Changes in extreme sea levels, combined with the growth of coastal population, are critical factors in evaluating the risks related to coastal flooding. Thus, studying the variability and trends of storm surges, a major contributor to extreme sea levels, becomes essential for coastal protection policies. We developed in the North Atlantic the first hourly surge hindcast covering the full 20th century (1900-2015) on a 0.1(degrees) grid, and called ClimEx hindcast. We validated the hindcast against 34 long-term tide gauges. The model shows overall very good performance for surges (Root Mean Square Error of 9.3 cm on average), and good performance for extreme surges, despite an overall underestimation. To investigate the variability and trends in storm surges, we performed a non-stationary extreme value analysis on modeled and observed storm surges. The seasonality of storm surges is highly dependent on the area. The seasonal amplitude varies from typically 10 cm, to more than 40 cm in the North Sea. The storm surge season occurs around December-January in the north of the domain (above 40(degrees) N), due to winter extra-tropical cyclones, and around September-October in the south-west, due to tropical cyclones. The dependence of storm surges with the North Atlantic Oscillation extends from the coasts to the deep ocean, and is positive above 50 degrees N and negative below. Observed storm surges show mostly non significant or small trends (< +/- 1 mm/yr), while the model displays positive trends almost everywhere, possibly due to inhomogeneities in the atmospheric forcing dataset prior to 1950.

Coastal subarctic systems are inhabited by bivalve and gastropods, which due to their lifecycle and longevity are reliable indicators of ecological alterations in the environment. Recent laboratory studies have shown that young life stages of invertebrates perceive natural sounds, and their settlement, behavior, and fitness could be altered by anthropogenic noise. Through a field study conducted on two sites differing by their noise pollution level (pristine [PS] or anthropized [AS]), we tested whether the distances (from 25 to 890 m) of anthropogenic noises might affect the diversity and early recruitment of multiple species in pristine and anthropized sites using artificial collectors moored on transects. Overall, environmental conditions (except sound levels) were homogeneous through the transects. The acoustic scenario differed between the PS (vessel noise, 132-138 dB re 1 μPa2 s) and AS (mix of pile driving and vessel noise, >140 dB re 1 μPa2 s) sites, with the AS site experiencing a higher level of sound exposure than the PS site. Species richness fluctuated with distance from the noise, but only in the anthropized site. Regarding species diversity and evenness, they varied with distance and month at both sites, displaying a clear negative effect of anthropogenic noises and shifting species composition. Specific early recruitment responses were observed for each species to anthropogenic noise, but with a different pattern for each site due to variations in sound pressure and exposure levels. The findings of our field study document, for the first time, that controlled anthropogenic noise emission leads to ecological shifts in community structure and population metrics of benthopelagic marine invertebrate species. To avoid disruptions in community structure and recruitment, we recommend that a noise threshold level for invertebrates should be below 140 dB re 1 μPa2 s.

The M2 tide displays large seasonal variability in Europe, particularly in the North Sea. The tide is there larger in summer than in winter. However, there is no consensus on the physical drivers leading to such large values, atmosphere circulation and stratification being two good candidates. We analyzed hourly sea level data from observations at 35 tide gauges in Europe. The amplitude of M2 seasonal cycle is the largest in the southern North Sea, reaching typically 4-6 cm. This cycle is well reproduced by a barotropic model, forced with the tidal potential and the atmosphere only. This suggests a minor role of the stratification. We show that large seasonal cycles in the southern North Sea are first due to gravitational nonlinear effects. The atmosphere also plays a role, but locally and in a smaller extent.

