Late Quaternary tephra stratigraphy and paleoenvironmental reconstruction based on lake sediments from North and Northeast Iceland

Abstract

Due to Iceland’s position in the middle of the North Atlantic, the island is highly sensitive to oceanic and atmospheric fluctuations, which lead to changes in the environment. These fluctuating environmental conditions in addition to Iceland’s high volcanic activity make it a strategic study area for paleoenvironmental and tephra studies. Lake sediments contain information about such past climate and environmental changes, and also have the ability to preserve tephra deposits. For this thesis, sediments cores were collected from four lakes: Torfdalsvatn, located on Skagi peninsula in North Iceland, and Þuríðarvatn, Nykurvatn and Ásbrandsstaðavatn, located near Vopnafjörður in Northeast Iceland. Multi-proxy analyses of the sediment records have been performed with the aim to construct a reliable alignment of individual core sections, to establish age models and tephra stratigraphy by identifying tephra marker layers, and to reconstruct the paleoenvironment during the Late Quaternary. Alignments for the core sections of the four lakes were established based on 14C ages, identified tephra layers and geochemical composition of the sediments. The alignments allowed the construction of continuous core records for each lake. Analysis of major element compositions from tephra layers contained in the Torfdalsvatn sediment core revealed four tephra marker layers, including Hekla 1104, Hekla 3, Hekla 4, and the Saksunarvatn Ash. In sediment records from Northeast Iceland the major element analysis of tephra layers showed that five tephra marker layers, including V1477, Hekla 3, Hekla 4, the Saksunarvatn Ash and Askja S, were deposited in the study area. Sedimentological and geochemical analysis of Torfdalsvatn revealed a clayey facies, which is believed to indicate that a glacial advance occurred on Skagi between ca. 12.0 to 10.3 cal. kyr BP. A gyttja facies found above the clay has been interpreted as a deposit formed during lacustrine conditions without the inflow of glacial meltwater, which would have coincided with warmer temperatures from 10.3 cal. kyr BP until presently. Skagi is therefore believed to have been fully deglaciated by 10.3 cal. kyr BP. A clayey facies in the bottom of the Ásbrandsstaðavatn core is believed to have formed in a glaciated environment in the Vopnafjörður area between 10.8-10.3 cal. kyr BP. After 10.3 cal. kyr BP the presence of gyttja suggests that lacustrine sedimentation persisted in Þuríðarvatn, Nykurvatn and Ásbrandsstaðavatn (Vopnafjörður area). Based on the findings it is believed that the Vopnafjörður area has been fully deglaciated by 10.3 cal. kyr BP.