Drivers of water exchange in the ORUST fjord system

2020 ◽  
Author(s):  
Sandra-Esther Brunnabend ◽  
Lars Axell ◽  
Maximo Garcia-Jove ◽  
Lars Arneborg
Keyword(s):  
Surface Water ◽  
Baltic Sea ◽  
Water Exchange ◽  
Sea Water ◽  
Water Masses ◽  
Open Boundary ◽  
Small Scale ◽  
Open Boundary Conditions ◽  
Near Surface ◽  
Fjord System

<p>The Orust fjord system, located on the west coast of Sweden, has openings on both ends and consists of several fjords that are connected by narrow and shallow channels. The fjord system includes the islands Orust and Tjörn as well as various smaller islands. The water exchange between the Kattegat and the different fjords is influenced by different factors, such as winds, tides, and density gradients. However, advection between the open sea and the complex fjord system are not yet well understood as lower resolution ocean models cannot resolve the small scale structures of the fjords and their connections. In addition, observations are rather sparse.</p><p>Therefore, the water exchange in the Orust fjord system is simulated using a high resolution (50 meter) NEMO3.6 ocean model setup, forced with the UERRA atmospheric reanalysis dataset. The lateral open boundary conditions for temperature, salinity, sea levels and velocities are provided by a low resolution (1.85 km) NEMO3.6 simulation, which spans the Baltic Sea and North Sea regions.</p><p>The model results are validated by comparison of modelled temperature, salinity, velocities and sea surface height with in-situ measurements. A detailed analysis of the different drivers of modelled water exchange between the Kattegat and the fjord system as well as between the different basins is presented. In general, the modelled water properties of the near surface layer in the fjord system are influenced by the Skagerrak surface water, which is controlled by the prevailing northward flowing Baltic Sea water. However, the residence times of water masses below the sill level are longer than the ones of the surface water masses as dense inflows of Skagerrak water in the basins create a strong stratification leading to weak vertical exchange.</p>

scholarly journals Is Interleaving in the Agulhas Current Driven by Near-Inertial Velocity Perturbations?

2007 ◽  
Vol 37 (4) ◽  
pp. 932-945 ◽  
Author(s):  
Lisa M. Beal
Keyword(s):  
Surface Water ◽  
Sea Water ◽  
Salinity Gradient ◽  
Water Masses ◽  
Vertical Shear ◽  
Small Scale ◽  
Exact Nature ◽  
Intermediate Water ◽  
Horizontal Shear ◽  
Agulhas Current

Abstract Recent observations taken at a number of latitudes in the Agulhas Current reveal that the water mass structure on either side of its dynamical core is distinctly different. Moreover, interleaving of these distinct water masses is observed at over 80% of the stations occupied in the current, particularly within the subsurface density layer between tropical surface water and subtropical surface water masses, and within the intermediate layer between the Antarctic Intermediate Water and Red Sea water masses. Direct velocity measurements allow for a comparison between the characteristic vertical length scales of the Agulhas intrusions and those of velocity perturbations found throughout the current. It is found that the interleaving scales match those of the velocity perturbations, which are manifest as high-wavenumber vertical shear layers and are identified as near-inertial oscillations. Furthermore, the properties of the intrusions indicate that double diffusion is not an important process in their development: they are generally not associated with a density anomaly, their slope and thickness fall outside the predicted maxima for instability, and a strong horizontal shear field acts to separate water parcels more quickly than intrusions would be able to grow by double-diffusive processes. Instead, the position, thickness, and slope of Agulhas intrusions relative to the background salinity and density field suggest that they are forced by rotating inertial velocities, with subsequent growth possibly driven by small-scale baroclinic instabilities. However, not all the evidence points conclusively toward advectively driven intrusions. For instance, there is a discrepancy between the observed salinity anomaly amplitude and the predicted inertial displacement given the background salinity gradient, which deserves further examination. Hence, there is a future need for more pointed observations and perhaps the development of an analytical or numerical model to understand the exact nature of Agulhas intrusions.