Broad embayment, such as some Fjords, can host the generation and propagation of internal Kelvin waves should the ratio of their Rossby radius to shelf-slope width be large. Here, we report on such a process in a broad, mid-latitude, fjord where the upper-layer dynamics are dominated by sub-inertial baroclinic motions. This fjord is of particular interest due to recent development of the aquaculture industry and to being historical fishing grounds. Using a fully non-linear, three-dimensional primitive equation numerical model we show that the large majority of the thermocline vertical fluctuations (80%) and much of the along-shore currents (50%) can be reproduced with a flat-bottom assumption. We use the model to determine the origin of the process, which is expressed by upwelling and downwelling disturbances traveling cyclonically around the bay. We find that the wind generates local and remote, from a large and deep neighboring bay, responses which travel as forced and freely propagating long, coastally trapped, internal waves into and around the fjord. The resulting dynamics within the fjord can therefore be complex, particularly in the fall season during which nearly continuous and directionally variable winds occur. Under such forcing conditions and given the irregularity of the regional coastline, signals combine to form temporally and spatially varying responses, enhancing or diminishing transient upwelling or downwelling and their associated along-shore current pulses.

Coastal cross-shelf transport drives the redistribution of sediment, nutrients and pollutants on continental shelves. Here, the cross-shelf volume flux is quantified from in situ measurements at two coastal sites on the Bay of Biscay (BoB) shelf. At both sites, a semidiurnal internal tide propagates onshore, and mode 1 nonlinear internal wave packets are observed. The Eulerian and Stokes drift contributions to the subtidal cross-shelf transport are estimated along density layers from ADCP, temperature sensors, and CTD measurements at 62 m water depth on the Landes plateau or SE-BoB (44° N) and 47 m water depth on the Armorican shelf or N-BoB (47° N). The Stokes drift transport has possible contributions from the internal tides, nonlinear internal waves and the surface waves and tide. At both sites, the vertical profile of the month-long averaged Stokes drift volume flux matches the shape of the semi-analytical Stokes drift volume flux due to a linear mode-1 internal tide. We demonstrate that nonlinear internal wave events can also contribute to the Stokes drift volume flux. We thereby attribute the Stokes drift volume flux at the study sites to internal wave pumping (IWP). At both sites, the IWP is responsible for a near-seabed onshore volume flux during stratified conditions and spring internal tides, that is equivalent to a wind-driven upwelling event generated by a 4 m s−1 wind. At N-BoB (47° N), IWP is the main contributor to the total cross-shelf volume flux under stratified conditions and a spring internal tide. At SE-BoB (44° N), IWP augments the near-seabed onshore volume flux during upwelling events and maintains a near-seabed onshore volume flux even during downwelling events.

We investigated regional changes in winter storm surges along the North Atlantic coasts, over the last century. We analyzed 35 tide gauges, with at least 80 years of data. We conducted a Generalized Extreme Value analysis on a 21-yr sliding window, to investigate variations in the 10-yr surge return level. Thanks to a standard clustering algorithm, we identified four regions with similar storm surge variations: the Northern Europe, the Northern U.S., the New York Bight and the Southern U.S.. The Northern Europe appears to be quite homogeneous, despite some discrepancies between the North Sea and the Baltic Sea. Surprisingly, storm surge variations in the New York Bight are close to the ones of the Northern Europe, suggesting connections across the North Atlantic. On the contrary, the New York Bight shows very different variations from the Northern U.S., despite located inside this coherent region. Large geographical areas with similar changes show that observed changes are mainly driven by large-scale processes. Close variations between storm surges and the Atlantic Multidecadal Oscillation suggest that the North Atlantic sea surface temperature may play a role. In addition, we found that 6

