titanium geophysics the application of induced polarization to sea floor mineral exploration titanium is abundant in the earth s crust but it can be economically extracted from only a limited group of minerals principally rutile tio2 and ilmenite fetio3 both found mainly in fossil beach complex placer deposits both minerals have only a weak magnetic susceptibility insufficient to permit correlation between magnetic surveys and known titanium rich deposits however ilmenite shows an unusually strong induced polarization ip response whereas the ip response of rutile is relatively weak ip spectral signatures for ilmenite acquired in laboratory and field settings are also distinctly different from those of other polarizing materials for instance pyrite a nonfloating towed streamer ip system was designed and deployed in surveys off the coasts of virginia and georgia when the cable lies on the sea floor calculations indicate that only about 8 percent of the injected current actually finds its way into the underlying sediment partly because of this high transmitted current to injecte

high resolution peatland water table changes for the past 200 years the influence of climate and implications for management management of peatlands for conservation purposes is often directed at mitigation of damaging impacts of past and present human activity assessment of such impacts is often based on perspectives from short term ecological data here we test a series of hypotheses for the causes of changes in mire hydrology and vegetation on the border mires in northern england using palaeoecological data for the last 200 years ecological data suggest peatlands surrounded by plantation forestry have become drier over the last 40 years this could be caused by direct hydrological impacts of the growing trees and associated drainage or indirectly by the cessation of grazing and burning a third hypothesis is that hydrological changes are the result of recent climatic change high resolution water table reconstructions from testate amoebae analysis supported by plant macrofossil analysis and dated by 210pb spheroidal carbonaceous particles scps and pollen data demonstrate that a site outside the direct in uence of fores

holocene palaeoclimates from peat stratigraphy macrofossil proxy climate records from three oceanic raised bogs in england and ireland quantified analyses of plant macrofossil remains have been made from three profiles of peat from raised bogs spanning a distance of 425 km from western ireland to northern england the reconstructed vegetation of each profile is related to changing bog surface wetness bsw and since the bogs are ombrotrophic these bsw changes are interpreted in terms of changing climate using age depth models based on a total of 49 radiocarbon dates a number of wetter and drier phases are identified and phase shifts to wetter and or cooler climates are defined prominent coincident changes to wetter conditions are dated in at least two of the profiles to ca 4400 4000 1750 1400 and 1000 cal bp and in all three profiles at 3200 2750 2350 2250 and around 700 cal bp these phases are related to proxy climate changes in other terrestrial data sets from northwest europe and a broad degree of synchroneity is demonstrated

widespread evidence of 1500 yr climate variability in north america during the past 14 000 yr there is debate concerning the spatial extent and magnitude of the recently identified 1500 yr climate oscillation existing evidence is largely restricted to the north atlantic and adjacent landmasses the spatial extent magnitude and effects of these climate variations within the terrestrial environment during the holocene have not been established we show that millennial scale climate variability caused changes in vegetation communities across all of north america with a periodicity of 1650 500 yr during the past 14 000 calendar years cal yr times of major transitions identified in pollen records occurred at 600 1650 2850 4030 6700 8100 10 190 12 900 and 13 800 cal yr b p consistent with ice and marine records we suggest that north atlantic millennial scale climate variability is associated with rearrangements of the atmospheric circulation with far reaching influences on the climate

