Holocene Chronology Research Articles

Human-environment interaction during the Mesolithic- Neolithic transition in the NE Iberian Peninsula. Vegetation history, climate change and human impact during the Early-Middle Holocene in the Eastern Pre-Pyrenees

The synthetic analysis of several pollen records from sub-Mediterranean lowland Pre-Pyrenean regions evidences expansion of forests during the Early Holocene in Northeastern Iberia and the establishment of dense deciduous broadleaf forests during the Holocene Climate Optimum. Pollen records show the broadleaf deciduous forests resilience against cooling phases during the Mid-Holocene period, with slight regressions of oak woodlands and expansion of conifers or xerophytic taxa contemporary to some cooling episodes (i.e. 8.2 and 7.2 kyr cal. BP). Major vegetation changes influenced by climate change occurred in the transition to the Late Holocene, in terms of the start of a succession from broadleaf deciduous forests to evergreen sclerophyllous woodlands.The lack of evidence of previous occupation seems to support the Neolithisation of the NE Iberian Peninsula as a result of a process of migration of farming populations to uninhabited or sparsely inhabited territories. In that context, remarkable changes in vegetation were recorded from 7.3 kyr cal. BP onwards in the Lake Banyoles area, where the establishment of permanent farming settlements caused the deforestation of oak woodlands. In La Garrotxa region, short deforestation episodes affecting broadleaf deciduous forests, together with expansion of grasslands and presence of Cerealia-t were documented in the period 7.4–6.0 kyr cal. BP. Finally, in the coastal area, where less evidence of Early Neolithic occupations is recorded, evidence of Neolithic impact is reflected in the presence of Cerealia-t in 6.5–6.2 kyr cal. BP, but no strong human transformation of landscape was carried out until more recent chronologies.

Taxonomic reassignment of the Paleolithic human navicular from Cueva de los Torrejones (Guadalajara, Spain)

Evidence of human activity and hominin remains are very scarce inland on the Iberian Peninsula. This fact raises the issue of the scarcity of evidence that Paleolithic Homo sapiens occupied this area outside of the littoral margins (Atlantic, Cantabrian, and Mediterranean coasts). Here, we comparatively describe a human right adult navicular bone recovered in the Cueva de los Torrejones site, located in the village of Tamajon (Guadalajara, Spain). This fossil was preliminarily established as belonging to Homo cf. neanderthalensis, due to the late Pleistocene faunal association, mainly because of the presence of Crocuta crocuta and Panthera pardus. The metrical and morphological study of the navicular T93-S3.27 from Cueva de los Torrejones clearly differentiates it from Neandertals and their ancestors, the hominins from Sima de los Huesos, allowing for this fossil to be taxonomically assigned with confidence as H. sapiens. The navicular from the Cueva de los Torrejones is absolutely and relatively medio-laterally narrow with a low wedging index as those of fossil and modern H. sapiens, and clearly different of Neandertals. The increased discoveries and publications of new naviculars belonging to genus Homo, together with the findings of P. pardus and C. crocuta in more recent chronologies in the Iberian Peninsula, are compatible with this reevaluation. We propose a probable chronology for this fossil between 12 and 15 ka and ca. 25 ka, based on the biostratigraphy and the oldest presence of H. sapiens in the Iberian Peninsula. This work confirms the human presence within the Iberian Peninsula during the Upper Paleolithic and reopens the question of the peopling of the inner Peninsula during this period.

Micromorphology of late Pleistocene and Holocene sediments and a new interpretation of the Holocene chronology at Anderson Pond, Tennessee, USA

AbstractThin-section (micromorphological) analysis of samples from the upper 1.5 m of a core obtained in 2007 from Anderson Pond, Tennessee, reveals a coherent but discontinuous record of late Pleistocene and Holocene climate change that supports some interpretations from previous pollen and charcoal analyses but indicates a revised Holocene chronology for this classic pollen site. Legacy sediments recording anthropogenic disturbance compose the upper 65 cm of the core (<160 cal yr BP) and are characterized by mixed, darker-colored, and coarser-grained deposits containing reworked soil aggregates, which sharply overlie finer-grained and lighter-colored, rooted middle Holocene sediments interpreted as a paleosol. These mid-Holocene sediments (95–65 cm; 7100–5600 cal yr BP) record extensive warm-dry subaerial soil conditions during the middle Holocene thermal maximum, manifested by illuviated clay lining root pores, and also contain abundant charcoal. Late Pleistocene sediments (150–95 cm), dark-colored and organic-rich, record open-water conditions and include siliceous aggregate grains at 143–116 cm (14,300–13,900 cal yr BP), recording intense fires. Thin sections are not commonly used in studies of paleoclimate from Quaternary lacustrine sediments, but we advocate for their inclusion in multianalytical approaches because they enhance resolution of depositional and pedogenic processes.

