GLACIAL LANDFORMS, SEDIMENTS | Micromorphology of Glacial Sediments

Hiemstra, John F.

doi:10.1016/b978-0-444-53643-3.00086-8

Cited by 3 publications

(1 citation statement)

References 31 publications

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“…Universal kriging was then used to calculate geographically interpolated surfaces with spatial linear dependence, especially useful for predicting environmental conditions for areas not included in the original layers (e.g., a newly available coastal region). For each input layer, we determined a variogram where the layer values were linearly dependent on the spatial coordinates (i.e., in R notation, bio ~ longitude + latitude) with the autofitVariogram function from the R package automaps ( Hiemstra and Hiemstra 2013 ). Next, universal kriging was implemented using the krige function from the R package gstat ( Pebesma 2019 ).…”

Section: Methodsmentioning

confidence: 99%

Identifying Climatic Drivers of Hybridization with a New Ancestral Niche Reconstruction Method

et al. 2023

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Applications of molecular phylogenetic approaches have uncovered evidence of hybridization across numerous clades of life, yet the environmental factors responsible for driving opportunities for hybridization remain obscure. Verbal models implicating geographic range shifts that brought species together during the Pleistocene have often been invoked, but quantitative tests using paleoclimatic data are needed to validate these models. Here, we produce a phylogeny for Heuchereae, a clade of 15 genera and 83 species in Saxifragaceae, with complete sampling of recognized species, using 277 nuclear loci and nearly complete chloroplast genomes. We then employ an improved framework with a coalescent simulation approach to test and confirm previous hybridization hypotheses and identify one new intergeneric hybridization event. Focusing on the North American distribution of Heuchereae, we introduce and implement a newly developed approach to reconstruct potential past distributions for ancestral lineages across all species in the clade and across a paleoclimatic record extending from the late Pliocene. Time calibration based on both nuclear and chloroplast trees recovers a mid- to late-Pleistocene date for most inferred hybridization events, a timeframe concomitant with repeated geographic range restriction into overlapping refugia. Our results indicate an important role for past episodes of climate change, and the contrasting responses of species with differing ecological strategies, in generating novel patterns of range contact among plant communities and therefore new opportunities for hybridization. The new ancestral niche method flexibly models the shape of niche while incorporating diverse sources of uncertainty and will be an important addition to the current comparative methods toolkit.

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Section: Methodsmentioning

confidence: 99%

Identifying Climatic Drivers of Hybridization with a New Ancestral Niche Reconstruction Method

et al. 2023

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New age constraints for the limit of the British–Irish Ice Sheet on the Isles of Scilly

Smedley

Scourse

Small

et al. 2017

J Quaternary Science

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The southernmost terrestrial extent of the Irish Sea Ice Stream (ISIS), which drained a large proportion of the last British-Irish Ice Sheet, impinged on to the Isles of Scilly during Marine Isotope Stage 2. However, the age of this ice limit has been contested and the interpretation that this occurred during the Last Glacial Maximum (LGM) remains controversial. This study reports new ages using optically stimulated luminescence (OSL) dating of outwash sediments at Battery, Tresco (25.5 AE 1.5 ka), and terrestrial cosmogenic nuclide exposure dating of boulders overlying till on Scilly Rock (25.9 AE 1.6 ka), which confirm that the ISIS reached the Isles of Scilly during the LGM. The ages demonstrate this ice advance on to the northern Isles of Scilly occurred at $26 ka around the time of increased ice-rafted debris in the adjacent marine record from the continental margin, which coincided with Heinrich Event 2 at $24 ka. OSL dating (19.6 AE 1.5 ka) of the post-glacial Hell Bay Gravel at Battery suggests there was then an $5-ka delay between primary deposition and aeolian reworking of the glacigenic sediment, during a time when the ISIS ice front was oscillating on and around the Llŷn Peninsula, $390 km to the north.

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Sediment fingerprinting and the mode of formation of singular and composite annual moraine ridges at two glacier margins, Jotunheimen, southern Norway

et al. 2015

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Sedimentary variation within and between annual moraine ridges formed at Storbreen and Styggedalsbreen, Jotunheimen, during the 1980s and 1990s is investigated with a focus on processes and mechanisms of moraine-ridge formation. Tops and bottoms of sediment slabs, deposited either as single annual moraines or incorporated into composite moraine ridges formed of several annual increments, were analysed and compared with possible source sediments with a view to sediment fingerprinting. Clast roundness and shape indicated mainly subglacial sediment origins while textural variability was mainly inherited from proglacial sediment sources, and macrofabrics and micromorphological characteristics revealed overprinting by various glaciofluvial, glaciolacustrine and periglacial processes. The evidence suggests one dominant mechanism of moraine-ridge formation involving the annual freeze-on and subsequent melt-out of overridden proglacial sediment slabs. This mechanism provides the basis of a simple model encompassing both singular and composite annual moraine-ridge formation, which appears appropriate for temperate glacier snouts characterized by deep seasonally frozen ground, close to the lower altitudinal limit of the zone of alpine permafrost.

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GLACIAL LANDFORMS, SEDIMENTS | Micromorphology of Glacial Sediments

Cited by 3 publications

References 31 publications

Identifying Climatic Drivers of Hybridization with a New Ancestral Niche Reconstruction Method

Identifying Climatic Drivers of Hybridization with a New Ancestral Niche Reconstruction Method

New age constraints for the limit of the British–Irish Ice Sheet on the Isles of Scilly

Sediment fingerprinting and the mode of formation of singular and composite annual moraine ridges at two glacier margins, Jotunheimen, southern Norway

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