Magnetic investigation of the mid-Holocene aged coastal lake Heimerdalsvatnet in the Lofoten Islands, northern Norway
Abstract
The coastal lake Heimerdalsvatnet is located on the island of Vestvågøya in the Lofoten Islands off the northern coast of Norway. Recently, Balascio et al. (2011) performed a comprehensive investigation of the lake using bathymetric and sub-bottom profiles, bulk geochemistry, diatom assemblages, molecular biomarkers, high resolution X-ray fluorescence (XRF) scans, and magnetic susceptibility to study its geologic history over the past 7800 years. They determined the lake had undergone a regressive sea level sequence and identified three distinct and separate units exemplifying the transition of a restricted marine environment within the lake to a completely freshwater lacustrine setting. Unit I, located at the bottom of the 5.8m sediment core, spans 7800-6500 years before present and is at a period of time when sea level was higher than the edge of the lake basin. Magnetic susceptibility is extremely low during this period, and it is theorized that this is due to stratification within the lake from a density difference between the marine salt water and the influx of freshwater. Unit II is broken into Unit IIa and IIb, making up the transitional period within the lake history from 6500 to 4900 years before present. This phase is marked by fluxes of higher and lower magnetic susceptibility and shifts between more freshwater to brackish water biological markers. Unit III (4900 years to present) has high magnetic susceptibility compared to the other two units, and represents the final stage of the lake as a completely freshwater environment. Questions remain about the lake, such as what was driving the changes in magnetic susceptibility? Was it dilution of the magnetic grains due to higher productivity of organisms within the lake, or is it related to dissolution of magnetite due to anoxic conditions caused by lake stratification? Rock magnetic investigations using magnetic susceptibility, hysteresis parameters, and Curie temperature analyses have led to a better understanding of the causes of the magnetic fluctuations within the lake. In addition to Heimerdalsvatnet providing a wealth of information about sea level changes in the Arctic, it can also offer a unique opportunity to study paleomagnetic data during the Holocene. Initial measurements (performed at the Laboratoire de paléomagnétisme sédimentaire of ISMER) showed reliable paleomagnetic data for the most recent Unit III. However, Units I and II are not as consistent as Unit III. The rock magnetic investigation outlined above is also being used to better constrain the causes of inconsistency within the paleomagnetic record and provide insight as to how the paleomagnetic data can be interpreted at older ages.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMGP41A1098M
- Keywords:
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- 1522 GEOMAGNETISM AND PALEOMAGNETISM / Paleomagnetic secular variation;
- 1540 GEOMAGNETISM AND PALEOMAGNETISM / Rock and mineral magnetism