Recent Glacial Cycles Research Articles

The polar ocean and glacial cycles in atmospheric CO2 concentration

Global climate and the atmospheric partial pressure of carbon dioxide () are correlated over recent glacial cycles, with lower during ice ages, but the causes of the changes are unknown. The modern Southern Ocean releases deeply sequestered CO(2) to the atmosphere. Growing evidence suggests that the Southern Ocean CO(2) 'leak' was stemmed during ice ages, increasing ocean CO(2) storage. Such a change would also have made the global ocean more alkaline, driving additional ocean CO(2) uptake. This explanation for lower ice-age , if correct, has much to teach us about the controls on current ocean processes.

Links between eccentricity forcing and the 100,000-year glacial cycle

The 100,000-year glacial cycles are generally thought to be driven by the eccentricity of the Earth’s orbit. Statistical analyses of climate variability and orbital forcing over the past five million years indicate that the glacial cycles are the result of an internal climate oscillation phase locked to the 100,000-year eccentricity cycle. Variations in the eccentricity (100,000 yr), obliquity (41,000 yr) and precession (23,000 yr) of Earth’s orbit have been linked to glacial–interglacial climate cycles. It is generally thought that the 100,000-yr glacial cycles of the past 800,000 yr are a result of orbital eccentricity1,2,3,4. However, the eccentricity cycle produces negligible 100-kyr power in seasonal or mean annual insolation, although it does modulate the amplitude of the precession cycle. Alternatively, it has been suggested that the recent glacial cycles are driven purely by the obliquity cycle5,6,7. Here I use statistical analyses of insolation and the climate of the past five million years to characterize the link between eccentricity and the 100,000-yr glacial cycles. Using cross-wavelet phase analysis, I show that the relative phase of eccentricity and glacial cycles has been stable since 1.2 Myr ago, supporting the hypothesis that 100,000-yr glacial cycles are paced8,9,10 by eccentricity4,11. However, I find that the time-dependent 100,000-yr power of eccentricity has been anticorrelated with that of climate since 5 Myr ago, with strong eccentricity forcing associated with weaker power in the 100,000-yr glacial cycle. I propose that the anticorrelation arises from the strong precession forcing associated with strong eccentricity forcing, which disrupts the internal climate feedbacks that drive the 100,000-yr glacial cycle. This supports the hypothesis that internally driven climate feedbacks are the source of the 100,000-yr climate variations12.

Comparative phylogeography of five avian species: implications for Pleistocene evolutionary history in the Qinghai-Tibetan plateau

Pleistocene climate fluctuations have shaped the patterns of genetic diversity observed in extant species. In contrast to Europe and North America where the effects of recent glacial cycles on genetic diversity have been well studied, the genetic legacy of the Pleistocene for the Qinghai-Tibetan (Tibetan) plateau, a region where glaciation was not synchronous with the North Hemisphere ice sheet maxima, remains poorly understood. Here, we compared the phylogeographical patterns of five avian species on the Qinghai-Tibetan plateau by three mitochondrial DNA fragments: the Tibetan snow finch (Montifringilla adamsi), the Blanford's snow finch (Pyrgilauda blanfordi), the horned lark (Eremophila alpestris), the twite (Carduelis flavirostris) and the black redstart (Phoenicurus ochruros). Our results revealed the three species mostly distributed on the platform region of the plateau that experienced population expansion following the retreat of the extensive glaciation period (0.5-0.175 Ma). These results are at odds with the results from avian species of Europe and North America, where population expansions occurred after Last Glacial Maximum (LGM, 0.023-0.018 Ma). A single refugium was identified in a restricted semi-continuous area around the eastern margin of the plateau, instead of multiple independent refugia for European and North American species. For the other two species distributed on the edges of the plateau (the twite and black redstart), populations were maintained at stable levels. Edge areas are located on the eastern margin, which might have had little or no ice cover during the glaciation period. Thus, milder climate may have mitigated demographic stresses for edge species relative to the extremes experienced by platform counterparts, the present-day ranges of which were heavily ice covered during the glaciation period. Finally, various behavioural and ecological characteristics, including dispersal capacities, habitat preference and altitude specificity along with evolutionary history might have helped to shape different phylogeographical structures appearing in these five species.

