summer enhancement of arctic sea ice volume anomalies in the september ice zone abstractbecause of its persistence on seasonal time scales arctic sea ice thickness sit is a potential source of predictability for summer sea ice extent sie new satellite observations of sit represent an opportunity to harness this potential predictability via improved thickness initialization in seasonal forecast systems in this work the evolution of arctic sea ice volume anomalies is studied using a 700 yr control integration and a suite of initialized ensemble forecasts from a fully coupled global climate model this analysis is focused on the september sea ice zone as this is the region where thickness anomalies have the potential to impact the sie minimum the primary finding of this paper is that in addition to a general decay with time sea ice volume anomalies display a summer enhancement in which anomalies tend to grow between the months of may and july this summer enhancement is relatively symmetric for positive and negative volume anomalies and peaks in july regardless of the initi

sea ice models for climate study retrospective and new directions scientific observations of sea ice began more than a century ago but detailed sea ice models appeared only in the latter half of the last century the high albedo of sea ice is critical for the earth s heat balance and ice motion across the ocean s surface transports fresh water and salt the basic components in a complete sea ice model must include vertical thermodynamics and horizontal dynamics including a constitutive relation for the ice advection and deformational processes this overview surveys topics in sea ice modeling from the global climate modeling perspective emphasizing work that significantly advanced the state of the art and highlighting promising new developments

assessing the importance of drilling predation over the palaeozoic and mesozoic abstract plausible predatory palaeozoic and mesozoic drillholes have been reported in the literature from 62 localities mainly from north america and western europe most of which were discovered in the last 20 years twenty nine of these reports include sufficient data to be statistically valid analyses of these data suggest that there was a highly significant increase in drillhole and hence predator size in the early devonian which may reflect a change in predatory taxa as part of the mid palaeozoic marine revolution in this study frequency of drillholes in particular species has been examined examination of drilling frequency suffered by individual taxa from a range of palaeozoic and mesozoic sites showing that these are highly variable just as they are between different holocene localities nevertheless levels of up to 50 in the palaeozoic and 40 in the mesozoic suggest that at least locally drillers did exert an important selection pressure analysis of the currently available data set reveals no significant change in drilling frequency over the palaeozoic and mesozoic there are fewer records of drilling predation from the palaeozoic and mesozoic than from the cenozoic at present however it is difficult to assess whether drilling was truly less widespread than in the cenozoic or whether at least part of the problem is taphonomic loss of information in particular in the late palaeozoic and mesozoic it is striking that relatively few reports involve molluscan prey despite their attractiveness as profitable prey with high flesh yield when compared with the apparently more frequently drilled brachiopods however study of the style of preservation of drilled molluscs that were mostly originally aragonitic suggests that drillholes are only preserved in faunas which are exceptionally preserved such that the original microstructure is still observable by contrast brachiopods which were either originally phosphatic or calcitic have much better preservation potentials and therefore may be more likely to show drillholes an understanding of the preservation biases involved in the recognition of drillholes may suggest suitable localities for further research more data from a suite of localities world wide are required for a more detailed analysis of patterns of drilling predation in the palaeozoic and mesozoic

variations in the age of arctic sea ice and summer sea ice extent 1 three of the past six summers have exhibited record low sea ice extent on the arctic ocean these minima may have been dynamically induced by changes in the surface winds based on results of a simple model that keeps track of the age of ice as it moves about on the arctic ocean we show that the areal coverage of thick multi year ice decreased precipitously during 1989 1990 when the arctic oscillation was in an extreme high index state and has remained low since that time under these conditions younger thinner ice anomalies recirculate back to the alaskan coast more quickly decreasing the time that new ice has to ridge and thicken before returning for another melt season during the 2002 and 2003 summers this anomalously younger thinner ice was advected into alaskan coastal waters where extensive melting was observed even though temperatures were locally colder than normal the age of sea ice explains more than half of the variance in summer sea ice extent

thinning and volume loss of the arctic ocean sea ice cover 2003 2008 1 we present our best estimate of the thickness and volume of the arctic ocean ice cover from 10 ice cloud and land elevation satellite icesat campaigns that span a 5 year period between 2003 and 2008 derived ice drafts are consistently within 0 5 m of those from a submarine cruise in mid november of 2005 and 4 years of ice draft profiles from moorings in the chukchi and beaufort seas along with a more than 42 decrease in multiyear my ice coverage since 2005 there was a remarkable thinning of 0 6 m in my ice thickness over 4 years in contrast the average thickness of the seasonal ice in midwinter 2 m which covered more than two thirds of the arctic ocean in 2007 exhibited a negligible trend average winter sea ice volume over the period weighted by a loss of 3000 km3 between 2007 and 2008 was 14 000 km3 the total my ice volume in the winter has experienced a net loss of 6300 km3 40 in the 4 years since 2005 while the first year ice cover gained volume owing to increased overall area coverage the overall decline in volume and thickness are explained almost entirely by changes in the my ice cover combined with a large decline in my ice coverage over this short record there is a reversal in the volumetric and areal contributions of the two ice types to the total volume and area of the arctic ocean ice cover seasonal ice having surpassed that of my ice in winter area coverage and volume became the dominant ice type it seems that the near zero replenishment of the my ice cover after the summers of 2005 and 2007 an imbalance in the cycle of replenishment and ice export has played a significant role in the loss of arctic sea ice volume over the icesat record

possible dynamic and thermal causes for the recent decrease in sea ice in the arctic basin 1 a dynamic thermodynamic sea ice model with 50 km spatial and 24 hour temporal resolution was used to investigate the spatial and temporal variability of the sea ice cover and the surface energy exchange in the arctic basin daily surface level air temperature and pressure data from national centers for environmental prediction for 1958 1997 and climatic data for cloudiness relative humidity snow precipitation and the heat flux from the deep ocean in the greenland barents and bering seas were used as external forcing the model is integrated using the method of large particles belotserkovskii 1984 the model satisfactorily reproduces the seasonal and interannual variability of the main characteristics of the sea ice the sea ice extent and exchange through the main straits and the surface heat exchange for different parts of the arctic basin in particular estimates of the year to year difference between mean sea ice thickness in september show good agreement with the essential thinning of sea ice in the canadian basin that rothrock et al 1999 found most of the decrease in sea ice thickness is caused by a decrease in ridge concentration and an increase in the area covered by undeformed ice numerical experiments show that only 20 of the ice decrease can be explained by an increase in surface level air temperature model results for the canadian and eurasian basins allow us to determine the main trends in the temporal variability of ice thickness in these regions our model results suggest that the recent thinning of the sea ice correlates with a decrease in the concentration of ridged ice in turn the concentration of ridged ice and the total sea ice volume in the canadian basin correlate with cyclonic and anticyclonic regimes of the wind driven ice motion the sharp decrease in modeled ice volume in the canadian basin after 1987 also coincides with a significant increase in the mean atmospheric vorticity index for the central arctic ocean

