detrital carbonate peaks on the labrador shelf a 13 7 ka template for freshwater forcing from the hudson strait outlet of the laurentide ice sheet into the subpolar gyre abstract the laurentide ice sheet lis was a large dynamic ice sheet in the early holocene the glacial events through hudson strait leading to its eventual demise are recorded in the well dated labrador shelf core md99 2236 from the cartwright saddle we develop a detailed history of the timing of ice sheet discharge events from the hudson strait outlet of the lis during the holocene using high resolution detrital carbonate ice rafted detritus ird 18o and sediment color data eight detrital carbonate peaks dcps associated with ird peaks and light oxygen isotope events punctuate the md99 2236 record between 11 5 and 8 0 ka we use the stratigraphy of the dcps developed from md99 2236 to select the appropriate r to calibrate the ages of recorded glacial events in hudson bay and hudson strait such that they match the dcps in md99 2236 we associate the eight dcps with h0 gold cove advance noble inlet advance initial retreat of the hudson strait ice stream hsis from hudson strait opening of the tyrrell sea and drainage of glacial lakes agassiz and ojibway the opening of foxe channel and retreat of glacial ice from foxe basin are represented by a shoulder in the carbonate data r of 350 years applied to the radiocarbon ages constraining glacial events h0 through the opening of the tyrell sea provided the best match with the md99 2236 dcps r values and ages from the literature are used for the younger events a very close age match was achieved between the 8 2 ka cold event in the greenland ice cores dcp7 8 15 ka bp and the drainage of glacial lakes agassiz and ojibway our stratigraphic comparison between the dcps in md99 2236 and the calibrated ages of hudson strait bay deglacial events shows that the retreat of the hsis the opening of the tyrell sea and the catastrophic drainage of glacial lakes agassiz and ojibway at 8 2 ka are separate events that have been combined in previous estimates of the timing of the 8 2 ka event from marine records sw iceland shelf core md99 2256 documents freshwater entrainment into the subpolar gyre from the hudson strait outlet via the labrador north atlantic and irminger currents the timing of freshwater release from the lis hudson strait outlet in md99 2236 matches evidence for freshwater forcing and lis icebergs carrying foreign minerals to the sw iceland shelf between 11 5 and 8 2 ka the congruency of these records supports the conclusion of the entrainment of freshwater from the retreat of the lis through hudson strait into the subpolar gyre and provides specific time periods when pulses of lis freshwater were present to influence climate

the northwest atlantic mid ocean channel of the labrador sea v sedimentology of a giant deep sea channel the northwest atlantic mid ocean channel namoc is one of the largest deep sea channels of the world s oceans during the late cenozoic glacial period the channel played a major role in the depositional history of the labrador sea and northwest atlantic in controlling sedimentation of a broad approx 500 m thick and 200 km wide lens of turbidites this sediment sequence interfingers laterally with the acoustically transparent pelagic and contourite facies found in the labrador basin the meandering channel is a depositional erosional feature formed by submarine mass flows predominantly turbidity currents the channel contains a meandering talweg that appears to be associated with a sequence of submarine point bars containing thick bedded coarse grained turbidites and gravel layers channel fill facies old channel positions on seismic profiles indicate that the channel has migrated laterally up to 30 km both to the west and to the east natural levees flank the channel for its entire length extendin

quantifying provenance of reservoir sediment using multiple composite fingerprints in an arid region experiencing both wind and water erosion abstract quantitative information on sediment sources is useful for developing targeted protection measures that effectively control soil erosion in a watershed in this study a multiple composite fingerprints method was tested and used for quantifying the sediment provenance of the danghe river and for providing effective sediment control strategies for the watershed in an arid region experiencing both wind and water erosion surface samples were taken from three geomorphic source areas of dunes gobi and upstream mountains and sediment samples from the watercourses near the reservoir to accommodate the wide range of sediment size distributions resulting from the fluvial and aeolian processes sediment contributions from each source were estimated for each of six particle size groups the results showed that the proportional contributions from each source to the reservoir sediments were 56 73 from upstream mountains 26 36 from gobi and 16 91 from dunes with the relative contributions in each size group following a similar trend the largest fraction of the sediment was from the 0 063 0 1 mm particle size group accounting for about 37 09 of the total in which 4 7 59 and 25 50 were from dunes gobi and upstream mountains our results also indicated that selective erosion existed in both erosion processes especially in wind erosion process and multiple particle size tracking should be used in the cases of severe selective erosion to improve the accuracy of estimation also the sediment contribution rate per unit area was the largest from dunes thus controlling wind blown sand to the river by stabilizing the dunes is recommended to reduce the reservoir siltation

origin of the northern atlantic s heinrich events as first noted by heinrich 1988 glacial age sediments in the eastern part of the northern atlantic contain layers with unusually high ratios of ice rafted lithic fragments to foraminifera shells he estimated that these layers are spaced at intervals of roughly 10 000 years in this paper we present detailed information documenting the existence of the upper five of these layers in odp core 609 from 50 n and 24 w their ages are respectively 15 000 radiocarbon years 20 000 radiocarbon years 27 000 radiocarbon years about 40 000 years and about 50 000 years we also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers although we are not of one mind regarding the origin of these layers we lean toward an explanation that the heinrich layers are debris released during the melting of massive influxes of icebergs into the northern atlantic these sudden inputs may be the result of surges along the eastern margin of the laurentide ice sheet

the quaternary geology of the labrador shelf the regional distribution of glacial and postglacial sediments on the labrador shelf was mapped by medium and high resolution seismics and shows a succession of tills that extend to the continental shelf edge at approximately 600 m the uppermost of these tills is less laterally extensive and does not occur on the labrador shelf bank tops in water depths less than 160 m we infer that the last glacial episode was less extensive than the preceding ones glaciomarine stratified silts and postglacial muds are found overlying the upper till in the deep basins that separate the banks the upper till glaciomarine silts and postglacial muds are interpreted to constitute one complete deglacial cycle radiocarbon age determination suggests this deglacial sequence began at approximately 20 000 years bp on the northernmost labrador shelf and hudson strait seismic evidence indicates a late glacial readvance locally deposited a till that overlies the glaciomarine sediments associated with the last glacial advance

isotope stratigraphy sedimentation rates deep circulation and carbonate events in the labrador sea during the last 200 ka high resolution stable isotope and accelerator mass spectrometry 14c measurements in 25 box and piston cores from the labrador sea allow the reconstruction of major paleoceanographical changes during the last 200 ka in this basin and also document the links between the interior of the laurentide ice sheet and the north atlantic ocean during this interval two deep circulation regimes are indicated by contrasting sedimentation rates on the slopes i the modern situation is characterized by a gyre of the north atlantic deep water nadw components into the basin which is responsible for the high energy western boundary undercurrent this regime also prevailed during the former true interglacials and possibly during shorter warm intervals e g bolling allerod ii a more frequent nadw free situation during glacial and interstadial intervals is marked by the presence of a vertically homogeneous water mass in the basin sedimentological records also indicate that carbonate events i e pulses of

origin and consequences of cyclic ice rafting in the northeast atlantic ocean during the past 130 000 years deep sea sediment cores recovered from the northeast atlantic ocean were examined in order to elucidate the influence of the earth s orbital parameters on major ice rafting analyses of coarse grained ice rafted debris and planktonic foraminifers revealed a strong reaction to the precession signal since 130 000 yr b p dropstone layers have been deposited each half period of a precessional cycle 11 000 1000 yr ice rafting occurs during times of winter minimum summer maximum insolation and summer minimum winter maximum insolation in the first case high summer insolation forces meltwater discharge from the ice sheets into the polar seas which subsequently enhances formation of sea ice during the winter in the second case growth of continental ice enhances iceberg production which also leads to a salinity reduction of surface seawater both situations result in a southward penetration of polar water thus the marine record of dropstones documents ice rafting not only during weichselian stades but also during cold events within interstades the regularity of ice rafting yields a useful framework to calibrate and elucidate climatic changes not only in the region of the north atlantic ocean but also in remote areas such as the pacific ocean and the antarctic

