circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

temporal analysis of water masses and sea ice formation rate west of the antarctic peninsula in 2008 estimated from southern elephant seals srdl ctd data abstract as an alternative method to collect oceanographic data in the polar oceans especially during winter when traditional methods are very difficult to be used sea mammals can be tagged with satellite relay data loggers with ctd capabilities srdl ctd using data from nine southern elephant seals ses mirounga leonina tagged during a field campaign of the meop br project the brazilian counterpart to the marine mammal exploration of the oceans pole to pole this work presents a temporal analysis of the water masses and the sea ice formation rate at the western part of the antarctic peninsula ap during 2008 we found that the seasonal and local processes controlling the surface and intermediate layers of the ocean produced differences in the water mass composition and the sea ice formation rates in our study region sea ice formation rates ranged from less than 1 cm day in deep sea waters off the northern part of the ap to 14 cm day at the vicinity of ice shelves such as the abbot and wilkins ice shelves further south in the ap maximum sea ice formation rates as expected occurred during autumn to winter after the successive collapse events of the wilkins ice shelf wis in 2008 the sea ice formation rate endured significant reductions even when sea ice concentrations were high in the region these reductions observed by ses in the vicinity of wis can be associated with freshwater input derived from shelf collapses the presence of the circumpolar deep water cdw over the continental shelf west of the ap affected the sea ice formation rate by both contributing to the observed low sea ice coverage and to the acceleration of the ice shelf melting another process that demonstrated influence on the formation of sea ice was the advection of more saline waters in the oceanic layer considered here for the application of salt balance equation this advection resulted in unrealistic sea ice formation rates in regions where there was no sea ice cover the data and results presented here can be used to feed and to validate climate ocean atmosphere coupled models the data can be combined with other more traditional meteorological and oceanographic data in order to provide a better understanding of both oceanic and ocean atmosphere coupled processes yet not very well known in our study region

the central anomaly magnetic high implications for ocean crust construction and evolution the central anomaly magnetic high camh is a long lineated short wavelength 10 km wide at the sea surface magnetic anomaly overlying many of the world s midocean spreading centers this anomaly is particularly well developed over the northern juan de fuca ridge including the northern symmetrical and endeavour segments the ubiquitous presence of this zone of high magnetic contrast directly in the zone of active oceanic plate formation is a key to our understanding of near axis crustal plate evolution recently obtained deep tow magnetometer data from segments of the juan de fuca spreading center have caused us to revise the present models of the source of the camh and to review the implications the new model would have on our understanding of the evolution of the magnetic structure of oceanic plates in this model we attribute the near axis magnetization contrast to tectonically controlled low temperature alteration of the upper vertical section of extrusive basement extensive and systematic fissuring of the upper extrusive rocks allows penetration of sea water and rapid alteration of the magnetic minerals in fissured areas approximately 3 km off axis the correlation between fissured crustal blocks and near bottom magnetic lows and unfissured crustal blocks with magnetic highs which is observed at the axis is also seen in a single off axis tow over an outer flanking ridge

heat flux through sea ice in the western weddell sea convective and conductive transfer processes the heat flux through the snow and sea ice cover and at the ice ocean interface were calculated at five sites in the western weddell sea during autumn and early winter 1992 the ocean heat flux averaged 7 2 w m2 from late february to early june and average ice air heat flux in the second year floes depended on the depth of the snow cover and ranged from 9 to 17 0 8 w m2 in late february three of the five sites had an ice surface which was depressed below sea level resulting at two of the sites in a partially flooded snow cover and a slush layer at the snow ice interface as this slush layer froze to form snow ice the dense brine which was rejected flowed out through brine drainage channels and was replaced by lower salinity nutrient rich seawater from the ocean upper layer we estimate that about half of the second year ice in the region was covered with this slush layer early in the winter as the slush layer froze over a 2 to 3 week period the convection within the ice transported salt from the ice to the upper ocean and increased total heat flux through the overlying ice and snow cover on an area wide basis approximately 10 cm of snow ice growth occurred within second year pack ice primarily during a 2 to 3 week period in february and march this ice growth near the surface of the ice provides a salt flux to the upper ocean equivalent to 5 cm of ice growth despite the thick about 1 m ice cover in addition to the ice growth in the small area less than 5 open water regions

warm weddell deep water west of maud rise a pool of relatively warm 1 0 c weddell deep water wdw immediately west of maud rise appears to be a quasi stationary feature the warm pool is derived from the flow of warm wdw around the flanks of maud rise an austral spring 1989 expedition of the r v akademik fedorov obtained detailed measurements of the warm pool it displays the general regional relationship of temperature maximum t max warmth to shallowness of the pycnocline as well as mixed layer oxygen concentration well below full saturation depression of oxygen values is a product of injection of wdw into the mixed layer during the ice covered winter period associated with this transfer are high vertical fluxes of heat and salt which limit the thickness of the sea ice cover in the winter the atmosphere is sufficiently cold to remove the wdw heat without massive sea ice melting though the regional ice thickness is restricted in the spring the atmospheric conditions cannot remove the ocean heat and ice melting ensues before the atmospheric heat budget alone can account for the ice melt this is clearly seen in the warm pool as very low mixed layer oxygen which is a reflection of high wdw entrainment and vertical heat flux and is normally associated with high mixed layer salinity here it is coupled instead with reduced salinity a result of approximately 0 5 m of ice melt the fedorov data confirm the role of oceanic heat flux in early removal of southern ocean sea ice at the end of winter in that the region of highest wdw entertainment is associated with greater amounts of melt water

volcanics and structure of the famous narrowgate rift evidence for cyclic evolution amar 1 a near bottom photographic survey on the mid atlantic ridge from the famous region south to transform b reveals structural and volcanologic evidence for an alternating widening and narrowing rift valley extension wedges appear to be propagating south from transform a and north from transform b these merge at mt mars where the rift valley is narrowest and shallowest narrowgate giving the valley a symmetrical hourglass shape three major volcanic en echelon lineaments trend n10 e 10 oblique to the strike of the inner walls faulting and fissuring are antisymmetrical across the rift valley in contrast to the major extension this contrasting antisymmetry reflects the surficial distribution of stress across crust of varying strengths whereas the large scale wedge phenomenon determines the periodicity of transition from a narrow valley to a wide valley using vector analysis the extension wedges are propagating at about 9 cm yr toward each other at this rate a narrow rift valley will be fully transformed into a wide rift in 0 64 m y

