pt paths from modal proportions application to the koralm complex eastern alps thermodynamic pseudosections portray those parts of a petrogenetic grid that are relevant to a given bulk composition and the reactions appearing on them can therefore be used directly to infer the pt path that the rock followed however for many normal bulk compositions the use of pseudosections is hampered by the fact that they display only few large fields of high thermodynamic variance in the pt range of interest here it is discussed how modal information on reaction progress within these fields can be used to determine pt path information for thermodynamically high variant metamorphic assemblages we use this information on reaction progress to contour pseudosections for modal proportions of minerals using the software package thermocalc the approach is applied to di tri and quadrivariant assemblages from the koralm complex in the eastern alps a pt path for these rocks is derived from modal considerations and compared with interpretations of mineral composition contours on the same pseudosection and with conventional thermobarometry it is shown that at least part of the complex must have cooled initially near isobarically from prevalent peak conditions around 700 c and 14 kbar before the rocks commenced a barroviantype decompression path

sea ice ocean feedbacks in the antarctic shelf seas abstractobserved changes in antarctic sea ice are poorly understood in part due to the complexity of its interactions with the atmosphere and ocean a highly simplified coupled sea ice ocean mixe

motion tracking of discontinuous sea ice the purpose of this paper is twofold 1 to develop a high resolution sea ice motion tracking system at the geospatial mesoscale 1 100 km2 and 2 to propose an algorithm that measures motion at close proximity to discontinuous regions here we present a motion tracking system that computes differential motion at 400 m resolution and validate the accuracy precision of this system via four studies the first study measures the accuracy against displacements measured from in situ global positioning system gps buoys deployed at the sea ice experiment dynamic nature of the arctic sedna and the surface heat budget of the arctic ocean sheba experiments the estimates are found to be statistically comparable with gps with an average error of 361 9 and 600 6 m for the experiments respectively the second study compares the estimated displacements to those measured by the radarsat geophysical processing system a precision error of 75 7 m is found between the two motion tracking systems the third study uses intensity warping of randomly sampled measurements to evaluate discontinuous motion tracking a one tailed wilcoxon signed rank test is used to validate these measurements at 0 01 results from this paper prove that anisotropic smoothing produces significantly smaller errors at discontinuous locations w 4240 and p 0 001 over conventional isotropic smoothing the fourth study compares displacements measured by anisotropic smoothing against manual measurements this paper demonstrates an average reduction of the estimation error by 50 m with the use of anisotropic smoothing over the conventional isotropic smoothing

amplified inception of european little ice age by sea ice ocean atmosphere feedbacks abstractthe inception of the little ice age 1400 1700 ad is believed to have been driven by an interplay of external forcing and climate system internal variability while the hemispheric signal seems to have been dominated by solar irradiance and volcanic eruptions the understanding of mechanisms shaping the climate on a continental scale is less robust in an ensemble of transient model simulations and a new type of sensitivity experiments with artificial sea ice growth the authors identify a sea ice ocean atmosphere feedback mechanism that amplifies the little ice age cooling in the north atlantic european region and produces the temperature pattern suggested by paleoclimatic reconstructions initiated by increasing negative forcing the arctic sea ice substantially expands at the beginning of the little ice age the excess of sea ice is exported to the subpolar north atlantic where it melts thereby weakening convection of the ocean consequently northward ocean heat transport is reduced reinf

bifurcations leading to summer arctic sea ice loss 1 there is significant interest in whether there could be a bifurcation sometimes referred to as a tipping point associated with arctic sea ice loss a low order model of arctic sea ice has recently been proposed and used to argue that a bifurcation associated with summer sea ice loss the transition from perennial to seasonal ice is unlikely here bifurcations are investigated in a variation of this model that incorporates additional effects including parameterizations of changes in clouds and heat transport as sea ice is lost it is shown that bifurcations can separate perennially and seasonally ice covered states in this model in a robust parameter regime although smooth loss of summer sea ice is also possible hysteresis and jumps associated with bifurcations involving winter sea ice loss are larger than those associated with summer sea ice loss finally in analogy with simulations in global climate models the low order model is integrated with time varying greenhouse gas forcing in both the regime in which summer sea ice is lost via bifurcations and the regime in which it is not the resulting time series are compared as a preliminary way of investigating ways in which these regimes could be distinguished from each other