arctic sea ice variability revisited this paper explores spatial and temporal relationships between variations in arctic sea ice concentration summer and winter and near surface atmospheric temperature and atmospheric pressure using multivariate statistical techniques trend empirical orthogonal function eof and singular value decomposition svd analyses are used to identify spatial patterns associated with covariances and correlations between these fields results show that 1 in winter the arctic oscillation still explains most of the variability in sea ice concentration from 1979 to 2006 and 2 in summer a decreasing sea ice trend centered in the pacific sector of the arctic basin is clearly correlated to an arctic wide air temperature warming trend these results demonstrate the applicability of multivariate methods and in particular svd analysis which has not been used in earlier studies for assessment of changes in the arctic sea ice cover results are consistent with the interpretation that a warming signal has now emerged from the noise in the arctic sea ice record during summer our analysis indicates that such a signal may also be forthcoming during winter

predatorial borings in late precambrian mineralized exoskeletons the late precambrian tube forming cloudina the earliest known animal to produce a mineralized exoskeleton shows evidence of having been attacked by shell boring organisms of more than 500 tubes from shaanxi province china 2 7 have rounded holes 40 to 400 micrometers in diameter the relation between the size of the holes and the width of the bored tubes suggests that the attacking organism was a predator selecting its prey for size if true this would be the oldest case of predation in the fossil record and would support the hypothesis that selection pressures from predation was a significant factor in the evolution of animal skeletons around the precambrian cambrian boundary

a pathway connecting the monsoonal heating to the rapid arctic ice melt abstractthis study provides a monsoonal link to the rapid arctic ice melt each year the planetary scale african asian monsoonal outflow near the tropopause carries a large anticyclonic gyre that has a longitudinal spread that occupies nearly half of the entire tropics in recent years the south asian summer monsoon has experienced increased rainfall over northwestern india and pakistan and it has also contributed to more intense local anticyclonic outflows from this region the western lobes of these intense upper high pressure areas carry outflows with large heat fluxes from the monsoon belt toward central asia and eventually to the region of the rapid ice melt of the canadian arctic in this study this spectacular pathway has been defined from airflow trajectories heat content and heat flux anomalies most of these show slow increasing trends in the last 20 years the monsoonal connection to the rapid arctic ice melt is a new contribution of this study this is shown from the passage of a vertical c

mystery of naticid predation history solved evidence from a living fossil species observations of living cernina fluctuata sowerby the sole extant species of the mesozoic and cenozoic prosobranch gastropod family ampullospiridae show that this species is an algal grazer and is not a shell drilling predatory naticid gastropod all jurassic and early cretaceous gastropods previously assigned to naticidae belong to ampullo spiridae and are now inferred to be herbivores not shell drillers this finding refutes the triassic origin and favors a cretaceous origin for naticid drilling predation a preliminary revision of cenozoic and cretaceous species previously assigned to naticidae suggests that naticids were absent prior to the cretaceous campanian and diversified at a modern level in eocene time this pattern of naticid diversification from the late cretaceous onward coincides roughly with the evidence of naticid predation the fossil record of naticid drill holes once of anomalously short duration now accurately reflects the geologic history of naticid predation activity

spatial and temporal variability of sea ice in the southern beaufort sea and amundsen gulf 1980 2004 1 changing extent location and motion of the arctic perennial pack affect the annual evolution of seasonal ice zones canadian ice service digital ice charts covering the southern beaufort sea and amundsen gulf are used to illustrate summer and winter conditions and trends between 1980 and 2004 for several sea ice stages of development results illustrate average sea ice conditions within the region in summer and winter for predominant sea ice types and changes in the relative concentration of sea ice types in summer and winter in summer a trend toward increased old sea ice concentration occurred near the mouth of amundsen gulf with a trend toward decreasing summer first year sea ice farther west in winter increasing thick first year sea ice extent appears to be replacing young sea ice within the flaw lead system in the region the dynamically driven breakup of sea ice in spring in the amundsen gulf is a highly variable event taking anywhere between 2 and 22 weeks to completely remove ice from the gulf the timing and duration of the open water season depends upon the extent and timing of old ice influx freezeup occurs very quickly proceeding from west to east with little temporal variability the results of this paper are used to set the context for the canadian arctic shelf exchange study cases in terms of sea ice dynamic and thermodynamic processes

semi empirical treatment of wave transformation outside and inside the breaker line a semi empirical method is developed which predicts the wave height shoaling up to the break point on laboratory and natural beaches linear shoaling is enhanced with empirical curves for the wave shape obtained from field measurements of wave height through the break point and the surf zone made on an ocean beach in southern australia from 1987 to 1989 wave height shoaling breaking and attenuation are unified in a mixed lagrangian eulerian numerical model of random wave height transformation which with the semi analytical enhancements provides improved predictions of the height transformation of individual waves through the surf zone this is demonstrated for a wide variety of cases from the field and laboratory

predicting regional and pan arctic sea ice anomalies with kernel analog forecasting predicting arctic sea ice extent is a notoriously difficult forecasting problem even for lead times as short as one month motivated by arctic intraannual variability phenomena such as reemergence of sea surface temperature and sea ice anomalies we use a prediction approach for sea ice anomalies based on analog forecasting traditional analog forecasting relies on identifying a single analog in a historical record usually by minimizing euclidean distance and forming a forecast from the analog s historical trajectory here an ensemble of analogs is used to make forecasts where the ensemble weights are determined by a dynamics adapted similarity kernel which takes into account the nonlinear geometry on the underlying data manifold we apply this method for forecasting pan arctic and regional sea ice area and volume anomalies from multi century climate model data and in many cases find improvement over the benchmark damped persistence forecast examples of success include the 3 6 month lead time prediction of arctic sea ice area the winter sea ice area prediction of some marginal ice zone seas and the 3 12 month lead time prediction of sea ice volume anomalies in many central arctic basins we discuss possible connections between kaf success and sea ice reemergence and find kaf to be successful in regions and seasons exhibiting high interannual variability

a model to interpret driftwood transport in the arctic abstract driftwood is frequently used to estimate past changes of sea ice extent and circulation in the arctic nevertheless driftwood observations are difficult to interpret because of the potentially complex relation with climate change in order to determine the origin of the observed changes we built a driftwood transport model dtm simulating the driftwood trajectories from the boreal forest to arctic coasts the model is driven by three main variables which are the sea ice velocity concentration and the sea surface current velocity that can be derived from observations or climate model outputs e g from a general climate model gcm overall the dtm model agrees with the observations although this comparison needs to be taken with caution because of the sparse data and the uncertainties of driftwood provenance through simulations performed with the dtm model we confirm the strong influence of the variability of the atmospheric circulation on the spatial driftwood distribution model simulations of the mid holocene period driven by six gcms show that small local changes in sea ice circulation a westward shift in the transpolar drift and a reduced beaufort gyre during the mid holocene compared to the present period suffice to explain the driftwood landing change during the mid holocene with a non negligible contribution from reduced sea ice concentration consequently a change in driftwood deposit should not be directly interpreted as large modifications in atmospheric circulation and the complexity of the response of driftwood trajectories to past climate changes clearly highlights the interest of using a model to interpret driftwood records

new example of devonian predatory boreholes and the influence of brachiopod spines on predator success three abundant devonian frasnian brachiopod species from the lime creek fm of iowa usa douvillina arcuata devonoproductus walcotti and pseudoatrypa devoniana contain boreholes pooled drilling frequency is 10 6 the boreholes are small usually 1 0 mm diameter cylindrical and drilled perpendicular to the shell surface the borings appear to be type a boreholes as described by ausich and gurrola 1979 j paleontol 53 335 344 based on multiple criteria including statistically significant stereotypy with respect to valve preference site on valve and size class of the prey the boreholes are inferred to be predatory or parasitic in origin for each species the predator preferred to attack the valve closest to the substrate regardless of whether that was the pedicle or brachial valve boreholes were concentrated over the muscle field on each of the three species the success percentage percent of complete holes was statistically lower 2 p 0 04 for the spinose devonoproductus walcotti 33 33 than for the non spinose but otherwise morphologically similar douvillina arcuata 54 22 in spite of the fact that d walcotti has a thinner shell this is the first quantitative evidence for an anti predatory function for brachiopod spines

