diatom productivity peak and increased circulation during latest quaternary alboran basin western mediterranean abstract diatoms were studied quantitatively in six latest quaternary 70 kyr b p to recent piston cores from the westernmost mediterranean the alboran basin and the atlantic region immediately to the west of the straits of gibraltar the atlantic cores completely lack diatoms in the alboran basin diatoms are common from late stage 3 27 5 kyr b p to termination ib 9 kyr b p and in recent core tops but are absent in the other latest quaternary intervals maximum accumulation of diatoms and highest abundance of species normally in sediments associated with increased productivity occurred during the latest quaternary deglaciation in the first phase of termination i 14 8 kyr b p in the modern alboran basin a region of high biological productivity occurs immediately east of the gibraltar straits this high productivity results from upwelling associated with the interaction between the atlantic inflow and the bottom topography near the spanish coast the upwelled nutrient rich waters are then advected to the east and southeast by the surficial anticyclonic gyral circulation late quaternary variations in diatom abundance are considered to reflect changes in this upwelling intensity with highest diatom abundances inferred to result from increased upwelling associated with an intensification of the anticyclonic gyral circulation highest inferred upwelling rates occurred during the first phase of latest quaternary deglaciation it is possible that an intensification of circulation within the mediterranean basin as a whole occurred from late stage 3 to mid termination i because widespread hiatus formation has been reported at this time in the straits of sicily due to an increase in the formation of intermediate waters diatoms were not preserved in other latest quaternary intervals due to insufficient productivity to counterbalance their dissolution

style and timing of glaciation in the lahul himalaya northern india a framework for reconstructing late quaternary palaeoclimatic change in the western himalayas

uranium series ages of travertines and timing of the last glaciation in the northern yellowstone area wyoming montana uranium series age determinations by mass spectrometric methods were done for travertines and associated carbonate veins related to clastic deposits of the last glaciation pinedale in the northern yellowstone area dramatic variations in the hydrologic head are inferred from variations in the elevation of travertine deposition with time and are consistent with the expected hydrologic effects of glaciation we determine the following chronology of the pinedale glaciation with the key assumption that travertine deposits and associated carbonate veins perched high above present thermal springs were deposited when glaciers filled the valley below these perched deposits 1 the early pinedale outlet glacier advanced well downvalley between 47 000 and 34 000 yr b p 2 the outlet glacier receded to an interstadial position between 34 000 and 30 000 yr b p 3 an extensive pinedale ice advance occurred between 30 000 and 22 500 yr b p 4 a major recession occurred between 22 500 and 19 500 yr b p 5 a minor readvance deckard flats culminated after 19 500 yr b p and 6 recession from the deckard flats position was completed before 15 500 yr b p this chronology is consistent with the general trend of climatic changes in the northern hemisphere as revealed by recent high resolution ice core records from the greenland ice sheet

glacier changes between 1971 and 2016 in the jankar chhu watershed lahaul himalaya india glacier changes in the jankar chhu watershed jcw of chandrabhaga chenab basin lahaul himalaya were worked out based on corona and sentinel 2a images between 1971 and 2016 the jcw consists of 153 glaciers 0 02 km 2 with a total area of 185 6 3 8 km 2 that include 82 glaciers with debris covered ablation zone comprising 10 9 of the total glacierized area as in 2016 change analysis based on corona 1971 landsat 2000 and sentinel 2a 2016 was restricted to 127 glaciers owing to the presence of cloud cover on 26 glaciers in 1971 a subset of glaciers was also mapped using landsat thematic mapper tm 1989 image the total glacier area decreased by 14 7 4 3 km 2 0 3 0 1 km 2 a the number of glaciers in the jcw increased by four between 1971 and 2016 due to fragmentation more recently 2000 16 recession rate has increased clean ice area decreased by 21 8 3 8 km 2 0 5 0 1 km 2 a while debris covered ice increased by 7 2 0 4 km 2 0 2 0 01 km 2 a field observations of select glaciers also support derived recession trend in the jcw retreat rates in the jcw have been observed to be much lower than previously reported

a late quaternary catastrophic flood in the lahul himalayas impressive flood deposits are described resulting from a catastrophic lake outburst in the upper chandra valley in the lahul himalaya northern india reconstructions of the former glacial lake glacial lake batal and the discharges were undertaken using landforms and sediment data the glacial dam burst released 1 496 km3 of water in 0 72 days with peak discharges of between 21 000 and 27000 m3 s at batal dating by osl suggests the flood occurred ca 36 9 if 8 4 to 43 4 2 10 3 ka ago this cataclysmic flood was responsible for major resedimentation and landscape modification within the chandra valley journal of quaternary suence

diatoms as hydrographic tracers example from bering sea sediments variations in the distribution of diatom species in surface sediments mirror distinct hydrographic regimes on the bering shelf spring salinity fronts divide the water column into four zones with different vertical structures and different productivity patterns four assemblages of diatoms can be distinguished in sediments underlying the zones

quaternary glaciations in the southern hemisphere an overview abstract large glacier systems in antarctica have existed at least since the early miocene glaciers in the patagonian andes advanced in the late miocene and fluctuated several times during the pliocene as did ice masses elsewhere in the southern hemisphere sedimentological evidence of glaciation during the early and middle quarternary is best preserved in volcanic regions patagonia new guinea africa but is poorly constrained by dating there is evidence of glaciation during oxygen isotope stages 10 8 and 6 in several parts of the southern hemisphere but the only well dated advance of the middle quarternary is that of stage 6 in the transantarctic mountains during the last glaciation montane glaciers in parts of the southern hemisphere were as large during isotope stage 4 as during isotope stage 2 the last glaciation maximum stage 2 is well dated in tasmania new zealand and patagonia culminating as 21 18 ka bp following slight recession from the lgm limits late glacial advances peaked at 15 14 ka bp and at 12 10 ka bp major holocene advances occurred on at least three occasions during the last 5 ka in areas presently glacier covered

assessment of geochemical and micropaleontological sedimentary parameters as proxies of surface water properties in the canary islands region abstract the canary islands region occupies a key position with respect to biogeochemical cycles with the zonal transition from oligotrophic to nutrient rich waters and the contribution of saharan dust to the particle flux we present the distribution of geochemical proxies toc carbonate 15n 13corg c n ratio and micropaleontological parameters diatoms dinoflagellates foraminifera pteropods in 80 surface sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre results of the surface sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or sst the distribution of total dinoflagellate cysts the planktic foraminifera species globigerina bulloides the diatom resting spore chaetoceros spp and toc concentration coincided well with the areas of strong filament production off cape ghir and cape yubi the warm water planktic foraminifera globigerinoides ruber white the diatom nitzschia spp and the 15n values showed the opposite trend with high values in the open ocean factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the canary islands region that represent the present surface water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre

study of temporal response 1976 2019 and associated mass movement event during 2017 of meru glacier bhagirathi valley garhwal himalaya india abstract impact of climate change on glaciers brings the favorable conditions of lakes formation within glacier moraines these lakes may produce outburst floods and transport the huge amount of debris debris flow in downstream settlements the present study addresses the current knowledge on mass movement activity occurred in the gangotri glacier area garhwal himalaya uttarakhand temporal response terminus retreat and frontal area loss of meru glacier during 1976 2019 using the images of landsat mss 1976 tm 1990 2011 etm 2001 oli 2019 and event of intense mass movement occurred along meru glacier during 2017 is assessed our estimations clearly reveals that the meru glacier is retreating continuously since 1976 with inconsistent rate considering the time span 1976 1990 1990 2001 2001 2011 2011 2019 the terminus receded with 12 42 m y 1 7 72 m y 1 6 00 m y 1 11 50 m y 1 and vacated the frontal area at the rate of 2330 70 m2 y 1 2185 88 m2 y 1 1425 18 m2 y 1 1452 66 m2 y 1 respectively field observations and high resolution imagery of liss iv suggest that the lower area of meru glacier experienced the event of intense mass movement in july 2017 this event breached the continuity of left morainic wall of bhagirathi valley this mass movement event influenced the initial course of bhagirathi river 1559 m length and also modified the morphology of the gaumukh region the precipitation data from indian meteorological department imd and satellite images of different years suggest that the multiple factors such as intense precipitation large amount of sediment transport from the upper reaches to lower area slope failure collapse of frontal part of meru glacier were the main causative factors for this event

