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1.
Modeling of oceanic nutrient fields indicates that the Southern Ocean may have a strong impact on the chemistry of the thermocline waters which upwell in the eastern tropical oceans and feed biological productivity there. The subantarctic is a primary source of equatorial undercurrent (EUC) waters. The Southern Ocean to equator connection has been shown through modeling to have a potential influence on atmospheric carbon dioxide content via an increase in the efficiency of the tropical biotic pump (silica leakage hypothesis). On the glacial–interglacial timescale the eastern equatorial Pacific (EEP) has a thermocline (EUC) carbon isotope record which is consistent with that idea and a stronger ice age biologic drawdown in the subantarctic. This carbon isotope record features glacial values more positive than those of the Holocene, which is the reverse of what is seen in the non-equatorial, stratified, ocean. We report planktonic carbon isotope records from the Pacific subantarctic in an effort to trace the unique EEP carbon isotope signature to its source. Our results are compatible with the subantarctic as a source of the tropical carbon isotope signature. Analysis of the glacial to Holocene isotopic pattern in terms of causative process indicates that an increased glacial subantarctic biotic pump accounts best for our observations. This supports the hypothesis of Southern Ocean drive on tropical biological production, and potential impact on the global carbon cycle.  相似文献   

2.
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.  相似文献   

3.
We present Globigerinoides ruber, G. sacculifer and Neogloboquadrina dutertrei oxygen isotope records from northwestern subtropical Atlantic Site 1058 spanning the mid Pleistocene ( 600 to 400 ka). The high temporal resolution of these records ( 800 yr) allows us to compare millennial-scale climate signals during one of the most extreme glacial periods of the Pleistocene (Marine Isotope Stage (MIS) 12) to an earlier, less extreme glacial (MIS 14), as well as to two full interglacial intervals (MIS 13 and MIS 15). We observe excellent agreement in the timing and amplitude of variations between the surface-most dwelling species G. ruber and Northern Hemisphere insolation during the two interglacial periods. There is some expression of Northern Hemisphere insolation during glacial MIS 14; however, during the more extreme glacial MIS 12 Northern Hemisphere insolation patterns are not apparent in any of the planktonic foraminiferal δ18O records. Insolation remains relatively high, but δ18O values increase toward the characteristic δ18O maximum of MIS 12 in all three of the records. On the millennial-scale, all three species display their highest amplitude δ18O variations (with a period between 4–6 kyr) during glacial MIS 12. Suborbital-scale variability is also statistically significant during glacial MIS 14, but the amplitude is smaller. These results support hypotheses linking millennial-scale climate fluctuations to the extent of continental glaciation. We propose that the relatively high degree of sea surface instability during one of the most extreme glacial periods of the Pleistocene arises from the competing effects of strong atmospheric winds related to the presence of a large ice sheet to the north and persistently high incident solar radiation during this interval of time.  相似文献   

4.
The glacial-to-interglacial shift in land carbon storage is important in understanding the global carbon cycle and history of the climate system. While organic carbon storage on land appears to have been much less than present during the cold, dry glacial maximum, calcrete (soil carbonate) carbon storage would have been greater. Here we attempt a global estimation of this change; we use published figures for present soil carbonate by biome to estimate changing global soil carbonate storage, on the basis of reconstruction of vegetation areas for four timeslices since the Last Glacial Maximum. It appears that there would most likely have been around a 30–45% decrease in calcrete carbon on land accompanying the transition between glacial and interglacial conditions. This represents a change of about 500–400 GtC (outer error limits are estimated at 750–200 GtC) . In order to be weathered into dissolved bicarbonate, this would take up an additional 500–400 GtC (750–200 GtC) in CO2 from ocean/atmosphere sources. An equivalent amount to the carbonate leaving the caliche reservoir on land may have accumulated in coral reefs and other calcareous marine sediments during the Holocene, liberating an equimolar quantity of CO2 back into the ocean-atmosphere system as the bicarbonate ion breaks up.  相似文献   

5.
The change in the global mean atmospheric pressure between glacial and interglacial periods is evaluated at sea level. This change originates in a modification of topography and in a possible variation in the atmospheric mass. In this calculation the atmosphere is at hydrostatic equilibrium, and the parameters describing the glacial period are varied in a plausible range. The result, with constant atmospheric mass, is a mean sea level pressure decrease of 9–15 hPa linked with the deglaciation. The corresponding pressure change at the reference level corresponding to the present day sea level does not exceed one hPa. When considering only the change in the atmospheric mass, an increase which does not exceed 2 hPa is found, linked with the deglaciation.  相似文献   