the magnetic structure of axial seamount juan de fuca ridge axial seamount is a large volcanically active seamount located in the eastern pacific on the central juan de fuca jdf ridge at 46 n 130 w sea surface magnetic anomaly data show that axial lies completely within crust formed during the brunhes normal polarity epoch the edifice however does not produce a simple positive magnetic anomaly related to the excess mass above mean seafloor several pronounced negative magnetic anomalies are associated with the seamount including both a circular shaped low located west of the summit and an elongate low trending nw on the southeast flank of the volcano these two anomalies form part of a nw se magnetic trough which extends across the seamount edifice oblique to the general jdf ridge trend of n20 e a third negative anomaly is observed on the northern flank of the seamount associated with north helium basin a deep elongate basin which indents the northeast flank of the seamount both inversion of sea surface magnetics data and forward modelling of topography constrained by magnetization values of dredged samples show that bathymetric effects can explain the helium basin anomaly but topography alone cannot produce the low magnetization values which extend across the seamount summit magnetization of crustal rocks does not vary spatially over the seamount so that negative anomalies at the summit can be explained by variations in the effective thickness of the magnetic source layer a simple forward model of uniform magnetization shows that the anomaly source layer would have to thin by 50 to less than 700 m thick in order to generate the observed magnetic response a thinned source layer is consistent with the presence of either a substantial magma chamber at depth beneath the summit of axial or a zone of substantial crustal alteration the shape of the anomaly implies the trend of either of these sources must be oriented obliquely to the general ridge trend but parallel to the direction of the absolute plate motion

investigation of a vine matthews magnetic lineation from a submersible the source and character of marine magnetic anomalies we report here the first attempt to map directly the boundary of a vine matthews magnetic stripe on the seafloor our objectives are to study the processes of oceanic crustal accretion as recorded in the reversal transition zone and to investigate the formation of the magnetic source of vine matthews magnetic anomalies our deep tow and alvin based magnetic studies focus on the matuyama brunhes reversal transition on the flanks of the east pacific rise near 21 n while the sea level magnetic anomalies are less than average in clarity for the east pacific rise a three dimensional inversion of deep tow data reveals a sharp strike linear polarity transition less than 1 8 km wide macdonald et al 1980a these measurements have been augmented by mounting a vertical magnetic gradiometer on alvin and making 280 reliable polarity determinations along and across the polarity transition zone even on long traverses across both sides of the boundary we find that nearly every magnetic target has the correct polarity i e the same polarity as the regional magnetic lineation this homogeneity in polarity of the magnetic lineations is surprising the magnetic polarity transition in the outcropping volcanic section is sharp and linear along strike delineated in some cases by a clear geologic contact of opposing flow fronts of different ages several weakly magnetized outcrops mapped within the transition zone may have erupted during the time in which the geomagnetic field was reversing the reversal boundary mapped on the seafloor from alvin is displaced 250 m to 500 m nw away from the spreading axis relative to the position of the average boundary as derived from inversion of the deep tow and sea level magnetic data this offset provides a means for estimating the spillover of lava flows away from the spreading axis during the time the crust was formed the combination of deep tow and alvin measurements suggests that circa 0 7 m y ago the crustal accretion zone magnetized volcanic intrusive and plutonic rocks was 2000 2800 m wide while the zone of recent volcanism alone was only 1000 2000 m wide the determination for the most recent reversal agrees well with submersible observations at the present spreading center where the zone of recent volcanism neovolcanic zone varies between 600 and 2000 m in width this very orderly picture for the formation of magnetic lineations and crustal accretion processes appears to conflict with complex deep sea drilling project dsdp magnetic results from the atlantic we suggest that the crustal generating processes and resulting magnetic structure vary significantly with spreading rate on the slow spreading mid atlantic ridge major episodes of volcanism are likely to be infrequent 104 years the magma chamber may be non steady state and the neovolcanic zone shifts or varies in width considerably this sporadic start and stop spreading process will contribute to a highly heterogeneous and complex crustal and magnetic structure as seen in dsdp holes in addition significant faulting and tilting may disrupt slow spreading crust for intermediate to fast spreading centers more frequent volcanism 50 600 years a nearly steady state magma chamber and a narrow stable neovolcanic zone will create a less complex magnetic and crustal structure both as seen from alvin and as inferred from clear sea level magnetic anomalies in the pacific

recurring polynyas over the cosmonaut sea and the maud rise two polynyas over the deep ocean were observed in the antarctic region during the winter of 1980 one near 43 e 66 s cosmonaut polynya and another near 2 e 64 s maud rise polynya the time history of these two polynyas was examined on an alternate day basis using ice concentration maps from the nimbus 7 scanning multichannel microwave radiometer smmr a quantitative analysis of a study area around it shows that the totally enclosed cosmonaut polynya attained a maximum size on july 25 1980 with an open water area of as much as 137 700 km2 this polynya lasted for a few weeks disappeared on august 16 1980 and was not observed for the rest of the winter similar polynyas in the same region have occurred for several years including 1973 1975 1979 1982 and 1986 the maud rise polynya on the other hand was observed as a reduction in ice concentration to about 37 within the smmr resolution of about 900 km2 however the open water area in the region amounted to 92 800 km2 on july 20 and the polynya recurred several times during the same winter period it is proposed that both polynyas are products of deep reaching convection which introduces warmer deep water into the surface layer in this way they are viewed as sensible heat polynyas in that they are maintained by oceanic heat the oceanographic settings of these two polynyas are similar the hydrographic data at both sites indicate the existence of localized doming of the pycnocline this brings warmer saltier deep water closer to the sea surface which has been demonstrated to be an effective preconditioner for deep reaching convection it is probable that the polynyas are terminated by invasion of sea ice from the sides which attenuates convection the capability of a polynya to survive an entire winter period may be related to its size the larger polynyas are better protected from convergence of the surrounding sea ice for example a simple model shows that a polynya with a diameter of about 100 km or greater is much more likely to survive a winter season than a smaller one

