Lateglacial and Holocene cosmogenic surface exposure age glacial chronology and geomorphological evidence for the presence of cold‐based glaciers at Nevado Sajama,Bolivia

Comparisons of palaeo‐equilibrium line altitudes between the Western and Eastern Cordilleras in the Central Andes are commonly based on the assumption that the tall outermost moraines visible in remotely sensed images of the Western Cordillera date to the Last Glacial Maximum (LGM). However, field investigation and geomorphic mapping at Nevado Sajama, Bolivia, indicates the tall moraines are relic features with shorter moraines overlying and in some cases extending beyond them. ³⁶Cl exposure ages from the shorter moraines suggest that they date to Lateglacial times ca. 16.9–10.2 ka. Although Lateglacial deposits have been found throughout the Central Andes, the extent of these deposits relative to LGM deposits varies both between the Western and Eastern Cordilleras and north‐to‐south along the Western Cordillera. In the Western Cordillera in the zone of easterly winds, the Lateglacial appears to be the most extensive glacial advance of the last glacial cycle. Geomorphic evidence also suggests that some Lateglacial moraines were deposited by cold‐based ice, a previously unreported finding in the tropical Andes. Retreat from other glacial features occurred at about 7.0–4.4 ka and 4.7–3.3 ka. These are the first directly dated Holocene glacial deposits in the Western Cordillera of Bolivia, and their presence suggests that the mid Holocene may not have been as warm and dry as previously thought. Copyright © 2008 John Wiley & Sons, Ltd.     

A new early Holocene cryptotephra from northwest Scotland

Clarification of the temporal relationships amongst records of environmental change is dependent on accurate timescales. Event markers such as tephra layers are extremely important for constraining chronologies and providing tie points. In this report we present evidence of a previously unknown early Holocene Icelandic cryptotephra from a lake in northern Scotland—the ‘An Druim Tephra’. The calibrated radiocarbon age of 9560 cal. yr BP for this new cryptotephra makes it an important addition to the suite of cryptotephras now recorded from the last glacial termination and early Holocene in northwest Europe. In addition we report evidence in support of a ‘Younger Borrobol Tephra’ from Lateglacial sediments of Allerød age. Copyright © 2005 John Wiley & Sons, Ltd.     

Last glacial–interglacial sea-ice cover in the SW Atlantic and its potential role in global deglaciation

Sea-ice growth and decay in Antarctica is one of the biggest seasonal changes on Earth, expanding ice cover from 4 × 10⁶ km² to a maximum of 19 × 10⁶ km² during the austral winter. Analyses of six marine sediment cores from the Scotia Sea, SW Atlantic, yield records of sea-ice migration across the basin since the Lateglacial. The cores span nearly ten degrees of latitude from the modern seasonal sea-ice zone to the modern Polar Front. Surface sediments in the cores comprise predominantly diatomaceous oozes and muddy diatom oozes that reflect Holocene conditions. The cores exhibit similar down-core stratigraphies with decreasing diatom concentrations and increasing magnetic susceptibility from modern through to the Last Glacial Maximum (LGM). Sediments in all cores contain sea-ice diatoms that preserve a signal of changing sea-ice cover and permit reconstruction of past sea-ice dynamics. The sea-ice records presented here are the first to document the position of both the summer and winter sea-ice cover at the Last Glacial Maximum (LGM) in the Scotia Sea. Comparison of the LGM and Holocene sea-ice conditions shows that the average winter sea-ice extent was at least 5° further north at the LGM. Average summer sea-ice extent was south of the most southerly core site at the LGM, and suggests that sea-ice expanded from approximately ～61°S to ～52°S each season. Our data also suggest that the average summer sea-ice position at the LGM was not the maximum extent of summer sea-ice during the last glacial. Instead, the sediments contain evidence of a pre-LGM maximum extent of summer sea-ice between ～30 ka and 22 ka that extended to ～59°S, close to the modern average winter sea-ice limit. Based on our reconstruction we propose that the timing of the maximum extent of summer sea-ice and subsequent retreat by 22 ka, could be insolation controlled and that the strong links between sea-ice and bottom water formation provide a potential mechanism by which Southern Hemisphere regional sea-ice dynamics at the LGM could have a global impact and promote deglaciation.     