Revisión radiocarbónica y cronocultural del Neolítico antiguo de la Balma Margineda (Aixovall, Andorra)

This work discusses the radiocarbon evidence from the Neolithic layers of the Balma Margineda (Andorra). Since the last excavation campaigns during the ‘90s, a total of ten 14C dates has been obtained. We discuss their stratigraphic provenance and suggest that only three of the ten 14C dates should be considered reliable. The new dates assign the Neolithic occupations to a more recent chronology. Moreover, we also present a brief revision of the ceramic and lithic materials from the in situ Neolithic layers, in order reinterpret the site using the most recent data on the Early Neolithic of Pyrenean region.

Biases in RCS tree ring chronologies due to sampling heights of trees

The Regional Curve Standardization (RCS) is one of the most employed standardization methods to remove biological signals in long tree ring chronologies. The approach assumes that an overall age-related growth trend typify all tree ring series to be included in a standardized tree ring chronology. Although several potential problems of the method have been examined, the influence of varying the sampling height along tree stems has not been evaluated. Considering that age-related growth trends may vary with stem height, biases may arise when combining samples from unknown or variable sampling heights, a frequent situation with subfossil logs. In this study we perform a detailed stem analysis of 15 lakeshore black spruce (Picea mariana Mill. B.S.P.) trees in the taiga of eastern Canada to describe how the age-related growth trend varies with stem height and evaluate associated biases in RCS chronologies built from living and subfossil trees. Results show that the age-related growth trends vary markedly and systematically along stems, potentially generating large methodological biases in RCS chronologies, especially near the recent chronology end. These biases may lead to erroneous reconstructions of recent climatic trends and cause false divergence between tree ring and climate series. We have developed a correction procedure that appears efficient in removing these biases from chronologies built with the lakeshore trees and associated subfossil logs.

Rebecca Weaver-Hightower and Peter Hulme, eds., Postcolonial Film: History, Empire, Resistance

Presenting “a cross-section of cutting edge postcolonial research on international cinema, research focused on more recent chronologies, new spaces and emerging technologies” (2), the book comprises twelve chapters, each analysing a single film plus an afterword. The selection of films spans forty-five years from Gillo Pontecorvo’s Italian-Algerian Battle of Algiers (1965) to Dakxin Bajrange Chhara’s The Lost Water: A Salt Worker’s Life (2010). Including fiction and documentary, the objective...

Asynchrony in key Holocene chronologies: Evidence from Irish bog pines

The Greenland Ice Core Chronology 2005 (GICC05) and the radiocarbon calibration curve (IntCal) are the foremost time scales used in paleoclimatic and paleoenvironmental studies of the most recent 10 k.y. Due to varying and often insufficient dating resolution, opportunities to test the synchrony of these two influential chronologies are rare. Here we present evidence for a phase of major pine recruitment on Irish bogs at ca. 8160 yr B.P. Dendrochronological dating of subfossil trees from three sites reveals synchronicity in germination across the study area, indicative of a regional forcing. The concurrent colonization of pine on peatland is interpreted in terms of drier surface conditions and provides the first substantive proxy data in support of a significant hydroclimatic change in the north of Ireland accompanying the 8.2 ka climate cooling event. The date of pine establishment does not overlap with the GICC05 age range for the event, and possible lags between responses are unlikely to explain the full difference. In light of recent studies highlighting a possible offset in GICC05 and IntCal dates, the Irish pine record supports the notion of ice core dates being too early during the period of study. If the suggested discrepancy in timing is an artifact of chronological error, it is likely to have affected interpretations of previous proxy comparisons and alignments.

