213-9 Foraminifera and Other Organisms Living an Extreme Life Beneath the Ross Ice Shelf, Antarctica

Session: Cushman Symposium: Microfossils of Extremophiles: Living in the Danger Zone

Presenting Author:

Robert Leckie

Authors:

Leckie, Robert Mark¹, Bombard, Samantha², Dameron, Serena³, Heins, Megan Kathleen⁴, Cortese, Giuseppe⁵, Dunbar, Gavin⁶, Coenen, Jason James⁷, Harwood, David M.⁸

(1) Department of Earth, Geographic, and Climate Sciences, Univ Massachusetts - Amherst, Amherst, MA, USA, (2) Department of Earth, Geographic, and Climate Sciences, University of Massachusetts, Amherst, MA, USA, (3) Department of Earth, Geographic, and Climate Sciences, University of Massachusetts, Amherst, MA, USA, (4) Department of Earth and Atmospheric Sciences, University of Nebraska, Lincoln, NE, USA, (5) GNS Science, Earth Sciences New Zealand, Lower Hutt, New Zealand, (6) Antarctic Research Centre, Victoria University, Wellington, New Zealand, (7) Earth and Atmospheric Sciences, University of Nebraska, Lincoln, NE, USA, (8) Dept of Earth & Atmospheric Sciences, Univ Nebraska - Lincoln, Lincoln, NE, USA,

Abstract:

Hot water drilling through the Ross Ice Shelf (RIS) in Antarctica has revealed much about the about the glacial history of Antarctica, including the RISP, ANDRILL, and SWAIS-2C projects, and NZARI Programme. Site HWD-2 was located 80°39.497′S, 174°27.678′E, ~320 km upstream of the calving front of the RIS in water depth of 787.5 m with an ice shelf thickness of 367.5 m and ~420 m water column cavity. Results presented here are from a surface sediment sample, 0-4 cm. All foraminifera were picked from the >63-micron fraction. A total of 647 specimens of foraminifera were found representing >45 species.

 

The near surface foram assemblage consists of 71.5% calcareous benthic specimens, 28.4% agglutinated, and <1% planktics. The two most common species are the agglutinate Textularia catenata (20.9%) and calcareous Globocassidulina subglobosa (18.4%), the latter a suspected proxy for CDW/mCDW in the Ross Sea. The family Miliolidae make up 24.5% of the assemblage (6+ species), while the Nodosariidae make up 16.3% (15+ species). Another agglutinated species, Cyclammina trullissata, is only known from the Holocene of RISP Site J-9. There are a number of likely in situ macroinvertebrates found in the foram samples, including a fairly diverse assemblage of ostracods, echinoderm fragments, sponge spicules, worm tubes(?), and a tiny bivalve. 

 

There is evidence of pelagic transport beneath the ice shelf based on the presence of rare specimens of juvenile planktic Neogloboquadrina pachyderma, sparse diatom specimens known from the Southern Ocean, including Fragilariopsis kerguelenensis, fragile radiolarians known from the calving front of the RIS, as well as pteropods. There is no obvious reworking of foraminiferal specimens, but most of the diatom specimens are reworked from Miocene deposits.

 

The aragonitic pteropods and calcareous benthic forams are well preserved; there is no strong dissolution and no strong traction current bottom transport, suggesting that the bottom water mass was not corrosive like HSSW. The benthic boundary layer may be a mix of HSSW and mCDW as observed near McMurdo Sound.

 

An important question is what food sources supported so many forams (eukaryotic protists) and diverse invertebrate animals? A previous study of microbial activity at HWD-2 identified a taxonomically distinct, chemosynthetically-driven microbial community adapted to a highly oligotrophic marine environment.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-10325

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