mid-Holocene Climatic Optimum Research Articles

Holocene paleoceanographic variability in Robertson Bay, Ross Sea, Antarctica: A marine record of ocean, ice sheet, and climate connectivity

Accelerating ocean-driven basal melting of Antarctic ice shelves in recent decades has implications for sea level rise and global overturning circulation. Here, we reconstruct oceanographic conditions at the confluence of the Ross Sea and the Southern Ocean by analyzing a multi-proxy Holocene marine sedimentary record collected from Robertson Bay. A ramped pyrolysis oxidation radiocarbon age-depth model provides a timeline for glacial behavior and oceanographic changes over the last 6700 years. The diatom assemblage, magnetic susceptibility, grain size, total organic carbon and nitrogen, trace elements, and bulk δ13C are used as proxies for changing ocean and glacial conditions, which we interpret in the context of modern oceanographic measurements.Our record shows evidence of persistent ice cover in the northwestern Ross Sea during the Antarctic mid-Holocene climate optimum (ca. 5 cal kyr BP). Based on this observation, we suggest that meltwater and iceberg discharge associated with ice sheet retreat in the Ross Sea region altered local oceanography during the mid-Holocene. The onset of modern style oceanographic conditions in Robertson Bay occurred at ca. 4 cal kyr BP. Stable late Holocene conditions in are punctuated by a period of enhanced polynya activity and upwelling of nutrient rich Circumpolar Deep Water ca. 0.8 cal kyr BP and an increase in the seasonal duration of sea ice after 0.7 cal kyr BP, during the Little Ice Age. The response of the marine environment in Robertson Bay to mid-Holocene ice sheet retreat and natural climate variability during the last millennium underscores the sensitivity of the Antarctic ice-ocean interface to projected changes in coming decades.

Geochemistry of a paleo-oxbow lake sediments and its implications for the late Holocene extreme overbank flooding history of the Yellow River within the Zoige Basin, NE Tibetan Plateau

Paleo-oxbow lake sediments can provide archives to reconstruct paleo-channel evolution and flooding history of the river. Multi-proxy approaches including detailed sediment stratigraphy, sedimentology and geochemistry have been implemented in a high-resolution sedimentary section of paleo-oxbow lake of the Yellow River within the Zoige Basin on the NE Tibetan Plateau, to reconstruct regional environmental changes and extreme overbank flooding history. Our results suggest that not only traditional sedimentological proxies, but also chemical elements can be applied in defining sequences with different genetic types, especially the paleoflood deposits in the paleo-oxbow profile. Two units of late-Holocence extreme overbank flooding deposits (OFDs) are identified in terms of the significantly higher proportions of sand, high contents of SiO2, Na2O, Ba, low contents of Al2O3, Fe2O3, MgO, K2O, Ti, Rb and high values of Zr/Fe, Zr/Rb ratios. These extraordinary flood events within the Zoige Basin were dated back to 2,960 ± 240–2,870 ± 270 a and 1840 ± 200–1700 ± 160 a, in response to the mid-Holocene climatic optimum to the late Holocene and the Dark Age Cold Period (DACP). And the strong rainfall caused by the abnormal atmospheric circulation during the period of climate transition and abrupt change may led to the frequent occurrence of extreme flood events in the source region of the Yellow River. These findings are important for understanding the response of regional fluvial system to high climatic instability and provide a new perspective for us to analyze the risk of flood disasters on the Tibetan Plateau under the background of climate change.

