Alonso Hernández-Guerra

• Catedrático at University of Las Palmas de Gran Canaria

The freshwater transport (Mov) by the Atlantic Meridional Overturning Circulation (AMOC) across 34.5°S is computed using observations from 49 eXpendable BathyThermograph (XBT) transects between 2002 and 2019. The Mov at 34.5°S serves as a possible indicator of the AMOC stability, with a negative (southward) freshwater transport indicating a possibl...

The circulation in the Atlantic Ocean is marked by the complex system of pathways of the Atlantic Meridional Overturning Circulation (AMOC). These currents change meridionally due to the interaction with nearby water masses. Hydrographic data provide the opportunity to characterize these currents for the whole water column with high-resolution data...

The Atlantic meridional overturning circulation (AMOC) is central to the climate of the Atlantic by redistributing mass, heat, and freshwater. Hydrographic sections help monitor its strength at different latitudes, and inverse box models provide estimates of AMOC, heat, and freshwater transports. We have used all available hydrographic zonal sectio...

The A20 line is a meridional hydrographic section located at 52ºW that cuts through the western North Atlantic Subtropical Gyre (NASG). It encloses the main paths of the Atlantic Meridional Overturning Circulation (AMOC). Using data from three A20 hydrographic cruises carried out in 1997, 2003 and 2012 together with Acoustic Doppler Current Profile...

The South Atlantic Ocean plays a key role in the heat exchange of the climate system, as it hosts the returning flow of the Atlantic Meridional Overturning Circulation (AMOC). To gain insights on this role, using data from three hydrographic cruises conducted in the South Atlantic Subtropical gyre at 34.5°S, 24°S, and 10°W, we identify water masses...

For the first time, four dedicated hydrographic cruises—one in each season—took place in 2015 around the Canary Islands to determine the seasonality of the flows at the eastern boundary of the North Atlantic Subtropical Gyre. The Canary Current (CC) is the eastern boundary current of the North Atlantic Subtropical Gyre and links the Azores Current...

The circulation in the Atlantic Ocean is marked by the complex system of pathways of the Atlantic Meridional Overturning Circulation (AMOC). These currents change meridionally due to the interaction with nearby water masses. Hydrographic data provide the opportunity to characterize these currents for the whole water column with high-resolution data...

The Atlantic Meridional Overturning Circulation (AMOC) plays a vital role in global climate, redistributing heat, and freshwater. It is predicted to decline due to anthropogenic climate change, with major implications for global climate. Accurately assessing AMOC strength with in situ observations has inspired a number of dedicated observing system...

The global upper ocean has been warming during the last decades accompanied with a chlorophyll‐a (Chl‐a) and productivity decrease. Whereas subtropical gyres show similar trends, Eastern Boundary Upwelling Systems are thought to increase in productivity due to increased trade winds. This study analyzes recent trends in sea surface temperature (SST)...

Poleward undercurrents are well-known features in Eastern Boundary upwelling systems. In the California Current upwelling system, the California poleward undercurrent has been widely studied, and it has been demonstrated that it transports nutrients from the equatorial waters to the northern limit of the subtropical gyre. However, in the Canary Cur...

Data from repeat hydrographic surveys over the 25‐year period 1993 to 2017, together with satellite altimetry data, are used to quantify the temporal and spatial variability of the North Icelandic Irminger Current (NIIC), East Icelandic Current (EIC), and the water masses they advect around northern Iceland. We focus on the warm, salty Atlantic Wat...

Four hydrographic cruises carried out between ~26.5 and 31°N in the eastern North Atlantic Subtropical Gyre in fall (2016 and 2017) and spring (2017 and 2018) are used to identify water masses and infer oceanic circulation. Geostrophic velocities are initially adjusted by referencing them to data from a Lower Acoustic Doppler Current Profiler (LADC...

The genesis and evolution of a sea-breeze front associated with a shallow convection episode at Fuerteventura Island (Canaries archipelago) are investigated using the Weather Research and Forecasting (WRF) numerical model. Three local and two non-local planetary boundary layer (PBL) parametrization schemes are used, and results of the numerical sim...

