| 1. |
- Amir Heidari, Payam, 1989, et al.
(författare)
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A state-of-the-art model for spatial and stochastic oil spill risk assessment: A case study of oil spill from a shipwreck
- 2019
-
Ingår i: Environment International. - : Elsevier BV. - 0160-4120 .- 1873-6750. ; 126, s. 309-320
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Tidskriftsartikel (refereegranskat)abstract
- Oil spills are serious environmental issues that potentially can cause adverse effects on marine ecosystems. In some marine areas, like the Baltic Sea, there is a large number of wrecks from the first half of the 20th century, and recent monitoring and field work have revealed release of oil from some of these wrecks. The risk posed by a wreck is governed by its condition, hazardous substances contained in the wreck and the state of the surrounding environment. Therefore, there is a need for a common standard method for estimating the risks associated with different wrecks. In this work a state-of-the-art model is presented for spatial and stochastic risk assessment of oil spills from wrecks, enabling a structured approach to include the complex factors affecting the risk values. A unique feature of this model is its specific focus on uncertainty, facilitating probabilistic calculation of the total risk as the integral expected sum of many possible consequences. A case study is performed in Kattegat at the entrance region to the Baltic Sea to map the risk from a wreck near Sweden. The developed model can be used for oil spill risk assessment in the marine environment all over the world.
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| 2. |
- Olofsson, Malin, et al.
(författare)
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Nitrate and ammonium fluxes to diatoms and dinoflagellates at a single cell level in mixed field communities in the sea
- 2019
-
Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9:1
-
Tidskriftsartikel (refereegranskat)abstract
- Growth of large phytoplankton is considered to be diffusion limited at low nutrient concentrations, yet their constraints and contributions to carbon (C) and nitrogen fluxes in field plankton communities are poorly quantified under this condition. Using secondary ion mass spectrometry (SIMS), we quantified cell-specific assimilation rates of C, nitrate, and ammonium in summer communities of large phytoplankton when dissolved inorganic nitrogen concentrations are low in temperate coastal regions. Chain-forming diatoms composed 6% of total particulate organic carbon, but contributed 20% of C assimilation, 54% of nitrate assimilation and 32% of ammonium assimilation within the plankton community. In contrast, large dinoflagellates composed 11% of total POC, and contributed 14% of the C assimilation, 4% of ammonium and 9% of nitrate assimilation within the plankton community. Measured cell-specific C and nitrate assimilation rate match the Redfield ratio and the maximal nitrate assimilation in Chaetoceros spp. predicted by mass transfer theory. However, average ammonium assimilation rates were 30 and 340% higher than predicted by mass transfer theory in Tripos/Ceratium and Chaetoceros, respectively, suggesting that microbial interactions in the phycosphere may facilitate substantial luxury ammonium uptake by Chaetoceros in environments with fluctuating nitrate concentrations.
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| 3. |
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| 4. |
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| 5. |
- Arneborg, Lars, 1969, et al.
(författare)
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Gravity Current Dynamics and Entrainment - A Process Study Based on Observations in the Arkona Basin
- 2007
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Ingår i: journal of physical oceanography. ; 37, s. 2094-2113
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Tidskriftsartikel (refereegranskat)abstract
- A 19 hour time series of dissipation, stratification and horizontal velocities has been obtained for a dense gravity current flowing into the Arkona Basin in the western Baltic Sea. The observations are compared with one-dimensional, quasi-steady theory, where the gravity component in the flow direction is balanced by bottom friction, while that in the cross flow direction is balanced by the Coriolis force. The observations deviate from the theory in that the bottom shear stress is more than twice as large as that required to balance the gravity. Several reasons for this discrepancy are discussed. A 1D turbulence model is also compared with the observations. Profiles of velocity, stratification and dissipation rates generally show similar variations with depth as the observations, although the observed dissipation rates are somewhat larger than the modeled and the modeled transverse velocities are much larger than the observed. Subsequently, the model is used to investigate the variation of the entrainment parameter for a large range of Ekman and Froude numbers. Within the modeled parameter space, the entrainment parameter can be collapsed onto a curve that is an increasing function of both the Froude and the Ekman numbers. There is one puzzling result of the observations that differs from the model results and earlier observations, namely that the observed entrainment rate increases dramatically during the observation period, where the Froude number decreases slightly. Some reasons for this increase are discussed.
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| 6. |
- Arneborg, Lars, 1969, et al.
(författare)
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MIXING IN FJORDS AND THE RELATION BETWEEN LOCAL ENERGY DISSIPATION AT A FJORD SILL AND RADIATED INTERNAL TIDES
- 2012
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Ingår i: TOS/ASLO/AGU 2012 Ocean Science Meeting abstract book, Salt Lake City, USA.
-
Konferensbidrag (refereegranskat)abstract
- Diapycnal mixing in a sill fjord is vital for renewal of the deep water inside the sill. Tides can cause such mixing, both by local turbulence at the sill associated with supercritical baroclinic flow and internal hydraulic jumps, and by radiation of internal tides away from the sill that dissipate elsewhere and cause turbulence and mixing there. Previous studies tend to look at these two processes as independent of each others, whereas they in reality are closely linked: The internal tide generation depends on the hydraulic conditions at the fjord sill, and the internal hydraulic jump strength depends on the upstream and downstream radiated columnar disturbances which over time constitute the internal tides. An effort is done to link the hydraulic theory and the internal tide generation theory, and the result is compared to recent intensive observations over the Oslo fjord sill, including high-resolution microstructure profiler transects and mooring data on and inside the sill.
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| 7. |
- Arneborg, Lars, 1969, et al.
(författare)
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Overturning and Dissipation caused by Baroclinic Tidal Flow near the Sill of a Fjord Basin
- 2009
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Ingår i: Journal of Physical Oceanography. ; 39, s. 2156-2174
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Tidskriftsartikel (refereegranskat)abstract
- Dissipation time series and moored velocity and density time series on the inner slopes of the Gullmar Fjord sill, showed that the internal tides generated at the sill radiated to the head of the fjord, were reflected, and radiated back to the sill, where they dissipated their energy mainly below sill level. A large amount of the dissipation was caused by a transitional flow at a particular phase of the internal tide, when the bottom layer descended down the sill slope and had to pass a constriction set up by a submarine hill. The inward, baroclinic, bottom layer flow transformed into a supercritical bottom jet, which separated from the bottom just downstream of the constriction. A large fraction of the dissipation took place in the successive rebounding region (the hydraulic jump) above the bottom jet, where overturns of the same size as the vertical extent of the rebounding region were observed. More than half of the dissipation was happening in the bottom boundary layer below the jet. During the transitional flow there were clear pulsations of the jet with periods of about 15 min. The amount of diapycnal mixing caused by the turbulence was reduced by the large fraction of dissipation within the bottom boundary layer, but maybe also by the high buoyancy Reynolds numbers within the rebounding region. When using a relatively new parameterization of mixing, the mixing was significantly reduced compared to using the traditional constant mixing efficiency method.
