Environmental changes on Yugorski Peninsula, Kara Sea, Russia, during the last 12,800 radiocarbon years

New pollen and radiocarbon data from an 8.6-m coastal section, Cape Shpindler (69°43′N; 62°48′E), Yugorski Peninsula, document the latest Pleistocene and Holocene environmental history of this low Arctic region. Twelve AMS ¹⁴C dates indicate that the deposits accumulated since about 13,000 until 2000 radiocarbon years BP. A thermokarst lake formed ca. 13,000–12,800 years BP, when scarce arctic tundra vegetation dominated the area. By 12,500 years BP, a shallow lake existed at the site, and Arctic tundra with Poaceae, Cyperaceae, Salix, Saxifraga, and Artemisia dominated nearby vegetation. Climate was colder than today. Betula nana became dominant during the Early Preboreal period about 9500 years BP, responding to a warm event, which was one of the warmest during the Holocene. Decline in B. nana and Salix after 9500 years BP reflects a brief event of Preboreal cooling. A subsequent increase in Betula and Alnus fruticosa pollen percentages reflects amelioration of environmental conditions at the end of Preboreal period (ca. 9300 years BP). A decline in arboreal taxa later, with a dramatic increase in herb taxa, reflects a short cold event at about 9200 years BP. The pollen data reflect a northward movement of tree birch, peaking at the middle Boreal period, around 8500 years BP. Open Betula forest existed on the Kara Sea coast of the Yugorski Peninsula during the Atlantic period (8000–4500 years BP), indicating that climate was significantly warmer than today. Deteriorating climate around the Atlantic–Subboreal boundary (ca. 4500 years BP) is recorded by a decline in Betula percentages. Sedimentation slowed at the site, and processes of denudation and/or soil formation started at the beginning of the Subatlantic period, when vegetation cover on Yugorski Peninsula shifted to near-modern assemblages.     

Mid–late Holocene monsoon climate retrieved from seasonal Sr/Ca and δO records of Porites lutea corals at Leizhou Peninsula, northern coast of South China Sea

South China Sea (SCS) is a major moisture source region, providing summer monsoon rainfall throughout Mainland China, which accounts for more than 80% total precipitation in the region. We report seasonal to monthly resolution Sr/Ca and δ¹⁸O data for five Holocene and one modern Porites corals, each covering a growth history of 9–13 years. The results reveal a general decreasing trend in sea surface temperature (SST) in the SCS from 6800 to 1500 years ago, despite shorter climatic cycles. Compared with the mean Sr/Ca–SST in the 1990s (24.8 °C), 10-year mean Sr/Ca–SSTs were 0.9–0.5 °C higher between 6.8 and 5.0 thousand years before present (ky BP), dropped to the present level by 2.5 ky BP, and reached a low of 22.6 °C (2.2 °C lower) by 1.5 ky BP. The summer Sr/Ca–SST maxima, which are more reliable due to faster summer-time growth rates and higher sampling resolution, follow the same trend, i.e. being 1–2 °C higher between 6.8 and 5.0 ky BP, dropping to the present level by 2.5 ky BP, and reaching a low of 28.7 °C (0.7 °C lower) by 1.5 ky BP. Such a decline in SST is accompanied by a similar decrease in the amount of monsoon moisture transported out of South China Sea, resulting in a general decrease in the seawater δ¹⁸O values, reflected by offsets of mean δ¹⁸O relative to that in the 1990s. This observation is consistent with general weakening of the East Asian summer monsoon since early Holocene, in response to a continuous decline in solar radiation, which was also found in pollen, lake-level and loess/paleosol records throughout Mainland China. The climatic conditions 2.5 and 1.5 ky ago were also recorded in Chinese history. In contrast with the general cooling trend of the monsoon climate in East Asia, SST increased dramatically in recent time, with that in the 1990s being 2.2 °C warmer than that 1.5 ky ago. This clearly indicates that the increase in the concentration of anthropogenic greenhouse gases played a dominant role in recent global warming, which reversed the natural climatic trend in East Asian monsoon regime.     

