EGU21-10173
https://doi.org/10.5194/egusphere-egu21-10173
EGU General Assembly 2021
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Calcification depth of deep-dwelling planktonic foraminifera from eastern North Atlantic: evidence from stable oxygen isotope ratios of shells from plankton tows 

Andreia Rebotim1,2, Antje H. L. Voelker2,3, Lukas Jonkers1, Joanna J. Waniek4, Michael Schulz1, and Michal Kucera1
Andreia Rebotim et al.
  • 1MARUM – Center for Marine Environmental Sciences, University of Bremen, 28359 Bremen, Germany
  • 2Divisão de Geologia e Georecursos Marinhos, Instituto Português do Mar e da Atmosfera, 1495-006 Lisboa, Portugal
  • 3CCMAR – Center of Marine Sciences, University Algarve , 8005-139 Faro, Portugal
  • 4IOW – Leibniz Institute for Baltic Sea Research Warnemünde, 18119 Rostock, Germany

Stable oxygen isotopes (δ18O) of planktonic foraminifera are one of the most used tools to reconstruct environmental conditions of the water column. Since different species live and calcify at different depths in the water column, the δ18O of sedimentary foraminifera reflects to a large degree the vertical habitat and interspecies δ18O differences and can thus potentially provide information on the vertical structure of the water column. To fully unlock the potential of foraminifera as recorders of past surface water properties, it is necessary to understand how and under what conditions the environmental signal is incorporated into the calcite shells of individual species. Deep-dwelling species play a particularly important role in this context, since their calcification depth reaches below the surface mixed layer. Here we report δ18O measurements made on four deep-dwelling Globorotalia species collected with stratified plankton tows in the Eastern North Atlantic. Size and crust effects on the δ18O signal were evaluated showing that a larger size increases the δ18O of Globorotalia inflata and Globorotalia hirsuta, and a crust effect is reflected in a higher δ18O in Globorotalia truncatulinoides. The great majority of the δ18O values can be explained without invoking disequilibrium calcification. When interpreted in this way the data imply depth-integrated calcification with progressive addition of calcite with depth to about 300 m for G. inflata and to about 500 m for G. hirsuta. In Globorotalia scitula, despite a strong subsurface maximum in abundance, the vertical δ18O profile is flat and appears dominated by a surface layer signal. In G. truncatulinoides, the δ18O profile follows equilibrium for each depth, implying a constant habitat during growth at each depth layer. The δ18O values are more consistent with the predictions of the Shackleton (1974) paleotemperature equation, except in G. scitula, which shows values more consistent with the Kim and O’Neil (1997) prediction.  In all cases, we observe a difference between the level where most of the specimens were present and the depth where most of their shell appears to calcify.

How to cite: Rebotim, A., Voelker, A. H. L., Jonkers, L., Waniek, J. J., Schulz, M., and Kucera, M.: Calcification depth of deep-dwelling planktonic foraminifera from eastern North Atlantic: evidence from stable oxygen isotope ratios of shells from plankton tows , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10173, https://doi.org/10.5194/egusphere-egu21-10173, 2021.