Recent Mediterranean Outflow Water and Atlantic Meridional Overturning Circulation correlations

The Atlantic Meridional Overturning Circulation (AMOC) is the main contributor to the heat interchange in the North Atlantic, carrying around 1.5 PW at 25°N, which helps to regulate the climate, especially in Europe. Any slowdown of the AMOC would produce an important decrease in the temperature in the regions around the North Atlantic and also in other parts of the world. A factor that affects the strength of the AMOC is the input of water. While an input of freshwater would produce a reduction in the transport of the AMOC, a supply of salty water, such as the Mediterranean Outflow Water (MOW), would enhance the formation of deep water, strengthening the AMOC, and even stabilizing it. The aim of this work is to determine if the variation of the volume of the MOW is having any effect in the fluctuation of the transport of the AMOC. In order to achieve this, we developed a method to estimate the volume of MOW in the North Atlantic using the Roemmich-Gilson Argo Climatology and compared it with the observations of the AMOC from the RAPID array. Although statistically, there was a low correlation, the similarities between the MOW and RAPID time series were evident, especially for the period 2012-2017. A possible explanation of this resemblance is that the changes that occur in the AMOC also affect the interchange between the Atlantic and the Mediterranean, and therefore the volume of MOW in the Atlantic

Ocean Circulation over Formigas and Ormonde Seamounts

Seamounts constitute an obstacle to the free ocean flow, modifying the patter of circulation. As a result of these alterations, a variety of hydrodynamical processes and phenomena may take place in seamounts, among others, Taylor columns/caps. These oceanographic effects may turn seamounts into very productive ecosystems with high biodiversity. Under these conditions seamounts provide a particularly good environment for the settle of some organisms, acting as stepping stones and contributing to its dispersal. In this study, we verify if these oceanographic effects explain the presence of cold-water corals of Mediterranean origin in the Atlantic. To achieve this, three seamounts in the path of the Mediterranean Outflow Water (MOW) through the Eastern North Atlantic were selected: the Gazul mud volcano, and the Ormonde and Formigas seamounts. In order to determine the hydrographic and dynamical conditions in each one of the three locations, CTD, LADPC and biochemical observations were carried out. Taylor columns were not observed in any of the three sampled areas. Although we found suggestions of upwelling/downwelling systems, their effect was barely noticed in the circulation pattern. The oceanographic processes in those areas are more influenced by the vertical distribution of water masses, which determine the stability of the water column. Moreover, the high values of the Brunt-Väisälä frequency around the MOW halocline can lead to the formation of internal waves. These perturbations in the water column can enhance the vertical mixing, producing suspension, which, in turn, could affect the vertical distribution of cold-water corals

Ocean Circulation over North Atlantic underwater features in the path of the Mediterranean Outflow Water: Ormonde and Formigas seamounts, and the Gazul mud volcano

Seamounts constitute an obstacle to the ocean circulation, modifying it. As a result, a variety of hydrodynamical processes and phenomena may take place over seamounts, among others, flow intensification, current deflection, upwelling, Taylor caps, and internal waves. These oceanographic effects may turn seamounts into very productive ecosystems with high species diversity, and in some cases, are densely populated by benthic organisms, such corals, gorgonians, and sponges. In this study, we describe the oceanographic conditions over seamounts and other underwater features in the path of the Mediterranean Outflow Water (MOW), where populations of benthic suspensions feeders have been observed. Using CTD, LADPC and biochemical measurements carried out in the Ormonde and Formigas seamounts and the Gazul mud volcano (Northeast Atlantic), we show that Taylor caps were not observed in any of the sampled features. However, we point out that the relatively high values of the Brunt–Väisälä frequency in the MOW halocline, in conjunction with the slope of the seamount flanks, set up conditions for the breakout of internal waves and amplification of the currents. This may enhance the vertical mixing, resuspending the organic material deposited on the seafloor and, therefore, increasing the food availability for the communities dominated by benthic suspension feeders. Thus, we hypothesize that internal waves could be improving the conditions for benthic suspension feeders to grow on the slope of seamounts.En prens

iMirabilis2: Cabo Verde oceanographic insights

Cabo Verde Islands are located between the North Equatorial Current (NEC) and the North Equatorial Counter Current (NECC). When the NECC reaches Africa, it splits in two currents, an eastward and a northward flow. This later flow joints the NEC forming a front known as the Cabo Verde Frontal Zone, that acts as a barrier between the North Atlantic Central Waters (NACW) and the South Atlantic Central Waters (SACW). In addition, this northward flow produces a cyclonic circulation in the region of Cabo Verde, called the Guinea Dome, and therefore an upwelling in this area. During the iMirabilis2 expedition, 22 CTD cast were performed in order to characterize the hydrographic conditions and to determine the water mass distribution in the main study areas, to find out its effects on the distribution of benthic organisms. Especial attention was put on the characterization of the Cadamosto seamount. Seamounts are underwater mountains which create a perturbation in the oceanic flow. This perturbation under idealized circumstances, known as Taylor columns, has the potential to isolate the oceanic circulation over the summit from the ocean circulation in the open waters. This can lead to the occurrence of upwelling phenomena that enrich the ecosystem. In this work, we show an overview of the preliminary results of the oceanographic studies conducted during the iMirabilis2 expedition