heinrich 0 on the east canadian margin source distribution and timing the last deglaciation was marked by intervals of rapid climatic fluctuations accompanied by glacial advances and retreats along the eastern margin of the laurentide ice sheet one of these climatic events the younger dryas cold reversal was accompanied by a detrital carbonate event referred to as heinrich event 0 h0 that deposited ice rafted debris and especially detrital carbonate rich dc sediment layers in the western and southern labrador sea the precise age duration source and geographical distribution of the h0 dc event however are not entirely clear a high sedimentation rate sequence cored off southern newfoundland yielded an age of 11 5 11 3 calibrated kyr b p for this layer thus pointing to its deposition directly following the younger dryas termination likely associated with rapid ice retreat and warming at the onset of the holocene at the study site the h0 layer contains increased concentrations of detrital carbonates calcite dolomite ratio 2 5 1 and a mature biomarker composition similar to that found in heinrich layers 1 2 4 and 5 which together suggest an origin from hudson strait grain size analysis indicates that the h0 sediments were transported to the study site mostly through shallow plumes along the labrador shelf with some hyperpycnal dispersal deeper along the slope and rise our data thus point to a large meltwater release caused by retreat of the ice margin in the hudson strait area the relvatively short duration of the h0 layer and its timing right after a major climatic transition combined with its ubiquitous regional occurrence makes it valuable for correlating different sediment records from the western labrador sea

cryosphere ocean interactions at the margin of the laurentide ice sheet during the younger dryas chron se baffin shelf northwest territories cores hu82 034 057 and hu84 035 008 resolution basin se baffin shelf contain 200 and 450 cm respectively of sediment that spans the younger dryas chron in both cores the interval is bracketed by 14c dates on foraminifera or molluscs these sites were close to the margin of the late wisconsin foxe ice sheet as it flowed toward the labrador sea prior to 11 ka both cores record moderate to high accumulations of foraminifera relatively high del 18o values in planktonic foraminifera and low values of detrital carbonate the diatom and percent opal records imply occasional seasonally open water conditions during part of the younger dryas chron both the diatom and opal analyses imply a shutoff of biogenic silica production suggesting surface water conditions affected by increased sea ice and or reduced nutrients in addition the younger dryas interval is marked by an increase in coarse sand and detrital carbonate a decrease in total organic carbon and foraminifera and high rates of sediment accumulation the inferred environment during the younger dryas is ice proximal in hu82 034 057 the foraminifera and other data suggest a change in conditions during the middle part of the younger dryas chron

changes in the western boundary undercurrent outflow since the last glacial maximum from smectite illite ratios in deep labrador sea sediments high resolution mineralogical studies were performed on late glacial and deglacial sediments from two deep piston cores from the labrador sea located at the inlet sw greenland rise and outlet labrador rise of the western boundary undercurrent wbuc gyre at the two sites smectites transported from the eastern iceland and irminger basins by the wbuc are observed clay mineral changes are used as proxies for the paleointensity reconstruction of the wbuc on the greenland rise a clay mineral index smectite illite s i ratio is defined a s i ratio of 1 characterized the last glacial maximum it increased after 17 ka and reached a maximum value of 4 during the early holocene the mineralogical changes are gradual and do not show any reversal during the younger dryas this pattern which is confirmed by first order estimations of smectite and illite fluxes suggests gradually increasing sedimentary fluxes and wbuc intensity since the last glacial maximum a peak in the velocity of the wbuc at 9 ka as recorded by clay assemblages is consistent with other regional studies based on pollen foraminifera or grain size measurements a massive dilution of smectites by illite and chlorite s i 3 occurs at 8 5 ka it corresponds to a period of rapid sediment accumulation and reflects an intensified illite rich detrital supply by meltwaters from the southern greenland ice margin on the labrador rise the smectite content varies between 20 and 60 with no obvious trend through time the mineralogical composition is strongly influenced by ice rafted deposition and by the abundance of fast deposit units cf heinrich layers in the north atlantic which contain abundant detrital carbonates spilled over from the north west atlantic mid ocean channel in such layers smectites are present but are diluted by the addition of illites chlorites and kaolinites this provides evidence for a discrete and continuous wbuc supply of fine particles from the irminger and iceland basins as far as the southeastern part of the labrador basin early deglacial smectite rich layers up to 60 are also observed at this site they indicate an increase in the outflow of the wbuc at 13 5 ka bolling allerod as previously reported from grain size or foraminiferal assemblage studies

lake agassiz outburst age and routing by labrador current and the 8 2 cal ka cold event abstract catastrophic drainage of glacial lake agassiz impounded by the laurentide ice sheet lis into hudson bay and strait is widely thought to have caused the 8 2 cal ka cold event though the path of its drainage in the north atlantic is poorly known analysis and compilation of 10 sediment cores from 8 sites distributed on the eastern canadian continental shelf and upper slope south of hudson strait revealed distinct beds with elevated detrital carbonate dc concentrations known by their distinct composition to originate from erosion of carbonate bedrock and carbonate rich glacial sediments in the hudson bay hudson strait region at all but one site radiocarbon ages bracketing and within the thickest and most widespread of these beds are coeval with the age constraints for the agassiz floods in hudson strait and southeastern hudson bay the dc distribution and concentration of this bed are consistent with southward transport in the labrador current transfer function analysis of dinoflagellate assemblage data from cores on the central labrador shelf in hudson bay and on the northeast newfoundland shelf reveal that early holocene seasonal ice cover was 5 6 months longer than at present requiring the application of a 200 year reduction to the radiocarbon age constraints on the lake agassiz outburst floods the age of the floods is reduced to about 8 33 cal ka 7 5 14 c ka from the previous determination of 8 47 cal ka 7 7 14 c ka with a similar reduction in their error ranges to 8 04 8 49 cal ka from 8 16 8 74 cal ka based on present current routing the agassiz floodwaters and icebergs are inferred to have travelled south in the labrador current and to have possibly become incorporated into the north atlantic current and transported to the nordic seas there the freshwater additions would have lessened deepwater production with a concomitant reduction in northward heat transport in the upper limb of the atlantic meridional overturning circulation thereby contributing to the 8 2 cal ka cold event variation in the calcite and dolomite content of the agassiz dc bed two salinity reductions during agassiz bed deposition and low level shorelines of lakes agassiz and ojibway suggest that more than one outburst was delivered during the final agassiz drainage the 8 2 cal ka cold event registered in greenland was coeval with a second or later flood which possibly accompanied the final collapse of the lis in hudson bay

revealing soil erosion characteristics using deposited sediment sources in a complex small catchment in the wind water erosion crisscross region of the chinese loess plateau abstract sediment sources in catchments under the control of check dams in the wind water erosion crisscross region are more complicated compared to other regions on the chinese loess plateau this is due to their general complexity which mainly results from variation in soil landform vegetation and erosion agents accordingly we used the composite fingerprinting approach to trace sediment sources in a typical small catchment in this region the aim was to reveal the erosion characteristics of the catchment throughout the trapping history of the check dam sediment sources were classified into three source paleosol loess and sand and four source paleosol gully loess gully slope bare of sand and slope covered by sand groups on the basis of soil and landform types respectively sediment sources throughout the whole trapping history of the check dam 1978 2010 could be classified into three stages according to variation in sedimentation rate results showed that depositional sediment in the check dam was primarily from gullies averaging 80 1 especially the paleosol gully 54 1 the large contribution of gullies indicated that the main erosion agents were streamflow from rainstorm events and gravity coal mining also had a significant impact on contribution of sediment sources especially for slopes since 1987 mining began to change the structure of hills in this region leading to slope fissures collapse and landslides at junctions where gullies meet slopes which increased the risk of slope erosion this has caused an increase in sediment from slopes bare of sand distributed under condition of continues implementation of soil conservation measures which converted sloping cropland into grassland or forest further studies are necessary to gain better insight into sediment transport and deposition within such complex environments as well as to distinguish between the effects of multiple erosion agents

iceberg discharges into the north atlantic on millennial time scales during the last glaciation high resolution studies of north atlantic deep sea cores demonstrate that prominent increases in iceberg calving recurred at intervals of 2000 to 3000 years much more frequently than the 7000 to 10 000 year pacing of massive ice discharges associated with heinrich events the calving cycles correlate with warm cold oscillations called dansgaard oeschger events in greenland ice cores each cycle records synchronous discharges of ice from different sources and the cycles are decoupled from sea surface temperatures these findings point to a mechanism operating within the atmosphere that caused rapid oscillations in air temperatures above greenland and in calving from more than one ice sheet

