Neoglacial Period Research Articles

Atlantic Water advection versus sea‐ice advances in the eastern Fram Strait during the last 9 ka: Multiproxy evidence for a two‐phase Holocene

A sediment core from the West Spitsbergen continental margin was studied to reconstruct climate and paleoceanographic variability during the last ~9 ka in the eastern Fram Strait (FS). Our multiproxy evidence suggests that the establishment of the modern oceanographic configuration in the eastern FS occurred stepwise, in response to the postglacial sea‐level rise and the related onset of modern sea‐ice production on the shallow Siberian shelves. The late Early and Mid‐Holocene interval (9 to 5 ka) was generally characterized by relatively unstable conditions. High abundance of the subpolar planktic foraminifer species Turborotalita quinqueloba implies strong intensity of Atlantic Water (AW) inflow with high productivity and/or high AW temperatures, resulting in a strong heat flux to the Arctic. A series of short‐lived cooling events (8.2, 6.9, and 6.1 ka) occurred superimposed on the warm late Early to Mid‐Holocene conditions. Our proxy data imply that simultaneous to the complete postglacial flooding of Arctic shallow shelves and the initiation of modern sea‐ice production, strong advance of polar waters initiated modern oceanographic conditions in the eastern FS at ~5.2 ka. The Late Holocene was marked by the dominance of the polar planktic foraminifer species Neogloboquadrina pachyderma, a significant expansion of sea ice/icebergs, and strong stratification of the water column. Although planktic foraminiferal assemblages as well as sea subsurface temperatures suggest a return of slightly strengthened advection of subsurface AW after 3 ka, a relatively stable cold‐water layer prevailed at the sea surface, and the study site was probably located within the seasonally fluctuating marginal ice zone during the Neoglacial period.

Sub-Boreal aggradation along the Apennine margin of the Central Po Plain: geomorphological and geoarchaeological aspects

The Apennine foothills at the southern limit of the Po Plain consist of a belt of coalescent, gravelly, alluvial fans, trending to the north, towards the depocenter of the plain. Their aggradation is generally considered to have been controled by climate and linked to the glacial periods of the Middle and Upper Pleistocene. At the transition from the Upper Pleistocene to the Holocene, aggradation of most of the alluvial fans stopped and their surface was subject to weathering, which resulted in deep, rubified Alfisols (Sols bruns fersiallitiques). These developed mainly during the Boreal and Atlantic periods. Beginning in the Sub-Boreal period, fine-textured alluvial deposits buried the distal margin of the alluvial fans and the soils developed on them. These deposits consist of fine-sized sediments of overbank facies, organised in fining upward sets and intercalated by buried Entisols, Inceptisols and Vertisols. The accumulation of alluvial sediments on the alluvial fans, after the prevailing weathering on their top, indicates a main change in the pedo-sedimentary processes and is related to the climatic change that occured between the end of the Postglacial Hypsithermal period and the beginning of the Neoglacial period. The soils on top of the alluvial fans and in later alluvial deposits show intensive human use and occupation from the Neolithic to the Early Bronze Age, and witness a significant change in land exploitation during the Atlantic/Sub-Boreal transition. During the Neolithic (Atlantic period), agricultural practices linked to shifting agriculture had minimal impact on the vegetation mantle and were limited to the plain areas. By contrast, during the Chalcolithic and the Early Bronze Age (Sub-Boreal period), a rather different mode of land use was adopted, as the result of the newly introduced transhumant pastoralism. Deforestation through slash and burn techniques was very intense and widespread, extending far beyond the boundary of the plain, deep inside the mountain range, affecting the Po Plain and the adjoining Apennines. This case study presents an argument for seeing climate change and human activity (deforestation by fire, agriculture and pastoralism) as synergic phenomena that shaped the prehistoric landscape.

The Holocene deposits of Lake Petit (2200 m a.s.l., Southern French Alps): climatic and anthropogenic controls on mountain sediment dynamics?

