Environmental history,palaeoecology and human activity at the early Neolithic forager/cultivator site at Kuahuqiao,Hangzhou, eastern China

The date and location of the adoption of rice cultivation by foraging cultures in China are of considerable current interest but its understanding is hampered by lack of information regarding its palaeoenvironmental context. We present detailed multi-proxy palaeoecological research at the earliest-dated site of rice cultivation in the coastal littoral of east China which has revealed the precise environmental setting of this early Neolithic settlement and its incipient cultivation at ca 7750 cal BP. Regional and local environmental changes governed the character of the site and the duration of human activity. After an episode of marine conditions, natural hydrological succession and terrestrialisation of the site preceded fire clearance of marsh fen-carr alder scrub that prepared the ground for cultivation and then maintained a reedswamp-type wet grassland in which rice was grown. Cropping of Typha stands may have formed part of the subsistence base before the site was overwhelmed by marine inundation ca 7200 cal BP, after which rice cultivation spread to Neolithic sites of Hemudu type elsewhere in the coastal lowlands. We suggest that integrated multi-proxy palaeoecological studies are vitally important for the full understanding of such key wetland archaeological sites.     

From Pleniglacial to Holocene: a 14C chronostratigraphy of environmental changes in the Konya Plain,Turkey

In the endoreic, semi-arid Konya basin on the central Anatolian plateaux, long-term hydrological evolution has left various landforms and lacustrine deposits reflecting the regional climatic evolution, as well as human influence on the local environments. This paper presents results from a cooperative programme grouping several institutes from Turkey and France, on lacustrine, marshy and aeolian sediment sequences of Upper Pleistocene and Holocene age. The detailed study of environmental evolution is based on the reconstruction as well as on the characterization of the extension and contraction phases of wetlands occupying the lowest parts of the Konya plain. A soil and a marsh layer are ¹⁴C dated ca. 28,000–25,000 yr bp. Three phases of Pleniglacial (from ca. 22,000 to 17,000 yr bp) high lake levels are distinguished. Complementary OSL dates on aeolian dunes confirm the occurrence of two drought periods: the first occurs around the start of the Late Glacial, the second after the Mid-Holocene climatic optimum, the latter being ‘in phase’ with a similar drought in other Eastern Mediterranean regions. After 17,000 yr bp, no lacustrine phase reached as high a level as the Pleniglacial lake. During the Late Glacial, a shallow freshwater lacustrine phase is identified from >12,500 to 11,000 yr bp. The Late Glacial to Holocene transition corresponds to a general absence of deposits and dateable material, thus suggesting a period of drought, to which no aeolian features have so far been related. The Holocene environmental evolution shows a period of marsh and shallow lake extansion from 6000 to 5500 yr bp; this wetter period is interrupted by the second drought (ca. 5500 yrs bp) as indicated by aeolian dune activity. During the Late Holocene, a renewal of marshes, as well as soil development on slopes, can be interpreted either as climatic changes or as impacts of human use of water and soil resources during prehistoric and historic times.     

Multi-proxy evidence for Holocene lake-level and salinity changes at An Loch Mór,a coastal lake on the Aran Islands,Western Ireland