Development of recent chronologies and evaluation of temporal variations in Pb fluxes and sources in lake sediment and peat cores in a remote, highly radiogenic environment, Cairngorm Mountains, Scottish Highlands

The use of stable Pb isotope analyses in conjunction with recent (210Pb and anthropogenic radionuclide) chronologies has become a well-established method for evaluating historical trends in depositional fluxes and sources of atmospherically deposited Pb using archival records in lake sediment or peat cores. Such studies rely upon (i) simple radioactive disequilibrium between unsupported 210Pb and longer-lived members of the 238U decay series and (ii) well-defined values for the isotopic composition of contaminant Pb and indigenous Pb in the study area. However, areas of high natural radioactivity can present challenging environments for such studies, with potential complications arising from more complex disequilibria in the 238U decay series and the occurrence, at local or regional level, of anomalous, ill-defined stable isotope ratios due to the presence of elevated levels of radiogenic Pb.Results are presented here for a study of a sediment core from a freshwater lake, Loch Einich, in the high natural radioactivity area of the Cairngorm Mountains of Scotland. 238U decay series disequilibria revealed recent diagenetic re-deposition of both U and 226Ra, the latter resulting in a requirement to use a modified calculation to derive a 210Pb chronology for the core. Confidence in the chronology was provided by good agreement with the independent 241Am chronology, but the 137Cs distribution was affected by significant post-depositional mobility in the organic-rich sediment. The systematics of variations in 230Th, 232Th and stable Pb isotope ratio distributions were used to establish the indigenous Pb characteristics of the sediment. The relatively high radiogenic content of the indigenous Pb resulted in complications in source apportionment, in particular during the 20th century, with multiple natural and anthropogenic sources precluding the use of a simple binary mixing model. Consequently, 206Pb/207Pb ratios in Scottish moss samples from an archive collection were used to provide the input term for atmospheric deposition in order to establish historical trends in indigenous and anthropogenic Pb fluxes.A test of the accuracy of the derived Pb fluxes was provided by analysis of a core from a nearby blanket peat deposit, Great Moss. Independent atmospheric and basal inputs gave a complex distribution of 210Pb in the peat, but this did not affect calculation of a 210Pb chronology. Once again, the 210Pb chronology was supported by the 241Am distribution.Temporal trends in anthropogenic Pb deposition derived for the Loch Einich sediment core were in generally good agreement with those for the Great Moss peat core, other peat cores and some other lake sediment cores from northern Scotland, providing confidence in the use of the archive moss data to characterise atmospheric deposition. However, sustained input of Pb to Loch Einich sediment at relatively high levels in the late 20th century, after the regional decline in atmospheric Pb deposition, suggested that catchment-derived Pb is now a significant component of the depositional flux for Loch Einich.

Tracking the impact of mid- to late Holocene climate change and anthropogenic activities on Lake Holzmaar using an updated Holocene chronology

The mid- to late Holocene interval is characterised by a highly variable climate in response to a gradual change in orbital insolation. The seasonal impact of these changes on the Eifel Maar region is not yet well documented largely due to uncertainties about the completeness of this archive (“missing varves” in the well known Lake Holzmaar) and a limited understanding of the factors (e.g. temperature, precipitation) influencing the seasonality archived within the lamination/varves. In this study we approach these challenges from a different perspective. Using detailed microfacies investigations we: (1) demonstrate that the ambiguity about the “missing varves” is related to the climate induced complex biotic and abiotic laminations that led to mis-identification of varves; (2) use a combination of detailed microfacies investigations (varve structure, seasonality of biotic and abiotic signals), lamination quality, varve counts on multiple cores, published and new radiocarbon dates to develop a continuous master chronology based on the Bayesian modelling approach. The dates of major climate, volcanic, and archaeological event(s) determined using our model are in good agreement with the independently determined ages of the same events from other archives, confirming the accuracy of our age model; (3) test the sensitivity of the seasonal proxies to the available data on mid-Holocene changes in temperature and precipitation; (4) demonstrate that the changes in lake eutrophicity are correlative with temperature changes in NW Europe and probably triggered by solar variability; and (5) show that the early Iron Age onset of eutrophication in Lake Holzmaar was climate induced and began several decades before the impact of anthropogenic activity was seen in the form of intensified detrital erosion in the catchment area. Our work has implications for understanding the impact of climate change and anthropogenic activities on limnological systems.