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

recent advances in fine particle magnetism implications for paleomagnetism it is becoming increasingly obvious in paleomagnetism that the older practice of using large numbers of samples to improve statistical measures of accuracy is often not adequate to reveal the signal of greatest geological importance blanket demagnetization treatments are now largely outdated except for the most ideally behaved samples a rapidly vanishing phenomenon in many locales variations in characteristic remanent directions between neighboring and supposedly contemporaneous but lithogically distinct rock units can no longer be simply treated as noise we now recognize that such differences may actually reflect rock magnetic effects rather than such factors as the short term behavior of the geomagnetic field or local variations in structure multiple overprints often the result of moderate reheating and or chemical alteration can result in an uncertain relationship between the timing of emplacement and the acquisition of remanence in the past rocks which presented such problems could often be avoided in favor of more straightforward units much of that geological cream has been skimmed however further progress in many areas particularly the determination of the apw path and reversal stratigraphy in the paleozoic will require a better understanding of magnetization processes in order to resolve the above mentioned problems and produce accurate and reliable results

nonuniform magnetization of jasper seamount paleopoles derived from seamounts have been used to reconstruct the tectonic history of ocean basins however the interpretation of seamount magnetization models and the validity of seamount paleopoles may be affected by inhomogeneous magnetization multibeam bathymetric data sea surface and deep tow magnetic field data and paleomagnetic analyses of dredged samples were used to examine the origin of nonuniform magnetization within jasper seamount 30 27 n 122 44 w models indicate that the seamount is predominantly reversely magnetized with local zones of normal polarity as corroborated by deep tow measurements lithologies likely to be volumetrically important in a seamount edifice show highly variable magnetic properties basalts have high intensities 0 5 27 0 a m high koenigsberger ratios q and low viscous remanence vrm acquisition low q ratios and high vrm acquisition coefficients of coarse grained material and volcaniclastics suggest that they may have substantial viscous and induced components models for jasper are characterized by low uniform intensities and far sided paleopoles the shallow model inclinations may be attributed to nondipolar components in the time averaged geomagnetic field the low intensities of the uniform models and the large nonuniform component in the seminorm solutions imply a complex distribution of magnetization sources within jasper this nonuniformity may result from either lithological variability or construction of the seamount spanning two or more polarity intervals

weddell gyre temperature maximum stratum at depths below 200 m relatively warm salty water spreads poleward from the antarctic circumpolar current acc this deep water mass is cooled through interaction with the atmosphere feeding the formation of dense bottom water which in turn influences much of the world ocean significant poleward spreading is accomplished within the weddell gyre of the atlantic sector of the southern ocean an extensive data set obtained in the 1980s within the weddell gyre provides a detailed view of the subsurface temperature maximum t max stratum defining the top of the deep water mass the seasonal sea ice growth and retreat pattern reflects the t max distribution there is evidence for subdivision of the t max into two cold centers which may reflect secondary circulation features within the gyre the primary inflow of warm deep water is derived from the southern edge of the acc near 20 30 e the inflow spreads to the west along 65 s and is divided into smaller pools of relatively warm water west of maud rise with a cold feature directly over the rise in a manner shown by models of topographically generated eddies variability of the t max stratum in the vicinity of maud rise arising from changes in the vigor of the large scale circulation may influence the regional vertical heat fluxes and be related to interannual variability of the sea ice cover and to the recurring polynya feature typical of the region

anthropogenic co2 estimates in the southern ocean storage partitioning in the different water masses the research leading to these results was supported through eu fp7 project carbochange changes in carbon uptake and emissions by oceans in a changing climate which received funding form the european commission s seventh framework under grant agreement no 264879 and by the spanish ministry of sciences and innovation and was co founded by the fondo europeo de desarrollo regional 2007 2012 feder through the catarina project ctm2010 17141 mar

the volcanic tectonic cycle of the famous and amar valleys mid atlantic ridge 36 47 n evidence from basalt glass and phenocryst compositional variations for a steady state magma chamber beneath the valley midsections amar 3 the 1978 amar expedition extended the investigation of the mid atlantic ridge that was begun by the 1973 1974 famous expedition from the northern end of the famous rift the original famous area to the narrow central and southern end of the famous rift narrowgate region and into the broad amar valley south of fracture zone b available field and geochemical data allow us to characterize in detail the volcanic tectonic cycle for these two segments of the mid ocean ridge system a dynamic model of the crust forming processes within these two rift valley segments is deduced from 1 variations in the chemical composition of the erupted basaltic liquids as preserved in chilled glassy margins 2 composition and petrographie relationships of megacrysts and phenocrysts that represent cumulus crystallization onto the floor of a shallow magma chamber of a primitive magma that has reached pyroxene saturation early in its evolution and 3 detailed stratigraphie and regional observations that characterize the periodicity of volcanic construction and superimposed tectonism related to the ongoing extension of the valley floor each volcanic cycle is composed of several eruptive episodes that are initially typified by rapidly extruded sheet flows of primitive composition the decreasing extrustion rates at the end of an eruptive event are associated with more evolved liquid compositions that reflect fractionation within the shallow conduits intermixing of magmas is indicated by the relatively limited variability in glass composition not explicable in terms of simple fractionation processes the common evidence of crystal resorption and the apparent disequilibrium between megacrysts phenocrysts and their enclosing glass this indicates control by a crustal magma chamber liquid and crystal compositions and textural relations can best be explained by a three stage crystallization history 1 crystallization of olivine plagioclase and clinopyroxene onto the floor of a magma chamber 2 partial resorption of mineral phases by a superheated undersaturated liquid above the floor 3 intratelluric crystallization of olivine and plagioclase clinopyroxene during rise of melt to the surface through the conduit system above the magma chamber a magma chamber model is suggested for the amar famous rift valleys that satisfies both seismic and geological constraints we propose that a small steady state magma chamber is maintained beneath the topographically higher midsections of each valley segment amar and narrowgate regions but that these thin and terminate near the intersecting fracture zones expansion and contracton of the central magma body is controlled by the fluctuating imbalance between magma supply and chamber crystallization the famous narrowgate rift is currently in a contraction period so that in the northern famous region primitive liquid has erupted at mount venus and mount pluto without intercepting and mixing into the steady state chamber that supplies the mixed magmas to the narrowgate region

