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Thank you to the 1396 reviewers who provided 2328 reviews during 2023 to ensure the quality and integrity of JGR‐Oceans manuscripts. Thank you to our 2023 peer reviewers Thank you to our 2023 peer reviewers

Semi‐enclosed marginal seas like the Baltic Sea are often characterized by permanently anoxic deep layers, and may therefore serve as important model systems to study the causes and consequences of the predicted global expansion of oxygen minimum zones. Here, we focus on the role of lateral intrusions in maintaining the “hypoxic transition zone” (HTZ) of the Baltic Sea, which characterizes the quasi‐permanent hypoxic region located between the oxygenized surface layer and the sulfidic deep‐water region. Based on long‐term deployments of an autonomous profiling system in the central Baltic Sea, we show that oxic mid‐water intrusions are ubiquitous features, providing the most important oxygen source for the HTZ, and largely control the vertical and lateral extent of the hypoxic areas. An oxygen budget for the HTZ suggests that oxygen turnover in the HTZ is, to first order, determined by a long‐term balance between sedimentary oxygen demand and oxygen import by intrusions. The downward mixing of oxygen into the HTZ is generally non‐negligible but unlikely to provide a first‐order contribution to the HTZ oxygen budget. On the long‐term average, mid‐water intrusions were shown to inject 30–60 Gmol of oxygen per year into the deep‐water region below the permanent halocline. This is approximately one order of magnitude larger than the average amount of oxygen imported during the massive deep‐water inflow events (Major Baltic Inflows) that occur on an approximately decadal time scale, highlighting the HTZ as a hotspot for biogeochemical turnover.

Thank you to the 1528 reviewers who provided 2647 reviews during 2022 to ensure the high quality and integrity of JGR‐Oceansmanuscripts. The editors thank the 2022 peer reviewersNew editorial practices reduce pressure on reviewersCo‐reviewer tool allows collaboration with students and postdocs The editors thank the 2022 peer reviewers New editorial practices reduce pressure on reviewers Co‐reviewer tool allows collaboration with students and postdocs

Intrusions of large amounts of dense and oxygen‐rich waters during so‐called Major Baltic Inflows (MBIs) form an essential component of the Baltic Sea overturning circulation and deepwater ventilation. Despite their importance, however, detailed observations of the processes occurring in the central basins duringan MBI are virtually lacking. Here data from a long‐term deployment of an autonomous profiling platform located in the center of one of the main basins are presented, providing the first direct and detailed view of the deepwater modifications and dynamics induced by one of the largest MBIs ever recorded (MBI 2014/2015). Approximately, 21 Gmol of oxygen were imported during three distinct inflow phases with an unexpectedly large contribution of oxic intrusions at intermediate depth. Oxygen consumption rates during the stagnation period immediately following the inflow phase was found to be 87 g m−2yr−1with a dominant contribution of sedimentary oxygen demand. The most energetic deepwater processes (topographic and near‐inertial waves) were only marginally affected by the inflow; however, subinertial energy levels associated with intrusions and eddies were strongly enhanced. Turbulence microstructure data revealed that the deep interior regions remain essentially nonturbulent even during the energetic conditions of an MBI, emphasizing the importance of boundary mixing. Warm intrusions frequently showed a temperature fine structure with vertical scales of the order of 0.1 m, without any signs of active turbulence. At the upper flanks of these intrusions, double‐diffusive staircases were often found to develop, suggesting an important alternative mixing process during inflow conditions. One of the largest Major Baltic Inflows sampled with an autonomous underwater winch including temperature microstructureOxygenation of the anoxic bottom water by an import of approximately 21 Gmol of oxygen; inflow can be divided into three distinct phasesNo increase in turbulence levels during the inflow, clear signs of diffusive convection and nonturbulent molecular smoothing

Tidal straining is known to be an important factor for the generation of residual currents and transports of suspended matter in the coastal ocean. Recent modeling studies and field experiments have revealed a new type of “slope‐induced” tidal straining, in which the horizontal density gradient required for this process is induced by the presence of a slope rather than by river runoff (as in classical tidal straining). Slope‐induced tidal straining is investigated here with the help of an idealized numerical model, and results are compared to a recent data set from the East China Sea providing first direct observational evidence. The focus of this study is on the effect of rotation that was ignored in previous investigations. The model is shown to reproduce the key features of the observations, in particular the strain‐induced generation of unstable stratification in the bottom boundary layer during periods of upslope flow. Rotation effects are found to significantly reduce the upslope tidal pumping of suspended material and also give rise to a newly identified pumping mechanism that results in a vigorous transport of suspended material along the slope. It is shown that slope‐induced tidal straining is likely to be relevant for a wide range of oceanic slopes exposed to tidal motions. Observational evidence of slope‐induced straining could be reproduced with a one‐dimensional numerical modelEarth rotation induces a significant along‐slope flux of suspended sedimentWhen the main current is orientated along‐slope, the tidal pumping contribution to the cross‐slope flux is reduced or inverted

