Glacier Expansion Research Articles

Fluctuations in Caspian sea level during the Quaternary: new evidence from palynology and climate modeling

Multi-proxy study of sediment cores retrieved from lakes below modern glaciers supports the first detailed Neoglacial chronology for Glacier National Park (GNP), Montana. Analysis focused on sedimentary properties sensitive to the extent and activity of upstream glacier ice, including: water, organic matter, carbonate, and biogenic silica content; bulk density; mass accumulation rate; phosphorus fractionation; magnetic susceptibility; L*a*b* color values; and grain size distribution. Results indicate that alpine glaciers in GNP advanced and retreated numerous times during the Holocene after the onset of Neoglaciation ca 6500 BP. The two oldest phases of glacier expansion were synchronous with the well-documented Garibaldi (5600–6900 BP) and Tiedemann-Peyto (1900–3700 BP) phases in western Canada. Younger phases correspond with the First Millennium Advance in western Canada, as well as glacier with advances in the Sierra Nevada. The culminating Little Ice Age (LIA) advance was the most recent and extensive of a series of advance/retreat cycles over the past millennium. Retreat from the LIA maximum was the most dramatic episode of ice retreat in at least the last 1000 years.

Permian Peri-glacial Deposits from Central Mongolia in Central Asian Orogenic Belt: A Possible Indicator of the Capitanian Cooling Event

A dropstone-bearing, Middle Permian to Early Triassic peri-glacial sedimentary unit was first discovered from the Khangai–Khentei Belt in Mongolia, Central Asian Orogenic Belt. The unit, Urmegtei Formation, is assumed to cover the early Carboniferous Khangai–Khentei accretionary complex, and is an upward-fining sequence, consisting of conglomerates, sandstones, and varved sandstone and mudstone beds with granite dropstones in ascending order. The formation was cut by a felsic dike, and was deformed and metamorphosed together with the felsic dike. An undeformed porphyritic granite batholith finally cut all the deformed and metamorphosed rocks. LA-ICP-MS, U–Pb zircon dating has revealed the following 206Pb/238U weighted mean igneous ages: (i) a granite dropstone in the Urmegtei Formation is 273 ± 5 Ma (Kungurian of Early Permian); (ii) the deformed felsic dike is 247 ± 4 Ma (Olenekian of Early Triassic); and (iii) the undeformed granite batholith is 218 ± 9 Ma (Carnian of Late Triassic). From these data, the age of sedimentation of the Urmegtei Formation is constrained between the Kungurian and the Olenekian (273–247 Ma), and the age of deformation and metamorphism is constrained between the Olenekian and the Carnian (247–218 Ma). In Permian and Triassic times, the global climate was in a warming trend from the Serpukhovian (early Late Carboniferous) to the Kungurian long and severe cool mode (328–271 Ma) to the Roadian to Bajocian (Middle Jurassic) warm mode (271–168 Ma), with an interruption with the Capitanian Kamura cooling event (266–260 Ma). The dropstone-bearing strata of the Urmegtei Formation, together with the glacier-related deposits in the Verkhoyansk, Kolyma, and Omolon areas of northeastern Siberia (said to be of Middle to Late Permian age), must be products of the Capitanian cooling event. Although further study is needed, the dropstone-bearing strata we found can be explained in two ways: (i) the Urmegtei Formation is an autochthonous formation indicating a short-term expansion of land glacier to the central part of Siberia in Capitanian age; or (ii) the Urmegtei Formation was deposited in or around a limited ice-covered continent in northeast Siberia in the Capitanian and was displaced to the present position by the Carnian.

Dendroglaciological investigations of mid- to late-Holocene glacial activity in the Mt. Waddington area, British Columbia Coast Mountains, Canada