Numerous archaeological studies carried out in high-elevation areas of the Southern French Alps have documented ancient human occupation of mountains, mainly characterized by pastoral and mining activities. Besides, the area was affected by both continental and Mediterranean climate instability throughout the Holocene. Lake Petit, located in the Mercantour massif, was investigated in order to reconstruct past interactions between humans, the environment and climate, using a multidisciplinary approach. This study was carried out on a 144 cm-long gravity core providing a continuous record spanning the last 5000 years. Our multi-proxy investigation (sedimentological, geochemical and palynological analyses), allowed us to reconstruct three main phases, evidencing a progressive destabilization of the local environment. The first phase (ca. 4800 to 4300 cal. BP) was characterized by relatively stable environmental conditions, as attested by a high lake productivity (deposition of pure diatomite) and by the local presence of trees (presence of conifer stomata). The second phase (ca. 4300 to 1500 cal. BP) could correspond to a drastic cleaning of landscapes since the lake record highlights an abrupt switch in sediment source marked by an input of terrestrial organic matter. Regular occurrences of anthropogenic pollen assemblages might indicate early pastoral activity in the lake vicinity, while wetter conditions characteristic of the Neoglacial period may have trigger hillslopes destabilization. The most recent phase (since ca. 1500 cal. BP) is marked by a final degradation of the environment: the lake productivity dramatically decreased contemporaneously with a fall of the AP/NAP pollen curve. This phase also exhibits the highest values of anthropogenic pollen taxa and concentrations of lead. It undoubtedly corresponded to one of an intensive agro-pastoral pressure as well to local mining activities.

Holocene hydro-climatic change and effects on carbon accumulation inferred from a peat bog in the Attawapiskat River watershed, Hudson Bay Lowlands, Canada

Multiple proxies from a 319-cm peat core collected from the Hudson Bay Lowlands, northern Ontario, Canada were analyzed to determine how carbon accumulation has varied as a function of paleohydrology and paleoclimate. Testate amoeba assemblages, analysis of peat composition and humification, and a pollen record from a nearby lake suggest that isostatic rebound and climate may have influenced peatland growth and carbon dynamics over the past 6700 cal yr BP. Long-term apparent rates of carbon accumulation ranged between 8.1 and 36.7 g C m−2 yr−1 (average = 18.9 g C m−2 yr−1). The highest carbon accumulation estimates were recorded prior to 5400 cal yr BP when a fen existed at this site, however following the fen-to-bog transition carbon accumulation stabilized. Carbon accumulation remained relatively constant through the Neoglacial period after 2400 cal yr BP when pollen-based paleoclimate reconstructions from a nearby lake (McAndrews et al., 1982) and reconstructions of the depth to the water table derived from testate amoeba data suggest a wetter climate. More carbon accumulated per unit time between 1000 and 600 cal yr BP, coinciding in part with the Medieval Climate Anomaly.

Using paleolimnology to track Holocene climate fluctuations and aquatic ontogeny in poorly buffered High Arctic lakes

Fossil diatom assemblages, and spectrally-inferred dissolved organic carbon (DOC) and sedimentary chlorophyll-a (SedChla) were analysed on lake sediment cores from two poorly buffered lakes on Pim Island (High Arctic Canada) to assess their responses to Holocene climate changes and to document lake ontogeny. Following deglaciation, diatom assemblages were dominated by small benthic Fragilaria sensu lato taxa. During the mid-Holocene, there was an abrupt shift to more circumneutral and slightly acidophilous taxa dominated by Achnanthes and Navicula taxa. In the most recent sediments, we recorded an increase in the planktonic taxon Cyclotella radiosa. This shift of the last century is the most ecologically unique in the Holocene record and is indicative of longer ice-free summers consistent with modern climate warming. Inferred DOC and SedChla track some of the main Holocene climatic trends documented in the region, including the Holocene Thermal Maximum and Neoglacial period; however, changes in lakewater DOC did not likely drive any of the recorded shifts in diatom assemblages. Compared to nearby well-buffered sites, our poorly buffered lakes recorded a more dynamic diatom response to Holocene environmental change. The decreasing trend in diatom-inferred pH is likely due to changes in the acid neutralizing capacity (ANC) driven by the release of alkalinizing base cations from the easily weathered glacial deposits in the early Holocene and later by climate-driven pH dynamics and within-lake dissolved inorganic carbon (DIC) dynamics. The diatom community composition in our study lakes is different and undergoes greater changes than in nearby well-buffered lakes suggesting that softwater lakes in the high Arctic may respond most sensitively to climate and other environmental stressors.

