heat flow in the baltic shield results of the lithospheric geothermal modelling abstract the results of heat flow measurements performed within the baltic shield and in its closest neighbourhood are reviewed the regional distribution of the heat flow density is presented as a heat flow map the characteristic heat flow density amounts to 35 40 mw m 2 and is notably smaller than heat flow in the surrounding areas the radiogenic heat production within the crust contributes to the observed surface heat flow by about 15 20 mw m 2 this permits to estimate the moho heat flow in the most stable parts of the shield to about 20 mw m 2 and over 25 30 mw m 2 in the surrounding platform to the south and east relatively low moho temperatures of 350 500 c characterize the crust mantle boundary of the shield increasing to 600 700 c beneath the shield margins the thermal thickness of the lithosphere of the shield can attain more than 200 km

role of the ocean in the decadal climate change in the north pacific 1 i have investigated features of decadal climate variability in the north pacific and clarified the role of the ocean in controlling them by analyzing historical data sets and executing experiments with a low order model detailed investigation of the variability of the wintertime aleutian low and water temperature in the subarctic frontal region implies a new scenario for the mechanism of the decadal variability the decadal variability can be interpreted as the transition process between two stable states cold and warm period in midlatitude atmosphere when the transition to a cold period occurs sea surface temperature in the subarctic frontal region begins to be lowered not only through the surface processes but by westward propagation of cold anomaly from eastern subarctic region as a baroclinic rossby wave as a result the meridional gradient of sea surface heat flux yq0 decreases its magnitude and then the forcing of the aleutian low is weakened when this weakening exceeds a threshold the transition from a cold to a warm period occurs abruptly after the transition to a warm period yq0 in turn increases its magnitude through the opposite processes to cause the reverse transition the timescale of this cycle is mainly determined by the propagation speed of a baroclinic rossby wave the el nino and southern oscillation variability both in the atmosphere and ocean can also affect the timescale by causing the thresholds for transitions to be temporarily exceeded experiments with a four variable low order model support the proposed mechanism of the decadal variability

late quaternary glacial interglacial changes in sediment composition at the east greenland continental margin and their paleoceanographic implications stable isotope records and sedimentological and organic geochemical investigations of marine sediments from the east greenland sea at 70 n provide important information about glacial interglacial variations of paleoenvironments through the last 225 kyr the oxygen isotope records established on the planktonic foraminifer n pachyderma sin show some excursions from the global climate pattern probably due to local regional overprint by meltwater supply the cold low saline east greenland current and fluctuations in sea ice covering were a crucial element controlling the carbonate production in the subsurface surface water column in the east greenland sea over the last 225 kyr the beginning of termination ia is ams 14c dated at about 15 8 kyr b p and interpreted as a greenland ice sheet meltwater signal the stage 2 3 boundary is dated at about 25 kyr b p the timing of the onset of the last deglacial meltwater event is about 800 years earlier than that of the barents shelf ice sheet meltwater signal recorded in the fram strait several major pulses of increased supply of coarse grained terrigenous material by glacio marine processes occurred during the last 225 kyr the supply of coarse grained ice rafted debris at the east greenland continental slope reached maximum values during the last glacial maximum stage 2 weichselian 15 19 kyr b p the drastic climatic change and the gradual retreat of continental ice masses glaciers during the last deglaciation termination i are clearly documented in the marine sedimentary sequences from shelf and upper slope environments this process resulted in distinctly decreased supply and deposition of ice rafted debris in the open shelf upper slope environments during termination i the sea ice cover also decreased causing an increase in surface water productivity indicated by increased organic carbon and biogenic opal deposition

structure and dynamics of decadal anomalies in the wintertime midlatitude north pacific ocean atmosphere system the structure and dynamics of decadal anomalies in the wintertime midlatitude north pacific ocean atmosphere system are examined in this study using the ncep ncar atmospheric reanalysis hadisst sst and simple ocean data assimilation data for 1960 2010 the midlatitude decadal anomalies associated with the pacific decadal oscillation are identified being characterized by an equivalent barotropic atmospheric low high pressure over a cold warm oceanic surface such a unique configuration of decadal anomalies can be maintained by an unstable ocean atmosphere interaction mechanism in the midlatitudes which is hypothesized as follows associated with a warm pdo phase an initial midlatitude surface westerly anomaly accompanied with intensified aleutian low tends to force a negative sst anomaly by increasing upward surface heat fluxes and driving southward ekman current anomaly the sst cooling tends to increase the meridional sst gradient thus enhancing the subtropical oceanic front as an adjustment of the atmospheric boundary layer to the enhanced oceanic front the low level atmospheric meridional temperature gradient and thus the low level atmospheric baroclinicity tend to be strengthened inducing more active transient eddy activities that increase transient eddy vorticity forcing the vorticity forcing that dominates the total atmospheric forcing tends to produce an equivalent barotropic atmospheric low pressure north of the initial westerly anomaly intensifying the initial anomalies of the midlatitude surface westerly and aleutian low therefore it is suggested that the midlatitude ocean atmosphere interaction can provide a positive feedback mechanism for the development of initial anomaly in which the oceanic front and the atmospheric transient eddy are the indispensable ingredients such a positive ocean atmosphere feedback mechanism is fundamentally responsible for the observed decadal anomalies in the midlatitude north pacific ocean atmosphere system

the effect of north pacific sea surface temperature anomalies on the january climate of a general circulation model abstract four perpetual january integrations of an atmospheric general circulation model have been performed in each of which a different sea surface temperature sst anomaly was specified in the north pacific the observed sst anomaly for the 1976 77 winter was chosen as the basic anomaly and 1200 day runs were carded out in which this anomaly was multiplied by 1 and 2 a fifth run was performed which combined the basic midlatitude sst anomaly from 1976 77 with a tropical pacific sst anomaly representative of the mature phase of a warm el nino southern oscillation enso episode an ensemble of eight independent 90 day averaged realizations was extracted from each simulation maps of ensemble mean differences from the model climatology are presented in this paper together with estimates of the statistical significance of some of the features which appear on these maps the model response to the basic sst anomaly and to twice the basic sst anomaly is a midiatitude teleconnection pattern the pacifi

impacts of el nino and la nina on the u s climate during northern summer the impacts of el nino and la nina on the u s climate during northern summer are analyzed separately composite analyses reveal that a continental scale anomalous high dominates over most of north america during la nina events and leads to hot and dry summers over the central united states however the impacts of el nino over north america are weaker and more variable a linear barotropic model is used to explore the maintenance of the anomalous patterns various forcing terms derived from observations via a single level vorticity budget analysis are used to drive the model when the barotropic model is driven by the total forcing rossby wave source plus transient eddy forcing plus nonlinear interactions the model simulations resemble the observed patterns and a strong and extensive anticyclone is reproduced in the la nina simulation the model responses to the individual forcing terms suggested that the vorticity stretching term fd and the transient eddy forcing contribute most to the responses over north america the stretching term fd excites a low in the el nino simulation and a high in the la nina simulation over north america however the transient eddy forcing favors an anomalous high over north america in both el nino and la nina simulations such that it weakens the el nino pattern and strengthens the la nina pattern

evidence for the influence of the agulhas current on regional atmospheric circulation patterns abstract the agulhas current is much the strongest western boundary current in the southern hemisphere transporting about 65 sv of warm water along the southeast coast of africa south of africa it retroflects back into the south indian ocean and flows east as the agulhas return current large amounts of heat are lost to the atmosphere from the warm waters of the southern agulhas current its retroflection and the return current particularly during winter and the transition seasons it is thought that this large exchange of heat may have a significant influence on the regional atmospheric circulation the tracks and intensity of transient weather disturbances such as extratropical cyclones and on rainfall received over large parts of neighboring southern africa in an attempt to investigate the potential influence of the agulhas current on the regional atmosphere two ensembles of year long integrations of an atmospheric general circulation model are analyzed in the first ensemble the sea surface tem