Dendroglaciological investigations near Mt. Waddington in the central British Columbia Coast Mountains provide an enhanced perspective of Holocene glacial activity. Field investigations at Confederation, Franklin, and Jambeau glaciers led to the discovery of subfossil wood mats encased in glacial deposits and glacially sheared stumps buried beneath till. Radiocarbon-dated wood collected from valley-bottom and lateral moraine sites at Confederation Glacier suggest that an early-Holocene advance occurred at c. 5665 cal. yr BP, followed by succeeding intervals of glacier expansion at c. 3700 and 3500 cal. yr BP. At Jambeau Glacier detrital wood mats buried close to the contemporary lateral moraine crests document glacier expansion at c. 3000 cal. yr BP. Detrital subfossil wood buried in lateral moraines at the confluence of Confederation and Franklin glaciers records distinct episodes of ‘Little Ice Age’ glacier expansion as early as c. 1212 cal. yr ad, and suggests the glacier surface continued to thicken until at least c. 1330–1410 cal. yr ad. An interval of downwasting and retreat followed, before late ‘Little Ice Age’ advances such as those at Jambeau Glacier were overwhelming valley-bottom forests by c. 1740 cal. yr ad. With the exception of the previously unrecognized advance of Confederation Glacier at c. 3700 cal. yr BP, our dendroglaciological findings corroborate the emerging record of Holocene glacier activity in the British Columbia Coast Mountains.

A lacustrine-based Neoglacial record for Glacier National Park, Montana, USA

Multi-proxy study of sediment cores retrieved from lakes below modern glaciers supports the first detailed Neoglacial chronology for Glacier National Park (GNP), Montana. Analysis focused on sedimentary properties sensitive to the extent and activity of upstream glacier ice, including: water, organic matter, carbonate, and biogenic silica content; bulk density; mass accumulation rate; phosphorus fractionation; magnetic susceptibility; L*a*b* color values; and grain size distribution. Results indicate that alpine glaciers in GNP advanced and retreated numerous times during the Holocene after the onset of Neoglaciation ca 6500 BP. The two oldest phases of glacier expansion were synchronous with the well-documented Garibaldi (5600–6900 BP) and Tiedemann-Peyto (1900–3700 BP) phases in western Canada. Younger phases correspond with the First Millennium Advance in western Canada, as well as glacier with advances in the Sierra Nevada. The culminating Little Ice Age (LIA) advance was the most recent and extensive of a series of advance/retreat cycles over the past millennium. Retreat from the LIA maximum was the most dramatic episode of ice retreat in at least the last 1000 years.

Glacier expansion in southern Patagonia throughout the Antarctic cold reversal

Resolving debated climate changes in the southern middle latitudes and potential teleconnections between southern temperate and polar latitudes during the last glacial-interglacial transition is required to help understand the cause of the termination of ice ages. Outlet glaciers of the Patagonian Ice Fields are primarily sensitive to atmospheric temperature and also precipitation, thus former ice margins record the extent and timing of past climate changes. 38 10 Be exposure ages from moraines show that outlet glaciers in Torres del Paine (51°S, south Patagonia, Chile) advanced during the time of the Antarctic cold reversal (ACR; ca. 14.6– 12.8 ka), reaching a maximum extent by ~14,200 ± 560 yr ago. The evidence here indicates that the South Patagonian Ice Field was responding to late glacial climate change distinctly earlier than the onset of the European Younger Dryas stadial (ca. 12.9 ka). Major glacier recession and deglaciation in the Torres del Paine region occurred by 12.5 ka and thus early in the Younger Dryas. We provide direct evidence for extensive ice in Patagonia at the very start of the ACR that agrees with atmospheric and marine records from the Southern Ocean and Antarctica. Atmospheric conditions responsible for the early late glacial expansion at Torres del Paine resulted from a climate reorganization that prompted a northern migration of the south westerly wind belt to the latitude of Torres del Paine at the onset of the ACR chronozone.

Late Holocene glacier expansion in the Cariboo and northern Rocky Mountains, British Columbia, Canada

