new tree ring dates for recent eruptions of mount st helens abstract distinctive patterns of growth rings in increment cores from old growth douglas fir pseudotsuga menziesii stands identify a d 1800 as a more precise date for the eruption of tephra layer t by mount st helens washington layer t was previously inferred to date to about a d 1802 growth patterns also establish a d 1480 as the date of eruption of the earlier layer wn previously estimated as dating to about a d 1500 the timing of radial tree growth places a small limitation on the seasonal resolution of these new tree ring dates

insolation values for the climate of the last 10 million years new values for the astronomical parameters of the earth s orbit and rotation eccentricity obliquity and precession are proposed for paleoclimatic research related to the late miocene the pliocene and the quaternary they have been obtained from a numerical solution of the lagrangian system of the planetary point masses and from an analytical solution of the poisson equations of the earth moon system the analytical expansion allows the direct determination of the main frequencies with their phase and amplitude numerical and analytical comparisons with the former astronomical solution ber78 are performed so that the accuracy and the interval of time over which the new solution is valid can be estimated the corresponding insolation values have also been computed this analysis leads to the conclusion that the new values are expected to be reliable over the last 5 ma in the time domain and at least over the last 10 ma in the frequency domain

extreme fires under warmer and drier conditions inferred from sedimentary charcoal morphotypes from opatcho lake central british columbia canada predictions of the extent of forest fires under warmer and drier conditions in boreal regions require knowledge of long term relationships between fire and climate however many long term studies

reconstruction of the late quaternary environment of the lower luni plains thar desert india geomorphological processes in the thar desert of india are largely climate driven in the lower reaches of the river luni the only major drainage system in the thar desert a fluvio aeolian sequence was located at a site called khudala sediments of this sequence represented a variety of depositional environments namely aeolian fluvially reworked aeolian overbank deposits gravels and occasional evidence of pedogenesis this provided a good opportunity to study aeolian fluvial interaction in the region and for deducing climatic records from the luminescence dating standpoint these sequences offered a good opportunity for a comparative study of thermoluminescence tl blue green light stimulated luminescence bgsl and infrared light stimulated luminescence irsl on different mineral separates of identical provenance but deposited under different environments broadly within experimental errors the tl ages agreed with bgsl and irsl ages on aeolian sands but differed substantially in the case of fluvially reworked and proximally deposited sands and silts the sequence provided a record spanning more than 100 ka with an aeolian phase at 100 ka a channel activation phase between 70 and 30 ka and a phase of climate instability between 13 and 8 ka this appears consistent with the records of monsoon performance during this period which includes the younger dryas it is also inferred that during the last glacial epoch geomorphological processes in the thar both aeolian and fluvial were dormant largely on account of their relationship with the southwest monsoon copyright 2001 john wiley sons ltd

a signal to noise index to quantify the potential for peak detection in sediment charcoal records article i nfo charcoal peaks in lake sediment records are commonly used to reconstruct fire histories spanning thousands of years but quantitative methods for evaluating the suitability of records for peak detection are largely lacking we present a signal to noise index sni that quantifies the separation of charcoal peaks signal from other variability in a record noise we validate the sni with simulated and empirical charcoal records and show that an sni n3 consistently identifies records appropriate for peak detection the sni thus offers a means to evaluate the suitability of sediment charcoal records for reconstructing local fires matlab and r functions for calculating sni are provided

the tephra stratigraphy of two lakes in south central british columbia canada and its implications for mid late holocene volcanic activity at glacier peak and mount st helens washington usa several mid late holocene glacier peak tephras along with mazama and mount st helens wn and p tephras were found in cores from cooley and rockslide lakes in southeastern british columbia 300 km northeast of glacier peak the sediments in cooley lake host the late holocene glacier peak a tephra 2010 calibrated cal years bp four separate glacier peak dusty creek gpdc tephras 5780 5830 cal years bp and a glacier peak set d tephra 6060 cal years bp this is the first report of glacier peak a and d tephras in british columbia the a tephra has been correlated on the basis of glass composition and age to a late holocene glacier peak tephra in the sediments of big twin lake 75 km northeast of glacier peak the glasses in the four gpdc tephra layers from cooley lake are compositionally indistinguishable from those in mount barr cirque and frozen lakes in southwestern british columbia the layers likely represent four eruptions taking place over 50 years although set d tephra has not been correlat