Predicting Spruce Taiga Distribution in Northeast Asia Using Species Distribution Models: Glacial Refugia, Mid-Holocene Expansion and Future Predictions for Global Warming

Spruce taiga forests in Northeast Asia are of great economic and conservation importance. Continued climate warming may cause profound changes in their distribution. We use prognostic and retrospective species distribution models based on the Random Forest machine learning method to estimate the potential range change of the dominant taiga conifer Jezo spruce (Picea jezoensis (Siebold & Zucc.) Carrière) for the year 2070 climate warming scenarios and for past climate epochs–the Last Glacial Maximum (LGM) (~21,000 years before present) and the mid-Holocene Climatic Optimum (MHO) (~7000 years before the present) using the MIROC-ESM and CCSM4 climate models. The current suitable climatic conditions for P. jezoensis are estimated to be 500,000 km2. Both climatic models show similar trends in past and future ranges but provide different quantitative areal estimates. During the LGM, the main part of the species range was located much further south than today at 35–45° N. Projected climate warming will cause a greater change in the distributional range of P. jezoensis than has occurred since the MHO. Overlapping climatic ranges at different times show that the Changbai Mountains, the central parts of the Japanese Alps, Hokkaido, and the Sikhote-Alin Mountains will remain suitable refugia for Jezo spruce until 2070. The establishment of artificial forest stands of P. jezoensis and intraspecific taxa in the future climate-acceptable regions may be important for the preservation of genetic diversity.

Implications of the loess record for Holocene climate and human settlement in Heye Catchment, Jiuzhaigou, eastern Tibetan Plateau, Sichuan, China

AbstractWe examine the Holocene loess record in the Heye Catchment on the margins of the Tibetan Plateau (TP) and China Loess Plateau (CLP) to determine: the region to which the Heye Catchment climate is more similar; temporal change in wind strength; and modification of the loess record by mass wasting and human activity. Luminescence and radiocarbon dating demonstrate loess deposited in two periods: >11–8.6 ka and <5.1 ka. The 8.6–5.1 ka depositional hiatus, which coincides with the Mid-Holocene Climatic Optimum, is more similar to the loess deposition cessation in the TP than to the loess deposition deceleration in the CLP. Grain-size analysis suggests the Heye loess is a mixture of at least three different grain-size distributions and that it may derive from multiple sources. A greater proportion of coarse sediments in the older loess may indicate stronger winds compared with the more recent depositional period. Gravel incorporated into younger loess most likely comes from bedrock exposed in slump scarps. Human occupation of the catchment, for which the earliest evidence is 3.4 ka, postdates the onset of slumping; thus the slumps may have created a livable environment for humans.

Vegetation and climate changes since the Last Glacial Maximum inferred from high-resolution pollen records from the Sichuan Basin, southwest China

Reconstructing the vegetation history of southwest China since the Last Glacial Maximum is crucial for understanding the evolution of the Indian summer monsoon. In this study, we present a high-resolution palynological investigation from a 5 m core from the Ganchi peatland (southwest margin of the Sichuan Basin, southwest China) in order to reconstruct regional vegetation and climate over the last 25 kyrs. The succession, from bottom to top, comprises lake, wetland, and peat deposits, and wetland/aquatic pollen types are found to be a sensitive indicator of palaeoenvironmental change. Deciduous broad leaf forests dominated by Betula were present between 25-18 cal kyrs BP, suggesting a cold and dry climate during the Last Glacial Maximum. After 18 cal kyrs BP, temperature and summer insolation increased gradually, marking the Lateglacial transition. Thermophilous and hygrophilous species expanded between 11-8 cal kyrs BP, indicating a progressively warmer and wetter climate. From 8-4 cal kyrs BP, evergreen forests developed, while Tsuga reached its maxim abundance, implying a warm and humid climate coincided with the mid-Holocene climatic optimum. Results indicate that residual ice sheets may have impeded the northward shift of the Intertropical Convergence Zone, resulting in peak Holocene warmth lagging behind peak summer insolation forcing. Vegetation change was primarily controlled by climate, with no obvious evidence of anthropogenic disturbance until the last 1 cal kyrs BP. Our study shows that vegetation and climate in the southwest margin of the Sichuan Basin were controlled by summer insolation and ice sheet dynamics, and also influenced by sea surface temperature in the Indian Ocean.