correlation between the pacific north american pattern and the eastward propagation of sea surface temperature anomalies in the north pacific lag correlation and singular value decomposition analyses reveal that the pacific north american pattern is correlated with eastward propagating sea surface temperature sst anomalies in the north pacific the eastward movement of sst anomalies is also clear in one point lag correlation maps and longitude time plot of low pass filtered time series the timescale for the sst anomalies to travel across the north pacific is 1 year it is speculated that the propagation is related to the air sea interactions in the north pacific these findings provide observational support for the atmospheric bridge theory proposed by lau and nath 1994

the north pacific as a regulator of summertime climate over eurasia and north america abstract the role of the north pacific as a regulator of boreal summer climate over eurasia and north america is investigated using observational data two summertime interannual climate modes associated with sea surface temperature sst variability in the north pacific are identified the first mode shows an elongated zone of warm cold sst anomalies in the central north pacific along 40 n with temporal variability significantly correlated with el nino during the preceding spring but its subsequent evolution is quite different from el nino the second mode exhibits a seesaw sst variation between the northern and southern north pacific and is independent of el nino both modes are linked to coherent sst anomalies over the north atlantic suggesting the presence of an atmospheric bridge linking the two extratropical oceans using the principal component of the most dominant mode as the north pacific index npi composite analyses show that the positive negative phase of npi features a warm cold

the linearity of the atmospheric response to north atlantic sea surface temperature anomalies a large number of uncoupled integrations with an idealized general circulation model are carried out to investigate the linearity of the atmospheric quasi equilibrium response to north atlantic sea surface temperature sst anomalies related to interdecadal variability a statistical approach is used to judge the linearity of the temporally averaged global atmospheric response with respect to the amplitudes of the sst anomaly patterns the results indicate that the assumption of a linear correlation of the corresponding magnitudes is in general not valid since the model though idealized provides all the characteristics of a full general circulation model gcm some important conclusions can be drawn for the design and interpretation of gcm sensitivity experiments

investigating the local atmospheric response to a realistic shift in the oyashio sea surface temperature front abstractthe local atmospheric response to a realistic shift of the oyashio extension sst front in the western north pacific is analyzed using a high resolution hr 0 25 version of the global community atmosphere model version 5 cam5 a northward shift in the sst front causes an atmospheric response consisting of a weak surface wind anomaly but a strong vertical circulation extending throughout the troposphere in the lower troposphere most of the sst anomaly induced diabatic heating is balanced by poleward transient eddy heat and moisture fluxes collectively this response differs from the circulation suggested by linear dynamics where extratropical sst forcing produces shallow anomalous heating balanced by strong equatorward cold air advection driven by an anomalous stationary surface low to the east this latter response however is obtained by repeating the same experiment except using a relatively low resolution lr 1 version of cam5 comparison to observations suggests that the hr respo

on variations in the subarctic circulation in the north pacific abstract anomalous southward shifts in the oyashio and subarctic circulation in the north pacific occur from winter to late spring and the wide extension of cold sea surface temperatures sst influences the atmospheric circulation over the north pacific this anomalous southward shift results from the barotropic response of the ocean to changes in the wind stress induced by the southward shift of the deepening aleutian low global changes in the ocean and atmosphere associated with these anomalous shift of the oyashio and subarctic circulation in the north pacific are examined in this study it is shown that both the area of sea ice in the okhotsk sea and the extent of snow cover over the eurasian continent decrease in winter in association with this anomalous shift the teleconnection between equatorial sst and the southward shift of the enhanced aleutian low was weak after 1989 as a result of a decadal climatic change even so the relationship between reductions in the areas of sea ice in the okhotsk sea and snow cover over the eurasian continent in the winter and the anomalous southward shift of the oyashio and the subarctic circulation persisted through the decadal change

modelling rates of sedimentation from icebergs abstract icebergs transport debris from ice masses into the glacimarine environment but iceberg production debris content and sedimentation rate will vary with glacier dynamics and the nature of marine waters a model incorporating glaciological and oceanographic parameters calculates the flux of debris calved in icebergs iceberg melt rates and sedimentation rates with distance from calving tidewater ice fronts the flux of basal debris calved through a 1 m width of tidewater margin is h d c 100 v c where h d and c are basal debris rich ice thickness and sediment content and v c is iceberg calving rate iceberg basal melting for any horizontal interval d x away from the calving glacier is dy m b d x v b where m b is iceberg melt rate and v b is horizontal iceberg velocity sediment release for any x increment depends on iceberg debris concentration and previous berg melt history model parameters vary with the nature of climatic conditions on a continuum from cold polar environments e g high canadian arctic antarctic peninsula through sub polar environments e g baffin island svalbard to more temperate environments e g se alaska these parameters include glacier flow velocity glacier thermal regime basal debris rich ice thickness and marine water temperature model results suggest that iceberg sedimentation rates are lowest for high polar settings and most rapid in warm maritime and some sub polar areas however icebergs in cold waters transport debris to significantly greater distances from the parent glacier the model provides calculations of order of magnitude rates of iceberg sedimentation in varying glacimarine settings

the modeled atmospheric response to midlatitude sst anomalies and its dependence on background circulation states abstract the atmospheric response to a midlatitude sst anomaly in the north pacific and its dependence on background flow are examined in a gcm experiments are conducted using the same warm sst anomalies but two different model states perpetual january and perpetual february the atmospheric responses to the sst anomalies are statistically significant in both january and february but are completely different the anomalous circulation in january is characterized by a trough decaying with height immediately downstream of the sst anomalies in february the anomalous circulation is dominated by a downstream ridge growing with height the patterns of the anomalous heights in the two months are nearly orthogonal vorticity and thermodynamic budgets are diagnosed to illustrate how the anomalous circulations are maintained over the sst anomalies low level convergence and ascent are observed in both months in january the anomalous convergence is balanced by a residual due primarily to the forcing by submont

winter observations of iceberg frequencies and sizes in the south atlantic ocean the numbers and apparent sizes of icebergs in the south atlantic ocean in midwinter were measured by radar and visually from f s polarstern during the 1986 winter weddell sea project cruise results show that in a heavy sea sea state 7 8 icebergs have to be at least 115 m in diameter to be detected at all and that detectability falls off severely for all bergs at ranges exceeding 8 n mi 15 km that most bergs had diameters of less than 1 km with a preferred size of 400 500 m and that a high density of icebergs in the latitude band 53 56 s at longitude 19 30 w contrasted with a virtual absence of bergs in the same latitude band at longitude 1 9 e the latter effect is ascribed to melt and wave induced deterioration causing the disappearance of this iceberg population between the two sets of longitudes

heat flow and thermal structure of the lithosphere across the baltic shield and northern tornquist zone abstract terrestrial heat flow data from archean and proterozoic provinces of the baltic shield its southwestern margin and the tectonic transition to the younger tectonic units of central europe northern segment of the european geotraverse are compiled and examined for local and regional variations a 2 d numerical lithospheric temperature and heat flux model is presented covering 1800 km of the deep seismic fennolora profile across the baltic shield and 500 km of eugeno s northern eugemi seismic lines across the northern tornquist zone and the danish and north german basins thermal lithosphere defined as the outer layer with relatively low temperatures t c in which heat transfer is dominantly by conduction is found to vary markedly in thickness from 85 110 km beneath basins and tornquist zone to about 150 km in central shield areas and 200 250 km in areas of low heat flow along the northern shield profile these results are in very good agreement with seismological information from surface wave dispersion analysis and the refraction wide angle seismic interpretation of fennolora data the combined thermal and seismologic evidence indicates that the uppermost mantle region stratified in seismic velocity is restricted to the upper relatively cold thermal layer which is interpreted to constitute shield lithosphere local and to some extent regional variations in surface heat flow are found to be closely related to variations in near surface radiogenic heat production for the southern baltic shield a heat flow heat production relationship of q 0 32 8 7 6 h 0 is derived regional increase in heat flow from northern and central shield provinces to the shield margin and the tornquist zone is interpreted to be related partly to differences in upper crustal heat generation partly and in southernmost areas mainly to an increased heat flux from the upper mantle upper mantle heat flux is estimated at 20 25 mw m 2 along the northern and central shield transect increasing to 30 40 mw m 2 beneath the shield margin basins and tornquist zone lithospheric thickness variations in this region of northern europe are found to be closely associated with variations in heat flux from the uppermost mantle and perhaps to a large extent controlled by geodynamically determined lateral differences in upper mantle heat flux earthquake focal depth data and information on crustal strength show baltic shield seismicity to be limited generally to the upper 20 25 km brittle part of the crust at temperatures less than 300 400 c maximum source depth of magnetic anomalies at temperatures near 600 c is in the deepest part of the crust near the crust mantle boundary in the southern region about 25 km depth along the tornquist zone and about 35 40 km in southern shield areas and in the uppermost mantle 60 70 km depth in the northern shield areas some petrologic implications are discussed the present deep crust is supposed to be at lower temperature pressure conditions than at early stages of formation however also the present deepest parts of the shield crust 35 40 km are within the stability field of eclogites the general absence of significant gravity anomalies in areas of marked crustal thickness variations indicate high density eclogites to be present in significant amounts in the deep shield crust

