pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

spatial patterns of variability in antarctic surface temperature connections to the southern hemisphere annular mode and the southern oscillation 1 the 17 year 1982 1998 trend in surface temperature shows a general cooling over the antarctic continent warming of the sea ice zone with moderate changes over the oceans warming of the peripheral seas is associated with negative trends in the regional sea ice extent effects of the southern hemisphere annular mode sam and the extrapolar southern oscillation so on surface temperature are quantified through regression analysis positive polarities of the sam are associated with cold anomalies over most of antarctica with the most notable exception of the antarctic peninsula positive temperature anomalies and ice edge retreat in the pacific sector are associated with el nino episodes over the past two decades the drift towards high polarity in the sam and negative polarity in the so indices couple to produce a spatial pattern with warmer temperatures in the antarctic peninsula and peripheral seas and cooler temperatures over much of east antarctica

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

the antarctic dipole and its predictability this study investigates the nature of interan nualvariability ofantarcticseaiceanditsrelationshipwith the tropical climate we nd that the dominant interan nual variance structure in the sea ice edge and surface air temperature elds is organized as a quasi stationary wave which we call the antarctic dipole adp it is charac terized by an out of phase relationship between the ice and temperature anomalies in the central eastern pacic and atlantic sectors of the antarctic the dipole consists of a strong standing mode and a weaker propagating motion within each basin s ice eld it has the same wavelength as the antarctic circumpolar wave acw and dominates the acw variance the dipole is clearly associated with tropical enso events it can be predicted with moderate skill using linear regression involving surface temperature two to four months ahead the prediction performs better in extreme warm cold years and best in la ni na years

onset of neoglaciation in the southern hemisphere a review of evidence documenting an early neoglacial mid holocene advance of mountain glaciers in south america and new zealand reveals that of 16 glaciers for which radiocarbon age control exists only two have associated dates that may approximate the culmination of an advance advances of the remaining glaciers are controlled only by minimum or maximum limiting ages additional dates for several new zealand glaciers are based on weathering rind measurements having large potential errors twelve of the glaciers now terminate or have terminated in lakes or in tidewater and are subject to instabilities associated with calving termini an extensive debris cover in the ablation zone of nearly half of the glaciers makes their moraine succession potentially suspect as a record of detailed climatic variation the two glaciers with seemingly reliable age control are located in valleys where large rock avalanches could affect glacier mass balance and lead to random advances or where rock avalanche deposits might easily be mistaken for moraines and tills the early neoglacial interval has been defined primarily based on this set of data the ages taken at face value suggest that the early neoglacial advance culminated between ca 5400 and 4900 cal yr ago ca 4600 4400 14c yr bp this chronology however should remain provisional until improved age control is obtained for a large population of glaciers based on closely bracketing radiocarbon dates and or an adequate number of cosmogenic isotope ages data from calving glaciers and those subject to rock avalanche activity should be avoided or assessed critically copyright 2000 john wiley sons ltd

millennial scale variability in southern hemisphere westerly wind activity over the last 5000 years in sw patagonia abstract here we report results from a high resolution palynological record and stratigraphic geochronologic data related to a neoglacial event in torres del paine national park southern chile 51 s 71 w to investigate climatic variations in southwest patagonia during the last 5000 years the record reveals a stepwise expansion of nothofagus dominated woodlands and forests with discrete pulses at 4400 2900 1300 and 570 cal yr bp superimposed upon this trend we identify a relative opening of the woodlands between 4100 2900 and 2300 1300 cal yr bp closed canopy forests dominated the landscape between 570 60 cal yr bp followed by a rapid decline at the end of the 19th century that coincided with intense fire activity and the appearance of rumex cf acetocella an exotic species introduced by european settlers we interpret these changes as variations in the intensity and or position of the southern margin of the westerly winds which culminated with a net eastward shift of the forest steppe ecotone during the little ice age we propose that millennial scale changes in either the latitudinal position and or the overall strength of the southern westerlies may be responsible for vegetation changes fire occurrence and the dynamic behavior of patagonian glaciers during the last 5000 years because the modern maximum in near surface wind velocities and precipitation is located between 48 and 50 s we suggest that the core of the southern westerlies may have achieved this modern position 570 years ago