Quaternary vegetation and climate changes on Banks Peninsula, South Island, New Zealand

Late Quaternary terrestrial and marine pollen records from the Canterbury Plains and Banks Peninsula suggest that climates during the peak of Marine Isotope Stage 7 (MIS 7) were similar to those prevailing during stage 5e and the Holocene. Podocarp forest (notably Prumnopitys taxifolia—matai) characterises each interglaciation. In contrast, marine records from DSDP 594 cores, off the east coast of Canterbury, indicate that stage 7 was dominated by montane forest (Libocedrus sp. and Phyllocladus). This suggests temperatures as much as 3 °C colder than indicated by the Banks Peninsula assemblage. Age control from both sites appears to be robust. Some of the differences may be related to the taphonomy of the pollen at both sites. DSDP 594 may reflect a more southerly catchment of fluvially and aeolian-derived pollen than does the Banks Peninsula site.Banks Peninsula was alternately separated from, and joined to, the mainland as Quaternary sea levels fell and rose. Assuming modern ocean current patterns, during interglacials the south–north Southland Current would have swept through the seaway separating the island from the mainland, diverting the flow of rivers embouching on the Canterbury coast, and moving sediments and fluvially transported pollen northwards. Little of this material would have reached DSDP 594, nor, if wind patterns were similar to those of today, would wind-borne pollen from Banks Peninsula have reached the site. It is probable that vegetation on the Peninsula was consistently distinct from that recorded at DSDP 594, which has a more southerly derivation.In contrast to the high mountain areas of the South Island, the low levels of grass pollen in the available record suggest that the Peninsula retained a woody vegetation over much of its area during glacial periods. This was favoured by the physiography of the area, with a variety of micro-climates, and by the extensive areas available for colonisation at times of low sea level. The podocarp forest of MIS 7 was replaced by an open shrubby vegetation in which Leptospermum and Kunzea (Leptospermum-type pollen) was locally dominant, and in which Plagianthus, Phyllocladus, Coprosma and Myrsine were prominent. Charcoal is associated with this change. Most of the recorded taxa, with the exception of Phyllocladus, are present on the Peninsula today. A gap in the pollen record coincides with the Last Interglacial and Last Glaciation, but a return of forest vegetation is documented in the later Holocene.The reconstructions do not exclude the possibility of a cooler stage 7. They do highlight the importance of excluding local/regional non-climatic effects before interpreting climate change from data sets, and reinforce the necessity of testing marine records against compatible terrestrial ones.     

Climatic change in Central Asia during MIS 3/2: a case study using biological responses from Lake Baikal

A Marine Isotope Stage (MIS) 3/early MIS 2 section from a structural high along the east coast of the North Basin of Lake Baikal was analysed for diatoms, C/N ratios, and organic carbon isotope ratios. Diatoms were present throughout MIS 3 and early MIS 2, with high concentrations of the planktonic taxa Cyclotella sp. c.f. gracilis between 54 and 51.5 kyr BP indicating relatively warm, interstadial, conditions. Following a %TOC inferred climatic cooling between 43.2 and 39.1 kyr BP, evidence of a more muted δ¹³C_(organic) and %TOC inferred climatic warming from c. 39.1–34.7 kyr BP coincides with a period of very high diatom concentrations, indicating high aquatic productivity, at the Buguldeika Saddle in the South Basin of Lake Baikal. No evidence exists for a ‘Kuzmin’ catchment erosional event in the North Basin during MIS 3. This, however, may reflect the location of the coring site away from major riverine inputs. Abrupt climatic cooling at the culmination of both warm phases in the North Basin are associated, on the basis of the palaeomagnetic age-model and correlations to existing sites in Lake Baikal, with the initiation of Heinrich events 5 (c. 50 kyr BP) and 4 (c. 35 kyr BP), respectively, in the North Atlantic. The amount of organic material declines across the MIS 3/MIS 2 transition while constant C/N ratios suggest organic material to be predominantly derived from phytoplankton. An increase in δ¹³C_(organic) at the MIS 3/MIS 2 transition may therefore indicate changes in aquatic productivity, pCO₂ or the inorganic carbon pool.     

