sedimentary pyrite formation an update sedimentary pyrite formation during early diagenesis is a major process for controlling the oxygen level of the atmosphere and the sulfate concentration in seawater over geologic time the amount of pyrite that may form in a sediment is limited by the rates of supply of decomposable organic matter dissolved sulfate and reactive detrital iron minerals organic matter appears to be the major control on pyrite formation in normal non euxinic terrigenous marine sediments where dissolved sulfate and iron minerals are abundant by contrast pyrite formation in non marine freshwater sediments is severely limited by low concentrations of sulfate and this characteristic can be used to distinguish ancient organic rich fresh water shales from marine shales under marine euxinic conditions sufficient h2s is produced that the dominant control on pyrite formation is the availability of reactive iron minerals calculations based on a sulfur isotope model indicate that over phanerozoic time the worldwide average organic carbon to pyrite sulfur ratio of sedimentary rocks has varied considerably high cs ratios during permo carboniferous time can be explained by a shift of major organic deposition from the oceans to the land which resulted in the formation of vast coal swamps at that time low cs ratios compared to today during the early paleozoic can be explained in terms of a greater abundance of euxinic basins combined with deposition of a more reactive type of organic matter in the remaining oxygenated portions of the ocean the latter could have been due to lower oceanic oxygen levels and or a lack of transportation of refractory terrestrial organic matter to the marine environment due to the absence of vascular land plants at that time

holocene variability in sea surface temperature and sea ice extent in the northern bering sea a multiple biomarker study abstract the bering sea as a transition between the arctic and the pacific oceans plays an important role in global climate change and biogeochemical cycles here we examined a variety of biomarkers in a core br07 from the northern continental slope of the bering sea in order to reconstruct summer sea surface temperature sst and sea ice extent during the period 11 2 ka thousands of calendar years ago the tex 86 l derived sst gradually decreased ca 1 6 c from early to mid holocene 11 3 8 0 ka but did not show a cooling or warming trend afterwards our sst data do not support the hypothesis of a holocene seesaw in temperature between the north atlantic and the north pacific several algal biomarkers including ip 25 and its derived indicators for sea ice brassicasterol for diatoms and dinosterol for dinoflagellates suggest that the sea ice extent gradually increased from early to late holocene interrupted by rapid changes at ca 2 8 2 6 and 5 5 5 0 ka the synchronous evolution between ip 25 and sst indicates a strong coupling between sea ice cover and climate change in the holocene

constraining pathways of microbial mediation for carbonate concretions of the miocene monterey formation using carbonate associated sulfate abstract carbonate concretions can form as a result of organic matter degradation within sediments however the ability to determine specific processes and timing relationships to particular concretions has remained elusive previously employed proxies e g carbon and oxygen isotopes cannot uniquely distinguish among diagenetic alkalinity sources generated by microbial oxidation of organic matter using oxygen nitrate metal oxides and sulfate as electron acceptors in addition to degradation by thermal decarboxylation here we employ concentrations of carbonate associated sulfate cas and 34scas along with more traditional approaches to determine the specific nature of concretion authigenesis within the miocene monterey formation integrated geochemical analyses reveal that at least three specific organo diagenetic reaction pathways can be tied to concretion formation and that these reactions are largely sample site specific one calcitic concretion from the phosphatic shale member at naples beach yields 34scas values near miocene seawater sulfate 22 vcdt abundant cas ca 1000 ppm depleted 13ccarb 11 vpdb and very low concentrations of fe ca 700 ppm and mn ca 15 ppm characteristics most consistent with shallow formation in association with organic matter degradation by nitrate iron oxides and or minor sulfate reduction cemented concretionary layers of the phosphatic shale member at shell beach display elevated 34scas up to 37 cas concentrations of 600 ppm mildly depleted 13ccarb 6 moderate amounts of mn ca 250 ppm and relatively low fe ca 1700 ppm indicative of formation in sediments dominated by sulfate reduction finally concretions within a siliceous host at montana de oro and naples beach show minimal cas concentrations positive 13c values and the highest concentrations of fe ca 11 300 ppm and mn ca 440 ppm consistent with formation in sediments experiencing methanogenesis in a highly reducing environment this study highlights the promise in combining cas analysis with more traditional techniques to differentiate among diagenetic reactions as preserved in the geologic record and shows potential for unraveling subsurface biospheric processes in ancient samples with a high degree of specificity