Paleochannel of the Yellow River within the Zoige Basin and its environmental significance on the NE Tibetan Plateau

Paleochannel sedimentary sequences can provide abundant information on regional environmental changes. A typical paleochannel (paleo-oxbow lake type) section of the Yellow River was identified within the Zoige Basin on the NE Tibetan Plateau. A multi-index approach was used to accurately identify sediments of different genetic types, such as riverbed deposits of the Yellow River, paleo-oxbow lake deposits, and overbank flood deposits (OFD) in the section. Based on optically stimulated luminescence (OSL) and AMS 14C dates, we examined the environmental evolution recorded by the section. The results show that: (1) The section is a record of environmental change since 4.17 ± 0.49 ka. During 4.17 ± 0.49 to 3.24 ± 0.26 ka, the ancient Yellow River occupied the channel. At 3.24 ± 0.26 ka, the paleochannel experienced a neck cutoff, and the fluvial environment began to change into the oxbow lake environment. After 2.45 ± 0.11 ka, the paleo-oxbow lake gradually disappeared. Subalpine meadow soil has developed at this site since 1.31 ± 0.05 ka. (2) Paleoenvironmental proxies indicate that the Zoige Basin was warmer and wetter before ~3.00 ka, and became drier and colder after ~3.00 ka, which may be mainly related to the weakening of the East Asian summer monsoon (EASM) and the strengthening of the Westerlies. (3) Two episodes of extreme overbank flooding occurred at 2.96 ± 0.24 to 2.87 ± 0.27 ka and 1.84 ± 0.20 to 1.70 ± 0.16 ka, correlated with climate shift period from the mid-Holocene climatic optimum to the late Holocene and the Dark Age Cold Period (DACP), respectively. Due to the relatively cold and dry climate in these periods, glaciers generally advanced on the Tibetan Plateau, and the contribution of snow and ice meltwater weakened. Therefore, the strong rainfall caused by the abnormal atmospheric circulation may be the main cause of these extreme overbank flooding.

Middle-late Holocene climate and hydrologic changes in the Gulf of Saros (NE Aegean Sea)

A multi-proxy analyses was applied on the sediment core from the Gulf of Saros (GoS) to identify and characterize climate and hydrological changes during the middle-to-late Holocene. The formation of two discrete Holocene sapropel layers in the GoS sediments was documented for the first time in the sediment core based on total organic carbon analysis. According to our paleo-proxy records, the lower Holocene sapropel was deposited under warm and humid climate conditions that gave rise to high delivery of terrestrial organic matter by numerous rivers in the northern catchment of the GoS. Biomarker and μ-XRF data were used to decipher climate variations during the middle to late Holocene. The general trends of sea-surface temperature records from the GoS and Sea of Marmara (SoM) at the beginning of late Holocene are in good agreement, underlying the influence of the Black Sea inflow. A relatively warm and wet climate together with a high sedimentation rate during the mid-Holocene Climatic Optimum resulted in high organic productivity and ensuing formation of the younger Holocene sapropel between 5.4 and 3.0 cal ka BP. Late Holocene European climate periods are evident in the Saros core records. The Roman Humid Period is represented by high variation in climate, indicating an earlier (2.5–2.3 cal ka BP) dry and a later (2.3–1.55 cal ka BP) wet periods. The abrupt return to drier condition during the Dark Ages Cold Period (1.6–1.3 cal ka BP) was followed by a wetter Medieval Climate Anomaly (1.1–0.7 cal ka BP). The paleo-proxy record of the core indicates a passage from a wetter to drier climate during the cold Little Ice Age period (730–110 cal yr BP), and highlights the influence of deforestation in the catchment of the GoS as a result of human activities during the last three centuries.

A new species of Cheironitis van Lansberge, 1875 from Jordan (Coleoptera, Scarabaeidae, Onitini).

BackgroundThe genus Cheironitis van Lansberge, 1875, currently contains 23 species from the Old World. During a survey for dung beetles in Jordan, specimens of an undescribed species were collected at the historical site of Petra.New informationA new species of Cheironitis (C.petraensis sp. n.) is described from the historical site of Petra, Jordan, illustrated and compared with its most closely related species. This new species is reminiscent of the African species of Cheironitis living in savannahs and could represent a relictual species of the mid-Holocene climatic optimum.