the use of mineral magnetism in the reconstruction of fire history a case study from lago di origlio swiss alps abstract the use of magnetic measurements in the detection of fire signals has been neglected since the work of rummery et al 1979 yet considerable developments have been made in the interpretation of magnetic measurements over the last 16 years this paper presents a study of the fire history of lago di origlio in the southern swiss alps the study utilises the technique of mineral magnetism alongside the stratigraphic pollen spore and charcoal records correlation between the various proxy records indicates that a magnetic fire record is present within the sediments for the last 4 ka the magnetic fire record has a distinct mineralogical and magnetic grain size signature that can be recognised against the background sedimentary signal the results suggest that magnetic measurements may be usefully employed in the reconstruction of fire history their application is rapid and non destructive and the results may provide additional information in relation to the links between catchment fire events and the sedimentary record

tracking recorded fires using charcoal morphology from the sedimentary sequence of prosser lake british columbia canada abstract quantitative analyses of variations in morphological features of charcoal were undertaken in a 210pb dated sediment core from prosser lake british columbia canada seven morphological types of charcoal were defined by particle shape major minor axis ratio apparent porosity and progradation to unburned material the distribution of morphotypes and total charcoal abundances were assessed as a proxy for fire events recorded between 1919 and 2000 and to subsequent mechanisms of transportation sedimentation to lake sediments charcoal morphotypes showed distinct relationships to recorded area burned by fires fragile charcoal fragments with highly irregular porosity termed type m displayed the strongest correlation to burned area r2 0 51 p 0 0001 and did not produce any false positive signal for fires recorded within a radius of 20 km around the lake we infer that high porosity and low density type m fragments are aerially transported and directly deposited on the lake and that the fragility of type m charcoal prevents significant quantities from being secondarily transported and incorporated into the sedimentary record we propose that charcoal morphology is an important but underutilized technique that can yield important insights into fire type proximity and transportation sedimentation processes

midge inferred holocene climate history of two subalpine lakes in southern british columbia canada to investigate postglacial environmental changes in both the coastal and interior wet belts of british columbia fossil midges were analysed from two subalpine lakes one adjacent to the lower fraser canyon frozen lake and the other in mount revelstoke national park eagle lake the midge stratigraphy for frozen lake revealed an abundance of rheophilous chironomid taxa and simuliidae larvae refecting the presence of an inflowing stream an abundance of chaoborus mandibles and microtendipes during the early holocene c 10100 7700 14c years bp c 11500 8500 cal years bp suggests warmer temperatures a subsequent decline in the warm indicators and relative increases in cold stenotherms heterotrissocladius and diamesa indicate cooling until present day this climate reconstruction is consistent with other quantitative and qualitative evidence for past climatic change in southern british columbia at eagle lake the warm indicators dicrotendipes and polypedilum are seen in the early holocene c 85

mount mazama eruption calendrical age verified and atmospheric impact assessed geochemical identification of mount mazama ash in the greenland ice sheet project 2 gisp2 ice core gives a calendrical age of 7627 150 cal yr b p 5677 150 b c for the eruption thus providing a more accurate early holocene stratigraphic time line than previously available the gisp2 record of volcanically derived sulfate suggests a total stratospheric aerosol loading between 88 and 224 mt spread over an 6 yr period following the eruption of mount mazama taking into account the likelihood of some tropospheric aerosol transport to greenland realistic estimates of the resulting atmospheric optical depth range from 0 6 to 1 5 these values may have produced a temperature depression of 0 6 to 0 7 c at mid to high northern latitudes for 1 3 yr after the eruption these results indicate that the 5677 b c eruption of mount mazama was one of the most climatically significant volcanic events of the holocene in the northern hemisphere we also calculate a maximum stratospheric cl release of 8 1 mt by the eruption which may have led to substantial stratospheric ozone depletion

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

environmental magnetism a practical guide j walden f oldfield j and smith eds technical guide no 6 quaternary research association london 1999 243 pp price 17 00 9 00 to qra members isbn 0 907780 42 3

analysis of hemlock pollen size in holocene lake sediments from new england abstract we explored the middle holocene decline of tsuga canadensis by measuring the diameters of pollen grains in two lake sediment cores from new england we hypothesized that a drop in pollen size at the time of the decline followed by an increase in pollen diameters as tsuga recovered during the late holocene might indicate reduced abundance of tsuga in the vicinity of the lake during the decline as smaller pollen grains travel farther than larger ones to provide context for this hypothesis we also measured the diameters of tsuga pollen grains in the surface sediments of sites spanning the modern day gradient of tsuga in new england both fossil records exhibited a reduction in pollen size during the interval of the middle holocene decline with diameters similar to those observed in the upper sediments of those sites yet larger than tsuga pollen grains in the surface sediments of coastal sites beyond the modern range of tsuga this pattern suggests that tsuga persisted in scattered low density populations during the middle holocene as it has remained on the landscape since european settlement