seasonality of southern ocean sea ice the sea ice cover of the southern ocean undergoes a rapid decrease from mid november to mid january the atmosphere to ocean heat flux is insufficient to account for this melting even in the presence of the high percentage of open water characteristic of the southern ocean sea ice it is estimated that sea air heat exchange in the 60 to 70 s zone can account for roughly 50 of the required spring heating the remainder must be supplied by the relatively warm deep water residing below the southern ocean pycnocline deep to surface water heat flux is accomplished by upwelling of the pycnocline due to the regional ekman divergence of the surface layer and by cross pycnocline mixing it is estimated that the required vertical mixing coefficient for the pycnocline is 1 5 cm2 s this value is considered as realistic in view of the relatively weak pycnocline which is a consequence of low levels of fresh water input to the surface layer it is suggested that the magnitude of fresh water input is a major factor in determining the degree of seasonality of southern ocean sea ice

formation and maintenance of a polynya in the weddell sea a dynamic thermodynamic sea ice mixed layer model for the weddell sea is complemented by a simple diagnostic model to account for local sea ice atmosphere interaction to consider the atmospheric influence on the oceanic mixed layer the pycnocline upwelling velocity is calculated using the theory of ekman pumping in several experiments formation and conservation of a polynya in the weddell sea are investigated intrusion of heat into the lower atmosphere above the polynya area is assumed to cause a thermal perturbation and a cyclonic thermal wind field superposed with daily ecmwf surface winds this modified atmospheric forcing field intensifies oceanic upwelling and induces divergent ice drift simulation results indicate that in case of a weak atmospheric cross polynya flow the formation of a thermal wind field can significantly extend the lifetime of a large polynya the repeated occurrence of the weddell polynya in the years 1974 76 thus appears to be an effect of feedback mechanisms between sea ice atmosphere and oceanic mixed layer

origin of detrital fluxes in the southeast indian ocean during the last climatic cycles because of a close relationship between detrital flux variations and magnetic susceptibility ms flux ms cm 3 of bulk sediment multiplied by the linear sedimentation rate variations in the southeast indian basin of the southern ocean ms flux profiles have been used to examine the spatial and temporal detrital flux changes in this basin during the last climatic cycle results indicate a general increase in detrital material input during the coldest periods suggesting a widespread phenomenon at least on the basin scale mineralogical data geochemical data and 87sr 86sr isotopic ratios have been used to determine the origin and transport mechanisms responsible for increased detrital flux during glacial periods mineralogical and geochemical data show that these glacial highs are due to increases in both kerguelen crozet volcanic and antarctic detrital inputs the 87sr 86sr isotopic composition of the 45 m fraction indicates that the kerguelen crozet province contributes to at least 50 of the coarse particule input to the west this contribution decreases eastward to reach less than 10 these tracers clearly indicate that the crozet kerguelen province was a major source region of detrital in the western part of the basin during glacial times in contrast material of antarctic origin is well represented in the whole basin fine and coarse fractions because of the minor amount of coarse particles in the sediments volcanic particles from kerguelen and crustal particles from antarctica have most probably been transported by the antarctic bottom water current and or the circumpolar deepwater current during glacial periods as is the case today nevertheless the presence of coarse particles even in low amount suggests also a transport by ice rafting sea ice and icebergs originated from both kerguelen and antarctic sources however the relative importance of both hydrographic and ice rafting modes of transport cannot be identified accurately with our data during low sea level stands glacial maximum periods increasing instability and erosion of the continental platform and shallow plateaus could have resulted in a more efficient transfer of crustal and volcano detrital material to the southeast indian basin at the same time extension of the grounded ice shelves over the continental margins and increase in the erosion rate of the antarctic ice sheet could have induced a greater input of ice rafted detritus ird to southern ocean basins enhancement of the circumpolar deepwater current strength might have also carried a more important flux of detrital material from kerguelen however an increase in the bottom water flow is not necessarily required

ice production and deep water entrainment in shelf break polynya off enderby land antarctica aircraft observations off enderby land antarctica verified that a coastal polynya forms even in severe winters and that new ice production continuously occurs there in the polynya water temperature profiles were measured for the first time using the aircraft launched expendable bathythermograph axbt the axbt data show that the thickness of the winter mixed layer is 350 m or more and that the layer temperatures are near the freezing point according to the water mass analysis of the winter mixed layer the active haline convection by the high ice production in the winter polynya contributes to the formation of more homogeneous and saline mixed layer than that under the fast ice cover where the ice grows slowly and convective mixing is calm furthermore the active convection leads to entrainment of the oxygen poor deep water under winter water consequently in the polynya located over the continental shelf break the oxygen content of the mixed layer is somewhat lower than that in a coastal polynya that forms on the continental shelf where the haline convection reaches to the sea bottom the oxygen undersaturation of the thick mixed layer in the shelf break polynya suggests that the deep water entrainment rate is more intense than that under the pack ice region in the weddell sea with a relatively thin mixed layer it is therefore important to consider such polynya processes which may contribute to water mass modification in the antarctic coastal region

on the total input of antarctic waters to the deep ocean a preliminary estimate from chlorofluorocarbon measurements 1 deep ocean inventories of dissolved chlorofluorocarbon 11 cfc 11 along representative sections off antarctica provide the first estimate of the overall strength of all dense water sources in the southern ocean their formation rates are reported for three density layers that span the main water masses involved in the lower limb of the thermohaline circulation thc the bottom layer is supplied via sinking of antarctic bottom water aabw produced at a few continental shelves the middle layer receives the offshore injection of ventilated modified circumpolar deep water mcdw produced along much of the lengthy antarctic slope front the top layer is ventilated by northward export of antarctic surface water into the upper circumpolar deep water of the antarctic circumpolar current average southern ocean inputs to the upper two layers of the deep ocean for the 1970 1990 period are derived on the basis of the cfc 11 distributions along meridional sections the mean cfc 11 saturations of all water mass ingredients and the inferred mixing leading to production of dense source waters about 5 4 1 7 sv 1 sv 10 6 m 3 s 1 of near freezing shelf water ventilate the bottom layer and 4 7 1 7 sv and 3 6 1 3 sv of cold antarctic surface water ventilate the middle and top layers therefore the total contribution of ventilated southern ocean waters to the lower limb of the global thc is about 14 sv this is close to the about 17 sv estimated for north atlantic near surface sources from cfc 11 inventories their entrainment of 7 4 2 4 sv of cfc poor subsurface lower circumpolar deep water during the formation and sinking of aabw and mcdw raises the total southern ocean input to the deep ocean to about 21 sv

glacial interglacial changes in global deepwater circulation variations in the areal extent of the cryosphere appear to exert an important control over glacial interglacial changes in the mode of formation and source areas for deepwater and bottom water masses during interglacials when ice extents are minimal these water masses form by mechanisms which are well documented for the present interglacial climatically related advances and retreats of sea ice in the northern hemisphere during glacials probably resulted in shifting loci of formation for each of the three types of north atlantic deep water nadw probable glacial advances of grounded ice sheets to the continental shelf margins in antarctica precluded formation of antarctic bottom water aabw at the presently active continental shelf sites because these shifts in source areas for aabw and nadw probably involved source waters with salinity temperature oxygen content and nutrient levels that differed from modern values deep and bottom waters are likely to have had different characteristics in glacials than they do during interglacials