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

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

atmospheric forcing of fram strait sea ice export a closer look fram strait is the primary region of sea ice export from the arctic and therefore plays an important role in regulating the amount of sea ice and freshwater within the arctic we investigate the variability of fram strait sea ice motion and the role of atmospheric circulation forcing using daily data during the period 1979 2006 the most prominent atmospheric driver of anomalous sea ice motion across fram strait is an east west dipole pattern of sea level pressure slp anomalies with centers of action located over the barents sea and greenland this pattern also observed in synoptic studies is associated with anomalous meridional winds across fram strait and is thus physically consistent with forcing changes in sea ice motion the association between the slp dipole pattern and fram strait ice motion is maximized at 0 lag persists year round and is strongest on time scales of 10 60 days the slp dipole pattern is the second empirical orthogonal function eof of daily slp anomalies in both winter and summer when the analysis is repeated with monthly data only the barents center of the slp dipole remains significantly correlated with fram strait sea ice motion however after removing the leading eof of monthly slp variability e g the north atlantic oscillation the full east west dipole pattern is recovered no significant slp forcing of fram strait ice motion is found in summer using monthly data even when the leading eof is removed our results highlight the importance of high frequency atmospheric variability in forcing fram strait sea ice motion

drill hole convergence and a quantitative analysis of drill holes in mollusks and brachiopods from the triassic of italy and poland abstract the history of predation is recorded primarily from drilling in cenozoic invertebrates quantitative data are uncommon from the triassic a period before the appearance and radiation of many known drill hole producers such as various gastropod families and octopods we present quantitative evidence of drilling from the late triassic carnian cassian formation of italy and the middle triassic anisian lower muschelkalk of poland documenting the first drill holes in triassic brachiopods a single brachiopod with a cylindrical complete drill hole was found in a brachiopod sample from of poland drilling percentage 0 3 n 365 the cassian formation yielded drill holes in gastropods bivalves and brachiopods indicating that more species are drilled than was known previously the minimum drilling percentage exclusive of incomplete drill holes of a sample from the stuores wiesen cassian formation is 1 7 n 116 5 prey selectivity is evident complete drill holes are primarily present in one gastropod species polygyrina lommeli 11 8 of specimens with a complete drill hole whereas other common species were not drilled single drill holes in brachiopods are cylindrical and complete and may be predatory in origin multiple drill holes in mollusks are common and drill holes are parabolic and often incomplete with a central boss resembling the shape of drill holes produced by extant naticid gastropods a survey of the paleozoic literature showed that such drill holes are also present in devonian and carboniferous brachiopods however naticids did not evolve until the cretaceous so we propose the term drill hole convergence for similar shaped drill holes produced by different organisms the triassic parabolic drill holes are not caused by domicile seeking or boring organisms instead we favor a predatory origin of these drill holes but we cannot entirely rule out parasitism surveying other triassic invertebrate assemblages should yield more evidence of drilling

north pole ice thickness and association with ice motion history 1977 1992 ice drafts measured by u s navy submarine sonar near the north pole from 1977 to 1992 were used together with arctic ocean drifting buoy data from 1979 to 1992 to investigate north pole ice thickness changes during this 15 year period a primary objective was to determine dynamical forcing mechanisms and associated time scales relevant to ice thickness variation north pole ice thickness showed much interannual variability and no systematic decrease of ice thickness was observed changes in ice thickness were closely associated with long term directional deviation of ice motion from geostrophic wind forcing and with ice convergence and divergence at the north pole during the 1 2 weeks prior to submarine measurement the geographic origin of ice within the arctic ocean was not associated with its eventual thickness at the north pole

the role of shortwave radiation in the 2007 arctic sea ice anomaly 1 recent satellite and re analysis model results on downwelling surface shortwave dssw radiation allow the investigation of its role in the arctic sea ice anomalies using satellite based information we revisit claims that reduced cloudiness and enhanced dssw are associated with the significant loss of sea ice during 2007 we account for the fact that the arctic ocean is not homogenous in terms of the characteristics of the sea ice anomalies we separate the arctic ocean region according to the spatial distribution of the sea ice anomalies and investigate the impact of dssw on the ice conditions accordingly the region which exhibits the strongest signal during the unprecedented 2007 reduction in sea ice is identified as 120 e to 210 e our analysis shows that the lowest cloud amount and the highest accumulated amount of dssw prior to the ice melt season june occur in 2005 for 2007 areas showing the largest accumulation of dssw do not correspond with negative sea ice concentration anomalies

predation in the paleozoic gastropod like drillholes in devonian brachiopods middle devonian articulate brachiopods ludlowville and moscow formations hamilton group new york have external tapered holes with a central boss that are indistinguishable from drillholes of naticid gastropods that are known from the triassic and later drillholes are specific to prey ribbed shells were avoided and specific to sites on prey healed drillholes suggest penetration of live prey as many as 44 percent of the preferred prey are drilled indicating a level of predation that has been reported only from post paleozoic strata

waves and climate change in the north east atlantic wave height in the north atlantic has been observed to increase over the last quarter century based on monthly mean data derived from observations empirical models have linked a large part of this increase in wave height with the north atlantic oscillation wave models provide a tool to study impacts of various climate change scenarios and investigate physical explanations of statistical results in this case we use a wave model of the ne atlantic model tests were carried out using synthetic wind fields varying the strength of the prevailing westerly winds and the frequency and intensity of storms the location of storm tracks and the storm propagation speed the strength of the westerly winds is most effective at increasing mean and maximum monthly wave height the frequency intensity track and speed of storms have little effect on the mean wave height but intensity track and speed significantly affect maximum wave height