Paired Measurements of Foraminiferal d18O and Mg/Ca Ratios of Indian Monsoons Reconstructed from Holocene to Last Glacial Record

The effect of seasonally reversing monsoons in the northern Indian Ocean is to impart significant changes in surface salinity (SS). Here, we report SS changes during the last 32 kyr in the Lakshadweep Sea (southeastern Arabian Sea) estimated from paired measurements of d18O and sea surface temperature (SST) using Globigerinoides sacculifer, an upper mixed layer dwelling foraminifera. The heaviest d18OG.sacculifer (–0.07±0.08‰) is recorded between 23 and 15 ka, which could be defined as the last glacial maximum (LGM). The d18OG.sacculifer shift between the LGM and Holocene is 2.07‰. The SST shows an overall warming of 2°C from the LGM to Holocene (28°C to 30°C). However, coldest SSTs are observed prior to LGM, i.e., ~27 ka. The SS was higher (~38 psu) throughout most of the recorded last glacial period (32.5–15 ka). This high salinity together with generally lower SSTs suggests a period of sustained weaker summer or stronger winter monsoons. The deglacial warming is associated with rapid reorganization of monsoons and is reflected in decreased salinity to a modern level of ~ 36.5 psu, within a period of ~5 kyr. This indicates intensification of summer monsoons during cold to warm climate transition.     

Holocene and Lateglacial relative sea‐level change in north‐west England: implications for glacial isostatic adjustment models

Relative sea‐level (RSL) change is reconstructed for central Cumbria, UK, based on litho‐ and biostratigraphical analysis from the Lateglacial to the late Holocene. The RSL curve is constrained using ten new radiocarbon‐dated sea‐level index points in addition to published data. The sea‐level curve identifies a clear Lateglacial sea‐level highstand approximately 2.3 m OD at c. 15–17 k cal a BP followed by rapid RSL fall to below ?5 m OD. RSL then rose rapidly during the early Holocene culminating in a mid‐Holocene highstand of approximately 1 m OD at c. 6 k cal a BP followed by gradual fall to the present level. These new data provide an important test for the RSL predictions from glacial isostatic adjustment models, particularly for the Lateglacial where there are very little data from the UK. The new RSL curve shows similar broad‐scale trends in RSL movement predicted by the models. However, the more recent models fail to predict the Lateglacial sea level highstand above present reconstructed by the new data presented here. Future updates to the models are needed to reduce this mismatch. This study highlights the importance for further RSL data to constrain Lateglacial sea level from sites in northern Britain. Copyright © 2012 John Wiley & Sons, Ltd.     

Mammal fauna during the Late Pleistocene and Holocene in the far northeast of Europe

The paper summarises materials on the mammal remains in northeastern Europe, dated by radiocarbon. Altogether, 23 local faunas of small mammals and 47 local faunas of large mammals were analysed. Multidimensional statistical analysis shows a strong correlation between changes in small mammal fauna composition and climate changes throughout time. The correlations with the spatial gradients, however, are less pronounced. The faunas are classified into three groups: (1) faunas of Holocene age; (2) Late Pleistocene ‘stadial’ assemblages; and (3) Late Pleistocene ‘interstadial’ assemblages. In some cases, changes in species abundance are better understood in terms of biotic interrelations rather than of climatic effects. The most pronounced change in small mammal fauna composition and structure occurred at the Preboreal/Boreal boundary, and a less conspicuous alteration took place at the LGM/Lateglacial transition. The most noticeable transformation in the large mammal fauna composition is dated to the early Holocene. Less significant changes are observed at the Middle Weichselian/LGM transition and at the LGM/Lateglacial transition. It is safely concluded that variations in the faunas of small and large mammals recorded in NE Europe during the last 35 000 years occurred synchronously and unidirectionally.     