Castle Creek Glacier in the Cariboo Mountains of British Columbia remained close to its Little Ice Age limit for most of the past 1500 years, without significant recession until the 20th century. This conclusion is based on radiocarbon-dated detrital and in-situ plant material overrun by the glacier, and the sedimentary record from informally named On–off Lake, which received clastic sediments only when Castle Creek Glacier crossed a hydrologic divide 330 m upvalley of the Little Ice Age limit. Plant macrofossils recovered from the transition between basal inorganic silt and overlying organic silty clay in a sediment core from the lake indicate that the glacier first retreated behind the divide ca. 10.92–9.70 ka. Ages of 8.97–8.61 and 5.58–5.53 ka on detrital wood from the glacier's forefield may record earlier advances, but the first unequivocal evidence of glacier expansion is from an overridden stump with an age of 4.96–4.45 ka. Continuous accumulation of gyttja within On–off Lake, however, indicates that Castle Creek Glacier did not cross the hydrologic divide at any time during the first half of the Holocene. Glacigenic sediments began to accumulate in the lake between 2.73 and 2.49 ka, indicating that Castle Creek Glacier expanded beyond the hydrologic divide at that time. A coincident advance is also recorded in the northern Rocky Mountains of British Columbia at Kwadacha Glacier, which overran a vegetated surface at 2.69–2.36 ka. Clastic sedimentation in On–off Lake ceased soon after the Bridge River volcanic eruption (2.70–2.35 ka), indicating that Castle Creek glacier retreat to a position upvalley of the divide at that time. Sedimentation resumed before 1.87–1.72 ka when the glacier advanced again past the hydrologic divide. Following a second retreat, Castle Creek Glacier advanced across the divide a final time at ca. 1.54–1.42 ka. The snout of the glacier remained less than 330 m upvalley of the Little Ice Age moraine until the early twentieth century when annual moraines indicate rapid frontal recession to a position upvalley of the hydrologic divide. These data collectively indicate that glaciers in the Cariboo Mountains of British Columbia nearly achieved their all-time Holocene limits as early as 2.73–2.49 ka and climatic conditions in the early 20th century abruptly ended a 1500-year period favoring glacier expansion.

Last Glacial Maximum climate in New Zealand inferred from a modelled Southern Alps icefield

We present a simulation of the New Zealand Southern Alps icefield at the Last Glacial Maximum (LGM, c. 30,000–20,000 calendar years ago (ka)) in an attempt to constrain the climate of that period. We use a 500 m-resolution ice-sheet model parameterised using empirical glaciological, climatological and geological data specific to the model domain to simulate the entire Southern Alps icefield. We find that an LGM cooling of at least 6–6.5 °C is necessary to bring about valley glaciers that extend beyond the mountains. However, climate–topography thresholds related to the elevation and hypsometry of individual catchments control the gradient of the rate of glacier expansion in the domain, and in order to remain within geologically reconstructed LGM limits we find that the LGM cooling was most likely associated with a precipitation regime up to 25% drier than today. Wetter-than-present scenarios give rise to equilibrium line depressions and ice extents that are incompatible with empirical evidence. These results perhaps indicate that either the westerly air masses affecting New Zealand during the LGM were drier than today, or that they were weaker or zonally displaced with respect to present.

Transient impacts of Little Ice Age glacier expansion on sedimentation processes at glacier-dammed Iceberg Lake, southcentral Alaska

Iceberg Lake, a glacier-dammed proglacial lake in southern Alaska, contains a 1,500+ year varve record complicated by a history of episodic lake-level changes associated with fluctuations in ice-dam thickness and position. To better understand the basinwide glaciolacustrine response to late Holocene climate variability, we collected five cores from two areas in the lake, including a previously unexamined deepwater area distal from inlet streams. Based on eight AMS 14C dates, and correlations among our cores and previously documented outcrops, we describe ~1,000 years of stratigraphy from each area. Deposition at both areas was dominated by fine-grained varves, but cores from the distal area uniquely contain coarser deposits, including rhythmites and graded sand beds, that we attribute to deposition of a subaqueous outwash fan-delta between ~1250 and 1650 AD. We attribute this event to thickening of the impounding glacier and consequent incursion of the glacier margin, and an associated lateral moraine, into the lake. This result suggests an early onset of the Little Ice Age (LIA) glacial advance in this region. Changes in basinwide circulation and sedimentation associated with this event probably caused minor thickening of varves used previously to reconstruct summer temperatures, reducing sensitivity of that record to early LIA cooling. The basinwide impact of this event illustrates the potentially significant spatial and temporal variability of lacustrine sedimentary processes in dynamic glacial landscapes.

