past glacial and interglacial conditions in the arctic ocean and marginal seas a review past changes in the arctic ocean and its marginal seas have been profound even during the last 10 000 years understanding these changes such as those occurring during the transition from glacial to interglacial climates are important for research on modern processes because this knowledge provides a framework and unique perspective in which to view the modern physical and biological processes this paper discusses our current understanding of past environmental change and processes relative to those currently in progress special emphasis is placed on the most recent transition from a glacial state to the modern interglacial conditions

1 500 year cycle in the arctic oscillation identified in holocene arctic sea ice drift decadal to centennial scale variability has been identified in the arctic oscillation but less is known about variations on the millennial scale a record of sea ice drift from off the alaskan coast shows a 1 500 year cycle in the phase of the arctic oscillation

effects of regional fast ice and iceberg distributions on the behaviour of the mertz glacier polynya east antarctica an observational account of research carried out in july august 1999 shows that grounded iceberg and related fast ice distributions and periodic break outs of fast ice in winter as well as at other times have an important impact on the size and behaviour of the mertz glacier polynya east antarctica and a smaller polynya to the east analysis of satellite and in situ data shows that a semi constant stream of thick broken out fast ice and other large floes from the east extends westwards from north of the glacier terminus to form a compact barrier to the net west northwesterly export of ice formed in the polynya an annual fast ice promontory to the west further narrows the outlet path as a result of this and high ice production rates the polynya periodically back fills significantly reducing the open water area present intervening flush outs by synoptic storm events clear the polynya region to some extent before it back fills again this cycle continued from mid march until early october in 1999 when a significant change in the regional ice drift occurred a preliminary comparison with data from 1998 indicates that the timing and magnitude of the processes may vary interannually similar morphological features were also observed in 1963 on a declassified photoreconnaissance satellite image

circumpolar mapping of antarctic coastal polynyas and landfast sea ice relationship and variability abstractsinking of dense water from antarctic coastal polynyas produces antarctic bottom water aabw which is the densest water in the global overturning circulation and is a key player in climate change as a significant sink for heat and carbon dioxide very recent studies have suggested that landfast sea ice fast ice plays an important role in the formation and variability of the polynyas and possibly aabw however they have been limited to regional and case investigations only this study provides the first coincident circumpolar mapping of antarctic coastal polynyas and fast ice the map reveals that most of the polynyas are formed on the western side of fast ice indicating an important role of fast ice in the polynya formation winds diverging from a boundary comprising both coastline and fast ice are the primary determinant of polynya formation the blocking effect of fast ice on westward sea ice advection by the coastal current would be another key factor these effects on the variability in

quaternary ice transport in the canadian arctic and extent of late wisconsinan glaciation in the queen elizabeth islands most of the ice rafted debris in channels off the queen elizabeth islands nunavut is of local origin particularly in the inner part of the archipelago but samples from the arctic shelf contain as much as 40 grains from sources as far away as 2000 km including the siberian shelves particle transport by drifting sea ice from distant shelves is an important process on the arctic continental shelf of the queen elizabeth islands in the interior of the queen elizabeth islands and in the viscount melville and lancaster sounds particle transport is limited to distances of approximately 200 km mixing is more common among grains of coarse silt to fine sand than in the 250 m fraction but even the latter contains debris from sources far apart during the late wisconsinan the northern southern and eastern queen elizabeth islands were covered by glaciers flowing radially from ice centers on the islands into the inter island channels queens channel was completely filled by ice and a glacier lobe moved

ephemeral formation of perennial sea ice in the arctic ocean during the middle eocene arctic sea ice is a key component of the modern climate system marine sediment analyses suggest that perennial sea ice in the arctic ocean first formed transiently about 44 million years ago

unabated bottom water warming and freshening in the south pacific ocean author posting american geophysical union 2019 this article is posted here by permission of american geophysical union for personal use not for redistribution the definitive version was published in journal of geophysical research oceans 124 3 2019 1778 1794 doi 10 1029 2018jc014775

hydrochemical and isotopic investigation of a tropical wetland system in the indian subcontinent the study reported here is a part of an attempt to establish a comprehensive hydrochemical and isotopic baseline for a tropical wetland system as background data for a range of applications surface water samples of vembanad lake were collected from 20 stations in three seasons during the period 2007 2009 the analytical results were subjected to different chemical classification techniques to understand processes affecting the chemical concentration of waters the piper diagram classified the water samples as 100 alkali group in pre monsoon followed by 15 in monsoon and 85 in post monsoon and for anions 100 samples were of strong acids followed by 90 in monsoon and 100 in post monsoon season the plot to decipher the mechanism controlling water chemistry placed the vembanad lake in the region of precipitation and rock dominance in the monsoon season and in the field of saline water dominance in pre monsoon and post monsoon season the positive values for the chloro alkaline indices in pre and post monsoon season promoted cation exchange in the system the stable isotopes of water samples ranged from 20 21 to 17 0 and 5 6 to 3 34 for 2h and 18o respectively the most depleted values observed in the monsoon are due to the amount effect the high enrichment observed in pre monsoon is primarily due to evaporation and salinity mixing the variation of isotopes in the whole system point toward the fact that salinity mixing can be indicated by the 18o variation and 2h indicates the evaporation effect the plot of 18o with chloride concentration showed precipitation dominance in the monsoon season mixing of saline water and evaporation in pre monsoon season whereas the post monsoon samples plot in both fresh and saline region

sediments in arctic sea ice implications for entrainment transport and release despite the arctic sea ice cover s recognized sensitivity to environmental change the role of sediment inclusions in lowering ice albedo and affecting ice ablation is poorly understood sea ice sediment inclusions were studied in the central arctic ocean during the arctic 91 expedition and in the laptev sea east siberian arctic region expedition 1992 results from these investigations are here combined with previous studies performed in major areas of ice ablation and the southern central arctic ocean this study documents the regional distribution and composition of particle laden ice investigates and evaluates processes by which sediment is incorporated into the ice cover and identifies transport paths and probable depositional centers for the released sediment in april 1992 sea ice in the laptev sea was relatively clean the sediment occasionally observed was distributed diffusely over the entire ice column forming turbid ice observations indicate that frazil and anchor ice formation occurring in a large coastal polynya provide a main mechanism for sediment entrainment in the central arctic ocean sediments are concentrated in layers within or at the surface of ice floes due to melting and refreezing processes the surface sediment accumulation in central arctic multi year sea ice exceeds by far the amounts observed in first year ice from the laptev sea in april 1992 sea ice sediments are generally fine grained although coarse sediments and stones up to 5 cm in diameter are observed component analysis indicates that quartz and clay minerals are the main terrigenous sediment particles the biogenous components namely shells of pelecypods and benthic foraminiferal tests point to a shallow benthic marine source area apparently sediment inclusions were resuspended from shelf areas before and incorporated into the sea ice by suspension freezing clay mineralogy of ice rafted sediments provides information on potential source areas a smectite maximum in sea ice sediment samples repeatedly occurred between 81 n and 83 n along the arctic 91 transect indicating a rather stable and narrow smectite rich ice drift stream of the transpolar drift the smectite concentrations are comparable to those found in both laptev sea shelf sediments and anchor ice sediments pointing to this sea as a potential source area for sea ice sediments in the central arctic ocean sea ice clay mineralogy is significantly different from deep sea clay mineral distribution patterns the contribution of sea ice sediments to the deep sea is apparently diluted by sedimentary material provided by other transport mechanisms

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

sea ice transport of riverine particles from the laptev sea to fram strait based on clay mineral studies the aim of this study was to identify pathways and processes of modern sediment transport from the siberian hinterland to the laptev sea and further to the arctic ocean clay mineral analyses were performed on riverine suspended particulate material spm surface sediments of the laptev sea shelf and sea ice sediments sis material collected during seven expeditions was included in this study clay mineral assemblages are used to decipher the distribution of riverine sediments on the shallow laptev sea shelf the entrainment of fine particles into newly forming ice and the transport of sis from the laptev sea towards the ablation areas a cluster analysis of our data set shows that the clay mineral assemblages of laptev sea shelf sediments and sis are controlled mainly by the input of riverine spm supplied by the khatanga lena and yana rivers whereas the western shelf clay mineral province is characterized by enhanced smectite concentrations supplied by the khatanga river the eastern laptev sea is dominated by illite discharged through the lena and yana rivers the sis smectite concentration serves as an indicator for sediment source areas on the circum arctic shelves subsequently the transpolar drift can be distinguished into a siberian branch fed from the eastern kara sea and the western laptev sea and a polar branch originating from the eastern laptev sea

regional changes in icescape impact shelf circulation and basal melting ice shelf basal melt is the dominant contribution to mass loss from antarctic ice shelves however the sensitivity of basal melt to changes in icescape grounded icebergs ice shelves and sea ice and related ocean circulation is poorly understood here we simulate the impact of the major 2010 calving event of the mertz glacier tongue mgt east antarctica and related redistribution of sea ice and icebergs on the basal melt rate of the local ice shelves we find that the position of the grounded tabular iceberg b9b controls the water masses that reach the nearby ice shelf cavities after the calving of the mgt and the removal of b9b warmer water is present both within the mgt cavity and on the continental shelf driving a 57 increase of the deep mgt basal melting major changes in icescape influence the oceanic heat flux responsible for basal ice shelf melting

examining the interaction between multi year landfast sea ice and the mertz glacier tongue east antarctica another factor in ice sheet stability the mertz glacier tongue mgt east antarctica has a large area of multi year fast sea ice myfi attached to its eastern edge we use various satellite data sets to study the extent age and thickness of the myfi and how it interacts with the mgt we estimate its age to be at least 25 years and its thickness to be 10 55 m this is an order of magnitude thicker than the average regional sea ice thickness and too thick to be formed through sea ice growth alone we speculate that the most plausible process for its growth after initial formation is marine frazil ice accretion the satellite data provide two types of evidence for strong mechanical coupling between the two types of ice the myfi moves with the mgt and persistent rifts that originate in the mgt continue to propagate for large distances into the myfi the area of myfi decreased by 50 following the departure of two large tabular icebergs that acted as pinning points and protective barriers future myfi extent will be affected by subsequent icebergs from the ninnis glacier and the imminent calving of the mgt fast ice is vulnerable to changing atmospheric and oceanic conditions and its disappearance may have an influence on ice tongue ice shelf stability understanding the influence of thick myfi on floating ice tongues ice shelves may be significant to understanding the processes that control their evolution and how these respond to climate change and thus to predicting the future of the antarctic ice sheet

