior of a wide, temperate, shelf sea. Cross-shelf sections of hydrography and nutrients, from a series of cruises between March 2014 and August 2015, along with time series of river discharge and river nutrient load are used to assess the seasonality of cross-shelf transports. Riverine nitrogen inputs are estimated to account for 30% of the nitrate available for the spring bloom on the inner shelf, and 10% in the mid- to outer-shelf. In the bottom layer in summer, high salinity, nutrient-rich waters are transported on-shelf as a result of wind-driven Ekman transport, cross-shelf pressure gradients and/or internal tidal wave Stoke’s drift. In the centre of the shelf this advection is responsible for 25% of the increase in bottom water nitrate seen between April and November 2014. The remaining nitrate increase suggests that about 50–62% of the nitrogen fixed into organic material during spring, summer and autumn phytoplankton growth is recycled in the bottom water over the 12 months between March 2014 and March 2015. In winter, when the water column is vertically mixed, there is a weak net off-shelf transport of about 1 m2 s−1, possibly driven by a reversal of the horizontal density gradient caused by excess cooling of shallower shelf waters. Overall, shelf nitrate concentrations are maintained by a combination of riverine supply, recycling of organic material, and summer on-shelf transports. We suggest that the main driver of inter-annual variability in pre-spring nitrate concentrations is variability in the depth of the winter mixed layer over the shelf slope.

Highlights • Seawater dissolved inorganic carbon and nutrients measured for 1.5 seasonal cycles. • Inventories not in steady state from one winter to the next (e.g. 10% nitrate loss) • Significant fraction of annual production stored in long-lived organic matter pool. • Organic matter could provide mechanism for “continental shelf pump” carbon export. Abstract Continental shelf seas may have a significant role in oceanic uptake and storage of carbon dioxide (CO2) from the atmosphere, through a ‘continental shelf pump’ mechanism. The northwest European continental shelf, in particular the Celtic Sea (50°N 8°W), was the target of extensive biogeochemical sampling from March 2014 to September 2015, as part of the UK Shelf Sea Biogeochemistry research programme (UK-SSB). Here, we use the UK-SSB carbonate chemistry and macronutrient measurements to investigate the biogeochemical seasonality in this temperate, seasonally stratified system. Following the onset of stratification, near-surface biological primary production during spring and summer removed dissolved inorganic carbon and nutrients, and a fraction of the sinking particulate organic matter was subsequently remineralised beneath the thermocline. Water column inventories of these variables throughout 1.5 seasonal cycles, corrected for air-sea CO2 exchange and sedimentary denitrification and anammox, isolated the combined effect of net community production (NCP) and remineralisation on the inorganic macronutrient inventories. Overall inorganic inventory changes suggested that a significant fraction (>50%) of the annual NCP of around 3 mol-C m–2 yr–1 appeared to be stored within a long-lived organic matter (OM) pool with a lifetime of several months or more. Moreover, transfers into and out of this pool appeared not to be in steady state over the one full seasonal cycle sampled. Accumulation of such a long-lived and potentially C-rich OM pool is suggested to be at least partially responsible for the estimated net air-to-sea CO2 flux of ∼1.3 mol-C m–2 yr–1 at our study site, while providing a mechanism through which a nutrient-conserving continental shelf pump for CO2 could potentially operate in this and other similar regions.

Autumn phytoplankton blooms represent key periods of production in temperate and high-latitude seas. Biogenic silica (bSiO2) production, dissolution, and standing stocks were determined in the Celtic Sea (United Kingdom) during November 2014. Dissolution rates were in excess of bSiO2 production, indicating a net loss of bSiO2. Estimated diatom bSiO2 contributed ≤10% to total bSiO2, with detrital bSiO2 supporting rapid Si cycling. Based on the average biomass-specific dissolution rate (0.2 day−1), 3 weeks would be needed to dissolve 99% of the bSiO2 present. Negative net bSiO2 production was associated with low-light conditions (−2·day−1). Our observations imply that dissolution dominates Si cycling during autumn, with low-light conditions also likely to influence Si cycling during winter and early spring.

The Deep Western Boundary Current in the subpolar North Atlantic is the lower limb of the Atlantic Meridional Overturning Circulation and a key component of the global climate system. Here, a mooring array deployed at 60°N in the Irminger Sea, between 2014 and 2016, provides the longest continuous record of total Deep Western Boundary Current volume transport at this latitude. The 1.8‐year averaged transport of water denser than σθ = 27.8 kg/m3 was −10.8 ± 4.9 Sv (mean ± 1 std; 1 Sv = 106 m3/s). Of this total, we find −4.1 ± 1.4 Sv within the densest layer (σθ > 27.88 kg/m3) that originated from the Denmark Strait Overflow. The lighter North East Atlantic Deep Water layer (σθ = 27.8–27.88 kg/m3) carries −6.5 ± 7.7 Sv. The variability in transport ranges between 2 and 65 days. There is a distinct shift from high to low frequency with distance from the East Greenland slope. High‐frequency fluctuations (2–8 days) close to the continental slope are likely associated with topographic Rossby waves and/or cyclonic eddies. Here, perturbations in layer thickness make a significant (20–60%) contribution to transport variability. In deeper water, toward the center of the Irminger Basin, transport variance at 55 days dominates. Our results suggest that there has been a 1.8 Sv increase in total transport since 2005–2006, but this difference can be accounted for by a range of methodological and data limitation biases.