Vegetation changes and their climatic implication for the late Pleistocene at Lake Poukawa, Hawkes Bay, New Zealand

A detailed vegetation history extending back to the Last Interglacial (Marine Isotope Substage 5e) is presented for Lake Poukawa, Hawkes Bay, New Zealand. This history is based on palynological analyses of a 198-m core record, age secured by uranium/thorium (U/Th) and optically stimulated luminescence (OSL) dates as well as tephrochronology. Vegetation of the penultimate glacial (Isotope Stage 6) probably consisted of a very sparse shrubby herbland of stunted podocarps (Phyllocladus sp.), daisies, grasses and sedges. Similar floras existed in each of the succeeding cool periods. Four interglacial/interstadial floras are preserved. The peak of the Last Interglacial (Substage 5e) was dominated by extensive lowland forest of tall forest podocarps (Podocarpus/Prumnopitys), most probably matai (Prumnopitys taxifolia) with red beech (Nothofagus fusca), secondary forest trees (Coprosma spp., Myrsine spp.) and tree ferns (Cyathea spp.). In the Poukawa basin itself, a swamp forest of the podocarp (Dacrycarpus dacrydioides) with the true palm (Rhopalostylis sapida) expanded. Substage 5e was significantly warmer and/or moister than the present day. Substage 5c/5a was marked by montane forest of red and silver beeches (N. fusca and N. menziesii), Phyllocladus spp. and secondary trees. A reduced representation of Podocarpus/Prumnopitys possibly consists of montane podocarp (Podocarpus hallii). We infer the temperature of Substage 5c/5a to have been 3.5–5 °C lower than the present day. Although Stage 3 flora are superficially similar to those of Substage 5c/5a, the beeches are relatively less dominant. The regional flora during Stage 1 is very similar to those of Substage 5e, but the density is lower with no swamp forest during the present interglaciation. This may represent a change in evapotranspiration balance around Poukawa, but may also be controlled by hydrological conditions within the basin.     

A late Quaternary lake record from the Qilian Mountains (NW China): evolution of the primary production and the water depth reconstructed from macrofossil, pollen, biomarker, and isotope data

The history (45–0 ka BP) of the aquatic vegetation composition of the shallow alpine Lake Luanhaizi from the NE Tibetan Plateau is inferred from aquatic plant macrofossil frequencies and aquatic pollen and algae concentrations in the sediments. C/N (range: 0.3–100), δ¹³C (range: −28 to −15‰), and n-alkane measurements yielded further information on the quantitative composition of sedimentary organic matter. The inferred primary production of the former lake ecosystem has been examined in respect of the alternative stable state theory of shallow lakes [Scheffer, M., 1989. Alternative stable states in eutrophic, shallow freshwater systems: a minimal model. Hydrobiological Bulletin 23, 73–83]. Switches between clear and turbid water conditions are explained by a colder climate and forest decline in the catchment area of Lake Luanhaizi. The macrofossil-based reconstruction of past water depth and salinity ranges, as well as other organic matter (OM) proxies allowed climatic inferences of the summer monsoon intensity during the late Quaternary. Around 45 ka BP, conditions similar to or even moister than present-day climate occurred. The Lake Luanhaizi record is further evidence against an extensive glaciation of the Tibetan Plateau and its bordering mountain ranges during the Last Glacial Maximum. Highest lake levels and consequently a strong summer monsoon are recorded for the early Holocene period, while gradually decreasing lake levels are reconstructed for the middle and late Holocene.     

