salt transport in the near surface layer in the monsoon influenced indian ocean using hycom 1 salt advection in the top 5 m layer of the monsoon influenced indian ocean has been studied with high resolution hybrid coordinate ocean model hycom simulated sea surface salinity sss during 2003 06 the effect of monsoon reversals and roles of ekman drift and geostrophic currents are emphasized the ekman drift component is found to be more important than the geostrophic component in exchange of salt in the basins an indication of the influence of winds and the associated surface currents the strongest differences in the salt advection terms occurred in the bay of bengal bob an indication of the significant role of advection for the distribution of freshwater and the ekman processes the inter tropical convergence zone itcz is seen to influence advection patterns via ekman drift along the equatorial region this results in the creation of two salt advection bands whose positions vary seasonally this study will help to interpret data from the recently launched soil moisture ocean salinity smos and future aquarius salinity missions for the indian ocean

controls of eustasy and diagenesis on the 238u 235u of carbonates and evolution of the seawater 234u 238u during the last 1 4 myr using a leaching protocol designed for the study of u isotopes in recent carbonates we measured the u isotope composition both 238 u 235 u and 234 u 238 u of modern and ancient corals n 6 a limestone and a dolostone as well as 43 shallow water carbonate sediments from the odp leg 166 site 1009 drill core on the slope of the bahamas platform although bulk corals record the seawater 238 u value within 0 02 differences of up to 0 30 in the 238 u of individual leachates suggest a control of the coral structure and a more positive 238 u 235 u ratio in the centers of calcification the drill core 238 u data shows that the 238 u 235 u ratio of shallow water carbonates is controlled mainly by 1 variations in sea level through the mixing of different amounts of platform derived sediments with 238 u 0 50 0 60 heavier than seawater and pelagic sediments with seawater like 238 u values 2 authigenic u enrichment via pore watercirculation and u reduction both on the platform and down to 5 m below the surface mbsf after deposition of the sediment and to a lesser extent by 3 early diagenetic processes i e carbonate dissolution and or recrystallization during sediment burial the global effect of these processes leaves the 238 u values of shallow water carbonates offset relative to that of seawater by carbonates sw 0 24 0 06 95 ci including all samples this shift can be used in seawater paleoredox reconstructions based on carbonates deposited on shallow water platform shelf and slope environments i e most of the carbonate sedimentary record prior to the mesozoic to account for the average effect of carbonate diagenesis assuming that the 238 u 235 u ratio of carbonate platform sediments directly records the seawater 238 u 235 u ratio would underestimate the extent of ocean seafloor anoxia by at least a factor 10 the rapid fluctuations in 238 u values due to sea level changes i is a factor that should be considered before interpreting 238 u variations as reflecting changes in oceanic paleoredox conditions and ii reinforces the need for statistically meaningful data sets the 234 u data suggest that the 234 u 238 u ratio of the seawater has remained within 20 of the modern seawater value during the last 1 1 4 myr furthermore we find that small scale 1 15 variations in seawater 234 u mirror sea level changes during the penultimate glacial interglacial period 140 to 200 ka thus confirming the record of lower 234 u sw during periods of low sea level stand and expanding it to at least the last two glacial interglacial events i e 0 23 ma such fluctuations in 234 u initial values should be taken into account when screening carbonate sediments u th ages on the basis of the initial 234 u 238 u ratios of the samples

interdecadal change in the north atlantic storm track during boreal summer around the mid 2000s role of the atmospheric internal processes the first eof mode eof1 of summer storm track activity over the north atlantic is characterized by a dipole structure with negative storm track anomalies over the south coast of greenland extending northeast across iceland to the norwegian sea and positive anomalies over coastal western europe this study shows that a significant interdecadal change in the north atlantic storm track during boreal summer occurred around the mid 2000s after the mid 2000s the eof1 occurs more frequently at its positive phase which is associated with an interdecadal increase in the geopotential height anomalies around greenland on the intra seasonal timescale the anticyclonic anomalies around greenland are crucial for the occurrence of positive eof1 events via triggering eastward propagating rossby waves therefore the interdecadal increase in the geopotential height anomalies around greenland tends to facilitate the occurrence of the positive eof1 event and is therefore a key driver of the interdecadal change in the summer storm track activity over the north atlantic further analysis indicates that the development of anticyclonic anomalies around greenland is maintained by the self interaction among the low and high frequency transients themselves moreover the anomalous synoptic eddy activities associated with the change in storm tracks can in turn amplify and maintain the rossby waves triggered by the anticyclonic anomalies around greenland in the synoptic scale eddy feedback process

the annual cycle in equatorial convection and sea surface temperature abstract the coupled atmosphere ocean system in the equatorial eastern pacific and atlantic exhibits a distinct annual cycle that is reflected in contrasting conditions at the times of the two equinoxes the contrasts are so strong that they dominate the annual march of zonally averaged outgoing longwave radiation for the equatorial belt the march equinox corresponds to the warm season when the equatorial cold tongues in the eastern pacific and atlantic are absent with the onset of summer monsoon convection over colombia central america and west africa in may june northward surface winds strengthen over the eastern pacific and atlantic the equatorial cold tongues reappear and the marine convection shifts from the equatorial belt to the intertropical convergence zones itczs along 8 n as the northern summer program the itczs remain strong and shift northward to new 10 n while sea surface temperature sst continues to drop over the cold tongues and the southern tropics perhaps in response to the

tonian cryogenian boundary sections of argyll scotland abstract the tonian cryogenian system boundary is to be defined at a gssp global boundary stratigraphic section and point beneath the first evidence of widespread glaciation a candidate lies within the dalradian supergroup of scotland and ireland which is least deformed and metamorphosed in argyll western scotland we present new stratigraphic profiles and interpretations from the isle of islay and the garvellach islands update the chemostratigraphy of the appin group tonian carbonates underlying the thick ca 1 km glacigenic port askaig formation paf and demonstrate an environmental transition at the contact the appin group forms a regionally extensive 4 km thick succession of limestones shales and sandstones deposited on a marine shelf on islay the upper part of the lithostratigraphy has been clarified by measuring and correlating two sections containing distinctive stratigraphic levels including molar tooth structure oolite stromatolitic dolomite and intraclastic microbial mounds significantly deeper erosion at the unconformity at the base of the overlying paf is demonstrated in the southern section carbonate facies show a gradual decline in 13 c vpdb from 5 to 2 upwards in ne garbh eileach garvellach islands a continuously exposed section of appin group carbonates 70 m thick here designated the garbh eileach formation gef lies conformably beneath the paf the gef and the gef paf boundary relationships are re described with new sedimentological logs petrological and stable isotope data interstratified limestone and dolomicrosparite with 13 c of 4 to 7 a feature named the garvellach anomaly replacing the term islay anomaly are overlain by dolomite in which the isotope signature becomes weakly positive up to 1 upwards shallow subtidal conditions become peritidal upwards with evidence of wave and storm activity gypsum pseudomorphs and subaerial exposure surfaces are common near the top of the gef the basal diamictite d1 of the paf is rich in carbonate clasts similar to slightly deeper water parts of the underlying succession d1 is typically several metres thick with interstratified sandstone and conglomerate but dies out laterally scattered siliciclastic coarse sandstone to pebble conglomerate with dropstones associated with soft sediment deformation is interbedded with carbonate below and above d1 dolomite beds with derived intraclasts and gypsum pseudomorphs are found above d1 or equivalent position where d1 is absent published and new sr isotope studies including successive leach data demonstrate primary tonian 87 sr 86 sr values of 0 7066 0 7069 on islay decreasing to 0 7064 0 7066 in the younger gef limestones on the garvellachs with 1700 2700 ppm sr other typically tonian characteristics of the carbonates are the sr rich nature of limestones molar tooth structure and dolomitized peritidal facies with evidence of aridity seabed surveys suggesting uniformly dipping strata and shallow borehole core material illustrate the potential for extending the tonian record offshore of the garvellachs a candidate tonian cryogenian gssp is proposed on garbh eileach within the smooth 13 c profile at the cross over to positive 13 c signatures 4 m below the first occurrence of ice rafted sediment and 9 m below the first diamictite although lacking radiometric constraints or stratigraphically significant biotas or biomarkers the scottish succession has a thick and relatively complete sedimentary record of glaciation coherent carbon and strontium chemostratigraphy lateral continuity of outcrops and 100 exposure at the proposed boundary interval

change in relationship between the east asian winter monsoon and the east asian jet stream during the 1998 99 regime shift abstracta composite analysis was conducted on the reanalysis dataset for 1979 2016 along with an idealized model experiment to show that the relationship between the east asian jet stream eajs a

strontium isotope stratigraphy for the late cretaceous a new curve based on the english chalk marine 87sr 86sr decreases from 0 70775 in the cenomanian to 0 70730 in the middle turonian before increasing in a near linear manner to 0 70775 in the early maastrichtian this variation has been defined using samples from the english chalk that are closely integrated with the macrofossil and microfossil biostratigraphy of northwestern europe with this new isotope curve a stratigraphic resolution is attainable in correlation that is typically 0 8 ma for the santonian and campanian stages isotopic and biostratigraphic correlations between dorset and norfolk in the uk agree within the limit of analytical error in 87sr 86sr authors