compilation of non annually resolved holocene proxy climate records stacked holocene peatland palaeo water table reconstructions from northern britain abstract the number and range of holocene palaeoclimate reconstructions from various regions of the world have increased dramatically over the last decade the data density for many regions and proxies now offers the potential of robust regional scale reconstructions that avoid the problems of records from individual sites and improve communication between palaeoclimate subdisciplines and climate modellers however there are problems with chronological uncertainties and quantification of proxies which make compilation of multiple records difficult here we explore a stacking and tuning approach to the derivation of regional records from peatland climate proxies to test its applicability to non annually resolved terrestrial records twelve individual records from northern britain based on water table reconstructions from testate amoebae analysis were divided into four regions records were detrended normalised and compared within regions to identify clear correlative events the original chronologies of the records were tuned using both these events and independent age markers the stacked record for northern britain indicates pronounced changes to wet conditions at 3600 2760 and 1600 cal yr bp with more minor changes at 3060 2050 1260 860 550 and 260 cal yr bp the main wet phases are highly correlated with mid european lake highstands wider north atlantic climate change inferred from ocean and ice core records and solar variability tuning and stacking of non annual terrestrial palaeoclimate records is a new approach to the compilation and reconciliation of individual records within coherent climatic regions and provides a tool for upscaling of palaeoclimate records for climate model data comparisons

a high resolution record of late holocene moisture variability from a michigan raised bog usa we reconstructed the late holocene surface moisture history and vegetation dynamics of a raised bog in michigan using testate amoebae peat humification pollen stomata and plant macrofossils our primary objective was to compare bog palaeohydrology with the water level history of lake michigan and to regional and local vegetation changes hydrologic histories inferred from testate amoebae and humification show similar trends and correspond with records of past water level variability in lake michigan the bog clearly shows effective moisture increases during the algoma highstand 3200 2300 cal bp and a later unnamed highstand 1900 1300 cal bp some higher frequency fluctuations are also similar the good correspondence indicates that bog hydrology and the water levels of lake michigan have been driven by changes in large scale atmospheric circulation patterns for at least the past 3500 years climate during the algoma highstand may have been spatiotemporally complex with increasing moisture oc

estimating carbon accumulation rates of undrained mires in finland application to boreal and subarctic regions equations based on empirical relationships of peat physical properties were used to estimate the average long term apparent rate of carbon accumulation lorca in finnish mire vegetation regions the results were generalized to the boreal and subarctic regions analyses of 1302 dated peat cores were used to infer carbon accumulation for each mire vegetation region of finland the area weighted lorca for finnish undrained mire areas was 18 5 g m 2 yr 1 and the total carbon sink 0 79 tg yr 1 1 tg 1012g the total carbon pool of finnish undrained mires was estimated as 2257 tg the aapa mire region included 80 of the total net accumulation rate of carbon and 85 of the total carbon reservoirs of finnish undrained mires lorca was signi cantly higher in the raised bog region 26 1 g m 2 yr 1 compared with the aapa mire region 17 3 g m 2 yr 1 and bogs generally had a higher lorca 20 8 g m 2 yr 1 than fens 16 9 g m 2 yr 1 the total c sink for boreal and subarctic mires was estimated at 66 tg yr 1 whi

dendroecological evidence of lake level changes during the last three centuries in subarctic quebec abstract dendroecological analysis of black spruces picea mariana mill bsp near the shore of clearwater lake in the eastern canadian subarctic yielded information on water level over the past three centuries tree positions growth froms layering tree ring patterns and ice scars provide direct evidence of a major rise in lake level from the 17th century to the present trees on the lake shore were progressively submerged by the increasing water level which reached a maximum in this century higher levels began around the mid 18th century when shoreline spruce trees started to lean because extensive wave erosion caused landward shore displacement high mortality of leaning spruce and abundant ice scar formation occurred during this century the rise in water level in inferred to have been caused by snowier winters occurring parallel to climatic warming

mire development pathways and palaeoclimatic records from a full holocene peat archive at walton moss cumbria england plant macrofossil data have been used to identify the successive mire communities occupying both central and marginal locations in the walton moss peatland complex during the last 10 500 years the reconstructed pathways of mire development indicate that early holocene fen and fen carr communities were succeeded by species indicative of deep mire water tables and oligotrophic conditions the character of the fen bog transition fbt is compared with similar records of peatland development from britain and scandinavia and with independent climate data for the early holocene the pseudohochmoor of central europe is suggested as an approximate modern analogue for the dry pioneer oligotrophic mire type and alternative explanations for its presence are explored the first major increase in ombrotrophic sphagna occurred at c 7800 cal bp overlying sphagnum peats provide a continuous record of climate change inferred from fluctuations in raised mire surface wetness the proxy palaeoclimate record reconstr