From the Allerød to the mid-Holocene: palynological evidence from the south basin of the Caspian Sea

Pollen and dinoflagellate cysts have been analysed in a core from the south basin of the Caspian Sea, providing a picture of respectively past vegetation and water salinity for the Late Pleistocene to middle Holocene. A relatively sharp lithological change at 0.86 m depth reflects a shift from detrital silts to carbonates-rich fine silts. From this depth upwards, a Holocene chronology is built based on ten radiocarbon dates on ostracod shells and bulk carbonates.From the vegetation point of view, the Late Pleistocene deserts and steppes were partially replaced in the most sheltered areas by an open woodland with Pinus, Juniperus-Hippophae-Elaeagnus and even Alnus-Quercus-Pterocarya and Fraxinus, related to the Allerød palynozone. This was interrupted by the Younger Dryas palynozone when Artemisia reaches a maximum in a first instance followed by a very dry phase with only a slight return of Pinus and Quercus and the rare presence of Ulmus-Zelkova. From 11.5 to 8.4 cal. ka BP, an open landscape dominated by shrubs such as Ephedra and progressively increasing Quercus appeared. The final spread of diverse evergreen and deciduous trees is delayed and occurs after 8.4 cal. ka BP. It is suggested that this delay is caused by an arid climate in the Early Holocene linked to high insolation and perhaps to a lake effect.The dinocyst assemblages fluctuate between slightly brackish (Pyxidinopsis psilata and Spiniferites cruciformis, 7 psu and lower) and more brackish (Impagidinium caspienense, ∼13 psu). In the Lateglacial (Khvalynian highstand), the assemblages remained dominated by relative low salinity taxa. A late and brief increase of salinity occurred prior to 11.2 cal. ka BP associated with the Mangyshlak lowstand. It is suggested that it was caused by a brief drop in meltwater flow from both the north and the southeast (Uzboy) and a likely evaporation increase. This lowstand occurs quasi at the same time as the end of a longer lowstand in the Black Sea. The freshest waters are then inferred as having occurred between 8.4 and ≤4.4 cal. ka BP, linked to a connection with the Amu Darya and the melting glaciers on the Pamir Mountains.The Caspian Sea is a sensitive environment, easily perturbed by global climatic changes, such as the Allerød and Holocene warming, and the Lateglacial and Younger Dryas cooling, as well as by regional changes in its hydrography, such as shifts in the Eurasian meltwater and the Volga and Amu Darya inflows.

Late Holocene chronology and geomorphic development of fluvial–tidal floodplains in the upper reaches of the lower Columbia River Valley, Washington and Oregon, USA

The upper reaches of the lower Columbia River Valley (125km in length) comprise an alluvial system that is transitional between fluvial and fluvial–tidal dominance. Sinuous channels separate elongate islands (1–8km in length) and floodplains (0.5–12.7km in total width). Thirty-six floodplain overbank deposits are analyzed for age and depth, which demonstrate an average sedimentation rate of 1.6mka−1 during the last 5–6ka. Older core records confirm that long-term depositional rates are controlled by relative sea level rise. Rising floodplain groundwater surfaces, which followed relative sea level rise (~1.25mka−1), submerged isolated floodplain depressions. Low sedimentation rates in the isolated depressions (0.6–1.1mka−1) maintained large ellipsoidal bullseye lakes (7–22km2 in area) dating back to 3.5–4.0ka. Increases in the widths of the floodplains and bullseye lakes are associated with broadening of the incised valley (4–13km width) in the Portland Basin. Dated basal overbank deposits (0.5–5.0ka in age) and their separation distances establish channel migration rates of 0.3–1.9kmka−1. Shallow burial rates relative to rapid channel migration rates resulted in reworking of late Holocene floodplains (50–75% erosion) since 5ka in the upper reaches of the lower Columbia River Valley.

Reassessing the evidence for tree-growth and inferred temperature change during the Common Era in Yamalia, northwest Siberia

