Antonio Gonzalez Ramos

The Cape Verde Frontal Zone in the eastern North Atlantic Subtropical Gyre is a complex region where the warmer North Atlantic Central Water interacts with the colder South Atlantic Central Water, forming the Cape Verde Front (CVF) with a sharp thermohaline gradient. The CVF exhibits high variability due to lateral intrusions, upwelling system filaments, and mesoscale and submesoscale eddy fields. In November 2017, the FLUXES project surveyed the CVZ extensively using shipborne conductivity, temperature, and depth (CTD) measurements, a SeaSoar and two deep gliders equipped with biochemical and dynamical instruments. The primary objective of this paper is to intercompare the spatial scales recovered by the different sampling methods in the CVF, incorporating Copernicus numerical model outputs. Wavelet analysis is used for a quantitative assessment of scales resolved by different sampling methods. The results highlight shipborne CTD depth, down to 1500 m, SeaSoar speed, with a 14 h sampling time, and specific capabilities of both the gliders and the SeaSoar in capturing small scales of between 1 and 5 km. The gliders slightly outperformed the SeaSoar in spatial resolution, emphasizing their effectiveness in revealing smaller features in this dynamic zone.

In recent decades, numerous marine species have changed their distribution ranges due to ocean warming. The Spotfin burrfish, Chilomycterus reticulatus, is a reef fish with a global distribution along tropical, subtropical and warm-temperate areas of the Pacific, Indian and Atlantic oceans. In this work, we analyzed the presence of this species, between 1990 and 2019, at two islands of the Canarian Archipelago under varying oceanographic conditions: El Hierro (the westernmost island, under more tropical conditions) and Gran Canaria (a central-east island, under more cooler conditions). We expected that, under increased ocean temperatures in recent decades, the number of sightings has increased in Gran Canaria relative to El Hierro. We compiled information from different sources, including interviews and local citizenship databases. A total of 534 sightings were reported: 38.58% from El Hierro and 61.43% from Gran Canaria. The number of sightings on Gran Canaria has significantly increased through time, at a rate of 0.1 sightings per year; at El Hierro, however, the number of sightings has not significantly changed over time. Sea Surface Temperature has linearly increased in both El Hierro and Gran Canaria islands over the last three decades. Positive Sea Surface Temperature anomalies, particularly in 1998 and 2010, including high winter minimum temperatures, provide an ideal oceanographic context to favour the arrival of new individuals and, consequently, the increase in the number of sightings in Gran Canaria. Still, potential donor areas of fish recruits remain unknown.

The eruption of a submarine volcano south of El Hierro Island (Canary Islands) in October 2011 led to major physical and chemical changes in the local environment. Large amounts of nutrients were found at specific depths in the water column above the volcano associated with suboxic layers resulting from the oxidation of reduced chemical species expelled during the eruptive phase. It has been suggested that the fertilization with these compounds enabled the rapid restoration of the ecosystem in the marine reserve south of the island once the volcanic activity ceased, although no biological evidence for this has been provided yet. To test the biological fertilization hypothesis on the pelagic ecosystem, we studied the evolution and variability in chlorophyll a, from in situ and remote sensing data, combined with information on phytoplankton and bacterial community structure during and after the eruptive episode. Remote sensing and in situ data revealed that no phytoplankton bloom took place neither during nor after the eruptive episode. We hypothesize that the fertilization by the volcano did not have an effect in the phytoplankton community due to the strong dilution of macro- and micronutrients caused by the efficient renewal of ambient waters in the zone.

Transoceanic Gliders are Autonomous Underwater Vehicles (AUVs) for which there is a developing and expanding range of applications in open-seas research, technology and underwater clean transport. Mature glider autonomy, operating depth (0–1000 meters) and low energy consumption without a CO₂footprint enable evolutionary access across ocean basins. Pursuant to the first successful transatlantic glider crossing in December 2009, the Challenger Mission has opened the door to long-term, long-distance routine transoceanic AUV missions. These vehicles, which glide through the water column between 0 and 1000 meters depth, are highly sensitive to the ocean current field. Consequently, it is essential to exploit the complex space-time structure of the ocean current field in order to plan a path that optimizes scientific payoff and navigation efficiency. This letter demonstrates the capability of dynamical system theory for achieving this goal by realizing the real-time navigation strategy for the transoceanic AUV named Silbo, which is a Slocum deep-glider (0–1000 m), that crossed the North Atlantic from April 2016 to March 2017. Path planning in real time based on this approach has facilitated an impressive speed up of the AUV to unprecedented velocities resulting in major battery savings on the mission, offering the potential for routine transoceanic long duration missions.

