the process of formation of ocean crust ocean crust is the outermost layer of earth under the oceans it is separated from the underlying mantle by a seismic transition zone called the moho a widely held view is that the moho represents a petrologic change from basaltic type rocks to a mantle composed mostly of olivine and pyroxene according to this view crust is formed by a steady segregation of basaltic melt derived from partial melting of the mantle into a crustal magma chamber wherein cooling and crystallization bring about steady state accretion to the continuously spreading plates there is sufficient disagreement between the predictions of this hypothesis and marine geophysical data to cause one to doubt the validity of this formation process at least two other processes are more compatible with the geophysical data in one the crust is formed from the episodic injection of basaltic dikes from a mantle reservoir and the moho is a primary petrologic boundary in the other the crust is treated as a mechanical boundary layer in which thermal contraction results in cracking by comparison in the mantle thermal contraction is accommodated by flow the upper part of the crust is formed from episodic extrusion and intrusion of basaltic melt the lower crust is formed by rapid hydrothermal alteration of mantle that may be continuously or episodically injected by viscous flow at temperatures below the melting temperature

linear prediction of sea ice anomalies stationary and cyclostationary statistical models are developed to predict arctic and antarctic sea ice anomalies using as predictors previous sea ice atmospheric and oceanic anomalies a prediction model hierarchy is developed by using first internal i e sea ice predictors including persistence lateral advection and diffusion and a cyclostationary model that allows the prediction coefficients to vary seasonally an external cyclostationary model hierarchy is developed next to investigate the ability of atmospheric winds heat flux proxies air temperatures and sea surface temperatures sst s to predict sea ice extent in the arctic the highest skill was generally achieved by the cyclostationary internal model attempts to forecast the ice data at 1 2 month intervals after removal of its autoregressive component using external predictors gave nonsignificant models at longer lead times e g 3 months the sst in the north pacific was superior to persistence for sea ice prediction in the western bering sea in the southern ocean especially off east antarctica the model that included lateral advection and diffusion outperformed both persistence and the cyclostationary internal model in the weddel sea and the ross sea persistence proved to be the best sea ice predictor no external models were tested for antarctic sea ice because of insufficient data

ocean circulation its effects on seasonal sea ice simulations a diagnostic ice ocean model of the arctic greenland and norwegian seas is constructed and used to examine the role of ocean circulation in seasonal sea ice simulations the model includes lateral ice motion and three dimensional ocean circulation the ocean portion of the model is weakly forced by observed temperature and salinity data simulation results show that including modeled ocean circulation in seasonal sea ice simulations substantially improves the predicted ice drift and ice margin location simulations that do not include lateral ocean movment predict a much less realistic ice edge

oceanic crustal thickness versus spreading rate a compilation of oceanic crustal thickness from seismic observations collected over the past two decades shows that the average crustal thickness away from plateaus is 6 km no systematic increase of crustal thickness with spreading rate is observed instead the data show large variations in crustal thickness at slow spreading ridges 3 8 km for half rates 30 mm yr the large variations at slow ridges and small variations at fast ridges are consistent with the results inferred from recent gravity studies of mid ocean ridges both data sets support the speculation of a transition from a 3 d structure of crustal accretion at slow ridges to a 2 d accretion pattern at fast ridges

past and recent tritium levels in arctic and antarctic polar caps tritium concentration was measured in snow deposited at the grip site central greenland and at the vostok station east antarctica from snow pits covering the period 1980 1990 the objective of the study was to investigate tritium concentrations in polar regions several decades after the bomb peak of the sixties and to put them in the context of available data for environmental tritium in the arctic and the antarctic over the last five decades the tritium content of the samples was measured by mass spectrometry using the helium 3 regrowth method in antarctica the tritium concentrations are in the range 70 110 tu the comparison of the bomb tritium history at different locations show that tritium levels increase moving inland where vapour pressure becomes extremely low and therefore more sensitive to the intrusion of stratospheric air masses highly enriched in tritium although most tritium fallout occurred in the northern hemisphere the tritium levels in central greenland in the 80 s in the range 10 40 tu are significantly lower than at vostok unlike antarctica no such continental effect is observed in greenland due to the higher water vapour content of the air masses as evidenced by the much higher snow accumulation rate whereas tritium fallout in antarctica appears to occur as a result of direct injections of stratospheric tritium during winter arctic fallout are the result of the dominant spring injection of stratospheric air at mid latitude in line with the deposition of other stratospheric tracers

