Holocene Warm Period Research Articles

Chinese Loess Plateau vegetation since the Last Glacial Maximum and its implications for vegetation restoration

Summary China has been investing heavily in afforestation programmes to control soil erosion on the vast Chinese Loess Plateau (CLP). This massive afforestation has led to a considerable increase in forest and a decrease in dust‐storm activity in some areas. However, there have also been some negative outcomes, including low tree survival rate, increased soil erosion, exacerbated water shortages and deep soil desiccation. One important explanation for these is the use of inappropriate species because of a lack of knowledge of the natural vegetation in the area, which has been largely destroyed by human activities. Natural vegetation in the most recent warm period (the early–mid‐Holocene) can serve as an analogue for the ongoing greening programme, particularly under the global warming scenario. In this study, the natural vegetation of the CLP since the Last Glacial Maximum (LGM) was reconstructed from pollen analyses of six loess sections. Our results show that herbs were dominant both in the cold–dry LGM and the warm–humid early–mid‐Holocene. During the LGM, vegetation in the north‐western CLP mainly consisted of Artemisia, Echinops‐type, Taraxacum‐type and Chenopodiaceae, and vegetation in the south‐eastern CLP was characterized by the same types but with a slightly higher incidence of Poaceae. During the early–mid‐Holocene, vegetation was more diverse, with Poaceae, Artemisia, Echinops‐type and Chenopodiaceae dominant in the north‐west, and Pinus, Corylus, Poaceae, Artemisia and Selaginella sinensis dominant in the south‐east. Synthesis and applications. The ecological restoration of herbs should be considered a priority, although trees and shrubs have been prioritized previously. To balance environmental conservation and farm‐income support objectives, we suggest planting Corylus, Juglans and Selaginella sinensis in the south‐eastern Chinese Loess Plateau (CLP) because of their edible value or medicinal properties. Given the considerable prevalence of Selaginella sinensis and the Asteraceae family in the pollen records, and their useful medicinal effects, the CLP has great potential to be a centre for Chinese medicinal herb production.

Tracing the Nd isotope evolution of North Pacific Intermediate and Deep Waters through the last deglaciation from South China Sea sediments

The intermediate and deep waters of the Pacific Ocean play a crucial role for regulating global climate changes on the millennium timescale. However, due to poor preservation of carbonate sediments in the deep Pacific, little attention has been received to better understand deep ocean circulation and its relationship with abrupt climate events. Here we present the first authigenic Nd isotope (εNd) record extracted from Fe–Mn oxyhydroxides of the South China Sea (SCS) sediments (SO17940-2, 1727m water depth) in order to investigate changes of intermediate and deep-water circulations in the Pacific Ocean since the Last Glacial Maximum (LGM).In general, the seawater εNd record extracted from the SCS sediments paralleled the existing Nd isotopes of fish teeth/debris from the eastern North Pacific core during the last deglaciation, demonstrating that our authigenic εNd can faithfully record the seawater εNd evolution in the deep Pacific Ocean. At the onset of the deglacial period, our data exhibit a clear negative shift in εNd towards a gradually increased component of Antarctica Intermediate Water (AAIW) and reached a maximal influx during the mid Heinrich Stadial 1 (HS1, ∼16kyr BP). Between the HS1 and Younger Dryas, deep-water circulation gradually shifted back to the modern condition during the Bølling-Allerød warm interval. A pronounced negative εNd excursion had occurred during the Pre-Boreal (PB), suggesting a rapid reorganization of deep-water ventilation in the Pacific Ocean and was predominated by AAIW. This is most likely due to poor ventilation in the western North Pacific associated with an intensified summer monsoon during the PB-early Holocene warm period. After the PB period, the seawater εNd values were once again dominated by Pacific Deep Water at the study site.

Oxygen isotope ratios in the shell of <i>Mytilus edulis</i>: archives of glacier meltwater in Greenland?