Continental climate in the East Siberian Arctic during the last interglacial: Implications from palaeobotanical records

To evaluate the consequences of possible future climate changes and to identify the main climate drivers in high latitudes, the vegetation and climate in the East Siberian Arctic during the last interglacial are reconstructed and compared with Holocene conditions. Plant macrofossils from permafrost deposits on Bol'shoy Lyakhovsky Island, New Siberian Archipelago, in the Russian Arctic revealed the existence of a shrubland dominated by Duschekia fruticosa, Betula nana and Ledum palustre and interspersed with lakes and grasslands during the last interglacial. The reconstructed vegetation differs fundamentally from the high arctic tundra that exists in this region today, but resembles an open variant of subarctic shrub tundra as occurring near the tree line about 350 km southwest of the study site. Such difference in the plant cover implies that, during the last interglacial, the mean summer temperature was considerably higher, the growing season was longer, and soils outside the range of thermokarst depressions were drier than today. Our pollen-based climatic reconstruction suggests a mean temperature of the warmest month (MTWA) range of 9–14.5 °C during the warmest interval of the last interglacial. The reconstruction from plant macrofossils, representing more local environments, reached MTWA values above 12.5 °C in contrast to today's 2.8 °C. We explain this contrast in summer temperature and soil moisture with a combination of summer insolation higher than present and climatic continentality in arctic Yakutia stronger than present as result of a considerably less inundated Laptev Shelf during the last interglacial.     

The Pleistocene evolution of the East Antarctic Ice Sheet in the Prydz bay region: stable isotopic evidence from ODP Site 1167

Ocean Drilling Program Leg 188, Prydz Bay, East Antarctica is part of a larger initiative to explore the Cenozoic history of the Antarctic Ice Sheet through direct drilling and sampling of the continental margins. In this paper, we present stable isotopic results from Ocean Drilling Program (ODP) Site 1167 located on the Prydz Channel Trough Mouth Fan (TMF), the first Antarctic TMF to be drilled. The foraminifer-based δ¹⁸O record is interpreted along with sedimentary and downhole logging evidence to reconstruct the Quaternary glacial history of Prydz Bay and the adjacent Lambert Glacier Amery Ice Shelf System (LGAISS). We report an electron spin resonance age date of 36.9±3.3 ka at 0.45 m below sea floor and correlate suspected glacial–interglacial cycles with the global isotopic stratigraphy to improve the chronology for Site 1167. The δ¹⁸O record based on planktonic (Neogloboquadrina pachyderma (s.)) and limited benthic results (Globocassidulina crassa), indicates a trend of ice sheet expansion that was interrupted by a period of reduced ice volume and possibly warmer conditions during the early–mid-Pleistocene (0.9–1.38 Ma). An increase in δ¹⁸O values after 900 ka appears to coincide with the mid-Pleistocene climate transition and the expansion of the northern hemisphere ice sheet. The δ¹⁸O record in the upper 50 m of the stratigraphic section indicates as few as three glacial–interglacial cycles, tentatively assigned as marine isotopic stages (MIS) 16–21, are preserved since the Brunhes/Matuyama paleomagnetic reversal (780 ka). This suggests that there is a large unconformity near the top of the section and/or that there may have been few extreme advances of the ice sheet since the mid-Pleistocene climate transition resulting in lowered sedimentation rates on the Prydz Channel TMF. The stable isotopic record from Site 1167 is one of the few available from the area south of the Antarctic Polar Front that has been linked with the global isotopic stratigraphy. Our results suggest the potential for the recovery of useful stable isotopic records in other TMFs.     

Aminostratigraphy of Middle and Late Pleistocene deposits in The Netherlands and the southern part of the North Sea Basin

A review of all available amino acid racemization D (alloisoleucine)/L (isoleucine) data from the whole shell of four molluscan species from Late and late Middle Pleistocene deposits of the Netherlands is presented. The data allow the distinction of 5 aminostratigraphical units, NAZ (Netherlands Amino Zone) A–E, each representing a temperate stage. The zones are correlated with marine isotope stages 1, 5e, 7, 9, and 11 respectively. Apart from NAZ-D (MIS 9), in all aminozones the marine transgression reached the present-day onshore area of the Netherlands. The transgression during NAZ-C (Oostermeer Interglacial: MIS 7) seems to be at least as widespread as its counterpart during NAZ-B (Eemian: MIS 5e) in the southern bight of the North Sea Basin. The stratigraphic position of the Oostermeer Interglacial is just below deposits of the Drente phase of the Saalian and because of this position the interglacial marine deposits have formerly erroneously considered to be of Holsteinian age. Neede, the ‘classic’ Dutch Holsteinian site, is dated in NAZ-E (MIS 11), like Noordbergum. Although the validity of these zones has been checked with independent data, some overlap between succeeding zones may occur. The relation between amino acid data from elsewhere in the North Sea Basin and the Netherlands amino zonation is discussed. The deposits at the Holsteinian stratotype Hummelsbüttel in North West Germany are dated in NAZ-D. This interglacial correlates with MIS 9. The Belvédère Interglacial, which is of importance for its archaeology, is in NAZ-D (MIS 9) and therefore of Holsteinian age as well. The lacustroglacial ‘pottery clays’ in the Noordbergum area are deposits from two glacial stages, which can be correlated with MIS 8 and 10 (the Elsterian). The pottery clay that is considered equivalent to the German ‘Lauenburger Ton’ correlates with MIS 10.     

