the mineralogy of ordinary chondrites and implications for asteroid spectrophotometry abstract the normative mineralogies of 94 ordinary chondrites have been calculated from high quality bulk chemical analyses relative proportions of olivine orthopyroxene and metal are more variable within the h l and ll classes than has been recognized previously mineralogy within each chondrite class varies systematically with oxidation state these data have important implications for the design of reflectance spectroscopy studies that match asteroid and meteorite spectral features and for quantitative spectral interpretations of asteroids they also provide a tool with which to predict mineral abundances in unsampled asteroids that formed under different redox conditions

historical ecology in beringia the south land bridge coast at st paul island a 14 m core of lake sediments from st paul island yields a long environmental history of the south coast of the bering land bridge tritium assay demonstrates that sands in the bottom 8 m of deposit are injected with modern water suggesting that a radiocarbon anomaly is the result of modern carbon introduced in groundwater the remaining radiocarbon chronology coupled with a time stratigraphic pollen zone boundary suggests that the record penetrates to the mid wisconsin interstadial pollen percentage data picea pollen influx and pollen species lists allow reconstruction of the land bridge vegetation which was tundra without shrubs or trees with bare ground and comparable to bering land bridge tundras found further north there was no coastal mild or wet strip plant associations comparable to those of the modern aleutians or pribilofs probably did not exist along the land bridge coast and the region was probably not suitable for breeding by fur seals and other marine mammals a cold dry continental air mass system reached to the coast itself the south land bridge coast did not offer an environment to aboriginal human populations that was significantly milder than that of the land bridge plains to the north at about 11 000 yr b p the wisconsin dry climate was replaced by a regimen comparable to that at the modern tree line of the interior and this climate in turn was replaced with the modern system at about 9500 yr b p climatic change was independent of fluctuating sea level

clay minerals as indicators of sources of terrigenous sediments their transportation and deposition bering basin russian alaskan arctic abstract cluster analysis of clay mineral abundances in surficial sediments from 52 stations revealed the presence of four station cluster groups within the bering basin and contiguous eastern aleutian trench forearc these results can be explained using two end members of terrigenous clay mineral sources and their admixtures the first end member cluster group i consists of the highest average concentration of illite 48 and chlorite plus kaolinite 40 and lowest of expandable minerals 12 in contrast the second end member cluster group iv has the highest concentration of expandable minerals 43 and lowest concentrations of illite 30 and chlorite plus kaolinite 27 the group i assemblages come from two regions the eastern aleutian trench forearc and the northwestern margin of the bering basin off koryak mountains east siberia clays in the former region are derived primarily from the meta sedimentary and meta volcanic rocks of the chugach mountains with infiltrations from alaska peninsula and are transported from the southeastern kodiak shelf of the gulf of alaska to the trench forearc by the alaska current alaskan stream similar clays are derived from the koryak mountains group iv clays located within the komandorsky and bowers basins and unmak plateau originated from the mio pliocene andesites and basalts of the eastern kamchatka peninsula and aleutian islands respectively it is postulated that group ii clays in the southcentral aleutian basin and bowers ridge basin area and group iii clays in the northern aleutian basin are mixtures obtained primarily from terrigenous sources of group i and iv the distribution patterns and boundaries of the cluster groups reflect the dispersal pathways of clays from the primary sources and the extent of their mixing by regional and local surface currents and mesoscale gyres eddies presumably the minor infiltration of anadyr river clays into group iii is a result of clay transport by episodic turbidity currents most of the clays derived from the alaska mainland and russia proper do not reach the bering basin as these clays are trapped within the bering sea shelf