sediment sources in a small agricultural catchment a composite fingerprinting approach based on the selection of potential sources abstract fingerprinting techniques have been widely used as a reasonable and reliable means for investigating sediment sources especially in relatively large catchments in which there are significant differences in surface materials however the discrimination power of fingerprint properties for small catchments in which the surface materials are relatively homogeneous and human interference is marked may be affected by fragmentary or confused source information using fingerprinting techniques can be difficult and there is still a need for further studies to verify the effectiveness of such techniques in these small catchments a composite fingerprinting approach was used in this study to investigate the main sources of sediment output as well as their relative contributions from a small catchment 30 km2 with high levels of farming and mining activities the impact of the selection of different potential sediment sources on the derivation of composite fingerprints and its discrimination power were also investigated by comparing the results from different combinations of potential source types the initial source types and several samples that could cause confusion were adjusted these adjustments improved the discrimination power of the composite fingerprints the results showed that the composite fingerprinting approach used in this study had a discriminatory efficiency of 89 2 for different sediment sources and that the model had a mean goodness of fit of 0 90 cultivated lands were the main sediment source the sediment contribution of the studied cultivated lands ranged from 39 9 to 87 8 with a mean of 76 6 for multiple deposited sediment samples the mean contribution of woodlands was 21 7 overall the sediment contribution from mining and road areas was relatively low the selection of potential sources is an important factor in the application of fingerprinting techniques and warrants more attention in future studies as is the case with other uncertainty factors

explained and unexplained spatial and temporal variability in rates of marine sediment accumulation along the northeast margin of the laurentide ice sheet 14 ka abstract changes in sediment accumulation rate sar cm ky for fifteen ams 14c dated late quaternary sites from along the ne margin of canada between 66 and 54 n are examined these 15 cores cover the last deglacial cycle of sediment input from the decaying laurentide ice sheet and subsequent postglacial marine sedimentation on these arctic and subarctic shelves and basins it is shown that the spatial and temporal variability of the 15 sar time series do not simply parallel the known glacial chronology deglaciation of the shelves initially occurred after heinrich event 1 h 1 14 5 ka all dates are in 14c yr subsequently there were major ice advances during the younger dryas yd h 0 10 11 ka and the noble inlet glacial events 8 6 ka with final collapse of the ice sheet ca 8 0 ka a total of 73 radiocarbon dates were used which led to 58 sar estimates the median sar is 69 cm ky however the distribution is strongly positively skewed because of short lived intervals of very high sar 5000 cm ky ca 5000 kg m 2 ky 1 on the labrador shelf high sar are associated with ice retreat from the noble inlet maximum 8 6 ka whereas on the se baffin shelf there is little response in the sediment system to this event conversely during the younger dryas heinrich 0 yd h 0 event high sars occur on the se baffin shelf but along the labrador shelf the interval 10 11 ka is marked by modest sars both the 11 10 and 8 6 8 ka rapid sediment accumulation events are marked by considerable increases in the detrital carbonate content hence bear similarities to the major heinrich events in the nw labrador sea these unexpected spatial and temporal differences in sediment deposition probably reflect changes in sediment transport trajectories associated with differences in ice glacial or sea ice extent and atmospheric oceanic circulations

the laurentide and innuitian ice sheets during the last glacial maximum the late wisconsinan advance of the laurentide ice sheet started from a middle wisconsinan interstadial minimum 27 30 14 c ka bp when the ice margin approximately followed the boundary of the canadian shield ice extent in the cordillera and in the high arctic at that time was probably similar to present ice advanced to its late wisconsinan stage 2 limit in the northwest south and northeast about 23 24 14 c ka bp and in the southwest and far north about 20 21 14 c ka bp in comparison to some previous reconstructions of ice extent our current reconstruction has substantially more late wisconsinan ice in the high arctic where an innuitian ice sheet is generally acknowledged to have existed in the atlantic provinces where ice is now thought to have extended to the continental shelf edge in most places and on eastern baffin island where ice probably extended to the fiord mouths rather than to the fiord heads around most of the ice margin the late wisconsinan maximum ice extent either exceeded the extent of earlier wisconsinan advances or it was similar to the early wisconsinan advance ice marginal recession prior to 14 14 ck a bp occurred mainly in deep water and along the southern terrestrial fringe however heinrich event 1 probably drew down the entire central ice surface at 14 5 14 c ka bp sufficiently to displace the labrador sector outflow centre 900 km eastward from the coast of hudson bay the onset of substantial ice marginal recession occurred about 14 14 c ka bp in the northwest southwest and south but not until about 10 11 14 c ka bp in the northeast and in the high arctic thus the period of maximum ice extent in north america generally encompasses the interval from b24 21 to 14 14 c ka bp or considerably longer than the duration of the lgm defined as occurring during a period of low global sea level as well as during a time of relative climate stability b18 14 c ka bp the interval of advance of much of the laurentide ice sheet to its maximum extent between b27 14 c ka bp and b24 14 c ka bp coincides with a suggested interval of rapid fall in global sea level to near lgmlevels r 2001 elsevier science ltd all rights reserved

late quaternary sedimentation in baffin bay baffin bay is a small ocean basin that connects the arctic and atlantic oceans the adjacent continental shelves have been extensively reworked during quaternary glaciation the shelf break generally lies between 200 and 500 m the continental slope passes directly into the abyssal plain of baffin bay basin without any major submarine canyon deep sea fan system being present except for a large smooth sediment apron in northern baffin bay on the basis of over 50 piston cores six quaternary sediment facies are distinguished from detrital mineralogy reflected in colour and sediment texture facies a b and c are predominantly ice rafted or are debris flow deposits each with a distinct mineralogy facies d is turbidites and bottom current sorted sands silts and muds facies e is hemipelagic sediment facies f consists of sediments ranging from slumps through debris flow deposits to fine grained turbidites with a distinctive provenance in northern baffin bay these sediment facies appear to be part

fingerprinting sediment sources in the water wind erosion crisscross region on the chinese loess plateau abstract sand sheet sources in the wind water erosion crisscross region of the chinese loess plateau have not been specifically identified spatially we selected a transect that cuts across the eastern edge of the mu us sandy land sand sheets distributed loess hills sand loess hills loess hills and adjacent rocky mountains to collect surface sediment samples temporally we selected a site on a sampling sand loess hill to collected depth incremental samples in a 320 cm depth soil profile to analyze sediment sources using the multiple composite fingerprinting approach we screened out a group of optimal composite fingerprints that correctly classified sediment sources at 100 greater than half of all sediment on sand loess hills originated from the sandy land area on the sampling transect and roughly half from the sandy land in the soil profile while the remaining sediment all originated from the loess hills and rocky mountains had no contributing effect coarse particles 100 m on sand loess hills were mainly transported from the mu us sandy land while fine particles were mainly from loess hills indicating the importance of aeolian activity in the transport of sand from the mu us sandy land to loess hills environmental changes chronicled by sediment deposition at approximately 12 85 ka bp in the soil profile were primarily attributed to climate change this study confirms that the composite fingerprinting approach is a feasible method for future studies on sediment sources in areas influenced by complex erosion agencies landforms and soil types

dansgaard oeschger events is there a signal off the hudson strait ice stream abstract it is generally accepted that the dramatic heinrich h events were principally sourced from the major hudson strait drainage basin of the laurentide ice sheet but it is not known whether the higher frequency dansgaard oeschger d o events have an imprint on sediments deposited during the inter h intervals in ice proximal slope sediments this paper examines this question by an analysis of data from cores on the se baffin slope because the proxies for heinrich events are so massive in scale we removed the major h events h 1 h 2 and h 4 from the records so as to better examine the structure of data in the intervening hemipelagic sediments the period of interest extends between 15 and 40 cal ka interstadial events 2 8 resolution varies with the proxy to between 210 and 700 yrs per sample in hu87033 009 from the lower slope a total of twelve variables for example 18o mass magnetic susceptibility calcite dolomite ratio number of ird 2 mm show a variety of multi millennial oscillations although not all of the same amplitude nor frequency several parameters show little correlation with the gisp2 18o record however a comparison of cie sediment color l from hu87033 009 and hu97048 007 from the upper slope with the gisp2 oxygen isotope record suggests that a substantial correlation exists between the records such changes might be associated with either detrital carbonate content or foraminiferal concentrations analysis suggests however that the first possibility is correct hence suggestive of a glaciological response of the hudson strait ice stream with d o events in the nw labrador sea the sediment records from around h 3 time 30 cal ka show excursions which might be correlative within this event but its amplitude is not unusual compared to events both before and after this reaffirms the argument that h 3 represents a different glaciological response a significant issue discussed in this paper is the inherent ambiguity of correlating records whose errors in the time domain approach that of a dominating periodicity in this case ca 1 5 kyr