satellite observations of antarctic sea ice thickness and volume 1 we utilize satellite laser altimetry data from nasa s ice cloud and land elevation satellite icesat combined with passive microwave measurements to analyze basin wide changes in antarctic sea ice thickness and volume over a 5 year period from 2003 2008 sea ice thickness exhibits a small negative trend while area increases in the summer and fall balanced losses in thickness leading to small overall volume changes using a 5 year time series we show that only small ice thickness changes of less than 0 03 m yr and volume changes of 266 km3 yr and 160 km3 yr occurred for the spring and summer periods respectively these results are in stark contrast to the much greater observed losses in arctic sea ice volume and illustrate the different hemispheric changes of the polar sea ice covers in recent years the uncertainties in the calculated thickness and volume trends are large compared to the observed basin scale trends this masks the determination of a long term trend or cyclical variability in the sea ice cover it is found that lengthening of the observation time series along with better determination of the interannual variability of sea ice and snow densities will allow for a more statistically significant determination of long term sea ice thickness and volume trends in the southern ocean

carbon oxygen and sulphur isotope variations in concretions from the upper lias of n e england carbon oxygen and sulphur isotope data for transects across two pyrite bearmg carbonate concretions and their host sediments from the upper lias of n e england show symmetrical zonation 13cpdb values of the calcite cement 12 9 to 15 4 indicate that most of it originated from organic matter by bacterial reduction of sulphate augmented with marine and to a lesser extent fermentation derived carbonate organic carbon 13cpdb 26 1 to 37 0 reflects the admixture of allochtho nous terrestrial organic matter with marine material and the selective preservation of isotopically light organic material through microbiological degradation two phases of pyrite are present in each concretion the earlier framboidal pyrite formed throughout the sediment prior to concretionary growth and has 34scd values of 22 to 26 indicating formation by open system sulphate reduction the later euhedral phase is more abundant and reaches values of 2 5 to 5 5 at concretion margins this phase of sulphate reduction provided the carbonate source for concretionary growth and occurred in a partially closed system the 13c and 34s data are consistent with mineralogical and chemical evidence which suggest that both concretions formed close to the sediment surface the 18o values of the calcite in one concretion 18opdb 2 3 to 4 8 indicate precipitation in pore waters whose temperature and isotopic composition was close to that of overlying seawater the other concretion is isotopically much lighter 18opdb 8 9 to 9 9 and large 18o differences between concretions in closely spaced horizons imply that local factors control the isotopic composition of pore waters

normalizing xrf scanner data a cautionary note on the interpretation of high resolution records from organic rich lakes x ray fluorescence xrf scanning of unlithified untreated sediment cores is becoming an increasingly common method used to obtain paleoproxy data from lake records xrf scanning is fast and delivers high resolution records of relative variations in the elemental composition of the sediment however lake sediments display extreme variations in their organic matter content which can vary from just a few percent to well over 50 as xrf scanners are largely insensitive to organic material in the sediment increasing levels of organic material effectively dilute those components that can be measured such as the lithogenic material the closed sum effect consequently in sediments with large variations in organic material the measured variations in an element will to a large extent mirror the changes in organic material it is therefore necessary to normalize the elements in the lithogenic component of the sediment against a conservative element to allow changes in the input of the elements to be addressed in this study we show that al which is the lightest element that can be measured using the itrax xrf scanner can be used to effectively normalize the elements of the lithogenic fraction of the sediment against variations in organic content we also show that care must be taken when choosing resolution and exposure time to ensure optimal output from the measurements

