| 1. |
- 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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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
-
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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| 5. |
- Arneborg, Lars, 1969, et al.
(författare)
-
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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| 6. |
- 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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| 7. |
- 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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| 8. |
- Forth, Michael, et al.
(författare)
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Effects of ecological engineered oxygenation on the bacterial community structure in an anoxic fjord in western Sweden
- 2015
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Ingår i: The ISME Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 9:3, s. 656-669
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-depleted bodies of water are becoming increasingly common in marine ecosystems. Solutions to reverse this trend are needed and under development, for example, by the Baltic deep-water OXygenation (BOX) project. In the framework of this project, the Swedish Byfjord was chosen for a pilot study, investigating the effects of an engineered oxygenation on long-term anoxic bottom waters. The strong stratification of the water column of the Byfjord was broken up by pumping surface water into the deeper layers, triggering several inflows of oxygen-rich water and increasing oxygen levels in the lower water column and the benthic zone up to 110μmoll−1.We used molecular ecologic methods to study changes in bacterial community structure in response to the oxygenation in the Byfjord. Water column samples from before, during and after the oxygenation as well as from two nearby control fjords were analyzed. Our results showed a strong shift in bacterial community composition when the bottom water in the Byfjord became oxic. Initially dominant indicator species for oxygen minimum zones such as members of the SUP05 clade declined in abundance during the oxygenation event and nearly vanished after the oxygenation was accomplished. In contrast, aerobic species like SAR11 that initially were restricted to surface waters could later be detected deep into the water column. Overall, the bacterial community in the formerly anoxic bottom waters changed to a community structure similar to those found in oxic waters, showing that an engineered oxygenation of a large body of anoxic marine water is possible and emulates that of a natural oxygenation event.
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| 9. |
- Green, Mattias, 1971, et al.
(författare)
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Physical oceanography and water exchange in the Northern Kvark Strait
- 2006
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Ingår i: Continental Shelf Research. - : Elsevier BV. - 0278-4343. ; 26:6, s. 721-732
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Tidskriftsartikel (refereegranskat)abstract
- The Northern Kvark connects the very fresh Bothnian Bay to the slightly saltier Bothilian Sea in the northern Baltic Sea. Intense field experiments were made in the strait in May 2003 and October-December 2004 to describe the physical oceanography of the strait. Three different hydrographic regimes were identified and first-order analyses were made on each regime, neglecting friction, rotation, and horizontal gradients. The strait is shown to be barotropically blocked about 45% of the time. The rest of the time there is vertical stratification, which can be described either by two homogenous layers or by linear density and velocity profiles. The flows in the two stratified regimes are shown to be hydraulically controlled. (C) 2006 Elsevier Ltd. All rights reserved.
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| 10. |
- Hansson, Daniel, 1980, et al.
(författare)
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Modelling the Orust fjord system on the Swedish west coast
- 2013
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Ingår i: Journal of Marine Systems. - : Elsevier BV. - 0924-7963. ; 113-114, s. 29-41
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Tidskriftsartikel (refereegranskat)abstract
- We use a numerical model to examine the dynamics controlling flushing of the basins of the Orust fjord system on the Swedish west coast over a period of 71 days in the autumn of 2010. This fjord system is known for its seasonal and permanent hypoxic basins; Koljöfjord, Byfjord and Havstensfjord. It is shown that wind direction determines in- and outflows of the basins. Westerly winds result in surface currents towards the interior of the system, and counter currents at the bottom. In contrast, easterly winds cause the export of surface water, which is compensated by upwelling of Skagerrak water. Although these easterly winds cause renewal to take place several times a month in southern Havstensfjord, it occurs only once or twice in the northern part, while Koljöfjord and Byfjord are ventilated about every 3 years. The reduction in density throughout the water column (i.e. weakening of the vertical stratification) is related to the amount of energy being supplied to the deepwater by internal waves, created by barotropic tides across the sills, and wind blowing across the surface. The model shows that, in the southern part of the system, tidal movement dominates the energy supply to the deepwater. Further into the system, the importance of wind energy increases. In Koljöfjord and Byfjord, wind accounts for about 40% of the supplied energy for deepwater mixing. Concurrent weekly measurements taken in each fjord basin reveal that the monthly monitoring programme currently in place cannot adequately resolve the dynamics of the fjords. Modelled and observed currents in Svanesund and Sunninge Strait show prominent baroclinic motion on time-scales between one day and one week, suggesting that monitoring programs that aim to support numerical modelling need to resolve these time scales.
