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Abstract:
Cosmogenic isotope 10Be is produced in the stratosphere and troposphere by spallation reactions involving interaction between highly energetic galactic cosmic ray and atmospheric isotopes such oxygen and nitrogen. Because the incoming flux of primary galactic cosmic ray is modulated by the strength of geomagnetic field and solar activity, the maximum production of cosmogenic 10Be appears during geomagnetic dipole lows. Atmospheric 10Be is eventually removed by aerosols and afterwards deposited on the Earth surface. In the Ocean it is rapidly scavenged by suspended mater and stored within the sedimentary column. In order to use pelagic archives for tracing back cosmogenic 10Be variations, which are prone to geomagnetic field change, 10Be is commonly normalized for sediment inhomogenities by stable isotope 9Be. Scaling the authigenic 10Be/9Be records, obtained from widely scattered locations, revealed the presence of several environmental components, likely driven by global ocean water masses circulation and regional processes. Detected additive site-dependent 10Be/9Be component is time-invariant over the last 300ka and seems to agree with the pattern of thermohaline circulation. The case study of North Atlantic site revealed the upward long-term and oscillatory trends of 10Be and 9Be records, pointing to the change of regional deep-water masses circulation. Unveiling these trends allows us not only to disentangle environmental and geomagnetic components of 10Be/9Be signal, but also to constrain the main drivers of beryllium isotopes distribution in the ocean.