Using underwater gliders we have identified canyon driven upwelling across the Celtic Sea shelf-break, in the vicinity of Whittard Canyon. The presence of this upwelling appears to be tied to the direction and strength of the local slope current, which is in itself highly variable. During typical summer time equatorward flow, an unbalanced pressure gradient force and the resulting disruption of geostrophic flow can lead to upwelling along the main axis of two small shelf break canyons. As the slope current reverts to poleward flow, the upwelling stops and the remnants of the upwelled features are mixed into the local shelf water or advected away from the region. The upwelled features are identified by the presence of sub-pycnocline high salinity water on the shelf, and are upwelled from a depth of 300 m on the slope, thus providing a mechanism for the transport of nutrients across the shelf break onto the shelf.

Temperature and current measurements from two moorings onshore of the Celtic Sea shelf break, a well-known hot spot for tidal energy conversion, show the impact of passing summer storms on the baroclinic wavefield. Wind-driven vertical mixing changed stratification to permit an increased on-shelf energy transport, and baroclinic energy in the semidiurnal band appeared at the moorings 1–4 days after the storm mixed the upper 50 m of the water column. The timing of the maximum in the baroclinic energy flux is consistent with the propagation of the semidiurnal internal tide from generation sites at the shelf break to the moorings 40 km away. Also, the ∼3 day duration of the peak in M2 baroclinic energy flux at the moorings corresponds to the restratification time scale following the first storm.

Here we describe, for the first time, the use of a miniaturized Lab-on-Chip (LoC) nutrient sensor deployed within an autonomous underwater vehicle (AUV; Kongsberg Seaglider) to collect high-resolution nitrate (nitrate + nitrite) data in a highly dynamic shelf sea environment. Seasonally stratified temperate shelf seas act as important carbon sinks, where primary production is controlled by the availability of nutrients such as nitrate. Spring phytoplankton blooms and sporadic mixing events can drastically modify the availability of nitrate on temporal scales from hours to days. Traditional sampling methods are unable to capture high frequency events that can be clearly observed using a wet-chemical microfluidic system deployed within a glider. We highlight firstly, an excellent agreement between the LoC and shipboard nitrate + nitrite measurements (r2 = 0.98 n = 11). Secondly, the LoC was able to observe a decrease in nitrate within the surface mixed layer from 5.74 μM (4th) to 1.42 μM (25th) during the onset of the spring bloom, whilst bottom layer concentrations remained constant (6.86 ± 0.16 μM), with an estimated analytical uncertaintly of

The combination of acoustic Doppler current profilers and the structure function methodology provides an attractive approach to making extended time series measurements of oceanic turbulence (the rate of turbulent kinetic energy dissipation ε) from moorings. However, this study shows that for deployments in the upper part of the water column, estimates of ε will be biased by the vertical gradient in wave orbital velocities. To remove this bias, a modified structure function methodology is developed that exploits the differing length scale dependencies of the contributions to the structure function resulting from turbulent and wave orbital motions. The success of the modified method is demonstrated through a comparison of ε estimates based on data from instruments at three depths over a 3-month period under a wide range of conditions, with appropriate scalings for wind stress and convective forcing.

Despite its size and importance the dispersal, variability and dynamics of the Congo River plume have until recently been minimally documented. In this paper we analyse remotely sensed sea surface temperature, sea level anomaly, salinity and chlorophyll concentration from 2010 to describe and quantify the extent, strength and seasonality of the plume and to explain its behaviour in relation to winds, ocean currents and fresh water discharge. Empirical Orthogonal Function (EOF) analysis reveals strong seasonal and coastal upwelling signals, potential bimodal seasonality and responses to fresh water discharge peaks in all data sets. Salinity and chlorophyll are significantly negatively correlated (− 0.4 to − 0.9) across a 500 km2 zone west of the river mouth. Lagged correlations with river discharge show the westward translation, dispersal and strengthening of a similar sized region of positive chlorophyll-discharge and negative salinity-discharge correlations. Peaks in chlorophyll lag the discharge by 1–4 months, although it is not possible from ocean colour alone to distinguish increases in chlorophyll resulting from the dispersal of nutrient rich river discharge from other physical and biological mechanisms that promote changes in surface chlorophyll, or indeed have confidence that the signal has not been contaminated by other optically active substances. The strongest plume-like signatures from EOF analysis are found in the salinity and colour data sets, which are then also analysed using a statistically based water mass detection technique to isolate the behaviour of the plume. The validity of the technique is checked against ARGO profiles. Throughout the year the main axis of the fresh water plume extends between 400 and 1000 km, northwest along the coastline, or west–southwest out into the open south Atlantic. Changes in the magnitude and direction of wind stress and hence wind driven surface currents are the principal driving force behind this far-field variability, although the strength and direction of the Angola and Benguela Coastal currents may also play a role. The mean surface salinity within the plume and its surface area have qualitative links to the seasonal cycle in river discharge and wind stress.

