Jökull - 01.01.2015, Side 83

Marine climate variability from Arnarfjörður, NW Iceland
W/m²W/m²°C wt% °C abundancedifference
(°C)
A2010-10-586
BWTTF
Haukadals-
vatn
TOC
HVT+HAK
combined
MD99-2275
SSTs
MD99-2275
IP25 GVF dTSI
C
E
Figure 7. BWT of Arnarfjörður compared to TOC and combined proxies from Hvítárvatn (HVT) and
Haukadalsvatn (HAK) (Geirsdóttir et al., 2013), Sea Surface temperatures (Sicre et al., 2008) and IP25 in-
dex (Massé et al., 2009) from core MD99-2275, north Iceland compared with Global Volcanic Forcing (GVF)
(Sigl et al., 2015) and Total solar irradiance (dTSI) (Steinhilber et al., 2009) (note that the sea ice index, TOC
and GVF has been inverted so that it trends in the same direction as the other records). – Botnhitastig úr Arnar-
firði ásamt TOC og samsett gögn úr Hvítárvatni (HVT) og Haukadalsvatni (HAK), yfirborðssjávarhita og IP25
gögn úr kjarna MD99-2275 norður af Íslandi borið saman við hnattræna eldvirkni og breytingar á inngeislun
sólar.
et al., 2008). The SST data do not indicate clear ev-
idence for colder conditions before the MWP as seen
in the proxies from Arnarfjörður but the transition
from the MWP to the LIA around 1300 CE is clearly
visible and defined by a general increase of Arctic wa-
ter indicator species at the transition (Knudsen et al.,
2012). The earliest temperature change was seen in
the bottom and subsurface waters, where a cooling
was reconstructed as early as 1150–1200 CE agree-
ing with the BWT changes in Arnarfjörður. Knud-
sen et al. (2012) concluded that changes in the deeper
water masses preceded long-term sea-surface and at-
mospheric changes at the MWP-LIA transition, and
that short-term variability may have been influenced
by the local wind circulation. High-resolution recon-
struction from four marine cores located at the eastern
Norwegian Sea and the adjacent Norwegian fjords, re-
flect temperature variability during the periods from
1225–1450 CE and 1650–1905 CE when tempera-
tures were 1.3–1.6◦C lower than present (Klitgaard-
Kristensen et al., 2004). They suggested that the cool-
ing starting around 1300 CE was associated with a
reduction in the strength of the thermohaline circu-
lation. This might indicate that Arnarfjörður leads the
cooling compared to the Norwegian shelf.
Variability in natural forcing in Arnarfjörður
Variability in natural forcing causes changes in the
climate. During the Holocene the long-term cool-
ing of northern high-latitude regions has been linked
to orbital forcing and its effects on insolation (e.g.
Solomina et al., 2015). However this signal is linear
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