semidiurnal tides on the laptev sea shelf with implications for shear and vertical mixing the arctic continental shelf seas hold a globally significant source of freshwater that impacts arctic ocean stratification circulation and climate this freshwater can be injected below the surface mixed layer by intense turbulent kinetic energy dissipation events as resolved by laptev sea microstructure observations the tides provide a major source of energy that can be dissipated and hence drive diapycnal mixing in the laptev sea multiyear adcp mooring records from locations across the shelf reveal that semidiurnal tides are dominated by them2 and s2 constituents with the largest amplitudes on the outer shelf throughoutmost of the shelf tides are clockwise polarized and sheared by stratification as characteristic near the m2 critical latitude interannual variations of the tidal and shear structures on the inner shelf aremainly determined by the stratification setting lena river freshwater plume in all locations m2 tides are enhanced under sea ice and therefore changes in the seasonal ice cover may lead to changes in tides and water column structure the main conclusions of this study are that i tides play a comparatively greater role year round on the outer shelf relative to the inner shelf ii a sea ice reduction will overall decrease the predictability of the currents especially on the inner shelf and iii the freshwater distribution directly impacts diapycnal mixing by setting the vertical tidal structure these combined effects imply that future sea ice loss will increase the variability and vertical mixing of freshwater particularly on the inner shelf where the lena river first enters the laptev sea

strontium isotope correlation of the basal maastrichtian stage in antarctica to the european and us biostratigraphic schemes new 87 sr 86 sr dating allows the correlation of a marker horizon within the prolific late cretaceous gunnarites antarcticus faunal assemblage of the cape lamb member snow hill island formation vega island antarctica with reference sections in europe and the usa this horizon is between 81 5 and 96 5 m above the base of the g antarcticus assemblage replicate analysis of six macrofossils from within it yielded a mean value for 87 sr 86 sr of 0 707 735 9 0 000 004 3 2 s e n 17 this ratio in turn yields a numerical age of 71 0 0 2 ma when compared to the standard 87 sr s6 sr reference curve for the latest cretaceous for which the campanian maastrichtian boundary is placed at 71 3 0 5 ma the value of 0 707 735 9 0 000 004 3 correlates to a level in the belemnella lanceolata belemnite zone of the chalk of northwestern germany that is 2 5 5 m beneath the base of the overlying b pseudobtusa zone and 7 5 m above the campanian maastrichtian belemnite boundary and to an interval within the ammonite zonation of the us western interior that spans the early maastrichtian baculites baculus and b eliasi zones but with a most likely level within the b eliasi zone an earliest maastrichtian age is thereby determined for the antarctic horizon and indeed for the entire g antarcticus assemblage gunnarites sensu lato is an important ammonite marker for the base of the maastrichtian throughout the southern high latitude regions and the associated large heteromorph ammonite diplomoceras may comprise a macrofossil link back to the maastrichtian type sections

evaluation of pan arctic melt freeze onset in cmip5 climate models and reanalyses using surface observations the seasonal melt freeze transitions are fun damental features of the arctic climate system the representation of the pan arctic melt and freeze onset north of 60 n is assessed in two reanalyse

wind and wave influences on sea ice floe size and leads in the beaufort and chukchi seas during the summer fall transition 2014 sea ice floe size distribution and lead properties in the beaufort and chukchi seas are studied in the summer fall transition 2014 to examine the impact on the sea ice cover from storms and surface waves floe size distributions are analyzed from medea landsat8 and radarsat 2 imagery with a resolution span of 1 100 m landsat8 imagery is also used to identify the orientation and spacing of leads the study period centers around three large wave events during august september 2014 identified by swift buoys and wavewatch iii model data the range of floe sizes from different resolutions provides the overall distribution across a wide range of ice properties and estimated thickness all cumulative floe size distribution curves show a gradual bending toward shallower slopes for smaller floe sizes the overall slopes in the cumulative floe size distribution curves from landsat8 images are lower than while those from radarsat 2 are similar to previously reported results in the same region and seasonal period the medea floe size distributions appeared to be sensitive to the passage of storms lead orientations regardless of length correlate slightly better with the peak wave direction than with the mean wave direction their correlation with the geostrophic wind is stronger than with the surface wind the spacing between shorter leads correlates well with the local incoming surface wavelengths obtained from the model peak wave frequency the information derived shows promise for a coordinated multisensor study of storm effects in the arctic marginal ice zone

construction of the silurian and devonian seawater 87sr 86sr curve the estimated path of seawater 87sr 86sr during the silurian and devonian is based on 86 analyses 84 whole rocks presented here and in other published results the seawater 87sr 86sr rose steadily throughout the silurian from a poorly constrained value near 0 70793 sw 114 at the ordovician silurian boundary the 87sr 86sr value at the silurian devonian boundary is near 0 70871 sw 36 based on an earliest devonian limestone suite from new york the 87sr 86sr falls through the early devonian to reach a low near 0 70772 sw 135 in the eifelian and givetian and rises to near 0 70803 sw 104 in famennian time the seawater 87sr 86sr at the devonian mississippian boundary is estimated to be near 0 70805 sw 102 the middle paleozoic sample suite is judged less suitable for defining seawater 87sr 86sr than those from other paleozoic periods the middle paleozoic seawater 87sr 86sr variation indicates domination of continental sr contributions during the silurian and later devonian the high ratio continental sr contribution is controlled by the climate and the area age and composition of exposed crystalline rocks the dominance of the oceanic low ratio sr during the early and part of middle devonian is coincident with a reported increase in continental volcanism the estimated rise and fall of sealevel leading to flooding or exposure of the continents does not appear to control seawater 87sr 86sr during the middle paleozoic

assessing the role of precursor cyclones on the formation of extreme greenland blocking episodes and their impact on summer melting across the greenland ice sheet a 30 year climatology of north atlantic cyclones from 1979 to 2008 is examined within the context of extreme greenland blocking and accelerated surface melting across the greenland ice sheet gris a distinct class of north atlantic cyclones known as precursor cyclones was identified as any extratropical cyclones originating to the west of greenland blocks prior to the peak of blocking intensity composite map analysis reveals that precursor cyclones contributed to a significant intensification of extreme greenland blocking episodes gbes through the process of upper level wave amplification across all seasons most extreme gbes are associated with multiple precursor cyclones prior to peaking in intensity and a majority of these cyclones have continental rather than oceanic origins over both the western and eastern sectors of greenland daily meltwater production simulated by the modele atmospherique regional regional climate model is greater during extreme gbes accompanied by precursor cyclones compared to extreme gbes lacking a precursor cyclone based on an analysis of air parcel trajectories and north atlantic sst anomalies enhanced surface melting during the summer particularly over southern and western greenland is strongly linked to the combination of vigorous adiabatic warming generated by subsiding air within the blocking anticyclones and warm air advection supplied by the precursor cyclones with the increased frequency of extreme gbes accompanied by precursor cyclones observed during a strong positive phase of the atlantic multidecadal oscillation recent long term increases in gris surface melting can be partially attributed to the interaction of these atmospheric and oceanic processes

continental heat anomalies and the extreme melting of the greenland ice surface in 2012 and 1889 recent decades have seen increased melting of the greenland ice sheet on 11 july 2012 nearly the entire surface of the ice sheet melted such rare events last occurred in 1889 and prior to that during the medieval climate anomaly studies of the 2012 event associated the presence of a thin warm elevated liquid cloud layer with surface temperatures rising above the melting point at summit station some 3212 m above sea level here we explore other potential factors in july 2012 associated with this unusual melting these include 1 warm air originating from a record north american heat wave 2 transitions in the arctic oscillation 3 transport of water vapor via an atmospheric river over the atlantic to greenland and 4 the presence of warm ocean waters south of greenland for the 1889 episode the twentieth century reanalysis and historical records showed similar factors at work however markers of biomass burning were evident in ice cores from 1889 which may reflect another possible factor in these rare events we suggest that extreme greenland summer melt episodes such as those recorded recently and in the late holocene could have involved a similar combination of slow climate processes including prolonged north american droughts heat waves and north atlantic warm oceanic temperature anomalies together with fast processes such as excursions of the arctic oscillation and transport of warm humid air in atmospheric rivers to greenland it is the fast processes that underlie the rarity of such events and influence their predictability

the role of summer surface wind anomalies in the summer arctic sea ice extent in 2010 and 2011 1 strong summertime anticyclonic wind anomalies over the arctic ocean with anomalous flow toward the fram strait during summer months of 2007 contributed to the record low the arctic sea ice extent observed in september of that year had the summer winds over the arctic during the summers of 2010 and 2011 been the same as those in 2007 september sea ice extent would have reached new record lows in those years as well by regulating the flow of ice toward and through the fram strait variations in low level winds over the arctic have contributed to the month to month year to year and decade to decade variability of sea ice extent

north american snow depth and climate teleconnection patterns abstract snow atmosphere relationships have been studied for nearly half a century but the primary focus has been on snow extent variability largely because of the relative scarcity of snow depth data a recently released north american snow depth dataset with extensive spatial coverage and multidecadal temporal duration provides a new opportunity to compare snow depth climate relationships with snow extent climate relationships over north america robust concurrent lead and lag correlations are observed between snow depth and two major climate modes the pacific decadal oscillation pdo and the pacific north america pna pattern across north america and throughout the snow season in contrast snow extent exhibits a less coherent relationship with pdo and pna except in late spring which can be interpreted as a residual of the snow depth climate mode relationship a regional signature for the snow depth pdo pna relationship is also identified centered over interior central western north america

summer arctic atmospheric circulation response to spring eurasian snow cover and its possible linkage to accelerated sea ice decrease abstractanticyclonic circulation has intensified over the arctic ocean in summer during recent decades however the underlying mechanism is as yet not well understood here it is shown that earlier spring eurasian snowmelt leads to anomalously negative sea level pressure slp over eurasia and positive slp over the arctic which has strong projection on the negative phase of the northern annular mode nam in summer through the wave mean flow interaction specifically earlier spring snowmelt over eurasia leads to a warmer land surface because of reduced surface albedo the warmed surface amplifies stationary rossby waves leading to a deceleration of the subpolar jet as a consequence rising motion is enhanced over the land and compensating subsidence and adiabatic heating occur in the arctic troposphere forming the negative nam the intensified anticyclonic circulation has played a contributing role in accelerating the sea ice decline observed during the last two decades the results here provid