crustal processes at spreading centers recent discoveries and research on mid ocean ridges mor s in the last four years have greatly increased our knowledge of this fundamental type of plate boundary the last iugg review of mor research was in 1975 aumento et al 1975 and its omission as a topic in 1978 may have reflected a feeling that spreading centers were reasonably well understood since that time however there has been a surfeit of important new observations and exciting research and there is now a turmoil of innovative ideas about the processes which create and leave their imprint on two thirds of the earth s crust new seismic measurements have been made and interpreted as evidence for the existence of shallow axial magma chambers amc beneath intermediate total opening rate 5 9 cm yr and fast 9 18 cm yr spreading centers fig 1 yet there is controversy as to whether they are steady state whether they persist beneath slow ridges as well in the steady state what the dimensions and shape of the chamber are its relation to oceanic crustal stratigraphy and its relation to observations in ophiolites black smoker hydrothermal vents have been discovered in the pacific spewing forth 350 c fluids blackened by polymetallic sulfide precipitates this discovery is embroiled in debate as to how long the vents last whether they occur at slow spreading rates as well whether the enormous heat flux of the vents freeze the magma chamber even at fast spreading rates their influence on geochemical balances in the ocean and the value of the sulfide deposits commercially it has been found that our initial view of mor s as two dimensional linear structures has served us well as an initial working model but must be significantly modified to account for variations in tectonic volcanic and hydrothermal activity along strike as well as for episodicity of these processes deep sea drilling project dsdp samples have raised fundamental questions about formation of the magnetic source layer hydrothermal circulation and fault mechanisms along the mor spreading centers which penetrate existing lithosphere along strike as propagating rifts have modified our views of how plate boundaries reorient themselves and how v shaped magnetic and topographic trends are formed we have also found that transform faults may modify spreading center processes for some distance away from their intersections with mor s and that rigid plate transform faults may fail to develop at fast spreading centers under certain conditions resulting in en echelon overlapping of spreading centers this review will focus on these developments and several others only example references to these topics will be given in the text and many important topics will not be discussed directly e g petrology and geochemistry mantle convection research on lithosphere older than 1 m y however i have tried to compile and have included an extensive bibliography for u s research on a broader range of mor topics for mid 1978 to mid 1982 which is the main purpose of this report pre 1978 references are occasionally included where appropriate abstracts are not included

snow accumulation rates in northern victoria land antarctica by firn core analysis a multiparametric chemical isotopic and physical study on three shallow firn cores sampled in northernvictoria land was carried out to obtain glaciological information and climatic data in this antarctic region sampling areas were accurately prospected to identify sites located at different altitudes and distances from the sea where the snow accumulation was not influenced by katabatic wind redistribution or summer melting stratigraphic isotopic 18 o and chemical h 2 o 2 msa and nssso 4 2 profiles were mutually examined for dating purposes and to determine the mean snow accumulation rates at three different stations annual accumulation rates of 85 420 kg m 2 a 1 were determined in the period 1971 92 an inverse pattern between accumulation rate and altitude was shown by the progression of the mean annual rates of 160 203 and 260 kg m 2 a 1 respectively in the highest medium and lowest stations the mean accumulation value of all northern victoria land data available 170 kg m 2 a 1 represents a decrease of up to 35 with respect to the estimated value most widely used until now our accumulation value is very close to that required for a zero net surface mass balance according to ice discharge a linear relationship with a gradient of 0 81 c has been found between mean 18 o values and mean annual surface temperature for different ice cores drilled in northern victoria land