arctic ice export events and their potential impact on global climate during the late pleistocene 1 ice sheets in the north american arctic and to a lesser extent those in northern eurasia calved large quantities of icebergs that drifted through fram strait into the greenland sea several times during the late pleistocene these icebergs deposited fe oxide grains 45 250 m and coarse lithic clasts 250 m matched to specific circum arctic sources four massive arctic iceberg export events are identified from the laurentide and the innuitian ice sheets between 14 and 34 ka calendar years in a sediment core from fram strait these relatively short duration 1 4 kyr events contain 3 5 times the background levels of fe oxide grains they began suddenly as indicated by a steep rise in the number of grains matched to an ice sheet source suggesting rapid purges of ice through fram strait due perhaps to collapse of ice sheets the larger events from the northwestern laurentide ice sheet are preceded by events from the innuitian ice sheet despite the chronological uncertainties the arctic export events appear to occur prior to heinrich events

patterns of ice rafted detritus in the glacial north atlantic 40 55 n the observation by heinrich 1988 that during the last glacial period much of the input of ice rafted detritus to the north atlantic sediments may have occurred as a succession of catastrophic events rekindled interest on the history of the northern ice sheets over the last glacial period in this paper we present a rapid method to study the distribution of these events both in space and time using whole core low field magnetic susceptibility we report on approximately 20 cores covering the last 150 to 250 kyr well defined patterns of ice rafted detritus appear during periods of large continental ice sheet extent although these are not always associated within their maxima most of the events may be traced across the north atlantic ocean for the six most recent heinrich layers hl two distinct patterns exist hl1 hl2 hl4 hl5 are distributed along the northern boundary of the glacial polar front over most of the north atlantic between 40 and 50 n hl3 is more restricted to the central and eastern part of the northern atlantic the nd sr isotopic composition of the material constituting different heinrich events indicates the different provenance of the two patterns hl3 has a typical scandinavia arctic icelandic young crust signature and the others have a large component of northern quebec and northern west greenland old crust material these isotopic results obtained on core su 9008 from the north american basin are in agreement with the study by jantschik and huon 1992 who used k ar dating of silt and clay size fractions of an eastern basin core me 68 89 these data confirm the large spatial scale of these events and the enormous amount of ice rafted detritus they represent

early holocene delevelling and deglaciation of the cumberland sound region baffin island arctic canada radiocarbon cosmogenic surface exposure and relative sea level data are used to examine deglaciation and glacioisostatic adjustment of cumberland sound and cumberland peninsula and southeastern baffin island in the context of a new model for the glacial history of the eastern canadian arctic over the last decade a multidisciplinary effort on easternmost baffin island has documented far greater ice expansion during the last glacial maximum than previously believed including low gradient glaciation in marine embayments coexisting with ice free or thin cold based ice on adjacent upland crystalline terrain this study documents that the cumberland sound region underwent about twice as much glacioisostatic movement during the last glacial maximum as shown in previous reconstructions however the loading impact of the laurentide ice sheet and local glaciation on adjacent cumberland peninsula was limited the mapped zero isoline on emergence shows that postglacial eustatic rise exceeded glacial isostatic uplift for much of the eastern peninsula a finding that is consistent with that of prior studies the center of loading and the major source of glacial ice for the entire cumberland sound region were foxe basin and western baffin island strandlines dated 10 500 and 8500 1 4 c yr b p show that slow deglaciation of cumberland sound was punctuated by at least two periods of faster grounding line retreat coastal southeastern cumberland peninsula was deglaciated before 9400 1 4 c yr b p and other areas surrounding cumberland sound were deglaciated after ca 9000 1 4 c yr b p these land areas experienced relatively slow glacial retreat and restrained rebound cosmogenic surface exposure ages on glacially scoured bedrock support the 1 4 c based inferred timing for deglaciation of the sound although inheritance of nuclides from prior exposure is evident in samples indicating limited bedrock erosion in many areas for central cumberland sound a rapid rise of relative sea level of 4 5 m 100 1 4 c yr 4 6 m 100 yr and a half life for crustal response of 720 1 4 c yr 1400 yr are consistent with those values obtained in other studies of isostatic adjustment around the edges of the former northern hemisphere ice sheets where lithospheric influences were relatively dominant

aeolian sediment fingerprinting using a bayesian mixing model identifying sand provenance in depositional aeolian environments e g dunefields can elucidate sediment pathways and fluxes and inform potential land management strategies where windblown sand and dust is a hazard to health and infrastructure however the complexity of these pathways typically makes this a challenging proposition and uncertainties on the composition of mixed source sediments are often not reported this study demonstrates that a quantitative fingerprinting method within the bayesian markov chain monte carlo mcmc framework offers great potential for exploring the provenance and uncertainties associated with aeolian sands eight samples were taken from dunes of the small 58 km2 ashkzar erg central iran and forty nine from three distinct potential sediment sources from the surrounding area these were analyzed for 61 tracers including 53 geochemical elements trace major and rare earth elements ree and 8 ree ratios kruskal wallis h tests and stepwise discriminant function analysis dfa allowed the identification of an optimum composite fingerprint based on six tracers rb sr 87sr la yb n ga and ce and a bayesian mixing model was applied to derive the source apportionment estimates within an uncertainty framework there is substantial variation in the uncertainties in the fingerprinting results with some samples yielding clear discrimination of components and some with less clear fingerprints quaternary terraces and fans contribute the largest component to the dunes but they are also the most extensive surrounding unit clay flats and marls however contribute out of proportion to their small outcrop extent the successful application of these methods to aeolian sediment deposits demonstrates their potential for providing quantitative estimates of aeolian sediment provenances in other mixed source arid settings and may prove especially beneficial where sediment is derived from multiple sources or where other methods of provenance e g detrital zircon u pb dating are not possible due to mineralogical constraints

wisconsinan late glacial environmental change on the southeast baffin shelf southeast baffin island and northern labrador the importance of the baffin labrador region is explained in terms of the channelling through this area of the mass flux of meltwater from the laurentide ice sheet and the probable effects of this on the thermohaline circulation of the north atlantic the chronology of glaciation and deglaciation in the region is summarised reference is made to recent marine records from the baffin shelf isotopic changes recorded in foraminiferal assemblages obtained from marine sediments in the baffin shelf labrador sea area indicate the timing and possible magnitude of meltwater fluxes during the period 14 0 11 0 ka bp

detrital carbonate rich sediments northwestern labrador sea implications for ice sheet dynamics and iceberg rafting heinrich events in the north atlantic much of the bed of the central and eastern sectors of the laurentide ice sheet was underlain by paleozoic carbonates we propose that pulses of detrital carbonate rich sediments in two cores from the northwestern labrador sea reflect episodes when an ice stream from the hudson strait extended to the shelf break and delivered sediment onto the slope and deep sea plain atomic mass spectroscopy 14 c dating of planktonic foraminifera in cores hu75 009 iv 55 2 4 km water depth and hu87 033 009 1 4 km water depth and 150 km north northwest indicates that the youngest event occurred between ca 14 and 15 ka and another occurred between 19 and 21 ka the two carbonate intervals in northwestern labrador sea cores are coeval with heinrich events 1 and 2 in the eastern north atlantic lat 45 50 n long 20 w where they are associated with an increase in lithic fragments and a drastic reduction in the numbers of foraminifera these changes have been linked with the massive production of icebergs associated with ice sheet surges our evidence indicates that heinrich events 1 and 2 are associated with the dynamics of the hudson strait ice stream and denote considerable glaciological instability

abrupt early holocene 9 9 9 6 ka ice stream advance at the mouth of hudson strait arctic canada radiocarbon dated glacial geologic evidence documents an abrupt advance of the northern margin of the labrador sector of the laurentide ice sheet during the last deglaciation ice flow directional indicators together with ice marginal features found onshore and offshore delimit an ice stream that advanced north northeast 300 km crossed the mouth of hudson strait and outer frobisher bay and overran summits 400 m above sea level on outer hall peninsula southeast baffin island fifty eight 14 c ages including 27 accelerator mass spectrometry ages on single shells indicate that the advance was extremely rapid the entire advance retreat cycle took place in an 300 yr 14 c interval 9 9 9 6 ka at its maximum extent the ice stream supported a calving margin 200 km long terminating in open water 500 m deep implying a massive iceberg release marine evidence for the outflow is preserved along the labrador sea shelf as thick carbonate rich glacial marine drift but has not been recognized farther east in the north atlantic either the discharge of icebergs was insufficient to produce a trans north atlantic carbonate rich heinrich layer or the icebergs tracked southward where they encountered warming sea surface temperatures although the advance seems to have been coincident with a brief interval of minor regional cooling it failed to trigger a significant climate perturbation suggesting that the ocean atmosphere system had attained its stable interglacial condition by that time