influence of the sea ice thickness distribution on polar climate in ccsm3 abstract the sea ice simulation of the community climate system model version 3 ccsm3 t42 gx1 and t85 gx1 control simulations is presented and the influence of the parameterized sea ice thickness distribution itd on polar climate conditions is examined this includes an analysis of the change in mean climate conditions and simulated sea ice feedbacks when an itd is included it is found that including a representation of the subgrid scale itd results in larger ice growth rates and thicker sea ice these larger growth rates represent a higher heat loss from the ocean ice column to the atmosphere resulting in warmer surface conditions ocean circulation most notably in the southern hemisphere is also modified by the itd because of the influence of enhanced high latitude ice formation on the ocean buoyancy flux and resulting deep water formation changes in atmospheric circulation also result again most notably in the southern hemisphere there are indications that the itd also modifies simulated sea

climate response to large high latitude and low latitude volcanic eruptions in the community climate system model 1 explosive volcanism is known to be a leading natural cause of climate change the second half of the 13th century was likely the most volcanically perturbed half century of the last 2000 years although none of the major 13th century eruptions have been clearly attributed to specific volcanoes this period was in general a time of transition from the relatively warm medieval period to the colder little ice age but available proxy records are insufficient on their own to clearly assess whether this transition is associated with volcanism this context motivates our investigation of the climate system sensitivity to high and low latitude volcanism using the fully coupled ncar community climate system model ccsm3 we evaluate two sets of ensemble simulations each containing four volcanic pulses with the first set representing them as a sequence of tropical eruptions and the second representing eruptions occurring in the mid high latitudes of both the northern and southern hemispheres the short term direct radiative impacts of tropical and high latitude eruptions include significant cooling over the continents in summer and cooling over regions of increased sea ice concentration in northern hemisphere nh winter a main dynamical impact of moderate tropical eruptions is a winter warming pattern across northern eurasia furthermore both ensembles show significant reductions in global precipitation especially in the summer monsoon regions the most important long term impact is the cooling of the high latitude nh produced by multiple tropical eruptions suggesting that positive feedbacks associated with ice and snow cover could lead to long term climate cooling in the arctic

complementary biomarker based methods for characterising arctic sea ice conditions a case study comparison between multivariate analysis and the pip 25 index abstract the discovery of ip25 as a qualitative biomarker proxy for arctic sea ice and subsequent introduction of the so called pip25 index for semi quantitative descriptions of sea ice conditions has significantly advanced our understanding of long term paleo arctic sea ice conditions over the past decade we investigated the potential for classification tree ct models to provide a further approach to paleo arctic sea ice reconstruction through analysis of a suite of highly branched isoprenoid hbi biomarkers in ca 200 surface sediments from the barents sea four ct models constructed using different hbi assemblages revealed ip25 and an hbi triene as the most appropriate classifiers of sea ice conditions achieving a 90 cross validated classification rate additionally lower model performance for locations in the marginal ice zone miz highlighted difficulties in characterisation of this climatically sensitive region ct model classification and semi quantitative pip25 derived estimates of spring sea ice concentration spsic for four downcore records from the region were consistent although agreement between proxy and satellite observational records was weaker for a core from the west svalbard margin likely due to the highly variable sea ice conditions the automatic selection of appropriate biomarkers for description of sea ice conditions quantitative model assessment and insensitivity to the c factor used in the calculation of the pip25 index are key attributes of the ct approach and we provide an initial comparative assessment between these potentially complementary methods the ct model should be capable of generating longer term temporal shifts in sea ice conditions for the climatically sensitive barents sea

