The present flora and vegetation of the moraines of the Klutlan Glacier,Yukon Territory,Canada: A study in plant succession     

H.J.B. Birks 《Quaternary Research》1980,14(1):60-86

The flora and vegetation of six ice-cored moraines of the Klutlan Glacier were analyzed in 65 plots by European plant-sociological techniques. The age of each plot was estimated from annual growth rings of shrubs or trees in the plots. Nine major vegetation types are distinguished: Crepis nana, Dryas drummondii, Hedysarum mackenzii, Hedysarum-Salix, Salix-Shepherdia canadensis, Picea-Salix, Picea-Arctostaphylos, Picea-Ledum, and Picea-Rhytidium. These contain plants aged 2–6, 9–23, 10–20, 24–30, 32–58, 58–80, 96–178, 177–240, and >163- >339 yr, respectively. Six other vegetation types are described from windthrow areas, drainage channels, volcanic tephra slopes, lake margins, fens, and drained lakes. The major vegetation types reflect a vegetational succession related to moraine age and stability, with the Crepis nana type as the pioneer vegetation developing through the other vegetation types to the Picea-Rhytidium type on the oldest moraines. Changes in species diversity and soil development, particularly humus accumulation, parallel the vegetational succession. This succession differs from patterns of revegetation of deglaciated landscapes in Alaska and British Columbia today and in Minnesota in late-Wisconsin times because of differences in climate, plant migration, and local ecology.  相似文献   

Modern pollen assemblages and vegetational history of the moraines of the Klutlan Glacier and its surroundings,Yukon Territory,Canada     

H.J.B. Birks 《Quaternary Research》1980,14(1):101-129

Modern pollen assemblages have been studied from surficial lake muds and moss polsters collected from five vegetated ice-cored moraines of the Klutlan Glacier. The youngest vegetated moraine (K-II) is characterized by high pollen values for Salix and Hedysarum, K-III by high Salix and Shepherdia canadensis and low Hedysarum and Picea, K-IV by high Betula, Salix, and Shepherdia, and K-V and the Harris Creek moraine (HCM) by high Picea. Variations are summarized by canonical variates analysis. A percentage pollen diagram from Gull Lake on the upland east of the glacier records vegetational development since the deposition of the White River volcanic ash 1220 ¹⁴C yr ago. An initial species-rich treeless vegetation was replaced by birch-alder-willow shrub-tundra, and this by open Picea glauca forest similar to present vegetation around the lake. Sites on HCM show two basic stratigraphies. Triangle Lake reflects vegetational succession from Salix-Shepherdia canadensis scrub similar to that on K-III today, through open Picea woodland of K-IV type, to closed Picea forests of K-V and HCM. Heart Lake and Cotton Pond reflect vegetational development following melting of ice underlying the spruce forests of HCM. These two types are summarized by positioning the fossil spectra on the first two canonical variate axes of the modern surface spectra.  相似文献   

A palaeoecological test of the land-use hypothesis for recent lake acidification in South-West Norway using hill-top lakes     

H. J. B. Birks  Frode Berge  J. F. Boyle  B. F. Cumming 《Journal of Paleolimnology》1990,4(1):69-85

Lakes perched on hill-tops have very small catchments. Their water chemistry is largely influenced by the chemical composition of precipitation and by the underlying bedrock geology. They are ideal sites for testing the hypothesis that land-use and associated soil changes are a major cause of recent lake acidification. On this hypothesis, hill-top lakes in SW Norway are predicted not to show any recent lake acidification because, by their very nature, the chemistry of such lakes is little influenced by land-use or soil changes.Palaeolimnological analyses of diatoms and chrysophytes show that prior to ca. 1914 the two hill-top lakes investigated were naturally acid with reconstructed lake-pH values of at least 4.8–5.1. Since ca. 1914 lake pH values declined to ca. 4.5–4.7. These results contradict the land-use hypothesis. All the available palaeolimnological evidence (diatoms, chrysophytes, pollen, sediment geochemistry, carbonaceous particles) is consistent with the acid-deposition hypothesis.In the absence of any evidence to support the land-use hypothesis as a primary cause of recent lake acidification and in the light of several independent refutations, it is perhaps time to put the land-use hypothesis for recent lake acidification to rest.  相似文献   