Curves for Holocene lake levels and salinity changes are presented for An Loch Mór, a small oligohaline lake on the Aran Islands off the west coast of Ireland, based on palaeoecological investigations of a 12 m long, lake-sediment core. New insights are also provided into Holocene sea-level change in the Galway Bay region. Particular emphasis has been placed on the ostracod fauna, both past and present. Salinity and lake-level changes were reconstructed from the fossil ostracod assemblages, based on the known tolerances of individual species and on the assemblages as a whole. Additional evidence was provided by other proxies including strontium–isotope ratios derived from ostracod shells and other carbonates, plant macrofossil and pollen analyses, and sedimentological changes. The early Holocene (pre-Boreal, i.e. 11.5–10 ka) was characterised by low lake levels and slightly elevated salinity values, probably the result of high evapotranspiration and low precipitation rather than elevated sea levels. Early Holocene plant and animal migration to the island does not seem to have been impeded but relative sea levels were not necessarily so low (below −40 m a.s.l.) that landbridges were present to the mainland. Between ca 10 and 8.5 ka, relatively high lake levels prevailed. At 8.3 and 7.5 ka, minor fluctuations (lowering) of the lake level occurred that are assumed to relate to early Holocene abrupt events. Beginning at 7.05 ka, lake levels declined sharply. A general trend towards rising lake levels started at ca 6.4 ka and accelerated at ca 5.6 ka as runoff increased as a result of Neolithic clearances. At ca 4.8 ka, lake levels began to rise once again, probably in response to changes in rainfall and/or evapotranspiration and runoff. Lower lake levels during the first half of the 1st millennium AD were probably a response to decreased runoff as a result of a drier climate coupled with regeneration of woody vegetation. The sharpest rise in both lake levels and salinity began during the ninth century AD, which is attributed to a rapid rise in relative sea level.     

Glacial to Holocene climate changes in the SE Pacific. The Raraku Lake sedimentary record (Easter Island, 27°S)

Easter Island (SE Pacific, 27°S) provides a unique opportunity to reconstruct past climate changes in the South Pacific region based on terrestrial archives. Although the general climate evolution of the south Pacific since the Last Glacial Maximum (LGM) is coherent with terrestrial records in southern South America and Polynesia, the details of the dynamics of the shifting Westerlies, the South Pacific Convergence Zone and the South Pacific Anticyclone during the glacial–interglacial transition and the Holocene, and the large scale controls on precipitation in tropical and extratropical regions remain elusive. Here we present a high-resolution reconstruction of lake dynamics, watershed processes and paleohydrology for the last 34 000 cal yrs BP based on a sedimentological and geochemical multiproxy study of 8 cores from the Raraku Lake sediments constrained by 22 AMS radiocarbon dates. This multicore strategy has reconstructed the sedimentary architecture of the lake infilling and provided a stratigraphic framework to integrate and correlate previous core and vegetation studies conducted in the lake. High lake levels and clastic input dominated sedimentation in Raraku Lake between 34 and 28 cal kyr BP. Sedimentological and geochemical evidences support previously reported pollen data showing a relatively open forest and a cold and relatively humid climate during the Glacial period. Between 28 and 17.3 cal kyr BP, including the LGM period, colder conditions contributed to a reduction of the tree coverage in the island. The coherent climate patterns in subtropical and mid latitudes of Chile and Eastern Island for the LGM (more humid conditions) suggest stronger influence of the Antarctic circumpolar current and an enhancement of the Westerlies. The end of Glacial Period occurred at 17.3 cal kyr BP and was characterized by a sharp decrease in lake level conducive to the development of major flood events and erosion of littoral sediments. Deglaciation (Termination 1) between 17.3 and 12.5 cal kyr BP was characterized by an increase in lake productivity, a decrease in the terrigenous input and a rapid lake level recovery, inaugurating a period of intermediate lake levels, dominance of organic deposition and algal lamination. The timing and duration of deglaciation events in Easter Island broadly agree with other mid- and low-latitude circum South Pacific terrestrial records. The transition to the Holocene was characterized by lower lake levels. The lake level dropped during the early Holocene (ca 9.5 cal kyr BP) and swamp and shallow lake conditions dominated till mid Holocene, partially favored by the infilling of the lacustrine basin. During the mid- to late-Holocene drought phases led to periods of persistent low water table, subaerial exposure and erosion, generating a sedimentary hiatus in the Raraku sequence, from 4.2 to 0.8 cal kyr BP. The presence of this dry mid Holocene phase, also identified in low Andean latitudes and in Patagonian mid latitudes, suggests that the shift of storm tracks caused by changes in the austral summer insolation or forced by “El Niño-like” dominant conditions have occurred at a regional scale. The palm deforestation of the Easter Island, attributed to the human impact could have started earlier, during the 4.2–0.8 cal kyr BP sedimentary gap. Our paleoclimatic data provides insights about the climate scenarios that could favor the arrival of the Polynesian people to the island. If it occurred at ca AD 800 it coincided with the warmer conditions of the Medieval Climate Anomaly, whereas if it took place at ca AD 1300 it was favored by enhanced westerlies at the onset of the Little Ice Age. Changes in land uses (farming, intensive cattle) during the last century had a large impact in the hydrology and limnology (eutrophication) of the lake.     

