Paleoecology of two marine oxygen isotope stage 7 sites correlated by the Sheep Creek tephra, northwestern North America

Pollen analysis at two sites, correlated by the presence of the 190,000 yr-old Sheep Creek tephra, documents fluctuations in vegetation and climate consistent with this date and indicates that the records span marine oxygen isotope stage 7 and the stage 6/7 transition. Dawson Cut, near Fairbanks, Alaska, provides a 5.2-m-long pollen record of interglacial boreal forest succeeded by shrub tundra and then forest/tundra. Ash Bend, Stewart River, central Yukon, provides a 9.5-m-long record of interglacial boreal forest succeeded by forest/tundra, shrub tundra, and herbaceous tundra. The replacement of forest at both sites by more open or tundra vegetation indicates warm interglacial conditions giving way to cold and arid climate. It is not clear whether stage 7 was warmer than the present. The warm-cool-warm climate oscillation evident at both sites may correlate to Lake Baikal substages 7a, 7b, and 7c. Sheep Creek tephra fell on forest/tundra vegetation.     

Recent Environmental Change and Atmospheric Contamination on Svalbard as Recorded in Lake Sediments – an Introduction

This paper outlines an interdisciplinary project on recent environmental change and atmospheric contamination on the high Arctic archipelago of Svalbard (76°30′N–80°30′N). It describes the rationale and aims of the project and summarises the location, climate, geology, vegetation, and land-use of Svalbard.     

Medieval Warming, Little Ice Age, and European impact on the environment during the last millennium in the lower Hudson Valley, New York, USA

Establishing natural climate variability becomes particularly important in large urban areas in anticipation of droughts. We present a well-dated bi-decadal record of vegetation, climate, land use, and fire frequency from a tidal marsh in the Hudson River Estuary. The classic Medieval Warm Period is evident through striking increases in charcoal and Pinus dominance from 800–1300 A.D., paralleling paleorecords southward along the Atlantic seaboard. Higher inputs of inorganic sediment during this interval suggest increased watershed erosion during drought conditions. The presence of the Little Ice Age ensues with increases in Picea and Tsuga, coupled with increasing organic percentages due to cooler, moister conditions. European impact is manifested by a decline in arboreal pollen due to land clearance, increased weedy plant cover (i.e., Ambrosia, Plantago, and Rumex), and an increase in inorganic particles to the watershed.     

A New Species of Ginkgo with Male Cones and Pollen Grains in situ from the Middle Jurassic of Eastern Xinjiang, China

Well-preserved Ginkgo pollen organs are analyzed from the Middle Jurassic Xishanyao Formation of the Turpan–Hami Basin, Xinjiang Uygur Autonomous Region, northwestern China, and are described as a new species, Ginkgo hamiensis Z.X. Wang et B.N. Sun sp. nov. The immature male cones are cylindrical and catkin-like, with two longitudinal stripes on the stalk. The pollen sacs are shaped like a long oval with two pollen sacs fused together for each microsporophyll, and the microsporophyll tip is a triangular cystidium. The pollen grains are oblong or fusiform and monocolpate; both ends are blunt or sharp. By comparison with previously reported fossil records of Ginkgo plants, we determined that the current fossils are different from all other reported species; thus, the present fossil is referred to as a new species of Ginkgo. The reproductive organs of the Ginkgo fossils described herein can provide valuable information for the study of Ginkgo plants. Further, there are two probable evolutionary trends in the Ginkgo pollen cones. One trend is that the number of pollen sacs changed from three or four during the Jurassic and Cretaceous to two at the present day; the other is that the number of pollen sacs has remained two from the Middle Jurassic to the present day. In addition, the pollen cones described herein are similar to the pollen cones of the extant Ginkgo, which strongly indicates that the morphology of Ginkgo plants may have remained highly conserved over millions of years.     

2500年来艾比湖的环境演变信息

通过对艾比湖缘1，8m浅孔的沉积相和孢粉组合，结合14C测年资料分析。指出近2500年来艾比湖的沉积环境总体是比较稳定的，但由于气候波动引起艾比湖水位曾发生较明显的变化。约在公元前300～400年，是艾比湖面积缩小时期；约公元前300—公元300年，即东周末至西晋，是艾比湖水位较高时期；约公元300—1400年，即东晋至15世纪初，是艾比湖的高水位时期；约15世纪初至17世纪中是艾比湖的水位下降期，但水位比现代仍然高；约17世纪中至19世纪初的小冰期是艾比湖的水位上升期。研究还提供了历史时期湖泊的盐度变化和湖周发生大火的信息。     

青海湖黑马河、泉湾湿地表土花粉与植被关系研究

对青海湖地区黑马河、泉湾湿地进行了植被样方调查,并由湖岸向外每间隔100～150 m采集表土与苔藓样品进行花粉分析。结果显示,黑马河、泉湾湿地表土花粉与对应样方植被关系密切,花粉组合能较好地反映样方植被特征,同时,桦木属、蒿属、藜科、白刺属、胡颓子科、麻黄科等花粉类型少量出现,为外来花粉。R值分析表明莎草科花粉相对呈高代表性,毛茛科、委陵菜属、禾本科、菊科、报春花科、玄参科等呈低代表性。该研究为在青海湖及其它地区利用花粉重建古植被提供了重要的参考依据。     

A statistical method for varve verification using seasonal pollen deposition

We developed a fast, inexpensive, statistically rigorous method of varve verification that uses prospective varve layer-splitting and seasonal pollen deposition. This method can be used on any sediment that contains seasonally deposited pollen, and avoids the need for radio-isotopic, optical, or thermoluminescence dating. The method uses a χ² test and non-parametric regression, together with recorded plant bloom times from pollen traps, to assess the differences in pollen abundances in light/dark (i.e. summer/winter-spring) sediment layers. A statistical test is required because such seasonally deposited data are inherently noisy, with a low signal-to-noise ratio. To illustrate this approach, visible laminations of Lake Mina, Minnesota, USA, were assessed in two separate regions of a core spanning 900 years. Results show that the laminations were deposited annually.     

