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

estimation of sea ice thickness and volume in the sea of okhotsk based on icesat data sea ice thickness in the sea of okhotsk is estimated for 2004 2008 from icesat derived freeboard under the assumption of hydrostatic balance total ice thickness including snow depth h t o t averaged over 2004 2008 is 95 cm the interannual variability of h t o t is large from 77 5 cm 2008 to 110 4 cm 2005 the mode of h t o t varies from 50 60 cm 2007 and 2008 to 70 80 cm 2005 ice thickness derived from icesat data is validated from a comparison with that observed by electromagnetic induction instrument em aboard the icebreaker soya near hokkaido japan annual maps of h t o t reveal that the spatial distribution of h t o t is similar every year ice volume of 6 3 10 11 m 3 is estimated from the icesat derived h t o t and amsr e derived ice concentration a comparison with ice area demonstrates that the ice volume cannot always be represented by the area solely despite the fact that the area has been used as a proxy of the volume in the sea of okhotsk the ice volume roughly corresponds to that of annual ice production in the major coastal polynyas estimated based on heat budget calculations this also supports the validity of the estimation of sea ice thickness and volume using icesat data

north atlantic ocean circulation and abrupt climate change during the last glaciation the most recent ice age was characterized by rapid and hemispherically asynchronous climate oscillations whose origin remains unresolved variations in oceanic meridional heat transport may contribute to these repeated climate changes which were most pronounced during marine isotope stage 3 the glacial interval 25 thousand to 60 thousand years ago we examined climate and ocean circulation proxies throughout this interval at high resolution in a deep north atlantic sediment core combining the kinematic tracer protactinium thorium pa th with the deep water mass tracer epibenthic 13c these indicators suggest reduced atlantic overturning circulation during every cool northern stadial with the greatest reductions during episodic hudson strait iceberg discharges while sharp northern warming followed reinvigorated overturning these results provide direct evidence for the ocean s persistent central role in abrupt glacial climate change

remapping the thickness distribution in sea ice models in sea ice models with multiple thickness categories the ice thickness distribution evolves in time the evolution of the thickness distribution as ice grows and melts is analogous to one dimensional fluid transport and can be treated by similar numerical methods one such method remapping is applied here thickness categories are represented as lagrangian grid cells whose boundaries are projected forward in time the thickness distribution is approximated as a linear or quadratic polynomial in each displaced category and ice area and volume are transferred between categories so as to restore the original boundaries in simple test problems and in a single column model with forcing typical of the central arctic remapping performs significantly better than methods previously used in sea ice models it is less diffusive than a scheme that fixes the ice thickness in each category and behaves better numerically than a scheme that represents the thickness distribution as a set of delta functions also remapping converges faster i e with fewer thickness categories than the alternative schemes with five to seven categories the errors due to finite resolution of the thickness distribution are much smaller than the errors due to other sources linear remapping performs as well as the more complex quadratic version and is recommended for climate modeling its computational cost is minimal compared to other sea ice model components

ross sea ice motion area flux and deformation abstract the sea ice motion area export and deformation of the ross sea ice cover are examined with satellite passive microwave and radarsat observations the record of high resolution synthetic aperture radar sar data from 1998 and 2000 allows the estimation of the variability of ice deformation at the small scale 10 km and to assess the quality of the longer record of passive microwave ice motion daily and subdaily deformation fields and radarsat imagery highlight the variability of motion and deformation in the ross sea with the passive microwave ice motion the area export at a flux gate positioned between cape adare and land bay is estimated between 1992 and 2003 a positive trend can be seen in the winter march november ice area flux that has a mean of 990 103 km2 and ranges from a low of 600 103 km2 in 1992 to a peak of 1600 103 km2 in 2001 in the mean the southern ross sea produces almost twice its own area of sea ice during the winter cross gate sea level pressure slp gra

