a 6 year record of baroclinic transport variability of the antarctic circumpolar current at 140 e derived from expendable bathythermograph and altimeter measurements 1 repeat hydrographic sections across the antarctic circumpolar current are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 dbar from temperature measurements with an error of a few per cent the mean transport distribution derived from 31 austral summer expendable bathythermograph xbt sections over a 6 year period consists of westward flow immediately south of tasmania a broad band of strong eastward flow between 50 and 55 s and three cores of eastward flow south of 55 s by defining a second empirical relationship between surface dynamic height and cumulative transport a continuous time series of baroclinic transport is derived from altimeter measurements of sea surface height transports derived from altimetry in this way agree well with simultaneous in situ estimates root mean square error in net transport is 4 106 m3 s 1 suggesting sea level anomalies largely reflect baroclinic changes above 2500 dbar the 10 day sampling of the altimeter transport time series shows the irregular xbt sampling aliases variability at unresolved timescales the standard deviation of net transport above and relative to 2500 m is 4 3 106 m3 s 1 the variability in net transport is largest 2 7 106 m3 s 1 in the quasi annual band periods of 4 months to 1 5 years slightly smaller 2 3 106 m3 s 1 in the mesoscale band 1 5 years 1 5 106 m3 s 1 changes in transport are correlated with local changes in both wind stress and wind stress curl in the quasi annual and interannual bands but the transport time series is too short to draw significant conclusions

paleoceanographic record of the last glacial interglacial cycle in the red sea and gulf of aden abstract hydrographic conditions in the red sea are strongly controlled by regional climatic conditions and the restricted water exchange with the gulf of aden indian ocean in turn intermediate and deep water masses in the gulf of aden reflect the nature of red sea outflow planktonic and benthic foraminiferal faunas and the lithology and mineralogy of red sea and gulf of aden sediments were studied in order to evaluate changes in water mass conditions in the two basins during the last 18 000 years the results indicate that changes in the local climate and circulation regime during this period resulted in significant hydrographic changes in surface and bottom waters in the red sea and intermediate waters in the gulf of aden during the last glacial maximum high aridity and glacio eustatic sea level lowering resulted in surface and bottom water salinities in the red sea which were considerably higher than at present in the gulf of aden glacial surface salinities and temperatures remained similar to holocene values while surface water productivity may have been lower surface salinities in the red sea decreased after 18 000 years b p as the connection between the red sea and gulf of aden was reestablished however bottom water salinities remained high until at least 11 000 years b p pluvial conditions during deglaciation enhanced the density difference between surface and bottom waters in the red sea and resulted in a decrease in the oxygen content of the bottom waters hydrographic conditions in the western gulf of aden reflect a change in the properties of outflowing red sea water during deglaciation

cycles steps and co2 paleoceanography in the united states from 1983 1986 the field of paleoceanography experienced continued growth during the last three years the first international conference on paleoceanography was held in zurich switzerland in july 1983 and a new journal devoted to the topic paleoceanography american geophysical union washington d c began publication in spring 1986 edited by dr james kennett of the university of rhode island nine legs of the r v glomar challenger concentrated upon paleoceanographic topics legs 71 75 in the south atlantic leg 81 in the north atlantic leg 85 in the equatorial pacific leg 86 in the northwest pacific and leg 90 in the southwest pacific several special symposia and conferences resulted in volumes of collected papers dealing with topics such as climate variability hansen and takahashi 1984 the global carbon cycle sundquist and broecker 1985 catastrophes and earth history berggren and van couvering 1984 orbital insolation and periodicity berger et al 1984 and coastal upwelling suess and thiede 1983 some very useful books have been published which summarize existing information on radiolaria anderson 1983 neogene planktonic foraminifera kennett and srinivasan 1983 calcareous nannofossils haq 1983 1984 and biostratigraphy bolli et al 1983

latest eocene early oligocene climate change and southern ocean fertility inferences from sediment accumulation and stable isotope data abstract the earliest oligocene 33 5 ma is marked by a major step in the long term transition from an ice free to glaciated world the transition characterized by both cooling and ice sheet growth triggered a transient but extreme glacial period designated oi 1 high resolution isotope records suggest that oi 1 lasted for roughly 400 000 yr the duration of magnetochron 13n before partially abating and that it was accompanied by an ocean wide carbon isotope anomaly of 0 75 one hypothesis relates the carbon isotope anomaly to enhanced export production brought about by climate induced intensification of wind stress and upwelling particularly in the southern ocean to understand how this climatic event affected export production in the southern ocean biogenic silica opal and carbonate accumulation rates were computed for the sub polar indian ocean using deep sea cores from odp site 744 kerguelen plateau our findings suggest that net productivity in this region increased by several fold in response to the oi 1 glaciation in addition calcareous primary producers dominant in the late eocene were partially replaced by opaline organisms suggesting a trend toward seasonally greater surface divergence and upwelling in this sector of the southern ocean we attribute these changes to intensification of atmospheric oceanic circulation brought about by high latitude cooling and the appearance of a full scale continental ice sheet on east antarctica higher terrigenous sediment accumulation rates support the idea that wind induced changes in regional productivity were augmented by an increased supply of glacial dust and debris that provided limiting micro nutrients e g iron rich dust particles we speculate that the rapid changes in biogenic sediment accumulation in the southern ocean and other upwelling dominated regions contributed to the ocean wide positive carbon isotope anomaly by temporarily increasing the burial rate of organic carbon relative to carbonate carbon the changes in burial rates in turn may have produced a positive feedback on climate by briefly drawing down atmospheric pco2