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| 8. |
- Arneborg, Lars, 1969, et al.
(författare)
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Persistent inflow of warm water onto the central Amundsen Shelf
- 2012
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Ingår i: Nature Geoscience. - : Springer Science and Business Media LLC. - 1752-0894 .- 1752-0908. ; 5:12, s. 876-880
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Tidskriftsartikel (refereegranskat)abstract
- The West Antarctic Ice Sheet contains enough ice to raise global sea level by several metres and, because it is grounded mainly below sea level, it is sensitive to ocean warming 1 . Accelerated thinning of glaciers that discharge into the Amundsen Sea over the past decades 2–4 has been proposed to be related to the presence of warmer waters beneath the ice shelves 4–6 . Three deep troughs crosscut the continental shelf of the Amundsen Sea, forming passages through which warm ocean waters can access the ice shelves, but oceanographic data has been limited. Here we present direct measurements from an ocean mooring and ship transect of the temperatures, salinities and velocities from one of these troughs in the central Amundsen Sea during the year 2010. The data show persistent inflow towards the ice shelf of relatively warm and salty water at the bottom of the trough throughout the year, and outflow of colder water above. Superposed on this background flow are barotropic current fluctuations that do not contribute significantly to the overall transport. In contrast to numerical models 7,8 , which show seasonal inflow changes in response to regional winds, we find that warm water is supplied to the Central Amundsen Shelf without strong seasonal variability.
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| 9. |
- Arneborg, Lars, 1969, et al.
(författare)
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Spatial variability of diapycnal mixing and turbulent dissipation rates in a stagnant fjord basin
- 2004
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Ingår i: Journal of Physical Oceanography. - 0022-3670. ; 34:7, s. 1679-1691
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Tidskriftsartikel (refereegranskat)abstract
- Two microstructure profilers, two ships, and four moorings with acoustic Doppler current profilers and conductivity-temperature loggers were used in an intensive effort to map the spatial and temporal variations of vertical mixing in the stagnant deep basin of Gullmar Fjord, Sweden. During three days in the beginning of August 2001 a continuous time series of turbulent kinetic energy dissipation profiles was obtained with one microstructure profiler at a fixed position near the deepest part of the fjord. During the same period the other microstructure profiler was used to obtain six sections of dissipation through the length of the basin. Two moorings were deployed in the fjord basin for one month from the end of July to the end of August. The mapping of dissipation rates reveals that the dissipation in the deep basin is confined to areas just inside the sill. More than 77% of the dissipation in the fjord basin happens above the sloping bottoms closest to the sill.
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| 10. |
- Arneborg, Lars, 1969, et al.
(författare)
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Strömklimat vid två potentiella testbäddar för strömenergi vid Orust
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Strömmätningar har utförts vid två positioner utanför Orust som ligger i Fyrbodalsområdet, för att skapa underlag för diskussioner om möjligheter och fördelar med etablering av en testbädd för marin strömenergi i Sverige. Båda positionerna uppfyller en stor del av önskemålen från Minesto, Sveriges mest etablerade företag för utvinning av el ur havsströmmar. Den ena, utanför Måseskär, är en relativt oskyddad position med ganska kraftiga strömmar nära ytan. Strömmarna är relativt variabla på tidsskalor från några dygn till veckor. Den andra, vid Svanesund innanför Orust, är en skyddad position dominerad av tidvattenrörelser. Variationerna i tiden är därför stora, med riktningsändringar fyra gånger per dygn, men dessa är förutsägbara, och variationerna över djupet är små. Däremot är fjordarna innanför Svanesund känsliga för strömhastigheter och vattentransporter genom sundet, vilka kommer att påverkas av strömenergietableringar. En testbädd där kräver därför miljökonsekvensanalyser för att undersöka hur stort energiuttag som kan göras utan att försämra fjordmiljön.
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| 11. |
- Arneborg, Lars, 1969, et al.
(författare)
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The rate of inflow and mixing during deep-water renewal in a sill fjord
- 2004
-
Ingår i: Limnology and Oceanography. - 0024-3590. ; 49:3, s. 768-777
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Tidskriftsartikel (refereegranskat)abstract
- We obtained high-resolution data on a deep-water renewal in the basin of Gullmar Fjord, Sweden, using an autonomous profiling platform. In the middle of the fjord, where the platform is anchored, renewal starts with the passage of a gravity current front and continues with a steady thickening of the new, oxygen-rich, low-nitrate bottom layer and an associated lifting of the old, oxygen-depleted, high-nitrate bottom water. The basin continuously fills to sill level during a period of 10 d. At the mouth of the fjord, a three-layer structure develops. Renewal is driven by the density difference between the intermediate water inside and the new deep water outside the fjord. The volume flux is well predicted by a hydraulic exchange model in which the upper layer plays a passive role. Local upwelling and downwelling of the upper halocline cause fluctuating baroclinic currents during renewal, but these seem to have little influence on the average volume flux of new deep water. Entrainment rates are small, and the associated volume flux increase seems to be balanced by detrainment.
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| 12. |
- Arneborg, Lars, 1969, et al.
(författare)
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Tidal Energy Loss, Internal Tide Radiation, and Local Dissipation for Two-Layer Tidal Flow over a Sill
- 2017
-
Ingår i: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 47:7, s. 1521-1538
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Tidskriftsartikel (refereegranskat)abstract
- A simple analytical model for tidal energy loss at fjord sills and its partitioning into local dissipation and radiated internal tides is presented. The analytical model builds on a two-layer assumption with quasi-steady nonlinear flow over the sill and wave radiation in the far field. When the interface is situated above sill level, upstream-and downstream-propagating internal waves are generated as the bottom-layer flow becomes partially blocked because of a hydraulic control over the sill. When this control sets in, energy is lost in the transition from supercritical flow over the sill to subcritical flow downstream of the sill. The analytical model is compared with observations at the Drobak sill in the Oslo Fjord and with idealized numerical simulations with a nonhydrostatic primitive equation model. The overall good agreement between observations, analytical model, and numerical model results indicates that the hydraulic control over the sill is a key player for both the generation of internal tides and the local energy loss. The tidal energy loss decreases with increasing height of the interface above the sill. At the same time, the fraction of energy dissipated locally increases from about 20% for the interface situated at sill level to > 50% when the upper-layer thickness is less than about 80% of the sill depth. These results correspond well with the observations in the Oslo Fjord where more energy is dissipated near the sill than is radiated away.