A ∼25 ka Indian Ocean monsoon variability record from the Andaman Sea

Recent paleoclimatic work on terrestrial and marine deposits from Asia and the Indian Ocean has indicated abrupt changes in the strength of the Asian monsoon during the last deglaciation. Comparison of marine paleoclimate records that track salinity changes from Asian rivers can help evaluate the coherence of the Indian Ocean monsoon (IOM) with the larger Asian monsoon. Here we present paired Mg/Ca and δ¹⁸O data on the planktic foraminifer Globigerinoides ruber (white) from Andaman Sea core RC12-344 that provide records of sea-surface temperature (SST) and δ¹⁸O of seawater (δ¹⁸O_sw) over the past 25,000 years (ka) before present (BP). Age control is based on nine accelerator mass spectrometry (AMS) dates on mixed planktic foraminifera. Mg/Ca-SST data indicate that SST was ∼3 °C cooler during the last glacial maximum (LGM) than the late Holocene. Andaman Sea δ¹⁸O_sw exhibited higher than present values during the Lateglacial interval ca 19–15 ka BP and briefly during the Younger Dryas ca 12 ka BP. Lower than present δ¹⁸O_sw values during the BØlling/AllerØd ca 14.5–12.6 ka BP and during the early Holocene ca 10.8–5.5 ka BP are interpreted to indicate lower salinity, reflect some combination of decreased evaporation–precipitation (E–P) over the Andaman Sea and increased Irrawaddy River outflow. Our results are consistent with the suggestion that IOM intensity was stronger than present during the BØlling/AllerØd and early Holocene, and weaker during the late glaciation, Younger Dryas, and the late Holocene. These findings support the hypothesis that rapid climate change during the last deglaciation and Holocene included substantial hydrologic changes in the IOM system that were coherent with the larger Asian monsoon.     

A terrestrial palynological record for the last two glacial cycles from southwestern New Zealand

A pollen profile from Okarito Pakihi Bog in south Westland, New Zealand extending from near present back to Marine Isotope Stage (MIS) 6 provides a continuous record of vegetation and climate change for the past two glacial cycles. Independent chronological control was obtained by AMS radiocarbon dating of organic sediments in the upper part of the sequence and OSL dating of inorganic silts in the lower part, with a unique tie point provided by the ca 26.5 cal ka Kawakawa Tephra. As was probably a common occurrence in this region, the basin developed as a moraine-dammed proglacial lake and remained lacustrine until the early Holocene, when a peat bog developed. Survival of the depositional site through subsequent multiple ice advances, unusual in a glaciated landscape, was probably assisted by lateral displacement of the basin relative to its source area, across the Alpine Fault.There is good correspondence between inferred periods of substantial treeline depression in the pollen profile and the record for ice advance in this region. More cooling events are evident in the pollen record, however, presumably due to the fragmentary nature of glacial geomorphology. The pollen record also shows broad consistency with the MIS record and hence with the Milankovitch orbital forcing model, but with some departures, including an early onset to the last glacial maximum (LGM). Several sub-Milankovitch scale events are also evident, including a mid-LGM warming and Lateglacial reversals during both the last and the penultimate deglaciation.     

Late Quaternary vegetation reconstruction from the Eastern Arc Mountains, Tanzania

Pollen, spore, macrofossil and stable isotope (C and N) analyses from a 266-cm sediment core collected from a swamp on the Eastern Arc Mountains, Tanzania, are used to reconstruct vegetation and environmental history. An estimated time scale based on five ¹⁴C ages records approximately 38,000 yr. This palaeorecord is the first from this biodiversity hotspot and importantly extends through the last glacial maximum (LGM). The altitudinal transition from montane to upper montane forest shifted from 1700-1800 m (38,000 ¹⁴C yr BP) to 1800-1900 m (35,000-29,000 ¹⁴C yr BP). From 29,000 to 10,000 ¹⁴C yr BP, it shifted from 1850-1950 m across the LGM to 1750-1800 m (during 10,000-3500 ¹⁴C yr BP), and to present-day elevations at 2000 m during the last 3500 ¹⁴C yr BP. The relative ecosystem stability across the LGM may be explained by the Indian Ocean's influence in maintaining continuous moist forest cover during a period of East African regional climate aridity. During the late Holocene, presence of abundant coprophilous fungi and algal blooms demonstrates increasing human impact. Neurospora spores indicate frequent fires, coinciding with clear signals of decline in Podocarpus and Psychotria trees that possibly represent selective logging.     