Sailing through the Late Pleistocene: unusual historical demography of an East Asian endemic, the Chinese Hwamei (Leucodioptron canorum canorum), during the last glacial period

Pleistocene climate fluctuations shaped the patterns of genetic diversity observed in extant species. In contrast to Europe and North America where the effects of recent glacial cycles on genetic diversity have been well studied, the genetic legacy of the Late Pleistocene for East Asia, a region of great topographical complexity and presumably milder historical climate, remains poorly understood. We analysed 3.86 kb of the mitochondrial genome of 186 Chinese Hwamei birds, Leucodioptron canorum canorum, and found that contrary to the conventional expectation of population decline during cold periods (stadials), the demographic history of this species shows continuous population growth since the penultimate glacial period (about 170,000 years ago). Refugia were identified in the south, coastal regions, and northern inland areas, implying that topographic complexity played a substantial role in providing suitable habitats for the Chinese Hwamei during cold periods. Intermittent gene flow between these refugia during the warmer periods (interstadials) might have resulted in a large effective population of this bird through the last glacial period.

Determining the origin and age of the Westland beech (Nothofagus) gap, New Zealand, using fungus beetle genetics

The formation and maintenance of the Nothofagus beech gap in the South Island, New Zealand, has been the focus of biogeographical debate since the 1920s. We examine the historical process of gap formation by investigating the population genetics of fungus beetles: Brachynopus scutellaris (Staphylinidae) inhabits logs and is absent from the beech gap, and Hisparonia hystrix (Nitidulidae) is contiguous through the gap and is found commonly on sooty mould growing on several plant species. Both species show distinctive northern and southern haplotype distributions while H. hystrix recolonized the gap as shown by definitive mixing. B. scutellaris shows two major haplotype clades with strong geographical concordance, and unlike H. hystrix, has clearly defined lineages that can be partitioned for molecular dating. Based on coalescence dating methods, disjunct lineages of B. scutellaris indicate that the gap was formed less than 200 000 years ago. Phylogenetic imprints from both species reveal similar patterns of population divergence corresponding to recent glacial cycles, favouring a glacial explanation for the origin of the gap. Post-gap colonization by H. hystrix may have been facilitated by the spread of Leptospermum scoparium host trees to the area, and they may be better at dispersing than B. scutellaris which may be constrained by fungal host and/or microhabitat. The gap-excluded species B. scutellaris is found in both beech and podocarp-broadleaf forests flanking the Westland gap and its absence in the gap may be related to incomplete recolonization following glacial retreat. We also discuss species status and an ancient polymorphism within B. scutellaris.

Phylogeographic analysis of complete mtDNA genomes from Walleye Pollock (Gadus chalcogrammusPallas, 1811) shows an ancient origin of genetic biodiversity

Ursvik et al. compared the complete mitochondrial DNA (mtDNA) genome sequences of Walleye Pollock (Gadus ( = Theragra) chalcogrammus) from the Pacific Ocean with a pair of fish from an isolated population of Norwegian pollock in the Barents Sea. They concluded that the Norwegian population was recently introduced from the Pacific. We test this hypothesis within a temporal framework provided by a phylogeographic analysis of complete genomes from the pollocks' sister species, Atlantic Cod (Gadus morhua), and their divergence 3.5 mya. Pollock have a coalescent ancestor 189 +/- 25 kya. The two Norwegian fish have a common ancestor 87 +/- 7 kya, which suggests an ancient origin rather than a recent human-mediated introduction. Mitochondrial genomic biodiversity in pollock antedates the most recent glacial cycle. The clade structure of the whole-genome tree indicates that previously described single-locus mtDNA haplotypes and haplogroups are typically paraphyletic.

The comparative study of range-wide genetic structure across related, co-distributed rainforest trees reveals contrasting evolutionary histories

Australia’s rainforests exhibit high taxonomic diversity and endemism, yet relatively little is known about patterns of genetic diversity across the flora. Habitat contractions caused by the aridification of the continent and the recent glacial cycles have left discrete genetic signatures on modern-day populations, with the nature of between-population differentiation likely to be influenced by a range of ecological and environmental factors. We used microsatellites to examine range-wide population genetic structure in two congeneric rainforest trees, Elaeocarpus angustifolius and E. largiflorens (Elaeocarpaceae), with similar habitat preference and dispersal potential. The aim was to investigate the relationships between genetic structure, geographic disjunction and morphological differentiation and attempt to clarify the likely evolutionary processes responsible for the observed patterns. We found substantial differences in the amount and type of genetic differentiation within the two co-distributed species. While Elaeocarpus largiflorens revealed an abrupt genetic disjunction front between two subspecies separated by a recognised biogeographic barrier (the Black Mountain Corridor), E. angustifolius showed lower genetic differentiation across a much wider geographic area. Our findings suggest that biogeographic features have different impacts on related species, and that generalisations on evolutionary patterns can be untenable without considering a range of factors. Also, on the basis of the available molecular data, a likely hypothesis is of pre-Pleistocene differentiation followed by reinforcement of differentiation patterns during recent glacial cycles (further studies are needed to conclusively date divergence).