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| 11. |
- Kelly, Julia, et al.
(författare)
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Modelling and upscaling ecosystem respiration using thermal cameras and UAVs: Application to a peatland during and after a hot drought
- 2021
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 0168-1923. ; 300
-
Tidskriftsartikel (refereegranskat)abstract
- Field-based thermal infrared cameras provide surface temperature information at very high spatial and temporal resolution and could complement existing phenological camera and spectral sensor networks. Since temperature is one of the main drivers of ecosystem respiration (ER), field-based thermal cameras offer a new opportunity to model and upscale ER in unprecedented detail. We present such an approach based on manual chamber CO2 flux measurements and thermal imagery from a tower-based camera and from Unmanned Aerial Vehicle (UAV) flights. Data were collected over two growing seasons, including the hot drought of 2018, for the two main vegetation microforms (hummock and hollow) of a hemi-boreal peatland in Sweden. Thermal imagery proved suitable for modelling ER in this ecosystem: ER model accuracies were similar when air, soil or surface temperature measurements were used as input. Our findings allowed us to upscale ER using UAV-derived thermal images and we present maps of ER at sub-decimeter resolution (<7 cm). The significantly different ER measured for each microform highlighted the importance of modelling their ER separately. Not accounting for these differences and the microforms' spatial distribution across the peatland led to a bias in upscaled ER of up to 18%. As a result of the severity and timing of the hot drought in 2018, we observed reductions in the ER of both microforms, but more so for hummocks (-48%) than for hollows (-15%), and modelled ER leveled off at high temperatures. These findings indicate that peatland carbon loss during hot droughts may be lower than expected and strongly relates to vegetation composition. The presented upscaling approach offers a new method to analyse how ER varies across a peatland or within a flux-tower footprint, and to interpret biases that occur when using coarse resolution satellite data to upscale chamber or tower-based flux measurements.
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| 12. |
- Liljebladh, Bengt, 1959, et al.
(författare)
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De döda vikingarna i Ikkafjorden
- 2022
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Ingår i: Havsutsikt. ; :1, s. 4-7
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 13. |
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| 14. |
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| 15. |
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| 16. |
- Sohn, Robert A., et al.
(författare)
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Explosive volcanism on the ultraslow-spreading Gakkel ridge, Arctic Ocean
- 2008
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 453:7199, s. 1236-1238
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Tidskriftsartikel (refereegranskat)abstract
- Roughly 60% of the Earth's outer surface is composed of oceanic crust formed by volcanic processes at mid-ocean ridges. Although only a small fraction of this vast volcanic terrain has been visually surveyed or sampled, the available evidence suggests that explosive eruptions are rare on mid-ocean ridges, particularly at depths below the critical point for seawater (3,000 m)1. A pyroclastic deposit has never been observed on the sea floor below 3,000 m, presumably because the volatile content of mid-ocean-ridge basalts is generally too low to produce the gas fractions required for fragmenting a magma at such high hydrostatic pressure. We employed new deep submergence technologies during an International Polar Year expedition to the Gakkel ridge in the Arctic Basin at 85° E, to acquire photographic and video images of 'zero-age' volcanic terrain on this remote, ice-covered ridge. Here we present images revealing that the axial valley at 4,000 m water depth is blanketed with unconsolidated pyroclastic deposits, including bubble wall fragments (limu o Pele)2, covering a large (>10 km2) area. At least 13.5 wt% CO2 is necessary to fragment magma at these depths3, which is about tenfold the highest values previously measured in a mid-ocean-ridge basalt4. These observations raise important questions about the accumulation and discharge of magmatic volatiles at ultraslow spreading rates on the Gakkel ridge5 and demonstrate that large-scale pyroclastic activity is possible along even the deepest portions of the global mid-ocean ridge volcanic system.