A 40,000-yr record of environmental change from Burial Lake in Northwest Alaska

Burial Lake in northwest Alaska records changes in water level and regional vegetation since ∼ 39,000 cal yr BP based on terrestrial macrofossil AMS radiocarbon dates. A sedimentary unconformity is dated between 34,800 and 23,200 cal yr BP. During all or some of this period there was a hiatus in deposition indicating a major drop in lake level and deflation of lacustrine sediments. MIS 3 vegetation was herb-shrub tundra; more xeric graminoid-herb tundra developed after 23,200 cal yr BP. The tundra gradually became more mesic after 17,000 cal yr BP. Expansions of Salix then Betula, at 15,000 and 14,000 cal yr BP, respectively, are coincident with a major rise in lake level marked by increasing fine-grained sediment and higher organic matter content. Several sites in the region display disrupted sedimentation and probable hiatuses during the last glacial maximum (LGM); together regional data indicate an arid interval prior to and during the LGM and continued low moisture levels until ∼ 15,000 cal yr BP. AMS ¹⁴C dates from Burial Lake are approximately synchronous with AMS ¹⁴C dates reported for the Betula expansion at nearby sites and sites across northern Alaska, but 1000-2000 yr younger than bulk-sediment dates.     

Radiocarbon dating and paleoclimatic significance of subfossil Limicolaria in northwestern Sudan

The discovery, identification, and radiocarbon dating of the large achatinid land snail Limicolaria kambeul chudeaui at six places in northwestern Sudan, north of the 100-mm isohyet, provide convincing evidence that at least 300 mm annual rainfall existed there 6000 yr ago. Since then the rainfall north of ca. 20°N lat in the eastern Sahara has certainly been <300 mm and probably <200 mm. Accelerator mass spectrometry has allowed the organic fraction, presumably conchiolin, to be accurately radiocarbon dated whereas carbonate fractions are ca. 600 yr too old. Comparative studies show the subfossil form, L. k. chudeaui, to be the most primitive in its species complex and to occupy a narrow east-west belt across Africa north of 15°N and west of 35°E. The northern limit of living forms lies within the southern part of the Sahelian zone in forest or forest-savanna. They cannot live in open grassland. Therefore, the distribution of L. k. chudeaui marks the former northern position of this zone during the middle Holocene, indicating a latitudinal shift of at least 5° (500 km).     

Mountain-block recharge, present and past, in the eastern Espa?ola Basin, New Mexico, USA

Noble gas recharge temperatures (NGTs) and radiocarbon ages were determined for 43 groundwater samples collected in the eastern Espa?ola Basin, New Mexico (USA), to identify mountain-block recharge in waters <10 thousand years (ka) old and to evaluate possible changes in mountain-block recharge over the past ??35?ka. For Holocene samples from the southeastern area, NGTs are dominantly 2?C4° cooler than the measured water-table temperature near the mountain front. Computed minimum mountain-block recharge fractions are dominantly 0.2?C0.5, consistent with previous large mountain-block recharge estimates. NGTs do not display the distinct low during the last glacial maximum observed in other paleorecharge studies; samples recharged 15?C25?ka ago are on average only 1.3° cooler than Holocene samples. Instead, samples with the coldest NGTs were recharged 25?C35?ka ago. A proposed explanation is that higher precipitation rates during the last glacial maximum resulted in a lower mean recharge elevation for the basin, essentially buffering the effect of the lower mean annual air temperature and producing NGTs similar to the Holocene. In the period preceding the last glacial maximum, precipitation rates more like today??s resulted in Holocene-like mountain-block recharge fractions, producing a mean NGT ??5° cooler than the Holocene, as expected.     

Towards a climate event stratigraphy for New Zealand over the past 30 000 years (NZ‐INTIMATE project)