Setting up the NEMO (Nucleus for European Modeling of the Ocean) for Baltic Sea region - open boundary conditions

2020 ◽  
Author(s):  
Jan Andrzejewski ◽  
Jaromir Jakacki ◽  
Maciej Muzyka ◽  
Anna Przyborska
Keyword(s):  
Boundary Conditions ◽  
Baltic Sea ◽  
North Sea ◽  
Water Exchange ◽  
Open Boundary ◽  
Open Boundary Conditions ◽  
The Baltic Sea ◽  
The North ◽  
Baltic Sea Region ◽  
The Baltic

<p>The Baltic Sea is inland, Shelf Sea in northern part of Europe. It is shallow with average depth of 52 meters and deepest point 459 meters located at Landsort Deep. Baltic Sea is connected with North Sea via the Danish Straits (comprising of Great Belt, Little Belt and Øresund). These systems ensure only limited exchange between oceanic waters and seawaters, which affect the low salinity in Baltic reservoir. Runoff from surrounding lands (approximately 200 rivers) and positive difference of precipitation minus evaporation additionally refreshes water and makes Baltic a brackish sea. The only charge of salt comes from the North Sea with so-called inflows or less frequent occurring Major Baltic Inflows (MBI). This exchange between Danish Straits is the key for properly working simulation. In this work the tool, well known as NEMO, was used to perform the numerical simulation for the Baltic Sea area. This presentation is focused on the first stage of validation of the model results for the Baltic Sea region where influence of open boundary conditions is noticeable as soon as possible. The main change in the model is the assimilation of sea surface height in Kattegat area. Also water outflow mass controlling from the Baltic Sea has been introduced. The properly working open boundary conditions affect the water exchange between Baltic Sea and North Sea, thus the MBI and minor salty inflows are well represented. This is very important part in modeling the Baltic<br>Sea, where narrow Danish Straits limits the water exchange which controls the salt budget, adding the salt with inflows and receiving brackish outflow out to the Ocean. This work presents comparison between model output with results measured in situ and from other validated model, the period which is compared is the Major Baltic Inflow in the beginning of 1993.</p>

scholarly journals Investigating patterns and controls of groundwater up-welling in a lowland river by combining Fibre-optic Distributed Temperature Sensing with observations of vertical hydraulic gradients

2012 ◽  
Vol 16 (6) ◽  
pp. 1775-1792 ◽  
Author(s):  
S. Krause ◽  
T. Blume ◽  
N. J. Cassidy
Keyword(s):  
Surface Water ◽  
Water Exchange ◽  
Structural Heterogeneity ◽  
Temperature Sensing ◽  
Small Scale ◽  
Lowland River ◽  
Fibre Optic ◽  
Distributed Temperature Sensing ◽  
Hydraulic Gradients ◽  
Cold Spots

Abstract. This paper investigates the patterns and controls of aquifer–river exchange in a fast-flowing lowland river by the conjunctive use of streambed temperature anomalies identified with Fibre-optic Distributed Temperature Sensing (FO-DTS) and observations of vertical hydraulic gradients (VHG). FO-DTS temperature traces along this lowland river reach reveal discrete patterns with "cold spots" indicating groundwater up-welling. In contrast to previous studies using FO-DTS for investigation of groundwater–surface water exchange, the fibre-optic cable in this study was buried in the streambed sediments, ensuring clear signals despite fast flow and high discharges. During the observed summer baseflow period, streambed temperatures in groundwater up-welling locations were found to be up to 1.5 °C lower than ambient streambed temperatures. Due to the high river flows, the cold spots were sharp and distinctly localized without measurable impact on down-stream surface water temperature. VHG patterns along the stream reach were highly variable in space, revealing strong differences even at small scales. VHG patterns alone are indicators of both, structural heterogeneity of the stream bed as well as of the spatial heterogeneity of the groundwater–surface water exchange fluxes and are thus not conclusive in their interpretation. However, in combination with the high spatial resolution FO-DTS data we were able to separate these two influences and clearly identify locations of enhanced exchange, while also obtaining information on the complex small-scale streambed transmissivity patterns responsible for the very discrete exchange patterns. The validation of the combined VHG and FO-DTS approach provides an effective strategy for analysing drivers and controls of groundwater–surface water exchange, with implications for the quantification of biogeochemical cycling and contaminant transport at aquifer–river interfaces.