Terrestrial stable isotope records of Late Quaternary paleoclimates in the eastern Mediterranean region

Terrestrial stable isotope records (¹³C/¹²C, ¹⁸O/¹⁶O, and D/H ratios) of late Quaternary paleoclimates in the eastern Mediterranean region are reviewed. Significant paleoclimatic reconstructions come from a variety of isotopic studies. Paleogroundwaters, although they cannot be accurately dated, show oxygen and hydrogen isotopic compositions highly depleted in heavier isotopes compared to modern meteoric waters in arid regions of southern Israel, Sinai and northeastern Africa and attest to a major difference in climatic regime some time in the Pleistocene. Th-U dating of land snails showing a similar ¹⁸O depletion indicates ages of 100,000 yr and ≥300,000 yr for this climatic regime in the Negev Desert of southern Israel. Carbon isotope records of organic matter have not been studied extensively in the region, except for the record of Holocene land snails in the Negev. These document a southward shift in pure C₃ plant communities in the middle and early Holocene relative to their present distribution and indicate wetter conditions at those times. An oxygen isotope curve for the Holocene, reflecting changes in the isotopic composition of precipitation, has been established from analysis of carbonate materials—land snail shells and speleothems. The curve indicates a depletion of ca. 2‰ in ¹⁸O centered around 7000 cal yr bp, with modern levels being reached by 5000 cal yr bp. Carbon isotope analysis of soil carbonates in paleosols developed in loess in the Negev show the existence of dramatic north–south climatic gradients at the times of formation of the soils (ca. 13,000, 28,000, and ≥37,000 ¹⁴C yr bp), as occur also today due to the waning influence of Mediterranean to the south. Some isotopic methods, widely used in other regions, have received little or no attention in the eastern Mediterranean region. These include oxygen and hydrogen isotopes in wood, phosphate oxygen and organic carbon in bones and teeth, and carbon in soil organic matter.     

Mesolithic agriculture in Switzerland? A critical review of the evidence

Accumulating palaeobotanical evidence points to agricultural activity in Central Europe well before the onset of the Neolithic, commonly dated at ca 5500–5200 cal BC. We reinvestigated an existing pollen profile from Soppensee with refined taxonomical resolution by further subdividing the Cerealia pollen type into Triticum t. and Avena t. because the sediments at this site currently provide the highest temporal resolution and precision for the period of interest among all sites in Switzerland. Our new results are in agreement with previous high-resolution investigations from Switzerland showing scattered but consistent presence of pollen of Cerealia, Plantago lanceolata, and other cultural plants or weeds during the late Mesolithic period (6700–5500 cal BC). Chronologically, this palynological evidence for sporadic agricultural activities coincides with a major break in material culture at ca 6700 cal BC (i.e. the transition from early to late Mesolithic). Here, we review possible arguments against palaeobotanical evidences of Mesolithic agriculture (e.g. chronological uncertainties, misidentification, contamination, long-distance transport) and conclude that none of these can explain the consistent pollen pattern observed at several sites. The palynological evidence can, of course, not prove the existence of pre-ceramic agriculture in Central Europe. However, it is so coherent that this topic should be addressed by systematic archaeobotanical analyses in future archaeological studies. If our interpretation should turn out to be true, our conclusions would have fundamental implications for the Neolithic history of Europe. Currently, it is intensely debated whether Central European agriculture developed locally under the influence of incoming ideas from areas where Neolithic farming had already developed earlier (e.g. southeastern Europe) or whether it was introduced by immigrating farmers. On the basis of our results, we suggest that agriculture developed locally throughout the late Mesolithic and Neolithic. Mesolithic trading networks connecting Southern and Central Europe also support the hypothesis of a slow and gradual change towards sessile agriculture, probably as a result of incoming ideas and regional cultural transformation.     