JGR‐Oceansreceives many more submissions from a broader demographic of authors than in the past and burnout among reviewers as well as potential bias among editors is threatening excellence and equity at the journal. To confront these issues, we have implemented some new editorial strategies that are anticipated to provide a fairer and more rewarding peer‐review experience for authors, as well as alleviate pressure on reviewers and deliver high quality science for readers. First, we have recruited a dozen new editors from across the world who better reflect our author demographic and who can make wiser and more inclusive decisions about the running of the journal. Second, we now require that each manuscript clearly communicate new understanding about the oceanbefore we send it out for review. This simple rubric deflects potentially biased editorial decisions based on author attributes and brings us closer to the original scope of JGR‐Oceans. Third, we are facilitating a culture of collaboration among reviewers and among ourselves, the editors, that brings more balanced decision‐making to reviews and manuscripts and provides authors more feedback. Our aim is to better help authors communicate their science with confidence and clarity. Finally, JGR‐Oceanshas always been a multi‐disciplinary journal and we are encouraging more submissions that convey new understanding of biogeochemical processes and human interact ocean variability and change. JGR‐Oceanshas diversified the editorial board and implemented new editorial strategies JGR‐Oceanshas diversified the editorial board and implemented new editorial strategies

Observations from the global ocean have long confirmed the ubiquity of thermohaline inversions in the upper ocean, often accompanied by a clear signal in biogeochemical properties. Their emergence has been linked to different processes such as double diffusion, mesoscale stirring, frontal subduction, and the recently discussed submesoscale features. This study uses the central Baltic Sea as a natural laboratory to explore the formation of salinity inversions in the thermocline region during summer. We use realistic high‐resolution simulations complemented by field observations to identify the dominant generation mechanism and potential hotspots of their emergence. We propose that the strongly stratified thermocline can host distinct salinity minima during summer conditions resulting primarily from the interaction between lateral surface salinity gradients and wind‐induced differential advection. Since this is a generic mechanism, such salinity inversions can likely constitute a typical feature of the upper ocean in regions with distinct thermoclines and shallow mixed layers. The upper ocean is characterized by a well‐mixed surface layer, below which temperature decreases rapidly with depth, forming the so‐called thermocline region. A corresponding salinity increase with depth is typically anticipated for stable density stratification to occur. Temperature and salinity inversions can, however, emerge in the upper ocean. Such thermohaline inversions have been observed in different regions of the world's oceans, and various mechanisms have been proposed to explain their generation. Here, the central basin of the Baltic Sea is used as a natural laboratory to explore the formation of distinct salinity minima in the thermocline region during summer conditions. Using high‐resolution numerical simulations and measurements from a field campaign, we show that inversions are abundant and can emerge throughout the entire basin. They increase with increasing wind speeds and concentrate mainly in regions with strong lateral salinity differences. We propose that thermocline salinity minima can occur during summer when the wind transports saltier water over less saline surface waters. This is a generic mechanism that can therefore be responsible for the formation of the salinity inversions observed worldwide in areas with distinct thermoclines and shallow mixed layers. Observations collected in the central Baltic Sea during summer indicate patches of distinct salinity minima in the thermocline regionRealistic high‐resolution simulations are used to explore the origin of the salinity minima and to identify the hotspots of their genesisLateral surface salinity gradients interacting with wind‐induced differential advection are shown to generate most of the inversions Observations collected in the central Baltic Sea during summer indicate patches of distinct salinity minima in the thermocline region Realistic high‐resolution simulations are used to explore the origin of the salinity minima and to identify the hotspots of their genesis Lateral surface salinity gradients interacting with wind‐induced differential advection are shown to generate most of the inversions

High‐resolution water column observations have been carried out in the Wadden Sea to understand suspended particulate matter (SPM) transport in well‐mixed tidal channels. These observations include more than 4000 consecutive CTD, microstructure shear and turbidity profiles from a free‐falling microstructure probe, as well as velocity data from an ADCP and SPM samples for calibration. A horizontal density gradient was established by a landward temperature gradient built up during an extraordinarily warm and calm spring season. Tidal averaging along σ‐layers (relative depth) provides the first direct observations of along‐channel estuarine circulation in the Wadden Sea, with net inflow near the bottom and outflow near the surface. Increased westerly (up‐estuary) winds during the second part of the campaign weakened and eventually even reversed estuarine circulation and yielded a net barotropic eastward transport. SPM concentrations showed a strong quarter‐diurnal signal with maxima near full flood and full ebb and were generally lower during the calm period and increased during the windy period, mainly due to wave‐related resuspension over nearby intertidal flats. The sediment flux analysis was based on a decomposition of the vertically integrated SPM flux into a barotropic advective component, an estuarine circulation component and a tidal pumping component. As a result, tidal pumping (due to ebb‐dominance weakly seaward) dominated the SPM flux during calm conditions, whereas barotropic advection dominated the strong landward SPM flux during the windy period. Along‐channel estuarine circulation is found to be of minor importance for the net SPM transport in such well‐mixed systems. Not estuarine circulation, but tidal pumping dominates SPM transport in well‐mixed estuarine systemsFirst direct observations of estuarine circulation in the Wadden SeaWind forcing has a substantial influence on estuarine circulation and SPM transport

