LICHEN GROWTH RATES ON GLACIER FORELANDS IN SOUTHERN NORWAY: PRELIMINARY RESULTS FROM A 25-YEAR MONITORING PROGRAMME     

BY HAZEL E. TRENBIRTH  JOHN A. MATTHEWS 《Geografiska Annaler: Series A, Physical Geography》2010,92(1):19-39

A unique 25-year lichen growth monitoring programme involving 2,795 individuals of the Rhizocarpon subgenus at 47 sites on 18 glacier forelands in the Jotunheimen–Jostedalsbreen regions of southern Norway is reported. The data are used to address fundamental questions relating to direct lichenometry: spatial and temporal variability in lichen growth rates, climatic effects on lichen growth rates, lichen growth models, and implications for lichenometric dating. Mean annual (diametral) growth rate ranged from 0.43 to 0.87 mm yr⁻¹ between sites, which is attributed primarily to local habitat differences. Interannual variability in annual mean growth rate exceeded 1.0 mm yr⁻¹ at some sites. Annual mean growth rates for all sites combined varied from 0.52 to 0.81 mm yr⁻¹ and was positively correlated with annual mean temperature and winter mean temperature (both r = 0.64, p <0.005) but not with summer seasonal temperature: positive correlations with annual and winter precipitation were less strong and the correlation with summer precipitation was marginally significant (r = 0.41 p <0.10). Growth-rate models characterized by annual growth rates that remain approximately constant or increase with lichen size up to at least 120 mm tended to fit the data more closely than a parabolic model. This is tentatively attributed to a long 'linear/mature' phase in the growth cycle. Comparison with growth rates inferred from indirect lichenometry suggest that such high measured growth rates could not have been maintained over the last few centuries by the largest lichens used in southern Norway for lichenometric dating. Several hypotheses, such as the effects of competition and climate change, which might explain this paradox, are discussed.  相似文献   

GROWTH OF CRUSTOSE LICHENS: A REVIEW     

BY RICHARD ARMSTRONG  TOM BRADWELL 《Geografiska Annaler: Series A, Physical Geography》2010,92(1):3-17

Crustose species are the slowest growing of all lichens. Their slow growth and longevity, especially of the yellow-green Rhizocarpon group, has made them important for surface-exposure dating (lichenometry). This review considers various aspects of the growth of crustose lichens revealed by direct measurement including: 1) early growth and development; 2) radial growth rates (RGR, mm yr⁻¹); 3) the growth rate–size curve; and 4) the influence of environmental factors. Many crustose species comprise discrete areolae that contain the algal partner growing on the surface of a non-lichenized fungal hypothallus. Recent data suggest that 'primary' areolae may develop from free-living algal cells on the substratum while 'secondary' areolae develop from zoospores produced within the thallus. In more extreme environments, the RGR of crustose species may be exceptionally slow but considerably faster rates of growth have been recorded under more favourable conditions. The growth curves of crustose lichens with a marginal hypothallus may differ from the 'asymptotic' type of curve recorded in foliose and placodioid species; the latter are characterized by a phase of increasing RGR to a maximum and may be followed by a phase of decreasing growth. The decline in RGR in larger thalli may be attributable to a reduction in the efficiency of translocation of carbohydrate to the thallus margin or to an increased allocation of carbon to support mature 'reproductive' areolae. Crustose species have a low RGR accompanied by a low demand for nutrients and an increased allocation of carbon for stress resistance; therefore enabling colonization of more extreme environments.  相似文献   

On the weakening of Hurricane Lili, October 2002     

T. N. KRISHNAMURTI  J. SANJAY †  T. S. V.VIJAYA KUMAR  ADAM J. O'SHAY  RICHARD J. PASCH 《地球，A辑:动力气象学与海洋学》2005,57(1):65-83

  相似文献   

Contemporary terminal-moraine ridge formation at a temperate glacier: Styggedalsbreen, Jotunheimen, southern Norway     