Palaeoecology of a late Allerød peat bed at Godøy,western Norway     

Hilary H. Birks  Geoffrey Lemdahl  John Inge Svendsen  Jon Y. Landvik 《第四纪科学杂志》1993,8(2):147-159

A peat bed found under solifluction deposits on Godøya island, western Norway, accumulated during a few decades around 11 000 yr BP, at the end of the Allerød period of the Late Weichselian. Palaeoecological investigations showed a local vegetation succession on wet sand culminating in a mire community dominated by Carex nigra. Periodic flooding brought in sand and silt, which decreased as drainage was impeded sufficiently for standing water to develop. The surrounding terrestrial vegetation was dominated by Salix scrub, with some open heath and alpine habitats nearby. Apart from two aquatic species, the 29 insect taxa recorded are characteristic of alpine heaths, plant litter (under Salix scrub) and stream-sides. Their remains, together with the terrestrial plant macrofossils, were washed into the mire from nearby. Because the fossils are locally derived, the environmental reconstructions are of the actual conditions at Godøy at ca. 11 000 yr BP. Palaeotemperature estimates from beetles and plants are in agreement. The coleopteran estimates (Mutual Climatic Range Method) suggest mean July temperatures of 10–13°C, slightly cooler than today (13.5°), and January temperatures between +1 and ?10°C, similar to or much colder than today. Summer temperature estimates from individual plant taxa indicate that temperatures during the Allerød period were similar to today's, but estimates from the reconstructed vegetation and timber-line positions give estimates up to 3.5° cooler. Temperatures fell 2.5–7.5°C at the Younger Dryas. This abrupt and severe cooling initiated the solifluction processes on Godøya that buried the peat. The Godøy peat bed and its contained fossils provide a rare glimpse of Allerød biota and environments at the local (site) scale.  相似文献   

In Memoriam: Herbert Edgar Wright,Jr.     

Daniel R. Engstrom  Hilary H. Birks  Richard W. Battarbee 《Journal of Paleolimnology》2016,56(1):73-78

  相似文献   

Hydrogeological investigation of Chappice Lake, southeastern Alberta: Groundwater inputs to a saline basin     

S.J. Birks  V. N. Remeda 《Journal of Paleolimnology》1999,21(2):235-255

Sediment cores from Chappice Lake, a hypersaline, groundwater-fed lake in southeastern Alberta, have been used in previous studies to reconstruct Holocene climate using lake levels as a source for proxy climate data. This assumes that the lake is fed by a shallow groundwater system sensitive to changes in climate. In this study we use the dynamics and chemistry of groundwater entering the lake to test this hypothesis.Groundwater inputs calculated from historical records using a simple water budget were highest during periods when the precipitation deficit was high. Over specific time intervals, the expected relationship between lake volumes and climate were not always found. Feedback loops between lake levels and groundwater input, and time lags within the system are the mechanisms proposed to explain these discrepancies.Field measurements suggest discharge of a local surficial groundwater system. Slug tests reveal a high conductivity system (K = 10-5 m/s) surrounding the lake. Hydraulic heads measured in standpipe, multilevel and minipiezometers installed around Chappice Lake show that the lake is situated in a closed hydraulic head contour. Hydraulic heads and water table elevations show strong annual fluctuations corresponding to seasonal changes in recharge. Horizontal hydraulic gradients measured in areas of groundwater springs indicate a strong horizontal component of flow towards the lake. Vertical hydraulic gradients are low and indicate the upward flow of water consistent with the discharge of a shallow, surfical groundwater system.Groundwater sampled from deposits surrounding Chappice Lake and springs feeding the lake have compositions similar to both shallow surficial aquifers and bedrock aquifers suggesting that the lake may be receiving inputs from both sources. However, evaporation simulations using PHRQPITZ, show that the evaporation of water typical of bedrock aquifers result in a mineral assemblage and brine composition different from that found at Chappice Lake. This suggests that discharge of a regional groundwater system can be eliminated as a dominant source over the lake's history. Evaporation simulations suggest that evaporation of groundwater from shallow surficial deposits can best explain the present mineral assemblage and brine chemistry and were likely the dominant source of water to the lake.Bedrock and shallow surficial groundwater sources have different chemistries and isotopic compositions. In hydrogeological settings such as Chappice Lake where more than one source may contribute to the lake, the relative importance of the different sources may change with changes in climate. If the source water composition to the lake changes, identifying changes in climate or hydrology based on changes in the composition of the lake preserved in sediment core will be made more difficult. This may complicate paleoclimate and paleohydrological reconstructions that rely on mineralogical and isotopic data.  相似文献   