two circulation regimes of the wind driven arctic ocean the major goal of this paper is to demonstrate the existence in the arctic ocean of two regimes of wind forced circulation we simulated the vertically averaged currents sea level heights and ice drift in the arctic ocean from 1946 to 1993 using a two dimensional wind forced barotropic model that includes frictional coupling between the ocean and ice the model has a spatial resolution of 55 5 km and is driven by winds river runoff and an imposed but realistic sea level slope between the pacific and the atlantic oceans there is a good agreement between velocities from observed buoy motions and velocities of modeled ice drift even though the model lacks ocean baroclinicity and ice thermodynamics the results indicate that wind driven motion in the central arctic alternates between anticyclonic and cyclonic circulation with each regime persisting for 5 7 years based upon our analysis of the modeled sea level and ice motion anticyclonic wind driven motion in the central arctic appeared during 1946 1952 1958 1963 1972 1979 and 1984 1988 and cyclonic motion appeared during 1953 1957 1964 1971 1980 1983 and 1989 1993 shifts from one regime to another are forced by changes in the location and intensity of the icelandic low and the siberian high the two regimes may help explain the significant basin scale changes in the arctic s temperature and salinity structure observed recently the great salinity anomaly and the variability of ice conditions in the arctic ocean

sea ice thickness distribution in fram strait hm nuclear submarine sovereign has obtained the first synoptic measurements of the ice thickness distribution in fram strait the main outflow from the arctic ocean the ice nearest the ice edge is of quite different character from ice in the interior of the strait with a greater proportion of first year ice and less pressure ridging an estimate of the ice flux through fram strait can be made from the distribution of mean ice drafts

sea ice motion from satellite passive microwave imagery assessed with ers sar and buoy motions observing the motion of sea ice from space is analogous to observing wind stress over the wet oceans both provide surface forcing for modeling ocean dynamics ice motion also directly provides the advective component of the equations governing the mass balance of the sea ice cover thus its routine observation from space would be of great value to understanding ice and ocean behavior to demonstrate the feasibility of creating a global multidecadal ice motion record from satellite passive microwave imagery and to quantitatively assess the errors in the estimated ice motions we have tracked ice every 3 days in the arctic ocean and daily in the fram strait and baffin bay during the 8 winter months from october 1992 to may 1993 and daily in the weddell sea during the 8 winter months from march to october 1992 the method which has been well used previously involves finding the spatial offset that maximizes the cross correlation of the brightness temperature fields over 100 km patches in two images separated in time by from 1 to 3 days the resulting ice motions are compared with contemporaneous buoyand sar derived ice motions the uncertainties in the displacement vectors between 5 and 12 km are better than the spatial resolution of the data both 85 ghz data with 12 km spatial resolution and 37 ghz data with 25 km resolution are tracked these trials with the 37 ghz data are new and show quite surprisingly that the error is only about 1 km larger with these data than with the 12 km 85 ghz data errors are typically larger than average in areas of lower ice concentration in the most dynamic regions particularly near the ice edge in the barents and greenland seas and in zones of high shear these passive microwave ice motions show a large increase in spatial detail over motion fields optimally interpolated from buoy and wind observations especially where buoy data are virtually absent such as near coasts and in some passages between the arctic ocean and its peripheral seas the feasibility of obtaining ice motion from the 37 ghz data in addition to the 85 ghz data should allow an important record of ice motion to be established for the duration of the scanning multichannel microwave radiometer smmr special sensor microwave imager ssm i and future microwave sensors that is from 1978 into the next millenium

what drove the dramatic retreat of arctic sea ice during summer 2007 1 a model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007 it is found that preconditioning anomalous winds and ice albedo feedback are mainly responsible for the retreat arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate during summer 2007 atmospheric changes strengthened the transpolar drift of sea ice causing more ice to move out of the pacific sector and the central arctic ocean where the reduction in ice thickness due to ice advection is up to 1 5 m more than usual some of the ice exited fram strait and some piled up in part of the canada basin and along the coast of northern greenland leaving behind an unusually large area of thin ice and open water thin ice and open water allow more surface solar heating because of a much reduced surface albedo leading to amplified ice melting the arctic ocean lost additional 10 of its total ice mass in which 70 is due directly to the amplified melting and 30 to the unusual ice advection causing the unprecedented ice retreat arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing

recent changes in the north atlantic it has long been recognized that the atlantic meridional overturning circulation moc is potentially sensitive to greenhouse gas and other climate forcing and that changes in the moc have the potential to cause abrupt climate change however the mechanisms remain poorly understood and our ability to detect these changes remains incomplete four main interrelated types of ocean change in particular are associated in the literature with greenhouse gas forcing these are a slowing of moc overturning rate changes in northern seas which might effect a change in atlantic overturning including changes in the freshwater flux from the arctic and changes in the transport and or hydrographic character of the northern overflows which ventilate the deep atlantic a change in the trans ocean gradients of steric height both zonal and meridional which might accompany a change in the moc and an intensification of the global water cycle though as yet we have no direct measure of the freshwater flux passing from the arctic to the atlantic either via the canadian arctic archipelago or along the east greenland shelf and no direct measure yet of the atlantic overturning rate we examine a wide range of time series from the existing hydrographic record for oceanic evidence of the other anticipated responses large amplitude and sustained changes are found or indicated by proxy over the past three to four decades in the southward transport of fresh waters along the labrador shelf and slope in the hydrography of the deep dense overflows from nordic seas in the transport of the eastern overflow through faroe bank channel and in the global hydrologic cycle though the type and scale of changes in ocean salinity are consistent with an amplification of the water cycle we find no convincing evidence of any significant concerted slowdown in the atlantic overturning circulation

simulating the ice thickness distribution in a coupled climate model climate simulations in a global coupled model are investigated using a dynamic thermodynamic sea ice and snow model with sophisticated thermodynamics and a subgrid scale parameterization for multiple ice thicknesses in addition to the sea ice component the model includes a full primitive equation ocean and a simple energy moisture balance atmosphere we introduce a formulation of the ice thickness distribution that is lagrangian in thickness space the method is designed to use fewer thickness categories because it adjusts to place resolution where it is needed most and it is free of diffusive effects that tend to smooth eulerian distributions experiments demonstrate that the model does reasonably well in simulating the mean arctic climate we find the climate of the arctic and northern north atlantic is sensitive to resolving the ice thickness distribution when comparing the model results to a simulation with a two level sea ice model the ice thickness distribution causes ice export through fram strait to be more variable and more strongly linked to meridional overturning in the north atlantic ocean the lagrangian formulation of the ice thickness distribution allows for the inclusion of a vertical temperature profile with relative ease compared to an eulerian method we find ice growth rates and ocean surface salinity differ in our model with a well resolved vertical temperature profile in the ice and snow and an explicit brine pocket parameterization compared to a simulation with semtner zero layer thermodynamics although these differences are important for the climate of the arctic the effects of an ice thickness distribution are more dramatic and extend into the northern north atlantic sensitivity experiments indicate that five ice thickness categories with 50 cm vertical temperature resolution capture the effects of the ice thickness distribution on the heat and freshwater exchange across the surface in the presence of sea ice in these simulations

monitoring ice thickness in fram strait time series of ice thickness in fram strait are evaluated together with ice drift for estimation of the ice flux from the arctic ocean ice draft was measured from moored sonars every 4 min suggesting a nominal sampling interval of 30 m on the basis of these data the annual cycle of many statistics can be resolved the modal ice thickness shows a maximum of 3 15 m in may and a minimum in september of 2 43 m indicating an annual variation range of 0 72 m this compares with model results comprehensive drillings and most of the submarine observations during the last 2 3 decades indicating no significant long term ice thickness change this is also concurrent with the lack of significant temperature changes in the arctic ocean during the same period the mean ice thickness in the central core of the ice stream shows an annual amplitude of 1 m with a minimum in september of 2 25 m and a maximum in april may of 3 25 m the mean thickness of ice only open water excluded is 3 27 m and compares with 3 29 m which is the mean thickness of ice only from 17 submarine tracks in the arctic ocean 1960 1982 the mean annual ice export which is equal to the mean annual net production of ice in the arctic ocean is 2850 km 3 yr 1 for the period 1990 1996 this efflux shows significant variations from year to year with a minimum in 1990 1991 of 2050 km 3 yr 1 and a maximum in 1994 1995 of 4700 km 3 yr 1 this significant variation of nearly 130 is mainly caused by an increased atmospheric forcing and to a lesser degree by an increase in the annual mean ice thickness of 20 over the same period