relationships between low frequency variability in the southern hemisphere and sea surface temperature anomalies abstract long term trends and interannual variations of circulation anomalies in the southern hemisphere are examined using the national centers for environmental prediction national center for atmospheric research reanalysis from 1949 to 1998 the changes in planetary circulation regimes are linked to global sea surface temperature anomalies sstas empirical orthogonal function eof analysis was performed on 500 hpa height anomalies the leading mode eof1 shows a strong zonal symmetry with a phase reversal between height anomalies in high and midlatitudes apart from zonal symmetry a zonal wavenumber 3 is evident with three centers located in three southern oceans in the low frequency band with fluctuations longer than 60 months eof1 is associated with the second rotated eof mode of sstas with positive loadings over three southern oceans and negative loadings in the north pacific and the north atlantic the next two modes are the pacific south american psa patterns they depict wave 3 patterns in

steppe expansion in patagonia abstract westward expansion of the patagonian steppe and retrocession of andean forests due to increasing aridity over the past one or two millennia has been a persistent theme in the ecological and paleoecological literature for at least half a century new evidence from pollen profiles tree ring analysis vegetation structure and photographic and documentary historical sources does not show the expansion of the steppe instead over the past century trees have invaded the steppe as a consequence mainly of human induced changes in the fire regime and trees have regenerated in forest areas that were heavily burnt at the onset of european colonization

annular modes in the extratropical circulation part i month to month variability the leading modes of variability of the extratropical circulation in both hemispheres are characterized by deep zonally symmetric or annular structures with geopotential height perturbations of opposing signs in the polar cap region and in the surrounding zonal ring centered near 458 latitude the structure and dynamics of the southern hemisphere sh annular mode have been extensively documented whereas the existence of a northern hemisphere nh mode herein referred to as the arctic oscillation ao has only recently been recognized like the sh mode the ao can be defined as the leading empirical orthogonal function of the sea level pressure field or of the zonally symmetric geopotential height or zonal wind fields in this paper the structure and seasonality of the nh and sh modes are compared based on data from the national centers for environmental prediction national center for atmospheric research reanalysis and supplementary datasets the structures of the nh and sh annular modes are shown to be remarkably similar not only in the zonally averaged geopotential height and zonal wind fields but in the mean meridional circulations as well both exist year round in the troposphere but they amplify with height upward into the stratosphere during those seasons in which the strength of the zonal flow is conducive to strong planetary wave mean flow interaction midwinter in the nh and late spring in the sh during these active seasons the annular modes modulate the strength of the lagrangian mean circulation in the lower stratosphere total column ozone and tropopause height over mid and high latitudes and the strength of the trade winds of their respective hemispheres the nh mode also contains an embedded planetary wave signature with expressions in surface air temperature precipitation total column ozone and tropopause height it is argued that the horizontal temperature advection by the perturbed zonal mean zonal wind field in the lower troposphere is instrumental in forcing this pattern a companion paper documents the striking resemblance between the structure of the annular modes and observed climate trends over the past few decades

30 year satellite record reveals contrasting arctic and antarctic decadal sea ice variability a 30 year satellite record of sea ice extents derived mostly from satellite microwave radiometer observations reveals that the arctic sea ice extent decreased by 0 30 0 03 x 10 exp 6 square kilometers per 10 yr from 1972 through 2002 but by 0 36 plus or minus 0 05 x 10 exp 6 square kilometers per 10yr from 1979 through 2002 indicating an acceleration of 20 in the rate of decrease in contrast the antarctic sea ice extent decreased dramatically over the period 1973 1977 then gradually increased over the full 30 year period the antarctic ice extent decreased by 0 15 plus or minus 0 08 x 10 exp 6 square kilometers per 10 yr the trend reversal is attributed to a large positive anomaly in antarctic sea ice extent in the early 1970 s an anomaly that apparently began in the late 1960 s as observed in early visible and infrared satellite images