Föhn, fire and grazing in Southern Tibet? A 20,000-year multi-proxy record in an alpine ecotonal ecosystem

The lithology, ostracods, palynomorphs and black carbon of a sediment core from a saline wetland in the southern Tibetan highlands (29°14′33.40″N/87°13′09.10″E, 4480 m a.s.l., A.R. Xizang, China) is analyzed and climate modelling applied with respect to core questions in Quaternary research: (1) Do meso-climatic effects of regional landscape structures like high mountains overrule the effects of global climates? (2) Did life persist during the LGM? (3) Which shifts in ecosystems can be detected? (4) Does the fire-record testify for the presence of humans and their environmental impact? (5) How old is Neolithisation in the world’s largest highlands?The results of this integrated multi-disciplinary investigation revealed (1) the meso-climatic effect of the Himalayan arc’s relief channeled westerlies with West-Himalayan forest-pollen types into the southern Tibetan highlands, with (2) higher winter-precipitation, slightly lower summer precipitation, and the persistence of life for plants, and herbivores and therefore probably hunters. (3) The most arid period occurred between 17.8 and 15 cal kyr B.P., possibly synchronous with the Heinrich 1 event. Around 14.8 cal kyr B.P. humidity increased with torrential rains of high erosive power on sparsely plant-covered slopes and lasted until 4 cal kyr B.P. (4) The continuous fire-record proved the availability of combustible matter and a constant fire source which is believed to be human-attributed. Charcoal peaks around 17, 16 and 13 cal kyr B.P. remained sporadic until 11.5 cal kyr B.P. and attained the highest values since 8.7 cal kyr B.P. Black carbon increased steadily until 11 cal kyr B.P. and sharply peaked with high fluctuations around 10 cal kyr B.P., indicating high frequency intensive fires at the beginning of the Holocene. Between 10 and 6 cal kyr B.P. fire frequency decreases, with a slight peak around 4 cal kyr B.P. (5) The dawn of pastoralism in the early Mid Holocene Climatic Optimum dated back to 8.7 cal kyr B.P. with a decline of grass-pollen and the synchronous emergence of grazing weeds, leaving a perception gap of 5000 years between the palaeo-ecological and the archaeological state of the art.

Middle Holocene Indian summer monsoon variability and its impact on cultural changes in the Indian subcontinent

Agriculture is a major contributor to the economic development of modern as well as ancient India and largely depends on the rainfall in the monsoon season. In order to understand the impact of climate variability on cultural changes in the Indian subcontinent, high resolution centennial to millennial scale middle Holocene Indian summer monsoon (ISM) variability was reconstructed from Bednikund lake, located in an alpine meadow of the Pindar basin, Chamoli, Central Himalaya. Increased ISM precipitations were found during ∼5930-3950 (mid-Holocene climate optimum), ∼3380–2830 (Minoan Warm Period), ∼2610–1860 (Roman Warm Period), ∼1050–760 (Medieval Climate Anomaly), and ∼320 cal yr BP to Present (Current Warm Period). The decreased ISM strengths were found during ∼3950-3380, ∼2830–2610, ∼1860–1050 (Dark Ages Cold Period), ∼760–580, and ∼500-320 cal yr BP (Little Ice Age). The covariance between our records of precipitation change and total solar irradiance for the middle to late Holocene and with Northern hemisphere (NH) temperature for the past two millennia suggested solar insolation as a primary forcing mechanism of ISM variability. The reconstructed paleoclimate combined with archaeology and historical records indicated that ancient Indian civilizations e.g., the Indus Valley (∼5200-3300 cal yr BP) and Vedic (∼3400-2400 cal yr BP) had established and thrived during periods of strengthened ISM precipitation, whereas their collapse closely corresponded to the decreased strength in ISM. From ∼2400 to 200 cal yr BP, the Indian subcontinent witnessed the rise and fall of various Kingdoms/dynasties. This period saw an exponential expansion/growth in agriculture, economy, population, languages, architecture, and religions in the Indian subcontinent. The agrarian-based economy showed little or no impact of monsoon weakening after ∼2400 cal yr BP possibly due to development and reforms in administrative policies, construction of irrigation systems such as dams, lakes and canals, use of technology for irrigation such as waterwheel, knowledge of double cropping, production of cash crops. The ancient civilizations of India were directly impacted by the strengthening and weakening of ISM, whereas for the later periods, civilizations were able to adapt to climate change.

