Superstatistical analysis of sea surface currents in the Gulf of Trieste, measured by HF Radar, and its relation to wind regimes, using the maximum entropy principle

Two years (2021&ndash;2022) of High Frequency Radar (HFR) sea surface current data in the Gulf of Trieste (Northern Adriatic Sea) are analysed. Two different time scales are extracted using superstatistical formalism: a relaxation time and a larger timescale over which the system is gaussian. A new analytical universality class of Probability Density Functions (PDFs) is proposed for ocean current data combining a gaussian PDF for the fast fluctuations and a convolution of exponential PDFs for the slowly evolving variance of the gaussian. The Gaussian PDF has maximum entropy for real-valued variables with a given variance. If a positive variable, as is a variance, has a specified mean, the maximum entropy solution is an exponential PDF. Here it is the sum of two exponentials, reflecting the two spatial degrees of freedom. In the Gulf of Trieste there are three distinct main wind forcing regimes: Bora, Sirocco and low wind, leading to a succession of different sea current dynamics on different time scales. The universality class PDF successfully fits the observed data over the two observation years and also for each wind regime separately with a different variance of the variance PDF, which is the only free parameter in all the fits.</p

Superstatistical analysis of sea surface currents in the Gulf of Trieste, measured by high-frequency radar, and its relation to wind regimes using the maximum-entropy principle

Two years (2021–2022) of high-frequency-radar (HFR) sea surface current data in the Gulf of Trieste (northern Adriatic Sea) are analysed. Two different timescales are extracted using a superstatistical formalism: a relaxation time and a larger timescale over which the system is Gaussian. We propose obtaining an ocean current probability density function (PDF) combining (i) a Gaussian PDF for the fast fluctuations and (ii) a convolution of exponential PDFs for the slowly evolving variance of the Gaussian function rather than for the thermodynamic β=1/σ2 in a system with a few degrees of freedom, as the latter has divergent moments. The Gaussian PDF reflects the entropy maximization for real-valued variables with a given variance. On the other hand, if a positive variable, as a variance, has a specified mean, the maximum-entropy solution is an exponential PDF. In our case the system has 2 degrees of freedom, and therefore the PDF of the variance is the convolution of two exponentials. In the Gulf of Trieste there are three distinct main wind forcing regimes: bora, sirocco, and low wind, leading to a succession of different sea current dynamics on different timescales. The universality class PDF successfully fits the observed data over the 2 observation years and also for each wind regime separately with a different variance of the variance PDF, which is the only free parameter in all the fits.</p

O termohalinim svojstvima i cirkulaciji Jonskog mora u toku 2010.-2013. na osnovi mjerenja Argo plutačama

From all available Argo floats and altimetry data, the surface, intermediate (350 m depth) and deep (1000 m) circulation patterns in the Ionian Sea were analysed in detail for four consecutive years (2010, 2011, 2012 and 2013). In addition, thermohaline properties from float measurements were described and compared considering among all, the Dense Water Overflow from the Adriatic, particularly the one due to the strong winter air-sea heat loss in 2012. In the flow field, energetic closed circulation structures with the spatial scale of about 100 km were present during the entire study period. More specifically, the Pelops Gyre is observed from the surface down to more than 1000 m depth. A multi-lobe anticyclonic feature in the centre of the Ionian basin located to the north of the Mid Ionian Jet was also well evident in the same depth interval. The sub-basin-wide cyclonic circulation in the northern Ionian was clearly documented only in the close vicinity of the basin flanks at all the three levels. The most prominent signal of the Adriatic Dense Water (AdDW) was evidenced at about 1000 m depth in the northwestern portion of the basin in late spring 2012. Afterwards, very likely the AdDW progressively sank along its way southward and its signal was not recorded anymore because of the limited range of the float profiles (max 2000 m).Na temelju raspoloživih podataka sistema argo sondi i podataka o visini morske razine, analizirani su površinski, intermedijarni (350 m) i duboki (1000 m) sustavi strujanja u Jonskom moru u toku 2010., 2011., 2012. i 2013. godine. Pritom su opisana i uspoređena termohalina svojstva dobivena iz profila argo sondi. r azmatrano je i širenje guste vode iz Jadranskog mora, naročito ono vezano uz iznimno velik gubitak topline s površine mora u toku zimskog razdoblja u 2012. godini. tokom perioda istraživanja, polja strujanja karakteriziraju vrtlozi čiji je promjer otprilike 100 km. vrtlog Pelops, posebice, opaža se od morske površine do 1000 m dubine. anticiklonalna struktura u središtu Jonskog mora, na sjevernoj strani struje tzv. Mid-Ionian Jet, sastavljena je od više manjih vrtloga i također se proteže do istih dubina. Ciklonalno strujanje dobro se uočava na sve tri razine u rubnom (dužobalnom) području unutar sjevernog Jonskog more. vrlo izrazit signal prisustva guste jadranske vode (Adriatic Dense Water, AdDW) opažen je na otprilike 1000 m dubine u sjeverozapadnom dijelu jonskog bazena u kasno proljeće 2012. godine. otuda, adDW vrlo vjerojatno postupno tone strujeći prema jugu, i njen se signal više ne opaža jer su argo mjerenja ograničena na maksimalnu dubinu od 2000 m

