Formation and pathways of dense water in the Nordic Seas

Sammendrag De nordiske hav er viktig for dannelsen av kalde, tette og dype vannmasser som strømmer sørover på tvers av Grønland-Skottland-ryggen og forsyner den dype grenen av omveltningssirkulasjonen i Atlanterhavet. På tross av at størrelsen på dypvannstransporten over ryggen er godt kjent, gjenstår det mange åpne spørsmål angående hvor og hvordan de dype vannmassene dannes og transporteres til ryggen. Det er også stor usikkerhet rundt variasjonene i dypvannsdannelse og hvilke implikasjoner dette har for omveltningssirkulasjonen. I denne oppgaven bruker vi observasjonsdata til å kvantifisere hvor dype vannmasser dannes, hvordan de strømmer mot Grønland-Skottland-ryggen, og hvordan dette har endret seg de siste 70 årene. Oppgaven retter et spesielt fokus mot Grønlandshavet, som er en viktig kilde til dypvannet i de nordiske hav. I Artikkel I benyttet vi hydrografiske observasjoner fra 1986 til 2016, sammen med en endimensjonal blandalagsmodell, til å undersøke mellomårlig variabilitet og langtidsendringer i dypvannsdannelsen i Grønlandshavet. Vi fant at perioden før midten av 1990-tallet var spesielt fersk og sterkt stratifisert, noe som resulterte i grunn konveksjon (<300 m), til tross for sterkt atmosfærisk pådriv. Saltinnholdet i Grønlandshavet økte etter midten av 1990-tallet på grunn av høyere saltholdighet i Atlanterhavsvannet som strømmer nordover inn i de nordiske hav. Dette førte til svekket stratifisering, dypere konveksjon (500–1500 m), og dannelse av en ny klasse dypvann som har vært hovedproduktet av konveksjonen i Grønlandshavet frem til i dag. Denne nye vannmassen er mindre tett enn dypvannet som ble produsert i Grønlandshavet før 1980-tallet. Den vertikale utstrekningen av den nye vannmassen er derfor begrenset til den øvre halvdelen av vannsøylen. Store mengder varme ekstraheres fra de nordiske hav til atmosfæren om vinteren. Omtrent 60–80% av varmen frigjøres under intense, kortvarige kaldluftsutbrudd (heretter omtalt som utbrudd). I Artikkel II brukte vi et unikt 10-årig (1999–2009) hydrografisk datasett fra profilerende instrumenter med 1–2 dagers tidsoppløsning til å kvantifisere, for aller første gang, den direkte påvirkningen av slike utbrudd på blandalaget i Grønlandshavet. Dette viste at responsen i blandalagsegenskapene var avhengig av styrken på utbruddene og når de inntraff. Kaldluftsutbrudd som inntraff tidlig på vinteren (november–januar) førte i hovedsak til en nedkjøling av blandalaget, mens utbrudd som inntraff senere på vinteren (februar–april) førte til en økning i blandalagsdyp. Idealiserte simuleringer med en endimensjonal blandalagsmodell antyder at tidspunktet når dyp konveksjon inntreffer avhenger av fordelingen av utbrudd, mens blandalagsegenskapene mot slutten av vinteren er mer avhengig av styrken og det totale antallet utbrudd gjennom vinteren. Responsen i blandalagsegenskapene var også avhengig av laterale varme og salt flukser. Disse ble kvantifisert og inkludert i blandalagsmodellen. Resultatene viste at deres kombinerte effekt er en reduksjon i blandalagsdybden på opptil flere hundre meter. I Artikkel III utviklet vi en inversjonsmodell med høy romlig oppløsning for vannmassene i de nordiske hav. Denne ble brukt til å identifisere opprinnelsen til de to største dypvannsstrømmene som passerer Grønland-Skottland-ryggen i Danmarkstredet og Færøybankkanalen. Inversjonsmodellen er basert på hydrografiske og geokjemiske vannegenskaper observert i perioden 2000–2019 og viser hvor dypvann dannes og hvordan de strømmer mot ryggen. Dypvannsstrømmen i Danmarkstredet består hovedsakelig av vannmasser fra Grønlandshavet (39±2%), Islandshavet (20±3%) og fra Norskehavet (19±2% ). Dypvann dannet i Grønlandshavet beveger seg sørover langs to distinkte strømningsveier: en ytre kjerne av Østgrønlandsstrømmen og en tidligere ukjent strømningsvei som krysser Jan Mayen-ryggen inn mot Islandshavet sør for Jan Mayen. Begge disse strømningsveiene forsyner Nordislandsjeten som består av 82±2% dypvann dannet i Grønlandshavet. Det meste av dypvannsstrømmen i Færøbankkanalen har sin opprinnelse i Grønlandshavet (46±8%) og Polhavet (25±9%). Disse vannmassene strømmer sørover mot kanalen med Island–Færøy-jeten og langs den østlige delen av Jan Mayenryggen. Den sistnevnte strømningsveien