bowhead whale acoustic activity in the southeast beaufort sea during late summer 2008 2010 autonomous passive acoustic recorders were deployed to record sounds of bowhead whales balaena mysticetus in the southeast beaufort sea for periods of 30 55 days during the late summer open water seasons of 2008 2010 recordings were made in three areas licensed for hydrocarbon exploration spanning the continental slope and adjacent outer shelf and in a shallow inner shelf area where bowheads have been observed congregating to feed in recent decades bowhead sounds were counted in samples comprising 10 of each recorded hour in mid august and september in all 3 years the rate of bowhead calling at outer shelf sites exceeded that at adjacent continental slope sites by one to two orders of magnitude higher rates of calling occurred on the slope in late july and early august than at later dates calling rates varied by an order of magnitude between years in the one area that was monitored in different years the highest rates of calling occurred on the inner shelf offshore of the northern tuktoyaktuk peninsula these trends are consistent with patterns of habitat use previously reported from aerial surveys in this and nearby areas of the beaufort sea and with the results of satellite tagging studies

evaluation of pan arctic melt freeze onset in cmip5 climate models and reanalyses using surface observations the seasonal melt freeze transitions are fun damental features of the arctic climate system the representation of the pan arctic melt and freeze onset north of 60 n is assessed in two reanalyse

has arctic sea ice loss contributed to increased surface melting of the greenland ice sheet abstractin recent decades the greenland ice sheet has experienced increased surface melt however the underlying cause of this increased surface melting and how it relates to cryospheric changes across the arctic remain unclear here it is shown that an important contributing factor is the decreasing arctic sea ice reduced summer sea ice favors stronger and more frequent occurrences of blocking high pressure events over greenland blocking highs enhance the transport of warm moist air over greenland which increases downwelling infrared radiation contributes to increased extreme heat events and accounts for the majority of the observed warming trends these findings are supported by analyses of observations and reanalysis data as well as by independent atmospheric model simulations using a state of the art atmospheric model that is forced by varying only the sea ice conditions reduced sea ice conditions in the model favor more extensive greenland surface melting the authors find a positive feedba

the cenozoic structural evolution of a fold and thrust belt northeastern brooks range alaska a cenozoic fold and thrust belt in the eastern structural province of the northeastern brooks range exposes polydeformed lowgrade metasedimentary and metavolcanic rocks of the pre mississippian basement and its sedimentary cover immediately adjacent to much younger foredeep deposits analysis of mesoscopic and map scale structures in the range front region suggests that at least one pre mississippian deformational event was recorded in the basement sequence by north vergent fold and thrust structures and associated penetrative structures most of later cenozoic shortening of the pre mississippian rocks was accommodated by thrust duplication with little development of penetrative mesoscopic structures although separated from the underlying basement rocks by a major regional decollement horizon cenozoic deformation in the overlying mississippian through lower cretaceous cover sequence also was primarily by thrust duplication although local and regional structural trends within the cover sequence suggest that cenozoic deformation was north northwest directed east west cenozoic structural trends within the pre mississippian rocks may reflect an inherited pre mississippian structural grain and or pre mississippian age structures reactivated during cenozoic deformation a regional balanced cross section of the eastern structural province was constructed by integrating the detailed structural data from the range front region with subsurface data from the foredeep basin to the north and reconnaissance surface data from the interior of the range this balanced cross section indicates that cenozoic shortening across the region was 101 km 63 mi over an undeformed length of 220 km 137 mi or 46

high resolution climatic evolution of coastal northern california during the past 16 000 years holocene and latest pleistocene oceanographic conditions and the coastal climate of northern california have varied greatly based upon high resolution studies ca every 100 years of diatoms alkenones pollen caco 3 and total organic carbon at ocean drilling program odp site 1019 41 682 n 124 930 w 980 m water depth marine climate proxies alkenone sea surface temperatures ssts and caco 3 behaved remarkably like the greenland ice sheet project gisp 2 oxygen isotope record during the balling allerod younger dryas yd and early part of the holocene during the yd alkenone ssts decreased by 3 c below mean bolling allerod and holocene ssts the early holocene ca 11 6 to 8 2 ka was a time of generally warm conditions and moderate caco 3 content generally 4 the middle part of the holocene ca 8 2 to 3 2 ka was marked by alkenone ssts that were consistently 1 2 c cooler than either the earlier or later parts of the holocene by greatly reduced numbers of the gyre diatom pseudoeunotia doliolus 10 and by a permanent drop in caco 3 to 3 starting at ca 5 2 ka coastal redwood and alder began a steady rise arguing for increasing effective moisture and the development of the north coast temperate rain forest at ca 3 2 ka a permanent ca 1 c increase in alkenone sst and a threefold increase in p doliolus signaled a warming of fall and winter ssts intensified higher amplitude and more frequent cycles of pine pollen alternating with increased alder and redwood pollen are evidence that rapid changes in effective moisture and seasonal temperature enhanced el nino southern oscillation enso cycles have characterized the site 1019 record since about 3 5 ka

