Authigenic Be-10/Be-9 ratios and Be-10-fluxes (Th-230(XS)-normalized) in central Baffin Bay sediments during the last glacial cycle: Paleoenvironmental implications

作者：Simon Quentin^*; Thouveny Nicolas; Bourles Didier L; Nuttin Laurence; Hillaire Marcel Claude; St Onge Guillaume

来源：Quaternary Science Reviews, 2016, 140: 142-162.

DOI：10.1016/j.quascirev.2016.03.027

• Be-10 cosmogenic nuclide
• Authigenic Be-10/Be-9 ratios
• (10)Befluxes (230)Thxs-normalization
• Baffin bay
• Late quaternary
• Glacial dynamics
• Stratigraphic markers
• Paleo-denudation rate
• Freshwater flux

Authigenic Be-10/Be-9 ratios and Be-10-fluxes reconstructed using the Th-230(xs), normalization, proxies of the cosmogenic radionuclide Be-10 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) Be-10 concentrations using the authigenic Be-9 isotope and Th-230(xs) methods yield equivalent results strongly correlated with sedimentological parameters (grain-size and mineralogy). Lower authigenic beryllium (Be) concentrations and Be-10/Be-9 ratios are associated with coarse grained carbonate-rich layers, while higher authigenic Be values are related to fine-grained felspar rich sediments. This variability is due to: i) sediment composition control over beryllium-scavenging efficiency and, ii) glacial history that contributed to modify the Be-10 concentration in Baffin Bay by input and boundary scavenging condition changes. Most paleo-denudation rates inferred from the Be-10/Be-9 ratio vary weakly around 220 +/- 76 tons.km(-2).yr(-1) (0.09 +/- 0.03 mm.yr(-1)) 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 km(3).yr(-1) (0.006 Sv), consistent with recent models, has been calculated in order to sustain glacially-derived Be-10 inputs into Baffin Bay. It is concluded that in such environments, the authigenic Be-10 measured mainly depends on climatic effects related to the glacial dynamics, which masks the Be-10 production variation modulated by geomagnetic field changes. Altogether, these results challenge the simple interpretation of Be-10-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 Be-10 signature.

• 出版日期2016-5-15