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| 13. |
- Arneborg, Lars, 1969
(författare)
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Turnover times for the water above sill level in Gullmar Fjord
- 2004
-
Ingår i: Continental Shelf Research. - : Elsevier BV. - 0278-4343. ; 24:4-5, s. 443-460
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Tidskriftsartikel (refereegranskat)abstract
- Daily hydrographic measurements between 1954 and 1986, monthly environmental monitoring data from the last decades, and high-resolution data from 2001 are combined to obtain statistics on the exchange of the water above sill level in Gullmar Fjord, Sweden. The analyses show: (i) that the average turnover time is 16-26 days for the water above the halocline (S < 28), and 40 days for the intermediate water below the halocline, (ii) that the exchange is dominated by baroclinic currents caused by vertical fluctuations of the halocline outside the fjord, and (iii) that the statistics for the turnover times are relatively independent of year and season. One implication of these results is that a coupling between climate variations and water quality in Gullmar Fjord, cannot be explained in terms of variations in the water exchange. (C) 2004 Elsevier Ltd. All rights reserved.
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| 14. |
- Bastviken, David, et al.
(författare)
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Determination of the piston velocity for water-air interfaces using flux chambers, acoustic Doppler velocimetry, and IR imaging of the water surface
- 2013
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202 .- 2169-8953. ; 118:2, s. 770-782
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Tidskriftsartikel (refereegranskat)abstract
- The transport of gasses dissolved in surface waters across the water-atmosphere interface is controlled by the piston velocity (k). This coefficient has large implications for, e.g., greenhouse gas fluxes but is challenging to quantify in situ. At present, empirical k-wind speed relationships from a small number of studies and systems are often extrapolated without knowledge of model performance. This study compares empirical k estimates from flux chamber and surface water gas concentration measurements (chamber method), eddy cell modeling and dissipation rates of turbulent kinetic energy (dissipation method), and a surface divergence method based on IR imaging, at a fetch limited coastal observation station. We highlight strengths and weaknesses of the methods, and relate measured k values to parameters such as wave height, and surface skin velocities. The chamber and dissipation methods yielded k values in the same order of magnitude over a 24h period with varying wind conditions (up to 10ms−1, closest weather station) and wave heights (0.01–0.30m). The surface divergence method most likely did not resolve the small turbulent eddies that cause the main divergence. Flux chamber estimates showed the largest temporal variability, with lower k values than the dissipation method during calm conditions, where the dissipation method failed as waves and instrument noise dominated over the turbulence signal. There was a strong correspondence between k from chambers, the RMS of surface velocities from IR imaging, and wave height. We propose a method to estimate area integrated values of k from wave measurements.
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| 15. |
- Björk, Göran, 1956, et al.
(författare)
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Seasonal oxygen depletion in a shallow sill fjord on the Swedish west coast
- 2017
-
Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963 .- 1879-1573. ; 175, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- During the summer of 2008, oxygen depleted water, between 5 and 12 m depth, was discovered in Sannasfjord on the Swedish west coast. The resulting sediments were black, benthic macrofauna were absent and Beggiatoa bacterial mats were a characteristic feature. This phenomenon, which was observed several years in a row, appears to be a relatively new phenomenon starting in the mid-1980s. In this study we attempt to find the underlying causes by investigating climatic effects (temperature, wind and precipitation), the local supply of nutrients from land, ecosystem change and the supply of organic material from the open Skagerrak. An analysis of long meteorological time series indicates that climatic effects are contributory, but probably not a dominating factor leading to hypoxia. Results from an advection-diffusion model solving for oxygen show that the observed increase in the river supply of nutrients has a high potential to generate hypoxia. Although complex and more difficult to quantify, it appears that ecosystem changes, with higher abundance of filamentous algae, may have played an important role. It is also possible that an enhanced supply of organic material from the open Skagerrak has contributed. (C) 2017 Elsevier B.V. All rights reserved.
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| 16. |
- Bondelind, Mia, 1980, et al.
(författare)
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Storlek och dynamik i sedimentbunden föroreningstransport i Göta älv orsakad av fartygspassage – inledande metodik-studie
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Flera olika källor bidrar till föroreningar i älven där till exempel metaller släpps ut via industrier och organiska ämnen släpps ut med avlopps-, dag- och kylvatten. Olika verksamheter har funnits längs med Göta älv under en lång tid och på många ställen finns föroreningar som via grundvattnet lakas ur jorden eller som tillförs älven genom skred. I sedimenten i älven har organiska miljögifter (t.ex. TBT, PCB, PAH och dioxiner) och metaller så som kadmium, koppar, bly, kvicksilver och zink uppmätts. Den årliga sedimenttransporten i Göta älv har uppskattas till 130-170 000 ton. Den totala mängden sediment som eroderas av fartyg har uppskattas till 40 000 ton per år, men då har inte hänsyn tagit till att en del av detta material har resuspenderats. Partiklarna i vattnet är potentiella föroreningsbärare då många tungmetaller fäster på partiklar, och smittämnen som bakterier, virus och parasitära protozoer är partiklar vilka kan utgöra en hälsorisk för konsumenterna. Turbiditetsmätningar längs Göta älv har visat ökade turbiditetsvärden efter fartygspassager i älven, men det är framförallt den initiala, kortvariga toppen som uppmärksammats. För att finna lämpliga åtgärder när det gäller provtagningar som underlag för masstransport och konsekvenser för råvattenintag behövs kunskaper om hela förloppet i tid och i djupled.Denna inledande studie har syftat till att undersöka metodik för att beskriva storlek och dynamik för den av fartyg orsakade turbiditetsökningen och eventuella föroreningstransporten i Göta älv. Studien har genomförs genom analyser av föroreningsinnehåll i vattenprover, hydrodynamisk modellering med anpassning för fartygspassagernas påverkan och mätning av vattenhastighet i älven vid Lärjeholm. Den huvudsakliga hypotesen är att föroreningstransporten varierar i djupled och att dynamiken i föroreningspassagen som vissa fartygspassager orsakar bör beaktas. Detta skulle kunna ge bättre underlag