Severe storms that hit the North Atlantic coasts over the last decades, such as Xynthia storm in Europe, showed the vulnerability of coastal populations to extreme sea levels. There is a need to quantify the changes in extreme sea levels, to enable the implementation of appropriate coastal adaptation measures. Extreme sea levels are the joint contribution of mean sea level, tide and storm surges. Several authors investigated changes in storm surges. Storm surges display strong interannual and multidecadal variability, but no clear long-term trends at most sites globally (Mawdsley and Haigh, 2016; Marcos and Woodworth, 2017). The objective of the present study is to characterize changes in extreme storm surges along the North Atlantic coasts, since 1850. We selected long-term tide gauges with at least 100 years of data, from GESLA-3 dataset (Haigh et al., 2022). This conducted to consider around 30 tide gauges along the U.S. and European coasts. Extreme storm surges were evaluated yearly, using different approaches: (1) the maximum value over a period (e.g. annual maximum), the n-th percentile (e.g. 99th percentile) and (3) the return level associated to a return period (e.g. 1 year return level); this last value is obtained by fitting a Generalized Extreme Value distribution on data. At each station, we characterized changes in extreme storm surges over the last century. We compared the different approaches. We estimated long-term trends and analyzed storm surge variability in link with large-scale atmospheric forcing (e.g. North Atlantic Oscillation index). Regions of similar variations were also identified. These results are a first step towards the understanding of the physical causes behind the observed changes of extreme storm surges in the North Atlantic. References[1] Marcos, M. & Woodworth, P. L (2017). Spatiotemporal changes in extreme sea levels along the coast of the North Atlantic and the Gulf of Mexico. J. Geophys. Res. Oceans 122, 7031–7048. https://doi.org/10.1002/2017JC013065[2] Mawdsley R. J. and Haigh I. D. (2016). Spatial and Temporal Variability and Long-Term Trends in Skew Surges Globally. Front. Mar. Sci. 3:29. https://doi.org/10.3389/fmars.2016.00029[3] Haigh I. D., Marcos M., Talke S. A., Woodworth P. L., Hunter J. R., Hague B. S., et al. (2022). GESLA Version 3: A major update to the global higher-frequency sea-level dataset. Geosci. Data J., 00, 1–22. https://doi.org/10.1002/gdj3.174

The Bay of Biscay (Bob) is a hot spot for the generation of internal tides and nonlinear internal waves (NLIW). However, no studies have focused on internal waves on the continental shelf of the Bob. Here, we present 22 days of collocated temperature, velocity and backscatter profiles within a water depth H of 65 m. The background stratification evolved from two pycnoclines, with the strongest one near the sea bed, to a continuous profile due to wind-driven upwelling.Under the double pycnocline situation, we observed trains of elevation emerging from each internal tidal front with amplitude reaching up to H/4 and propagating at speeds between 0.1 and 0.35 m/s. Sporadically depression waves were measured within the train and can propagate substantially faster (between 0.36 and 0.54 m/s). With the continuous stratification, the trains of NLIWs of elevation and containing opposite polarities were no longer observed.These observations suggest that depression waves can cross the train of elevation waves. Resulting interactions could have significant impacts on sediment dynamics over the shelf. The double pycnocline regime and the impact of the stratification modification due to wind will be investigated numerically in future work.

This data set includes all the data from the ETOILE campaign (https://doi.org/10.17600/17010800) used in the paper: Moncuquet A., N. L. Jones, A. P. Zulberti, F. Dufois, L. Bordois, P. Lazure. Observations of mode-one nonlinear internal waves of opposite polarity in changing background conditions, submitted to Journal of Geophysical Research in September 2023. ========================================================================== The ETOILE campaign (https://doi.org/10.17600/17010800) has been designed to study internal dynamics in the Bay of Biscay. The data archived here are from 2 moorings with ADCPs and temperature/pressure sensors deployed from 09/07/2017 to 02/08/2017. It also includes vertical profiles of CTD measurements performed between the 25th of and 29th of July 2017 using a moving vessel profiler (MVP). Outer shelf mooring (2L) The 2L mooring was moored along the 150 m isobath. The 2L mooring had 9 thermistors distributed between 70cm above the bottom and 20 m below the surface, with an acquisition frequency of 1 minute. The bottoms mounted ADCP (RDI Sentinel 300 kHz) was deployed with an acquisition frequency of 2s. The ADCP and the mooring line were separated by 1.4km and respectively located at 43°59.9N, 2°02.537W and 44°00.1N, 2°01.5W. The folder named "2L_mooring" includes the following files: - 2L_MooringLine.mat: a matlab format file with pressure and temperature data. - ADCP_2L_UVW.mat: a matlab format file with ADCP velocity data in earth coordinates. - ADCP_2L_EAS.mat: a matlab format file with ADCP backscatter data. - ADCP_2L_PG.mat: a matlab format file with ADCP "Percentage Good" RDI values. Inner shelf mooring (2C) The 2C mooring was moored along the 60 m isobath. The 2C mooring had 6 thermistors distributed between 70cm above the bottom and 20 m below the surface, with an acquisition frequency of 1 minute. The bottoms mounted ADCP (RDI Sentinel 300 kHz) was deployed with an acquisition frequency of 2s. The ADCP and the mooring line were collocated and located at 44°00N, 1°31W. The folder named "2C_mooring" includes the following files: - 2C_MooringLine.mat: a matlab format file with pressure and temperature data. - ADCP_2C_UVW.mat: a matlab format file with ADCP velocity data in earth coordinates. - ADCP_2C_EAS.mat: a matlab format file with ADCP backscatter data. - ADCP_2C_PG.mat: a matlab format file with ADCP "Percentage Good" RDI values. MVP profiles The MVP is a self-profiling system capable of measuring pressure P, conductivity sigma, temperature T, salinity S and density rho, behind a travelling vessel at high frequency. The MVP profiled along a 52 km long transect down to 300 m depth for the first two days at a boat speed of 4 knots. The last two days the MVP profiled down to 100 m along a 15 km long transect at a boat speed of 6 knots. A bottom safe margin of 13 m was used to prevent the MVP from hitting the bottom. The folder named "MovingVesselProfiler" includes the MVP files in a native ascii format, with one file per profile (including both downcast and upcast). The file headers includes all the metadata including the time and position of each profile.

