Preprints
https://doi.org/10.5194/cp-2021-87
https://doi.org/10.5194/cp-2021-87

  03 Aug 2021

03 Aug 2021

Review status: this preprint is currently under review for the journal CP.

Variability in Neogloboquadrina pachyderma stable isotope ratios from isothermal conditions: implications for individual foraminifera analysis

Lukas Jonkers1, Geert-Jan A. Brummer2, Julie Meilland1, Jeroen Groeneveld3, and Michal Kucera1 Lukas Jonkers et al.
  • 1MARUM Center for Marine Environmental Sciences, University of Bremen, Bremen, Germany
  • 2Royal Netherlands Institute for Sea Research, Texel, the Netherlands
  • 3Department of Geology, Hamburg University, Hamburg, Germany

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.

Lukas Jonkers et al.

Status: open (extended)

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  • RC1: 'Comment on cp-2021-87', Anonymous Referee #1, 21 Sep 2021 reply

Lukas Jonkers et al.

Lukas Jonkers et al.

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Short summary
The variability in the geochemistry among individual foraminifera is used to reconstruct seasonal to interannual climate variability. This method requires that each foraminifera shell accurately records environmental conditions, which we test here using a sediment trap time series. 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.