för planering och utvärdering av provtagningar. Det kan också ge en möjlighet att minska föroreningsmängden i det råvatten som tas in vid Göteborg stads råvattenintag vid Lärjeholm genom att lägga intaget på lämpligt djup i förhållande till föroreningstransporten. Tänkbara åtgärder för att ta in mindre föroreningar i intaget är ändrat intagsdjup eller stängning vid vissa båtpassager.Resultaten från denna begränsade studie ska tolkas med försiktighet, men visar att den relativt kraftiga ökning av grumlighet och partikelbundna föroreningar som kan observeras i samband med fartygspassager på grund av sin korta varaktighet har liten betydelse jämfört med den ökning som kan kvarstå under åtskilliga timmar. Blyhalten kan till exempel dubbleras och en ökning kvarstå under mer än tre timmar. Föroreningshalter av t ex bly kan under den första timmen efter passagen öka med djupet för att under de följande timmarna vara mer jämnt fördelade i djupprofilen. De partiklar som resuspenderas vid fartygspassager tycks till stor del ha en så låg sedimentationshastighet att de under normal fartygstrafik inte hinner sedimentera innan nästa passage. Hydrodynamisk modellering kan vara ett kraftfullt verktyg för att prediktera flödesmönster, erosion och turbiditetsökning vid fartygspassager. Med en modell kan olika scenarier utvärderas och rekommendationer utfärdas utifrån resultaten. Mätning av turbulens, strömmar och turbiditet under och bakom fartygen bör genomföras för att undersöka om sedimentet resuspenderas i fartygets bana och sedan dispergera in till älvkanten. Undersökning bör genomföras om vissa partier i älven ger upphov till större mängd upprivet sediment som sedan transporteras ned förbi intaget. En möjlighet skulle kunna vara att minska resuspensionen genom att anpassa fartygens hastigheter efter storlek och last, samt om de går motströms eller medströms. Detta skulle ge ytterligare underlag för representativa stickprover efter fartygspassager för beräkning av masstransport med djup- och tidsberoende.
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| 17. |
- Burchard, H., et al.
(författare)
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Dynamics of medium-intensity dense water plumes in the Arkona Basin, Western Baltic Sea
- 2005
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Ingår i: Ocean Dynamics. - : Springer Science and Business Media LLC. - 1616-7341 .- 1616-7228. ; 55:5-6, s. 391-402
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the dynamics of medium-intensity inflow events over Drogden Sill into the Arkona Sea are investigated. Idealised model simulations carried out with the General Estuarine Transport Model suggest that most of the salt transport during such inflow events occur north of Kriegers Flak, a shoal with less than 20 in water depth Surrounded by water depths of more than 40 in. This assumption about the pathway is supported by recent ship-based observations in the Arkona Sea during a medium-intensity inflow event. The propagation of a saline bottom plume could be observed during several days after having passed Drogden Sill. In the area north of Kriegers Flak the plume was about 10 m thick, and propagated with more than 0.5 m s(-1) and a salinity of tip to 20 psu (with ambient water salinity being 8 psu) eastwards. Although the model simulations were idealised, the Structural agreement between the observation and model result was good, The structure and pathways of these medium-intensity inflow events are of specific interest due to the plans for erecting extensive offshore wind farms in the Arkona Sea which may under certain circumstances lead to increased entrainment of ambient water into the bottom Plumes.
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| 18. |
- Erlandsson, Carina P., et al.
(författare)
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The sensitivity of minimum oxygen concentrations in a fjord to changes in biotic and abiotic external forcing
- 2006
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Ingår i: Limnology and Oceanography. - 0024-3590. ; 51:1, part 2, s. 631-638
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Tidskriftsartikel (refereegranskat)abstract
- We investigated the possible biotic and abiotic causes of the observed long-term decrease of oxygen minimum concentrations in the deep water of Gullmar Fjord. Physical factors explained about 40% of the decreased minimum oxygen concentrations since the 1950s. The North Atlantic Oscillation and more regional climate variations account for an important part of this change. The effect of the climate variations was mainly on the timing of the renewal of the basin water. The consumption rate of oxygen in the basin water has increased by 50% since the 1950s. This biotic effect explained about 60% of the decrease in minimum oxygen concentrations. The likely dominating source of oxygen-consuming matter was (remote) production in the Skagerrak, suggesting that there has been a long-term increase of particulate organic carbon in the Skagerrak water.
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| 19. |
- Fredriksson, Sam, 1966, et al.
(författare)
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An evaluation of gas transfer velocity parameterizations during natural convection using DNS
- 2016
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Ingår i: Journal of Geophysical Research - Oceans. - 0148-0227 .- 2156-2202. ; 121:2, s. 1400-1423
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Tidskriftsartikel (refereegranskat)abstract
- Direct numerical simulations (DNS) of free surface flows driven by natural convection are used to evaluate different methods of estimating air-water gas exchange at no-wind conditions. These methods estimate the transfer velocity as a function of either the horizontal flow divergence at the surface, the turbulent kinetic energy dissipation beneath the surface, the heat flux through the surface, or the wind speed above the surface. The gas transfer is modeled via a passive scalar. The Schmidt number dependence is studied for Schmidt numbers of 7, 150 and 600. The methods using divergence, dissipation and heat flux estimate the transfer velocity well for a range of varying surface heat flux values, and domain depths. The two evaluated empirical methods using wind (in the limit of no wind) give reasonable estimates of the transfer velocity, depending however on the surface heat flux and surfactant saturation. The transfer velocity is shown to be well represented by the expression, k(s) = A (Bv)(1/4) Sc2(n), where A is a constant, B is the buoyancy flux, m is the kinematic viscosity, Sc is the Schmidt number, and the exponent n depends on the water surface characteristics. The results suggest that A = 0.39 and n approximate to 1/2 and n approximate to 2/3 for slip and no-slip boundary conditions at the surface, respectively. It is further shown that slip and no-slip boundary conditions predict the heat transfer velocity corresponding to the limits of clean and highly surfactant contaminated surfaces, respectively.
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| 20. |
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| 21. |
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| 22. |
- Fredriksson, Sam, 1966, et al.