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

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

Climate and human impact during the past 2000 years as recorded in the Lagunas de Yala,Jujuy, northwestern Argentina

²¹⁰Pb, ¹³⁷Cs and ¹⁴C dated sediments of two late Holocene landslide lakes in the Provincial Park Lagunas de Yala (Laguna Rodeo, Laguna Comedero, 24°06′S, 65°30′W, 2100 m asl, northwestern Argentina) reveal a high-resolution multi-proxy data set of climate change and human impact for the past ca. 2000 years. Comparison of the lake sediment data set for the 20th century (sediment mass accumulation rates MARs, pollen spectra, nutrient and charcoal fluxes) with independent dendroecological data from the catchment (fire scars, tree growth) and long regional precipitation series (from 1934 onwards) show that (1) the lake sediment data set is internally highly consistent and compares well with independent data sets, (2) the chronology of the sediment is reliable, (3) large fires (1940s, 1983/1984–1989) as documented in the local fire scar frequency are recorded in the charcoal flux to the lake sediments and coincide with low wet-season precipitation rates (e.g., 1940s, 1983/1984) and/or high interannual precipitation variability (late 1940s), and (4) the regional increase in precipitation after 1970 is recorded in an increase in the MARs (L. Rodeo from 100 to 390 mg cm⁻² yr⁻¹) and in an increase in fern spores reflecting wet vegetation. The most significant change in MARs and nutrient fluxes (C_org and P) of the past 2000 years is observed with the transition from the Inca Empire to the Spanish Conquest around 1600 AD. Compared with the pre-17th century conditions, MARs increased by a factor of ca. 5 to >8 (to 800 _{+130, −280} mg cm⁻² yr⁻¹), PO₄ fluxes increased by a factor of 7, and C_org fluxes by a factor of 10.5 for the time between 1640 and 1930 AD. 17th to 19th century MARs and nutrient fluxes also exceed 20th century values. Excess Pb deposition as indicated by a significant increase in Pb/Zr and Pb/Rb ratios in the sediments after the 1950s coincides with a rapid expansion of the regional mining industry. Excess Pb is interpreted as atmospheric deposition and direct human impact due to Pb smelting.     

Holocene glacier history of Bjørnbreen and climatic reconstruction in central Jotunheimen,Norway, based on proximal glaciofluvial stream-bank mires

Holocene variations of Bjørnbreen, Smørstabbtinden massif, west-central Jotunheimen are reconstructed from the lithostratigraphy of two alpine stream-bank mires flooded episodically by meltwater. The approach uses multiple sedimentological indicators (weight loss-on-ignition, mean grain size, grain-size fractions, bulk density, moisture content and magnetic susceptibility), an a priori model of overbank deposition of suspended glaciofluvial sediments, a detailed chronology based on 56 radiocarbon dates, and a Little Ice Age sedimentological analogue. Rapid, late-Preboreal deglaciation was indicated by immigration of Betula pubescens by 9700 cal. BP. An interval of at least 3000 years in the early Holocene when glaciers were absent was interrupted by two abrupt episodes of glacier expansion around the time of the Finse Event, the first at ca 8270–7900 cal. BP (Bjørnbreen I Event) and the second at ca 7770–7540 cal. BP (Bjørnbreen II Event). Neoglaciation began shortly before ca 5730 cal. BP with gradual build-up to the maximum of the Bjørnbreen III Event at ca 4420 cal. BP. Later maxima occurred at ca 2750 cal. BP (Bjørnbreen IV Event) and at 1300, 1260, 1060 and 790 cal. BP (all within the Bjørnbreen V Event). Glaciers were smaller than today and possibly melted away on several occasions in the late Holocene (ca 3950, 1410 and 750 cal. BP). Minor maxima also occurred at ca 660 and 540 cal. BP, within the late Mediaeval Warm Period and the early Little Ice Age, respectively. The Little Ice Age maximum was dated to 213±25 BP (ca 205 cal. BP). The relative magnitudes of the main glacier maxima were determined: Erdalen Event>Little Ice Age Event (Bjørnbreen VI)>Bjørnbreen I (Finse Event) ≈ Bjørnbreen II>Bjørnbreen V⩾Bjørnbreen IV>Bjørnbreen III. These episodic events of varying magnitude and abruptness were used in conjunction with an independent summer-temperature proxy to reconstruct variations in equilibrium-line altitude (ELA) and a Holocene record of winter precipitation. Since the Preboreal, ELA varied within a range of about 390 m, and winter precipitation ranged between 40 and 160% of modern values. Winter precipitation variations appear to have been the main cause of these century- to millennial-scale Holocene glacier variations.     