Extreme sea levels are the joint contribution of mean sea level, tide and storm surges. The ClimEx project investigates changes in tide and storm surges over the last century, along the North Atlantic coasts. Concerning the tide, we investigated the long-term changes of the principal tidal component M2, from 1846 to 2018 (Pineau-Guillou et al., 2021). The M2 variations are consistent at all the stations in the North-East Atlantic. The changes started long before the 20th century and are not linear. Regarding the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M2 variations in the North-East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. A possible underlying mechanism is discussed. Concerning the storm surges, we found a clear shift in the storm surge season at Brest (France), between 1950 and 2000 (Reinert et al., 2021). Extreme storm surge events occurred three weeks earlier (mid-December instead of beginning of January) in the winter 2000 than in the 1950s. Analysis of additional stations in Europe reveals a large-scale process (Roustan et al., 2022). Temporal shifts are positive (later events) in northern Europe, and negative (earlier events) in southern Europe. Such a tendency is similar to the one already reported for European river floods between 1960 and 2010 (Blöschl et al., 2017). References[1] Pineau-Guillou L., Lazure P. and Wöppelmann G. (2021). Large-scale changes of the semidiurnal tide along North Atlantic coasts from 1846 to 2018. Ocean Sci., 17, 17–34. https://doi.org/10.5194/os-17-17-2021[2] Reinert M., Pineau-Guillou L., Raillard N., Chapron B. (2021). Seasonal shift in storm surges at Brest revealed by extreme value analysis. J. Geophys. Res. Oceans, 126, e2021JC017794. https://doi.org/10.1029/2021JC017794[3] Roustan J.-B., Pineau-Guillou L., Chapron B., Raillard N., Reinert M. (2022). Shift of the storm surge season in Europe due to climate variability. Sci. Rep., 12, 8210. https://doi.org/10.1038/s41598-022-12356-5[4] Blöschl G., Hall J., Parajka J., Perdigão R. A. P., Merz B., Arheimer B. et al. (2017). Changing climate shifts timing of European floods. Science, 357(6351), 588–590. https://doi.org/10.1126/science.aan25

As one of the foremost global forcings, tidal circulation exerts a pervasive influence on biological and physical processes occurring in the world's oceans on hourly to decadal time scales. This research identified the 18.6-year periodic variation in the lunar orbital plane within an annually resolved 140-year (1875 to 2015) shell growth master chronology measured from 21 live collected Arctica islandica, a bivalve known to be one of the longest lived non-colonial animals. The potential ecological implications of this result warranted detailed inventory of underlying physical processes. The absence of long-term in situ hydrological data for the bivalve's habitat was circumvented by the use of satellite data and numerical modeling which show that coastal regions of the Northwest Atlantic shelf clearly record diurnal tidal currents influenced by the 18.6-year nodal lunar cycle. The approach described here demonstrates that combining physical and biological data can help to identify subtle ecological processes over long time-scales for accurately disentangling the latter from variation introduced by anthropogenic climate change.

