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Special Issue "Ocean Exchange and Circulation"

A special issue of Water (ISSN 2073-4441). This special issue belongs to the section "Hydraulics".

Deadline for manuscript submissions: closed (29 April 2019).

Special Issue Editors

Guest Editor
Dr. Miroslav Gacic

National Institute of Oceanography and Experimental Geophysics, Borgo Grotta Gigante 42-C, I-34010 Trieste, Italy
Website | E-Mail
Interests: ocean circulation; dense water formation; strait exchange; coastal circulation; experimental oceanography; Mediterranean long-term variability
Guest Editor
Dr. Manuel Bensi

National Institute of Oceanography and Experimental Geophysics, Borgo Grotta Gigante 42-C, I-34010 Trieste, Italy
Website | E-Mail
Interests: abyssal circulation; thermohaline properties; mesoscle variability; experimental oceanography; polar oceanography; Mediterranean circulation

Special Issue Information

Dear Colleagues,

Ocean circulation generated by the wind and/or by density gradients contributes to water property exchange between different parts of the ocean or between semi-enclosed seas and adjacent oceanic areas. Different space and time scales characterize ocean exchange and circulation. In addition to the mean circulation, basin-scale, and sub-basin flows, mesoscale eddies and internal processes (e.g., mixing induced by bottom roughness, internal waves, etc.) contribute to re-distribution of ocean properties and energy. Thermohaline oceanic circulation is driven by the winter convection and dense-water formation processes that are thus directly influenced by winter climatic conditions. Long-term and climatic changes in circulation and in the vertical mixing processes directly influence the variability of the biogeochemical properties of the ocean. A special role in trapping and/or transporting the biogeochemical properties of sea water is played by travelling eddies; however, this is yet to be quantified. This issue is open to all papers addressing the processes, which are associated with ocean circulation and mixing in both oceanic areas and semi-enclosed seas. It will also deal with the implications of circulation on biogeochemical properties and marine pollution.

Dr. Miroslav Gacic
Dr. Manuel Bensi
Guest Editors

Manuscript Submission Information

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Keywords

  • ocean circulation
  • long-term variability
  • vertical mixing
  • mesoscale eddies
  • biogeochemical properties

Published Papers (7 papers)