dynamic and thermodynamic characteristics of atmospheric response to anomalous sea ice extent in the sea of okhotsk abstract influence of sea ice extent anomalies within the sea of okhotsk on the large scale atmospheric circulation is investigated through an analysis of the dynamic and thermodynamic characteristics of the response in an atmospheric general circulation model to specified anomalous sea ice cover significant response appears not only around the sea of okhotsk but also downstream over the bering sea alaska and north america in the form of a stationary wave train in the troposphere this remote response associated with wave activity flux emanating from the okhotsk area to the downstream is regarded as a stationary rossby wave generated thermally by the anomalous turbulent heat fluxes from the ocean surface as a result of the anomalous sea ice cover the pacific storm track in the model that extends zonally at 35 n is located too far south of the sea of okhotsk to exert substantial feedback forcing on the local and remote response since a similar stationary wave train is identified in the composite di

evolution of the ocean crust results from recent seismic experiments we present results from recent analyses of seismic refraction and sea floor microseismicity studies in the pacific and atlantic oceans which lend support to the hypothesis that processes responsible for the construction of ophiolite suites are similar to phenomena extant at midocean ridges seismicity at fast spreading ridges is characterized by very low magnitude 0 1 and shallow 2 3 km microearthquakes and long term oscillations or harmonic tremor a detailed seismic refraction experiment on a fast spreading portion of the east pacific rise supports the hypothesis of the existence of a crustal magma chamber analyses of these data indicate that the chamber is largely unperturbed by the presence of conjugate spreading centres and the inverted deltashaped zone of partial melt is characterized by a half width in excess of 6 km finally a new approach for obtaining upper crustal velocities when applied to data characterized by the presence of shear waves provides several counter examples to the hypothesis that the shallow crust evolves with time

sea ice motion measurements from seasat sar images satellite imaging radar is expected to become the prime instrument for mapping the distribution and motion of sea ice on a periodic basis the observational independence from weather fog and clouds and the fact that it provides its own illumination are decisive advantages that imaging radar has in the remote sensing of sea ice the seasat spacecraft launched in 1978 included such an imaging radar and approximately one fourth of all seasat sar observations are of sea ice in the beaufort sea data from seven sequential orbits of the satellite were selected to study the capabilities and limitations of spaceborne radar application to sea ice mapping the results are encouraging 1 there is no difficulty in identifying homologue ice features on sequential radar images 2 the accuracy is entirely controlled by accuracy of the orbit data and the geometric calibration of the sensor 3 conventional radargrammetric methods serve well for satellite radar ice mapping 4 ground control points can be used to calibrate the ice location and motion measurements in the cases where orbit data and sensor calibration are lacking ice motion was found to be approximately 6 4 0 5 km per day however higher accuracies are feasible with better timing calibration of the sensor events and knowledge of the orbit the accuracy of pixel location was also determined over land areas it was found that with the use of one control point in 10 000 km2 the accuracy is about 150 m with higher density of control points 7 in 1000km2 the location accuracy improves to the image resolution i e 25 m this is applicable for both optical and digital data

research on snow and ice this review unlike its predecessor martinelli et al 1979 is an intentionally selective survey of recent advances in selected areas of snow and ice research i have chosen to concentrate on studies relating to large scale aspects of the cryosphere and to consider their wider significance for other disciplines results obtained by new measurement techniques and the application of remote sensing methods are also stressed at the same time the broad lines of advance in glaciological research as represented in books conference themes and major field or laboratory programs are noted and a detailed bibliography is appended