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

pdo related wintertime atmospheric anomalies over the midlatitude north pacific local versus remote sst forcing abstractobserved wintertime atmospheric anomalies over the central north pacific associated with the pacific decadal oscillation pdo are characterized by a cold trough warm ridge structure tha

the general circulation model response to a north pacific sst anomaly dependence on time scale and pattern polarity abstract a general circulation model was integrated with perpetual january conditions and prescribed sea surface temperature sst anomalies in the north pacific a characteristic pattern with a warm region centered northeast of hawaii and a cold region along the western seaboard of north america was alternately added to and subtracted from the climatological sst field long 1350 day runs as well as short 180 day runs each starting from different initial conditions were performed the results were compared to a control integration with climatological ssts the model s quasi stationary response does not exhibit a simple linear relationship with the polarity of the prescribed sst anomaly in the short runs with a negative sst anomaly over the central ocean a large negative height anomaly with an equivalent barotropic vertical structure occurs over the gulf of alaska for the same sst forcing the long run yields a different response pattern in which an anomalous high prevails over northern canada and

subsurface iceberg melt key to greenland fjord freshwater budget liquid freshwater fluxes from the greenland ice sheet affect ocean water properties and circulation on local regional and basin wide scales with associated biosphere effects the exact impact however depends on the volume timing and location of freshwater releases which are poorly known in particular the transformation of icebergs which make up roughly 30 50 of the loss of the ice sheet mass to liquid freshwater is not well understood here we estimate the spatial and temporal distribution of the freshwater flux for the helheim sermilik glacier fjord system in southeast greenland using an iceberg melt model that resolves the subsurface iceberg melt by estimating seasonal variations in all the freshwater sources we confirm quantitatively that iceberg melt is the largest annual freshwater source in this system type we also show that 68 78 of the iceberg melt is released below a depth of 20 m and seasonally about 40 100 of that melt is likely to remain at depth in contrast with the usual model assumptions iceberg melt also peaks two months after all the other freshwater sources peak our methods provide a framework to assess individual freshwater sources in any tidewater system and our results are particularly applicable to coastal regions with a high solid ice discharge in greenland iceberg melt is the largest annual freshwater source in a south greenland fjord with release largely below 20 m depth according to iceberg model simulations furthermore iceberg melt peaks later in the year than other sources of freshwater

distribution of icebergs in the atlantic and indian ocean sectors of the antarctic region and its possible links with enso 1 the spatial distribution and multiyear variability of iceberg concentration in the atlantic and indian ocean sectors of the antarctic region have been studied using ship borne observations of iceberg occurrence the collected dataset includes more than 40 000 reports predominantly from russian and australian research vessels made over the last 36 years 1970 2005 the analysis of the data has revealed a gradual decrease in the iceberg concentration away from the coast of antarctica and a substantial variation along the coast line large concentration of icebergs was found in the weddell sea and north east of the antarctic peninsula several regions in the atlantic and indian ocean sector of antarctica have been identified where yearly anomalies of the iceberg occurrence exhibit a noticeable correlation with el ni o southern oscillation enso events the strongest enso effect was observed in the region east of drake passage where the iceberg concentration increased by about 50 during years of the negative southern oscillation index soi phase the change in the iceberg amount is explained by an increased iceberg drift into this region from the southern part of weddell sea and from pacific ocean the latter is caused by anomalous surface pressure high and associated anti clockwise circulation around the pressure anomaly developing in the south eastern part of pacific ocean during the negative phase of enso

the glacier influenced scoresby sund fan east greenland continental margin evidence from gloria and 3 5 khz records a major submarine fan gradient about 2 offshore of the scoresby sund fjord system is indicated by the crescentic shape of the shelf break gloria long range side scan sonar imagery was obtained over about 20 000 km2 of the fan along with 1000 km of 3 5 khz records three acoustic facies were defined from gloria backscatter signatures and sea floor morphology and sediment acoustic character on 3 5 khz records facies 1 includes a series of acoustically transparent features 0 5 2 km in width elongate downslope with irregular surface topography which are interpreted as debris flows this makes up the bulk of relatively recent sedimentation on the upper fan diamictic sediments in a core support a debris flow origin facies 2 is featureless on gloria images 3 5 khz profiles reveal irregular former sea floor morphology above which is a draping unit 15 m thick this northern region of the fan is a less active area where hemipelagic sediments and limited ice rafted debris overlie older material formed by past debris flow activity the more distal area of the adjacent ocean basin has a flat floor with parallel sub bottom reflectors of facies 3 this facies is probably an area of low energy hemipelagic sedimentation punctuated by occasional ice rafting and turbidity current activity the debris flows interpreted from gloria and 3 5 khz data are basic building blocks in the long term development of the scoresby sund fan glacier influenced fan volume is about 15 000 5000 km3 based on seismic reflection studies during full glacials in east greenland the inland ice sheet advances to fill the scoresby sund fjord system and extends across the shelf to reach the shelf break in some glacial cycles debris flows form in areas of most rapid sediment flux the scoresby sund fan is relatively similar to the storfjorden fan on the eastern polar north atlantic margin but differs from the larger bear island fan in having a steeper fan gradient much smaller debris flows and no large scale slides

simulation of the response of the north pacific ocean to the anomalous atmospheric circulation associated with el nino during el nino events when positive sea surface temperature sst anomalies form in the equatorial pacific sst anomalies also tend to develop in the north pacific this study attempts to model and explain the large scale features of the observed sst anomaly field in the north pacific during the fall and winter of the el nino year the experiment design consists of a mixed layer ocean model of the north pacific which is forced by atmospheric surface fields from two sets of community climate model ccm integrations the el nino set with prescribed positive sst anomalies in the tropical pacific and the control set which is obtained from an extended ccm integration with prescribed climatological ssts the response of the midlatitude ocean to atmospheric surface fields associated with el nino is obtained by compositing each set of model integrations el nino and control and then taking the difference between the composites the ocean model is able to reproduce the general features of the observed midlatitude sst anomaly pattern warm water in the northeast pacific and an elliptically shaped cold pool in the central pacific in these regions a large fraction of the temperature anomalies are significant at the 95 level as indicated by a two tailed t test the ocean temperature anomalies simulated by the model are primarily caused by changes in the sensible and latent heat flux and to a lesser extent the longwave radiation flux entrainment of cold water from below the mixed layer also influences ocean temperatures however the entrainment anomaly pattern has a complex spatial structure which does not always coincide with the simulated mixed layer temperature anomalies