A comparison and integration of tree-ring and alluvial records of fire history at the Missionary Ridge Fire, Durango, Colorado, USA

We used tree-ring and alluvial sediment methods to reconstruct past fire regimes for a mixed conifer forest within a 1 km2 drainage basin which was severely burned by a wildfire near Durango, Colorado. Post-fire debris flow events incised the valley-filling alluvial sediments in the lower basin, and created exposures of fire-related of deposits of late-Holocene age. Tree-ring and alluvial sediment fire history records were created separately, and then compared and integrated to create a ~ 3000 year record of past fire activity. The tree-ring record showed that from AD 1679 to 1879, there were frequent surface fires, while patches of high-severity fire occurred during widespread fire years. The alluvial record showed that a low- to moderate-and mixed-severity fire regime has likely been dominant over the past ~ 2600 calibrated calendar years before present, as shown by locally episodic deposition of charcoal-rich, fine-grained sediments. Radiocarbon dating suggested that in two stratigraphic sections, there was rapid deposition of several fine-grained sediment layers. One of these episodes occurred during the Medieval Climatic Anomaly (AD 900—1300). A charcoal-rich debris flow deposit in the oldest exposed part of the stratigraphic record dated to ~ 2600 calibrated calendar years before present. This event was potentially equivalent in magnitude to the debris-flow events following the recent wildfire in the study area, and is evidence of a high-severity fire that burned a large proportion of the study basin. The timing of this event coincides with a period of less frequent, yet more severe wildfires in a nearby lake sediment record, and is associated with the end of a Neoglacial period of cooler and wetter temperatures.

Diatom-inferred climatic and environmental changes over the last ∼ 9000 years from a low Arctic (Nunavut, Canada) tundra lake

Diatom assemblage changes over the Holocene were examined from a 14C-dated sediment core retrieved from Lake TK-2, a small low Arctic lake located ca. 200 km north of the forest–tundra ecotone in mainland Nunavut, Canada. Notable changes in the diatom assemblages were recorded throughout the core, suggesting that the Holocene epoch in this region has been environmentally and climatically dynamic. The earliest diatom assemblages (ca. 9000 cal yr BP) were dominated by taxa that are atypical of post-glacial assemblages commonly recorded throughout the Arctic, and may suggest that early Holocene conditions at Lake TK-2 were relatively warmer. A shift to dominance by small, benthic, opportunistic Fragilaria taxa followed (after ca. 8550 cal. yr BP), more typical of Arctic assemblages during initial lake ontogeny, suggesting the onset of cooler, more alkaline conditions. An abrupt and short-lived marked decrease in diatoms between ca. 8550 and 8500 cal. yr BP, with corresponding changes in physical and chemical indicators (e.g., sedimentation rate, siliciclastic content, % organic matter content), provides potential evidence for the 8.2 k cooling anomaly, an event rarely recognized from other paleolimnological studies in the Canadian north. Following ca. 7000 cal. yr BP, a substantial shift occurred to a more complex and diverse diatom assemblage that now included more acidophilic taxa. This compositional change is likely indicative of a natural, long-term loss of alkalinity in the lake, and marks the onset of the Holocene Thermal Maximum, consistent with the timing of this warm period for this region. The relatively stable diatom assemblage composition during the Neoglacial period was punctuated by fluctuations in key species potentially correlative with the so-called Medieval Warm Period and Little Ice Age. In the most recent sediments, the post-industrial expansion of the small, planktonic Cyclotella stelligera complex, and a concurrent decline in the heavily-silicified Aulacoseira lirata complex, are similar to shifts that are increasingly being recognized as geographically widespread diatom responses to recent climate warming. The Lake TK-2 diatom record provides important insights into the Holocene environmental history of this understudied region of the Canadian Arctic. Furthermore, it is one of the few Arctic lakes in which the 8.2 k cold event is possibly expressed.

Holocene Antarctic climate variability from ice and marine sediment cores: Insights on ocean–atmosphere interaction

Holocene climate variability in the southeast Atlantic sector of the Southern Ocean and Antarctic is assessed and quantified through integration of available marine sediment core and Antarctic ice core data. We use summer sea surface temperature (SSST) and sea ice presence (SIP) reconstructions from two marine sediment cores recovered north (50 °S) and south (53.2 °S) of the present day Antarctic Polar Front (APF), as well as an atmospheric temperature and sea ice proxy from the EPICA ice core from Dronning Maud Land (EDML). We find reasonably good agreement in the timing of climate evolution in the analyzed series. Almost all records show a gradual glacial-to-Holocene climate transition, interrupted by the Antarctic cold reversal around 13 000 cal yr BP, and early Holocene climatic optimum (HCO) at about 11 000 cal yr BP. During the early HCO, the seasonal ice cover retreats to south of 53 °S; it then readvances in the course of the mid- to late Holocene. The maximum winter sea ice edge position during the recent 10 000 years varied mainly within 51–53 °S, with sporadic growth to north of 50 °S, a position similar to that during the last glacial. The onset of the Neoglacial period after ca 4000 yr BP is associated with a steepening of the SSST gradient between the marine core sites, strengthening of the westerlies and cooling in the inland ice sheet. The agreement in timing between elevated SSST during the early HCO and decreased deuterium excess in EDML and other ice cores from different locations in the East Antarctic suggests that the retreat of sea ice during the early HCO and weakening of the APF was a general feature of the East Antarctic climate during that time.