mechanisms forcing an antarctic dipole in simulated sea ice and surface ocean conditions abstract the mechanisms forcing variability in southern ocean sea ice and sea surface temperature from 600 years of a control climate coupled model integration are discussed as in the observations the leading mode of simulated variability exhibits a dipole pattern with positive anomalies in the pacific sector associated with negative anomalies in the atlantic it is found that in the pacific ocean circulation changes associated with variable wind forcing modify the ocean heat flux convergence and sea ice transport resulting in sea surface temperature and sea ice anomalies the pacific ice and ocean anomalies persist over a number of years due to reductions in ocean shortwave absorption reinforcing the initial anomalies in the atlantic sector no single process dominates in forcing the anomalies instead there are contributions from changing ocean and sea ice circulation and surface heat fluxes while the absorbed solar radiation in the atlantic is modified by the changing surface albedo the anomalies

interpretation of recent antarctic sea ice variability 1 trends in the satellite derived antarctic sea ice concentrations 1979 2002 show pronounced increase decrease in the central pacific sector bellingshausen western weddell sector by 4 10 per decade confidence levels for these regional trends exceed 95 positive polarities of the antarctic oscillation aao lead to more less ice in the eastern ross amundsen sector bellingshausen northern weddell sector which are qualitatively opposite to the impacts of positive polarities of the el nino southern oscillation enso the mechanisms responsible for the covariability between the ice and the a aao and b enso are demonstrated over the last 24 years a positive aao trend and a slightly negative enso trend produce a spatial pattern of ice changes similar to the regional ice trends however the magnitude of the ice changes associated with the aao and enso is much smaller than the regional ice trends more local or less understood large scale processes should be investigated for the explanations

changing fire regimes in the temperate rainforest region of southern chile over the last 16 000 yr abstract a high resolution macroscopic charcoal record from lago melli 42 46 s 73 33 w documents the occurrence of forest fires in the lowlands of isla grande de chiloe southern chile over the last 16 000 yr our data suggest that fire activity in this region was largely modulated by the position intensity of the southern westerlies at multi millennial time scales fire activity was infrequent or absent between 16 000 11 000 and 8500 7000 cal yr bp and was maximal between 11 000 8500 and 3000 0 cal yr bp a mosaic of valdivian north patagonian rainforest species started at 6000 cal yr bp along with a moderate increase in fire activity which intensified subsequently at 3000 cal yr bp the modern transition between these forest communities and the occurrence of fires are largely controlled by summer moisture stress and variability suggesting the onset of high frequency variability in summer precipitation regimes starting at 5500 cal yr bp because negative anomalies in summer precipitation in this region are teleconnected with modern el nino events we propose that the onset of el nino like variability at 5700 6200 cal yr bp led to a reshuffling of rainforest communities in the lowlands of isla grande de chiloe and an increase in fire activity

paleoenvironments and paleoclimates in tierra del fuego and southernmost patagonia south america abstract a continuous paleoclimatic history for the past 14 000 years is presented based on palynological records from south of latitude 50 s in south america prior to 12 500 yr b p dry empetrum heathlands not mesic tundra dominated throughout the high southern latitudes indicating high winds annual precipitation of less than 300 mm and freezing temperatures year round after 12 500 yr b p steppe replaced the heathlands suggesting decrease in wind intensity increase in effective moisture and increase in temperatures when forests expanded at 9000 yr b p along the rainward side and at 8000 yr b p in the rainshadow side of the andes precipitation reached holocene levels judging from the greater openness of the early holocene forests including those in the rainward part of the region precipitation levels probably ranged between 500 and 800 mm comparable to those from today s forest steppe transition after a pronounced mid holocene dry event the late holocene forests appeared more closed than the early holocene forests suggesting greater effective moisture probably related to cooler temperatures the high latitude paleoclimatic history differs from that of lower latitudes as far as the actual amplitude of change and the climatic signal is concerned low moisture levels prior to 12 500 yr b p between latitudes 45 and 55 c suggest that the westerly stormtracks responsible for precipitation patterns in southern south america may have been located year round closer to the equator than today the precipitation increase at 12 500 yr b p that extended only as far south as 50 s indicates that the stormtracks had shifted poleward but did not reach tierra del fuego by 9000 yr b p the stormtracks had shifted to the high southern latitudes but the large seasonal latitudinal shift comparable to the modern situation equatorwards in winter and polewards in summer did not develop until after 4500 yr b p