The Identification and Nomenclature of the Surface Water Masses in the Tasman Sea (Data to the End of 1954)

1957 ◽  
Vol 8 (4) ◽  
pp. 369 ◽  
Author(s):  
DJ Rochford
Keyword(s):  
Surface Water ◽  
Sea Water ◽  
Maximum Velocity ◽  
Water Masses ◽  
Late Winter ◽  
The South ◽  
Coral Sea ◽  
Tasman Sea ◽  
East And West ◽  
Western Side

In this paper an examination of all available data on the hydrological characteristics of the Tasman Sea, prior to and including the year 1954, has permitted the identification and naming of eight surface water masses. Certain of their properties and general features of their season and region of occurrence and method of formation are summarized. Although little quantitative data are available some general features of the circulation of these water masses in the Tasman Sea are deduced from a study of their seasonal occurrence in relation to source regions. The Coral Sea water mass (chlorinity 19.60-19.70‰, temperature 20-26� C) flows from a source region in the north-west Coral Sea along the western side of the Tasman Sea and reaches maximum velocity off Sydney in October-December. The South Equatorial (chlorinity 19.50-19.60‰, temperature 24-26� C) also flows south along the western side of the Tasman Sea but reaches maximum velocity between February and March. These two water masses constitute the East Australian current. The Sub-Antarctic (chlorinity 19.15-19.30‰, temperature 10-14°C) is found at the surface in the south-eastern Tasman Sea between July and September. The Central Tasman (chlorinity 19.65-19.75‰, temperature 15-20‰C) flows to the west from its region of formation and generally flows north along the southern New South Wales coast in late winter. The South-west Tasman (chlorinity 19.50- 19.60‰, temperature 12-15°C) flows to the east in latitude 38�S. and curves south in a clockwise gyral off eastern Tasmania between October and December. The Xorth Bass Strait (chlorinity 19.66-19.75‰ temperature 12-17�C) flows from South Australia to the eastern approaches of Bass Strait. The East Central New Zealand (chlorinity 19.10-19.30‰, temperature 15-20°C) flows west through Cook Strait into the Tasman Sea in midsummer. The East and West Tasmanian (chlorinity 19.40- 19.50‰ temperature 10-14°C) form in midwinter in the southern part of Bass Strait and flow along the east and west coasts in the spring.

scholarly journals High-resolution measurements of elemental mercury in surface water for an improved quantitative understanding of the Baltic Sea as a source of atmospheric mercury

2017 ◽  
Author(s):  
Joachim Kuss ◽  
Siegfried Krüger ◽  
Johann Ruickoldt ◽  
Klaus-Peter Wlost
Keyword(s):  
Surface Water ◽  
High Resolution ◽  
Baltic Sea ◽  
Elemental Mercury ◽  
Ambient Air ◽  
Atmospheric Mercury ◽  
Small Scale ◽  
The Baltic Sea ◽  
Marginal Seas ◽  
The Baltic