the enhanced geothermal system of soultz sous forets a study of the relationships between fracture zones and calcite content the enhanced geothermal system egs of soultz sous forets france is made of three boreholes gpk2 gpk3 and gpk4 the hydraulic connection between the wells which is crucial to get an efficient geothermal exchanger may be unfortunately hindered by the more or less complete sealing of fractures by hydrothermal neoformed minerals this paper takes over the recent work of the authors that quantified the amounts of calcite on a random sampling within the three boreholes in order to assess the role of this mineral on the exchanger zone and in particular its influence on the permeability of the flow pathways in the present study we focused the sampling on the fracture zones that have been identified as flow pathways now all the three wells show high above 10 wt and moderate to low between 2 0 and 7 0 wt calcite anomalies in gpk2 fracture zones with a high conductivity are characterized by high calcite content and those with a low conductivity by low calcite content the fracture zones of gpk3 show the opposite relationship the most efficient flow pathways have a low calcite content whilst the less conductive show a high calcite content fluid flow in gpk4 is mainly accommodated by the fracture zone at 4775 m md that is not calcite rich the other fracture zones of gpk4 which are interpreted with a similar and low conductivity show low moderate and high calcite contents these data show clearly that gpk2 is different from gpk3 and gpk4 these two later being more comparable it suggests that the fracture zones themselves may be of different type and that the connectivity to the fracture network may be different too this difference of behaviour is consistent with microseismicity data showing that gpk2 is characterized by a rather compact and well structured network of medium scale fracture whereas gpk3 and gpk4 are altogether characterized by more localized and discrete fracture zones some issues remain such as the occurrence of calcite anomalies with no evident relationship with fracture zones as well as the occurrence of identified flow pathways with no abnormal calcite content

distribution of oxygen isotopes in the water masses of drake passage and the south atlantic measurements of the ratio of stable isotopes of oxygen 18o and 16o from samples collected on world ocean circulation experiment sections sr1b eastern drake passage and a11 punta arenas to cape town are used together with hydrographic data to deduce information about the formation and variability of south atlantic and southern ocean water masses the drake passage surface waters south of the polar front pf are isotopically light 18o around 0 4 owing to the influence of meteoric waters the salinity and 18o of the a11 surface waters yield an apparent freshwater end member which is much isotopically lighter than the local precipitation thus advection of these waters from farther south dominates over local effects in determining the surface water properties the drake passage section shows unusual proximity of the two main fronts of the antarctic circumpolar current the pf and subantarctic front saf and we observe cold fresh and isotopically light water derived from the temperature minimum winter water at the saf this water is of the correct density to freshen the intermediate water north of the saf and thus play a role in the formation of the comparatively fresh antarctic intermediate water aaiw of the south atlantic this confirms the role of antarctic water in forming the south atlantic variety of aaiw across the a11 section the oxygen isotope and salinity data at the aaiw core show very similar traces with waters in the malvinas current loop showing lowest values of both at the eastern boundary of the south atlantic the input of red sea water from east of south africa is observed via the presence of anomalously isotopically heavy aaiw we deduce potentially significant temporal variability in the isotopic composition of weddell sea deep water wsdw by comparing the drake passage data to earlier data covering the outflow of the weddell sea the a11 data show wsdw consistent with such variability indicating that its effects could persist in the waters as they flow north into the western south atlantic we speculate that such variability could be due to small changes in the amount of glacial ice melt in wsdw

decadal variability of east australian current transport inferred from repeated high density xbt transects a ctd survey and satellite altimetry a time series of the net geostrophic transport through the tasman sea representing the flow of the east australian current eac extension is determined from a full depth ctd section 15 years of high density xbt transects and satellite altimetry data a section between sydney and wellington px34 has been occupied four times per year since 1991 with high resolution xbt sampling two methods to infer baroclinic transport from proxy data along the section are presented the first uses shallow xbt transects to derive geostrophic transport relative to a deep 2000 m reference level in the second approach synts the subsurface temperature and salinity structure are inferred from satellite surface height and temperature fields using a model developed from historical in situ observations the baroclinic transport is then computed in the usual manner the methods are validated using both a full depth ctd occupation of the px34 section and further transects crossing the eac in the northern tasman sea there is close agreement between the 49 xbt and synts px34 transport estimates obtained between 1992 and 2006 the time series of transport through the sydney wellington section shows a range of temporal signals from eddyscale seasonal interannnual to decadal in particular we note that the net eac flow ranges from 5 sv in 1995 to a maximum of 16 sv in 2000 2001 this decadal variation confirms the eac response to a spin up of the south pacific circulation forced by changes in the basin wide winds and matches the changes in oceanic properties observed in the tasman sea

wellbore reservoir coupled simulation to study thermal and fluid processes in a co2 based geothermal system identifying favorable and unfavorable conditions in comparison with water using co2 as a heat transmission fluid to extract geothermal energy is currently considered as a way to achieve co2 resource utilization and geological sequestration as a novel heat transmission fluid the thermophysical properties of co2 are quite different from those of water co2 has many advantages such as larger mobility and buoyancy resulted from the lower density and viscosity this will reduce the consumption of pressure driving the circulation and save the energy of external equipment the cycle even can be achieved by siphon phenomenon under a negative circulating pressure difference however there are still some disadvantages for co2 as the heat transmission fluid such as small heat capacity leading to a less heat at the same mass flow rate at the same time because of the lager expansion and compression coefficient for co2 changes in temperature and pressure may cause a more complex flow and thermodynamic processes the lager compressibility makes it possible to get high temperature at the bottom of the injection well whereas the lager expansion coefficient makes the temperature drop rapidly along the production well therefore how to scientifically control the production pressure to guarantee sufficient high temperatures at the head of production well and thereby improve the efficiency of heat extraction are the key issues needed to be further addressed the geological and geothermal conditions correspond to the central depression of the songliao basin located in the northest of china this depression has a high geothermal gradient and heat flow in this article a classic idealized five spot reservoir model coupled with wellbores is used for simulations and analyses the objectives of the present work are 1 to investigate the fluid flow and thermal processes of supercritical co2 along the wellbore and in the reservoir 2 to understand the heat extracting mechanism 3 to identify advantages and disadvantages of using co2 as the heat transmission fluid and 4 to provide a theoretical basis for the selection of heat transmission fluid