shelf erosion and glacial ice proximity in the labrador sea during and after heinrich events h 3 or 4 to h 0 as shown by foraminifera

sediments sedimentation rates and environments southeast baffin shelf and northwest labrador sea 8 26 ka ten 14c dated cores are described from the labrador sea continental slope and hatton and resolution basins on the southeast baffin shelf based on sharply defined detrital carbonate layers in the labrador sea cores we propose that the laurentide ice sheet reached the shelf break at both 20 and 15 14c ka 24 3 and 18 2 sidereal ka and contributed significant sediment to the northwest labrador sea both times the flux was 720 kg m2 ka during these periods of maximum ice extent the laurentide ice sheet retreated from its 15 ka position at the shelf break to the inner shelf between 14 and 12 14c ka ice proximal conditions recognized by relatively light 18o on near surface planktonic foraminifera high detrital carbonate and benthic foraminiferal faunas dominated by elphidium excavatum forma clavata cassidulina reniforme prevailed until at least 10 14c ka the ice readvanced toward resolution basin and across part of hatton basin at 11 14c ka accelerator mass spectrometry dates on core tops i

gravity erosion on the steep loess slope behavior trigger and sensitivity abstract gravity erosion is a dominant geomorphic process on the widespread steep loess slopes yet it is not well understood due to the complexity of failure occurrence and behavior this study conducted a series of experiments in the laboratory to test the stability of different slope geometries and rainfalls and then performed a sensitivity analysis to quantitatively explore the triggering mechanisms of mass failure on the steep loess slope a topography meter designed by the authors was used to quantitatively measure the process of gravity erosion and the increase rate analysis method presented by the authors was also used to analyze the sensitivity of gravity erosion the following three types of gravity erosion were observed landslide avalanche and mudslide in an event of rainfall various types of gravity erosion might emerge in the same period and mass failures with the same mode and similar size often adjacently appeared sometimes a group of mass failures might happen on a large slowly slipping block then the increase rate analysis method was used to evaluate variations in the gravity erosion with respect to changes in other causal parameters of rainfall duration intensity and slope height gradient climate driven factors and topography triggers had prominent influences on gravity erosion whether for the total amount or the peak amount in an experiment the largest sensitivity parameter on both landslides and mudslides was that of rainfall duration in comparison topography was relatively less influential for the total amount in an experiment the sensitivity parameters of rainfall duration on the landslide and mudslide were 24 9 and 19 5 respectively while the sensitivity parameter of rainfall intensity on the avalanche was 2 2 for the peak amount in an experiment the sensitivity parameter of rainfall duration on the landslide and mudslide were 5 5 and 15 6 respectively meanwhile the sensitivity parameter of slope gradient on the avalanche was 4 6 the experimental results obtained here provide an insight into the pre failure mechanisms and processes of steep loess slopes

abrupt changes in marine conditions sunneshine fiord eastern baffin island nwt during the last deglacial transition younger dryas and h 0 events

varying sediment sources hudson strait cumberland sound baffin bay to the nw labrador sea slope between and during heinrich events 0 to 4 core hu97048 007pc was recovered from the continental labrador sea slope at a water depth of 945 m 250 km seaward from the mouth of cumberland sound and 400 km north of hudson strait cumberland sound is a structural trough partly floored by cretaceous mudstones and paleozoic carbonates the record extends from 10 to 58 ka on board logging revealed a complex series of lithofacies including buff colored detrital carbonate rich sediments heinrich h events frequently bracketed by black facies we investigate the provenance of these facies using quantitative x ray diffraction on drill core samples from paleozoic and cretaceous bedrock from the se baffin island shelf and on the 2 mm sediment fraction in a transect of five cores from cumberland sound to the nw labrador sea a sediment unmixing program was used to discriminate between sediment sources which included dolomite rich sediments from baffin bay calcite rich sediments from hudson strait and discrete sources from cumberland sound results indicated that the bulk of the sediment was derived from cumberland sound but baffin bay contributed to sediments coeval with h 0 younger dryas whereas hudson strait was the source during h events 1 4 contributions from the cretaceous outcrops within cumberland sound bracket h events thus both leading and lagging hudson strait sourced h events copyright 2012 john wiley sons ltd

rapid fluctuations of the laurentide ice sheet at the mouth of hudson strait new evidence for ocean ice sheet interactions as a control on the younger dryas ice directional features and erratic lithologies of the last glaciation demonstrate that a major outlet glacier of the laurentide ice sheet flowed nne across outer hudson strait rather than se down the strait as previously hypothesized ice advanced more than 600 km from a labradorean source crossing hudson strait and outer frobisher bay and advancing onto hall peninsula the highest summits on loks land circa 400 m asl a large island at the se tip of hall peninsula were inundated by labradorean ice three distinct late wisconsin advances have been recognized the earliest most extensive advance crossed frobisher about 11 5 kyr b p and was maintained for circa 1 kyr differences in the extent of amino acid racemization in shells from interstadial and deglacial sites on eastern loks land limit the duration of the most extensive late wisconsin advance s to a brief interval of no more than 2 kyr radiocarbon dates on in situ shells and on shells incorporated in till indicate that frobisher bay was ice free from at least 10 5 to 10 2 kyr b p after which a second labradorean advance the gold cove readvance attained nearly the same extent as the earlier advance the readvance was short lived and the bay was deglaciated before 9 5 kyr b p a final readvance occurred during the cockburn substage 9 to 8 kyr b p but ice failed to cross frobisher bay the maximum extent of the labradorean advance coincides with the onset of younger dryas cooling based on a minimum cross sectional area and reasonable estimates of ice velocity the iceberg flux to the north atlantic ocean at this time was between 300 to 2400 km year 1 about the same as the freshwater influx from the diversion of lake agassiz drainage to the st lawrence the input of a significant volume of ice into the north atlantic via the labrador sea would have cooled sea surface and air temperatures increased sea surface albedo and diminished the effectiveness of wind mixing of surface waters thereby reducing the volume of water required to effectively cap the north atlantic we suggest that a combination of a massive iceberg flux and increased st lawrence discharge may have been required to initiate younger dryas cooling when the outflow of lake agassiz was again routed down the st lawrence at 9 5 kyr b p a second younger dryas event failed to occur because by that time labradorean ice had retreated within hudson strait and was unable to generate a substantial climate altering volume of icebergs the possibility of an iceberg flood in the north atlantic could be tested by measuring the concentration of ice rafted detritus ird traditionally defined as quartz feldspar grains 125 m in deep sea cores however sediment entrained by the labradorean ice is dominated by detrital carbonate and only a small fraction of the noncarbonate component is 125 m hence a revised definition of ird is required to evaluate the iceberg flood hypothesis

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

erosion source discrimination in a rural australian catchment using compound specific isotope analysis csia compound specific isotope analysis csia has been used to assess the ability of 13c signatures of fatty acid compounds to discriminate erosion sources in a rural australian catchment the study focussed on a high flow event 10 year recurrence interval which occurred in the logan albert catchment in january 2008 and augmented a previous sediment tracing study using fallout radionuclides and major minor element geochemistry it is found that surface soil from forest pasture and cultivated land uses are well discriminated using csia furthermore sub surface soil sources associated with channel bank erosion and exposed subsoils gullies and hillslope scalds occurring specifically in the mid western logan catchment could also be discriminated selected fatty acid and bulk carbon 13c data were used in the isosource mixing model to determine erosion sources contributing sediment the results were compared with results obtained using other sediment tracers for the lower logan river the csia tracing results are consistent with fallout radionuclide and element geochemistry tracing with channel bank erosion being confirmed as the major sediment source moreover csia has quantified the significant contribution of exposed subsoils originating on hillslopes and drainage lines from the mid western region of the logan catchment in the albert river catchment about 40 of sediment comes from forest land use although more than half of this may come from sub surface sources these results have demonstrated that csia has the potential to significantly enhance the ability of sediment tracing studies to determine the extent that different land uses and erosion processes are contributing eroded soil to rivers allowing an assessment of soil erosion and transport model predictions copyright 2012 john wiley sons ltd