drought variability in the pacific northwest from a 6 000 yr lake sediment record we present a 6 000 yr record of changing water balance in the pacific northwest inferred from measurements of carbonate 18o and grayscale on a sediment core collected from castor lake washington this subdecadally resolved drought record tracks the 1 500 yr tree ring based palmer drought severity index reconstructions of cook et al cook er woodhouse ca eakin cm meko dm stahle dw 2004 science 306 1015 1018 in the pacific northwest and extends our knowledge back to 6 000 yr b p the results demonstrate that low frequency drought pluvial cycles with occasional long duration multidecadal events are a persistent feature of regional climate furthermore the average duration of multidecadal wet dry cycles has increased since the middle holocene which has acted to increase the amplitude and impact of these events this is especially apparent during the last 1 000 yr we suggest these transitions were driven by changes in the tropical and extratropical pacific and are related to apparent intensification of the el nino southern oscillation over this interval and its related effects on the pacific decadal oscillation the castor lake record also corroborates the notion that the 20th century prior to recent aridity was a relatively wet period compared to the last 6 000 yr our findings suggest that the hydroclimate response in the pacific northwest to future warming will be intimately tied to the impact of warming on the el nino southern oscillation

regionalization of fire regimes in the central rocky mountains usa article i nfo fire is one of the most important natural disturbances in the coniferous forests of the us rocky mountains the rocky mountains are separated by a climatic boundary between 40 and 45 n which we refer to as the central rocky mountains crm to determine whether the fire regime from the crm was more similar to the northern rocky mountains nrm or southern rocky mountains srm during the holocene a 12 539 yr old sediment core from long lake wyoming located in the crm was analyzed for charcoal and pollen these data were then compared to charcoal records from the crm nrm and srm during the younger dryas chronozone the fire regime was characterized as frequent at long lake the early and middle holocene fire regime was charac terized as infrequent a brief interval from 4000 to 3000 cal yr bp termed the populus period had a frequent fire regime and remained frequent through the late holocene at long lake in comparison to sites from the nrm and srm the fire regime at long lake was most similar to the srm during the past 12 539 cal yr bp these results suggest the disturbance regime in the crm has a greater affinity with those of the srm

tree ring evidence for a two year interval between recent prehistoric explosive eruptions of mount st helens distinctive annual ring patterns in trees in a forest stand 10 km east of mount st helens indicate that the volcano9s voluminous layer we tephra was erupted after the a d 1481 growth season late in 1481 or early during 1482 combined with earlier research that established a d 1480 as the date of eruption of the underlying similar layer wn tephra the new tree ring data provide evidence that these two major explosive tephra eruptions about 500 yr ago were separated by about 2 yr during that eruptive sequence a voluminous explosive eruption was therefore followed by more than 1 yr of minor explosive activity before another voluminous eruption occurred this record suggests that mount st helens might produce a second large explosive eruption during its current period of activity examinations of the tephra deposits that correlate with narrowring patterns in trees at mount st helens also demonstrate that distinctive ring patterns can form in trees across a large range of tephra layer thicknesses the examinations also suggest that tephra coarseness interacts with tephra layer thickness in determining the effects that tephra fallout will have upon forest trees

early holocene thermal maximum in western north america new evidence from castle peak british columbia conifer logs and branches of early holocene age are common on the surface and in sediments above timberline at castle peak in the southeastern coast mountains of british columbia a study of this wood and associated peat and colluvium has shown that local timberline from 9 1 to 8 2 ka was at least 60 m and perhaps more than 130 m higher than today mean growing season temperature at castle peak during this period thus may have been 0 4 0 8 c warmer than at present this is consistent with theoretical considerations based on milankovitch forcing of climatic change and is supported by other paleoecological data from the southern canadian cordillera and adjacent northwestern united states a generally warm climate may have persisted until about 5 6 ka followed by late holocene cooling

