stability of the atlantic meridional overturning circulation and stratification in a zonally averaged ocean model effects of freshwater flux southern ocean winds and diapycnal diffusion the atlantic meridional overturning circulation amoc is a crucial component of the global climate system in this study using a zonally averaged ocean model we reexamine the sensitivity of this circulation and ocean density structure in general to several types of external forcing the basin of the model extends from northern high latitudes to antarctica and includes an implicit representation of a circumpolar channel in the south and ocean circulation is driven by surface buoyancy fluxes and wind forcing in contrast to earlier two dimensional studies of the amoc our approach involves a careful treatment of the residual mean circulation comprising the eulerian mean and eddy induced flows which is especially important for the southern ocean dynamics using boundary conditions consistent with present day observations the model reproduces realistic ocean stratification and meridional overturning the structure intensity and stability of the overturning are then extensively studied using three control parameters the strength of westerly wind stress over the southern ocean the magnitude of freshwater fluxes imposed on the northern atlantic and ocean diapycnal diffusivity in a realistic parameter range we estimate the amoc sensitivity to changes in the southern ocean winds on the order of 1 sv per 20 increase in the wind stress the overturning also increases with diapycnal diffusivity but the dependence is weaker than in the absence of the winds the model can undergo a shutdown of the overturning subject to a hysteresis when either the freshwater forcing gradually increases or the wind stress decreases the hysteresis loop disappears for large values of isopycnal diffusivity changes in the amoc intensity are accompanied by changes in the volume transport of the antarctic circumpolar current specifically the amoc collapse leads to a strengthening of this transport ultimately our calculations produce stability maps for the steady states of the meridional overturning circulation and provide a general framework that potentially can be used to compare different models or to understand past abrupt climate changes related to reorganization of the amoc

mountain ranges favour vigorous atlantic meridional overturning 1 we use a global ocean atmosphere general circulation model oagcm to show that the major mountain ranges of the world have a significant role in maintenance of the atlantic meridional overturning circulation amoc a simulation with mountains has a maximum amoc of 18 sv 1 sv 106 m3 s 1 compared with 0 sv for a simulation without mountains atlantic heat transport at 25 n is 1 1 pw with mountains compared to 0 2 pw without the difference in amoc is due to major changes in surface heat and freshwater fw fluxes over the atlantic in the pacific changed surface fluxes lead to a meridional overturning circulation of 10 sv our results suggest that the effects of mountains on the large scale atmospheric circulation is to force the ocean towards a state with a vigorous amoc and with no overturning in the pacific

three dimensional simulation and inversion of borehole temperatures for reconstructing past climate in complex settings 1 the majority of inversion methods used for inferring past ground surface temperatures gst from borehole temperature depth profiles rely on the assumption that heat flow is in the vertical direction only this means that accounting for certain effects caused by the local terrain of a borehole is not possible and consequently many borehole profiles cannot be used with confidence here we describe a methodology to avoid this problem by solving the heat conduction forward problem in 3 d using finite elements fe in order to make the inversion approach computationally tractable we reduce the dimensions of this fe model using proper orthogonal decomposition the inverse problem is cast in a probabilistic bayesian framework for which the posterior probability distribution of the past gsts is sampled using a reversible jump markov chain monte carlo algorithm this allows the resolution of the gst history over time to be explored by varying the parameterization of the gst model synthetic examples calculated with moderate topographies demonstrate the efficacy of the bayesian 3 d inversion method and the results are compared with those using a 1 d approach for moderate topography the latter can lead to spurious gst reconstructions a further synthetic example demonstrates that the effect of incorrectly assuming lateral geological homogeneity is negligible the inversion method is also compared with a more standard inversion method a significant advantage of the bayesian approach is that uncertainties in all of the model parameters can be accounted for leading to a more realistic interpretation of the range of gst histories supported by the data the methods presented here should allow a broader range of geothermal data to be used for paleoclimate reconstruction purposes in the future