entrainment driven modulation of southern ocean mixed layer properties and sea ice variability in cmip5 models the evolution of the upper southern ocean hydrographic structure in response to the representative concentration pathways 4 5 rcp 4 5 forcing scenario is analyzed using model data drawn from the coupled model intercomparison project phase 5 cmip5 archive a robust freshening trend is evident associated with an increase in stratification and decoupling of the upper ocean as the mixed layer gains buoyancy at a faster rate than the underlying ocean the magnitudes of the individual terms of the salinity and heat budgets are evaluated convection driven entrainment from the thermocline into the mixed layer is found to play a significant role in modulating the mixed layer salinity whilst the heat budget of the mixed layer is dominated by a primary balance between atmospheric warming and the entrainment modulated supply of oceanic heat from below the mixed layer the relationship between oceanic heat storage below the mixed layer ice thickness and atmospheric temperature is investigated and a very disparate response noted amongst the models considered here based on this analysis we hypothesize that the balance between the entrainment modulated supply of oceanic heat from below the mixed layer and the heat supplied by the atmosphere may play an important role in determining the simulated sea ice variability

late twentieth century simulation of arctic sea ice and ocean properties in the ccsm4 abstractto establish how well the new community climate system model version 4 ccsm4 simulates the properties of the arctic sea ice and ocean results from six ccsm4 twentieth century ensemble simulations are compared here with the available data it is found that the ccsm4 simulations capture most of the important climatological features of the arctic sea ice and ocean state well among them the sea ice thickness distribution fraction of multiyear sea ice and sea ice edge the strongest bias exists in the simulated spring to fall sea ice motion field the location of the beaufort gyre and the temperature of the deep arctic ocean below 250 m which are caused by deficiencies in the simulation of the arctic sea level pressure field and the lack of deep water formation on the arctic shelves the observed decrease in the sea ice extent and the multiyear ice cover is well captured by the ccsm4 it is important to note however that the temporal evolution of the simulated arctic sea ice cover over the

the mechanisms of the atlantic meridional overturning circulation slowdown induced by arctic sea ice decline abstractwe explore the mechanisms by which arctic sea ice decline affects the atlantic meridional overturning circulation amoc in a suite of numerical experiments perturbing the arctic sea ice ra

effective bulk composition changes due to cooling a model predicting complexities in retrograde reaction textures diffusive processes are a strong function of temperature thus during cooling of rocks mineral grains may develop zoning profiles as successively larger parts of the grain close to the diffusive exchange with the rock one of the consequences of this process is that during cooling successively larger parts of zoned minerals depending on grain size are effectively removed from the reacting part of the rock volume thus the effective bulk composition of metamorphic rocks changes during cooling and the rate of its change will be a function of grain size because the sequence of metamorphic reactions seen by a given rock is a strong function of its bulk composition this process may have the consequence that two rocks of identical overall bulk composition but of different grain size may experience a different sequence of reactions qualitatively identical peak paragenesis may therefore react to form qualitatively different retrograde reaction textures the model is applied to examples in the pelitic system there garnet is usually the slowest diffusing phase developing zoning profiles during cooling and the effective removal of garnet from the reacting rock volume will cause changes of the effective bulk composition it is shown that during cooling of pelitic rocks from amphibolite facies conditions typical aluminous peak parageneses of garnet muscovite kyanite biotite may react to form either staurolite chlorite or muscovite or different combinations thereof depending on grain size during cooling from the granulite facies aluminous peak parageneses of garnet cordierite sillimanite may form biotite either on the expense of cordierite or garnet also depending on grain size the two examples are illustrated with a series of reaction textures reported for amphibolite and granulite terrains in the literature

