18We present a new 3D unstructured-grid model (SCHISM) which is an upgrade from an existing model (SELFE). 19The new advection scheme for the momentum equation includes an iterative smoother to reduce excess mass 20 produced by higher-order kriging method, and a new viscosity formulation is shown to work robustly for generic 21 unstructured grids and effectively filter out spurious modes without introducing excessive dissipation. A new higher-22 order implicit advection scheme for transport (TVD 2 ) is proposed to effectively handle a wide range of Courant 23 numbers as commonly found in typical cross-scale applications. The addition of quadrangular elements into the 24 model, together with a recently proposed, highly flexible vertical grid system (Zhang et al. 2015), leads to model 25 polymorphism that unifies 1D/2DH/2DV/3D cells in a single model grid. Results from several test cases 26 demonstrate the model's good performance in the eddying regime, which presents greater challenges for 27 unstructured-grid models and represents the last missing link for our cross-scale model. The model can thus be used 28 to simulate cross-scale processes in a seamless fashion (i.e. from deep ocean into shallow depths). 29 30 31 32 54 accuracy, efficiency and robustness. For instance, the eddying regime sets a high standard for numerical dissipation 55 and stability (control of modes), whereas the order of numerical schemes is less important in the estuarine 56 applications, as the strong forcing therein favors stable and often lower-order numerical schemes. For such 57 applications, more emphasis should be placed on faithfully resolving geometric and bathymetric features that act as 58 the 1 st -order forcing for the underlying processes. The rich diversity of the processes as found from shallow to large 59 depths likely precludes a 'one-size-fits-all' approach, and different numerical options may prove to be useful in 60 different regimes. This has been the guiding principle when we built our cross-scale model. 61As far as the model (SELFE) we have been developing for the past 15 years is concerned, we have made steady 62 progress in the baroclinic regime in the shallows (ZB08; Burla 2010). Although all implicit models have inherent 63 numerical diffusion, SELFE seems to have struck a good balance between numerical dissipation (due to implicit 64 time stepping), numerical dispersion (due to Finite Element Method), and stability demanded by such type of 65 applications. However, the following areas need to be improved before it can become a bona fide cross-scale model. 66First, the stratification is often under-estimated. This is related to the transport scheme as well as the vertical grid 67 Zhang et al. Page 3system used (which is a hybrid system with part terrain-following S coordinates and part Z coordinates). The 68 situation improves significantly with the introduction of TVD scheme for transport, and recently a flexible LSC 2 69 vertical grid (Zhang et al. 2015). Second, the model has not been applied in the eddying re...

This work is dedicated to the study of the climate variability of the Mediterranean Sea, in particular the study of the Eastern Mediterranean Transient (EMT) which occurred in the early 1990s. Simulations of the 1961–2000 period have been carried out with an eddy‐permitting Ocean General Circulation Model of the Mediterranean Sea, driven by realistic interannual high‐resolution air‐sea fluxes. Using different databases for the river runoff, Black Sea inflow, and Atlantic thermohaline characteristics at climatological or interannual scales, we assess the effects of the non‐atmospheric hydrological forcings on the simulation of the interannual variations of the Mediterranean circulation. The evolution of the basin‐scale heat content is in very good agreement with the observations (especially in the surface and intermediate layers), while the agreement is lower for the evolution of the salt content. Convection events in the Aegean Sea are noticed in the simulations between 1972 and 1976, in the late 1980s, and around the EMT period. The formation rates of Cretan Deep Water (CDW) are different during these periods, allowing or preventing the spreading of CDW into the eastern Mediterranean. The sequence of the EMT events is well reproduced: the high winter oceanic surface cooling and net evaporation over the Aegean Sea in the early 1990s, the high amount of dense CDW formed during these winters, and then the overflow and the spreading of this CDW in the eastern Mediterranean. Among the preconditioning processes suggested in the literature, we find that changes in the Levantine surface circulation, possibly induced by the presence in the Cretan Passage of anticyclonic eddies and a lasting period with reduced net precipitation over the eastern Mediterranean, lead to an increase of the salt content of the Aegean Sea. Changes in the Black Sea freshwater inflow or in the characteristic of the Atlantic Water entering at the Gibraltar Strait also modify the thermohaline state of the Aegean Sea before the EMT. But, as none of these preconditioning factors has a lasting impact on lowering the vertical stratification of the Aegean Sea, we conclude that concerning the EMT, the major triggering elements are the atmospheric fluxes and winds occurring in winters 1991–1992 and 1992–1993.

Abstract. In this paper we provide an overview of new knowledge on oxygen depletion (hypoxia) and related phenomena in aquatic systems resulting from the EU-FP7 project HYPOX ("In situ monitoring of oxygen depletion in hypoxic ecosystems of coastal and open seas, and landlocked water bodies", www.hypox.net). In view of the anticipated oxygen loss in aquatic systems due to eutrophication and climate change, HYPOX was set up to improve capacities to monitor hypoxia as well as to understand its causes and consequences.Temporal dynamics and spatial patterns of hypoxia were analyzed in field studies in various aquatic environments, including the Baltic Sea, the Black Sea, Scottish and Scandinavian fjords, Ionian Sea lagoons and embayments, and Swiss lakes. Examples of episodic and rapid (hours) occurrences of hypoxia, as well as seasonal changes in bottom-water oxygenation in stratified systems, are discussed. Geologically driven hypoxia caused by gas seepage is demonstrated. Using novel technologies, temporal and spatial patterns of watercolumn oxygenation, from basin-scale seasonal patterns to meter-scale sub-micromolar oxygen distributions, were resolved. Existing multidecadal monitoring data were used to demonstrate the imprint of climate change and eutrophication on long-term oxygen distributions. Organic and inorganic proxies were used to extend investigations on past oxygen conditions to centennial and even longer timescales that cannot be resolved by monitoring. The effects of hypoxia on faunal communities and biogeochemical processes were also addressed in the project. An investigation of benthic fauna is presented as an example of hypoxia-devastated benthic communities that slowly recover upon a reduction in eutrophication in a system where naturally occurring hypoxia overlaps with anthropogenic hypoxia. Biogeochemical investigations reveal that oxygen intrusions have a strong effect on the microbially mediated redox cycling of elements. Observations and modeling studies of the sediments demonstrate the effect of seasonally changing oxygen conditions on benthic mineralization pathways and fluxes. Data quality and access are crucial in hypoxia research. Technical issues are therefore also addressed, including the availability of suitable sensor technology to resolve the gradual changes in bottom-water oxygen in marine systems that can be expected as a result of climate change. Using cabled observatories as examples, we show how the benefit of continuous oxygen monitoring can be maximized by adopting proper quality control. Finally, we discuss strategies for state-of-the-art data archiving and dissemination in compliance with global standards, and how ocean observations can contribute to global earth observation attempts.

Abstract. TOPEX/Poseidon (T/P) altimeter data in the Black

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