Distinguishing between tills from Valdaian ice sheets in the Arkhangelsk region, Northwest Russia

Recent studies in the Arkhangelsk region, northwest Russia, have identified at least three consecutive tills all associated with the last Valdaian (Weichselian) glaciation. The Scandinavian ice sheet deposited a Late Valdaian till (ca. 17 ka BP), whereas two tills were deposited in the Early–Middle Valdaian by the Barents/Kara Sea ice sheet (ca. 45–60 ka BP) and an older ice sheet with an eastern centre (ca. 74 ka BP). This article expands on previous stratigraphical work on the discrimination of regional till units by a combination of compositional characteristics and directional properties. Tills associated with the Scandinavian ice sheet were deposited by a glacier advancing from west or northwest, transporting predominantly material from the Fennoscandian shield and the White Sea area. The Barents/Kara Sea ice sheet moved from the north and northeast, whereas the oldest ice advance came from the east–southeast. Although, the two oldest tills both contain material with an eastern provenance, the Viryuga Till is dominated more by local carbonate-rich material. This study demonstrates that detailed investigation of till units facilitate the distinction of glacial events imperative for the reconstructing of the last glaciation in northern Russia.     

A Holocene and latest Pleistocene pollen record from Lake Poukawa, Hawke's Bay, New Zealand

Lake Poukawa is a small, shallow lake lying in the middle of extensive peatland in the Poukawa depression, central Hawke's Bay. Holocene peats (10 m at deepest point) overlie more than 200 m of sand, silt, clastic debris and infrequent thin peats and lacustrine sediments deposited during the late Pleistocene. Pollen analyses are presented for: a peat possibly dating to a late stage of the last interglacial or a warm interstadial of the last glacial; cool climate last glacial sediments; and a Holocene peat. The last interglacial or interstadial peat records a cool climate Nothofagus podocarp forest. During the last glacial, sparse shrubland and grassland grew within the depression under much drier and colder conditions than now. There is no pollen record for the Late Glacial and early Holocene period as conditions remained too dry for peat formation. Avian fossils indicate scrub and grassland persisted through until at least 10,600 years BP, and scrub or open forest may have prevailed until c. 6500 years BP. Closed podocarp broadleaved forest (Prumnopitys taxifolia dominant) occupied the depression from at least 6500 years BP until its destruction by Polynesian settlers after 800 years BP. Water levels rose from 6500 to 4500 years BP, culminating in the establishment of the present fluctuating lake-peatland system. Dry conditions in the Late Glacial and early Holocene may reflect a predominant northwesterly air flow, and a change to more easterly and southerly air flow in the mid- to late Holocene resulted in increased rainfall.     