We show that inflows of oxygenated waters into sulfidic layers have a strong impact on biogeochemical transformation at oxic/anoxic transition zones. Taking the pelagic methane dynamics in the Gotland Basin as an example, we performed our studies when one of the largest inflows ever recorded entered the Baltic Sea in March 2015. An inflowing gravity current transported oxic waters into the sulfidic deep layers and freshly generated a near‐bottom secondary redox interface. At the upper slope, where the inflowing water masses were vigorously turbulent and the main and secondary redox interfaces in close contact to each other, methane oxidation rates inside the transition zone were found to be higher compared to the weakly turbulent basin interior. At the main redox interface in the basin center, lateral intrusions of oxygenated waters into intermediate water depth may have stimulated the growth of the methanotrophic community and their activity. Dense gravity currents increase mixing in stagnant basins in the central Baltic SeaIntrusions of oxygenated water impact methane dynamics in anoxic basinsMixing intensity, methane oxidation, and abundance of methanotrophs show a positive correlation

Thank you to the 1,371 reviewers who provided 2,661 reviews during 2021 to ensure the same quality and integrity of JGR‐O manuscripts. The editors thank the 2021 peer reviewers The editors thank the 2021 peer reviewers

Recent results from a tracer release experiment have shown that, similar to many lakes and ocean basins, deep‐water mixing in the Baltic Sea is largely determined by mixing processes occurring in the energetic near‐bottom region. Due to the complexity and small vertical extent of this region, however, previous modeling studies of the Baltic Sea have so far not been able to provide a numerically and physically sound representation of boundary mixing. Here we discuss first results from a nested high‐resolution simulation of the central Baltic Sea that aims at a realistic description of the turbulent bottom boundary layer with the help of new numerical techniques (adaptive coordinates) and state‐of‐the‐art turbulence modeling. Using a comprehensive data set from the Baltic Sea Tracer Release Experiment, we show that the model is able to reproduce the key dynamical processes (near‐inertial waves, topographic waves, and a rim current) with excellent accuracy. Boundary mixing triggered by these processes was found to result in simulated basin‐scale mixing rates in close agreement with observations, including a seasonal variability that has been emphasized in previous studies. These results may be relevant also for the description of mixing in large lakes and other stratified basins. Successful remodeling of interior/boundary mixing processesDominant subinertial motion is a double‐gyre structured topographic wavePassive tracer mixing study using an ensemble experiment

Recently discovered, ocean submesoscales have attracted considerable attention due to their ability to change the upper ocean stratification, affect vertical transport, and induce a downscale cascade of energy toward dissipation. In this paper, we highlight the effect of submesoscale fronts and filaments on surface layer properties and dynamics during storm events, extending previous idealized simulations toward real‐ocean applications. Here, we use the Baltic Sea as a natural laboratory to study the rich submesoscale activity of this system with the help of realistic high‐resolution numerical simulations. These simulations reveal a wealth of cold submesoscale filaments with sharp lateral buoyancy gradients, strong surface convergence, and high vertical velocities. Highly heterogeneous Mixed Layer Depth (MLD) modulations are associated with these features, maintaining locally reduced MLDs even during storm events due to vigorous submesoscale restratification. The interaction of near‐surface turbulence and submesoscale restratification results in strong and highly efficient mixing inside the submesoscale fronts. Focusing on a typical filament, it is shown that frontogenesis is associated with the convergent cross‐front circulation arising from a turbulent thermal wind balance, consistent with previous studies. We show that the sharp fronts generated by this process may become symmetrically unstable, and show enhanced (modeled) energy dissipation rates that are in good quantitative agreement with existing theoretical estimates. Recent studies have revealed that horizontal density differences on scales of 0.1–10 km (submesoscales) are ubiquitous in the surface mixed layer and play an essential role in its evolution. Submesoscale features can restratify, that is, bring warm water above cold water and shallow the depth of the mixed layer, which along with their high vertical velocities, makes them particularly relevant for biology. In this study, we highlight the effect of submesoscales on the restratification process and near‐surface turbulence during the lifetime of storms, thereby extending previous idealized simulations toward real‐ocean applications. We analyze a realistic high‐resolution numerical simulation focusing on the central Baltic Sea, an area where observations from a field campaign confirm that it constitutes a hotspot of submesoscale activity, hence forming an ideal natural laboratory. The simulation reveals a strong lateral temperature gradient that persists during autumn. The basin is found to be rich in submesoscale features that create shallow and heterogeneous Mixed Layer Depths (MLDs). The MLD presents high temporal variability, with the submesoscales being able to maintain shallow MLDs during storms and induce rapid restratification when the wind subsides. Submesoscale restratification tends to counteract the destratification effect caused by atmospheric forcing, yielding stably stratified patches. Using realistic simulations a strong surface front, characterized by intense submesoscale activity, was identified in the central Baltic SeaSubmesoscales maintain shallow mixed layers during storms and induce rapid restratification afterward creating stably stratified patchesThe interaction of near‐surface turbulence and submesoscale restratification results in highly efficient mixing inside submesoscale fronts Using realistic simulations a strong surface front, characterized by intense submesoscale activity, was identified in the central Baltic Sea Submesoscales maintain shallow mixed layers during storms and induce rapid restratification afterward creating stably stratified patches The interaction of near‐surface turbulence and submesoscale restratification results in highly efficient mixing inside submesoscale fronts