late holocene paleoecohydrology and carbon accumulation estimates from two boreal peat bogs in eastern canada potential and limits of multi proxy archives abstract the stratigraphy of four peat sequences collected in two peat bogs located in the eastmain river watershed 52 n 76 w james bay lowlands quebec canada was investigated to reconstruct past hydroclimatic conditions of peat accumulation and associated carbon dynamics during the late holocene analyses of macrofossils testate amoebae peat humification c n ratio and bulk density were performed at high resolution along each peat core allowing the potential of each proxy indicator under varying nutrient status and hydroclimatic conditions to be evaluated some synchronous changes were recorded both within and between peatlands suggesting the influence of allogenic factors in the development of these peatlands other reconstructed changes have highlighted autogenic succession processes related to the local geomorphic and hydrologic context highest peat carbon accumulation rates lorca were correlated with either wet conditions or high woody debris percentages suggesting that residence time of the biomass in the acrotelm and the nature of plant material can both influence carbon accumulation rates in peat bogs this study provides the first high resolution paleoecohydrological reconstructions from the mid boreal ecoregion of eastern canada a region in which peatlands occupy 30 to 60 of the land surface

a relationship between dunes fire and climate recorded in the holocene deposits of quebec during the past 5 000 yr bp the tropics have experienced an increase in aridity and aeolian activity in both maritime and continental areas1 4 in contrast the onset and subsequent development of post hypsithermal climates in northern latitudes were primarily conducive to global cooling it is suggested here that aeolian activity in cold environments represents a direct response to this long term cooling trend that began after 6 000 5 000 yr bp at the end of the climatic optimum5 9 this study establishes the holocene chronology of sand dunes near the outer forest limit in northern quebec fig 1 i show here that fires initiate the aeolian activity and that the fire dune relationship is typical of cooling period on this basis a palaeoclimatic reconstruction since the climatic optimum is proposed

a 2800 year palaeoclimatic record from tore hill moss strathspey scotland the need for a multi proxy approach to peat based climate reconstructions analyses of plant macrofossils testate amoebae and humification have been carried out on a 2800 year core from tore hill moss a raised bog in the strathspey region of scotland all three analyses were carried out at the same 4 cm intervals allowing exact correlation and the core was dated by nine accelerator mass spectrometry radiocarbon dates and the glen garry tephra layer the results have been combined and compared to present a bog surface wetness bsw record within which the limitations of each proxy method can be assessed and this has highlighted the advantages of a combined rather than a single proxy approach significant wet shifts are recorded at ca cal 560 bc 60 bc ad 430 ad 570 ad 700 ad 1090 and ad 1640 significant shifts to drier periods are also suggested ca cal ad 220 ad 500 and ad 820 some of the recorded shifts and phases are related to phases of wetter and drier climate such as the sub boreal sub atlantic transition the dark age deterioration and the romano british warm period the dark ages are notable as a period of rapid peat accumulation and frequent water table fluctuations time series analysis revealed a significant wet shift cycle of 560 years from the testate amoebae data

an 8500 cal year multi proxy climate record from a bog in eastern newfoundland contributions of meltwater discharge and solar forcing analyses of plant macrofossils testate amoebae and the degree of peat humification have been combined into a single composite reconstruction of bog surface wetness bsw on a coastal plateau bog in eastern newfoundland the reconstruction reveals 14 distinctive phases of near surface water tables commencing at 8270 7500 6800 5700 5200 4900 4400 4000 3100 2500 2050 1700 600 and 200 cal bp which may be used to infer changes in the atmospheric water balance of eastern newfoundland the first two major phases of pool development follow the final drainage of glacial lake agassiz at 8400 cal bp and the ungava lakes between ca 7500 6900 cal bp respectively from 7500 cal bp to the present there appears to be a strong correlation within dating errors between reconstructed bsw and the stacked ice rafted debris ird record in the north atlantic ocean both records may reflect long term changes in air masses comparisons of the bsw reconstruction with records of cosmogenic isotope flux also suggest a persistent link between reduced solar irradiance and increased bsw during the holocene

