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Abstract:
Knowledge about the timing, amplitude and spatial
gradients of Holocene environmental variability in the
circum-Baltic region is key to understanding its responses
to ongoing climate change. Based on a multi-dating and
proxy approach, we reconstruct changes in productivity using
total organic carbon (TOC) contents in sediments of Lake
Kälksjön (KKJ) from west–central Sweden spanning the last
9612 (+255 − 114) years. An exception is the period from
1878 CE until today, in which sedimentation was dominated
by anthropogenic lake level lowering and land use. In-lake
productivity was higher during periods of warmer winters
with shortened ice cover and prolonged growing seasons.
A multi-millennial increase in productivity throughout the
last ∼ 9600 years is associated with progressively warmer
winters in northwestern Europe, likely triggered by the coinciding
increase in Northern Hemisphere winter insolation.
Decadal to centennial periods of higher productivity in KKJ
tend to correspond to warmer winters during a more positive
North Atlantic Oscillation (NAO) polarity, as reconstructed
for the last 8000 years. In consequence, we assume
our decadal to centennial productivity record from KKJ sediments
for the complete ∼ 9600 years to provide a qualitative
record of NAO polarity. A shift towards higher productivity
variability at ∼ 5450 cal a BP is hypothesized to reect a reinforcement
of NAO-like atmospheric circulation variability,
possibly driven by more vigorous changes in North Atlantic
deep-water formation.