analysis of the projected regional sea ice changes in the southern ocean during the twenty first century using the set of simulations performed with atmosphere ocean general circulation models aogcms for the fourth assessment report of the intergovernmental panel on climate change ipcc ar4 the projected regional distribution of sea ice for the twenty first century has been investigated averaged over all those model simulations the current climate is reasonably well reproduced however this averaging procedure hides the errors from individual models over the twentieth century the multimodel average simulates a larger sea ice concentration decrease around the antarctic peninsula compared to other regions which is in qualitative agreement with observations this is likely related to the positive trend in the southern annular mode sam index over the twentieth century in both observations and in the multimodel average despite the simulated positive future trend in sam such a regional feature around the antarctic peninsula is absent in the projected sea ice change for the end of the twenty first century the maximum decrease is indeed located over the central weddell sea and the amundsen bellingshausen seas in most models changes in the oceanic currents could play a role in the regional distribution of the sea ice especially in the ross sea where stronger southward currents could be responsible for a smaller sea ice decrease during the twenty first century finally changes in the mixed layer depth can be found in some models inducing locally strong changes in the sea ice concentration

the impact of a changing southern hemisphere annular mode on antarctic peninsula summer temperatures since the mid 1960s rapid regional summer warming has occurred on the east coast of the northern antarctic peninsula with near surface temperatures increasing by more than 2 degrees c this warming has contributed significantly to the collapse of the northern sections of the larsen ice shelf coincident with this warming the summer southern hemisphere annular mode sam has exhibited a marked trend suggested by modeling studies to be predominantly a response to anthropogenic forcing resulting in increased westerlies across the northern peninsula observations and reanalysis data are utilized to demonstrate that the changing sam has played a key role in driving this local summer warming it is proposed that the stronger summer westerly winds reduce the blocking effect of the antarctic peninsula and lead to a higher frequency of air masses being advected eastward over the orographic barrier of the northern antarctic peninsula when this occurs a combination of a climatological temperature gradient across the barrier and the formation of a fohn wind on the lee side typically results in a summer near surface temperature sensitivity to the sam that is 3 times greater on the eastern side of the peninsula than on the west sam variability is also shown to play a less important role in determining summer temperatures at stations west of the barrier in the northern peninsula similar to 62 degrees s both at the surface and throughout the troposphere this is in contrast to a station farther south similar to 65 degrees s where the sam exerts little influence

antarctic ocean and sea ice response to ozone depletion a two time scale problem theresponseofthesouthernoceantoarepeatingseasonalcycleofozonelossisstudiedintwocoupledclimate models and is found to comprise both fast and slow processes the fast response is similar to the interannual signature of the southern annular mode sam on sea surface temperature sst onto which the ozone hole forcing projects in the summer it comprises enhanced northward ekman drift inducing negative summertime sst anomalies around antarctica earlier sea ice freeze up the following winter and northward expansion of the sea ice edge year round the enhanced northward ekman drift however results in upwelling of warm waters from below the mixed layer in the region of seasonal sea ice with sustained bursts of westerly winds induced by ozone hole depletion this warming from below eventually dominates over the cooling from anomalous ekman drift the resulting slow time scale response years to decades leads to warming of ssts around antarctica and ultimately a reduction in sea ice cover year round this two time scale behavior rapid cooling followed by slow but persistent warming is found in the two coupled models analyzed one with an idealized geometry and the other with a complex global climate model with realistic geometry processes that control the time scale of the transition from cooling to warming and their uncertainties are described finally the implications of these results are discussed for rationalizing previous studies of the effect of the ozone hole on sst and sea ice extent