Holocene carbon burial by lakes in SW Greenland

AbstractThe role of the Arctic in future global change processes is predicted to be important because of the large carbon (C) stocks contained in frozen soils and peatlands. Lakes are an important component of arctic landscapes although their role in storing C is not well prescribed. The area around Kangerlussuaq, SW Greenland (66–68°N, 49–54°W) has extremely high lake density, with ∼20 000 lakes that cover about 14% of the land area. C accumulation rates and standing stock (kg C m−2), representing late‐ to mid‐Holocene C burial, were calculated from AMS 14C‐dated sediment cores from 11 lakes. Lake ages range from ∼10 000 cal yr bp to ∼5400 cal yr bp, and reflect the withdrawal of the ice sheet from west to east. Total standing stock of C accumulated in the studied lakes for the last ∼8000 years ranged from 28 to 71 kg C m−2, (mean: ∼42 kg C m−2). These standing stock determinations yield organic C accumulation rates of 3.5–11.5 g C m−2 yr−1 (mean: ∼6 g C m−2 yr−1) for the last 4500 years. Mean C accumulation rates are not different for the periods 8–4.5 and 4.5–0 ka, despite cooling trends associated with the neoglacial period after 4.5 ka. We used the mean C standing stock to estimate the total C pool in small lakes (<100 ha) of the Kangerlussuaq region to be ∼4.9 × 1013 g C. This C stock is about half of that estimated for the soil pool in this region (but in 5% of the land area) and indicates the importance of incorporating lakes into models of regional C balance at high latitudes.

Holocene palaeoecological reconstruction of three boreal peatlands in the La Grande Rivière region, Québec, Canada

Pollen and macrofossil analyses from central peat cores along with 23 radiocarbon dates were used in palaeoecological reconstructions for three peatlands (LG1, LG2 and LG3) within the lower La Grande Rivière watershed in northern boreal Québec. Basal ages from LG3 and LG2 indicate up to an 1100 years later and possibly more abrupt Tyrrell Sea retreat in the LG3 area compared with the timeline for the region. Both autogenic and allogenic factors were found to have influenced local vegetation succession and rates of peat accumulation. Internal autogenic factors such as peat accumulation were key elements for the general peatland developmental pathway that followed the classic hydrosere sequence (pond-fen-bog). Regional climate and hydrography are the main external factors associated with changes in vegetation assemblages, surface wetness and consequently rates of peat accumulation. The LG2 and LG3 peatlands began developing shortly after 7000 cal. BP as shallow ponds with herbaceous freshwater aquatic and emergent taxa. Both sites rapidly evolved into fens with brown mosses. The autogenic transition from fen to bog occurred at both sites between 6000 and 5500 cal. BP. A long-term decrease in peat accumulation rates corresponding to a gradual densification of the local tree and shrub cover occurred at the LG2 and LG3 sites between 5000 and 1500 cal. BP. These changes were simultaneous at the two sites and therefore suggest the influence of external factors such as a shift to cooler and drier climatic conditions from the middle to late Holocene (Neoglacial period). Development of the LG1 site was delayed by a much later Tyrrell Sea retreat and started with a relatively long eutrophic aquatic phase. Both internal factors (minerotrophic conditions) and external factors (local topography and climate) contributed to the somewhat slower pace of vegetation succession. Synchronous increased peat accumulation rates in the last 1500 years at the three sites are attributable to regional vegetational shifts possibly due to the influence of recent climatic conditions and lower peat compaction of the acrotelm.

