Ecological Regime Shifts in Lake Kälksjön, Sweden, in Response to Abrupt Climate Change Around the 8.2 ka Cooling Event

A detailed diatom record from Lake Ka¨ lksjo¨ n, westcentral
Sweden, reveals two periods of abrupt
ecological change correlative with the 8.2 ka cooling
event. Using a combination of abrupt step
changes and piece-wise linear regressions, the
diatom data were analyzed for change points over
time, and two sudden and large events that are
described as regime shifts were detected. During
the first event at c. 8040 cal. y BP, a doubling in
diatom biomass took place over 5–10 years. This
increase in primary productivity can be connected
to an erosion event in the catchment that resulted
in an abrupt increase in nutrient supply to the lake.
The second event was characterized by a substantial
shift within the planktonic diatom community
from taxa indicative of colder conditions to
those indicating warm over 5–10 years at c.
7850 cal. y BP. This event was superimposed on a
successive change from periphytic to planktonic
diatom dominance over a 250-year period and a
gradual diversification of the periphytic community
that spanned c. 150 years. Rapid climate warming
following the 8.2 ka event likely caused these
changes and both regime shifts are examples of
externally driven abrupt ecological change. This
study demonstrates that it is possible to detect,
quantify and test for regime shifts in paleoecological
data, and it highlights the need for high sampling
resolution and precise chronological control.
High-resolution paleoecological reconstructions of
ecological regime shifts in response to climate
change can provide useful analogues of future
changes in ecosystem structure and functioning