Eccentricity cycles shown by early Pleistocene planktonic foraminifers of the Omma Formation, Sea of Japan

There is a continuous record of planktonic foraminifers for oxygen isotope stages 50 to 26 (ca. 1.5–1.0 Ma) in the early Pleistocene Omma Formation near Kanazawa City, Central Japan, on the Sea of Japan coast. The warm-water species Globigerinoides ruber entered the Sea of Japan with the Tsushima Current during all interglacial periods and went locally extinct in the succeeding glacial periods. This implies that the marine climate of the Sea of Japan varied predominantly with the 41,000-year period of Earth's orbital obliquity. However, the relative abundances of G. ruber in marine isotope stages 47, 43 and 31 are significantly higher than those in other interglacial stages. These stages correspond to periods when eccentricity-modulated precession extremes were aligned with obliquity maxima. The Tsushima Current is a branch of the warm Kuroshio Current which is the strong northwestern component of the subtropical North Pacific Ocean gyre. Our data imply that the early Pleistocene climate in the northwestern Pacific was influenced not only by obliquity cycles but also by eccentricity cycles. This study also supports the climate model regarding eccentricity's role in the origin of low-frequency climate changes before the late Pleistocene ice ages.     

Past 100 ky surface salinity-gradient response in the Eastern Arabian Sea to the summer monsoon variation recorded by δO of G. sacculifer

Northward flowing coastal currents along the western margin of India during winter–spring advect low-salinity Bay of Bengal water in to the Eastern Arabian Sea producing a distinct low-salinity tongue, the strength of which is largely governed by the freshwater flux to the bay during summer monsoons. Utilizing the sedimentary records of δ¹⁸O_{G. sacculifer}, we reconstructed the past salinity-gradient within that low-salinity tongue, which serves as a proxy for the variation in freshwater flux to the Bay of Bengal and hence summer monsoon intensity.The north–south contrast in the sea level corrected (residual)-δ¹⁸O_{G. sacculifer} can be interpreted as a measure of surface salinity-contrast between those two locations because the modern sea surface temperature and its past variation in the study region is nearly uniform. The core-top residual-δ¹⁸O_{G. sacculifer} contrast of 0.45‰ between the two cores is assumed to reflect the modern surface salinity difference of 1 psu and serves as a calibration for past variations.The residual-δ¹⁸O_{G. sacculifer} contrast varies between 0.2‰ at 75 ky B.P. (i.e., late-Marine Isotope Stage 5) and 0.7‰ at 20 ky B.P. (i.e., Last Glacial Maximum), suggesting that the overall salinity difference between the northern- and southern-end of the low-salinity tongue has varied between 0.6 and 1.6 psu. Considerably reduced difference during the former period than the modern suggests substantially intensified and northward-extended low-salinity tongue due to intense summer monsoons than today. On the other hand, larger difference (1.6 psu) during the latter period indicates that the low-salinity tongue was significantly weakened or withdrawn due to weaker summer monsoons. Thus, the salinity-gradient in the eastern Arabian Sea low-salinity tongue can be used to understand the past variations in the Indian summer monsoons.     

Detrital input and early diagenesis in sediments from Lake Baikal revealed by rock magnetism

A rock magnetic study was performed on sediment cores from six locations in Lake Baikal. For a comprehensive approach of the processes influencing the rock magnetic signal, additional data are presented such as total organic carbon (TOC), total sulphur (TS), opal, water content and relative variations in iron and titanium measured on selected intervals. In glacial sediments, the magnetic signal is dominated by magnetite, which is considered to be of detrital origin. This predominance of magnetite is interrupted by distinct horizons of authigenic greigite, probably confined to reductive microenvironments. In interglacial stages, besides dilution by biogenic silica and a decreasing detrital input, the weakness of the rock magnetic signal is also due to a reductive dissolution of magnetic particles. The magnetic assemblage is strongly linked to the redox history of interglacial sediment. In the oxidised bottom sediments of Lake Baikal, a biogenic magnetite is observed [Peck, J.A., King, J.W., 1996. Magnetofossils in the sediments of lake Baikal, Siberia. Earth Planet. Sci. Lett. 140 (1–4), 159–172]. After burial under the redox front, the magnetite is preferentially dissolved, and detrital hematite remains dominant when the sedimentation rate is low and when the residence time of the magnetite close to the redox boundary is long. During these low sedimentation rate conditions, the redox front is preserved [Granina, L., Müller, B. and Wehrli, B., 2004. Origin and dynamics of Fe and Mn sedimentary layers in Lake Baikal. Chem. Geol. 205 (1-2), 55-72]. At constant sedimentation rate and fast burial, the magnetite is preserved or transformed into greigite when sulphate-reducing conditions are reached in the sediment. In interglacial sediments, the magnetic assemblages depict changes in the sedimentation rate, which are traced using the ratio of magnetite over hematite (S-ratio). At the beginning of interglacials, the sedimentation rate is constant with an assemblage magnetite+greigite (high S-ratio), and at the end of some interglacials, the sedimentation rate decreases with a predominance of hematite (low S-ratio).     