GEOMORPHOLOGICAL DYNAMICS OF THE ELEVATED GEOSYSTEMS OF THE BORBOREMA HIGHLANDS, NORTHEAST OF BRAZIL, FROM OPTICALLY STIMULATED LUMINESCENCE DATING OF HILLSLOPE SEDIMENTS

The geomorphological dynamics of the elevated compartments of the Borborema Highlands, northeastern Brazil, were assessed through the analysis of hillslope sediments. The chosen study area was the Baixa Verde massif, in the State of Pernambuco. The main morphostratigraphic features were identified on the basis of their relevance to the reconstruction of the geomorphological dynamics. First hillslope deposits in the shape of colluvial fans, or infills of hollows and zero order catchments were identified. Following field study of the stratigraphic interactions in four sampling areas within the massif, samples were collected for a number of laboratory tests: sedimentological analysis, soil micromorphology and Optically Stimulated Luminescence (OSL) dating. A fragment of charcoal found on the top of a gravel layer was radiocarbon- dated. The sampling procedures were aimed at the characterization of the several depositional units. The results of the dating of 14 sampling sites point to the occurrence of discrete events of hillslope material remobilization within the last 20,000 years as a dynamic response of the geomorphological systems to the following events: the Last Glacial Maximum (LGM), the Pleistocene/Holocene transition, the mid-Holocene climatic optimum and the recent anthropic period and its short term climatic oscillations.

Vegetation, climate and human impact since 20 ka in central Yunnan Province based on high-resolution pollen and charcoal records from Dianchi, southwestern China

High-resolution pollen and charcoal records from Dianchi in central Yunnan Province, southwestern China are presented in this study and reveal variations in vegetation, fire, lake environments, and climate over the last 20,000 years (20 ka). The results show that the climate during the period 20.0–18.0 ka was relatively cold, and rainfall in winter and early spring was relatively lower than the present, which belongs to the Last Glacial Maximum (LGM) . After 18.0 ka, the temperature increased gradually, indicating the onset of deglacial warming in central Yunnan Province, though the mean annual temperature before 10.8 ka was still at least 1.5 °C lower than today. The climate began to obviously warm from ∼10.8 ka and was at least 2 °C higher than today and relatively humid between 10.0 and 5.4 ka, denoting the early-Holocene Thermal Maximum. A major vegetation change around Dianchi occurred at ∼5.4 ka and was most likely caused by the climate cooling and drying with no obvious evidence for cultivation activities except for some possible evidence of human fire use or selective deforestation from the pollen assemblage. Significant cultivation activities in Yunnan Province indicated by the first obvious increases in Poaceae (>40 μm) and Poaceae (25–40 μm) pollen percentages began at ∼2.4 ka. In central Yunnan Province, there was a continuous deglacial warming that occurred between 18.0 and 12.5 ka without marked interruption during the interval of Heinrich Event 1 (H1). Additionally, the Holocene Thermal Maximum occurred in the early Holocene. The results from this study are different from the western region of southwestern China where the paleoclimate studies have clearly detected the H1, the B/A, and the YD events, and revealed a mid-Holocene climatic optimum.