structural style and its relation to hydrocarbon exploration in the songliao basin northeast china the songliao basin in northeast china is a mesozoic rift basin characterized by mesozoic and cenozoic hydrocarbon systems the songliao basin was initiated by southeast to northwest lithospheric extension during the late jurassic the extensional phase was dominated by two fault sets l shallow to moderately dipping normal faults and 2 steeply dipping transfer faults the extensional structures are characterized by half grabens a second short extensional tectonic overprinting phase occurred during the early qingshankou early albian 100 to 97 ma faults that occur in the quantou formation and the qingshankou formation are growth faults t2 faults which trend mostly nnw and occur predominantly at the sites of basement faults and structural bend zones located between sag and uplift and basement uplifts the basin broadly subsided during the denglouku quantou aptian 125 to 100 ma and the late qingshankou late albian 97 to 94 ma to yaojia nenjiang cenomanian to campanian 94 to 73 ma respectively positive inverted structures developed during the late cretaceous to the cenozoic in the songliao basin these are classified into two types positive inversion structures controlled by reactivation of early normal faults and inversion structures not controlled by earlier faults the major extensional structures exerted a range of controls on both sedimentation and deformation during the subsequent phases of basin evolution two thermotectonic rifting events during the late jurassic and early qingshankou play a major role in organic matter thermal evolution the timing of formation of structural traps in the basin matches that of hydrocarbon generation and migration structural traps formed during late jurassic early qingshankou and late cretaceous to paleocene 73 to 56 ma late jurassic organic rich source rock reached its peak oil generation from the time of deposition of member deng 3 4 of the denglouku formation 119 to 116 ma to that of member qing 1 of the qingshankou formation 100 to 97 ma qing 1 of the qingshankou formation and nen 1 of the nenjiang formation organic rich source rocks reached their peak oil generation from the time of deposition of the upper mingshui formation to that of the upper yi an formation and from the time of deposition of the taikang formation to that of deposition of the quarternary respectively

quaternary carbonate record from the equatorial indian ocean and its relationship with productivity changes abstract the caco3 content in quaternary deep sea sediments from pacific and atlantic oceans have been suggested to respond differently to glacial interglacial cycles caco3 contents are highest during glacials in the pacific but highest during interglacials in the atlantic ocean it is not yet clear as to whether a pacific or an atlantic pattern of caco3 fluctuations dominates the indian ocean we have analyzed the ocean drilling program odp site 709a from the western equatorial indian ocean for the last 1370 ka to determine the relationships between percentages and fluxes of caco3 and quaternary paleoclimatic changes we also analyzed the coarse 25 m and fine 18 o of the planktonic foraminifera globigerinoides ruber this indicates that caco3 fluctuations at this site do not show either a pacific or an atlantic pattern of caco3 fluctuations fluxes of caco3 0 38 to 2 46 g cm 2 ka 1 in total sediment and ba al ratios 0 58 to 3 93 g cm 2 ka 1 show six fold variability through the last 1370 ka which points out that productivity changes are significant at this site fluxes of the fine caco3 component demonstrate a 26 fold change 0 02 to 0 52 g cm 2 ka 1 whereas the coarse caco3 component exhibit eight fold change 0 13 to 1 07 g cm 2 ka 1 this suggests that productivity variations of calcareous nannofossils are greater in comparison with the foraminifera on the other hand mean values of coarse caco3 fluxes are higher compared to those of fine caco3 which reveals that the foraminifera contribute more to the bulk caco3 flux than the calcareous nannofossils in the equatorial indian ocean

an equivalent barotropic mode in the fine resolution antarctic model abstract both the 6 year time mean flow and the eddy kinetic energy in the fine resolution antarctic model are found to be approximately self similar in the vertical with the velocity showing a rapid decay with depth a simple argument is given as to why this would be expected to occur in this and other numerical models and an analysis is given as to the degree of steering of the mean flow by topography

carbonate sedimentation beneath the antarctic circumpolar current during the late quaternary abstract calcium carbonate content and planktonic foraminiferal fragmentation have been studied in four late quaternary eltanin piston cores e48 22 e48 28 e49 18 and e49 23 taken from the southeast indian ridge between 3200 and 3400 m waterdepth beneath the antarctic circumpolar current the calcium carbonate records in the two southernmost cores e49 18 and e49 23 show distinct glacial interglacial cycles with the glacial intervals and intermediate cool intervals having low carbonate values relative to the interglacial times however the carbonate records of e48 22 and e48 28 are largely independent of the paleoclimatic records and may be influenced by input of volcanic ash from the st paul or amsterdam islands located less than 700 km upwind of the cores planktonic formainiferal fragmentation considered to be a dissolution index indicates that dissolution generally increased during glacial intervals relative to the interglacial intervals in e49 18 and e49 23 in e48 22 and e48 28 the dissolution records do not follow glacial interglacial patterns but instead dissolution was greatest during oxygen isotope stage 9 the stage 9 8 boundary the early part of stage 8 and during stage 7 no relationship exists between benthonic formainiferal changes and the fragmentation records in three cores e48 22 e48 28 and e49 23 indicating that deep water circulation changes had minimal or no influence on these dissolution records however in e49 18 the benthonic foraminiferal and the dissolution records are closely matched from oxygen isotope stages 12 to 5 t 440 000 120 000 yrs b p deep water circulation changes may have influenced the dissolution record in e49 18 or the two variables may be unrelated but may have independently responded to glacial interglacial climatic changes

an altimetry based gravest empirical mode south of africa 1 development and validation 1 hydrographic transects of the antarctic circumpolar current acc south of africa are projected into baroclinic stream function space parameterized by pressure and dynamic height this produces a two dimensional gravest empirical mode gem that captures more than 97 of the total density and temperature variance in the acc domain weekly maps of absolute dynamic topography data derived from satellite altimetry are combined with the gem to obtain a 16 year time series of temperature and salinity fields the time series of thermohaline fields are compared with independent in situ observations the residuals decrease sharply below the thermocline and through the entire water column the mean root mean square rms error is 0 15c 0 02 and 0 02 kg m 3 for temperature salinity and density respectively the positions of acc fronts are followed in time using satellite altimetry data these locations correspond to both the observed and gem based positions the available temperature and salinity information allow one to calculate the baroclinic zonal velocity field between the surface and 2500 dbar this is compared with velocity measurements from repeat hydrographic transects at the goodhope line the net accumulated transports of the acc derived from these different methods are within 1 3 sv of each other similarly gem produced cross sectional velocities at 300 dbar compare closely to the observed data with the rms difference not exceeding 0 03 m s 1 the continuous time series of thermohaline fields described here are further exploited to understand the dynamic nature of the acc fronts in the region and which is given by swart and speich 2010

