Abstract For more than five decades, the Mediterranean Sea has been identified as a region of so‐called thermohaline circulation, namely, of basin‐scale overturning driven by surface heat and freshwater exchanges. The commonly accepted view is that of an interaction of zonal and meridional conveyor belts that sink at intermediate or deep convection sites. However, the connection between convection and sinking in the overturning circulation remains unclear. Here we use a multidecadal eddy‐permitting numerical simulation and glider transport measurements to diagnose the location and physical drivers of this sinking. We find that most of the net sinking occurs within 50 km of the boundary, away from open sea convection sites. Vorticity dynamics provides the physical rationale for this sinking near topography: only dissipation at the boundary is able to balance the vortex stretching induced by any net sinking, which is hence prevented in the open ocean. These findings corroborate previous idealized studies and conceptually replace the historical offshore conveyor belts by boundary sinking rings . They challenge the respective roles of convection and sinking in shaping the oceanic overturning circulation and confirm the key role of boundary currents in ventilating the interior ocean.
MOOSE is a multidisciplinary integrated Ocean observing system part of the French national Research Infrastructure for coastal ocean and seashore observations (ILICO-RI). It was established in 2010 to monitor the Northwestern Mediterranean Sea in the context of rapid climate change and its impacts on marine ecosystems.
Addressing the need for clear communication in Mediterranean oceanography, this study presents a revised and comprehensive catalogue of water mass acronyms. Although there is no universal set of standard rules for assigning acronyms to water masses, as these can vary among different research groups, regions, or scientific communities, scientists generally aim for clarity and consistency when naming and abbreviating water masses to facilitate communication within the scientific community. The team of experts, guided by the CIESM (the Mediterranean Science Commission) C2 Committee on the Physics and Climate of the Ocean, reviewed existing literature and established new acronyms and naming guidelines. This standardized system, emphasizing clarity and consistency, replaces the current variable practices employed by different research groups.
We present here a unique oceanographic and meteorological data set focus on the deep convection processes. Our results are essentially based on in situ data (mooring, research vessel, glider, and profiling float) collected from a multiplatform and integrated monitoring system (MOOSE: Mediterranean Ocean Observing System on Environment), which monitored continuously the northwestern Mediterranean Sea since 2007, and in particular high-frequency potential temperature, salinity, and current measurements from the mooring LION located within the convection region. From 2009 to 2013, the mixed layer depth reaches the seabed, at a depth of 2330m, in February. Then, the violent vertical mixing of the whole water column lasts between 9 and 12 days setting up the characteristics of the newly formed deep water. Each deep convection winter formed a new warmer and saltier “vintage” of deep water. These sudden inputs of salt and heat in the deep ocean are responsible for trends in salinity (3.3 ± 0.2 × 10−3/yr) and potential temperature (3.2 ± 0.5 × 10−3 C/yr) observed from 2009 to 2013 for the 600–2300 m layer. For the first time, the overlapping of the three “phases” of deep convection can be observed, with secondary vertical mixing events (2–4 days) after the beginning of the restratification phase, and the restratification/spreading phase still active at the beginning of the following deep convection event.
The winter of 2012 experienced peculiar atmospheric conditions that triggered a massive formation of dense water on the continental shelf and in the deep basin of the Gulf of Lions. Multi-platforms observations enabled, with an unprecedented resolution, a synoptic view of dense water formation and spreading at basin scale. Five months after its formation, the dense water of coastal origin created a distinct bottom layer up to few hundreds of meters thick over the central part of the NW Mediterranean basin, which was overlaid by a layer of newly formed deep water produced by open-sea convection. These observations highlight the role of intense episodes of both dense shelf water cascading and open-sea convection to the alteration of the characteristics of the NW Mediterranean deep waters.
The cruise KH 2018-709 aboard the Research Vessel Kronprins Haakon was the second process cruise of the project the Nansen Legacy. The cruise contributed to task T1-2, on process studies to investigate the atmospheric, oceanographic, radiative and other physical controls on sea ice and stratification, with a general aim to identify and quantify the processes that control the heat budget north of Svalbard and in the Barents Sea. The cruise aimed to deploy oceanographic moorings and gliders, an AUV, a remotely piloted unmanned aircraft, controlled meteorological balloons, collect underway measurements from ship-mounted ocean current profilers, wind profilers, radiometer and wave sensors, and collect ocean stratification, currents, and microstructure profiles along selected transects across the north Spitsbergen shelf and slope. Additionally, wave sensors were deployed at ice floes from ice edge into pack ice. This report provides an overview of the methods employed and the data collected.
The HYdrological cycle in the Mediterranean Experiment (HyMeX) Special Observing Period 2 (SOP2, January 27–March 15, 2013) was dedicated to the study of dense water formation in the Gulf of Lion in the northwestern Mediterranean. This paper outlines the deep convection of winter 2012–2013 and the meteorological conditions that produced it. Alternating phases of mixing and restratification are related to periods of high and low heat losses, respectively. High-resolution, realistic, three-dimensional models are essential for assessing the intricacy of buoyancy fluxes, horizontal advection, and convective processes. At the submesoscale, vertical velocities resulting from symmetric instabilities of the density front bounding the convection zone are crucial for ventilating the deep ocean. Finally, concomitant atmospheric and oceanic data extracted from the comprehensive SOP2 data set highlight the rapid, coupled evolution of oceanic and atmospheric boundary layer characteristics during a strong wind event.