velocity measurements on daugaard jensen gletscher scoresby sund east greenland the surface movement of daugaard jensen gletscher east greenland a fast moving outlet glacier from the greenland ice sheet was determined by means of theodolite measurements using intersections from observation stations on bedrock once or twice a day during a ten day period with a gap of about three weeks the observation programme was resumed for another three days which allowed long term mean velocities to be calculated as references for a study of velocity fluctuations on time scales in the range 2 10 days various methods of analysing non synchronous theodolite measurements on fast moving glaciers are discussed and previously reported large velocity fluctuations are critically reviewed it is concluded that on the time scales studied velocities in the frontal region of daugaard jensen gletscher fluctuate by up to 15 however on one occasion a velocity increase of more than 50 was observed lasting for about 7 5 hours this event is inferred to be the result of a sudden increase in the water pressure of the subglacial drainage system caused by the tapping of an ice dammed lake behind the glacier front the more moderate velocity fluctuations are most likely also due to changes of the subglacial hydraulic system

jakobshavns glacier drainage basin a balance assessment maximum and minimum estimates are made of the drainage basin feeding the jakobshavns glacier by using surface elevation maps derived from seasat altimetry benson s 1962 net balance measurements are used to calculate the balance flow within the basin comparisons of the balance flux at the terminus with estimates of actual flux suggest the basin is in overall equilibrium or slightly thickening this agrees with measurements along the nearby egig traverse balance velocities accelerate rapidly within 100 km of the coast farther upstream balance velocities are consistent with both measured velocities along the egig traverse and calculated deformation velocities it is estimated that jakobshavns glacier discharges between 4 8 and 7 6 of the annual net balance over greenland and drains between 3 7 and 5 8 of the ice sheet area

response of the atmosphere ocean mixed layer system to anomalous ocean heat flux convergence we investigate the role of the extratropical oceans in climate variability rather than following the traditional approach of studying the atmospheric response to prescribed sea surface temperature sst anomalies we focus on the role of anomalous ocean heat transport we employ an atmosphere model coupled to a fixed depth slab ocean mixed layer model forced by a field of ocean heat flux convergence ohfc we study the response of this coupled atmosphere ocean mixed layer system to an idealized ohfc anomaly we find that the ohfc forcing is mainly balanced by anomalous surface latent heat flux i e enhanced evaporation notably the anomalous sst is not co located with the forcing nor with the anomalous air sea flux nor with the anomalous diabatic heating contrary to conventional wisdom in our experiment the influence of the extratropical ocean on the atmosphere is not manifest primarily in an sst signature the anomalous diabatic heating is associated with a downstream surface low pressure anomaly in line with the simple theory of the steady response to extratropical heating transient eddy anomalies play only a minor role the principal sst anomaly appears to be a passive response to this anomalous atmospheric flow our results suggest that the traditional narrow focus on sst as the key variable involved in ocean atmosphere interaction may offer only a limited perhaps even misleading guide to the influence of the extratropical oceans on climate variability copyright 2002 royal meteorological society

simple coupled midlatitude climate models a set of simple analytical models is presented and evaluated for interannual to decadal coupled ocean atmosphere modes at midlatitudes the atmosphere and ocean are each in sverdrup balance at these long timescales the atmosphere s temperature response to heating determines the spatial phase relation between sst and sea level pressure slp anomalies vertical advection balancing heating produces high low slp lying east of warm cold sst anomalies as observed in the antarctic circumpolar wave acw the decadal north pacific mode and the interannual north atlantic mode zonal advection in an atmosphere with a rigid lid produces low slp east of warm sst however if an ad hoc equivalent barotropic atmospheric response is assumed high slp lies east of warm sst relaxation to heating produces behavior like the observed north atlantic decadal pattern with low slp over warm sst meridional advection in the atmosphere cannot produce the observed sst slp patterns the dominant balance in the ocean s temperature equation determines the phase speed of the modes the coupled mode is nondispersive in all models examined here indicating the need for additional processes for modes with an sst slp offset as observed in the acw and north pacific ekman convergence acting as a heat source causes eastward propagation relative to the mean ocean flow sverdrup response to ekman convergence acting on the mean meridional temperature gradient causes westward propagation relative to the mean ocean flow when the ocean temperature adjusts through surface heat flux alone the mode is advected by the mean ocean flow and is damped relaxation to heating in the atmosphere when operating with sverdrup response in the ocean produces the only complete solution presented here that exhibits growth with an e folding timescale of order 100 days this solution appears appropriate for the north atlantic decadal mode in northern hemisphere basins with meridional boundaries the same sets of dynamics create the observed sst slp phase relation an additional factor is the creation of sst anomalies through variations in the western boundary current strengths which are related to the zonally integrated wind stress curl over the whole basin if barotropic and hence fast adjustment is assumed the resulting positive feedback can maintain or strengthen the coupled anomalies in the north pacific and interannual north atlantic modes

relict sea floor ploughmarks record deep keeled antarctic icebergs to 45 s on the argentine margin abstract this paper reports ploughmarks on the argentine continental margin up to 44 50 s the most northerly morphological evidence of giant icebergs in the southern atlantic more than 2500 ploughmarks up to 32 km long 685 m wide and more than 20 m deep have been observed at modern water depths up to 646 m taking into account these iceberg sizes and ocean current directions which appear to have remained similar from the last full glacial to the present interglacial the icebergs that produced the ploughmarks are interpreted to be calved from fast flowing ice streams draining huge basins of the west antarctic ice sheet and the western antarctic peninsula during the last glacial maximum lgm about 20 000 years ago ploughmarks at the deepest water depths correspond to icebergs more than 500 m thick and at least 2 km wide given a sea level rise of 120 m since the lgm the icebergs after having drifted northeast in the antarctic circumpolar current were transported northward by the falklands malvinas current a total distance of 2000 to 4000 km the waters north of the falkland islands in particular were probably several degrees colder than today to prevent rapid iceberg melting and deterioration

mechanisms determining the atmospheric response to midlatitude sst anomalies abstract previous gcm experiments demonstrated that a model atmosphere produces two different responses to a midlatitude warm sst anomaly over the pacific under perpetual january and february conditions to elucidate the mechanisms responsible for the different gcm responses and their dependence on the background flow experiments with two idealized models are conducted experiments with a linear baroclinic model reveal that the gcm responses at equilibrium are primarily maintained by the anomalous eddy forcing the anomalous flow induced directly by an idealized initial heat source exhibits little sensitivity to the background flow eddy feedbacks on the heating induced anomalous flow are examined using a linear storm track model the anomalous eddy forcing produced by the storm track model is sensitive to the basic state the eddy forcing in january acts to shift the heating induced upper level ridge toward the northeast of the gulf of alaska while in february it acts to reinforce the ridge this sugge

geophysical evidence of deep keeled icebergs on the rockall bank northeast atlantic ocean high resolution multibeam swath bathymetric data acquired from the rockall bank reveal an abundance of linear to slightly sinuous seabed incisions these features interpreted as relict iceberg scours provide for the first time evidence that the rockall bank was intensively scoured by iceberg keels while the shallower portion of the rockall bank lacks evidence of iceberg scouring on the western and southern flanks between 250 and 450 m water depth the seabed is almost completely covered by thousands of cross cutting scours more isolated scours up to 800 m wide and 25 km long are also observed down to nearly 600 m water depth based on a full glacial sea level low stand of 120 m these isolated scour marks must have been carved bygigantic icebergs with keels up to 500 m deep and able to create incisions up to 15 m deep in the seabed analysis of scour orientation length width and depth indicates that these mega icebergs were likely calved from large fast flowing ice sheet outlets draining circum north atlantic ice sheets prevailing scour orientations suggest a number of possible ice sheet sources including southeast and southern greenland and the donegal barra ice stream of the last british irish ice sheet the bimodal distribution of the scour depth observed across the rockall bank suggest either different icebergs provenances or physical and climatic controlson icebergs draft

metamorphism in basement rocks and the implications for the tectonic evolution nasafjall window scandinavian caledonides the rocks of the nasafjall window comprise proterozoic granitoids with a metasedimentary cover of late precambrian to ordovician age the mierkenis group the metamorphic grade in the window varies from greenschist facies in the eastern part of the window to amphibolite facies in the western part the metamorphic maximum is syn to post kinematic in relation to the formation of the thrust related pervasive foliation this suggests a rapid basement heating in response to the late silurian to early devonian nappe emplacement the caledonian metamorphism terminated in middle devonian times and the retrograde phase was characterized by decompression this implies that the later stage of the thrusting was not associated with an increase in thickness of the nappe pile above the rocks of the nasafjall window