Global Sea Level Projections to 2100 Using Methodology of the Intergovernmental Panel on Climate Change

Forecasts of sea-level rise by 2100 have such a wide range that objective planning is difficult. In 2007, the Intergovernmental Panel on Climate Change (IPCC) forecast a sea-level rise from 1990 to 2100 between 0.18 and 0.59 m, but they did not completely consider contributions from Greenland and Antarctica in determining the upper limit. Recent projections by others have been larger, typically 1–2 m, with Greenland and Antarctica being the greatest contributors. However, these projections are usually maximum possible rises without probabilities of occurrence, whereas the maximum IPCC projection is at the 95% confidence level with a 2.5% probability of being equaled or exceeded. Project planning and design generally require projections with associated probabilities to determine risk. This paper shows what worldwide tide gauge data tell us about sea-level rise trends and accelerations in the twentieth century, and satellite altimeter recordings tell us about the rise since the early 1990s. Using IPCC methodology, sea level projections with associated probabilities are made from 1990 to 2100. Projections of Greenland and Antarctica contributions are estimated based on satellite measurements of current ice-mass-loss trends and accelerations, and then they are added to contributions from thermal expansion and melting of glaciers and ice caps based on the latest information. Sea-level rise projections from 1990 to 2100 are 0.18, 0.48, and 0.82 m at 5, 50, and 95% confidence levels, respectively.

Mid-Holocene glacier expansion between 7500 and 4000 cal. yr BP in the British Columbia Coast Mountains, Canada

The mid-Holocene behaviour of five glaciers in the British Columbia Coast Mountains was reconstructed from radiocarbon ages and stratigraphic analysis. Subfossil wood evidence at Canoe, Fyles, Jacobsen, Tchaikazan and Icemaker glaciers suggests these glaciers were expanding into standing forests prior to 6630, 4900 and 4200 cal. yr BP. Stratigraphically constrained woody detritus at Fyles Glacier records the progradational history of a Gilbert-type delta forming in response to glacial expansion between 7020 and 5470 cal. yr BP. This research provides the first evidence for mid-Holocene glacial expansion in the central and northern British Columbia Coast Mountains. Proxy records describing mid-Holocene climates in the British Columbia Coast Mountains indicate a trend towards slightly cooler and possibly wetter conditions than present. Glacial expansion occurring between 7500 and 4000 cal. yr BP has regional correlatives, suggesting coherent broad-scale climate forcing mechanisms influenced glacial mass balance at this time.

Dendroglaciological reconstruction of late-Holocene glacier activity at White and South Flat glaciers, Boundary Range, northern British Columbia Coast Mountains, Canada

Holocene glacier activity in the northern British Columbia Coast Mountains, Canada, is described following investigations in the recently deglaciated forefields of White and South Flat glaciers spilling from the Cambria Icefield. Glacially overridden stumps and detrital wood was radiocarbon and dendrochronologically dated to describe an advance between ad 250 and 650. Expansion and thickening of White Glacier by ad 765 resulted in creation of an ice-dammed lake in South Flat valley that persisted until ad 1080. Following this the lake drained, before refilling in the early ‘Little Ice Age’ prior to ad 1300. Shortly thereafter White and South Flat glaciers became confluent and flowed over the valley side toward White Lake. The characteristics of the site and the preservation of 1500 yr old deposits indicate that the two glaciers remained confluent throughout the remainder of the ‘Little Ice Age’, only separating following terminal retreat early in the 20th century. The late-Holocene glacial history of White and South Flat glaciers appears synchronous with those of other glaciers in northern portion of Pacific Northwest.

Recognition and paleoclimatic implications of late-Holocene glaciation on Mt Taranaki, North Island, New Zealand

Evidence for the timings of inter-hemispheric climate fluctuations during the Holocene is important, with mountain glacier moraine systems routinely used as a proxy for climate. In New Zealand such evidence for glacier expansion during the late Holocene is fragmentary and is limited to glaciers in a narrow zone within the Southern Alps. Here, we present the first evidence for late-Holocene glacier expansion on the North Island of New Zealand in the form of two unconsolidated debris ridges on the south side of the stratovolcano, Mt Taranaki/Mt Egmont, at ~1920 m a.s.l. The two ridges are aligned north–south along the western and eastern sides of a small basin (Rangitoto Flat), which is formed between the main Taranaki cone (to the north), and the parasitic cone of Fanthams Peak (to the south). The approximate age of the ridges is constrained by dated eruptive events and the relationship between ridge locations and the spatial positioning of adjacent volcanic landforms. We propose the ridges formed as two lateral moraines on the margins of a cirque glacier during the final construction phase of Fanthams Peak between 3.3 and 0.5 ka BP, during late-Holocene time. This time interval accords with published cosmogenic 10Be dating of moraine-building episodes in the Southern Alps, indicating the Mt Taranaki moraines are a response to the same regional climatic forcings.