svinger østover til den norske kontinentalskråningen, som den deretter følger sørover til Færøy-Shetland-kanalen. Denne strømningsveien kan bidra med 24±3% av dypvannet i Færøybankkanalen, mens Island–Færøyjeten forsyner 58±3%. Disse resultatene øker vår forståelse av hvor de dype vannmassene dannes og hvordan de transporteres til Grønland-Skottland-ryggen. Fokuset i Artikkel IV var langtidsendringer i dypvannet i de nordiske hav. Til å undersøke dette ble observasjonsdata over en 70-års periode (1950–2019) benyttet, sammen med inversjonsmodellen for periodene 1950–1979 og 2000–2019. Resultatene avslørte at dypvannsreservene i de nordiske hav har blitt varmere og mindre tett på grunn av økt temperatur i det innstrømmende Atlanterhavsvannet og opphør av konveksjon til bunnen av Grønlandshavet etter 1980-tallet. Dette har påvirket hele tetthetsstrukturen i de nordiske hav. Den reduserte konveksjonen har ført til en nedgang i tettheten og bidraget fra Grønlandshavet til dypvannsstrømmen gjennom Færøybankkanalen. Derimot har bidraget til Danmarkstredet fra den nye, mindre tette vannmassen i Grønlandshavet økt. Våre analyser av egenskapene og sammensetningen av dybvannsstrømmene på tvers av Grønland-Skottland-ryggen demonstrerer at det er viktig å ta hensyn til både romlige og tidsmessige variasjoner i dypvannsdannelse for å forstå langtidsendringene. Dersom trenden mot varmere og mindre tette dypvannsreserver fortsetter i fremtiden, forventes en tetthetsreduksjon i omveltningssirkulasjonen i de nordiske hav. Til sammen har de fire artiklene i denne oppgaven økt vår kunnskap om dannelsen, strømingsveiene, og variabiliteten til dypvannet i de nordiske hav i betydelig grad. Denne kunnskapen er kritisk for å kunne bedre forstå dypvannstrømmene på tvers av Grønnland-Skottland-ryggen, deres bidrag til omveltningssirkulasjonen i Atlanterhavet og hva vi kan forvente av disse i et framtidig varmere klima.Abstract Dense water formed in the Nordic Seas flows southward across the Greenland-Scotland Ridge and sinks to great depths in the North Atlantic to supply the lower limb of the Atlantic Meridional Overturning Circulation. While the exchange flows across the ridge have been monitored for several decades, gaps in our knowledge remain regarding where and how the dense overflow waters are formed and transported to the ridge. Questions also remain regarding the variability in dense-water formation and its implications for the dense-water reservoir and overflows from the Nordic Seas, which are critical to understand the overturning in the Nordic Seas. Based on observational data, this thesis quantifies the origin and upstream pathways of the overflow waters, as well as how and why they have changed over the past 70 years. A particular focus was on the variability in dense-water formation in the Greenland Sea, where a major portion of the overflow waters originate. In Paper I, we focused on the interannual and long-term changes in dense-water formation in the Greenland Sea based on hydrographic observations from 1986 to 2016 and a one-dimensional mixed-layer model. We found that the period prior to the mid-1990s was particularly fresh and strongly stratified, resulting in predominantly shallow convection (<300 m), despite strong atmospheric forcing. Increased salinity, linked to higher salinity in the Atlantic Water inflow into the Nordic Seas, weakened the water column stability after the mid-1990s. This transition led to increased convection depths (500–1500 m) and the formation of a new, less dense class of intermediate water that has been the main product of convection in the Greenland Sea until present. Although the volume of the new water mass increased from the 1990s to the 2000s, its vertical extent has been constrained to the upper half of the Greenland Sea water column, above the remnants of the denser Greenland Sea deep water that was the main product of convection prior to the 1980s. Approximately 60–80% of the heat lost to the atmosphere during winter is related to intense, short-lived events called cold-air outbreaks (CAOs). In Paper II, we utilized a unique 10-year (1999–2009) hydrographic record from moored profilers with 1–2 days temporal resolution to examine, for the first time, the direct impact of CAOs on the mixed-layer development in the Greenland Sea. This revealed