physical characteristics of summer sea ice across the arctic ocean sea ice characteristics were investigated during july and august on the 1994 transect across the arctic ocean properties examined from ice cores included salinity temperature and ice structure salinities measured near zero at the surface increasing to 3 4 at the ice water interface ice crystal texture was dominated by columnar ice comprising 90 of the ice sampled surface albedos of various ice types measured with radiometers showed integrated shortwave albedos of 0 1 to 0 3 for melt ponds 0 5 for bare discolored ice and 0 6 to 0 8 for a deteriorated surface or snow covered ice aerial photography was utilized to document the distribution of open melt ponds which decreased from 12 coverage of the ice surface in late july at 76 n to almost none in mid august at 88 n most melt ponds were shallow and depth bore no relationship to size sediment was pervasive from the southern chukchi sea to the north pole occurring in bands or patches it was absent in the eurasian arctic where it had been observed on earlier expeditions calculations of reverse trajectories of the sediment bearing floes suggest that the southernmost sediment was entrained during ice formation in the beaufort sea while more northerly samples probably originated in the east siberian sea some as far west as the new siberian islands

particulate matter in pack ice of the beaufort gyre ice observations and sediment samples were collected in the beaufort gyre in 1988 fine sediment occurred in very small patches of turbid ice as thin spotty surface layers in mud pellets or in old snowdrifts the latter were widespread south of 74 n containing an estimated 22 tonnes of silt and clay km 2 average particle concentration in sea ice 40 mg l 1 was much higher than in sea water 0 8 mg l 1 or in new snow but the sediment load was significantly smaller and of finer texture compared to that observed in a shelfal source area after a major entrainment event

air sea co2 exchange in the ross sea antarctica although the ross sea is one of the most productive regions in antarctica it is not clear to what extent this region is an atmospheric co2 sink we calculate instantaneous co2 flux rates with in situ pco2 and wind speed data from 20 cruises in the ross sea in addition we estimate annual co2 fluxes into the ross sea with nutrient budgets from a late summer cruise we find that the ross sea is a lesser atmospheric co2 sink 7 5 0 5 tg c yr 1 1 3 0 1 mol c m 2 yr 1 than previously reported 13 tg c yr 1 1 7 to 4 2 mol c m 2 yr 1 one exception is terra nova bay tnb in the western ross sea with co2 flux rates 4 8 0 3 mol c m 2 january march that are 3 4 times greater than the ross sea mean the majority of the co2 flux into tnb occurs during the late summer with instantaneous co2 flux rates up to 246 mmol c m 2 d 1 these extraordinary co2 flux rates are caused by the unique coupling of strong katabatic winds and low surface pco2 values although strong katabatic winds deepen the mixed layer and entrain co2 rich water from below late season net community productivity maintains low surface water pco2 levels while tnb only covers 1 3600 km2 of the ross sea continental shelf extraordinary air to sea co2 fluxes during the late summer may be regular features in many of the major sea ice production polynyas 148 000 km2 combined including antarctic bottom water formation regions

dissolved iron and iron ii distributions beneath the pack ice in the east antarctic 120 e during the winter spring transition distributions of dissolved iron dfe and its reduced form fe ii to a depth of 1000 m were investigated under the seasonal pack ice off east antarctica during the sea ice physics and ecosystem experiment sipex 2 sea ice voyage in september october 2012 concentrations of dfe were elevated up to five fold relative to southern ocean background concentrations and were spatially variable the mean dfe concentration was 0 44 0 4 nm with a range from 0 09 to 3 05 nm profiles of dfe were more variable within and among stations than were macronutrients suggesting that coupling between these biologically essential elements was weak at the time of the study brine rejection and drainage from sea ice are estimated to be the dominant contributors to elevated dfe concentrations in the mixed layer but mass budget considerations indicate that estimated dfe fluxes from brine input alone are insufficient to account for all observed dfe melting icebergs and shelf sediments are suspected to provide the additional dfe fe ii was mostly below the detection limit but elevated at depth near the continental shelf implying that benthic processes are a source of reduced fe in bottom waters the data indicate that dfe builds up under the seasonal sea ice cover during winter and that reduction of fe may be hampered in early spring by several factors such as lack of electron donors low biological productivity and inadequate light below the sea ice the accumulated dfe pool in the mixed layer is expected to contribute to the formation of the spring bloom as the ice retreats

provenance of terrigenous detritus of the surface sediments in the bering and chukchi seas as derived from sr and nd isotopes implications for recent climate change in the arctic regions abstract strontium and nd isotope analysis of the detrital fractions extracted from the marginal sea sediments in the arctic was applied to examine regional and temporal changes in the inflow and transportation of terrigenous material in the chukchi and bering seas over the past 100 years regional distributions of the sr and nd isotopes of the surface sediments show higher sr isotope ratios and lower nd isotope ratios in the chukchi sea 87 sr 86 sr 0 7106 0 7150 e nd 10 1 to 8 3 and lower sr isotope ratios and higher nd isotope ratios in the eastern bering sea 0 7045 0 7109 8 6 to 3 0 in addition the rb and sr contents and ree patterns e g eu eu changed noticeably across the bering strait these variations mean that the sediments in the bering and chukchi seas have clearly distinct sources the terrigenous detritus in the chukchi sea is mainly derived from northeastern siberia 87 sr 86 sr 0 711 e nd 9 and bering strait inflow essentially from the yukon river and additionally from the mackenzie river basin including the canadian shield 0 732 0 734 14 the detritus in the eastern bering sea mainly consists of two components the continental material from the yukon river basin mainly underlain by mesozoic and paleozoic rocks in the alaskan mainland 0 708 0 709 9 to 8 and the aleutian arc volcanics 0 703 6 to 10 transported northward by the alaska coastal and bering shelf waters the eastern bering sediments over the past 100 years show slight variations of the sr isotope ratio and relatively wide variations of the nd isotope ratio and the variations and trends of the time series of the northeastern bering sea in the sr nd isotope diagram are probably controlled by changes in the grain size of the detritus from the yukon river basin some of the e nd time series show periodic fluctuations correlating with the annual mean surface air temperature sat for the arctic the e nd value is low in the high sat period and high in the low sat period in the warm period the yukon river was likely to supply a higher amount of the fine grain material with a relatively low e nd value such as surficial overburden probably because partial melting of continental glaciers and permafrosts in the alaskan mainland increased more detailed analysis with high time resolution is needed to clearly understand the effects the sat have on the arctic continental and marine environments

change in dense shelf water and adelie land bottom water precipitated by iceberg calving antarctic bottom water supplies the deep limb of the global overturning circulation and ventilates the abyssal ocean antarctic bottom water has warmed freshened and contracted in recent decades but the causes remain poorly understood we use unique multiyear observations from the continental shelf and deep ocean near the mertz polynya to examine the sensitivity of this bottom water formation region to changes on the continental shelf including the calving of a large iceberg postcalving the seasonal cycle of dense shelf water dsw density almost halved in amplitude and the volume of dsw available for export reduced in the deep ocean the density and volume of adelie land bottom water decreased sharply after calving while oxygen concentrations remained high indicating continued ventilation by dsw this natural experiment illustrates how local changes in forcing over the antarctic continental shelf can drive large and rapid changes in the abyssal ocean

polynya dynamics drive primary production in the larsen a and b embayments following ice shelf collapse 1 the climate driven collapses of the larsen a and b ice shelves have opened up new regions of the coastal antarctic to the influence of sea ice resulting in increases in seasonal primary production in this study passive microwave remote sensing of sea ice concentration and satellite imagery of ocean color are employed to quantify the magnitude of and variability in open water area and net primary productivity npp in the larsen embayments between 1997 and 2011 numerical model output provides context to analyze atmospheric forcing on the coastal ocean following ice shelf disintegration the embayments function as coastal sensible heat polynyas the larsen a and b are as productive as other antarctic shelf regions with seasonally averaged daily npp rates reaching 1232 and 1127 mg c m 2 d 1 and annual rates reaching 200 and 184 g c m 2 yr 1 respectively a persistent cross shelf gradient in npp is present with higher productivity rates offshore contrasting with patterns observed along the west antarctic peninsula embayment productivity is intimately tied to sea ice dynamics with large interannual variability in npp rates driven by open water area and the timing of embayment opening opening of the embayment is linked to periods of positive southern annular mode and stronger westerlies which lead to the vertical deflection of warm maritime air over the peninsula and down the leeward side causing increases in surface air temperature and wind velocity high productivity in these new polynyas is likely to have ramifications for organic matter export and marine ecosystem evolution

a key source area and constraints on entrainment for basin scale sediment transport by arctic sea ice combining field measurements remote sensing and numerical modelling a key site for ice entrainment and basinwide dispersal of sediments by sea ice has been identified near the new siberian islands the total ice bound sediment export of 18 5 x 10 6 t for an entrainment event documented in 1994 95 is of the same order of magnitude as annual sediment supply to the deep sea sector of the eurasian arctic and the greenland sea satellite imagery and ancillary data indicate that ice advection from this source may play an important role in sedimentation downstream in the transpolar drift

erosion by rivers and transport pathways in the ocean a provenance tool using 40ar 39ar incremental heating on fine grained sediment measured from 39 ar and 37 ar respectively are consistent with typical values for k and ca bearing minerals calculations show that the bulk mineralogy is reflected in the outgassing k ca spectra and identify plagioclase as the dominant mineral contributing to the plateau defining portion of the age spectra a second model predicts bulk sediment ages from integrated bedrock cooling age area estimates in order to examine whether bulk sediment plateau ages are representative of the average cooling age of rocks from a given river basin calculated and observed ages are notably similar in three river basins when topographic and lithologic effects are accounted for overall this technique shows considerable promise not only in tracking individual terrigenous sources in the marine realm but also for understanding processes such as erosion and sediment transport in terrestrial systems