6.
A pollen record from the core sediments collected in the northern part of Lake Baikal represents the latest stage of the Taz (Saale) Glaciation, Kazantsevo (Eemian) Interglacial (namely the Last Interglacial), and the earliest stage of the Zyryanka (Weichselian) Glaciation. According to the palaeomagnetic-based age model applied to the core, the Last Interglacial in the Lake Baikal record lasted about 10.6 ky from 128 to 117.4 ky BP, being more or less synchronous with the Marine Isotope Stage 5e. The reconstructed changes in the south Siberian vegetation and climate are summarised as follows: a major spread of shrub alder (Alnus fruticosa) and shrub birches (Betula sect. Nanae/Fruticosae) in the study area was a characteristic feature during the late glacial phase of the Taz Glaciation. Boreal trees e.g. spruce (Picea obovata) and birch (Betula sect. Albae) started to play an important role in the regional vegetation with the onset of the interglacial conditions. Optimal conditions for Abies sibirica–P. obovata taiga development occurred ca. 126.3 ky BP. The maximum spread of birch forest-steppe communities took place at the low altitudes ca. 126.5–125.5 ky BP and Pinus sylvestris started to form forests in the northern Baikal area after ca. 124.4 ky BP. Re-expansion of the steppe communities, as well as shrubby alder and willow communities and the disappearance of forest vegetation occurred at about 117.4 ky BP, suggesting the end of the interglacial succession. The changes in the pollen assemblages recorded in the sediments from northern Baikal point to a certain instability of the interglacial climate. Three phases of climate deterioration have been distinguished: 126–125.5, 121.5–120, and 119.5–119 ky BP. The penultimate cooling signal may be correlated with the cool oscillation recorded in European pollen records. However, such far distant correlation requires more careful investigation.  相似文献   

7.
A new theory is proposed to explain global cooling at the onset of Pleistocene glacial periods. Atmospheric CO2 drawdown is considered to be the driving force behind global cooling, brought about by heightened productivity at the equatorial divergences and along continental margins, particularly in upwelling regions. Eutrophication appears to be triggered when global warming during late interglacial periods causes accelerated melting of the West Antarctic Ice Sheet. This would release large reserves of silicate-enriched subglacial meltwaters into the surrounding oceans where entrainment would take place into deep and intermediate currents forming in Antarctic and subantarctic waters. Subsequent advection, mixing and upwelling of silicate-enriched deep and intermediate waters into the coastal zones and open-ocean divergences results in the proliferation of large, rapidly-sinking diatom species with a high affinity for dissolved silicate. These blooms enhance rates of recycling of N and P in upwelling regions and accelerate rates of organic carbon production, export and sequestration in shelf and slope sediments and in the deep sea. The resultant atm. CO2 drawdown initiates global cooling. Consequent expansion of Northern Hemisphere glaciers lowers sea level, while increased temperature and pressure gradients between equatorial and polar regions intensify meridional winds. The former process exposes nutrient-enriched coastal sediments to wave erosion, thereby releasing new nutrient supplies, while the latter process enhances upwelling. The combined effect is to greatly increase rates of org. C production and export from continental margins and further accelerate atm. CO2 drawdown. Glacial-period cooling is also enhanced by a number of other positive feedbacks, including changes in albedo, water vapour and cloud cover. Episodic warming intervals during glacial periods may be related to insolation changes associated with orbital precession and tilt cycles, but processes involved in deglaciation and reversion to the interglacial climatic regime are complex and not yet fully understood.  相似文献   

8.
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9.
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.  相似文献   

