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 (t_1/2=5730 a) and ²³⁰Th (t_1/2=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.