low drilling frequency in norian benthic assemblages from the southern italian alps and the role of specialized durophages during the late triassic abstract drillholes represent one of the clearest lines of evidence for predation of benthic invertebrates in the fossil record and are frequently used as a primary proxy for predation intensity in the fossil record drillholes are abundant in the late cretaceous and cenozoic but their occurrence is patchy in older deposits of the mesozoic the inconsistent record of drillholes in pre cretaceous deposits of mesozoic age are problematic for interpretations of predation prey dynamics and adaptive radiations and the role of taphonomy or diagenesis have not been resolved here we present drilling percentages for assemblages of well preserved shelly benthic invertebrates mainly comprised of bivalves and rare gastropods from the upper norian upper triassic in northern italy in order to compare these values with reported drilling percentages from the carnian san cassiano formation a rare triassic sedimentary unit that has yielded many drilled fossils the norian fossil deposits reported here are comparable to those of the san cassiano in terms of depositional environment preservation and region and can be reasonably compared to the drilling percentage of fossils from the san cassiano the sampled deposits are collected from marly limestone horizons in the argillite di riva di solto in the southern italian alps deposited in the lombardian basin and which are interbedded with shale units containing well preserved fish and arthropod fossils enabling a correlation between paleoecological structure of the shelly benthos and the demersal pelagic predator diversity over four hundred bivalve fossils yielded a drilling percentage of 0 24 1 406 which is typical for fossil assemblages of this age but the single occurrence of a drillhole in this study is in marked contrast to the many drilled specimens reported from the san cassiano formation deposit in italy the drilled specimen with complete drillhole was an infaunal bivalve and no incomplete drillholes were observed in other specimens thus drilling percentages for the triassic are consistently low but present suggesting that drilling predation was an ecologically minimal influence to benthic communities and unlikely to have driven the significant ecological changes observed in benthic communities during the late triassic although drilling predation occurred during the late triassic we present an updated database of specialized durophagous predators including fishes sharks and reptiles that are likely to have been more ecologically influential on benthic communities during the norian stage fishes in particular

solar partitioning in a changing arctic sea ice cover the summer extent of the arctic sea ice cover has decreased in recent decades and there have been alterations in the timing and duration of the summer melt season these changes in ice conditions have affected the partitioning of solar radiation in the arctic atmosphere ice ocean system the impact of sea ice changes on solar partitioning is examined on a pan arctic scale using a 25 km 25 km equal area scalable earth grid for the years 1979 2007 daily values of incident solar irradiance are obtained from ncep reanalysis products adjusted by era 40 and ice concentrations are determined from passive microwave satellite data the albedo of the ice is parameterized by a five stage process that includes dry snow melting snow melt pond formation melt pond evolution and freeze up the timing of these stages is governed by the onset dates of summer melt and fall freeze up which are determined from satellite observations trends of solar heat input to the ice were mixed with increases due to longer melt seasons and decreases due to reduced ice concentration results indicate a general trend of increasing solar heat input to the arctic ice ocean system due to declines in albedo induced by decreases in ice concentration and longer melt seasons the evolution of sea ice albedo and hence the total solar heating of the ice ocean system is more sensitive to the date of melt onset than the date of fall freeze up the largest increases in total annual solar heat input from 1979 to 2007 averaging as much as 4 a 1 occurred in the chukchi sea region the contribution of solar heat to the ocean is increasing faster than the contribution to the ice due to the loss of sea ice

sea ice thickness variability in the chukchi sea spring and summer 2002 2004 abstract measurements of sea ice thickness were obtained from drill holes an ice based electromagnetic induction instrument iem and a ship borne electromagnetic induction instrument sem during the early melt season in the southern chukchi sea in 2002 and 2004 and in late summer 2003 at the time of minimum ice extent in the northern chukchi sea an ice roughness criterion was applied to distinguish between level and rough or ridged ice ice thickness modes in the probability density functions pdfs derived from drill hole and iem measurements agreed well with modes at 1 5 1 6 and 1 8 1 9 m for all data from level ice the pdfs derived from sem measurements show that the primary modes are at 0 1 and 1 1 m in 2003 and 0 7 m in 2004 in 2002 and 2004 significant fractions between one third and one half of level ice were found to consist of rafted ice segments snow depth varied significantly between years with 2004 data showing more than half the snow cover on level ice to be at or below 0 05 m depth in late spring ice growth simulations and examination of ice drift and deformation history indicate that impacts of atmospheric and oceanic warming on level ice thickness in the region over the past few decades are masked to a large extent by variability in snow depth and the contribution of deformation processes in comparison with submarine sonar ice thickness data from previous decades a reduction in ice thickness by about 0 5 1 m is in part explained by the replacement of multi year with first year ice over the chukchi and beaufort shelves

hardgrounds reworked concretion levels and condensed horizons in the jurassic of western india their significance for basin analysis jurassic sediments in the shallow pericratonic basins of kachchh and rajasthan western india exhibit numerous signs of reduced sedimentation omission erosion and in situ reworking in combination with synsedimentary cementation hardgrounds developed on carbonate shoals in the bathonian of rajasthan whilst reworked concretion levels are characteristic of offshore siliciclastic sediments of the callovian of kachchh a prominent marker horizon the oxfordian dhosa oolite member occurs throughout much of the kachchh sub basin and is a highly condensed unit characterized by hardgrounds intraformational cobbles reworked concretions stromatolitic iron crusts iron oncoids and shell lags hardgrounds reworked concretion levels and condensation horizons are interpreted as the preserved relicts of transgressive pulses such pulses were possibly controlled by eustatic rise of sea level of at least equal importance however was a tectonic control which is demonstrated by the presence of small neptunian dykes boulder beds derived from small submarine cliffs and rapid lateral facies and thickness changes in the dhosa oolite member these indications of extensional tectonics are thought to be connected to rifting and initial sea floor spreading between africa and india

a record minimum arctic sea ice extent and area in 2002 1 arctic sea ice extent and area in september 2002 reached their lowest levels recorded since 1978 these conditions likely resulted from 1 anomalous warm southerly winds in spring advecting ice poleward from the siberian coast 2 persistent low pressure and high temperatures over the arctic ocean in summer promoting ice divergence and rapid melt

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

recent changes in arctic sea ice melt onset freezeup and melt season length 1 in order to explore changes and trends in the timing of arctic sea ice melt onset and freezeup and therefore melt season length we developed a method that obtains this information directly from satellite passive microwave data creating a consistent data set from 1979 through present we furthermore distinguish between early melt the first day of the year when melt is detected and the first day of continuous melt a similar distinction is made for the freezeup using this method we analyze trends in melt onset and freezeup for 10 different arctic regions in all regions except for the sea of okhotsk which shows a very slight and statistically insignificant positive trend 0 4 d decade 1 trends in melt onset are negative i e toward earlier melt the trends range from 1 0 d decade 1 for the bering sea to 7 3 d decade 1 for the east greenland sea except for the sea of okhotsk all areas also show a trend toward later autumn freeze onset the chukchi beaufort seas and laptev east siberian seas observe the strongest trends with 7 d decade 1 for the entire arctic the melt season length has increased by about 20 days over the last 30 years largest trends of over 10 d decade 1 are seen for hudson bay the east greenland sea the laptev east siberian seas and the chukchi beaufort seas those trends are statistically significant at the 99 level