effect of ocean gateways on the global ocean circulation in the late oligocene and early miocene 1 we investigate the effect of changes in the tectonic boundary conditions on global ocean circulation patterns using a fully coupled climate model in an idealized setup we compare situations corresponding to the late oligocene the early miocene and present day the model results show the existence of a flow reversal through the panama seaway between the oligocene and miocene this flow reversal is induced by global tectonic changes related to the widening of the southern ocean passages and the closing of the tethys seaway it mainly involves the wind driven ocean circulation in agreement with previous model studies the global thermohaline circulation in the oligocene and miocene simulations is significantly different from the present day conveyor circulation as there is deepwater formation in both the north atlantic and the north pacific oceans in particular in the oligocene simulation the salinity contrast between the atlantic and pacific oceans is reduced because of water mass exchange through the low latitude connections between the two oceans

significance of a midlatitude sst frontal zone in the formation of a storm track and an eddy driven westerly jet abstract in a set of idealized aquaplanet experiments with an atmospheric general circulation model to which zonally uniform sea surface temperature sst is prescribed globally as the lower boundary condition an assessment is made of the potential influence of the frontal sst gradient upon the formation of a storm track and an eddy driven midlatitude polar front jet pfj and on its robustness against changes in the intensity of a subtropical jet stj in experiments with the frontal midlatitude sst gradient as that observed in the southwestern indian ocean transient eddy activity in each of the winter and summer hemispheres is organized into a deep storm track along the sst front with an enhanced low level baroclinic growth of eddies in the winter hemisphere another storm track forms just below the intense stj core but it is confined to the upper troposphere with no significant baroclinic eddy growth underneath the near surface westerlies are strongest near the midlatitude sst front as observe

a diagnostic indicator of the stability of the atlantic meridional overturning circulation in ccsm3 a diagnostic indicator dmov is proposed in this paper to monitor the stability of the atlantic meridional overturning circulation amoc the dmov is a diagnostic for a basinwide salt advection feedback and defined as the difference between the freshwater transport induced by the amoc across the southern border of the atlantic ocean and the overturning liquid freshwater transport from the arctic ocean to the north atlantic as validated in the community climate system model version 3 ccsm3 for an amoc in the conveyor state a positive dmov freshwater convergence in the atlantic basin indicates a monostable amoc and a negative dmov freshwater divergence indicates a bistable amoc based on dmov the authors investigate the amoc stability in the last glacial maximum lgm and analyze the modulation of the amoc stability by an open closed bering strait moreover the authors estimate that the real amoc is likely to be bistable in the present day since some observations suggest a negative dmov freshwater divergence is currently in the atlantic basin however this estimation is very sensitive to the choice of the observational data

atlantic pacific seesaw and its role in outgassing co2 during heinrich events 1 paleoproxy records indicate that a marked weakening of the atlantic meridional overturning circulation amoc during heinrich events was often accompanied by a notable atmospheric co2 increase however previous modeling studies display conflicting atmospheric co2 responses to an amoc shutdown here we use model simulations combined with paleoproxy records to show that depending on the deep and bottom water transport in the northern and southern pacific ocean during an amoc weakening the ocean can act either as a sink or a source of carbon results from idealized meltwater experiments as well as from a transient experiment covering heinrich stadial 4 suggest that a shutdown of the amoc during heinrich stadials 4 hs4 and 1 hs1 led to an enhancement of antarctic bottom water aabw and north pacific deep water npdw transport we show that enhanced deep and bottom water transport in the pacific ocean ventilates deep pacific carbon through the southern ocean thus contributing to a rise in atmospheric co2 this mechanism yields a good agreement between paleoproxy records and modeling results thus highlighting the possible establishment of an atlantic pacific seesaw during heinrich stadials enhanced aabw and npdw transport could account for most of the observed atmospheric co2 increase during hs4 and for about 30 of the atmospheric co2 increase during hs1

wind effect on the atlantic meridional overturning circulation via sea ice and vertical diffusion effects of wind and fresh water on the atlantic meridional overturning circulation amoc are investigated using a fully coupled climate model the amoc can change significantly when perturbed by either wind stress or freshwater flux in the north atlantic this study focuses on wind stress effect our model results show that the wind forcing is crucial in maintaining the amoc reducing wind forcing over the ocean can cause immediately weakening of the vertical salinity diffusion and convection in the mid high latitudes atlantic resulting in an enhancement of vertical salinity stratification that restrains the deep water formation there triggering a slowdown of the thermohaline circulation as the thermohaline circulation weakens the sea ice expands southward and melts providing the upper ocean with fresh water that weakens the thermohaline circulation further the wind perturbation experiments suggest a positive feedback between sea ice and thermohaline circulation strength which can eventually result in a complete shutdown of the amoc this study also suggests that sea ice variability may be also important to the natural amoc variability on decadal and longer timescales