The discovery of the southernmost ultra-high-resolution Holocene paleoclimate sedimentary record in Antarctica

The response of the Antarctic ice sheet to climate warming is the main source of uncertainty regarding future global sea level rise, since little is known about its present and past dynamics. The last deglaciation is the most recent interval of large-scale climate warming, during which the Northern and Southern Hemisphere ice sheets retreated, and sea level rose globally, although at a non-uniform rate. Geologic records from the polar regions are fundamental in determining the factors that caused the major changes in ice sheets during the last deglacial under different boundary conditions. Here, we combine morpho-bathymetric and seismic data with sediment cores and oceanographic measurements to reconstruct the processes that influenced the deposition of the southernmost, most extensive, ultrahigh-resolution record of the Holocene in Edisto Inlet fjord (Ross Sea, Antarctica). We find that post-glacial sedimentation resulted in a layered diatom mud up to 110 m thick that was locally redistributed by bottom currents over confined drifts-moats in the central part of the fjord. After the Holocene climatic optimum, the fjord was not carved by ground ice, and there continued to be internal fjord water circulation associated with Ross Sea circulation. These results support a retreat of coastal glaciers by about 11 kiloyears ago (ka) from the continental shelf of North Victoria Land

Biogeochemical properties of Adriatic dense waters

Distribution and characteristics of dense waters in the Adriatic Sea were monitored during their formation in winter 2008, and later, in autumn at the end of the seasonal stratification period in the Adriatic Sea. Different types of dense waters were identified on the basis of their physical features. In order to characterised their biogeochemical properties dissolved oxygen, nutrient, and particulate organic matter (chlorophyll a, particulate organic carbon, particulate nitrogen and phosphorus) were analysed

Coastal high-frequency radars in the Mediterranean ??? Part 1: Status of operations and a framework for future development

Due to the semi-enclosed nature of the Mediterranean Sea, natural disasters and anthropogenic activities impose stronger pressures on its coastal ecosystems than in any other sea of the world.With the aim of responding adequately to science priorities and societal challenges, littoral waters must be effectively monitored with high-frequency radar (HFR) systems. This land-based remote sensing technology can provide, in near-real time, fine-resolution maps of the surface circulation over broad coastal areas, along with reliable directional wave and wind information. The main goal of this work is to showcase the current status of the Mediterranean HFR network and the future roadmap for orchestrated actions. Ongoing collaborative efforts and recent progress of this regional alliance are not only described but also connected with other European initiatives and global frameworks, highlighting the advantages of this cost-effective instrument for the multi-parameter monitoring of the sea state. Coordinated endeavors between HFR operators from different multi-disciplinary institutions are mandatory to reach a mature stage at both national and regional levels, striving to do the following: (i) harmonize deployment and maintenance practices; (ii) standardize data, metadata, and quality control procedures; (iii) centralize data management, visualization, and access platforms; and (iv) develop practical applications of societal benefit that can be used for strategic planning and informed decision-making in the Mediterranean marine environment. Such fit-for-purpose applications can serve for search and rescue operations, safe vessel navigation, tracking of marine pollutants, the monitoring of extreme events, the investigation of transport processes, and the connectivity between offshore waters and coastal ecosystems. Finally, future prospects within the Mediterranean framework are discussed along with a wealth of socioeconomic, technical, and scientific challenges to be faced during the implementatio

EuroGOOS roadmap for operational coastal downstream services

The EuroGOOS Coastal working group examines the entire coastal value chain from coastal observations to services for coastal users. The main objective of the working group is to review the status quo, identify gaps and future steps needed to secure and improve the sustainability of the European coastal service provision. Within this framework, our white paper defines a EuroGOOS roadmap for sustained “community coastal downstream service” provision, provided by a broad EuroGOOS community with focus on the national and local scale services. After defining the coastal services in this context, we describe the main components of coastal service provision and explore community benefits and requirements through sectoral examples (aquaculture, coastal tourism, renewable energy, port, cross-sectoral) together with the main challenges and barriers to user uptake. Technology integration challenges are outlined with respect to multiparameter observations, multi-platform observations, the land-coast-ocean continuum, and multidisciplinary data integration. Finally, the technological, financial, and institutional sustainability of coastal observing and coastal service provision are discussed. The paper gives special attention to the delineation of upstream and downstream services, public-private partnerships and the important role of Copernicus in better covering the coastal zone. Therefore, our white paper is a policy and practice review providing a comprehensive overview, in-depth discussion and actionable recommendations (according to key short-term or medium-term priorities) on the envisaged elements of a roadmap for sustained coastal service provision. EuroGOOS, as an entity that unites European national operational oceanography centres, research institutes and scientists across various domains within the broader field of operational oceanography, offers to be the engine and intermediary for the knowledge transfer and communication of experiences, best practices and information, not only amongst its members, but also amongst the different (research) infrastructures, institutes and agencies that have interests in coastal oceanography in Europe