137cs and 210pb transport and geochronologies in urbanized reservoirs with rapidly increasing sedimentation rates sedimentation rates have been measured in three reservoirs in northeastern ohio u s a by means of 137cs and 210pb geochronologies volumetric surveys and varve counting these various methods while only partially overlapping for each reservoir show dramatic three fold increases in rates of sediment accumulation in each system between about 1940 and 1977 mass sedimentation rates are very nearly proportional to the size of the population in the region and possess a doubling time of roughly 19 yr in these systems with changing sedimentation rates the preferred model for use with 210pb geochronologies is one which assumes a constant activity of material added to surface sediments in systems possessing large watershed reservoir area ratios increasing erosion is evidently accompanied by a proportionate increase in the erosion of excess 210pb high near surface activities of 137cs are due to system integration effects with time constants the order of 10 yr to a few decades total accumulation of fallout 137cs and excess 210pb far exceed direct atmospheric loadings thus indicating the importance of watershed contributions and implying annual retention of the radionuclides in the reservoirs of between 15 and 80 in lake rockwell sedimentary fluxes of zn pb and cu have increased with time the flux of cu in particular has increased very markedly since 1970 and concentrations are high in surface materials due in large part to addition of cuso4 an algicide to the water because of increased rates of sedimentation the remaining useful life of lake rockwell has decreased from 203 to 67 yr while the remaining useful life of mayfair lake is now less than 5 yr

dinocyst based reconstructions of sea ice cover concentration during the holocene in the arctic ocean the northern north atlantic ocean and its adjacent seas abstract sea ice cover extent expressed in terms of mean annual concentration was reconstructed from the application of the modern analogue technique to dinocyst assemblages the use of an updated database which includes 1492 sites and 66 taxa yields sea ice concentration estimates with an accuracy of 1 1 10 holocene reconstructions of sea ice cover were made from dinocyst counts in 35 cores of the northern north atlantic and arctic seas in the canadian arctic the results show high sea ice concentration 7 10 with little variations throughout the interval in contrast in arctic areas such as the chukchi sea and the barents sea the reconstructions show large amplitude variations of sea ice cover suggesting millennial type oscillations with a pacing almost opposite in western vs eastern arctic other records show tenuous changes with some regionalism either in trends or sea ice cover variability during the mid holocene and notably at 6 0 5 ka minimum sea ice concentration is recorded in the eastern fram strait northern baffin bay and labrador sea however this minimum cannot be extrapolated at the scale of the arctic and circum arctic the comparison of recent observations and reconstructions suggests larger variations in the arctic sea ice cover during the last decades than throughout the holocene

antarctic bottom water warming and freshening contributions to sea level rise ocean freshwater budgets and global heat gain abstractfreshening and warming of antarctic bottom water aabw between the 1980s and 2000s are quantified assessing the relative contributions of water mass changes and isotherm heave the analysis uses highly accurate full depth ship based conductivity temperature depth measurements taken along repeated oceanographic sections around the southern ocean fresher varieties of aabw are present within the south pacific and south indian oceans in the 2000s compared to the 1990s with the strongest freshening in the newest waters adjacent to the antarctic continental slope and rise indicating a recent shift in the salinity of aabw produced in this region bottom waters in the weddell sea exhibit significantly less water mass freshening than those in the other two southern basins however a decrease in the volume of the coldest deepest waters is observed throughout the entire southern ocean this isotherm heave causes a salinification and warming on isobaths from the bottom up to the shallow potential tem

large multidecadal salinity trends near the pacific antarctic continental margin abstract ocean temperature and salinity measurements on and near the antarctic continental shelf in the southwest pacific sector are evaluated for evidence of temporal change shelf water in the southwest ross sea has declined in salinity by 0 03 decade 1 from 1958 to 2008 while its temperatures have increased in proportion to the influence of salinity on the sea surface freezing point modified deep water intrusions that reach the central ross ice shelf have freshened at a similar rate and cooled by 0 5 c since the late 1970s salinity has decreased by 0 08 decade 1 in the westward coastal and slope front currents consistent with increased melting of continental ice upstream in the amundsen sea overturning of those near surface waters during winter sea ice formation and mixing across the slope front is sufficient to account for the 5 decade shelf water salinity change a strong correlation between the freshening and change in the southern annular mode index suggests a link with the large scale atmosp