The development of research into the history of tree growth and inferred summer temperature changes in Yamalia spanning the last 2000 years is reviewed. One focus is the evolving production of tree-ring width (TRW) and tree-ring maximum-latewood density (MXD) larch (Larix sibirica) chronologies, incorporating different applications of Regional Curve Standardisation (RCS). Another focus is the comparison of independent data representing past tree growth in adjacent Yamalia areas: Yamal and Polar Urals, and the examination of the evidence for common growth behaviour at different timescales. The sample data we use are far more numerous and cover a longer time-span at Yamal compared to the Polar Urals, but Yamal has only TRW, while there are both TRW and MXD for the Polar Urals. We use more data (sub-fossil and from living trees) than in previous dendroclimatic studies in this region. We develop a new TRW chronology for Yamal, more than 2000 years long and running up to 2005. For the Polar Urals we develop new TRW and MXD chronologies that show good agreement at short (<15 years) and medium (15–100 years) timescales demonstrating the validity of attempts to reconcile the evidence of longer-timescale information that they provide. We use a “conservative” application of the RCS approach (two-curve signal-free RCS), guarding against the possibility of “modern sample bias”: a possible inflation of recent chronology values arising out of inadvertent selection of mostly relatively fast-growing trees in recent centuries. We also transform tree indices to have a normal distribution to remove the positive chronology skew often apparent in RCS TRW chronologies. This also reduces the apparent magnitude of 20th century tree-growth levels.There is generally good agreement between all chronologies as regards the major features of the decadal to centennial variability. Low tree-growth periods for which the inferred summer temperatures are approximately 2.5 °C below the 1961–90 reference are apparent in the 15-year smoothed reconstructions, centred around 1005, 1300, 1455, 1530, particularly the 1810s where the inferred cooling reaches −4 °C or even −6 °C for individual years, and the 1880s. These are superimposed on generally cool pre-20th century conditions: the long-term means of the pre-1900 reconstructed temperature anomalies range from −0.6 to −0.9 °C in our alternative reconstructions. There are numerous periods of one or two decades with relatively high growth (and inferred summer temperatures close to the 1961–1990 level) but at longer timescales only the 40-year period centred at 250 CE appears comparable with 20th century warmth. Although the central temperature estimate for this period is below that for the recent period, when we take into account the uncertainties we cannot be highly confident that recent warmth has exceeded the temperature of this earlier warm period. While there are clear warm decades either side of 1000 CE, neither TRW nor MXD data support the conclusion that temperatures were exceptionally high during medieval times. One previous version of the Polar Urals TRW chronology is shown here to be in error due to an injudicious application of RCS to non-homogeneous sample data, partly derived from root-collar samples that produce spuriously high chronology values in the 11th and 15th centuries. This biased chronology has been used in a number of recent studies aimed at reconstructing wider scale temperature histories. All of the chronologies we have produced here clearly show a generally high level of growth throughout their most recent 80 years. Allowing for chronology and reconstruction uncertainty, the mean of the last 100 years of the reconstruction is likely warmer than any century in the last 2000 years in this region.

LA ARQUEOFAUNA DEL SUDESTE DE SIERRA BAGUALES DURANTE EL HOLOCENO: EL SITIO CERRO LEÓN 3 (SANTA CRUZ, ARGENTINA)

this paper presents the study of the archaeofaunal remains recovered at the Cerro Leon 3 archaeological site ( santa Cruz, argentina), with early to Late holocene chronology. the measurement of taxonomic and skeletal part abundance, the general patterns of bone frequency and the distribution as well as pre and postdepositional modifications are assessed. the integration of archaeofaunal analyses

Testing climate–proxy stationarity throughout the Holocene: an example from the varved sediments of Lake Meerfelder Maar (Germany)

Lake Meerfelder Maar (Germany) provides a varved record from the Last Glacial/Interglacial transition back to ca 1500 years BP. This study shows results for the Holocene sequence from new cores collected in 2009 based on varve counting, microfacies and micro-XRF analyses. The main goal of combining those analyses is to provide a new approach for interpreting long-term palaeolimnological proxy data and testing the climate–proxy stationarity throughout the current interglacial period. Varve counting provides a new independent Holocene chronology (MFM2012) with an estimated counting error of 1–0.5% and supported by 14C dating. Varve structure and thickness and geochemical composition of the varves give information about the main environmental processes that affect the lake and its catchment as well as the possible climate variability behind. Varves are couplets of i) a spring/summer laminae composed of monospecific diatom blooms and ii) an autumn/winter sub-layer made of minerogenic material and reworked sediments. Thickness of the varves and sub-layers reflect lake variability and allow seasons to be distinguished as well as seasonal proxies. Changes in the winter minerogenic influx into the lake are reflected by Ti intensities and the Si/Ti ratio as an indicator for diatom concentration, which can be used as a proxy for water circulation during the early spring. Long-term variability of geochemical composition shows a reduction of the detrital material input (Ti) at 5000 varve yrs BP and a visible sensitivity to water mixing (Si/Ti) during the Late Holocene. Variations of Ti intensities during the early and mid-Holocene do not show a clear relationship with climate. In contrast, higher values of the Si/Ti ratio together with thicker varves have been interpreted as wind-stress phases, which coincide with centennial variability of European cold/wet episodes during the Late Holocene. Our findings show that a long-term change in the lake and/or variability of the climate system can influence proxy sensitivity of a lacustrine record.