It is widely recognised that the acquisition of high‐resolution palaeoclimate records from southern mid‐latitude sites is essential for establishing a coherent picture of inter‐hemispheric climate change and for better understanding of the role of Antarctic climate dynamics in the global climate system. New Zealand is considered to be a sensitive monitor of climate change because it is one of a few sizeable landmasses in the Southern Hemisphere westerly circulation zone, a critical transition zone between subtropical and Antarctic influences. New Zealand has mountainous axial ranges that amplify the climate signals and, consequently, the environmental gradients are highly sensitive to subtle changes in atmospheric and oceanic conditions. Since 1995, INTIMATE has, through a series of international workshops, sought ways to improve procedures for establishing the precise ages of climate events, and to correlate them with high precision, for the last 30 000 calendar years. The NZ‐INTIMATE project commenced in late 2003, and has involved virtually the entire New Zealand palaeoclimate community. Its aim is to develop an event stratigraphy for the New Zealand region over the past 30 000 years, and to reconcile these events against the established climatostratigraphy of the last glacial cycle which has largely been developed from Northern Hemisphere records (e.g. Last Glacial Maximum (LGM), Termination I, Younger Dryas). An initial outcome of NZ‐INTIMATE has been the identification of a series of well‐dated, high‐resolution onshore and offshore proxy records from a variety of latitudes and elevations on a common calendar timescale from 30 000 cal. yr BP to the present day. High‐resolution records for the last glacial coldest period (LGCP) (including the LGM sensu stricto) and last glacial–interglacial transition (LGIT) from Auckland maars, Kaipo and Otamangakau wetlands on eastern and central North Island, marine core MD97‐2121 east of southern North Island, speleothems on northwest South Island, Okarito wetland on southwestern South Island, are presented. Discontinuous (fragmentary) records comprising compilations of glacial sequences, fluvial sequences, loess accumulation, and aeolian quartz accumulation in an andesitic terrain are described. Comparisons with ice‐core records from Antarctica (EPICA Dome C) and Greenland (GISP2) are discussed. A major advantage immediately evident from these records apart from the speleothem record, is that they are linked precisely by one or more tephra layers. Based on these New Zealand terrestrial and marine records, a reasonably coherent, regionally applicable, sequence of climatically linked stratigraphic events over the past 30 000 cal. yr is emerging. Three major climate events are recognised: (1) LGCP beginning at ca. 28 000 cal. yr BP, ending at Termination I, ca. 18 000 cal. yr BP, and including a warmer and more variable phase between ca. 27 000 and 21 000 cal. yr BP, (2) LGIT between ca. 18 000 and 11 600 cal. yr BP, including a Lateglacial warm period from ca. 14 800 to 13 500 cal. yr BP and a Lateglacial climate reversal between ca. 13 500 and 11 600 cal. yr BP, and (3) Holocene interglacial conditions, with two phases of greatest warmth between ca. 11 600 and 10 800 cal. yr BP and from ca. 6 800 to 6 500 cal. yr BP. Some key boundaries coincide with volcanic tephras. Copyright © 2007 John Wiley & Sons, Ltd.     

Late Devensian environments in the Vale of Mowbray, North Yorkshire, UK: evidence from palynology

Two radiocarbon-dated Lateglacial pollen diagrams from the Vale of Mowbray (northern Vale of York) are presented from sites in the lowlands between the washlands courses of the rivers Swale and Ure in North Yorkshire, an area with little previous palynological research despite its proximity to the Devensian glacial advance limits in eastern England. The profiles, from Snape Mires and Nosterfield, include the Loch Lomond Stadial (Younger Dryas) and the Holocene transition, while that from Snape Mires also includes the period from the early part of the Lateglacial Interstadial. This profile differs from most published Interstadial diagrams from the Yorkshire region in having a long-delayed expansion of tree and shrub taxa. Juniperus (juniper) remains important after vegetation development takes place and the pollen record includes evidence of two cold climate oscillations before the maximum development of Betula (birch) woodland near the end of the Lateglacial Interstadial. At both profiles Artemisia (mugwort) frequencies are lower during the Loch Lomond Stadial than at many regional sites, probably due to edaphic factors in these lowland locations. The two sites provide valuable environmental data that enable comparison between the more wooded Lateglacial vegetation to the south in the Vale of York and Humberside and the more open contemporaneous vegetation to the north in the Durham and Northumberland lowlands.     