Multi-platform study of the extreme bloom of the barrel jellyfish Rhizostoma pulmo (Cnidaria: Scyphozoa) in the northernmost gulf of the Mediterranean Sea (Gulf of Trieste) in April 2021

On 7 April 2021, an exceptional bloom of the scyphomedusa Rhizostoma pulmo was observed in the Gulf of Trieste (Italy). Blooms of this species in the northern Adriatic Sea have been reported since the late 1800s: the density of jellyfish observed in 2021 reached more than 10 specimens per square metre. We analyse the bloom from a multi-platform approach using observations and model data at different timescales. We attempt to explain the intensity of the bloom as a consequence of thermohaline and hydrodynamical conditions in the gulf. Meteo-oceanographic conditions that may have contributed to the exceptional aggregation of jellyfish observed along the northernmost coast of the Adriatic Sea are discussed in detail. Specifically, our results indicate that this bloom was enabled by (1) the presence of a high number of jellyfish in the gulf, probably linked to the anomalously warm sea conditions in spring 2020 and winter 2021, which may have favoured a longer reproductive period and enhanced survival of adult R. pulmo, respectivelyand (2) strong wind events, such as the bora wind for the Gulf of Trieste, which enhanced upwelling and mixing processes in the gulf, bringing the jellyfish from the deeper waters to the surface and clustering them along the coast

EVOLUTION OF DYNAMICS IN THE EASTERN MEDITERRANEAN AFFECTING HYDROGRAPHIC PROPERTIES IN THE IONIAN AND ADRIATIC SEAS (1995-1999)

Basin-wide hydrographic observations performed in the eastern Mediterranean during the past 2 decades attest changes in the thermohaline circulation as well as new aspects concerning the onset and the follow up of the major transient event that occurred at the beginning of the 1990s, i.e., the change of the dense water formation site from the Adriatic to the Aegean Sea. Since 1999, the upper thermohaline circulation has indicated the restoring of the opposite flows of the Atlantic Water and the Levantine Intermediate Water, which were greatly reduced in the period 1987–1995. In the deep layer the comparison between water mass structures observed in 1995, during the mature status of the transient, and those observed in 1999 shows a damping of the event and a regained role of the Adriatic Sea as a primary source of dense waters. Separate calculations of the salt content in the Ionian and in the Levantine Seas show an overall salt redistribution. During 1987–1995 a salt loss of about 25 1012 kg was computed for the upper 800 m, constituting only 27% of the salt gain in the deep layer over most of the eastern Mediterranean. On the contrary, during 1995–1999 the restored upper thermohaline circulation caused a salt redistribution between the two basins of about the same amount, but in the opposite sense, while an extra quantity of 12 1012 kg was deposited in the deep layer. In addition, calculations of the salt concentration in the convection region of the southern Adriatic reveal a remarkable amount of the salt, not yet totally transferred into the deep layers by its interior dynamics because of mild winters

Surface transport in the Northeastern Adriatic Sea from FSLE analysis of HF radar measurements

International audienceThis study focuses on the surface transport in the Northeastern Adriatic Sea and the related hydrodynamic connectivity with the Gulf of Trieste (GoT) under calm or typical wind conditions: Bora (from the NE) and Sirocco (from the SE). The surface transport in the area has been investigated by evaluating the Finite-Size Lyapunov Exponents (FSLE) on the current field measured by the High Frequency (HF) coastal radar network. FSLE allow us to estimate Lagrangian Coherent Structures (LCSs), which provide information on the transport patterns associated with the flow and identify regions characterized by different dynamics. This work includes the development and set-up of the FSLE algorithm applied for the first time to the specific Adriatic area considered. The FSLE analysis during calm wind reveals an attractive LCS crossing the GoT entrance, marking the convergence between the Northern Adriatic and the outflowing gulf waters. During Bora episodes this attractive LCS is displaced westward with respect to the calm wind case, indicating that Bora drives an extended coherent outflow from the GoT. On the other hand, Sirocco wind piles up the water along the northern end of the basin. In this area an attractive LCS is found, extending mainly in the SW-NE direction. The sirocco-induced inflow of Adriatic waters in the GoT is mainly driven along its northern (Italian) side, as evidenced by the orientation of the LCS. Under Sirocco condition, as in the Bora case, there is no barrier in front of the gulf. No relevant LCSs are observed in the southern radar coverage area except for Bora cases, when a repulsive LCS develops in front of the Istrian coast separating water masses to the North and the South of it