mid wisconsin laurentide ice sheet growth and decay implications for heinrich events 3 and 4 a close look at the sedimentology of heinrich event 4 from the northwest labrador sea indicates that an extended ice margin perhaps greater than before heinrich events 1 or 2 h 1 and h 2 existed in the hudson strait region pre heinrich event 4 h 4 and that on the basis of characteristics of the sediment unit heinrich event 4 was different than heinrich events 1 or 2 i e larger ice sheet collapse longer duration dirtier icebergs other data from across the southern and eastern margin of the laurentide ice sheet as well as greenland and the north atlantic support this interpretation possibly indicating a relative mid wisconsin glacial maximum pre heinrich event 4 many of these data also indicate that heinrich event 4 35 ka resulted in serious climatic and oceanographic reorganizations we suggest that heinrich event 4 gutted the hudson strait leaving it devoid of ice for heinrich event 3 we further hypothesize that heinrich event 3 did not originate from axial ice transport along the hudson strait thus heinrich event 3 may be more analogous to the proposed northward advancing ice from ungava bay during heinrich event 0 than to the more typical down the strait flow during h 1 h 2 and h 4 consequently the climatic and oceanographic impacts resulting from heinrich events are highly susceptible to the type origin and magnitude of ice sheet collapse something which varied per heinrich event during the last glacial period

aeolian process induced hyper concentrated flow in a desert watershed ephemeral desert channels are characterized by very high rates of sediment transport during infrequent flood events here we show that aeolian process induced hyper concentrated ahc flows occur in the sudalaer desert watershed in the ordos plateau of china which primarily transport 0 08 0 25 mm non cohesive aeolian sand and have a peak suspended sediment concentration of 1 1 1 4 x 10 6 mg l 3 aeolian sand supply and storage in the channel play a crucial role in causing hyper concentrated flow our results indicate that non cohesive aeolian sand can be entrained from the bed and suspended in the turbulent flow when the channel bed slope exceeds a critical threshold 0 0003 we also show that if the frequency ratio of wind blown sandstorms to rainstorms t w t p exceeds beta gamma gamma 0 alpha p v 3 a l where alpha is the wind blown sand transport coefficient beta is the runoff coefficient gamma gamma 0 is the increase in suspension concentration caused by addition of aeolian sands p is the density of rainstorms v is the wind speed of sandstorms a is the runoff generating area l is the aeolian sand filled channel length an ahc flow occurs during the passage of a flood in a desert channel since high frequency aeolian processes provide an adequate quantity of transportable sediment and promote ahc flow most of the infrequent rainfall induced floods occurring in arid zones can develop as ahc flows c 2014 elsevier b v all rights reserved

abrupt deglaciation events and holocene palaeoceanography from high resolution cores cartwright saddle labrador shelf canada the uppermost quaternary sediments in cartwright saddle labrador shelf are acoustically laminated with reflectors that can be traced over long distances two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the laurentide ice sheet lis during deglaciation variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr the temporal sampling interval reaches decadal resolution in the last deglacial period 7 9 ka analyses of total carbonate content sediment magnetic variables foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca 10 9 9 2 8 8 7 9 and 7 ka with 450 yr correction there was no distinct change in sediment character during much of the younger dryas chronozone in the 18o record the 8 8 ka event is a dramatic 1 shift toward lower values which we associate with the noble inlet glacial event within hudson strait we do not see the pronounced low 18o event at 7 1 ka reported off nova scotia but surprisingly neither the nova scotia records nor other records in the labrador sea capture the impressive 8 8 ka change serious consideration must be given to the final collapse of the lis as the cause of the 8 2 cal ka cold event recorded in greenland and northwest europe copyright 1999 john wiley sons ltd

tracing sediment sources in a tropical highland catchment of central mexico by using conventional and alternative fingerprinting methods land degradation is intense in tropical regions where it causes for instance a decline in soil fertility and reservoir siltation two fingerprinting approaches i e the conventional approach based on radionuclide and geochemical concentrations and the alternative diffuse reflectance infrared fourier transform spectroscopy method were conducted independently to outline the sources delivering sediment to the river network draining into the cointzio reservoir in mexican tropical highlands this study was conducted between may and october in 2009 in subcatchments representative of the different environments supplying sediment to the river network overall cointzio catchment is characterized by very altered soils and the dominance of andisols and acrisols both fingerprinting methods provided very similar results regarding the origin of sediment in huertitas subcatchment dominated by acrisols where the bulk of sediment was supplied by gullies in contrast in la cortina subcatchment dominated by andisols the bulk of sediment was supplied by cropland sediment originating from potrerillos subcatchment characterized by a mix of acrisols and andisols was supplied in variable proportions by both gullies and rangeland cropland in this latter subcatchment results provided by both fingerprinting methods were very variable our results outline the need to take the organic carbon content of soils into account and the difficulty to use geochemical properties to fingerprint sediment in very altered volcanic catchments however combining our fingerprinting results with sediment export data provided a way of prioritizing the implementation of erosion control measures to mitigate sediment supply to the cointzio reservoir supplying drinking water to morelia city copyright 2012 john wiley sons ltd

monitoring of gully erosion on the loess plateau of china using a global positioning system abstract with the development of a technique global positioning system gps has become progressively less expensive lighter and easier to use the accuracy of gps has been improved and it appears applicable to the continuously monitoring morphology changes on the earth surface with small and slow change the objective of this study is to use gps to measure the morphology of gullies in a small catchment near suide shaanxi province china there are three main gully types in the study area bank gullies floor gullies and hill slope gullies and this study mainly focuses on the hill slope gullies the hill slope gullies in the study area are mainly discontinuous and are developing rapidly the gully density in the study area is very large the retreat rate of hill slope gullies is 0 16 2 02 m year 1 the relationships between the upslope drainage area a and the critical slope gradient s for hill slope gullies is s 0 1839a 0 2385 the values of as2 range from 41 to 814 m2 for the hill slope gully headcuts and most of them fell into the range of 100 300 m2 both of these relationships are suggested as indexes for estimating the location of gully headcuts

surface oceanographic changes in the eastern labrador sea nannofossil record of the last 31 000 years abstract calcareous nannofossils in two ams 14c dated piston cores from the eastern labrador sea yield oceanographic information of the last 31 kyr moderate nannofossil productivity and abundance of north atlantic warm water taxa in the southern labrador sea core 91 045 094p suggest cool surface ocean condition between 31 and 26 thousand years ago ka the irminger current was absent in this interval thus we attribute this cool condition to weak advection of north atlantic water from the southeast we found evidence of cold and or seasonally ice covered surface conditions between 26 and 13 ka in the southern labrador sea and between 31 and 12 6 ka in the northeastern labrador sea core 90 013 013p increase of nannofossil productivity and abundance of north atlantic taxa at about 10 7 ka in core 91 045 094p suggests that the southern labrador sea was influenced by warm north atlantic surface water the polar water of the labrador current had little or no influence on the surface ocean in this area before 9 ka the labrador current started to flow or intensify after 9 ka and became strong by 8 4 ka the northeastern labrador sea remained cold until 8 4 ka perhaps because of discharge of cold meltwater from the greenland ice sheet at this time productivity increased sharply and the assemblage of nannofossils changed these suggest a significant improvement in surface ocean conditions and the establishment of the warm irminger current which marked the onset of the modern circulation pattern characterized by warm west greenland current and strong labrador current

a heinrich like event h 0 dc 0 source s for detrital carbonate in the north atlantic during the younger dryas chronozone in the north atlantic we define h 0 as a heinrich like event which occurred during the younger dryas chron on the se baffin shelf prior to 11 ka surface water productivity was reasonably high as measured by the numbers of diatom and planktic foraminifera per gram but an abrupt increase in detrital carbonate dc 0 event from approximately 15 up to 50 carbonate by weight occurred at 11 14c ka and continued to circa 10 ka these deposits 2 6 m thick are dominated by detrital calcite and silt and clay sized sediments during this event dc 0 h 0 ice extended onto the inner shelf but did not reach the shelf break and probably originated from a center over labrador ungava as a consequence the pattern of ice rafted debris and sediment provenance shown by h o in the north atlantic is different from that during h 1 14 5 ka or h 2 20 ka when the ice sheet extended along the axis of hudson strait and may have reached the shelf break for example there is no concrete evidence for dc o is cores on the floor of the labrador sea due east of hudson strait hu75 55 56 but h o has been noted in cores off newfoundland and west of ireland a coeval carbonate event to dc 0 but this one dominated by dolomite occurs in hu82 su5 on the west side of davis strait with a source either from northern baffin bay or cumberland sound although other sources for north atlantic detrital carbonate cannot be totally excluded our evidence suggests that h 0 represents the expression of glaciological instability of the laurentide ice sheet within the general region of hudson strait and probably to the north cumberland sound and northernmost baffin bay there is one younger dc event dated circa 8 4 ka present in sediments along the labrador margin and in hudson strait which represents the final collapse of the ice sheet within hudson strait and hudson bay

