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Biodiversity signature of the Last Glacial Maximum at South Georgia, Southern Ocean

Biodiversity signature of the Last Glacial Maximum at South Georgia, Southern Ocean
Biodiversity signature of the Last Glacial Maximum at South Georgia, Southern Ocean
Aim
High-latitude biodiversity distributions can preserve signals of the timing and geography of past glaciations, and as such ground truth ice-sheet models. Discrete polar archipelagos offer the fewest confounding factors for testing historic ice position records in extant biodiversity. At South Georgia, two competing geological hypotheses suggest that either the Last Glacial Maximum (LGM) ice was extensive, nearly covering the continental shelf (H1 Big ice) or restricted to the inner fjords (H2 Little ice). We examined the past configuration of the South Georgia ice cap using seabed biodiversity.

Location
South Georgia, Southern Ocean.

Methods
We used a bespoke camera lander (SUCS) and Agassiz trawl deployments across ‘big ice’ and ‘little ice’ hypothesized positions of LGM grounded ice around the South Georgia continental shelf. We investigated faunal assemblage structure and richness, especially of brooders, and modelled low dispersal taxa, for example, those with limited pelagic larvae (bryozoans and sponges).

Results
We found a striking ‘line’ of major richness discontinuity, with significantly higher richness, especially of brooders and low dispersal model taxa, mainly conforming to the ‘big ice’ hypothesized position. What few bryozoans and sponges occurred inside this line were a subset of those outside.

Main conclusions
Benthic biodiversity is consistent with extensive LGM grounded ice advancing to near the shelf break in most, but not all locations around South Georgia's shelf, for example, the eastern shelf area. We suggest that most of the shelf is still undergoing recolonization from when grounded ice covered the shelf ~20 kyr ago. Our alternative hypothesis of LGM ice position, H3 ‘Limited-Extensive ice’, best fitted our data and is easily further testable, but if verified, shows that shelf recolonization following glaciation is much slower than previously thought. This contrasts with surprisingly rapid colonization of continental shelves after ice-shelf collapses, but these are not grounded, which may be crucial to polar recolonization rates.
benthos, biodiversity, continental shelf, glaciation, Last Glacial Maximum, moraine, polar, recolonization, Southern Ocean
0305-0270
2391-2399
Barnes, David K. A.
4e32233e-f977-48d4-93ec-5e4ac1f73e91
Sands, Chester J.
955f6259-4110-4374-b004-ee77758f37fd
Hogg, Oliver T.
43f3bdc0-7667-488d-9f9f-963f15f33a10
Robinson, Ben J.O.
3819b2d1-7109-4397-b924-66b36d9a9554
Downey, Rachel V.
d50c2cc0-656c-4290-8d21-119062f19423
Smith, James A.
c16ec974-92e7-4f9f-ba92-9e4233fe58b2
Barnes, David K. A.
4e32233e-f977-48d4-93ec-5e4ac1f73e91
Sands, Chester J.
955f6259-4110-4374-b004-ee77758f37fd
Hogg, Oliver T.
43f3bdc0-7667-488d-9f9f-963f15f33a10
Robinson, Ben J.O.
3819b2d1-7109-4397-b924-66b36d9a9554
Downey, Rachel V.
d50c2cc0-656c-4290-8d21-119062f19423
Smith, James A.
c16ec974-92e7-4f9f-ba92-9e4233fe58b2

Barnes, David K. A., Sands, Chester J., Hogg, Oliver T., Robinson, Ben J.O., Downey, Rachel V. and Smith, James A. (2016) Biodiversity signature of the Last Glacial Maximum at South Georgia, Southern Ocean. Journal of Biogeography, 43 (12), 2391-2399. (doi:10.1111/jbi.12855).

Record type: Article

Abstract

Aim
High-latitude biodiversity distributions can preserve signals of the timing and geography of past glaciations, and as such ground truth ice-sheet models. Discrete polar archipelagos offer the fewest confounding factors for testing historic ice position records in extant biodiversity. At South Georgia, two competing geological hypotheses suggest that either the Last Glacial Maximum (LGM) ice was extensive, nearly covering the continental shelf (H1 Big ice) or restricted to the inner fjords (H2 Little ice). We examined the past configuration of the South Georgia ice cap using seabed biodiversity.

Location
South Georgia, Southern Ocean.

Methods
We used a bespoke camera lander (SUCS) and Agassiz trawl deployments across ‘big ice’ and ‘little ice’ hypothesized positions of LGM grounded ice around the South Georgia continental shelf. We investigated faunal assemblage structure and richness, especially of brooders, and modelled low dispersal taxa, for example, those with limited pelagic larvae (bryozoans and sponges).

Results
We found a striking ‘line’ of major richness discontinuity, with significantly higher richness, especially of brooders and low dispersal model taxa, mainly conforming to the ‘big ice’ hypothesized position. What few bryozoans and sponges occurred inside this line were a subset of those outside.

Main conclusions
Benthic biodiversity is consistent with extensive LGM grounded ice advancing to near the shelf break in most, but not all locations around South Georgia's shelf, for example, the eastern shelf area. We suggest that most of the shelf is still undergoing recolonization from when grounded ice covered the shelf ~20 kyr ago. Our alternative hypothesis of LGM ice position, H3 ‘Limited-Extensive ice’, best fitted our data and is easily further testable, but if verified, shows that shelf recolonization following glaciation is much slower than previously thought. This contrasts with surprisingly rapid colonization of continental shelves after ice-shelf collapses, but these are not grounded, which may be crucial to polar recolonization rates.

Full text not available from this repository.

More information

e-pub ahead of print date: 1 September 2016
Published date: 1 December 2016
Keywords: benthos, biodiversity, continental shelf, glaciation, Last Glacial Maximum, moraine, polar, recolonization, Southern Ocean
Organisations: Ocean and Earth Science

Identifiers

Local EPrints ID: 400419
URI: http://eprints.soton.ac.uk/id/eprint/400419
ISSN: 0305-0270
PURE UUID: 3cf0e4e9-89d4-47e9-9004-062211122a09

Catalogue record

Date deposited: 13 Sep 2016 08:59
Last modified: 15 Jul 2019 20:07

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