This paper describes the physical oceanography of Fortune Bay, a broad, mid-latitude fjord located in Newfoundland (Canada). Fortune Bay is subject to a strong seasonal stratification (0-16 degrees C sea-surface temperature range with up to 1 degrees C/m vertical gradient) influenced by local freshwater runoff, wind forcing and shelf inputs. Sea-ice is seldom present in the bay and unlikely to be of importance on the seasonal stratification and mixing processes. Fortune Bay is warmer than its adjacent shelf both at the surface (by about 2 degrees C) and at intermediate depths (by about 1 degrees C from 50-150 m). While the former is likely due to local freshwater runoff stratification influence, the latter is probably related to the warm, deep water input occurring in winter below sill depth and subsequently mixed with the intermediate layer via the input of a colder water mass flowing in summer and which eventually reaches the bottom as well. Currents are dominated by the 'weather band' (2-20 d) and characterized by energetic pulses associated with downwelling and upwelling events. Mean circulation is rather weak and the seasonal pattern obtained here did not reveal either the presence of a distinct estuarine circulation nor a strong influence of the main coastal current. Tidal currents are weak also and no inertial signal was observed. Estimates of water exchange between the inner and outer part of the bay were calculated using several methods and led to residence times of the order of a few to several months for the upper layers and of the order of a year for the bottom layer with a probable strong seasonal variability (larger residence time in summer for the upper layers). The "baroclinic pumping" processes, which include the downwelling/upwelling events, appear to be important players but more work is needed to better understand their nature and actual contribution. Crown Copyright (C) 2022 Published by Elsevier B.V.

In response to ongoing global climate change, marine ecosystems in the northwest Atlantic are experiencing one of the most drastic increases in sea surface temperatures in the world. This warming can increase water column stratification and decrease surface nutrient concentrations, in turn impacting primary productivity and phytoplankton assemblages. However, the exact impacts of these changes on sources and quality of organic matter as well as its transfers to the benthic compartment remain uncertain. This survey characterized organic matter sources and quality within a highly-stratified sub-Arctic coastal system (Saint-Pierre and Miquelon) and described its transfer towards a biomass-dominant primary consumer, the sand dollar Echinarachnius parma. This study analyzed fatty acid and stable isotope (delta C-13 and delta N-15) composition of surface and bottom Particulate Organic Matter (s-POM and b-POM, respectively), Sedimentary Organic Matter (SOM) and sand dollar tissue along a near shore to offshore gradient during two contrasting seasons associated either with sharp or weak water column stratification (i.e. High vs Low Stratification Periods). Results revealed high relative abundances of polyunsaturated fatty acids (notably macro- and microalgae markers) in POM during the Low Stratification Period while the High Stratification Period was characterized by elevated relative abundance of saturated fatty acids indicating a higher organic matter degradation state. In addition, strong seasonal differences were also observed in food availability with four-fold higher concentrations in total suspended solids during Low vs High Stratification Periods. These results suggested thus multiple negative effects of stratification on pelagic-benthic coupling and POM quality. Lower nutrient repletion of surface waters during period of sharp stratification diminishes pelagic-benthic coupling by reducing food availability, POM quality and vertical transfer of organic matter. By contrast, the sediment-based diet of E. parma showed a low spatiotemporal variability reflecting the homogenous composition of the SOM. This study suggests that intensified water column stratification due to increasing sea surface temperatures may modify the pelagic-benthic coupling and future quality and composition of POM pools.