structure of the earth oceanic crust and uppermost mantle the past four years have witnessed the introduction of a variety of new instruments and methods for the study of the seismic structure of the oceanic crust and lithosphere the application of these and existing tools has led to the discovery of a number of new phenomena and to a fuller understanding of the genesis and evolution of the oceanic ithosphere borehole seismic instrumentation has become more widely employed ocean bottom seismographs while generally decreasing in number have become significantly more reliable and useful and multichannel seismic systems have been employed in innovative experiments ranging from studies of fracture zones to the regular detection of magma chambers beneath rise axes the techniques available for the analysis of seismic data have become more sophisticated waveforms collected in seismic experiments can now be used directly in constructing and evaluating seismic velocity models and travel time data are regularly inverted directly for structure trial and error modeling has become increasingly unimportant marine seismologists are becoming increasingly involved in understanding the coupling between the ocean and the underlying oceanic lithosphere this has led to a more complete understanding of seafloor noise processes and the partitioning of energy between acoustic and elastic waves

a convective model for the weddell polynya abstract mechanisms are considered which may induct the large over 105 km2 area of open water or polynya which frequently occurs within the weddell sea winter sea ice we propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water the latter by salt rejection during ice formation in a preconditioned area static instability with intense vertical mixing can occur the upwelled warm salty deep water can then supply enough heat to melt the ice or prohibit its formation even in the middle of winter a simple two level model is derived to test this theory and is found to agree well with observations the process is found to be irregular due to different times of ice onset from one year to the next and to a lesser extent from variations in surface heating and cooling further it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year the system will either gain or lose salt yearly an

recent increase in south pole snow accumulation this paper summarizes the 37 year history of net accumulation measurements at the geographic south pole obtained by numerous investigators using a variety of techniques these data lead to the conclusion that annual net snow accumulation has increased in the vicinity of south pole station sps since 1955 the records were examined for evidence of a station effect and it is concluded that not all of the observed increase can be attributed to snow drift associated with the presence of the station furthermore the accumulation increase at the south pole appears consistent with increases observed at other locations on the east antarctic plateau and in the peninsula region as well these data suggest that the recent accumulation increase at sps may be regionally extensive over the east antarctic plateau

monthly and seasonal variability in the ocean ice atmosphere systems of the north pacific and the north atlantic four regional indices of sea ice variability and thirty years of monthly sea surface temperature sst and sea level pressure slp data are used to evaluate the large scale interactions within the ocean ice atmosphere systems of the north pacific and the north atlantic a direct association between positive negative sst anomalies and light heavy ice in the bering sea is indicated the sst ice coupling in the northern alaskan waters is also statistically significant the sst anomalies in both the north pacific and the north atlantic appear as persistent responses to atmospheric forcing the slp distributions over both oceans correlate significantly with the arctic slp distribution although the midlatitude atmospheric circulation shows no systematic tendency to lead or lag the arctic circulation sea ice fluctuations correlate most highly with the atmospheric forcing over antecedent periods of approximately 9 months in the northern alaskan waters 3 4 months in the bering sea and 5 7 months in the east greenland sea the strength of the 9 month mean onshore air flow component describes over 70 of the northern alaskan ice variance

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

simulated low frequency modes of circulation in the arctic ocean the variability of the arctic circulation is investigated for a 43 year period 1951 1993 from a coupled ice ocean model empirical orthogonal function eof analysis shows that the variability of the sea surface height ssh and vertically integrated transport is organized so that in the leading mode the whole arctic operates as a single gyre the mode is associated with the arctic oscillation ao thompson and wallace 1998 and it explains over 70 of the variance in the vertically integrated transport and 25 of the ssh variability the physical interpretation of this mode is derived to arise from its close connection to the atlantic inflow to the arctic the mode shows a major shift toward cyclonic circulation in the end of the 1980s which is associated with a large multiyear pulse of atlantic water to the arctic thus this event appears as the likely initiation of the atlantic layer warming observed during the recent years carmack et al 1995 overall the first mode shows strong decadal variability as reported by proshutinsky and johnson 1997 the second mode of the oceanic circulation which explains 9 of the variance in the transport contains two gyres with opposing cyclonicity in the eurasia and canada basins it projects onto the north atlantic oscillation nao pattern and displays a 14 year cycle which is known to exist in the midlatitude north atlantic surface temperatures deser and blackmon 1993 a further examination reveals that this mode describes the variability of the flow through the barents sea which is modulated by the water mass modification due to the local heat flux variability the apparent nao connection is provided by a simultaneous correlation between the time series of this second mode and the leading heat flux mode in the north atlantic which is associated with nao