Post-Messinian drainage changes triggered by tectonic and climatic events (eastern Southern Alps, Italy)

The Messinian–Quaternary history of tectonic and climatic control on sedimentation in the eastern Southern Alps, northern Italy, was reconstructed using an integrated petrographic and sedimentological analysis of five sedimentary successions. These units mainly consist of fluvial conglomerates of the Tagliamento sequence, deposited within the eastern Southern Alps since the Upper Miocene (“Messinian Salinity Crisis”). At that time, the closure of marine gateways between the Atlantic Ocean and the Mediterranean Sea caused a drop in sea level, causing exchanged fluvial erosion and widening of the Alpine catchments. Sediment composition in the Upper Miocene to Lower Pliocene units shows an abrupt change in the source areas: from sediments characterized by carbonate rock fragments to detritus rich in low-grade metamorphic grains. In spite of tectonic activity within the eastern Southern Alps, no major modifications in sediment supply took place during the Pliocene–Early Pleistocene time span. In the Middle Pleistocene the first major expansion of the Alpine glaciers triggered a change in drainage patterns and a marked increase in erosion rates. Predominantly climatic control on sedimentation in the Tagliamento basin and the erosion of the Carnic Alps produced sediments rich in quartz, siltstone and metamorphic rock fragments, deposited in the Upper Pleistocene unit and in modern river sediments.

Foreword: International Space Science Institute (ISSI) Workshop on the Earth’s Cryosphere and Sea Level Change

Rising sea level is perhaps the most severe consequence of climate warming, as much of the world’s population and infrastructure is located near current sea level (Lemke et al. 2007). A major rise of a metre or more would cause serious problems. Such possibilities have been suggested by Hansen and Sato (2011) who pointed out that sea level was several metres higher than now during the Holsteinian and Eemian interglacials (about 250,000 and 120,000 years ago, respectively), even though the global temperature was then only slightly higher than it is nowadays. It is consequently of the utmost importance to determine whether such a sea level rise could occur and, if so, how fast it might happen. Sea level undergoes considerable changes due to natural processes such as the wind, ocean currents and tidal motions. On longer time scales, the sea level is influenced by steric effects (sea water expansion caused by temperature and salinity changes of the ocean) and by eustatic effects caused by changes in ocean mass. Changes in the Earth’s cryosphere, such as the retreat or expansion of glaciers and land ice areas, have been the dominant cause of sea level change during the Earth’s recent history. During the glacial cycles of the last million years, the sea level varied by a large amount, of the order of 100 m. If the Earth’s cryosphere were to disappear completely, the sea level would rise by some 65 m. The scientific papers in the present volume address the different aspects of the Earth’s cryosphere and how the different changes in the cryosphere affect sea level change. It represents the outcome of the first workshop held within the new ISSI Earth Science Programme. The workshop took place from 22 to 26 March, 2010, in Bern, Switzerland, with the objective of providing an in-depth insight into the future of mountain glaciers and the large land ice areas of Antarctica and Greenland, which are exposed to natural and anthropogenic climate influences, and their effects on sea level change. The participants of the workshop are experts in different fields including meteorology, climatology, oceanography, glaciology and geodesy; they use advanced space-based observational studies and state-of-the-art numerical modelling.

A 5200-year record of freshwater availability for regions in western North America fed by high-elevation runoff

[1] Shrinking glaciers and snowpacks are reducing discharge in rivers that drain the central Rocky Mountain region – water that supports downstream societies and ecosystems of western North America. However, a new 5200-year record of Lake Athabasca water-level variations, which serves as a sensitive gauge of past changes in alpine-sourced river discharge, reveals that western Canadian society has developed during a rare period of unusually abundant water ‘subsidized’ by prior glacier expansion. As the ‘alpine water tap’ closes, much drier times are ahead. Future water availability is likely to become similar to the mid-Holocene when Lake Athabasca dropped 2–4 m below the twentieth-century mean. Regions dependent on high-elevation runoff (i.e., western North America) must prepare to cope with impending water scarcity of magnitude not yet experienced since European settlement.