Abstract. Melting of the Greenland Ice Sheet (GrIS) is accelerating and will contribute significantly to global sea level rise during the 21st century. Instrumental data on GrIS melting only cover the last few decades, and proxy data extending our knowledge into the past are vital for validating models predicting the influence of ongoing climate change. We investigated a potential meltwater proxy in Godthåbsfjord (West Greenland), where glacier meltwater causes seasonal excursions with lower oxygen isotope water (δ18Ow) values and salinity. The blue mussel (Mytilus edulis) potentially records these variations, because it precipitates its shell calcite in oxygen isotopic equilibrium with ambient seawater. As M. edulis shells are known to occur in raised shorelines and archaeological shell middens from previous Holocene warm periods, this species may be ideal in reconstructing past meltwater dynamics. We investigate its potential as a palaeo-meltwater proxy. First, we confirmed that M. edulis shell calcite oxygen isotope (δ18Oc) values are in equilibrium with ambient water and generally reflect meltwater conditions. Subsequently we investigated if this species recorded the full range of δ18Ow values occurring during the years 2007 to 2010. Results show that δ18Ow values were not recorded at very low salinities (< ~ 19), because the mussels appear to cease growing. This implies that Mytilus edulis δ18Oc values are suitable in reconstructing past meltwater amounts in most cases, but care has to be taken that shells are collected not too close to a glacier, but rather in the mid-region or mouth of the fjord. The focus of future research will expand on the geographical and temporal range of the shell measurements by sampling mussels in other fjords in Greenland along a south–north gradient, and by sampling shells from raised shorelines and archaeological shell middens from prehistoric settlements in Greenland.

Climatic trends for the last 70 ky BP in the SE Pacific: the Rano Aroi and Rano Raraku records from Easter Island

This paper discusses a complete record of vegetation history since the Bølling (GI-1e) warming (14,500 cal yr BP) up to the Holocene in Latvia. To date, this is the only complete record of such age in the eastern Baltic area and the northernmost area for which Bølling records are present. Combining pollen evidence, pollen accumulation rates (PAR) and plant macrofossil data, we assess the local and regional vegetation development, and we attempt to separate the true Lateglacial vegetation signal by removing the obviously redeposited thermophilous pollen; however, we remove not only their signal, we discuss the possibilities of separating the redeposition signal of the so-called “local Lateglacial trees”, pine and birch, by looking at their corrosion and degradation. The results show that the Bølling warming in the eastern Baltic area was a treeless tundra community consisting of the shrubs Betula nana, Dryas octopetala and Salix polaris. The Older Dryas cold spell is clearly recognised as a decline in the total concentration of plant macrofossils and PARs at between 14,200 and 13,500 cal yr BP. At 13,460 cal yr BP, the B. nana macrofossils disappear, and tree birch (Betula sect. Albae) appears, marking the start of tree birch forest. The presence of pine forest is confirmed by a variety of macrofossils, including bark, wood, needles and seeds, since 13,400 cal yr BP, at the same time at which pine stomata are found. The first identified pine stomata finds are associated with a Pinus PAR over 3000 grains cm−2 yr−1 and pine macrofossil finds with a Pinus PAR over 4000 grains cm−2 yr−1. During the warmest period of the GI-1a (Allerød) at 13,000–12,700 cal yr BP, a pine forest with deciduous trees (birch – Betula pendula and aspen – Populus tremula) developed in the study area. The Younger Dryas (GS-1) cooling strongly affected the floral composition in eastern Latvia. The PAR of the tree taxa declined abruptly from a maximum value at 12,700 to below 1000 grains cm−2 yr−1 at 12,600 cal yr BP. The response time for the pine forest to collapse was 100 years according to the PAR data. Pine macrofossils disappear simultaneously with the pollen signal at 12,600 cal yr BP, yet occasional Pinus stomata are recorded throughout the Younger Dryas (GS-1). The landscape was treeless shrub tundra again, with D. octopetala, S. polaris, B. nana and Juniperus present. Picea is introduced in the region within the cold Younger Dryas and is represented by stomata (12,400–12,200 cal yr BP), needles, seeds and wood (since 12,050 cal yr BP up to the Holocene). The Pleistocene/Holocene boundary at 11,650 cal yr BP is marked by changes both in vegetation composition and sediment type. The organic rich gyttja accumulated instead of silts and clays, and the start of the Holocene warm period permitted forest re-expansion in eastern Latvia.

