The upper, deep, abyssal and overturning circulation in the Atlantic Ocean at 30°S in 2003 and 2011

Mass transports for the thermocline, intermediate, deep and abyssal layers in the Atlantic Ocean, at 30°S and for 2003 and 2011, have been estimated using data from GO-SHIP hydrographic transoceanic sections and applying three inverse models with different constraints. The uppermost layers comprise South Atlantic Central Water (SACW) and Antarctic Intermediate Water (AAIW), with a net northward transport in the range of 12.1–14.7 Sv in 2003 and 11.7–17.7 Sv in 2011, which can be considered as the northward returning limb of the Meridional Overturning Circulation (MOC). The western boundary Brazil Current transports twice as much SACW in 2003 (−20.2 ± 0.7 Sv) than in 2011 (−9.7 ± 0.7 Sv). A poleward current consisting of AAIW and Upper Circumpolar Deep Water (UCDW) flows beneath the Brazil Current. The eastern boundary Benguela Current, characterized by a high mesoscale eddy activity, transports 15.6 ± 0.9 Sv in 2003 and 11.2 ± 0.8 Sv in 2011, east of the Walvis Ridge. In the ocean interior, the northward flow is mainly located east of the Mid Atlantic Ridge (MAR) where Agulhas Rings (ARs), observed in both 2003 and 2011, transport warm and salty water from the Indian to the Atlantic Ocean. For the deep layers, the southward transport of North Atlantic Deep Water (NADW) occurs as the Deep Western Boundary Current and also in the eastern basin. The western and eastern basins transport similar amounts of NADW to the south during both years, although the eastern pathway changes substantially between both years. The total NADW transport, which is also considered the MOC, is in the range 16.3–24.5 Sv in 2003 and 17.1–29.6 Sv in 2011, hence with no significant change

Fixed and Drifting Buoys around the National Spanish Waters

Improving the knowledge of the seas surrounding the Iberian Peninsula, Balearic and Canary islands is one of the objectives for the Spanish oceanographic community. For that purpose, a number of fixed and drifting buoys have been deployed in the last 25 years. Parameters measured included sea surface temperature and salinity, ocean current velocity, air temperature, humidity, wave characteristic and wind velocity. The national aim is to increase the quantity, quality, coverage and timeliness of atmospheric and oceanographic data. These observations are used immediately to improve forecast and therefore increase marine safety

The Mediterranean Overflow in the Gulf of Cadiz: A rugged journey

The pathways and transformations of dense water overflows, which depend on small-scale interactions between flow dynamics and erosional-depositional processes, are a central piece in the ocean’s large-scale circulation. A novel, highresolution current and hydrographic data set highlights the intricate pathway travelled by the saline Mediterranean Overflow as it enters the Atlantic. Interaction with the topography constraints its spreading. Over the initial 200 km west of the Gibraltar gateway, distinct channels separate the initial gravity current into several plunging branches depth-sorted by density. Shallow branches follow the upper slope and eventually detach as buoyant plumes. Deeper branches occupy mid slope channels and coalesce upon reaching a diapiric ridge. A still deeper branch, guided by a lower channel wall marked by transverse furrows, experiences small-scale overflows which travel downslope to settle at mid-depths. The Mediterranean salt flux into the Atlantic has implications for the buoyancy balance in the North Atlantic. Observations on how this flux enters at different depth levels are key to accurately measuring and understanding the role of Mediterranean Outflow in future climate scenarios

Gravest Empirical Mode to be used by Inverted Echo Sounders in order to determine the zonal flows in the South Atlantic

Four Pressure-equipped Inverted Echo Sounders (PIES) were deployed at about 10°W, between 19 and 35°S, the South Atlantic Gateway (SAGA), in order to determine the zonal flows in the South Atlantic. Those PIES will allow to observe the circulation of two water masses, the South Atlantic Central Water (SACW) and the North Atlantic Deep Water (NADW), that flow in opposite directions across the South Atlantic, between Cape town and Brazil, through the SAGA. The measurements from the PIES, together with historical hydrographic data, permit to estimate the profiles of temperature and salinity of the water column, and therefore the density. Besides, using the thermal-wind equation, it is possible to retrieve the geostrophic velocity from an array of PIES. In order to get those estimations of temperature and salinity, it is necessary to determine the Gravest Empirical Mode (GEM), a relationship between the acoustic travel time observed by the PIES and the historical observations of salinity and temperature in the study area. In this work, we will show the GEM estimated for the SAGA, calculated using historical hydrographic data from CTDs and Argo Float, as well as, the estimations of the error in the geostrophic transport