high resolution records of late holocene climate change and carbon accumulation in two north west european ombrotrophic peat bogs the peat stratigraphy plant macrofossils colorimetric humification pollen non pollen microfossils carbon nitrogen ratios of three replicate cores from a raised peat bog in the uk walton moss and a single core from a raised peat bog in denmark lille vildmose were examined in an attempt to investigate the relation between long term climate change and changes in species composition of the peat forming vegetation nine wet shifts identified in the monoliths from walton moss and lille vildmose mainly occurred during periods of increasing atmospheric c 14 content because fluctuations in holocene atmospheric radiocarbon concentrations have been shown to be due to variations in solar activity the little ice age lia climatic deteriorations registered in both peat bogs were probably driven by changes in solar activity climatic deteriorations in the three replicate cores from walton moss are not all consistently registered and may reflect the internal variability in the extent of hollow lawn hummock microforms within raised peat bog ecosystems the lowest carbon accumulation values for the walton moss monoliths between ca cal ad 1300 and 1800 and between ca cal ad 1490 and 1580 for lille vildmose occurred during the course of lia climatic deteriorations peat bog primary productivity may have been reduced during the lia owing to lower spring summer temperatures and shorter growing seasons for the peat forming plants species specific higher decomposition rates may have also caused the lower carbon accumulation rates in the peat bogs during the lia c 2002 elsevier science b v all rights reserved

a sensitive high resolution record of late holocene climatic change from a raised bog in northern england proxy climatic data in the form of plant macrofossils have been analysed from a 5 m core from bolton fell moss cumbria uk detailed analysis of peat from the upper 50 cm of this core is used to demonstrate a strong correlation between changes in the relative proportion of taxa and known climatic changes over the last 1000 years the record of changes in bog vegetation contained within the peat profile is used to reconstruct changes in bog surface wetness for the latter half of the holocene as bog surface wetness is directly controlled by the prevailing climatic conditions this reconstruction can be viewed as a proxy climate record twelve radiocarbon age estimates on the 5m core suggest that between 50 and 500 cm peat accumulated at a relatively constant rate of 12 4 yr cm 1 the regular sampling intervals thus provide a time series of past bog surface wetness spectral analyses of this series indicates that wetness changes are cyclic with a ca 800 year periodicity

replicability and variability of the recent macrofossil and proxy climate record from raised bogs field stratigraphy and macrofossil data from bolton fell moss and walton moss cumbria england replication of results is a basic tenet of science but in palaeoecology this is very time consuming and the signal is subject to noise the derivation of proxy climate signals from ombrotrophic peat was carried out originally using samples from open peat faces where the stratigraphic relationships could be easily observed now that such sections are rare and often degraded there is a need to demonstrate that data can be replicated from core profiles ten short cores taken from two adjacent bogs have been analysed for macrofossils and show a coherent series of changes which are also similar to previous profiles from the same sites it is concluded that variation between profiles is slight and less than observations of present vegetation mosaics might suggest recommendations for a standard approach to fieldwork on raised bogs that emphasises the utility of subfossil pool layers are proposed and the need for a secure chronology is stressed 1998 john wiley sons ltd