acceleration of the contribution of the greenland and antarctic ice sheets to sea level rise 1 ice sheet mass balance estimates have improved substantially in recent years using a variety of techniques over different time periods and at various levels of spatial detail considerable disparity remains between these estimates due to the inherent uncertainties of each method the lack of detailed comparison between independent estimates and the effect of temporal modulations in ice sheet surface mass balance here we present a consistent record of mass balance for the greenland and antarctic ice sheets over the past two decades validated by the comparison of two independent techniques over the last 8 years one differencing perimeter loss from net accumulation and one using a dense time series of time variable gravity we find excellent agreement between the two techniques for absolute mass loss and acceleration of mass loss in 2006 the greenland and antarctic ice sheets experienced a combined mass loss of 475 158 gt yr equivalent to 1 3 0 4 mm yr sea level rise notably the acceleration in ice sheet loss over the last 18 years was 21 9 1 gt yr2 for greenland and 14 5 2 gt yr2 for antarctica for a combined total of 36 3 2 gt yr2 this acceleration is 3 times larger than for mountain glaciers and ice caps 12 6 gt yr2 if this trend continues ice sheets will be the dominant contributor to sea level rise in the 21st century

anomalous blocking over greenland preceded the 2013 extreme early melt of local sea ice the arctic marine environment is undergoing a transition from thick multi year to first year sea ice cover with coincident lengthening of the melt season such changes are evident in the baffin bay davis strait labrador sea bdl region where melt onset has occurred 8 days decade 1 earlier from 1979 2015 a series of anomalously early events has occurred since the mid 1990s overlapping a period of increased upper air ridging across greenland and the northwestern north atlantic we investigate an extreme early melt event observed in spring 2013 below the 1981 2010 melt climatology with respect to preceding sub seasonal mid tropospheric circulation conditions as described by a daily greenland blocking index gbi the 40 days prior to the 2013 bdl melt onset are characterized by a persistent strong 500 hpa anticyclone over the region gbi 1 on 75 of days this circulation pattern advected warm air from northeastern canada and the northwestern atlantic poleward onto the thin first year sea ice and caused melt about 50 days earlier than normal the episodic increase in the ridging atmospheric pattern near western greenland as in 2013 exemplified by large positive gbi values is an important recent process impacting the atmospheric circulation over a north atlantic cryosphere undergoing accelerated regional climate change

geomorphological records of extreme floods and their relationship to decadal scale climate change extreme rainfall and flood events in steep upland catchments leave geomorphological traces of their occurrence in the form of boulder berms debris cones and alluvial fans constraining the age of these features is critical to understanding i landscape evolution in response to past present and future climate changes and ii the magnitude frequency of extreme ungauged floods in small upland catchments this research focuses on the cambrian mountains of wales uk where lichenometric dating of geomorphological features and palaeohydrological reconstructions is combined with climatological data and documentary flood records our new data from wales highlight a distinct flood rich period between 1900 and 1960 similar to many other uk lichen dated records however this study sheds new light on the underlying climatic controls on upland flooding in small catchments although floods can occur in any season their timing is best explained by the summer north atlantic oscillation snao and shifts between negative wetter than average conditions with regular cyclonic flow and flooding and positive phases drier than average conditions with less frequent cyclonic flow and flooding which vary from individual summers to decadal and multidecadal periods recent wet summer weather flooding and boulder berm deposition in the uk 2007 2012 are related to a pronounced negative phase shift of the snao there is also increasing evidence that recent summer weather extremes in the mid latitudes may be related to arctic amplification and rapid sea ice loss if this is the case continuing and future climate change is likely to mean that i unusual weather patterns become more frequent and ii upland uk catchments will experience heightened flood risk and significant geomorphological changes

an exercise in forecasting loop current and eddy frontal positions in the gulf of mexico 1 as part of a model evaluation exercise to forecast loop current and loop current eddy frontal positions in the gulf of mexico the princeton regional ocean forecast system profs is tested to forecast 14 4 week periods aug 25 99 sep 20 00 during which a powerful eddy eddy juggernaut eddy j separated from the loop current and propagated southwestward to initialize each forecast profs assimilates satellite sea surface height ssh anomaly and temperature sst by projecting them into subsurface density using a surface subsurface correlation that is a function of the satellite ssh anomaly the closest distances of the forecast fronts from seven fixed stations in the northern gulf over a 4 week forecast horizon are then compared against frontal observations derived primarily from drifters model forecasts beat persistence and the major source of error is found to be due to the initial hindcast fields

implications of fractured arctic perennial ice cover on thermodynamic and dynamic sea ice processes decline of the arctic summer minimum sea ice extent is characterized by large expanses of open water in the siberian laptev chukchi and beaufort seas and introduces large fetch distances in the arctic ocean long waves can propagate deep into the pack ice thereby causing flexural swell and failure of the sea ice this process shifts the floe size diameter distribution smaller increases floe surface area and thereby affects sea ice dynamic and thermodynamic processes the results of radarsat 2 imagery analysis show that a flexural fracture event which occurred in the beaufort sea region on 6 september 2009 affected 40 000 km2 open water fractional area in the area affected initially decreased from 3 7 to 2 7 but later increased to 20 following wind forced divergence of the ice pack energy available for lateral melting was assessed by estimating the change in energy entrainment from longwave and shortwave radiation in the mixed layer of the ocean following flexural fracture 11 54 mj m 2 of additional energy for lateral melting of ice floes was identified in affected areas the impact of this process in future arctic sea ice melt seasons was assessed using estimations of earlier occurrences of fracture during the melt season and is discussed in context with ocean heat fluxes atmospheric mixing of the ocean mixed layer and declining sea ice cover we conclude that this process is an important positive feedback to arctic sea ice loss and timing of initiation is critical in how it affects sea ice thermodynamic and dynamic processes

sea surface salinity variability during the indian ocean dipole and enso events in the tropical indian ocean an ocean reanalysis that covers the period from 1871 2008 is used to analyze interannual variability of sea surface salinity sss in the tropical indian ocean the reanalysis sss and the sss anomaly patterns during indian ocean dipole iod and el nino southern oscillation enso events are compared with patterns from argo sss data the mean seasonal sss variation is large in the northern bay of bengal compared to variations in the arabian sea and equatorial indian ocean during a positive iod event positive sss anomalies are found along the sumatra coast due to the combination of wind driven upwelling of subsurface high salinity waters enhanced evaporation and anomalous surface circulation the opposite is true to a lesser extent during negative iod events a dipole mode index for salinity dmis based on sss data and a new index based on the average of salinity in a region off the coast of sumatra is introduced to monitor sss variability during iod and enso events the impact of concomitant el nino events on a positive iod event is large with freshening a negative sss anomaly in the equatorial indian ocean and salting positive sss anomaly off the southern sumatra coast the impact of intense freshening reaches into the southwestern tropical indian ocean the impact of concomitant la nina with negative iod is also large with an intense freshening in the southeastern arabian sea and salting off the northern sumatra coast

the extreme melt across the greenland ice sheet in 2012 1 the discovery of the 2012 extreme melt event across almost the entire surface of the greenland ice sheet is presented data from three different satellite sensors including the oceansat 2 scatterometer the moderate resolution imaging spectroradiometer and the special sensor microwave imager sounder are combined to obtain composite melt maps representing the most complete melt conditions detectable across the ice sheet satellite observations reveal that melt occurred at or near the surface of the greenland ice sheet across 98 6 of its entire extent on 12 july 2012 including the usually cold polar areas at high altitudes like summit in the dry snow facies of the ice sheet this melt event coincided with an anomalous ridge of warm air that became stagnant over greenland as seen in melt occurrences from multiple ice core records at summit reported in the published literature such a melt event is rare with the last significant one occurring in 1889 and the next previous one around seven centuries earlier in the medieval warm period given its rarity the 2012 extreme melt across greenland provides an exceptional opportunity for new studies in broad interdisciplinary geophysical research

is the dipole anomaly a major driver to record lows in arctic summer sea ice extent recent record lows of arctic summer sea ice extentare found to be triggered by the arctic atmospheric dipoleanomaly da pattern this local second leading mode ofsea level pressure slp anomaly in the arctic produced astrong meridional wind anomaly that drove more sea ice outof the arctic ocean from the western to the eastern arcticinto the northern atlantic during the summers of 1995 1999 2002 2005 and 2007 in the 2007 summer the daalso enhanced anomalous oceanic heat flux into the arcticoceanviaberingstrait whichacceleratedbottomandlateralmelting of sea ice and amplified the ice albedo feedback acoupled ice ocean model was used to confirm the historicalrecord lows of summer sea ice extent

autumn atmospheric response to the 2007 low arctic sea ice extent in coupled ocean atmosphere hindcasts the autumn and early winter atmospheric response to the record low arctic sea ice extent at the end of summer 2007 is examined in ensemble hindcasts with prescribed sea ice extent made with the european centre for medium range weather forecasts state of the art coupled ocean atmosphere seasonal forecast model robust warm anomalies over the pacific and siberian sectors of the arctic as high as 10 c at the surface are found in october and november a regime change occurs by december characterized by weaker temperatures anomalies extending through the troposphere geopotential anomalies extend from the surface up to the stratosphere associated to deeper aleutian and icelandic lows while the upper level jet is weakened and shifted southward over the continents it is intensified over both oceanic sectors especially over the pacific ocean on the american and eurasian continents intensified surface highs are associated with anomalous advection of cold warm polar air on their eastern western sides bringing cooler temperatures along the pacific coast of asia and northeastern north america transient eddy activity is reduced over eurasia intensified over the entrance and exit regions of the pacific and atlantic storm tracks in broad qualitative agreement with the upper level wind anomalies potential predictability calculations indicate a strong influence of sea ice upon surface temperatures over the arctic in autumn but also along the pacific coast of asia in december when the observed sea ice extent from 2007 is prescribed throughout the autumn a higher correlation of surface temperatures with meteorological re analyses is found at high latitudes from october until mid november this further emphasises the relevance of sea ice for seasonal forecasting in the arctic region in the autumn