centennial scale climate change from decadally paced explosive volcanism a coupled sea ice ocean mechanism northern hemisphere summer cooling through the holocene is largely driven by the steady decrease in summer insolation tied to the precession of the equinoxes however centennial scale climate departures such as the little ice age must be caused by other forcings most likely explosive volcanism and changes in solar irradiance stratospheric volcanic aerosols have the stronger forcing but their short residence time likely precludes a lasting climate impact from a single eruption decadally paced explosive volcanism may produce a greater climate impact because the long response time of ocean surface waters allows for a cumulative decrease in sea surface temperatures that exceeds that of any single eruption here we use a global climate model to evaluate the potential long term climate impacts from four decadally paced large tropical eruptions direct forcing results in a rapid expansion of arctic ocean sea ice that persists throughout the eruption period the expanded sea ice increases the flux of sea ice exported to the northern north atlantic long enough that it reduces the convective warming of surface waters in the subpolar north atlantic in two of our four simulations the cooler surface waters being advected into the arctic ocean reduced the rate of basal sea ice melt in the atlantic sector of the arctic ocean allowing sea ice to remain in an expanded state for 100 model years after volcanic aerosols were removed from the stratosphere in these simulations the coupled sea ice ocean mechanism maintains the strong positive feedbacks of an expanded arctic ocean sea ice cover allowing the initial cooling related to the direct effect of volcanic aerosols to be perpetuated potentially resulting in a centennial scale or longer change of state in arctic climate the fact that the sea ice ocean mechanism was not established in two of our four simulations suggests that a long term sea ice response to volcanic forcing is sensitive to the stability of the seawater column wind and ocean currents in the north atlantic during the eruptions

analysis of the projected regional sea ice changes in the southern ocean during the twenty first century using the set of simulations performed with atmosphere ocean general circulation models aogcms for the fourth assessment report of the intergovernmental panel on climate change ipcc ar4 the projected regional distribution of sea ice for the twenty first century has been investigated averaged over all those model simulations the current climate is reasonably well reproduced however this averaging procedure hides the errors from individual models over the twentieth century the multimodel average simulates a larger sea ice concentration decrease around the antarctic peninsula compared to other regions which is in qualitative agreement with observations this is likely related to the positive trend in the southern annular mode sam index over the twentieth century in both observations and in the multimodel average despite the simulated positive future trend in sam such a regional feature around the antarctic peninsula is absent in the projected sea ice change for the end of the twenty first century the maximum decrease is indeed located over the central weddell sea and the amundsen bellingshausen seas in most models changes in the oceanic currents could play a role in the regional distribution of the sea ice especially in the ross sea where stronger southward currents could be responsible for a smaller sea ice decrease during the twenty first century finally changes in the mixed layer depth can be found in some models inducing locally strong changes in the sea ice concentration

open ocean convection observations theory and models we review what is known about the convective process in the open ocean in which the properties of large volumes of water are changed by intermittent deep reaching convection triggered by winter storms observational laboratory and modeling studies reveal a fascinating and complex interplay of convective and geostrophic scales the large scale circulation of the ocean and the prevailing meteorology two aspects make ocean convection interesting from a theoretical point of view first the timescales of the convective process in the ocean are sufficiently long that it may be modified by the earth s rotation second the convective process is localized in space so that vertical buoyancy transfer by upright convection can give way to slantwise transfer by baroclinic instability moreover the convective and geostrophic scales are not very disparate from one another detailed observations of the process in the labrador greenland and mediterranean seas are described which were made possible by new observing technology when interpreted in terms of underlying dynamics and theory and the context provided by laboratory and numerical experiments of rotating convection great progress in our description and understanding of the processes at work is being made

processes controlling surface bottom and lateral melt of arctic sea ice in a state of the art sea ice model we present a modelling study of processes controlling the summer melt of the arctic sea ice cover we perform a sensitivity study and focus our interest on the thermodynamics at the ice atmosphere and ice ocean interfaces we use the los alamos community sea ice model cice and additionally implement and test three new parametrization schemes i a prognostic mixed layer ii a three equation boundary condition for the salt and heat flux at the ice ocean interface and iii a new lateral melt parametrization recent additions to the cice model are also tested including explicit melt ponds a form drag parametrization and a halodynamic brine drainage scheme the various sea ice parametrizations tested in this sensitivity study introduce a wide spread in the simulated sea ice characteristics for each simulation the total melt is decomposed into its surface bottom and lateral melt components to assess the processes driving melt and how this varies regionally and temporally because this study quantifies the relative importance of several processes in driving the summer melt of sea ice this work can serve as a guide for future research priorities