Given the huge disparity in the chance of survival for children with cancer born in low income countries (LICs) compared with those in high income ones, there is an urgent need to assist those striving to support, palliate and offer curative treatment in resource limited settings. International twinning partnerships offer the opportunity to provide advice, expertise, support and technology transfer from established paediatric oncology units to developing ones in order to help them overcome the challenges facing them. It may help them to avoid the mistakes made over the last 50 years during which childhood cancer survival has progressed in high income countries from little expectation of cure to 75–80% long term survival. Projects must be locally driven by the team in the LIC, but volunteers and funding organisations can help to make progress possible. There is mutual benefit for all concerned.

Sea surface temperature satellite imagery and a regional hydrodynamic model are used to investigate the variability and structure of the Liverpool Bay thermohaline front. A statistically based water mass classification technique is used to locate the front in both data sets. The front moves between 5 and 35 km in response to spring–neap changes in tidal mixing, an adjustment that is much greater than at other shelf-sea fronts. Superimposed on top of this fortnightly cycle are semi-diurnal movements of 5–10 km driven by flood and ebb tidal currents. Seasonal variability in the freshwater discharge and the density difference between buoyant inflow and more saline Irish Sea water give rise to two different dynamical regimes. During winter, when cold inflow reduces the buoyancy of the plume, a bottom-advected front develops. Over the summer, when warm river water provides additional buoyancy, a surface-advected plume detaches from the bottom and propagates much larger distances across the bay. Decoupled from near-bed processes, the position of the surface front is more variable. Fortnightly stratification and re-mixing over large areas of Liverpool Bay is a potentially important mechanism by which freshwater, and its nutrient and pollutant loads, are exported from the coastal plume system. Based on length scales estimated from model and satellite data, the erosion of post-neap stratification is estimated to be responsible for exporting approximately 19% of the fresh estuarine discharge annually entering the system. Although the baroclinic residual circulation makes a more significant contribution to freshwater fluxes, the episodic nature of the spring–neap cycle may have important implications for biogeochemical cycles within the bay.

Observations made near the Celtic Sea shelf edge are used to investigate the interaction between wind-generated near-inertial oscillations and the semidiurnal internal tide. Linear, baroclinic energy fluxes within the near-inertial (f) and semidiurnal (M2) wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone. Over the 2 week deployment period, the semidiurnal tide drove 28–48 W m−1 of energy directly on-shelf. Little spring-neap variability could be detected. Horizontal near-inertial energy fluxes were an order of magnitude weaker, but nonlinear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semidiurnal internal tide led to a 25–43% increase in positive on-shelf energy flux. The phase relationship between f and M2 determines whether this nonlinear interaction enhances or dampens the linear tidal component of the flux, and introduces a 2 day counter-clockwise beating to the energy transport. Two very clear contrasting regimes of (a) tidally and (b) inertially driven shear and energy flux are captured in the observations.

[1] We show that discrete lenses of anomalously high-salinity water, originating from the shelf edge and trapped within the seasonal pycnocline, are advected 100 km or more onto the Celtic Sea continental shelf. We propose that the lenses are created by increased diapycnal mixing at the shelf edge associated with breaking high-frequency internal wave packets. Quasi-synoptic hydrography sections show the lenses to be 3–5 km wide, their temporal persistence confirmed by moored instrumentation and a series of CTD casts. Estimates of the propagation speed of these features (∼0.020 m s−1) compare favorably with the magnitude of observed residual currents. Residual current variability within the pycnocline is dominated by vertical structures most consistent with the second baroclinic mode. The residual flow is therefore thought to be predominantly driven by non-linear second mode internal tidal waves. These are observations of a shelf edge exchange process not previously identified.

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.

A detailed analysis of the Southland Front, a shelf-break system off the southeast coast of South Island, New Zealand is presented. The position, temperature, temperature range and width of the front are determined using a new statistical front detection algorithm and 21 years worth of Advanced Very High Resolution Radiometer satellite sea surface temperature (SST) data. Overall, the front is strongest (highest SST gradients) in the summer and winter, and the across front gradient decreases northward in all seasons, consistent with an equatorward decrease in stability and divergence of isobaths. The surface expression of the front moves further offshore during the winter months and is found closest inshore in the summer. Seasonality of the front is strongly controlled by the annual cycle of subtropical and subantarctic water mass temperatures. Both the temperature and strength of the front are interannually variable, and correlated with the El Nino-Southern Oscillation (ENSO); they both decrease during El Nino, and increase during La Nina events. ENSO indices lead changes in the fronts temperature by up to 6 months. Conversely, the gradient may change up to 6 months in advance of peak ENSO indices. The strength and sign of correlations is seasonally dependent.