Holocene climate change in the Bransfield Basin, Antarctic Peninsula: evidence from sediment and diatom analysis

AbstractWe present the first study from the Bransfield Basin that extends through the Holocene, recording the variable climate history back to the decoupling of the ice sheet from the continental shelf ~10 650 calendar years before present (cal yr bp). Detailed sediment analysis reveals three stratigraphic units in PC-61 concomitant with three sedimentary environments, similar to sedimentary facies reported elsewhere: 1) subglacial, 2) glacial proximal/sub-ice shelf, and 3) open marine. These interpretations are based on a variety of sedimentological criteria, supported by ten AMS radiocarbon dates and detailed diatom analysis. We note two significant volcanic ash layers (tephra) at 3870 and 5500 cal yr bp from nearby Deception Island. Based on diatom assemblage analysis, we identify five separate climate regimes, highlighting a significantly shorter Mid-Holocene Climatic Optimum than reported by other studies (6800–5900 cal yr bp). This period is marked by the highest Eucampia antarctica var. antarctica and Fragilariopsis curta abundance, total diatom abundance, sediment accumulation rates, and low magnetic susceptibility. We also identify a less pronounced Neoglacial period relative to other studies, which includes an increase of Cocconeis/Rhizosolenia spp. assemblage related to unstable surface water conditions. Such observations probably reflect important regional variations in atmospheric or ocean circulation patterns.

Sea ice expansion in the Bering Sea during the Neoglacial: evidence from archaeozoology

The Neoglacial was a period of cold that lasted more than 2000 years during the mid-Holocene, from approximately 4700 to 2500 years ago. Although proxy data from a number of sources document the regional onset and duration of cold conditions in the Northern Hemisphere during this period, none have suggested an expansion of sea ice in the Bering Sea. Here we provide new evidence that Neoglacial sea ice expansion in the Bering Sea was substantial enough to have altered the distribution of North Pacific pinnipeds and cetaceans, using prehistoric skeletal remains recovered from an archaeological site on the island of Unalaska in the eastern Aleutians (Amaknak Bridge, occupied from c. 3500—2500 yr BP (radiocarbon years before present, uncalibrated)). Comprehensive archaeozoological analysis of the Amaknak Bridge fauna indicates that sea ice in the Bering Sea must have reached a more southerly position at the height of the Neoglacial and persisted longer than it does today. We infer from this evidence that for most of the Neoglacial period, sea ice must have surrounded the Pribilof Islands until early summer and blocked the Bering Strait until late summer. Such an expansion and seasonal persistence of sea ice would have prevented fur seals from using the Pribilofs as a summer breeding rookery and whales from making summer migrations into arctic waters to feed, as they do today. We suggest this expansion of sea ice in the Bering Sea during the Neoglacial may explain several unresolved phenomena of mammalian distributions, genetic partitioning and extinctions in the North Pacific.

Relative surface age‐dating of rock glacier systems near Hólar in Hjaltadalur, northern Iceland

AbstractSchmidt‐hammer rebound values and photogrammetric measurements of surface displacement were used to date two active polymorphic (high‐altitude) and two relict monomorphic (low‐altitude) rock glaciers near Hólar in Hjaltadalur, Tröllaskagi peninsula, northern Iceland (65° 40′ N, 19° 00′ W). Both low‐altitude rock glaciers are of Late Weichselian or Preboreal origin (ca. 10.3–9.2 k yr BP) with minor later reshaping until the early Neoglacial period (‘Vatnsdalur I’; ca. 5.2 k yr BP). Both high‐altitude rock glaciers consist of an upper lobe overriding a lower lobe corresponding to initiation during different cool phases. The initiation of the lower lobes can possibly be attributed to the ‘GH‐8.2 event’ (8.6–8.0 k cal. yr BP). They reached their terminal position at the end of the ‘Vatnsdalur I’ stage. The upper lobes of the high‐altitude rock glaciers were initiated sometimes between the ‘Vatnsdalur I’ but substantially before the ‘Vatnsdalur II’ (ca. 3.0–3.2 k yr BP) stages and underwent modification during each following Holocene glacier expansion episode, culminating the last time in the Little Ice Age. Thus, it is suggested that similar looking rock glaciers occurring elsewhere in the Tröllaskagi peninsula may have a similar complex history. Therefore, they may not be seen as rather simple landforms developed during the Little Ice Age. Copyright © 2007 John Wiley & Sons, Ltd.

Reconstruction of the ice age glaciation in the southern slopes of Mt. Everest, Cho Oyu, Lhotse and Makalu (Himalaya) (part 2)