Late Holocene glacial activity in Manatee Valley, southern Coast Mountains, British Columbia, Canada

The dendroglaciologic and lichenometric research methodologies employed in this study provide a perspective of glaciological conditions from 5 ka to present in a remote headwater area of the British Columbia Coast Mountains. Since Holocene ice fronts of four glaciers at this site periodically extended below treeline, previous glacier advances overrode and buried forests beneath till deposits. This study suggests that glaciers were expanding into standing forests at 4.76 and 3.78 ka. Following glacier expansion at 3.78 ka, a period of recession ensued when glaciers withdrew upvalley long enough for the development of deep pedogenic surfaces and the growth of trees exceeding 300 years. Investigations at Beluga and Manatee glaciers benchmark a subsequent episode of significant glacial expansion at 2.42 ka referred to as the “Manatee Advance”. This advance has regional correlatives and is distinguished from the Tiedemann Advance at Manatee Glacier by documentation of substantive ice front retreat between the two episodes. Examination of Little Ice Age (LIA) deposits in the study area allowed for presentation and application of a revised Rhizocarpon spp. lichen growth curve. Lichenometric surveys of lateral moraines associated with Beluga, Manatee, and Oluk glaciers provided limited insight into their early LIA behaviour but record advances during the 15th and 16th centuries. Locally, glaciers achieved their maximum LIA size prior to an early to mid 18th century moraine-building event. This reconstruction of Holocene glacial history offers insights consistent with the emerging record of glacier activity described for other southern British Columbia Coast Mountain glaciers.

Statistical Analysis of Global Surface Air Temperature and Sea Level Using Cointegration Methods

Global sea levels are rising which is widely understood as a consequence of thermal expansion and melting of glaciers and land-based ice caps. Due to physically-based models being unable to simulate observed sea level trends, semi-empirical models have been applied as an alternative for projecting of future sea levels. There is in this, however, potential pitfalls due to the trending nature of the time series. We apply a statistical method called cointegration analysis to observed global sea level and surface air temperature, capable of handling such peculiarities.We find a relationship between sea level and temperature and find that temperature causally depends on the sea level, which can be understood as a consequence of the large heat capacity of the ocean. We further find that the warming episode in the 1940s is exceptional in the sense that sea level and warming deviates from the expected relationship. This suggests that this warming episode is mainly due to internal dynamics of the ocean rather than external radiative forcing. On the other hand, the present warming follows the expected relationship, suggesting that it is mainly due to radiative forcing. In a second step, we use the total radiative forcing as an explanatory variable, but unexpectedly find that the sea level does not depend on the forcing. We hypothesize that this is due to a long adjustment time scale of the ocean and show that the number of years of data needed to build statistical models that have the relationship expected from physics exceeds what is currently available by a factor of almost ten.

Rhodolith transport and immobilization on a volcanically active rocky shore: Middle Miocene at Cabeço das Laranjas on Ilhéu de Cima (Madeira Archipelago, Portugal)

Extraordinary deposits of fossil rhodoliths occur at the Cabeço das Laranjas (Portuguese~Hill of the Oranges) in a small fault block at the northwest end of Ilhéu de Cima off Porto Santo in the Madeira Archipelago. Stratigraphic repetitions of densely packed rhodolith beds up to 2.6m thick are associated with a receding rocky shoreline, and are interpreted as the result of hurricanes. The initial storm deposit sits unconformably on basalt and eroded basalt boulders associated with tuff and volcaniclastic breccia. Approximately 90,000 rhodoliths of Middle Miocene age (14–15Ma) are exposed on the upper surface of the initial deposit over a 450-m2 shelf exhumed from the hill's southeast side. Ranging in diameter from ≤3cm to 20cm, many of the rhodoliths generated by crustose coralline red algae are now iron stained and resemble a mass of oranges in gross appearance. Sea stacks and large boulders rise through the thick basal rhodolith bed to form small catchment areas that held the deposit in place after the storm's passage. The succeeding rhodolith deposits are variably separated by layers with mixed carbonate and volcanic sand, pure volcanic lapilli, and volcaniclastic tephra mixed with tuff showing swaley cross-stratification. Three out of four rhodolith beds are truncated against the flank of the adjoining rocky shore. Only the youngest (fourth) rhodolith layer is fully exposed around the perimeter of the hill and can be shown to cross a basalt barrier that is traceable for 70m in cross section as an erosional ramp dipping from 6° to 8° southeast. The entire fossil-rich sequence is capped by a basalt flow showing columnar disjunction. Based on thin-section analysis, three genera of coralline red algae are recognized in the basal rhodolith deposit: Sporolithon, Lithothamnion, and Neogoniolithon. Associated biodiversity is low, represented by 16 kinds of marine invertebrates dominated by encrustations and borings on the rhodoliths and very few free body fossils. The Madeira region of the North Atlantic may have been susceptible to major cyclonic storms immediately after the Middle Miocene Climate Optimum, when a northward shift of the Inter-tropical Convergence Zone was stimulated by a steeper temperature gradient in the southern hemisphere related to expansion of continental glaciers on Antarctica.