holocene variability in sea ice cover primary production and pacific water inflow and climate change in the chukchi and east siberian seas arctic ocean in this study we present new detailed biomarker based sea ice records from two sediment cores recovered in the chukchi sea and the east siberian sea these new biomarker data may provide new insights on processes controlling recent and past sea ice changes the biomarker proxy records show i minimum sea ice extent during the early holocene ii a prominent mid holocene short term high amplitude variability in sea ice primary production and pacific water inflow and iii significantly increased sea ice extent during the last ca 4 5k cal a bp this late holocene trend in sea ice change in the chukchi and east siberian seas seems to be contemporaneous with similar changes in sea ice extent recorded from other arctic marginal seas the main factors controlling the millennial variability in sea ice and surface water productivity are probably changes in surface water and heat flow from the pacific into the arctic ocean as well as the long term decrease in summer insolation the short term centennial variability observed in the high resolution middle holocene record is probably related to solar forcing our new data on holocene sea ice variability may contribute to synoptic reconstructions of regional to global holocene climate change based on terrestrial and marine archives

reconstruction of ice conditions in the northern chukchi sea during recent centuries geochemical proxy compared with observed data abstract this paper presents the first results of the quantitative reconstruction of ice conditions in the arctic based on a comparison of the data for periods of meteorological observations with variations in the chemical compositions of the sediments accumulated during the same times the biogenic elements br ca and sr and some redox sensitive as and fe elements are the most informative for the reconstruction of changes in ice conditions with positive correlations and the lithogenic elements k and ti are predominantly negatively correlated the reconstruction results for the last 300 400 years of average annual air temperature anomalies for all cores in general terms coincide with the reconstruction for the northern hemisphere the common features of all reconstructions are low temperatures during the little ice age lia and a rapid warming in the middle of the 19th century and in the last decades of the 20th and first decades of the 21st centuries the results of the reconstruction of the duration of the ice free period generally coincide with the temperature changes for the last two centuries although for lia there is an inverse correlation between the variations in temperature and the duration of the ice free period a possible reason for this may be changes in the structure of the surface currents in the chukchi sea and the northern part of the bering sea because of which the inflow of warm and freshened waters through the bering strait to the arctic increased occasionally

holocene sea ice conditions and circulation at the chukchi alaskan margin arctic ocean inferred from biomarker proxies two sediment cores from the chukchi sea margin were investigated for the arctic sea ice biomarker ip25 along with marine and terrestrial sterols and glycerol dialkyl glycerol tetraethers gdgts this is the first paleoclimatic application of ip25 in the chukchi alaskan region of the arctic which is key for understanding arctic pacific interactions and is experiencing rapid sea ice retreat under present warming sea ice and related circulation conditions were characterized in this study with a multicentury resolution for the long term holocene record to multidecadal for the last several centuries sea ice was found to be present during the entire record but with considerable spatial and temporal variability after very low deglacial ip25 values possibly related to permanent sea ice and or an iceberg dominated environment cores from the upper slope and shelf show ip25 maxima interpreted as representing a relative proximity to the sea ice margin in the early ca 8 9 ka and middle ca 5 6 ka holoce

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

oxygen and carbon isotopic composition of marine carbonate concretions an overview abstract compilation of stable isotope data 18o and 13c for marine calcite siderite and dolomite concretions from a large number of studies reveals consistent and unanticipated isotopic trends although many of the dolomites have 18o values that are compatible with precipitation from unaltered seawater at low temperatures most of the calcites and siderites are far too depleted in 12o for such an origin this is surprising as most of the concretions appear to have formed very early in the diagenetic history of the sediments often within several meters of the sediment water interface the most likely cause of the anomalously depleted oxygen values is a decrease in pore water 18o values during early diagenesis a result perhaps of a significant influx of meteoric water into the marine shelf environment or water mineral interaction e g precipitation of 18o enriched minerals the carbon isotopic field for dolomite is quite different from that for calcite and siderite highly positive 13c values are fairly common only for dolomites this indicates that while dolomite concretions often form in sediments where methanogenesis is rapid precipitation of calcite and siderite concretions is restricted to sediments where either n methanogenesis takes place or where methanogenesis is not extensive enough to generate highly positive pore fluid 13c values this variation in carbon isotopic composition among the different minerals suggests that the rates of organic carbon oxidation and sedimentation may control the mineralogy of carbonate concretions high organic carbon oxidation rates favor dolomite and lower oxidation rates favor calcite or siderite