a statistical approach to source determination of lithic and fe oxide grains an example from the alpha ridge arctic ocean abstract discriminant function analysis dfa of microprobe data on 12 elements in nine fe oxide mineral types was used to match each fe oxide grain from an arctic ocean core to similarly analyzed grains in probable source areas for ice rafted detritus this approach to provenance allows us to determine the proportion of multiple sources with a high degree of statistical probability counts of microscopically identified dropstones 250 m from centimeter thick samples of the core and from source area samples provide a direct link to the sediment source multiple types of dfa e g direct vs stepwise on the dropstone data provide slightly different sources for many samples from the core this is due to multiple sources for each core sample and provides a more accurate picture of ources than one dfa procedure alone most of the lithic grains were derived from the northwestern queen elizabeth islands centered around ellef ringnes island and from the vicinity of victoria and banks islands whereas the microprobe data from individual fe oxide grains led to these same source areas they always showed that several sources contributed to each centimeter thick core sample significant input from both the dominant source areas to the same intervals in the core indicates that the ice sheets or ice caps covering these different areas coexisted during several pre wisconsin glaciations

an arctic perspective on dating mid late pleistocene environmental history to better understand pleistocene climatic changes in the arctic integrated palaeoenvironmental and palaeoclimatic signals from a variety of marine and terrestrial geological records as well as geochronologic age control are required not least for correlation to extra arctic records in this paper we discuss from an arctic perspective methods and correlation tools that are commonly used to date arctic pleistocene marine and terrestrial events we review the state of the art of arctic geochronology with focus on factors that affect the possibility and quality of dating and support this overview by examples of application of modern dating methods to arctic terrestrial and marine sequences event stratigraphy and numerical ages are important tools used in the arctic to correlate fragmented terrestrial records and to establish regional stratigraphic schemes age control is commonly provided by radiocarbon luminescence or cosmogenic exposure ages arctic ocean deep sea sediment successions can be correlated over large distances based on geochemical and physical property proxies for sediment composition patterns in palaeomagnetic records and increasingly biostratigraphic data many of these proxies reveal cyclical patterns that provide a basis for astronomical tuning recent advances in dating technology calibration and age modelling allow for measuring smaller quantities of material and to more precisely date previously undatable material i e foraminifera for c 14 and single grain luminescence however for much of the pleistocene there are still limits to the resolution of most dating methods consequently improving the accuracy and precision analytical and geological uncertainty of dating methods through technological advances and better understanding of processes are important tasks for the future another challenge is to better integrate marine and terrestrial records which could be aided by targeting continental shelf and lake records exploring proxies that occur in both settings and by creating joint research networks that promote collaboration between marine and terrestrial geologists and modellers

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

a comparison between multiproxy and historical data ad 1990 1840 of drift ice conditions on the east greenland shelf 66 n the reduction in sea ice along the se greenland coast during the last century has severely impacted ice rafting to this area in order to reconstruct ice rafting and oceanographic conditions in the area of denmark strait during the last 150 years we conducted a multiproxy study on three short 20 cm sediment cores from outer kangerdlugssuaq trough 300 m water depth the proxy based data obtained have been compared with historical and instrumental data to gain a better understanding of the ice sheet ocean interactions in the area a robust chronology has been developed based on 210pb and 137cs measurements on core po175gkc 9 66 2 n 32 w and expanded to the two adjacent cores based on correlations between calcite weight percent records our proxy records include sea ice and phytoplankton biomarkers and a variety of mineralogical determinations based on the 2 mm sediment fraction including identification with quantitative x ray diffraction ice rafted debris counts on the 63 150 m sand fraction

modeling water mass formation in the mertz glacier polynya and adelie depression east antarctica 1 high rates of sea ice growth and brine rejection in the mertz glacier polynya drive the production of dense continental shelf waters in the adelie depression we consider the rate of outflow of waters having sufficient density to sink into the neighboring abyssal ocean and form adelie land bottom water albw along with weddell and ross sea bottom waters the albw is an important source of antarctic bottom water the relevant processes are modeled using a variant of the max planck institute ocean model mpiom under daily ncep ncar reanalysis forcing for the period 1991 2000 the orthogonal curvilinear horizontal grid allows for the construction of a global domain with high resolution in our region of interest the modeled mertz glacier polynya is realistic in location and extent exhibiting low ice thickness 0 4 m and low ice fraction 50 the net surface ocean to atmosphere heat flux exceeds 200 w m2 and is dominated by sensible heat exchange in wintertime may through september inclusive 7 5 m of sea ice forms over the adelie depression at a rate of 4 9 cm d 1 this results in annual average volumetric production of 99 km3 of sea ice the associated brine release drives dense shelf water formation the off shelf flow of dense water exhibits strong interannual variability in response to variability in both atmospheric forcing and ocean preconditioning averaged over the period 1991 2000 the off shelf flow of dense water is 0 15 sv for a period of strong outflow 1993 1997 this increases to 0 24 sv most of the outflow occurs during july through october at a rate of 0 40 0 63 sv over the period 1991 2000 1993 1997 the peak mean monthly outflow can exceed 1 sv

hydrochemical variability associated with rainfall regime a case study in the coastal wetland of the outer rio de la plata estuary argentina in coastal wetlands the interaction between groundwater surface water and marine or estuarine water determines the water chemistry variations in the water balance may be of influence as well the objective of this work was to assess how the rainfall regime affects the hydrological and geochemical processes that regulate the quality of surface and groundwater in the samborombon bay coastal wetland we analyzed the water balances and chemical data of surface and groundwater during a dry and a wet period results show that the rainfall regime regulates water quality in the three hydrological units defined for the region i e groundwater in the coastal plain groundwater in the shell ridges and surface water in the coastal plain in the water balance corresponding to a dry period real evapotranspiration is similar to precipitation in such conditions in the coastal plain the halite and gypsum salts precipitate subsequently the rain or the tidal flow dissolves them and they enter the water table by infiltration the lowering of the water table favors the oxidation of sedimentary pyrite and the contribution of sulfates the oversaturation of calcium carbonates in groundwater causes their precipitation both in the coastal plain and in the shell ridges the chemistry of surface water depends on the influence generated by the tidal inflow and groundwater discharge during the wet periods precipitation is higher than real evapotranspiration leading to the infiltration of water excess toward the water table and the increase in surface runoff this causes a decrease in the concentration of ions dissolved by dilution this rainfall regime hinders the formation of evaporite salts gypsum and halite and leads to the undersaturation of groundwater with respect to calcite allowing the dissolution of carbonates as regards the chemical composition of the surface water in the coastal plain the surface runoff in the drainage basin is more significant than the groundwater discharge and the tidal inflow it can be concluded that the alternation of dry and wet periods in the samborombon bay wetland causes the rainfall regime to be a determining factor in the different hydrological and geochemical processes affecting the quality of surface and groundwater

spatial variability of antarctic bottom water in the australian antarctic basin from 2018 2020 captured by deep argo author s thomas george advisor s purkey sarah abstract there are two varieties of antarctic bottom water present in the australian antarctic basin aab locally produced adelie land bottom water albw and distantly produced ross sea bottom water rsbw between 2014 and 2018 rsbw has rebounded from a multi decade freshening trend the return of the salty rsbw to the aab is revealed by six deep argo floats that have occupied the region from january of 2018 to march of 2020 the floats depict a zonal variation in temperature and salinity in the bottom waters of the aab driven by the inflow of rsbw a simple optimum multiparameter analysis based on potential temperature and salinity gives a sense of scale to the composition of the bottom waters which are nearly 80 the new salty rsbw in the south east corner of the basin by 2019 and generally less than 40 to the west closer to the albw outflow region and the abyssal plain

dense shelf water production in the adelie depression east antarctica 2004 2012 impact of the mertz glacier calving summer repeated hydrographic surveys and 4 years of mooring observations are used to characterize for the first time the interannual variability of the bottom water in the mertz glacier polynya mgp on the east antarctic shelf 142 e 146 e until 2010 large interannual variability was observed in the summer bottom salinity with year to year changes reaching 0 12 in commonwealth bay the region with the highest sea ice production the summer variability was shown to be linked to the efficiency of the convection during the preceding winter the recent freshening of the bottom waters subsequent to the mertz glacier calving was well beyond the range of the precalving interannual variability within 2 years after the event the bottom water of the shelf became too light to possibly contribute to renewal of the antarctic bottom water rough estimates of the freshwater budget of the adelie depression indicate that the freshening necessary to compensate for net sea ice production in the mgp did not change drastically after the mertz calving the year to year salinity changes appeared to respond to the mgp activity yet prior to the calving the convective system in the polynya was also partly controlled by the late winter bottom salinity through a mechanism leading to a sequence of alternatively fresher and more saline bottom waters over the period 2007 2010 exceptional events like the mertz calving seem to be able to switch over the system into a less stratified state where convection responds more directly to changes in the surface forcing

a biomarker based reconstruction of sea ice conditions for the barents sea in recent centuries variations in sea ice occurrence for the barents sea since c ad 1700 have been determined by analysis of the abundance of the sea ice biomarker ip25 in three marine sediment box cores obtained from locations in the north southeast and southwest parts of the region depth age models for each core were established using excess 210pb activity profiles comparisons between these depth age models with those reported previously for the barents sea suggest that the proxy sea ice record may alternatively extend back to c ad 1500 1600 sedimentation accumulation rates and bulk densities were combined with ip 25 concentrations resulting in temporal changes to ip25 fluxes which have been interpreted in terms of sea ice variability the ip25 sea ice proxy data are also compared with other bulk organic geochemical parameters total organic carbon and c n ratios and with sediment particle size distributions the data indicate ice free conditions for the southwest barents sea for the past c 300 yr consistent

carbonate chemistry in the mertz polynya east antarctica biological and physical modification of dense water outflows and the export of anthropogenic co2 1 dense shelf water dsw is formed in east antarctica from enhanced sea ice production driven by air sea interaction in coastal polynyas cross shelf export and downslope mixing of this dsw produces antarctic bottom water contributing to the lower limb of the global overturning circulation we present biogeochemical observations from the mertz polynya region in summer 2007 2008 with additional observations from spring 2001 and winter 1996 the seasonal changes in mixed layer carbonate chemistry are driven by a combination of air sea co2 exchange biological activity and the formation and melt of sea ice the air sea fluxes in 2008 were 15 mmol c m 2 d 1 and net community production estimated from the summertime surface dissolved inorganic carbon dic deficit ranged from 0 9 to 1 2 mol c m 2 yr 1 we show that biological modification of carbonate chemistry over the shelf in summer preconditions the dsw outflows from the adelie depression this process appears to supply both organic material and water depleted in co2 and with enhanced carbonate saturation state relative to inflowing water to coral communities on the slope we combined model based transports of exported dsw with the natural and anthropogenic cant carbon concentrations and estimate that the annual outflows of dic and cant from the mertz polynya range from 320 to 560 tg c yr 1 and from 3 to 6 tg cant yr 1 respectively the formation and export of dense water from this region and by extension all similar polynyas around antarctica is an effective mechanism for the transfer of anthropogenic carbon into the deep ocean

