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De siste tiårenes forskning tyder på at endringer i havstrømmene nord for Island har en nær sammenheng med brå klimaendringer i den nordiske region. Selv om Island ligger sentralt til i det nord-atlantiske klimasystemet har det frem til nylig vært lite detaljerte opplysninger å finne om paleomiljøendringer i dette området. De senere årenes forskning på havstrømmenes rolle i brå klimaendringer har imidlertid satt den nord-islandske sokkelen i nytt fokus. Kombinasjonen stor varmetransport inn fra sør, og den polare lokaliseringen, fører til at regionen er svært sensitiv for naturlige klimavariasjoner og spesielt sårbar for eksterne pådrivere. En ny marin sedimentkjerne fra den nord-islandske sokkelen (GS15-198-33) er benyttet til høyoppløselig rekonstruksjon av oseanske forhold i overgangen fra «middelalderens varmeperiode» til «den lille istid». En foraminiferbasert (Melonis barleeanum) Mg/Ca analyse og ẟ^[18]O analyse gir detaljert informasjon om egenskapsendringer i bunnvannet over Húnaflói. Studieområdet ligger ideelt til for å kunne gi detaljert informasjon om endringer i dominans mellom den nord-islandske Irmingerstrømmen og Østgrønlandsstrømmen. Endringer i dominans mellom disse forårsaker breddegradsendringer i Polarfronten og har stor klimatisk innflytelse på hele regionen. De instrumentelle dataene er supplert med informasjon om brefluktuasjoner i Drangajökull som ligger like ved studielokaliteten. Det er også søkt i historiske kilder etter førstehåndsberetninger om endringer i vær og klimaforhold i overgangen til «den lille istid». Mine resultater viser en brå endring i vannmassene på den nord-islandske sokkelen rundt 1275-1300 evt. Etter et skifte tilbake til en atlantisk varmere modus, endres temperaturene brått igjen i tiden rundt 1500 evt. Etter dette gjenspeiler ikke forholdene i bunnstrømmen det som skjer på overflaten eller i atmosfæren. Masteroppgave i geovitenskap MAMN-GEOV GEOV399

Extending oceanographic data beyond the instrumental period is highly needed to better characterize and understand multi-decadal to centennial natural ocean variability. Here, a stable isotope record at unprecedented temporal resolution (1 to 2 years) from a new marine core retrieved off western North Iceland is presented. We aim to better constrain the variability of subsurface, Atlantic-derived Subpolar Mode Water (SPMW), using near surface-dwelling planktic foraminifera and Arctic Intermediate Water (AIW) mass changes using benthic foraminifera over the last ~165 years. The reconstruction overlaps in time with instrumental observations and a direct comparison reveals that the δ18O record of Neogloboquadrina pachyderma is reliably representing temperature fluctuations in the SPMWs. Trends in the N. pachyderma δ13C record match the measured phosphate concentration in the upper 200 m on the North Icelandic Shelf well. Near surface-dwelling foraminifera trace anthropogenic CO2 in the Iceland Sea by ~ 1950 ± 8, however, a reduced amplitude shift in the Marine Suess effect is identified. We argue that this is caused by a contemporary ongoing increase in marine primary productivity in the upper ocean due to enhanced Greenland’s freshwater discharge that has contributed to a nutrient-driven fertilization since the 1940s/50s (Perner et al., 2019). Multi-decadal variability is detected. We find that the 16-year periodicity evident in SPMW and AIWs based on the δ18O of N. pachyderma and M. barleeanum is a signal of SST anomalies propagated into the Nordic Seas via the Atlantic inflow branches around Iceland. Spectral analyses of the planktic foraminiferal δ13C signal indicate intermittent 30-year cycles that are likely reflecting the ocean response to atmospheric variability, presumably the East Atlantic Pattern. A long-term trend in benthic δ18O suggests that Atlantic-derived waters are expanding their core within the water column from the subsurface into deeper intermediate depths towards the present day. This is a result of increased transport by the North Icelandic Irminger Current to the North Iceland Shelf over the historical era.

Extending oceanographic data beyond the instrumental period is highly needed to better characterize and understand multi-decadal to centennial natural ocean variability. Here, a stable isotope record at unprecedented temporal resolution (1 to 2 years) from a new marine core retrieved off western North Iceland is presented. We aim to better constrain the variability of subsurface, Atlantic-derived Subpolar Mode Water (SPMW), using near surface-dwelling planktic foraminifera and Arctic Intermediate Water (AIW) mass changes using benthic foraminifera over the last ~165 years. The reconstruction overlaps in time with instrumental observations and a direct comparison reveals that the δ18O record of Neogloboquadrina pachyderma is reliably representing temperature fluctuations in the SPMWs. Trends in the N. pachyderma δ13C record match the measured phosphate concentration in the upper 200 m on the North Icelandic Shelf well. Near surface-dwelling foraminifera trace anthropogenic CO2 in the Iceland Sea by ~ 1950 ± 8, however, a reduced amplitude shift in the Marine Suess effect is identified. We argue that this is caused by a contemporary ongoing increase in marine primary productivity in the upper ocean due to enhanced Greenland's freshwater discharge that has contributed to a nutrient-driven fertilization since the 1940s/50s (Perner et al., 2019). Multi-decadal variability is detected. We find that the 16-year periodicity evident in SPMW and AIWs based on the δ18O of N. pachyderma and M. barleeanum is a signal of SST anomalies propagated into the Nordic Seas via the Atlantic inflow branches around Iceland. Spectral analyses of the planktic foraminiferal δ13C signal indicate intermittent 30-year cycles that are likely reflecting the ocean response to atmospheric variability, presumably the East Atlantic Pattern. A long-term trend in benthic δ18O suggests that Atlantic-derived waters are expanding their core within the water column from the subsurface into deeper intermediate depths towards the present day. This is a result of increased transport by the North Icelandic Irminger Current to the North Iceland Shelf over the historical era.