modelling iceberg trajectories sedimentation rates and meltwater input to the ocean from the eurasian ice sheet at the last glacial maximum we model iceberg flow paths from the eurasian ice sheet and the associated meltwater production and sedimentation rates within the norwegian greenland sea during the last glaciation results from a numerical ice sheet model an atmospheric general circulation model and an ocean general circulation model are collated and used to provide iceberg production rate wind field and surface current forcings to an iceberg trajectory model the iceberg model then determines how icebergs issuing from the eurasian ice sheet travel across the ocean and eventually melt in addition the release of iceberg sediments is also predicted the results show that iceberg trajectories are complex and that common features of iceberg movement are clustering in zones of convergence and exit into the north atlantic through the iceland faeroes channel eurasian icebergs do not penetrate into the interior of the arctic ocean the gathering of icebergs produces a complex meltwater pattern that does not follow the conceptual idea of decreasing meltwater production with distance from the ice sheet margin sedimentation results are compared with the meltwater configuration and are found to be a poor indicator of past zones of iceberg melt with zones of sedimentation extending significantly less far

the antarctic circumpolar wave a combination of two signals abstract a simplified view of the possible mechanisms behind the antarctic circumpolar wave acw interannual variability is provided by a frequency domain decomposition of several observed atmospheric and oceanic variables two significant interannual signals with different temporal and spatial characteristics are identified in the southern ocean and most of the variance of the acw in the interannual band can be accounted for by a linear combination of them the first signal has a period of oscillation of around 3 3 yr and a zonal wavenumber 3 structure across the southern ocean it involves self sustained fluctuations inherent in the southern ocean and driven by coupled air sea interactions in which the atmosphere and the ocean mutually force one another this signal is represented by an atmospheric standing oscillation with centers at fixed locations around antarctica and a propagating oceanic pattern in which the surface antarctic circumpolar current plays an essential role the second signal has a

northern hemisphere atmospheric response to changes of atlantic ocean sst on decadal time scales a gcm experiment analyses indicate that the atlantic ocean sea surface temperature sst was considerably colder at the beginning than in the middle of the century in pa rallel a systematic change in the north atlantic sea level pressure slp pattern was observed to find out whether the sst and slp changes analyzed are consis tent which would indicate that the sst change was real and not an instrumental artifact a response experiment with a low resolution t21 atmospheric gcm was per formed two perpetual january simulations were con ducted which differ solely in the atlantic ocean 40 s 60 n sst the cold simulation utilizes the ssts for the period 1904 1913 the warm simulation uses the ssts for the period 1951 1960 also a con trol run with the model s standard sst somewhat be tween the cold and warm sst was made for the response analysis a rigorous statistical approach was taken first the null hypothesis of identical horizontal distributions was subjected to a multivariate signifi cance test second the level of recurrence was esti mated the multivariate statistical approaches are based on hierarchies of test models we examined three different hierarchies a scale dependent hierarchy based on spherical harmonics s and two physically motivated ones one based on the barotropic normal modes of the mean 300 hpa flow b and one based on the eigenmodes of the advection diffusion operator at 1000 hpa a the intercomparison of the cold and warm experiments indicates a signal in the geostrop

a response climatology of idealized midlatitude thermal forcing experiments with and without a storm track several gcm studies indicate that eddy activity may have a considerable influence on the atmospheric response to midlatitude sea surface temperature anomalies the effect of eddy activity on the atmospheric equilibrium response to idealized midlatitude thermal forcing is analyzed for an atmosphere with or without an idealized storm track experiments using a simplified global circulation model forced by thermal anomalies of different sign and location are discussed consistent with the linear theory the geopotential height field displays a baroclinic response with a shallow low high somewhat downstream of the warm cold anomaly farther downstream an equivalent barotropic response occurs with positive negative amplitude increasing with height eddy feedbacks have weak impact on the baroclinic part but the equivalent barotropic response is strongly enhanced if the bandpass filtered streamfunction tendency is in phase with the linear geopotential height response this is the case in an experiment with a warm anomaly near 408n located southwesterly of the idealized storm track in the corresponding experiment with a cold anomaly the two patterns are out of phase and the equivalent barotropic response is slightly reduced it is weakened strengthened if a warm cold anomaly is shifted about 108 poleward or equatorward relative to the idealized storm track midlatitude heat sources generate wave trains that extend equatorward and poleward developing large scale correlations between the flow at remote locations teleconnections the space time variability can be changed considerably by eddy feedbacks developing stronger variance for large scale retrogressive traveling and standing waves partially blocking like events develop

multi decadal record of ice dynamics on daugaard jensen gletscher east greenland from satellite imagery and terrestrial measurements this is the publisher s version also available electronically from http www ingentaconnect com

lithospheric thermal structure in the baltic shield summary steady state heat conduction modelling was carried out to calculate the crustal temperature field and thermal lithosphere thickness in the baltic shield the radiogenic sources at the surface were fixed depending on the age of the crust below the uppermost 10 kilometres a relationship between heat generation and p wave velocity was applied and seismic structure was used to define individual crustal blocks of specific thermal parameters small scale surface heat flow density anomalies are interpreted as lateral variations of heat generation within the upper part of the crust whereas the large anomaly in the southern part of the shield is attributed to an anomalously high mantle heat flow density the results are shown on maps outlining mantle heat flow density moho temperature and thermal lithosphere thickness a relationship between subcrustal temperature and moho depth was found except for southern sweden the lithospheric thickness is found to exceed 200 km in the bothnian gulf northern central finland and part of the kola peninsula where temperatures at the moho are less than 500 c the temperature gradient at the top of the mantle has on the average a value of 7 5 mk m and the mantle heat flow density varies from 19 to 25mwm 2 towards the south the lithospheric thickness decreases until it attains a value lower than 100km under southern sweden in this latter area the moho temperature and mantle heat flow density are remarkably high 700 900 c and 30 45 mw m 2 respectively as well as the temperature gradient which amounts to 10 mk m

the dynamical basis of regional vertical motion fields surrounding localized tropical heating abstract a series of real data integrations of the national center for atmospheric research community climate model with tropical heat anomalies display regions of pronounced subsidence and drying surrounding the anomaly the present emphasis is upon subsidence and drying centers located several thousand kilometers westward and poleward of the heating these features are repeatedly found in several different series of medium to extended range forecast experiments including cases of tropical atlantic heating and tropical east pacific heating this highly predictable sinking response is established within the first five days of these integrations the normal modes of a set of primitive equations linearized about a resting basic state are used to partition model response into gravity inertia and rossby modes the results show that most of the vertical motion response can be explained by gravity mode contributions the sensitivity of the response is examined through a series of numerical experiments with a s

a general circulation model study of the atmospheric response to extratropical sst anomalies observed in 1950 79 abstract a 30 year experiment with an atmospheric general simulation model has been performed the lower boundary condition at all oceanic grid points between 38 s and 60 n has been prescribed to follow the observed month to month variation of the sea surface temperature sst field during the 1950 79 period much of the model diagnosis presented here pertains to the midlatitude atmospheric response to recurrent sst patterns in the north pacific and north atlantic in winter the principal modes of variability of the seasonally averaged 515 mb height and sst fields have been identified using rotated principal component rpc analysis the extrema of the first atmospheric mode reside over the north atlantic and eurasia whereas the second mode is associated with height anomalies in the north pacific north american sector cross correlation analysis reveals that these two atmospheric modes am linked to leading patterns of the sst field in the north atlantic and north pacific respectively it is also demonst