late quaternary detrital carbonate dc layers in baffin bay marine sediments 67 74 n correlation with heinrich events in the north atlantic abstract episodes of glaciation in the region north of baffin bay resulted in the erosion of paleozoic carbonate outcrops in nw greenland and the canadian high arctic these events are recognized in the marine sediments of baffin bay bb as a series of detrital carbonate rich dc layers bbdc layers thin southward within baffin bay thus the contribution of baffin bay ice rafted carbonate rich sediments to the north atlantic is probably slight especially compared with sediment output from hudson strait during heinrich events we reexamine cf aksu 1981 a series of nine piston cores from the axis of baffin bay and across the davis strait sill and provide a suite of 21 ams 14 c dates on foramininfera which bracket the ages of several dc layers the onset of the last dc event is dated in six cores and has an age of ca 12 4 ka in northern and central baffin bay a thick dc layer occurs at around 4 m in the cores and is dated 40 ka there were three to six dc intervening events the youngest bbdc event possibly a double event lags heinrich event 1 h 1 off hudson strait dated at 14 5 ka but it is coeval with the pronounced warming seen in gisp2 records from the greenland ice sheet during interstadial 1 we hypothesize that bbdc episodes are coeval with major interstadial 18 o peaks from gisp2 and other greenland ice core records and are caused by or associated with the advection of atlantic water into baffin bay cf hiscott et al 1989 and the subsequent rapid retreat of ice streams in the northern approaches to baffin bay

hyper concentrated flow response to aeolian and fluvial interactions from a desert watershed upstream of the yellow river abstract aeolian and fluvial interactions afis are critical earth surface processes in arid zones especially in desert watersheds the response of hyper concentrated flows to seasonal alternate afis shows very high rates of sediment transport and has important environmental and ecological consequences from local to global scales here we present the aeolian processes induced hyper concentrated ahc flows that occurred in the sudalaer desert watershed upstream of the yellow river which primarily transport non cohesive coarse aeolian sand 0 08 mm and show a peak suspended sediment concentration ssc of 1 1 to 1 4 106 mg l 3 our field study and theoretical analysis indicate that non cohesive coarse aeolian sand downstream in the channel can be entrained from the bed and can be suspended in the turbulent flow by the significant runoff generated upstream with a ssc 0 value of 0 5 106 mg l 3 severe aeolian processes can provide an abundant coarse sediment supply in the channel which once entrained can also trigger and promote the development of ahc flows we define for the first time the ratio of the weight percentage of coarse sediment to fine sediment c 0 08 mm c

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

the northwest atlantic mid ocean channel of the labrador sea iv petrography and provenance of the sediments the northwest atlantic mid ocean channel namoc of the labrador sea is associated with a 500 m thick sequence of well bedded turbidites along the axis of the labrador and newfoundland basins and extends onto the western sohm abyssal plain the specific source areas of these terrigenous turbidites on the shelves and landmasses surrounding the labrador sea were not known hitherto because the morphological connections in the head region of the namoc with canyons on the slope are masked by young ice rafted and bottom current transported sediments petrographic analysis of channel sands and gravels suggests a dominant canadian source for the channel segment north of the confluence with the imarssuak mid ocean channel imoc based on the predominance of lower paleozoic detrital carbonates the imoc provides sediment from sources around the west reykjanes basin i e the east coast of greenland and iceland however source specific minerals or rock fragments from the tertiary alkali basalts of southwest greenla

sediment fingerprinting in agricultural catchments a critical re examination of source discrimination and data corrections fine sediment source fingerprinting techniques have been widely applied in agricultural river catchments successful source discrimination in agricultural environments depends on the key assumption that land use source signatures imprinted on catchment soils are decipherable from those due to other landscape factors affecting soil and sediment properties in this study we re examine this critical assumption by investigating i the physical and chemical basis for source discrimination and ii potential factors that may confound source un mixing in agricultural catchments including particle size and organic matter effects on tracer properties the study is situated in the river tamar a predominantly agricultural catchment 920 km2 in south west england that has also been affected by mining source discrimination focused on pasture and cultivated land uses and channel banks monthly time integrated suspended sediment samples were collected across seven catchments for a 12 month period physical and chemical properties measured in source soils and sediment included fallout radionuclides 137cs excess 210pb major and minor element geochemical constituents total organic carbon and particle size source discrimination was entirely dependent on differences in tracer property concentrations between surface and sub surface soils this is based on fallout radionuclide concentrations that are surface elevated while many geochemical properties are surface depleted due to weathering and pedogenetic effects although surface soil contamination can reverse this trend however source discrimination in the study catchments was limited by i rotation of cultivated and pasture fields resulting in reduced differences between these two sources and ii the cultivated source signature resembling a mix of the pasture and channel bank sources for many tracer properties furthermore a combination of metal pollution from abandoned historic mines and organic enrichment of sediment from upland areas of peaty soils resulted in the non conservative behaviour of some tracer properties in several catchments differences in the particle size and organic carbon content of source soils could explain much of the variation in these properties in downstream sediment rather than selective transport effects inconsistent relationships between particle size organic carbon and tracer property concentrations further undermined the basis for the use of widely applied corrections to tracer datasets sensitivity analysis showed that correcting source tracer data for differences in organic matter can produce large changes to source contribution estimates that cannot be justified and such corrections should not be used confounding factors related to poor source discrimination and non conservative behaviour are highly likely to affect sediment fingerprinting studies in many agricultural catchments as a result estimates of source contributions in many fingerprinting studies may contain significant unquantified errors

heinrich event 0 dc 0 in sediment cores from the northwest labrador sea recording events in cumberland sound layers of ice rafted limestone debris rich sediment were deposited in the northwest labrador sea and the north atlantic during the last glacial period 10 80 ka these sediments were deposited by heinrich events h events which record catastrophic collapses of the laurentide ice sheet in the region of the hudson strait these intervals of detrital carbonate rich sediments are referred to as detrital carbonate layers dc in the northwest labrador sea accelerator mass spectrometry ams 14c dates provide a strong constraint on the timing for these events h 1 dc 1 and h 2 dc 2 dc 0 also known as h 0 correlative to the younger dryas cooling event is not as distinct a sediment unit in the northwest labrador sea as dc 1 and dc 2 an analysis of sediments from two cores hu75009 iv 055 and hu75009 iv 056 off the mouth of the hudson strait in the northwest labrador sea basin sheds new light on the missing dc 0 sediment unit timing for the dc 0 event in cores 055 and 056 is bracketed between 11

early deglacial onset of southwestern greenland ice sheet retreat on the continental shelf abstract the greenland ice sheet gris advanced onto the continental shelf during the last glacial period while deglacial records for when the gris withdrew onto the modern coastline are relatively abundant the timing of early gris retreat on the shelf is poorly constrained here we use planktic foraminiferal 18 o sediment grain size sedimentation rates and 14 c ages in southeastern davis strait core hu87033 008 to develop an early deglaciation chronology of the southwestern gris while on the continental shelf sedimentation rates and especially silt and clay fractions are high between 20 5 and 17 1 ka suggesting that the southwestern gris margin was near or at the shelf break where it released subglacially derived sediment laden meltwater a peak in sedimentation rates of 110 cm ka 1 between 19 3 ka and 18 6 ka combined with an initial decrease in planktic 18 o of 0 5 per mil suggests an early deglacial pull back of the gris margin from the shelf break with a concurrent increase in surface ocean meltwater discharge a subsequent planktic 18 o decrease of 1 0 per mil combined with a drop in silt and clay sedimentation rates at 18 17 ka likely record further gris retreat inland from the shelf break terrestrial 10 be surface exposure ages indicate that the gris margin remained on the continental shelf until 11 ka yet the cause of this subsequent ice margin stability on the inner shelf is not known our new records provide the first evidence that the southwestern gris margin may have begun to deglaciate at the same time as other northern hemisphere ice sheets as labrador sea water temperatures likely remained near glacial values until 15 ka we suggest that initial southwestern gris retreat was in response to rising global sea level from retreat of other ice sheets and or the initial deglacial rise in boreal summer insolation