dynamics of the barents kara ice sheet as revealed by quartz sand grain microtextures of the late pleistocene arctic ocean sediments abstract during the entire quaternary ice sheets advanced and retreated across the circum arctic margins in a series of climate related glacial interglacial cycles it is critical to obtain evaluation of the nature of initiated glaciers at the arctic margins after the pronounced interglacial periods in this study this will be done by inferring from glacially generated quartz sand grain surface microtextures and related sedimentology extracted from the central arctic ocean sediments these microtextures can be correlated with the generation and fluctuations in the extent of the late pleistocene eurasian ice sheet i e barents kara ice sheet the central arctic ocean sediments in the lomonosov ridge having been deposited after the late pleistocene interglaciations and having had no internal hiatuses provide an excellent time window for usage of quartz sand grain surface textures for evaluating possible evolving glaciers and continental ice sheets this is based on the fact that iceberg and sea ice transported quartz sand grains and their mechanically formed surface textures created under high cryostatic stress are diagnostic for glacier thickness and dynamics having been existed in sediment source areas sand sized quartz grains in deep marine sediments favour iceberg or sea ice transportation with characteristic content of microtextures formed prior this transportation the sand grain surface microtextures and their frequencies of the selected submarine lomonosov ridge sediments during marine isotope stage mis 5 to mis 3 are analysed using a scanning electron microscope sem coring during the arctic ocean 96 expedition core 96 12 1pc provided alternating clay to silty clay sediments which are characterised by prominent silt to sand size containing intervals the specific glacial crushing and high cryostatic stress generated features such as high angularity conchoidal fractures steps and sub parallel linear fractures were observed from quartz sand grain surfaces continental ice generation and extent are evident soon after the eemian interglaciation and the following mis 4 stage shows the highest frequencies of glacigenic microtextures the microtexture generation under high cryostatic pressure underneath ice more than 1 km thick can be taken as concurrent signal of the temporal expansion of the northernmost continental ice sheets which could easily have reached the shelf break of the barents kara and western laptev seas during that time

phytoplankton biomass and photosynthetic competency in the summertime mertz glacier region of east antarctica abstract vertical profiles of water temperature salinity beam transmission density pressure wind speed wind direction phytoplankton biomass chlorophyll a chl a plus phaeophytin a and photosynthetic competency by fast repetition rate fluorometry are presented for the mertz glacier region east antarctica for a 3 week period during the austral summer 2000 2001 injection of low salinity water from the melting of the ice pack formed a shallow ca 25 m mixed layer offshore two distinct deep mixing features were observed associated to varying degrees with high chlorophyll levels and high photosynthetic competency along the adelie land coast a deep mixing layer 1400 m with chl a concentrations of 386 mg m 2 and elevated fv fm 0 5 was observed at the eastern end of the study area along a seaward extension of fast ice a bloom of phaeocystis antarctica bloom formed within a shallow 24 m mixed layer with surface chl a concentrations of ca 8 mg m 3 and elevated fv fm 0 5 this feature also had high surface salinity 34 and was contiguous with a deep mixing feature 236 m frrf parameters fv fm and psii were strongly suppressed in surface waters

taxonomic variability of phytoplankton and relationship with production of cdom in the polynya of the amundsen sea antarctica abstract to evaluate the relationship between the phytoplankton composition and the cdom production in the amundsen sea we examined the taxonomic variability of phytoplankton nutrients and chromophoric dissolved organic matter cdom participating in two research cruises ana02c february 2012 and ana04b january 2014 for both cruises the peak concentrations of chlorophyll a chl a were measured in the amundsen sea polynya asp where the average chl a concentration was 2 31 g l 1 1 01 g l 1 in february 2012 and 3 92 g l 1 3 14 g l 1 in january 2014 the major phytoplankton groups were diatoms and prymnesiophytes while the minor groups were cryptophytes chlorophytes dinophytes chrysophytes and cyanophytes the phytoplankton compositions in the sea ice zone siz the asp and ice shelf is was distinct the predominance of phaeocystis antarctica p antarctica 70 90 was observed at all stations except in the siz in january 2014 while the cdom concentrations a355 ranged from 0 07 to 0 98 m 1 the average values of a355 of the euphotic layer in the asp was 0 51 m 1 0 19 m 1 which was much higher than any other region of the southern ocean cdom showed strong correlation with chl a but no relationship with salinity which implies that biological processes were the main source of cdom among the major phytoplankton taxa p antarctica was confirmed as the most important contributor to the production of cdom according to the high correlation between marker pigment hex fuco and cdom the unusually high cdom in the asp is expected to give as impact on the environment in various aspects as a nature of cdom absorption of solar radiation at the surface can result in the increase of sea surface temperature ssts which will accelerate the ice melting also the photo oxidation of cdom can serve as a feedback to increasing atmospheric co2 concentrations after peak bloom in austral summer

mineralogical geochemical and magnetic signatures of surface sediments from the canadian beaufort shelf and amundsen gulf canadian arctic mineralogical geochemical magnetic and siliciclastic grain size signatures of 34 surface sediment samples from the mackenzie beaufort sea slope and amundsen gulf were studied in order to better constrain the redox status detrital particle provenance and sediment dynamics in the western canadian arctic redox sensitive elements mn fe v cr zn indicate that modern sedimentary deposition within the mackenzie beaufort sea slope and amundsen gulf took place under oxic bottom water conditions with more turbulent mixing conditions and thus a well oxygenated water column prevailing within the amundsen gulf the analytical data obtained combined with multivariate statistical notably principal component and fuzzy c means clustering analyses and spatial analyses allowed the division of the study area into four provinces with distinct sedimentary compositions 1 the mackenzie trough canadian beaufort shelf with high phyllosilicate fe oxide magnetite and al k ti fe cr v zn p contents 2 southwestern banks island characterized by high dolomite k feldspar and ca mg loi contents 3 the central amundsen gulf a transitional zone typified by intermediate phyllosilicate magnetite k feldspar dolomite and al k ti fe mn v zn sr ca mg loi contents and 4 mud volcanoes on the canadian beaufort shelf distinguished by poorly sorted coarse silt with high quartz plagioclase authigenic carbonate and si zr contents as well as high magnetic susceptibility our results also confirm that the present day sedimentary dynamics on the canadian beaufort shelf is mainly controlled by sediment supply from the mackenzie river overall these insights provide a basis for future studies using mineralogical geochemical and magnetic signatures of canadian arctic sediments in order to reconstruct past variations in sediment inputs and transport pathways related to late quaternary climate and oceanographic changes keywords mineralogy elemental geochemistry magnetic properties surface sediment sediment provenance redox condition canadian beaufort shelf amundsen gulf

physical and biogeochemical controls on the variability in surface ph and calcium carbonate saturation states in the atlantic sectors of the arctic and southern oceans polar oceans are particularly vulnerable to ocean acidification due to their low temperatures and reduced buffering capacity and are expected to experience extensive low ph conditions and reduced carbonate mineral saturations states in the near future however the impact of anthropogenic co2 on ph and will vary regionally between and across the arctic and southern oceans here we investigate the carbonate chemistry in the atlantic sector of two polar oceans the nordic seas and barents sea in the arctic ocean and the scotia and weddell seas in the southern ocean to determine the physical and biogeochemical processes that control surface ph and high resolution observations showed large gradients in surface ph 0 10 to 0 30 and aragonite saturation state ar 0 2 to 1 0 over small spatial scales and these were particularly strong in sea ice covered areas up to 0 45 in ph and 2 0 in ar in the arctic sea ice melt facilitated bloom initiation in light limited and iron replete dfe 0 2 nm regions such as the fram strait resulting in high ph 8 45 and ar 3 0 along the sea ice edge in contrast accumulation of dissolved inorganic carbon derived from organic carbon mineralisation under the ice resulted in low ph 8 05 and ar 1 1 in areas where thick ice persisted in the southern ocean sea ice retreat resulted in bloom formation only where terrestrial inputs supplied sufficient iron dfe 0 2 nm such as in the vicinity of the south sandwich islands where enhanced ph 8 3 and ar 2 3 were primarily due to biological production in contrast in the adjacent weddell sea weak biological uptake of co2 due to low iron concentrations dfe 0 2 nm resulted in low ph 8 1 and ar 1 6 the large spatial variability in both polar oceans highlights the need for spatially resolved surface data of carbonate chemistry variables but also nutrients including iron in order to accurately elucidate the large gradients experienced by marine organisms and to understand their response to increased co2 in the future

quantitative mineralogy of surface sediments on the iceland shelf and application to down core studies of holocene ice rafted sediments abstract quantitative x ray diffraction analyses on the 2 mm sediment fraction from the iceland shelves are reported for subglacial diamictons seafloor surface sediments and the last 2000 cal yr bp from two cores the overall goal of the paper is to characterize the spatial variability of the mineralogy of the present day surface sediments 18 non clay minerals and 7 clay minerals compare that with largely in situ erosional products typified by the composition of subglacial diamictons and finally examine the late holocene temporal variability in mineral composition using multi mineral compositions the subglacial diamictons are dominated in the non clay mineral fraction by the plagioclase feldspars and pyroxene with 36 7 6 1 and 17 9 3 5 wt respectively with smectites being the dominant clay minerals the surface seafloor sediments have similar compositions although there are substantial amounts of calcite plus there is a distinct band of sites from nw to n central iceland that contain 1 6 wt of quartz this latter distribution mimics the modern and historic pattern of drift ice in iceland waters principal component analysis of the transformed wt log ratio non clay minerals is used to compare the subglacial surface and down core mineral compositions fifty eight percent of the variance is explained by the first two axes with dolomite microcline and quartz being important foreign species these analyses indicate that today the nw n central iceland shelf is affected by the import of exotic minerals which are transported and released from drift ice the down core mineralogy indicates that this is a process that has varied over the last 2000 cal yr bp