A reconstruction of the thawing of the permafrost during the last 170 years on the Taimyr Peninsula (East Siberia, Russia)

Reconstructing the temporal and spatial changes in climate on a seasonal basis during the past few centuries may help us better understand the modern-day interplay between natural and anthropogenic climate variability. The objective of this paper is to reconstruct the thawing of the permafrost at 71°N in Arctic Siberia during the termination of the Little Ice Age and the subsequent Recent Warming period. Sediment samples from two lakes on the Taimyr Peninsula were analysed by high-resolution X-ray fluorescence spectroscopy at a scan resolution of 1mm, and pollen analyses were conducted. The depth-age models of the cores were constructed using 210Pb and 137Cs activity according to the constant rate of supply (CRS) model. The lake sediment cover of these lakes began to form ca. 1840. We defined three periods of increased permafrost thawing during the last 170years. The first maximum of permafrost melting occurred from 1870 to 1880, the second episode was from 1900 to 1930 and the third began between 1960 and 1965. During these periods, the maxima of permafrost melting occurred with a specific time lag following.

Using stochastic population process models to predict the impact of climate change

More than ten years ago a paper was published in which stochastic population process models were fitted to time series of two marine polychaete species in the western Wadden Sea, The Netherlands (Van der Meer et al., 2000). For the predator species, model fits pointed to a strong effect of average sea surface winter temperature on the population dynamics, and one-year ahead model forecasts correlated well with true observations (r=0.90). During the last decade a pronounced warming of the area occurred. Average winter temperature increased with 0.9°C. Here we show that despite the high goodness-of-fit whilst using the original dataset, predictive capability of the models for the recent warm period was poor.

Climate and cyclic hydrobiological changes of the Barents Sea from the twentieth to twenty-first centuries

The Barents Sea is a transition zone between North Atlantic and Arctic waters, so its marine ecosystem is highly sensitive to climate dynamics. Understanding of marine biota response to climate changes is necessary to assess the environmental stability and the state of marketable biological resources. These processes are analyzed using a database from the Murmansk Marine Biological Institute which holds oceanographic and hydrobiological data sets collected for more than 100 years along the meridional Kola Transect in the Barents Sea. The data demonstrate high variability in thermal state of the upper layer of the Barents Sea, which is regulated by varying the inflow of Atlantic water and by regional climate. At irregular intervals, cold periods with extended seasonal ice cover are followed by warm periods. The most recent warm period started in the late 1980s and reached its maximum from 2001 to 2006. These cyclic changes in hydrologic regime across the twentieth century and first decade of the twenty-first century are reflected (with a specific lag of 1–5 years) by changes in species composition, as well as abundance and distribution of boreal and arctic groups of macrozoobenthos and fish fauna. For instance, cod and cod fisheries in the Barents Sea are closely linked to the marine climate. Furthermore, Kamchatka crab stock recruitment benefited from the warm climate of 1989 and 1990. In general, studies in this region have shown that climatic dynamics may be assessed using biological indices of abundance, biomass, and migration of marine organisms, including commercial species.

Coral reefs in the South China Sea: Their response to and records on past environmental changes

This paper reviews both the recent and longer-term (Holocene) ecological history of coral reefs in the South China Sea (SCS). (1) Local ecological monitoring since the 1960s shows that the coral reefs in the South China Sea have declined dramatically, reflecting the rapid decrease of living coral cover and the great loss of symbiotic zooxanthellae. Collectively, this has led to a significant decrease of annual CaCO3 production. Heavy anthropogenic activities and global warming are recognized as major triggers of the observed coral reef degradation. Observations show that the modern coral reefs in the SCS are a source of atmospheric CO2 in summer. (2) Coral reefs of the SCS have been widely used to reveal longer-term environmental variations, including Holocene high-resolution sea surface temperature (SST) and abrupt climate events, millennial-scale El Nino variations, millennial- and centennial-scale sea level oscillations, strong and cyclic storm activities, East Asian monsoon intensities, variation in seawater pH, and recent seawater pollution. (3) Coral reefs of the southern SCS have experienced repeated episodes of bleaching over the last 200 years due to high SST and intense El Nino events; coral reefs of the northern SCS suffered high levels of mortality during several abrupt winter cold-water bleaching events during the middle Holocene warm period. On average, recovery after the middle Holocene cold-bleaching took 20–30 years; recovery following other middle Holocene environmental stresses took approximately 10-20 years. Such findings have significantly contributed to the understanding of the present ecological pressures faced by the coral reefs in the SCS, the histories of Holocene climate/environment changes, and the long-term models of coral reef responses to various past environmental changes.

