The morphotypes of Neogloboquadrina pachyderma : Isotopic signature and distribution patterns in the Canadian Arctic Archipelago and adjacent regions

• Published in: Marine Micropaleontology
• Main Authors: El Bani Altuna, Naima, Pieńkowski, Anna J., Eynaud, Frederique, Thiessen, Rabecca
• Other Authors: Environnements et Paléoenvironnements OCéaniques (EPOC), Observatoire aquitain des sciences de l'univers (OASU), Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Sciences et Technologies - Bordeaux 1 (UB)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-École Pratique des Hautes Études (EPHE), Université Paris Sciences et Lettres (PSL)-Université Paris Sciences et Lettres (PSL)-Centre National de la Recherche Scientifique (CNRS)
• Format: Article in Journal/Newspaper
• Language: English
• Published: HAL CCSD 2018
• Subjects: [SDE]Environmental Sciences; Arctic Archipelago; Arctic; Canadian Arctic Archipelago; Foraminifera*; Neogloboquadrina pachyderma; Planktonic foraminifera
• Online Access: https://hal.science/hal-04558164; https://doi.org/10.1016/j.marmicro.2018.05.004

International audience Neogloboquadrina pachyderma represents a key planktonic foraminifera species in the boreal Atlantic and has been extensively used as a paleoceanographic tool in polar to subpolar environments. The species shows an intraspecific morphological variability, displaying at least 5 different morphotypes previously documented from northern and southern oceans. The present work focuses on the distribution of these morphotypes in modern surface sediment samples from the Canadian Arctic Archipelago (CAA). Our results, obtained for the first time for this area, show the prevalence of morphotypes 1, 2 and 3 (abundance on average 19%, 48% and 22%, respectively). Two types of assemblages were observed in the inner and outer parts of the Northwest Passages on the basis of the abundance and diversity of morphotypes. Their geographical and vertical positions regarding the water depth in the CAA argue for a strong influence of water mass stratification on morphotype distribution. The detailed morphometric study of test morphology together with SEM imagery provides a way to re-evaluate and complete previous classifications of N. pachyderma morphotypes. This morphological approach is supported by stable isotope analyses that document a link between δ18O and δ13C and morphotype mean sizes. This relationship is interpreted as indicative of water column position, with large morphotypes living in relatively shallower (but also fresher, colder and more productive) waters compared to small morphotypes. The former interpretation is further supported by the increased pore concentration in larger morphotypes, which is tentatively interpreted as a strategy to increase buoyancy and to adapt to lower salinity. Consequently, we propose that a coupled approach of using morphology and stable isotopes may constitute an improved tool for oceanographic reconstructions (particularly water column stratification) when used with N. pachyderma assemblages. Furthermore, the additional morphometric criteria defined in the current ...