The Holocene boreal forest dynamics in the western range limit of the Siberian Larch (Larix sibirica): evidence from stomata, pollen and charcoal records from small hollows

The development of research into the history of tree growth and inferred summer temperature changes in Yamalia spanning the last 2000 years is reviewed. One focus is the evolving production of tree-ring width (TRW) and tree-ring maximum-latewood density (MXD) larch (Larix sibirica) chronologies, incorporating different applications of Regional Curve Standardisation (RCS). Another focus is the comparison of independent data representing past tree growth in adjacent Yamalia areas: Yamal and Polar Urals, and the examination of the evidence for common growth behaviour at different timescales. The sample data we use are far more numerous and cover a longer time-span at Yamal compared to the Polar Urals, but Yamal has only TRW, while there are both TRW and MXD for the Polar Urals. We use more data (sub-fossil and from living trees) than in previous dendroclimatic studies in this region. We develop a new TRW chronology for Yamal, more than 2000 years long and running up to 2005. For the Polar Urals we develop new TRW and MXD chronologies that show good agreement at short (<15 years) and medium (15–100 years) timescales demonstrating the validity of attempts to reconcile the evidence of longer-timescale information that they provide. We use a “conservative” application of the RCS approach (two-curve signal-free RCS), guarding against the possibility of “modern sample bias”: a possible inflation of recent chronology values arising out of inadvertent selection of mostly relatively fast-growing trees in recent centuries. We also transform tree indices to have a normal distribution to remove the positive chronology skew often apparent in RCS TRW chronologies. This also reduces the apparent magnitude of 20th century tree-growth levels.There is generally good agreement between all chronologies as regards the major features of the decadal to centennial variability. Low tree-growth periods for which the inferred summer temperatures are approximately 2.5 °C below the 1961–90 reference are apparent in the 15-year smoothed reconstructions, centred around 1005, 1300, 1455, 1530, particularly the 1810s where the inferred cooling reaches −4 °C or even −6 °C for individual years, and the 1880s. These are superimposed on generally cool pre-20th century conditions: the long-term means of the pre-1900 reconstructed temperature anomalies range from −0.6 to −0.9 °C in our alternative reconstructions. There are numerous periods of one or two decades with relatively high growth (and inferred summer temperatures close to the 1961–1990 level) but at longer timescales only the 40-year period centred at 250 CE appears comparable with 20th century warmth. Although the central temperature estimate for this period is below that for the recent period, when we take into account the uncertainties we cannot be highly confident that recent warmth has exceeded the temperature of this earlier warm period. While there are clear warm decades either side of 1000 CE, neither TRW nor MXD data support the conclusion that temperatures were exceptionally high during medieval times. One previous version of the Polar Urals TRW chronology is shown here to be in error due to an injudicious application of RCS to non-homogeneous sample data, partly derived from root-collar samples that produce spuriously high chronology values in the 11th and 15th centuries. This biased chronology has been used in a number of recent studies aimed at reconstructing wider scale temperature histories. All of the chronologies we have produced here clearly show a generally high level of growth throughout their most recent 80 years. Allowing for chronology and reconstruction uncertainty, the mean of the last 100 years of the reconstruction is likely warmer than any century in the last 2000 years in this region.

Tree-ring analysis of ancient baldcypress trees and subfossil wood

Ancient baldcypress trees found in wetland and riverine environments have been used to develop a network of exactly dated annual ring-width chronologies extending from the southeastern United States, across Mexico, and into western Guatemala. These chronologies are sensitive to growing season precipitation in spite of frequently flooded site conditions, and have been used to reconstruct moisture levels the southeastern United States and Mexico for over 1000 years. The El Nino/Southern Oscillation (ENSO) is a major influence on the climate reconstructions derived from these baldcypress chronologies, especially in Mexico where some of the most extreme reconstructed droughts occurred during El Nino events. In the Southeast, the ENSO influence on climate and tree growth changes sign from spring to summer, and this change in dynamical forcing is recorded by sub-seasonal chronologies of earlywood and latewood width. Most existing baldcypress chronologies have been extended with tree-ring data from “subfossil” wood recovered from surface and submerged deposits. Well-preserved subfossil logs have also been recovered in quantity from buried deposits of great age, and may permit development of long continuously dated Holocene chronologies and discontinuous “floating” Pleistocene chronologies. The extensive subfossil baldcypress swamp discovered 6 m below the streets of Washington D.C. was overrun by a transgression of the Potomac estuary, possibly during the previous super interglacial (marine OIS 5e), and provides direct evidence for one potential impact of unmitigated anthropogenic warming and sea level rise.