the explosive diversification of the diatom genus chaetoceros across the eocene oligocene and oligocene miocene boundaries in the norwegian sea abstract eocene to middle miocene stratigraphic changes in species richness abundance and valve size of chaetoceros resting spores in the norwegian sea dsdp site 338 were investigated in order to understand past productivity and paleoenvironmental changes in upwelling regions as a result drastic resting spore events were recognized in a 6 myr interval across the eocene oligocene boundary eo event the oligocene miocene boundary om event and in the early middle miocene emm event the eo event was characterized by explosive diversification at both the morpho generic and specific levels an increase in abundance and a decrease in valve size from the upper eocene through the lowest oligocene the om event was defined by a two fold increase in species richness during the emm event spore abundance decreased rapidly and species richness and valve size decreased gradually these changes may indicate changes in the nutrient supply especially in upwelling regions the increased species richness suggests a change from a stable water column with a constant nutrient supply in the eocene to an unstable one with a sporadic nutrient supply by increased vertical mixing in the oligocene based on evaluation of the ecologic differences between dinoflagellate cysts and chaetoceros resting spores the role of main primary producer might have switched from dinoflagellates and or nannoplankton in the eocene to diatoms especially chaetoceros in the oligocene in the norwegian sea increased resting spore species richness during the om event may show that environmental changes such as global cooling and nutrient mixing led to a diversification of the spore producing genus chaetoceros the emm event might have been affected by changes in paleoceanographic conditions perhaps a decrease in nutrient supply this study presents the first paleoceanographic analysis using not only the total resting spore abundance but also the abundances of individual species and establishes the value of spore taxonomy and diatom analysis including spores

the quaternary glacial history of the lahul himalaya northern india this paper presents the first glacial chronology for the lahul himalaya northern india the oldest glaciation the chandra glacial stage is represented by glacially eroded benches at altitudes greater than 4300 m above sea level this glaciation was probably of a broad valley type the second glaciation the batal glacial stage is represented by highly weathered and dissected lateral moraines which are present along the chandra valley and some of its tributaries this was an extensive valley glaciation the third major glaciation the kulti glacial stage is represented by well preserved moraines in the main tributary valleys of the chandra valley this represents a less extensive valley glaciation two minor glacial advances the sonapani i and ii are represented by small sharp crested moraines which are within a few hundred metres or few kilometres of the present day glaciers the change in style and extent of glaciation is attributed to an increase in aridity throughout the quaternary due either to global climatic change or uplift of the pir panjal mountains to the south of lahul which restricted the northward penetration of the south asian summer monsoon 1996 john wiley sons ltd

an upwelling case study on florida s west coast using a combination of satellite sea surface temperature imagery in situ currents temperature and sea level data and a numerical circulation model we describe an upwelling event observed along florida s west coast although ubiquitous features of continental shelves descriptions of coastal upwellings or downwellings are generally complicated by the continuum of processes in which they occur for the case study presented the winds were light and the baroclinic background currents were steady for several days prior to the event these conditions allow the evolution of a specific winddriven upwelling event to be viewed as an initial value problem the data and the numerical model analysis show that the route of adjustment by the sea level and currents is a classical ekman geostrophic one sea level drops due to an offshore ekman transport causing a geostrophic alongshore jet and the associated onshore flow within the bottom ekman layer accounts for the appearance of cold water at the surface this surface manifestation occurs as an elongated feature centered about the 25 m isobath that spans roughly half of the florida peninsula from just north of tampa bay to key west the coldest water is observed offshore from tampa bay and we explain this region of locally maximum upwelling on the basis of the coastline and isobath geometries

the role of the indian summer monsoon and the mid latitude westerlies in himalayan glaciation review and speculative discussion new dates for late quaternary glaciations in the himalayas show that during the last glacial cycle glaciations were not synchronous throughout the region rather in some areas glaciers reached their maxima at the global glacial maximum of c 18 20 ka bp whereas in others glaciers were most extensive at c 60 30 ka bp comparison of these data with palaeoclimatic records from adjacent regions suggest that on millennial timescales himalayan glacier fluctuations are controlled by variations in both the south asian monsoon and the mid latitude westerlies

cosmogenic radionuclide dating of glacial landforms in the lahul himalaya northern india defining the timing of late quaternary glaciation the timing of glaciation in the lahul himalaya of northern india was ascertained using the concentrations of cosmogenic 10be and 26al from boulders on moraines and drumlins and from glacially polished bedrock surfaces five glacial stages were identified sonapani i and ii kulti batal and chandra of these cosmogenic exposure ages were obtained on samples representative of the batal and kulti glacial cycles stratigraphical relationships indicate that the sonapani i and ii are younger no age was obtained for the chandra glacial advance batal glacial stage deposits are found throughout the valley indicating the presence of an extensive valley glacial system during the kulti stage glaciers advanced ca 10 km beyond their current positions moraines produced during the batal stage ca 12 15 5 ka are coeval with the northern hemisphere late glacial interstadial bolling allerod deglaciation of the batal glacial stage was completed by ca 12 ka and was followed by the kulti glacial stage during the early holocene at ca 10 11 4 ka on millennial time scales glacier oscillations in the lahul himalaya apparently reflect periods of positive mass balance coincident with times of increased insolation during these periods the south asian summer monsoon strengthened and or extended its influence further north and west thereby enhancing high altitude summer snowfall copyright 2001 john wiley sons ltd

the quaternary glacial history of the zanskar range north west indian himalaya abstract three glacial stages and a minor advance are recognised from the zanskar range of the north western indian himalaya a glaciated palaeosurface 280 m above river level a r l with associated erratics represents the oldest and most extensive glaciation the chandra stage this ice covered a landscape of broad gentle valleys probably as an ice cap with an erratic distribution indicating that the ice shed lay to the south over the high himalaya a change in valley form from broad glacial troughs to narrow v shaped gorges along with large subdued moraine ridges delimits a separate later extensive valley glaciation the batal stage with its maximum at 78 0 12 3 ka bp distinct sets of moraine ridges represent a less extensive younger glaciation the kulti stage which dates close to the global last glacial maximum a minor advance the sonapani is represented by sharp crested moraine ridges within 2 km of current ice bodies possibly belonging to the little ice age glacier elevation indexes geis calculated for this and adjacent areas show a rise in elevation from the south west to the north east but dip again to the indus valley for both the batal and kulti stages reflecting attenuation of the south westerly monsoon and possible channelling of westerly depressions along the broad upper indus valley gei depression are 500 and 300 m for the batal and kulti stages respectively the change in extent and style from the chandra stage to the later glaciations may be related to uplift of more southerly ranges blocking monsoon precipitation and incision of the landscape such that ice reached lower altitudes over shorter horizontal distances why ice extent was greater during oxygen isotope stage ois 4 than 2 is not clear although recent high resolution plaeomonsoon records show complex peaks in monsoon intensity and it is possible that there was a more favourable combination of precipitation and temperature earlier rather than later during the last glaciation

equilibrium line altitudes of the last glacial maximum for the himalaya and tibet an assessment and evaluation of results abstract contemporary equilibrium line altitudes elas for glaciers in the high mountains of the himalaya and tibet have considerable variation because the region is influenced by two major climatic systems the mid latitude westerlies and the south asian summer monsoon and glaciers are subject to strong topographic controls reconstructions of past elas based on the former extent of glaciers are numerous but were estimated using a variety of methods some of which are not appropriate for high altitude glaciers which are strongly influenced by topography and have extensive supraglacial debris cover furthermore few of the reconstructions have adequate chronological control because of the difficulty of dating glacial landforms in high altitude regions where organic matter for radiocarbon dating is sparse or absent cosmogenic radionuclide surface exposure and optically stimulated luminescence dating are providing data to define the timing of glaciation and these together with objective analysis of glacier dynamics may allow better estimates of ela changes in the future however there are currently only two regions the hunza valley and the khumbu himal which are sufficiently well dated to allow reconstructions of last glacial maximum glacier extent and hence elas these two regions cannot provide an adequate assessment of ela changes for the himalayan tibetan region

rapid last glacial maximum deglaciation in the indian himalaya coeval with midlatitude glaciers new insights from 10be dating of ice polished bedrock surfaces in the chandra valley nw himalaya despite a large number of dated glacial landforms in the himalaya the ice extent during the global last glacial maximum lgm from 19 to 23 ka is only known to first order new cosmogenic 10be exposure ages from well preserved glacially polished surfaces combined with published data and an improved production rate scaling model allow reconstruction of the lgm ice extent and subsequent deglaciation in the chandra valley of nw india we show that a 1000 m thick valley glacier retreated 150 km within a few thousand years after the onset of lgm deglaciation by comparing the recession of the chandra valley glacier and other himalayan glaciers with those of northern and southern hemisphere glaciers we demonstrate that post lgm deglaciation was similar and nearly finished prior to the bolling allerod interstadial our study supports the view that many himalayan glaciers advanced during the lgm likely in response to global variations in temperature