A World Ocean Circulation Experiment Hydrographic Program along with a Global Repeat Hydrography Program occupied sections along 66°W in the North West Atlantic Ocean in 2003 and 2012. Hydrographic variables, tracers and LADCP measurements were collected in situ. This section together with the North American and South American Coasts create a close...

Transports of suspended particulate (POCsusp) and dissolved (DOC) organic carbon are inferred from a box-model covering the eastern boundary of the North Atlantic subtropical gyre. Corresponding net respiration rates (R) are obtained from a net organic carbon budget that is based on the transport estimates, and includes both vertical and lateral fl...

A South Atlantic ring is studied through remote sensing altimetry, hydrographic stations, and drifters' trajectories. The ring's core was characterized by warmer and saltier Indian Ocean waters. At the time of the cruise, the ring's signature extended radially out to 124 km and vertically down to 2000 m, and its core absolute dynamic topography (AD...

Decadal differences in the Falkland Plateau are studied from the two full-depth hydrographic data collected during the ALBATROSS (April 1999) and MOC-Austral (February 2010) cruises. Differences in the upper 100 dbar are due to changes in the seasonal thermocline, as the ALBATROSS cruise took place in the austral fall and the MOC-Austral cruise in...

The Atlantic meridional overturning circulation (AMOC) is continually monitored along 26°N by the RAPID-MOCHA array. Measurements from this array show a 6.7 Sv seasonal cycle for the AMOC, with a 5.9 Sv contribution from the upper-mid-ocean. Recent studies argue that the dynamics of the eastern Atlantic is the main driver for this seasonal cycle; s...

Decadal differences in the Falkland Plateau are studied from full-depth hydrographic data collected during the ALBATROSS (April 1999) and MOC2-Austral (February 2010) cruises. Differences in the upper 100 dbar are due to changes in the seasonal thermocline, as the ALBATROSS cruise took place in the austral fall while the MOC-Austral in summer. The...

Hydrographic data, SSH from altimetry, thermosalinograph and drifters measurements were acquired along an Agulhas ring during March 2010. Hydrographic survey and drifters deployment were done 5 months after the ring formation. The ring is clearly visible from altimetry and salinity from thermosalinograph data since the surface properties in the cor...

The meridional circulation and transports at 30°S in the Pacific and Indian Oceans for the years 2002-2003 and 2009 are compared, using GO-SHIP hydrographic section data with an inverse box model and several choices of constraints. Southward heat transport across the combined Indian-Pacific sections, reflecting net heating north of these sections,...

CTD and LADCP data measured in October 2014 are used to describe water masses, geostrophic circulation and mass transport in the Eastern Boundary of the North Atlantic Subtropical Gyre. Initial geostrophic velocities are adjusted to velocities from the LADCP data to estimate an initial velocity at the reference layer. Final reference velocities and...

This study examines the seasonal cycle of the Atlantic Meridional Overturning Circulation (AMOC) and its eastern boundary contributions. The cycle has a magnitude of 6 Sv, as measured by the RAPID/MOCHA/WBTS project array at 26°N, which is driven largely by the eastern boundary. The eastern boundary variations are explored in the context of the reg...

Ocean acidification is directly related to increasing atmospheric CO2 levels due to human activities and the active role of the global ocean in absorbing part of this anthropogenic CO2. Here we present an assessment of the pH changes that have occurred along 24.5°N in the Subtropical North Atlantic through comparison of pH observations conducted in...

Transatlantic hydrographic sections along latitudes 7.5N and 24.5N have been repeated with about 20 years difference, at the beginning of the 1990s and 2010s. For each period, an inverse model is applied to the closed box bound by both sections. The model imposes mass conservation for individual layers, defined by isoneutral surfaces, and the whole...

The source of the Canary Current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre (29–37°N, 9–24°W). The Portugal Current is observed between 13.5 and 14.8°W at 37°N carrying inline image Sv southward. This current presumably merges with the eastward trans...

Transatlantic hydrographic sections along latitudes 7.5N and 24.5N have been repeated with about 20 years di erence, at the beginning of the 1990s and 2010s. For each period, an inverse model is applied to the box bound by both sections. The model imposes mass conservation for individual layers, de ned by isoneutral surfaces, and the whole water co...