on long term thickening of the oceanic crust a number of studies of seismic refraction data have resulted in suggestions that the oceanic crust thickens with age perhaps over a long time span it is difficult to reconcile notions of crustal thickening with many of our ideas about crustal structure and formation in this study we have re evaluated data compiled from a number of sources to obtain crustal thickness and age parameters for 105 different refraction profiles in the pacific an attempt was made to exclude data which might have poorly determined values of crustal thickness the crust does appear to thicken with age to 30 or 40 m y but the effect is very subtle once probable biases are removed from the data crustal thickening is not significant to a 95 confidence limit if ten m y samples are used however if one takes sample intervals of 0 30 m y and 30 100 m y there appears to be some difference in the average crustal thickness even in the latter case the amount of thickening is far less than previous studies have suggested only 45 km thus evidence for the long term addition of mass to the crust remains tenuous

the interpretation of the icelandic sea ice record the representativeness of the icelandic sea ice record one of the longest climate indicators for the north atlantic sector is assessed by statistical analysis correlation of the sea ice index with ice concentration data for the adjacent seas suggests that the index is a reasonable measure of the ice cover of a large area of the northern north atlantic sector associations with surface air temperature and sea level pressure are strong but regional rather than hemispheric in scale the immediate causes of the variable advance of ice onto the icelandic coasts are clear in the analysis of the atmospheric circulation data severe ice conditions are associated with enhanced anticyclonicity in the icelandic region and stronger northerly and westerly winds over the greenland sea it is concluded that the icelandic index is a useful indicator of the state of the atmospheric flow north of iceland and of the character of the east greenland current one of the major avenues of meridional heat exchange in the climate system

multichannel seismic evidence for variations in crustal thickness across the molokai fracture zone in the mid pacific coincident multichannel seismic reflection and refraction data from a n s transect near oahu hawaii provide evidence for thickening of the pacific crust by 1 2 1 km south of the large offset 16 m y molokai fracture zone fz tau p stacks tau sum inversions and forward modeling of the refraction data indicate that the crustal thickening occurs primarily within the lower portion of seismic layer 2 assuming isostatic balance the differences in crustal thickness predict that seafloor having the same age will have different elevations across the fz observations of sea floor depths across the fz east of the hawaiian islands are consistent with this prediction implying that the processes which have generated the crustal differences have been stable for over 50 m y previous correlations between the chemical composition of ridge crest basalts crustal thickness and ridge crest elevation have been attributed to variations in the thermal regime of the upper mantle under mid ocean spreading centers in accord with this hypothesis we propose that the observed differences in crustal structure across the molokai fz may have been produced by small 25 c differences in the thermal regime of the upper mantle beneath the ancestral east pacific rise discontinuous intracrustal reflections located about 1 6 s below the sediment basement interface are observed in migrated reflection data south of oahu these reflections are similar in character to the lower crustal horizon r event observed in the western north atlantic shallower intracrustal reflections possibly from within seismic layer 2 are also observed the observation of these intracrustal reflections in both the atlantic and pacific oceans suggests that they are a fundamental signature of the crustal accretion process at a variety of spreading rates and that they are mappable using modern seismic reflection refraction methods