increased ocean heat convergence into the high latitudes with co2 doubling enhances polar amplified warming we isolate the role of the ocean in polar climate change by directly evaluating how changes in ocean dynamics with quasi equilibrium co2 doubling impact high latitude climate with co2 doubling the ocean heat flux convergence ohfc shifts poleward in winter in both hemispheres imposing this pattern of perturbed ohfc in a global climate model results in a poleward shift in ocean to atmosphere turbulent heat fluxes both sensible and latent and sea ice retreat the high latitudes warm while the midlatitudes cool thereby amplifying polar warming furthermore midlatitude cooling is propagated to the polar midtroposphere on isentropic surfaces augmenting the positive lapse rate feedback at high latitudes these results highlight the key role played by the partitioning of meridional energy transport changes between the atmosphere and ocean in high latitude climate change

impact of a reduced arctic sea ice cover on ocean and atmospheric properties abstractthe arctic sea ice cover declined over the last few decades and reached a record minimum in 2007 with a slight recovery thereafter inspired by this the authors investigate the response of atmospheric and oceanic properties to a 1 yr period of reduced sea ice cover two ensembles of equilibrium and transient simulations are produced with the community climate system model a sea ice change is induced through an albedo change of 1 yr the sea ice area and thickness recover in both ensembles after 3 and 5 yr respectively the sea ice anomaly leads to changes in ocean temperature and salinity to a depth of about 200 m in the arctic basin further the salinity and temperature changes in the surface layer trigger a great salinity anomaly in the north atlantic that takes roughly 8 yr to travel across the north atlantic back to high latitudes in the atmosphere the changes induced by the sea ice anomaly do not last as long as in the ocean the response in the transient and equilibrium simulations w

isolating the atmospheric circulation response to arctic sea ice loss in the coupled climate system abstractin this study coupled ocean atmosphere land sea ice earth system model esm simulations driven separately by sea ice albedo reduction and by projected greenhouse dominated radiative forcing are combined to cleanly isolate the sea ice loss response of the atmospheric circulation a pattern scaling approach is proposed in which the local multidecadal mean atmospheric response is assumed to be separately proportional to the total sea ice loss and to the total low latitude ocean surface warming the proposed approach estimates the response to arctic sea ice loss with low latitude ocean temperatures fixed and vice versa the sea ice response includes a high northern latitude easterly zonal wind response an equatorward shift of the eddy driven jet a weakening of the stratospheric polar vortex an anticyclonic sea level pressure anomaly over coastal eurasia a cyclonic sea level pressure anomaly over the north pacific and increased wintertime precipitation over the west coast of north america many

a petrogenetic grid for pelitic schists in the system sio 2 al 2 o 3 feo mgo k 2 o h 2 o a quantitative petrogenetic grid for pelitic schists in the system kfmash that includes the phases garnet chlorite biotite chloritoid cordierite staurolite talc kyanite andalusite sillimanite and pyrophyllite with quartz h2o and muscovite or k feldspar in excess is presented the grid is based on thermodynamic data of berman et al 1985 and berman 1988 for endmember kfash and kmash equilibria and natural fe mg partitioning for the kfmash system calculation of p t slopes and the change in fe fe mg along reactions in the kfmash system were made using the gibbs method in addition the effect on the grid of mno and cao is evaluated quantitatively the resulting grid is consistent with typical buchan and barrovian parageneses at medium to high grades at low grades the grid predicts an extensive stability field for the paragenesis chloritoid biotite which arises because of the unusual facing of the reaction chloritoid biotite quartz h2o garnet chlorite muscovite which proceeds to the right with increasing t in the kfmash system however the reaction proceeds to the left with increasing t in the mnkfash system so the assemblage chloritoid biotite is restricted to bulk compositions with high fe fe mg mn typical metapelites will therefore contain garnet chlorite at low grades rather than chloritoid biotite