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

the bering sea and paleoceanography abstract this paper serves as an introduction to the bering sea preceding the 14 contributed papers contained in this volume several parts of the paper are allocated for current reviews of the bering sea included in the review topics are geomorphology surface water circulation and the importance of the formation of intermediate waters representative results of previous paleoceanographic studies are also presented in particular focusing on spatial and temporal distributions of biosiliceous microfossils as well as isotopic analyses of carbon and nitrogen concerning changes in productivity and nutrients motivations behind the scientific expeditions conducted which resulted in the many papers included here are briefly discussed in order to illustrate the recent trend in paleoceanography in the bering sea and the adjacent regions brief summaries or highlights of each of the contributed papers are given in order to provide an overview of the volume

diatom evidence on wisconsin and holocene events in the bering sea abstract previous work on surface modern sediments has defined diatom species which appear to be good indicators of various oceanographic ecologic conditions in the north pacific ocean and marginal seas three long cores from the eastern and northern sides of the aleutian basin show changes in species assemblage which can be interpreted in terms of changes in the ocean environment during the last glaciation wisconsin and the holocene the early and late wisconsin maxima were times of prolonged annual sea ice cover and a short cool period of phytoplankton productivity during the ice free season the middle wisconsin interstade at least in the southern bering sea had greater seasonal contrast than today with some winter sea ice cover an intensified temperature minimum and high spring productivity variations in clastic and reworked fossil material imply varying degrees of transport to the basin by alaskan rivers the results of jouse from the central bering sea generally correspond with those presented here although there are problems with direct comparison

clay mineral assemblages from late quaternary deposits on vancouver island southwestern british columbia canada resume dans le secteur de l ile de vancouver les formations de dashwood drift cowichan head quadra sand et vashon drift se sont deposees au cours des periodes glaciaires et non glaciaires du pleistocene terminal elles presentent des variations importantes du cortege argileux dont certaines sont relatives aux fluctuations climatiques les periodes glaciaires sont caracterisees par des chlorites riches en fer des illites toutes deux bien cristallisees et des smectites avec une morphologie rappelant celle de smectites developpees a partir de roches volcaniques la mineralogie des argiles des depots non glaciaires est plus complexe elle est marquee en outre par la presence de vermiculite kaolinite halloysite et de mineraux interstratifies irreguliers ces assemblages sont mediocrement preserves et montrent une degre d alteration pedologique plus eleve par rapport aux assemblages glaciaires les variations importantes enregistrees dans les depots nonglaciaires sont egalement dues a des facteurs secondaires tels la sedimentation differentielle les sources sedimentaires variantes et des possibles modification diagenetiques toutefois ces facteurs ne semblent pas obliterer de maniere significative les empreintes climatiques des mineraux argileux cette etude permet egalement de differencier des sediments remanies sous regime glaciaire de determiner les relations entre les unites lithologiques d une meme coupe et d etablir l origine des mineraux argileux rencontres

a climate related oxidizing event in deep sea sediment from the bering sea abstract many cores from the deep basins of the bering sea have a thin oxidized zone within otherwise reduced sediment this oxidized zone began to form about 6000 yr ago and represents an interval of about 3200 yr mineralogically the oxidized and reduced sediments are similar but chemically they differ concentrations of fe and c are lower and concentrations of mn ba co mo and ni are higher in the oxidized than in the reduced sediment mn is enriched about 10 fold in the oxidized zone relative to its concentration in the reduced sediment mo about threefold and ba co and ni about twofold these data suggest that the oxidized zone developed diagenetically as the result of the balance between the flux of organic matter and the available dissolved oxygen in bottom and interstitial waters we propose that the bering sea was substantially ice covered when global glacial conditions prevailed during the transition to global interglacial conditions seasonal meltwater from thawing sea ice formed a lens of fresh water that decreased organic productivity during the winter seasons however sea ice reformed and caused downwelling of dense oxygen rich waters to recharge bottom waters the combination of lower organic productivity and more oxygen rich bottom water allowed oxidized sediment to accumulate once full interglacial conditions were established the volume of sea ice produced was insufficient to affect either productivity or the supply of dissolved oxygen and so bottom conditions again became reducing similar events probably occurred during the onset of global glacial conditions and similar oxidized layers probably formed at these times such oxidized zones are highly unstable however in a reducing environment and once buried beyond the influence of bacterial and infaunal activities are depleted of their available oxygen and converted to reduced sediment