Late Holocene monsoon climate as evidenced by proxy records from a lacustrine sediment sequence in western Guangdong,South China

The study of a 300-cm-thick exposed lacustrine sediment section in the Hedong village in Zhaoqing area which is located in sub-tropical west Guangdong Province in South China, demonstrates that the lacustrine sedimentary sequence possibly contains evidence for exploring variation of Asian monsoon climate. Multi-proxy records, including the humification intensity, total organic carbon, and grain size fractions, reveal a general trend towards dry and cold conditions in the late Holocene that this is because of a decrease in solar insolation on an orbital scale. Three intensified Asian summer monsoon (ASM) intervals (∼3300–3000 cal yr BP, ∼2600–1600 cal yr BP, and ∼900–600 cal yr BP), and three weakened ASM intervals (∼4000–3300 cal yr BP, ∼3000–2600 cal yr BP, and ∼1600–900 cal yr BP) are identified. Our humification record (HD_cal) shows a good correlation on multi-centennial scale with the tree ring Δ¹⁴C record, a proxy of solar activity. A spectral analysis of HD_cal reveals four significant cycles, i.e., ∼1250 yr, 300 yr, 110 yr, and 70 yr, and most of these cycles are related to the solar activity. Our findings indicate that solar output and oceanic–atmospheric circulation probably have influenced the late Holocene climate variability in the study region.     

Oceanic and atmospheric forcing of early Holocene ice shelf retreat,George VI Ice Shelf,Antarctica Peninsula

We use lake sediment records from an epishelf lake on Alexander Island to provide a detailed picture of the Holocene history of George VI Ice Shelf (GVI-IS). Core analyses included; micropaleontology (diatoms/foraminifera), stable isotope (δ¹⁸O, δ¹³C), geochemistry (total organic carbon (TOC), total nitrogen (TN), C/N ratios) and grain-size analyses. These data provide robust evidence for one period of past ice shelf absence during the early Holocene. The timing of this period has been constrained by 10 AMS ¹⁴C dates performed on mono-specific foraminifera samples. These dates suggest that GVI-IS was absent between c 9600 cal yr BP and c 7730 cal yr BP. This early Holocene collapse immediately followed a period of maximum Holocene warmth that is recorded in some Antarctic ice cores and coincides with an influx of warmer ocean water onto the western Antarctic Peninsula (AP) shelf at c 9000 cal yr BP. The absence of a currently extant ice shelf during this time interval suggests that early Holocene ocean-atmosphere variability in the AP was greater than that measured in recent decades.     

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 25,000 yr, 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. 1200 yr, 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 3400 cal yr BP, and an explicitly drier phase from 9000 to 3700 cal yr BP. Modern conditions with shorter dry seasons became established after 3400 cal yr 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.     