isotopic evidence for hydrologic change related to the westerlies in sw patagonia chile during the last millennium abstract the southern hemisphere westerly winds influence the spatial distribution of precipitation in southern south america and play a significant role in the global carbon cycle yet little is known about how this important atmospheric circulation feature has varied in the past here we present a sediment core record of late holocene variability from lago guanaco a small closed basin lake located in torres del paine national park chilean patagonia the park is located in the core of the modern wind field and variations in the intensity of the atmospheric circulation directly influence the hydrology of this region we combine stable isotopic measurements of biogenic carbonate and bulk organic matter to identify two periods of increased evaporation between 900 550 and 400 50 calendar years before present cal yr bp the first interval is coincident with the medieval climate anomaly mca while the more recent period is broadly coincident with the timing of the little ice age lia during the lia interval we observe simultaneous monotonic increases in the 18 o of biogenic carbonate and nothofagus dombeyi type pollen which we interpret as indicative of significant changes in the intensity of the southern westerlies during the last millennium the isotopic and palynological variations in the guanaco record are coincident with geochemical variations found in an antarctic ice core record from siple dome suggesting that the signal preserved in lago guanaco is regional rather than local and that the lia intensification was accompanied by a poleward shift in the southern margin of the westerlies in addition we interpret four periods of increased lake productivity centered on 900 650 500 and 200 cal yr bp from simultaneous increases in the 13 c of bulk organic material and biogenic carbonate these increases in lake productivity are most likely tied to increases in summer temperatures

an analysis of the atmospheric processes driving the large scale winter sea ice variability in the southern ocean the response of the sea ice in the southern ocean to the variability of the atmosphere on the period 1979 2004 is investigated using both model and observational data on the one hand our results show that in line with previous investigations the classical modes of atmospheric variability do not explain a large part of the winter sea ice extent variability integrated over the entire southern ocean on the other hand the regression between the ice extent and the atmospheric pressure displays a pattern with low pressure areas over the south atlantic over the indian ocean and on the southwestern part of the pacific ocean and a high pressure area over the antarctic region extending toward both the southeastern pacific and the region south of australia this pattern which does not correlate significantly with any of the known modes of atmospheric variability induces changes in the sea ice extent by influencing the air temperature the ice production and both the meridional and the zonal ice velocity however there is no clear link between the different centers of action of this pattern furthermore the correlation of the sea ice extent between the different sectors is generally low as a conclusion we must consider that the sea ice extent in the southern ocean over the last 30 years does not behave as a single entity its variability is the result of the combination of regional sea ice changes each sector should thus be examined separately

simulated changes in the extratropical southern hemisphere winds and currents 1 the results from 12 global climate models show a remarkably consistent strengthening and poleward shifting of the zonal wind stress through the 20th and 21st centuries at extratropical southern hemisphere latitudes changes in the zonal circulation of the ocean in the region are broadly consistent with the changes in zonal wind stress in particular the climate models simulate a strengthening and a poleward shift of the antarctic circumpolar current the strengthening of the zonal wind stress also results in intensifying northward ekman transport across the antarctic circumpolar current which in the unblocked latitudes of drake passage implies increasing southward geostrophic transport in the ocean below about 2000 m zonal wind stress changes such as these may be expected to enhance the mesoscale eddy activity in the southern ocean

interpretation of recent southern hemisphere climate change climate variability in the high latitude southern hemisphere sh is dominated by the sh annular mode a large scale pattern of variability characterized by fluctuations in the strength of the circumpolar vortex we present evidence that recent trends in the sh tropospheric circulation can be interpreted as a bias toward the high index polarity of this pattern with stronger westerly flow encircling the polar cap it is argued that the largest and most significant tropospheric trends can be traced to recent trends in the lower stratospheric polar vortex which are due largely to photochemical ozone losses during the summer fall season the trend toward stronger circumpolar flow has contributed substantially to the observed warming over the antarctic peninsula and patagonia and to the cooling over eastern antarctica and the antarctic plateau