Aquatic macrophyte vegetation development in Kråkenes Lake, western Norway, during the late-glacial and early-Holocene   总被引：1，自引：0，他引：1  

Hilary H. Birks 《Journal of Paleolimnology》2000,23(1):7-19

Macrofossil analyses were carried out on the late-glacial and early-Holocene sediments of the radiocarbon-dated master core at Kråkenes Lake, western Norway, to investigate the aquatic vegetation changes. Ranunculus sect. Batrachium and Nitella were the earliest pioneers after deglaciation ca. 12,300 ¹⁴C yr BP. The Allerød vegetational succession was very slow during ca. 1000 ¹⁴C yrs in a cool climate and conditions that were similar to those above tree-line in Norway today. The rapid cooling at the start of the Younger Dryas stadial caused extensive disturbance, and with the development of an active cirque glacier in the catchment, plants and animals were almost exterminated from the lake by inflow of permanently cold and turbid water. Rising temperatures caused the glacier to melt at the end of the Younger Dryas. The biotic response to the rapid warming was immediate, with pioneer Ranunculus sect. Batrachium and Nitella expanding within 1-3 decades, closely followed by other elodeids. The lake witnessed a remarkable isoetid succession, with phases dominated by Limosella aquatica, Subularia aquatica, Elatine hydropiper, Isoetes echinospora, and, later, I. lacustris. About 800 yrs into the Holocene most of the macrophytes declined. The short-lived isoetids became extinct, but other taxa probably survived vegetatively. The reasons for this decline are unknown, but are probably related to nutrient depletion in combination with other factors. About 550 yrs later, I. lacustris and Nymphaea colonised, and a stable flora and vegetation developed. This study illustrates the large and rapid changes that occurred over the first 1400 yrs of the Holocene in the macrophyte flora and vegetation in Kråkenes Lake before stability was attained, pointing to the value of a palaeoecological study in tracing aquatic successions over time, and highlighting our lack of knowledge of the underlying ecological factors responsible for such rapid and marked changes.  相似文献   

Late-glacial climatic oscillations as recorded in Swiss lake sediments     

A. F. Lotter Eawag  U. Eicher  U. Siegenthaler  H. J. B. Birks 《第四纪科学杂志》1992,7(3):187-204

Regional pollen assemblage zones for the late-glacial period of the Swiss Plateau are introduced and defined. They include four major zones (Artemisia, Juniperus—Hippophaë, Betula, Pinus PAZ) with several subzones. Pollen and oxygen-isotope analyses on lacustrine sediments from several lakes in the area reveal four distinct phases of climatic oscillation in the time period of 13 000-9500 yr BP. The first oscillation, termed the Aegelsee fluctuation, occurs shortly before 12 000 yr BP and varve counts suggest its duration was ca. 100 yr. It is characterised by a short decrease in the oxygen isotopes as well as a short increase in NAP associated with a depression in birch pollen values. The second oscillation, which occurs in the δ¹⁸O record shortly before the deposition of the Laacher See Tephra (ca. 11 000 yr BP), is termed the Gerzensee fluctuation. It occurs during a pine-dominated phase and its vegetational effects cannot be determined palynologically. The most prominent regressive phase is the Younger Dryas biozone (ca. 10 700-10 000 yr BP) characterised by an increase in heliophilous NAP and low δ¹⁸O values. The Younger Dryas biozone can often be subdivided palynologically into two parts: a first part rich in grasses and juniper and a second part with higher Filipendula and birch values. During the Preboreal biozone another distinct oscillation is evidenced only in the oxygen isotope ratios. Comparison of the Swiss oxygen isotope profiles with the Greenland Dye 3 record suggests that not only the three major shifts in the δ¹⁸O curves but also the minor ones are closely comparable, suggesting some common climatic control.  相似文献   