precision logging of temperature gradients and the extraction of past climate abstract with new equipment it is now possible to obtain borehole logs which allow resolution of temperature gradients differing by 0 1 0 2 mk m over a distance of about 0 5 m at a logging rate of 8 m min since such a detailed profile of temperature gradient versus depth is easily obtained disturbances to the equilibrium gradient can now be readily identified in order to identify the forms of surface temperature variation which disturb the equilibrium regime in boreholes to depths of more than 100 m some tests are proposed in which a polynomial curve is fitted to the observed temperature gradient the real roots of the first and second derivative equations of this fitted curve are then used to estimate the types of surface thermal disturbances aplication of these tests to a well characterized borehole indicates that there were increases in temperature of 1 k approx 250 years ago 3 6 k approx 25 years ago and 5 0 k approx 8 years ago the first disturbance may be associated with the ending of the little ice age while the last two are associated with the completion of large buildings nearby in 1958 and 1967

deepwater formation in the north pacific during the last glacial termination between approximately 17 500 and 15 000 years ago the atlantic meridional overturning circulation weakened substantially in response to meltwater discharges from disintegrating northern hemispheric glacial ice sheets the global effects of this reorganization of poleward heat flow in the north atlantic extended to antarctica and the north pacific here we present evidence from north pacific paleo surface proxy data a compilation of marine radiocarbon age ventilation records and global climate model simulations to suggest that during the early stages of the last glacial termination deep water extending to a depth of approximately 2500 to 3000 meters was formed in the north pacific a switch of deepwater formation between the north atlantic and the north pacific played a key role in regulating poleward oceanic heat transport during the last glacial termination

a model of variations in the north atlantic oscillation 1 the major source of interannual variability in the atmospheric circulation over the north atlantic ocean is the north atlantic oscillation nao which is associated with the strength of the winter surface westerly winds over the ocean during the last century the nao has shown pronounced multi annual and multi decadal variations fluctuations that have been accompanied by changes in the marine and terrestrial ecosystems of the north atlantic region this paper presents a simple model which reproduces the major trends in the nao index from 1866 to 2004 the model is based on climatic resonators that are forced by the global mean temperature and the southern oscillation of the pacific ocean so the ocean component of the model shows similar variations to time series from the north atlantic

an atlantic pacific ventilation seesaw across the last deglaciation it has been proposed that the rapid rise of atmospheric co2 across the last deglaciation was driven by the release of carbon from an extremely radiocarbon depleted abyssal ocean reservoir that was vented to the atmosphere primarily via the deep and intermediate overturning loops in the southern ocean while some radiocarbon observations from the intermediate ocean appear to confirm this hypothesis others appear to refute it here we use radiocarbon measurements in paired benthic and planktonic foraminifera to reconstruct the benthic planktonic 14c age offset i e ventilation age of intermediate waters in the western equatorial atlantic our results show clear increases in local radiocarbon based ventilation ages during heinrich stadial 1 hs1 and the younger dryas yd these are found to coincide with opposite changes of similar magnitude observed in the pacific demonstrating a seesaw in the ventilation of the intermediate atlantic and pacific oceans that numerical model simulations of north atlantic overturning collapse indicate was primarily driven by north pacific overturning we propose that this atlantic pacific ventilation seesaw would have combined with a previously identified north atlantic southern ocean ventilation seesaw to enhance ocean atmosphere co2 exchange during a collapse of the north atlantic deep overturning limb whereas previous work has emphasized a more passive role for intermediate waters in deglacial climate change merely conveying changes originating in the southern ocean we suggest instead that the intermediate water seesaw played a more active role via relatively subtle but globally coordinated changes in ocean dynamics that may have further influenced ocean atmosphere carbon exchange