drill hole analysis reveals evidence of targeted predation on modern brachiopods abstract if drill holes are made in prey either by mistaken or opportunistic predators or parasites rather than those which do so on a more regular basis we might predict that such drill holes will commonly be incomplete or repaired and show no evidence of behavioural familiarity such as size selection or constancy of attack site these predictions were used to examine the patterns of drill holes found in bulk samples of death assemblages of modern rhynchonelliform brachiopods from around new zealand four samples yielding data for five different taxa four terebratulides and one rhynchonellide were examined in each the proportion of incomplete or repaired holes was low samples of terebratella sanguinea fiordland and gyrothyris mawsoni antipodes islands show statistically significant evidence of both size selection and preferential drill hole siting the sample of notosaria nigricans waikawa shows only evidence of size selection examination of drill hole morphology and the co occurring gastropod fauna suggests that the distinctive countersunk holes in t sanguinea and g mawsoni were likely made by the trophonid gastropod xymene ambiguus aquarium experiments demonstrate that the ranellid gastropod argobuccinum tumidum is also capable of feeding on brachiopods but that the resulting hole is not likely to be readily recognisable in death assemblages

quaternary paleoceanography of the central arctic based on integrated ocean drilling program arctic coring expedition 302 foraminiferal assemblages the integrated ocean drilling program iodp arctic coring expedition acex hole 4c from the lomonosov ridge in the central arctic ocean recovered a continuous 18 m record of quaternary foraminifera yielding evidence for seasonally ice free interglacials during the matuyama progressive development of large glacials during the mid pleistocene transition mpt 1 2 0 9 ma and the onset of high amplitude 100 ka orbital cycles 500 ka foraminiferal preservation in sediments from the arctic is influenced by primary sea ice organic input and other environmental conditions and secondary factors syndepositional long term pore water dissolution taking these into account the acex 4c record shows distinct maxima in agglutinated foraminiferal abundance corresponding to several interglacials and deglacials between marine isotope stages mis 13 37 and although less precise dating is available for older sediments these trends appear to continue through the matuyama the mpt is characterized by nearly barren intervals during major glacials mis 12 16 and 22 24 and faunal turnover mis 12 24 abundant calcareous planktonic mainly neogloboquadrina pachyderma sin and benthic foraminifers occur mainly in interglacial intervals during the brunhes and very rarely in the matuyama a distinct faunal transition from calcareous to agglutinated foraminifers 200 300 ka in acex 4c is comparable to that found in arctic sediments from the lomonosov alpha and northwind ridges and the morris jesup rise down core disappearance of calcareous taxa is probably related to either reduced sea ice cover prior to the last few 100 ka cycles pore water dissolution or both

a fossil record full of holes the phanerozoic history of drilling predation the evolutionary history of drilling predation despite a long and rich fossil record precambrian holocene contains a 120 m y gap late triassic early cretaceous drilled bivalve and brachiopod shells from jurassic deposits of hungary india and four localities documented in the literature indicate that drillers may have existed continuously throughout the mesozoic they may have been descendants of paleozoic predators unknown mesozoic carnivores or precursors of modern drillers a literature database suggests three major phases in the phanerozoic history of drilling predators 1 the paleozoic phase latest precambrian carboniferous dominated by rare to moderately frequent drillings in brachiopods and sessile echinoderms 2 the mesozoic phase permian early cretaceous with very rare or even facultative drillers that had little impact on marine benthic communities but nevertheless may have been present continuously and 3 the cenozoic phase late cretaceous holocene dominated by frequent gastropod drillings in mollusks

modern sedimentation on the shoreface and inner continental shelf at wrightsville beach north carolina u s a abstract the geologic framework and surficial morphology of the shoreface and inner continental shelf off the wrightsville beach north carolina barrier island were mapped using high resolution sidescan sonar bathymetric and seismic reflection surveying techniques a suite of over 200 diver vibracores and extensive seafloor observations by divers the inner shelf is a sediment starved active surface of marine erosion modern sediments where present form a patchy veneer over tertiary and quaternary units the lithology of the underlying units exerts a primary control on the distribution texture and composition of surficial sediments as well as inner shelf bathymetry the shoreface is dominated by a linear cross shore morphology of rippled scour depressions rsds extending from just seaward of the surf zone onto the inner shelf on the upper shoreface the rsds are incised up to 1 m below surrounding areas of fine sand and have an asymmetric cross section that is steeper sided to the north on the inner shelf the rsds have a similar but more subdued cross sectional profile the depressions are floored primarily by shell hash and quartz gravel vibracore data show a thick up to 1 5 m sequence of rsd sediments that unconformably overlies ancient coastal lithosomes in this sediment starved inner shelf setting rippled scour depressions probably form initially on preexisting coarse sediment substrates such as modern lag deposits of paleofluvial channel lithosomes or ancient tidal inlet thalwegs interannual observations of seafloor morphologic change and the longer term record contained in vibracores suggest that the present seafloor morphology is either relatively stable or represents a recurring preferential morphologic state to which the seafloor returns after storm induced perturbations the apparent stability is interpreted to be the result of interactions at several scales that contribute to a repeating self reinforcing pattern of forcing and sedimentary response which ultimately causes the rsds to be maintained as sediment starved bedforms responding to both along shore and across shore flows sediment accumulation from over 30 years of extensive beach nourishment at wrightsville beach appears to have exceeded the local shoreface accommodation space resulting in the leaking of beach and shoreface sediment to the inner shelf a macroscopically identifiable beach nourishment sediment on the shoreface and inner shelf was used to identify the decadal scale pattern of sediment dispersal the nourishment sediment is present in a seaward thinning wedge that extends from the beach over a kilometer onto the inner shelf to waters depths of 14 m this wedge is best developed offshore of the shoreline segment that has received the greatest volume of beach nourishment

response of sea ice to the arctic oscillation abstract data collected by the international arctic buoy programme from 1979 to 1998 are analyzed to obtain statistics of sea level pressure slp and sea ice motion sim the annual and seasonal mean fields agree with those obtained in previous studies of arctic climatology the data show a 3 hpa decrease in decadal mean slp over the central arctic ocean between 1979 88 and 1989 98 this decrease in slp drives a cyclonic trend in sim which resembles the structure of the arctic oscillation ao regression maps of sim during the wintertime january march ao index show 1 an increase in ice advection away from the coast of the east siberian and laptev seas which should have the effect of producing more new thin ice in the coastal flaw leads 2 a decrease in ice advection from the western arctic into the eastern arctic and 3 a slight increase in ice advection out of the arctic through fram strait taken together these changes suggest that at least part of the thinning of sea ice recently observed ov

salinity trends on the siberian shelves 1 we present an analysis of observed long term 100 year salinity trends on the freshwater dominated siberian continental shelves a multiple regression was performed in the white sea ws the kara sea ks the laptev sea ls and the east siberian sea ess since 1930 the ws has gained freshwater while the ess has lost it consistent with river discharge trends over this period over the past 20 years increases in both river discharge and direct precipitation can explain observed salinity decreases in the ws but not in the ks salinity trends in the ls and ess indicate that ocean circulation plays a dominate role in these areas where in recent years freshwater has been diverted eastward along the coast rather than northward toward the deep ocean