holocene palaeoecological reconstruction of three boreal peatlands in the la grande riviere region quebec canada pollen and macrofossil analyses from central peat cores along with 23 radiocarbon dates were used in palaeoecological reconstructions for three peatlands lg1 lg2 and lg3 within the lower la grande riviere watershed in northern boreal quebec basal ages from lg3 and lg2 indicate up to an 1100 years later and possibly more abrupt tyrrell sea retreat in the lg3 area compared with the timeline for the region both autogenic and allogenic factors were found to have influenced local vegetation succession and rates of peat accumulation internal autogenic factors such as peat accumulation were key elements for the general peatland developmental pathway that followed the classic hydrosere sequence pond fen bog regional climate and hydrography are the main external factors associated with changes in vegetation assemblages surface wetness and consequently rates of peat accumulation the lg2 and lg3 peatlands began developing shortly after 7000 cal bp as shallow ponds with herbaceous freshwater aquatic and e

all age depth models are wrong but how badly the uncertainty and error associated with fitted age depth models were investigated by fitting a range of models to sets of simulated radiocarbon dates based on varved sediments and comparing the modelled relationship with the varve timescale with large numbers of dates cubic smooth splines out perform other models with few dates no model reliably provides a good fit to reality and calculated confidence intervals are over optimistic c 2003 elsevier ltd all rights reserved

multiproxy late holocene peat records from ireland towards a regional palaeoclimate curve two new peat based climate records from ireland covering the late holocene are presented the sequences are dated by a strong chronological framework formed by ams radiocarbon dates and scps three proxy indicators testate amoebae macrofossils and humification have been determined allowing the limitations and strengths of each to be identified and utilised to provide a bog surface wetness bsw record for both sites age depth models take into account the potential for accumulation rates to vary with bog vegetation the records from each site have been used to derive a combined bsw record that displays changes to a wetter cooler climate from ca ad 30 1920 bp ca ad 310 1640 bp ca ad 805 1145 bp ca ad 1040 910 bp and ca ad 1300 650 bp changes follow closely those identified in a northern britain composite bsw record and largely correspond with lake level data in central france suggesting the main changes in water balance were coherent over a large region correspondence with increases in ird and slower iceland scotland overflow water isow suggests that these changes were related to oceanic forcing influencing the track of dominant westerly air flow over ireland copyright 2007 john wiley sons ltd

sphagnum δ13c values as indicators of palaeohydrological changes in a peat bog late holocene peat stratigraphy of a canadian boreal peat bog was examined to evaluate the poten tial of sphagnum 13 c values as surface moisture proxy indicators isotopic measurements were compared to tes tate amoebae inferred water table depth reconstructions plant macrofossil assemblages and past decompo sition levels inferred by colorimetric humification ams radiocarbon dates were coupled with 210 pb dates to establish peat chronology although the mechanisms underlying carbon fractionation processes in peatlands are not well understood we demonstrate that sphagnum 13 c values have potential for palaeohydrological recon structions since variations presented by the isotopic values can generally be correlated with the other proxy records especially during drier episodes

proxy climate record for the last 1000 years from irish blanket peat and a possible link to solar variability recent research has shown that ombrotrophic mires can yield a proxy climate signal based on changes in the degree of peat humification 1 2 and that oceanic margin sites show the most sensitive record 3 we compare humification records for the last 1000 yr from two radiocarbon dated blanket peat profiles from western ireland and show several corresponding periods of climatic fluctuations periods favouring reduced peat decomposition suggestive of wetter and or cooler climatic conditions seem to coincide with periods of reduced sunspot activity and atmospheric14c anomalies whilst climatologists have continued to debate a link between solar variability on a century timescale and climate change the exact nature of that link remains elusive 4 7 the results from ireland demonstrate that data derived from mires could be relevant to the debate as to the extent of solar forcing in natural climatic variability and the curves shown provide a continuous record to add to previous evidence for the so called medieval optimum and little ice age 8 the record may imply that during the past millennium climatic change at the oceanic margin of the northeast atlantic largely corresponded to inferred variations in solar output