recent changes in the exchange of sea ice between the arctic ocean and the canadian arctic archipelago 1 sea ice is exchanged between the arctic ocean and canadian arctic archipelago caa but has not been quantified over long time periods the corresponding mechanisms responsible for recent variability and change also remain unidentified to address this we estimated the sea ice area flux between the arctic ocean and the m clure strait and queen elizabeth islands qei from 1997 to 2012 for the months of may to november over the period there was a mean flux of 1 103 km2 21 103 km2 at the m clure strait and mean flux of 8 103 km2 8 103 km2 at the qei positive and negative flux signs correspond to arctic ocean ice inflow and outflow respectively the m clure strait had a mean flux of 5 103 km2 from may to september and a mean flux of 7 103 km2 from october to november the qei gates had a mean flux of 4 103 km2 from august to september with negligible ice exchange from may to july and october to november more frequent high sea level pressure anomalies over the beaufort sea and canadian basin since 2007 have reduced arctic ocean multiyear ice myi inflow into the m clure strait the presence of myi in the caa originating from the arctic ocean has been maintained by inflow at the qei which has increased since 2005 these recent increases in arctic ocean myi inflow into the qei can be attributed to increased open water area within the caa that have provided more leeway for inflow to occur

observations reveal external driver for arctic sea ice retreat 1 the very low summer extent of arctic sea ice that has been observed in recent years is often casually interpreted as an early warning sign of anthropogenic global warming for examining the validity of this claim previously ipcc model simulations have been used here we focus on the available observational record to examine if this record allows us to identify either internal variability self acceleration or a specific external forcing as the main driver for the observed sea ice retreat we find that the available observations are sufficient to virtually exclude internal variability and self acceleration as an explanation for the observed long term trend clustering and magnitude of recent sea ice minima instead the recent retreat is well described by the superposition of an externally forced linear trend and internal variability for the externally forced trend we find a physically plausible strong correlation only with increasing atmospheric co2concentration our results hence show that the observed evolution of arctic sea ice extent is consistent with the claim that virtually certainly the impact of an anthropogenic climate change is observable in arctic sea ice already today

observed atlantification of the barents sea causes the polar front to limit the expansion of winter sea ice abstractbarents sea water bsw is formed from atlantic water that is cooled through atmospheric heat loss and freshened through seasonal sea ice melt in the eastern barents sea the bsw and fresh

wind and wave climate in the arctic ocean as observed by altimeters abstracttwenty years 1996 2015 of satellite observations were used to study the climatology and trends of oceanic winds and waves in the arctic ocean in the summer season august september the atlantic side seas exposed to the open ocean host more energetic waves than those on the pacific side trend analysis shows a clear spatial regional and temporal interannual variability in wave height and wind speed waves in the chukchi sea beaufort sea near the northern alaska and laptev sea have been increasing at a rate of 0 1 0 3 m decade 1 found to be statistically significant at the 90 level the trend of waves in the greenland and barents seas on the contrary is weak and not statistically significant in the barents and kara seas winds and waves initially increased between 1996 and 2006 and later decreased large scale atmospheric circulations such as the arctic oscillation and arctic dipole anomaly have a clear impact on the variation of winds and waves in the atlantic sector comparison

a sea ice free summer arctic within 30 years an update from cmip5 models interpreted as sea ice extent less than 1 0 million km 2 w e consider this estimate to be still valid based on projections of updated climate models cmip5 and observational data similar to previous models cmip3 cmip5 still shows a wide spread in hindcast and projected sea ice loss among different models further there is no consensus in the scientific literature for the cause of such a spread in results for cmip3 and cmip5 while cmip5 model mean sea ice extents are closer to observations than cmip3 the rates of sea ice reduction in most model runs are slow relative to recent observations all cmip5 models do show loss of sea ice due to increased anthropogenic forcing relative to preindustrial control runs applying the same technique of model selection and extrapolation approach to cmip5 as we used in our previous paper the interval range for a nearly sea ice free arctic is 14 to 36 years with a median value of 28 years relative to a 2007 baseline this suggests a nearly sea ice free arctic in the 2030s citation wang m and j e overland 2012 a sea ice free summer arctic within 30 years an update from cmip5 models geophys res lett 39 l18501