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Research

Open AccessArticle
Picoplankton Distribution and Activity in the Deep Waters of the Southern Adriatic Sea
Water 2019, 11(8), 1655; https://doi.org/10.3390/w11081655
Received: 19 July 2019 / Revised: 7 August 2019 / Accepted: 8 August 2019 / Published: 10 August 2019
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Abstract
Southern Adriatic (Eastern Mediterranean Sea) is a region strongly dominated by large-scale oceanographic processes and local open-ocean dense water formation. In this study, picoplankton biomass, distribution, and activity were examined during two oceanographic cruises and analyzed in relation to environmental parameters and hydrographic [...] Read more.
Southern Adriatic (Eastern Mediterranean Sea) is a region strongly dominated by large-scale oceanographic processes and local open-ocean dense water formation. In this study, picoplankton biomass, distribution, and activity were examined during two oceanographic cruises and analyzed in relation to environmental parameters and hydrographic conditions comparing pre and post-winter phases (December 2015, April 2016). Picoplankton density with the domination of autotrophic biomasses was higher in the pre-winter phase when significant amounts of picoaoutotrophs were also found in the meso-and bathy-pelagic layers, while Synechococcus dominated the picoautotrophic group. Higher values of bacterial production and domination of High Nucleic Acid content bacteria (HNA bacteria) were found in deep waters, especially during the post-winter phase, suggesting that bacteria can have an active role in the deep-sea environment. Aerobic anoxygenic phototrophic bacteria accounted for a small proportion of total heterotrophic bacteria but contributed up to 4% of bacterial carbon content. Changes in the picoplankton community were mainly driven by nutrient availability, heterotrophic nanoflagellates abundance, and water mass movements and mixing. Our results suggest that autotrophic and heterotrophic members of the picoplankton community are an important carbon source in the food web in the deep-sea, as well as in the epipelagic layer. Besides, viral lysis may affect the activity of the picoplankton community and enrich the water column with dissolved organic carbon. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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Open AccessArticle
Sea Surface Circulation Structures in the Malta-Sicily Channel from Remote Sensing Data
Water 2019, 11(8), 1589; https://doi.org/10.3390/w11081589
Received: 20 June 2019 / Revised: 17 July 2019 / Accepted: 25 July 2019 / Published: 31 July 2019
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Abstract
The Malta-Sicily Channel is part of the Sicily Channel system where water and thermohaline properties between the Eastern and Western Mediterranean basins take place. Several mesoscales features are detached from the main circulation due to wind and bathymetric forcing. In this paper, surface [...] Read more.
The Malta-Sicily Channel is part of the Sicily Channel system where water and thermohaline properties between the Eastern and Western Mediterranean basins take place. Several mesoscales features are detached from the main circulation due to wind and bathymetric forcing. In this paper, surface circulation structures are studied using different remotely sensed datasets: satellite data (absolute dynamic topography, Cross-Calibrated Multi-Platform wind vector analysis, satellite chlorophyll and sea surface temperature) and high frequency radar data. We identified high frequency motions (at short time scales—hours to days), as well as mesoscale structures fundamental for the understanding of the Malta-Sicily Channel circulation dynamics. One of those is the Malta-Sicily Gyre; an anticyclonic structure trapped between the Sicilian and Maltese coasts, which is poorly studied in the literature and often confused with the Malta Channel Crest and the Ionian Shelf Break Vortex. In order to characterize this gyre, we calculated its kinetic properties taking advantage of the fine-scale temporal and spatial resolution of the high frequency radar data, and thus confirming its presence with an updated version of the surface circulation patterns in the area. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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Open AccessArticle
New Insights of the Sicily Channel and Southern Tyrrhenian Sea Variability
Water 2019, 11(7), 1355; https://doi.org/10.3390/w11071355
Received: 31 May 2019 / Revised: 24 June 2019 / Accepted: 27 June 2019 / Published: 29 June 2019
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Abstract
The dynamics of the Sicily Channel and the southern Tyrrhenian Sea are highly influenced by the seasonal variability of the Mediterranean basin-wide circulation, by the interannual variability of the numerous mesoscale structures present in the Channel, and by the decadal variability of the [...] Read more.
The dynamics of the Sicily Channel and the southern Tyrrhenian Sea are highly influenced by the seasonal variability of the Mediterranean basin-wide circulation, by the interannual variability of the numerous mesoscale structures present in the Channel, and by the decadal variability of the adjacent Ionian Sea. In the present study, all these aspects are investigated using in-situ (Lagrangian drifter trajectories and Argo float profiles) and satellite data (Absolute Dynamic Topography, Sea Level Anomaly, Sea Surface Temperature, wind products) over the period from 1993 to 2018. The availability of long time series of data and high-resolution multi-sensor surface currents allow us to add new details on the circulation features and on their driving mechanisms and to detect new permanent eddies not yet described in literature. The structures prevailing in winter are mainly driven by wind, whereas those prevailing in summer are regulated by topographical forcing on surface currents. The strength of the surface structures located at the western entrance of the Ionian Sea and of the mesoscale activity along the northern Sicily coast is modulated by the large-scale internal variability. The vertical hydrological characteristics of these mesoscale eddies are delineated using the Argo float profiles inside these structures. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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Open AccessArticle
A Census of the 1993–2016 Complex Mesoscale Eddy Processes in the South China Sea
Water 2019, 11(6), 1208; https://doi.org/10.3390/w11061208
Received: 16 March 2019 / Revised: 27 May 2019 / Accepted: 5 June 2019 / Published: 10 June 2019
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Abstract
Mesoscale eddy process with at least one splitting and/or merging event can be defined as either a complex process or a simple process. Investigation of the difference between these two categories could provide new insights into how different factors, such as the seabed [...] Read more.