post glacial variability of sea ice cover river run off and biological production in the western laptev sea arctic ocean a high resolution biomarker study abstract multi proxy biomarker measurements were applied on two sediment cores ps51 154 ps51 159 to reconstruct sea ice cover ip25 biological production brassicasterol dinosterol and river run off campesterol sitosterol in the western laptev sea over the last 17 ka with unprecedented temporal resolution the absence of ip25 from 17 2 to 15 5 ka in combination with minimum concentration of phytoplankton biomarkers suggests that the western laptev sea shelf was mostly covered with permanent sea ice very minor river run off and restricted biological production occurred during this cold interval from 16 ka until 7 5 ka a long term decrease of terrigenous riverine organic matter and a coeval increase of marine organic matter reflect the gradual establishment of fully marine conditions in the western laptev sea caused by the onset of the post glacial transgression intensified river run off and reduced sea ice cover characterized the time interval between 15 2 and 12 9 ka including the bolling allerod warm period 14 7 12 9 ka prominent peaks of the dip25 index coinciding with maximum abundances of subpolar foraminifers are interpreted as pulses of atlantic water inflow on the western laptev sea shelf after the warm period a sudden return to severe sea ice conditions with strongest ice coverage between 11 9 and 11 ka coincided with the younger dryas 12 9 11 6 ka at the onset of the younger dryas a distinct alteration of the ecosystem reflected in a distinct drop in terrigenous and phytoplankton biomarkers was detected during the last 7 ka the sea ice proxies reflect a cooling of the laptev sea spring summer season this cooling trend was superimposed by a short term variability in sea ice coverage probably representing bond cycles 1500 500 ka that are related to solar activity changes hence atmospheric circulation changes were apparently able to affect the sea ice conditions on the laptev sea shelf under modern sea level conditions

carbon isotopic compositions of 28 30 bisnorhopanes and other biological markers in a monterey crude oil abstract an immature tar like oil api 3 13 c 23 6 vs pdb from the miocene monterey formation offshore california was selected for a study of carbon isotopic signatures of individual biomarkers the three principal stereoisomers of 28 30 bisnorhopane c 28 have within analytical precision identical carbon isotopic compositions average 13 c 32 3 0 4 and are considerably depleted in 13 c compared to the whole oil these 28 30 bisnorhopanes bnh differ isotopically from c 29 and c 30 17 h hopanes 25 8 and 26 1 and c 31 c 35 extended hopanes 13 c 27 7 and suggest different precursors for the c 28 hopanes than for c 29 c 35 hopanes the relative depletion of bnh of almost 9 compared to the isotopic composition of the whole oil suggests that these hopanes derive from chemoautotrophic bacteria possibly not yet identified h 2 s oxidizers which utilize 13 c depleted substrates the c 29 and c 30 hopanes are within analytical precision isotopically identical 26 and similar to algal derived compounds e g c 27 steranes 25 9 which is consistent with a cyanobacterial source for these hopanes an archaebacterial biomarker 1 1 biphytane 13 c 25 5 likely derived from methanogens is also isotopically similar to c 27 sterane norpristane pristane and phytane liberated by desulfurization of the aromatic and polar maltene fractions show isotopic compositions similar to the same isoprenoids in the free lipids of the bitumen total range from 24 5 to 27 5 this isotopic similarity supports a common origin for the free and sulfur bound forms of these isoprenoids this origin could be algal and or archaebacterial lipids which both show isotopic compositions within the range of the c 18 c 20 isoprenoids like other marine derived organic matter this monterey oil does not show the strong 13 c depletion typical for methylotroph derived compounds characteristically found in organic matter of lacustrine origin this may indicate fundamental differences of methane recycling processes in marine sulfate dominated as compared to lacustrine environments