holocene climate fire vegetation interactions at a subalpine watershed in southeastern british columbia canada abstract vegetation assemblages and associated disturbance regimes are spatially heterogeneous in mountain ecosystems throughout the world due to the complex terrain and strong environmental gradients given this complexity numerous sites describing postglacial vegetation and fire histories are needed to adequately understand forest development and ecosystem responses to varying climate and disturbance regimes to gain insight into long term historical climate fire vegetation interactions in southeastern british columbia canada sedimentological and paleoecological analyses were performed on a sediment core recovered from a small subalpine lake the pollen assemblages stomata and macroremains indicate that from 9500 to 7500 cal yr bp pinus dominated forests occurred within the catchment and alnus was also present climate was an important control of fire and fire frequency was highest at this time peaking at 8 fires 1000 yr 1 yet charcoal accumulation rates were low indicative of low terrestrial biomass abundance from 7500 to 4600 cal yr bp pinus decreased as picea abies and larix increased and fire frequencies decreased to 3 6 fires 1000 yr 1 since 7500 cal yr bp the fire regime varied at a millennial scale driven by forest biomass abundance and fuel accumulation changes local scale bottom up controls of fire increased in relative importance since at least 6000 cal yr bp

latest pleistocene and holocene glacier fluctuations in western canada we summarize evidence of the latest pleistocene and holocene glacier fluctuations in the canadian cordillera our review focuses primarily on studies completed after 1988 when the first comprehensive review of such evidence was published the cordilleran ice sheet reached its maximum extent about 16 ka and then rapidly decayed some lobes of the ice sheet valley glaciers and cirque glaciers advanced one or more times between 15 and 11 ka by 11 ka or soon thereafter glacier cover in the cordillera was no more extensive than at the end of the 20th century glaciers were least extensive between 11 and 7 ka a general expansion of glaciers began as early as 8 4 ka when glaciers overrode forests in the southern coast mountains it culminated with the climactic advances of the little ice age holocene glacier expansion was not continuous but rather was punctuated by advances and retreats on a variety of timescales radiocarbon ages of wood collected from glacier forefields reveal six major periods of glacier advance 8 59 8 18 7 36 6 45 4 40 3 97 3 54 2 77 1 71 1 30 ka and the past millennium tree ring and lichenometric dating shows that glaciers began their little ice age advances as early as the 11th century and reached their maximum holocene positions during the early 18th or mid 19th century our data confirm a previously suggested pattern of episodic but successively greater holocene glacier expansion from the early holocene to the climactic advances of the little ice age presumably driven by decreasing summer insolation throughout the holocene proxy climate records indicate that glaciers advanced during the little ice age in response to cold conditions that coincided with times of sunspot minima priority research required to further advance our understanding of late pleistocene and holocene glaciation in western canada includes constraining the age of late pleistocene moraines in northern british columbia and yukon territory expanding the use of cosmogenic surface exposure dating techniques using multi proxy paleoclimate approaches and directing more of the research effort to the northern canadian cordillera

paleofire reconstruction for high elevation forests in the sierra nevada california with implications for wildfire synchrony and climate variability in the late holocene abstract here we present two high resolution records of macroscopic charcoal from high elevation lake sites in the sierra nevada california and evaluate the synchroneity of fire response for east and west side subalpine forests during the past 9200 yr charcoal influx was low between 11 200 and 8000 cal yr bp when vegetation consisted of sparse pinus dominated forest and montane chaparral shrubs high charcoal influx after 8000 cal yr bp marks the arrival of tsuga mertensiana and abies magnifica and a higher than present treeline that persisted into the mid holocene coeval decreases in fire episode frequency coincide with neoglacial advances and lower treeline in the sierra nevada after 3800 cal yr bp independent fire response occurs between 9200 and 5000 cal yr bp and significant synchrony at 100 to 1000 yr timescales emerges between 5000 cal yr bp and the present especially during the last 2500 yr indistinguishable fire return interval distributions and synchronous fires show that climatic control of fire became increasingly important during the late holocene fires after 1200 cal yr bp are often synchronous and corroborate with inferred droughts holocene fire activity in the high sierra nevada is driven by changes in climate linked to insolation and appears to be sensitive to the dynamics of the el nino southern oscillation

charcoal and fly ash particles from lake lucerne sediments central switzerland characterized by image analysis anthropologic stratigraphic and environmental implications abstract in order to link the charcoal record from sedimentary archives with the combustion processes that reflect past anthropogenic activity a novel method based on automated image analysis was developed it allows a detailed quantification and morphological analysis of the combustion derived products that were emitted in the area of lake lucerne central europe throughout the last 7200 years charcoal particle distribution reconstructed from the composite sedimentary record shows that the charcoal input is primarily linked to redistribution of detrital m size charcoal degradation products from surface runoff into the large lake basin however the independent distribution of the coarser charcoal fraction 38 m exhibits four major periods of large scale fire activity around 5500 3300 2400 and 530 cal bp these events are synchronous with major anthropogenic changes lake dwellings land use changes technological innovations although it is possible that these major fire episodes could have been indirectly triggered by climatic deterioration and unfavorable environmental conditions during the late nineteenth century a great increase in slag particles and magnetic spherules of fly ash occurred due to the steamboat navigation on lake lucerne the successive burning of wood after ad 1838 coal after ad 1862 and diesel after ad 1931 by the steamboat traffic produced specific particle shapes providing valuable chronological markers for dating the recent sediments and a proxy for fossil fuel combustion

