Search

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

Since the beginning of the 1980s, deep convection has ceased in the Greenland Sea. The effects of this halt on the intense warming and salinification of Greenland Sea deep waters and on the “dome collapse” (sinking of the dome) have been intensively studied. However, their causes and the potential outflow of Greenland Sea deep and bottom waters toward southern adjacent basins have remained less investigated and are the focus of this work. Combining oceanic and atmospheric in situ data, together with satellite and reanalysis data, it is found that there is not a unique factor responsible for the halt of deep convection in the Greenland Sea. Changes in the Ekman pumping seem to only explain one tenth of the observed deepening of isopycnals of 1,300 m in the central Greenland Sea (dome collapse). Since the early 1980s, in addition, a decrease in the mean net heat loss from the ocean to the atmosphere and in the intensity and number of intense heat loss events would have contributed to the decrease in both the intensity of convective mixing and the generation of dense deep waters. The generation of waters not sufficiently dense to contribute to the reservoir of water below the Greenland Sea dome would have led to its emptying and sinking. More importantly, it is found that in situ evidence of a sustained bottom-water upwelling driven by a secondary circulation cell whose major role in ventilating and draining the Greenland Sea deep and bottom waters has been largely underestimated., Sí

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

In April – November 2009, surface salinity data provide a good coverage of most of the south-east Bay of Biscay and nearby Aquitaine/Armorican shelves. By late April most of the shelf, in particular south of 46°N, is covered by a fresh surface layer amounting to a fresh water volume of 49·10 9 m 3 . At that time, a moderate amount of fresh water has spread over the Landes Plateau. By mid-June, this shelf water penetrates over the Cape Ferret Canyon north of the Landes Plateau. By mid-July, it is found west of the Landes Plateau to at least 4°W, with an estimated fresh-water content of 11 – 14·10 9 m 3 . Drifters deployed on June 17 in the Cape Ferret Canyon, or later on the shelves, con fi rm the spreading of shelf fresh-water over the deep ocean. Lagrangian tracking using altimetric products, also con fi rms the transport by a quasi-stationary circulation. Operational numerical simula- tions (PREVIMER, IBI, HYCOM) display this spread of the freshwater, but in different areas. In particular, all have some fresh water escaping westward near the coast in the Basque region, which is not observed. Later in the summer season, the fresh water spreads westward to south-westward and along the shelf break to at least 5.5°W in late September.

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

In order to reinforce its contribution to the ocean monitoring, the Spanish Institute of Oceanography (IEO) deployed in June 2007 an oceanic-meteorological buoy (AGL Buoy, 43°50.67' N; 003°46.20' W, and 40 km offshore, www.boyaagl.st.ieo.es/) in the southern Bay of Biscay. The buoy is equipped with a suite of field-proven sensors for the measurement of atmospheric and hydrological parameters at the air-sea interface but also with other more experimental biogeochemical and radiative heat fluxes sensors. The measurements from the first group of sensors only require a validation procedure to obtain high quality in situ data time series. For the second, obtaining a reliable data set from these measurements requires a considerable effort on data analysis and careful calibration. Because the importance to obtain high quality in situ data, especially for high frequency time-series less available nowadays yet, the different validation/calibration procedures developed for the AGL buoy are described in this work.