diffuse spectral reflectance of surficial sediments indicates sedimentary environments on the shelves of the bering sea and western arctic abstract visible diffuse spectral reflectance dsr has been described by previous workers as an efficient tool for extracting lithological compositions clay minerals iron oxyhydroxides carbonates and diatoms in sedimentary material the spatial patterns of these components are essential to understanding the processes driving their distribution and accumulation in the marine environment some of these processes include sea ice variability nutrient supply current flow patterns current strength sediment supply provenance and bathymetry the dsr derivatives and varimax rotated principal component analysis vpca of the spectral data collected from 234 core samples identified five leading components that account for variations in sediment lithology of the surface samples from the bering sea and western arctic these spectral components were then matched to spectral standards to identify the mineral assemblages responsible for them the components responsible for the vpca trends are chlorite muscovite goethite phycoerythrin phycocyanin smectite calcite dolomite and illite chlorophyll a the spatial pattern of the inorganic components is indicative of provenance and processes controlling their transportation and depositional patterns while the organic components are indicative of areas of primary productivity and driving mechanisms the chlorite muscovite assemblage which is sourced dominantly from the yukon river has maximum values on the bering sea shelf this is the source of the chlorite muscovite transport to the chukchi sea the chlorite muscovite assemblage also has a main transport route to the aleutian basin in the northern bering sea shelf the chukchi sea on the western arctic ocean shelf is a region of highly reducing condition this is based on the lowest values for the goethite phycoerythrin phycocyanin assemblage supported by the high carbonate concentrations at this location the carbonate distribution pattern on the bering sea shelf also appears to be tidally influenced this is because their spatial pattern divides the bering shelf into three domains which are similar to the three hydrographic domains on the bering shelf a function of tidal influence the smectite assemblage reaches maximum values along the coast of the chukotka peninsula in the chukchi sea denoting the chukotka peninsula as a major source area of smectite and supporting the notion for volcanically derived sediment to the chukchi sea another likely source of smectite to the chukchi sea is via the bering strait the illite in the illite chlorophyll a assemblage shows maximum values and distribution on the western arctic ocean shelf indicating the western arctic ocean shelf to be a main province of illite all the high values of the illite chlorophyll a component on the bering sea shelf are chlorophyll a from diatoms our results support the usefulness of the dsr method as an effective and efficient tool for provenance analysis and understanding the processes controlling sediment and biologic distribution in this case in the marine environment

water mass transformation by sea ice in the upper branch of the southern ocean overturning sea ice formation is a key factor in the lower branch of the southern ocean overturning circulation observation based data in conjunction with a water mass transformation framework reveal that sea ice plays a central role in the upper branch too

800 yr long records of annual air temperature and precipitation over southern siberia inferred from teletskoye lake sediments a unique 800 yr long record of annual temperatures and precipitation over the south of western siberia has been reconstructed from the bottom sediments of teletskoye lake altai mountains using an x ray fluorescence scanner xrf providing 0 1 mm resolution timeseries of elemental composition and x ray density xrd br content appears to be broadly correlative with mean annual temperature variations because of changes in catchment vegetation productivity sr rb ratio reflects the proportion of the unweathered terrestrial fraction xrd appears to reflect water yield regime and sediment flux sedimentation is rather continuous because annual clastic supply and deposited mass are the same the artificial neural networks method was applied to convert annual sedimentary time series of xrd br content and sr rb ratio to annual records of temperature and precipitation using a transfer function comparison of these reconstructed siberian records with the annual record of air temperature for the northern hemisphere shows similar trends in climatic variability over the past 800 yr estimated harmonic oscillations of temperature and precipitation values for both historical and reconstructed periods reveal subdecadal cyclicity

climate science southern ocean freshened by sea ice the southern ocean has become less salty during the past few decades an analysis of sea ice transport in the ocean suggests that this phenomenon can be explained by coupled changes in sea ice drift and thickness see letter p 89 the southern ocean has freshened over the past few decades but the underlying mechanisms involved have remained unclear alex haumann and colleagues bring together multiple lines of evidence and despite large uncertainties in the underlying datasets they find that northward transport of sea ice formed around the antarctic coast can explain the bulk of the observed freshening

sea ice transport driving southern ocean salinity and its recent trends the southern ocean has freshened over the past few decades but the underlying mechanisms involved have remained unclear alex haumann and colleagues bring together multiple lines of evidence and despite large uncertainties in the underlying datasets they find that northward transport of sea ice formed around the antarctic coast can explain the bulk of the observed freshening