After Bakun (1990) formulated his hypothesis of upwelling intensification caused by increasing global warming, contradictory results have been published on whether primary productivity is increasing or decreasing in Eastern Boundary Upwelling Ecosystems (EBUE). The present work is focused in comparing three net primary production (NPP) models—the VGPM (Vertically Generalized Production Model), the Eppley-VGPM and the CbPM (Carbon-based Production Model)—in the Canary Current (CanC) EBUE during the 1998–2015 period, making use of both SeaWiFS (Sea-viewing Wide Field-of-view Sensor) and MODIS (MODerate-resolution Imaging Spectroradiometer) derived data. We looked for the first time for seasonal to interannual trends of NPP under a regional perspective, with the aim of searching for temporal patterns that could support or reject the intensification hypothesis. According to previous studies based on the seasonality of the upwelling regime, the CanC EBUE was divided into three subregions: a seasonal upwelling zone (SUZ; 13–20°N), a permanent upwelling zone (PUZ; 20–26°N) and a weak permanent upwelling zone (WPUZ; 26–33°N). Although differences in the output of the models are important, both at regional and subregional scales, our analyses do not show significant increasing trends in NPP with any of the productivity models used. Our results are in accordance with previous published studies that indicate, that unlike other EBUE, winds have weakened (or at least not intensified) in the CanC upwelling over time scales ranging up to 60 years. Nevertheless, the comparison made in this work shows disagreements between some of the best-known NPP models and calls for a validation effort in this region. Seasonal to decadal anomalies of NPP and sea-surface temperature (SST) are estimated and analyzed in relation to selected climate indices, yielding only significant correlations between SST and the North Atlantic Oscillation (NAO) indices.

With recent developments in battery technology and ocean energy harvesting systems, biological fouling, or biofouling, a process referring to the gradual accumulation of organisms on underwater surfaces, has gained a foothold as the primary adversary in long-duration autonomous underwater vehicle (AUV) flights of the Challenger glider mission. Limiting biofouling on long-duration AUVs is essential to the success of the flight. Inverse relationships and correlations were drawn between biofouling, vertical velocity of the AUV, and in turn, steering capability. As organisms settle and grow on the AUV, the hydrodynamics of the vessel changed, resulting in larger volume and more drag, adding buoyancy discrepancies as well. The increased drag results in a lower vertical velocity, and therefore less water flow over the rudder, or fin, directly causing the reduction in steering capability. Additionally, the organisms were not evenly distributed about the AUV, causing an imbalance in the drag. The fin then needed to maintain an offset to counteract this imbalance, resulting in less overall range in fin movement, further reducing the ability to steer. Analysis of the data from four separate legs of ocean basin crossings has shown that as the AUV begins to foul, it needs to maintain a vertical velocity of greater than 12 cm/s to maintain viable steering. Overall the fin will move more as it attempts to compensate for biofouling, which will use additional power throughout the duration of the flight, bringing power budgets back into the equation. Although the biofouling issues facing long-duration AUVs are subject to the same settling processes as boats and ships, porting commercially available antifoulant technologies from larger, faster vessels to the AUVs has proven challenging. Non-like metals combined with biofilms can result in increased galvanic corrosion, so copper coating compounds on steel components and aluminum AUV hull are not ideal, particularly with limited space and weight for sacrificial anodes. Ablative paints, by design, can wear away, causing possible ballast issues while failing to prevent fouling. Biocides, for obvious reasons, have not been in the list of candidates for consideration in the ongoing battle against biological growth. We introduced some behavioral modifications in the flight characteristics of the AUV that provided some assistance. For example, we avoided the majority of the warmer and illuminated euphotic zone, where primary production occurred, or zones above a certain temperature range that could hamper organism growth, even if it was not possible to prevent settling. This paper will explore the differences in biofouling, flight environment, preventative measures, and lessons learned on the four legs of ocean basin crossings completed by two separate Slocum electric gliders, part of the Rutgers AUV fleet.

The Copernicus Marine Environment Monitoring Service (CMEMS) Ocean State Report (OSR) provides an annual report of the state of the global ocean and European regional seas for policy and decision-makers with the additional aim of increasing general public awareness about the status of, and changes in, the marine environment. The CMEMS OSR draws on expert analysis and provides a 3-D view (through reanalysis systems), a view from above (through remote-sensing data) and a direct view of the interior (through in situ measurements) of the global ocean and the European regional seas. The report is based on the unique CMEMS monitoring capabilities of the blue (hydrography, currents), white (sea ice) and green (e.g. Chlorophyll) marine environment. This first issue of the CMEMS OSR provides guidance on Essential Variables, large-scale changes and specific events related to the physical ocean state over the period 1993–2015. Principal findings of this first CMEMS OSR show a significant increase in global and regional sea levels, thermosteric expansion, ocean heat content, sea surface temperature and Antarctic sea ice extent and conversely a decrease in Arctic sea ice extent during the 1993–2015 period. During the year 2015 exceptionally strong large-scale changes were monitored such as, for example, a strong El Niño Southern Oscillation, a high frequency of extreme storms and sea level events in specific regions in addition to areas of high sea level and harmful algae blooms. At the same time, some areas in the Arctic Ocean experienced exceptionally low sea ice extent and temperatures below average were observed in the North Atlantic Ocean.