intensification of geostrophic currents in the canada basin arctic ocean abstractcontinuous sampling of upper ocean hydrographic data in the canada basin from various sources spanning from 2003 through 2011 provides an unprecedented opportunity to observe changes occurring in a major feature of the arctic ocean in a 112 km radius circle situated near the center of the traditional beaufort gyre geopotential height referenced to 400 dbar increased by about 0 3 gpm from 2003 to 2011 and by the end of the period had increased by about 65 from the climatological value near the edges of the domain considered the anomalies in dynamic height are much smaller indicating steeper gradients a rough dynamic topography constructed from profiles collected between 2008 and 2011 shows the center of the gyre to have shifted south by about 2 in latitude along the 150 w meridian geostrophic currents are much stronger on the periphery of the gyre reaching amplitudes 5 6 times higher than climatological values at grid points just offshore from the beaufort and chukchi shelf slopes esti

interannual variability of arctic landfast ice between 1976 and 2007 abstractanalysis of weekly sea ice charts produced by the u s national ice center from 1976 to 2007 indicates large interannual variations in the averaged winter landfast ice extent around the arctic basin during the 32 yr period of the record landfast ice cover was relatively extensive from the early to mid 1980s but since then has declined in many coastal regions of the arctic particularly after the early 1990s while the barents baltic and bering seas show increases in landfast ice area the overall change for the northern hemisphere is negative about 12 27 2 8 103 km2 yr 1 or 7 1 5 decade 1 relative to the long term mean except in a few coastal regions the seasonal duration of landfast ice is shorter overall particularly in the laptev east siberian and chukchi seas the decreased winter landfast ice extent is associated with some notable changes in ice growth and melt patterns in particular the slowed landfast ice expansion during fall and early winter since 1990 the observed

record of intense predatory drilling from upper jurassic bivalves of kutch india implications for the history of biotic interaction abstract the study of past biotic interactions is important not only to understand the paleoecological history of a community but also to test the evolutionary role of such interactions drill holes in invertebrate exoskeletons provide one of the very few scenarios where biotic interaction could be studied directly and the related hypotheses could be tested with statistical rigor hence the documentation and interpretation of the spatio temporal patterns of drill hole frequencies has been the subject of extensive paleontological research the two main gastropod groups responsible for the drilling predation in modern marine environment arose in cretaceous as supported by their body fossil however the drill holes have been reported from the fossils of as far back as precambrian age the trend shows an overall low but variable intensity in paleozoic and mesozoic and a significant increase in cenozoic there are few reported cases of drilled bivalves from the mesozoic although in those instances frequencies are fairly low most of the previous records of drilling predation during paleozoic and mesozoic come from north america and western europe here we report 148 drilled bivalve specimens of a single species from the upper jurassic horizon in western india this is highest in number for any taxon ever recorded since precambrian to cretaceous the frequency of drilling constitutes 30 of shells of the same species examined this drilling frequency is highest when compared to all the reported mesozoic drilling frequencies in bivalves the shapes of the drill holes are indicative of gastropod predation the drilling gastropods responsible for these lethal attacks are also similar to their modern counterparts in terms of their highly selective prey choice and site specificity these results suggest that 1 mesozoic bivalves were preyed upon by drilling gastropods often with high intensities and 2 the specialized characters of modern drilling predators were also present in mesozoic this largely unexplored record of bivalve drill holes from the middle mesozoic contradicts the general trend of mesozoic quiescence as claimed by most researchers

sorted bed forms as self organized patterns 2 complex forcing scenarios 1 we employ a numerical model to study the development of sorted bed forms under a variety of hydrodynamic and sedimentary conditions results indicate that increased variability in wave height decreases the growth rate of the features and can potentially give rise to complicated a priori unpredictable behavior this happens because the system responds to a change in wave characteristics by attempting to self organize into a patterned seabed of different geometry and spacing the new wavelength might not have enough time to emerge before a new change in wave characteristics occurs leading to less regular seabed configurations the new seabed configuration is also highly dependent on the preexisting morphology which further limits the possibility of predicting future behavior for the same reasons variability in the mean current magnitude and direction slows down the growth of features and causes patterns to develop that differ from classical sorted bed forms spatial variability in grain size distribution and different types of net sediment aggradation degradation can also result in the development of sorted bed forms characterized by a less regular shape numerical simulations qualitatively agree with observed geometry spacing and height of sorted bed forms also in agreement with observations is that at shallower depths sorted bed forms are more likely to be affected by changes in the forcing conditions which might also explain why in shallow waters sorted bed forms are described as ephemeral features finally simulations indicate that the different sorted bed form shapes and patterns observed in the field might not necessarily be related to diverse physical mechanisms instead variations in sorted bed form characteristics may result from variations in local hydrodynamic and or sedimentary conditions

boring predation and mesozoic articulate brachiopods abstract a systematic survey of all the mesozoic brachiopods in the large collections of the sedgwick museum cambridge university has revealed more than 213 predatory boreholes from a wide range of largely british localities it seems likely that this type of predation was not infrequent at least locally as evidenced by the proportion of bored valves at some localities and the degree of stereotypy shown in borehole positioning the size of the boreholes and their neat circular cross sections suggest that they were made by large epifaunal predators using chemical attack and those of post albian age may be comfortably if not confidentally assigned to muricid gastropods although it is likely that bivalves with their greater flesh yields were the preferred prey item in most mesozoic shelly benthic communities it is apparent that boring predators may have resulted in a significant predation pressure on articulate brachiopods

thinning of the arctic sea ice cover comparison of sea ice draft data acquired on submarine cruises between 1993 and 1997 with similar data acquired between 1958 and 1976 indicates that the mean ice draft at the end of the melt season has decreased by about 1 3 m in most of the deep water portion of the arctic ocean from 3 1 m in 1958 1976 to 1 8 m in the 1990s the decrease is greater in the central and eastern arctic than in the beaufort and chukchi seas preliminary evidence is that the ice cover has continued to become thinner in some regions during the 1990s

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

arctic sea ice reemergence the role of large scale oceanic and atmospheric variability abstractarctic sea ice reemergence is a phenomenon in which spring sea ice anomalies are positively correlated with fall anomalies despite a loss of correlation over the intervening summer months this work employs a novel data analysis algorithm for high dimensional multivariate datasets coupled nonlinear laplacian spectral analysis nlsa to investigate the regional and temporal aspects of this reemergence phenomenon coupled nlsa modes of variability of sea ice concentration sic sea surface temperature sst and sea level pressure slp are studied in the arctic sector of a comprehensive climate model and in observations it is found that low dimensional families of nlsa modes are able to efficiently reproduce the prominent lagged correlation features of the raw sea ice data in both the model and observations these families provide an sst sea ice reemergence mechanism in which melt season spring sea ice anomalies are imprinted as sst anomalies and stored over the summer months allowing for