what drove the dramatic retreat of arctic sea ice during summer 2007 1 a model study has been conducted of the unprecedented retreat of arctic sea ice in the summer of 2007 it is found that preconditioning anomalous winds and ice albedo feedback are mainly responsible for the retreat arctic sea ice in 2007 was preconditioned to radical changes after years of shrinking and thinning in a warm climate during summer 2007 atmospheric changes strengthened the transpolar drift of sea ice causing more ice to move out of the pacific sector and the central arctic ocean where the reduction in ice thickness due to ice advection is up to 1 5 m more than usual some of the ice exited fram strait and some piled up in part of the canada basin and along the coast of northern greenland leaving behind an unusually large area of thin ice and open water thin ice and open water allow more surface solar heating because of a much reduced surface albedo leading to amplified ice melting the arctic ocean lost additional 10 of its total ice mass in which 70 is due directly to the amplified melting and 30 to the unusual ice advection causing the unprecedented ice retreat arctic sea ice has entered a state of being particularly vulnerable to anomalous atmospheric forcing

sipex 2012 extreme sea ice and atmospheric conditions off east antarctica abstract in 2012 antarctic sea ice coverage was marked by weak annual mean climate anomalies that consisted of opposing anomalies early and late in the year some setting new records which were interspersed by near average conditions for most of the austral autumn and winter here we investigate the ocean ice atmosphere system off east antarctica prior to and during the sea ice physics and ecosystems experiment sipex 2012 by exploring relationships between atmospheric and oceanic forcing together with the sea ice and snow characteristics during august and september 2012 just prior to sipex 2012 atmospheric circulation over the southern ocean was near average setting up the ocean ice atmosphere system for near average conditions however below average surface pressure and temperature as well as strengthened circumpolar winds prevailed during june and july 2012 this led to a new record 19 48 10 6 km 2 in maximum antarctic sea ice extent recorded in late september in contrast to the weak circum antarctic conditions the east antarctic sector including the sipex 2012 region experienced positive sea ice extent and concentration anomalies during most of 2012 coincident with negative atmospheric pressure and sea surface temperature anomalies heavily deformed sea ice appeared to be associated with intensified wind stress due to increased cyclonicity as well as an increased influx of sea ice from the east this increased westward ice flux is likely linked to the break up of nearly 80 of the mertz glacier tongue in 2010 which strongly modified the coastal configuration and hence the width of the westward coastal current combined with favourable atmospheric conditions the associated changed coastal configuration allowed more sea ice to remain within the coastal current at the expense of a reduced northward flow in the region around 141 145 e in addition a westward propagating positive anomaly of sea ice extent from the western ross sea during austral winter 2012 has been identified to have fed into the westward current of the sipex 2012 region a pair of large grounded icebergs appears to have modified the local stress state as well as the structure of the ice pack upstream and also towards the dalton glacier tongue together with the increased influx of sea ice into the regions this contributed to the difficulties in navigating the sipex 2012 region

detection of mesoscale thermal fronts from 4km data using smoothing techniques gradient based fronts classification and basin scale application abstract in order to optimize frontal detection in sea surface temperature fields at 4 km resolution a combined statistical and expert based approach is applied to test different spatial smoothing of the data prior to the detection process fronts are usually detected at 1 km resolution using the histogram based single image edge detection sied algorithm developed by cayula and cornillon in 1992 with a standard preliminary smoothing using a median filter and a 3 3 pixel kernel here detections are performed in three study regions off morocco the mozambique channel and north western australia and across the indian ocean basin using the combination of multiple windows cmw method developed by nieto demarcq and mcclatchie in 2012 which improves on the original cayula and cornillon algorithm detections at 4 km and 1 km resolution are compared fronts are divided into two intensity classes weak and strong according to their thermal gradient a preliminary smoothing is applied prior to the detection using different convolutions three type of filters median average and gaussian combined with four kernel sizes 3 3 5 5 7 7 and 9 9 pixels and three detection window sizes 16 16 24 24 and 32 32 pixels to test the effect of these smoothing combinations on reducing the background noise of the data and therefore on improving the frontal detection the performance of the combinations on 4 km data are evaluated using two criteria detection efficiency and front length we find that the optimal combination of preliminary smoothing parameters in enhancing detection efficiency and preserving front length includes a median filter a 16 16 pixel window size and a 5 5 pixel kernel for strong fronts and a 7 7 pixel kernel for weak fronts results show an improvement in detection performance from largest to smallest window size of 71 for strong fronts and 120 for weak fronts despite the small window used 16 16 pixels the length of the fronts has been preserved relative to that found with 1 km data this optimal preliminary smoothing and the cmw detection algorithm on 4 km sea surface temperature data are then used to describe the spatial distribution of the monthly frequencies of occurrence for both strong and weak fronts across the indian ocean basin in general strong fronts are observed in coastal areas whereas weak fronts with some seasonal exceptions are mainly located in the open ocean this study shows that adequate noise reduction achieved by a preliminary smoothing of the data considerably improves the frontal detection efficiency as well as the global quality of the results consequently the use of 4 km data enables frontal detections similar to 1 km data using a standard median 3 3 convolution in terms of detectability length and location this method is easily applicable to large regions or at the global scale with far less constraints of data manipulation and processing time using 4 km data relative to 1 km data

effective use of cerium anomalies as a redox proxy in carbonate dominated marine settings abstract rare earth elements and yttrium rey have a distinct distribution pattern in seawater and this pattern may be faithfully preserved in carbonate sediments and rocks anomalous concentrations of redox sensitive cerium ce compared with neighbouring rey originate in oxic water column conditions and as such ce anomalies can provide a potentially useful redox proxy in carbonate dominated marine settings the methods used to extract rey from carbonates vary widely and may suffer from widespread leaching of rey from accessory non carbonate minerals and organic matter limiting the application of ce anomalies for palaeo redox reconstruction we have systematically compared different methods on 195 carbonate samples with varying purity carbonate from both modern and ancient environments we used sequential leaching experiments in nitric acid to identify the most seawater like portion of the carbonate sample where contributions from non carbonate minerals and organic matter are minimised we also compared the results of sample dissolution in different types and strengths of acid our results confirm that rey concentrations can be inadvertently contaminated by partial leaching of clays and fe oxyhydr oxides during a single step digestion and we suggest a pre leach of 20 of the sample followed by a partial leach of 40 of the sample to selectively dissolve carbonate we suggest that rey studies are optimised in carbonates with 85 caco 3 and show that dolomites behave differently during the leaching process and must be treated separately we present rey patterns for modern carbonate rich sediments from a range of environments and show that seawater rey are faithfully preserved in some non skeletal carbonate but modified leaching procedures are necessary for impure unlithified or organic rich carbonate sediments we combine rey with fe speciation data to identify how fe oxides and clays contribute to the rey signal and explore how the two proxies can be used together to provide a complex and high resolution redox reconstruction in carbonate dominated marine environments

strontium isotope stratigraphy in the late cretaceous numerical calibration of the sr isotope curve and intercontinental correlation for the campanian the white chalk exposed in quarries at lagerdorf and kronsmoor northwestern germany provides a standard section for the european upper cretaceous the sr 87 sr 86 values of nannofossil chalk and belemnite calcite increase upward through 330 m of section from less than or equal to 0 70746 in the upper santonian to greater than or equal to 0 70777 in the lower maastrichtian the data define three linear trends separated by major points of inflection at stratigraphic heights in the section of 162 m 75 5 ma in the upper campanian galerites vulgaris zone and at 6 m 82 9 ma just above the base of the campanian in the inoceramus lingua goniateuthis quadrata zone the temporal rate of change of sr 87 sr 86 was constant through each of the linear segments of our isotope curve when viewed at the resolution of our average sampling interval 0 15 m y fine structure if rear may record brief 100 kyr excursions of srsr sr 87 sr 86 from values expected from the overall trends in lagerdorf the boundary between the santonian and campanian stages taken here as the level of first occurrence of the belemnite gonioteuthis granulataquadrata has an sr 87 sr 86 of 0 707473 5 this is within error of the values of 0 707457 16 for this boundary in the u s western interior base of the scaphites leei iii zone and 0 707479 9 for this boundary in the english chalk top of the marsupites testudinarius zone in kronsmoor the boundary between the campanian and maastrichtian stages taken here as the level of first occurrence of the belemnite belemnella lanceolata has an sr 87 sr 86 of 0 707723 4 this is within error of the values of 0 707725 20 for this boundary in the u s western interior base of the baculites eliasi zone and 0 707728 5 for this boundary in the english chalk defined as in germany

decadal changes in the north pacific oceanic frontal zones as revealed in ship and satellite observations 1 influence of decadal climate changes upon the north pacific subarctic and subtropical oceanic frontal zones np safz and np stfz respectively is documented both satellite and ship measured sea surface temperature sst data reveal the strong confinement of wintertime decadal sst anomalies to those frontal zones the satellite data indicate that the wintertime np safz tended to be narrow and shift northward under the weakened surface westerlies during a warm event in the early 1990s the opposite was the case under the enhanced westerlies during a cool event in the mid 1980s decadal scale modulations in the frontal intensity are also evident in the satellite data a diagnosis based on a simple linearized mixed layer model suggests that the observed anomalous frontal intensity was contributed by the sign reversal of anomalous wind stress curl through the ekman processes and by an anomaly dipole of the net heat flux around the safz these decadal scale modulations in the np safz and their relationships with decadal fluctuations in the local surface westerlies are confirmed in the ship measured data over the 4 recent decades it is found that the safz happens to be a region where the decadal variability in the surface westerlies are unlikely to be masked by the higher frequency fluctuations as it almost coincides with the ridge trough line of the remote atmospheric response to the el nino southern oscillation

abrupt evolution of the summer northern hemisphere annular mode and its association with blocking 1 using reanalysis data from the national centers for environmental prediction national center for atmosperic research boulder colorado for the period from 1958 to 2005 we statistically analyzed the relationships of the summer northern hemisphere annular mode summer nam with hemispheric scale anomalous summer weather and the occurrence of blocking highs the anomalous positive nam low pressure anomaly in the arctic and high pressure anomaly in midlatitudes accounts well for the hemispheric scale weather associated with anomalous blocking between the polar and subtropical jets whereas blocking rarely occurs during negative nam periods the double jet stream structure is more evident during periods of anomalous positive nam than during periods of negative nam the surface temperatures associated with the anomalous positive nam clearly show europe to be hot and east asia to be cool as was the case during the anomalous summer of 2003 the occurrence of a positive summer nam is therefore consistent with the hemispheric scale anomalous summer weather associated with blocking in 2003 we investigated the abrupt evolution of atmospheric patterns and the geographic distribution of blocking highs associated with the development maintenance and decay periods of an anomalous positive nam during the development period blocking tends to occur over europe and the atlantic ocean but no significant blocking signature is evident over eastern eurasia during the maintenance stage blocking tends to occur in the far east during the decay stage blocking over the pacific region is obvious this longitudinal migration of blocking phenomena may be used to predict the evolution through time of the nam