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

evidence for restricted ice extent during the last glacial maximum in the koryak mountains of chukotka far eastern russia field evidence in the koryak mountains lake mainitz region of far eastern russia supports three pleistocene glacial advances the early wisconsinan and pre wisconsinan glaciations are represented by broad lobate moraines extending as much as 30 km north of the koryak mountains field evidence demonstrates that the terminal lateral and medial moraines as well as meltwater channels dead ice topography kettles and outwash plains mark the extent of ice during the last glacial maximum lgm during which glaciers reached no more than 20 km beyond their present limits those emanating from the southern koryak mountains may have reached the bering sea numerical and relative dating techniques support these results and test the theoretical models of the lgm in western beringia erratics on moraines and glaciofluvial terraces common to all valleys at 13 13 8 m above river level yield 36 cl exposure ages ranging from 10 08 to 25 78 ka the koryak mountains lake mainitz record of glaciation is spatially and temporally consistent with the glaciation pattern across central beringia found in other terrestrial and marine records glacier growth in the koryak mountains was sustained by possible increased summer sea surface temperatures and precipitation in the northwest pacific region evidence from the northern koryak mountains lat 64 n long 177 e indicates that the extent of ice in western beringia was limited to mountain and valley glaciers during the lgm this fieldbased research contradicts m g grosswald s theoretical beringian ice sheet hypothesis

changes in redox conditions in deep sea sediments of the subarctic north pacific ocean possible evidence for the presence of north pacific deep water cores of upper quaternary and holocene sediment from the subarctic north pacific north of about 48 n contain one or more layers of oxidized brown sediment interbedded within predominantly reduced green sediment the brown layers are enriched in several trace elements especially mn mo ni and co relative to the green layers where multiple oxidized layers are present the intensity of the brown coloration and the magnitude of trace element enrichment often decrease with depth suggesting that the oxidized layers are unstable and are being chemically reduced at depth the oxidized layers represent a change in redox conditions between the north pacific red clay province and the subarctic biosiliceous green clay province the redox change may have been caused by an increase in supply of dissolved oxygen to bottom waters during glacial interglacial transitions as the result of the periodic formation of a seasonal bottom water mass in the northeastern pacific ocean

latitudinal control of astronomical forcing parameters on the high resolution clay mineral distribution in the 45 60 n range in the north atlantic ocean during the past 300 000 years the clay mineralogy of four 5 5 to 13 5 m long cores sampled between 45 and 60 n in the north atlantic ocean has been investigated at high latitudes within a well constrained chronostratigraphic scale cross correlation spectral analyses have been performed on both clay mineral and 18o planktonic records detrital clay minerals display strong signals which are coherent with the 18o record within the three main milankovitch frequency bands eccentricity obliquity and precession the climatic control on clay mineral sedimentation largely depends on the latitudinal location of the sediment cores the 100 000 year signal occurs as a uniformly acting factor whereas the 41 000 year signal dominates clay sedimentation at high latitudes and the 23 000 year signal dominates at midlatitudes we suggest that the latitudinal variations of the orbital forcing on the detrital clay mineral distribution in the north atlantic ocean not only result from climatic control of the intensity of physical and chemical weathering but also from latitudinal control on the detrital clay supply linked to influences of the high latitude wind driven and midlatitude ocean driven transportation processes respectively

sea ice cover sea surface salinity and halo thermocline structure of the northwest north atlantic modern versus full glacial conditions abstract seasonal sea ice develops along the eastern continental margins in the northern north atlantic where freshwater and or meltwater outflow are responsible for relatively low salinity in surface waters and very pronounced water mass stratification sea ice constitutes a major parameter in the marine ecosystem since the duration and extent of its seasonal spreading constrain the plankton distribution and the related microfossil assemblages on the sea floor organic walled dinoflagellate cysts that are highly resistant to dissolution were recovered from surface sediments of the northern north atlantic and used to develop transfer functions best analogue method for the reconstruction of the seasonal spreading and duration of sea ice cover in addition to salinity and temperature of the warmest month of the year application of the best analogue approach to cores from the labrador sea reveals large variations in sea ice cover and sea surface conditions throughout the last glacial stage and during the early holocene isotopic analyses in epipelagic and mesopelagic planktonic foraminifers also suggest important changes in salinity and temperature gradients between the surface and sub surface water masses specific study of the last glacial maximum lgm time slice 16 20 ka on a 14 c time scale in the northwestern north atlantic shows much more extensive sea ice than at present with perennial sea ice lying along the continental margins of eastern canada seasonal spreading of the cover of sea ice offshore was accompanied by large seasonal contrasts in temperature with very cold winters but relatively warm summers a pattern linked to strong stratification between a buoyant low saline surface layer having a low thermal inertia and the underlying intermediate oceanic waters