<p>FUMSECK (Facilities for Updating the Mediterranean Submesoscale - Ecosystem Coupling Knowledge) is a one-week cruise, which took place in spring 2019, in the gulf of Genoa (NW Mediterranean Sea), onboard the R/V T&#233;thys II. It was conducted in preparation of the BioSWOT-Med cruise in the SW Mediterranean Sea in 2022, planned as part of the ``Adopt a Cross Over'' initiative organising simultaneous oceanographic cruises around the world during the SWOT fast sampling phase. During FUMSECK we tested various technological innovations for the study of fine-scale dynamics and their coupling with biogeochemistry.</p><p>By their interactions, the fine scales could induce some ageostrophic and tridimensional dynamics, which are a critical point for the understanding of the vertical exchanges and their effect on biogeochemistry. Therefore, the fine scales play a key role in the oceans global balance and, despite their low intensity, clearly impact processes such as nutriment vertical transfer and carbon export. However, their ephemeral nature complicates their in situ measurements, which are nevertheless essential for their understanding and for the confirmation of the models&#8217; prediction and the satellite observations. Furthermore, measuring vertical velocities in situ represents a real challenge since they are several orders of magnitude below the horizontal ones.</p><p>The FUMSECK cruise benefited from the automatic Lagrangian SPASSO treatment of the satellite data with an onshore team providing a daily bulletin of analysis and guidance on the fine-scale structures in the studied area. The distribution of phytoplankton functional groups at a small spatio-temporal scale was measured by automated flow cytometry with imaging. This technology allows to address the distribution of phytoplankton at fine scales within its hydrodynamic context. Several methods of measuring vertical velocities have been deployed, using different ADCP at fixed depth and in profile, FF-ADCP (Free Fall ADCP), the VVP (Vertical Velocities Profiler) prototype developed at MIO, and a SeaExplorer glider. These methods have shown promising results for in situ measurement of vertical velocities. Overall results show an abrupt change of population associated with a fine-scale structure appearance in relation with a storm event.</p><p>In addition, in order to study the physical part of the biological carbon pump, we experienced the release, following, pumping and detection by cytometry of a sample of biodegradable micro-particles that mimic the phytoplankton, and established a proof-of-concept for this method. Finally, we studied the MVP (Moving Vessel Profiler) instruments behaviour and reduced significantly a rotative effect.</p><p>We will describe the instrumental and analysis methodology deployed during FUMSECK in the study area of the Ligurian Sea, including the Northern Current, and present the results on the fine-scale dynamics and their impact on biology.</p>
<p><span>The study of oceanic vertical velocities arises increasing interest in the oceanographic community. The general interest in the determination of vertical velocities is rooted in their key role for global oceanic balance and their impact on the vertical transfer of nutrients, heat and carbon despite their generally low magnitude </span><span>of </span><span><em>O</em></span><span>(1-100 m day<sup>-1</sup>)</span><span>. With the pressing global warming issues linked to the disturbance of the carbon cycle by anthropogenic activities, estimating vertical velocities becomes an essential information for a better representation of biogeochemical budgets, especially in coastal areas. </span><span>Considering the challenges in directly measuring vertical velocities, numerous studies </span><span>have been</span><span> conducted in highly energetic regions, with estimation of large vertical motions. I</span><span>nstead, i</span><span>n this study, we have estimated vertical velocities based on a method suitable for low-intensity regions, where we expected a magnitude of few mm s</span><sup><span>-1 </span></sup><span>up to cm s</span><sup><span>-1</span></sup><span>.</span></p><p><span>We have develop</span><span>ed</span><span> a new method for direct </span><span><em>in situ</em></span><span> measurement of vertical velocities using data from different Acoustic Doppler Current Profilers (conventional four-beam vs new generation Sentinel-V five-beam ADCPs) following different sampling techniques (lowered vs free falling). We collected data during the FUMSECK cruise in May 2019 in the Ligurian Sea (Northwestern Mediterranean Sea). </span><span>O</span><span>ur analyses provided profiles of vertical velocities of the order of mm s</span><sup><span>-1</span></sup><span>, as expected, with standard deviations of a few mm s</span><sup><span>-1</span></sup><span>. While the fifth beam of the Sentinel-V showed a better accuracy than conventional ADCPs, the free-fall technique provided more accurate measurements compared to the lowered technique.</span></p><p><span>In parallel </span><span>to</span><span> this </span><span><em>in situ</em></span><span> analysis, </span><span>we use the three-hourly fields of the SYMPHONIE circulation model that we implemented over the FUMSECK area during the period of the measurement campaign, using a grid of 1 km horizontal resolution and 60 hybrid "z-sigma" vertical levels. </span><span>Combining </span><span><em>in situ</em></span><span> and numerical data in this study allows us to have a synoptic vision of the temporal evolution of vertical velocities.</span></p><p><span>Some of these measurements were gathered along</span><span> the density front of</span><span> the Northern Current known to be active in terms of vertical dynamics.</span> <span>The Northern Current f</span><span>low</span><span>s</span><span> along the coast; measuring vertical velocities in </span><span>its</span><span> region represents a new way to approach nearshore oceanic processes. </span><span>Moreover, this new information should also represent a key point for the future improvement of altimetry near the coast, especially </span><span>in</span><span> the context of the launch of new generation SWOT altimetry.</span></p><p><span><span>Finally, this innovative study paves the way to measure </span><span>vertical velocities directly </span><span><em>in situ</em></span><span>, by coupling the free-fall technique with a five-beam ADCP. Consequently, we plan to apply these findings in&#160;</span><span>areas characterized by&#160;</span><span>either low or&#160;</span><span>intense vertical dynamics</span>&#160;to improve both the observational and modeling components of oceanic processes.</span></p>