the atmospheric circulation and sea surface temperature in the north atlantic area in winter their interaction and relevance for iberian precipitation abstract the ocean surface atmosphere relationships in the north atlantic area in northern winter are empirically examined by canonical correlation analysis cca this analysis is performed from two different points of view first the connection between atmospheric circulation anomalies in terms of monthly mean sea level pressure slp and monthly standard deviation of slp slp and sea surface temperature sst anomalies of the atlantic ocean are directly examined second the air sea relationships are indirectly studied through their influence upon precipitation in an area likely to be influenced by the north atlantic the iberian peninsula the canonical correlation analysis yields two pairs of patterns that describe the coherent variations of the combined sst slp fields one pair of patterns for the sst slp fields and one pair of patterns for the slp slp fields all patterns are dominant in describing variance a lag cross correlation analysis of the time coefficients indicates that monthly mea

the differences between early and midwinter atmospheric responses to sea surface temperature anomalies in the northwest atlantic abstract using an atmospheric global spectral model it is shown that the winter atmosphere in the midlatitudes is capable of reacting to prescribed sea surface temperature sst anomalies in the northwest atlantic with two very different responses the nature of the response is determined by the climatological conditions of the winter regime experiments are performed using either the perpetual november or january conditions with or without the prescribed sst anomalies warm sst anomalies in november result in a highly significant anomalous ridge downstream over the atlantic with a nearly equivalent barotropic structure in january the response is a statistically less significant trough the presence of the sst anomalies also causes a northward southward shift of the atlantic storm track in the november january cases a diagnostic analysis of the anomalous heat advection in the simulations reveals that in the january cases the surface heating is offset primarily by the strong horizontal cold advect

sensitivity of the systematic error of extended range forecasts to sea surface temperature anomalies abstract the sensitivity of the systematic error of extended range forecasts to sea surface temperature sst anomalies is investigated general circulation model gcm experiments were performed to quantify error patterns for warm normal and cold sst anomalies in the equatorial central pacific the model underestimates the strength of tropical convection during warm el nino southern oscillation enso episodes and has large zonal mean errors in midlatitudes the model captures the negative pacific north american teleconnection pna pattern during the cold enso episodes but the simulated amplitude is too weak the time mean errors during warm and cold enso events bear little resemblance to the errors estimated from a 10 yr integration which includes both warm and cold episodes the time mean error of a 10 yr integration is a good estimate of the systematic model error only for those years when ssts are close to climatology

the ice cover in the greenland and norwegian seas the seasonal sea ice cover of the northern north atlantic is reviewed comprising the ice of the east greenland current the ice cover around svalbard and the ice of the barents sea as far east as franz josef land the review considers various types of ice cover 1 the fast ice along the coasts and in fjords including sikussak or very old fast ice of exceptional thickness 2 the transition zone between the fast ice and the main pack including the positions and causes of recurring winter polynyas and the nature of the shear zone in ne greenland 3 the constitution dynamics and seasonal extent of the drifting pack ice including interannual variations 4 the processes of air ice ocean interaction which occur in the marginal ice zone where the pack ice is influenced by an open ocean boundary

model experiments on the impact of pacific sea surface temperature anomalies on blocking frequency abstract sensitivity experiments with a perpetual january version of a low resolution general circulation model are conducted to investigate the influence of pacific sea surface temperature sst anomalies on blocking in the northern hemisphere six 1200 day integrations each of which contains a different specified sst anomaly superimposed upon a fixed climatological sst distribution are compared with a 1200 day control simulation to examine the impact of both equatorial pacific and midlatitude north pacific anomalous forcing an ensemble of eight independent 90 day realizations is extracted from each simulation distributions of the ensemble mean differences in the total number of blocking days from the control simulation are presented along with estimates of the statistic significance of these differences pacific sst anomalies do not strongly affect the total number of days in which a block is present anywhere over the north pacific basin but they apparently can affect the preferred regions over th

the relationship between sea surface temperature anomalies and atmospheric circulation in gcm experiments several 19 year integrations of the hamburg version of the ecmwf t21 general circulation model driven by the monthly mean sea surface temperature sst observed in 1970 1988 were examined to study extratropical response of the atmospheric circulation to sst anomalies in the northern hemisphere in winter in the first 19 years run sst anomalies were prescribed globally gago run and in two others sst monthly variability was limited to extratropical regions moga run and to tropics toga run respectively a canonical correlation analysis cca which select from two time dependent fields optimally correlated pairs of patterns was applied to monthly anomalies of sst in the north alantic and pacific oceans and monthly anomalies of sea level pressure and 500 hpa geopotential height in the northern hemisphere in the gago run the best correlated atmospheric pattern is global and is characterized by north south dipole structures of the same polarity in the north atlantic and the north pacific sectors in the moga and toga experiments the atmospehric response is more local than in the gago run with main centers in the north atlantic and north pacific respectively the extratropical response in the gago run is not equal to the sum of the responses in the moga and toga runs the artificial meridional sst gradients at 25 30 n probably influence the results of the moga and toga runs the atmopsheric modes found by the cca were compared with the normal modes of the barotropic vorticity equation linearized about the 500 hpa winter climate the normal modes with smallest eigenvalues are similar to the model leading variability modes and canonical patterns of 500 hpa geopotential height the corresponding eigenvectors of the adjoint operator which represent an external forcing optimal for exciting normal modes have a longitudinal structure with maxima in regions characterized by enhanced high frequency baroclinic activity over both oceans

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

the timing of initiation of fast flowing ice streams during a glacial cycle inferred from glacimarine sedimentation fast flowing ice streams drain huge basins within modern ice sheets and are a mechanism for rapid iceberg production and mass loss some ice streams are known to be unstable and to switch between fast flow and stagnation numerical ice sheet models and geophysical observations of large scale streamlined glacial landforms and large glacier derived sedimentary fans along high latitude continental margins indicate the presence of ice streams in quaternary ice sheets high resolution ams dated sedimentary records from an inter fan area on the svalbard continental margin yield evidence on the timing of initiation of fast glacier flow during a glacial cycle of ice sheet growth and decay sedimentation rates and iceberg rafted debris influx show that debris delivery to the svalbard margin was relatively high during the period of late weichselian ice sheet growth from about 30 000 18 000 yr bp both parameters fell dramatically in inter fan areas when full glacial conditions with ice at the continental shelf edge were established at about 18 000 yr bp this shift is interpreted to mark the initiation of a fast flowing ice stream the convergence of flow from the surrounding ice sheet into this ice stream and the consequent slowing of ice flow and sediment delivery to the inter fan area beyond the ice stream margins this provides a constraint on the timing of icestream initiation during the cycle of ice sheet growth and decay 4 2002 elsevier science b v all rights reserved

iceberg scouring in scoresby sund and on the east greenland continental shelf modern and relict scours produced by iceberg keels have been reported from a number of high latitude continental shelves in the northern hemisphere and antarctica but observations are largely absent from the east greenland shelf about 18 km3 yr 1 of icebergs are calved into the scoresby sund fjord system east greenland these icebergs have submarine keels with drafts up to 550 m modern iceberg contacts with the sea floor are inferred from calculated keel depths and stationary icebergs identified on sequential landsat imagery acoustic profiles parasound 3 5 khz of the sea floor show that scouring is a significant process in water depths 550 m iceberg scouring intensity varies inversely with water depth the most intense scouring occurs at depths of 300 400 m iceberg scours were observed on over 25 000 km2 of the east greenland shelf at 69 72 n and 75 n scours are being actively produced on the modern shelf but relict scours probably dating back to the late weichselian are also present the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg scouring is important over a significant proportion of the 500 000 km2 area above the shelf break around greenland

sea floor scour at the mouth of hudson strait by deep keeled icebergs from the laurentide ice sheet physical evidence on the dimensions of icebergs released from the mouth of hudson strait into the northwest atlantic during the last heinrich event h 0 is presented side scan sonar imagery shows scour marks up to 700 m wide and longer than 28 km these scour marks were carved by gigantic icebergs megabergs with keel drafts possibly as great as 660 m capable of scouring trenches 20 to 25 m deep into the seabed these icebergs were likely calved from the grounding margin of a thick possibly as thick as 640 m rapidly flowing glacial margin during the h 0 heinrich event 11 ka bp along with the relatively few megabergs released were large numbers of smaller icebergs that calved from the ice margin at the same time and were also produced from break up of the megabergs scouring of the seabed by the large and smaller icebergs happened at the same time with megabergs scouring only in the deep waters of hatton basin and the smaller bergs scouring only on the eastern shallow margin of the basin at the continental shelf break