Quantitative climate and vegetation trends since the late glacial on the northeastern Tibetan Plateau deduced from Koucha Lake pollen spectra

Quantitative information on vegetation and climate history from the late glacial-Holocene on the Tibetan Plateau is extremely rare. Here, we present palynological results of a 4.30-m-long sediment record collected from Koucha Lake in the Bayan Har Mountains, northeastern Tibetan Plateau. Vegetation change has been traced by biomisation, ordination of pollen data, and calculation of pollen ratios. The application of a pollen-climate calibration set from the eastern Tibetan Plateau to Koucha Lake pollen spectra yielded quantitative climate information. The area was covered by alpine desert/steppe, characteristic of a cold and dry climate (with 50% less precipitation than today) between 16,700 and 14,600 cal yr BP. Steppe vegetation, warm (∼ 1°C higher than today) and wet conditions prevailed between 14,600 and 6600 cal yr BP. These findings contradict evidence from other monsoon-influenced areas of Asia, where the early Holocene is thought to have been moist. Low effective moisture on the northeastern Tibetan Plateau was likely due to high temperature and evaporation, even though precipitation levels may have been similar to present-day values. The vegetation changed to tundra around 6600 cal yr BP, indicating that wet and cool climate conditions occurred on the northeastern Tibetan Plateau during the second half of the Holocene.     

Late Quaternary tephrostratigraphy and pollen stratigraphy of Uwa Formation,Shikoku Island,SW Japan: Reconsidering the MIS 11 super-interglacial horizon

We investigated a late Quaternary terrestrial sedimentary sequence (Uwa Formation) in core IC2, from a site adjacent to that of the reported core IC on NW Shikoku Island, SW Japan, and developed its tephra and pollen stratigraphy to refine the age model of the formation. First, we identified 19 horizons with high glass shard concentrations in the IC2 core sediments as possible tephras or cryptotephras, and correlated them with reported tephras on the basis of the major- and trace-element compositions of their glass shards. All correlated widespread tephras and cryptotephras were products of volcanoes in the Kyushu volcanic zone (Aso, Kakuto, Aira, Ata, and Kikai calderas). Second, we confirmed the presence in core IC2 of two pollen zones dominated by Quercus subgen. Cyclobalanopsis, which is an indicator of very warm interglacial vegetation. In the Japanese Islands, these two vegetation zones have usually been considered to characterize marine isotopic stages (MISs) 1 and 11. A previous study of the Uwa Formation correlated the upper pollen zone to MIS 1, but the lower zone was not correlated to MIS 11; rather, it was inferred to be older than MIS 12 because it was stratigraphically below the “Oda” tephra (equivalent to a distal Kasamori 5 [Ks5] tephra [MIS 12]). In this study, however, noting that the Naruohama-IV tephra (Nh-IV; MIS 10d) and Ks5 cannot be distinguished by their shard chemistries, we inferred that the suggested “Oda” tephra actually correlates to Nh-IV, rather than to the Ks5 tephra. By re-assigning the “Oda” tephra to Nh-IV, we could correlate the underlying Quercus subgen. Cyclobalanopsis-abundant zone to MIS 11 and, consequently, a pair of pollen zones indicating cool and warm conditions below the MIS 11 pollen zone to MISs 12 and 13, respectively. The resulting age model whereby tephra and pollen constraints are integrated showed a roughly constant sedimentation rate from MIS 13, without any long-term gaps; further, our MIS 13 horizon in core IC2 corresponds to the reported 1 Ma tephra horizon in core IC. Therefore, these findings represent a dramatic change in the Uwa Formation age model and validate the Uwa Formation as one of the most useful terrestrial archives of Quaternary tephrostratigraphy and paleoclimatic fluctuation in SW Japan.     

Full-glacial — late-glacial palaeoclimate of the Southern Andes: evidence from pollen,beetle and glacial records

Palaeoecological studies carried out in the Chilean Lake District and Chilotan Archipelago (41°–43°S) record full-glacial and late-glacial pollen assemblages beginning just after 21000 and beetle assemblages after 18000, both sets extending until 10000 ¹⁴C yr BP. Pollen records indicate that Subantarctic Parkland, the vegetation of the early millennia of record, changed after about 14000 yr BP to become open woodland and later North Patagonian Evergreen Forest. Assemblages of plants and beetles, responding more or less in unison to a strong rise in temperature (≥ 6°C), behaved in accord at around 14000 until 13000–12500 yr BP, the beetle fauna displaying a marked increase in obligate forest types. During full-glacial conditions (17400–16100 and 15300 and 14400 yr BP) and in the late-glacial interval (after about 13000 yr BP), however, climate evidently coerced populations dissimilarly, the pollen sequence showing an increase in plant taxa indicative of colder climate, whereas the beetle fauna underwent little or no variation. Contrasting climate modes implied by plants and beetles may be attributed to differential responses to apparent low-order temperature changes (≤ 2–3°C).