Records of ocean/atmosphere dynamics over the past centuries are essential to understand processes driving climate variability. This is particularly true for the Northwest Atlantic which is a key region with an essential role in global climate regulation. Over the past two decades, coralline red algae have been increasingly used as environmental and climatic archives for the marine realm and hold the potential to extend long-term instrumental measurements. Here, we investigate the possibility to extract climate and environmental information from annual growth patterns and geochemical composition of the coralline red algae, Clathromorphum compactum, from Saint-Pierre & Miquelon (SPM), a French archipelago southwest of Newfoundland. However, measurements of C. compactum growth trends is challenging due to difficulties in identifying annual growth lines directly. So far, growth pattern investigations were commonly performed based on geochemical data of coralline calcite matrix. Nonetheless, this method is expensive and therefore prevents from analyzing a large number of specimens that would be representative of the population. For this reason, we enhanced the growth line readability by staining polished sections with Mutvei's solution and performed growth analysis based on direct increment width measurements. Geochemical analyses were also carried out in order to validate the assumption that growth lines observed after staining were formed on an annual basis. Moreover, growth pattern and trace element composition were measured on multiple axes of several individuals in order to assess the intra- and interspecimen variability and validate their use for paleoenvironmental reconstructions. Finally, relationships between the C. compactum sclerochronological records from SPM and environmental datasets covering different geographical areas allow a better knowledge of flow dynamics in the Northwest Atlantic and confirm the findings related to Arctica islandica from the same location.

Submesoscale processes have a determinant role in the dynamics of oceans by transporting momentum, heat, mass, and particles. Furthermore, they can define niches where different phytoplankton species flourish and accumulate not only by nutrient provisioning but also by modifying the water column structure or active gathering through advection. In coastal areas, however, submesoscale oceanic processes act together with coastal ones, and their effect on phytoplankton distribution is not straightforward. The present study brings the relevance of hydrodynamic variables, such as vorticity, into consideration in the study of phytoplankton distribution, via the analysis of in situ and remote multidisciplinary data. In situ data were obtained during the ETOILE oceanographic cruise, which surveyed the Capbreton Canyon area in the southeastern part of the Bay of Biscay in early August 2017. The main objective of this cruise was to describe the link between the occurrence and distribution of phytoplankton spectral groups and mesoscale to submesoscale ocean processes. In situ discrete hydrographic measurements and multi-spectral chlorophyll a (chl a) fluorescence profiles were obtained in selected stations, while temperature, conductivity, and in vivo chl a fluorescence were also continuously recorded at the surface. On top of these data, remote sensing data available for this area, such as high-frequency radar and satellite data, were also processed and analysed. From the joint analysis of these observations, we discuss the relative importance and effects of several environmental factors on phytoplankton spectral group distribution above and below the pycnocline and at the deep chlorophyll maximum (DCM) by performing a set of generalized additive models (GAMS). Overall, salinity is the most important parameter modulating not only total chl a but also the contribution of the two dominant spectral groups of phytoplankton, brown and green algae groups. However, at the DCM, among the measured variables, vorticity is the main modulating environmental factor for phytoplankton distribution and explains 19.30 % of the variance. Since the observed distribution of chl a within the DCM cannot be statistically explained without the vorticity, this research sheds light on the impact of the dynamic variables in the distribution of spectral groups at high spatial resolution.

We investigated the long-term changes of the principal tidal component M-2 along North Atlantic coasts, from 1846 to 2018. We analysed 18 tide gauges with time series starting no later than 1940. The longest is Brest with 165 years of observations. We carefully processed the data, particularly to remove the 18.6-year nodal modulation. We found that M-2 variations are consistent at all the stations in the North-East Atlantic (Cuxhaven, Delfzijl, Hoek van Holland, Newlyn, Brest), whereas some discrepancies appear in the North-West Atlantic. The changes started long before the 20th century and are not linear. The secular trends in M-2 amplitude vary from one station to another; most of them are positive, up to 2.5 mm/yr at Wilmington since 1910. Since 1990, the trends switch from positive to negative values in the North-East Atlantic. Concerning the possible causes of the observed changes, the similarity between the North Atlantic Oscillation and M-2 variations in the North-East Atlantic suggests a possible influence of the large-scale atmospheric circulation on the tide. Our statistical analysis confirms large correlations at all the stations in the North-East Atlantic. We discuss a possible underlying mechanism. A different spatial distribution of mean sea level (corresponding to water depth) from one year to another, depending on the low-frequency sea-level pressure patterns, could impact the propagation of the tide in the North Atlantic basin. However, the hypothesis is at present unproven.