arctic ice ocean simulation with optimized model parameters approach and assessment 1 we present an optimized 1992 2008 coupled ice ocean simulation of the arctic ocean a green s function approach adjusts a set of parameters for best model data agreement overall model data differences are reduced by 45 the optimized simulation reproduces the negative trends in ice extent in the satellite records volume and thickness distributions are comparable to those from the ice cloud and land elevation satellite 2003 2008 the upper cold halocline is consistent with observations in the western arctic the freshwater budget of the arctic ocean and volume heat transports of pacific and atlantic waters across major passages are comparable with observation based estimates we note that the optimized parameters depend on the selected atmospheric forcing the use of the 25 year japanese reanalysis results in sea ice albedos that are consistent with field observations simulated pacific water enters the bering strait and flows off the chukchi shelf along four distinct channels this water takes 5 10 years to exit the arctic ocean at the canadian arctic archipelago nares or fram straits atlantic water entering the fram strait flows eastward merges with the st ana trough inflow and splits into two branches at the southwest corner of the makarov basin one branch flows along lomonosov ridge back to fram strait the other enters the western arctic circulates cyclonically below the halocline and exits mainly through the nares and fram straits this work utilizes the record of available observations to obtain an arctic ocean simulation that is in agreement with observations both within and beyond the optimization period and that can be used for tracer and process studies

winter atmospheric circulation in the arctic basin and possible relationships to the great salinity anomaly in the northern north atlantic variations in synoptic activity are assessed in terms of potential influences on ice transport and indicators of shifts in the arctic atmospheric circulation related to the great salinity anomaly of the northern north atlantic winter pressure anomalies suggest an increased contribution to the fram strait sea ice flux by multiyear ice from along the northern coasts of greenland and ellesmere island this may be related to a teleconnection involving changes in anticyclonicity over the central arctic ocean and canadian arctic archipelago

variability of fram strait ice flux and north atlantic oscillation we estimate the winter sea ice export through the fram strait using ice motion from satellite passive microwave data sea ice motion october may is obtained by tracking the displacement of common features in sequential 85 and 37 ghz brightness temperature fields the average winter area flux over the 18 year record 1978 1996 is 670 000 km2 7 of the area of the arctic ocean the winter area flux ranges from a minimum of 450 000 km2 in 1984 to a maximum of 906 000 km2 in 1995 the daily monthly and interannual variabilities of the ice area flux are high there is an upward trend in the ice area flux over the 18 year record the average winter volume flux over the winters of october 1990 through may 1995 is 1745 km3 ranging from a low of 1375 km3 in the 1990 flux to a high of 2791 km3 in 1994 the sea level pressure gradient across the fram strait explains more than 80 of the variance in the ice flux over the 18 year record we use the coefficients from the regression of the time series of area flux versus pressure gradient across the fram strait and ice thickness data to estimate the summer area and volume flux the average 12 month area flux and volume flux are 919 000 km2 and 2366 km3 we find a significant correlation r 0 86 between the area flux and positive phases of the north atlantic oscillation nao index over the months of december march correlation between our 5 years of volume flux estimates and the nao index gives r 0 56 during the high nao years a more intense icelandic low increases the gradient in the sea level pressure by almost 1 mbar across the fram strait thus increasing the atmospheric forcing on ice transport correlation is reduced during the negative nao years because of decreased dominance of this large scale atmospheric pattern on the sea level pressure gradient across the fram strait

the east greenland coastal current structure variability and forcing abstract the subtidal circulation of the southeast greenland shelf is described using a set of high resolution hydrographic and velocity transects occupied in summer 2004 the main feature is the east greenland coastal current egcc a low salinity high velocity jet with a wedge shaped hydrographic structure characteristic of other surface buoyancy driven currents the egcc was observed along the entire greenland shelf south of denmark strait while the transect north of the strait showed only a weak shelf flow this observation in conjunction with water mass considerations and other supporting evidence suggests that the egcc is an inner branch of the east greenland current egc that forms south of denmark strait it is argued that bathymetric steering is the most likely reason why the egc apparently bifurcates at this location repeat sections occupied at cape farewell between 1997 and 2004 show that the alongshelf wind stress can have an influence on the structure and strength of the egcc and egc on timescales of 2 3 days accounting for the wind induced effects the volume transport of the combined egcc egc system is roughly constant 2 sv over the study domain from 68 n to cape farewell near 60 n the corresponding freshwater transport increases by roughly 60 over this distance 59 96 msv referenced to a salinity of 34 8 this trend is consistent with a simple freshwater budget of the egcc egc system that accounts for meltwater runoff melting sea ice and icebergs and net precipitation minus evaporation