10.
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11.
Storini  Marisa  Sýkora  Július 《Solar physics》1997,176(2):417-430
The existence of a 22-year heliomagnetic cycle was inferred long ago not only from direct measurements of the solar magnetic field but also from a cyclic variability of a number of the solar activity phenomena. In particular, it was stated (a rule derived after Gnevyshev and Ohl (1948) findings and referenced as the G–O rule in the following) that if sunspot number Rz cycles are organized in pairs of even–odd numbered cycles, then the height of the peak in the curve of the yearly-averaged sunspot numbers Rz-y is always lower for a given even cycle in comparison with the corresponding height of the following odd cycle. Exceptions to this rule are only cycles 4 and 8 which, at the same time, are the nearest even cycles to the limits of the so-called Dalton minimum of solar activity (i.e., the 1795–1823 time interval). In the present paper, we are looking for traces of the mentioned G–O rule in green corona brightness (measured in terms of the Fexiv 530.3 nm emission line intensity), using data covering almost five solar cycles (1943–1994). It was found that the G–O rule seems to work within the green-line corona brightness, namely, when coronal intensity measured in an extended solar middle-latitude zone is considered separately from the rest of the solar surface. On the other hand, the same G–O rule is valid at the photospheric level, as the heliographic latitudinal dependence of sunspot numbers (1947–1984) shows.  相似文献   

12.
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).  相似文献   

13.
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.  相似文献   

14.
Sediment samples were collected from a borehole in the northern South China Sea with the depositional age back to 400 ka BP, for grain size and geochemical analyses to constrain the sediment provenance and paleoenvironmental variability. Geochemical indices of Th/Sc, Ti/Nb and Th/Nb ratios suggest that the Zhujiang (Pearl River) was the main provenance of the inner shelf sediments of Hong Kong deposited during interglacial periods, whereas the locally-derived granitoids contributed significantly to the exposed inner shelf through the incision of local streams during glacial periods. Furthermore, the influence of the Zhujiang-derived sediments on the inner shelf of Hong Kong varied spatially and temporally with different sea-level changes during the past 400 kyr. Chemical weathering indices suggest hot and wet climate conditions were dominant in South China during interglacial periods of marine isotope stages (MIS) 7, 9 and 11 whereas a dry and cold paleoclimate prevailed during glacial periods of MIS 6 which accounts for weak chemical weathering and coarse-grained deposition on the inner shelf. The Holocene and last interglacial period did not see more intense chemical weathering in the Zhujiang drainage basin than other interglacial periods. Although the high resolution paleoenvironmental changes can not be easily reconstructed due to ubiquitous unconformity in the sedimentary strata and weak age controls compared to the deep sea sedimentation, the present study sheds new lights on the understanding of the transport process of the Zhujiang sediment in the deep ocean and provides a teleconnection of East Asian palaeomonsoon activity between South China, the inland and open sea areas.  相似文献   

15.
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.  相似文献   

16.
As part of a multiproxy investigation, phytoliths were extracted from sediments in a 197-m core in Hawkes Bay, New Zealand. They provide a continuous vegetation–climate record spanning the time period from at least the last interglacial (marine oxygen isotope stage 5) to the present. The phytolith record demonstrates that grass/cyperaceae grew during warmer periods and woody taxa dominated the site during colder periods.During the present interglacial, the Poukawa basin is occupied by a shallow lake surrounded by an extensive fen. During colder–drier periods, the floor of the basin dried out and woody taxa occupied the basin floor. This contrasts with the pollen record, which demonstrates a converse pattern. The apparent discrepancy reflects the purely local provenance of the phytolith assemblage.Significant changes in phytolith assemblages occur at the same depth as major tephras, indicating a sharp decline in trees and shrubs and a surge in grass and cyperaceae. A series of successional changes follow each major tephra fall. Initially, the woody taxa are killed off and replaced by grass and cyperaceae that rapidly colonise the fresh surface. Trees and or shrubs succeed the grass and cyperaceae after a significant lag.  相似文献   

17.
Growth patterns of the last ice age coral terraces at Huon Peninsula   总被引：1，自引：0，他引：1  
At Huon Peninsula, Papua New Guinea, prolific coral growth during the last-glacial was episodic and in response to a series of sea-level rises. The resultant step-like coral terraces are currently situated from 20 m up to 140 m above sea-level due to continuous tectonic uplift of the Peninsula. The sea-level rises were in response to periodic partial disintegration of Northern Hemisphere ice sheets associated with severe climate swings and occurred within decadal timescales. The relatively rapid 15 m to 35 m rise in sea-levels exposed new head-room for corals to colonize. The resulting terrace structures contain individual corals that do not appear to have grown sequentially in time and with elevation. Additionally, following the peak, sea level fell relatively slowly over several thousand years and corals grew and filled in the flanks of the terrace such that younger corals now occupy lower elevations. We have labeled these structures “pack-up” reefs. This is in contrast to coral terraces formed during major sea-level rises from glacial to interglacial or glacial to interstadial transitions where the rate of sea level rise is commensurate with coral growth rates and corals can keep up with sea-level rise by growing on top of each other in a time orderly sequence. Deriving sea-level information from pack-up terraces is difficult and is likely to be ambiguous. The periodic fluctuations in climate were associated with atmospheric radiocarbon swings that seem to have varied smoothly with time. The same corals that show a scatter in stratigraphic temporal ordering appear regularly distributed in time and with radiocarbon content attesting to the veracity of the age measurements and at the same time confirm the disordered distribution of corals in “pack-up” type reefs.  相似文献   

