Larsen-C Benthos

Benthic biodiversity under Antarctic ice-shelves – baseline assessment of the seabed exposed by the 2017 calving of the Larsen-C Ice Shelf

Start date
22 December, 2017
End date
21 December, 2018

On 12 July 2017, the Larsen-C Ice Shelf calved one of the largest iceberg originating from the Antarctic Peninsula ever recorded. As iceberg A68 moves north, it  leaves behind an area of 5,800 km2 of seabed newly exposed to open marine conditions. Much of this area has very likely remained ice-covered for centuries and may have been covered since the last inter-glacial (<100kyr) period. The calving of A68 offers a unique scientific opportunity for fundamental research to address questions around the mobility and colonisation capacity of seafloor species and past climate variability.

As iceberg A68 moves north, it will leave an area of 5,800 km2 of seabed newly exposed to open marine conditions

This NERC-funded Urgency project Larsen-C Benthos aimed to test the hypothesis that under-ice-shelf benthic biodiversity resembles nutrient-poor deep-sea communities by examining the life and habitats formerly under the iceberg A68 in the western Weddell Sea. Unfortunately, heavy sea ice conditions thwarted their attempts at reaching the Larsen C Ice Shelf.

Marine biologist and Principal Investigator, Dr Katrin Linse, from British Antarctic Survey who led the team said:

“We knew that getting through the sea ice to reach Larsen C would be difficult. Naturally, we were disappointed not to get there but safety must come first. The captain and crew have been fantastic and pulled out all the stops to get us to the ice shelf, but our progress became too slow, with just 8kms traveled in 24 hours and we still had over 400kms to travel. Mother Nature had not been kind to us on our mission!

“But we had a ‘Plan B’, we headed north to areas which have never been sampled for benthic biodiversity. The Prince Gustav Channel Ice Shelf and neighbouring Larsen A Ice Shelf collapsed in 1995. We sampled deeper than we planned at Larsen C – down to 1000 metres – and found lots of exciting animals living on the seafloor.”

A map of the sea ice and new sampling location in the Prince Gustav Channel

In September 2017 the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) designated the newly-exposed marine area (adjacent to Larsen C Ice Shelf, Subarea 48.5) as a Stage 1 Special Area for Scientific Study. This allows the area to be protected from potential commercial exploration for an initial period of two years, which is likely to be extended to ten years following further consideration by CCAMLR Members. Read more here.

 

Map of the Antarctic Peninsula showing the Special Area for Scientific Study

 

Larsen-C Benthos was  a British Antarctic Survey (BAS) led expedition supported by a NERC Urgency Grant (NE/R012296/1) including scientists from three UK universities (Aberdeen, Newcastle, and Southampton) and the Natural History Museum in London. This core team was supported by national and international scientists and overall included participants from 6 different countries and 9 institutes. The expedition took place on board the BAS research ship the RRS James Clark Ross in early 2018.

A selection of seafloor animals collected by the Larsen C Benthos expedition in the Prince Gustav Channel

Our governing hypothesis is:

“Until the calving of the Larsen-C iceberg, A68, the benthic fauna on the seabed beneath ice shelf has likely comprised oligotrophic assemblages resembling deep-sea Weddell Sea assemblages. The calving of A68, and the exposure of the seabed it covered to open-marine and sea-ice conditions will initiate a rapid colonisation by new species that will transform the benthic ecosystem significantly within 3-5 years.”

To test our hypothesis and document the faunal baseline under Larsen-C, we will deploy trawls (epibenthic sledge (EBS), Agassiz trawl (AGT), bongo net (BN)), mega-corer (MUC), towed camera systems (SUCS & DWCS), CTD, and single and multi-beam echosounders at each station. As the seabed under A68 is uncharted, areas around the proposed stations will be surveyed by swath bathymetry to map seafloor topography. With our holistic sampling approach we will collect information on the assemblage structure, biodiversity and abundance of the in-, epi-, and suprabenthic meio-, macro- and megafauna. This will provide a baseline for assessing ecosystem function with samples of potential food sources such as phyto- and zooplankton as well as organic matter in the sediments and comprise a suite of biological, sedimentological and biogeochemical parameters.

 

Our key objectives and tasks are:

  • Sample and characterize macro- and mega-faunal biodiversity in the benthic community below A68; Faunal collection and appropriate sample fixation for taxonomic identification, molecular genetic and genomic analyses of phylogeography, evolutionary history and metagenomics. Characterisation of assemblages formerly under A68 and their spatial distribution at a range of scales in relation to distance from the former ice front. Faunal community analysis from photo and video imagery with taxonomic identification validated with physical specimen samples.
  • Assess the initial benthic trophic structure and carbon flow below A68. 1) Sample fixation appropriate for food web analysis (natural isotopes δ13C, δ 15N and δ 34S) of macro- and megafauna, and food sources such as plankton and organic matter in the sediment. 2) In-vivo 13C uptake experiments of infaunal meio- and macrofauna in multicorer-tube microcosms.
  • Document and describe the pre-collapse system to provide a springboard for future studies and grant opportunities. Archiving of pre-collapse samples will be vital.

Biological and environmental data will be analysed with multivariate statistics and compared to assemblages and ecosystems reported from the Southern Ocean shelf, slope and deep-sea, especially those from Larsen-A/B and the bathyal and abyssal Weddell Sea.


Science and Technology team

Carwyn Davies

Co-Investigators

Adrian Glover – Natural History Museum

Alan Jamieson – Newcastle University

Will Reid – Newcastle University

Ursula Witte – University of Aberdeen

Project Partners

Jon Copley – University of Southampton

Dieter Piepenburg – Alfred Wegener Institute

External collaborators

Angelika Brandt – Senckenberg Institute

Ann Vanreusel – University of Ghent

Anni Makela – University of Aberdeen

Luisa Federwisch – Alfred Wegener Institute

Melanie Mackenzie – Museum Victoria

Simon Dreutter – Alfred Wegener Institute

Thomas Dahlgren – University of Gothenburg and Uni Research

 


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