the 2017 reversal of the beaufort gyre can dynamic thickening of a seasonal ice cover during a reversal limit summer ice melt in the beaufort sea during winter 2017 the semi permanent beaufort high collapsed and the anticyclonic beaufort gyre reversed the reversal drove eastward ice motion through the western arctic causing sea ice to converge against banks island and halted the circulation of multiyear sea ice via the gyre preventing its replenishment in the beaufort sea prior to the reversal an anomalously thin seasonal ice cover had formed in the beaufort following ice free conditions during september 2016 with the onset of the reversal in january 2017 convergence drove uncharacteristic dynamic thickening during winter by the end of march despite seasonal ice comprising 97 of the ice cover the reversal created the thickest roughest and most voluminous regional ice cover of the cryosat 2 record within the beaufort sea previous work has shown that winter ice export can precondition the region for increased summer ice melt but that a short reversal during april 2013 contributed to a reduction in summer ice loss hence the deformed ice cover at the end of winter 2017 could be expected to limit summer melt in spite of this the beaufort ice cover fell to its fourth lowest september area as the gyre re established during april and divergent ice drift broke up the pack negating the reversal s earlier preconditioning our work highlights that dynamic winter thickening of a regional sea ice cover for instance during a gyre reversal offers the potential to limit summer ice loss but that dynamic forcing during spring dictates whether this conditioning carries through to the melt season

dependence of the arctic ocean ice thickness distribution on the poleward energy flux in the atmosphere 1 the sensitivity of the arctic ocean ice cover on the atmospheric poleward energy flux d is studied using a coupled column model of the ocean ice and atmosphere in the model the ice cover is described by a thickness distribution and the atmosphere is a simple two stream gray body in radiative equilibrium it is shown that the thickness distribution in combination with the albedo function gives a strong nonlinear response to positive perturbations of d the response on d is sensitive to the albedo parameterization and the shape of the thickness distribution controlled by ridging and divergence an increase of about 9 w m 2 from a standard value of d 103 w m 2 has a dramatic effect reducing the ice thickness by more than 2 m and generates a large open water fraction during summer the reduction of ice thickness is characterized by a clear transition between two regimes going from a regime where first year ice survives the next summer melt period to a seasonal ice regime where the first year ice melts completely it is shown that the existence of seasonal ice regime is dependent on the surface mixed layer thickness the model enters a completely ice free state if the thickness of the mixed layer is increased above a threshold value the adjustment timescale for the ice cover is 6 years for small positive and negative perturbations in d for larger positive perturbations of about 10 w m 2 the adjustment timescale is up to 20 years

the role of sea ice and other fresh water in the arctic circulation salinity stratification is critical to the vertical circulation of the high latitude ocean we here examine the control of the vertical circulation in the northern seas and the potential for altering it by considering the budgets and storage of fresh water in the arctic ocean and in the convective regions to the south we find that the present day greenland and iceland seas and probably also the labrador sea are rather delicately poised with respect to their ability to sustain convection small variations in the fresh water supplied to the convective gyres from the arctic ocean via the east greenland current can alter or stop the convection in what may be a modern analog to the halocline catastrophes proposed for the distant past the north atlantic salinity anomaly of the 1960s and 1970s is a recent example it must have had its origin in an increased fresh water discharge from the arctic ocean similarly the freshening and cooling of the deep north atlantic in recent years is a likely manifestation of the increased transfer of fresh water from the arctic ocean into the convective gyres finally we note that because of the temperature dependence of compressibility a slight salinity stratification in the convective gyres is required to efficiently ventilate the deep ocean

differential bedload transport rates in a gravel bed stream a grain size distribution approach two methods that were recently proposed for calculating fractional bedload transport rates in gravel bed streams are examined closely both of them employ the oak creek bedload data the diplas pd method is guided by dimensional analysis and therefore can be used to predict bedload transport in different gravel rivers the only requirement for using this method is the knowledge of the subsurface material size distribution of the stream of interest the expression for the fractional bedload transport obtained by the shih and komar sk method for oak creek cannot be used for other streams its use for a given stream requires information that is rarely available for the oak creek case both methods demonstrate similar predictive ability