Centennial- to millennial-scale monsoon changes since the last deglaciation linked to solar activities and North Atlantic cooling

Abstract. Rapid monsoon changes since the last deglaciation remain poorly constrained due to the scarcity of geological archives. Here we present a high-resolution scanning X-ray fluorescence (XRF) analysis of a 13.5 m terrace succession on the western Chinese Loess Plateau (CLP) to infer rapid monsoon changes since the last deglaciation. Our results indicate that Rb∕Sr and Zr∕Rb are sensitive indicators of chemical weathering and wind sorting, respectively, which are further linked to the strength of the East Asian summer monsoon (EASM) and the East Asian winter monsoon (EAWM). During the last deglaciation, two cold intervals of the Heinrich event 1 and Younger Dryas were characterized by intensified winter monsoon and weakened summer monsoon. The EAWM gradually weakened at the beginning of the Holocene, while the EASM remained steady till 9.9 ka and then grew stronger. Both the EASM and EAWM intensities were relatively weak during the Middle Holocene, indicating a mid-Holocene climatic optimum. Rb∕Sr and Zr∕Rb exhibit an antiphase relationship between the summer and winter monsoon changes on a centennial timescale during 16–1 ka. Comparison of these monsoon changes with solar activity and North Atlantic cooling events reveals that both factors can lead to abrupt changes on a centennial timescale in the Early Holocene. During the Late Holocene, North Atlantic cooling became the major forcing of centennial monsoon events.

Hydrological reconstruction of extreme palaeoflood events 9000–8500 a BP in the Danjiang River Valley, tributary of the Danjiangkou Reservoir, China

The Danjiang River, a major tributary of the Danjiangkou Reservoir, is famed for the current national South-to-North Water Diversion project. Palaeohydrological investigations were carried out in the Danjiang River valley. A set of palaeoflood slackwater deposit (SWD) beds was identified embedded in Holocene loess soil sequences within riverbank cliffs based on sedimentary criteria and analytical results. These palaeoflood SWDs were deposited from the suspended sediment load of overbank flooding. These extreme palaeoflood events were dated to between 9000 and 8500 a BP from optically simulated luminescence (OSL) dating and pedostratigraphical correlation. The palaeoflood peak stages were calculated between 404.4 and 412.5 m using the slackwater flow depth method. The palaeoflood peak discharges were calculated between 8570 and 23,350 m3/s using the HEC-RAS model. These results have extended the flood data sequence of the Danjiang River to a 10,000-year time-scale. The ages of the palaeoflood events coincide well with the contemporaneous global climatic events at 8500 a BP, a time that the monsoonal climate shifted from the early Holocene dry conditions to the mid-Holocene climatic optimum. These findings will play an important role in flood risk estimation, the development of water resources, and will be significant in understanding the effects global climatic variations on hydrological systems in catchment of the Danjiangkou Reservoir.

Main patterns of present-day zonal vegetation development in Kaliningrad Oblast, Russian Federation (southeastern Baltic), inferred on palynological data

This article is devoted to the question of zonal vegetation formation on the territory of Kaliningrad Oblast, Russian Federation, during the Mid- and Late Holocene. Based on palynological data, the main variants of zonal phytocoenoses are defined. It is stated that the formation of present-day zonal vegetation in the region can be derived from the species-rich deciduous forests which became dominant in the study area up to the middle of the Atlantic (7000-6000 cal BP). These plant communities, the key elements of which belong to species of the ‘nemoral complex’ ( Quercus , Ulmus , Tilia , Corylus ), could be considered the climax vegetation corresponding to the mid-Holocene Climatic Optimum. Their further development during the Late Holocene consisted of several structural shifts, such as the invasion of hornbeam ( Carpinus betulus ) during the Sub-Boreal; the invasion of spruce ( Picea abies ) during the Sub-Boreal in the southern part of the region and during the Atlantic and Sub-Boreal in the northern part; the distribution of beech ( Fagus sylvatica ) as a characteristic species of deciduous forests in the southern part of the region during the Atlantic and Sub-Boreal. The lowland habitats, especially in the Neman Delta landscape area, had been occupied by communities of the black alder ( Alnus glutinosa ). These processes led to the formation of three variants of nemoral zonal vegetation on the territory of the region: 1) oak-linden-hornbeam forests, 2) spruce-broadleaved forests with an admixture of hornbeam, 3) black alder communities. All three variants were dominant during the Mid- and Late Holocene (≈ 5000-1300 cal BP). In the later period, a common decline of broadleaved species is recorded with a simultaneous increase of conifers, apparently as a response to climate cooling. Regarding present-day climate conditions, the boundary of Fagus distribution range in the region should be set more northeastwards than currently. Substantial structural alterations occurred in the nemoral forests under anthropogenic impact during the last 300 years, though in the Neman Delta area this transition started later (150-200 years ago) due to difficult access to the area.

