Evaluating Holocene climate change in northern Norway using sediment records from two contrasting lake systems

We analyzed Holocene sedimentary records from two lakes in the Lofoten Islands, northern Norway to evaluate environmental changes during the Holocene related to northern North Atlantic climate dynamics. The lakes are located in different geomorphological settings, and thus provide a contrast in their response to regional climate change. Environmental changes at both lakes were interpreted based on magnetic susceptibility, organic-matter flux, C/N, dCorg, Ti concentrations, and mass accumulation rates. Chronologies were established using 16 AMS radiocarbon dates, and average deposition rates in both environments are higher than 0.2 mm/year throughout the Holocene. At Vikjordvatnet, sedimentary geochemical properties define three distinct phases of sedimentation related to changes in aquatic productivity and gradual landscape development. Following deglaciation, during the early Holocene (11.6–7.2 ka), aquatic productivity increased and the landscape stabilized as regional temperatures increased in response to higher summer insolation and increasing inflow of warm Atlantic water into the Norwegian Sea. Centennial-scale intervals of decreased organic-matter flux, from 10.9 to 10.2 ka and 9.2 to 8.0 ka, record episodes of instability during the early Holocene. These may represent regional cooling events related to freshwater forcing and a slowdown of the northward transport of warm water into the North Atlantic. During the mid-Holocene (7.2–4.8 ka) organic-matter properties show less variability and the timing of this phase corresponds with the regional Holocene thermal maximum. The late Holocene sediments (4.8 ka–present) record a transition to colder climate conditions. The record from Fiskebølvatnet captures periodic changes in clastic input related to runoff and exhibits highfrequency variations over the last 9.5 ka. The most significant change in sedimentation was during the late Holocene (4.3 ka–present) when the frequency and magnitude of runoff events show an abrupt transition to wetter conditions. The timing of this shift corresponds to other regional reconstructions that indicate wetter and colder conditions during the late Holocene.