late pleistocene holocene paleoenvironmental changes inferred from the diatom record of the ulleung basin east sea sea of japan abstract the diatom floral record from two piston cores 00ghp 01 and 00ghp 07 taken from the southwestern margin of the ulleung basin east sea sea of japan reveals a series of well defined changes in glacio eustatic sea level and paleoceanographic conditions during the late pleistocene holocene six assemblage zones and two barren zones in 00ghp 01 and four assemblage zones in 00ghp 07 are erected respectively on the basis of frequency of variations in and occurrences of biostratigraphically significant diatom species all assemblage zones have been strongly influenced by the tsushima warm current twc the twc has an important affect on controlling the distribution and composition of diatom flora which in turn reveal the history of the twc in this area the distribution pattern of diatoms in the diatom assemblages reveals sea surface temperature and salinity affected by the sediments type and terrigenous material input diatom temperature td values show that the site of 00ghp 01 in the ulleung basin has been influenced by a relatively enhanced twc twice during the deposition of lowermost and uppermost intervals a relatively weak twc was recorded in the middle interval since the latest pleistocene the diatom assemblages of 00ghp 07 represent an apparently continuous late quaternary record spanning the last glacial maximum bolling allerod younger dyras and holocene high abundance of a low salinity coastal water diatom paralia sulcata may reflect the influx of the east china sea water through the korean strait to the east sea sea of japan during the last glacial maximum the sea level was low enough that selected basin with shallow sills along the margin of the east sea sea of japan became isolated from the pacific ocean salinity also decreased due to increased freshwater input from rivers draining the surrounding lands the density stratified water column may have prevented vertical mixing and resulted in anoxic bottom water conditions

comment cosmogenic radionuclide dating of glacial landforms in the lahul himalaya northern india defining the timing of late quaternary glaciation l a owen l gualtieri r c finkel m w caffee d i benn and m c sharma 2001 journal of quaternary science16 555 563

palaeoclimatic reconstruction by using the varvite sediments of bharatpur upper lahaul valley nw himalaya india a 6 m thick varvite profile exposed at bharatpur 77 27 e 32 48 n altitude 4692 m in the nw himalaya was investigated to understand the past climatic signatures during the late quaternary period the radiocarbon chronology brackets the varvite sedimentation between 24 3 and 7 2 ka bp and the sedimentary sequence is bounded by river born gravel at the top and glacial outwash at the bottom the proxies used were lithology chronology ams radiocarbon dating geochemical analysis loss on ignition loi and mineral magnetism other parameters e g chemical index of alteration cia chemical index of weathering ciw al2o3 sio2 fe2o3 cao mgo and al na ratio were also used based on the combined data set six phases of warm and cold climatic conditions are reconstructed the mean cia ciw and al na ratios reveal that the sediments were incorporated from sedimentary rocks by moderate silicate chemical weathering process based on the available chronology the basal most glacial outwash event can be estimated as ca 24 3 ka bp and the laminated section shows continuity of sedimentation from the late quaternary to holocene the period between ca 24 3 and 22 6 ka can be regarded as an arid phase from ca 22 6 20 5 ka bp a slight increase in monsoonal precipitation is observed followed by decreased precipitation from ca 20 5 to 18 ka bp the period from ca 18 to 15 7 reveals warm and humid climatic conditions we suggest that a cold event from ca 15 7 to 11 5 may correspond to the younger dryas yd which in turn is followed by a phase of maximum moisture of the holocene climate optimum hco ca 11 5 7 2 ka bp in the study area the increased cia during deglaciation and hco suggest high chemical weathering whereas the lgm last glacial maximum and yd are represented by the low cia the observed climatic phases events are in agreement with the records from other parts of the himalaya

spatio temporal fluctuations over chorabari glacier garhwal himalaya india between 1976 and 2017 abstract the current research work deals with the health of chorabari glacier between 1976 and 2017 using multi spectral and multi dated satellite data series of landsat mss tm and etm and resourcesat ii liss iv result closely reveals that the studied glacier receding continuously with inconsistent rate for the last 41 years and rate of receding dominates significantly after 2012 it lost 306 43 61 m total length 7 46 1 48 m a 1 0 074 km2 frontal area 0 0018 km2 a 1 0 31 km2 24 glaciated area 0 007 km2 a 1 0 015 km3 32 60 glaciated volume the upward migration of sla snow line altitude from 5265 m to 5290 m also suggests that the melting process were prevailing during the study tenure an existence of supra glacial lakes and its successive growth over the surface of chorabari glacier further justifies that the temperature of the surroundings has increased significantly and influences the melting process as well the melting process between 1976 and 1990 of the studied glacier directly influenced by the frequent episodes of precipitation and temperature anomalies of central himalayan region during 1960 1990 while the melting process after 1990 is directly influenced by the increase in average mean temperature and decrease in average mean precipitation of garhwal himalayan region the tree ring data of garhwal himalaya region also well matches the precipitation data of imd indian meteorological department the overall analysis explains that the chorabari glacier is retreating continuously since 1976

the quaternary glacial history of nanga parbat abstract during one or more times throughout the quaternary an extensive glacier system occupied the valleys of the nanga parbat massif glacial landforms in the astor valley provide evidence for two separate glacial advances with ice advancing more than 15 km down valley from the present ice fronts elsewhere in the massif geomorphic and sedimentological evidence provide evidence for a less extensive glaciation where glaciers advanced no more than 12 km beyond their present positions intense erosion and mass movement has destroyed any depositional evidence for earlier pleistocene glaciations however truncated spurs hanging valleys steep valley sides and over deepened trunk valleys provide evidence of an earlier more extensive glaciation small moraines near the snouts of the present glaciers provide evidence for at least three limited glacial advances that post date the extensive valley glacier system on the basis of geomorphology sedimentology and relative weathering characteristics glacial landforms are correlated across the nanga parbat massif furthermore the age of the maximum extent of valley glaciation is tentatively assigned to early in the last glacial cycle with two late pleistocene readvances or periods of stagnation followed by three periods of limited glacial advance during the holocene

quaternary glacial history of the karakoram mountains and northwest himalayas a review abstract the style and extent of glaciation in the nw himalayas and karakoram mountains of pakistan and the himalayas in nw india are reviewed at least three glacial events progressively less extensive with time can be recognised in most regions the timing and status of these glacial successions is poorly known this is partially due to poor dating constraints but also arises from a lack of adherence to strict stratigraphic procedures recommendations are made for a more rigorous approach to the study of himalayan quaternary glacial histories

late pleistocene holocene vegetation and indian summer monsoon record from the lahaul northwest himalaya india abstract the high resolution holocene paleomonsoon records from northwest nw himalaya are limited the carbon isotope 13 c total organic carbon toc and pollen analysis were therefore carried out from a peat lake sediment sequence developed in alpine meadows of the chandra valley lahaul nw himalaya in order to reconstruct centennial to millennial scale vegetational changes and indian summer monsoon ism variability during the holocene the chronology of peat lake sediments is constrained with 9 ams 14 c dates the recovered non arboreal pollen nap suggested that during holocene alpine desert steppe meadows and shrubs growing along the stream had developed in the lahaul valley whereas arboreal pollens ap e g pinus quercus cedrus and ulmus presently growing in the southern hill slopes of pir panjal range indicated moisture carrying monsoonal air flow from the south the increased 13 c and low toc values between 12 880 and 11 640 calibrated years before present cal yr bp suggested weakening of ism and low organic carbon production corresponding to the younger dryas yd cold event the gradual depletion in carbon isotope ratio from 11 640 to 8810 cal yr bp indicated enhanced precipitation in the chandra valley in response of increased ism strength in early holocene the short spell of cold and dry climate with gradual decrease in ism intensity between ca 10 398 and 9778 cal yr bp is closely linked with bond event 7 the other prominent cold dry events recorded in present study are i 8810 to 8117 cal yr bp roughly corresponding to global 8 2 ka cold event ii 4808 to 4327 cal yr bp closely preceding the global 4 2 ka cold arid period and iii 1303 to 1609 cal ad corresponding to little ice age lia event the expansion of thermophillous broad leaved taxa viz betula utilis alnus nepalensis quercus semicarpifolia and juglans regia and effective growth of meadow vegetation such as grasses caryophyllaceae and artemisia along with marshy elements i e polygonum and liliaceae between 6732 and 3337 cal yr bp marked warm and wet holocene climate optimum hco period the warm and moist climate from 1158 647 cal yr bp corresponded with global medieval warm period mwp

controversy regarding the existence of a large ice sheet on the qinghai xizang tibetan plateau during the quaternary period