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| 17. |
- Spokes, L., et al.
(författare)
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MEAD: An interdisciplinary study of the marine effects of atmospheric deposition in the Kattegat
- 2006
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 140:3, s. 453-462
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Tidskriftsartikel (refereegranskat)abstract
- This paper summarises the results of the EU funded MEAD project, an interdisciplinary study of the effects of atmospheric nitrogen deposition on the Kattegat Sea between Denmark and Sweden. The study considers emissions of reactive nitrogen gases, their transport, transformations, deposition and effects on algal growth together with management options to reduce these effects. We conclude that atmospheric deposition is an important source of fixed nitrogen to the region particularly in summer, when nitrogen is the limiting nutrient for phytoplankton growth, and contributes to the overall eutrophication pressures in this region. However, we also conclude that it is unlikely that atmospheric deposition can, on its own, induce algal blooms in this region. A reduction of atmospheric nitrogen loads to this region will require strategies to reduce emissions of ammonia from local agriculture and Europe wide reductions in nitrous oxide emissions. (c) 2005 Elsevier Ltd. All rights reserved.
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| 18. |
- 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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| 19. |
- Staalstrom, A., et al.
(författare)
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Propagation and dissipation of internal tides in the Oslofjord
- 2012
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Ingår i: Ocean Science. - : Copernicus GmbH. - 1812-0784 .- 1812-0792. ; 8:4, s. 525-543
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Tidskriftsartikel (refereegranskat)abstract
- Observations of velocity, pressure, temperature and salinity in the inner Oslofjord have been analysed to provide new information about the relationships between internal tides generated by tidal currents across the Drobak Sill and dissipation and diffusivity in the fjord. The most energetic vertical displacement of density surfaces inside the sill is associated with the first internal mode that has maximum amplitude around sill depth. The amplitude of the vertical displacement around sill depth correlates with the amplitude of the surface elevation, and, at a distance of 1 km inside the sill, the ratio between the amplitudes is 38, decreasing to 11 at a distance of 10 km. The greatest vertical displacements inside the sill, however, are found at 40 m depth. These latter internal waves are not associated with a first-mode internal tide, but are rather associated with higher internal modes controlled by stratification. The energy flux of the internal wave propagating from the Drobak Sill into the inner fjord on the east side of the Haoya Island is estimated to vary in the range 155-430 kW. This is the same order of magnitude as the estimated barotropic energy loss over the Drobak Sill (250 kW), but only 4-10% of the total barotropic flux. Approximately 40-70 % of the internal energy flux is lost within a distance of 10 km from the sill. The mean diffusivity below 90m depth in this area (similar to 20 cm(2) s(-1)) is more than four times higher than in the rest of the fjord (similar to 5 cm(2) s(-1) or less).
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| 20. |
- Stigebrandt, Anders, 1942, et al.
(författare)
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A new Phosphorus Paradigm for the Baltic Proper
- 2014
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Ingår i: Ambio. - : Springer Science and Business Media LLC. - 0044-7447 .- 1654-7209. ; 43:5, s. 634-643
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Tidskriftsartikel (refereegranskat)abstract
- The external phosphorus (P) loading has been halved, but the P content in the water column and the area of anoxic bottoms in Baltic proper has increased during the last 30 years. This can be explained by a temporary internal source of dissolved inorganic phosphorus (DIP) that is turned on when the water above the bottom sediment becomes anoxic. A load-response model, explaining the evolution from 1980 to 2005, suggests that the average specific DIP flux from anoxic bottoms in the Baltic proper is about 2.3 g P m-2 year-1. This is commensurable with fluxes estimated in situ from anoxic bottoms in the open Baltic proper and from hydrographic data in the deep part of Bornholm Basin. Oxygenation of anoxic bottoms, natural or manmade, may quickly turn off the internal P source from anoxic bottoms. This new P-paradigm should have far-reaching implications for abatement of eutrophication in the Baltic proper.