synchronous variability in the southern hemisphere atmosphere sea ice and ocean resulting from the annular mode zonally symmetric fluctuations of the midlatitude westerly winds characterize the primary mode of atmospheric variability in the southern hemisphere during all seasons this is true not only in observations but also in an unforced 15 000 yr integration of a coarse resolution r15 coupled ocean atmosphere model here it is documented how this mode of atmospheric variability known as the southern annular mode sam generates ocean circulation and sea ice variations in the model integration on interannual to centennial timescales that are tightly in phase with the sam the positive phase of the sam is associated with an intensification of the surface westerlies over the circumpolar ocean around 608s and a weakening of the surface westerlies farther north this induces ekman drift to the north at all longitudes of the circumpolar ocean and ekman drift to the south at around 308s through mass continuity the ekman drift generates anomalous upwelling along the margins of the antarctic continent and downwelling around 458s the anomalous flow diverging from the antarctic continent also increases the vertical tilt of the isopycnals in the southern ocean so that a more intense circumpolar current is also closely associated with positive sam in addition the anomalous divergent flow advects sea ice farther north resulting in an increase in sea ice coverage finally positive sam drives increases in poleward heat transport at about 308s while decreases occur in the circumpolar region ocean and sea ice anomalies of the opposite sign occur when the sam is negative the ocean and sea ice fluctuations associated with the sam constitute a significant fraction of simulated ocean variability poleward of 308s year round the robustness of the mechanisms relating the sam to oceanic variability suggests that the sam is likely an important source of large scale variability in the real southern hemisphere ocean

the great salinity anomaly in the northern north atlantic 1968 1982 the widespread freshening of the upper 500 800m layer of the northern north atlantic which this paper describes represents one of the most persistent and extreme variations in global ocean climate yet observed in this century though a range of explanations have been advanced to explain this event including in situ changes in the surface moisture flux this paper describes the great salinity anomaly as largely though not entirely an advective event traceable around the atlantic subpolar gyre for over 14 years from its origins north of iceland in the mid to late 1960s until its return to the greenland sea in 1981 1982 the overall propagation speed around this subpolar gyre is estimated at about 3cm s 1 of the total salt deficit associated with the anomaly as it passed south along the labrador coast in 1971 1973 about 72 109 tonnes a deficit equivalent to about two thirds of this figure 47 109 tonnes ultimately passed through the faroe shetland channel to the barents sea arctic ocean and greenland sea during the mid 1970s possible effects on deep water formation and on the representativeness of historical section data are discussed

physical and biological characteristics of the pelagic system across fram strait to kongsfjorden abstract the fram strait is very important with regard to heat and mass exchange in the arctic ocean and the large quantities of heat carried north by the west spitsbergen current wsc influence the climate in the arctic region as a whole a large volume of water and ice is transported through fram strait with net water transport of 1 7 3 2 sv southward in the east greenland current and a volume ice flux in the range of 0 06 0 11 sv the mean annual ice flux is about 866 000 km2 yr 1 the kongsfjorden krossfjorden fjord system on the coast of spitsbergen or at the eastern extreme of fram strait is mainly affected by the northbound transport of water in the wsc mixing processes on the shelf result in transformed atlantic water in the fjords and the advection of atlantic water also carries boreal fauna into the fjords the phytoplankton production is about 80 g c m 2 yr 1 in fram strait and has been estimated both below and above this for kongsfjorden the zooplankton fauna is diverse but dominated in terms of biomass by calanoid copepods particularly calanus glacialis and c finmarchicus other important copepods include c hyperboreus metridia longa and the smaller more numerous pseudocalanus p minutus and p acuspes microcalanus m pusillus and m pygmaeus and oithona similis the most important species of other taxa appear to be the amphipods themisto libellula and t abyssorum the euphausiids thysanoessa inermis and t longicaudata and the chaetognaths sagitta elegans and eukrohnia hamata a comparison between the open ocean of fram strait and the restricted fjord system of kongsfjorden krossfjorden can be made within limitations the same species tend to dominate but the fram strait zooplankton fauna differs by the presence of meso and bathypelagic copepods the seasonal and inter annual variation in zooplankton is described for kongsfjorden based on the record during july 1996 2002 the ice macrofauna is much less diverse consisting of a handful of amphipod species and the polar cod the ice associated biomass transport of ice amphipods was calculated based on the ice area transport at about 3 55 106 ton wet weight per year or about 4 2 105 t c yr 1 this represents a large energy input to the greenland sea but also a drain on the core population residing in the multi year pack ice myi in the arctic ocean a continuous habitat loss of myi due to climate warming will likely reduce dramatically the sympagic food source the pelagic and sympagic food web structures were revealed by stable isotopes the carbon sources of particulate organic matter pom being ice pom and pelagic pom revealed different isotopic signals in the organisms of the food web and also provided information about the sympagic pelagic and pelagic benthic couplings the marine food web and energy pathways were further determined by fatty acid trophic markers which to a large extent supported the stable isotope picture of the marine food web although some discrepancies were noted particularly with regard to predator prey relationships of ctenophores and pteropods