diatom assemblages as upwelling indicators in surface sediments off portugal abstract diatom abundance and assemblage composition have been determined for 169 surface sediment samples from the portuguese margin an area where seasonal upwelling occurs each year from april to october absolute diatom abundance distribution patterns reflect the more intense and or persistent and more homogeneous upwelling north of the nazare canyon the position of the inner upwelling front south of lisbon and the eastern continuation of the coastal upwelling jet along the algarve coast distribution patterns of species and of ecologically defined groups meroplanktonic oceanic freshwater and marine benthic support the hypothesis that diatom species and assemblages are good indicators of the changing character of the upwelling system small species of the genus thalassiosira occur in areas of persistent upwelling where availability of nutrients is more constant and or higher paralia sulcata ehr cleve is an abundant species whose mean cell diameter increases as nutrient availability decreases resting spores mainly of chaetoceros ehrenberg record the position of the zone where higher variability occurs the inner upwelling front

timing and nature of holocene glacier advances at the northwestern end of the himalayan tibetan orogen abstract holocene glacial chronostratigraphies are developed for four glaciated valleys at the northwestern end of the himalayan tibetan orogen using geomorphic mapping and cosmogenic 10be surface exposure dating the study areas include the hamtah valley in the lahul himalaya and the karzok lato and upper stok valleys in zanskar five local glacial stages are dated to 10 4 6 1 3 3 2 1 0 9 0 7 0 4 and 0 3 0 2 ka based on 49 new moraine boulder ages large age dispersions are evident for each of the local glacial stages this is especially the case for 6 1 3 3 and 2 1 0 9 ka which is likely a result of prior and or incomplete exposures in very young moraine boulders an additional compilation of 187 published 10be moraine boulder ages help define seven himalayan holocene regional glacial stages hhs for the northwestern end of the himalayan tibetan orogen these hhs date to 10 9 9 3 8 2 7 4 6 9 4 3 4 5 2 8 2 7 1 8 1 8 0 9 and

review of the timing and extent of glaciers during the last glacial cycle in the bordering mountains of tibet and in east asia new accelerator mass spectrometry 14c ams14c electron spin resonance esr and thermoluminescence tl dates for glacial successions in tibetan bordering mountains and in east asia show that glacier extent during the early middle mis3 4 parts of the last glacial cycle was larger than that of the late stage mis2 in last glacial cycle glaciation was not synchronous with the north hemisphere ice sheet maxima and changes in oceanic circulation that predominately control global climate there exist three seasonal precipitation patterns that control the accumulation and ablation on glaciers in the study areas areas dominated by westerlies including the east asia coastal islands experience glacier advance mainly because of increased winter precipitation these glaciers expand during glacial stages in contrast in areas dominated by summer precipitation in the interior of mainland except in the monsoonal high precipitation zone in southeast tibet and the hengduan mountain range tend not to develop large glaciers during major glacial stages

evidence for an early glacial maximum in the french vosges during the last glacial cycle the last glacial maximum is observed to have occurred between 18 000 and 20 000 years ago throughout northern europe here we present evidence for the surprising result that in the region of the french vosges the regional ice sheet advanced during the early part of the last glacial cycle and this expansion was considerably larger than that which occurred during the last glacial maximum from these results we conclude that the glacial maximum may not have occurred at the same time worldwide contrary to what has usually been assumed1

high frequency holocene glacier fluctuations in the himalayan tibetan orogen abstract holocene glacial chronostratigraphies in glaciated valleys spread throughout the himalayan tibetan orogen including the himalaya tibet pamir and tian shan are developed using a landsystems approach detailed geomorphic mapping and new and published 10be surface exposure dating new studies in the kulti valley of lahul and the parkachik valley of the nun kun massif of the himalaya of northern india define three glacier advances at 14 7 12 2 0 5 ka in addition to one historically dated late 19th century advance in the kulti valley and one late holocene advance at 0 2 ka in the parkachik valley three major climatic groups subdivided into five climatic zones are defined across the orogen using cluster analysis ca and principal component analysis pca to identify glaciated regions with comparable climatic characteristics to evaluate the timing and extent of holocene glacier advances across these regions our regional analyses across the himalayan tibetan orogen suggest at least one lateglacial 15 3 11 8 ka and five himalayan tibetan holocene glacial stages hths at 11 5 9 5 8 8 7 7 7 0 3 2 2 3 1 0 and

increased upwelling off portugal during the last glaciation diatom evidence abstract quantitative studies have been carried out on opaline microfossils and diatom assemblage composition and preservation in two latest quarternary 100 ka to p d cores from the continental slope of portugal the sites are located in an area of modern summer coastal upwelling created by northerly trade winds the spatial patterns and intensity of this upwelling system are accurately recorded by the diatom abundances and taxonomic composition in the surface sediments the diatom record in these sequences indicates that coastal upwelling intensity was similar to present day during late holocene interglacial stage 3 and late stage 5 higher during stage 2 and lower in the early holocene paleoproductivity estimates are consistent with the diatom accumulation rates from stage 3 to the recent this indicates that both the diatom and the organic carbon content of the sediments mainly reflect the biological productivity in the euphotic zone

estimating groundwater discharge into the northeastern gulf of mexico using radon 222 abstract submarine groundwater discharge sgd may provide important chemical constituents to the ocean but the dispersed nature of this process makes locating and quantifying its input extremely difficult since groundwater contains 3 4 orders of magnitude greater radon than seawater 222rn may be a useful tracer of this process if all other sources of radon to bottom waters can be evaluated we report development of a sgd tracing tool based on radon inventories in a coastal area of the northeastern gulf of mexico we evaluated factors that influence the concentration of radon in the water column i e production decay horizontal transport and loss across the pycnocline using a linked benthic exchange horizontal transport model total 222rn benthic fluxes 2420 dpm m 2 day 1 measured with in situ chambers are of the magnitude required to support measured sub pycnocline 222rn inventories while estimates of molecular diffusion show that this input is relatively small 230 dpm m 2 day 1 using this model approach together with measurements of the radon inventory we estimated a regional subsurface fluid flow ranging from 180 to 710 m3 sec 1 into the 620 km2 study area this discharge equivalent to an upward advective velocity of approximately 2 10 cm day 1 dispersed over this entire study area is equivalent to approximately 20 first magnitude springs

terrain changes caused by the 15 17 june 2013 heavy rainfall in the garhwal himalaya india a case study of alaknanda and mandakini basins abstract exceptional early high monsoon rains between 15 and 17 june 2013 combined with discharge from snowmelt water caused widespread floods in every major river of the garhwal himalaya this catastrophic event triggered widespread landslides and devastation in the region affecting the movement of the people that led to stranding of pilgrims in various pilgrimage routes this event caused many casualties and irreparable damage to the infrastructures and property in the garhwal himalaya a large volume of debris was deposited in kedarnath town 3 9 10 6 m 3 and a huge amount of debris was removed from rambara and surrounding areas 2 6 10 8 m 3 the study also found that villages like lambaghar bhyundar alaknanda river valley and rambara mandakini river valley were completely washed away leaving no trace of earlier settlement govindghat and pulna villages in the alaknanda river valley were also badly damaged approximately 0 3 10 6 and 0 72 10 6 m 3 of debris was deposited respectively similarly in the mandakini valley kedarnath and sonprayag towns were also badly damaged and 3 9 10 6 and 1 4 10 6 m 3 of debris was deposited in the area respectively simultaneously the moraine dammed chorabari lake breached releasing 6 1 10 5 m 3 of water with an average rate of 1429 m 3 s discharge of lake the towns of pandukeshwar in the alaknanda valley and gaurikund in the mandakini valley were partially damaged however no evidence of such magnitude of destruction was reported from the yamuna river valley during the same period this catastrophic event changed the landscape in many parts of uttarakhand making the whole region more fragile and vulnerable a disaster of such magnitude was perhaps not witnessed by the region for at least the last 100 years

neotectonics and glacial deformation in the karakoram mountains and nanga parbat himalaya abstract the karakoram mountains and the nanga parbat himalaya are one of the most rapidly rising mountain areas in the world with uplift rates in the order of 2 mm yr large scale regional warping is the most likely form of uplift with the greatest rates around the nanga parbat haramosh massif only two active faults have been recognised in the pakistan karakoram the rakhiot and the misgar valley fault the rakhiot fault zone is a neotectonic expression of the rapid uplift centred around the nanga parbat syntaxis deformation structures in quaternary and recent sediments in the rakhiot area are not produced solely by neotectonic processes but also by processes in the glacial depostional environment and slope related processes structures present vary from neotectonic shear zones folds thrusts and high angled faults glacially produced folds thrusts shears and joints and debris slides bounded by discrete shear zones the distinction between these structures is vital in making valid neotectonic models for high active mountain belts