Amazon diversity in light of the paleoecological record

Disjunct distributions of Amazonian species have been explained previously by a refugial theory which postulates that Amazonian rain forest was preserved in large highland regions throughout the Pleistocene. No direct, radiocarbon dated evidence exists for the last glacial maximum with which to test this theory. The only radiocarbon dates of Pleistocene age from the Amazon basin are of fossiliferous deposits in the proposed Napo refugium of the West, where both pollen assemblages and wood samples indicate that forest with cool Andean elements existed there at two intervals in the last cycle of northern hemisphere glaciation, implying a temperature depression of at least 4°C in the Amazon lowlands.Under modern climatic conditions, lateral erosion by river meander, together with surface erosion, serves as a rejuvenating mechanism for the rain forests of Peru and Ecuador. The instability of late Holocene Amazonian climates is demonstrated by documenting a precipitation event in the eastern Andean cordillera that caused widespread flooding of western Amazonian forests 800–1300 BP. Late Holocene pollen histories from widely dispersed parts of central Amazonia distinguish between vegetation histories in the drainage of northern, south-western and western watersheds, but all show histories of fluctuating intensities of dry seasons. Radiocarbon dating of charcoal layers in soils of Venezuelan Amazonia demonstrates the apparently random incidence of wild fires at wide intervals over at least the last 6 ka.The high species richness of Amazonia is a result of numerous opportunities for vicariance because of a very large total area, wide variety of habitats and intermediate levels of disturbance, particularly by hydrological processes, that has varied on timescales from years to millennia. Amazonian disjunct distributions probably reflect regional environmental discontinuities in both interglacial and glacial times.     

Lateglacial and early Holocene summer temperatures in the southern Swiss Alps reconstructed using fossil chironomids

We present a Lateglacial and early Holocene chironomid‐based July air temperature reconstruction from Foppe (1470 m a.s.l.) in the Swiss Southern Alps. Our analysis suggests that chironomid assemblages have responded to major and minor climatic fluctuations during the past 17 000 years, such as the Oldest Dryas, the Younger Dryas and the Bølling/Allerød events in the Lateglacial and the Preboreal Oscillation at the beginning of the Holocene. Quantitative July air temperature estimates were produced by applying a combined Norwegian and Swiss temperature inference model consisting of 274 lakes to the fossil chironomid assemblages. The Foppe record infers average July air temperatures of ca. 9.9 °C during the Oldest Dryas, 12.2 °C during most of the Bølling/Allerød and 11.1 °C for the Younger Dryas. Mean July air temperatures during the Preboreal were 14 °C. Major temperature changes were observed at the Oldest Dryas/Bølling (+2.7 °C), the Allerød/Younger Dryas (?2 °C) and the Younger Dryas/Holocene transitions (+3.9 °C). The temperature reconstruction also shows centennial‐scale coolings of ca. 0.8–1.4 °C, which may be synchronous with the Aegelsee (Greenland Interstadial 1d) and the Preboreal Oscillations. A comparison of our results with other palaeoclimate records suggests noticeable temperature gradients across the Alps during the Lateglacial and early Holocene. Copyright © 2011 John Wiley & Sons, Ltd.     

Glaciations and paleoclimate of Mount Erciyes,central Turkey,since the Last Glacial Maximum,inferred from 36Cl cosmogenic dating and glacier modeling

Forty-four boulders from moraines in two glacial valleys of Mount Erciyes (38.53°N, 35.45°E, 3917 m), central Turkey, dated with cosmogenic chlorine-36 (³⁶Cl), indicate four periods of glacial activity in the past 22 ka (1 ka = 1000 calendar years). Last Glacial Maximum (LGM) glaciers were the most extensive, reaching 6 km in length and descending to an altitude of 2150 m above sea level. These glaciers started retreating 21.3 ± 0.9 ka (1σ) ago. They readvanced and retreated by 14.6 ± 1.2 ka ago (Lateglacial), and again by 9.3 ± 0.5 ka ago (Early Holocene). The latest advance took place 3.8 ± 0.4 ka ago (Late Holocene). Using glacier modeling together with paleoclimate proxy data from the region, we reconstructed the paleoclimate at these four discrete times. The results show that LGM climate was 8–11 °C colder than today and moisture levels were somewhat similar to modern values, with a range between 20% more and 25% less than today. The analysis of Lateglacial advance suggests that the climate was colder by 4.5–6.4 °C based on up to 1.5 times wetter conditions. The Early Holocene was 2.1–4.9 °C colder and up to twice as wet as today, while the Late Holocene was 2.4–3 °C colder and its precipitation amounts approached to similar conditions as today. Our paleoclimate reconstructions show a general trend of warming for the last 22 ka, and an increase of moisture until Early Holocene, and a decrease after that time. The recent glacier terminates at 3450 m on the northwest side of the mountain. It is a remnant from the last advance (possibly during the Little Ice Age). Repeated measurements of glacier length between 1902 and 2008 reveal a retreat rate of 4.2 m per year, which corresponds to a warming rate of 0.9–1.2 °C per century.     