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

the impact of climatic and atmospheric teleconnections on the brine inventory over the laptev sea shelf between 2007 and 2011 export of brine enriched water from siberian shelves is thought to be a key parameter in maintaining the arctic halocline which isolates the fresh and cold surface water from the warm atlantic water and thus prevent dramatic change in the arctic sea ice thermodynamic in this study we used five years of oxygen isotope and hydrological summer surveys to better understand the factors controlling the brine inventory and distribution over the laptev sea shelf the inventory was maximal in 2011 and 2007 and minimal in 2010 the brine inventory interannual variations are coherent with the winter arctic oscillation index that was maximal in 2011 and 2007 and minimal in 2010 which is known to modulate arctic winds and sea ice export pattern while we should remain cautious since our record is limited to 5 years our results suggest that the combined effect of the arctic oscillation and of the arctic dipole is the main factor controlling the annual variations in the inventory of brine enriched waters from the laptev sea shelf between 2007 and 2011 especially during extreme negative arctic oscillation and arctic dipole conditions as in 2010

coupled δ44 40ca δ88 86sr and 87sr 86sr geochemistry across the end permian mass extinction event abstract we report high resolution high precision 44 40ca 88 86sr and 87sr 86sr records spanning the permian triassic boundary ptb from the meishan and dajiang carbonate successions in south china the goal of the study was to understand the behavior of ca and sr isotopes during a time period in earth history characterized by severe biological and environmental perturbations including a major mass extinction flood basalt volcanism ocean acidification and sea level fluctuations dajiang displays negative 44 40ca and 88 86sr excursions and invariant 87sr 86sr ratios in the

a satellite derived climatology of the itcz abstract this paper presents fundamental climatological characteristics of the intertropical convergence zone itcz in a simple concise manner using the highly reflective cloud hrc dataset this satellite derived dataset uses both visible and infrared observations to measure the frequency of occurrence of large scale convective systems over the global tropics at a 1 spatial resolution these dataset characteristics make the hrc particularly well suited for climatological analysis of the itcz because the dataset is based on estimates of organized deep convective cloud systems rather than observations of clouds as a whole and it provides the spatial resolution needed to identify thew large wale convective structures furthermore the dataset covers a time period extending nearly two decades which provides for a fairly robust climatology and the opportunity to examine seasonal and interannual variability of both the convection and the latitude of the itcz

accelerated contribution of the paleo congo river to global seawater 87 sr 86 sr change following eocene oligocene collapse of the african surface

wind and wave climate in the arctic ocean as observed by altimeters abstracttwenty years 1996 2015 of satellite observations were used to study the climatology and trends of oceanic winds and waves in the arctic ocean in the summer season august september the atlantic side seas exposed to the open ocean host more energetic waves than those on the pacific side trend analysis shows a clear spatial regional and temporal interannual variability in wave height and wind speed waves in the chukchi sea beaufort sea near the northern alaska and laptev sea have been increasing at a rate of 0 1 0 3 m decade 1 found to be statistically significant at the 90 level the trend of waves in the greenland and barents seas on the contrary is weak and not statistically significant in the barents and kara seas winds and waves initially increased between 1996 and 2006 and later decreased large scale atmospheric circulations such as the arctic oscillation and arctic dipole anomaly have a clear impact on the variation of winds and waves in the atlantic sector comparison

evidence for wave resonance as a key mechanism for generating high amplitude quasi stationary waves in boreal summer several recent northern hemisphere summer extremes have been linked to persistent high amplitude wave patterns e g heat waves in europe 2003 russia 2010 and in the us 2011 floods in pakistan 2010 and europe 2013 recently quasi resonant amplification qra was proposed as a mechanism that when certain dynamical conditions are fulfilled can lead to such high amplitude wave events based on these resonance conditions a detection scheme to scan reanalysis data for qra events in boreal summer months was implemented with this objective detection scheme we analyzed the occurrence and duration of qra events and the associated atmospheric flow patterns in 1979 2015 reanalysis data we detect a total number of 178 events for wave 6 7 and 8 and find that during roughly one third of all high amplitude events qra conditions were met for respective waves our analysis reveals a significant shift for quasi stationary waves 6 and 7 towards high amplitudes during qra events lagging first qra detection by typically one week the results provide further evidence for the validity of the qra hypothesis and its important role in generating high amplitude waves in boreal summer

early miocene subtropical water temperatures in the southeast pacific abstract cenozoic climate of western south america is strongly controlled by features like andean uplift and the humboldt current the first strontium isotope age data from central and southern chile provide a latest oligocene to late early miocene age for classic warm water mollusk faunas reaching as far south as 45 s comparison with the biogeography of congeneric living species indicates that sea surface temperatures off central and southern chile during that time were at least 5 c higher than today i e minimum annual mean sea surface temperatures for darwin s navidad fauna at 34 s are estimated as 20 c as expected the number of tropical taxa decreases towards the south but several are still present as far south as 45 s the ages scatter relatively broadly between 24 and 16 ma partly even within individual localities shallow water and deeper water faunas are revealed to have similar ages when considered in light of convincing micropaleontological evidence for late miocene to early pliocene depositional ages the sr isotope data support a hypothesis that the mollusk fauna is reworked

salinity variability in the arabian sea argo floats deployed in the arabian sea provided an opportunity to look at the temporal variability of the core depth of arabian sea high salinity water mass ashsw at three locations in the north central and southern arabian sea these three locations show distinctly different variability patterns at the northern location we see a prominent semi annual cycle whereas at the central location an annual cycle dominates comparison with topex jason sea level data shows that this difference can be attributed to the influence of rossby waves at the central location in the southern arabian sea the variability in core depth is also dominated by an annual mode but there are 2 high frequency components near the madden julian oscillation frequencies thus the salinity distribution in the arabian sea apparently is influenced by both remote forcing and ocean atmospheric coupling

meteorological conditions in a thinner arctic sea ice regime from winter to summer during the norwegian young sea ice expedition n ice2015 atmospheric measurements were made over arctic sea ice north of svalbard from winter to early summer january june 2015 during the norwegian young sea ice n ice2015 expedition these measurements which are available publicly represent a comprehensive meteorological data set covering the seasonal transition in the arctic basin over the new thinner sea ice regime winter was characterized by a succession of storms that produced short lived less than 48 h temperature increases of 20 to 30 k at the surface these storms were driven by the hemispheric scale circulation pattern with a large meridional component of the polar jet stream steering north atlantic storms into the high arctic nonstorm periods during winter were characterized by strong surface temperature inversions due to strong radiative cooling radiatively clear state the strength and depth of these inversions were similar to those during the surface heat budget of the arctic ocean sheba campaign in contrast atmospheric profiles during the opaquely cloudy state were different to those from sheba due to differences in the synoptic conditions and location within the ice pack storm events observed during spring summer were the result of synoptic systems located in the barents sea and the arctic basin rather than passing directly over n ice2015 these synoptic systems were driven by a large scale circulation pattern typical of recent years with an arctic dipole pattern developing during june surface temperatures became near constant 0 c on 1 june marking the beginning of summer atmospheric profiles during the spring and early summer show persistent lifted temperature and moisture inversions that are indicative of clouds and cloud processes

radiogenic isotopes systematics and applications to earth surface processes and chemical stratigraphy radiogenic isotopes have wide application to chemical stratigraphy geochronology provenance studies and studies of temporal changes in earth surface processes this paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals these seawater isotope curves can be used for stratigraphic correlation and to assess changes through earth history in processes such as tectonic uplift climate change biogeochemical cycling ocean circulation crustal growth and surface water evolution understanding the modern biogeochemical cycle of the element isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles the main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration sample impurities and errors in age assignments rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves applications are discussed for the rb sr sm nd la ce lu hf re os u th pb k ar and cosmogenic isotope systems d 2003 elsevier b v all rights reserved

warm season subseasonal variability and climate extremes in the northern hemisphere the role of stationary rossby waves abstractthis study examines the nature of boreal summer subseasonal atmospheric variability based on the new nasa modern era retrospective analysis for research and applications merra for the period 1979 2010 an analysis of the june july and august subseasonal 250 hpa meridional wind anomalies shows distinct rossby wave like structures that appear to be guided by the mean jets on monthly subseasonal time scales the leading waves the first 10 rotated empirical orthogonal functions reofs of the 250 hpa wind explain about 50 of the northern hemisphere wind variability and account for more than 30 60 of the precipitation surface temperature variability over a number of regions of the northern middle and high latitudes including the u s northern great plains parts of canada europe and russia the first reof in particular consists of a rossby wave that extends across northern eurasia where it is a dominant contributor to monthly surface temperature and precipitation variability and