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| 21. |
- Stigebrandt, Anders, 1942, et al.
(författare)
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An Experiment with Forced Oxygenation of the Deepwater of the Anoxic By Fjord, Western Sweden
- 2015
-
Ingår i: Ambio. - : Springer Netherlands. - 0044-7447 .- 1654-7209. ; 44:1, s. 42-54
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Tidskriftsartikel (refereegranskat)abstract
- In a 2.5-year-long environmental engineering experiment in the By Fjord, surface water was pumped into the deepwater where the frequency of deepwater renewals increased by a factor of 10. During the experiment, the deepwater became long-term oxic, and nitrate became the dominating dissolved inorganic nitrogen component. The amount of phosphate in the water column decreased by a factor of 5 due to the increase in flushing and reduction in the leakage of phosphate from the sediments when the sediment surface became oxidized. Oxygenation of the sediments did not increase the leakage of toxic metals and organic pollutants. The bacterial community was the first to show changes after the oxygenation, with aerobic bacteria also thriving in the deepwater. The earlier azoic deepwater bottom sediments were colonized by animals. No structural difference between the phytoplankton communities in the By Fjord and the adjacent Havsten Fjord, with oxygenated deepwater, could be detected during the experiment.
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| 22. |
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| 23. |
- Stockmann, Gabrielle. J. J., et al.
(författare)
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Mineral Changes to the Tufa Columns of Ikka Fjord, SW Greenland
- 2022
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Ingår i: Minerals. - : MDPI AG. - 2075-163X. ; 12:11
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Tidskriftsartikel (refereegranskat)abstract
- The submarine tufa columns of Ikka Fjord in Southwest Greenland have been studied during multiple field campaigns since 1995. The fjord contains close to thousand columns previously shown to consist of the metastable carbonate mineral ikaite (CaCO3·6H2O), which requires near-freezing conditions to remain stable over longer periods of time. During a field campaign to Ikka Fjord in the summer of 2019, seawater temperatures of 6–9 °C and visual physical changes to the columns were observed. These are the highest recorded seawater temperatures measured in Ikka Fjord in over three decades of research. In response, three selected columns at three different locations were sampled at their bases, middle, and top sections for mineralogical analysis. These samples were supplemented by a four further column samples and an extensive hydrographical campaign during fieldwork in the summer 2021. Here, we report the results of the mineralogical analyses performed by X-ray diffraction and µ-Raman Spectroscopy on these column samples. The results show that the columns analysed now consist of the less hydrated carbonate minerals, monohydrocalcite (CaCO3·H2O), aragonite, and calcite (CaCO3). One of the columns has completely altered into monohydrocalcite, whereas the other columns have crusts of ikaite and cores of monohydrocalcite ± aragonite and calcite. This change is interpreted as a dehydration reaction and mineral alteration from ikaite to monohydrocalcite continuing to aragonite ± calcite in response to being bathed in warming seawater. Hydrographic profilers and static dataloggers recorded seawater temperatures of 4–8 °C in the column-containing fjord areas during June–August 2021. The upper parts of the columns are particularly exposed to temperatures > 6 °C, considered to be the long-term stability threshold of ikaite in Ikka Fjord. The mineral dehydration reactions are irreversible. It is therefore predicted in a warming Arctic, ikaite will only appear as new growth on the columns for a short period, and that with time, the columns of Ikka Fjord will change mineralogy into mainly monohydrocalcite.
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| 24. |
- Stranne, Christian, 1979, et al.