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

morphometric analysis of predatory drillholes abstract quantitative studies of post jurassic predatory drillholes assume that drill holes were made by either naticid or muricid gastropods however other potential predators can leave similar traces and the traditional method of discrimination based on differences in vertical shape of drillholes cylindrical vs countersunk is not always applicable poor preservation or thin shells may prevent identification a multivariate morphometric approach including principal component analysis pca canonical variate analysis cva and size free discriminant analysis is suggested here as a supplementary method i test the approach by analyzing 98 drillholes made in the valves of the thin shelled bivalve mulinia coloradoensis collected from subfossil deposits in northeastern baja california using traditional criteria 10 10 2 of 98 drillholes were not correctly identified morphometric analyses indicate that in planar view muricid and naticid drillholes do not differ in shape however they perfectly discriminate in size the cylindrical drillholes oichnus simplex attributed to muricid predators are significantly smaller than countersunk ones oichnus paraboloides made most likely by naticid gastropods the results do not necessarily undermine the validity of the traditional ichnotaxonomy muricids tend to produce smaller drillholes than naticids nevertheless the vertical shape of a drillhole may be a function of both the type of predator and the size of hole drilled more than half of the unidentified drillholes 6 out of 10 from an independent group characterized by a more oval shape octopod drilling the traditional method supported by the morphometric methods employed here is a powerful tool for analysis of drillholes it may be valuable not only as a tool for analysis of muricid and naticid drillholes but also as a method for comparative analysis of drillholes of unknown source found throughout the phanerozoic fossil record

formation of ripple bands in a wave convergence zone abstract sidescan sonographs of the whangarei harbor ebb tidal delta in northeastern new zealand revealed distinct bands of ripples of short wavelength lying in bands on otherwise undistinguished flat sand the ripple bands occurred in a confined and patchworked region across the delta extending some 4 km offshore and 1 0 km wide combined surface gravity wave refraction studies numerical hydrodynamic modeling and field measurements indicated that both the ripples and the bands were wave induced the ripples were found to have symmetrical profiles and wavelengths increasing shorewards both indicative of a wave generation mechanism the bands were aligned with the dominant surface wave orientation and typical bed orbital velocities exceeded the sediment threshold speed while tidal currents were perpendicular to the crests and velocities were below the sediment threshold the wave refraction study showed that the ebb tidal delta bathymetry concentrates surface gravity wave energy along a distended zone across the delta and this distinctive band of wave height reinforcement corresponded with the location of the bands of ripples numerical hydrodynamic modeling demonstrated that the shoaling waves induce a net shoreward circulation capable of transporting winnowed fines away from the ripple bands the regional wave height reinforcement and the associated shoreward current can explain the zonal nature of the bands the measured coarseness of the ripple sediments compared with neighboring sites and the presence of the bands in topographic lows

wave mechanisms responsible for grain sorting and non uniform ripple distribution across two moderate energy sandy continental shelves abstract mechanisms responsible for observed ripple geometry and grain size trends at two open coast sites are considered the field sites are two moderate energy sandy shelves on the inner continental shelf out to 50 m depth at east gippsland in southeastern australia and at pakiri in northeast new zealand both are characterised by bands of medium sediments inshore and offshore separated at 20 45 m depth by a zone with significantly coarser grain size 0 9 mm cf 0 3 mm video observations of the seabed at 126 sites on the east gippsland shelf revealed that the band was also characterised by larger wavelength ripples 1 0 m cf 0 3 m the size of the band stretching over an average of 20 km from 20 45 m depth and its presence at both field sites suggests that the observed characteristics are a long term response to physical forcing possibly in near equilibrium with modern processes numerical modelling demonstrated that grain sorting on the shelf is initiated by the presence of maxima in predicted ripple activity and seabed roughness around 35 m depth the local grain size evidently increases due to winnowing of the fines positive feedback through dependence of ripple size on grain size causes further lengthening of ripple wavelength until the pattern has evolved to become highly pronounced on the shelf and self sustaining but limited by reducing sediment mobility as grain size increases

temporal patterns in the efficiency of naticid gastropod predators during the cretaceous and cenozoic of the united states coastal plain abstract the hypothesis of escalation predicts that highly armored more escalated prey will be selectively eliminated at mass extinctions if recovery faunas were dominated by less escalated species a relative decrease in the defensive abilities of prey should follow mass extinctions we tested this hypothesis by examining two indices of the relative efficiency of drilling naticid gastropod predators and their molluscan prey the percent of drill holes that were incomplete and the percent of holes occurring in multiply bored shells both represent unsuccessful drilling attempts due to interruption of the drilling process by physical or biological factors including escape tactics of the prey excessive prey thickness or predator inefficiency if recovery faunas were more vulnerable to predation the incidence of incomplete or multiple drill holes should decline following mass extinctions the data do not support this hypothesis of a total of 16 comparisons across four extinction boundaries two showed a significant decrease in failed drilling following mass extinctions in accord with the hypothesis oligocene gastropods had fewer incomplete drill holes than did eocene gastropods and the frequency of multiply bored gastropod specimens was less in the pleistocene than in the pliocene two comparisons yielded a significant increase in failed drilling in the recovery fauna contrary to the hypothesis bivalve recovery faunas in the oligocene and miocene showed significantly greater proportions of multiply bored specimens than did their pre extinction counterparts no overall trend in unsuccessful drilling was apparent in the cretaceous through cenozoic data incomplete and multiple drilling were relatively rare in the cretaceous paleocene and most of the eocene 0 12 failed drilling was significantly more common during the oligocene up to 20 and returned to lower levels for most of the remainder of the cenozoic

drivers of declining sea ice in the arctic winter a tale of two seas 1 while the summer perennial arctic sea ice has declined markedly in recent decades the maximum extent of the winter ice cover had decreased only slightly until the past few years when it also receded dramatically this investigation reveals that the timing of maximum extent varies greatly and the drivers of ice edge location differ strikingly between two of the areas where it varies most the bering and barents seas between 1979 and 2005 in the bering sea the ice edge is influenced mainly by anomalies in easterly winds associated with the aleutian low which was particularly strong during the 1980s the barents sea ice edge in contrast is driven primarily by two factors anomalies in sea surface temperature particularly close in time to the maximum extent and by southerly wind from the south anomalies integrated back to mid and early winter the hemispheric mean decline in winter ice extent is due in large part to increasing sea surface temperatures in the barents sea and adjoining waters which are consistent with increased concentrations of greenhouse gases

atmospheric circulation and its effect on arctic sea ice in ccsm3 simulations at medium and high resolution the simulation of arctic sea ice and surface winds changes significantly when community climate system model version 3 ccsm3 resolution is increased from t42 2 8 to t85 1 4 at t42 resolution arctic sea ice is too thick off the siberian coast and too thin along the canadian coast both of these biases are reduced at t85 resolution the most prominent surface wind difference is the erroneous north polar summer anticyclone present at t42 but absent at t85 an offline sea ice model is used to study the effect of the surface winds on sea ice thickness in this model the surface wind stress is prescribed alternately from reanalysis and the t42 and t85 simulations in the offline model ccsm3 surface wind biases have a dramatic effect on sea ice distribution with reanalysis surface winds annual mean ice thickness is greatest along the canadian coast but with ccsm3 winds thickness is greater on the siberian side a significant difference between the two ccsm3 forced offline simulations is the thickness of the ice along the canadian archipelago where the t85 winds produce thicker ice than their t42 counterparts seasonal forcing experiments with ccsm3 winds during spring and summer and reanalysis winds in fall and winter relate the canadian thickness difference to spring and summer surface wind differences these experiments also show that the ice buildup on the siberian coast at both resolutions is related to the fall and winter surface winds the arctic atmospheric circulation is examined further through comparisons of the winter sea level pressure slp and eddy geopotential height at both resolutions the simulated beaufort high is quite weak weaker at higher resolution eddy heights show that the wintertime beaufort high in reanalysis has a barotropic vertical structure in contrast high ccsm3 slp in arctic winter is found in association with cold lower tropospheric temperatures and a baroclinic vertical structure in reanalysis the summertime arctic surface circulation is dominated by a polar cyclone which is accompanied by surface inflow and a deep ferrel cell north of the traditional polar cell the arctic ferrel cell is accompanied by a northward flux of zonal momentum and a polar lobe of the zonal mean jet these features do not appear in the ccsm3 simulations at either resolution