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

ridge segmentation and the magnetic structure of the southern mid atlantic ridge 26 s and 31 35 s implications for magmatic processes at slow spreading centers along axis profiles of three dimensional magnetic inversions for the mid atlantic ridge mar 31 35 s show low magnetization near the middle of ridge segments and high magnetization at the segment tips for three adjacent spreading segments thus there is an inverse relation between axial magnetization and axial topography the ridge segment at 26 s on the mar has the same inverse relationship between magnetization and topography the common occurrence of this relationship suggests that it reflects a fundamental process of crustal accretion at the mar we analyze the rock magnetic properties from 42 locations within the four ridge segments in the south atlantic to constrain the inherent trade off between source intensity and source thickness in the magnetization model the natural remanent magnetization nrm intensities from the four ridge segments averaged together correlate with the magnetic inversion profiles this finding implies that changes in the magnetization of the extrusives may account for much of the observed magnetic anomaly amplitude variation a direct correlation of feo content and magnetization suggests that magnetic anomaly amplitudes may be an indicator of feti rich basalts at the slow spreading mar even though the iron content of the basalts from high magnetization areas is not as high as observed at pacific spreading centers despite the different magma plumbing systematics of the pacific spreading centers and the mar it appears that the segment scale magma system of the mar also results in segment scale crustal magnetization variations further evidence that the axial magnetic variations result from source intensity variations is that older isochrons have higher intensities near the ridge discontinuities similar to the behavior on axis between 0 and 5 ma the decay in magnetization is 50 independent of location within a spreading segment

magnetic properties of three segments of the mid atlantic ridge at 37 n famous narrowgate and amar amar 2 during the amar 1978 expedition over 200 separate basalt samples were collected by alvin and dredge from the narrowgate and amar segments of the mid atlantic ridge near 37 n to determine the origin of reversely magnetized rocks previously recognized in the famous rift area to the north and to study the variations in rock magnetic properties that occur along the strike of the mid atlantic ridge magnetic intensity determinations of rocks collected in the famous area indicate that intensity decays with time by a factor of 5 in less than 106 years rocks with low intensities have high curie temperatures tc indicating that low temperature oxidation of the magnetic minerals takes place soon after the basalts are extruded and is pervasive in crust older than 106 years magnetic intensity jnrm of the uppermost oceanic crust can be expressed as a function of age t by the expression j 5 82t 1 3 by measuring jnrm of the surface rocks from the three valley segments the relative ages of the surface rocks from the famous amar and narrowgate areas can be estimated to be 1 104 years 3 104 years and 4 104 years respectively one exception is mt mars located in the center of the narrowgate area that has high jnrm values 84 10 3 emu cm3 and low tc values 165 c suggesting that this is an area where volcanic activity is becoming reactivated following a period of quiescence of the 55 oriented samples collected eight are reversely magnetized although three of the reversed samples have curie temperatures above 300 c and may have undergone self reversal the other five reversed samples have magnetic properties similar to normally magnetized rocks and may have been misoriented or extruded during a short reversed event within the brunhes epoch because most of the surficial rock samples are normally magnetized it is suggested that the previously recognized reversed zones which appear in a deep tow magnetometer profile that crossed the narrowgate area are located at depth and are the result of the spreading axis moving into older matuyama crust that is now covered by more recent volcanism

magnetic properties of the bay of islands ophiolite suite and implications for the magnetization of oceanic crust rock magnetic properties opaque mineralogy and degree of metamorphism were determined for 101 unoriented samples from the north arm and blow me down massifs of the bay of islands ophiolite complex newfoundland the weathered and metamorphosed extrusive basalt samples have a weak secondary magnetization arising from oxidation and exsolution of ilmenite of unknown origin the initial magnetization of the underlying sheeted dike complex appears to have been destroyed by hydrothermal alteration soon after formation the magnetic intensity of the gabbroic samples increases as the degree of alteration increases with the highly altered upper metagabbros having an average intensity of 3 10 3 emu c3 because magnetization of the metagabbro samples is related to nonpervasive variable alteration these crustal units are unlikely to make a significant contribution to lineated magnetic anomalies a compilation of our results and other studies suggests a model in which oceanic crust magnetization results from an upper extrusive basalt source layer roughly 600 m thick with no contribution from a deeper source layer recognizable from these bay of islands data

magnetization during low temperature oxidation of seafloor basalts no large scale chemical remagnetization difficulty in removing the effects of grain size dependence have hampered interpretations of magnetic property changes during low temperature oxidation of titanomaghemite for the present study samples were collected perpendicular to cracks in seafloor basalts to produce subsamples of essentially constant grain size but varying degree of low temperature oxidation within a few centimeters coarse grained samples and those showing evidence of high temperature oxidation were excluded increasing curie temperature was used as the most reliable measure of increasing maghemitization intensity of natural remanent magnetization jnrm consistently decreased with increasing low temperature oxidation indicating that any increase in jnrm with age of oceanic crust must be due to other factors coercive force hc increased until curie temperatures reached 250 c and then in samples exhibiting single domain behavior decreased drastically because coercive force depended on degree of oxidation in this complex manner chemical remanent magnetization crm in even slightly oxidized grains should have a different coercivity than the original thermal remanent magnetization trm most deep sea drilling project samples in this study have experienced tectonic rotations or field reversals within 1 0 m y of extrusion thus field controlled crm if present should have different coercivities and a discrete direction and be discernible during alternating field af demagnetization alternating field demagnetizations showed no evidence for significant acquisition of field controlled crm viscous remanent magnetization vrm was the dominant secondary magnetization in samples with several components of remanence in very fine grained basalts vrm was difficult to remove by af demagnetization and may be the source of increased dispersion in highly oxidized oceanic basalts mechanisms which may in part be responsible for coercivity and vrm changes are 1 an increase in the critical size of domain transitions during low temperature oxidation and 2 incipient phase separation into fe rich and ti rich areas the fe rich areas being superparamagnetic the latter mechanism explains the increase in saturation magnetization js and concomitant decrease in jnrm when curie temperatures are above 360 c