(författare)
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Analysis and modeling of hydrothermal plume data acquired from the 85°E segment of the Gakkel Ridge
- 2010
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Ingår i: Journal of Geophysical Research. - 0148-0227. ; 115:C06028
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Tidskriftsartikel (refereegranskat)abstract
- We use data from a CTD plume-mapping campaign conducted during the Arctic Gakkel Vents (AGAVE) expedition in 2007 to constrain the nature of hydrothermal processes on the Gakkel Ridge at 85 degrees E. Thermal and redox potential (Eh) anomalies were detected in two discrete depth intervals: 2400-2800 m (Interval 1) and 3000-3800 m (Interval 2). The spatial and temporal patterns of the signals indicate that the Interval 1 anomalies were most likely generated by a single large, high-temperature (T > 100 degrees C) vent field located on the fault terraces that form the NE axial valley wall. In contrast, the Interval 2 anomalies appear to have been generated by up to 7 spatially distinct vent fields associated with constructional volcanic features on the floor of the axial valley, many of which may be sites of diffuse, low-temperature (T < 10 degrees C) discharge. Numerical simulations of turbulent plumes rising in a weakly stratified Arctic Ocean water column indicate that the high-temperature field on the axial valley wall has a thermal power of 1.8 GW, similar to the Trans-Atlantic Geotraverse and Rainbow fields in the Atlantic Ocean, whereas the sites on the axial valley floor have values ranging from 5 to 110 MW.
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| 25. |
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| 26. |
- Strömberg, Jarl-Ove, et al.
(författare)
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Northern krill, Meganyctiphanes norvegica, come up to see the last eclipse of the millennium?
- 2002
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Ingår i: Journal of the Marine Biological Association of the United Kingdom. - 0025-3154. ; 82:5, s. 919-920
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Tidskriftsartikel (refereegranskat)abstract
- Most krill species undergo diel vertical migration (DVM) which is to some extent influenced by light intensity. During a solar eclipse (11 August 1999) the upward and downward movement of krill, Meganyctiphanes norvegica, inhabiting a Swedish fjord followed closely changes in light intensity. Here the eclipse was partial (77%) and the weather overcast and yet krill at 70-90 m depth were able to detect, and respond to very small changes in light. This observation of an event during mid-day which is not pre-programmed confirms light as an important triggering mechanism for krill DVM.
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| 27. |
- Urrutia-Cordero, P., et al.
(författare)
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SITES AquaNet: An open infrastructure for mesocosm experiments with high frequency sensor monitoring across lakes
- 2021
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Ingår i: Limnology and Oceanography-Methods. - : Wiley. - 1541-5856. ; 19:6, s. 385-400
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Tidskriftsartikel (refereegranskat)abstract
- For aquatic scientists mesocosm experiments are important tools for hypothesis testing as they offer a compromise between experimental control and realism. Here we present a new mesocosm infrastructure-SITES AquaNET-located in five lakes connected to field stations in Sweden that cover a similar to 760 km latitudinal gradient. SITES AquaNet overcomes major hindrances in aquatic experimental research through: (i) openness to the scientific community, (ii) the potential to implement coordinated experiments across sites and time, and (iii) high-frequency measurements (temperature, photosynthetic photon flux density, turbidity and dissolved oxygen, chlorophyll a and phycocyanin concentrations) with an autonomous sensor system. Moreover, the infrastructure provides operational guidance and sensor expertise from technical staff, and connections to a multi-layered monitoring programme ("SITES Water") for each lake. This enables ecological observations from whole lake ecosystems to be compared with experimental studies aiming at disentangling major drivers and mechanisms underlying observed changes. Here we describe the technical properties of the infrastructure along with possibilities for experimental manipulations to tackle pressing issues in aquatic ecology and global change science. As a proof of concept, we also present a first mesocosm experiment across all five field sites with a cross-factorial design to evaluate responses of the sensor measurements to press/bottom-up (constant light reduction) and pulse/top-down (temporary fish predation) disturbances. This demonstrates the suitability of the infrastructure and autonomous sensor system to host modularized experiments and exemplifies the power and advantages of the approach to integrate a network of mecsocosm facilities with manageable costs across large geographic areas.
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