control of organic carbon accumulation in the late quaternary equatorial atlantic ocean drilling program sites 664 and 663 productivity versus terrigenous supply organic geochemical records of the last 940 kyr are presented for equatorial atlantic ocean drilling program odp sites 663 and 664 and discussed with regard to the development of ocean productivity and african paleoclimate proportions of marine and terrigenous organic matter om are estimated from elemental pyrolytic isotopic and petrologic data spectral analyses reveal a strong power at the eccentricity and obliquity band indicating a close response of tropical organic sedimentation to the climatic evolution at high latitudes the orbital covariance of organic carbon with biogenous opal and terrigenous records favor that glacially enhanced dust supply and surface water mixing were primary controls for deposition of organic carbon wind borne supply of terrigenous om contributes 26 to 55 and 0 to 39 to the bulk om based on microscopic and isotopic records respectively admixture of c4 plant matter was approximated to contribute up to 16 to the bulk organic fraction during peak glacial conditions

a model assessment of satellite observed trends in polar sea ice extents 1 for more than three decades now satellite passive microwave observations have been used to monitor polar sea ice here we utilize sea ice extent trends determined from satellite data for both the northern and southern hemispheres for the period 1972 73 2004 and assess and interpret them using results from simulations by eleven climate models in the northern hemisphere nh observations show a statistically significant decrease of sea ice extent and an acceleration of sea ice retreat during the past three decades however from the modeled natural variability of sea ice extents in control simulations we conclude that the acceleration is not statistically significant and should not be extrapolated into the future most of the models like the observations show an absence of a prominent seasonal cycle in the trend values both observations and model simulations show that climate variability in sea ice extent in the southern hemisphere sh is much larger than in the nh and that the sh sea ice extent trends are not statistically significant citation vinnikov k y d j cavalieri and c l parkinson 2006 a model assessment of satellite observed trends in polar sea ice extents geophys res lett 33 l05704 doi 10 1029 2005gl025282

influence of coupling on atmosphere sea ice and ocean regional models in the ross sea sector antarctica air sea ice ocean interactions in the ross sea sector form dense waters that feed the global thermohaline circulation in this paper we develop the new limited area ocean sea ice atmosphere coupled model tango to simulate the ross sea sector tango is built up by coupling the atmospheric limited area model mar to a regional configuration of the ocean sea ice model nemo a method is then developed to identify the mechanisms by which local coupling affects the simulations tango is shown to simulate realistic sea ice properties and atmospheric surface temperatures these skills are mostly related to the skills of the stand alone atmospheric and oceanic models used to build tango nonetheless air temperatures over ocean and winter sea ice thickness are found to be slightly improved in coupled simulations as compared to standard stand alone ones local atmosphere ocean feedbacks over the open ocean are found to significantly influence ocean temperature and salinity in a stand alone ocean configuration the dry and cold air produces an ocean cooling through sensible and latent heat loss in a coupled configuration the atmosphere is in turn moistened and warmed by the ocean sensible and latent heat loss is therefore reduced as compared to the stand alone simulations the atmosphere is found to be less sensitive to local feedbacks than the ocean effects of local feedbacks are increased in the coastal area because of the presence of sea ice it is suggested that slow heat conduction within sea ice could amplify the feedbacks these local feedbacks result in less sea ice production in polynyas in coupled mode with a subsequent reduction in deep water formation