Climate-related variations in the occurrence and distribution of mackerel (Scomber scombrus) in Icelandic waters

Abstract Astthorsson, O. S., Valdimarsson, H., Gudmundsdottir, A., and Óskarsson, G. J. 2012. Climate-related variations in the occurrence and distribution of mackerel (Scomber scombrus) in Icelandic waters. – ICES Journal of Marine Science, 69: . Based on long-term investigations on sea temperature in Icelandic waters, five climatic periods are defined from the mid-1880s until today. These are a cold period between 1880 and 1920, a warm period between 1921 and 1964, a cold period between 1965 and 1971, one of intermediate conditions (alternating warm and cold) between 1972 and 1995, and finally a warm period from 1996 until today. Mackerel were first reported from Icelandic waters in 1895, were then found intermittently until 1996, and from then appeared almost every year and since 2007 in large numbers in many areas around Iceland. The occurrence of mackerel appears to be confined mainly to warm periods in the North Atlantic Ocean and around Iceland. The unprecedented occurrence and extended distribution of the species began at the onset of the recent warm period during the mid-1990s and, in recent years, 0-group and age 1 mackerel have also been observed in Icelandic waters. This expansion in distribution resulted initially in a bycatch fishery, which then developed into a direct fishery within the Icelandic Exclusive Economic Zone, increasing from ∼1700 t in 2006 to ∼120 000 t in 2009 and 2010.

Lateglacial vegetation dynamics in the eastern Baltic region between 14,500 and 11,400 cal yr BP: A complete record since the Bølling (GI-1e) to the Holocene

This paper discusses a complete record of vegetation history since the Bølling (GI-1e) warming (14,500calyrBP) up to the Holocene in Latvia. To date, this is the only complete record of such age in the eastern Baltic area and the northernmost area for which Bølling records are present. Combining pollen evidence, pollen accumulation rates (PAR) and plant macrofossil data, we assess the local and regional vegetation development, and we attempt to separate the true Lateglacial vegetation signal by removing the obviously redeposited thermophilous pollen; however, we remove not only their signal, we discuss the possibilities of separating the redeposition signal of the so-called “local Lateglacial trees”, pine and birch, by looking at their corrosion and degradation. The results show that the Bølling warming in the eastern Baltic area was a treeless tundra community consisting of the shrubs Betula nana, Dryas octopetala and Salix polaris. The Older Dryas cold spell is clearly recognised as a decline in the total concentration of plant macrofossils and PARs at between 14,200 and 13,500calyrBP. At 13,460calyrBP, the B. nana macrofossils disappear, and tree birch (Betula sect. Albae) appears, marking the start of tree birch forest. The presence of pine forest is confirmed by a variety of macrofossils, including bark, wood, needles and seeds, since 13,400calyrBP, at the same time at which pine stomata are found. The first identified pine stomata finds are associated with a Pinus PAR over 3000grainscm−2yr−1 and pine macrofossil finds with a Pinus PAR over 4000grainscm−2yr−1. During the warmest period of the GI-1a (Allerød) at 13,000–12,700calyrBP, a pine forest with deciduous trees (birch –Betula pendula and aspen –Populus tremula) developed in the study area. The Younger Dryas (GS-1) cooling strongly affected the floral composition in eastern Latvia. The PAR of the tree taxa declined abruptly from a maximum value at 12,700 to below 1000grainscm−2yr−1 at 12,600calyrBP. The response time for the pine forest to collapse was 100 years according to the PAR data. Pine macrofossils disappear simultaneously with the pollen signal at 12,600calyrBP, yet occasional Pinus stomata are recorded throughout the Younger Dryas (GS-1). The landscape was treeless shrub tundra again, with D. octopetala, S. polaris, B. nana and Juniperus present. Picea is introduced in the region within the cold Younger Dryas and is represented by stomata (12,400–12,200calyrBP), needles, seeds and wood (since 12,050calyrBP up to the Holocene). The Pleistocene/Holocene boundary at 11,650calyrBP is marked by changes both in vegetation composition and sediment type. The organic rich gyttja accumulated instead of silts and clays, and the start of the Holocene warm period permitted forest re-expansion in eastern Latvia.