multiyear sea ice variability in the eastern bering sea an update time series of sea surface temperature sst percent ice cover degree day and surface wind anomalies are updated from niebauer 1980 for the period 1974 1982 from the eastern bering sea these data are used to provide further documentation of the recent short term 1977 present climatic warming trend in the region of the eastern bering sea the data analysis indicates that the warming trend is statistically significant and that it ended in 1979 details of the anomalies in sst ice and surface and 700 mbar winds are updated for the individual winters of 1979 82 are compared and contrasted to the recent multiyear warming trend and are discussed in relation to longer term studies of air ice sea interactions in this region

a model of the atmospheric boundary layer over the marginal ice zone a one layer primitive equation model is presented for the atmospheric boundary layer over the marginal ice zone miz the model simulates the slow rate of inversion growth and rate of warming of the boundary layer seaward of an ice edge for off ice winds observed on two cruises in the bering sea by the noaa r v surveyor the horizontal temperature gradient in the boundary layer caused by the oceanic heat flux seaward of an ice edge induced an increase in wind speed with a maximum increase of 8 at 50 km seaward of the edge at 100 km off ice a momentum balance is established between accelerative terms boundary layer baroclinity momentum entrainment synoptic scale scale pressure gradient and decelerative terms surface drag and the local pressure force resulting from inversion rise wind velocity in the boundary later over the miz during off ice winds is sensitive to changes in surface roughness when an miz is modeled as a smooth interior cd 2 10 3 and a 30 km wide rough marginal ice zone cd 3 8 10 3 with an unstable surface layer over the ocean the model shows a decrease in wind speed of 9 at the windward side of the miz and an 18 increase in wind speed from 5 km interior to the ice edge to 40 km seaward of the edge these results suggest an atmospheric mechanism for rafting at the windward side of the marginal ice zone divergence of the ice at the edge and ice band formation seaward of the edge

snow accumulation variability from seasonal surface observations and firn core stratigraphy eastern wilkes land antarctica annual accumulation records were derived from two firn cores drilled at gd03 69 00 s 115 30 e 1835m and gd15 69 00 s 130 48 e 2155m which are separated by 750 km along the 2000 m contour in eastern wilkes land the accumulation records spanning the period 1930 85 show that annual accumulation has increased by 25 from 1960 to 1985 resulting in the highest accumulation rates in the 55 year records annual accumulation layers were identified in the firn cores using a firn stratigraphic model based on the observed characteristics and variability of the seasonal snow surface layer together with seasonal oxygen isotope ratios the accumulation records support other evidence for a similar recent increase across antarctica the greater increase over the long term mean for 1930 85 in eastern wilkes land was observed at gd15 which is located on a northeast aspect slope near terre adelie it is suggested that the increase is the result of changes in the general atmospheric circulation pattern which have produced a higher annual frequency of precipitation events

concentration gradients and growth decay characteristics of the seasonal sea ice cover the growth and decay characteristics of sea ice in the northern and southern hemispheres are presented quantitatively by using brightness temperature data from the nimbus 5 electrically scanning microwave radiometer the areal extent of 15 ice cover follows a basically symmetrical seasonal cycle in the northern hemisphere ranging from 8 106 km2 in summer to 16 106 km2 in winter in contrast the seasonal cycle in the southern hemisphere is asymmetrical with longer periods of growth than decay and areal extent ranging from 4 106 km2 in summer to 20 106 km2 in winter at different longitudes the occurrences of the maximum rates of advance of the ice edge differ by up to 2 months and similarly for retreat the distribution of the rate of change in the latitudinal position of the ice edge using as a reference point the 50 ice concentration line near the ice ocean boundary follows a quasi gaussian function with peak at about 60 km month and with a standard deviation of about 120 km month however for some months rates as large as a 940 km month change in the latitudinal position are observed when the movement of the ice edge tends to be in the eastward or westward direction as for example in the weddell sea the gradient of ice concentration near the ice edge has considerable variability following a poisson distribution with peaks at about 0 89 ice concentration per kilometer as derived from the 3 day averages and 0 62 ice concentration per kilometer from the monthly averages during the growth cycle the dominant change in ice cover is the advance of consolidated ice behind the advancing ice edge while during decay the retreat of the ice edge is accompanied by massive reduction of ice concentration within the ice pack the monthly changes in ice edge position in the southern hemisphere are also shown to have good correlation with the rates of advance and retreat of the 271 k surface temperature isotherms inferred from climatological temperature data