(författare)
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Near-surface physics during convection affecting air-water gas transfer
- 2016
-
Ingår i: IOP Conference Series: Earth and Environmental Science. - : IOP Publishing. - 1755-1307 .- 1755-1315. ; 35:1, s. 012007-
-
Konferensbidrag (refereegranskat)abstract
- The gas flux at the water surface is affected by physical processes including turbulence from wind shear, microscale wave breaking, large-scale breaking, and convection due to heat loss at the surface. The main route in the parameterizations of the gas flux has been to use the wind speed as a proxy for the gas flux velocity, indirectly taking into account the dependency of the wind shear and the wave processes. The interest in the contributions from convection processes has increased as the gas flux from inland waters (with typically lower wind and sheltered conditions) now is believed to play a substantial role in the air-water gas flux budget. The gas flux is enhanced by convection through the mixing of the mixed layer as well as by decreasing the diffusive boundary layer thickness. The direct numerical simulations performed in this study are shown to be a valuable tool to enhance the understanding of this flow configuration often present in nature.
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| 23. |
- Fredriksson, Sam, 1966, et al.
(författare)
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Surface shear stress dependence of gas transfer velocity parameterizations using DNS
- 2016
-
Ingår i: Journal of Geophysical Research: Oceans. - 2169-9275 .- 2169-9291 .- 0148-0227 .- 2156-2202. ; 121:10, s. 7369-7389
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Tidskriftsartikel (refereegranskat)abstract
- Air-water gas-exchange is studied in direct numerical simulations (DNS) of free-surface flows driven by natural convection and weak winds. The wind is modeled as a constant surface-shear-stress and the gas-transfer is modeled via a passive scalar. The simulations are characterized via a Richardson number Ri=Bν/u*4 where B, ν, and u* are the buoyancy flux, kinematic viscosity, and friction velocity respectively. The simulations comprise 0Ric or kg=Ashearu*Sc-n, Ri
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| 24. |
- Gröger, M., et al.
(författare)
-
Summer hydrographic changes in the Baltic Sea, Kattegat and Skagerrak projected in an ensemble of climate scenarios downscaled with a coupled regional ocean–sea ice–atmosphere model
- 2019
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Ingår i: Climate Dynamics. - : Springer Science and Business Media LLC. - 0930-7575 .- 1432-0894. ; 53, s. 5945-5966
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Tidskriftsartikel (refereegranskat)abstract
- © 2019, The Author(s). This model study investigates summer hydrographic changes in response to climate projections following the CMIP5 RCP8.5 scenario. We use the high resolution regional coupled ocean–sea ice–atmospheremodel RCA4–NEMO to downscale an ensemble of five global climate projections with a main focus on the Baltic Sea and neighboring shelf basins to the west. We find consistently across the ensemble a northward shift in the mean summer position of the westerlies at the end of the twenty-first century compared to the twentieth century. Associated with this is an anomalous precipitation pattern marked by increased rainfall over northern Europe and dryer conditions over the continental central part. In response to these large-scale atmospheric changes, a strong freshening mainly resulting from a higher net precipitation over the year combined with higher annual mean runoff is registered for the Baltic Sea and adjacent seas. The strongest freshening takes place in the southern Skagerrak region where stronger winds enhance the cyclonic circulation and by this, recirculation of fresher waters from the Baltic Sea strengthens. In the Baltic Sea freshening leads to a reduction in basin averaged salinities between 0.6 and 2.3gkg−1 throughout the ensemble. Likewise, the sea surface temperature response in the Baltic Sea varies between + 2.5 and + 4.7K depending on the applied global model scenario. The climate induced changes in atmospheric forcing have further consequences for the large-scale circulation in the Baltic Sea. All ensemble members indicate a strengthening of the zonal, wind driven near surface overturning circulation in the southwestern Baltic Sea towards the end of the twenty-first century whereas the more thermohaline driven overturning at depth is reduced by ~ 25%. In the Baltic Proper, the meridional overturning shows no clear climate change signal. However, three out of five ensemble members indicate at least a northward expansion of the main overturning cell. In the Bothnian Sea, all ensemble members show a significant weakening of the meridional overturning. The entire ensemble consistently indicates a basin-wide intensification of the pycnocline (9–35%) for the Baltic Sea and a shallowing of the pycnocline depth in most regions as well. In the Baltic Sea, which is dominated by mesohaline conditions under the historical period, the changes in salinity at the end of the twenty-first century have turned wide areas to be dominated by oligohaline conditions as a result of climate change. Potential consequences for biogeochemical conditions and implications for biodiversity are discussed.
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| 25. |
- Ha, H.K., et al.
(författare)
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Circulation and modification of warm deep water on the central Amundsen Shelf
- 2014
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Ingår i: Journal of Physical Oceanography. - 0022-3670. ; 44:5, s. 1493-1501
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Tidskriftsartikel (refereegranskat)abstract
- The circulation pathways and subsurface cooling and freshening of warm deep water on the central Amundsen Sea shelf are deduced from hydrographic transects and four subsurface moorings. The Amundsen Sea continental shelf is intersected by Dotson Trough (DT) leading from the outer shelf to the deep basins on the inner shelf. During the measurement period, warm deep water was observed to flow southward on the eastern side of DT in approximate geostrophic balance. A northward outflow from the shelf was also observed along the bottom in the western side of DT. Estimates of the flow rate suggest that up to one third of the inflowing warm deep water leaves the shelf area below the thermocline in this deep outflow. The deep current was 1.2°C colder and 0.3 psu fresher than the inflow, but still warm, salty and dense compared to the overlying water mass. The temperature and salinity properties suggest that the cooling and freshening process is induced by subsurface melting of glacial ice, likely from basal melting of Dotson and Getz ice shelves. New heat budgets are presented, with a southward oceanic heat transport of 3.3 TW on the eastern side of the DT, a northward oceanic heat transport of 0.5-1.6 TW on the western side, and an ocean-to-glacier heat flux of 0.9-2.53 TW, equivalent to melting glacial ice at the rate of 83- 237 km3yr-1 . Recent satellite-based estimates of basal melt rates for the glaciers suggest comparable values, 145 km3yr-1 (Getz) and 45 km3yr-1 35 (Dotson) (Rignot et al. 2013).
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| 26. |
- Karlsson, Therese, 1987, et al.