1] Dinitrogen (N 2) fixation and dissolved organic nitrogen (DON) release rates were measured on fractionated samples (>10 mm and <10 mm) along 24.58N in the subtropical North Atlantic. Net N 2 fixation rates (N 2 assimilation into biomass) ranged from 0.01 to 0.4 nmol N L À1 h À1 , and DON release rates ranged from 0.001 to 0.09 nmol N L À1 h À1 ....

[1] The source of the Canary Current has been inferred from an inverse box model applied to the hydrographic data of a survey carried out in 2009 in the northeast subtropical gyre (29–37°N, 9–24°W). The Portugal Current is observed between 13.5 and 14.8°W at 37°N carrying Sv southward. This current presumably merges with the eastward transport of t...

Meridional transports in the Atlantic Ocean at 7.5N and 24.5N in 1992-1993 and 2010-2011

[This corrects the article DOI: 10.1038/srep00486.].

Del 18 al 29 de octubre de 2010 se llevó a cabo la campaña oceanográfica PROMECA en la parte occidental de la Cuenca Canaria con en el buque oceanográfico García del Cid, figura 1. Uno de los objetivos principales del proyecto se centra en el estudio del sistema de afloramiento noroccidental africano en la región de Cabo Ghir. En dicha región se re...

The eastern boundary of the North Atlantic subtropical gyre (NASG) is an upwelling favorable region characterized by a mean southward flow. The Canary Upwelling Current (CUC) feeds from the interior ocean and flows south along the continental slope off NWAfrica, effectively providing the eastern boundary condition for the NASG.We followa joint appr...

NCEP Wind-stress and temperature and salinity data from Argo have been used together with a steady model to estimate the meridional velocity and volume and heat transport in the Equatorial Indian Ocean for a seven years period (2003-2009). Total volume transport of the wind stress curl shows a northward and southward flow for theWinter and Summer M...

On October 10 2011 an underwater eruption gave rise to a novel shallow submarine volcano south of the island of El Hierro, Canary Islands, Spain. During the eruption large quantities of mantle-derived gases, solutes and heat were released into the surrounding waters. In order to monitor the impact of the eruption on the marine ecosystem, periodic m...

An inverse model to estimate the origin of the Canary Current in Autumn 2009

Changes in environmental parameters such as sea surface temperature, chlorophyll concentration and aerosol optical depth, need to be considered since they are believed to be directly related to climate change. A detailed study has been conducted to obtain several maps highlighting those areas presenting a greater variation. This way, a regional eva...

High-resolution data collected southeast of the Canary Islands during late winter 2006 are analyzed to describe the hydrography and three-dimensional circulation in the coastal transition zone off NW Africa. The data are optimally interpolated over a regular grid, the geostrophic velocity field is calculated and the Q-vector formulation of the omeg...

High spatial resolution hydrographic data, including Lowered Acoustic Doppler Current Profiler (LADCP) measurements, were acquired along a meridional section at 24.5W in October 2009. The data are analyzed in detail with the purpose of definitively defining and quantifying the zonal Azores Current System. The Azores Current and Azores Countercurren...

The upwelling index (UI) obtained from sea surface temperature (SST) images for the period 1987–2006 and remote sensing wind stress were used to analyse the features of the coastal upwelling region off northwest Africa. The seasonal distribution shows a persistent upwelling throughout the year from 20° N to 33° N, seasonal behaviour from 12° N to s...

The ocean surface velocity field in the Cape Blanc region, off Northwest Africa, is investigated with the maximum cross-correlation MCC method applied to channel-4 Advanced Very High Resolution Radiometer satellite images. An initial sensitivity analysis allows us to select the four parameters that provide maximum area coverage and the best velocit...

We have compared historical data from the Nimbus-7 Coastal Zone Color Scanner (CZCS) with recent in situ measurements at the European Station for Time-Series in the Ocean, Canary Islands (ESTOC). CZCS data show an annual winter phytoplankton maximum in January but with a large interannual variation. In sediment traps moored at ESTOC we observed win...

Strong interest in multidecadal changes in ocean temperature and heat transport has resulted in the occupation of the North Atlantic Ocean hydrographic transect along 24.5oN five times since 1957, more than any other transoceanic section in the world. This latitude is chosen because it is where the northward ocean transport of heat in the Atlantic...