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

decadal variability in high northern latitudes as simulated by an intermediate complexity climate model a 2500 year integration has been performed with a global coupled atmospheric sea ice ocean model of intermediate complexity with the main objective of studying the climate variability in polar regions on decadal time scales and longer the atmospheric component is the ecbilt model a spectral t21 three level quasi geostrophic model that includes a representation of horizontal and vertical beat transfers as well as of the hydrological cycle ecbilt is coupled to the clio model which consists of a primitive equation free surface ocean general circulation model and a dynamic thermodynamic sea ice model comparison of model results with observations shows that the ecbilt clio model is able to reproduce reasonably well the climate of the high northern latitudes the dominant mode of coupled variability between the atmospheric circulation and sea ice cover in the simulation consists of an annular mode for geopotential height at 800 hpa and of a dipole between the barents and labrador seas for the sea ice concentration which are similar to observed patterns of variability in addition the simulation displays strong decadal variability in the sea ice volume with a significant peak at about 18 years positive volume anomalies are caused by 1 a decrease in ice export through fram strait associated with more anticyclonic winds at high latitudes 2 modifications in the freezing melting rates in the arctic due to lower air temperature and higher surface albedo and 3 a weaker heat flux at the ice base in the barents and kara seas caused by a lower inflow of warm atlantic water opposite anomalies occur during the volume decrease phase of the oscillation

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

arctic salinity anomalies and their link to the north atlantic during a positive phase of the arctic oscillation abstract many of the changes observed during the last two decades in the arctic ocean and adjacent seas have been linked to the concomitant abrupt decrease of the sea level pressure in the central arctic at the end of the 1980s the decrease was associated with a shift of the arctic oscillation ao to a positive phase which persisted throughout the mid 1990s the arctic salinity distribution is expected to respond to these dramatic changes via modifications in the ocean circulation and in the fresh water storage and transport by sea ice the present study investigates these different contributions in the context of idealized ice ocean experiments forced by atmospheric surface wind stress or temperature anomalies representative of a positive ao index wind stress anomalies representative of a positive ao index generate a decrease of the fresh water content of the upper arctic ocean which is mainly concentrated in the eastern arctic with almost no compensation from the western arctic sea ice contributes to about two third of this salinification another third being provided by an increased supply of salt by the atlantic inflow and increased fresh water export through the canadian archipelago and fram strait the signature of a saltier atlantic current in the norwegian sea is not found further north in both the barents sea and the fram strait branches of the atlantic inflow where instead a widespread freshening is observed the latter is the result of import of fresh anomalies from the subpolar north atlantic through the iceland scotland passage and enhanced advection of low salinity waters via the east icelandic current the volume of ice exported through fram strait increases by 20 primarily due to thicker ice advected into the strait from the northern greenland sector the increase of ice drift velocities having comparatively less influence the export anomaly is comparable to those observed during events of great salinity anomalies and induces substantial freshening in the greenland sea which in turn contributes to increasing the fresh water export to the north atlantic via denmark strait with a fresh water export anomaly of 7 msv the latter is the main fresh water supplier to the subpolar north atlantic the canadian archipelago contributing to 4 4 msv the removal of fresh water by sea ice under a positive winter ao index mainly occurs through enhanced thin ice growth in the eastern arctic winter sat anomalies have little impact on the thermodynamic sea ice response which is rather dictated by wind driven ice deformation changes the global sea ice mass balance of the western arctic indicates almost no net sea ice melt due to competing seasonal thermodynamic processes the surface freshening and likely enhanced sea ice melt observed in the western arctic during the 1990s should therefore be attributed to extra winter atmospheric effects such as the noticeable recent spring summer warming in the canada alaska sector or to other modes of atmospheric circulations than the ao especially in relation to the north pacific variability