(författare)
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The unaccountability case of plastic pellet pollution
- 2018
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Ingår i: Marine Pollution Bulletin. - : Elsevier BV. - 0025-326X. ; 129:1, s. 52-60
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Tidskriftsartikel (refereegranskat)abstract
- Plastic preproduction pellets are found in environmental samples all over the world and their presence is often linked to spills during production and transportation. To better understand how these pellets end up in the environment we assessed the release of plastic pellets from a polyethylene production site in a case study area on the Swedish west coast. The case study encompasses; field measurements to evaluate the level of pollution and pathways, models and drifters to investigate the potential spread and a revision of the legal framework and the company permits. This case study show that millions of pellets are released from the production site annually but also that there are national and international legal frameworks that if implemented could help prevent these spills. Bearing in mind the negative effects observed by plastic pollution there is an urgent need to increase the responsibility and accountability of these spills.
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| 27. |
- Linders, Torsten, 1971, et al.
(författare)
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Enhanced diapycnal mixing during intermediate flushing of a deep sill fjord
- 2012
-
Ingår i: Ocean Sciences Meeting.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A flushing event occurred during a 24 h period, with strong inflow at intermediate levels. This coincided with enhanced dissipation rates at the levels of inflow in a wedge extending 6 km into the fjord. The density and dissipation rate fields reveal nonlinear, oblique internal wave beams with typical horizontal length scales from 0.3 to 3 km. The beams extend from the bottom and from the halocline near the entrance towards the center of the inflowing layer, bounding the wedge of enhanced dissipation. Data from the entire 24 h period show that the dissipation rate has a rather consistent Richardson number dependency, with higher dissipation rates for lower Richardson numbers. However, for buoyancy-frequency and shear the picture is little bit more mixed. Dissipation rates appear to be independent of the shear – for values of shear squared below 10-4 s-2.
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| 28. |
- Meier, H. E. M., et al.
(författare)
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Ventilation of the Baltic Sea deep water: A brief review of present knowledge from observations and models
- 2006
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Ingår i: Oceanologia. - 0078-3234. ; 48, s. 133-164
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Tidskriftsartikel (refereegranskat)abstract
- The ventilation of the Baltic Sea deep water is driven by either gale-forced barotropic or baroclinic salt water inflows. During the past two decades, the frequency of large barotropic inflows (mainly in winter) has decreased and the frequency of medium-intensity baroclinic inflows (observed in summer) has increased. As a result of entrainment of ambient oxygen-rich water, summer inflows are also important for the deep water ventilation. Recent process studies of salt water plumes suggest that the entrainment rates are generally smaller than those predicted by earlier entrainment models. In addition to the entrance area, the Slupsk Sill and the Slupsk Furrow are important locations for the transformation of water masses. Passing the Slupsk Furrow, both gravity-driven dense bottom flows and sub-surface cyclonic eddies, which are eroded laterally by thermohaline intrusions, ventilate the deep water of the eastern Gotland Basin. A recent study of the energy transfer from barotropic to baroclinic wave motion using a two-dimensional shallow water model suggests that about 30% of the energy needed below the halocline for deep water mixing is explained by the breaking of internal waves. In the deep water decade-long stagnation periods with decreasing oxygen and increasing hydrogen sulphide concentrations might be caused by anomalously large freshwater inflows and anomalously high mean zonal wind speeds. In different studies the typical response time scale of average salinity was estimated to be between approximately 20 and 30 years. The review summarizes recent research results and ends with a list of open questions and recommendations.
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| 29. |
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| 30. |
- Nylund, Amanda, 1989, et al.
(författare)
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Hydrographical implications of ship-induced turbulence in stratified waters, studied through field observations and CFD modelling
- 2023
-
Ingår i: Frontiers in Marine Science. - 2296-7745. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Ship-related energy pollution has received increasing attention but almost exclusively regarding radiated underwater noise, while the effect of ship-induced turbulence is lacking in the literature. Here we present novel results regarding turbulent wake development, the interaction between ship-induced turbulence and stratification, and discuss the impact of turbulent ship wakes in the surface ocean, in areas with intense ship traffic. The turbulent wake development was studied in situ, using Acoustic Doppler Current Profilers (ADCP) and conductivity, temperature, depth (CTD) observations of stratification, and through computational fluid dynamics (CFD) modelling. Our results show that the turbulent wake interacts with natural hydrography by entraining water from below the pycnocline, and that stratification influences the turbulent wake development by dampening the vertical extent, resulting in the wake water spreading out along the pycnocline rather than at the surface. The depth and intensity of the turbulent wake represent an unnatural occurrence of turbulence in the surface ocean. The ship-induced turbulence can impact local hydrography, nutrient dynamics and increase plankton mortality due to physical disturbance, especially in areas with intense traffic. Therefore, sampling and modelling of e.g., contaminants in shipping lanes need to consider hydrographic conditions, as stratification may alter the depth and spread of the wake, which in turn governs dilution. Finally, the frequent ship traffic in estuarine and coastal areas, calls for consideration of ship-induced turbulence when studying hydrographic processes.
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| 31. |
- Nylund, Amanda, 1989, et al.
(författare)
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In situ observations of turbulent ship wakes and their spatiotemporal extent
- 2021
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Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0792 .- 1812-0784. ; 17:5, s. 1285-1302
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Tidskriftsartikel (refereegranskat)abstract
- In areas of intensive ship traffic, ships pass every 10ĝ€¯min. Considering the amount of ship traffic and the predicted increase in global maritime trade, there is a need to consider all types of impacts shipping has on the marine environment. While the awareness about, and efforts to reduce, chemical pollution from ships is increasing, less is known about physical disturbances, and ship-induced turbulence has so far been completely neglected. To address the potential importance of ship-induced turbulence on, e.g., gas exchange, dispersion of pollutants, and biogeochemical processes, a characterisation of the temporal and spatial scales of the turbulent wake is needed. Currently, field measurements of turbulent wakes of real-size ships are lacking. This study addresses that gap by using two different methodological approaches: in situ and ex situ observations. For the in situ observations, a bottom-mounted acoustic Doppler current profiler (ADCP) was placed at 32ĝ€¯m depth below the shipping lane outside Gothenburg harbour. Both the acoustic backscatter from the air bubbles in the wake and the dissipation rate of turbulent kinetic energy were used to quantify the turbulent wake depth, intensity, and temporal longevity for 38 ship passages of differently sized ships. The results from the ADCP measurements show median wake depths of 13ĝ€¯m and several occasions of wakes reaching depths >ĝ€¯18ĝ€¯m, which is in the same depth range as the seasonal thermocline in the Baltic Sea. The temporal longevity of the observable part of the wakes had a median of around 10ĝ€¯min and several passages of >ĝ€¯20ĝ€¯min. In the ex situ approach, sea surface temperature was used as a proxy for the water mass affected by the turbulent wake (thermal wake), as lowered temperature in the ship wake indicates vertical mixing in a thermally stratified water column. Satellite images of the thermal infrared sensor (TIRS) onboard Landsat-8 were used to measure thermal wake width and length, in the highly frequented and thus major shipping lane north of Bornholm, Baltic Sea. Automatic information system (AIS) records from both the investigated areas were used to identify the ships inducing the wakes. The satellite analysis showed a median thermal wake length of 13.7ĝ€¯km (nCombining double low line144), and the longest wake extended over 60ĝ€¯km, which would correspond to a temporal longevity of 1ĝ€¯h 42ĝ€¯min (for a ship speed of 20ĝ€¯kn). The median thermal wake width was 157.5ĝ€¯m. The measurements of the spatial and temporal scales are in line with previous studies, but the maximum turbulent wake depth (30.5ĝ€¯m) is deeper than previously reported. The results from this study, combined with the knowledge of regional high traffic densities, show that ship-induced turbulence occurs at temporal and spatial scales large enough to imply that this process should be considered when estimating environmental impacts from shipping in areas with intense ship traffic.