forcing of late cenozoic northern hemisphere climate by plateau uplift in southern asia and the american west geologic evidence indicates that net vertical uplift occurred on a large kilometer scale and at accelerating rates during the middle and late cenozoic in plateaus of southern asia and the american west based on this evidence general circulation model sensitivity tests were run to isolate the unique effects of plateau uplift on climate the experiments simulated significant climatic changes in many places some far from the uplifted regions the basic direction of most of these simulated responses to progressive uplift is borne out by changes found in the geologic record winter cooling of north america northern europe northern asia and the arctic ocean summer drying of the north american west coast the eurasian interior and the mediterranean winter drying of the north american northern plains and the interior of asia and changes over the north atlantic ocean conducive to increased formation of deep water the modeled changes result from increased orographic diversion of westerly winds from cyclonic and anticyclonic surface flow induced by summer heating and winter cooling of the uplifted plateaus and from the intensification of vertical circulation cells in the atmosphere caused by exchanges of mass between the summer heated and winter cooled plateaus and the mid latitude oceans disagreements between the geologic record and the model simulations in alaska and the southern rockies and plains may be related mainly to the lack of narrow mountain barriers in the model orography taken together the observed regional trends comprise much of the pattern of late cenozoic climatic deterioration in the northern hemisphere that culminated in the plio pleistocene ice ages the success of the uplift sensitivity experiment in simulating the correct pattern and sign of most of the observed regional climatic trends points to uplift as an important forcing function of late cenozoic climatic change in the northern hemisphere at time scales longer than orbital variations however the modest amplitude of the uplift induced cooling simulated at high latitudes indicates a probable need for additional climatic forcing

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

the fate of diatom valves in the subantarctic and polar frontal zones of the southern ocean sediment trap versus surface sediment assemblages abstract an array of deep ocean sediment traps was initiated in 1997 within the australian sector of the southern ocean and serviced annually for over a decade the subantarctic site is ongoing as part of the southern ocean time series here we expand on previous findings obtained from the shallow traps 1000 m depth in the polar frontal zone pfz and subantarctic zone saz by examining the chemical composition and diatom assemblages collected by sediment traps deployed at bathypelagic depths in the pfz 1500 m depth years 1997 1998 1999 2000 and 2003 2004 and saz 2000 and 3800 m year 1999 2000 additionally the diatom assemblages of the surface sediments below the traps were analyzed to document how the seasonal signal is recorded in the sedimentary record analysis of the changes of the bsi poc ratios with depth at both sites confirms previous work suggesting that the decoupling between si and c cycles in the southern ocean is not different from other biogeochemical provinces of the world s ocean comparison of the seasonal flux pattern registered by the traps indicates that the diatom assemblages in the sediments of the antarctic zone and pfz mainly represent the summer period in contrast the assemblages found in the sediments of the saz are a reflection of the spring and summer months a period characterized by a larger variability in chemical and physical parameters the strong correlation between the poc fluxes and the relative abundance of a group of diatom species mainly pseudo nitzschia and small fragilariopsis in the pfz traps suggest that there is an intimate relationship between the development of these species and the poc pulses to the deepest layers of the water column in this region interestingly analysis of the diatom assemblages in the surface sediments reveals that the strong dissolution in the sediment water interface removed the signal of these carbon sinkers from the sedimentary record leaving the sediment assemblage enriched in heavily silicified species

a 13 000 year record of environmental magnetic variations in the lake and peat deposits from the chandra valley lahaul implications to holocene monsoonal variability in the nw himalaya abstract an 13 000 year old record of in situ peat bog and lacustrine sediments from a post glacial lake in the chandra valley of the lahaul himalaya is studied to generate the record of environmental magnetic signatures in response to indian summer monsoon ism variability in the nw himalaya the chronology of studied chandra peat trench cpt profile is based on 9 ams 14c calibrated dates cal yr bp the piece wise linear regression analysis of age depth model indicates non linear sedimentation with higher rates from 4142 cal yr bp to the present and lower accumulation during 12 880 4142 cal yr bp the mineral magnetism showed three dominant assemblages of magnetic minerals with varying concentrations in peat lake sediment sequence i e 1 mixed ferri and antiferromagnetic minerals between 12 880 and 11 019 cal yr bp 2 dominant antiferromagnetic mineralogy from 11 019 to 3172 cal yr bp and 3 significantly increased concentrations of mixed ferri and antiferromagnetic minerals from 3172 cal yr bp to the present with characteristically increased ferrimagnetic concentrations after 2032 cal yr bp the characteristic increase in antiferromagnetic mineral concentration accompanied by decreased ferrimagnetic concentration from 10 398 to 5770 cal yr bp suggest possible oxidation of magnetite to hematite under warmer climate conditions and corresponds to increased ism intensity during early to mid holocene warm wet climate in the nw himalaya the distinctly increased concentration of antiferromagnetic minerals from 6732 to 5770 cal yr bp indicates mid holocene climate optimum hco in the lahaul himalaya the strengthening and weakening of ism recorded in environmental magnetic signatures during 1260 852 cal yr bp 690 1098 ad and between 852 and 239 cal yr bp 1098 1711 ad corresponds to medieval warm period mwp and little ice age lia events respectively

temporal fluctuations and frontal area change of bangni and dunagiri glaciers from 1962 to 2013 dhauliganga basin central himalaya india abstract glaciers have been receding for the last 100 years in many glaciated regions of the world and the rate of recession has accelerated during the last 60 years recent assessments of changes in glaciers in the himalaya have usually recognized their variable rate of recession the present study deals with snout retreat frontal area vacation and estimation of the equilibrium line altitude ela of bangni and dunagiri glaciers in the dhauliganga basin central himalaya india using multi image satellite data landsat mss 1976 landsat tm 1990 landsat etm 2005 and survey of india topographic maps 1962 1 50 000 along with field surveys 2012 to 2014 for the period of 1962 2013 the meteorological data of the india meteorological department imd and trmm suggested that the central himalaya received less precipitation between 1960 and 1990 because of the less precipitation glaciers receded rapidly during this period the present study shows that bangni and dunagiri glaciers retreated 2080 162 m and 484 38 m with average rates of 41 3 2 m a 1 and 9 0 6 m a 1 between 1962 and 2013 respectively during this period bangni and dunagiri glaciers lost about 17 and 11 of their length respectively the result also suggested that bangni glacier vacated 598 948 12 257 m2 frontal area while dunagiri glacier vacated 170 428 7833 m2 frontal area between 1962 and 2013 moreover the estimated ela change for bangni glacier was 64 30 m upward during the study period the geological survey of india gsi 1998a b suggested that the ela of dunagiri glacier rose 28 m between 1984 and 1992 and that the glacier lost 16 106 m3 w e ice with an average rate of loss of 1 04 m w e a 1 the geomorphology of the dunagiri valley reflected that bangni and dunagiri glaciers were joined together in the past nevertheless these two glaciers retreat at different rates indicating that climate change is not the only factor in glacier retreat but that geometry size shape slope and orientation of the glacier and basin topography also plays a major role

a note on the extent of glaciation throughout the himalaya during the global last glacial maximum abstract quantitative chronologies for the impressive glacial successions that occur throughout the himalaya have until recently been almost totally lacking within the last decade two new techniques have promised to remedy this situation these techniques optically stimulated luminescence and cosmogenic nuclide surface exposure dating enable the age of many glacial features to be determined and have allowed us to study the extent and timing of himalayan glaciation in the late quaternary new data show that the local last glacial maximum lgm occurred during the early part of the last glacial cycle in most areas during marine isotope stage 3 mis 3 mis 3 was a time of increased insolation when the south asian summer monsoon strengthened and penetrated further north into the himalaya the concomitant increased precipitation occurring as snow at high altitudes produced positive glacier mass balances thereby allowing glaciers to advance on the other hand during the global lgm 18 24 ka himalayan glaciation was very restricted in extent generally extending

siliceous sedimentary record of the last 280 kyr in the canary basin nw africa abstract siliceous microfossils were quantified in four sedimentary sequences off northwest africa in order to disclose the productivity story of the last 280 kyr three sediment cores retrieved along an e w profile at about 29 n geob4240 geob4241 and geob4242 and one core geob4216 from the highly productive area off cape ghir in the canary island region at 29 n along all but the most offshore sequences geob4242 coincidence of high diatom accumulation rates dar and high abundances of chaetoceros spores the upwelling related species indicate glacial stages isotope stages is 4 and 2 as more productive than the interglacial intervals is5 and holocene the dar in the coastal area of the canary basin during is2 is of the same order of magnitude 10 8 valves cm 2 kyr 1 reported for cape blanc and one order of magnitude higher than reported for the iberian margin the deviation observed between the offshore higher dar at is3 and 6 and the coastal diatom records higher dar at is2 and 4 may be a reflection of local productivity generated by wind input of nutrients and advection from coastal sources the occurrence of dar spikes at the timing of some heinrich events seems to support the hypothesis of productivity maxima associated with the presence of meltwater off nw africa as previously proposed by other authors