midge inferred holocene summer temperatures in southeastern british columbia canada abstract using fossil midge stratigraphies we inferred holocene summer temperatures at three subalpine lakes in eastern british columbia the late glacial sediment indicated cool conditions with an abundance of microspectra atrofasciata radialis type fossils at thunder lake and redmountain lake and sergentia at windy lake sergentia and tanytarsus lugens corynocera oliveri type were dominant in the early holocene together with chironomus at redmountain lake at thunder and windy lakes the early holocene was dominated by warm adapted taxa such as microtendipes quantitative midge temperature inference models reconstruct a 4 to 8 c rise in mean july air temperature for windy and thunder lakes at the pleistocene holocene transition early holocene temperatures averaged 3 to 4 c warmer than those extant today in contrast no long term temperature trend was evident at redmountain lake this site may not reflect actual trends in air temperature due to runoff from a persistent snow pack in the watershed comparison of midge and pollen data suggests an inverse relationship between summer temperature and precipitation through the middle to late holocene

summary of pre 1980 tephra fall deposits erupted from mount st helens washington state usa mount st helens has been a prolific source of tephra fall deposits for about 40 000 years these tephra deposits 1 record numerous explosive eruptions 2 form important regional time stratigraphic marker beds and 3 record repeated changes in composition within and between eruptive periods

neoglacial glacier fluctuations in the canadian rockies abstract the little ice age was the most extensive neoglacial glacier advance in the canadian rockies evidence of earlier less extensive neoglacial glacier advances is based on wood recovered from several glacier forefields wood flushed out of athabasca glacier 7550 8230 yr b p three dates and dome glacier 6120 6380 yr b p two dates indicates that forests occurred upvalley of present glacier termini during the hypsithermal detrital logs from peyto 14 dates saskatchewan 3 dates robson 3 dates and yoho 1 date glaciers plus in situ slumps at peyto and robson glaciers have yielded 14 c dates between 2490 and 3300 yr b p 12 dates between 2800 and 2990 this wood is derived from sources at or upvalley from present glacier termini and represents forests overridden by glaciers between ca 3100 and 2500 yr b p treeline was higher than present immediately prior to this advance this advance which did not extend beyond the little ice age maximum position is designated the peyto advance and correlated with the tiedemann advance in western british columbia earliest little ice age advances at peyto and robson glaciers are dated ca 800 600 yr b p at positions ca 500 m upvalley from little ice age limits

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

abrupt holocene climate change and potential response to solar forcing in western canada several abrupt climate events during the holocene including the widely documented oscillation at 8 2 thousand years before present ka are attributed to changes in the north atlantic thermohaline circulation additional mechanisms such as interactions between atmospheric circulation ice sheet dynamics and the influence of solar irradiance also have been proposed to explain abrupt climatic events but evidence remains elusive this study presents evidence from multi proxy analyses on the holocene sediments of eleanor lake interior british columbia climatic inferences from our decadal resolution record of biogenic silica bsi abundance are supported by changes in diatom and pollen assemblages from the same core and correlations with existing regional climate records the bsi record reveals abrupt and persistent climatic shifts at 10 2 9 3 and 8 5 ka the latter two of which are coeval with major collapses of the laurentide ice sheet the record also reveals a short term cooling at 8 2 ka that is distinct from the 8 5 ka event and similar in magnitude to several other late holocene coolings bsi is correlated with solar irradiance indices r 0 43 0 61 but the correlation is opposite in sign to that expected from direct solar forcing and weakens after 8 ka possible mechanisms causing the abrupt and persistent climate changes of the early holocene include 1 sudden losses of ice and proglacial lake extent causing a shift in the meridional structure of atmospheric circulation 2 a possible link between solar minima and el nino like conditions that are correlated with warm spring temperature in interior british columbia and 3 the influence of solar irradiance variability on the position of the polar jet possibly via effects on the strength of the glacial anticyclone