low energy deposition in the chicxulub crater during the impact to post impact transition article i nfo the crater fill units that were deposited during the terminal stages of the formation of the shallow marine chicxulub crater in northern yucatan were interpreted by some authors as products of a catastrophic resurge of water this interpretation contrasts markedly with the dominant sand grain size b300 m and the abundant small scale current cross bedding structures indicative of low energy deposition to solve this discrepancy we applied first principles of physical sedimentology in an analysis of grain size and sedimentary structures to determine current velocities and minimum water depths required to generate the observed sedimentary bedforms we combine this approach with numerical modeling of crater formation in order to explore the dimensions of the ejecta ring wall being formed by a chicxulub impactor in water depths of 1000 m we find that the ejecta wall reaches heights in the order of 1200 m above sea floor and 200 m above sea level it thus prevented the resurge of water into the crater cavity and consequently also the subsequent formation of a collapse wave the ring wall significantly retarded the refilling of the crater cavity with seawater and refilling took place by permeation through and localized erosion of the ring wall this resulted in low energy currents with velocities between 1 5 and 0 18 m s 1 slowly reentering the crater and depositing the cm scale low energy laminated and crossbedded sandy terminal impact deposits

peatland development in relation to holocene climatic change in manitoba and saskatchewan canada two peat cores from the southern boreal forest in south central manitoba and central saskatchewan canada were analyzed for microfossils macrofossils and physicochemical properties regional vegetation and local peatland development at these sites show the influence of warm and dry climatic conditions during the middle holocene pollen assemblages at the base of the manitoba site indicate the presence of grassland parkland vegetation in the area prior to 4230 bp at the saskatchewan site boreal forest was present throughout the development of the peatland from before 5020 bp to present both the manitoba and saskatchewan records suggest a more open deciduous character of the regional vegetation cover during the middle holocene in the southernmost part of the expanding boreal forest in comparison with the modern southern mixed wood boreal forest the presence of a typha latifolia domimted marsh phase in the initial stages of development of both peatlands is indicative of marked water level fluctuati

a 7500 year peat based palaeoclimatic reconstruction and evidence for an 1100 year cyclicity in bog surface wetness from temple hill moss pentland hills southeast scotland analyses of plant macrofossils peat humification and testate amoebae were used to reconstruct a proxy climate record spanning the last 7500 years from an ombrotrophic bog temple hill moss in southeast scotland the plant macrofossil data were subjected to detrended correspondence analysis dca which modelled effectively the significant wet shifts within the record a mean water table depth transfer function was applied to the testate amoebae data to provide quantifiable changes the three proxy records show coherent phase changes which are interpreted as variability in past effective precipitation two tephra horizons glen garry and lairg a were used in conjunction with radiocarbon dates to construct an age depth model producing a robust geochronology from which a time series was calculated the palaeoclimatic reconstruction identified major wet shifts throughout the holocene with specific events occurring around cal 6650 5850 5300 4500 3850 3400 2800 2450 1450 1350 and 250 150 bp spectral analysis of the plant macrofossil dca and colorimetric humification data produced a millennial scale periodicity of 1100 years the same periodicity has also been found in a palaeoclimatic reconstruction from a site in cumbria walton moss and may be linked with millennial scale periodicities found in oceanic palaeoclimatic records

millennial scale rhythms in peatlands in the western interior of canada and in the global carbon cycle abstract anatural 1450 yr global holocene climate periodicity underlies a portion of the present global warming trend calibrated basal radiocarbon dates from 71 paludified peatlands across the western interior of canada demonstrate that this periodicity regulated western canadian peatland initiation peatlands the largest terrestrial carbon pool and their carbon budgets are sensitive to hydrological fluctuations the global atmospheric carbon budget experienced corresponding fluctuations as recorded in the holocene atmospheric co 2 record from taylor dome antarctica while the climate changes following this 1450 yr periodicity were sufficient to affect the global carbon budget the resultant atmospheric co 2 fluctuations did not cause a runaway climate co 2 feedback loop this demonstrates that global carbon budgets are sensitive to small climatic fluctuations thus international agreements on greenhouse gasses need to take into account the natural carbon budget imbalance of regions with large climatically sensitive carbon pools