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Fig. 2 NAOSIM-derived time-slice sea-ice anomaly for 6 ka to pre-industrial (PI) times in the
Fram Strait area (map) and P
B
IP
25
(where B refers to the use of brassicasterol for calculating the
PIP
25
index) records of three sediment cores from the same area. Gray shadings and red solid
regression lines highlight the individual P
B
IP
25
trends from 6 ka to PI times. Sea-ice concentration
estimates for MSM5/5-712-2 are derived from the P
B
IP
25
vs. satellite sea-ice data correlation
of M
ller et al. (
2011
). Both proxy (P
B
IP
25
) and model results (dark green colours on the map)
point to a 30 % sea-ice increase in the eastern Fram Strait between 6 ka and PI times (red dashed
lines denote the increase in sea-ice concentrations from ca 40 % to 70 %). Only a minimum sea-ice
increase is reconstructed (solid red regression lines)/modeled (light green colours on the map) for
the northern and western Fram Strait core sites
ü
3 Key Findings
The novel sea-ice proxy IP
25
, a biomarker associated exclusively to diatoms living
in sea ice, has opened new possibilities for reconstructions of past sea-ice coverage
in the (sub-)Arctic. The method, originally based only on IP
25
concentrations in
sediments, has been further developed by combining data from IP
25
and phyto-
plankton-derived biomarkers. This combination
—
resulting in the so-called PIP
25
index
—
allows a (semi-)quantitative reconstruction of past sea-ice cover (M
ü
ller
et al.
2009
,
2011
; Stein et al.
2012
). This approach was
first applied to core PS2837
from north of Svalbard (Fig.
1
), close to the modern summer sea-ice margin (M
ller
et al.
2009
). Variable contents of both biomarker types demonstrated that even the
position of a seasonally
ü
fluctuating sea-ice margin can be reliably detected. A study
on recent (surface) sediments in combination with numerical modeling results of
the sea-ice distribution (M
ller et al.
2011
) showed that both methods successfully
reproduce the degree and spatial distribution of the average ice coverage in
the Fram Strait and Nordic Seas although in places local effects can distort the
results.
ü
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