dissolution methods for strontium isotope stratigraphy guidelines for the use of bulk carbonate and phosphorite rocks diverse carbonate dissolution methods have been applied to bulk carbonate rocks in order to target least altered components for strontium isotope stratigraphy sis this is especially important for precambrian and cambrian studies for which no suitable skeletal material is available one proven method for bulk limestones involves the removal of up to a third of the powdered sample using an acid pre leach before partial dissolution of the rest of the sample using a weak acid or acid buffer solution we applied a similar technique to dissolve a range of lithologies limestone dolostone and phosphorite and compared the strontium isotopic composition of various leaches to contemporaneous seawater our results vindicate this approach and allow us to conclude that some dolomitic and phosphatic rock components may retain a near primary seawater 87sr 86sr composition once contaminant strontium from secondary calcite and other phases has been removed commonly applied trace element e g mn sr mg ca and isotopic c o screening cut offs were also examined in the light of these results and proved unreliable particularly in the case of dolostones and partially dolomitized limestones we recommend that rigid sample selection and sequential leaching procedures be applied to all sis studies of bulk materials and propose a general protocol for strontium isotope studies on marine authigenic rocks which may also be applicable to rare earth element and other geochemical studies of marine authigenic minerals in the future

two major cenozoic episodes of phosphogenesis recorded in equatorial pacific seamount deposits seamount phosphorites have been recognized since the 1950s but this is the first study to provide an in depth exploration of the origin and history of these widespread deposits representative samples from equatorial pacific cretaceous seamounts were analyzed for chemical mineralogical and stable isotope compositions the phosphorites occur in a wide variety of forms but most commonly carbonate fluorapatite cfa replaced middle eocene and older carbonate sediment in a deep water environment 1000 m element ratios distinguish seamount phosphorites from continental margin plateau and insular phosphorites uranium and thorium contents are low and total rare earth element ree contents are generally high ree ratios and shale normalized patterns demonstrate that the rees and host cfa were derived from seawater strontium isotopic compositions compared with inferred cenozoic seawater curves define two major episodes of cenozoic phosphatization late eocene early oligocene 39 34 ma and late oligocene early miocene 27 21 ma three minor events are also indicated the major episodes occurred at times of climate transition the first from a nonglacial to glacial earth and the second from a predominantly glacial to warm earth the paleoceanographic conditions that existed at those times initiated and sustained development of phosphorite by accumulation of dissolved phosphorus in the deep sea during relatively stable climatic conditions when oceanic circulation was sluggish fluctuations in climate sealevel and upwelling that accompanied the climate transitions may have driven cycles of enrichment and depletion of the deep sea phosphorus reservoir as temperature gradients in the oceans increased antarctic glaciation expanded and oceanic circulation and upwelling intensified expansion and intensification of the oxygen minimum zone may have increased the capacity for midwater storage of phosphorus supplied by dynamic upwelling around seamounts however the bottom waters never became anoxic during the phosphogenic episodes fluctuations in the ccd and lysocline co2 fluxes and changes in bottom water circulation and temperatures may have bathed the seamount carbonates in more corrosive waters which coupled with increased supplies of dissolved phosphorus promoted replacement processes the late eocene early oligocene phosphogenic episode recorded in seamount deposits is not matched by large phosphorite deposits in the geologic record whereas the late oligocene early miocene episode and middle miocene event are matched by large deposits distributed globally the seamount phosphorites are exposed at the surface of the seamounts and have been for most of the neogene and oligocene the phosphorites do not show signs of etching that would indicate substantial undersaturation of seawater phosphate with respect to cfa mass balance calculations indicate that about 5 4 19 1012 g of p2o5 are locked up in equatorial pacific seamount phosphorites that amount is equivalent to about 2 7 years of the present annual input from rivers

c o sr and pb isotope systematics of carbonate sequences of the vindhyan supergroup india age diagenesis correlations and implications for global events abstract the vindhyan supergroup of central india records a substantial portion of proterozoic time and contains some of the most disputed precambrian cambrian fossil discoveries despite the significance of these fossil finds many issues including reliable geochronology remained unresolved similarly the geochemical aspects of the sedimentary sequences and their implications to the evolution of proterozoic oceans have been studied only at a reconnaissance level here we report the results of the pb pb dating for the rohtasgarh limestone from the lower vindhyan supergroup giving an age of 1601 130 ma an estimate that is in accord with the recent u pb zircon dating of the lower vindhyan supergroup by rasmussen et al geology 30 2002 103 and ray et al geology 30 2002 131 sr isotope stratigraphy of carbonates from the upper vindhyan supergroup suggests a mid neoproterozoic 750 650 ma age for these formations this in turn argues for a long hiatus between the deposition of the lower and upper vindhyan supergroups our results conflict with the reports of cambrian age small shelly fossils and ediacaran fossils from the upper vindhyan rocks at the same time they suggest that the alleged trace fossils in the lower vindhyan rocks must be of paleoproterozoic age the most common 18 o values for calcitic components from limestone formations of the supergroup range from 10 to 7 similar to paleo neoproterozoic carbonates worldwide the modes of 13 c in the lower and upper vindhyan supergroups are 0 2 and 3 2 respectively again consistent with the worldwide dataset the secular patterns of carbon isotope trends do not support the earlier assumptions that the carbonate sequences at the southern margin correlate with those at the western or northern margins of the vindhyan basin c and sr isotope data provide new calibration points for the seawater evolutionary curves particularly for the paleoproterozoic for strontium isotopes the data from the lower vindhyan supergroup suggest that seawater departed probably less rapidly from mantle values than was previously believed

strontium isotope stratigraphy of kita daito jima atoll north philippine sea implications for neogene sea level change and tectonic history abstract a detailed chronology of a 432 m core from kita daito jima an atoll on the philippine sea plate has been obtained by strontium isotope stratigraphy the atoll carbonate extends to late oligocene age the top 100 m plio pleistocene section of the core has been dolomitized and dolomite also extends to middle miocene sediments sr isotopes identify two dolomitization events at 2 and 5 ma atoll growth appears to have been continuous between 18 8 and 24 3 ma and the fit of the growth history to a standard model provides a successful confirmation of darwin s subsidence theory the atoll growth appears to have commenced about 42 ma ago 6 ma after volcanism producing a 2 km column of atoll carbonate in agreement with bathymetry the subsidence model defines an apparent loss of 360 m of the sedimentary record since the early middle miocene boundary the amount in excess of the 100 m associated with sea level fall is attributed to plio pleistocene uplift at rates of 20 30 m ma associated with the forebulge of the philippine sea plate prior to its subduction uplift rates have also been estimated using a the heights of dated last interglacial coral reefs on kita daito jima and nearby minami daito jima 17 m ma and 29 m ma b sr isotope ages of calcites from surface samples on minami daito jima 21 m ma and c contrasts in elevation with okino daito jima 100 km away 22 m ma the locations of hiatuses and ages of dolomitization indicate sea level falls of 80 m at 17 16 ma 30 m at 16 15 ma 125 m at 11 ma and 90 m at 5 ma and at 2 ma the data have been combined with those from enewetak atoll to produce a curve of sea level change for the neogene

variability and trends in anticyclonic circulation over the greenland ice sheet 1948 2013 melting and mass loss on the greenland ice sheet have accelerated in recent years possible causes include broader arctic warming reduced snow ice cover lowered ice sheet albedo and changes in atmospheric circulation anticyclonic ridging over greenland leads to southerly advection of warm air and clear sky conditions promoting high melt rates to examine the relative importance of ridging we examine direct measures of summer 500 hpa anticyclonic circulation strength and frequency in greenland from 1948 to 2013 isolating the atmospheric circulation signal from 500 hpa geopotential height variations anticyclonic circulation anomalies account for 38 49 of the interannual variability and trend in summer air temperature and melt indices vorticity detrended geopotential height anomalies explain an additional 13 27 of the variance we identify an abrupt persistent shift to strong anticyclonic circulation in central greenland beginning in 2001 which has contributed to recent increases in greenland ice sheet melt

an itcz like convergence zone over the indian ocean in boreal late autumn 1 we examined the convective activity over the tropical indian ocean in boreal autumn using satellite observation data in november and december we detected an intertropical convergence zone like itcz like precipitation zone between maldives and somalia that is unobserved in the other periods of the year it accompanied a high sea surface temperature sst north of the equator and a cold tongue near the equator similar to the itczs over the pacific and atlantic oceans however the formation mechanism of the sst anomalies over the indian ocean is not the same as that in the pacific and atlantic oceans the high sst region forms in early november corresponding to weak sea surface wind during the monsoon transition the low sst along the equator appears associated with the upwelling of the subsurface water

strontium isotope stratigraphy for late cretaceous time direct numerical calibration of the sr isotope curve based on the us western interior the 87sr 86sr of sr in macrofossil carbonate from upper cretaceous strata deposited in the western interior seaway usa provides a sr isotope curve for late cretaceous time cenomanian early maastrichtian the curve is calibrated biostratigraphically against the most refined ammonite zonation known for the interval and calibrated numerically with 39ar 40ar dates for 20 bentonites within the sequence marine 87sr 86sr decreased from 0 70743 in the late middle cenomanian to a late cretaceous minimum of 0 70730 in the late turonian 89 ma from the minimum 87sr 86sr increased through a middle campanian inflexion minimum at 77 ma maximum at 78 80 ma to reach 0 70772 at the campanian maastrichtian boundary thereafter 87sr 86sr increased through a very short inflexion in the latest early maastrichtian to the limit of our sampling in the earliest late maastrichtian the inflexions provide global event markers for correlation for most of the period covered by our curve resolution in dating and correlation of 0 8 ma should be achievable with our 2 s d precision in measurement of 18 10 6 our 87sr 86sr data show no evidence of having been affected by influxes of freshwater into the us western interior seaway from rivers including those that drained the sevier orogenic belt

