Foraminiferal Patterns in Deglacial Sediment in the Western Ross Sea, Antarctica: Life Near Grounding Lines

Abstract

Improved multibeam swath bathymetry allows targeted coring of glacial landforms aiming at improving our understanding of sedimentary facies that developed in glacimarine settings during the post-Last Glacial Maximum (LGM) deglaciation. Coupled with radiocarbon dates, we explore foraminiferal records from 18 sediment cores from the western Ross Sea largely from sites near paleo-grounding lines. We investigate post-LGM foraminiferal assemblages from glacimarine environments, including those proximal and more distal to paleo-grounding lines, including environments influenced by subglacial meltwater outflow and further removed from direct glacial influence and subject to different oceanographic conditions. Agglutinated benthic foraminiferal assemblages dominate open marine facies deposited under the presence of High Salinity Shelf Water and significant primary production, while calcareous foraminiferal assemblages characterize grounding line-proximal settings, some of which were potentially influenced by Modified Circumpolar Deep Water. Rapid deposition of meltwater plume deposits inhibited and, in some cases, significantly altered foraminifera abundance and diversity. Broadly in the Ross Sea, it appears that the high bathymetric gradient of grounding zone wedges is a key factor promoting rich benthic foraminiferal communities in habitats proximal to grounding lines. Therefore, we demonstrate that paleo-grounding line settings may archive high quality in situ foraminiferal data, which is imperative for paleoenvironmental and geochemical studies on glaciated continental margins worldwide.

Environmental and Oceanographic Conditions at the Continental Margin of the Central Basin, Northwestern Ross Sea (Antarctica) Since the Last Glacial Maximum

“…This agglutinated taxon has been documented in the diatomaceous sediments of the Ross Sea troughs by [54,80,94] (as M. arenacea) during the Late Pleistocene-Holocene transition. The exclusive presence M. earlandi and the disappearance of the calcareous foraminifera are normally related to the lower carbonate ion concentration in the deep water, presumably under the influence of the HSSW [14,80].…”

“…As already observed in the previous unit from the early Holocene onwards, calcareous foraminifera are nearly absent in Unit 3 as well and the only benthic species present is M. earlandi. The presence of this agglutinated taxon together with the percentage values of F. kerguelensis indicates the maintenance of open water conditions [54,80,[94][95][96] at least until 6.5 ka, even though a slight increase and oscillating abundance of ice-related and cold-water species (F. obliquecostata, E. antarctica, and S. speculum var. coronata) are observed, especially in the offshore site, suggesting a decreased inflow of CDW.…”

“…At the same time, the benthic foraminifera are abundant and are mainly represented by E. exigua, A. weddellensis, Nonionella spp., and subordinately by C. lobatulus, G. biora, G. subglobosa and T. earlandi. This benthic foraminifera association is normally used to represent sub-ice shelf environments, from proximal to distal, although the presence of A. weddellensis and E. exigua suggests a more open marine environment [80]. These two small species could also indicate the occasional influence of CDW for this area, as suggested by [80,81].…”

“…This benthic foraminifera association is normally used to represent sub-ice shelf environments, from proximal to distal, although the presence of A. weddellensis and E. exigua suggests a more open marine environment [80]. These two small species could also indicate the occasional influence of CDW for this area, as suggested by [80,81].…”

Foraminifer and Ostracod Occurrence in a Cool-Water Carbonate Factory of the Cape Adare (Ross Sea, Antarctica): A Key Lecture for the Climatic and Oceanographic Variations in the Last 30,000 Years

“…In contrast, in high latitude areas, glacial processes are known for test transport, leading to the accumulation of allochthonous fossil assemblages in deep shelf settings [16]. However, even in high dynamic environments such as those located near grounding lines and related grounding zone wedges (GZWs), microfossils can be considered autochthonous, provided they meet certain preservation criteria [18,19]. Reworked and transported foraminifers are, in fact, recognised when their tests appear damaged, with different coloration, and/or with sediment filling [20].…”