that the mixed-layer response depended on when the CAO events occurred and on their intensity. Early in winter (November–January) the response was primarily a cooling of the mixed layer, while later in winter (February–April) the mixed layer mainly deepened. Idealized simulations with a one-dimensional mixed-layer model suggest that the temporal distribution of CAOs impacts the timing of the onset of the deepening phase, while the end-of-winter mixed-layer depth and hydrographic properties are more sensitive to the integrated heat loss over the winter, which is determined by the total number and intensity of CAOs. Considerable variability was observed in the mixed-layer response to CAOs, highlighting the importance of lateral heat and salt fluxes. These were quantified and included in the mixed-layer model, which suggests that their combined effect is a reduction in the end-of-winter mixed-layer depth of up to several hundred meters. In Paper III we developed a regional high-resolution water-mass inversion for the Nordic Seas to determine the origin and upstream pathways of the two main overflow plumes passing the Greenland-Scotland Ridge in Denmark Strait and the Faroe Bank Channel. The inversion is based on the geographical distribution of hydrographic and geochemical water properties from observations covering the period 2000–2019 and resolves the pathways that connect the overflow plumes to their origins. The Denmark Strait overflow is mainly composed of water originating in the Greenland Sea (39±2%), the Iceland Sea (20±3%), and in the Atlantic Domain (19±2%) of the Nordic Seas. Dense water from the Greenland Sea propagates southward along two distinct pathways: an outer core of the East Greenland Current and along a previously unknown pathway that crosses the Jan Mayen Ridge into the Iceland Sea just south of Jan Mayen. Both of these pathways feed the North Icelandic Jet that consists of 82±2% dense-water formed in the Greenland Sea. Most of the Faroe Bank Channel overflow originates in the Greenland Sea (46±8%) and the Arctic Ocean (25±9%) and propagates toward the channel with the Iceland-Faroe Slope Jet and along the eastern margin of the Jan Mayen Ridge. The latter pathway turns eastward over to the Norwegian continental slope, which it then follows southward to the Faroe-Shetland Channel. This pathway can account for 24±3% of the Faroe Bank Channel overflow, while the Iceland-Faroe Slope Jet supplies 58±3%. These results improve our understanding on the origin and upstream pathways of the overflows, in particular regarding the dense-water pathways from the Greenland Sea and how the overflow water approaches the Faroe-Shetland Channel. The focus in Paper IV was long-term variability in the Nordic Seas reservoir and overflows using a 70-year long (1950–2019) observational record and the regional water-mass inversion for the two periods 1950–1979 and 2000–2019. The results revealed that the Nordic Seas reservoir has warmed and become less dense due to changes in the Atlantic Water inflow and the cessation of bottom-reaching convection in the Greenland Sea. This has, in turn, impacted the entire density structure in the Nordic Seas. The transition from bottom to intermediate-depth convection has reduced the density and supply from the Greenland Sea to the Faroe Bank Channel overflow, while the contribution of the less dense intermediate water to the overflow through Denmark Strait has increased. Our analyses of the overflow water composition and properties demonstrate that it is important to take both the spatial and temporal variability in dense-water formation into account when examining the long-term changes in the overflows. The Atlantic Water has warmed and become less dense over the past 2-3 decades. If this trend continues in the future, it is expected to further decrease the density of the overturning the Nordic Seas. Collectively, the four papers in this thesis have significantly advanced our knowledge about the formation and pathways of dense water in the Nordic Seas, their variability, and the contributions to the overflow waters across the Greenland-Scotland Ridge from an observational point of view. As such, the thesis provides an important step forward to understand the overturning in the Nordic Seas and its variability.Doktorgradsavhandlin