This dataset is from the study entitled "The Physical Oceanography of Fortune Bay, an overview" which is being submitted to Regional Studies in Marine Science journal for publication (submission: July 2021).It consists of processed data that was used to make the analysis as well as some of the main tabulated results (i.e. statistics).Data published previously were also used for this study (see references).Details of the files are provided in a README.txt and details on the data processing and analysis are provided in the manuscript to be published.

Abstract. Mesoscale dynamics play a major role in several ocean processes, not only in the transport of momentum, heat, mass, particles and microorganisms but also in the provisioning of nutrients into the euphotic zone. Mesoscale processes can define niches where specific phytoplankton species flourish. However, this effect is not straightforward in coastal areas, which are submitted to a more complex interplay between different oceanic processes. In this context, the ETOILE campaign surveyed the CapBreton canyon area in the South-East of Bay of Biscay in early August 2017. The main objective of this study was to link the occurrence and distribution of phytoplankton with the mesoscale ocean processes. On top of the remote sensing data available for this area, such as High Frequency radar or satellite data, in situ discrete hydrographic measurements were carried out by a CTD and a Moving Vessel Profiler. Likewise, multi-spectral fluorescence casts were performed in selected stations. Other parameters such as temperature, conductivity and in vivo multi-spectral fluorescence were also continuously recorded at surface. From our observations, we discuss on the distinct effect and importance of different factors affecting the phytoplankton distribution. Overall, salinity is the most important parameter modulating not only algae distribution but also the composition of the community in terms of spectral groups. Although below the mixed layer salinity still impacts significantly phytoplankton, vorticity comes into play and becomes the dominant factor determining both distribution and composition. The present study brings into consideration the relevance of the hydrodynamical variables in the study of phytoplankton.

While the dynamics of narrow fjords, i.e. narrow with respect to their internal Rossby radius, have been widely studied, it is only recently that interest in studying the physics of broad fjords was sparked due to their importance in glacial ice melting (in Greenland, especially). Here, we present a comprehensive set of data collected in Fortune Bay, a broad, mid-latitude fjord located on the northwest Atlantic shores. Aside from being wide (15–25 km width) and deep (600 m at its deepest), Fortune Bay also has the characteristics of having steep slopes, having weak tides and being strongly stratified from spring to fall. Thus, and since strong along-shore winds also characterize the region, this system is prone to interesting dynamics, generally taking the form of transient upwelling and downwelling travelling along its shores, similar to processes encountered in broad fjords of higher latitudes. The dataset collected to study those dynamics consists of water column physical parameters (temperature, salinity, currents and water level) and atmospheric forcing (wind speed and direction, atmospheric pressure, air temperature, and solar radiation) taken at several points around the fjord using oceanographic moorings and land-based stations. The program lasted 2 full years and achieved a good data return of 90 %, providing a comprehensive dataset not only for Fortune Bay studies but also for the field of broad fjord studies. The data are available publically from the SEANOE repository (https://doi.org/10.17882/62314; Donnet and Lazure, 2020).

Despite its major role as a global climate regulator, little is known about the recent evolution of the North Atlantic Ocean, especially prior to the fifties, principally because of the lack of long-term instrumental data. Moreover, the North Atlantic Ocean is undergoing rapid changes at the physical scale leading to modifications at the biological scale increasing interest to monitor the environment. The phytoplankton is the base of the ocean life and its perturbation can lead to further changes in the food chain. Recording its dynamics implies to observe both its spatial and temporal variations. This study brings forward the use of the Ba/Ca ratio from shells of the long-living bivalve Arctica islandica collected in the Northwestern Atlantic Ocean near Saint-Pierre and Miquelon (SPM) as a recorder of the past and present phytoplankton dynamics. A high inter and intra-reproducibility and synchrony between Ba/Cashell profiles were demonstrated allowing the reconstruction of a 124 years annually-resolved Ba/Cashell master chronology (from 1893 to 2016). This master chronology was positively correlated to the surface chlorophyll a measured by satellite sensor at regional (around SPM) and global scales (Northwestern Atlantic).