Can patchiness explain habitat variability in planktonic foraminifera?

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Chemical properties of planktonic foraminifera shells record physical and chemical conditions in the upper ocean during their calcification. Trace element and isotopic signatures locked in the shells can be used to reconstruct key parameters of the upper ocean in the past. To unlock the full potential of these signals, the position in the water column where calcification occurs has to be constrained. Observations from stratified plankton tows and geochemical analyses of shells from the sediment revealed that living and calcification depth varies among species as well as within species. The factors that control this variability are difficult to identify and the understanding is further complicated by hypotheses involving habitat depth changes through life in pace with diurnal to reproductive cycles. All of those concepts rely on the assumption that the distribution of the studied species is spatially uniform. In the presence of patchiness, many of the observed patterns and habitat variability could be explained by unpredictable spatial heterogeneity. Here we propose to use stratified plankton samples collected in a unique and unprecedented sampling design during RV METEOR expedition M140 to determine the existence and the extent of patchiness in planktonic foraminifera. By combining assemblage counts with a new highly resolved 3D automated image segmentation technique in replicate samples we will determine where in the water column individuals of different sizes within species live and by analyzing their isotopic signatures, we will determine how temporarily stable these habitats are. These results will critically constrain the extent of population structuring of marine microzooplankton, allowing a more realistic representation of their habitat in models and proxies, and facilitating correct interpretation of observational data obtained by point sampling for global carbon budget estimations.