spatial and temporal variability of central indian ocean salinity fronts observed by smos soil moisture and ocean salinity smos sea surface salinity sss measurements in addition to other data are used to study the occurrence of salinity fronts in the poorly sampled indian ocean which exhibits unique seasonal wind and current reversals the strength and extent of salinity fronts are analyzed to understand their variabilities salinity fronts computed from smos compare favorably with those computed from argo floats data with smos showing higher magnitudes and more detailed structure of the fronts than argo strong salinity fronts are observed along the equatorial region with meridional migration of the fronts following the migration of the intertropical convergence zone itcz and meridional ocean currents linked with these fronts are less saline subsurface waters that are sustained by the itcz influenced precipitation and warm near surface layer during the 2010 negative indian ocean dipole event the equatorial front was influenced more by the increased sss along the equator rather than precipitation additional factors such as advective processes aid the dynamics of fronts in the tropical indian ocean zonal currents advect less saline waters from the eastern indian ocean into the central indian ocean additionally the indonesian throughflow transports less saline waters to the region south of the equator which eventually influence sss front dynamics

an analysis of sst gradients off the peruvian coast the impact of going to higher resolution abstract the peruvian coastal upwelling system pcus is one of the most productive fisheries in the world upwelling events are associated with changes in the magnitude and location of frontal structures sst gradients from four different data sets ncdc remss ostia and mur are compared in two test areas off the pcus paita 5 s and pisco 14 s in both areas gradients derived from the mur data set show greater magnitudes as well as larger seasonal cycles off pisco the magnitude of the seasonal cycle of 2 2 c 100 km in mur is larger than the one derived from the lower resolution data sets all data sets at pisco exhibit a seasonal cycle that peaks in late austral summer and early fall hovmoller diagrams calculated at 5 5 s 10 5 s and 14 5 s show clearly defined offshore maxima in the cross shore gradients for all the data sets upwelling scales determined by the distance to the first maxima vary depending on the data set used at 5 5 s upwelling scales vary from 10 km for mur to 50 km for ncdc at 14 5 s the scales vary from 20 km for mur to 40 km for ostia all four data sets show similar large scale structures associated with the peruvian upwelling however mur shows finer scale structures that are most likely due to submesoscale to mesoscale eddies sub sampled mur 1 km data at the 25 km 9 km and 4 km resolutions compare well in magnitude and phase with the lower resolution products agreement in gradient magnitude between the lower resolution data sets and the mur sub sampled at their respective resolutions implies that the pixel to pixel analysis noise in mur is at a similar level as the other data sets

the recent shift in early summer arctic atmospheric circulation 1 the last six years 2007 2012 show a persistent change in early summer arctic wind patterns relative to previous decades the persistent pattern which has been previously recognized as the arctic dipole ad is characterized by relatively low sea level pressure over the siberian arctic with high pressure over the beaufort sea extending across northern north america and over greenland pressure differences peak in june in a search for a proximate cause for the newly persistent ad pattern we note that the composite 700 hpa geopotential height field during june 2007 2012 exhibits a positive anomaly only on the north american side of the arctic thus creating the enhanced mean meridional flow across the arctic coupled impacts of the new persistent pattern are increased sea ice loss in summer long lived positive temperature anomalies and ice sheet loss in west greenland and a possible increase in arctic subarctic weather linkages through higheramplitude upper level flow the north american location of increased 700 hpa positive anomalies suggests that a regional atmospheric blocking mechanism is responsible for the presence of the ad pattern consistent with observations of unprecedented high pressure anomalies over greenland since 2007 2012 american geophysical union all rights reserved

sr isotopic composition of paleoproterozoic 13c rich carbonate rocks the tulomozero formation se fennoscandian shield abstract rb sr systematics has been studied in 13c rich carbonate rocks of the paleoproterozoic 2 09 0 07 ga tulomozero formation in the northern onega lake area the se fennoscandian shield the formation is divided into eight members a f consisting of greenschist facies grade variegated sandstones siltstones mudstones stromatolitic dolostones and subordinate crystalline limestones samples of carbonate rocks were obtained from two overlapping drillholes intersecting the entire thickness of the tulomozero formation prior to isotope analysis the rocks powders were treated with 1n ammonium acetate for partial removal of the late epigenetic carbonate phases major resetting of the rb sr systems in the tulomozero carbonate rocks appears to take place during the svecofennian regional metamorphic event and it was screened by using mn sr fe sr mg ca and 18o 16o ratios high sr content up to 2080 g g in limestones and 530 g g in dolostones coupled with low fe mn 0 40 in dolostones of the upper part of member b and of members g and h is indicative of seawater influxes sea transgression into the tulomozero basin the 87sr 86sr values in the least altered mn sr

rb sr sm nd k ca o and h isotopic study of cretaceous tertiary boundary sediments caravaca spain evidence for an oceanic impact site isotopic ratios and trace element abundances were measured on samples of ir enriched clay at the cretaceous tertiary boundary and in carbonate and marl from 5 cm below and 3 cm above the boundary samples were leached with acetic acid to remove carbonate and with hydrochloric acid leachates and residues were measured the sr nd o and h isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials the data indicate that most of the clay material was derived from a terrestrial source with relatively low87sr 86sr and high143nd 144nd ratios the 18o data suggest that the detritus has been modified by submarine weathering k ca and rb sr systematics as well as o isotope ratios of k feldspar spherules within the boundary clay suggest that they are predominantly authigenic and may have formed after the time of deposition however sm nd and rb sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus the isotopic evidence for foreign terrestrial detritus in the boundary clay the low rare earth element concentrations and high ni concentration support the hypothesis of a terminal cretaceous asteroidal impact that produced a global layer of fallout the data are most easily explained if the impact site was on oceanic crust rather than continental crust and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere 3 km this would probably require a single large impactor

regional dependence in the timing of onset of rapid decline in arctic sea ice concentration arctic sea ice concentration from satellite passive microwave measurements is analyzed to assess the form and timing of the onset of decline of recent ice loss and the regional dependence of the response the timing of the onset is estimated using an objective method and suggests differences of up to 20 years between the various subregions a clear distinction can be drawn between the recent onset times of the atlantic sector beginning in 2003 and the much earlier onset times associated with the pacific sector where the earliest transition to rapid loss is found in 1992 rates of decline prior to and following the transition points are calculated and suggest that the postonset rate of loss is greatest in the barents sea and weakest in the pacific sector covariability between the seasons is noted in the sic response both at interannual and longer time scales for two case regions potential mechanisms for the onset time transitions are briefly analyzed in the barents sea the onset time coincides with a redistribution of the pathways of ice circulation in the region while along the alaskan coast the propagation of the regional signal can be traced in the age of the sea ice the results presented here indicate a series of spatially self consistent regional responses and may be useful in understanding the primary drivers of recent sea ice loss

subseasonal atmospheric regimes and ocean background forcing of pacific arctic sea ice melt onset one observed fingerprint of pacific arctic environmental change induced by climate warming and amplified local feedbacks is a shift toward earlier onset of sea ice melt shorter freeze periods impact the melt season energy balance with cascading effects on ecological productivity and human presence in the region through this study a non linear technique self organizing maps is utilized to investigate the subseasonal role of regional pressure patterns and associated lower tropospheric wind regimes on melt onset in the beaufort and chukchi seas focus is directed on the frequency and duration 3 consecutive days of offshore onshore and zonal weak flow that tend to precede anomalous late and early and average times of melt background north pacific climate forcing ascribed from the pacific decadal oscillation pdo phase and bering strait oceanic heat flux measurements provide a surface thermal context to the composite wind fields in early melt onset years onshore northerly winds occur approximately 1 3 fewer days with offsetting increases in zonal and offshore flow in the beaufort and chukchi seas during these cases the beaufort high pattern tends to set up more frequently around the southeastern beaufort sea region yielding winds of a southerly and or easterly nature that are enhanced by cyclone activity to the south or downstream chukchi sea weather analyses in particular suggest that interacting precursor mechanisms involving warm air advection off snow free arctic lands and from southerly latitudes coupled with a slightly positive pdo state and anomalous poleward oceanic heat transfer condition the seasonal ice pack for increasingly early melt

atmospheric response in summer linked to recent arctic sea ice loss since 2007 a large decline in arctic sea ice has been observed the large scale atmospheric circulation response to this decline is investigated in era interim reanalyses and hadgem3 climate model experiments in winter post 2007 observed circulation anomalies over the arctic north atlantic and eurasia are small compared to interannual variability in summer the post 2007 observed circulation is dominated by an anticyclonic anomaly over greenland which has a large signal to noise ratio climate model experiments driven by observed sst and sea ice anomalies are able to capture the summertime pattern of observed circulation anomalies although the magnitude is a third of that observed the experiments suggest high ssts and reduced sea ice in the labrador sea lead to positive temperature anomalies in the lower troposphere which weaken the westerlies over north america through thermal wind balance the experiments also capture cyclonic anomalies over northwest europe which are consistent with downstream rossby wave propagation