Can you make it through the month? An instrumental single case study of intercultural learning through the use of a video game in an upper secondary EAL classroom in Norway

Erfaringsbasert masteroppgave i undervisning med fordypning i engelskENGMAU650VID-MAUEN

Literature circles as an approach to exploring multimodality through graphic novels in the 5th grade EAL classroom: A case study.

Dette masterprosjektet undersøkte hvordan man kan bruke grafiske noveller til å utforske multimodalitet i en 5. klasse og hva elevenes perspektiver på læringsutbytte og læringsprosessen i dette prosjektet var.Erfaringsbasert masteroppgave i undervisning med fordypning i engelskENGMAU650VID-MAUEN

Biodegradation of Naturally Occurring Substances in Produced Water - Revision of data for the DREAM model

A literature review was conducted to obtain more reliable primary (biotransformation) and ultimate (biomineralization) biodegradation rates for compounds in produced water for the DREAM model, than the current biodegradation data. During the literature review, it became apparent that many compounds lacked quality ultimate biodegradation rates, which is preferred in the model. Therefore, ultimate biodegradation rates for these compounds were estimated based on their primary biodegradation rates and a FACTOR. These data and calculations are described in the report below. Calculated ultimate biodegradation rates are compared to rates found in the literature. This report also includes two separate Excel spreadsheets that summarize the prima ry and ultimate biodegradation data obtained during the literature review and their corresponding experimental details. A Q10 approach was applied to calculated ultimate biodegradation rates to display rates at three relevant temperatures (5, 13, and 20°(). The ultimate biodegradation rates included in this report will substantially improve the DREAM model, but the majority of these rates are extrapolated estimates. Additional biodegradation tests are recommended to correlate these calculations with laboratory experiments.StatoilpublishedVersio

Do investors penalize lack of prevention of ESG incidents?

I examine market reaction on 1987 global ESG incidents over ten years, from 2010 to 2020. To evaluate if investor value negative ESG information consistently, independent on company traits, event study of mean cumulative abnormal returns is applied. ESG incident do not cause market reaction. Investor values ESG incidents differently, depending on company traits. I find that investors value negative ESG information for companies that show lack in preventive measures on ESG incidents. Companies with lack of preventive measures experience a negative effect on abnormal returns and underperform compared to companies that show favorable traits.I examine market reaction on 1987 global ESG incidents over ten years, from 2010 to 2020. To evaluate if investor value negative ESG information consistently, independent on company traits, event study of mean cumulative abnormal returns is applied. ESG incident do not cause market reaction. Investor values ESG incidents differently, depending on company traits. I find that investors value negative ESG information for companies that show lack in preventive measures on ESG incidents. Companies with lack of preventive measures experience a negative effect on abnormal returns and underperform compared to companies that show favorable traits.MasteroppgaveECON391MASV-SØKPROF-SØ

Biodegradation of weathered crude oil by microbial communities in solid and melted sea ice.

