The potential of high-resolution stable isotope records in the bivalve Angulus benedeni benedeni's shells to investigate Pliocene seasonality

Obtaining temperature data from the mid-Piacenzian warm period (mPWP) is a key factor in understanding the coming changes brought upon by anthropogenic climate change. The mPWP, a high-CO₂ world with a paleogeography similar to modern times, has been used to validate and improve model retrodictions, which in turn enables assessing the prediction strength of these models¹. For the first time, stable isotope analysis has been applied to the extinct tellinid bivalve Angulus benedeni benedeni, originating from the mid-Piacenzian of the Lillo Formation of Belgium in the southern North Sea basin. Multi-annual oxygen isotope records with a seasonal resolution obtained from its shell indicate that this species could live for up to a decade and formed monthly growth increments. From this oxygen isotope record, a clumped-isotope-based mean annual temperature of 12.6 ± 3.6°C was reconstructed. This is 2.1°C warmer than today^2,3, 2.6°C warmer than the pre-industrial North Sea², and in line with global Pliocene temperature estimates of +2-4°C compared to the pre-industrial climate^4,5. The pristine nature of the aragonitic shell material was verified through electron backscatter diffraction analysis (EBSD), and backed up by light microscopy, X-ray diffraction, and X-ray fluorescence. The various microstructures as obtained from the EBSD maps have been described, and they provide a template of pristine A. benedeni benedeni material to which potentially altered shells may be compared. The bivalve A. benedeni benedeni is suitable for high resolution isotope-based paleoclimatic reconstruction and it can be used to unravel the marine conditions in the Pliocene North Sea basin at a seasonal scale, yielding enhanced insight into imminent western European climate conditions.

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