Shelf/fjord exchange driven by coastal-trapped waves in the Arctic

publishedVersio

Necessary conditions for warm inflow towards the Filchner Ice Shelf, Weddell Sea

Understanding changes in Antarctic ice shelf basal melting is a major challenge for predicting future sea level. Currently, warm Circumpolar Deep Water surrounding Antarctica has limited access to the Weddell Sea continental shelf; consequently, melt‐rates at Filchner‐Ronne Ice Shelf are low. However, large‐scale model projections suggest that changes to the Antarctic Slope Front and the coastal circulation may enhance warm inflows within this century. We use a regional high‐resolution ice shelf cavity and ocean circulation model to explore forcing changes that may trigger this regime shift. Our results suggest two necessary conditions for supporting a sustained warm inflow into the Filchner Ice Shelf cavity; (i) an extreme relaxation of the Antarctic Slope Front density gradient, and (ii) substantial freshening of the dense shelf water. We also find that the on‐shelf transport over the western Weddell Sea shelf is sensitive to the Filchner Trough overflow characteristics

Results from the intercalibration of optical low light calibration sources 2011

Following the 38th Annual European Meeting on Atmospheric Studies by Optical Methods in Siuntio in Finland, an intercalibration workshop for optical low light calibration sources was held in Sodankylä, Finland. The main purpose of this workshop was to provide a comparable scale for absolute measurements of aurora and airglow. All sources brought to the intercalibration workshop were compared to the Fritz Peak reference source using the Lindau Calibration Photometer built by Wilhelm Barke and Hans Lauche in 1984. The results were compared to several earlier intercalibration workshops. It was found that most sources were fairly stable over time, with errors in the range of 5–25%. To further validate the results, two sources were also intercalibrated at UNIS, Longyearbyen, Svalbard. Preliminary analysis indicates agreement with the intercalibration in Sodankylä within about 15–25%

Results from the intercalibration of optical low light calibration sources 2011

Following the 38th Annual European Meeting on Atmospheric Studies by Optical Methods in Siuntio in Finland, an intercalibration workshop for optical low light calibration sources was held in Sodankylä, Finland. The main purpose of this workshop was to provide a comparable scale for absolute measurements of aurora and airglow. All sources brought to the intercalibration workshop were compared to the Fritz Peak reference source using the Lindau Calibration Photometer built by Wilhelm Barke and Hans Lauche in 1984. The results were compared to several earlier intercalibration workshops. It was found that most sources were fairly stable over time, with errors in the range of 5–25%. To further validate the results, two sources were also intercalibrated at UNIS, Longyearbyen, Svalbard. Preliminary analysis indicates agreement with the intercalibration in Sodankylä within about 15–25%.publishedVersio

Stabilization of dense Antarctic water supply to the Atlantic Ocean overturning circulation

The lower limb of the Atlantic overturning circulation is resupplied by the sinking of dense Antarctic Bottom Water (AABW) that forms via intense air–sea–ice interactions next to Antarctica, especially in the Weddell Sea. In the last three decades, AABW has warmed, freshened and declined in volume across the Atlantic Ocean and elsewhere, suggesting an ongoing major reorganization of oceanic overturning. However, the future contributions of AABW to the Atlantic overturning circulation are unclear. Here, using observations of AABW in the Scotia Sea, the most direct pathway from the Weddell Sea to the Atlantic Ocean, we show a recent cessation in the decline of the AABW supply to the Atlantic overturning circulation. The strongest decline was observed in the volume of the densest layers in the AABW throughflow from the early 1990s to 2014; since then, it has stabilized and partially recovered. We link these changes to variability in the densest classes of abyssal waters upstream. Our findings indicate that the previously observed decline in the supply of dense water to the Atlantic Ocean abyss may be stabilizing or reversing and thus call for a reassessment of Antarctic influences on overturning circulation, sea level, planetary-scale heat distribution and global climate

Overvåking av hydrogenslfid i Sælenvannet, Bergen kommune, 2010

Målinger av hydrografiske og kjemiske parametere og gjennomgang av meteorologiske data har i perioden 23. februar til 18. mars 2010 vært utført i Sælenvatnet for å beskrive tilstanden før tiltak iverksettes. Lite nedbør i perioden fra midten av desember til midten av januar ga liten ferskvannstilførsel via Sælenelva og resulterte i fjerning av det øvre brakkvannslaget. Stille og kaldt vær ga isdannelse, og nedkjølt og saltere overflatevann økte dette vannets tetthet og la grunnlaget for en omrøring. Fjerningen av det øvre brakkvannslaget og en sannsynlig omrøring har ført til at vann med høyt hydrogensulfid­innhold har blitt brakt opp til overflaten med avdamping av hydrogensulfid til luften som resultat. Innstrømming av salt og kaldt og dermed tungt vann fra Nordåsvannet har sannsynligvis også ført til at lettere vann med høy konsentrasjon av hydrogensulfid har blitt presset opp mot overflaten og forlenget perioden med lukt av hydrogen­sulfid­ rundt Sælenvatnet. Ved første måling 23. februar 2010 ble det målt hydrogensulfid i vannmassene helt opp til overflaten. Etter hvert dannet det seg et stadig tykkere og oksygenholdig brakkvannslag nær overflaten. Økende tetthet nedover i vannmassene i løpet av måleperioden har ført til en stabilisering av vannsøylen og en innestenging av det hydrogensulfidholdige vannet slik at luktproblemene har forsvunnet.Bergen kommune, Vann- og avløpsetaten, Postboks 7700, 5020 Berge

Shelf/fjord exchange driven by coastal‐trapped waves in the A

In this article, we show that the class of low frequency (subinertial) waves known as coastal-trapped waves (CTWs) are a significant agent of water volume exchange in a west Svalbard fjord, and by extension more widely along the west Svalbard and east Greenland margins where similar conditions prevail. We show that CTWs generated by weather systems passing across the sloping topography of the shelf break propagate into the fjord, steered by the topography of an across-shelf trough. The CTWs have characteristic periods of ∼2 days, set by the passage time of weather systems. Phase speeds and wavelengths vary seasonally by a factor of two, according to stratification: winter (summer) values are Cp = 0.25 ms−1 (0.5 ms−1) and λ = 40 km (84 km). CTW-induced flow velocities in excess of 0.2 ms−1 at 100 m water depth are recorded. Observationally scaled CTW model results allow their explicit role in volume exchange to be quantified. Of the estimated exchange terms, estuarine exchange is weakest (Qest=0.62x103 m3s-1), followed by barotropic tidal pumping (Qbt=2.5x103 m3s-1)with intermediary exchange dominating (Qi=2.4x104 m3s-1). Oscillatory flows display greatest activity in the 1–5 day period band, and CTW activity is identified as the likely source of variability in the 40–60 h period band. Within that band, intermediary exchange driven by CTWs is estimated as QiCTW_ave=0.82x104 m3s-1; an exchange rate exceeding both barotropic and estuarine exchange estimates