Aberrant coiling signatures reveal the specialised reproductive strategy of the planktonic foraminifera Neogloboquadrina pachyderma under Central Arctic perennial sea ice

Abstract

The perennially sea-ice covered Central Arctic Ocean (CAO) hosts a single planktonic foraminifera species, Neogloboquadrina pachyderma, a polar specialist that predominantly exhibits sinistral-coiling. Widely used as a palaeoceanographic proxy for polar conditions, it displays a range of morphologies, including an uncommon dextral form which resembles its subpolar relative, Neogloboquadrina incompta. The biological significance of dextral coiling in N. pachyderma remains unclear, complicating climate reconstructions and interpretations of its reproduction in the CAO. While culture studies link coiling direction to a biphasic life cycle involving an asexual stage producing both coiling types, supporting field data are lacking. This study analysed N. pachyderma collected from eight plankton net and four box core stations in the CAO beneath permanent sea ice. Morphometric and genetic analyses identified six N. pachyderma morphotypes concentrated in the upper 100 m, dominated by relatively small specimens (80–125 μm). Unusually high proportions of dextral coilers (up to 32 %) were observed in the water column, compared to ∼6 % in the underlying sediment. Proloculus (first chamber) size-analysis and Gaussian Mixture Modelling revealed three proloculus-size means in the water column, suggesting the presence of an asexual clonal schizont generation alongside the typical sexual-asexual cycle. These observations provide the first in situ evidence of schizont reproduction in natural N. pachyderma populations, a strategy that may facilitate rapid population growth and adaptability in the CAO. These results clarify the biological significance of coiling direction in N. pachyderma's life cycle, and reduce the risk of misidentifying N. incompta in Arctic palaeoclimatic studies.