variability of the antarctic circumpolar current transport through the fawn trough kerguelen plateau abstract the kerguelen plateau is a major topographic obstacle to the eastward flowing antarctic circumpolar current acc while approximately two third of the acc transport is diverted to the north most of the remaining flow engulfs in the fawn trough the only deep passage across the plateau as part of the track transport across the kerguelen plateau project three mooring lines of current meters were deployed in the fawn trough for one year in february 2009 underneath ground track 94 of the jason 2 satellite altimeter full depth ctd ladcp casts carried out during the deployment cruise were previously analyzed to provide a comprehensive description of the regional circulation featuring in particular a volume transport of 43 sv across the fawn trough park et al 2009 here we present a time series of the transport in the fawn trough estimated from current meter observations featuring a mean eastward transport of 34 sv possibly biased low by at most 5 sv and a root mean squared variability of 6 sv consistent with ladcp estimates 43 sv in february 2009 and 38 sv in january 2010 in addition we analyze to what extent the transport can be directly monitored from along track satellite altimeter data which would enable study of the variability of the fawn trough current from a now 20 year long archive the ability to reconstruct the flow from a limited set of moored instruments as well as from altimeter derived surface geostrophic velocity is further assessed from synthetic data extracted from a high resolution peri antarctic simulation while a canonical method to derive transport from altimetry previously applied to the malvinas current gives here unsatisfactory comparisons with in situ estimates an ad hoc approach using only the two northernmost mooring lines yields an estimate well correlated 0 8 with in situ transport at subseasonal time scales during the one year period of observations at interannual time scales however both methods provide significantly correlated 0 7 transport estimates suggesting that long term transport fluctuations across the kerguelen plateau can be confidently estimated from altimetry these consistently indicate a measurable impact of the outstanding 1997 1998 el nino southern oscillation enso event yielding an increase of the annual mean transport of 3 sv possibly with a one year lag the transport estimate based on the ad hoc approach is significantly correlated 0 6 with the southern annular mode sam index at interannual time scales suggesting that an intensification of the circumpolar winds drives an increase in the transport across the kerguelen plateau

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

circumpolar structure and distribution of the antarctic circumpolar current fronts 2 variability and relationship to sea surface height 1 in part 1 of this study we showed that the antarctic circumpolar current acc consisted of multiple fronts each of which was consistently associated with a particular contour of sea surface height ssh or approximate streamline in part 2 we have used maps of ssh to examine the variability of the acc fronts between 1992 and 2007 the ssh label associated with each frontal branch is nearly constant around the circumpolar belt the front labels are also nearly constant in time the bands of enhanced ssh gradient i e fronts occur along the same streamlines throughout the 15 year period of observations both short and long period changes of the ssh frontal labels of the acc are small based on a tight relationship between dynamic height and cumulative baroclinic transport of the acc the baroclinic transport variability of the individual branches of the acc is also expected to be small the major change in the total acc baroclinic transport occurs in the drake passage the streamline associated with the northern branch of the saf saf n does not pass through drake passage and the waters carried by this branch are not observed there instead the transport of the saf n turns north in the pacific to supply the export of water to the indian ocean north and south of australia strong eddy activity in the southeast pacific acts to dissipate the hydrographic signature of the saf n there in the atlantic the saf n reappears as the same streamline is again associated with enhanced ssh gradients to the east of the brazil malvinas confluence zone while the large changes in ssh have occurred in the southern ocean between 1992 and 2007 there are strong regional differences because the acc fronts are robustly associated with particular ssh contours the changes in ssh reflect shifts in the position of the acc fronts in the circumpolar average each of the acc fronts has shifted to the south by about 60 km the changes in ssh in the southern ocean are largely due to changes in ocean circulation rather than warming and freshening by atmospheric fluxes much larger changes in ssh are observed in some locations of the southern ocean particularly where the fronts interact with large scale topography the northern branch of the pf pf n near the kerguelen plateau is an extreme example where the pf n followed a path around the northern end of kerguelen plateau between 1992 and 1997 passed through the fawn trough after 2003 and oscillated between the two paths between 1997 and 2003

glacial terminations in the oxygen isotope record of deep sea cores hypothesis of massive antarctic ice shelf destruction abstract glacial terminations i and ii in the deep sea core foraminiferal oxygen isotope ratios though not similar in form are each characterized by a short interval of about 3 ka during which a large negative change occurred in the ratios after correcting for temperature effects we estimate that each change was equivalent to a glacial disintegration capable of causing a 50 60 m eustatic sea level rise in the termination i interval 16 13 ka b p the estimated equivalent sea level rise is much larger than that suggested by the best evidence of deglacial ice loss from the laurentide ice sheet which is thought to dominate pleistocene glacial ice volume changes moreover in termination ii about 125 ka b p the estimated equivalent sea level rise is much larger than that inferred from the stratigraphy of coral reefs and beaches on new guinea and other locations which suggests quite high sea levels for 10 ka prior to this termination to reconcile these severely conflicting lines of evidence we propose that the rapid negative isotope ratio changes were largely caused by the disintegration of massive floating antarctic ice shelves which masqueraded as land ice in the oceanic isotope ratios but which contributed no sea level change we propose that such shelves were formed when oceanic circulation changes in the north atlantic under glacial conditions greatly reduced the formation of relatively warmer north atlantic deep water and its injection into circumpolar antarctic regions and that the shelves disintegrated rapidly with the resumption of large scale formation of this deep water and its input into the antarctic we find that high sea levels in the 125 135 ka b p interval prior to termination ii which imply very little northern ice then are well supported by dated coral reef stratigraphy although these ages were not accepted by the climap study of the last interglacial ocean minimal northern ice volumes at that time imply that strong milankovitch summer insolation is not always required for northern deglaciation a promising additional deglacial mechanism is the prolonged viscous depression of the crust beneath the laurentide ice sheet combined with atmospheric oceanic circulation factors

