- 1Department of Geography, School of Environment, Education and Development, The University of Manchester, Oxford Road, Manchester M13 9PL, United Kingdom
- 2Scott Polar Research Institute, University of Cambridge, Lensfield Road, Cambridge CB2 1ER, United Kingdom
This paper examines the structure of glacial cycles, with a particular focus on the definition and complexity of cold stages in the stratigraphical record. The Middle and Late Pleistocene cold stages correspond to the classic orbitally-driven 100 ka glacial cycles. Closer examination of the global glacier-climate record also reveals that cold stages are structured within larger glacial cycles beyond the classic 100 ka pattern. ‘Mega’-glacial cycles closely correspond to 400 ka eccentricity cycles and the last two such cycles were bounded by MIS 19, 11 and 1. The last of these mega-cycles encompasses the Saalian Complex Stage in Europe, as well as the last cold stage (Weichselian Stage and equivalents) and has significant implications for how cold stages are defined.
The irregular pacing of quasi-100 ka glacial cycles is likely to represent an internal mechanism related to ice-sheet evolution through cold stages and their interaction with ocean and atmospheric circulation. Internal climate drivers also explain short-term climatic fluctuations within cold stages such as Dansgaard-Oeschger cycles and various other short-term interstadial-stadial transitions, such as the during the Late-glacial and the Younger Dryas Stadial, for example. Since the effects of global climate change are not manifested uniformly through time and space, such climatic effects result in diachronous boundaries in the geological record as well as spatial variability. This is especially characteristic of the Quaternary record where sediments and landforms record climate change over relatively short time intervals. This complexity, inherent in climate stratigraphy upon which the Quaternary stratigraphical record is built, poses challenges for regional and especially global correlations. In many studies cross-correlation within glacial cycles is achieved via the marine or ice-core records, especially for the last glacial cycle. However, whilst useful as records of time through the Quaternary, these records do not always reflect other processes on Earth. For example, it is now known that glacier behaviours around the world do not conform closely with the marine isotopic records, the latter being dominated by fluctuations in the Laurentide Ice Sheet over North America, overprinted by local factors.
Whilst orbital forces caused by the Earth’s interaction with other planetary orbits in our Solar System are pivotal in modulating and pacing climate change, the most important driver of the magnitude of climate change that we see in the Quaternary are largely internal factors. It is the coincidence of these drivers with orbital parameters that explain the structure and characteristics of glacial cycles. Whilst similarities between global climate patterns between glacial cycles are apparent, such as the saw-tooth pattern of change observed in marine isotope records, the complexity within these cycles differs within every cycle. Thus, every glacial cycle is unique. This means that stratigraphical frameworks for subdividing, ordering and correlating structural elements of Pleistocene cold stages will also be unique for each glacial cycle and requires careful consideration and definition. This is especially important for correct correlation of intra-cold stage climatic stratigraphical events across regions and ultimately for comparison with global climate temporal frameworks such as the marine or ice-core records.
How to cite: Hughes, P. and Gibbard, P.: Anatomy of a cold stage: deconstructing the structure of Pleistocene glacial cycles, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12509, https://doi.org/10.5194/egusphere-egu25-12509, 2025.
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