dynamical nonlinearity in the atmospheric response to atlantic sea surface temperature anomalies 1 large ensembles 100 members of atmospheric general circulation model experiments are forced throughout the northern hemisphere cold season by four different sea surface temperature sst fields the observed climatology the so called sst tripole pattern and its tropical and its extratropical subcomponents late winter responses to these anomalies are of modest amplitude in comparison with the amplitudes of climatological stationary waves but are because of the large ensemble significant despite their modest amplitudes the responses display additive nonlinearity in that the sum of the separate responses to the component anomalies differs significantly from the response to the tripole neither the heating field nor the basin averaged zonal winds display this nonlinearity it is most evident in a sub basin scale wave train and most significant in its impact on the amplitude of the geopotential response these results indicate that even for modest forcing responses to patterns of sst anomalies cannot necessarily be understood as the sums of responses to constituent anomalies

geographical distribution and volume of antarctic icebergs derived from ship observation data information on the occurrence spatial distribution and morphometric characteristics of antarctic icebergs is needed in a large number of applications including navigation heat and freshwater balance calculations biochemistry of the ocean and climatology using over 60 000 ship observations of icebergs in the southern ocean collected since the end of the 1940s we have produced a detailed map of the distribution of antarctic icebergs as well as maps of related statistics including the standard deviation minimum and maximum values of the iceberg concentration and the probability of iceberg free observations the study incorporated small and medium sized icebergs with a length of 2 and 16 893 km 3 with uncertainties of 32 33

iceberg production debris rafting and the extent and thickness of heinrich layers h 1 h 2 in north atlantic sediments the pattern of heinrich layer distribution for the last two events h 1 14 5 and h 2 21 1 ka mapped from magnetic susceptibility analysis of more than 50 north atlantic ocean cores provides the most detailed information to date on their extent and thickness an integrated spatial average thickness for the layers is 10 15 cm and there is a strong distance decay eastward the pattern of deposition over the north atlantic is similar for events h 1 and h 2 indicating that icebergs followed similar drift tracks rates of iceberg production and sediment flux from the hudson strait drainage basin of the north american laurentide ice sheet the major iceberg source for the events were calculated by using a mass balance approach this provides an envelope of sedimentation rates and the prediction that it would take between 50 and 1250 yr of iceberg sediment delivery to accumulate a heinrich layer averaging 10 cm thick over the north atlantic depending on the model assumptions used the most likely duration of heinrich events is 250 1250 yr

linkage between the pacific decadal oscillation and the low frequency variability of the pacific subtropical cell the decadal variability of pacific subtropical cell stc and its linkages with the pacific decadal oscillation pdo are investigated in the present study based on a simple ocean data assimilation soda 2 2 4 it is found that on decadal time scales the western boundary and interior pycnocline transports are anticorrelated and the variation of the interior component is more significant which is consistent with previous studies the decadal variability of stc in the northern hemisphere is found to be strongly associated with pdo associated with a positive negative phase of pdo the relaxation acceleration of the northeast trades slows down spins up the stc within a few years through baroclinic adjustment in conjunction with the subduction of the cold warm mixed layer anomalies in the extratropics the cold warm water is then injected into the thermocline and advected further southwestward to the tropics along the isopycnal surfaces leading to the slowdown spin up of stc due to zonal pressure gradient change at low latitude along with the stc weakening strengthening a significant warming cold anomaly appears in the tropics and it is advected to the midlatitude by the kuroshio and north pacific currents thus feeding back to the atmosphere over the north pacific in contrast to the northern hemisphere it is found the stc in the south only passively responds to the pdo the mechanism found here highlights the role of the stc advection of extratropical anomalies to the tropics and horizontal gyre advection of the tropical anomalies to the extratropics in decadal variability of the stc and pdo

impact of localized tropical and extratropical sst anomalies in ensembles of seasonal gcm integrations a series of 120 day ensemble integrations of a general circulation model designed to assess the impact of geographically localized sea surface temperature sst anomalies in both the tropics and extratropics are described these experiments contribute firstly to an appraisal of the relative roles of tropical and extratropical sst anomalies on interannual variability of the large scale circulation in the northern extratropics and secondly to an assessment of the role of quasi stationary diabatic heating anomalies on model systematic error including blocking activity overall it is found that sst anomalies associated with el nino and la nina have a larger and more reproducible impact on the extratropics than the chosen extratropical sst anomalies these extratropical anomalies were localized to the north west pacific and north west atlantic with realistic amplitude however unlike earlier studies a response to the extratropical north pacific sst anomalies has been obtained over the north pacific which is correlated with the sign of the imposed sst anomaly the response to extratropical sst anomalies in the north west atlantic are similar to the results obtained from an earlier study the downstream responses to the extratropical pacific and atlantic sst anomalies are qualitatively similar to one another overall it is concluded that the northern large scale flow is influenced by such extratropical sst anomalies the response to idealized tropical sst anomalies was also studied in particular a localized anomaly over indonesia had a very substantial impact on the hadley circulation on zonal flow and on blocking frequency over the north pacific and europe this response was such as to reduce model systematic error locally in the vicinity of the sst anomaly remotely around the tropics and remotely in the extratropics a similar though weaker impact on euro atlantic blocking was obtained with an idealized caribbean sst anomaly further statistical and dynamical analyses suggested that the extratropical response to the indonesian sst anomaly occurs through the creation of two distinct planetary scale regimes in one of which the formation of blocks is much favoured by increased ridges on the north eastern side of the oceans

holocene glacimarine sedimentation inner scoresby sund east greenland the influence of fast flowing ice sheet outlet glaciers abstract holocene glacimarine sedimentation associated with fast flowing outlet glaciers draining the greenland ice sheet is investigated using sedimentary and acoustic data from inner scoresby sund east greenland sedimentation in inner scoresby sund is dominated by three processes which are influenced by differences in proximity to fast flowing outlet glaciers extent of glacier ice cover and fjord bathymetry 1 sediment gravity flow principally in the form of turbidity currents and debris flows 2 suspension sedimentation from turbid meltwater plumes and 3 iceberg rafting these processes result in texturally and sedimentologically heterogeneous lithofacies proportionally fine grained muds laminated stratified and massive facies dominate cores recovered from inner scoresby sund accounting for 80 of the total whereas diamict facies account for only 15 abundant fine grained muds demonstrate that meltwater flux and sedimentation is significant in this high arctic glacimarine environment in settings proximal to fast flowing outlet glaciers with increasing distance from these glacier termini muds are replaced progressively by iceberg rafted coarse grained sediment the dominance of this iceberg rafted sediment in outer scoresby sund reflects both its more distal location from fast flowing glacier termini and the high calving flux associated with these ice masses laminated muds deposited by turbidity currents and suspension settling from overflow plumes in inner scoresby sund are similar to lithofacies produced in temperate and subpolar glacimarine systems this implies a similarity in sedimentation processes and resulting facies across a wide spectrum of climatically glaciologically fast flowing and non fast flowing ice masses and oceanographically variable glacimarine settings recognition of laminated fine grained facies in the geological record therefore does not necessarily indicate a temperate palaeo glacial setting however the predominance of iceberg rafted diamict facies in ice distal sedimentary records suggests the former presence of relatively cold environmental conditions in which iceberg sedimentation played a dominant role

modeling iceberg rafted sedimentation in high latitude fjord environments 1 an iceberg model sedberg has been developed to simulate sedimentation in high latitude glaciated fjords sediments deposited in fjords provide an important record of glaciological response to changing climatic conditions the model simulates the formation drift and melt of a population of icebergs utilizing monte carlo based techniques with a number of underlying parametric probability distributions to describe the stochastic behavior of iceberg formation and dynamics the model captures iceberg dynamics and melt in fjord environments and has been applied to kangerdlugssuaq fjord in east greenland as an example of an iceberg dominated sedimentary environment sedimentation has been simulated over the past 1500 years encompassing the climatic intervals of the medieval warm period mwp and the little ice age lia model results have been compared with the observed sedimentary record the model demonstrates that the glaciological regime e g basal debris thickness mean annual calving rate mean iceberg size plays a more important role than the direct influence of climate ocean and air temperatures on iceberg sedimentation rate although often changes in climate result in changes to the glaciological regime