Abstract Oil spilled in the Arctic may drift into ice-covered areas and become trapped until the ice melts. To determine if exposure to oil during freezing may have a priming effect on degradation of the oil, weathered dispersed oil (2-3 mg/L) was frozen into solid ice for 200 days at -10 °C, then melted and incubated for 64 days at 4 °C. No degradation was measured in oil frozen into ice prior to melting. Both total amount of oil and target compounds were biotransformed by the microbial community from the melted ice. However, oil released from melted ice was degraded at a slower rate than oil incubated in fresh seawater at the same temperature (4 °C), and by a different microbial community. These data suggest negligible biodegradation of oil frozen in sea ice, while oil-degrading bacteria surviving in the ice may contribute to biodegradation when the ice melts

Formation and pathways of dense water in the Nordic Seas based on a regional inversion

Dense waters formed in the Nordic Seas spill across gaps in the Greenland-Scotland Ridge into the abyss of the North Atlantic to feed the lower limb of the Atlantic Meridional Overturning Circulation. The overflow water transport is well known, but open questions remain regarding where and how the dense overflow waters are formed and transported to the ridge. Here we develop a regional high-resolution version of an inverse method called Total Matrix Intercomparison, which combines hydrographic and geochemical tracer observations between 2000 and 2019 to resolve the pathways that connect the overflows to their origins. Consistent with previous studies we find two main pathways feeding the Denmark Strait Overflow Water (DSOW): the East Greenland Current and the North Icelandic Jet. Most of the water supplied by the North Icelandic Jet originates in the Greenland Sea (82 ± 2%) and flows southward along an outer core of the East Greenland Current, as well as along a previously unknown pathway crossing the Jan Mayen Ridge into the Iceland Sea. In total, 39 ± 2% of the DSOW originates in the Greenland Sea, while the Iceland Sea and the Atlantic Domain of the Nordic Seas account for 20 ± 3% and 19 ± 2%, respectively. The majority of the Faroe Bank Channel Overflow Water originates in the Greenland Sea (46 ± 8%) and the Arctic Ocean (25 ± 9%). These dense waters approach the sill in the Iceland-Faroe Slope Jet and along the eastern side of the Jan Mayen Ridge. The inversion reveals unprecedented details on the upstream sources and pathways of the overflows, which have not previously been obtained using observations.publishedVersio

Biodegradation in seawater of PAH and alkylphenols from produced water of a North Sea Platform

Operational planned discharges of produced water (PW) to the marine environment from offshore oil production installations, contain low concentrations of dispersed oil compounds, like polycyclic aromatic hydrocarbons (PAH) and alkylated phenols (APs). Biotransformation in natural seawater (SW) of naphthalene/PAH and phenol/AP in field-collected PW from a North Sea platform was investigated in this biodegradation study. The PW was diluted in SW from a Norwegian fjord, and the biodegradation study was performed in slowly rotating carousels at environmental conditions (13⁰C) over a period of 62 days. Naphthalene/PAH and phenol/AP biotransformation was determined by first-order rate kinetics, after normalization against the recalcitrant biomarker 17α(H),21β(H)-Hopane. The results from this study showed total biotransformation half-lives ranging from 10 to 19 days for groups of naphthalenes and PAH, while half-lives for APs (C0- to C9-alkylated) were 10 to 14 days. Biotransformation half-lives of single components ranged from 8 to >100 days for naphthalenes and PAHs (median 16 days), and from 6 to 72 days (median 15 days) for phenols and AP. Four of the tested PAHs (chrysene, benzo(b)fluoranthene, benzo(e)pyrene, benzo(g,h,i,)perylene) and one AP (4-tert-butylphenol) showed biotransformation half-lives >50 days. This is one of a few studies that has investigated the potential for biodegradation of PW in natural SW. Methods and data from this study may be used as a part of Risk Based Approaches (RBA) for assessments of environmental fate of PW released to the marine environment and as part of the persistence related to risk.acceptedVersio