Variasjoner i stormaktivitet fra midt- til sein-holosen på Langøya, Vesterålen

• Main Author: Prestegård, Ingvild
• Format: Master Thesis
• Language: Norwegian Bokmål
• Published: The University of Bergen 2020
• Subjects: Vesterålen; Flygesand; eolisk influks; klima; ekstremvær; CT-skanning; stormaktivitet; holosen; 733111; Fjærvoll; Langøya; Norway; Nøkktjønna; Sandy Beach; North Atlantic; Northern Norway
• Online Access: https://hdl.handle.net/1956/21314

In this study, mid- to late Holocene storminess has been reconstructed from lacustrine sediments from Nøkktjønna. Nøkktjønna is situated 1,5 km from the shoreline at Fjærvoll on Langøya, Vesterålen in Northern Norway. Mapping of the study area has revealed large amounts of aeolian deposits as both sand dunes and sand sheets. This indicates that sand drift is active when strong enough wind speeds are present. A wide range of methods have been applied to capture variations in storminess. The content of mineral grains in the sediment core has been quantified by sieving ignition residue through two different mesh sizes (125 – 250 µm, >250 µm) and by conducting a threshold analysis of the results from CT-scanning. The results from the different datasets show relatively good correlation, especially from the upper part of the core. Considering the setting of Nøkktjønnas drainage basin, the mineral grains present in the sediment core are suggested to be deposited by aeolian transport. The most likely source area is the sandy beach deposits at Fjærvollsanden 1,5 km west of Nøkktjønna. Five periods of high aeolian influx are suggested to indicate increased storminess. These periods occurred from 4085 – 4060 cal. yr BP (24 – 23,5 cm), 3450 – 3350 cal. yrs BP (18,5 – 18 cm), 2860 – 2760 cal. yrs BP (15,5 – 15 cm), 1400 – 715 cal. yrs BP (8 – 4,5 cm ) and 320 – 30 cal. yrs BP (2,5 – 0,5 cm), where the two last periods are the longest and most intense. The increased influx in the two periods can possibly be associated to changes in the storm tracks combined with increased anthropogenic influence. The highest influx rates occur at the end of the Little Ice Age (AD 1630 – 1920). The results from this study correlate relatively well to other reconstructions from the North Atlantic Region. This indicates that aeolian influx to Nøkktjønna is affected by the big scale atmospheric and oceanic circulation patterns. I dette studiet er variasjoner i stormaktivitet rekonstruert for midt- til sein-holosen med utgangspunkt i analyse ...