Mesoscale eddy process with at least one splitting and/or merging event can be defined as either a complex process or a simple process. Investigation of the difference between these two categories could provide new insights into how different factors, such as the seabed topography, Kuroshio intrusion, and winds, affect the origin, migration, and decay of the mesoscale eddies. This study compared the characteristics of the complex against the simple eddy processes in the South China Sea (SCS) from 1993 to 2016. We comprehensively analyzed the eddy processes with regards to their characteristic points, trajectories, and networks. The simple and complex processes share many similarities but do show significantly different behaviors. Both the simple and complex processes mainly start from the eastern SCS. However, the complex processes mainly vanish in the western SCS whereas the simple processes disappear almost everywhere across the SCS. The complex processes last longer and migrate more than the simple processes. Lastly, the complex processes mainly move westward within the community. The complex processes can be further categorized into complex anticyclonic and cyclonic eddy processes. Spatially, the splitting and merging events mainly occur in the southwest of Taiwan, northwest of the Luzon Island, and the southeast of Vietnam. Temporally, the merging and splitting events mainly occur in the fall. The interaction among the communities reveals the different migration patterns of the complex anticyclonic and cyclonic eddy processes in the SCS. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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Open AccessArticle
Deep Flow Variability Offshore South-West Svalbard (Fram Strait)
Water 2019, 11(4), 683; https://doi.org/10.3390/w11040683
Received: 22 February 2019 / Revised: 22 March 2019 / Accepted: 29 March 2019 / Published: 2 April 2019
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Abstract
Water mass generation and mixing in the eastern Fram Strait are strongly influenced by the interaction between Atlantic and Arctic waters and by the local atmospheric forcing, which produce dense water that substantially contributes to maintaining the global thermohaline circulation. The West Spitsbergen [...] Read more.
Water mass generation and mixing in the eastern Fram Strait are strongly influenced by the interaction between Atlantic and Arctic waters and by the local atmospheric forcing, which produce dense water that substantially contributes to maintaining the global thermohaline circulation. The West Spitsbergen margin is an ideal area to study such processes. Hence, in order to investigate the deep flow variability on short-term, seasonal, and multiannual timescales, two moorings were deployed at ~1040 m depth on the southwest Spitsbergen continental slope. We present and discuss time series data collected between June 2014 and June 2016. They reveal thermohaline and current fluctuations that were largest from October to April, when the deep layer, typically occupied by Norwegian Sea Deep Water, was perturbed by sporadic intrusions of warmer, saltier, and less dense water. Surprisingly, the observed anomalies occurred quasi-simultaneously at both sites, despite their distance (~170 km). We argue that these anomalies may arise mainly by the effect of topographically trapped waves excited and modulated by atmospheric forcing. Propagation of internal waves causes a change in the vertical distribution of the Atlantic water, which can reach deep layers. During such events, strong currents typically precede thermohaline variations without significant changes in turbidity. However, turbidity increases during April–June in concomitance with enhanced downslope currents. Since prolonged injections of warm water within the deep layer could lead to a progressive reduction of the density of the abyssal water moving toward the Arctic Ocean, understanding the interplay between shelf, slope, and deep waters along the west Spitsbergen margin could be crucial for making projections on future changes in the global thermohaline circulation. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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Open AccessArticle
The Four Patterns of the East Branch of the Kuroshio Bifurcation in the Luzon Strait
Water 2018, 10(12), 1822; https://doi.org/10.3390/w10121822
Received: 17 November 2018 / Revised: 1 December 2018 / Accepted: 6 December 2018 / Published: 10 December 2018
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Abstract
Based on the self-organizing map (SOM) method, a suite of satellite measurement data, and Hybrid Coordinate Ocean Model (HYCOM) reanalysis data, the east branch of the Kuroshio bifurcation is found to have four coherent patterns associated with mesoscale eddies in the Pacific Ocean: [...] Read more.
Based on the self-organizing map (SOM) method, a suite of satellite measurement data, and Hybrid Coordinate Ocean Model (HYCOM) reanalysis data, the east branch of the Kuroshio bifurcation is found to have four coherent patterns associated with mesoscale eddies in the Pacific Ocean: anomalous southward, anomalous eastward, anomalous northward, and anomalous westward. The robust clockwise cycle of the four patterns causes significant intraseasonal variation of 62.2 days for the east branch. Furthermore, the study shows that the four patterns of the east branch of the Kuroshio bifurcation can influence the horizontal and vertical distribution of local sea temperature. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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Open AccessArticle
Numerical Investigations of Tsunami Run-Up and Flow Structure on Coastal Vegetated Beaches
Water 2018, 10(12), 1776; https://doi.org/10.3390/w10121776
Received: 23 October 2018 / Revised: 28 November 2018 / Accepted: 29 November 2018 / Published: 3 December 2018
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Abstract
Tsunami waves become hazardous when they reach the coast. In South and Southeast Asian countries, coastal forest is widely utilized as a natural approach to mitigate tsunami damage. In this study, a depth-integrated numerical model was established to simulate wave propagation in a [...] Read more.
Tsunami waves become hazardous when they reach the coast. In South and Southeast Asian countries, coastal forest is widely utilized as a natural approach to mitigate tsunami damage. In this study, a depth-integrated numerical model was established to simulate wave propagation in a coastal region with and without forest cover. This numerical model was based on a finite volume Roe-type scheme, and was developed to solve the governing equations with the option of treating either a wet or dry wave front boundary. The governing equations were modified by adding a drag force term caused by vegetation. First, the model was validated for the case of solitary wave (breaking and non-breaking) run-up and run-down on a sloping beach, and long periodic wave propagation was investigated on a partially vegetated beach. The simulated results agree well with the measured data. Further, tsunami wave propagation on an actual-scale slope covered by coastal forest Pandanus odoratissimus (P. odoratissimus) and Casuarina equisetifolia (C. equisetifolia) was simulated to elucidate the influence of vegetation on tsunami mitigation with a different forest open gap. The numerical results revealed that coastal vegetation on sloping beach has significant potential to mitigate the impacts from tsunami waves by acting as a buffer zone. Coastal vegetation with open gaps causes the peak flow velocity at the exit of the gap to increase, and reduces the peak flow velocity behind the forest. Compared to a forest with open gaps in a linear arrangement, specific arrangements of gaps in the forest can increase the energy attenuation from tsunami wave. The results also showed that different cost-effective natural strategies in varying forest parameters including vegetation collocations, densities, and growth stages had significant impacts in reducing the severity of tsunami damage. Full article
(This article belongs to the Special Issue Ocean Exchange and Circulation)
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