nature and timing of quaternary glaciation in the himalayan tibetan orogen abstract much effort has been made in recent years to define the timing and extent of quaternary glaciation throughout the himalayan tibetan orogen these studies are challenging because of the logistical and political inaccessibility of the region and the inherent problems associated with the application of numerical dating techniques nevertheless the studies are providing abundant evidence for significant glacial advances throughout the last several glacial cycles and are beginning to accurately define the extent and timing of glaciation in selected regions studies are showing that himalayan tibetan glaciers in arid regions during the last glacial cycle reached their maximum extent early in the cycle and that global last glacial maximum glacier advances were significantly less extensive however along the more monsoonal influenced greater himalaya there is increasing evidence to suggest that glaciation was more extensive later in the last glacial cycle but this has yet to be fully assessed in addition the new studies are showing that throughout most himalayan tibetan regions significant glacier advances occurred during the lateglacial and early holocene with minor advances in some regions during the mid holocene the still relatively poor chronological control in the himalayan tibetan orogen however makes it difficult to construct correlations across the region and with regions elsewhere in the world this in turn makes it hard to assess the relative importance of the different climatic mechanisms that force glaciation across the himalayan tibetan orogen and to quantify paleoclimate change in this high altitude subtropical region the lateglacial and holocene glacial records however are particularly well preserved in several himalayan tibetan regions glacial successions such as these have the greatest potential to be examined in detail using newly developing numerical dating and geomorphic and sedimentologic methods to derive high resolution terrestrial records of glaciation that will help in paleoclimatic reconstruction for high altitude subtropical regions

observations on rock glaciers in the himalayas and karakoram mountains of northern pakistan and india abstract rock glaciers are abundant in the lahul and garhwal himalayas of northern india and the karakoram mountains of northern pakistan they exhibit morainic and protalus forms and are restricted altitudinally and climatically to sites above approximately 4000 m asl and regions where annual precipitation is less than 1000 mm in these areas morainic rock glaciers are large usually 1 km long 100 m wide and 15 m thick they are advancing over recent fluvial terraces and modern floodplains the morainic rock glaciers record the advance of ice cored moraines following retreat of glaciers likely since the little ice age these rock glaciers form a major component of the landscape and are important conveyors of debris down valley under the influence of gravity

variability of current temperature and bottom pressure across the west florida continental shelf winter 1981 1982 observations are analyzed from four current meter moorings deployed on the broad continental shelf in the northeastern gulf of mexico from november 29 1981 to february 8 1982 71 days consistent with recent modeling studies the shelf circulation responds within an inertial period to the alternating up and down coast synoptic scale wind forcing average response to a 0 5 dyn cm 2 alongshore wind stress as measured at the coast is 20 cm s 1 off cedar key and 40 cm s 1 in the north where the shelf narrows off cape san bias lower layer currents veer counterclockwise with depth as in a bottom ekman layer e folding scale 8 m the pressure field decays offshore e folding scale 160 km and yields a geostrophic current in good agreement with the observed alongshelf flow cross shelf and vertical variations of the tidal signals compare nicely with results from barotropic theory calculations indicate that most of the shoreward propagating tidal energy must be dissipated in depths of 20 m within 50 km of shore

influence of debris cover on terminus retreat and mass changes of chorabari glacier garhwal region central himalaya india recent studies of himalayan glacier recession indicate that there is wide variability in terminus retreat rate and mass balance in the different sectors of the mountain range primarily linked to the topography and climate of the region variable retreat rates of glacier termini and inadequate supporting field data e g mass balance ice thickness velocity etc in the himalayan glaciers make it difficult to develop a coherent picture of climate change impacts in this study the results of a detailed mapping campaign and ground based measurements of ablation rate terminus retreat and ice loss are reported for the period 2003 10 in addition background information from an old glacier map survey of india 1962 was compiled and terminus recession measurements were carried out from 1990 field photographs of chorabari glacier central himalaya our ablation stake network results suggest that the influence of debris cover is significant for chorabari glacier mass balance and terminus retreat the terminus survey finds that the glacier is retreating but at a lower rate than many other non debris covered glaciers in the region the recession and ablation data particularly in the upper ablation area at higher altitudes suggest that the ice volume loss of the glaciers is of greater magnitude than the slow terminus retreat and if the process continues the lowermost part of the glacier may reduce to a quasi stationary position while significant ice loss continues

climate change and coastal hydrographic response along the atlantic iberian margin tagus prodelta and muros ria during the last two millennia the tagus prodelta w portugal and the muros ro a nw spain are areas of high deposition rates registering high resolution palaeoclimatic records for western iberia we compare the climatic conditions of the two areas over the last two millennia based on proxies of temperature sea surface temperatures and oxygen isotopes continental input grain size iron and magnetic susceptibility and productivity inorganic and organic carbon carbon isotopes benthic foraminifera and diatoms biogeochemical changes in the tagus prodelta reflect widely recognized north atlantic climatic periods encompassing the roman period ad 0 350 the dark ages ad 400 700 the mediaeval warm period mwp ad 800 1200 and the little ice age lia ad 1300 1750 the atmospheric north atlantic oscillation nao drives the tagus prodelta multidecadal long term variability in precipitation river input during cold periods negative nao and marine upwelling during warmer periods positive nao a scheme that is reversed in the galician region the muros ro a shows only local hydrodynamics until ad 1150 including a suboxic event in the inner ro a around ad 500 700 since ad 1150 atlantic warm upwelled waters have ventilated the outer ro a but only reach the inner ro a at ad 1750 the twentieth century records are also interpreted as a reflex of the inverse nao mode in both areas resulting in amplification of the lia biogeochemical water conditions centennial scale solar activity appears to be another important forcing mechanism or the only one if solar activity drives the nao and bond cycles behind changes in the hydrography of the tagus prodelta and primary production bottom ventilation and organic carbon degradation in the muros ro a

summertime coastal currents in the northeastern gulf of mexico abstract observations of currents and temperature at a mooring on the 18 m isobath 30 km south of the florida shoreline are discussed for the 31 day period 15 august 15 september 1978 tidal currents having average amplitudes of 10 cm s 1 account for 85 of the observed kinetic energy low frequency currents with maximum speeds of 10 cm s 1 appear to be at least partly driven by local wind stress events of magnitude 0 2 dyn cm 2 frictional effects give rise to a veering with depth in the ekman sense of both the low frequency flow and the energetic counterclockwise rotating twice daily tidal currents propagation of both the tidal signal and low frequency coastal sea level fluctuations amplitudes 5 cm is westward through the study area

mid depth oxygen drawdown during heinrich events evidence from benthic foraminiferal community structure trace fossil tiering and benthic δ13c at the portuguese margin abstract the distribution of trace fossils and benthic foraminiferal assemblages in two sediment cores from 2160 m water depth at the northern and 1100 m at the southern portuguese continental margin was used to reconstruct the bottom water oxygenation during the last 40 ka emphasis was given to the heinrich events during which enhanced meltwater flux associated with the iceberg surges reduced or even halted deep water formation in the north atlantic condensed trace fossil tiering structures and high proportions of low oxygen tolerant benthic foraminifera suggest a major drawdown of bottom water oxygenation during heinrich events using the benthic foraminiferal oxygenation index bfoi of kaiho 1991 1994 that links benthic foraminiferal communities to ambient bottom water oxygenation we extracted apparent oxygen concentrations from benthic assemblages bfoi values suggest low oxic conditions during heinrich events 1 and 4 with mean oxygen levels of 2 6 to 2 8 ml l 1 and high oxic conditions with 4 1 ml l 1 during heinrich event 2 at the shallower site high proportions of low oxygen tolerant foraminiferal species and bfoi minima are recorded a few centimetres below the maximum concentrations of ice rafted debris indicating that the original microhabitat depth of dysoxic species is preserved beneath the heinrich layers even though bioturbation continued during the events trace fossil tiering calibrated with the redox boundary in low oxic environments and dysoxic ichnotaxa commonly associated with black shales indicate oxygen levels lower than those implied by the bfoi oxygenation estimates derived from trace fossil tiering denote low oxic conditions during h1 13 3 ka with oxygen concentrations slightly above 1 ml l 1 and dysoxic conditions during h2 20 6 ka h3 27 ka and h4 33 5 ka with oxygen concentrations between 0 1 and 1 ml l 1 during the younger dryas bottom waters likely were low oxic negative excursions of benthic carbon isotope values provide independent control on the oxygen drawdown during heinrich events considering a bottom water oxygenation of 6 1 to 6 5 ml l 1 during the last glacial the benthic 13 c minima reveal an oxygen depletion to values between 3 4 and 5 0 ml l 1 during h1 through h4 at the shallower core site differences between estimates from benthic 13 c bfoi and trace fossil tiering suggest that benthic foraminiferal communities are rather robust to oxygen depletion if the level does not fall below 3 ml l 1 whereas burrowing organisms react sensitively to depth variations of the redox boundary in near surface sediments due to even small changes of bottom water oxygenation

