Title:
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Landscape interaction with climate change: the Late glacial of the Usk Valley, South Wales
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Determining the climate change required for a glaciological response from a landscape can demonstrate
regional gradients and the potential forcing factors of palaeoclimate. This investigation considers the
interaction of a marginal landscape for glaciation, the Usk Valley and Brecon Beacons, with the rapid
climate shifts during the Lateglacial, the transition period (-15-9ka BP) following the Last Glacial Maximum
(LGM). The study relies on the 'Iandsystems concept' to derive important palaeoglaciological information
on the style of glaciation.
This study concludes that the Usk Valley was not linked to a 'Welsh' ice-sheet and was relatively
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isolated from other source-areas. Initial deglaciation occurred earlier than other regions of the British Isles,
with active retreat of warm based ice controlled by topography. Local icefields and tributary glaciation
along the Valley length were critical for supporting Usk glacier mass-balance. Paraglacial processes are
major components of the landsystem with new process-form models allowing the recognition of modified
glacial landforms, aiding the reconstruction of former ice-margins.
Acomplex event stratigraphy is identified, with an earty readvance before 19420±64 Cal 14CBP
('Uandelti Readvance Phase'). Two subsequent renewed glaciation events ('Younger' and 'Older Cwm
Oergwm Events') date to the earty Lateglacial and are correlated to cold events recorded in alocal basin
(Waen Ddu) and regional palaeoecological records. These events manifested under polythermal and cold
based conditions. Response to Younger Dryas climate was marginal, with an overlap of glacial, periglacial
and paraglacial processes. 3-D modelling of topoclimate shows that shortwave radiation was the principal
control over the nature of the renewed-glacial response.
This complex landscape response suggests the region may be unique, with small-scale climate
events recorded because of the marginal and isolated nature of LGM glaciation. Consequently, the region
may provide an important case-study for determining climate gradients across the British Isles during the
last glacial cycle.
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