Timing and style of Late Pleistocene glaciation in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau

AbstractGlacial landforms and sediments provide evidence for the existence of two Late Pleistocene major glacial advances in the Queer Shan, northern Hengduan Mountains in the eastern Tibetan Plateau. In the current study, optically stimulated luminescence and electron spin resonance dating results reveal that the two glacial advances occurred during Marine Isotope Stage (MIS) 3 and the Last Glacial Maximum (LGM) in MIS 2, respectively. Geomorphic evidence shows that the glacial advance during MIS 3 was more extensive than that in MIS 2. This glacial advance is synchronous with other glaciated areas in the Himalaya and Tibet, but contrasts with global ice volumes that reached their maximum extent during the LGM. Glaciers in the Queer Shan are of the summer accumulation type and are mainly fed by precipitation from the south Asian monsoon. Palaeoclimate proxies show that during MIS 3 the south Asian monsoon strengthened and extended further north into the Tibetan Plateau to supply more precipitation as snow at high altitudes. This in turn led to positive glacier mass balances and caused glaciers to advance. However, during the LGM, despite cooler temperature than in MIS 3, the weakened south Asian monsoon and the associated reduced precipitation were not as favourable for glacier expansion as in MIS 3. Copyright © 2010 John Wiley & Sons, Ltd.

Extent, age and dynamics of Marine Isotope Stage 3 glaciations in the southwestern Baltic Basin

Houmark‐Nielsen, M. 2010: Extent, age and dynamics of Marine Isotope Stage 3 glaciations in the southwestern Baltic Basin. Boreas, 10.1111/j.1502‐3885.2009.00136.x. ISSN 0300‐9483The southwestern Baltic region is known as a major crossroad for the expansion of Pleistocene glaciers from the Scandinavian Ice Sheet (SIS). At the peak of the Last Glacial Maximum (LGM, 25–20 kyr BP), steady‐flowing inter‐stream glaciers expanded radially from the major ice divide over central Scandinavia. During the subsequent deglaciation phase (20–15 kyr BP), streaming ice was flowing through the Baltic gateway onto the North European lowland. The lithology and directional ice‐flow properties of pre‐LGM till formations of Baltic provenance in Denmark (the Ristinge till and Klintholm till) suggest that the ice‐sheet dynamics during the Marine Isotope Stage (MIS) 3 glacier expansion were similar to those for the post‐LGM advances. Increasing geological evidence indicates that glaciers extended onto the Circum‐Baltic lowlands during MIS 3. Reconstructions of flow paths and estimates of the basal ice‐sheet coupling in Denmark suggest that southward flow of the SIS through the Baltic was probably the result of ice streaming. Despite methodological uncertainties, available OSL and 14C dates indicate that glaciers advanced at least twice during the mild second half of the Middle Weichselian (c. 75–25 kyr BP), most probably in connection with Dansgaard‐Oeschger (D‐O) events 14–13 (54–46 kyr BP) and 8–5 (35–30 kyr BP). The chronology and dynamics of glacier expansion in the southwestern Baltic in response to long‐term cooling trends, the contemporary presence of a low Arctic biota in large parts of Scandinavia and of possible leads or lags in relation to North Atlantic climate changes during MIS 3 are discussed.