Late Quaternary environmental and landscape dynamics revealed by a pingo sequence on the northern Seward Peninsula, Alaska

A terrestrial sediment sequence exposed in an eroding pingo provides insights into the late-Quaternary environmental history of the northern Seward Peninsula, Alaska. We have obtained the first radiocarbon-dated evidence for a mid-Wisconsin thermokarst lake, demonstrating that complex landscape dynamics involving cyclic permafrost aggradation and thermokarst lake formation occurred over stadial–interstadial as well as glacial–interglacial time periods. High values of Picea pollen and the presence of Larix pollen in sediments dated to 50–40 ka BP strongly suggest the presence of forest or woodland early in MIS 3; the trees grew within a vegetation matrix dominated by grass and sedge, and there is indirect evidence of grazing animals. Thus the interstadial ecosystem was different in structure and composition from the Holocene or from the preceding Last Interglacial period. An early Holocene warm period is indicated by renewed thermokarst lake formation and a range of fossil taxa. Multiple extralimital plant taxa suggest mean July temperatures above modern values. The local presence of spruce during the early Holocene warm interval is evident from a radiocarbon-dated spruce macrofossil remain and indicates significant range extension far beyond the modern tree line. The first direct evidence of spruce in Northwest Alaska during the early Holocene has implications for the presence of forest refugia in Central Beringia and previously assumed routes and timing of post-glacial forest expansion in Alaska.

Has the Problem of a Permanent El Niño been Resolved for the Mid-Pliocene?

AbstractThe mid-Pliocene, the most recent warm geo-logical period, is thought to be indicative of the fate of the Earth's climate under global warming. Earlier evidence has suggested that permanent El Nino-like conditions existed in the mid-Pliocene, though the concept of a permanent El Nino remains controversial. Here, the authors analyzed Nino3.4 SST in pre-industrial and mid-Pliocene simulations with the low-resolution version of the Norwegian Earth System Model (NorESM-L). The simulated mid-Pliocene Nino3.4 SST, with a smaller standard deviation, indicated that a weaker ENSO existed in the mid-Pliocene relative to the pre-industrial experiment. Compared with earlier modeling studies, our simulations show that the problem of ENSO's standard deviations in the mid-Pliocene remains unresolved, although the mean and the period of ENSO in the mid-Pliocene have been re-solved by earlier geological and modeling studies.

Environmental changes in southeastern Amazonia during the last 25,000 yr revealed from a paleoecological record

New pollen, micro-charcoal, sediment and mineral analyses of a radiocarbon-dated sediment core from the Serra Sul dos Carajás (southeast Amazonia) indicate changes between drier and wetter climatic conditions during the past 25,000yr, reflected by fire events, expansion of savanna vegetation and no-analog Amazonian forest communities. A cool and dry last glacial maximum (LGM) and late glacial were followed by a wet phase in the early Holocene lasting for ca. 1200yr, when tropical forest occurred under stable humid conditions. Subsequently, an increasingly warm, seasonal climate established. The onset of seasonality falls within the early Holocene warm period, with possibly longer dry seasons from 10,200 to 3400calyr BP, and an explicitly drier phase from 9000 to 3700calyr BP. Modern conditions with shorter dry seasons became established after 3400calyr BP. Taken together with paleoenvironmental evidence from elsewhere in the Amazon Basin, the observed changes in late Pleistocene and Holocene vegetation in the Serra Sul dos Carajás likely reflect large-scale shifts in precipitation patterns driven by the latitudinal displacement of the Inter-Tropical Convergence Zone and changes in sea-surface temperatures in the tropical Atlantic.

