Detecting the Surface Signature of Riverine and Effluent Plumes along the Bulgarian Black Sea Coast Using Satellite Data

The clear and reliable detection of effluent plumes using satellite data is especially challenging. The surface signature of such events is of a small scale; it shows a complex interaction with the local environment and depends greatly on the effluent and marine water constitution. In the context of remote sensing techniques for detecting treated wastewater discharges, we study the surface signature of small river plumes, as they share specific characteristics, such as higher turbidity levels and increased nutrient concentration, and are fresh compared to the salty marine water. The Bulgarian Black Sea zone proves to be a challenging study area, with its optically complex waters and positive freshwater balance. Additionally, the Bulgarian Black Sea coast is a known tourist destination with an increased seasonal load; thus, the problem of the identification of wastewater discharges is a topical issue. In this study, we analyze the absorption components of the Inherent Optical Properties (IOPs) for 84 study points that are located at outfall discharging areas, river estuaries and at different distances from the shoreline, reaching the open sea area at a bottom depth of more than 2000 m. The calculations of IOPs take into account all available Sentinel 2 cloudless acquisitions for three years from 2017 until 2019 and are performed using the Case-2 Regional CoastColour (C2RCC) processor, implemented in the Sentinel Application Platform (SNAP). The predominant absorber for each study area and its temporal variation is determined, deriving the specific characteristics of the different areas and tracking their seasonal and annual course. Optical data from the Galata AERONET-OC site are used for validating the absorption coefficient of phytoplankton pigment. A conclusion regarding the possibility of distinguishing riverine, marine and coastal water is derived. The study provides a sound basis for estimating the advantages and drawbacks of optical satellite data for tracking the extent of effluent and fluvial plumes with unknown concentrations of optically significant seawater constituents.

Does the interior of the ocean hide a major part of the eddy field?

<p>In ocean research, mesoscale eddies typically are detected through surface signatures based on satellite data. The assumption is that most eddies are surface intensified and have a vertical structure consistent with a surface intensified mode. However, in-situ eddy observations, especially in the tropical oceans, showed that the vertical eddy structure is often more complex than previously assumed (higher baroclinic modes), and a diverse subsurface eddy field is present, which does not show any surface signatures at all. Our objective here is a first step towards a quantification of the occurrence of subsurface relative to surface eddies. To do this, we use an actively eddying model to compare the subsurface eddy field to its surface signatures in order to be able to estimate which vertical eddy structures prevail and how much of the eddy field is hidden in the subsurface. In addition, the model results are compared against an unprecedented assemblage of observations of subsurface eddies in the tropical oceans. In a first step we focus on eddies in the model that are detectable at the surface for more than 120 days. We found that around 60 % of the detected eddies have a vertical structure associated with a surface intensified mode as previously assumed which are characterized by a strong surface signature. Around 40 % of the eddy field have a vertical structure associated to a higher baroclinic mode. They are often called “intrathermocline” eddies and are characterized by a rather weak surface signature. In a second step we track subsurface eddies (lifetime > 120 days) in the model by identifying density layer thickness anomalies and connect them with possible surface signatures. Around 30 % of the total eddy field of the model, are hidden in the subsurface with no detectable surface signature. In conclusion, our results show that subsurface eddies form a substantial contribution to the total eddy field. Consequently it is difficult to estimate the impact of the eddy field on the ocean when only working with surface based satellite data.</p>

Apoptotic Extracellular Vesicles (ApoEVs) Safeguard Liver Homeostasis and Regeneration via Assembling an ApoEV-Golgi Organelle

SummaryApoptosis is an integral physiological cell death process that occurs frequently and generates a huge number of apoptotic extracellular vesicles (apoEVs). However, whether apoEVs are necessary for maintaining organ homeostasis remains unclear. Here, we show that circulatory apoEVs engraft in liver and undergo specialized internalization by hepatocytes (HCs) based on surface signature of galactose and N-acetylgalactosamine. Furthermore, apoEVs rescue liver injury in apoptotic-deficient Fas mutant and Caspase-3 knockout mice, which is exerted by restoring the featured hepatic ploidy homeostasis. Surprisingly, apoEVs form a chimeric organelle complex with recipient Golgi apparatus via SNARE-mediated membrane interaction, which consequently facilitates microtubule organization and HC cytokinesis. Notably, through Golgi recovery and ploidy transition, apoEVs contribute to liver regeneration and protect against acute hepatic failure. Collectively, these results identify a previously unrecognized role for apoEVs and the specific mechanisms by which they safeguard liver homeostasis, and suggest the potential of apoEV-based therapy for liver disorders.

Korteweg-deVriès limitations for the interpretation of SAR images in the Strait of Gibraltar: impact of different stratifications on ISW surface signature.