Severe storms happen every year in the North coast of Spain. If certain weather and oceanic conditions match, they can be quite destructive, both for ships and structures on the sea and buildings, cars, people or city furniture on land. Systems of meteorological and oceanographic observations are fundamental tools for improve the prediction models and help to reduce the impact of storms on ships, coastal structures and people and improve the security at sea and along the coast. On November 2010 a severe storm took place at the southern Bay of Biscay causing important damage. The relevant aspects of this storm will be studied and compared with previous storms in December 2007, March 2008 and January 2009, leaving this last one a record wave of 26.13m measured at the Augusto Gonzalez de Linares (AGL) buoy. On June 2007, the IEO moored the AGL ocean-meteorological Buoy, 22 miles north of Santander over about 2850m depth, at the position 43°50.67'N, 3°46.2'W to complete the ocean information with the ocean-atmosphere interaction. This buoy is integrated seamlessly in the national buoy network, contributing with its data to oceanographic research, operative ocean-meteorological predictions and seasonal climate predictions. This applications will also be shown in this paper. The AGL buoy is equipped with several sensors, meteorological, oceanographic and biologic. Some relevant parameters than can be obtained from these sensors are: air temperature, wind speed and direction, humidity, air pressure, water temperature, wave height and direction, wave periods, current speed and direction in the first 100m of water, salinity, fluorescence and dissolved oxygen concentration. All the data obtained from the buoy is stored internally and some other parameters are transfered hourly to the Santander IEO center via satellite. The data stored in the buoy is recovered and deployed on every buoys maintenance operation, which takes place three times a year. During the storms in 2007, 2008 and 2009 the AGL buoy measured significant wave heights of more than 10m for all of them, translating to maximum wave heights of 15.22m, 19.77m and 26.13m respectively. The storm in 2010 produced smaller significant wave heights than the previous ones, but during almost all the storm period (November 8th, 9th and 10th) this parameter was always above 6 meters. This persistence made it more destructive in economic terms. Sustained strong winds generated also a continuous pattern of high height waves which reached the coast during spring tides and where the mean water level was also at a maximum value, 0.34 meters over the mean of the corresponding month and 0.46 meters over the annual mean, and, finding tidal residuals up to 0.40 meters at high water level. The weather conditions that raised these waves will be studied and compared deeply in this paper. For this purpose, the help of meteorological models is invaluable.

17 páginas, 9 figuras, 5 tablas., We analyzed the effect of physical forcing on zooplankton biomass distribution in the Strait of Gibraltar as a function of tidal phase. A set of 5 Longhurst-Hardy-Plankton-Recorder (LHPR) casts were made along the main channel of the Strait during different phases of the tidal cycle to determine how the hydrological processes taking place in the strait (mainly internal wave generation) influenced the distribution and taxonomic composition of zooplankton biomass. A CTD coupled to the LHPR net allowed a detailed study of the hydrological patterns created by the generation and development of the internal waves. Plankton samples were analyzed using a semi-automatic method for zooplankton discrimination (plankton visual analyzer) which is able to differentiate each individual within a sample into specific taxonomic groups. The results show that the internal wave generation on the main channel of the strait induces divergent processes causing a reduction of the zooplankton biomass. Flow patterns within the internal waves lead to alternating bands of high and low zooplankton biomass with varying taxonomic composition. Changes in taxonomic composition appear to be the result of spatial differentiation between smaller (weak-swimming) and larger (strong-swimming) taxa. This work demonstrates the necessity to consider and understand physical processes when addressing biological patterns, especially in regions with intense hydrodynamic regimes., This work was funded by the Spanish National Research Program, Project CTM2005-08142-C03-01 and CTM2008-06124. D.M. was supported by the Spanish Postdoc Fellowship Program (contract no. EX2008-0394).

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

From 1991, shelf and slope waters of the Southern Bay of Biscay are regularly sampled in a monthly hydrographical line north of Santander to a maximum depth of 1000m, as part of the IEO Radiales project. From 2003, a deep hydrological standard sections (part of the VACLAN project) is occupied twice a year extending the Santander section 90 miles offshore. Measurements include CTDO2, nutrients and currents from vessel-mounted ADCP and LADCP. The data base in the area hold by IEO is complemented with a current meters line moored in 2003 at 43deg48'N, 3deg 47'W sampling temperature, salinity and currents at the core of Central, Mediterranean and Labrador Sea water. On June 2007, an ocean-meteorological Buoy was moored at the Santander Section, 22 miles north of Santander at about 2850m depth, to complete the ocean information with the ocean-atmosphere interaction. The Santander section and AGL Buoy data highlight that heat and salt show a quite different behaviour in terms of their balance in the upper layers of the Bay of Biscay. At interannual and seasonal timescales temperature is mainly determined by the atmospheric forcing while salinity is more closely linked to advection processes. Finally, a severe storm developed in the Bay of Biscay on January 24, 2009 is described. The AGL buoy registered an individual maximum wave of 26.1m, the largest ever recorded by the Spanish buoy Networks.