16Since October 19, 2016, and

<p>The Makarov Basin halocline receives contributions from diverse water masses of Atlantic, Pacific, and East Siberian Sea origin. Changes in surface circulation (e.g., in the Transpolar Drift and Beaufort Gyre) have been documented since the 2000s, while the upper ocean column in the Makarov Basin has received little attention. The evolution of the upper and lower halocline in the Makarov Basin and along the East Siberian Sea slope was examined combining drifting platforms observations, shipborne hydrographic data, and modelled fields from a global operational physical model.</p><p>In 2015, the upper halocline in the Makarov Basin was warmer, fresher, and thicker compared to 2008 and 2017, likely resulting from the particularly westward extension of the Beaufort Gyre that year. From 2012-onwards, cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian slope, with a sharp shift from 155 to 170°E above the 1000 m isobath in winter 2011-2012, followed by a progressive eastward motion after winter 2015-2016 and reached the western Chukchi Sea in 2017. In parallel, an active mixing between upwelled Atlantic water and shelf water along the slope, formed dense warm water which also supplied the Makarov Basin lower halocline.</p><p>The progressive weakening of the halocline, together with shallower Atlantic Waters, is emblematic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime now may extend toward the Amerasian Basin.</p><p><br><br></p>

<div>The investigation is devoted to the development of a regional eddy-resolving model of the ocean of the Subpolar North Atlantic in order to reliably reproduce the components and properties of the Subpolar Gyre and the Atlantic meridional overturning circulation. Using the tools of the NEMO4 model, a configuration was created and, based on the literature, new parametrizations were proposed and implemented in the model: correction of the friction stress (current feedback for forced models), cool skin and warm sublayer in surface turbilent fluxes scheme. Also we formulated the best scheme of horizontal impulse advection from the point of view of reproducing mesoscale vortices. Last but noe least the local-sigma coordinate was implemented in the area of underwater cascading (overflow). For the first time, the eddy-resolving global ocean reanalysis GLORYS12V1 was validated against the independent observational data. The implementation of the local sigma coordinate allowed to reproduce the flow function of the Atlantic meridional overturning circulation in a model with a stepped representation of bathymetry. All the parametrization and scheme innovations led to an improvement in the solution, with the exception of the cool skin parametrization. Physical processes representation in the model is discussed. </div>

<p>We use 25 years of ocean reanalysis to revisit the Malvinas Current, a major route of Antarctic Intermediate Waters, from the South (Drake Passage) to the North (Brazil-Malvinas Confluence) from the synoptic to interannual time scales. The MC mean surface velocity structure evolves as the geometry of the continental slope changes. Over the Malvinas Plateau, the slope is gentle, the MC is rather wide and is organized in two jets. As the slope steepens further north, the jets narrow, intensify and merge at 45°S. The MC appears as stable current over the 25 years connecting two of the major regions with high eddy kinetic energy (Drake Passage and the Brazil Malvinas Confluence). The MC plays a minor role in the velocity variations observed at the confluence at seasonal and interannual scales. Velocity variations at the confluence are related with changes in the intensity of the Brazil Current (BC), in particular, the summer intensification (+15 cm/s at the surface) of the BC (34°-36°S over the slope) advects into a winter intensification and southward displacement of the BC overshoot (40/44°S-54°W).  </p><p>The Malvinas Plateau is a key region for eddy activity dissipation and for water mass properties modification. Winter deep mixed layers occasionally reach 600 m south of 50°S on the Malvinas Plateau, and show large interannual variations. We compute the volume transport in the layer associated with the Subantarctic Surface Waters (SASW), Subantarctic Mode Waters (SAMW) and Antarctic Intermediate waters (AAIW) over sections spanning the 55 -41°S latitudinal range. The transport time series along the Patagonian slope have a mean of 27.1+- 0.1 Sv and a standard deviation decreasing from south (51°S) to north (45°S) from 4.6 and 3.4 Sv. Variations of SASW/SAMW/AAIW transport are small at the seasonal scale; in contrast, the transport times series vary over a range of 5 Sv at the interannual scale.  In general the transport time series covary and show an absolute minimum in 2004 of the order of 23+-2 Sv. This minimum was associated with a unique southward displacement of the BC overshoot leading to a blocking event at 48°S disconnecting the MC from its source in March, followed by a feeding event in May supplying polar waters reducing the SASW/SAMW/AAIW layer volume. Over the 25 years there is a significant freshening trend and no trend in volume transport. </p>

No abstract