20th Century sea-level change along the eastern US: Unravelling the contributions from steric changes, Greenland ice sheet mass balance and Late Pleistocene glacial loading

We have considered the influence of ocean temperature and salinity changes, mass changes of the Greenland ice sheet (GIS) and the isostatic response of the solid earth to the most recent glacial cycle on 20th century sea-level change along the US east coast with the intention of better understanding the observed signal as well as determining the potential of the tide gauge data for constraining the recent (past 50–100 yr) mass balance of the GIS and earth viscosity structure. Our results show that the signal due to steric changes is large and displays a complex spatial variation which can account for a significant portion of the observed signal. In contrast, that due to changes in the GIS is relatively small and insensitive to the specific geometry of the mass balance model adopted. As a consequence, the tide gauge data alone are not capable of providing useful constraints on either the magnitude or form of recent GIS mass balance. Our inference of mantle viscosity structure based on the tide gauge data was affected dramatically when the steric effect was accounted for: An earth model with an upper mantle viscosity of 8 × 10 19 Pa s and a lower mantle viscosity of 5 × 10 22 Pa s produced the best fit to the steric-corrected data; the optimal fit to the uncorrected data was obtained for upper and lower mantle viscosities of 5 × 10 20 Pa s and 10 22 Pa s, respectively.

Eight glacial cycles from an Antarctic ice core.

The Antarctic Vostok ice core provided compelling evidence of the nature of climate, and of climate feedbacks, over the past 420,000 years. Marine records suggest that the amplitude of climate variability was smaller before that time, but such records are often poorly resolved. Moreover, it is not possible to infer the abundance of greenhouse gases in the atmosphere from marine records. Here we report the recovery of a deep ice core from Dome C, Antarctica, that provides a climate record for the past 740,000 years. For the four most recent glacial cycles, the data agree well with the record from Vostok. The earlier period, between 740,000 and 430,000 years ago, was characterized by less pronounced warmth in interglacial periods in Antarctica, but a higher proportion of each cycle was spent in the warm mode. The transition from glacial to interglacial conditions about 430,000 years ago (Termination V) resembles the transition into the present interglacial period in terms of the magnitude of change in temperatures and greenhouse gases, but there are significant differences in the patterns of change. The interglacial stage following Termination V was exceptionally long--28,000 years compared to, for example, the 12,000 years recorded so far in the present interglacial period. Given the similarities between this earlier warm period and today, our results may imply that without human intervention, a climate similar to the present one would extend well into the future.

A long-term perspective on ungulate–vegetation interactions

The fossil record of vegetation and ungulates places present conditions and trends in a temporal perspective. Ungulate–vegetation interactions during the last 500 000 years were primarily driven by the climatic variation of the glacial–interglacial cycle. There were distinctive faunas associated with each temperate period and a loss of species diversity only in the present interglacial. Climate change and human activities have interacted during the most recent glacial cycle, accelerating extinction rates. This unique course of events has the consequence that no stable, ‘base-line’ conditions can be recognised. A review of the full-glacial ‘mammoth-steppe’ debate suggests that ungulate populations were limited by available forage, but a mosaic of habitat supported a diverse fauna in Beringia. In the debate over early–mid Holocene ‘wood pasture’, past ungulate populations are one of a range of disturbance factors, including burning, that influenced regional vegetation composition and structure in northern Europe. These debates concerning the scale and impacts of past ungulate–vegetation interactions will not be fully resolved until more is known about past ungulate population sizes. Modelling past scenarios would enhance the value of retrospective studies and help provide goals for management of near-natural ecosystems.

Architecture and depositional pattern of the Quaternary deep-sea fan of the Amazon

The Quaternary deep-sea fan of the Amazon is composed of four superimposed lens-shaped channel–levee Complexes covering most of the fan surface and controlled by allocyclic processes: high amplitude sea-level variations of recent glacial cycles, induced river-fed turbiditic currents that discharged directly into the submarine canyon during low sea-level. In contrast, individual channel–levee systems and associated terminal lobes are governed by two distinct autocyclic processes: (1) an initial phase of avulsion and adjustment with unconfined sand deposition (High Amplitude Reflection Packets), and (2) down-fan progressive aggradation/progradation of a graded channel–levee/lobe system, when a new equilibrium profile is reached. During the latter phase, the system acts as a particularly efficient sand cleaning and separating factory that is responsible for the high reservoir potential of such turbidites.

