Integrated micropaleontological (planktic and benthic foraminifera, diatoms, and silicoflagellates) analysis, together with textural and geochemical results of a deep-sea core from the Hallett Ridge (northwestern Ross Sea), provides new data for late Quaternary (23–2 ka) paleoenvironmental and paleoceanographic reconstructions of this region. Results allow us to identify three time intervals: the glacial–deglacial transition, the deglacial period, and the interglacial period.

Morphologically similar benthic foraminifera taxa are difficult to separate, resulting in incorrect identifications, complications understanding species-specific ecological preferences, and flawed reconstructions of past environments. Here we provide descriptions and illustrated guidelines on how to separate some key Arctic–North Atlantic species to circumvent taxonomic confusion, improve understanding of ecological affinities, and work towards more accurate palaeoenvironmental reconstructions.

The study presents (1) a validation of a method which was previously published allowing us to recognize different Ammonia phylotypes (T1, T2 and T6) based only on their morphology and (2) a refined biogeographical distribution presented here supporting the putatively invasive character of phylotype T6. Results suggest that phylotype T6 is currently spreading out and supplanting autochthonous phylotypes T1 and T2 along the coastlines of the British Isles and northern France.