numerical simulation of the weddell sea pack ice to investigate the role of ice dynamics on the seasonal cycle of antarctic sea ice a series of 2 year simulations of the weddell sea pack ice are carried out the simulations employ the dynamic thermodynamic model developed by hibler 1979 and use a 1 day time step on an 18 15 grid with a resolution of 222 km daily atmospheric data from 1979 are used to drive the simulations with atmospheric temperature fields modified to reflect buoy observations the simulations yield a seasonal cycle of ice with maximum and minimum extents close to that observed except for portions of the western weddell the advance of the ice is found to be primarily thermodynamic in nature while the rapid decay depends critically on the presence of both leads and lateral ice advection the average fraction of open water is substantial even in winter and varies from a minimum of 10 in september to a maximum of 35 in march these values are in general agreement with estimates from satellite microwave data in early summer the ice motion causes a residual tongue of ice to extend eastward from the antarctic peninsula in agreement with observations mean ice thicknesses are consistent with observations and vary from about 3 m in the perennial ice in the western weddell to 1 m in first year ice in the eastern weddell possible feedback between the ice extent and atmosphere are investigated by simulations with the surface air temperatures constrained to below freezing values in the presence of ice these coupled simulations yield a more realistic rapid decay in summer with dynamics included but an unrealistically small decay without dynamics simulated ice drift results yield mean drift rates of about 5 km day in good agreement with buoy drift observations but with slightly inadequate northward transport in the western weddell near the ice edge the drift rates are relatively insensitive to the ice strength near the coast however lower strengths are found to yield a decrease in northward drift rates

effects of el nino southern oscillation and north pacific weather patterns on interannual variability in the subarctic bering sea extraordinary interannual variability in ice cover air and sea surface temperatures sst and surface winds in the eastern bering sea have been observed over recent years to investigate the causes of this interannual variability long term 20 30 years time series of air ocean and ice parameters from the bering sea were cross correlated with the southern oscillation index soi an index of el nino southern oscillation enso events in the tropical southern hemisphere as well as with an index of pacific north american pna events in the north pacific five to thirty percent of the interannual variability linear regression with various smoothing in the bering sea data sets with the exception of surface winds is explained by the soi when the bering sea data lags the soi for comparison 29 52 of the variability in the sst off south america can be explained by the soi the signs of the correlations all suggest that warming in the bering sea follows negative anomalies in the soi that is enso events positive anomalies in the soi which tend to precede el nino events were found to precede cooling in the bering sea significant correlation persists for 18 20 months higher order polynomial regressions between the soi and bering sea data can explain up to 40 of the bering sea variability the mechanism for the connection between enso events and bering sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the aleutian low the aleutian low is intensified and eastward of normal in association with el nino i e warm events but is weaker and westward of normal during cool events it is the regional winds associated with the variable position of the aleutian low that cause the regional warming and cooling events this seesaw in the aleutian low is also used to explain the out of phase ice conditions between the bering sea and the sea of okhotsk pna events are also associated with an intensified aleutian low as well as 700 mbar ridging over northwestern north america causing southerly flow over alaska however while correlation between enso events and pna was significant the correlation between the bering sea and pna was marginal except for surface winds here surface winds from the north were significantly correlated with the pna this apparent inconsistency as well as the lack of correlation of surface winds with the soi is explained by the lack of preferred site of the aleutian low during enso events this lack of preferred site helps explain why the major el nino event of 1982 1983 had little apparent effect on the bering sea