Geochemical record of the Holocene Jomon transgression and human activity in coastal lagoon sediments of the San'in district, SW Japan

Coastal lagoon muds were analyzed to evaluate changes in sedimentary environments by the Jomon transgression from the lower to middle Holocene age and human activities. Core samples from Lake Shinji, Southwest Japan were utilized, which cover the entire Holocene Nakaumi Formation (ca. 23-m thick), and comprise the Lower, Middle, Upper and Uppermost members. Total sulfur (TS) contents and Fe₂O₃/Al₂O₃ ratios increase from the boundary of Middle and Upper members, which is 1 m below the Kikai-Akahoya (K-Ah) volcanic ash of 6300 years BP. This change coincides to the pollen flora zone boundary of the Pinus–Abies and the Cyclobalanopsis–Castanopsis, suggesting transition to a warming climate. Chemical index of alteration (CIA) values [(ratio of Al to Al+Ca+Na+K)×100] and Rb/K ratios also show gradual increase from the middle part of the Upper member, due to its derivation from highly weathered source material probably formed under warming and rainy condition. Al₂O₃/TiO₂ and SiO₂/TiO₂ show little variation from the Lower to the Upper members, probably related to consistent feldspar composition in the source rocks, and homogeneously mixed clays. In the Uppermost member (from 1500 years), sharp increases in Ti/Zr and decreases in both Nb/Y and Zr/Y occurred, suggesting heavy mineral fractionation. This change was caused by iron sand processing called Kannanagashi and charcoal-making in the most mountainous regions. Soil erosion by these processes brought changes in mud composition, shown by the enrichment in Al₂O₃, and depletion in Zr and Cr. Human activities thus had severe impacts on sedimentary environments compared with the natural changes since the Jomon transgression.     

A river erosion estimate on the Loess Plateau: a case study from Luohe River, a second-order tributary of the Yellow River

Based on fieldwork and terrace ages, which were determined using ¹⁴C, TL and paleosol stratigraphy, a general model was established for the development of the Yellow River terrace system. The ages for the terraces and valley flats of the Yellow River system are T₆—1.67–0.85 Ma BP, T₅—0.85–0.47 Ma BP, T₄—0.47–0.10 Ma BP, T₃—0.10–0.007 Ma BP, T₂—7.0–0.7 ka BP, T₁—0.7–0.3 ka BP, the higher valley flat—0.3–0.15 ka BP and the lower valley flat 0.15–0 ka BP, respectively. Each terrace or valley flat and corresponding paleo-valley represents a river erosion/deposition cycle. Using this model and selected geomorphic parameters of terraces and paleo-valleys from 10 typical cross sections of Luohe River, a tributary of the Yellow River, an attempt is made here to estimate paleo-river erosion since the Pleistocene on the Loess Plateau.     

Climatic pacing of Mediterranean fire histories from lake sedimentary microcharcoal

The microcharcoal content (particles < 180 µm) of overlapping sedimentary sequences from two crater lake basins in central Turkey are used to reconstruct the regional fire history of the East Mediterranean oak–grass parkland zone from the Last Glacial Maximum to the present-day. These results are correlated with stable isotope and pollen data from the same cores in order to assess the changing role of climate, vegetation and human activity in landscape burning. This indicates that climatically-induced variation in biomass availability was the main factor controlling the timing of regional fire activity during the Last Glacial–Interglacial climatic transition, and again during Mid-Holocene times, with fire frequency and magnitude increasing during wetter climatic phases. Spectral analysis of the Holocene part of the record from Eski Acıgöl indicates significant cyclicity with a periodicity of ~ 1500 years that may be linked with large-scale climate forcing. Although proto-agricultural societies were established in this region as early as 10,000 years ago, it is only during the last two to three millennia that the pacing of wildfire cycles appears to have become decoupled from climate and linked instead to human-induced changes in land cover and fuel load availability.     