a combined radiometric and mineral magnetic approach to recent geochronology in lakes affected by catchment disturbance and sediment redistribution abstract as a result of empirical testing of 210 pb dating models in a wide variety of lakes we conclude that there are many situations where despite major changes in sedimentation rates as a result of lake or catchment disturbance the crs constant flux model provides a sound basis for establishing recent chronology factors which may complicate or vitiate the assumptions of the model include short water residence time bioturbation for which we propose a modified dating model discontinuous or disturbed sedimentation sediment resuspension and shifts in sediment source in the case of the last three processes we illustrate ways in which the problems can be identified and evaluated using mineral magnetic measurements we propose an evaluative approach to 210 pb dating projects with emphasis on independent dating evidence on tests of internal consistency and on the use of data from several correlatable cores

varves in marine sediments a review the global compilation of reported marine varved sedimentary records throughout the quaternary contains 52 sites marine varve deposition and preservation typically depend on environmental and sedimentological conditions such as a sufficiently high sedimentation rate severe depletion of dissolved oxygen in bottom water to exclude bioturbation by macrobenthos and a seasonally varying sedimentary input to yield a recognizable rhythmic varve pattern additional oceanographic factors include the strength and depth range of the oxygen minimum zone omz and regional anthropogenic eutrophication from point sources such as large polluted rivers quaternary marine varves are not only found in those parts of the open ocean that comply with these conditions but also in fjords embayments and estuaries with thermohaline density stratification and nearshore marine lakes with strong hydrologic connections to ocean water this review critically describes settings and sedimentological characteristics of marine sites where varves have been reported broader applications of marine varve records are discussed for example in terms of radiocarbon calibration on high resolution time scales constraining paleoceanographic variability and global change teleconnections diagnosing factors affecting modern fish population dynamics based on past performance detailing biogeochemical cycles and deciphering complex factors influencing marine productivity varves in saline water bodies without hydrologic connection to the global ocean are not included in this review and instead pertain to the companion review on lacustrine varves where also general and fundamental principles of varve deposition classification and dating are covered zolitschka et al 2015 the postulated occurrence of varves in pre quaternary rocks is critically discussed in this review with representative examples in the case of non evaporitic laminations in fine grained ancient marine rocks such as banded iron formations and black shales laminations may not be varves but instead may have multiple alternative origins such as event beds or formation via bottom currents that transport and sort silt sized particles clay floccules and organic mineral aggregates in the form of migrating bedload ripples

temporal and spatial variability in coastline response to declining sea ice in northwest alaska abstract arctic sea ice is declining in extent leaving coastlines exposed to more storm wave events there is an urgent need to understand how these changes affect geomorphic processes along arctic coasts here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct storm wave dominated reaches of the chukchi sea coastline over the last 64 years one study area encompasses the west to southwest facing coarse clastic shoreline and ice rich bluffs of cape krusenstern cakr the other covers the north facing sandy shorelines on barrier islands ice rich bluffs and the cape espenberg spit in the bering land bridge national park bela both study areas lie within the zone of continuous permafrost which exists both on and offshore and outcrops as ice rich bluffs along the bela coast we mapped changes in coastal geomorphology over three observation periods 1950 1980 1980 2003 and 2003 2014 using aerial and satellite imagery we then compared these geomorphic changes to changes in sea ice coverage which declined 10 days per decade between 1979 and 2016 in the southern chukchi sea changes in coastal geomorphology in both bela and cakr exhibited high spatial variability over the study period between 2003 and 2014 shorelines of barrier islands in bela exhibited the highest mean rates of change 1 5 m yr 1 while coarse clastic barrier beaches in cakr showed only minimal change overall shorelines in both bela and cakr became more dynamic increasing erosion or increasing accumulation after ca 2003 with spatial variability in shoreline changes roughly doubling between the first period of observation 1950 1980 and the last 2003 2014 this increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice affected coastlines