a physical mechanism of the precipitation dipole in the western united states based on pdo storm track relationship it is known that the western united states us precipitation displays a north south contrast i e the so called precipitation dipole during el nino and la nina winters furthermore the pacific decadal oscillation pdo has been known to modulate this precipitation dipole however the underlying physical mechanism regulating this modulation is not well understood this study revisits previous studies and suggests a physical mechanism of precipitation dipole modulation based on the pdo storm track relationship we found that both jet stream and storm track tend to move northward southward over the north pacific during negative positive pdo winters contributing to the increase of precipitation over the northwestern southwestern us respectively this relationship is robust regardless of el nino southern oscillation enso possibly facilitating modulation of the precipitation dipole moreover changes in oceanic baroclinicity associated with the pdo phase are suggested to be responsible for anchorage of storm tracks over the north pacific

the role of meridional density differences for a wind driven overturning circulation experiments with the coupled climate model climber 3 which contains an oceanic general circulation model show deep upwelling in the southern ocean to be proportional to the surface wind stress in the latitudinal band of drake passage at the same time the distribution of the southern ocean upwelling onto the oceanic basins is controlled by buoyancy distribution the inflow into each basin being proportional to the respective meridional density difference we observe approximately the same constant of proportionality for all basins and demonstrate that it can be directly related to the flow geometry for increased wind stress in the southern ocean the overturning increases both in the atlantic and the indo pacific basin for strongly reduced wind stress the circulation enters a regime where atlantic overturning is maintained through pacific upwelling in order to satisfy the transports set by the density differences previous results on surface buoyancy and wind stress forcing obtained with different models are reproduced within one model in order to distill a consistent picture we propose that both southern ocean upwelling and meridional density differences set up a system of conditions that determine the global meridional overturning circulation

the ocean s role in setting the mean position of the inter tropical convergence zone through study of observations and coupled climate simulations it is argued that the mean position of the inter tropical convergence zone itcz north of the equator is a consequence of a northwards heat transport across the equator by ocean circulation observations suggest that the hemispheric net radiative forcing of climate at the top of the atmosphere is almost perfectly symmetric about the equator and so the total atmosphere plus ocean heat transport across the equator is small order 0 2 pw northwards due to the atlantic ocean s meridional overturning circulation however the ocean carries significantly more heat northwards across the equator order 0 4 pw than does the coupled system there are two primary consequences first atmospheric heat transport is southwards across the equator to compensate 0 2 pw southwards resulting in the itcz being displaced north of the equator second the atmosphere and indeed the ocean is slightly warmer by perhaps 2 c in the northern hemisphere than in the southern hemisphere this leads to the northern hemisphere emitting slightly more outgoing longwave radiation than the southern hemisphere by virtue of its relative warmth supporting the small northward heat transport by the coupled system across the equator to conclude the coupled nature of the problem is illustrated through study of atmosphere ocean ice simulations in the idealized setting of an aquaplanet resolving the key processes at work

impact of north atlantic freshwater forcing on the pacific meridional overturning circulation under glacial and interglacial conditions abstractthe pacific meridional overturning circulation pmoc is not well known compared to the atlantic meridional overturning circulation amoc due to its absence today however considering pm

synchronization of north pacific and greenland climates preceded abrupt deglacial warming some proposed mechanisms for transmission of major climate change events between the north pacific and north atlantic predict opposing patterns of variations others suggest synchronization resolving this conflict has implications for regulation of poleward heat transport and global climate change new multidecadal resolution foraminiferal oxygen isotope records from the gulf of alaska goa reveal sudden shifts between intervals of synchroneity and asynchroneity with the north greenland ice core project ngrip 18 o record over the past 18 000 years synchronization of these regions occurred 15 500 to 11 000 years ago just prior to and throughout the most abrupt climate transitions of the last 20 000 years suggesting that dynamic coupling of north pacific and north atlantic climates may lead to critical transitions in earth s climate system