In the Khumbu-and Khumbakarna Himalaya an ice stream network and valley glacier system has been reconstructed for the last glacial period (Wurmian, Last Ice Age, Isotope stage 4–2, 60–18 Ka BP, Stage 0) with glaciogeomorphological and sedimentological methods. It was a part of the glacier system of the Himalaya and has communicated across transfluence passes with the neighbouring ice stream networks toward the W and E. The ice stream network has also received inflow from the N, from a Tibetan ice stream network, by the Kyetrak-Nangpa-Bote Koshi Drangka (Valley) in the W, by the W-Rongbuk glacier valley into the Ngozumpa Drangka (Valley), by the Central Rongbuk glacier valley into the Khumbu Drangka (Valley) and by the antecedent Arun Nadi transverse-valley in the E of the investigation area. The ice thickness of the valley glacier sections, the surface of which was situated above the snow-line, amounted to 1000–1450 m. The most extended parent valley glaciers have been measured a:rox. 70 km in length (Dudh Koshi glacier), 67 km (Barun-Arun glacier) and 80 km (Arun glacier). The tongue end of the Arun glacier has flowed down to c. 500 m and that of the Dudh Koshi glacier to c. 900 m asl. At heights of the catchment areas of 8481 (or 8475) m (Makalu), i.e., 8848 (or 8872) m (Mt. Everest, Sagarmatha, Chogolungma) this is a vertical distance of the Ice Age glaciation of c. 8000 m. The steep faces towering up to 2000 m above the neve areas of the 6000–7000 m-high surfaces of the ice stream network were located 2000–5000 m above the ELA. Accordingly, their temperatures were so low, that their rock surfaces were free of flank ice and ice balconies. From the maximum past glacier extension up to the current glacier margins, 13 (altogether 14) glacier stages have been differentiated and in part 14C-dated. They were four glacier stages of the late glacial period, three of the neoglacial period and six of the historical period. By means of 130 medium-sized valley glaciers the corresponding ELA-depressions have been calculated in comparison with the current courses of the orographic snow-line. The number of the glacier stages since the maximum glaciation a:rox. agrees with that e.g. in the Alps and the Rocky Mountains since the last glacial period. Accordingly, it is interpreted as an indication of the Wurmian age (last glacial period) of the lowest ice margin positions. The current climatic, average glacier snow-line in the research area runs about 5500 m asl. The snow-line depression (ELA) of the last glacial period (Wurm) calculated by four methods has run about 3870 m asl, so that an ELA-depression of c. 1630 m has been determined. This corresponds to a lowering of the annual temperature by c. 8, i.e.,10°C according to the specific humid conditions at that time.

Reconstruction of the Ice Age glaciation in the southern slopes of Mt. Everest, Cho Oyu, Lhotse and Makalu (Himalaya) (Part 1)

In the Khumbu-and Khumbakarna Himalaya an ice stream network and valley glacier system has been reconstructed for the last glacial period (Wurmian, Last Ice Age, Isotope stage 4–2, 60–18 Ka BP, Stage 0) with glaciogeomorphological and sedimentological methods. It was a part of the glacier system of the Himalaya and has communicated across transfluence passes with the neighbouring ice stream networks toward the W and E. The ice stream network has also received inflow from the N, from a Tibetan ice stream network, by the Kyetrak-Nangpa-Bote Koshi Drangka (Valley) in the W, by the W-Rongbuk glacier valley into the Ngozumpa Drangka (Valley), by the Central Rongbuk glacier valley into the Khumbu Drangka (Valley) and by the antecedent Arun Nadi transverse-valley in the E of the investigation area. The ice thickness of the valley glacier sections, the surface of which was situated above the snow-line, amounted to 1000–1450 m. The most extended parent valley glaciers have been measured approx. 70 km in length (Dudh Koshi glacier), 67 km (Barun-Arun glacier) and 80 km (Arun glacier). The tongue end of the Arun glacier has flowed down to c. 500 m and that of the Dudh Koshi glacier to c. 900 m asl. At heights of the catchment areas of 8481 (or 8475) m (Makalu), i.e., 8848 (or 8872) m (Mt. Everest, Sagarmatha, Chogolungma) this is a vertical distance of the Ice Age glaciation of c. 8000 m. The steep faces towering up to 2000 m above the neve areas of the 6000–7000 m-high surfaces of the ice stream network were located 2000–5000 m above the ELA. Accordingly, their temperatures were so low, that their rock surfaces were free of flank ice and ice balconies. From the maximum past glacier extension up to the current glacier margins, 13 (altogether 14) glacier stages have been differentiated and in part 14C-dated. They were four glacier stages of the late glacial period, three of the neoglacial period and six of the historical period. By means of 130 medium-sized valley glaciers the corresponding ELA-depressions have been calculated in comparison with the current courses of the orographic snow-line. The number of the glacier stages since the maximum glaciation approx. agrees with that e.g. in the Alps and the Rocky Mountains since the last glacial period. Accordingly, it is interpreted as an indication of the Wurmian age (last glacial period) of the lowest ice margin positions. The current climatic, average glacier snow-line in the research area runs about 5500 m asl. The snow-line depression (ELA) of the last glacial period (Wurm) calculated by four methods has run about 3870 m asl, so that an ELA-depression of c. 1630 m has been determined. This corresponds to a lowering of the annual temperature by c. 8, i.e., 10°C according to the specific humid conditions at that time.