One of the longest current meter time series in the Lanzarote Passage in the eastern boundary of the North Atlantic Subtropical Gyre has been used to determine and quantify the 9-year mean transport, the inter-annual and seasonal mass transport variability for the three water masses present in the area. Results show North Atlantic Central Water (NA...

Two 9-yr current-meter and salinity records, together with climatological data, reveal marked seasonal variability of the intermediate flow at a key location in the Canary Basin. The region is characterized by a summer (July-September) and early fall (October) northward progression of Antarctic Intermediate Water followed by a fall (November-Decemb...

Here we present results from sediment traps that separate particles as a function of their settling velocity, which were moored in the Canary Current region over a 1.5-year period. This study represents the longest time series using “in situ” particle settling velocity traps to date and are unique in providing year-round estimates. We find that, at...

Acoustic Doppler Current Profilers (ADCPs) have proven to be a useful oceanographic tool in the study of ocean dynamics. Data from D279, a transatlantic hydrographic cruise carried out in spring 2004 along 24.5 degrees N, were processed, and lowered ADCP (LADCP) bottom track data were used to assess the choice of reference velocity for geostrophic...

The variability of the Canary Current is a widely studied topic regarding its role as eastern boundary of the North Atlantic Subtropical Gyre. The Canary region provides indeed an interesting study area in terms of estimating variability scales of the Subtropical Gyre as well as the water masses dynamics. RAPROCAN (RAdial PROfunda de CANarias - Can...

Using a variety of oceanographic data, including direct volume transports in the Florida Strait, and Argo float profiles and drift velocities at 24°N and 36°N in the North Atlantic, inverse calculations are presented in which the net meridional transport, down to a depth of approximately 1600 m, is estimated at both latitudes for a 5-year period 20...

We report, from remote sensing and in situ observations, a new type of permanent structure in the eastern subtropical Atlantic Ocean, that we call the “Canary Eddy Corridor”. The phenomenon, is a zonal long-lived (>3 months) mesoscale eddy corridor, whose source is the flow perturbation of the Canary Current and the Trade Winds at the Canary Island...

Changes in the coastal upwelling ecosystems need to be accounted for as these structures are responsible for an important percentage of the global fish catch, for the primary and secondary productivity and for the atmosphere-ocean exchange. In this sense, our work aims to assess its impact in the coastal upwelling regions located in the northwest A...

We have estimated the lateral transport and consumption, from surface to 3000 m, of suspended particulate organic carbon (POC), through a box model approach, in the Canary Current region (subtropical northeast Atlantic). Our results show that lateral POC fluxes are up to 3 orders of magnitude higher than vertical fluxes. In the mesopelagic ocean, t...

The relation of upwelling areas with climate variability is an important issue as these areas, where relatively cold and nutrient-rich waters reach the sea surface, both trap heat excess and become increased biological and physical carbon pumps. Here, we investigate the spatio-temporal evolution of the northwest African Upwelling System, with empha...

The distribution of fish larvae in relation to a filament shed from the Northwest African coastal upwelling was studied in February 2001. During the cruise, the filament was located between 27°N and 28°N, extending from the African coastal upwelling zone to the south of Fuerteventura Island (Canary Islands). This filament was trapped and remained o...

The ocean involves a complex set of physical, chemical, biological, and geological processes, interacting with each other to influence our climate and natural environment. One of the most important disciplines in oceanography is the study of the ocean dynamics and, particularly, the ocean surface circulation. One can estimate this by the automated...

Mass transports in the Bay of Biscay for thermocline, intermediate and deep water masses are estimated from a box inverse model applied to hydrographic data from a quasi-synoptic survey carried out in August 2005. The model obeys conservation statements for mass in a volume of ocean bounded by 43 full depth CTD stations in the horizontal, and neutr...

A historical data set is used to describe the coastal transition zone off Northwest Africa during spring 1973 and fall 1975, from 17° to 26°N, with special emphasis on the interaction between subtropical (North Atlantic Central Waters) and tropical (South Atlantic Central Waters) gyres. The near-surface geostrophic circulation, relative to 300 m, i...