modeling obliquity and co2effects on southern hemisphere climate during the past 408 ka abstractthe effect of obliquity and co2 changes on southern hemispheric climate is studied with a series of numerical modeling experiments using the earth system model of intermediate complexity loch vecode ecbilt clio agism model loveclim and a coupled general circulation model model for interdisciplinary research on climate miroc it is shown in time slice simulations that phases of low obliquity enhance the meridional extratropical temperature gradient increase the atmospheric baroclinicity and intensify the lower and middle troposphere southern hemisphere westerlies and storm tracks furthermore a transient model simulation is conducted with loveclim that covers the greenhouse gas ice sheet and orbital forcing history of the past 408 ka this simulation reproduces reconstructed glacial interglacial variations in temperature and sea ice qualitatively well and shows that the meridional heat transport associated with the orbitally paced modulation of middle troposphere westerlies and storm tr

modelling teleconnections between the north atlantic and north pacific during the younger dryas evidence for a cooling event synchronous with the younger dryas 12 000 calendar years before present has been found in the north pacific ocean north of 30 n in records of surface1 5 and subsurface water properties6 7 these changes may be related to a temporary shut down of north atlantic deep water formation and associated surface cooling over the north atlantic it has remained unclear however whether this north atlantic cooling was communicated to the north pacific ocean through the atmosphere or the ocean here we report results of a sensitivity experiment with a coupled ocean atmosphere general circulation model that support a primarily atmospheric forcing of north pacific climate variations changes in wind strongly affect coastal upwelling at the north american west coast and surface cooling by the atmosphere causes better ventilation of the thermocline waters of the northeast pacific this effect is amplified by oceanic progagation to the pacific of the signal arising from collapse of north atlantic deep water formation these teleconnections may also explain earlier north pacific and western north american millenial scale cooling events of a similar nature8 12

robustness of multiple equilibria in the global ocean circulation 1 in an idealized atlantic pacific ocean model we study the steady state solutions versus freshwater input in the northern north atlantic we find that four different states the conveyor c the southern sinking ss the northern sinking ns and the inverse conveyor ic appear as two disconnected branches of solutions where the c is connected with the ss and the ns with the ic we argue that the latter has the intriguing consequence that the parameter volume for which multiple steady states exist is greatly increased

large fluctuations of dissolved oxygen in the indian and pacific oceans during dansgaard oeschger oscillations caused by variations of north atlantic deep water subduction a s and s h were supported by the paleoclimate program of the national science foundation as part of the paleovar project atm 0602395

effects of topography and climatic changes on the temperature in borehole gfu 1 prague abstract in october 1992 a 150 m borehole was drilled on the ground of the geophysical institute prague for purposes of long term temperature observations since the borehole is intended for a detailed study of the change during downward propagation of the ground surface temperature gst an evaluation of the topographic effect and the unsteady state component is necessary as a first step the effect of topography was studied by solving the heat conduction equation in 2 d models the gst model presumed a lapse rate of 5 mk m superposed on the gst dependence on the slope orientation which raises the gst on the southern slope by 0 5 k and lowers it by the same amount on the northern one as a second step the model was subjected to 1 k warming of the surface 70 yr ago which is in the range of expected changes and the computed profile was inverted by a 1 d algorithm to reconstruct the gst neglecting the influence of topography the reconstructed warming gives a value of 1 05 k 74 yr ago in view of these results the inversion of the measured profile was made without applying the topographic correction if a step change in the gst is presumed a warming of 1 2 k 70 yr ago is most probable an assumption of a linear change gives a warming of 1 1 k 120 yr ago the meteorological data recorded at praha klementinum support the latter case

mechanisms for millennial scale global synchronization during the last glacial period global climate during the last glacial period was punctuated by abrupt warmings and occasional pulses of freshwater into the north atlantic that disrupted deepwater production these massive freshwater pulses known as heinrich events arose in part from instabilities within the laurentide ice sheet paleoevidence from the north atlantic suggests that these events altered the production of deep water and changed downstream climate throughout the northern hemisphere in the tropical western pacific sea surface temperatures and salinity varied together with ocean and climate changes at high latitudes here we present results from coupled modeling experiments that shed light on a possible dynamical link between the north atlantic ocean and the western tropical pacific this link involves a global oceanic standing wave pattern brought about by millennial scale glacial density variations in the north atlantic atmospheric teleconnections triggered by meridional sea surface temperature gradients and local air sea interactions furthermore our modeling results are compared with hydrological records from the cariaco basin the indian ocean the sulu sea and northern australia