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

patterns of sea ice retreat in the transition to a seasonally ice free arctic abstractthe patterns of sea ice retreat in the arctic ocean are investigated using two global climate models gcms that have profound differences in their large scale mean winter atmospheric circulation and sea ice drift patterns the community earth system model large ensemble cesm le presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century the community climate system model version 4 ccsm4 exhibits a low bias in its mean sea level pressure over the arctic region with a deeper icelandic low a dynamical mechanism is presented in which large scale mean winter atmospheric circulation has significant effect on the following september sea ice extent anomaly by influencing ice divergence in specific areas a lagrangian model is used to backtrack the 80 n line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the pacific and eurasian sectors of the arctic i

did unusually sunny skies help drive the record sea ice minimum of 2007 1 we conduct experiments with an ice ocean model to answer the question whether and to what degree unusually clear skies during the summer of 2007 contributed to the record sea ice extent minimum in the arctic ocean during september of 2007 anomalously high pressure over the beaufort sea during summer 2007 appears associated with a strong negative cloud anomaly this anomaly is two standard deviations below the 1980 2007 average established from a combination of two different satellite based records cloud anomalies from the modis sensor are compared with anomalies from the ncep ncar reanalysis and are found in good agreement in spatial patterns and magnitude however these experiments establish that the negative cloud anomaly and increased downwelling shortwave flux from june through august did not contribute substantially to the record sea ice extent minimum this finding eliminates one aspect of the unusual weather that may have contributed to the record minimum

a case of intense predatory drilling of brachiopods from the middle miocene of southeastern poland abstract the documentation of biotic interactions in the fossil record is important not only to understanding the earth s paleoecological history but also to testing the evolutionary role of such interactions drill holes in invertebrate shells provide one of the most direct and easily interpretable signals of such interactions and the documentation and interpretation of the spatio temporal patterns of drill hole frequencies in a variety of invertebrate taxa has been the subject of extensive paleontological research for brachiopods the most recent summaries suggest that the record of drill holes extends back to the early paleozoic shows an increase in the devonian and remains highly variable through the rest of the paleozoic there are few reported cases of drilled brachiopods from the mesozoic although in those few instances on record frequencies can be as high as in the paleozoic to date only a few drilled brachiopods have been reported from the record of the cenozoic here we report on over 500 drilled brachiopod specimens constituting 39 9 of all brachiopod shells examined from a single middle miocene locality in southeastern poland this drilling frequency is high when compared to two additional middle miocene localities in poland where frequencies are 2 0 and 3 7 these results suggest that 1 cenozoic brachiopods were predated upon by drilling gastropods often with high intensities and 2 in the miocene drilling frequencies could be highly variable even at proximate localities the largely unexplored record of brachiopod drill holes across the late mesozoic and cenozoic could provide additional evidence for the mesozoic marine revolution

winter coastal divergence as a predictor for the minimum sea ice extent in the laptev sea abstractseasonal predictability of the minimum sea ice extent sie in the laptev sea is investigated using winter coastal divergence as a predictor from february to may the new ice forming in wi

arctic sea ice retreat in 2007 follows thinning trend the minimum of arctic sea ice extent in the summer of 2007 was unprecedented in the historical record a coupled ice ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective it is found that even though the 2007 ice extent was strongly anomalous the loss in total ice mass was not rather the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987 since then the simulated mean september ice thickness within the arctic ocean has declined from 3 7 to 2 6 m at a rate of 0 57 m decade 1 both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing the combined impact of these two trends caused a large reduction in the september mean ice concentration in the arctic ocean this created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the pacific side to the atlantic side of the basin and more than usual into the greenland sea this exposed large areas of open water resulting in the record ice extent anomaly

summer retreat of arctic sea ice role of summer winds 1 the unprecedented retreat of first year ice during summer 2007 was enhanced by strong poleward drift over the western arctic induced by anomalously high sea level pressure slp over the beaufort sea that persisted throughout much of the summer comparison of the tracks of drifting buoys with monthly mean slp charts shows a substantial ekman drift by means of linear regression analysis it is shown that ekman drift during summer has played an important role in regulating annual minimum arctic sea ice extent in prior years as well in combination the preconditioning by events in prior years as represented by an index of may multi year ice and current atmospheric conditions as represented by an index of july august september slp anomalies over the arctic basin account for 60 of the year to year variance of september sea ice extent since 1979

shell beds as tools in basin analysis the jurassic of kachchh western india skeletal concentrations are ubiquitous in bathonian oxfordian shallow water sediments of the pericratonic basins of kachchh and rajasthan western india by analysing the biofabric of the concentrations and the taphonomic signatures of individual components it is possible to distinguish between the final concentration process recorded by the biofabric and events taking place prior to final deposition recorded by taphonomic signatures the skeletal concentrations are grouped in nine genetic types ranging from fair weather wave concentrations to storm concentrations and condensed concentrations they mainly reflect biological and hydraulic processes and in some instances permit estimates of their duration and show a rough zonation along a bathymetric gradient plotted against the stratigraphic sections the skeletal concentrations show in accordance with other sedimentological data three orders of bathymetric trends the first two orders are shallowing deepening cycles which possibly correspond to eustatic changes in sea level the third order represents parasequences with a strongly asymmetric sedimentary record skeletal concentrations are a useful additional tool in basin analysis but are best used in combination with other data

reduced ice thickness in arctic transpolar drift favors rapid ice retreat 1 helicopter borne electromagnetic sea ice thickness measurements were performed over the transpolar drift in late summers of 2001 2004 and 2007 continuing ground based measurements since 1991 these show an ongoing reduction of modal and mean ice thicknesses in the region of the north pole of up to 53 and 44 respectively since 2001 a buoy derived ice age model showed that the thinning was mainly due to a regime shift from predominantly multi and second year ice in earlier years to first year ice in 2007 which had modal and mean summer thicknesses of 0 9 and 1 27 m measurements of second year ice which still persisted at the north pole in april 2007 indicate a reduction of late summer second year modal and mean ice thicknesses since 2001 of 20 and 25 to 1 65 and 1 81 m respectively the regime shift to younger and thinner ice could soon result in an ice free north pole during summer