Il segnale climatico e le sue variazioni negli anelli di accrescimento degli alberi da siti estremi al contorno della regione mediterranea

Climatic signal and its variations in the tree rings from extreme environments bordering the Mediterranean region.Tree rings from climatically extreme environments, such as the Alpine treeline the arid and desert environments, allow the annually-resolved reconstruction of the climatic parameters most limiting tree growth in these areas. Climate proxies from the regions bordering the Mediterranean basin could provide a valuable contribution to palaeoclimate reconstructions in the area. Recent tree-ring chronologies of alpine conifers from the Italian Central Alps and discontinuous upper-mid Holocene chronologies of Cupressus dupreziana from the Libyan Sahara, confirm the possibility of obtaining meaningful palaeoclimatic information and quantitative reconstructions of the diverse climate parameters from annual tree rings. The Alpine tree-ring chronologies contain a summer-temperature signal, while the Libyan chronologies highlight the fluctuations of water availability in the Central Sahara over time. The information contained in these records can therefore contribute to a better definition of the past Mediterranean climate, showing how, by using dendrochronological data from sites limited by temperatures and by precipitations, relevant climatic information can also be derived from the bordering regions.

ICE-5G and ICE-6G models of postglacial relative sea-level history applied to the Holocene coral reef record of northeastern St Croix, U.S.V.I.: investigating the influence of rotational feedback on GIA processes at tropical latitudes

Fossil coral reefs along the northeastern coast of St Croix in the Caribbean Sea provide an 8000 year record of dated and interpreted Holocene sea-level change. We herein compare this record with the predictions of models of glacio-hydro-isostatic adjustment for St Croix and for additional sites at similar latitudes in the Greater and Lesser Antilles region. RSL predictions are based upon the model ICE-5G (VM2), and with a modified model ICE-6G (VM5A), both including and excluding the influence of rotational feedback. Misfits between the modeled sea levels and the local geologic data are most apparent for models without rotational feedback, particularly in the prediction of a +2 to +4 m unsupported mid-Holocene misfit at ∼4 ka, as well as a small-amplitude highstand that extends from 2.5 to 1.5 ka. Incorporation of the influence of rotational feedback provides the best fit to the data, largely eliminating the unsupported mid-Holocene misfit between the data field and the sea-level histories predicted by the models without rotational feedback, and fitting data older than 5 kyr more closely than a previously published latitudinally-averaged sea-level curve for the western Atlantic. The St Croix data therefore demonstrate that rotational influence extends at least 27° further south from its 45° N mid-latitude extremum along the US east coast, and identifies tropical latitudes as influenced by proglacial forebulge collapse. Implications for reef-based sea-level reconstruction include the ability to accurately model sea levels at specific tropical sites with partial Holocene chronologies using the ICE-6G (VM5A) model with rotational feedback. Latitudinally-averaged sea-level curves are therefore of limited use in understanding the relative importance of contributing physical influences on postglacial sea-level history.

Radiocarbon chronology of the late-glacial Puerto Bandera moraines, Southern Patagonian Icefield, Argentina