Abstract. Marginal seas are directly subjected to anthropogenic and natural influences from land in addition to receiving inputs from the atmosphere and open ocean. Together these lead to pronounced gradients and strong dynamic changes. However, in the case of mercury emissions from these seas, estimates often fail to adequately account for the spatial and temporal variability of the elemental mercury concentration in surface water (Hg0wat). In this study, a method to measure Hg0wat at high resolution was devised and subsequently validated. The better-resolved Hg0wat dataset, consisting of about one measurement per nautical mile, yielded insight into the sea's small-scale variability and thus improved the quantification of the sea's Hg0 emissions, a major source of atmospheric mercury. Research campaigns in the Baltic Sea were carried out between 2011 and 2015 during which Hg0 both in surface water and in ambient air were measured. For the former, two types of equilibrators were used. A membrane equilibrator enabled continuous equilibration and a bottle equilibrator assured that equilibrium was reached for validation. The measurements were combined with data obtained in the Baltic Sea in 2006 from a bottle equilibrator only. The Hg0 sea-air flux was newly calculated with the combined dataset based on current knowledge of the Hg0 Schmidt number, Henry's law constant, and a widely used gas-exchange transfer velocity parameterization. By using a newly developed pump-CTD with increased pumping capability in the Hg0 equilibrator measurements, Hg0wat could also be characterized in deeper water layers. A process study carried out near the Swedish island Øland in August 2015 showed that the upwelling of Hg0-depleted water contributed to Hg0 emissions of the Baltic Sea. However, a delay of a few days after contact between the upwelled water and light was apparently necessary before the biotic and abiotic transformations of ionic to volatile Hg0 produced a distinct sea-air Hg0 concentration gradient. This study clearly showed spatial, seasonal, and interannual variability in the Hg0 sea-air flux of the Baltic Sea. The average annual Hg0 emission was 0.90 ± 0.18 Mg for the Baltic Proper and to 1.73 ± 0.32 Mg for the entire Baltic Sea, which is about half the amount entrained by atmospheric deposition. A comparison of our results with the Hg0 sea-air fluxes determined in the Mediterranean Sea and in marginal seas in East Asia were to some extent similar but they partly differed in terms of the deviations in the amount and seasonality of the flux.

scholarly journals A New Characterization of the Upper Waters of the central Gulf of México based on Water Mass Hydrographic and Biogeochemical Characteristics

2019 ◽  
Author(s):  
Gabriela Yareli Cervantes-Diaz ◽  
Jose Martín Hernández-Ayón ◽  
Alberto Zirino ◽  
Sharon Zinah Herzka ◽  
Victor Camacho-Ibar ◽  
...  
Keyword(s):  
Surface Water ◽  
Gulf Of Mexico ◽  
Surface Waters ◽  
Water Mass ◽  
Biogeochemical Cycles ◽  
Water Masses ◽  
Near Surface ◽  
Deep Waters ◽  
Mesoscale Processes

Abstract. In the Gulf of Mexico (GoM) at least three near-surface water masses are affected by mesoscale processes that modulate the biogeochemical cycles. Prior studies have presented different classifications of water masses where the greater emphasis was on deep waters and not on the surface waters (σθ 

scholarly journals Observations on sea-ice and surface-water geochemistry–implications for importance of sea ice in geochemical cycles in the northern Baltic Sea

2001 ◽  
Vol 33 ◽  
pp. 311-316 ◽  
Author(s):  
M. A. Granskog ◽  
J. Virkanen
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Baltic Sea ◽  
Trace Element ◽  
Sea Water ◽  
Ice Cores ◽  
The Other ◽  
Ice Formation ◽  
Nutrient Concentrations ◽  
Element Concentrations

AbstractSea-ice and surface-water samples collected in January-April 1999 in coastal areas in the northern Baltic Sea were analyzed for particle, nutrient and trace-element concentrations and salinity. Stratigraphic analyses of ice cores were also carried out. Bulk nutrient and trace-element concentrations in sea ice fluctuated widely. Nutrient concentrations in sea ice normalized to sea-water salinities showed that sea ice had, almost without exception, an excess of nutrients compared to underlying waters. For phosphorus and phosphate this can be explained by particle incorporation and snow-ice formation, whereas for nitrogen and the sum of nitrite and nitrate snow-ice formation and other mechanisms are important. The levels of Al, Cu, Fe and Ni in the ice were similar to those observed in underlying waters. Pb was observed in detectable concentrations in the ice only. This indicates that sea ice contributes lead to underlying waters during melting, and in some degree also affects the other elements. Furthermore, the observations indicate that incorporation of lead into the ice cover is governed by different processes than for the other elements studied.

scholarly journals Aegean Sea Water Masses during the Early Stages of the Eastern Mediterranean Climatic Transient (1988–90)