western arctic ocean temperature variability during the last 8000 years 1 we reconstructed subsurface 200 400 m ocean temperature and sea ice cover in the canada basin western arctic ocean from foraminiferal do ostracode mg ca ratios and dinocyst assemblages from two sediment core records covering the last 8000 years results show mean temperature varied from 1 to 0 5 c and 0 5 to 1 5 c at 203 and 369 m water depths respectively centennial scale warm periods in subsurface temperature records correspond to reductions in summer sea ice cover inferred from dinocyst assemblages around 6 5 ka 3 5 ka 1 8 ka and during the 15th century common era these changes may reflect centennial changes in the temperature and or strength of inflowing atlantic layer water originating in the eastern arctic ocean by comparison the 0 5 to 0 7 c warm temperature anomaly identified in oceanographic records from the atlantic layer of the canada basin exceeded reconstructed atlantic layer temperatures for the last 1200 years by about 0 5 c citation farmer j r t m cronin a de vernal g s dwyer l d keigwin and r c thunell 2011 western arctic ocean temperature variability during the last 8000 years geophys res lett 38 l24602 doi 10 1029 2011gl049714

reconstructing ice conditions in the southern chukchi sea during the last millennium based on chemical composition of sediments and diatom assemblages abstract using transfer functions this study reconstructed the ice free period ifp that occurred 4 7 kya in the southern chukchi sea based on the comparison between the observed data and the chemical composition of sediments accumulated during the observation period during the analysis a double normalization of the chemical element contenton rubidium and minimax was implemented for the first time it was established that the duration of the ifp varied between 90 and 140 days year the highest values are observed in the 21st century and 4 5 kya coinciding with pacific water inflow through the bering strait the reconstruction of water masses based on diatom thanatocoenosis has revealed the considerable impact of the alaskan coastal current on the duration of the ifp the penetration of its waters to the west during the following time periods 2750 2550 1450 800 350 0 cal yr bp led to an increase in the duration of the ifp in the central part of the sea by 10 15 days relative to background values as a result the identified variations in the duration of the ifp in the southern chukchi sea do not coincide with global climate events of the last millennium but are clearly demonstrated by an increase in the ifp during the little ice age currently the influence of the alaskan coastal water is summed up by the effect of increasing global temperatures and pacific water inflow which has led to a sharp increase in the ifp in the last few decades

210pb derived chronology and the fluxes of 210pb and 137cs isotopes into continental shelf sediments east chukchi sea alaskan arctic abstract eleven sediment cores and eight sediment trap samples from the continental shelf of the eastern chukchi sea were analyzed for 210pb cs and 2226ra in selected samples the organic carbon content and stable carbon isotope ratios were also determined the excess 210pb 210pbxs concentrations in the 1 cm core tops are generally lower than those of surficial sediments of subarctic shelves and arctic lakes the sediment inventory derived depositional fluxes of 210ph vary between 0 09 and 0 38 dpm cm 2y 1 with a mean of 0 18 dpm cm 2 y 1 the apparent mass sediment accumulation rates which vary between 31 and 324 mg cm 2 y 1 with a mean value of 133 mg cm 2 y 1 are about an order of magnitude lower than the yearly particle flux obtained from the sediment trap experiments this difference between the relatively long term and short term yearly accumulation rates is likely due to the occasional resuspension of fine particles in the continental shelf areas and their advective transport to sites other than their initial deposition the sediment inventory of 137cs varied between 0 64 and 4 09 dpm cm 2 with a mean of 2 18 dpm cm 2 a comparison of this inventory with the expected fallout inventory of 137cs suggests that there had been no detectable input of 137cs to the study area from the former ussr nuclear dump sites

rapid sea level rise and holocene climate in the chukchi sea three new sediment cores from the chukchi sea preserve a record of local paleoenvironment sedimentation and flooding of the chukchi shelf 50 m by glacial eustatic sea level rise radiocarbon dates on foraminifera provide the first marine evidence that the sea invaded hope valley southern chukchi sea 53 m as early as 12 ka the lack of significant sediment accumulation since ca 7 ka in hope valley southeastern chukchi shelf is consistent with decreased sediment supply and fluvial discharge to the shelf as deglaciation of alaska concluded abundant benthic foraminifera from a site west of barrow canyon indicate that surface waters were more productive 4 6 ka and this productivity varied on centennial time scales an offshore companion to this core contains a 20 m record of the holocene these results show that carefully selected core sites from the western arctic ocean can have a temporal resolution equal to the best cores from other regions and that these sites can be exploited for high resolution studies of the paleoenvironment