Based on hydrographic sections carried out during the last decade in the Canary region at 29° 10′N, we show that there has been a statistically significant rise in temperature and salinity on isobars between 1500 and 2300 db. The maximum increase, found at 1600 db, is occurring at a rate of 0.29°C and 0.047 per decade. Isobaric change decomposition...

The Cape Verde Frontal Zone separates North and South Atlantic Central Waters in the eastern North Atlantic Subtropical Gyre. CTD-O2 and shipboard ADCP data from three hydrographic sections carried out in September 2003 are used to study the structure of the front. Results show the relation between spatial variations of water masses and currents, d...

The Ocean section at 24.5°N has a doubtless interest for climate studies because it is the place where the northward ocean transport of heat throughout the Atlantic has its maximum. Data from the Argo network and from five previous oceanographic cruises are used to quantify the temperature and salinity variation at this latitude. Results show that...

We use hydrographic and buoy data to compare the initial temperature fields and Lagrangian evolution of water parcels in two vortices generated by the southward flowing Canary Current passing around the island of Gran Canaria Island. One vortex is anticyclonic, shed in June 1998 as the result of an incident current of about 0.05ms−1, and the second...

Ocean studies in the 1970s provided an improved knowledge of the coastal upwelling region off NW Africa while in the 1980s and 1990s they led to a good description of the open ocean flow patterns in the Canary Basin. It was not until the late 1990s that major research addressed the open-coastal ocean coupled response. Here we examine the mean and s...

The distribution and abundance of fish larvae was studied along the eastern and southern shelf of Gran Canaria Island (Canary Islands) from July 2000 to June 2001. Oblique bongo hauls were carried out fortnightly during the daytime, coinciding with days of full and new moon. During February, the area was sampled every 2–5 days. About 17.3% of the i...

A trans-oceanic section at 24.5°N in the North Atlantic has been sampled at a decadal frequency. This work demonstrates that the wind-driven component of the Meridional Overturning Circulation (MOC) may be monitored using autonomous profiling floats deployed in the eastern North Atlantic Subtropical Gyre. More than 500 CTD vertical profiles from th...

[1] The large-scale Canary Basin circulation is estimated from a box inverse model applied to hydrographic data from a quasi-synoptic survey carried out in September 2003. The cruise consisted of 76 full depth CTD and oxygen stations. Circulation is required to nearly conserve mass and anomalies of salinity and heat within layers bounded by neutral...

Ocean hydrological sections provide a very useful mean to study the ocean circulation as well as to determine water mass properties and to estimate fluxes. One basic method for their analysis is the spatial interpolation of data, obtained from a set of predefined stations, into a regular grid for contouring isolines and for further calculations. Th...

An atmospheric correction algorithm for the retrieval of sea surface temperature (SST) from the Canary Islands–Azores–Gibraltar area is developed by using a matchup dataset from Advanced Very High Resolution Radiometer (AVHRR) multiple-infrared window channel data and in situ SST data. The improvements and restrictions introduced in the systematic...

1] We use the trajectory of three buoys dragged below the surface mixed layer, together with sea surface temperature imagery, to examine the evolution of an anticyclonic warm-core eddy since its generation by the Canary Islands. Two buoys remain within the eddy during some 100 days, and the third one remains almost 200 days, while drifting southwes...

The surface and upper-thermocline waters of the Canary Basin are characterised by very strong coupling between the open ocean and the coastal upwelling region. Such coupling has its origin in water inflow into the upwelling region north of the Canary Islands and its recirculation south along the continental slope, which is the true Canary Current....

We present hydrographic data for several sections located along the African coastline and off Cape Ghir, carried out at times of weak surface winds (October 1995 and September 1997). The main sections are near the continental slope, at mean distances between 100 and 150 km from the coastline. North of Cape Ghir (31°N) the geostrophic transport (ref...

During Fall 1995 and Fall 1997 two hydrographic cruises were done with the RN Hespérides between the Iberian Peninsula and the Canary ArchipeIago, with special coverage of the Cape Ghir Filament region. XBT, CTD and ADCP measurements are reported for these cruises . Synoptic XBT measurements, using opportunify ships, were also taken along several s...

In March 2002, 20 Argo profilers were deployed in the Subtropical North Atlantic, within the European project Gyroscope. In this contribution we compare the θ-distribution on a hydrographical section along the 24.5°N parallel using two different data sets. The first set consists of the first data transmitted by an array of autonomous profilers depl...

