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 Current upwelling system, the Canary intermediate poleward undercurrent (CiPU) has not been properly characterized, despite recent studies arguing that the dynamics of the eastern Atlantic play an important role in the Atlantic meridional overturning circulation, specifically on its seasonal cycle. Here, we use trajectories of Argo floats and model simulations to characterize the CiPU, including its seasonal variability and its driving mechanism. The Argo observations show that the CiPU flows from 26°N, near Cape Bojador, to approximately 45°N, near Cape Finisterre, and flows deeper than any poleward undercurrent in other eastern boundaries, with a core at a mean depth of around 1000 dbar. Model simulations manifest that the CiPU is driven by the meridional alongshore pressure gradient due to general ocean circulation and, contrary to what is observed in the other eastern boundaries, is still present at 1000 dbar due the pressure gradient between the Antarctic Intermediate Waters in the south and Mediterranean Outflow waters in the north. The high seasonal variability of the CiPU, with its maximum strength in fall, and the minimum in spring, is due to the poleward extension of AAIW, forced by Ekman pumping in the tropics.

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 and compute absolute geostrophic circulation using inverse modeling. In the upper layers, the currents describe the South Atlantic anticyclonic gyre with the northwest flowing Benguela Current (26.3 ± 2.0 Sv at 34.5°S, and 21.2 ± 1.8 Sv at 24°S) flowing above the Mid‐Atlantic Ridge (MAR) between 22.4°S and 28.4°S (−19.2 ± 1.4 Sv), and the southward flowing Brazil Current (−16.5 ± 1.3 Sv at 34.5°S, and −7.3 ± 0.9 Sv at 24°S); the deep layers feature the southward transports of Deep Western Boundary Current (−13.9 ± 3.0 Sv at 34.5°S, and −8.7 ± 3.8 Sv at 24°S) and Deep Eastern Boundary Current (−15.1 ± 3.5 Sv at 34.5°S, and −16.3 ± 4.7 Sv at 24°S), with the interbasin west‐to‐east flow close to 24°S (7.5 ± 4.4 Sv); the abyssal waters present northward mass transports through the Argentina Basin (5.6 ± 1.1 Sv at 34.5°S, and 5.8 ± 1.5 Sv at 24°S) and Cape Basin (8.6 ± 3.5 Sv at 34.5°S–3.0 ± 0.8 Sv at 24°S) before returning southward (−2.2 ± 0.7 Sv at 24°S to −7.9 ± 3.6 Sv at 34.5°S), without any interbasin exchange across the MAR. In addition, we compute the upper AMOC strength (14.8 ± 1.0 and 17.5 ± 0.9 Sv), the equatorward heat transport (0.30 ± 0.05 and 0.80 ± 0.05 PW), and the freshwater flux (0.18 ± 0.02 and −0.07 ± 0.02 Sv) at 34.5°S and 24°S, respectively.

<p>The European Union aims to achieve carbon neutrality by 2050. Therefore, it is crucial to increase the use of renewable energy. One clean energy source is the wind, and during the last decades, several countries have developed wind farms, not only on land but also in the ocean. Most offshore wind farms have been installed in shallow waters; however, recently, open ocean offshore floating wind farms are being installed in deep waters due to stronger and steadier wind occurring in these areas. Thus, offshore wind turbines are a potential new source of underwater noise. Noise can propagate underwater having the potential to affect marine mammals and fish, among others. Floating wind turbines are known to reduce the installation and decommissioning noise in contrast to fixed-bottom turbines but, nevertheless, the noise produced by the operation of the turbines and the anchoring systems have been scarcely studied, and it is still unknown whether added noise could significantly affect behavior or even hearing capacity in the long term. In the framework of the JONAS European project we anticipate a regional use case with a future installation of a commercial offshore wind farm, to determine how noise would propagate in the region, from installation to operation, and potentially impact (or not) local fauna, focusing initially on mammal groups. In this study, we use the RAM model (Range-dependent acoustic model) which is a parabolic equation (PE) code that calculates the propagation of sound in the ocean using the split-step Padé solution. RAM needs information about the temperature and salinity in the water column to calculate sound speed profiles, as well as the bathymetry and a geo-acoustic model of the bottom. It returns the transmission loss depending on the depth and distance to the source. We have applied the RAM model to an area located in the southeast of Gran Canaria Island, where a plan for a floating wind farm is under consideration. Results and suggestions about the negative impact on marine mammals known to live in this location are presented.</p>

At the eastern region of the North Atlantic Subtropical Gyre, the Canary Current (CC) connects the Azores Current with the North Equatorial Current (Hernández-Guerra et al., 2005;Pérez-Hernández et al., 2013) (Figure 1a). The first studies carried out in the region used historical hydrographic data to determine the existence of a seasonal change in the structure of the eastern subtropical gyre. These studies found a CC flowing closer to the African coast in summer and through the western islands in winter (Stramma & Isemer, 1988;Stramma & Müller, 1989). Using one hydrographic cruise per season carried out between Madeira and north of the Canary Islands (at 28-32°N) in and 1998, Machín et al. (2006 reported that the CC presents a seasonal cycle characterized by a southward mass transport of −1.7 ± 1.0 Sv in winter, −2.8 ± 1.0 Sv in spring, −2.9 ± 1.1 Sv in summer, and −4.5 ± 1.2 Sv in fall with a shift westward from spring to fall. Pérez-Hernández et al. (2013) confirmed that CC migrates west of the Canary Islands in fall and described a mass transport of −5.8 ± 0.2 Sv southward. In addition, both Fraile-Nuez and Hernández-Guerra (2006) using Argo data, and Mason et al. (2011)

<p>The A20 is a meridional hydrographic section located at 52ºW on the western North Atlantic Subtropical Gyre that encloses the path of the water masses of the Atlantic Meridional Overturning Circulation (AMOC). Using data from three A20 hydrographic cruises carried out in 1997, 2003 and 2012 together with LADCP-SADCP data and the velocities from an inverse box model, the circulation of the western North Atlantic Subtropical Gyre is estimated. The main poleward current of the AMOC is the Gulf Stream (GS) which carries 129.0±10.5 Sv in 2003 and 110.4±12.2 Sv in 2012. Due to the seasonality, the GS position is shifted southward in 2012 - relative to that of 2003 - as both cruises took place in different seasons. In opposite direction, the Deep Western Boundary Current (DWBC) crosses the section twice, first at 39.3-43.2ºN (-34.9±7.5 Sv in 2003 and -25.3±9.4 Sv in 2012) and then at 7.0-11.7ºN (42.0±8.0 Sv in 2003 and 48.0±8.1 Sv in 2012). Additionally, two zonal currents contribute with westward transport below 20ºN: the North Equatorial Current and the North Brazil Current; with a net value of -28.0±4.1 Sv in 2003 and -36.7±3.6 Sv in 2012.</p>