sea ice and oceanic processes on the ross sea continental shelf we have investigated the spatial and temporal variability of antarctic sea ice concentrations on the ross sea continental shelf in relation to oceanic and atmospheric forcing sea ice data were derived from nimbus 7 scanning multichannel microwave radiometer smmr brightness temperatures from 1979 1986 ice cover over the shelf was persistently lower than above the adjacent deep ocean averaging 86 during winter with little month to month or interannual variability the large spring ross sea polynya on the western shelf results in a longer period of summer insolation greater surface layer heat storage and later ice formation in that region the following autumn newly identified pennell and ross passage polynyas near the continental shelf break appear to be maintained in part by divergence above a submarine bank and by upwelling of warmer water near the slope front warmer subsurface water enters the shelf region year round and will retard ice growth and enhance heat flux to the atmosphere when entrained in the strong winter vertical circulation temperatures at 125 m depth on a mooring near the ross ice shelf during july 1984 averaged 0 15 c above freezing sufficient to support a vertical heat flux above 100 w m2 monthly average subsurface ocean temperatures along the ross ice shelf lag the air temperature cycle and begin to rise several weeks before spring ice breakout the coarse smmr resolution and dynamic ice shelf coastlines can compromise the use of microwave sea ice data near continental boundaries

winter mixed layer entrainment of weddell deep water observations from the somov during the us ussr weddell polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60 s greenwich meridian region has an oxygen content of 7 4 ml 1 this is 86 of full oxygen saturation representing an oxygen deficit relative to full saturation of 1 1 ml 1 the source of this deficit is believed to be a consequence of oxygen poor 4 5 ml 1 weddell deep water wdw entrainment by the winter mixed layer assuming effective cutoff of ocean atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors a mixing ratio of 1 3 for wdw to beginning of winter surface water is required to explain the end of winter mixed layer oxygen content accompanying the wdw transfer into the mixed layer is heat transfer of approximately 7 103 cal cm2 2 9 108 j m2 during the five winter months of sea ice coverage as well as salt transfer which requires 34 cm of fresh water to produce typical mixed layer salinity during the seven ice free months when entrainment is expected to be minor diffusive heat and salt flux continues a mean annual heat flux of 12 w m2 is suggested with an annual demand for freshwater of 46 cm yr consideration of the winter period salinity budget indicates net sea ice melting of 20 cm which can be attributed to regional convergence of sea ice the remaining freshwater is derived from excess precipitation and possibly iceberg melt oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a fully saturated condition

restriction of convective depth in the weddell sea 1 the depth open ocean convection can reach around maud rise in the weddell sea is estimated based on the entrainment assumption using hydrographic data obtained in winter 1986 during which no distinct polynya was observed while the water column is stable at all ctd stations when observed additional cooling makes the mixed layer water heavier than the underlying water at any depth in an adiabatic sense however convective plume cannot reach the ocean bottom since it loses positive density anomaly due to thermobaricity by entraining the warm deep water wdw on its downward way the deeper convection is located over maud rise where the maximum temperature of the wdw max is about 0 5 c while the shallower one in the warm water cell region where max is more than 1 0 c the mean convective depth is much shallower than the ocean depth and the ventilated depth during the weddell polynya years 3 4 km

the structure and paleomagnetism of north atlantic ocean layer 2 segregation vesicle determinations segregation vesicles contain solidified residual melt the segregation vesicle technique of seafloor basalt orientation is based on the assumptions that 1 the orientation of this residue is mainly gravity controlled and forms a geopetal feature and 2 rocks remain relatively stationary during the time of segregation solidification and magnetization by application of this technique it is possible to determine the horizontal cooling of certain seafloor basalts recovered in drill cores and then correct the magnetic direction for the dip of the rocks determine the true thickness of lithologic units measured perpendicular to the dip and estimate the dip direction with some degree of confidence this technique was applied to dsdp holes 332a 332b 334 395 395a and 396b which penetrated 117 to 583 m into basaltic basement crust of the north atlantic ocean segregation vesicles occur in 26 to 50 of the samples collected from each hole primarily upright dips of 4 to 41 were measured in holes 3

a coupled one dimensional sea ice ocean model a prognostic one dimensional mixed layer pycnocline model describing the vertical structure of the upper ocean is coupled to a thermodynamic sea ice model the coupled prognostic model is compared with the more usual sea ice model overlying a fixed mixed layer with constant oceanic heat flux and is then applied to investigate the effect of temporal and regional variations of the entrained oceanic heat flux on the sea ice cover in both polar regions in the southern ocean a standard simulation is compared with two perturbation experiments which both describe the occurrence of a polynya in the arctic ocean the effect of possible soviet river diversions is investigated finally the response of the coupled model to paleoclimatic forcing and boundary conditions is presented

the transport of the weddell gyre across the prime meridian abstract current meter observations from instruments moored from 1996 to 2001 are used to determine the structure and the volume transport of the weddell gyre on the greenwich meridian the record length mean volume transport is 45 sv to the east within the northern and 56 sv to the west within the southern limb of the weddell gyre thus 11 sv must leave the gyre circulation west of the greenwich meridian and enter it east of it the deficit occurs with 8 sv mainly in the circumpolar deep water cdw warm deep water wdw layer surface waters and weddell sea deep water wsdw contribute 2 and 3 sv respectively in contrast to this 3 sv more of weddell sea bottom water wsbw flow in the northern limb to the east than in the southern limb to the west which suggests a wsbw formation rate of about 3 sv in the western weddell sea in the southern boundary of the antarctic circumpolar current acc a volume transport of 35 16 sv was found using geostrophic calculations adjusted with two measurements of the absolute velocity the large heat content of the northern limb points to an extensive heat exchange between the weddell sea and the world ocean west of the prime meridian hence the heat transport as well as the volume transport suggest that the water masses of the weddell gyre are not exclusively replaced in its eastern part but that there is a significant exchange of water masses to the west of the prime meridian