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| 32. |
- Nylund, Amanda, 1989, et al.
(författare)
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Modellering av omblandning i fartygs kölvatten, för ökad förståelse av belastning på havsmiljön till följd av utsläpp från fartyg
- 2020
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- Östersjön är ett av världens mest intensivt trafikerade områden och i vissa delar sker en fartygspassage i genomsnitt var tolfte minut. Fartygen kan betraktas som flytande industrier som släpper ut föroreningar, försurande och övergödande ämnen som produceras i olika ombordssystem, såsom svart-, grå-, ballast-, läns-, kyl- och skrubbervatten, giftiga båtbottenfärger och propellerhylsolja. De senaste årens ökade förståelse för att sjöfartens utsläpp inte är negligerbara för havsmiljön belyses i Miljömålsberedningens betänkande Havet och människan (2020), där det bland annat föreslås att Havs- och vattenmyndigheten bör få i uppdrag att integrera övervakning av sjöfartens påverkan på havsmiljön i sin verksamhet. För att kunna göra detta på ett effektivt sätt är det nödvändigt att förstå hur föroreningar som släpps ut från fartyg sprids vidare i havsmiljön. Med utgångspunkt från denna kunskap kan miljöövervakningsprogram utformas och i förlängningen åtgärder vidtas för att minska påverkan från sjöfart på havsmiljön, exempelvis genom förbud mot utsläpp eller omledning av farleder i känsliga områden. I befintliga modelleringar av utsläpp från fartyg görs antagandet att utsläppen sker i ytan, vilket får till följd att beräkningen av spridningen i miljön i stor utsträckning kommer att styras av rådande vind- och strömförhållanden i ytskiktet. Detta kan vara acceptabelt, exempelvis vid modellering av lättare oljeprodukter, men för andra ämnen är det nödvändigt att förstå hur omblandningen i kölvattnet sker för att mer korrekt kunna beräkna hur föroreningarna sprider sig i miljön; strömförhållanden kan variera avsevärt i både riktning och styrka på 5–10 m djup, jämfört med i ytan. Syftet med den här förstudien var att undersöka förutsättningarna att kombinera beräkningsströmningsdynamik (Computational Fluid Dynamics (CFD)) som vanligtvis används för att göra högupplösta 3D modelleringar av strömningen runt skrov och propeller på fartyg, med regionala oceanografiska modeller. Användningen av den högupplösta 3D Reynolds- Medelvärdesbildad Navier-Stokes (3D RANS) modellen är dock beräkningsintensiv och brukar endast användas för att modellera närvaken, upp till någon fartygslängd akter om fartyget. För att kunna brygga över skalorna i fjärrvaken (ca 0,8–3 km) akter om fartyget är det därför lämpligt att försöka förenkla beräkningarna, vilket kan göras genom semi-empirisk modellering och 2D modellering av ett tvärsnitt av vaken över tid, vilka i begränsad omfattning validerats mot 3D RANS resultaten. Vidare har in-situ mätningar med en Acoustic Doppler Current Profiler (ADCP) använts för att validera utbredningen av det turbulenta vakområdet. Resultaten av förstudien, både från modellering och fältmätningarna, visar tydligt att utsläpp i fartygsvaken kan spridas på olika djup och i olika riktning som en effekt av omblandningen som sker i vaken. Vidare är hydrografin viktig för hur och var spridningen i vaken sker och fältmätningarna indikerar att när det finns en stark skiktning kommer det omblandade vattnet i fartygsvaken att spridas i sidled, längs med skiktningen, istället för nedåt mot botten. Ur miljöövervakningsperspektiv är det därför viktigt att känna till skiktningen och djupet i relation till farledernas placering, då det får konsekvenser för spridningen av föroreningar från farleden och därmed även var provtagning bör ske. Slutsatsen från förstudien är att det föreslagna ramverket, kombinationen av olika teoretiska modeller och in-situ mätningar, har stor potential för att kunna leverera indata till regionala oceanografiska modeller, för att kunna modellera den storskaliga spridningen av föroreningar från fartyg och farleder. Denna information är också kritisk för utformning av övervakningsprogram, där det är avgörande att mätningar görs där föroreningar från fartyg kan förväntas att återfinnas.
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| 33. |
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| 34. |
- Staalstrom, A., et al.
(författare)
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Observations of Turbulence Caused by a Combination of Tides and Mean Baroclinic Flow over a Fjord Sill
- 2015
-
Ingår i: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 45:2, s. 355-368
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Tidskriftsartikel (refereegranskat)abstract
- This study investigates the dissipation rates and flow conditions at the Drobak Sill in the Oslofjord. The area was transected 13 times with a free-falling microstructure shear probe during 4 days in June 2011. At the same time, an ADCP was deployed inside the sill. During most tidal cycles, internal hydraulic jumps with high dissipation rates were found on the downstream side of the sill. However, the internal response varied strongly between different tidal cycles with similar barotropic forcing. In the beginning of the observational period, ebb tides had no hydraulic jumps, and in the end one of the flood tides did not have a hydraulic jump. During the same period, the mean baroclinic exchange flow changed from inflow to outflow in the bottom layer. The authors conclude that the conditions at the sill are on the edge of forming hydraulic jumps and that the mean baroclinic exchange may push the flow above or below the limit of a hydraulic jump depending on the situation. This conclusion is supported by two-layer hydraulic theory. The volume-integrated dissipation rates within 500m from the sill crest compare well with estimates of energy loss in the lower layer calculated from the Bernoulli drop under the assumption of no energy loss in the upper layer. Finally, the mean dissipation rate at the sill was compared with the radiation of internal tidal energy away from the sill, and it was found that about 60%-90% of the total energy loss was dissipated locally.
