Towards dating marine sediments using 26Al

Radiometric dating methods are indispensable tools for providing a common and precise timescale for different paleo-environmental archives and their climate records. The cosmogenic radionuclides 26Al and 10Be decay with half-lives of 0.7 Ma (26Al) and 1.4 Ma (10Be), respectively, allowing radiometric dating of climate archives far beyond the range of 14C (t1/2=5730 a) and 230Th (t1/2=75 ka). While 10Be has become a common tool in marine geology, 26Al has been studied significantly less. Low atmospheric 26Al production rates and high stable 27Al concentrations result in very low 26Al/27Al ratios, often near the detection limit of accelerator mass spectrometry (AMS). However, with its half-life of 0.7 Ma 26Al would be perfectly suited to bridge a gap of the currently available radiometric dating methods and may allow for constructing better age models in the 1-3 Ma range. Recently, new developments in the field of AMS enable measurements of low 26Al/27Al ratios by isobar suppression using selective photodetachment via ion laser interaction (ILIAMS at University of Vienna). We use these advances to study 26Al/27Al of globally distributed core-top marine sediments. In combination with the corresponding 10Be/9Be we can now assess the spatial variability of authigenic 26Al/27Al and 26Al/10Be in core-top marine sediments as an important premise for the use of 26Al as a dating tool. Based on these measurements we are able to identify suitable locations for further studies on the behaviour of 26Al/27Al and 26Al/10Be during deposition in the sediment. Ackn.: Parts of the measurements were supported by the RADIATE project from the EU Research and Innovation programme HORIZON 2020 under grant agreement No 824096. Parts of this research were carried out at the Ion Beam Centre (IBC) at the Helmholtz-Zentrum Dresden-Rossendorf e. V., a member of the Helmholtz Association.