Testing models of mid to late Holocene sea-level change,North Queensland,Australia

Understanding the nature of global ice-equivalent eustatic sea-level changes during the mid to late Holocene is important to our understanding of how ice sheets will respond to future climate change. This study re-analyses the indicative meaning and age control of existing relative sea-level (RSL) data from Cleveland Bay, North Queensland, Australia and presents new RSL data from a foraminifera-based transfer function as a preliminary test of global geophysical models in this region during the mid to late Holocene. The foraminifera-based transfer function produces reliable RSL estimates, consistent through the mid to late Holocene at different locations in Cleveland Bay. Analysis of the combined RSL database reveals that RSL rose above present between 8 and 6.2 ka cal. BP, with the peak of the sea-level highstand c. 2.8 m above present at c. 5 ka cal. BP, remaining relatively stable above +1.5 m from 6.2 until at least 2.3 ka cal. BP, falling to present in the last millennia. This long period of sea level above present in the mid to late Holocene suggests a gradual rather than abrupt end to global ice melt, which must have continued into the late Holocene. This new analysis also shows no evidence for episodic fluctuations within the highstand, although they cannot be entirely ruled out by this study. This study demonstrates that more sea-level data needs to be collected from locations uncontaminated by glacio-isostasy, hydro-isostasy and tectonic effects, in order to better constrain the late Holocene melt histories of the large polar ice sheets.     

Holocene glacier and deep water dynamics,Adélie Land region,East Antarctica

This study presents a high-resolution multi-proxy investigation of sediment core MD03-2601 and documents major glacier oscillations and deep water activity during the Holocene in the Adélie Land region, East Antarctica. A comparison with surface ocean conditions reveals synchronous changes of glaciers, sea ice and deep water formation at Milankovitch and sub-Milankovitch time scales. We report (1) a deglaciation of the Adélie Land continental shelf from 11 to 8.5 cal ka BP, which occurred in two phases of effective glacier grounding-line retreat at 10.6 and 9 cal ka BP, associated with active deep water formation; (2) a rapid glacier and sea ice readvance centred around 7.7 cal ka BP; and (3) five rapid expansions of the glacier–sea ice systems, during the Mid to Late Holocene, associated to a long-term increase of deep water formation. At Milankovich time scales, we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier–sea ice–ocean system throughout the Holocene, in the Adélie Land region. In addition, the orbitally-forced seasonality seems to control the coastal deep water formation via the sea ice–ocean coupling, which could lead to opposite patterns between north and south high latitudes during the Mid to Late Holocene. At sub-Milankovitch time scales, there are eight events of glacier–sea ice retreat and expansion that occurred during atmospheric cooling events over East Antarctica. Comparisons of our results with other peri-Antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier–sea ice–ocean interactions and their Holocene evolutions reflect a more global Antarctic Holocene pattern.     

Glacial–interglacial productivity and environmental changes in Lake Biwa,Japan: A sediment core study of organic carbon,chlorins and biomarkers

Temporal changes in paleoproductivity of Lake Biwa (Japan) over the past 32 kyr have been studied by analyzing bulk organic carbon and photosynthetic pigments (chlorins) in the BIW95-5 core. Primary productivity was estimated on the assumption of C/N_org values of 8 for autochthonous organic matter (OM) and 25 for allochthonous OM and using an equation developed for the marine environment. The estimate indicates that primary productivity ranges from 50 to 90 g C m^?2 yr^?1 in the Holocene, while it is ～60 g C m^?2 yr^?1 on average in the last glacial. Pheophytin a and pheophorbide a are the major chlorins. A downcore profile of chlorin concentration normalized to autochthonous organic carbon (OC) shows a decreasing trend. Chlorin productivity was corrected by removal of the effect of post-burial chlorin degradation. The temporal profile of chlorin productivity thereby obtained resembles that from autochthonous OC.The difference in primary productivity between the Holocene and the glacial for the lake is markedly smaller than that for Lake Baikal situated in the boreal zone. This difference between the two lakes is probably caused by the difference in their climatic conditions, such as temperature and precipitation. Precipitation at Lake Biwa is relatively large during the glacial and the Holocene because of the continuous influence of the East Asian monsoon. Lake Baikal precipitation is generally small as a result of control by the continental (Siberia) climate regime. In addition, a significant difference in productivity between the glacial and the Holocene for Lake Baikal may be essentially controlled by the hydrodynamic systems in the lake.Lake Biwa terrigenous OM input events occurred at least five times over the period 11–32 kyr BP, suggesting enhanced monsoon activity. Molecular examination of the layer with a large input of terrigenous OM during the Younger Dryas indicates that concentrations of terrigenous biomarkers such as n-C₂₇–C₃₁ alkanes, lignin phenols, cutin acids, ω-hydroxy acids and C₂₉ sterols are high, suggesting that soil OM with peat-like material entered the lake as a result of flooding. An enhanced sedimentation rate in the last 3000 years might have been partially caused by agricultural activity around the lake.     

