LA-MC-ICP-MS study of boron isotopes in individual planktonic foraminifera: A novel approach to obtain seasonal variability patterns

Boron isotope (delta B-11) analysis using bulk foraminifera samples is a widely used method to reconstruct paleo sea water pH conditions. Although, these analyses exhibit high analytical precision, short term information is lost due to the pooling of tests with distinct and diverse boron isotope signatures resulting in average values for the time interval encompassed in the sample. Here we present and assess the analysis of delta B-11 of individual foraminifera by means of Laser Ablation Multi-Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) to obtain seasonal variability patterns and to test the limits of precision of LA-MC-ICP-MS on the planktonic foraminifera Orbulina universa. The results show that relative seasonal differences (of similar to 11%0) can be captured from either uncleaned or cleaned individual O. universa tests with an average precision of +/- 2.9 parts per thousand (2 SE). The delta B-11 variability among foraminifera representing the same season is on average 7.4%o (2 SD) irrespective of cleaning state. With our approach, analyses on oxidatively cleaned o. universa do not require the use of a matrix matched standard to obtain B isotope values in the range of those expected for solution multispecimen analyses. Our results are useful for considering the potential spread caused by foraminifera vital effects and for obtaining information of seasonal ranges of pH and possible bias related to seasonally hidden within conventional solution based delta B-11 analyses.