Publication Date:
2019-07-17
Description:
Changes in intensity and composition of bioturbation and trace fossils in deep-sea settings are directly related
to changes in environmental parameters such as food availability, bottom water oxygenation, or substrate
consistency. Because trace fossils are practically always preserved in situ, and are often present in environments
where other environmental indicators are scarce or may have been compromised or removed by diagenetic
processes, the trace fossils provide an important source of paleoenvironmental information in regions
such as the deep Arctic Ocean. Detailed analysis of X-ray radiographs from 12 piston and gravity cores from a
transect spanning from the Makarov Basin to the Yermak Plateau via the Lomonosov Ridge, the Morris Jesup
Rise, and the Gakkel Ridge reveal both spatial and temporal variations in an ichnofauna consisting of
Chondrites, Nereites, Phycosiphon, Planolites, Scolicia, Trichichnus, Zoophycos, as well as deformational biogenic
structures. The spatial variability in abundance and diversity is in close correspondence to observed patterns
in the distribution of modern benthos, suggesting that food availability and food flux to the sea floor are the
most important parameters controlling variations in bioturbation in the Arctic Ocean. The most diverse
ichnofaunas were observed at sites on the central Lomonosov Ridge that today have partially ice free conditions
and relatively high summer productivity. In contrast, the most sparse ichnofauna was observed in the
ice-infested region on the Lomonosov Ridge north of Greenland. Since primary productivity, and therefore
also the food flux at a certain location, is ultimately controlled by the geographical position in relation to
ice margin and the continental shelves, temporal variations in abundance and diversity of trace fossils have
the potential to reveal changes in food flux, and consequently sea ice conditions on glacial–interglacial
time scales. Down core analysis reveal clearly increased abundance and diversity during interglacial/
interstadial intervals that were identified through strongly enhanced Mn levels and the presence of microand
nannofossils. Warm stages are characterized by larger trace fossils such as Scolicia, Planolites or Nereites,
while cold stages typically display an ichnofauna dominated by small deep penetrating trace fossils such as
Chondrites or Trichichnus. The presence of biogenic structures in glacial intervals clearly show that the Arctic
deep waters must have remained fairly well ventilated also during glacials, thereby lending support to the
hypothesis that the conspicuous brown layers rich in Mn which are found ubiquitously over the Arctic basins
are related to input from rivers and coastal erosion during sea level high-stands rather than redox processes
in the water column and on the sea floor. However, the X-ray radiograph study also revealed the presence of
apparently post-sedimentary, diagenetically formed Mn-layers which are not directly related to Mn input
from rivers and shelves. These observations thus bolster the hypothesis that the bioturbated, brownish
Mn-rich layers can be used for stratigraphic correlation over large distances in the Arctic Ocean, but only if
post sedimentary diagenetic layers can be identified and accounted for in the Mn-cycle stratigraphy.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
Format:
application/pdf
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