distribution of water masses and meltwater on the continental shelf near the totten and moscow university ice shelves warm waters flood the continental shelf of the amundsen and bellingshausen seas in west antarctica driving rapid basal melt of ice shelves in contrast waters on the continental shelf in east antarctica are cooler and ice shelves experience relatively low rates of basal melt an exception is provided by the totten and moscow university ice shelves on the sabrina coast where satellite derived basal melt rates are comparable to west antarctica recent oceanographic observations have revealed that relatively warm 0 4 c modified circumpolar deep water mcdw enters the cavity beneath the totten ice shelf through a 1100 m deep trough delivering sufficient heat to drive rapid basal melt here we use observations from a recent summer survey to show that mcdw is widespread on the continental shelf of the sabrina coast forming a warm up to 0 3 c and saline 34 5 34 6 bottom layer overlaid by cold freezing point and fresh salinity 34 3 winter water dense shelf water is not observed a 1000 deep m trough allows water at 1 3 c to reach the moscow university ice shelf cavity to drive basal melt freshening by addition of glacial meltwater is widespread on the southern shelf at depths above 300 400 m with maximum meltwater concentrations up to 4 5 ml l 1 observed in outflows from the ice shelf cavities our observations indicate that the ocean properties on the sabrina coast more resemble those found on the continental shelf of the amundsen and bellingshausen seas than those typical of east antarctica

local and regional controls on holocene sea ice dynamics and oceanography in nares strait northwest greenland abstract nares strait is one of three channels that connect the arctic ocean to baffin bay unique sea ice conditions in the strait lead to the formation of landfast ice arches at its northern and southern ends these ice arches regulate arctic sea ice and freshwater export through the strait and promote the opening of the north water polynya the present study addresses the paucity of pre satellite records of environmental conditions in the nares strait area and aims at reconstructing holocene sea ice conditions and ocean circulation in the strait the investigation is based on a marine sediment core strategically retrieved from under the current ice arch in kane basin to the south of nares strait and provides a continuous record spanning the past ca 9 kyrs we use benthic foraminiferal assemblages and sea ice biomarkers to infer changes in holocene ocean circulation and sea ice conditions in kane basin the establishment of the modern ocean circulation in kane basin is related to ice sheet retreat and postglacial rebound while changes in sea ice cover concur with major shifts in the arctic oscillation ao our results suggest that sea ice cover in kane basin was highly variable between ca 9 0 and 8 3 cal ka bp before increasing probably in link with the 8 2 cold event and the opening of nares strait a short period of minimum sea ice cover and maximum atlantic bottom water influence occurred between ca 8 1 and 7 5 cal ka bp when kane basin was deeper than for the remaining of the holocene as atmospheric temperatures dropped sea ice cover intensified in kane basin between ca 7 5 and 5 5 cal ka bp but strong winds under prevailing positive like ao conditions likely prevented the formation of ice arches in nares strait during this time our micropaleontological data show that atlantic water was progressively excluded from kane basin by the postglacial isostatic rebound increasingly cooler atmospheric temperatures and a shift towards more negative phases of the ao may have promoted the establishment of ice arches in nares strait between ca 5 5 and 3 0 cal ka bp instabilities in the kane basin ice arch ca 3 0 cal ka bp coincide with a shift towards prevailing positive phases of the ao while a brief recovery of the ice arch occurred during more negative like ao conditions between ca 1 2 and 0 2 cal ka bp

glacier tongue calving reduced dense water formation and enhanced carbon uptake 1 dense shelf water formed in the mertz polynya supplies the lower limb of the global overturning circulation ventilating the abyssal indian and pacific oceans calving of the mertz glacier tongue mgt in february 2010 altered the regional distribution of ice and reduced the size and activity of the polynya the salinity and density of dense shelf water declined abruptly after calving consistent with a reduction of sea ice formation in the polynya breakout and melt of thick multiyear sea ice released by the movement of iceberg b9b and the mgt freshened near surface waters the input of meltwater likely enhanced the availability of light and iron supporting a diatom bloom that doubled carbon uptake relative to precalving conditions the enhanced biological carbon drawdown increased the carbonate saturation state outweighing dilution by meltwater input these observations highlight the sensitivity of dense water formation biological productivity and carbon export to changes in the antarctic icescape

sources of sediment found in sea ice from the western arctic ocean new insights into processes of entrainment and drift patterns 1 the geochemical fingerprint of entrained fe oxide mineral grains in arctic ocean sea ice is used to determine precise sources of this sediment this approach substantiates the importance of the laptev sea as a source of sea ice and even the presence of russian ice in the beaufort sea off alaska fe oxide grains from the laptev sea were found in floes in the beaufort sea chukchi borderland and central arctic ocean demonstrating the importance of sea ice in distributing itself throughout the arctic ocean and the potential of transporting sediment from russian rivers to north american shelves banks island shelf is the most important source of sediment sampled from ice floes in the beaufort sea northern chukchi sea and chukchi borderland area although most of the entrained sediment fits the criteria for suspension freezing in shallow water the presence of winter polynyas with offshore winds and not the size of shallow areas appears to be the critical factor for sea ice entrainment seven of the 18 ice floes sampled contained fe oxide grains from more than one source area the two most common sources that are found in the same ice floes are banks island and the laptev sea multiple sources in ice floes suggest that either mingling of fragmented ice floes occurs or that a source area containing grains from both these sources has yet to be located the addition of fine sand sized windblown sediment is not thought to be significant

variability of sea ice cover in the chukchi sea western arctic ocean during the holocene 1 dinocysts from cores collected in the chukchi sea from the shelf edge to the lower slope were used to reconstruct changes in sea surface conditions and sea ice cover using modern analogue techniques holocene sequences have been recovered in a down slope core b15 2135 m 75 44 n sedimentation rate of 1 cm kyr 1 and in a shelf core p1 201 m 73 41 n sedimentation rate of 22 cm kyr 1 the shelf record spanning about 8000 years suggests high frequency centennial oscillations of sea surface conditions and a significant reduction of the sea ice at circa 6000 and 2500 calendar cal years b p the condensed offshore record b15 reveals an early postglacial optimum with minimum sea ice cover prior to 12 000 cal years b p which corresponds to a terrestrial climate optimum in bering sea area dinocyst data indicate extensive sea ice cover 10 months yr 1 from 12 000 to 6000 cal years b p followed by a general trend of decreasing sea ice and increasing sea surface salinity conditions superimposed on large amplitude millennial scale oscillations in contrast 18o data in mesopelagic foraminifers neogloboquadrina pachyderma and benthic foraminifers cibicides wuellerstorfi reveal maximum subsurface temperature and thus maximum inflow of the north atlantic water around 8000 cal years b p followed by a trend toward cooling of the subsurface to bottom water masses sea surface to subsurface conditions estimated from dinocysts and 18o data in foraminifers thus suggest a decoupling between the surface water layer and the intermediate north atlantic water mass with the existence of a sharp halocline and a reverse thermocline especially before 6000 years b p the overall data and sea ice reconstructions from core b15 are consistent with strong sea ice convergence in the western arctic during the early holocene as suggested on the basis of climate model experiments including sea ice dynamics matching a higher inflow rate of north atlantic water

freshening drives contraction of antarctic bottom water in the australian antarctic basin antarctic bottom water aabw in the australian antarctic basin has become fresher and lighter since the late 1960s with largest changes observed near the sources of aabw the volume of aabw with neutral density n 28 30 kg m 3 decreased by 50 between 1969 1971 and 2008 2012 thinning at a rate of 100 m per decade contraction of dense aabw was balanced primarily by expansion of water lighter than n 28 15 kg m 3 prior to 1995 and by inflation of less dense classes of aabw after 1995 oxygen concentrations remained unchanged in the densest aabw and increased on neutral surfaces for aabw with n 28 31 kg m 3 between 1995 and 2011 2012 consistent with continued ventilation over this time period the observed changes in potential temperature salinity density volume and oxygen of aabw can be accounted for by freshening of the source waters but cannot be explained by changes in formation rate alone key points freshening drives contraction of antarctic bottom water aabw aabw has contracted by about 50 and thinned more than 100 m per decade since 1970 small increase in oxygen on isopycnals suggests continued ventilation of aabw 2014 american geophysical union all rights reserved

recent changes in arctic ocean sea ice motion associated with the north atlantic oscillation examination of a new ice motion dataset of the arctic ocean over a recent eighteen year period 1978 1996 reveals patterns of variability that can be linked directly to the north atlantic oscillation the intensity of the icelandic low one of its centers of action modulates the sea level pressure distribution over a broad region of the arctic ocean and the greenland iceland norwegian and barents seas over the winters of 1988 through 1995 the oscillation has remained in its positive phase contributing to coherent large scale changes in the intensity and character of ice transport in the arctic ocean the significant changes include the weakening of the beaufort gyre the increase in ice export through the fram strait the increase in ice import from the barents kara seas the enhanced eastward transport of sea ice from the laptev sea the weakening of the transpolar drift stream and the reduction in ice extent in the nordic seas all of these changes affect the regional and total sea ice mass balance of the arctic ocean

arctic vs north atlantic water mass exchanges in fram strait from pb isotopes in sediments surface sediment samples n 10 collected between spitzbergen and greenland and two cores raised east c04 and west c16 from fram strait were analyzed for their chemical and isotopic pb compositions to trace the source of sediments and water masses exchanging between the arctic and the north atlantic oceans in surface sediments variable major and trace element concentrations suggest variations in both the mineralogy carbonate and quartz dilution of other silicate minerals and source regions of detrital supplies based on th zr and to a lesser extent on th u ratios each core site shows specific but nearly constant th zr ratios indicating homogeneous source supplies at both core sites pb concentrations and isotopic compositions display similar patterns homogeneous low pb and radiogenic crustal signals below 5 10 cm contrasting with high pb and less radiogenic anthropogenic inputs at core tops however the differing pre anthropogenic pb isotopic ratios in c04 and c16 confirm the involve

the distribution of dissolved and total dissolvable aluminum in the beaufort sea and canada basin region of the arctic ocean 1 vertical profiles of the concentrations of dissolved al d al and total dissolvable al t al are reported from a transect extending from the continental shelf of the beaufort sea into the canada basin in the arctic ocean sampling was performed in late summer and early autumn 2007 a year of historically extensive sea ice melt vertical profiles of d al displayed surface maxima 1 3 nmol kg 1 subsurface minima 300 m depth suggest that al is likely lost through particle scavenging in the interior of the canada basin concentrations of t al show that particulate al 0 2 m is the dominant form of al in the water column except at greater depths at the most offshore stations lateral transport of d al and t al off the shelf likely results from the offshore progression of cyclonic eddies spawned inshore oscillating upwelling and downwelling favorable winds and brine rejection during sea ice formation that can drive currents sufficiently energetic to resuspend shelf sediments