evidence for massive discharges of icebergs into the north atlantic ocean during the last glacial period sediments in the north atlantic ocean contain a series of layers that are rich in ice rafted debris and unusually poor in foraminifera1 here we present evidence that the most recent six of these heinrich layers deposited between 14 000 and 70 000 years ago record marked decreases in sea surface temperature and salinity decreases in the flux of planktonic foraminifera to the sediments and short lived massive discharges of icebergs originating in eastern canada the path of the icebergs clearly marked by the presence of ice rafted detrital carbonate can be traced for more than 3 000 km a remarkable distance attesting to extreme cooling of surface waters and enormous amounts of drifting ice the cause of these extreme events is puzzling they may reflect repeated rapid advances of the laurentide ice sheet perhaps associated with reductions in air temperatures yet temperature records from greenland ice cores appear to exhibit only a weak corresponding signal moreover the 5 10 000 yr intervals between the events are inconsistent with milankovitch orbital periodicities raising the question of what the ultimate cause of the postulated cooling may have been

upper cenozoic history of the labrador sea baffin bay and the arctic ocean a paleoclimatic and paleoceanographic summary foraminifera palynomorphs and stable isotopes in planktonic foraminifera have been studied in piston cores from the northern labrador sea southern baffin bay and the alpha ridge region of the central arctic ocean foraminifera in cores from the labrador sea and southern baffin bay show glacial interglacial 18o values similar to those reported from the norwegian and greenland seas in contrast to the eastern north atlantic ocean however peaks of subarctic foraminifera and dinoflagellates in the western north atlantic cores show that relatively warm atlantic surface water continued to flow into the northern labrador sea during the early glaciation growth phases of isotopic stages 2 4 6 and 8 boreal and subarctic pollen suggest that warm atlantic air flowed into the northern labrador sea and baffin bay during the ice sheet growth phases the advection of warm air masses and the presence of open waters during the summer probably provided moisture for the growth of the laurentide innuitian and greenland ice sheets isotopic and microfossil records in arctic cores can also be tentatively correlated with major high latitude north atlantic glacial interglacial events magnetostratigraphic palynological and amino acid dating however shows that sedimentation on the alpha ridge has been very slow during the past 0 73 m y therefore events of less than 20 000 years duration cannot be clearly discerned interpretation of pre pleistocene paleoenvironments is further limited by the sparseness of calcareous and siliceous microfossils

provenance of sediment in the labrador current a record of hinterland glaciation over the past 125 ka the labrador current flows southward along the continental margin off eastern canada and is the principal source of sediment to the outer continental margin areas where ice sheets did not cross the continental shelf we present multi proxy mineralogical and geochemical records based principally on x ray diffraction and x ray fluorescence for core 2011031 059 from northern flemish cap to determine changes in supply and hence to reconstruct provenance evolution during the last glacial cycle the calcite to dolomite ratios in heinrich layers ranged from 2 to 4 suggesting carbonate layers derived from hudson strait as early as marine isotope stage mis 5a d mineral abundance shows three time dependent predominant sediment sources other than in heinrich layers i baffin bay shelves and adjacent land in mis 5 and 1 with high ca sr kaolinite and feldspars and low clay minerals and calcite dolomite ratios ii labrador in mis 3 with low clays and grey color and iii north east newfoundland shelf in mis 2 and 4 with higher concentrations of clay minerals red sandstones and transition elements these results allow a reconstruction of principal ice streams supplying the north west atlantic over the last full glacial cycle

horizontal wind erosion flux and potential dust emission in arid and semiarid regions of china a major source area for east asia dust storms abstract arid and semiarid regions of china are important sources of dust for storms that affect east asia and the western pacific ocean however little is known about the process spatial variation and quantity of the emission and transportation of windblown sand dust from such areas in 2009 a large number of passive sand traps were set on different landscape surfaces across the arid and semiarid regions of china to monitor the horizontal wind erosion flux and establish the potential of dust emission the monitoring data suggest that the taklamakan desert has the greatest wind erosion flux the mean wind erosion flux of the marginal sand seas hinterland sand seas gobi type desert and degraded land of oases in this area is 45 07 32 37 31 11 and 19 83 kg day 1 m 2 respectively during the aeolian transport process the mean limit of a suspended load particle size is 0 066 mm aeolian sediment mean grain size and sorting are 0 11 mm and 1 40 respectively and potential pm10 dust emission rate is 0 969 kg day 1 m 2 the qaidam basin and dunhuang areas and the hexi corridor and alax areas also have strong wind erosion flux the mean wind erosion flux for the gobi type deserts in these areas is 11 57 and 39 16 kg day 1 m 2 respectively while for the degraded land of oases it is 14 78 and 12 68 kg day 1 m 2 respectively during the aeolian sediment transport process the mean limit of a suspended load particle size is 0 083 mm aeolian sediment mean grain size and sorting are 0 18 mm and 1 82 respectively and potential pm10 dust emission rate is 1 011 kg day 1 m 2 the mu us sandy land steppes of the northern yinshan mountains hunshandake sandy land and its surrounding steppes and horqin sandy land have the weakest wind erosion flux the mean value of which is 10 53 5 43 2 88 and 1 94 kg day 1 m 2 respectively during the aeolian sediment transport process the mean limit of a suspended load particle size is 0 12 mm aeolian sediment mean grain size and sorting are 0 25 mm and 2 1 respectively and potential pm10 dust emission rate is 0 103 kg day 1 m 2

meltwater and deglaciation se baffin shelf ne margin laurentide ice sheet between 13 5 and 7 ka from o and c stable isotopic data stable isotopic values on planktonic foraminifera in a suite of cores from basins across the se baffin shelf are used to extract a record of meltwater events during termination i deglaciation resolution and hatton basins lie on the se baffin shelf at water depths 500 m seaward of major conduits for ice drainage from the eastern sector of the laurentide ice sheet lis accelerator mass spectrometry 14c dates are used to constrain our chronology of events in ten cores in resolution basin three cores have 14c ams dates on foraminifera of 20 ka at their bases whereas hatton basin cores terminate in sediments 13 kyr sedimentation rates varied between 0 1 to 4 5 m ka stable oxygen and carbon isotopic ratios were obtained on 146 samples of the planktonic foraminifera neogloboquadrina pachyderma ehrenberg sinistral from seven of the ten cores no evidence was found to indicate that test morphology or size affected 18o between 7 and 13 5 ka the surface water on the shelf was on average 1 lower than the open ocean signal significant temporal variations were found in both 18o and 13c evidence for significant low 18o events occurred between 13 and 8 ka the 13c record from the planktonic foraminifera suggests a threefold division of events between 13 and 7 ka with positive values between 10 8 and 13 0 ka negative values between 9 and 10 8 ka and positive values from 7 to 9 ka the 18o data suggest the presence of meltwater on the shelf some 3 000 years prior to the first late glacial dates on terrestrial deglaciation at circa 10 4 ka hudson strait must be the real key to the importance of the calving process during deglaciation because it is potentially the largest marine outlet for the laurentide ice sheet and because it leads into the very center of the ice sheet the rates of calving through hudson strait during the period of initial 18o rise unfortunately are unknown w f ruddiman 1987 p 151

carbonate leaching processes in the red clay formation chinese loess plateau fingerprinting east asian summer monsoon variability during the late miocene and pliocene 1 high resolution variations in carbonate minerals from the jiaxian red clay section located at the northern limit of the present east asian summer monsoon easm on chinese loess plateau were quantified using fourier transform infrared spectroscopy we analyzed a large quantity of sediments dated from the late miocene to pliocene 8 2 2 6 ma the carbonates in this interval show high frequency variations alternating between leached and calcareous horizons the low carbonate contents and high values of magnetic susceptibility and high rb sr ratios were found in the leached zones a pattern that is consistent with that observed in the overlying quaternary loess paleosol sequences this pattern suggests that east asian monsoon eam rainwater enhanced leaching and accumulation processes of carbonate minerals in the red clay formation in a way similar to the loess paleosol sequence seven alternating leached and calcareous zones are identified suggesting oscillations of the easm and east asian winter monsoon intervals the calcareous zones were also found to have high zr rb ratio these indications of shifts from a strong easm to east asian winter monsoon dominance correlate well with the cooling transition indicated by deep sea 18o isotopes this evidence suggests that the eam was active during the late miocene and pliocene and was similar to the quaternary monsoon the presence of a strong eam during the pliocene warm period also raises questions about the hypothesis that past and future warm climate conditions could produce a permanent el nino like state