the atlantic freshwater budget as a diagnostic for the existence of a stable shut down of the meridional overturning circulation 1 which physical processes effectively determine the stability regime of the atlantic meridional overturning circulation moc is not yet fully understood we investigate the role of the oceanic freshwater transport into the basin employing a coupled model of intermediate complexity by modifying the longitudinal variation of surface salinities near the southern border at 33 s the amount of salt flowing out of the atlantic via the brazil current can be regulated in turn this will influence whether the moc exports or imports salt water the latter is associated with a basin scale salinity overturning feedback which can be either positive or negative pulse experiments strongly suggest that its sign determines the existence of a monostable or bistable regime in our model

strong and deep atlantic meridional overturning circulation during the last glacial cycle extreme abrupt northern hemisphere climate oscillations during the last glacial cycle 140 000 years ago to present were modulated by changes in ocean circulation and atmospheric forcing1 however the variability of the atlantic meridional overturning circulation amoc which has a role in controlling heat transport from low to high latitudes and in ocean co2 storage is still poorly constrained beyond the last glacial maximum2 3 4 here we show that a deep and vigorous overturning circulation mode has persisted for most of the last glacial cycle dominating ocean circulation in the atlantic whereas a shallower glacial mode with southern sourced waters filling the deep western north atlantic prevailed during glacial maxima3 5 our results are based on a reconstruction of both the strength and the direction of the amoc during the last glacial cycle from a highly resolved marine sedimentary record in the deep western north atlantic parallel measurements of two independent chemical water tracers the isotope ratios of 231pa 230th and 143nd 144nd 6 7 8 which are not directly affected by changes in the global cycle reveal consistent responses of the amoc during the last two glacial terminations any significant deviations from this configuration resulting in slowdowns of the amoc were restricted to centennial scale excursions during catastrophic iceberg discharges of the heinrich stadials severe and multicentennial weakening of north atlantic deep water formation occurred only during heinrich stadials close to glacial maxima with increased ice coverage probably as a result of increased fresh water input in contrast the amoc was relatively insensitive to submillennial meltwater pulses during warmer climate states and an active amoc prevailed during dansgaard oeschger interstadials greenland warm periods

the role of the pmoc in modulating the deglacial shift of the itcz based on an energy constraint framework the effect of the pacific meridional overturning circulation pmoc has been investigated on the meridional shift of the intertropical convergence zone itcz during heinrich event 1 the global itcz displaces southward in response to a shutdown of the atlantic meridional overturning circulation amoc however the pmoc resumes and induces an enhanced northward meridional heat transport mht further analyses show that the resumption of the pmoc and its associated mht can relieve the decrease of oceanic cross equatorial heat transport by the collapsed amoc and lower the compensating decline of atmospheric cross equatorial meridional heat transport by 0 09pw leading to an offset of the southward shift of the global itcz by 0 5 regionally the developed pmoc does not affect the southward movement of the atlantic itcz much since the latter is dominated by the collapsed amoc that induces the change of atlantic mht in contrast the pmoc induced northward heat transport largely abates the hemispheric temperature contrast in the tropical pacific and reduces the southward itcz shift by as much as 5 in the eastern pacific

precise temperature monitoring in boreholes evidence for oscillatory convection part 1 experiments and field data temperature was monitored in two boreholes in kamchatka russia in years 2001 2003 ten min reading sampling interval was selected for the first half year run followed by shorter 12 days experiment with 5 s reading interval a similar experiment was repeated later in the test borehole sporilov prague czech republic where four temperature time series were performed with reading intervals varying from 1 to 20 s all temperature time series except the record from the bottom of the hole displayed intermittent non periodic oscillations of temperature of up to several hundredths of degree with sharp gradients and large fluctuations over all observed time intervals no such oscillation was detected at the bottom of the hole the spectral analysis revealed a high level of stochasticity in the measured signal calculated spectra showed band pass behavior without any definite peaks which might characterize certain periodicity local growth of the second moment technique revealed the presence of at least two distinct temperature forming processes one of them can be related to heat transfer in the structurally and compositionally complex subsurface the second process which presents the bulk of the measured signal probably reflects certain intra hole convection we hypothesized that the oscillatory regime of such convection is responsible for the stochastic nature of measured temperatures results of numerical modeling describing the fluctuation of water cells in a vertical slot support the idea of thermally unstable water column in a hole the instability of which produces a complex oscillation system model solutions and their discussion is presented in part ii of this work

