Larsen-C Benthos

What Larsen-C Benthos did

The Larsen-C Benthos project planned to study benthic biodiversity on the seabed exposed by the 2017 calving of the Larsen-C Ice Shelf. On 12 July 2017, iceberg A68 broke away, creating 5,800 km² of seabed newly exposed to the open ocean. Much of this area had likely been under ice for centuries, possibly since the last interglacial period.

The project tested the idea that under-ice benthic communities are similar to nutrient-poor deep-sea ecosystems. The team planned to study life and habitats under the former Larsen-C Ice Shelf in the western Weddell Sea.

Heavy sea ice prevented the team from reaching Larsen C. Progress slowed to 8 km in 24 hours, and they still had over 400 km to go. Safety was prioritised, so the team switched to a ‘Plan B.’ 

They moved north to previously unsampled areas, including the Prince Gustav Channel of which the southern end had been a former part of the Larsen A Ice Shelf, which had collapsed in 1995.

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.

In the Prince Gustav Channel, the team sampled down to 1,250 metres, deeper than planned at Larsen C, and discovered many exciting seafloor animals.

Why this matters

The project provided the first scientific data on previously ice-covered seafloor in the western Weddell Sea. Sampling in new areas revealed benthic communities that had not been studied before.

In September 2017, CCAMLR designated the newly exposed marine area as a Stage 1 Special Area for Scientific Study. This protected it from commercial activities for an initial two-year period, likely to extend to ten years.

How the project worked

• Ship-based expedition: the team sailed on the BAS research ship RRS James Clark Ross in early 2018.
• Sampling: scientists collected seafloor animals and studied habitats down to 1,000 metres.
• Plan B approach: when Larsen C was inaccessible, the team sampled the Prince Gustav Channel and Larsen A Ice Shelf areas.
• Collaboration: national and international scientists participated, contributing expertise in benthic biology and ecosystem analysis.

Science objectives

The project aimed to:

• assess benthic biodiversity in the Prince Gustav Channel
• evaluate benthic communities undergoing succession after ice shelf collapse
• collect baseline data for future monitoring, including on microplastic pollution
• inform conservation and management decisions for the region

Who was involved

The project was led by BAS scientists and funded by a Natural Environment Research Council (NERC) Urgency Grant (NE/R012296/1).

The core team included scientists from:

• University of Aberdeen 
• Newcastle University
• University of Southampton
• Natural History Museum

Participants came from six countries and nine institutes in total.

Our governing hypothesis was:

“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.

To test our hypothesis and document the faunal baseline under Larsen-C, we deployed 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 was uncharted, areas around the proposed stations were surveyed by swath bathymetry to map seafloor topography. With our holistic sampling approach we collected information on the assemblage structure, biodiversity and abundance of the in-, epi-, and suprabenthic meio-, macro- and megafauna. This provided 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 comprised a suite of biological, sedimentological and biogeochemical parameters.

Our key objectives and tasks were:

• 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 would be vital. Biological and environmental data were 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

Bjoerg Apeland

Mechanical Engineer

Carwyn Davies

Mechanical Engineer

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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The data collected by this expedition will be used to produce official reports and will be made publicly available through the official SCAR biodiversity data portal – biodiversity.aq.