Understanding the controls behind the calcification and distribution of planktonic foraminifera in the modern ocean is important when using these organisms for paleoceanographic reconstructions. This study combines shell geochemistry, light microscopy, and X-ray micro-computed tomography to dissect various parameters of Trilobatus trilobus shells from surface sediments and explore the factors influencing their biometry. The goal is to understand which aspects of the marine environment are critical for the calcification and vertical distribution of this species. T. trilobus is found to produce larger, thinner and overall lighter shells in the equatorial regions compared to the subtropical gyre regions where the shells were up to 4% smaller, more than 60% thicker and approximately 45% heavier. The skeletal mass percentage together with other calcification metrics (shell weight, thickness) are found to depend primarily on ambient seawater salinity rather than carbonate chemistry. In line with their degree of calcification, based on geochemically reconstructed apparent calcification depths, this group of organisms is found shallower into the water column at the equator and the subtropical gyres, while its habitat deepens in between these regions at the extra-equatorial sites. Furthermore, it is demonstrated that T. trilobus, in the (central) Atlantic, occupies a density layer slightly below the salinity maximum isopycnal at various depths, presumably by adjusting its shell properties.

High-resolution X-ray tomographic data of shells of planktonic foraminifera species Trilobatus trilobus from samples VM27-261, VM19-308, VM16-206, VM23-112, VM22-26, RC13-189, RC13-188, RC24-10, RC24-11, RC24-16, RC24-17, VM22-175, RC16-77, RC16-36, RC08-19, RC08-23 from the central Atlantic Ocean. The specimens are from the 300-355 μm sieve fraction and the average scanning resolution is ~1.2 μm. The exact voxel size and other scan info are included in each zip file. The analyses were performed using a GE/Phoenix v|tome|x s 240 CT scanner at the Geozentrum Nordbayern. The planktonic tests were fixed in a customized cylindrical container together with a calcite microcrystal that can be used to standardize the CT number (grey levels) of the scanned specimens. A high-resolution setting (voltage of 80 kV, current 80 μA, detector array size of 1024×1024, 1501 projections/360°, 2.5 s/projection) enabled the acquisition of 3D images with an isotropic pixel size. Phoenix datos|x 2.0 software was used to correct and reconstruct tomographic data that uses the general principle of Feldkamp cone beam algorithm to reconstruct image cross sections from the filtered back projections.