strontium isotope 87sr 86sr stratigraphy of ordovician bulk carbonate implications for preservation of primary seawater values the present study on bulk carbonate 87 sr 86 sr stratigraphy represents a companion work to earlier research that presented a conodont apatite based ordovician seawater 87 sr 86 sr curve for the tremadocian katian stages 485 445 ma here we directly compare the curve based on conodont apatite including some new data not published in earlier work with a new curve based on 87 sr 86 sr results from bulk carbonate from the tremadocian sandbian stages we sampled eight lower to upper ordovician carbonate successions in north america to assess the reliability of bulk carbonate to preserve seawater 87 sr 86 sr and its utility for 87 sr 86 sr chemostratigraphy a high resolution 87 sr 86 sr curve based on 137 measurements of bulk conodont apatite is used as a proxy for seawater 87 sr 86 sr 87 sr 86 sr seawater in total 230 bulk carbonate samples that are paired to conodont samples were measured for 87 sr 86 sr in order to determine the conditions under which 87 sr 86 sr seawater is preserved in bulk carbonate results indicate that well preserved bulk carbonate can faithfully record the 87 sr 86 sr seawater trend but that its 87 sr 86 sr values are commonly more variable than those of conodont apatite on average bulk carbonate samples of the same age vary by 10 20 10 5 compared to 5 10 10 5 for conodont apatite the amount of isotopic alteration of bulk carbonate from seawater 87 sr 86 sr 87 sr 86 sr was determined by taking the difference between 87 sr 86 sr values of bulk carbonate and the approximated seawater trend based on the least radiogenic conodont 87 sr 86 sr values cross plots comparing 87 sr 86 sr values to bulk carbonate sr concentration sr and conodont color alteration indices cai an estimate of the thermal history of a rock body indicate that bulk carbonate is most likely to preserve 87 sr 86 sr seawater minimally altered when either 1 bulk carbonate sr is greater than 300 ppm or 2 carbonate rocks experienced minimal thermal alteration with burial temperatures less than 150 c carbonates with intermediate sr e g between 130 and 300 ppm can also yield 87 sr 86 sr seawater values but results are less predictable and local diagenetic conditions may play a greater role modeling results support the argument that seawater 87 sr 86 sr can be preserved in bulk carbonates with low sr if pore water rock ratios are low 87 sr 86 sr is similar to the seawater 87 sr 86 sr value preserved in limestone bulk carbonate samples that meet these criteria can be useful for high resolution measurements of 87 sr 86 sr seawater with a sample variation on par with fossil materials 5 particularly for successions where well preserved fossil material i e conodonts or brachiopods is not available such as precambrian strata sequences recording mass extinction events or otherwise fossil barren facies these criteria and model predictions based on bulk carbonate sr must be considered in the context of whether a limestone accumulated under calcite seas e g ordovician with relatively high seawater sr ca or aragonite seas in which case the diagenetic transformation of aragonite to calcite may result in incorporation of non seawater sr

divergent patterns of recent sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region abstract over the past three decades of the observed satellite record there have been significant changes in sea ice cover across the bering chukchi and beaufort seas of the pacific arctic region par satellite data reveal that patterns in sea ice cover have been spatially heterogeneous with significant declines in the chukchi and beaufort seas yet more complex multi year variability in the bering sea south of st lawrence island these patterns in the chukchi and beaufort seas have intensified since 2000 indicating a regime shift in sea ice cover across the northern portion of the par in particular satellite data over 1979 2012 reveal localized decreases in sea ice presence of up to 1 64 days year canada basin and 1 24 days year beaufort sea which accelerated to up to 6 57 days year canada basin and 12 84 days year beaufort sea over the 2000 2012 time period in contrast sea ice in the bering sea shows more complex multi year variability with localized increases in sea ice presence of up to 8 41 days year since 2000 the observed increases in sea ice cover since 2000 in the southern bering sea shelf region are observed in wintertime whereas sea ice losses in the canada basin and beaufort sea have occurred during summer we further compare sea ice variability across the region with the national centers for environmental prediction ncep north american regional reanalysis narr wind and air temperature fields to determine the extent to which this recent variability is driven by thermal vs wind driven processes results suggest that for these localized areas that are experiencing the most rapid shifts in sea ice cover those in the beaufort sea are primarily wind driven those offshore in the canada basin are primarily thermally driven and those in the bering sea are influenced by elements of both sea ice variability and its drivers across the par provides critical insight into the forcing effects of recent shifts in climate and its likely ultimate profound impacts on ecosystem productivity across all trophic levels

the arctic oscillation signature in the wintertime geopotential height and temperature fields the leading empirical orthogonal function of the wintertime sea level pressure field is more strongly coupled to surface air temperature fluctuations over the eurasian continent than the north atlantic oscillation nao it resembles the nao in many respects but its primary center of action covers more of the arctic giving it a more zonally symmetric appearance coupled to strong fluctuations at the 50 hpa level on the intraseasonal interannual and interdecadal time scales this arctic oscillation ao can be interpreted as the surface signature of modulations in the strength of the polar vortex aloft it is proposed that the zonally asymmetric surface air temperature and mid tropospheric circulation anomalies observed in association with the ao may be secondary baroclinic features induced by the land sea contrasts the same modal structure is mirrored in the pronounced trends in winter and springtime surface air temperature sea level pressure and 50 hpa height over the past 30 years parts of eurasia have warmed by as much as several k sea level pressure over parts of the arctic has fallen by 4 hpa and the core of the lower stratospheric polar vortex has cooled by several k these trends can be interpreted as the development of a systematic bias in one of the atmosphere s dominant naturally occurring modes of variability

identification of connate water in interstitial solution of chalk sediment interstitial solution was recovered from core samples of a borehole through 472 m of the upper cretaceous chalk formation in eastern england the solution has been analysed for major and some minor components and also for oxygen and hydrogen isotopic composition samples of the carbonate rock have also been analysed following acid dissolution the general feature of interstitial solution chemistry is a progressive dilution of dissolved species with decreasing depth from a near marine composition found in the deepest samples which are identified as connate water departures from the expected dilution trend are interpreted as evidence for diagenetic reactions during burial or as a result of freshwater circulation following subaerial uplift sr2 li and f have been enriched in interstitial solution and k has been slightly depleted the profile of chalk chemistry with depth shows no conclusive evidence for changes in the mg and sr content of the bulk carbonate due to freshwater diagenesis the 18o and d of the interstitial water reflect the same mixing as that shown by dissolved species however an apparent depletion of 18o and d in the deepest fluids with respect to the expected marine isotopic composition is tentatively explained as a result of the differences in diffusion rates of aqueous oxygen and hydrogen and of ionic solutes

dissolution methods for strontium isotope stratigraphy whole rock analysis the preparation of samples for strontium isotope stratigraphy sis by whole rock dissolution results in contributions of sr from contaminant phases as well as from the target carbonate phase here we highlight and quantify the errors in 87sr 86sr values that might result when calcium carbonate is dissolved using an inappropriate method we report the variation in 87sr 86sr value of sr released from four samples of differing calcite content and degrees of cementation when subject to different methods of dissolution we show that errors of up to 0 000076 in 87sr 86sr which correspond to errors of 3 68 ma in age can be avoided by careful preleaching of the samples

patterns of sea ice retreat in the transition to a seasonally ice free arctic abstractthe patterns of sea ice retreat in the arctic ocean are investigated using two global climate models gcms that have profound differences in their large scale mean winter atmospheric circulation and sea ice drift patterns the community earth system model large ensemble cesm le presents a mean sea level pressure pattern that is in general agreement with observations for the late twentieth century the community climate system model version 4 ccsm4 exhibits a low bias in its mean sea level pressure over the arctic region with a deeper icelandic low a dynamical mechanism is presented in which large scale mean winter atmospheric circulation has significant effect on the following september sea ice extent anomaly by influencing ice divergence in specific areas a lagrangian model is used to backtrack the 80 n line from the approximate time of the melt onset to its prior positions throughout the previous winter and quantify the divergence across the pacific and eurasian sectors of the arctic i

variability of salt flux in the indian ocean during 1960 2008 abstract this paper describes near surface horizontal salt flux in the indian ocean during 1960 2008 using the simple ocean data assimilation reanalysis version 2 2 4 the long term mean salt flux shows seasonal reversals that are more pronounced in the northern indian ocean than in the southern indian ocean mean zonal salt flux is of a higher magnitude than the mean meridional salt flux wyrtki jets influence zonal salt flux in the equatorial region meridional salt flux is northward along the northeast ne african coast and western bay of bengal bob during the southwest monsoon season the opposite holds during the ne monsoon season empirical orthogonal function analyses of salt flux show that the indian ocean dipole iod primarily controls interannual variability with flux being westward during positive dipole events and eastward during negative dipole events the co occurrence of iod with the el nino southern ocean results in enhanced salt flux especially along the equatorial region spatially the most variable regions are the ne african coast eastern arabian sea bob and equatorial regions this study will help interpret salinity data for the indian ocean from the recently launched soil moisture ocean salinity and aquarius satellite salinity missions

arctic sea ice retreat in 2007 follows thinning trend the minimum of arctic sea ice extent in the summer of 2007 was unprecedented in the historical record a coupled ice ocean model is used to determine the state of the ice and ocean over the past 29 yr to investigate the causes of this ice extent minimum within a historical perspective it is found that even though the 2007 ice extent was strongly anomalous the loss in total ice mass was not rather the 2007 ice mass loss is largely consistent with a steady decrease in ice thickness that began in 1987 since then the simulated mean september ice thickness within the arctic ocean has declined from 3 7 to 2 6 m at a rate of 0 57 m decade 1 both the area coverage of thin ice at the beginning of the melt season and the total volume of ice lost in the summer have been steadily increasing the combined impact of these two trends caused a large reduction in the september mean ice concentration in the arctic ocean this created conditions during the summer of 2007 that allowed persistent winds to push the remaining ice from the pacific side to the atlantic side of the basin and more than usual into the greenland sea this exposed large areas of open water resulting in the record ice extent anomaly

combined osmium and strontium isotopic study of the cretaceous tertiary boundary at sumbar turkmenistan a test for an impact vs a volcanic hypothesis osmium and strontium isotopic ratios at the cretaceous tertiary boundary at sumbar turkmenistan display a negative hyperbolic covariation superimposed on the long term trend which displays a positive covariation the minimum ratio for os and the maximum ratio for sr occur at the boundary clay volcanism with a mantle or crustal source cannot account for the isotopic data the low 187 o s 188 o s and the high 87 sr 86 sr ratios can be explained by an impact whereby os was derived from the bolide and the 87 sr 86 sr ratio was enhanced by acid rain and or a tsunami following the event