when will the summer arctic be nearly sea ice free 1 the observed rapid loss of thick multiyear sea ice over the last 7 years and the september 2012 arctic sea ice extent reduction of 49 relative to the 1979 2000 climatology are inconsistent with projections of a nearly sea ice free summer arctic from model estimates of 2070 and beyond made just a few years ago three recent approaches to predictions in the scientific literature are as follows 1 extrapolation of sea ice volume data 2 assuming several more rapid loss events such as 2007 and 2012 and 3 climate model projections time horizons for a nearly sea ice free summer for these three approaches are roughly 2020 or earlier 2030 10 years and 2040 or later loss estimates from models are based on a subset of the most rapid ensemble members it is not possible to clearly choose one approach over another as this depends on the relative weights given to data versus models observations and citations support the conclusion that most global climate model results in the cmip5 archive are too conservative in their sea ice projections recent data and expert opinion should be considered in addition to model results to advance the very likely timing for future sea ice loss to the first half of the 21st century with a possibility of major loss within a decade or two

annual cycle of downward particle fluxes on each side of the gakkel ridge in the central arctic ocean two mooring arrays carrying sediment traps were deployed from september 2011 to august 2012 at 83n on each side of the gakkel ridge in the nansen and amundsen basins to measure downward particle fl

the early winter sea ice variability under the recent arctic climate shift this study reveals that sea ice in the barents and kara seas plays a crucial role in establishing a new arctic coupled climate system the early winter sea ice before 1998 shows double dipole patterns over the arctic peripheral seas this pattern referred to as the early winter quadrupole pattern exhibits the anticlockwise sequential sea ice anomaliespropagationfromthe greenland sea to the barents kara seas andto the bering sea from october to december this early winter in phase ice variability contrasts to the out of phase relationship in late winter the mean temperature advection and stationary wave heat flux divergence associated with the atmospheric zonal wave 2 pattern are responsible for the early winter in phase pattern since the end of the last century the early winter quadrupole pattern has broken down because of the rapid decline of sea ice extent in the barents kara seas this remarkable ice retreat modifies the local ocean atmosphere heat exchange forcing an anomalous low air pressure over the barents kara seas the subsequent collapse of the atmospheric zonal wave 2 pattern is likely responsible for the breakdown of the early winter sea ice quadrupole pattern after 1998 therefore the sea ice anomalies in the barents kara seas play a key role in establishing new atmosphere sea ice coupled relationships in the warming arctic

a record of holocene sea ice variability off west greenland and its potential forcing factors abstract we present a reconstruction of holocene sea ice variability from sediment core ga306 gc3 from the holsteinsborg dyb off west greenland which provides an index of palaeoceanographic and palaeoenvironmental conditions within this climatically sensitive region during the last 6700 yr the reconstructed sea ice record combined with previously published proxy data suggests that relatively warm conditions with reduced sea ice extent prior to 5000 cal yr bp were associated with the holocene thermal maximum subsequent cooling and extensive sea ice cover between ca 5000 and 4000 cal yr bp was followed by even colder conditions and persistent sea ice cover during the neoglacial cooling phase particularly after ca 1500 cal yr bp there is a positive correlation between west greenland sea ice cover and solar activity over the past 5000 yr but the correlation is much weaker prior to 5000 cal yr bp in addition there is a strong link between west greenland sea ice and changes in the abundance of arctic benthic foraminifera species related to different water masses of the west greenland current during the entire interval even prior to 5000 cal yr bp our findings indicate that sea ice variability off west greenland was driven not only by solar activity but also by ocean circulation the strength of cold polar water from the east greenland current and warm atlantic water from the irminger current

multiple episodes of cenozoic denudation in the northeastern brooks range fission track data from the okpilak batholith alaska the northeastern brooks range of alaska is a complex mesozoic to cenozoic northward verging fold and thrust belt in response to regional compression shortening in the upper crust has occurred thr