drivers of antarctic sea ice volume change in cmip5 models antarctic sea ice trends have to date been linked to surface winds through sea ice motion and atmospheric thermal advection this paper analyzes sea ice volume in 10 cmip5 model configurations under pre industrial and historical climate forcings to compare the relative importance of ice motion and thermodynamic processes we find that the models responses to historical forcings is dependent on their sea ice motion formulation models with low magnitude sea ice motion tend to have historical trends that are dominated by thermodynamic processes whilst sea ice models with higher magnitude motion have more spatially variable relative contributions from dynamic and thermodynamic processes trends at the sea ice edge during the season of sea ice advance are generally dominated by dynamic processes whereas during retreat thermodynamic trends dominate the models show more disagreement in the sea ice interior this analysis highlights the different estimates and patterns of sea ice volume among global climate models and offers insight into the drivers of sea ice volume change as well as the subsequent implications for simulated atmosphere sea ice ocean interactions

a heuristic model of dansgaard oeschger cycles part i description results and sensitivity studies abstracta simple model for studying the dansgaard oeschger d o cycles of the last glacial period is presented based on the t dokken et al hypothesis for d o cycles the model is a column model representing the nordic seas and is composed of ocean boxes stacked below a one layer sea ice model with an energy balance atmosphere no changes in the large scale ocean overturning circulation are invoked parameterizations are included for latent heat polynyas and sea ice export from the column the resulting heuristic model was found to cycle between stadial and interstadial states at times scales similar to those seen in the proxy observational data with the presence or absence of perennial sea ice in the nordic seas being the defining characteristic for each of these states the major discrepancy between the modeled oscillations and the proxy record is in the length of the interstadial phase which is shorter than that observed the modeled oscillations were found to be robust to parameter changes inclu

consistent past half century trends in the atmosphere the sea ice and the ocean at high southern latitudes simulations performed with the climate model loveclim aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations are able to reasonably reproduce the observed changes in the lower atmosphere sea ice and ocean during the second half of the twentieth century although the simulated ice area slightly increases over the period 1980 2000 in agreement with observations it decreases by 0 5 106 km2 between early 1960s and early 1980s no direct and reliable sea ice observations are available to firmly confirm this simulated decrease but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean the simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation however the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the ross sea and the salinity decrease on the ross sea continental shelf parts of those changes are likely related to the response of the system to the external forcing modifications in the wind pattern influencing the ice production melting rates also play a role in the simulated surface salinity decrease

the continuum of drought in southwestern north america abstractdrought has severe consequences for humans and their environment yet we have a limited understanding of the drivers of drought across the full range of time scales on which it occurs here

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

modeled trends in antarctic sea ice thickness abstractunlike the rapid sea ice losses reported in the arctic satellite observations show an overall increase in antarctic sea ice concentration over recent decades however observations of decadal trends in antarctic ice thickness and hence ice volume do not currently exist in this study a model of the southern ocean and its sea ice forced by atmospheric reanalyses is used to assess 1992 2010 trends in ice thickness and volume the model successfully reproduces observations of mean ice concentration thickness and drift and decadal trends in ice concentration and drift imparting some confidence in the hindcasted trends in ice thickness the model suggests that overall antarctic sea ice volume has increased by approximately 30 km3 yr 1 0 4 yr 1 as an equal result of areal expansion 20 103 km2 yr 1 or 0 2 yr 1 and thickening 1 5 mm yr 1 or 0 2 yr 1 this ice volume increase is an order of magnitude smaller than the arctic decrease and about half the size of the increased freshwater s