Climate change and human impact on the Song Hong (Red River) Delta, Vietnam, during the Holocene

On the basis of the results of palynological research on two cores from the Song Hong (Red River) delta in the sub-tropical zone of Asia, centennial- to millennial-scale climate changes and human impacts during the Holocene were clarified. Three cycles of cooling and warming were identified during the last 5000 yr: a cool and wet climate during 4530–3340 cal. yr BP, 2100–1540 cal. yr BP, and 620–130 cal. yr BP, a warm and dry climate during 3340–2100 cal. yr BP, 1540–620 cal. yr BP and the present warm climate. The first and last cooling events correspond to global Holocene cooling events, the Neoglacial Period and the Little Ice Age, respectively. Each persisted for 500–1000 yr, and they occurred at intervals of 1500–2000 yr. Pollen records also reflect human impacts on this area, which intensified after 3340 cal. yr BP when large quantities of cultivated Gramineae taxa, possibly including the main wet rice species, Oryza sativa, secondary forest, and other upland cultivated taxa appear in the record.

The Maximum Ice Age (Würmian, Last Ice Age, LGM) Glaciation of the Himalaya – A Glaciogeomorphological Investigation of Glacier Trim-lines, Ice Thicknesses and Lowest Former Ice Margin Positions in the Mt. Everest–Makalu–Cho Oyu Massifs (Khumbu and Khumbakarna Himal) Including Informations on Late-glacial, Neoglacial, and Historical Glacier Stages, their Snow-line Depressions and Ages

In the Khumbu- and Khumbakarna Himalaya an ice stream network and valley glacier system has been reconstructed for the last glacial period (Wurmian, Last Ice Age, Isotope stage 4–2, 60–18 Ka BP, Stage 0) with glaciogeomorphological and sedimentological methods. It was a part of the glacier system of the Himalaya and has communicated across transfluence passes with the neighbouring ice stream networks toward the W and E. The ice stream network has also received inflow from the N, from a Tibetan ice stream network, by the Kyetrak–Nangpa–Bote Koshi Drangka in the W, by the W-Rongbuk glacier valley into the Ngozumpa Drangka, by the Central Rongbuk glacier valley into the Khumbu Drangka and by the antecedent Arun Nadi transverse-valley in the E of the investigation area. The ice thickness of the valley glacier sections, the surface of which was situated above the snow-line, amounted to 1000–1450 m. The most extended parent valley glaciers have measured approx. 70 km in length (Dudh Koshi glacier), 67 km (Barun–Arun glacier) and 80 km (Arun glacier). The tongue end of the Arun glacier has flowed down to ca. 500 m and that of the Dudh Koshi glacier to ca. 900 m a.s.l. At heights of the catchment areas of 8481 (or 8475) m (Makalu), i.e. 8848 (or 8872) m (Mt. Everest, Sagarmatha, Chogolungma) this is a vertical distance of the Ice Age glaciation of ca. 8000 m. The steep faces towering up to 2000 m above the neve areas of the 6000–7000 m-high surfaces of the ice stream network were located 2000–5000 m above the ELA. Accordingly, their temperatures were so low, that their rock surfaces were free of flank ice and ice balconies. From the maximum past glacier extension up to the current glacier margins, 13 (altogether 14) glacier stages have been differentiated and in part 14C-dated. They were four glacier stages of the late-glacial period, three of the neoglacial period and six of the historical period. By means of 130 medium-sized valley glaciers the corresponding ELA-depressions have been calculated in comparison with the current courses of the orographic snow-line. The number of the glacier stages since the maximum glaciation approx. agrees with that e.g. in the Alps and the Rocky Mountains since the last glacial period. Accordingly, it is interpreted as an indication of the Wurmian age (last glacial period) of the lowest ice margin positions. The current climatic, i.e. average glacier snow-line in the research area runs about 5500 m a.s.l. The snow-line depression (ELA) of the last glacial period (Wurm) calculated by four methods has run about 3870 m a.s.l., so that an ELA-depression of ca. 1630 m has been determined. This corresponds to a lowering of the annual temperature by ca. 8, i.e. 10 °C according to the specific humid conditions at that time.