rates and magnitudes of paraglacial fan formation in the garhwal himalaya implications for landscape evolution the development of paraglacial fans studied in the upper bhagirathi valley garhwal himalaya northern india relates to the retreat of the gangotri glacier over the last 200 years these fans demonstrate the speed by which mass movement and fluvial processes may lead to the modification and readjustment of the himalayan landscapes during deglaciation the paraglacial fans in this region grew within approximately 100 years of deglaciation and there after were modified by small debris flows and entrenched by fluvial incision on the basis of the preservation of moraines which were deposited during the last glacial total resedimentation of glacial sediments by mass movement and fluvial processes is estimated to occur over approximately 100 000 years in this region a knowledge of the magnitude and frequency of development of paraglacial fans is essential for hazard mitigation and management in himalayan environments where glaciers are presently retreating and are likely to retreat in the near future if global warming occurs

probability of moraine survival in a succession of glacial advances emplacement of glacial moraines normally results in obliteration of any older moraines deposited by less extensive glacial advances a process we call obliterative overlap a probability analysis of the likely impact of obliterative overlap on the completeness of the glacial record assumes that moraines were deposited at various distances from their glacial source areas randomly over time assuming randomness and obliterative overlap after 10 glacial episodes the most likely number of surviving moraines is only three the record of the pleistocene is in agreement with the probability analysis the 10 glaciations during the past 0 9 m y inferred from the deep sea record resulted in moraine sequences in which only two or three different aged moraine belts can generally be distinguished

late quaternary glacial advances in the tons river valley garhwal himalaya india and regional synchronicity the glacial history of the tons river valley reveals significant changes in the glacier extent during the late quaternary driven by regional and global climatic changes the successions of moraines in glaciated valley of the upper tons river garhwal himalaya provide evidence of at least five glacial advances during the late quaternary period this study discusses about the synchronicity of himalayan glaciers and comparison between results of optically stimulated luminescence osl and cosmogenic radio nuclide crn 10be dates the osl dates of moraine sediments deposited by glacier in the upper tons valley show parallelism with the ages deduced from the crn of 10be by scherler et al in the same area the five episodes of glacier advances are dated at 20 3 16 2 8 1 2 6 0 7 and 3 0 6 kyr between marine isotope stages miss i and ii two of the more extensive phases of glaciation were during the early and later parts of mis ii which attributed to the lower temperature and enhanced the mid

diatom taphocoenoses in the coastal upwelling area off south west africa abstract the diatom floral composition of 124 sediment samples from the south east atlantic records the influence of coastal upwelling on sediment composition off south west africa inner shelf samples between 19 and 24 s are rich in diatom valves and the patterns of diatom species distribution in these samples are related to the coastal upwelling process comparison with recent phytoplankton data shows that the sediment assemblages preserve many of the important species of the diatom biocoenoses including chaetoceros resting spores delphineis karstenii thalassiosira eccentrica and thalassionema nitzschioides delphineis karstenii a pioneer species in enriched coastal water occurs nearshore and chaetoreros resting spores are widespread with highest relative abundance values in some more offshore samples the abundance of the thalassiosira eccentrica group and of thalassionema nitzschioides in sediment samples in and near walvis bay reflects the recurrence of intense upwelling off this part of the coast an abundance of large centric species has been reported in hydrological conditions characteristic of newly upwelled waters and correspondingly actinocyclus octonarius and some large coscinodiscus species occur in the sediments in nearshore patches or belts

a 220 000 year climatic record for the east equatorial atlantic ocean and equatorial africa evidence from diatoms and opal phytoliths in the zaire congo deep sea fan accumulation rates of microfossil associations are independent of each other and in addition to percentages give indispensable information about the significance of micropaleontological data marine diatoms reveal that coastal upwelling in the zaire fan region was strong during glacial stages and weaker during interglacial stages oceanic upwelling was intense in stages 6 and 2 and at the stage 5d 5c transition but not in stage 4 the benguela current did not penetrate into the gulf of guinea during the last 220 000 years the phfd index based on the contribution of freshwater diatoms and phytoliths is a measure of aridity in equatorial africa the production in the low salinity river plume was high in the most humid periods on land and low when the continent was arid on the long term nutrient supply of the zaire river to the ocean was probably larger in humid than in arid periods periods of strong seasonal variability in river fluxes and coastal upwelling coincide with arid intervals except in the very humid interval with strong seasonal contrasts 35 000 20 000 years b p

palaeoproductivity changes and upwelling variability in the galicia mud patch during the last 5000 years geochemical and microfloral evidence theholocenepalaeoclimatichistoryofthegaliciancontinentalshelfhasbeeninvestigatedthrough theanalysesofdiatomremains othersiliceouscompounds biogenicsilica bsi andmetalscontentinamul tiproxyapproachtoagravitycorerecoveredfromthegaliciamudpatch nwiberianpeninsula coveringthe last 5000 years downcore changes in diatom assemblages composition and abundance reflect changes in diatomproductionrelatedtolong short termvariationsinclimate regionaloceanography upwellingstrength and river influx off the coast of nw spain and portugal palaeoclimatic variability was related to the relative strengths and position of the azores high and iceland low pressure cells metals and microflora fluctuations are interpreted as changes in the riverine influence and upwelling intensity paced by oceanographic atmos pheric and climatic changes lack of diatoms between 4700 3300 and 1800 1200 cal yr bp could be linked to early diagenetic processes taking place in the sediment after burial biogenic barium baexcess metals and diatomassemblages showageneralincreaseofmarineproductivityforthelast1200cal yrbp between800 and500cal yrbphighproductionofthemicrofloraistriggeredbyinfluxofriver derivednutrientsundercon ditionsofswwindsandstormsresultingfromanaonegative likephase thebiosiliceousandgeochemical signatures of sediments from the last 500 cal yr bp indicate conditions of enhanced upwelling and increased

late holocene climate response and glacial fluctuations revealed by the sediment record of the monsoon dominated chorabari lake central himalaya we studied a periglacial lake situated in the monsoon dominated central himalaya where an interplay of monsoonal precipitation and glacial fluctuations during the late holocene is well preserved a

loessic silt deposits in the western himalayas their sedimentology genesis and age abstract loess is abundant in the foreland basins of the himalayas however it is poorly developed within the intermontane basins of the western himalayas and karaloram selected sections were studied from the swat himalaya and the karakoram mountains fieldwork and sedimentological analysis including grain size mineralogy and microfabric showed that the loessic sediments have been reworked and some have undergone weak pedogeneses these silts are not true loess rather a loessic colluvium thermoluminescence tl dates from the loessic sediments in sections from the swat valley provided younger ages than earlier workers had suggested this is consistent with reworking of the loess in these areas it is concluded that care must be taken when using loessic silts for tl in similar mountainous terranes

at the land s end marine resources and the importance of fluctuations in the coastline in the prehistoric hunter gatherer economy of portugal abstract this paper focuses on the importance of aquatic resources in economy and subsistence strategies during the middle and upper palaeolithic of portugal modern theoretical biases in archaeology have led to a marginalization of marine resources and a dismissal of their use by palaeolithic hunter gatherers geological and archaeological data show that changes in the position of the coastline had a direct impact on the visibility of marine resources in the archaeological record marine regressions and transgressions have significantly altered the record of pleistocene coastal settlement using recent studies on changes in upwelling intensity during the last glacial we offer a new perspective on palaeolithic hunter gatherer economy that emphasizes the importance of the coast as a focus of subsistence and settlement

