Dataset Information

Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland.

ABSTRACT: Knowledge about the Holocene evolution of the Greenland ice sheet (GrIS) is important to put the recent observations of ice loss into a longer-term perspective. In this study, we use six new threshold lake records supplemented with two existing lake records to reconstruct the Holocene ice marginal fluctuations of the Qassimiut lobe (QL) - one of the most dynamic parts of the GrIS in South Greenland. Times when the ice margin was close to present extent are characterized by clastic input from the glacier meltwater, whereas periods when the ice margin was behind its present day extent comprise organic-rich sediments. We find that the overall pattern suggests that the central part of the ice lobe in low-lying areas experienced the most prolonged ice retreat from ~9-0.4?cal. ka BP, whereas the more distal parts of the ice lobe at higher elevation re-advanced and remained close to the present extent during the Neoglacial between ~4.4 and 1.8?cal. ka BP. These results demonstrate that the QL was primarily driven by Holocene climate changes, but also emphasises the role of local topography on the ice marginal fluctuations.

SUBMITTER: Larsen NK

PROVIDER: S-EPMC4778018 | biostudies-literature | 2016 Mar

REPOSITORIES: biostudies-literature

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Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland.

Larsen Nicolaj K NK Find Jesper J Kristensen Anders A Bjørk Anders A AA Kjeldsen Kristian K KK Odgaard Bent V BV Olsen Jesper J Kjær Kurt H KH

Scientific reports 20160304

Knowledge about the Holocene evolution of the Greenland ice sheet (GrIS) is important to put the recent observations of ice loss into a longer-term perspective. In this study, we use six new threshold lake records supplemented with two existing lake records to reconstruct the Holocene ice marginal fluctuations of the Qassimiut lobe (QL) - one of the most dynamic parts of the GrIS in South Greenland. Times when the ice margin was close to present extent are characterized by clastic input from the ...[more]

PMID: 26940998

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Project description:Measuring microbial abundance in glacier ice and identifying its controls is essential for a better understanding and quantification of biogeochemical processes in glacial ecosystems. However, cell enumeration of glacier ice samples is challenging due to typically low cell numbers and the presence of interfering mineral particles. We quantified for the first time the abundance of microbial cells in surface ice from geographically distinct sites on the Greenland Ice Sheet (GrIS), using three enumeration methods: epifluorescence microscopy (EFM), flow cytometry (FCM), and quantitative polymerase chain reaction (qPCR). In addition, we reviewed published data on microbial abundance in glacier ice and tested the three methods on artificial ice samples of realistic cell (10(2)-10(7) cells ml(-1)) and mineral particle (0.1-100 mg ml(-1)) concentrations, simulating a range of glacial ice types, from clean subsurface ice to surface ice to sediment-laden basal ice. We then used multivariate statistical analysis to identify factors responsible for the variation in microbial abundance on the ice sheet. EFM gave the most accurate and reproducible results of the tested methodologies, and was therefore selected as the most suitable technique for cell enumeration of ice containing dust. Cell numbers in surface ice samples, determined by EFM, ranged from ~ 2 × 10(3) to ~ 2 × 10(6) cells ml(-1) while dust concentrations ranged from 0.01 to 2 mg ml(-1). The lowest abundances were found in ice sampled from the accumulation area of the ice sheet and in samples affected by fresh snow; these samples may be considered as a reference point of the cell abundance of precipitants that are deposited on the ice sheet surface. Dust content was the most significant variable to explain the variation in the abundance data, which suggests a direct association between deposited dust particles and cells and/or by their provision of limited nutrients to microbial communities on the GrIS.

Dataset Information

Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland.

Publications

Holocene ice marginal fluctuations of the Qassimiut lobe in South Greenland.

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