Can biochar and hydrochar stability be assessed with chemical methods?

Field application of biochar is intended to increase soil carbon (C) storage. The assessment of C storage potential of biochars lacks methods and standard materials. The reactivity of biochars and hydrochars may be one possible means of evaluating their environmental stability. The aim of this study was to evaluate the reactivity of biochar produced by gasification (GS) and hydrochar produced by hydrothermal carbonisation (HTC). The approach included analysis of the two different char types produced from the same three feedstocks. Moreover, we analysed the reactivity of Holocene charcoal (150 and 2000 yr old) to evaluate whether or not their use as standard materials to represent stable biochar is meaningful. We assessed carbon loss following oxidation with acid dichromate as well as hydrolysis with HCl. Our results showed that chemical reactivity is not a straightforward approach for characterising the stability of biochar and hydrochar. Acid hydrolysis showed little difference between HTCs and GSs, despite the contrasting elemental composition. Using acid dichromate oxidation, we determined that GSs contained ca. 70% of oxidation resistant C while the proportion for HTCs was < 10%. The different feedstocks had a slight, but significant, influence on the reactivity of GSs and HTCs. The content of oxidation resistant C decreased in the order 100 yr old charcoal = GSs > 2000 yr old charcoal > HTCs > feedstock and was related to elemental composition. This shows that acid dichromate oxidation may allow differentiation of the reactivity of modern biochars but that there is not necessarily a relationship between reactivity and age of Holocene charcoals. As the chemical reactivity of biochars may change with exposure time in soil, it is poorly suited for assessing their environmental residence time.     

Sedimentary evidence of soil organic matter input to the Curuai Amazonian floodplain

A multi-proxy study has been performed on a sediment core from the Curuai floodplain, Central Amazonia. The combination of elemental, isotopic and molecular analysis of a 110 cm core (a record of ca. the last 100 yr) allowed reconstruction of the hydrological conditions of organic matter (OM) deposition. Two units could be delineated. The first (UI) was composed of three sub-units: UIa (0–15 cm), composed of highly degraded organic particles originating from the surrounding soil and indicative of restricted transport; UIb (15–48 cm), during which the region was permanently flooded and the material stored came from soil runoff, mainly from alluvial forest; and UIc (48–88 cm) composed of material from Amazon River suspended sediment, itself originating from OM degradation in forest soil. In UII (88–111 cm), the OM originated mainly from the forest soil and other plant remains in the floodplain. The data reveal that, during the four distinct depositional periods, the sedimentary OM alternated between land derived soil and alluvial vegetation due to changes in hydrodynamics.     

Holocene vegetation and climate changes from a peat pollen record of the forest – steppe ecotone,Southwest of Patagonia (Argentina)

Pollen analysis from a peat-bog sequence located at 50° 24′ S, 72° 42′ W in the Subantarctic forest – Patagonian steppe ecotone gives information about vegetation and climate changes in Southwestern Patagonia since the glacier retreat. After 11 000 cal yr BP a change from grass steppe to open Nothofagus forest indicates that climatic conditions became rapidly warmer. Development of a closed Nothofagus forest between 5800 and 3200 cal yr BP is interpreted as precipitation increase. During the late Holocene colder climate conditions prevail in response to Neoglacial events. After ca 3000 cal yr BP Nothofagus forest became opener, and after 800 cal yr BP grass steppe expanded. Changes in the forest-steppe ecotone composition as well as the ecotone longitudinal shifts suggest changes in temperature and precipitation. Present-day mean annual precipitation between 300 and 400 mm is associated with grass steppe, and 500–600 mm with a greater forest representation. During the last century, low presence of forest in the area may be related to European settlement and repeated flooding caused by periodic advances of Perito Moreno glacier.     

