T02_P04

The impact of leaching on foraminifera radiocarbon ages

Grotheer H^1,2,  Mollenhauer G^1,2

¹Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany, ²University Bremen, MARUM, Bremen, Germany

Reliable radiocarbon ages of foraminifera are a prerequisite to generate robust high-resolution age-depth models or to obtain precise understanding of past carbon cycle dynamics. With the advance of small-scale radiocarbon measurements instrumental precision and levels of contamination become increasingly important to consider as with decreasing sample size the precision becomes progressively poorer, and the effect of contamination increases proportionally. To reduce the effect of carbon contamination, an attempt can be made to remove it by chemical pretreatment. An alternative might be mathematical corrections based on processing blanks of the same sample material and assuming constant contamination.

Here we report on radiocarbon analyses of monospecific foraminifera samples compared between different blank corrections and sample treatments I) to examine whether chemical pre-treatment and mathematical blank correction are comparable, and II) to determine limitations hindering reliable radiocarbon dating with ever smaller sample sizes. The data show that chemical pre-treatment does remove surface contamination and that the same effect on data reliability can be achieved by mathematically correcting for blank values determined from sample size-matched blank foraminifera. Theoretical considerations show that chemical pretreatment only has a beneficial effect where the isotopic difference between chemically untreated and pre-treated samples exceed the analytical precision