JOHN A. MATTHEWS  DANNY McCARROLL  RICHARD A. SHAKESBY 《Boreas: An International Journal of Quaternary Research》1995,24(2):129-139

Terminal-moraine ridges up to 6 m high have been forming at the snout of Styggedalsbreen for two decades. Based on intermittent observations during this period, combined with a detailed study of ridge morphology, sedimentary structures and composition during the 1993 field season, a model of terminal-moraine formation that involves the interaction of glacial and glacio-fluvial processes at a seasonally oscillating ice margin is presented. In winter, subglacial debris is frozen-on to the glacier sole; in summer, ice-marginal and supraglacial streams deposit sediments on the wasting ice tongue. The ice tongue overrides an embryonic moraine ridge during a late-winter advance and a double layer of sediment (diamicton overlain by sorted sands and gravels) is added to the moraine ridge during the subsequent ablation season. Particular ridges grow incrementally over many years and exert positive feedback by enhancing snout up-arching during the winter advance and constraining the course of summer meltwater streams close to the ice margin. The double-layer annual-meltout model is related to moraine formation by the stacking of subglacial frozen-on sediment slabs (Krüger 1993). Moraine ridges of this type have a complex origin. are not push moraines, and may be characteristic of dynamic high-latitude and high-altitude temperate glaciers.  相似文献   

The significance of pollen-rich inorganic lake sediments in the Cratére du Nouveau-Quèbec area, Ungava, Canada     

PIERRE J. H. RICHARD  MICHEL A. BOUCHARD  PIERRE GANGLOFF 《Boreas: An International Journal of Quaternary Research》1991,20(2):135-149

Unexpectedly high pollen concentrations characterize the basal, silty part of the postglacial sediments accumulated in two lakes from the Cratère du Nouveau-Quebéc area, Ungava. These lacustrine silts and their pollen content result from early postglacial washing of a pollen bearing till. The till must therefore ahve incorporated pollen that relates to events prior to the last glacial event. The matrix of the till deposits surrounding the lakes shows outstandingly high pollen concentrations. It is hypothesized that because of the proximity of the ice divide during the last (and earlier) ice advance(s) in Ungava, the previously depoisited till and the pollen that haad accumulated in its matrix during the interglacial interval(s) were preserved in relict till plains or recycled into the till of teh last glaciation. The crater's age has been established at 1.4 Ma and holds a minimum thickness of 95 m of sediments. It is very likely filled with successive tills or related glacigenic deposits perhaps representing the whole length of time since the crater was formed. Alike the most recent till, these deposits should pollen. there is thus the prospect ofr a 1.4 Ma old pollen record for Ungava.  相似文献   

Cretaceous-Tertiary crossroads of migration in the Sahel     

RICHARD MOODY  PETER SUTCLIFFE 《Geology Today》1990,6(1):19-23

A series of expeditions undertaken over the last three years by a team of geologists from Kingston Polytechnic and the British Museum (Natural History) has increased our understanding of the Cretaceous and Tertiary palaeogeography of Central West Africa. The latest expedition discovered a dinosaur graveyard of Lower Cretaceous (Wealden) age. Studies of these and other fossils within the sedimentary rocks of the Iullemmeden Basin in Niger and Mali have shed new light on the Trans-Saharan Seaway migration route during the Cretaceous and Tertiary periods.  相似文献   

Why ocean heat transport warms the global mean climate     

CELINE HERWEIJER  RICHARD SEAGER  MICHAEL WINTON  AMY CLEMENT 《地球，A辑:动力气象学与海洋学》2005,57(4):662-675

  相似文献   

Spatial Requirements for the Continuation of Social Democracy in New Zealand     

RICHARD V. WELCH 《New Zealand geographer》1982,38(1):3-8

  相似文献   

Variable Variscan thermal rejuvenation in the St Malo region, Cadomian Orogen, France: evidence from ⁴⁰Ar/³⁹Ar mineral ages     

R. DAVID DALLMEYER  MICHAEL BROWN  RICHARD S. D'LEMOS  ROBIN A. STRACHAN 《Journal of Metamorphic Geology》1993,11(1):137-154