is the wind stress forcing essential for the meridional overturning circulation 1 we use a global couple d atm osphere ocean sea ice model of interm ediate complexity to demonstrate that wind forcing i s a crucial element to sustain meridional overturning flow i n t he atlantic neglecting wind stress in our multi century lon g simulations leads to a complete shutdown of the conveyor belt ci r culation this r esult may have tremendous impacts f or an assessment of the sensitivity of 2 d clima t e models which typicall y do not capture wind driven gyres it is argued that wind effects may be a key element in determining the f ate and length of a collapsed thc state possible paleo implications will be discussed

first heat flow density assessments in cuba abstract the first determinations of heat flow density in cuba are reported precise temperature loggings were carried out in 12 holes in the western and central parts of cuba along the northwestern shore the mean temperature gradient ranges from 14 16 mk m in the pinar del rio province and 18 22 mk m east of habana to 30 mk m in northern matanzas in the central basin it ranges from 23 24 mk m west of ciego de avila to 28 39 mk m east of sancti spiritus rock samples for laboratory determination of thermal conductivity could be collected only from two holes in pinar del rio their mean conductivity amounts to 4 1 w m 1 k 1 from other holes no core samples were available and characteristic rocks were collected from surface outcrops in the vicinity of each hole the measured conductivity ranges from 0 8 to 3 0 w m 1 k 1 heat flow density assessments revealed very low heat flow near habana and south of varadero 30 40 mw m 2 and relatively higher but still rather subnormal values in pinar del rio 60 mw m 2 and in the central basin 50 65 mw m 2 the generally low heat flow density found in western and central parts of the island thus seems to agree well with the results of marine observations in surrounding areas reported by other authors

thermal conductivity determinations on solid rock a comparison between a steady state divided bar apparatus and a commercial transient line source device abstract two apparatuses were used to measure thermal conductivities on pairs of contiguous samples from 17 specimens of solid rock the usgs divided bar apparatus a steadystate comparative method and the shotherm quick thermal meter qtm which employs a transient strip heat source both devices were calibrated relative to fused silica both devices have a reproducibility of 5 or better depending to some extent on the physical nature of the specimen being tested for solid rocks specimen preparation for the divided bar is much more tedious and expensive than for the qtm which seems insensitive to minor surface roughness the qtm does however require quite large specimens 30 mm 60 mm 100 mm as a minimum for rocks with even larger specimens 50 mm 100 mm 100 mm required for higher conductivity material 3 5 w m 1 k 1 and greater experimental times are comparable however the qtm is a self contained unit that can be transported easily and set up quickly and requires no more space than a standard desk top from a formal statistical comparison it appears that over a large range of conductivities 1 4 to 5 w m 1 k 1 and rock types the two instruments will yield the same value of thermal conductivity for isotropic rocks

sea surface temperature variability and sea ice extent in the subarctic northwest pacific during the past 15 000 years past changes in north pacific sea surface temperatures and sea ice conditions are proposed to play a crucial role in deglacial climate development and ocean circulation but are less well known than from the north atlantic here we present new alkenone based sea surface temperature records from the subarctic northwest pacific and its marginal seas bering sea and sea of okhotsk for the time interval of the last 15 kyr indicating millennial scale sea surface temperature fluctuations similar to short term deglacial climate oscillations known from greenland ice core records past changes in sea ice distribution are derived from relative percentage of specific diatom groups and qualitative assessment of the ip25 biomarker related to sea ice diatoms the deglacial variability in sea ice extent matches the sea surface temperature fluctuations these fluctuations suggest a linkage to deglacial variations in atlantic meridional overturning circulation and a close atmospheric coupling between the north pacific and north atlantic during the holocene the subarctic north pacific is marked by complex sea surface temperature trends which do not support the hypothesis of a holocene seesaw in temperature development between the north atlantic and the north pacific key points millennial scale changes in sst in the north pacific during the last 15 kyr changes in sea ice extent suggest a close coupling to sst fluctuations middle to late holocene ssts show no clear sst trend in the north pacific