Abstract
Individual foraminifera analysis (IFA) holds promise to reconstruct seasonal to interannual oceanographic variability. Even though planktonic foraminifera are reliable recorders of environmental conditions on a population level, whether they also are on the level of individuals is unknown. Yet, one of the main assumptions underlying IFA is that each specimen records ocean conditions with negligible noise. Here we test this assumption using stable isotope data measured on groups of four shells of Neogloboquadrina pachyderma from a 16–19 days resolution sediment trap time series from the subpolar North Atlantic. We find a within-sample variability of 0.11 and 0.10 ‰ for δ18O and δ13C respectively that show no seasonal pattern and exceed water column variability in spring when conditions are homogeneous down to 100s of metres. We assess the possible effect of life cycle characteristics and delay due to settling on foraminifera δ18O variability with simulations using temperature and δ18Oseawater as input. These simulations indicate that the observed δ18O variability can partially be explained by environmental variability. Individual N. pachyderma are thus imperfect recorders of temperature and δ18Oseawater. We estimate the excess noise on δ18O to be 0.11 ± 0.06 ‰. The origin and nature of the recording imprecision require further work, but our analyses highlight the need to take such excess noise into account when interpreting the geochemical variability among individual foraminifera.
Highlights
Planktonic foraminifera hold the promise to provide palaeo-environmental information at high temporal resolution, owing to their life cycle, which is in the order of weeks to months and calcification that takes place 40 over hours to days
Even in the absence of environmental variability, planktonic foraminifera display variability in their stable isotope ratios that needs to be considered in the interpretation of individual foraminifera data. 35
Analytical issues aside (Fehrenbacher et al, 2020), the uncertainty associated with Individual foraminifera analysis (IFA) is often viewed from the perspective of whether the population is well enough characterised, how habitat tracking may affect the results or how variability at different time scales can be distinguished (Leduc et al, 2009; Thirumalai et al, 2013; Glaubke et al, 2021; Metcalfe et al, 2020) and only few consider calibration issues associated with individual planktonic foraminifera (Glaubke et al, 2021)
Summary
Planktonic foraminifera hold the promise to provide palaeo-environmental information at high temporal resolution, owing to their life cycle, which is in the order of weeks to months and calcification that takes place 40 over hours to days This potential is exploited in individual foraminifera analysis (IFA), when instead of measuring groups of shells, shells are measured individually and the variability among the individual shells is used to reconstruct environmental variability during deposition of the sample. The variability in Mg/Ca and δ18O in foraminifera populations from sediment samples often exceeds the variability that can be expected based on local hydrography (Leduc et al, 2009; Groeneveld et al, 2019) Whilst such evidence from 60 sediment may be ambiguous due to uncertainty in the age of the sample and the exact habitat of the foraminifera analysed, laboratory studies suggest that foraminifera geochemistry is affected by temperature-independent variability (de Nooijer et al, 2014; Spero and Lea, 1993; Dueñas-Bohorquez et al, 2011). These observations are not conclusive in their own right, but together they suggest that there are reasonable grounds to assess if the composition of individual foraminifera can be used as a precise environmental indicator
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