We report radiocarbon dates that constrain the timing of the deposition of the late-glacial Puerto Bandera moraine system alongside the western reaches of Lago Argentino adjacent to the Southern Patagonian Icefield. Close maximum-limiting radiocarbon ages ( n = 11) for glacier advance into the outer moraines, with a mean value of 11,100 ± 60 14C yrs BP (12,990 ± 80 cal yrs BP), were obtained from wood in deformation (soft) till exposed beneath flow and lodgment till in Bahía del Quemado on the northeast side of Brazo Norte (North Branch) of western Lago Argentino. Other exposures of this basal deformation till in Bahía del Quemado reveal incorporated clasts of peat, along with larger inclusions of deformed glaciofluvial and lacustrine deposits. Radiocarbon dates of wood included in these reworked peat clasts range from 11,450 ± 45 14C yrs BP to 13,450 ± 150 14C yrs BP (13,315 ± 60 to 16,440 ± 340 cal yrs BP). The implication is that, during this interval, glacier fronts were situated inboard of the Puerto Bandera moraines, with the peat clasts and larger proglacial deposits being eroded and then included in the basal till during the Puerto Bandera advance. Minimum-limiting radiocarbon ages for ice retreat come from basal peat in cores sampled in spillways and depressions generated during abandonment of the Puerto Bandera moraines. Glacier recession and subsequent plant colonization were initiated close behind different frontal sectors of these moraines prior to: 10,750 ± 75 14C yrs BP (12,660 ± 70 cal yrs BP) east of Brazo Rico, 10,550 ± 55 14C yrs BP (12,490 ± 80 cal yrs BP) in Peninsula Avellaneda, and 10,400 ± 50 14C yrs BP (12,280 ± 110 cal yrs BP) in Bahía Catalana. In addition, a radiocarbon date indicates that by 10,350 ± 45 14C yrs BP (12,220 ± 110 cal yrs BP), the Brazo Norte lobe (or former Upsala Glacier) had receded well up the northern branch of Lago Argentino, to a position behind the Herminita moraines. Furthermore, glacier termini had receded to just outboard of the outer Holocene moraines at Lago Frías and Lago Pearson (Anita) prior to 10,400 ± 40 14C yrs BP (12,270 ± 100 cal yrs BP) and 9040 ± 45 14C yrs BP (10,210 ± 50 cal yrs BP), respectively. The most extensive recession registered during the early Holocene was in Agassiz Este Valley, where the Upsala Glacier had pulled back behind the outer Holocene moraine, reaching close to the present-day glacier terminus before 8290 ± 40 14C yrs BP (9300 ± 80 cal yrs BP). The radiocarbon-dated fluctuations of the Lago Argentino glacier in late-glacial time, given here, are in accord with changes in ocean mixed layer properties, predominately temperature, derived from the isotopic record given here of ODP Core 1233, taken a short distance off shore of the Chilean Lake District. It also matches recently published chronologies of late-glacial moraines in the Southern Alps of New Zealand on the opposite side of the Pacific Ocean from Lago Argentino. Finally, the timing of the late-glacial reversal of the Lago Argentino glacier fits the most recent chronology for the culmination of the Antarctic Cold Reversal (ACR) in the deuterium record of the EPICA Dome C ice core from high on the East Antarctic Plateau. Therefore, we conclude that the climate signature of the ACR was widespread in both the ocean and the atmosphere over at least the southern quarter of the globe.

Environmental responses to Lateglacial climatic fluctuations recorded in the sediments of pre‐Alpine Lake Mondsee (northeastern Alps)

AbstractInvestigation of the sedimentary record of pre‐Alpine Lake Mondsee (Upper Austria) focused on the environmental reaction to rapid Lateglacial climatic changes. Results of this study reveal complex proxy responses that are variable in time and influenced by the long‐term evolution of the lake and its catchment. A new field sampling approach facilitated continuous and precisely controlled parallel sampling at decadal to sub‐annual resolution for µ‐XRF element scanning, carbon geochemistry, stable isotope measurements on ostracods, pollen analyses and large‐scale thin sections for microfacies analysis. The Holocene chronology is established through microscopic varve counting and supported by accelerator mass spectrometry 14C dating of terrestrial plant macrofossils, whereas the Lateglacial age model is based on δ18O wiggle matching with the Greenland NGRIP record, using the GICC05 chronology. Microfacies analysis enables the detection of subtle sedimentological changes, proving that depositional processes even in rather large lake systems are highly sensitive to climate forcing. Comparing periods of major warming at the onset of the Lateglacial and Holocene and of major cooling at the onset of the Younger Dryas reveals differences in proxy responses, reflecting threshold effects and ecosystem inertia. Temperature increase, vegetation recovery, decrease of detrital flux and intensification of biochemical calcite precipitation at the onset of the Holocene took place with only decadal leads and lags over a ca. 100 a period, whereas the spread of woodlands and the reduction of detrital flux lagged the warming at the onset of the Lateglacial Interstadial by ca. 500–750 a. Cooling at the onset of the Younger Dryas is reflected by the simultaneous reaction of δ18O and vegetation, but sedimentological changes (reduction of endogenic calcite content, increase in detrital flux) were delayed by about 150–300 a. Three short‐term Lateglacial cold intervals, corresponding to Greenland isotope substages GI‐1d, GI‐1c2 and GI‐1b, also show complex proxy responses that vary in time. Copyright © 2011 John Wiley &amp; Sons, Ltd.