fluctuations of the south patagonian ice field during the last glaciation and the holocene mapping along a transect from the southeastern margin of the south patagonian ice field in torres del paine national park chile to the limits of fresh moraines of the last glacial cycle indentified eight glacier advances the four younger ones have been dated by dendrochronology tephrochronology and radiocarbon dating although the bases of 10 m deep bogs were sampled close limiting radiocarbon dates were not obtained because bog formation in this rain shadow area appears not to have commenced until ca 12000 yr ago the outermost little ice age moraine formed during the seventeenth century and three inner ones were deposited around ad 1805 1845 and after 1890 densely vegetated older moraines contiguous with little ice age deposits are possibly of late holocene age tephra from the eruption of reclus volcano at ca 11 880 yr bp was incorporated by a readvance that deposited large multiple moraines 10 16 km from the modern ice front the oldest basal peat found inside the moraine has been dated to ca 9200 yr bp these bracketing dates indicate that some eastern outlet glaciers of the ice field advanced at a time when some western tidewater outlet glaciers terminated inside their modern limits this questions the view of j h mercer and other that patagonian glaciers did not readvance during the late glacial interval a stadial event also occurred when the glaciers were some 18 20 km from their modern positions and is closely dated to ca 11880 yr bp because reclus pumice flushed down glacier forms thick upper beds in outwash deltas deposited in proglacial lakes the four older moraines pre date the late glacial eruption of reclus but are not dated closely comparison of their spatial extent with well dated moraines in the chilean lakes region suggests that they may mark advances culminating at ca 14000 yr bp ca 20000 yr bp and earlier

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

definition of antarctic oscillation index following walker s work about his thmous three oscillations published during the 1920 30s many papers were written about atmospheric oscillations a iburth atmospheric oscillation in the middle and high southern latitudes was lbund and nanted the grotarctic oscillation ao a refiers to a large scale alternation of atmospheric mass between the mid latitudes and high latitudes surthce pressure in order to understand the spatial structure of sea level pressure variation in detail empirical orthogonal fitnction analysis is applied an objective index of the antarctic oscillation index aoi is defined as the diffierence of zonal mean sea level pressure between 40os and 65os the aoi has the potential tbr clarifying climate regimes in the southern hemisphere similar to how the na and the npo has been used in the northern hemisphere were there other oscillation s besides nao npo and s especially in the southern hemisphere it had been supposed that there might be other atmospheric oscillation s in the high southern latitudes although as early as in the first quarter of this century walker 1928 had stated that just as in the north atlantic there is a pressure opposition between the azores and iceland there is an opposition between the high pressure belt across chile and the argentine on the one hand and the low pressure area of weddell sea and the bellingshausen sea on the other the scarcity of data in the southern hemisphere hindered the search tbr new oscillation s during the last two decades more comprehensive data over the southern hemisphere became available and more analyses were carried out see kidson 1975 rogers and van loon 1982 mo and l 7 ite 1985 2 4o 1986 connolley 1997 gong and wang 1998 a tburth atmospheric oscillation in the middle and high southern latitudes was tbund and nanted as the antarctic oscillation a wang 1992 gong and wang 1998 the term ao relrs to a large scale alternation of atmospheric mass between the mid latitude sur hce pressure

evaluation of the simulation of the annual cycle of arctic and antarctic sea ice coverages by 11 major global climate models 1 comparison of polar sea ice results from 11 major global climate models gcms and satellite derived observations for 1979 2004 reveals that each of the models is simulating annual cycles that are phased at least approximately correctly in both hemispheres each is also simulating various key aspects of the observed ice cover distributions such as winter ice not only throughout the central arctic basin but also throughout hudson bay despite its relatively low latitudes however some of the models simulate too much ice others simulate too little ice in some cases depending on hemisphere and or season and some match the observations better in one season versus another several models do noticeably better in the northern hemisphere than in the southern hemisphere and one does noticeably better in the southern hemisphere in the northern hemisphere all simulate monthly average ice extents to within 5 1 106 km2 of the observed ice extent throughout the year in the southern hemisphere all except one simulate the monthly averages to within 6 3 106 km2 of the observed values all the models properly simulate a lack of winter ice to the west of norway however most obtain more ice immediately north of norway than the observations show suggesting an under simulation of the north atlantic current the spread in monthly averaged ice extents among the 11 model simulations is greater in the southern hemisphere than in the northern hemisphere and greatest in the southern hemisphere winter and spring