Climatic changes in areas adjacent to the North Atlantic during the last glacial-interglacial transition (14-9 ka BP): A contribution to IGCP-253     

J. John Lowe  B. Ammann  H. H. Birks  S. Bjrck  G. R. Coope  L. Cwynar  J.-L. de Beaulieu  R. J. Mott  D. M. Peteet  M. J. C. Walker 《第四纪科学杂志》1994,9(2):185-198

This paper presents a summary of the evidence for climatic changes during the last glacial-interglacial transition (14-9 ka BP) in land areas adjacent to the North Atlantic. It is a synthesis of the results of the 12 regional summaries compiled by contributors to the North Atlantic Seaboard Programme of IGCP-253 that are published separately in this issue of Journal of Quaternary Science. Eighteen palaeotemperature curves are compared and arranged in three transects, one from southern Europe to Spitsbergen, a second from Ireland to Poland, and the third from southern New England to the Labrador-Baffin Shelf area. Ten maps are presented that summarise the synoptic climatic conditions of the region in 500-year time periods. The purpose of the exercise is to examine the extent to which any emerging patterns support the Ruddiman and Mclntyre model of large-scale shifts in the position of the oceanice Polar Front during the last glacial-interglacial transition. Some broad agreement emerges, although the influence of oceanic changes is diminished in areas that lay in close proximity to the Laurentide and Fennoscandian ice sheets. Attention is drawn to limitations in the compilations and to the potential for improved models in the future.  相似文献   

The ecological implications of a Yakutian mammoth's last meal   总被引：1，自引：0，他引：1  

Bas van Geel  Andr Aptroot  Claudia Baittinger  Hilary H. Birks  Ian D. Bull  Hugh B. Cross  Richard P. Evershed  Barbara Gravendeel  Erwin J.O. Kompanje  Peter Kuperus  Dick Mol  Klaas G.J. Nierop  Jan Peter Pals  Alexei N. Tikhonov  Guido van Reenen  Peter H. van Tienderen 《Quaternary Research》2008,69(3):361-376

Part of a large male woolly mammoth (Mammuthus primigenius) was preserved in permafrost in northern Yakutia. It was radiocarbon dated to ca. 18,500 ¹⁴C yr BP (ca. 22,500 cal yr BP). Dung from the lower intestine was subjected to a multiproxy array of microscopic, chemical, and molecular techniques to reconstruct the diet, the season of death, and the paleoenvironment. Pollen and plant macro-remains showed that grasses and sedges were the main food, with considerable amounts of dwarf willow twigs and a variety of herbs and mosses. Analyses of 110-bp fragments of the plastid rbcL gene amplified from DNA and of organic compounds supplemented the microscopic identifications. Fruit-bodies of dung-inhabiting Ascomycete fungi which develop after at least one week of exposure to air were found inside the intestine. Therefore the mammoth had eaten dung. It was probably mammoth dung as no bile acids were detected among the fecal biomarkers analysed. The plant assemblage and the presence of the first spring vessels of terminal tree-rings of dwarf willows indicated that the animal died in early spring. The mammoth lived in extensive cold treeless grassland vegetation interspersed with wetter, more productive meadows. The study demonstrated the paleoecological potential of several biochemical analytical techniques.  相似文献