linkage of north atlantic and southern ocean deep water circulation during glacial intervals the antarctic circumpolar current acc is one of the major current systems in the world ocean affecting circulation in all of the major ocean basins the acc flows eastwards around antarctica from the surface to 4 000 m depth with a transport on the order of 125 sverdrups1 deep sea benthic foraminifera from one piston core e49 18 from the south east indian ocean sector of the southern ocean were analysed to determine deep water mass circulation conditions within the acc during the late quaternary i report here that benthic foraminiferal faunal patterns closely match northern hemisphere ice volume changes shown by planktonic foraminiferal oxygen isotopic stratigraphy the glacial interglacial faunal oscillations are interpreted to reflect the presence of a deep water mass in the acc during glacial times which differs from modern circumpolar deep water i suggest that deep water circulation changes within the acc during the interval 440 000 to the present are directly linked to changes in north atlantic deep water nadw circulation

sedimentation processes on the antarctic continental margin at kapp norvegia during the late pleistocene sedimentological analyses concerning ice rafted debris grain size distribution biogenous components and clay mineral composition of four sediment cores from the antarctic continental margin off kapp norvegia reveal a cyclical pattern of three different sediment facies these are classified into warm and cold types representing warm and cold a climatic periods and short transition period from cold to warm events

monitoring drake passage with elephant seals frontal structures and snapshots of transport conductivity temperature pressure satellite relay data loggers ctd srdls were attached to southern elephant seals mirounga leonina on the island of south georgia during the animals migration the ctdsrdls recorded and transmitted hydrographic profiles at a rate of approximately two profiles per day to an average depth of about 547 m representing transect type sections with a spatial resolution of 16 47 km along the migratory routes of the seals two sections are used to clearly identify the locations of the antarctic circumpolar current fronts across drake passage providing in situ data complementary to satellite and other techniques an empirical relationship between upper ocean temperature and baroclinic mass transport is used to determine the transport through drake passage at the times of the sections and these transports are compared with estimates derived by other techniques an absolute geostrophic velocity section across drake passage is calculated using ctd srdl data and data of absolute geostrophic surface velocities from altimetry the mean total baroclinic transports in june 2004 and april 2005 are estimated to be 124 3 106 6 14 3 106 m3 s21 and 112 3 106 6 14 3 106 m3 s21 respectively

eocene oligocene paleoceanography in the antarctic ocean atlantic sector maud rise odp leg 113 site 689b and 690b abstract middle eocene to late oligocene sediments from near the crest site 689b water depth 2080 m and flank water depth 2914 m of the maud rise 62 s have been investigated by coarse fraction analysis and have revealed the following 1 1 the middle eocene 50 40 ma was a period of pure carbonate sedimentation with good preservation of carbonate microfossils no opal 40 m is present 2 2 in the late eocene 40 36 5 ma opal fossils mainly radiolaria and some diatoms 40 m appeared for the first time three maxima in opal sedimentation eocene oligocene boundary middle early oligocene and early late oligocene boundary are separated by increases in carbonate sedimentation the dissolution of carbonate fossils is strong in the opal rich layers opal sedimentation is attributed to cooling and probably more vigorous atmospheric circulation and increased upwelling 3 3 carbonate dissolution increased with water depth in the oligocene whereas in the middle eocene excellent carbonate preservation in the deeper site 690b and stronger dissolution in the shallower site 689b is attributed to different bottom water characteristics the middle eocene bottom water probably was formed by strong evaporation at low latitudes whereas by the earliest oligocene formation of antarctic bottom water aabw had set in 4 4 current influence not on top but on the flank of the maud rise could be recorded by means of larger grain sizes of benthonic and planktonic microfossils 5 5 ice rafted debris was not found quartz and other minerals are very rare and not larger than 125 m and may have been supplied by ice as well as by wind or by deep currents mica contents were up to 10 times higher in the middle eocene on the flank compared to on the crest of the maud rise indicating deep current supply

bottom current speed in the vema channel recorded by particle size of sediment fine fraction abstract the particle size distribution of the carbonate free silt fraction was determined in forty two core top samples from the east flank of the vema channel in order to allow comparison of the mean particle size with near bottom current speed based on nearby ctd and current meter observations the silt mean particle size fluctuates insignificantly between 1450 3950 m but coarsens markedly below 4000 m under antarctic source bottom currents the top of the zone of coarse sizes approximates the top of lower circumpolar water lcpw at 4000 m the steep gradient to coarsest sizes in the axis of the channel marks the transition to antarctic bottom water aabw the vertical profile of mean particle size on the east flank correlates in general respects with the vertical velocity gradient in the channel axis although the core sites on the east flank are as far as 200 miles from the current meter arrays nevertheless this relationship is used to infer that the non carbonate particle sizes deposited on the east flank of the channel may be an indication of bottom current speed and therefore the mean size is used to reconstruct profiles of mean current speed for three time slices 18 120 and 140 ka b p during glacial isotopic stages 2 and 6 the particle sizes deposited on the east flank of the channel are characterized by finer sizes at nearly all depths and the zone of coarse sizes corresponding to lcpw and aabw deepens during interglacial isotopic stage 5e the particlesize profile is very similar to the modern profile however lcpw and aabw appear to be deeper than at present the finer particle sizes deposited at nearly all depths during glacial periods indicates that the velocity of deep circulation in the atlantic was reduced in response to the ice ages deep circulation during isotopic stage 5e closely resembled modern circulation however aabw production rates may have been less that at present

geochemistry of natural gases in deep strata of the songliao basin ne china chemical composition and stable carbon isotopic studies were undertaken for 27 gas samples from deep strata of the xujiaweizi depression in the songliao basin to investigate their origin gas molecular and carbon isotopic compositions show great variety methane is the main component for all studied samples and its content ranges from 57 4 to 98 2 with an average of 90 1 gas wetness ranges from 0 8 to 16 7 with an average of 2 7 the main non hydrocarbon gases are carbon dioxide and nitrogen with an average of 4 0 and 3 2 respectively carbon isotope data suggest that these deep strata gases are mainly coal type gases mixed with minor amounts of associated oil type gases coal type gases are characterized by heavier carbon isotopic values and drier chemical compositions these gases were generated from the lower cretaceous shahezi formation coals interbedded shales with type iii kerogen during the postmature stage of hydrocarbon generation oil type gases are characterized by lighter carbon isotope and higher wetness which were generated from the lower cretaceous shales with type ii kerogen in the shallow strata during the early mature stage of hydrocarbon generation mixing of two different gases causes unusual carbon isotopic distribution patterns with lighter isotopic values in higher numbered carbons in most gases the discovery of coal type gases in the songliao basin provides new prospects for the exploration in this region