Abstract The St Malo region in north-west France contains migmatites and anatectic granites derived by partial melting of metasedimentary protoliths during Cadomian orogenesis at c. 540 Ma. Previously reported Rb–Sr model ages for muscovite and biotite range from c. 550 to c. 300 Ma, and suggest variable resetting of mineral isotopic systems. These rocks display microscopic evidence for variably intense Cadomian intracrystalline plastic strain but record no obvious evidence of penetrative Palaeozoic regional deformation. ⁴⁰Ar/³⁹Ar mineral ages have been determined to evaluate better the extent, timing and significance of Palaeozoic overprinting. Eleven muscovite concentrates and one whole-rock phyllite have been prepared from various units exposed in the St Malo and adjacent Mancellian regions. In the Mancellian region, muscovite from two facies of the Bonnemain Granite Complex record ⁴⁰Ar/³⁹Ar plateau ages of c. 527 and 521 Ma. An internally discordant ⁴⁰Ar/³⁹Ar release spectrum characterizes muscovite from protomylonitic granite within the Cadomian Alexain-Deux Evailles-Izé Granite Complex, and probably records the effects of Variscan displacement along the North Armorican Shear Zone. Muscovite concentrates from anatectic granite and from Cadomian mylonites along ductile shear zones within the north-western sector of the St Malo region exhibit internally discordant ⁴⁰Ar/³⁹Ar release spectra which suggest variable and partial late Palaeozoic rejuvenation. By contrast, muscovite concentrates from samples of variably mylonitic Brioverian metasedimentary rocks exposed within the south-eastern sector of the St Malo region display internally concordant apparent age spectra which define plateaux of 326–320 Ma. A whole-rock phyllite sample from Brioverian metasedimentary rocks exposed along the eastern boundary of the St Malo region displays an internally discordant argon release pattern which is interpreted to reflect the effects of a partial late Palaeozoic thermal overprint. Muscovite from the Plélan granite, part of the Variscan Plélan-Bobital Granite Complex, yields a ⁴⁰Ar/³⁹Ar plateau age of c. 307 Ma. The ⁴⁰Ar/³⁹Ar results indicate that Cadomian rocks of the St Malo region have undergone a widespread and variable Palaeozoic (Carboniferous) rejuvenation of intracrystalline argon systems which apparently did not affect the Mancellian region. This rejuvenation was not accompanied by penetrative regional deformation, and was probably of a static thermal–hydrothermal origin. The heat source for rejuvenation was probably either the result of heating during Variscan extension or advection from Variscan granites which are argued to underlie the St Malo region.  相似文献   

Bulk composition and mineral parageneses of sapphirine-bearing rocks along a gabbro-lherzolite contact at Finero, Ivrea Zone, N Italy     

JANE D. SILLS  DIETRICH ACKERMAND  RICHARD K. HERD  BRIAN F. WINDLEY 《Journal of Metamorphic Geology》1983,1(4):337-351

Sapphirine occurs in a 3-5 m wide zone between amphibole-lherzolite and garnetiferous metagabbro at Finero in the Ivrea Zone, NW Italian Alps. Layers consisting of plag + hb + sa + cpx + opx + sp + gt are interbanded with spinel pyroxenites, which may contain sapphirine replacing spinel. All minerals are very magnesian, with X_Mg between 0.78 and 0.92. Bulk rock analyses suggest that precursors to the sapphirine-bearing rocks were igneous cumulates of plagioclase + olivine + hornblende + spinel. Up to 16wt% CaO does not inhibit sapphirine formation and it is the unusually Mg-rich nature of the host rocks which allows sapphirine development. The early igneous assemblage was replaced by one of cpx + sa + hb +± plag at a pressure of 9 ± 1 kbar and temperatures of 900 ± 50°C. Subsequent rapid uplift caused the instability of gt, gt + hb, hb and sa + cpx to form opx + plag ± sp ± sa symplectites.  相似文献