antarctic ice sheet loss driven by basal melting of ice shelves accurate prediction of global sea level rise requires that we understand the cause of recent widespread and intensifying glacier acceleration along antarctic ice sheet coastal margins atmospheric and oceanic forcing have the potential to reduce the thickness and extent of floating ice shelves potentially limiting their ability to buttress the flow of grounded tributary glaciers indeed recent ice shelf collapse led to retreat and acceleration of several glaciers on the antarctic peninsula but the extent and magnitude of ice shelf thickness change the underlying causes of such change and its link to glacier flow rate are so poorly understood that its future impact on the ice sheets cannot yet be predicted here we use satellite laser altimetry and modelling of the surface firn layer to reveal the circum antarctic pattern of ice shelf thinning through increased basal melt we deduce that this increased melt is the primary control of antarctic ice sheet loss through a reduction in buttressing of the adjacent ice sheet leading to accelerated glacier flow the highest thinning rates occur where warm water at depth can access thick ice shelves via submarine troughs crossing the continental shelf wind forcing could explain the dominant patterns of both basal melting and the surface melting and collapse of antarctic ice shelves through ocean upwelling in the amundsen and bellingshausen seas and atmospheric warming on the antarctic peninsula this implies that climate forcing through changing winds influences antarctic ice sheet mass balance and hence global sea level on annual to decadal timescales

late summer biogeochemistry in the mertz polynya east antarctica a marked reconfiguration of the mertz polynya following the 2010 calving of the mertz glacier tongue has been associated with a decrease in the size and activity of the polynya we report observations of the oceanic carbonate co 2 system in late summer 2013 the third post calving summer season estimates of seasonal net community production ncp based on inorganic carbon deficits and the oxygen argon ratio indicate that the waters on the shelf to the east of commonwealth bay adjacent to the mertz glacier remain productive compared to pre calving conditions the input of residual or excess alkalinity from melting sea ice is found to contribute to the seasonal enhancement of carbonate saturation state and ph in shelf waters mean rates of ncp in 2012 2013 are more than twice as large as those observed in the pre calving summers of 2001 and 2008 and suggest that the new post calving configuration of the polynya favors enhanced net community production and a stronger surface ocean sink for atmospheric co 2 due at least in part to the redistribution of sea ice and associated changes in summer surface stratification

widespread freshening in the seasonal ice zone near 140 e off the adelie land coast antarctica from 1994 to 2012 long term water mass changes during 1994 2012 are examined from nine repeat hydrographic sections in the seasonal ice zone along 140 e off antarctica significant freshening trends are detected within most of the water masses from the bottom to surface bottom water freshened by 0 008 0 009 decade 1 below isopycnal surfaces and its layer thickness decreased by 120 160 dbar decade 1 throughout the study period in addition to general thinning the layer thickness was anomalously thin in 2012 suggesting a possible link with the sudden calving of the mertz glacier tongue and subsequent reduction in sea ice production winter water freshened by 0 03 decade 1 throughout the study period with significant interannual variability in the offshore region a long term increase in precipitation can explain a substantial portion of the freshening trend the lower circumpolar deep water on the continental slope underwent freshening at the same rate as the bottom water during the last two decades modified shelf water also shows robust freshening at a rate of 0 03 decade 1 combined with the freshening of near surface and bottom water masses in this region these data indicate freshening of the entire water column over the continental slope this widespread freshening is broadly consistent with the enhancement of the global hydrological cycle together with a possible acceleration of land ice melting key points antarctic bottom water freshened off adelie coast antarctica during 1994 2012 precipitation increase can cause a significant part of winter water freshening the freshening is consistent with the enhancement of global hydrological cycle 2013 american geophysical union all rights reserved

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

imprint of late pleistocene continental processes visible in ice rafted grains from the central arctic ocean abstract ice rafted quartz sand grains of sediment samples representing marine isotope stages mis 3 and 4 from the lomonosov ridge arctic ocean are here analysed with a scanning electron microscope sem to characterise processes in the sediment source area the microtextural characteristics of the grains were observed and their microtexture frequencies calculated specific sets of microtextures were identified and classified group i iii using principal component analysis pca and cluster analysis the statistically analysed microtextural data were used to identify signals of continental processes that operated during the late pleistocene mis 4 to mis 3 in the eurasian arctic the microtextures of group i generally formed as a result of prolonged fluvial alluvial or aeolian transport the glacial microtextures of groups ii and iii indicate subglacial conditions and transport based on the data two principal components seem to characterise late pleistocene continental environmental conditions glacial and non glacial there is a signal of non glacial continental processes in the ice rafted grains at around 62 64 and 67 ka ago a signal of subglacial processes was observed in the grains at around 26 34 42 and 45 ka and concurrent with non glacial at around 62 and 64 ka ago we suggest that these signals in mis 4 sediments are related to deglaciation with an increased supply of glacial sediment to the arctic ocean whereas during mis 3 they were probably related more to iceberg calving from the oscillating barents kara ice sheet

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

sea ice growth and water mass modification in the mertz glacier polynya east antarctica during winter in july september 1999 an extensive oceanographic survey 87 conductivity temperature and depth measuring stations was conducted in the mertz glacier polynya over the adelie depression off the antarctic coast between 145 and 150 e we identify and describe four key water masses in this polynya highly modified circumpolar deep water hmcdw winter water ww ice shelf water isw and high salinity shelf water hssw combining surface velocity data from an acoustic doppler current profiler with three hydrographic sections we found the hmcdw to be flowing westward along the shelf break 0 7 sv the ww and hssw flowing eastwards underneath mertz glacier 2 0 sv and that there was a westward return flow of isw against the continent 1 2 sv using a simple box model for the exchanges of heat and fresh water between the principal water masses we find that the polynya was primarily a latent heat polynya with 95 of the total heat flux caused by sea ice formation this heat flux results from a fresh water equivalent sea ice growth rate of 4 9 7 7 cm d 1 and a mass exchange between hmcdw and ww of 1 45 sv the inferred ocean heat flux is 8 14 w m 2 and compares well with other indirect estimates

suspended sediment and fresh water discharges in the ob and yenisey rivers 1960 1988 of the world s great rivers the ob and yenisey rank among the largest suppliers of fresh water and among the smallest suppliers of suspended sediment to the coastal ocean sediment in the middle reaches of the rivers is mobilized from bordering terraces and exchanged between channels and flood plains sediment in the lower reaches of these great rivers is deposited and stored permanently on a millennial time scale in flood plains sediment discharges already small under natural conditions are diminished further by large manmade reservoirs that trap significant proportions of the moving solids the long winter freeze and sudden spring breakup impose a peakedness in seasonal water runoff and sediment discharge that contrasts markedly with that in rivers of the tropics and more temperate climates very little sediment from the ob and yenisey rivers is being transported to the open waters of the arctic ocean under present conditions

enigmatic origin of the largest known carbon isotope excursion in earth s history carbonate rocks from the middle ediacaran period in locations all over the globe record the largest excursion in carbon isotopic compositions in earth history this finding suggests a dramatic reorganization of earth s carbon cycle named the shuram excursion for its original discovery in the shuram formation oman the anomaly closely precedes impressive events in evolution including the rise of large metazoans and the origin of biomineralization in animals instead of a true record of the carbon cycle at the time of sedimentation the carbon isotope signature recorded in the shuram excursion could be caused by alteration following deposition of the carbonate sediments a scenario supported by several geochemical indicators however such secondary processes are intrinsically local which makes it difficult to explain the coincident occurrence of carbon isotope anomalies in numerous records around the globe both possibilities are intriguing if the shuram excursion preserves a genuine record of ancient seawater chemistry it reflects a perturbation to the carbon cycle that is stronger than any known perturbations of the modern earth if however it represents secondary alteration during burial of sediments then marine sediments must have been globally preconditioned in a unique way to allow ordinary and local processes to produce an extraordinary and widespread response

chemical fingerprinting a precise and efficient method to determine sediment sources abstract an accurate method of determining source locations for detrital sediment is presented using the chemical composition of fe oxide minerals like a fingerprint this method is an improvement in the use of fe oxide minerals for provenance determinations because it requires less time and fewer source samples a rigorous test of the method uses a database of more than 38 000 grains from known locations the average error of matching grains back to 45 source locations designated for this database is less than 2 the method allows for proportional matching of a grain to multiple sources if other grains in the source database meet the compositional match criteria which helps reduce the error of incorrect matches most provenance studies do not involve source basins as large as the entire arctic ocean where sediment can be ice rafted several thousand kilometers for most studies only a few samples 100 grain analyses sample would be required to characterize a source if strategically placed such as near a river mouth deposits more than 40 million years old can be traced to specific sources using this method because fe oxide grains are relatively stable in most deposits