wisconsin holocene paleoenvironment of the bering sea evidence from diatoms pollen oxygen isotopes and clay minerals abstract a core from the southeastern bering sea contains a depositional record of the wisconsin glacial interval and the holocene four lithologic units show distinctive changes in diatom species palynomorphs oxygen isotopes in diatom silica and clay minerals unit 4 the oldest probably represents the glacial advance of the early wisconsin and records extensive sea ice cover and a soggy herbaceous tundra on the exposed continental shelf unit 3 represents the stades and interstades of the middle wisconsin including an early period of high seasonal variability and a later period with expansion of winter sea ice in the basin and of tundra onshore unit 2 represents the late wisconsin glacial maximum and subsequent deglaciation with a tundra covered shelf sea ice cover increased to a maximum during which the surface waters were probably covered by sea ice throughout the year subsequent to the sea ice maximum the isotope ratios record a major meltwater event unit 1 represents the holocene with expansion of shrub tundra or scrub forest in the coastal upland and waters of increased temperature and salinity in the bering sea

late quaternary sea level change in southern beringia postglacial emergence of the western alaska peninsula abstract postglacial sea level trends have varied dramatically across the bering platform because of differences in coastal and shelf geologic settings emergent shorelines and basal peats along the western alaska peninsula indicate that relative sea level has fallen since regional deglaciation occurred ca 13 000 cal yr bp age elevation determinations on four shorelines 25 m 10 ka 16 m 9 6 6 ka 6 m 2 1 ka and 2 3 m 1 8 0 6 ka in the vicinity of cold and morzhovoi bays provide an estimate of the pace and timing of of sea level change since the last glacial maximum lgm 22 17 ka isostatic recovery and shoreline regression following the disintegration of continental and alpine ice has been interrupted by transgressive conditions at least twice since deglaciation changes in the balance between eustatic sea level rise and isostatic uplift resulted in the reactivation of marine scarps during the early to middle holocene but terrace cutting and a gap in the archaeological record about 2 1 ka suggest that sudden tectonic displacements also influence the record reconstructions of coastal paleogeography constrain the timing and distribution of regional archaeological settlement periods of shoreline erosion during stillstands or transgressions and the episodic reorganization of intertidal environments that accompanies tectonic displacements have conditioned site preservation potential and long term adaptive strategies

orbital and millennium scale environmental changes in the southern bering sea during the last glacial holocene geochemical and paleontological evidence the d 18 o benthic foraminiferal curve and ams 14 c radiocarbon data provide a representative age model for a southern bering sea sediment core gc 11 downcore profiles of d 18 oo fn pachyderma s and u auberiana carbonate and organic carbon contents species changes in the planktonic foraminifera assemblages and some diatom species show orbital mis 1 2 and 3 and millennium scale variability influenced by the alaska current flowing into the studied region three warmer episodes in the southern bering sea environment were assumed to be synchronous with do interstadials 8 12 and 14 in gisp 2 chronology during mis 3 more severe climate and environmental conditions in the southern bering sea during mis 2 occurred synchronously with the lgm within a 17 19 ka time span two well pronounced environmental warming events productivity spikes and changes in the pore water geochemistry separated by younger dryas cooling were observed at the base of mis 1 coeval with mwp 1a and 1b regional glacial primary productivity based on the calculation of the organic carbon mar similar to that found in the far northwestern pacific exceeded the late holocene values under conditions close to the present day r 2005 elsevier ltd all rights reserved