quaternary glacial history of nw garhwal central himalayas a first account of the quaternary glacial history is presented for northwest garhwal central himalaya on the basis of sediments and landforms one glacial stage has been recognised this is called the bhagirathi glacial stage when extensive valley glaciers advanced down the bhagirathi valley to jhala 40 5 km from the snout of gangotri glacier the ela depression during this stage was ca 640 m the bhagirathi glacial stage is constrained by optically stimulated luminescence dates of ca 63 ka and 5 ka bp and this glaciation is considered equivalent to the last glaciation elsewhere in the world the maximum extent of ice occurred ca 63 ka bp this however does not correlate with the last glacial maximum for the northern hemisphere ice sheets 20 18 ka bp a series of sharp crested moraines are present between 1 to 3 km beyond the snouts of most of the present glaciers these moraines formed during the mid holocene 5 ka bp termed here the shivling glacial advance small moraines are inset into these and are dated at about 200 to 300 bp the bhujbas glacial advance ca 300 to 200 bp and considered equivalent to the little ice age in other parts of the world ela depressions of between 40 100 m and 20 60 m occurred during the shivling and bhujbas glacial advances respectively since the bhujbas glacial advance there has been progressive retreat of glaciers initially by downwasting and retreat and then by simple retreat this retreat has accelerated during the last few decades impressive paraglacial fans are associated with deglaciation representing very rapid resedimentation during and soon after ice retreat

multiyear subinertial and seasonal eulerian current observations near the florida big bend coast abstractmultiyear in situ eulerian acoustic doppler current profiler measurements were obtained at 5 10 and 19 m depths off the big bend coast and in 19 m off the florida peninsula to the south analysis on subinertial time scales dominated by weatherband frequencies led to the following conclusions at the 19 m big bend site k tower consistent with coastally trapped wave ctw theory the along isobath flow is not proportional to the local along isobath wind stress but rather to the alongshore wind stress to the south along the west florida shelf wfs at the southern 19 m site consistent with previous work the along isobath flow is driven by but is weakened by an alongshore pressure gradient brake via ctw dynamics this brake is due to the abrupt end of the wfs at the florida keys by contrast along isobath flow at the shallow 5 m site is driven by the local wind in a constant stress turbulent frictional layer because of the freshwater flux near the coast density usually increases s

the little ice age in the himalaya a review of glacier advance driven by northern hemisphere temperature change northern hemisphere cooling between 1400 and 1900 in the common era ce resulted in the expansion of glaciers during a period known as the little ice age lia early investigation of recent advances of himalayan glaciers assumed that these events were synchronous with lia advances identified in europe based on the appearance and position of moraines and without numerical age control however applications of quaternary dating techniques such as terrestrial cosmogenic nuclide dating have allowed researchers to determine numerical ages for these young moraines and clarify when glacial maxima occurred this paper reviews geochronological evidence for the last advance of glaciers in the himalaya the 66 ages younger than 2000 years 0 2000 ce calculated from 138 samples collected from glacial landforms demonstrate that peak moraine building occurred between 1300 and 1600 ce slightly earlier than the coldest period of northern hemisphere air temperatures the timing of lia advances varied spatially lik

mid to late holocene climate response from the triloknath palaeolake lahaul himalaya based on multiproxy data abstract a 2 13 m thick palaeolake sequence deposited between the right lateral moraine and the valley wall of triloknath glacier has been studied at high resolution to understand the past climatic changes in lahaul himalaya the osl and ams 14c chronology suggests that the lake building activity was initiated post cooling phase since 6484 cal ybp the combination of sedimentological geochemical and environmental magnetic parameters helped to infer five first order climatic zones the influx of magnetic minerals along with a notable increase in antiferromagnetic mineralogy appearance of hematite and higher chemical index of alteration cia values during 5925 cal ybp to 5676 cal ybp suggests warm and wet conditions owing to enhanced indian summer monsoon ism precipitation corresponding to the mid holocene warming further reduction in the magnetic mineral concentration with few peaks of antiferromagnetic mineralogy and higher cia values suggests warmer episodes within an overall cold climate and the finer ferrimagnetic grain size suggests intermittent low energy and ponding conditions during 3904 cal ybp to 2365 cal ybp this was followed by fluctuating cold arid conditions in response to reduced ism precipitation during 2365 cal ybp and 1758 cal ybp further between 1758 cal ybp to the present episodic warming pedogenic enhancement and increased monsoon precipitation have been recorded a major warm episode medieval warm period as depicted from enhanced antiferromagnetic mineralogy and higher cia values has been recorded between 742 cal yrs bp and 593 cal ybp the sudden drop in the magnetic mineral concentration as well as the cia value around 300 cal ybp 1650 ce is likely because of colder conditions prevailing during the little ice age lia the study illustrates high sensitivity of the lake sediment sequence to witness the climatic episodes experienced in the glaciated regime of the triloknath glacier

bottom currents and fluviomarine sedimentation on the mississippi prodelta shelf february may 1984 surface winds and currents temperature and water transparency at heights of 1 and 5 m above bottom in 60 m of water were measured during the period from february 23 to may 2 1984 at a site on the mississippi delta the objective was to better understand the influence of near bottom flow on the character of sedimentation on the prodelta shelf data analysis showed currents to be parabathic with periodicities of 5 and 20 days flow showed a strong east west polarization with net flow 0 4 cm s onshore at the lower level and 0 5 cm s offshore at the upper with easterly flow water temperature declined indicating upwelling and current veering between 1 and 5 m was 12 15 in the sense of a bottom ekman layer with westerly flow water temperature increased indicating downwelling and veering was of the same magnitude but in the sense of a surface ekman layer flow and suspended sediment data suggest that during the period of study deposition of sediment from the turbid plume of the mississippi river was continuous calculations of sediment settling velocities indicate that the surface plume of turbid river water transported in suspension particles with hydraulic equivalent diameters ranging from clay to fine sand size computations of friction velocity indicate that here on the outer prodelta shelf the observed bottom currents were not competent to erode bottom sediment short period 1 3 days fluctuations in mean bottom turbidity may be due to variations in the supply of suspended sediment as the surface plume moves laterally in response to the wind and in at least some cases to a vertical redistribution of sediment in suspension by currents too weak to initiate resuspension these fluctuations are probably responsible for the silty and sand laminae generally a millimeter thick or less observed in bottom cores the thickness of the annual flood deposit may approach 1 m in the vicinity of the plume

diatom record of late quaternary climatic change in the eastern equatorial atlantic and tropical africa over the last 160 000 years diatom productivity in the equatorial atlantic has been high during glacial stages 2 4 and 6 and moderate during parts of substages 5b and 5d approximately 96 000 and 117 000 years b p productivity of diatoms is particularly low in substage 5e and in the middle of stage 1 higher productivity implies more vigorous trade winds during glacial intervals leading to stronger upwelling and enhanced lateral advection of surface waters the influence of the benguela current near the equator was strongest during stage 2 a separate regime of coastal upwelling may have existed in the gulf of guinea at this time upwelling and advection may not always respond to the same forcing as sea surface temperature results support the hypothesis that ethmodiscus rex oozes result from high diatom productivity runoff from the zaire and niger rivers was highest at the stage 2 1 transition and just prior to the stage 6 5 transition due to intensification of the african monsoon several other times of increased runoff are indicated periods of increased surface water circulation in the eastern equatorial atlantic appear to correspond to times of aridity in tropical africa conversely intervals of decreased circulation in the eastern equatorial atlantic coincide with times of humidity in tropical africa precessional forcing of continental climate is suggested however precessional forcing of surface ocean circulation can be neither confirmed nor refuted based on the records examined here influx of antarctic bottom water to the eastern equatorial atlantic has been insignificant throughout the last 160 000 years

relative dating of quaternary moraines rongbuk valley mount everest tibet implications for an ice sheet on the tibetan plateau abstract relative dating studies applied to high altitude moraines 5000 5500 m in the rongbuk valley on the northern flank of mt everest reveal strong contrasts in the weathering characteristics of the boulders exposed along moraine crests these differences serve to define three intervals of major pleistocene glaciation that on the basis of the degree of weathering are interpreted to extend back to at least the penultimate glaciation and probably encompass at least one still older glaciation either interpretation indicates that some of these moraines are considerably older than their previously assigned ages the magnitude of equilibrium line lowering during neoglacial and late pleistocene times is calculated to be ca 50 100 and 350 450 m respectively the data described here are incompatible with the recently proposed model kuhle 1987 for large scale ice sheet development on the tibetan plateau the reconstructed equilibrium line lowering in the everest region is only 30 of that cited in the ice sheet model moreover the flow patterns and geometry of the former rongbuk glaciers are in opposition to those proposed by the model based on the data from the everest region it appears that valley glaciation rather than ice sheet growth characterized the southern margin of the tibetan plateau during the middle and late pleistocene glaciations