Detection of a possible change point in atmospheric variability in the North Atlantic and its effect on Scandinavian glacier mass balance

Climate change, resulting from an increase in global temperatures, is likely to have a large impact on glaciers and glacier meltwater during the course of the present century resulting in significant contributions to sea level rise. Globally, glaciers are in retreat, partly as a response to the return to warmer conditions after the last neoglacial period during the Little Ice Age but also because of the almost continuous increases evident in global temperature since then. In contrast, Scandinavian glaciers, particularly maritime glaciers, were maintaining equilibrium or advancing over the closing decades of the last century possibly resulting from an increased moisture flux over the North Atlantic. While the more continental glaciers were still declining, the rate of decline diminished during the late 1980s. This coincides with an accelerated rate of increase evident on the maritime glaciers in southwestern Norway. A change point in atmospheric variability in the North Atlantic is identified as having occurred during this period. This change point is associated with an intensification of westerlies over Europe, particularly since the late 1980s, which significantly contributes to increases in temperature and precipitation over northern Europe while suppressing the penetration of warm, moist air into more southern European locations. Regional variations in temperature and precipitation from selected Scandinavian stations are also found to be consistent with the changes in the large-scale modes of atmospheric variability in the North Atlantic. Copyright © 2005 Royal Meteorological Society

A high-resolution Holocene sediment record from Húnaflóaáll, N Iceland margin: centuryto millennial-scale varability since the Vedde tephra

MD99-2269 is a 25 m long core from Hunaflóadll, a deep trough which runs northward towards the shelf break from the narrow neck of land which joins the Northwest Peninsula of Iceland with the ‘mainland’. The core was recovered from the thickest part of an elongate shelf sediment body, underlain by glacial diamictons with ages 26 ka BP. 3.5 kHz profiles indicate the presence of a reflector, RI, which can be traced over long distances. Twelve AMS radiocarbon dates and the presence of the Saksunarvatn tephra (which is the origin for the RI reflector at 21 m core depth) define a linear depth/age relation with an accumulation rate of 200 cm/ky. The date on the core top is ‘modem’. X-radiographs indicate that the sediments are principally massive. bioturbated muds. The data were measured at resolutions of between 5 and 40 yr/sample. Our primary data represent aspects of (a) multisensor track measurements, (b) colour, (c) grain size, (d) sediment properties and (e) sediment magnetic properties. Principal component analysis (PCA) was used to simplify the analysis of these five data sets, and resulted in nine significant axes compared to over 70 original variables. The explained variance on the first axes varied between 47 and 96%. These time series were reduced to a common 50-yr sample interval which were then also subject to PCA. Using the resulting PC scores we present three primary axes of environmental variability in Hunaflóaall that have century-scale quasi-periodicities, and demonstrate that these are highly correlated with specific ‘raw’ variables. We focus on variables linked to changes in grain size and productivity and show regional coherence (cores B997-321 and 330) in the coercivity/grain size measure ARMJ(20)/ARMJ(0), which have a close similarity to the detrended A14C series. This provides a potential link to the vigour of the thermohaline circulation to the north of the Iceland shelf in the Iceland and Greenland Seas. Our data indicate increased variability in our proxies during the Neoglacial period.

Vegetation and climate changes in the Changjiang (Yangtze River) Delta, China, during the past 13,000 years inferred from pollen records

A high-resolution pollen record from 2 boreholes from the Changjiang (Yangtze River) delta shows a series of well-defined changes in vegetation and climate over the last 13,000 yr . In latest Pleistocene to early Holocene time (12,900– 10,300 cal yr BP), pollen dominated by the xerophytic herb Artemisia and common conifers indicate coniferous forest and grasslands and a cool, dry climates, possibly represented by the Younger Dryas. From 10,300 to 9000 cal yr BP, a warm, wet climate fostered the development of mixed broadleaved evergreen–deciduous forests to grow on the grasslands and surrounding hills and uplands. From 9000 to 7600 cal yr BP, the dominance of conifers and the reduction in broadleaved evergreen trees pollen suggest cool, dry conditions. The mid-Holocene “hypsithermal” (7600– 4800 cal yr BP) is represented by a large expansion of subtropical evergreen–deciduous broadleaved forests. Between 4800 and 1300 cal yr BP, which corresponds to a Neoglacial period elsewhere, conifers are dominant, along with common herbs, whereas the area with broadleaved evergreen trees shrink under the cool, dry conditions. The first occurrence of Fagopyrum pollen at 4500 cal yr BP suggests human influence. The significant change in arboreal and herbaceous pollen after 1300 cal yr BP reflects widespread intensive human influence.