sources and dispersal patterns of clay minerals in surface sediments from the continental shelf areas off alaska the three mineral suites were recognized in the gulf of alaska the glaciomarine sediments of fjords and the eastern shelf consist typically of the primary phyllosilicates micas and chlorites derived locally from argillite graywacke and metavolcanics under conditions of mild chemical weathering more glycol expandable clay minerals gecm in the north gulf substantiate clay supply to that region primarily from the yakataga and poul creek formations and to a lesser extent from the copper river the northern gulf clay mineral suite is transported to central prince william sound and northeast kodiak shelf by the alaska coastal current in the western gulf clay minerals adjacent to the alaska peninsula are derived principally from the susitna river via cook inlet whereas those of the outer shelf presumably have their provenance in kodiak island and the katmai ash submarine deposit in the southeast bering sea a progressive northwestward decrease in gecm from 65 to 11 is caused by a gradually decreased sediment export from the alaska peninsula and the aleutians with a possible minor increase in illite from the kuskokwin river the yukon river is the predominant clay source for the north bering sea as signified by an abrupt increase in that area of gecm 20 to 35 and of kaolinite chlorite ratios clay mineralogy indicates that the central chukchi sea is the major repository of the yukon clays suggesting that clay mineral stratigraphic studies have implications for interpretation of the quaternary paleogeography of beringia in the beaufort sea nearshore influence of different fluvial inputs and their dispersals by currents are sharply defined the lack of a definite pattern to the distribution of clay minerals in the outer continental shelf may be due to haphazard transport of clays by ice rafting and or reworking and redistribution of sediments resulting from ice gouging of the sea substrate movement of sediment to the west in the alaskan portion of the inner shelf of beaufort sea is evident an apparent seaward increase in illite gecm ratio in the colville delta is tentatively ascribed to regeneration of degraded illite micas by k fixation in saline waters an isolated area of sediment rich in expandable clay minerals in the central beaufort shelf presumably is relict

the effect of species on lacustrine δ18odiatom and its implications for palaeoenvironmental reconstructions the oxygen isotope composition of diatom silica 18odiatom is increasingly being used to reconstruct climate from marine and lacustrine sedimentary archives although diatoms are assumed to precipitate their frustule in isotopic equilibrium with their surrounding water it is unclear whether internal processes of a given species affect the fractionation of oxygen between the water and the diatom we present 18odiatom data from two diatom size fractions 3 38 and 38 m characterized by different species in a sediment core from heart lake alaska differences in 18odiatom between the two size fractions varies from 0 to 1 2 with a mean offset of 0 01 n 20 fourier transform infrared spectroscopy confirms our samples consist of pure biogenic silica sio2 and 18odiatom trends are not driven by contamination the maximum offset is outside the range of error but the mean is within analytical error of the technique 1 06 demonstrating no discernible species dependent fractionation in 18odiatom we conclude that lacustrine 18odiatom measurements offer a reliable and valuable method for reconstructing 18owater considering the presence of small offsets in our two records we advise interpreting shifts in 18odiatom only where the magnitude of change is greater than the combined analytical error

late pleistocene glaciation of the southwestern ahklun mountains alaska glacial deposits in the southwestern ahklun mountains southwestern alaska record two major glacier advances during the late pleistocene the arolik lake and klak creek glaciations took place during the early and late wisconsin respectively during the arolik lake glaciation outlet glaciers emanated from an ice cap centered over the central portion of the ahklun mountains and expanded beyond the present coast during the klak creek glaciation ice cap outlet glaciers terminated 60 km upvalley from arolik lake moraines the area also supported numerous alpine glaciers that expanded from small massifs during both episodes of glaciation these alpine glaciers apparently reached their maximum positions sometime after the retreat of the ice cap outlet glaciers equilibrium line altitudes for reconstructed alpine glaciers of the klak creek glaciation average 390 6 100 m elevation in the western ahklun mountains which is at most 500 m and possibly only 200 m below the estimated modern equilibrium line altitude the maximum late pleistocene advance in the southwestern ahklun mountains occurred during the early wisconsin similar to advances elsewhere in western alaska but in contrast to the isotopic signal in the deep sea record of global ice volume the restricted extent of klak creek glaciers might reflect the increased distance to the bering sea resulting from eustatic sea level regression and decreased evaporation resulting from lower s ea surface t emperatures a nd i ncreased s ea ice extent 2000 university of washington