How the aggressiveness of rainfalls in the Mediterranean lands is enhanced by climate change

Rainfall and overland flow are fundamental processes for Earth’s ecosystems but can also be land disturbing forces, particularly when triggered by extreme hydro-meteorological events. Examples of these extremes are rainstorms and related phenomena due to rainfall aggressiveness. They produce high-impact land processes such as soil erosion and nutrient losses. Economic and social consequences of these processes can be quite severe. However, hydrological extremes and their environmental implications are still poorly understood, particularly if analyzed in the context of climate change. Here, we analyze a 300 year long times series of historical rainfall patterns across the Mediterranean in the last three centuries and we investigate changes in the erosive forcing as related to climate changes. Our results show that the erosive forcing increased towards the end of the Little Ice Age (~1850) over western and central Mediterranean and that has been increasing in the recent warming period at low Mediterranean latitudes, due to a higher frequency of intensive storms. Such increased concentrated precipitation may lead to an intensification of land degradation processes triggered by soil erosion and transport across a range of scales from hillslopes to small catchments.

On the recent strengthening of the relationship between Palmer Drought Severity Index and teak ( Tectona grandis L. F.) tree-ring width chronology from Maharashtra, India: A case study

Tree growth-climate relationship analysis revealed the important role of soil moisture availability in development of annual growth rings. Winter season (October–March) Palmer Drought Severity Index (PDSI) is an important factor in developing annual tree-rings during subsequent growing seasons. The chronology was strongly correlated with winter PDSI in recent few decades, more so than in the earlier period, indicating that tree growth is more dependent on climate. Many low growth years detected during El Nino events are probably related to moisture deficiency. The result indicates that the tree growth is mostly affected by the soil moisture availability during the recent warm periods over the region.

Simulation of sea surface temperature changes in the Middle Pliocene warm period and comparison with reconstructions

The Middle Pliocene (ca 3.12–2.97 Ma) is a recent warm period in the Earth’s history. In many respects, the warmth of the Middle Pliocene is similar to the probable warm situation of the late 21st century predicted by climate models. Understanding the Middle Pliocene climate is important in predicting the future climate with global warming. Here, we used the latest reconstructions for the Middle Pliocene—Pliocene Research Interpretation and Synoptic Mapping (PRISM) version 3—to simulate the Middle Pliocene climate with a fully coupled model Fast Ocean Atmosphere Model. From comparison of the results of simulations with reconstructions, we considered two important scientific topics of Middle Pliocene climate modeling: extreme warming in the subpolar North Atlantic and a permanent El Niño in the tropical Pacific. Our simulations illustrate that the global annual mean sea surface temperature (SST) in the Middle Pliocene was about 2.3°C higher than that in the pre-industrial era. The warming was stronger at mid- and high latitudes than at low latitudes. The simulated SST changes agree with SST reconstructions in PRISM3 data, especially for the North Atlantic, North Pacific and west coast of South America. However, there were still discrepancies between the simulation of the SST and reconstructions for the subpolar North Atlantic and tropical Pacific. In the case of the Atlantic, the weakened meridional overturning circulation in the simulation did not support the reconstruction of the extremely warm condition in the subpolar North Atlantic. In the case of the tropical Pacific, the whole ocean warmed, especially the eastern tropical Pacific, which did not support the permanent El Niño suggested by the reconstruction. From evaluation of the modeling and reconstruction, we suggest that the above discrepancies were due to uncertainties in reconstructions, difficulties in paleoclimate modeling and deficiencies of climate models. The discrepancies should be reduced through consideration of both the modeling and data.

Periodic oscillations in millennial global-mean temperature and their causes

Time series of solar radiation and north Pacific sea surface temperature (SST) index were used to analyze their causality relationship with various periodic oscillations in reconstructed millennial global-mean temperature series. The three long-term periods of the Medieval Warm Period (MWP), Little Ice Age (LIA) and recent Global Warming Period (GWP) were distinct in the temperature series. 21-year, 65-year, 115-year and 200-year oscillations were derived from the temperature series after removing three long-term climatic temperatures. The phases of temperature oscillations significantly lagged behind oceanic SST and solar radiation variability. The recent decadal warm period was caused by the quasi-21-year temperature oscillation. At this century-cross period, the four oscillations reached their peaks simultaneously, which did not occur during the last millennium. Based on the long-term trend during the GWP and the four periodic oscillations, global-mean temperature is expected to drop to a new cool period in the 2030s and then a rising trend would be towards to a new warm period in the 2060s.