Determining the age of the universe

Closely-spaced 3.5 kHz seismic profiles were collected over the north-easterly trending ridge and swale system 50 km east-southeast of Atlantic City, New Jersey. They yield information on the Late Quaternary depositional history of the area, and on the origin of the ridge system. Four of the sub-bottom reflectors identified were sufficiently persistent to warrant investigation and interpretation. These reflectors, which have been cored, lithologically identified, and radiocarbon dated, are stratigraphically higher than the reflectors dealt with by the majority of previous studies. The upper three reflectors are definitely mid- and post-Wisconsin in age and present a record of the most recent glacial cycle. The upper three units associated with the observed reflectors appear to exert a pronounced influence on the bathymetry. The gently corrugated ridge system of Holocene sand is formed over the regionally flat-lying upper unit, an Early Holocene lagoonal silty clay. The characteristically flat, broad depressions of the area are floored by this lagoonal material. Locally, however, marine scour has cut through the silty clay into an underlying unit of unconsolidated fine Pleistocene sand. Several stages of trough development appear to be represented. After penetrating the lagoonal clay, troughs are initially narrow, but when incised through the sand into a lower, Pleistocene, silty-clay unit, the troughs become notably wider. As downcutting is inhibited by the lower clay, the upper clay is undercut as the trough widens in a fashion similar to a desert blowout.The sub-bottom reflectors indicate that ridge development on the central shelf has involved aggradation as well as erosion. Some ridges seem to have grown by vertical and lateral accretion from small cores. The internal structure of other ridges suggests that they formed by the coalescence of several small ridges. Others appear to have undergone appreciable lateral migration.The ridges appear to be in a state of continuing adjustment to the hydraulic regime of the deepening post-Pleistocene water column.

Asynchronous maximum advances of mountain and continental glaciers

The last maximum glacier advance in many mountain ranges appears to have predated the last maximum advance of the Wisconsinan continental ice sheets (∼20,000 years B.P.). Published evidence from widely spaced localities in North and South America, Europe, Asia, and Hawai'i suggests that some mountain glaciers extended farther during one or more stades early in the last glaciation, roughly 115,000–30,000 years B.P., than at its end, when low global temperature and high precipitation presumably were most favorable for the growth of glaciers. Variations in the timing of glacier advances in different mountain ranges suggest that alpine glaciers are dependent on regional climate as well as global conditions. Their study might provide sensitive tests for theories of global climate change. Glacial deposits are often used as time markers in neotectonic and geomorphic studies, and their ages sometimes are inferred from distant measurements or from proxy histories of global climate change. Undated geomorphic features such as moraines, sharply incised streams, and river terraces, which commonly have been associated with the last maximum glacier advance (∼20,000 years B.P.) or last deglaciation ( ∼13,000 years B.P.), may actually be older by a factor of 2 to 4 (or more). Conversely, deposits assigned to the maximum advances of the penultimate global glaciation ( ∼130,000 years B.P.) may actually date from early in the most recent glacial cycle and be younger by a comparable factor. Rates of faulting or folding estimated from displacements or deformation and the assumed ages of such geomorphic features might be too great (or too small) by corresponding factors.

Ridge development as revealed by sub-bottom profiles on the central New Jersey shelf

Closely-spaced 3.5 kHz seismic profiles were collected over the north-easterly trending ridge and swale system 50 km east-southeast of Atlantic City, New Jersey. They yield information on the Late Quaternary depositional history of the area, and on the origin of the ridge system. Four of the sub-bottom reflectors identified were sufficiently persistent to warrant investigation and interpretation. These reflectors, which have been cored, lithologically identified, and radiocarbon dated, are stratigraphically higher than the reflectors dealt with by the majority of previous studies. The upper three reflectors are definitely mid- and post-Wisconsin in age and present a record of the most recent glacial cycle. The upper three units associated with the observed reflectors appear to exert a pronounced influence on the bathymetry. The gently corrugated ridge system of Holocene sand is formed over the regionally flat-lying upper unit, an Early Holocene lagoonal silty clay. The characteristically flat, broad depressions of the area are floored by this lagoonal material. Locally, however, marine scour has cut through the silty clay into an underlying unit of unconsolidated fine Pleistocene sand. Several stages of trough development appear to be represented. After penetrating the lagoonal clay, troughs are initially narrow, but when incised through the sand into a lower, Pleistocene, silty-clay unit, the troughs become notably wider. As downcutting is inhibited by the lower clay, the upper clay is undercut as the trough widens in a fashion similar to a desert blowout. The sub-bottom reflectors indicate that ridge development on the central shelf has involved aggradation as well as erosion. Some ridges seem to have grown by vertical and lateral accretion from small cores. The internal structure of other ridges suggests that they formed by the coalescence of several small ridges. Others appear to have undergone appreciable lateral migration. The ridges appear to be in a state of continuing adjustment to the hydraulic regime of the deepening post-Pleistocene water column.