assimilating satellite concentration data into an arctic sea ice mass balance model 1979 1985 using satellite ice concentration data observed buoy velocities and a thermodynamic ice growth model we compute the time histories of the thickness distributions of four ice types level and ridged first year ice and level and ridged multiyear ice these histories are computed for seven regions covering the arctic ocean with a 10 day time step for 1979 through 1985 a blend of observed buoy motions and wind driven free drift velocities drives the advective and ridging parts of the model while climatological growth and melt rates determine the ice thickness the model adjusts the thickness distributions so that the modeled concentrations of open water first year ice and multiyear ice match the concentrations derived by kalman filtering of satellite passive microwave observations the major adjustment is to reduce modeled ice concentrations in summer and particularly in the peripheral seas to account for unmodeled melt the model includes an ice salinity parameterization which along with changes in ice volume gives the salt or freshwater flux from the ice our results show that the arctic ice cover consists primarily of multiyear ice 60 by area and 82 by volume and that most of this ice is ridged the average ice thickness is 2 7 m with a seasonal variation of 30 and an interannual variation of 10 the study also shows that for each cell and the arctic as a whole the changes in ice volume caused by growth minus melt approximately balance the changes caused by import minus export the annual ice export through fram strait varies from 1100 to 3000 km3 primarily because of variations in ice velocity all regions except the chukchi sea have a net ice growth a net export and a net salt input to the ocean surface the annual mean salt flux to the ocean surface from net ice production is 7 3 kg m 2 downward fluxes along the transpolar drift stream are larger than elsewhere the largest downward flux of 33 kg m 2 yr 1 in the nansen basin can be attributed to the strong divergence near fram strait a companion paper steele et al this issue uses these fluxes and ice velocities to derive the arctic ocean freshwater balance

fram strait sea ice outflow 1 we summarize 24 years 1978 2002 of ice export estimates and examine over a 9 year record the associated variability in the time varying upward looking sonar uls thickness distributions of the fram strait a more thorough assessment of the pmw passive microwave ice motion with 5 years of synthetic aperture radar sar observations shows the uncertainties to be consistent with that found by kwok and rothrock 1999 giving greater confidence to the record of ice flux calculations interesting details of the cross strait motion profiles and ice cover characteristics revealed by high resolution sar imagery are discussed the average annual ice area flux over the period is 866 000 km2 yr between the 1980s and 1990s the decadal difference in the net exported ice area is 400 000 km2 approximately half the annual average except for the years with extreme negative nao correlation of winter ice area export with the nao index remains high r2 0 62 with thickness estimates from uls moorings we estimate the average annual ice volume flux 8 years to be 2218 km3 yr 0 07 sv over the 9 year uls ice thickness data set there is an overall decrease of 0 45 m in the mean ice thickness over the entire time series and a decrease of 0 23 m over the winter months december through march correspondingly the mode of the my ice thickness exhibits an overall decrease of 0 55 m and a winter decrease of 0 42 m these are significant trends whether these trends are indicative of the thickness trends of the arctic ocean is examined as the time varying behavior of the monthly uls thickness distributions can be related not only to the seasonal cycle in the basal growth and melt but also to the magnitude and pattern of ice motion in the arctic ocean and the proximity of the uls moorings to the ice edge

composition of freshwater in the spring of 2014 on the southern labrador shelf and slope the labrador current is an important conduit of freshwater from the arctic to the interior north atlantic subpolar gyre here we investigate the spatial variability of the freshwater sources over the southern labrador shelf and slope during may june 2014 using measurements of seawater properties such as temperature salinity nutrients and oxygen isotopic composition we estimate the respective contributions of saline water of atlantic and pacific origins of brines released during sea ice formation and of freshwater from sea ice melt and meteoric water origins on the southern labrador shelf we find a large brine signal and pacific water influence indicating a large contribution of water from the canadian arctic the brine signal implies that more than 4 m of sea ice formed upstream either in the arctic or in baffin bay and the northern labrador sea over the midshelf and slope at 52 n we find a stronger influence of slope water from the west greenland current with a smaller contribution of pacific water and no brine signal thus there is advection of water from the slope region to the midshelf between 55 n and 52 n very freshwater with high meteoric content is found close to the coast in june 2014 observations from 1995 and 2008 suggest a higher fraction of brine and pacific water on the shelf compared to that observed in 2014