foraminifera distribution of provinces in the gulf of mexico recent benthic foraminifera distribution patterns form the basis of much palaeoenvironmental particularly palaeobathymetric interpretation used by geologists we have recently summarized the distribution of recent benthic foraminifera on the atlantic continental margin of north america1 2 and report here the results of an analysis of all published data from the gulf of mexico to obtain a synthesis of foraminiferal distribution in the gulf of mexico a computerized catalogue of all published occurrences presence or absence data was compiled cluster analysis of these data isolated four large marginally overlapping areas or provinces exhibiting a spatial correlation with gulf of mexico water masses a fifth smaller discrete area biofacies was found at the mouth of the mississippi delta

application of the geomechanical facies approach and comparison of exploration and evaluation methods used at soultz sous forets france and spa urach germany geothermal sites earth reservoirs are increasingly exploited today with the extraction of resources such as heat and hydrocarbons and the large scale emplacement of waste such as co2 sequestration the characterization site investigation predictive modeling and long term monitoring are dependent on the processes being investigated and modeled in most cases complex coupled processes have to be addressed in a geologically complex rock mass system in this paper we present a conceptual holistic framework known as geomechanical facies linking all the scales of investigation characterization and reservoir development methods we demonstrate this concept on the work undertaken during the design and development of the enhanced geothermal systems egs systems at the forefront of european hot dry rock hdr technology soultz sous forets france and spa urach germany soultz sous forets is situated within granitic rocks and an active tectonic graben system in the central part of the rhine graben it presents conditions of lithology temperature stress hydraulics and geochemistry that are very different from those at spa urach located in a very dense gneiss formation in the south german crystalline complex spa urach exhibits more elastic behavior and is set tectonically within an almost inactive strike slip stress field described in more detail in sects drill core analysis and hydraulic stimulation at spa urach this paper compares the exploration and field development methods used at these two sites against the back drop of the geomechanical facies concept issues addressed include the key parameters for flow and heat transport properties coupled hydro mechanical process identification the success of the hdr reservoir as a heat exchanger and exploration techniques applicable to the different facies identification of the key geomechanical facies gives an indication as to which technologies will prove more efficient in the application of hdr technology the results of this study will hopefully help in developing heat recovery schemes for the long term economical operation of future hdr plants and egs as well as assist in the understanding of engineered geosystems

upper ocean temperature and the baroclinic transport stream function relationship in drake passage repeat hydrographic sections across the antarctic circumpolar current acc in drake passage are used to derive an empirical relationship between upper ocean temperature and the baroclinic transport stream function cross validation shows this relationship can be used to infer baroclinic transport above and relative to 2500 m from expendable bathythermograph xbt temperature measurements with an error of a few per cent transport errors of less than 2 sv are obtained if temperature at depths between 600 and 1600 m is used to define the relationship temperature at depths above 300 m provides an unreliable index of transport because of variability in temperature salinity t s properties produced by air sea interaction the scatter in the relationship between temperature and stream function from repeat observations along a single line is similar in magnitude to the scatter observed when data from the broader drake passage area are considered in both cases variability about the mean temperature stream function relationship reflects advection of water with anomalous t s properties the tight relationship between temperature and stream function in drake passage and south of australia suggests baroclinic transports can be inferred from xbt temperatures with high accuracy in the southern ocean providing a cost effective means of monitoring acc variability however care must be taken at the end points particularly in the drake passage where the strong flow of the subantarctic front sometimes lies over the continental slope

a two dimensional gravest empirical mode determined from hydrographic observations in the subantarctic front abstract south of australia where the baroclinicity in the subantarctic front extends almost to the seafloor the geopotential height of the sea surface and the vertical acoustic travel time exhibit a tight empirical relationship to each other and to the entire vertical structure of temperature t p salinity s p and specific volume anomaly p measurements of provide proxy estimates of the profiles tg p sg p and g p based on a two dimensional gravest empirical mode gem representation of the vertical structure fitted to 212 hydrographic stations a seasonal model was fitted in the near surface layers using additional historical data at each depth in the range 150 3000 dbar more than 96 of the variance in both the t and fields is captured by the gem representation during the subantarctic flux and dynamics experiment mar 1995 mar 1997 inverted echo sounders ies and current meters were moored in a 2d array along the woce sr3 transect south of australia at each i

a circumpolar gravest empirical mode for the southern ocean hydrography historical hydrographic data from the southern ocean are projected into a baroclinic stream function space generating a three dimensional gravest empirical mode gem parameterized by pressure geopotential height and longitude the low dimensional gem projection is intrinsically steady vertically coherent and equivalent barotropic the gem fields capture more than 97 of the total density and temperature variance in the antarctic circumpolar current region

a study on the interaction of mud acid with rock for chemical stimulation in an enhanced geothermal system in order to explore the thermal energy from the low permeability hot dry rocks both thermal and shear stimulations were employed to create connective fracture networks that allow fluid flow in the reservoir which is the concept of enhanced geothermal system egs however strong hydraulic stimulation may lead to preferential short circuiting flow paths where the fluid transports too fast to take in sufficient heat from the reservoir to solve this problem the chemical stimulation was proposed recently which injects aqueous chemical agents such as acids into reservoir to enlarge the fractures by dissolving the minerals in the rocks this study examines in the laboratory the effects of using mud acid to enhance the permeability of the rock cores that were recovered from yingcheng formation in songliao basin china the results suggest that the permeability in the core increases with the injection rate of the mud acid the core scanning electron microscope analysis shows that the increase in permeability is mainly induced by the dissolution of k feldspar and albite secondary amorphous silica was formed due to the acid rock interaction the chemical stimulation in the laboratory can be reproduced by reactive transport simulation the experimental and numerical studies confirmed that the injection of mud acid allows the permeability enhancement during field chemical stimulation for an egs reservoir

changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode 1 we present the first direct evidence that interannual changes in ocean transport through drake passage are forced by variability in the southern annular mode sam this evidence is derived from two decades 1980s and 1990s of subsurface pressure measurements from the tide gauge at faraday station western antarctic peninsula combined with the output of an ocean general circulation model in recent decades the sam has moved toward a higher index state stronger circumpolar winds this trend is not simply monotonic but is the product of a long term change in the seasonality of the sam whilst we cannot address directly the effect of the long term trend on circumpolar transport bottom pressure data from drake passage during the 1990s demonstrate that ocean transport showed the same changes in seasonality as did the sam this offers a mechanism for atmospheric climate change to influence directly the largescale ocean circulation indexterms 4207 oceanography general arctic and antarctic oceanography 4215 oceanography general climate and interannual variability 3309 4532 oceanography physical general circulation 1635 global change oceans 4203 4556 oceanography physical sea level variations citation meredith m p p l woodworth c w hughes and v stepanov 2004 changes in the ocean transport through drake passage during the 1980s and 1990s forced by changes in the southern annular mode geophys res lett 31 l21305 doi 10 1029 2004gl021169

productivity of the glacial ocean discussion of the iron hypothesis an increase in the productivity of the glacial age southern ocean has been postulated to explain the decrease in pc0 of the atmosphere observed in ice cores a plausible mechanism has been proposed elsewhere that productivity is limited by the availability of fe in this region and that the greater supply of eolian dust during glacial time removed this limit recently published evidence from cores from the southern ocean suggests that in fact there was no change in productivity in the assumed manner glacial age productivity was indeed greatly increased in the equatorial pacific and in the eastern boundary upwelling systems the cause presumably was the mechanical action of glacial age winds rather than a greater supply of fe however a role of increased supply of micronutrients from the continents in the increase of equatorial productivity during glacial time cannot be excluded such enhancement from increased supply of dust would have the interesting corollary of more efficient export transfer to depth possibly contributing to nutrient depletion in glacial age deep intermediate waters there is some indication as well of a general decrease in nutrient content in the tropical thermocline in the western pacific during the last several million years a depletion that may have been fostered by increasing supply of dust from emerging asian highlands alternative explanations are available the case for fe as a major modifier of productivity and biogenic sedimentation on geological time scales cannot be made in the absence of criteria diagnostic for fe supply as opposed to stirring and upwelling

monitoring the transport of the antarctic circumpolar current at drake passage abstract data from an extensive moored instrument array and three hydrographic cruises are used to calculate a time series of the net transport through the upper 2500 m of the drake passage the baroclinic geostrophic transport was monitored with heavily instrumented moorings at each side of the passage pressure gauge measurements at the northern and southern ends of the passage provided a reference speed at 500 m to adjust the relative transport the net transport of the upper 2500 m for the 370 day record ending in january 1980 averaged 121 106 m3 s 1 the total transport through the entire cross sectional area of drake passage is probably between 118 and 146 106 m3 s 1 fluctuations in the relative transport are related to changes in latitude of the northernmost front in the passage the subantarctic front variability of the net transport is coherent with the zonally averaged eastward wind stress

transport and variability of the antarctic circumpolar current in drake passage the baroclinic transport of the antarctic circumpolar current acc above 3000 m through drake passage is 107 3 10 4 sv and has been steady between 1975 and 2000 for six hydrographic sections 1993 2000 along the world ocean circulation experiment woce line sr1b the baroclinic transport relative to the deepest common level is 136 7 7 8 sv the acc transport is carried in two jets the subantarctic front 53 10 sv and the polar front pf 57 5 5 7 sv southward of the acc the southern antarctic circumpolar current transports 9 3 2 4 sv we observe the pf at two latitudes separated by 90 km this bimodal distribution is related to changes in the circulation and properties of antarctic bottom water three realizations of the instantaneous velocity field were obtained with lowered adcps from these observations we obtain near bottom reference velocities for transport calculations net transport due to these reference velocities ranges from 28 to 43 sv consistent with previous estimates of variability the transport in density layers shows systematic variations due to seasonal heating in near surface layers volume transport weighted mean temperatures vary by 0 40 c from spring to summer a seasonal variation in heat flux of about 0 22 pw finally we review a series of papers from the international southern ocean studies program the average yearlong absolute transport is 134 sv and the standard deviation of the average is 11 2 sv the error of the average transport is 15 to 27 sv we emphasize that baroclinic variability is an important contribution to net variability in the acc

response of deep sea benthic foraminifera to late quaternary climate changes southeast indian ocean offshore western australia the late quaternary benthic foraminifera of four deep sea cores off western australia odp 122 760a odp122 762b bmr96gc21 and rc9 150 have been examined for evidence of increased surface productivity to explain the anomalously low sea surface paleotemperatures inferred by planktic foraminifera for the last and penultimate glaciations the 13c trends ofcibicidoides wuellerstorfi and differences between the 13c trends of planktics globigerinoides sacculifer and benthicsc wuellerstorfi in the four cores indicate that during stage 6 bottom waters were significantly depleted in 13c and strong 13c gradients were established in the water column while during stage 2 and the last glacial maximum 13c trends did not differ greatly from that of the holocene two main assemblages of benthic foraminifera were identified by principal component analyses one dominated byuvigerina peregrina another dominated byu proboscidea abundance of these uvigerinids and of taxa preferring an infaunal microhabitat and ofepistominella exigua andbulimina aculeata indicate that episodes of high influx of particulate organic matter were established in most sites during glacial episodes and particularly so during stage 6 while evidence for upwelling during the last glacial maximum is less strong the penultimate glaciation upwellings were established within the areas of low sea surface paleotemperature indicated by planktic foraminifera during the last interglacial climax upwelling appears to have been established in an isolated region offshore from a strengthened leeuwin current off north west cape last glacial maximum 13c values ofc wuellerstorfi at waterdepths of less than 2000 m show smaller than global mean glacial interglacial changes suggesting the development of a deep hydrological front a similar vertical stratification bathyal front was also established during the penultimate glaciation

paleo oceanography global ocean evolution paleoceanography one of the youngest branches of earth sciences is concerned with the development of oceanic circulation through geologic time this is a multifaceted and integrated endeavor since none of the subdisciplines is easily separated from the others the field is holistic in character and includes the history and effects of bottom intermediate and surface circulation patterns planktonic and benthonic biogeographic development and rates of organic evolution the history of biogenic productivity and dissolution and their effect on sediment distribution and the consequences of sea level change paleoceanography was largely born of the deep sea drilling project dsdp and continues to be nourished by it because problems are of global scope the appetite for new sediment core material is large and is being supplied by numerous expeditions of dsdp this article is a brief overview of a number of advances that have occurred in paleoceanography and related fields during the period from 1979 to 1982 because of page limitations all publications cannot be cited which is not meant to indicate any lack of importance