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

comparing sea ice sediment load with beaufort sea shelf deposits is entrainment selective abstract modern dispersal of sea ice rafted debris ird is important for the arctic ocean sediment budget from sources to sinks sediment entrainment occurs mainly through the action of small ice crystals frazil attaching to sedimentary particles in shallow water a mechanism that could be selective the principal source for entrainment of ird by suspension freezing into the beaufort gyre western arctic ocean is the adjacent shallow 250 m lithology and carbon and carbonate content of ird in the beaufort gyre were compared to sediments from the probable source surface in order to determine whether preferential entrainment occurs with any of these sediment parameters ird is generally much finer grained than the source surface showing that silt and clay size particles are preferentially entrained by frazil ice although anchor ice can locally incorporate very high percentages of sand and coarser clasts the coarsest ird is also the most poorly sorted the clay mineralogy of the 2 m ird fraction is very similar to that of the source surface indicating no selective entrainment within the clay fraction the lithology of sand in ird also matches that of the source surface although the number of coarse grains is too small 100 in most samples for a statistically meaningful count the average organic carbon content of ird is three times higher than that of the source surface but we attribute this to summer algal growth on ice floes rather than to selective entrainment a relatively low carbonate content in ird may be because much of the carbonate in the source is of silt size while about 50 of the ird measured is clay size the low carbonate content may also reflect solution under acidic summer conditions on sea ice selective export of silt and clay size particles by ice rafting from the shallow shelf with time should lead to the formation of a slightly coarser lag even though some of the dirty ice drops its sediment load in the entrainment area further mineralogical and lithological analysis on ird promises to become a useful tool for the study of sediment dispersal paths by drift ice in the arctic today and in the past and also for the study of sources of anthropogenic pollutants found in sea ice

antarctic bottom water from the adelie and george v land coast east antarctica 140 149 e 1 we report on observations of dense shelf water overflows and antarctic bottom water aabw formation along the continental margin of the adelie and george v land coast between 140 e and 149 e vertical sections and bottom layer water mass properties sampled during two rvib nathaniel b palmer hydrographic surveys nbp00 08 december 2000 january 2001 and nbp04 08 october 2004 describe the spreading of cold dense shelf water on the continental slope and rise from two independent source regions the primary source region is the adelie depression exporting high salinity dense shelf water through the adelie sill at 143 e an additional eastern source region of lower salinity dense shelf water from the mertz depression is identified for the first time from bottom layer properties northwest of the mertz sill and mertz bank 146 e 148 e that extend as far as the buffon channel 144 75 e in summer regional analysis of satellite derived ice production estimates over the entire region from 1992 to 2005 suggests that up to 40 of the total ice production for the region occurs over the mertz depression and therefore this area is likely to make a significant contribution to the total dense shelf water export concurrent time series from bottom mounted microcats and adcp instruments from the mertz polynya experiment april 1998 to may 1999 near the adelie sill and on the upper continental slope 1150 m and lower continental rise 3250 m to the north describe the seasonal variability in downslope events and their interaction with the ambient water masses the critical density for shelf water to produce aabw is examined and found to be 27 85 kg m 3 from the adelie depression and as low as 27 80 kg m 3 from the mertz depression this study suggests previous dense shelf water export estimates based on the flow through the adelie sill alone are conservative and that other regions around east antarctica with similar ice production to the mertz depression could be contributing to the total aabw in the australian antarctic basin

an isotopic palaeoenvironmental study of human skeletal remains from the nile valley stable isotope measurements were carried out on human skeletal remains from the nile valley ranging in age from about 7000 to 1750 yr b p and on a set of other samples among which are archaeological food remains bone samples were analyzed for 18o po3 4 18o co2 3 and 13c co 3 of carbonate hydroxylapatite and 13c and 15n of collagen food remains and tissue samples were analyzed for their 13c and 15n values the isotopic composition of bone collagen apatite and food remains partially representative of the diet in ancient egypt suggest a mixed diet including c3 plant food and probably animal resources both fresh water fish and c3 animals a rather surprising observation is the lack of differences between isotopic composition of remains of different social classes spanning from the very poor village of gebelein to the middle class of the rich town of asyut to the distinguished people who underwent mummification processes after their death from the palaeoclimatological point of view the 18o po3 4 values ranging from 20 6 to 24 5 seem to reflect the isotopic composition of nile river water also related to relative humidity rather than real climatic temperature variations through time the oxygen isotope compositions of carbonate and phosphate of the same samples from 30 2 to 32 5 and from 20 6 to 22 2 respectively suggest isotopic equilibrium conditions thus confirming the possibility of also using the carbonate measurements for palaeoclimatological studies at least in the case of recent and well preserved samples

mid to late pleistocene ice drift in the western arctic ocean evidence for a different circulation in the past the provenance of ice rafted debris ird in four arctic sediment cores implies that icebergs from the northwestern laurentide ice sheets drifted across the western arctic ocean along the 180 0 meridian toward fram strait during mid to late pleistocene deglaciations within the last 700 000 years this iceberg drift was different from the present day beaufort gyre circulation and resembled a dislocated transpolar drift tpd sea ice mainly followed the iceberg trajectories but also frequently drifted from the russian shelves eastward into the amerasian basin

mysterious iron nickel zinc arctic spherules an investigation into the sources of ice rafted detritus in the central arctic ocean using microprobe analyses of detrital fe oxide minerals discovered unique magnetic spherules in 20 of 144 potential source sample sites from the shelves and coastal areas around this ocean the spherules occur only in samples from the queen elizabeth islands canada these grains are characterized by a 45 60 m diameter pitting throughout and are occasionally found as multiple joint spherules they have the optical properties of magnetite and most remarkably contain both zno and nio in subequal amounts of up to 25 the ni suggests either an anthropogenic or meteoritic source these spherules were probably ice rafted into the central arctic ocean where they are found in sediments of holocene age and back to at least 780 ka eliminating an anthropogenic source because zn is too volatile to survive entry of a meteor through the earth s atmosphere these spherules were probably formed during impact of an fe ni meteor i

a shift in heavy and clay mineral provenance indicates a middle miocene onset of a perennial sea ice cover in the arctic ocean during the arctic coring expedition acex a 428 m thick sequence of upper cretaceous to quaternary sediments was penetrated the mineralogical composition of the upper 300 m of this sequence is presented here for the first time heavy and clay mineral associations indicate a major and consistent shift in provenance from the barents kara western laptev sea region characterized by presence of common clinopyroxene to the eastern laptev east siberian seas in the upper part of the section characterized by common hornblende amphibole sea ice originating from the latter source region must have survived at least one summer melt cycle in order to reach the acex drill site if considering modern sea ice trajectories and velocities this shift in mineral assemblages probably represents the onset of a perennial sea ice cover in the arctic ocean which occurred at about 13 ma thus suggesting a coeval freeze in the arctic and antarctic regions

how iceberg calving and grounding change the circulation and hydrography in the filchner ice shelf ocean system the formation of bottom water in the southern weddell sea is strongly influenced by the flow of ice shelf water isw out of the filchner ronne ice shelf cavity the breakout of three giant icebergs in 1986 and their grounding on the shallow berkner bank modified the circulation and water mass formation in the filchner trough and the adjacent sea areas hydrographic measurements along the filchner ice shelf front carried out with rv polarstern in 1995 show significant changes in the water mass characteristics and flow patterns in the filchner trough in comparison to measurements from the early 1980s changes in the trough will affect the flow over the sill to the deep weddell abyssal plain we combine a three dimensional ocean circulation model with conductivity temperature depth and stable isotope measurements to investigate the details of the circulation in front of and beneath the filchner ice shelf we assess the impact of stranded icebergs and a more southerly ice shelf front position caused by a 1986 iceberg calving event on the circulation and observed water mass properties results indicate variations of the flow pattern in the filchner trough and on berkner bank where high salinity shelf water the feedstock for isw is produced the calving and grounding impacts illustrate the sensitivity of the ice shelf ocean system to perturbations in local bathymetric settings

arctic perennial ice cover over the last 14 million years knowledge of the long term history of the perennial ice is an important issue that has eluded study because the cenozoic core material needed has been unavailable until the recent arctic coring expedition acex detrital fe oxide mineral grains analyzed by microprobe from the last 14 ma 164 m of the acex composite core on the lomonosov ridge were matched to circum arctic sources with the same mineral and 12 element composition these precise source determinations and estimates of drift rates were used to determine that these sand grains could not be rafted to the acex core site in less than a year thus the perennial ice cover has existed since 14 ma except for the unlikely rapid return to seasonal ice between the average sampling interval of about 0 17 ma both north america and russia contributed significant fe grains to the acex core during the last 14 ma

the distribution and formative processes of latent heat polynyas in east antarctica a study of polynya characteristics in east antarctica was undertaken using ice concentrations derived from special sensor microwave imager data for the period july 1987 august 1994 the areas of polynyas were defined as having an ice concentration 75 the analysis revealed a total of 28 coastal polynyas within the study region the spatial and temporal variability in areal extent was quantified the timing of mean maximum areal extent varied from june to october the bathymetry and wind regime at each polynya site was examined to gauge the relative importance of these parameters in polynya formation and maintenance in 20 locations shallow banks and shoals form grounding zones for icebergs and anchoring sites for fast ice which form barriers to the predominantly westward drift of the pack ice elsewhere north south coastal protrusions or alignments form similar barriers the subsequent removal of newly formed sea ice from the lee of such barriers by katabatic and synoptic winds maintains areas of reduced ice concentration and open water very few coastal polynyas are attributed solely to katabatic outflow the combined influence of bathymetry topography and winds is responsible for the characteristics of the majority of polynyas many were considered to be marginal characterised by occasional periods when the ice concentration falls below 75 an analysis of annual winter totals of areas with ice concentrations 75 shows no trends in total polynya areal extent over the period 1987 94 known locations of emperor penguin aptenodytes forsteri rookeries were also found to be associated with the locations of coastal polynyas

changes in water properties and flow regime on the continental shelf off the adelie george v land coast east antarctica after glacier tongue calving oceanic changes before and after the relocation of iceberg b9b and calving of the mertz glacier tongue mgt in february 2010 are examined on the continental shelf off the adelie land george v land coast east antarctica summer hydrographic observations including stable oxygen isotope ratio 18o in 2001 2008 and 2011 2015 and results of a numerical model are used along the western flank of the mgt temperature decreased between 2001 and 2015 for most of the water column in the adelie depression 18o generally decreased especially at the mgt draft depths on the northern side west of the mgt temperature salinity and 18o decreased in the intermediate layer east of the mgt in contrast temperature increased between 2001 and 2011 at intermediate depths salinity increased in the intermediate and deep layers and 18o slightly decreased in the deep layer but did not change much around 300 dbar the numerical experiment exhibits a change in ocean circulation revealing an increase in modified circumpolar deep water mcdw inflow in the east and a decrease in the west the contrasting changes in mcdw intrusion are consistent between the observations and numerical model and are indicative of the effect of removal of the ice barriers the contrast is overlain by overall decreases in salinity and 18o which suggests an increase in the continental meltwater fraction of 5 20 and might reveal a wide ranging influence from west antarctica the oxygen isotope ratio is hence effective in monitoring the increase in continental melt over the antarctic shelf