tertiary ice sheet dynamics the snow gun hypothesis we observe strong negative correlation between tertiary low to mid latitude planktonic foraminiferal 18o and the difference between these data and coeval benthic foraminiferal 18o late quaternary data do not show this correlation coupling statistical model 18o comparisons and evidence for antarctic ice and ocean temperature variation we infer that tertiary ice volume recorded by tropical planktonic 18o increased as the deep ocean warmed because the isotopic signatures of deepwater temperature variation and ice volume change were of opposite sign the sum of these signals in tertiary benthic 18o became lost in the noise this renders low correlation between tertiary planktonic and benthic 18o time series compared to late quaternary data we contend that tertiary ice sheet growth was commonly driven by warming of deep water from low to mid latitude marginal seas snow gun hypothesis in contrast late quaternary ice sheets grew as deep water formed at high latitude cooled because tectonic forcing and orbital forcing at low latitude primarily controlled production and temperature variations of this warm saline deep water these influences largely dictated tertiary ice volume fluctuations through the tertiary we infer ice volume fluctuations to be an important component of sea level history on timescales between 103 and 107 years

reply to comments on magnetic properties of three segments of the mid atlantic ridge at 37 n famous narrowgate and amar amar 2 by nancy a van wagoner and h paul johnson

marine tectonics processes at mid ocean ridges the use of multibeam echo sounders and various side looking sonar systems has greatly increased our knowledge and understanding of mid ocean ridge mor processes since the last iugg review on mid ocean ridge research macdonald 1983 the extensive use of swath mapping tools such as sea beam deep tow seamarc i and ii the application of multichannel seismic reflection techniques to the detection of axial magma chambers and the use of satellite data in the study of oceanic lithosphere have rejuvenated marine tectonics and have generated and stimulated a large number of important contributions this review will focus on what we feel were the major developments in marine tectonics with an emphasis on mid ocean ridges in the last four years certain topics such as marine seismicity and satellite studies are only briefly mentionned for reference and will be covered in greater detail in other reviews because of the exponential growth in the number of publications related to mors during 1982 1986 only a few references pertinent to each of the major research topics will be quoted in the text as examples but the reader will find an extensive bibliography at the end of the text references published prior to 1982 were added only where appropriate

fronts transport and weddell gyre at 30 e between africa and antarctica a detailed description of the frontal structure of major currents and estimates of transport between africa and antarctica at 30 e were made on the basis of a finely resolved hydrographic section made during the 1996 civa 2 cruise particular emphasis was put on a refinement of the eastern boundary of the weddell gyre by analyzing also supplementary hydrographic data from the 1993 civa 1 cruise and the best available historical hydrographic data in the weddell and enderby basins contrary to the general belief our results show that the weddell gyre extends far beyond 30 e reaching at least as far east as the enderby land promontory 53 e from this point westward currents along the antarctic continental margin constitute the gyre s southern boundary thus closing the cyclonic circulation of the gyre at its easternmost end as the most convincing evidence for this refined circulation scheme significant westward transport south of 65 s has been identified from the civa 1 acoustic doppler current profiler data we have shown also using an inertial jet model that the blocked feature of the weddell cold regime 57 s to the west of 25 e is due to the topographic control of flow by local bathymetry during the civa 2 cruise 70 of the antarctic circumpolar current acc was concentrated near the polar front 51 s with surface speeds reaching up to 70 cm s 1 the baroclinic current field in the subpolar area south of the weddell front 58 s for civa 2 and 57 s for civa 1 is featureless 3 cm s 1 but yielding a nonnegligible eastward transport of 15 sv 1 sv 106 m3 s 1 this bottom referenced baroclinic transport is entirely compensated by a substantial westward barotropic transport south of 65 s the acc transport across the 30 e section during the civa 2 cruise is estimated to be 160 sv

diatom assemblages in surface sediments of the northwestern weddell sea antarctic peninsula a study of 42 surface sediment samples from the northwestern weddell sea documents the relationship between the modern distribution of diatom assemblages and present oceanographic conditions in the region three diatom assemblages were identified using r mode principal components analysis and cluster analysis while q mode cluster analysis was used to distinguish two geographically distinct biofacies based on the relative abundance of diatom species the biofacies of the former larsen a ice shelf lais is more closely associated with a sea ice diatom assemblage while the biofacies of the prince gustav channel northern peninsula pgc np is associated with two open coastal diatom assemblages this division is consistent with variance observed in the current oceanographic setting whereby the lais is generally characterized by a longer seasonal duration of sea ice coverage and lower primary productivity relative to the pgc np which is marked by a shorter seasonal duration of sea ice coverage and greater surface water productivity this relationship is further reflected in the distribution of the paleoenvironmentally significant diatom species fragilariopsis curta thalassiosira antarctica and chaetoceros subg hyalochaete spp as well as in absolute abundance data specifically f curta and the morphological form t antarctica t1 are representative of greater seasonal duration of sea ice coverage and lower productivity chaetoceros subg hyalochaete spp and the morphological form t antarctica t2 are associated with decreased seasonal duration of sea ice cover and greater surface water productivity a setting that is further reflected in high absolute diatom abundances these findings provide a basis for future paleoceanographic work in the region especially as studies of surface sediment diatom assemblages are vital to establishing a link between downcore diatom assemblages and those presently found in the water column

comments on magnetic properties of three segments of the mid atlantic ridge at 37 n famous narrowgate and amar amar 2 by nancy a van wagoner and h paul johnson

ocean heat flux in the central weddell sea during winter abstract seasonal sea ice which plays a pivotal role in air sea interaction in the weddell sea a region of large deep water formation with potential impact on climate depends critically on heat flux from the deep ocean during the austral winter of 1994 an intensive process oriented field program named the antarctic zone flux experiment measured upper ocean turbulent fluxes during two short manned ice drift station experiments near the maud rise seamount region of the weddell sea unmanned data buoys left at the site of the first manned drift provided a season long time series of ice motion mixed layer temperature and salinity plus a truncated high resolution record of temperature within the ice column direct turbulence flux measurements made in the ocean boundary layer during the manned drift stations were extended to the ice ocean interface with a mixing length model and were used to evaluate parameters in bulk expressions for interfacial stress a rossby similarity drag law and ocean to