Climate and marine biogeochemistry during the Holocene from transient model simulations

Abstract. Climate and marine biogeochemistry changes over the Holocene are investigated based on transient global climate and biogeochemistry model simulations over the last 9500 years. The simulations are forced by accelerated and non-accelerated orbital parameters, respectively, and atmospheric pCO2, CH4, and N2O. The analysis focusses on key climatic parameters of relevance to the marine biogeochemistry, and on the physical and biogeochemical processes that drive atmosphere–ocean carbon fluxes and changes in the oxygen minimum zones (OMZs). The simulated global mean ocean temperature is characterized by a mid-Holocene cooling and a late Holocene warming, a common feature among Holocene climate simulations which, however, contradicts a proxy-derived mid-Holocene climate optimum. As the most significant result, and only in the non-accelerated simulation, we find a substantial increase in volume of the OMZ in the eastern equatorial Pacific (EEP) continuing into the late Holocene. The concurrent increase in apparent oxygen utilization (AOU) and age of the water mass within the EEP OMZ can be attributed to a weakening of the deep northward inflow into the Pacific. This results in a large-scale mid-to-late Holocene increase in AOU in most of the Pacific and hence the source regions of the EEP OMZ waters. The simulated expansion of the EEP OMZ raises the question of whether the deoxygenation that has been observed over the last 5 decades could be a – perhaps accelerated – continuation of an orbitally driven decline in oxygen. Changes in global mean biological production and export of detritus remain of the order of 10 %, with generally lower values in the mid-Holocene. The simulated atmosphere–ocean CO2 flux would result in atmospheric pCO2 changes of similar magnitudes to those observed for the Holocene, but with different timing. More technically, as the increase in EEP OMZ volume can only be simulated with the non-accelerated model simulation, non-accelerated model simulations are required for an analysis of the marine biogeochemistry in the Holocene. Notably, the long control experiment also displays similar magnitude variability to the transient experiment for some parameters. This indicates that also long control runs are required when investigating Holocene climate and marine biogeochemistry, and that some of the Holocene variations could be attributed to internal variability of the atmosphere–ocean system.

Integration of Linearbandkeramik cattle husbandry in the forested landscape of the mid-Holocene climate optimum: Seasonal-scale investigations in Bohemia

Domestic animals and plants were introduced to Europe from the Near East and subsequently spread across Europe, entailing adaptations to different environments with consequences for the biology of organisms, agropastoral technical systems and socio-economic organisation. Agriculture was introduced to Central Europe by Linearbandkeramik (LBK) societies between 5600 and 4900 cal. BC, in predominantly forested environments. LBK farming systems involved intensive permanent field cultivation in natural openings. Milking was practiced as evidenced from cattle mortality profiles and lipid residues in ceramics. Questions arise as to what extent LBK cattle husbandry relied on woodland, and as to whether the seasonal scarcity of fodder conditioned cattle reproduction cycles, with consequences on milk availability. Results from the δ13C and δ18O analysis of cattle tooth enamel at Chotěbudice and Černý Vůl (Bohemia, Czech Republic) suggest a limited use of dense forest for cattle herding, even on a seasonal scale: cattle were kept in the open component of the forest/steppe mosaic landscape. Winter forest browsing/provision of leafy fodder was evidenced in one specimen. At Chotěbudice, cattle births mainly occurred over a two to three-month period, suggesting environmental constraints on cattle fertility cycles, and possibly seasonal fodder scarcity. A direct consequence of this would be a shorter period of milk availability throughout the year.