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| 35. |
- Umlauf, L., et al.
(författare)
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Dynamics of rotating shallow gravity currents passing through a channel. Part I: Observation of transverse structure
- 2009
-
Ingår i: Journal of Physical Oceanography. ; 39, s. 2385-2401
-
Tidskriftsartikel (refereegranskat)abstract
- We present a detailed data set describing a quasi-stationary bottom gravity current, approximately 10 m thick and 10 km wide, passing through a channel-like constriction in the Western Baltic Sea. The data include full-depth, synoptic, and highly resolved transects of stratification and turbulence parameters, as well as detailed velocity transects across the gravity current at different down-channel locations. Our velocity data reveal a persistent transverse circulation, creating a characteristic wedge-shaped density structure in the interface. A strong asymmetry was also found in the interior of the gravity current, where we observed the evolution of a dynamically significant transverse density gradient to the right of the down-channel flow. Spectral analysis of the near-bottom velocities showed a surprisingly strong contribution to the bottom stress from low-frequency motions with periods up to 30 minutes that are possibly related to internal wave effects. Cross-channel transects of shearmicrostructure were used to investigate the transverse variation of local entrainment rates and bottom stresses. These data indicate that frictional control is essential for this class of gravity currents that are characterized by subcritical Froude numbers, small entrainment, strong rotational effects, and small thickness compared to the bottom Ekman layer.
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| 36. |
- Umlauf, L., et al.
(författare)
-
Dynamics of rotating shallow gravity currents passing through a channel. Part II: Analysis
- 2009
-
Ingår i: Journal of Physical Oceanography. ; 39, s. 2402-2416
-
Tidskriftsartikel (refereegranskat)abstract
- The physics of frictional control for channelized rotating gravity currents are analyzed using an extensive data set including hydrographic, current, and microstructure measurements from the Western Baltic Sea. Rotational effects in these gravity currents, characterized by Ekman numbers of the order of one and sub-critical Froude numbers, induce a complex transverse circulation that strongly affects the internal dynamics. The key component of this circulation is a geostrophically balanced transverse jet in the interface that modifies the entrainment process by (i) laterally draining the interface and (ii) providing additional interfacial shear comparable to the down-channel shear. The recirculation of mixed interfacial fluid into the interior distorts the internal density structure of the gravity current, and creates a thermal wind shear in the interior that is comparable to the observed shear. Using a theoretical model, this effect is shown to be responsible for the three-layer structure of the transverse velocity with the near-bottom velocity and stress directed opposite to the Ekman transport. Our analysis confirms the key assumption in available models for frictional control in rotating gravity currents: the transverse Ekman transport is balanced by the geostrophic transport due to the down-channel tilt of the interface.
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| 37. |
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| 38. |
- Wåhlin, Anna, 1970, et al.
(författare)
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Some Implications of Ekman Layer Dynamics for Cross-Shelf Exchange in the Amundsen Sea MMERMANN R, 2010, EARTH SYSTEM SCI DAT, V0002
- 2012
-
Ingår i: Journal of Physical Oceanography. - : American Meteorological Society. - 0022-3670 .- 1520-0485. ; 42:9, s. 1461-1474
-
Tidskriftsartikel (refereegranskat)abstract
- The exchange of warm, salty seawater across the continental shelves off West Antarctica leads to subsurface glacial melting at the interface between the ocean and the West Antarctic Ice Sheet. One mechanism that contributes to the cross-shelf transport is Ekman transport induced by along-slope currents over the slope and shelf break. An investigation of this process is applied to the Amundsen Sea shelfbreak region, using recently acquired and historical field data to guide the analyses. Along-slope currents were observed at transects across the eastern and western reaches of the Amundsen slope. Currents in the east flowed eastward, and currents farther west flowed westward. Under the eastward-flowing currents, hydrographic isolines sloped upward paralleling the seabed. In this layer, declining buoyancy forces rather than friction were bringing the velocity to zero at the seabed. The basin water in the eastern part of the shelf was dominated by water originating from 800-1000-m depth off shelf, suggesting that transport of such water across the shelf frequently occurs. The authors show that arrested Ekman layers mechanism can supply deep water to the shelf break in the eastern section, where it has access to the shelf. Because no unmodified off-shelf water was found on the shelf in the western part, bottom layer Ekman transport does not appear a likely mechanism for delivery of warm deep water to the western shelf area. Warming of the warm bottom water was most pronounced on the western shelf, where the deep-water temperature increased by 0.6 degrees C during the past decade.
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| 39. |
- Wåhlin, Anna, 1970, et al.
(författare)
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Variability of Warm Deep Water Inflow in a Submarine Trough on the Amundsen Sea Shelf
- 2013
-
Ingår i: Journal of Physical Oceanography. - 0022-3670 .- 1520-0485. ; 43:10, s. 2054-2070
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Tidskriftsartikel (refereegranskat)abstract
- The ice shelves in the Amundsen Sea are thinning rapidly, and the main reason for their decline appears to be warm ocean currents circulating below the ice shelves and melting these from below. Ocean currents transportwarm densewater ontothe shelf,channeledby bathymetric troughs leadingto the deep inner basins. A hydrographic mooring equipped with an upward-looking ADCP has been placed in one of these troughs on the central Amundsen shelf. The two years (2010/11) of mooring data are here used to characterize the inflow of warm deep water to the deep shelf basins. During both years, the warm layer thickness and temperature peaked in austral fall. The along-trough velocity is dominated by strong fluctuations that do not vary in the vertical. These fluctuations are correlated with the local wind, with eastward wind over the shelf and shelf break giving flow toward the ice shelves. In addition, there is a persistent flow of dense lower Circumpolar Deep Water (CDW) toward the ice shelves in the bottom layer. This bottom-intensified flow appears to be driven by buoyancy forces rather than the shelfbreak wind. The years of 2010 and 2011 were characterized by a comparatively stationary Amundsen Sea low, and hence there were no strong eastward winds during winter that could drive an upwelling of warm water along the shelf break. Regardless of this, there was a persistent flow of lower CDW in the bottom layer during the two years. The average heat transport toward the ice shelves in the trough was estimated from the mooring data to be 0.95 TW.
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| 40. |
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