3d seismic evidence of buried iceberg ploughmarks from the mid norwegian continental margin reveals largely persistent north atlantic current through the quaternary over 7500 buried linear and curvilinear depressions interpreted as iceberg ploughmarks were identified within the quaternary naust formation from an extensive three dimensional seismic dataset that covers 40 000 km2 of the mid norwegian continental margin the morphology and net orientation of ploughmarks were mapped and analysed these features are up to 28 km long 700 m wide and are incised up to 31 m deep on average ploughmarks are incised 5 m deep with median width of 185 m and median lengths ranging from 1 2 to 2 7 km for individual palaeo surfaces width to depth ratio ranges from 8 1 to 400 1 and is on average 36 1 the presence of ploughmarks buried deeply within some palaeo slope surfaces implies the occasional presence of very large icebergs since the middle quaternary suggesting that thick ice sheet margins with fast flowing ice streams were present in order to calve icebergs of such dimensions into the norwegian sea the wide geographical distribution of ploughmarks suggests unrestricted iceberg drift and an open norwegian sea during the periods of iceberg calving since the early quaternary ploughmark trajectory analysis demonstrates that the ocean current circulation now dominated by the northeasterly flowing norwegian atlantic current nwac has largely persisted throughout the quaternary despite the overall strikingly consistent pattern of iceberg drift ploughmark mapping also shows evidence for short lived nwac reductions possibly related to major phases of iceberg discharge and or meltwater pulses from the fennoscandian ice sheet during the middle and late quaternary

dynamics of the extratropical response to a tropical atlantic sst anomaly abstract previous atmospheric general circulation model agcm experiments revealed that atmospheric responses to a tropical atlantic sea surface temperature anomaly ssta were asymmetric with respect to the sign of the ssta a positive ssta produced a south north dipole in geopotential heights much like the north atlantic oscillation nao while a negative ssta yielded an eastward propagating wave train with the northern lobe of the nao absent here these height responses are decomposed into components that are symmetric or antisymmetric with respect to the sign of the ssta the symmetric or notionally linear component is a nearly south north dipole projecting on the nao while the antisymmetric or notionally nonlinear component is a different dipole experiments with a diagnostic linear baroclinic model lbm suggest that both components are maintained primarily by transient eddy forcing dynamical mechanisms for the formation of the two components are explored using the lbm and a nonlinear baro

midlatitude atmosphere ocean interaction during el nino part ii the northern hemisphere atmosphere abstract the influence of midlatitude air sea interaction on the atmospheric anomalies associated with el nino is investigated by coupling the community climate model to a mixed layer ocean model in the north pacific prescribed el nino conditions warm sea surface temperatures sst in the tropical pacific cause a southward displacement and strengthening of the aleutian low this results in enhanced reduced advection of cold asian air over the west central northwest pacific and northward advetion of warm air over the eastern pacific allowing air sea feedback in the north pacific slightly modified the el nino induced neu surface wind air temperature and precipitation anomalies the anomalous cyclonic circulation over the north pacific is more concentric and shifted slightly to the east in the coupled simulations air sea feedback also damped the air temperature anomalies over most of the north pacific and reduced the precipitation rate above the cold sst anomaly that develops in the central pacifi

linear and nonlinear winter atmospheric responses to extreme phases of low frequency pacific sea surface temperature variability this study examines northern hemisphere winter djfm atmospheric responses to opposite strong phases of interdecadal low frequency lf pacific sea surface temperature sst forcing which resembles el nino southern oscillation enso on a longer time scale in observations and gfdl and cam4 model simulations over the pacific north america pna sector linear observed responses of 500 hpa height z500 anomalies resemble the pna teleconnection pattern but show a pna like nonlinear response because of a westward z500 shift in the negative lf relative to the positive lf lf phase significant extratropical linear responses include a north atlantic oscillation nao like z500 anomaly a dipole like z500 anomaly over northern eurasia associated with warming over mid high latitude eurasia and a southern annular anomaly pattern associated with warming in southern land areas significant nonlinear z500 responses also include a nao like anomaly pattern models forced by lf and lf sst anomalies reproduce many aspects of observed linear and nonlinear responses over the pacific north america sector and linear responses over southern land but not in the north atlantic european sector and eurasia both models simulate pna like linear responses in the north pacific north america region similar to observed but show larger pna like lf responses resulting in a pna nonlinear response the nonlinear pna responses result from both nonlinear western tropical pacific rainfall changes and extratropical transient eddy feedbacks with lf tropical pacific forcing only lftp and lftp climatological sst elsewhere cam4 simulates a significant nao response to lftp including a linear negative and nonlinear positive nao response

a theory of interdecadal climate variability of the north pacific ocean atmosphere system abstract a linear coupled model for the atmosphere upper ocean system is proposed to highlight the mechanisms of decadal to interdecadal climate variability in the north pacific in this model wind stress anomalies over the north pacific are related to anomalies in the meridional temperature gradient of the upper ocean the latter depends upon air sea thermodynamical feedbacks and meridional heat transport by upper ocean currents slow adjustment of the oceanic gyre circulation to the change in wind stress is accomplished by the forced baroclinic oceanic rossby waves which carry out the meridional heat transport uncoupled ocean dynamic adjustment can produce a weak decadal to interdecadal peak in the power spectrum of the meridional transport under temporal white noise wind stress forcing with organized spatial structure coupled dynamics produce a basin scale interdecadal oscillatory mode this mode arises from the dynamic coupling and the memory of the system residing in the slow gyre circulation ad

geothermal flow and phenomena in two swedish localities north of the arctic circle summary temperature measurements in eight holes reaching vertical depths between 287 and 1100m below ground surface in the malmberget area lat 67 10 n long 20 40 e gr and the kiruna area lat 67 52 n long 20 9 e gr in the swedish precambrian are reported the mean equilibrium heat flow in this part of the swedish shield after climatic correction is 52 6 1 7mwm 2 the mean uncorrected heat flow is 46 6 mwm 2 comparison with other shield areas shows that in common with the s african and indian shields the north swedish shield has a greater heat flow than the remaining shield areas of the world

laminated sediments in glacimarine environments diagnostic criteria for their interpretation abstract fine grained laminated deposits are often reported from contemporary and ancient glacimarine sedimentary sequences laminated glacimarine sediments form by a variety of processes including suspension settling from turbid overflow plumes turbidity current deposition and contour current activity subglacial deformation of pre existing sediments may also produce laminated deposits in the form of glacitectonite and deformation till the development of diagnostic criteria for genetic discrimination of laminated glacimarine sediments is important both for their correct interpretation in sedimentary sequences and also for the accurate reconstruction of former glacier extent and geometry as laminated sediments may form in subglacial ice proximal and ice distal environments this paper reviews the processes by which laminated glacimarine sediments form and their resulting sedimentology the aim is to provide a synthesis of diagnostic sedimentological criteria for laminated glacimarine deposits that will assist in the interpretation of such sediments in the geological record laminated sediments are genetically differentiated on the basis of sedimentary structures bedding contacts stratigraphic relationships and macrofaunal content bioturbation these attributes also facilitate discrimination between glacimarine and glacilacustrine rhythmites the paper concludes by discussing the glaciological significance of laminated glacimarine sediments in terms of glacier hydrology reconstructions of former ice dynamics and basal thermal regime