land sea linkage of holocene paleoclimate on the southern bering continental shelf detailed diatom records within surface and core sediments from the southern bering continental shelf sbcs reveal that the holocene evolution of sea ice distribution is associated with low pressure patterns holocene sea ice distribution over the sbcs was mainly controlled by the location of the aleutian low the corresponding paleoceanographic and paleoclimate conditions can be divided into three stages 1 the early holocene before 7000 cal yr bp was characterized by extensive sea ice distribution under two low pressure cells which covered the western bering sea and the gulf of alaska respectively 2 between 3000 and 7000 cal yr bp the low pressure system over the gulf of alaska became weak causing total sea ice mass over the sbcs to retreat 3 in the past 3000 years prevailing southwesterly winds over the sbcs due to the developing aleutian low have reduced further sea ice cover on the sbcs these paleoclimatic changes were probably a response to enso variation the timings of water mass exchanges on the sbcs coincided with sea level change along the alaskan peninsula as a result subsequent morphologic alterations have also influenced the paleoceanographic condition of the sbcs the effect of the surface coastal water and bottom marine water on the sbcs intensified about 6000 cal yr bp when sea level increased

mine water hydrogeology and geochemistry this book is a collection of keynote reviews and detailed case studies covering the principal areas of active research and state of the art industrial practice in the field of mine water management it addresses both issues of water quantity such as the impact of iongwall mining on the piezometry and hydraulic properties of overlying aquifers and water quality spanning an array of sites from deep coal mines to open pit base metal mines as well as a wealth of hybrid integrated studies in which hydrogeological and geochemical aspects are considered and managed together the papers presented in this book are intended for practicing geologists and engineers involved in the management of active and abandoned mine sites all over the world it is also of interest to academic geoscientists and students with interests in low temperature aqueous geochemistry and the hydrogeology of complex quasi karstic groundwater flow systems

paleoenvironments of the strait of georgia british columbia during the last deglaciation microfaunal and microfloral evidence the strait of georgia is situated between vancouver island and the western canadian mainland it was deglaciated quickly around 12 500 14c yr bp by in situ downwasting the subsequent marine invasion has left glacimarine sediments with foraminifers diatoms and dinocysts characterizing successive paleoenvironments recognizable basinwide the first paleoenvironment represents near ice conditions under the influence of the turbid meltwater plume marked by low algal productivity and few foraminifers mostly elphidium excavatum just off the plume the second environment shows a peak of nonionellina labradorica possibly resulting from an observed sudden increase in diatom numbers mostly ice dwelling forms implying a long annual sea ice cover further away cassidulina reniforme increases n labradorica decreases while other calcareous foraminifer species colonize the area there are fewer ice diatoms more marine planktonic diatoms and dinocysts become more abundant finally after 12 000 14c yr bp calcareous foraminifers are gradually replaced because of dissolution of calcium carbonate by a low diversity arenaceous assemblage at the same time abundant planktonic diatoms and dinocysts indicate warmer surface temperature the succession of fossils and environments compares well with modern horizontal off glacier successions observed in fjords of the european arctic

surface water productivity and sediment transport by bering strait throughflow in the chukchi shelf the western arctic ocean during the holocene diverse paleoceanographic proxies from three sediment cores gc12ex jpc35 and jpc30 collected from the chukchi shelf north of the bering strait elucidate the holocene paleoceanographic changes surface water productivity and sediment transport caused by the bering strait throughflow from the bering sea into the chukchi sea lithology of three sediment cores identified the same three units based on comparison and correlation to adjacent age dated cores as well as ams 14c dates of core gc12ex the boundary between unit 1 and unit 2a is dated about 8500 cal yr bp and the boundary between unit 2a and unit 2b is also dated about 4500 cal yr bp consistent down core profiles of the geochemical and isotopic properties among the three cores differentiate the paleoceanographic conditions corresponding to lithologic units based on the biogenic opal total organic carbon and 13c values unit 1 is characterized by low surface water marine productivity under relatively shallow water with weak transport of b