influence of the southern annular mode on the sea ice ocean system 1 the global sea ice ocean model orca2 lim driven by the ncep ncar national centers for environmental prediction national center for atmospheric research reanalysis daily 2 m air temperatures and 10 m winds and by monthly climatologies for precipitation cloud cover and relative humidity is used to investigate the impact of the southern annular mode sam on the antarctic sea ice ocean system our results suggest that the response of the circumpolar southern ocean consists of an annular and a nonannular component for the sea ice cover the non annular component seems to be the most important the annular component strongly affects the overall patterns of the upper ocean circulation when the sam is in its positive phase a northward surface ekman drift a downwelling at about 45 degreess and an upwelling in the vicinity of the antarctic continent are simulated the non annular component has a significant impact at the regional scale especially in the weddell ross amundsen and bellingshausen seas in those regions the pressure pattern associated with the sam induces meridional winds which advect warmer air in the weddell sea and around the antarctic peninsula and colder air in the amundsen and ross seas this implies a dipole response of sea ice to the sam with on average a decrease in ice area in the weddell sea and around the antarctic peninsula and an increase in the ross and amundsen seas during years with a high sam index the long term trend in the observed sea ice area does not appear to be related to the trend in the sam index

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

consistent past half century trends in the atmosphere the sea ice and the ocean at high southern latitudes simulations performed with the climate model loveclim aided with a simple data assimilation technique that forces a close matching of simulated and observed surface temperature variations are able to reasonably reproduce the observed changes in the lower atmosphere sea ice and ocean during the second half of the twentieth century although the simulated ice area slightly increases over the period 1980 2000 in agreement with observations it decreases by 0 5 106 km2 between early 1960s and early 1980s no direct and reliable sea ice observations are available to firmly confirm this simulated decrease but it is consistent with the data used to constrain model evolution as well as with additional independent data in both the atmosphere and the ocean the simulated reduction of the ice area between the early 1960s and early 1980s is similar to the one simulated over that period as a response to the increase in greenhouse gas concentrations in the atmosphere while the increase in ice area over the last decades of the twentieth century is likely due to changes in atmospheric circulation however the exact contribution of external forcing and internal variability in the recent changes cannot be precisely estimated from our results our simulations also reproduce the observed oceanic subsurface warming north of the continental shelf of the ross sea and the salinity decrease on the ross sea continental shelf parts of those changes are likely related to the response of the system to the external forcing modifications in the wind pattern influencing the ice production melting rates also play a role in the simulated surface salinity decrease

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

late quaternary climatic history of the chilean channels based on fossil pollen and beetle analyses with an analysis of the modern vegetation and pollen rain fossil beetles and pollen were examined from an intermorainal bog at puerto eden isla wellington chile latitude 49 08 s longitude 74 25 w wood from near the base of the section has an age of 12 960 150 yr bp occurrence of flightless beetle species in the basal peat sample is evidence that some members of the biota survived the last glacial maximum in refugia the assumption that the chilean channels were entirely ice covered is incorrect plants and insects that invaded the deglaciated terrain were those of an empetrum heathland in which patches of nothofagus forest were restricted to sheltered locations the climate supporting the heathland is inferred to have been windier and probably drier than that of the present day from 13 000 yr bp to 9500 yr bp nothofagus forest expanded possibly in response to less windiness and more available moisture neither the fossil beetle nor pollen data support a return to significantly colder conditions between 11 000 and 10 000 yr bp at the time of the younger dryas stade from 9500 to 5500 yr bp the climate was as wet as that of the present day based on an increased representation of the pollen of moorland plants and of aquatic beetle species from 5500 to 3000 yr bp the climate was drier as indicated by the expansion of empetrum heath and the reduction in mesic habitats from 3000 yr bp to the present day mesic habitats dominated as the climate returned to a wetter mode the alternatively wetter and drier episodes are attributed to latitudinal shifts in the position of storm tracks in the belt of southern westerlies

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