Narrow baroclinic fronts are observed in the surface mixed layer (SML) of the Baltic Sea following an autumn storm. The fronts are subjected to hydrodynamic instabilities that lead to submesoscale and turbulent motions while restratifying the SML. We describe observations from an ocean glider that combines currents, stratification, and turbulence microstructure in a high horizontal resolution (150–300 m) to analyze such fronts. The observations show that SML turbulence is strongly modulated by frontal activity, acting as both source and sink for turbulent kinetic energy. In particular, a direct route to turbulent dissipation within the front is linked to shear instability caused by elevated nongeostrophic shear. The turbulent dissipation of frontal kinetic energy is large enough that it could be a significant influence in the evolution of the front and demonstrates that small‐scale turbulence can act as a significant sink of submesoscale kinetic energy. An autonomous ocean glider observed turbulence, currents, and stratification in surface mixed layer submesoscale fronts following a stormSubmesoscale fronts provide both a damping and generation of surface mixed layer turbulenceShear instability within the front could represent a significant energy transfer in frontal evolution

Deep water mixing processes in the largest basin of the Baltic Sea (Gotland Basin) are investigated here with the help of long‐term moored instrumentation and turbulence microstructure measurements. Budgets for heat and salinity reveal a strong temporal variability in the deep water mixing coefficients that is shown to be coupled to the wind forcing down to time scales of individual wind events. Consistent with the results from a simultaneously conducted tracer release experiment, near‐boundary turbulence was identified as the key processes for basin‐scale mixing. Turbulent bottom boundary layers were found to be thick and stable in the flat, deep part of the basin, where highest dissipation rates were observed, and comparatively thin, less energetic, and highly variable on the slopes due to a permanent tendency for boundary layer restratification. In the absence of internal tides, strongly damped basin‐scale topographic waves with periods of a few days, a deep rim current, and, to a smaller extent, near‐inertial waves were identified as the main energy sources for boundary mixing. These results are likely to be relevant also for other medium‐sized stratified basins. Deep water mixing rates coupled to wind eventsSubinertial motions (topographic waves) dominate deep water kinetic energiesTurbulence microstructure measurements confirm importance of boundary mixing

In this study, results from the Baltic Sea Tracer Release Experiment (BATRE) are described, in which deep water mixing rates and mixing processes in the central Baltic Sea were investigated. In September 2007, an inert tracer gas (CF3SF5) was injected at approximately 200 m depth in the Gotland Basin, and the subsequent spreading of the tracer was observed during six surveys until February 2009. These data describe the diapycnal and lateral mixing during a stagnation period without any significant deep water renewal due to inflow events. As one of the main results, vertical mixing rates were found to dramatically increase after the tracer had reached the lateral boundaries of the basin, suggesting boundary mixing as the key process for basin‐scale vertical mixing. Basin‐scale vertical diffusivities were of the order of 10−5m2s−1(about 1 order of magnitude larger than interior diffusivities) with evidence for a seasonal and vertical variability. In contrast to tracer experiments in the open ocean, the basin geometry (hypsography) was found to have a crucial impact on the vertical tracer spreading. The e‐folding time scale for deep water renewal due to mixing was slightly less than 2 years, the time scale for the lateral homogenization of the tracer patch was of the order of a few months. Mixing rates in the Gotland Basin are dominated by boundary mixing processesThe time scale for Gotland Basin deep water renewal is approximately 2 yearsMixing rates determined from the tracer CF3SF5