Southern high latitude climate variability in the Late Cretaceous greenhouse world

A palynological study of oil exploration wells in the Gippsland Basin southeastern Australia has provided a record of southern high latitude climate variability for the last 12 million years of the Cretaceous greenhouse world. During this time, the vegetation was dominated by a cool to temperate flora of Podocarpaceae, Proteaceae and Nothofagidites spp. at a latitude of 60°S. Milankovitch forced cyclic alternations from drier to wetter climatic periods caused vegetation variability from 72 to 77 Ma. This climate change was probably related to the waxing and waning of ephemeral (100 ky) small ice sheets in Antarctica during times of insolation minima and maxima. Drying and cooling after 72 Ma culminated from 68 to 66 Ma, mirroring trends in global δ¹⁸O data. Quantitative palynofloral analyses have the potential to provide realistic proxies for small-scale climate variability in the predominantly ice-free Late Cretaceous.     

Temperature changes on the Tibetan Plateau during the past 600 years inferred from ice cores and tree rings

The climatological signal of δ¹⁸O variations preserved in ice cores recovered from Puruogangri ice field in the central Tibetan Plateau (TP) was calibrated with regional meteorological data for the past 50 years. For the period AD 1860–2000, 5-yearly averaged ice core δ¹⁸O and a summer temperature reconstruction derived from pollen data from the same ice core were compared. The statistical results provide compelling evidence that Puruogangri ice core δ¹⁸O variations represent summer temperature changes for the central TP, and hence regional temperature history during the past 600 years was revealed. A comparison of Puruogangri ice core δ¹⁸О with several other temperature reconstructions shows that broad-scale climate anomalies since the Little Ice Age occurred synchronously across the eastern and southern TP, and the Himalayas. Common cold periods were identified in the 15th century, 1625–1645 AD, 1660–1700 AD, 1725–1775 AD, 1795–1830 AD, 1850–1870 AD, 1890–1920 AD, 1940–1950 AD, and 1975–1985 AD. The period 1725–1775 AD was one of the most prolonged cool periods during the past 400 years and corresponded to maximum Little Ice Age glacier advance of monsoonal temperate glaciers of the TP.     

Continental European Eemian and early Würmian climate evolution: comparing signals using different quantitative reconstruction approaches based on pollen

Analyses of Eemian climate dynamics based on different reconstruction methods were conducted for several pollen sequences in the northern alpine foreland. The modern analogue and mutual climate sphere techniques used, which are briefly presented, complement one another with respect to comparable results. The reconstructions reveal the occurrence of at least two similar thermal periods, representing temperate oceanic conditions warmer and with a higher humidity than today. Intense changes of climate processes become obvious with a shift of winter temperatures of about 15 °C from the late Rissian to the first thermal optimum of the Eemian. The transition shows a pattern of summer temperatures and precipitation increasing more rapidly than winter temperatures. With the first optimum during the Pinus–Quercetum mixtum–Corylus phase (PQC) at an early stage of the Eemian and a second optimum period at a later stage, which is characterised by widespread Carpinus, climate gradients across the study area were less intense than today. Average winter temperatures vary between −1.9 and 0.4 °C (present-day −3.6 to 1.4 °C), summer temperatures between 17.8 and 19.6 °C (present-day 14 to 18.9 °C). The timberline expanded about 350 m when compared to the present-day limit represented by Pinus mugo. Whereas the maximum of temperature parameters is related to the first optimum, precipitation above 1100 mm is higher during the second warm period concomitant to somewhat reduced temperatures. Intermediate, smaller climate oscillations and a cooling becomes obvious, which admittedly represent moderate deterioration but not extreme chills. During the boreal semicontinental Eemian Pinus–Picea–Abies phase, another less distinct fluctuation occurs, initiating the oscillating shift from temperate to cold conditions.