reconstructing the origin and trajectory of drifting arctic sea ice recent studies have indicated that drifting arctic sea ice plays an important role in the redistribution of sediments and contaminants here we present a method to reconstruct the back ward trajectory of sea ice from its sampling location in the eurasian arctic to its possible site of ori gin on the shelf based on historical drift data from the international arctic buoy program this method is verified by showing that origins derived from the backward trajectories are generally con sistent with other indicators such as comparison of the predicted backward trajectories with known buoy drifts and matching the clay mineralogy of sediments sampled from the sea ice with that of the seafloor in the predicted shelf source regions the trajectories are then used to identify regions where sediment laden ice is exported to the transpolar drift stream from the new siberian islands and the central kara plateau calculation of forward trajectories shows that the kara sea is a major contributor of ice to the barents sea and the southern limb of the transpolar drift stream

summer plankton production and nutrient consumption patterns in the mertz glacier region of east antarctica abstract we report on a biological and nutrient survey conducted off the eastern adelie and george v coasts of east antarctica in late december 2000 and january 2001 the region was dominated by the mertz glacier tongue mgt and its associated polynya that controlled the amount of open water through the season and influenced stratification near forming and melting ice as in other regions of the southern ocean large concentrations of nitrate phosphate and silicic acid were found chlorophyll levels varied from 0 3 mg m 3 in pack ice and slope regions to greater than 10 mg m 3 in a phaeocystis bloom encountered among grounded ice northeast of the mgt net utilization rates of nutrients were derived from the deficit between measured concentrations and estimated winter values nitrate n n and silicic acid utilization rates ranged from 2 to 12 and 14 to 30 mmol m 2 d 1 respectively and were greatest in commonwealth bay the ratio of nitrate to phosphate utilization was low 10 lower silicic acid to n n ratios were found in regions with substantial populations of phaeocystis sp in the eastern grounded ice region however there was significant variation in the silicic acid to n n utilization that may be induced by mixed layer iron levels that varied from

microfeatures of modern sea ice rafted sediment and implications for paleo sea ice reconstructions distinguishing sea ice rafted debris sird from iceberg rafted debris is crucial to an interpretation of ice rafting history however there are few paleo sea ice proxies this study characterizes quartz grain microfeatures of modern sird from the arctic ocean and compares these results with microfeatures from representative glacial deposits to potentially differentiate sird from ice rafted sediments which have been recently subjected to glacial processes this allows us to evaluate the use of grain microfeatures as a paleo sea ice proxy sird grains were largely subrounded with medium relief pervasive silica dissolution and a high abundance of breakage blocks and microlayering the glacial grains were more angular with lower relief and higher abundances of fractures and striations gouges discriminate analysis shows a distinct difference between sird and glacial grains with 7 of the sird grains containing typical glacial microtextures suggesting this method is a useful means of inferring paleo sea ice presence in the marine record we propose that differences in microfeatures of sird and glacial ice rafted debris reflect differences in sediment transport and weathering histories sediment transported to a coastal setting and later rafted by sea ice would be subject to increased chemical weathering whereas glaciers that calve icebergs would bypass the coastal marine environment thus preserving their glacial signature

modeling ocean cryosphere interactions off adelie and george v land east antarctica abstractocean cryosphere interactions along the adelie and george v land agvl coast are investigated using a coupled ocean sea ice ice shelf model the dominant feature of the mertz glacier tongue mgt located at approximately 145 e was a highly productive winter coastal polynya system until its calving in february 2010 dramatically changed the regional icescape this study examines the annual mean seasonal and interannual variabilities of sea ice production basal melting of the mgt ice shelves large icebergs and fast ice dense shelf water dsw export and bottom water properties on the continental slope and rise and assesses the impacts of the calving event the interannual variability of the winter coastal polynya regime is dominated by the regional offshore winds and air temperature which are linked to activity of the amundsen sea low pressure system this is the main driver of the interannual variability of dsw exported from the agvl region the calving event led to a decrease in sea

mapping of sea ice production for antarctic coastal polynyas 1 active sea ice production in antarctic coastal polynyas causes dense water formation finally leading to antarctic bottom water aabw formation this study gives the first mapping of sea ice production in the antarctic ocean based on heat flux calculation with ice thickness data derived from satellite data the highest ice production occurs in the ross ice shelf polynya region the ice production there decreased by 30 from the 1990s to the 2000s which can be one candidate for causing the recent freshening of aabw the cape darnley polynya in east antarctica is found to be the second highest production area suggesting a possible aabw formation area according to our estimation around 10 of southern ocean sea ice is produced in the major antarctic coastal polynyas the mapping provides surface heat and salt flux conditions in the ice covered region which have not been well understood

relationship between δ18o values for skeletal apatite from reindeer and foxes and yearly mean δ18o values of environmental water abstract the oxygen isotope composition of bone and tooth phosphate of 50 fox specimens and 30 reindeer specimens from various locations with different climatic and environmental conditions was measured the existing relationship between these values and the mean oxygen isotope composition of local meteoric water has been calculated in the case of foxes specimens belonging to two genera vulpes and alopex and three different species were measured the samples fit a straight line whose equation can be used for paleoclimatological studies either in arctic or in temperate regions for reindeer rangifer a relatively large range of isotopic values was obtained from each location suggesting imperfect equilibrium conditions with environmental water the calculated equation can be used for semi quantitative information on local paleowaters at high latitudes only

physiographic influences on dense shelf water cascading down the antarctic continental slope abstract predicting the source areas for antarctic bottom water aabw requires knowledge of how cold dense water masses form and move from the antarctic shelves to the continental slope here we use a review of nearly 50 years of direct hydrographic observations to infer the main broad scale influences on the distribution of dense shelf water dsw overflows that cascade down the continental slope around antarctica the dynamics and distribution of large ice shelves coastal polynyas and the physiography of the antarctic continental shelves are each considered the catalogue we present increases the number of dsw observations to 27 adds 20 additional stations where this process is likely to have occurred and identifies 41 areas where dsw appears to be absent our pan antarctic multi decadal review enhances the understanding of the formation and export of dsw and highlights the variability and complexity of ice ocean systems on high latitude continental margins the study also provides a context for understanding recent episodes of antarctic ice shelf instability and how the relationship between dsw and aabw may evolve with climatic and oceanographic changes

stronger ocean circulation and increased melting under pine island glacier ice shelf the ice shelf buttressing antarctica s pine island glacier has been melting rapidly observations taken between 1994 and 2009 show that meltwater production has increased by about 50 since 1994 as a result of a stronger circulation below the ice shelf

dissolved oxygen change and freshening of antarctic bottom water along 62 s in the australian antarctic basin between 1995 1996 and 2012 2013 abstract significant warming and freshening signals observed in the world s deep oceans are generally stronger southward in the australian antarctic basin along 62 s near the southern edge of the western pacific and indian oceans we compared water properties of antarctic bottom water observed in 1995 1996 and 2012 2013 the basin collects newly ventilated dense water from the western pacific sector of the antarctic coast and the ross sea compared on pressure surfaces freshening of more than 0 003 g kg in absolute salinity 0 003 in practical salinity scale 1978 or pss 78 was found below 3000 dbar the freshening was stronger 0 02 g kg or 0 02 in pss 78 eastward and towards the bottom suggesting that it originated from the regions of new bottom water production we also detected warming 0 2 c on pressure surfaces below the surface layer freshening of similar magnitudes were observed on density surfaces neutral densities 1028 1 kg m 3 adiabatic southward migration of water masses observed by satellite altimetry can explain the warming but not the freshening a notable increase in dissolved oxygen on density surfaces was found near the bottom the increase appears due to density decrease of near bottom water which can be explained by a change in the mixing ratio of bottom water from near the adelie depression adelie land bottom water albw higher oxygen with that from the more distant ross sea ross sea bottom water rsbw lower oxygen an increased contribution of albw and a decreased contribution of rsbw this change might be associated with a decrease in the rsbw supply following an earlier ice calving event in the polynya region oxygen rich 242 mol kg and dense 1028 35 kg m 3 bottom water observed in 1995 1996 in troughs near 130 e disappeared in 2012 2013 which also might reflect changes in bottom water production along the coast possibly in mertz and dibble polynyas

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

entrainment and export of laptev sea ice sediments siberian arctic sea ice sediments sis sediments rafted by ice and shelf surface deposits from the siberian laptev sea were analyzed to study turbulent entrainment processes this study focused on the silt and clay fractions on average representing 63 4 and 30 4 total 93 7 of the bulk sis respectively generally the sis contains 50 more silt than the shelf deposits while the clay percentages in both sample groups are similar sand sized particles are less abundant in sis than in bottom sediment although sis is clearly enriched in silt no evidence was found for preferential ice entrainment of any silt subfraction coarse medium fine statistical tests of sis and shelf silt parameters and the similar clay mineral compositions of both sample groups provide evidence for entrainment of laptev bottom deposits into newly forming ice the entrainment is related to the mechanism known as suspension freezing accordingly coarser clasts sand and plant debris may be lifted upward by buoyant anchor ice while coarse silt particles are supposed to be transported to the surface by rising frazil aggregates additionally turbulent interaction of convergent langmuir circulation and near surface frazil ice streaks is proposed to support ice entrainment of the finest particles 6 4 phi 12 m entrainment and export of sis from the laptev sea were assessed for ten individual flaw leads extended narrow polynyas separating fast and drifting ice using particle concentrations in ice samples and new ice formation rates the results show that roughly 20 mt of sis can be annually exported from the laptev sea by lead ice only thus formation and export of sediment laden lead ice may play a major geological role in siberian arctic shelf erosion and coastal retreat

a holocene record of changing arctic ocean ice drift analogous to the effects of the arctic oscillation 1 the arctic oscillation ao controls the configuration of the transpolar drift tpd if thicker ice from the beaufort gyre were exported the volume of fresh water sea ice in the nordic seas would significantly increase decreasing the formation of north atlantic deep water this would cool large parts of the northern hemisphere and affect global climate therefore in order to understand how the global climate system functions it is imperative to know how the tpd changed over the last millennium or more the provenance of grains in a sediment core located near the confluence of the tpd and the beaufort gyre provides a direct proxy for changes in seaice drift owing to these circulation systems the core has more than 200 cm of holocene sediment with intervals dominated by grains from the russian shelves alternating with intervals of abundant grains from north american sources grains matched to russian shelves indicate that the tpd was shifted toward north america similar to what occurs during a more positive phase of the ao this condition alternated with intervals where few grains matched to russian sources presumably because the tpd was restricted to the russian half of the arctic far from the core site during the last 1300 years increased influx of russian grains occurred approximately every 50 150 years this fluctuation might represent the long term oscillation of the ao which modulates the same tpd shift today