Pore fluid modeling approach to identify recent meltwater signals on the west Antarctic Peninsula

The sensitivity of sea level to melting from polar ice sheets and glaciers during recent natural and anthropogenic climate fluctuations is poorly constrained beyond the period of direct observation by satellite. We have investigated glacial meltwater events during the Anthropocene by adapting the pioneering approach of modeling trends in δ18O in the pore waters of deep‐sea cores, previously used to constrain the size of ice sheets during the Last Glacial Maximum. We show that during recent warm periods, meltwater from glacier retreat drains into the coastal fjords, leaving a signature of depleted δ18O values and low Cl concentrations in the pore water profiles of rapidly accumulating sediments. Here we model such pore water profiles in a piston core to constrain the timing and magnitude of an ice sheet retreat event at Caley Glacier on the west Antarctic Peninsula, and the result is compared with local ice front movement. This approach of pore water modeling was then applied in another kasten core and tested by a series of sensitivity analyses. The results suggest that our approach may be applied in fjords of different sedimentary settings to reconstruct the glacier history and allow insight into the sensitivity of polar glaciers to abrupt warming events.

Evolution of a debris-charged glacier landsystem, Kvíárjökull, Iceland

Please click here to download the map associated with this article. A time-series of 1:12,500 scale maps of the snout and foreland of the Icelandic glacier Kvíárjökull provides a spatial and temporal assessment of landform evolution from a debris-charged glacier snout over a 58 year period between 1945 and 2003. In addition to providing a valuable record of glacier recession over a period of recent global warming, the maps enable the elaboration of existing conceptual models of the debris-charged glacier landsystem based on measurable process-form relationships. Features were identified using a combination of DEM visualization, morphometric analysis, stereoscopic viewing of aerial photographs and field verification. The maps contain twelve colour coded surficial geology units displayed as polygons and various geomorphological features represented by a combination of lines and points. The spatial and temporal evolution of the landforms on the glacier foreland indicate that the snout of Kvíárjökull has been undergoing active retreat and incremental stagnation over the study period. The maps serve as excellent modern landsystem analogues for palaeoglaciological reconstructions in similar climatic and topographic settings.

Differences between tree species seedling and adult altitudinal distribution in mountain forests during the recent warm period (1986–2006)

Spatial fingerprints of climate change on tree species distribution are usually detected at latitudinal or altitudinal extremes (arctic or alpine tree line), where temperatures play a key role in tree species distribution. However, early detection of recent climate change effects on tree species distribution across the overall temperature gradient remains poorly explored. Within French mountain forests, we investigated altitudinal distribution differences between seedling (≤50 cm tall and >1 yr old) and adult (>8 m tall) life stages for 17 European tree taxa, encompassing the entire forest elevation range from lowlands to the subalpine vegetation belt (50–2250 m a.s.l.) and spanning the latitudinal gradient from northern temperate to southern Mediterranean forests. We simultaneously identified seedlings and adults within the same vegetation plots. These twin observations gave us the equivalent of exactly paired plots in space with seedlings reflecting a response to the studied warm period (1986–2006) and adults reflecting a response to a former and cooler period. For 13 out of 17 species, records of the mean altitude of presence at the seedling life stage are higher than that at the adult life stage. The low altitudinal distribution limit of occurrences at the seedling life stage is, on average, 29 m higher than that at the adult life stage which is significant. The high altitudinal distribution limit also shows a similar trend but which is not significant. Complementary analyses using modelling techniques and focusing on the optimum elevation (i.e. the central position inside distribution ranges) have confirmed differences between life stages altitudinal distribution. Seedlings optima are mostly higher than adults optimum, reaching, on average, a 69 m gap. This overall trend showing higher altitudinal distribution at the seedling life stage in comparison to the adult one suggests a main driver of change highly related to elevation, such as climate warming that occurs during the studied period. Other drivers of change that could play an important role across elevation or act at more specific scales are also discussed as potential contributors to explain our results.