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

a century of accumulation and temperature changes in dronning maud land antarctica a mass balance program was initiated in the vestfjella heimefrontfjella area of western dronning maud land during the austral summer of 1988 1989 as a part of this program spatial and temporal variations in snow accumulation and temperature stable isotopes are measured using shallow firn cores in this paper we present surface accumulation data and discuss the climatic implications of the stable isotope records from two shallow firn cores one 30 m deep core obtained about 200 km from the coast at 700 m asl 73 36 s 12 26 w covers the period 1932 1991 the other core was drilled at about 500 km from the coast at 2900 m asl 75 00 s 2 00 e and covers the period 1865 1991 the recent accumulation increase that has been reported from several areas of the antarctic continent is not present in either of these records instead our coastal record suggests a significant decrease in accumulation with the strongest trend from about 1975 there is a positive trend in the oxygen isotope signal in both cores which in the coastal core corresponds to a temperature increase of about 1 8 c since the early 1930s and in the high altitude core to about 0 8 c since 1865 however it is likely that part of this increase in 18o is due to a change of moisture source

on the development and cause of the weddell polynya in a sea ice simulation abstract occurrence of the weddell polynya a large open water area in the midst of the wintertime pack ice of the southern ocean is examined through a sequence of numerical simulations of the sea ice cover using mean climatological input data the numerical model realistically simulates the emergence of the polynya through the encircling of an open water region by ice in addition with only the wind fields altered the model successfully simulates winter seasons totally lacking a weddell polynya since the vertical ocean heat flux inserted into the model is spatially invariant these results call into question without actually refuting those explanations of the polynya based exclusively on oceanographic factors on the other hand the failure of the modeled polynya to survive the winter season without significant weakening as the observed polynya did in each of the years 1974 76 suggests that the oceanography and or the ocean atmosphere feedbacks are essential to the polynya maintenance even if not

variability in oceanic crustal thickness and structure multichannel seismic reflection results from the northern east pacific rise multichannel seismic reflection data acquired between 8 50 and 9 50 n and between 12 30 and 13 30 n along the east pacific rise provide a three dimensional view of the young oceanic crust seafloor to moho reflection travel times vary by up to 0 9 s within our study areas the total range of crustal travel times in the 9 n area is 1 55 to 2 45 s the total range in the 13 n area is 1 60 to 2 05 s the variation is systematic indicating thinner crust locally associated with overlapping spreading centers oscs and in the 9 n area segment scale variation along crustal isochrons crustal travel time is found to be a valid proxy for oceanic crustal thickness outside of the axial low velocity volume thickness can be calculated from time to 500 m even in the axial region thickness can be calculated to 1 km if low velocity zone position is known crustal thicknesses calculated from travel times vary by 2 6 km in the 9 n area and by 1 5 km in the 13 n area the majority of this variation is attributed to seismic layer 3 the lower crust segment scale variation of 1 8 km 5 5 to 7 3 km thickness is observed in the 9 n area with thinnest crust formed between 9 40 and 9 50 n and thickest formed between 9 15 and 9 20 n results imply a three dimensional pattern of magma supply to the 9 n segment the osc at 9 03 n is associated with major disruptions of the segment scale pattern in the form of local thin areas within the discordant zone the smaller osc at 12 54 n is not associated with dramatic changes in thickness of the surrounding crust in the absence of oscs the process of crustal formation displays more temporal uniformity along flow lines than spatial uniformity along isochrons within a segment thicker crust does not always correlate with shallower ridge bathymetry broader axial cross section or more negative mantle bouguer or subcrustal gravity anomaly variable thickness of the crust mantle transition region as well as crustal flow in the axial region may be responsible for this unexpected result we hypothesize that the geophysical signature of diapiric mantle upwelling beneath a fast spreading ridge is relatively thin crust associated with a thick moho transition zone and a subcrustal gravity low such a diapiric upwelling center appears to be now located beneath the east pacific rise near 9 40 to 9 50 n