Developing a palaeoceanographic proxy based on the dimensions of Adercotryma glomeratum populations: a case study in Drake Passage region (Antarctic Peninsula)

The Drake Passage is a highly hydrodynamic region that is difficult to navigate due to adverse weather conditions and intense surface currents. This study investigates how the bottom hydrodynamic regime influences the size of foraminiferal tests on the Antarctic Peninsula. For this, the species Adercotryma glomeratum (an agglutinated species of foraminifera) was chosen, as it was the only species abundant in the seven selected stations. Five stations (EB-1 to EB-5) are located in a region with a depth of ~ 480 m and two in a deep area of ~ 3,800 m (DK-1 and DK-2). All the tests were individually measured along their long axis and classified according to size. The most frequently recorded size range of A. glomeratum varied between ≈ 90–180 µm. The average test size and standard deviation were lower at stations EB-1 to EB-5, with coarser-grained sediments. The cluster analysis based on grain size, morphometric data of A. glomeratum , and depth shows that the largest sizes of this species tend to occur in fine-grained sediments at stations DK-1 and DK-2. The fine-grained sediments at stations DK-1 and DK-2 indicate the presence of calmer bottom conditions. These results suggest that in deep-sea environments, the stable areas, under calmer hydrodynamic conditions, enable longer life cycles of living foraminifera and the development of populations with bigger individuals, namely of A. glomeratum. The data obtained in this work suggest that the size of A. glomeratum populations can be used as an indicator of the stability/instability of the environment. Thus, the size of the individuals that make up the populations of A. glomeratum , and probably other foraminiferal species, can be used in paleoenvironmental reconstructions as a trace of disturbances or environmental stability in deep-sea settings, such as that of the Southern Ocean.