The Bonneville Estates Rockshelter rodent fauna and changes in Late Pleistocene–Middle Holocene climates and biogeography in the Northern Bonneville Basin,USA

Excavations at Bonneville Estates Rockshelter, Nevada recovered rodent remains from stratified deposits spanning the past ca. 12,500 ¹⁴C yr BP (14,800 cal yr BP). Specimens from horizons dating to the late Pleistocene and early Holocene include species adapted to montane and moist and cool habitats, including yellow-bellied marmot (Marmota flaviventris) and bushy-tailed woodrat (Neotoma cinerea). Shortly after 9000 ¹⁴C BP (10,200 cal yr BP) these mammals became locally extinct, or nearly so, taxonomic diversity declined, and the region became dominated by desert woodrats (Neotoma lepida) and other species well-adapted to xeric, low-elevation settings. The timing and nature of changes in the Bonneville Estates rodent fauna are similar to records reported from nearby Homestead and Camels Back caves and provide corroborative data on terminal Pleistocene–early Holocene environments and mammalian responses to middle Holocene desertification. Moreover, the presence of northern pocket gopher (Thomomys talpoides) at Bonneville Estates adds to a sparse regional record for that species and, similar to Homestead Cave, it appears that the ca. 9500 ¹⁴C yr BP (10,800 cal yr BP) replacement of the northern pocket gopher by Botta's pocket gopher in the Great Salt Lake Desert vicinity was also in response to climate change.     

Holocene environmental and climatic changes at Gorgo Basso,a coastal lake in southern Sicily,Italy

We used a new sedimentary record to reconstruct the Holocene vegetation and fire history of Gorgo Basso, a coastal lake in south-western Sicily (Italy). Pollen and charcoal data suggest a fire-prone open grassland near the site until ca 10,000 cal yr BP (8050 cal BC), when Pistacia shrubland expanded and fire activity declined, probably in response to increased moisture availability. Evergreen Olea europaea woods expanded ca 8400 to decline abruptly at 8200 cal yr BP, when climatic conditions became drier at other sites in the Mediterranean region. Around 7000 cal yr BP evergreen broadleaved forests (Quercus ilex, Quercus suber and O. europaea) expanded at the cost of open communities. The expansion of evergreen broadleaved forests was associated with a decline of fire and of local Neolithic (Ficus carica–Cerealia based) agriculture that had initiated ca 500 years earlier. Vegetational, fire and land-use changes ca 7000 cal yr BP were probably caused by increased precipitation that resulted from (insolation-forced) weakening of the monsoon and Hadley circulation ca 8000–6000 cal yr BP. Low fire activity and dense coastal evergreen forests persisted until renewed human activity (probably Greek, respectively Roman colonists) disrupted the forest ca 2700 cal yr BP (750 BC) and 2100 cal yr BP (150 BC) to gain open land for agriculture. The intense use of fire for this purpose induced the expansion of open maquis, garrigue, and grassland-prairie environments (with an increasing abundance of the native palm Chamaerops humilis). Prehistoric land-use phases after the Bronze Age seem synchronous with those at other sites in southern and central Europe, possibly as a result of climatic forcing. Considering the response of vegetation to Holocene climatic variability as well as human impact we conclude that under (semi-)natural conditions evergreen broadleaved Q. ilex–O. europaea (s.l.) forests would still dominate near Gorgo Basso. However, forecasted climate change and aridification may lead to a situation similar to that before 7000 cal yr BP and thus trigger a rapid collapse of the few relict evergreen broadleaved woodlands in coastal Sicily and elsewhere in the southern Mediterranean region.