Lacustrine Records of Holocene Climate History and Human-Driven Landscape Evolution in the Lofoten Islands, Norway

Lake sediments are useful paleoenvironmental archives; however their sensitivity to change depends on lake and catchment-specific characteristics. Here I present analyses of lacustrine records from two contrasting lakes on Vestvågøy in the Lofoten Islands, Norway to investigate regional responses to Holocene climate changes and human-driven landscape evolution. Sediment cores spanning the last c. 7 kyr were collected from Lauvdalsvatnet, a small lake (~0.17 km2) with a steep-sided catchment and large catchment-to-lake-area ratio (~18.8), and Ostadvatnet, a larger lake (~1.2 km2) with a smaller catchment-to-lake-area ratio (~5.2) and lower slope catchment. Sediment analyses included magnetic susceptibility, organic-matter content, bulk density, biogenic silica, CNS elemental analysis, x-radiography and scanning X-ray fluorescence. Chronologies are based on radiocarbon dating of terrestrial macrofossils. In the Lauvdalsvatnet record, which is finely laminated and displays high-frequency variability in all sediment properties throughout, clastic sedimentation indicators increase c. 5.5 ka, and decline c. 2.8 ka. Biogenic silica values abruptly decline c. 3.8 ka. During the late Holocene, a large peak then abrupt, lasting decline in organic-matter content occurs c. 1.9 ka, followed by fluctuations in magnetic susceptibility and increased sedimentation rates starting c. 0.5 ka. In the Ostadvatnet record, C/N values are heightened from c. 3.8-2.8 ka, synchronous with peaks in detrital sedimentation indicators in Lauvdalsvatnet. In the late Holocene portion of the Ostadvatnet record, high-amplitude fluctuations in organic-matter concentration begin c. 2.5 ka, followed by decreasing C/N values and increasing magnetic susceptibility since c. 1.9 ka. I attribute changes in Lauvdalsvatnet sediment characteristics during the mid to late Holocene to changes in precipitation and weathering patterns c. 5.5 and 2.8 ka, and decreasing temperatures beginning c. 3.7 ka associated with regional termination of the Holocene Thermal Maximum. Ostadvatnet was less sensitive to mid-Holocene climate changes, likely due its lower catchment-to-lake-area ratio and the lower slope of its catchment. Both lakes record changes in sediment properties after c. 2.5 ka, which are likely related to the onset of local agriculture and early human population expansion. These results have implications for understanding when and how climate in the Lofoten region responded to past global changes, including during the Holocene thermal maximum and neoglacial transition. They also suggest that onset of agriculture in the central corridor of Vestvågøy c. 2.5 ka preceded settlement in at least one peripheral valley, improving understanding of early human-landscape interactions.