Lateglacial and early Holocene lake sediments from the northern Apennines, Italy – pollen stratigraphy and radiocarbon dating

Radiocarbon-dated pollen profiles are presented from two basins in Prato Spilla, near Val Parma in the northern Apennines. One basin contains a complete Holocene succession, the other a full Lateglacial to mid-Holocene record. The data provide the most comprehensive Lateglacial-early Holocene pollenstratigraphic succession yet reported from the northern Apennines accompanied by an internally consistent radiocarbon chronology. They provide fresh impetus for (a) a discussion of the strength of the Younger Dryas 'signal' in pollen-stratigraphic profiles from southern Europe, (b) an assessment of the palaeovegetation of northern Italy during the last glacial-interglacial transition, and (c) the altitude of the snowline in the region during the Younger Dryas.     

Postglacial fire,vegetation, and climate history across an elevational gradient in the Northern Rocky Mountains,USA and Canada

A 13,100-year-long high-resolution pollen and charcoal record from Foy Lake in western Montana is compared with a network of vegetation and fire-history records from the Northern Rocky Mountains. New and previously published results were stratified by elevation into upper and lower and tree line to explore the role of Holocene climate variability on vegetation dynamics and fire regimes. During the cooler and drier Lateglacial period, ca 13,000 cal yr BP, sparsely vegetated Picea parkland occupied Foy Lake as well as other low- and high-elevations with a low incidence of fire. During the warmer early Holocene, from ca 11,000–7500 cal yr BP, low-elevation records, including Foy, indicate significant restructuring of regional vegetation as Lateglacial Picea parkland gave way to a mixed forest of Pinus-Pseudotsuga-Larix. In contrast, upper tree line sites (ca >2000 m) supported Pinus albicaulis and/or P. monticola-Abies-Picea forests in the Lateglacial and early Holocene. Regionally, biomass burning gradually increased from the Lateglacial times through the middle Holocene. However, upper tree line fire-history records suggest several climate-driven decreases in biomass burning centered at 11,500, 8500, 4000, 1600 and 500 cal yr BP. In contrast, lower tree line records generally experienced a gradual increase in biomass burning from the Lateglacial to ca 8000 cal yr BP, then reduced fire activity until a late Holocene maximum at 1800 cal yr BP, as structurally complex mesophytic forests at Foy Lake and other sites supported mixed-severity fire regimes. During the last two millennia, fire activity decreased at low elevations as modern forests developed and the climate became cooler and wetter than before. Embedded within these long-term trends are high amplitude variations in both vegetation dynamics and biomass burning. High-elevation paleoecological reconstructions tend to be more responsive to long-term changes in climate forcing related to growing-season temperature. Low-elevation records in the NRM have responded more abruptly to changes in effective precipitation during the late Holocene. Prolonged droughts, including those between 1200 and 800 cal yr BP, and climatic cooling during the last few centuries continues to influence vegetation and fire regimes at low elevation while increasing temperature has increased biomass burning in high elevations.     

Constraints on hydrological and paleotemperature variations in the Eastern Mediterranean region in the last 140 ka given by the δD values of speleothem fluid inclusions

Speleothem fluid inclusions potentially provide vital data on the paleohydrological conditions in glacial and interglacial periods. We show here that δD analyses of fluid inclusions from speleothems in three caves in the Eastern Mediterranean region (Israel) provide a basis for understanding hydrological and temperature variations in the last 140 ka. Using measured δD fluid inclusion values and temperature ranges constrained by the present-day Mediterranean Meteoric Water Line (MMWL) and the global MWL, we show a strong compatibility between the land and marine temperature records, with the highest land temperatures occurring at 120–130 ka (17–22°C) and the present (18°C) and the lowest temperatures during the LGM, about 10°C lower than present. Interglacial waters are constrained to follow the MMWL and most glacial waters also plot close to the MMWL, with a slight shift towards the MWL. However, during two remarkable brief periods at the termination of the LGM, the waters plot on the MWL, suggesting that both sharp cooling and an increase in relative humidity above the EM Sea reduced d-excess values to those of the global system.