seasonal control of petermann gletscher ice shelf melt by the ocean s response to sea ice cover in nares strait petermann gletscher drains 4 of the greenland ice sheet gris area with 80 of its mass loss occurring by basal melting of its ice shelf we use a high resolution coupled ocean and sea ice model with a thermodynamic glacial ice shelf to diagnose ocean controlled seasonality in basal melting of the petermann ice shelf basal melt rates increase by 20 in summer due to a seasonal shift in ocean circulation within nares strait that is associated with the transition from landfast sea ice to mobile sea ice under landfast ice cold near surface waters are maintained on the eastern side of the strait and within petermann fjord reducing basal melt and insulating the ice shelf under mobile sea ice warm waters are upwelled on the eastern side of the strait and mediated by local instabilities and eddies enter petermann fjord enhancing basal melt down to depths of 200 m the transition between these states occurs rapidly and seasonal changes within nares strait are conveyed into the fjord within the same season these results suggest that long term changes in the length of the landfast sea ice season will substantially alter the structure of petermann ice shelf and its contribution to gris mass loss

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

seasonal sea ice cover during the warm pliocene evidence from the iceland sea odp site 907 abstract sea ice is a critical component in the arctic and global climate system yet little is known about its extent and variability during past warm intervals such as the pliocene 5 33 2 58 ma here we present the first multi proxy ip25 sterols alkenones palynology sea ice reconstructions for the late pliocene iceland sea odp site 907 our interpretation of a seasonal sea ice cover with occasional ice free intervals between 3 50 3 00 ma is supported by reconstructed alkenone based summer sea surface temperatures as evidenced from brassicasterol and dinosterol primary productivity was low between 3 50 and 3 00 ma and the site experienced generally oligotrophic conditions the east greenland current and east icelandic current may have transported sea ice into the iceland sea and or brought cooler and fresher waters favoring local sea ice formation between 3 00 and 2 40 ma the iceland sea is mainly sea ice free but seasonal sea ice occurred between 2 81 and 2 74 ma sea ice extending into the iceland sea at this time may have acted as a positive feedback for the build up of the greenland ice sheet gis which underwent a major expansion 2 75 ma thereafter most likely a stable sea ice edge developed close to greenland possibly changing together with the expansion and retreat of the gis and affecting the productivity in the iceland sea

the response of the bering sea gateway during the mid pleistocene transition abstract the mid pleistocene transition and the response of sea ice in the subarctic north pacific are examined using a diatom record from the north eastern bering sea slope iodp core u1344a high percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions thalassiosira antarctica var borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0 9 to1 2 ma after which it dominates the assemblage until 0 6 ma the decline of neodenticula seminae indicative of alaskan stream water inflow is in agreement with neighbouring core u1343e confirming the reduction of bering sea circulation after 0 9 ma we propose that during the mpt a stepped advancement of sea ice occurs in the bering sea as a response to increased moisture delivery to the high latitudes an extended period of diatom productivity between 0 75 and 0 65 ma marks major deglacial conditions towards the end of the mpt by 0 6 0 55 ma the work highlights the important role played by sea ice and supports the contention of a colder mpt in the subarctic pacific

style controls and timing of fold and thrust deformation of the jago stock northeastern brooks range alaska involvement of the devonian jago stock in cenozoic fold and thrust deformation of the northeastern brooks range illustrates the influence of a relatively small isolated crystalline body on the mechanical stratigraphy and subsequent deformatioml behavior of an otherwise layered sedimentary package the small size of the stock allowed it and the structurally coupled overlying mississippian kekiktuk conglomerate to deform nonpenetratively as a horse in a regional duplex in contrast to the semiductile behavior of the nearby but much larger okpilak batholith shear was localized in the upper part of the stock and the conglomerate due to partial detachment of the overlying carboniferous lisbume group north vergent thrust related folds formed in the mechanically layered lisburne group carbonates instead of the symmetrical unfaulted detachment folds more typical of the region because an underlying regional detachment horizon in the mississippian kayak sme is depositionally absent over the stock unusually competent contact metamorphosed pre mississippian metasedimentary rocks were thrust over the stock and its cover because a ramp formed at the edge of the stock ad cut upsection through the lisburne group due to the absence of kayak shale a ar13 r age of foliated white mica indicates thrusting of the stock by 61 ma fission track ages indicate cooling at 44 and 28 ma these ages indicate a cooling history that implies 11 h of unroofing since 61 ma only 1 5 km of which can be explained by the inferred duplex structure the remining 9 5 km of unroofing is most likely due to subduplex structural thickening above a deep regional detachment

mid holocene drylands a multi model analysis using paleoclimate modelling intercomparison project phase iii pmip3 simulations this study examines changes in aridity levels during the mid holocene approximately 6000 cal yr ago using multi model simulations from the paleoclimate modelling intercomparison project phase ii