clay mineral evidence of nepheloid layer contributions to the heinrich layers in the northwest atlantic abstract the clay fraction of four cores drilled in the north atlantic ocean was studied at a very high resolution over the last 150 ka in order to record the mineralogical signature of heinrich events factor analysis of clay mineralogy establishes that three independent factors represent the main variations a detrital factor illite chlorite kaolinite a smectite factor and a mixed layer factor ivml illite vermiculite mixed layered clay the clay mineral fraction of core su90 38 drilled in the northeastern atlantic basin did not record any heinrich event whereas large changes in the clay mineral fraction occurred during heinrich events h1 h2 h4 and h5 in the three cores from the northwestern atlantic basin cores su90 08 su90 11 and su90 12 heinrich layers are characterized by increases in the detrital factor in cores su90 08 and su90 11 and sharp increases in the mixed layer factor in cores su90 11 and su90 12 the geographical setting of the cores the pattern of surface intermediate and deep water circulation and the main sources of clay minerals allow recognition of two major mechanisms involved in the deposition of the heinrich layers 1 an increased supply of detrital clay minerals by the icebergs and 2 a specific input of illite vermiculite mixed layer clay minerals by a nepheloid layer

increased production of cosmogenic 10be during the last glacial maximum beryllium 10 half life 1 5 myr is produced by spallation of nitrogen and oxygen atoms by cosmic rays in the upper atmosphere its production rate is proportional to the flux of cosmic rays which is modulated by solar activity and the strength of the earth s magnetic field1 2 weakening of the magnetic field allows more cosmic rays to impinge on the earth s atmosphere thereby increasing 10be production here we report that the ocean wide average accumulation rate of 10be in pacific sediments which reflects the global average production rate of 10be ref 3 was at least 25 greater during the height of the most recent ice age 24 000 16 000 yr ago than during the holocene the past 10 000 yr the higher production rate of 10be records the lower intensity of the geomagnetic field during that period and is consistent with the hypothesis developed to explain the younger 14c ages of fossil corals compared with ages obtained by u th dating4 these results also point to a more general need to consider variations in production rate in geochronological studies using other cosmogenic nuclides

glacial interglacial changes in nutrient supply and stratification in the western subarctic north pacific since the penultimate glacial maximum abstract in piston cores from the open subarctic pacific and the okhotsk sea diatom bound 15n 15ndb biogenic opal calcium carbonate and barium were measured from coretop to the previous glacial maximum mis 6 glacial intervals are generally characterized by high 15ndb 8 and low productivity whereas interglacial intervals have a lower 15ndb 5 7 6 3 and indicate high biogenic productivity these data extend the regional swath of evidence for nearly complete surface nutrient utilization during glacial maxima consistent with stronger upper water column stratification throughout the subarctic region during colder intervals an early deglacial decline in 15ndb of 2 at 17 5 ka previously observed in the bering sea is found here in the open subarctic pacific record and arguably also in the okhotsk and a case can be made that a similar decrease in 15ndb occurred in both regions at the previous deglaciation as well the early deglacial 15ndb decrease best explained by a decrease in surface nutrient utilization appears synchronous with southern hemisphere associated deglacial changes and with the heinrich 1 event in the north atlantic this 15ndb decrease may signal the initial deglacial weakening in subarctic north pacific stratification and or a deglacial increase in shallow subsurface nitrate concentration if the former it would be the north pacific analogue to the increase in vertical exchange inferred for the southern ocean at the time of heinrich event 1 in either case the lack of any clear change in paleoproductivity proxies during this interval would seem to require an early deglacial decrease in the iron to nitrate ratio of subsurface nutrient supply or the predominance of light limitation of phytoplankton growth during the deglaciation prior to bolling allerod warming