an assessment of biomarker based multivariate classification methods versus the pip25 index for paleo arctic sea ice reconstruction abstract the development of various combinative methods for arctic sea ice reconstruction using the sympagic highly branched isoprenoid hbi ip25 in conjunction with pelagic biomarkers has often facilitated more detailed descriptions of sea ice conditions than using ip25 alone here we investigated the application of the phytoplankton ip25 index pip25 and a recently proposed classification tree ct model for describing temporal shifts in sea ice conditions to assess the consistency of both methods based on biomarker data from three downcore records from the barents sea spanning millennial timescales we showcase apparent and potential limitations in both approaches and provide recommendations for their identification or prevention both methods provided generally consistent outcomes and within the studied cores captured abrupt shifts in sea ice regimes such as those evident during the younger dryas as well as more gradual trends in sea ice conditions during the holocene the most significant discrepancies occurred during periods of highly unstable climate change such as those characteristic of the younger dryas holocene transition such intervals of increased discrepancy were identifiable by significant changes of hbi distributions and correlations to values not observed in proximal surface sediments we suggest that periods of highly fluctuating climate that are not represented in modern settings may hinder the performance and complementary application of pip25 and ct based methods and that data visualisation techniques should be employed to identify such occurrences in downcore records additionally due to the reliance of both methods on biomarker distributions we emphasise the importance of accurate and consistent biomarker quantification

the influence of sea ice on ocean heat uptake in response to increasing co2 two significant changes in ocean heat uptake that occur in the vicinity of sea ice cover in response to increasing co2 are investigated with community climate system model version 3 ccsm3 a deep warming below 500 m and extending down several kilometers in the southern ocean and warming in a 200 m layer just below the surface in the arctic ocean ocean heat uptake caused by sea ice retreat is isolated by running the model with the sea ice albedo reduced artificially alone this integration has a climate response with strong ocean heat uptake in the southern ocean and modest ocean heat uptake in the subsurface arctic ocean the arctic ocean warming results from enhanced ocean heat transport from the northern north atlantic at the time of co2 doubling about 1 3 of the heat transport anomaly results from advection of anomalously warm water and 2 3 results from strengthened inflow at the same time the overturning circulation is strengthened in the northern north atlantic and arctic oceans wind stress changes cannot explain the circulation changes which instead appear related to strengthened convection along the siberian shelves deep ocean warming in the southern ocean is initiated by weakened convection which is mainly a result of surface freshening through altered sea ice and ocean freshwater transport below about 500 m changes in convection reduce the vertical and meridional temperature gradients in the southern ocean which significantly reduce isopycnal diffusion of heat upward around antarctica the geometry of the sea ice cover and its influence on convection have a strong influence on ocean temperature gradients making sea ice an important player in deep ocean heat uptake in the southern ocean

evolution of the southern ocean winter mixed layer and sea ice open ocean deepwater formation and ventilation an analytical model has been developed to describe the nature of the winter ocean sea ice interaction in the southern ocean to determine the principal processes responsible for maintaining stability in this marginally stable region and to predict the response to changes in the external forcing and initial conditions the model accurately describes the sparse winter observations and the general temporal evolution of the ice mixed layer depth and salinity for the period following the elimination of the seasonal pycnocline by rapid fall ice growth a scale analysis and sensitivity study reveal the system parameter dependence this indicates that the magnitude of entrainment is proportional to fst h0 s where fs is the external salt flux h0 the depth of the winter mixed layer and s the salinity gradient through the pycnocline thermodynamic ice growth reflects predominantly the competition between the oceanic diffusive heat gain across the base of the mixed layer and the loss to the atmosphere through the ice and leads a strong thermal gradient across the pycnocline leads to a significant diffusive flux which balances most of the heat lost to the atmosphere this limits the amount of ice growth possible and plays the principal role in maintaining the system stability since the ice growth is required for destabilization through haline rejection during the growth process the system is also sensitive to the large ratio of heat to salt in the pycnocline this introduces a negative feedback where increasing ice growth induces entrainment by the associated salt flux which in turn drives an entrainment heat flux which compensates for heat lost to the atmosphere this moderates the ability to grow ice and drive further entrainment the absolute strength of the salinity gradient on the other hand dictates the effectiveness which a same magnitude external salt flux will have in driving entrainment the effectiveness with which changes in these parameters as well as several other external parameters can influence the southern ocean stability is explicitly evaluated through the sensitivity study and analysis