2006 ◽  
Vol 36 (9) ◽  
pp. 1841-1859 ◽  
Author(s):  
I. Gertman ◽  
N. Pinardi ◽  
Y. Popov ◽  
A. Hecht
Keyword(s):  
Surface Water ◽  
Deep Water ◽  
Water Mass ◽  
Sea Water ◽  
Eastern Mediterranean ◽  
Aegean Sea ◽  
Water Masses ◽  
Intermediate Water ◽  
Central Basin ◽  
Cretan Sea

Abstract The Aegean water masses and circulation structure are studied via two large-scale surveys performed during the late winters of 1988 and 1990 by the R/V Yakov Gakkel of the former Soviet Union. The analysis of these data sheds light on the mechanisms of water mass formation in the Aegean Sea that triggered the outflow of Cretan Deep Water (CDW) from the Cretan Sea into the abyssal basins of the eastern Mediterranean Sea (the so-called Eastern Mediterranean Transient). It is found that the central Aegean Basin is the site of the formation of Aegean Intermediate Water, which slides southward and, depending on their density, renews either the intermediate or the deep water of the Cretan Sea. During the winter of 1988, the Cretan Sea waters were renewed mainly at intermediate levels, while during the winter of 1990 it was mainly the volume of CDW that increased. This Aegean water mass redistribution and formation process in 1990 differed from that in 1988 in two major aspects: (i) during the winter of 1990 the position of the front between the Black Sea Water and the Levantine Surface Water was displaced farther north than during the winter of 1988 and (ii) heavier waters were formed in 1990 as a result of enhanced lateral advection of salty Levantine Surface Water that enriched the intermediate waters with salt. In 1990 the 29.2 isopycnal rose to the surface of the central basin and a large volume of CDW filled the Cretan Basin. It is found that, already in 1988, the 29.2 isopycnal surface, which we assume is the lowest density of the CDW, was shallower than the Kassos Strait sill and thus CDW egressed into the Eastern Mediterranean.

scholarly journals Planktic foraminifera and structure of surface water masses at the SW Svalbard margin in relation to climate changes during the last 2000 years

2018 ◽  
Author(s):  
Katarzyna Zamelczyk ◽  
Tine Lander Rasmussen ◽  
Markus Raitzsch ◽  
Melissa Chierici
Keyword(s):  
Surface Water ◽  
Sea Ice ◽  
Time Scale ◽  
Climate Changes ◽  
Water Masses ◽  
Warm Period ◽  
Sea Surface ◽  
Planktic Foraminifera ◽  
Near Surface ◽  
Surface Conditions

Abstract. We present a high-resolution record of properties in the subsurface (250–100 m), near surface (100–30 m) and surface (30–0 m) water masses at the SW Svalbard margin in relation to climate changes during the last 2000 years. The study is based on planktic foraminiferal proxies including the distribution patterns of planktic foraminiferal faunas, δ18O and δ13C values measured on Neogloboquadrina pachyderma, Turborotalita quinqueloba, and Globigerinita uvula, Mg / Ca-, δ18O- and transfer function-based sea surface temperatures, mean shell weights and other geochemical and sedimentological data. We compared paleo-data with modern planktic foraminiferal fauna distributions and the carbonate chemistry of the surface ocean. The results showed that cold sea surface conditions prevailed at ~ 400–800 AD and ~ 1400–1950 AD are associated with the local expression of the Dark Ages Cold Period and Little Ice Age, respectively. Warm sea surface conditions occurred at ~ 21–400 AD, ~ 800–1400 AD and from ~ 1950 AD until present and are linked to the second half of the Roman Warm Period, Medieval Warm Period and recent warming, respectively. On the centennial to multi-centennial time scale, sea surface conditions seem to be governed by the inflow of Atlantic water masses (subsurface and surface) and the presence of sea-ice and the variability of sea-ice margin (near surface water masses). However, the close correlation of sea surface temperature recorded by planktic foraminifera with total solar irradiance implies that solar activity could have exerted a dominant influence on the sea surface conditions on the decadal to multidecadal time scale.

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