A HOLOCENE RECORD OF ENVIRONMENTAL CHANGE FROM BÖVATNET, LOFOTEN ISLANDS, ARCTIC NORWAY

The Lofoten Island archipelago (67-69°N) is a mountainous region, with numerous coastal and alpine lakes, off the northwestern coast of Norway. Bövatnet is a small lake (0.6 km², 37 m a.s.l.), located within a glacial, northwest trending valley on the island Vestvågøy. The lake is 1 km down valley from a well-developed cirque that opens to the northeast. A decadal-scale late Holocene sedimentary record has been generated from a 1.37 m sediment core and a 0.25 m surface core collected from the northwestern portion of the lake. The lower 0.56 m of the record is a light gray diamicton with cm-sized suspended clasts. This unit sharply transitions into a dark brown, fine-grained, organic-rich unit that extends to the top of the core. The chronology for the core is based on one radiocarbon date from 70 cm (4620 cal yr BP) and cryptotephra found at 66 cm and 13.6 cm that were geochemically matched to the Icelandic eruptions of Hekla IV (2310 BC) and Oraefajokull (AD 1362), respectively. Cores were sampled every 2 mm to a depth of 81 cm (providing a time resolution of 10-15 years per sample) and analyzed for total organic carbon (TOC), total nitrogen, d¹³C, and d¹⁵N. TOC ranges from 0.4% to 7.2% with the highest values near the top of the core. Values increase above the minerogenic unit, but overall show a decreasing trend during most of the late Holocene. C/N ratios indicate that the record of organic carbon is dominated by algal biomass with brief periods of terrestrial influence that increase in frequency towards to the top of the core. Corresponding peaks in d¹³C and dips in d¹⁵N support the interpreted changes in the source of organic matter. These intervals may represent large runoff events or times of decreased lake productivity. The lower section of the core is somewhat enigmatic and could represent a catastrophic slope failure or glacial activity. Other regional paleoclimate records from northern Scandinavia identify the mid-Holocene as a warm period, making a glacial origin for this section seem unlikely; however, the extreme shading and orientation of the upper valley may have allowed a glacier to persist despite regional warming.