the role of oscillating southern hemisphere westerly winds southern ocean coastal and open ocean polynyas abstractan oscillation in intensity of the southern hemisphere westerly winds is a major characteristic of the southern annular mode its impact upon the sea ice ocean interactions in the weddell and ross seas is investigated by a sea ice ocean general circulation model coupled to an energy balance model for three temporal scales and two amplitudes of intensity we find that the oscillating wind forcing over the southern ocean plays a significant role both in regulating coastal polynyas along the antarctic margins and in triggering open ocean polynyas the formation of coastal polynya in the western weddell and ross seas is enhanced with the intensifying winds resulting in an increase in the salt flux into the ocean via sea ice formation under intensifying winds an instantaneous spin up within the weddell and ross sea cyclonic gyres causes the warm deep water to upwell triggering open ocean polynyas with accompanying deep ocean convection in contrast to coastal polynyas open ocean polynyas in the we

variation of magnetic directions within pillow basalts abstract relative directions of magnetization have been measured within individual pillow basalts collected from the atlantic ocean and caribbean sea the angle between the magnetic directions was determined and is referred to as the directional difference although one pillow contained a directional difference of 44 the remaining ten pillows had differences less than 14 the maximum orientation and measurement error was 7 dispersion on the scale found in these fine grained pillow basalts would not appreciably affect the magnetic anomaly pattern on the sea floor we detected no reversals of magnetization despite the sometimes large and variable low temperature oxidation comparison of directions within homogeneous segments of the pillow viscous remanent magnetization vrm acquisition experiments and alternating field af demagnetization indicate a large portion of the dispersion was due to the acquisition of a viscous component in the larger grained less oxidized portion of the pillows evidence from one variably weathered pillow suggests that extreme low temperature oxidation may lead to the acquisition of a secondary component with high coercivities 20 80 mt we could not determine whether this was a chemical remanent magnetization crm or a vrm acquired by single domain grains near the superparamagnetic threshold hysteresis properties confirmed by microscopic examination indicated that the magnetic grain size in all the pillows was at least as small as pseudo single domain

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

water drag coefficient of first year sea ice in may 1977 eddy flux measurements of momentum were made with a three component ultrasonic current meter in the oceanic boundary layer under a first year floe of fast sea ice in barrow strait n w t by using eddy correlation methods values of horizontal reynolds stress were computed from each of 20 data runs of about 1 hour duration during which the mean current was reasonably steady a least squares analysis in which water stress was assumed proportional to the square of the mean current yielded a value for the 1 m water drag coefficient of 1 32 10 3 with a standard deviation of 0 06 10 3 the diameter of the floe was greater than 1 km and its mean thickness was 128 cm with a standard deviation of 4 cm and a maximum deviation of 7 cm

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

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

modern and late quaternary pollen spectra of fiord sediments eastern baffin island arctic canada abstract pollen spectra of thirty surface samples from baffin island fiords are dominated by abetula filicales cyperaceae gramineae association that is somewhat representative of local or regional vegetation however betula and filicales are over represented andsalix cyperaceae and ericales are under represented compared to their importance in the present vegetation two possible causes for this disparity related to the fluvial processes that furnish most pollen to fiords are 1 fluvial reworking of older sediment that contains abundantbetula and filicales and 2 greater resistance of these taxa to corrosion and degradation during fluvial transport the pollen stratigraphy of five piston cores from fiords contains two types of pollen assemblages in the lower portions of the cores exotic pollen types and pre quaternary palynomorphs are abundant the upper portions of the cores contain an assemblage roughly representative of the present vegetation in which cyperaceae and gramineae are abundant and exotic and pre quaternary types are reduced or absent the lower assemblage was deposited during the late glacial deglacial transition and deglaciation ca 12 000 to 6000 b p when eastern baffin island had little vegetation cover and long distance transport and reworking were virtually the only pollen sources a feature of several cores is a major peak in dinoflagellates about 5000 b p this event may be related to the postglacial marine climatic optimum in the eastern canadian arctic between 5000 and 3000 b p

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

antarctic sea ice microwave signatures and their correlation with in situ ice observations the general characteristics and microwave radiative properties of sea ice in the weddell sea region during the onset of spring are studied by using the nimbus 7 scanning multichannel microwave radiometer smmr and other satellite sensors in conjunction with in situ observations from the mikhail somov the position of the ice edge the gradient of ice concentration and the width of the marginal ice zone are inferred from the microwave data and are found to be consistent with ship observations especially at 18 ghz the sensitivities of the various smmr frequencies to surface and other effects are investigated by using multi spectral cluster analysis the results show considerable variability in emissivity especially at 37 ghz likely associated with varying degrees of surface wetness ice concentrations are derived by using two methods one that assumes fixed emissivities for consolidated ice and an iterative procedure that accounts for the variable emissivities observed by using the procedure that allows the emissivities to be variable gives ice concentrations that are more consistent with qualitative field observations

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

a study of the palaeomagnetism of subglacial basalts sw iceland a comparison with oceanic crust summary subglacial volcanic sequences in iceland were used as analogues of oceanic crust to get an indication of the degree of primary heterogeneity of magnetic directions that can be expected within subaqueous volcanic sequences erupted in both deep and shallow water in the icelandic sequences the degree 6f tilt brecciation and the amount of hyaloclastite are known so it is possible to test for primary magnetic heterogeneity we measured magnetic directions of 119 oriented core samples 2 5 cm diameter collected from five sites in sw iceland where there is good exposure in quaternary subglacial volcanic sequences sample sites vary from compact pillowed flows most analogous to deep water volcanic sequences to pillow breccia with up to 40 per cent interpillow hyaloclastite more analogous to shallow water sequences magnetic directions of multiple samples from 16 individual pillows have angular differences of 2 66 with most being less than lo of the five sites sampled two sites have inclinations that approximate that of the centred axial dipole one site has steeper inclinations and two sites have shallower inclinations when the site averages of magnetic direction with their circles of ag5 are plotted there is little overlap there is little correlation between either the scatter of magnetic measurements or the percentage of non dipolar inclinations and the occurrence of pillow breccias hyaloclastite or depositional dips we doubt the tectonic significance of small amounts of tilt 30 estimated from drill cores on the basis of palaeomagnetic inclination as it is not uncommon for rocks to rotate by as much as 30 after they cool through the curie temperature or for such a scatter to be the result of secular variation with this in mind the same caution must be applied when orienting seafloor basalts for palaeomagnetic or structural studies using geopetal features such as drain away ledges or segregation vesicles because the rocks may rotate after these features form at 1200 1000 c but before the rocks cool through the curie temperature