clay mineral dispersal patterns in the north bering and chukchi seas abstract characterization of the clay mineralogic constituents of the m e s d equivalent spherical diameter size fraction of contemporary marine and fluvial sediments from the north bering sea chukchi sea region and adjacent land areas has resulted in delineation of suites dominated by broadly defined illitic and expandable group components with lesser amounts of chlorite and kaolinite distribution patterns elucidated indicate net northward transport of sediments relatively enriched in the expandable group with predominant terrigen ous source from the yukon river system this material is distributed across the study area in a medial zone along a general north south trend with peripherally decreasing relative amounts of this expandable group component and concomitant relative increases in the illitic components these patterns are consistent with known physical oceanographic and regional geologic relationships in terms of sediment sources transport processes and depositional mechanisms the foregoing suggest further that consideration of the stratigraphic relationships of these clay mineral component types as a function of time in relevant marine sediments north and south of the present bering strait should be informative with respect to regional quaternary paleogeography as related to global sea level fluctuations during glacial and interglacial episodes

late pleistocene mountain glaciation in alaska key chronologies moraine sequences of mountain glaciers can be used to infer spatial and temporal patterns of climate change across the globe alaska is an accessible high latitude location in the northern hemisphere and contains a rich record of alpine glaciation here we highlight the key chronologies from three mountain ranges in alaska that reveal the timing and spatial extent of late pleistocene glaciation and pay particular attention to age of the penultimate glaciation the most extensive glacier advance of the last glaciation occurred prior to the last global glacial maximum cosmogenic exposure ages from moraine boulders in three sites spanning 800km indicate that this penultimateadvancemostlikelyculminatedduringmarineisotopestage mis 4orearlymis3 during mis 2 more limited glacier expansion generated multiple moraines that span from prior to the global last glacial maximum lgm through the lateglacial period glaciers retreated from their terminal positions ca 27 25ka in arctic alaska and ca 22 19ka in southern alaska moraines in at least two ranges date to 12 11ka indicating a glacial advance during the younger dryas period reconstructed equilibrium line altitudes of both penultimate and mis 2 glaciers were lowered only 300 600m much less than elsewhere in the americas alaska is documented to have been more arid during mis 2 perhaps due in large part to the exposure of the bering chukchi platform during eustatic sea level lowering the restricted ice extent is also consistent with the output of climate models that simulate a lack of significant summer cooling copyright 2008 john wiley sons ltd

chlorine 36 and 14c chronology support a limited last glacial maximum across central chukotka northeastern siberia and no beringian ice sheet abstract the pekulney mountains and adjacent tanyurer river valley are key regions for examining the nature of glaciation across much of northeast russia twelve new cosmogenic isotope ages and 14 new radiocarbon ages in concert with morphometric analyses and terrace stratigraphy constrain the timing of glaciation in this region of central chukotka the sartan glaciation last glacial maximum was limited in extent in the pekulney mountains and dates to 20 000 yr ago cosmogenic isotope ages 30 000 yr as well as non finite radiocarbon ages imply an estimated age no younger than the zyryan glaciation early wisconsinan for large sets of moraines found in the central tanyurer valley slope angles on these loess mantled ridges are less than a few degrees and crest widths are an order of magnitude greater than those found on the younger sartan moraines the most extensive moraines in the lower tanyurer valley are most subdued implying an even older probable middle pleistocene age this research provides direct field evidence against grosswald s beringian ice sheet hypothesis

clay mineral stratigraphy during the last 2 4ma at iodp exp 323 site u1343 in the bering sea abstract the clay mineral composition at iodp exp 323 site u1343 in the bering sea was analyzed so as to unravel their provenance over glacial interglacial cycles for the last 2 4 ma smectite was negatively correlated with the sum of illite and chlorite therefore their ratio s i c was used as an indicator of clay mineral composition changes in general the s i c ratio was rather similar for glacial and interglacial periods during most of the last 2 4 ma in addition these results overlap with those of surface sediments in the modern east aleutian basin which suggests that smectite rich clay particles are delivered from the aleutians by the northward bering slope current bsc rather than from rivers in western alaska however some clay mineral compositions of the glacial periods after the mid pleistocene transition mpt 1 25 0 7 ma were characterized by low illite and relatively high smectite during this period extensive ice rafting might have transported the smectite rich clay particles to site u1343 from the glacial shelf off alaska and or from glacial rivers from that area