<p>Internal Solitary Waves (ISW) are particularly large amplitude internal waves which may propagate in the ocean over tens of kilometres while preserving their shape via a balance between non-linearity and non-hydrostatics effects. These waves may have wide impacts on the ocean dynamics (mixing or inducing vertical currents) and on human activities (fisheries, underwater acoustic or offshore activities).</p><p>ISW can be detected on satellite scenes. For instance, they may induce surface currents and thus enhance or damp the capillary waves at the sea surface which signed on the Synthetic Aperture Radar (SAR) scenes. On SAR images, ISW appear as successions of bright and dark bands over a grey background. From these images, the amplitude of the ISW and the depth of the pycnocline may be inferred using the Korteweg-DeVries (KdV) theoretical framework. Several SAR images interpretation methods have been developed based on curve fitting or Peak-to-Peak methods (Zheng et al., 2001) or parametric autoregressive techniques (Le Caillec, 2006). The KdV theory relies on the weakly nonlinear approximation and a Two-Layers Ocean Model (TLOM).</p><p>In Gibraltar Strait, the tidal dynamic leads to strong periodic currents. The exchanges between the Mediterranean sea and the Atlantic ocean occurred according a two layer scheme that maintains large density gradient located at the interface between Atlantic and Mediterranean Waters.  At some tidal outflow, an internal hydraulic jump is formed above Camarinal sill, when the tidal ouflow slackens, it is released and leads to the formation of eastward propagating internal solitary waves. The site is thus considered as an ISW “hot-spot”. Part of the energy carried by these waves propagates eastward into the Alborean Sea, although the stratification may differ from the TLOM.</p><p>If the stratification differs from TLOM, a given surface signature of ISW could match to several configurations of the pycnocline geometry and ISW amplitude, depending on the associated stratification.</p><p>In order to assess the impact of the stratification on the surface signature of the ISW, we implemented an idealized 2DV (one vertical and one longitudinal directions) configuration with the Coastal and Regional Ocean modelling COmmunity model (CROCO) using its non-Boussinesq (pseudo compressible) capability. The bathymetry and the density profile are inspired from oceanic observations. The tidal forcing is simplified to a pure monochromatic M2 tide.</p><p>First, simulations are initialized with a two-layer density profile and different pycnocline depths. Then, we added continuous stratification in each of the two (surface/bottom) layers. We tested also several tidal regimes in order to represent the various strengths between the neap and spring tide. SAR images interpretation techniques are then tested in each configurations. Pycnocline depths and ISW amplitudes computed from SAR methods are then compared with the ones initially simulated by the CROCO model.</p><p> </p><p>Le Caillec, J.-M., 2006. Study of the SAR signature of internal waves by nonlinear parametric autoregressive models. IEEE Trans. Geosci. Remote Sens. 44, 148–158. https://doi.org/10.1109/TGRS.2005.859954</p><p>Zheng, Q., Yuan, Y., Klemas, V., Yan, X.-H., 2001. Theoretical expression for an ocean internal soliton synthetic aperture radar image and determination of the soliton characteristic half width. J. Geophys. Res. Oceans 106, 31415–31423. https://doi.org/10.1029/2000JC000726</p>

Coupling of Arctic ozone and stratospheric dynamics and its influence on surface climate: the role of CFC concentrations.

<p>Arctic stratospheric ozone has been shown to exert a statistically significant influence on Northern Hemispheric surface climate. This suggests that Arctic ozone is not only passively responding to dynamical variability in the stratosphere, but actively feeds back into the circulation through chemical and radiative processes. However, the extent and causality of the chemistry-dynamics coupling is still unknown. Since many state-of-the-art climate models lack a sufficient representation of ozone-dynamic feedbacks, a quantification of this coupling can be used to improve intra-seasonal weather and long-term climate forecasts.</p><p>We assess the importance of the ozone-dynamics coupling by performing simulations with and without interactive chemistry in two Chemistry Climate Models. The chemistry-dynamics coupling was examined in two different sets of time-slice simulations: one using pre-industrial, and one using year-2000 boundary conditions. We focus on the impact of sudden stratospheric warmings (SSW) and strong vortex events on stratosphere-troposphere coupling, since these go along with strong ozone anomalies and therefore an intensified ozone feedback.  We compare the runs with and without interactive chemistry.</p><p>For pre-industrial conditions, simulations without interactive ozone show a more intense and longer lasting surface signature of SSWs compared to simulations with interactive chemistry. Conversely, for year-2000 conditions, the opposite effect is found: interactive chemistry amplifies the surface signature of SSWs. Following these results, atmospheric CFC concentrations, which differ greatly in the pre-industrial and year-2000 runs, determine the sign of the ozone-circulation feedback, and thus have a strong impact on chemistry-climate coupling. Implications for modeling of stratosphere-troposphere coupling and future projections are discussed.</p>