Depositional environment and climate changes during the Holocene in Grande Valley, Fildes Peninsula, King George Island, Antarctica

AbstractA 9.24 m sediment core, GA-2, was collected on the coastal platform of Grande Valley, a relatively narrow and shallow fjord in Fildes Peninsula, King George Island, Antarctica. The sediment was formed between 6600 and 2000 cal. yrbpaccording to accelerator mass spectrometry (AMS)14C dating of five bulk sediment samples. The comprehensive proxy indicators (grain size, loss on ignition at 550°C, magnetic susceptibility, elements) were analysed, and three separate depositional environments and an alternating climate change pattern were identified. Grande Valley experienced a warm marine environment between 6600 and 5800 cal. yrbp, a minor cooling between 5800 and 4800 cal. yrbp, the transition from cool to warm during 4800–4400 cal. yrbp, a mid-Holocene climatic optimum between 4400 and 2700 cal. yrbp, and the onset of the Neoglacial at 2700 cal. yrbp. This study reconstructed the environmental history of Grande Valley during the mid–late Holocene, provides the missing marine record of historical climate for the western coast of Fildes Peninsula and lays the foundation for further study of the climate and environment changes therein. Our finding that the sea level wasc.12 m a.m.s.l. at 2000 cal. yrbpallows for detailed reconstruction of Holocene sea level variations.

Loess deposits of the upper Hanjiang River valley, south of Qinling Mountains, China: Implication for the pedogenic dynamics controlled by paleomonsoon climate evolution

Aeolian deposits in the Chinese Loess Plateau (CLP) provide a detailed archive for reconstructing the pedogenic intensity as well as the East Asian monsoon climate change. However, study on the loess in the upper Hanjiang River valley, south of Qinling Mountains has seldom been comprehensively reported. Located at the transition zone between temperate and subtropical monsoon climate, the study area is more sensitive to the climate change. In this paper, three loess-paleosol profiles at the first terrace of the upper Hanjiang River were studied in detail. High-resolution investigations, including field observations, optically stimulated luminescence (OSL) dating, and measurements of magnetic susceptibility (MS), grain-size (GS), color variation, loss-on-ignition (LOI) and chemical elements were carried out. The results show that the stratigraphic sequences, in order from the top to the bottom, are topsoil (TS), recent loess (L0), paleosol (S0), transitional loess (Lt), Malan loess (L1) and fluvial deposits (T1-al). The pedogenic intensity varies significantly in different layers and presents such a tendency of S0 > L0 > Lt > L1. This indicates four distinct stages in the paleoclimate evolution: a cold-dry period (55.0–11.5 ka B.P.); a phase of gradual transition to warm-wet (11.5–8.5 ka B.P.); the maximum warm-wet period (8.5–3.0 ka B.P.); and a phase of gradually shifting to cool-dry (3.0–0.0 ka B.P.). The climate change trends are similar with the loess records from the CLP and the stalagmite and peat records in southern China. But the paleosol development in the study is probably a better indicator of the strength of summer monsoon climate change during the mid-Holocene Climatic Optimum. This study also provides basic data for exploring the pedogenesis and climate differences in the East Asian monsoon climate zones.

Pollen Evidence of a Humid Mid-Holocene Climate from Bahar Nuur, Inner Mongolia

A high-resolution pollen-based bioclimatic reconstruction from Bahar Nuur Lake in Inner Mongolia, China, supported by 15 AMS dates, is compared with other records in the Ordos Plateau and stalagmite record from Dongge cave in order to better understand the Holocene climate history in semi-arid East Asian monsoon margin area better. A humid climate prevailed in the Ordos Plateau during 6.3-4.4 ka BP, as indicated by high broadleaf-tree pollen percentages and pollen concentrations. Due to a strong Asian monsoon, the mid-Holocene climatic optimum exhibited a delayed vegetative response on the Ordos Plateau.