18.
The North Taymyr ice-marginal zone (NTZ) is a complex of glacial, glaciofluvial and glaciolacustrine deposits, laid down on the northwestern Taymyr Peninsula in northernmost Siberia, along the front of ice sheets primarily originating on the Kara Sea shelf. It was originally recognised from satellite radar images by Russian scientists; however, before the present study, it had not been investigated in any detail. The ice sheets have mainly inundated Taymyr from the northwest, and the NTZ can be followed for 700–750 km between 75°N and 77°N, mostly 80–100 km inland from the present Kara Sea coast.The ice-marginal zone is best developed in its central parts, ca. 100 km on each side of the Lower Taymyr River, and has there been studied by us in four areas. In two of these, the ice sheet ended on land, whereas in the two others, it mainly terminated into ice-dammed lakes. The base of the NTZ is a series of up to 100-m-high and 2-km-wide ridges, usually consisting of redeposited marine silts. These ridges are still to a large extent ice-cored; however, the present active layer rarely penetrates to the ice surface. Upon these main ridges, smaller ridges of till and glaciofluvial material are superimposed. Related to these are deltas corresponding to two generations of ice-dammed lakes, with shore levels at 120–140 m and ca. 80 m a.s.l. These glacial lakes drained southwards, opposite to the present-day pattern, via the Taymyr River valley into the Taymyr Lake basin and, from there, most probably westwards to the southern Kara Sea shelf.The basal parts of the NTZ have not been dated; however, OSL dates of glaciolacustrine deltas indicate an Early–Middle Weichselian age for at least the superimposed ridges. The youngest parts of the NTZ are derived from a thin ice sheet (less than 300 m thick near the present coast) inundating the lowlands adjacent to the lower reaches of the Taymyr River. The glacial ice from this youngest advance is buried under only ca. 0.5 m of melt-out till and is exposed by hundreds of shallow slides. This final glaciation is predated by glacially redeposited marine shells aged ca. 20,000 BP (14C) and postdated by terrestrial plant material from ca. 11,775 and 9500 BP (14C)–giving it a last global glacial maximum (LGM; Late Weichselian) age.  相似文献   

19.
The relationship between the Ricker Hills Tillite (RHT), which represents the northernmost outcrop of lithified continental glacial deposits in Victoria Land, is discussed with respect to the glacial landscape assemblage of the Ricker Hills, a nunatak at the internal border of the Transantarctic Mountains. A warm-based ice sheet deposited the tillite and induced syn- to post-depositional glacial deformation under wet conditions both of the tillite and of the bedrock. The thickness of the ice sheet on the nunatak is estimated to have been 600 m, at most. The area had been deeply eroded before deposition of the RHT as documented by the low elevation of tillite outcrops located in overdeepened depressions of the nunatak. Micropaleontological analysis evidences only the presence of Permian to Jurassic palynomorphs. X-ray diffraction and SEM–EDS analyses of clay minerals in the RHT indicate continental chemical weathering under wet conditions after the RHT deposition. As documented by clay mineral assemblage variation in CRP drillholes, the progressive cooling of the Antarctic continent allowed chemical weathering in “warm” conditions until the Late Oligocene period in southern Victoria Land, leading to a chronological constrain for RHT deposition. Conservatively estimating the sea level to have been between the tillite outcrops and the erosional trimline limiting horns in the Ricker Hills, at the time of RHT deposition, we suggest that the maximum uplift of the area would not have exceeded 900–1500 m since at least Late Oligocene.  相似文献   

20.
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.  相似文献   

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