Geoscience Reference
In-Depth Information
1 Introduction
The Arctic Ocean and sub-Arctic play a fundamental role in the global ocean-climate
system. Siberian and North American rivers discharge enormous amounts of fresh-
water to the Arctic Ocean which, in combination with cold atmospheric temperatures,
enables the formation and persistence of the Arctic sea-ice cover which is severely
threatened today by global warming. The Fram Strait between Greenland and
Svalbard is the main
“
Arctic Gateway
”
for water mass exchange between the Arctic
Ocean and the northern North Atlantic (Fig.
1
). In the east, relatively warm (2
7
°
C)
-
and saline (S > 35) Atlantic Water
flows northward. In the west, cold, sea-ice covered
low-saline Arctic surface waters are exported to the Nordic Seas. Given the strong
E-W contrasts, saline Atlantic Water is preconditioned for convective overturning
and deepwater renewal. The position of the sea-ice margin is strongly controlled
by the intensity and temperature of advected Atlantic Water but little is known about
the Holocene (last
fill this knowledge gap
and analyze the amplitudes of natural Arctic climate variations on (sub-)millennial
timescales, expressed as, e.g., temporal and spatial variations of Atlantic Water
temperature and sea-ice cover, high-resolution sedimentary records from the Arctic
Gateway were investigated by micropaleontological and geochemical methods.
Simulations with a coupled atmosphere-ocean circulation model were used to
investigate the role of river discharge and to extend the spatial range of sea-ice
reconstructions which are originally derived from (local) sediment core data series.
12 ka) variability of these parameters. To
∼
2 Materials and Methods
Sediment investigations were performed on selected long cores with multidecadal
resolution from the continental margin of the eastern Fram Strait (78.9
°
N
81.2
°
N;
-
Fig.
2
) and the shelf off East Greenland (73.1
N). The cores were subsampled to
reach a (sub-)centennial resolution. The stratigraphy is based on a series of radio-
carbon datings. For sedimentological, micropaleontological and isotopic investi-
gations, sediment preparations and analyses followed standard procedures
described by Werner et al. (
2011
,
2013
). To investigate the organic-geochemical
content, sediments were analyzed for total organic carbon, carbonate and biomarker
composition according to procedures described by M
°
ü
ller et al. (
2011
,
2012
).
Model simulations were performed with the coupled atmosphere-ocean general
circulation model ECHO-G using acceleration techniques for the Holocene and the
regional North Atlantic/Arctic Ocean
Sea Ice Model (NAOSIM). Details of the
-
model set-up are given by M
ller et al. (
2011
) and Wagner et al. (
2011
). Forcing
occurred solely by solar variations from orbital parameters between 7 ka and 1800
CE and additionally by anthropogenic greenhouse gases thereafter. The high-res-
olution NAOSIM simulations focus on the sea-ice distribution in the Greenland Sea
and Fram Strait. Downscaling procedures were described by M
ü
ü
ller et al. (
2011
)
and St
ä
rz et al. (
2012
).
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