late quaternary caco3 production and preservation in the southern ocean implications for oceanic and atmospheric carbon cycling recent geochemical models invoke ocean alkalinity changes particularly in the surface southern ocean to explain glacial age pco2 reduction in such models alkalinity increases in glacial periods are driven by reductions in north atlantic deep water nadw supply which lead to increases in deep water nutrients and dissolution of carbonate sediments and to increased alkalinity of circumpolar deep water upwelling in the surface southern ocean we use cores from the southeast indian ridge and from the deep cape basin in the south atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by circumpolar deep water this suggests that deep southern ocean carbonate ion concentrations were lower in glacial stages than in interglacials rather than higher as suggested by the polar alkalinity model broecker and peng 1989 our observations show that changes in southern ocean caco3 preservation are coherent with changes in the relative flux of nadw suggesting that southern ocean carbonate chemistry is closely linked to changes in deepwater circulation the pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient depleted water nadw to the southern ocean and with an increase of nutrients in deep water masses carbonate mass accumulation rates on the southeast indian ridge 3200 3800 m and in relatively shallow cores 3000 m from the kerguelen plateau and the south pacific were significantly reduced during glacial stages by about 50 the reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in caco3 corg flux ratios acting as another mechanism which would raise the alkalinity of southern ocean surface waters the polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant even if overall productivity in the southern ocean were held constant a decrease in the caco3 corg ratio would result in increased alkalinity and reduced pco2 in southern ocean surface waters during glacials this ecologically driven surface alkalinity change may enhance deepwater mediated changes in alkalinity and amplify rapid changes in pco2

the subantarctic and polar fronts in relation to deep water masses through the southwestern atlantic the two principal fronts within the antarctic circumpolar current acc the subantarctic front saf and the polar front pf are investigated with respect to their spatial patterns and relations to deep water masses from the northern drake passage to the western and southern argentine basin observations from four recent cruises in adjoining and overlapping regions are supplemented with satellite infrared imagery and trajectories from surface drifters east of drake passage the width of the polar frontal zone pfz increases rapidly when the saf turns sharply northward as a part of the falkland malvinas current while the pf remains oriented mainly toward the northeast found within this region of the pfz are mesoscale eddies the upper layers of which consist of subantarctic mode water from the pacific the contrasts in upper layer water properties that identify the saf can be traced the entire length of the falkland current to the brazil falkland confluence zone and then southward to the southern argentine basin there the saf turns eastward and later but perhaps not always merges with the pf north of ewing bank to form a single intense current core strongly influenced by bottom topography at times this eastward current loops southward through a gap in the falkland ridge into the georgia basin thereby supplying relatively warm and salty subantarctic water to the antarctic zone east of the gap the two fronts become separated and are once again distinct features in the vicinity of the islas orcadas rise at depth within drake passage and the western scotia sea the saf and pf are not lateral boundaries between distinct water masses but are instead identified by enhanced vertical displacements of property isopleths with the northward turn of the saf east of drake passage a thick layer of circumpolar deep water cdw is advected over the falkland plateau into the argentine basin there it is joined by waters entering the argentine basin via a deep spreading route through the georgia basin denser cdw deep water from the weddell sea and episodically deep water from the southeastern pacific ocean together these waters form a northward flow off the patagonian shelf that extends from the sea surface to the bottom most of which turns back toward the south with the falkland current return also flowing south along the seaward side of the falkland current return well away from the western boundary is the main core of north atlantic deep water nadw detatched masses of nadw are observed within the cdw at the western boundary as well as within the acc south of the saf in the south central argentine basin

the baroclinic transport of the antarctic circumpolar current south of africa five hydrographic transects at nominal longitudes 0 e and 30 e and fourteen expendable bathythermograph xbt sections near the former longitude are used to study the baroclinic transport of the antarctic circumpolar current acc between africa and antarctica the bottom referenced geostrophic transport between the subtropical front and the acc southern boundary is 147 10 sv estimating the transport from the xbts using a technique previously employed south of australia proves delicate because of an irregular bathymetry and water mass variations it nevertheless confirms acc transports around 150 sv gathering these and other estimates from the atlantic sector suggests that while north atlantic deep water is injected in the current west of 35 w a partially compensating loss of deep circumpolar water occurs east of this longitude another transport increase from 0 e to 30 e might reflect southward transfer across the subtropical front south of the agulhas retroflection

carbonate dissolution and abyssal hydrography in the atlantic ocean abstract surface sediment samples from two regions in the eastern atlantic angola basin and cape verde basin and two regions in the western atlantic brazil basin and vema channel were examined to evaluate the relationship among carbonate dissolution abyssal hydrography and carbonate chemistry of the water column at each of these locations the position of the lysocline was determined carbonate saturation 1 was calculated and major deep water mass boundaries were identified as previously observed the correlation among these variables is strikingly different between the eastern and western atlantic in the vema channel and the brazil basin there is a first order correlation among the position of the lysocline the benthic thermocline aabw nadw boundary and the transition from saturation to undersaturation with respect to carbonate this relationship breaks down in the eastern atlantic where there is no noticeable benthic thermocline and the lysocline occurs significantly deeper than the saturation undersaturation transition

volume transport of the antarctic circumpolar current from bottom pressure measurements abstract meausrements from bottom pressure gauges located at the north and south sides of drake passage are used to extend the one year time series of volume transport of the antarctic circumpolar current acc given previously by whitworth a small error in that paper is corrected and a revised transport time series is presented which shows the importance of including the transport in the northern and southern margins of drake passage direct measurements of vertical shear averaged across the passage are in good agreement with geostrophic shear and suggest that the acc is in geostrophic balance although most of the acc transport is in the baroclinic field transport fluctuations are mainly barotropic transport estimates based on pressure difference alone differ from the estimates of whitworth by less than 10 106 m3 s 1 fluctuations in transport of almost half of the mean value occur over periods as short as two weeks