Authigenic 10Be/9Be ratios and 10Be-fluxes (230Thxs-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications
Résumé
Authigenic 10Be/9Be ratios and 10Be-fluxes reconstructed using the 230Thxs normalization, proxies of the
cosmogenic radionuclide 10Be production rate in the atmosphere, have been measured in a sedimentary
core from Baffin Bay (North Atlantic) spanning the last 136 ka BP. The normalization applied on the
exchangeable (authigenic) 10Be concentrations using the authigenic 9Be isotope and 230Thxs methods
yield equivalent results strongly correlated with sedimentological parameters (grain-size and mineralogy).
Lower authigenic beryllium (Be) concentrations and 10Be/9Be ratios are associated with coarsegrained
carbonate-rich layers, while higher authigenic Be values are related to fine-grained felsparrich
sediments. This variability is due to: i) sediment composition control over beryllium-scavenging
efficiency and, ii) glacial history that contributed to modify the 10Be concentration in Baffin Bay by
input and boundary scavenging condition changes. Most paleo-denudation rates inferred from the
10Be/9Be ratio vary weakly around 220 ± 76 tons.km2.yr1 (0.09 ± 0.03 mm.yr1) corresponding to
relatively steady weathering fluxes over the last glacial cycle except for six brief intervals characterized
by sharp increases of the denudation rate. These intervals are related to ice-surging episodes coeval with
Heinrich events and the last deglaciation period. An average freshwater flux of 180.6 km3.yr1 (0.006 Sv),
consistent with recent models, has been calculated in order to sustain glacially-derived 10Be inputs into
Baffin Bay. It is concluded that in such environments, the authigenic 10Be measured mainly depends on
climatic effects related to the glacial dynamics, which masks the 10Be production variation modulated by
geomagnetic field changes. Altogether, these results challenge the simple interpretation of 10Be-concentration
variation as a proxy of Interglacial/Glacial (interstadial/stadial) cycles in Arctic and sub-Arctic
regions. They rather suggest the effect of higher-frequency paleoclimatic changes and local glacial dynamics
on 10Be signature.
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