We quantify the mass transport in the Northeastern Subtropical Gyre in each season using an innovatory Lagrangian profiler floats (Apex and Provor). These floats drift with the current at 1700 meter depth, coming up to the surface every 10 days recording temperature and salinity, which is transmitted via satellite to a receiving station. We apply a...

We show the mean and seasonal ocean circulation in the Canary basin, as result from an inverse model. For this purpose, a high-quality data set, obtained during the CANIGO (Canary Islands, Azores and Gibraltar Observations) project, has been used. It is composed of CTD casts carried out in four cruises along the four seasons. Basically, mean surfac...

The dominant periods in time series of sea surface temperature (SST) of the south-eastern North Atlantic are determined and related to atmospheric forcing and ocean dynamics. We analyse five-day composite images of a 10.5-year-long (from 10 July 1981 to 31 December 1991) time series of Advanced Very High Resolution Radiometer (AVHRR) onboard NOAA s...

Observations from a four-year current meter mooring at 28°44′N, 13°28′W in the Lanzarote passage are used to describe the transport variability of the Eastern Boundary Current of the North Atlantic Subtropical Gyre. Three different water masses are found in the passage: North Atlantic Central Water in the upper levels (roughly 0–600m), Antarctic In...

The variability of the Canary Current is investigated using bimonthly expandable bathythermograph sections from Gran Canaria Island to the African coast between November 1996 and September 1998. The geostrophic transport of the easternmost branch of the Canary Current is estimated by integrating the thermal wind equation using the layer of neutral...

To study the Eastern Boundary Current system off Northwest Africa in detail several CTD/ADCP-sections and long-term mooring work were carried out in the channel between Lanzarote and Africa. The observations are compared with a fine resolution model, which was developed in the framework of the CANIGO project. The water masses, which are observed in...

On December 1999 and interdisciplinary survey was carried out in the central basin of the Bransfield Strait. The survey was focussed towards the interdisciplinary sampling (hydrography and distribution/structure of the planktonic community) of the Strait. Several high spatial resolution transects were carried out through regions where in- tense mes...

Sea surface temperature (SST) images illustrate that the surface waters of the Strait of Gibraltar episodically become several degrees cooler than the surrounding waters in the Mediterranean Sea and Atlantic Ocean. It appears that such a variation cannot be due to skin warming effects, the main possible cause being that the flow becomes unstable an...

A World Ocean Circulation experiment Hydrographic Program section along 66°W in the North Atlantic was made in 1997. In addition to the usual variables (hydrographic and tracer) measured in WOCE onetime sections, we made lowered acoustic doppler current profiler (LADCP) measurements at nearly all of the stations. The section closed off a portion of...

A methodology to obtain the sea surface temperature (SST) in the Canary-Azores-Gibraltar area has been developed. The final accuracy of the AVHRR-based SST retrievals depends both on the accuracy of the measured radiance and the accuracy of the SST retrieval algorithm that converts the measured radiance into sea surface temperature. The procedure m...

Publicación online disponible en: http://www.icm.csic.es/scimar/index.php CTD sections carried out in September 1998 are used to describe the water masses, geostrophic circulation and mass transport in the easternmost branch of the Canary Current. The surface water mass (<600 m) consists of North Atlantic Central Water (NACW) flowing south with a n...

Publicación online disponible en: http://www.icm.csic.es/scimar/index.php Two years of periodic XBT data, along seven transects covering the Canary Basin, were examined to analyse the seasonal cycle of the upper layers of the warmwatersphere. This is characterised by seasonal storage/release of heat in the surface mixed layer and by the winter form...

A meridional hydrographic section was made in August-September 1997 at 66°W from the coast of Venezuela to Woods Hole aboard the R/V Knorr. In this report, we concentrate on near surface measurements in the Caribbean. The data show two distinct water masses with different origins. From approximately 14°N to Puerto Rico, Caribbean Surface Water and...

The present knowledge of the marine phanerogams of the Canary Islands is poorly documented. Earlier studies of the marine phytobenthos along the Canarian coasts provides little information on seagrass ecosystems and their distributional patterns. This contribution summarizes the available information about the three species reported for the islands...