topographically induced baroclinic eddies near a coastline with application to he northeast pacific abstract a mathematical model is developed to describe the interaction between variable bottom topography and a steady horizontally sheared baroclinic coastal current the topography modeled in this study consists of an offshore seamount and a seaward protrusion of the continental slope the fluid motions are assumed to conserve potential vorticity on the f plane and expressions for the pressure density velocity and mass transport fields are obtained using a normal mode analysis and the appropriate green s function for the horizontal problem the theory is applied to the northeast pacific ocean in an attempt to model the anticyclonic eddy which has been observed by tabata west of sitka alaska the numerical calculations of the model and the observed location dimensions velocities and transports of the sitka eddy are in good agreement the axial velocities and dimensions of the calculated eddy field are largest for upstream surface and bottom currents of approximately 5 7 and 1 2 cm s 1 respectivel

pore properties as indicators of breakdown mechanisms in experimentally weathered limestones the results are reported of four experimental weathering tests freeze thaw wetting and drying slake durability and salt weathering on five different types of limestone effective porosity mercury intrusion porosimetry and scanning electron microscopy were used to evaluate changes in pore properties while weight loss and fracture density were used to assess deterioration severity a primary aim was to observe modifications in porosity due to weathering and to draw inferences about the internal rock deterioration mechanisms taking place it is concluded that the five limestones not only show a wide range of resistance to weathering in general but considerable difference in resistance to particular weathering processes consequently when assessing durability it is essential to consider rock properties in the context of the weathering process to which the rock is subject the type of deterioration indicator used is also important in interpretation of durability a variety of pore modification mechanisms operate including changes in pore connectivity pore infilling and the introduction of additional void space there are indications that changes to the internal pore structure of rocks due to weathering may be a precursor to more substantial macrodeterioration copyright 2001 john wiley sons ltd

salt weathering in dual porosity building dolostones abstract the influence of rock fabric on physical weathering due to the salt crystallization of selected brecciated dolostones is discussed these dual porosity dolostones are representative of heterogeneous and anisotropic building rocks and present highly complex and heterogeneous rock fabric features the pore structure of the matrix and clasts is described in terms of porosity and pore size distribution whereas the relative strength for each textural component is assessed using the knoop hardness test the whole characterisation process was carried out using the same samples as those used in the standard salt durability test en 12370 including connected porosity the water saturation coefficient fissure density compressional wave velocity and waveform energy results show the most important rock fabric elements to be considered are the matrix and clast properties and the nature of fissures firstly a relatively weak matrix was the focus of major granular disintegration as it presents high porosity low pore radius and reduced strength secondly narrow micro fissures appear to be important in the decay process due to the effectiveness of crystallization pressure generated by salt growth on the contrary macro fissures do not contribute greatly to rock decay since they act as sinks to consume the high supersaturations caused by growth of large crystals additionally an analysis of stress generated by crystallization was carried out based on the general situation of a lenticular crystal geometry finally the relationships between whole petrophysical properties and durability were established using a principal component analysis this analysis has clearly established that the durability of rocks affected by salt crystallization mechanisms diminishes in weaker and anisotropic rocks with high porosity and fissure density

monsoon fluctuations in two 20 000 yr b p oxygen isotope pollen records off southwest india abstract two marine pollen diagrams for sediments off the southwest coast of india provide a 20 000 yr history of the nearby continental vegetation determined by the monsoon climate within the framework of the isotopic stratigraphy two important phases of the evolution of the monsoon climate are a very arid period about 22 000 18 000 yr b p and a very humid period culminating at 11 000 yr b p the very arid period corresponds to the lowest pollen representation of mangrove vegetation which is used here as an indirect indicator of monsoonal runoff this aridity is due to a very weak southwest airflow a great reduction of summer monsoonal rainfall and reduced runoff of the western ghats rivers the extension of the monsoon over india after the last glacial maximum has been a gradual process following the northward progression of the intertropical convergene zone the very humid period corresponding to the highest pollen representation of mangrove vegetation and the heaviest summer rainfall is a climatic response to the maximum summer insolation of the northern hemisphere at 11 000 yr b p

holocene hydrological changes in se iran a key region between indian summer monsoon and mediterranean winter precipitation zones as revealed from a lacustrine sequence from lake hamoun abstract core sediments from the dry lake bed of hamoun were subdivided into 3 main sedimentary units using a multi proxy approach e g petrography grain size analysis total organic matter and caco 3 determination to reconstruct the palaeoenvironment of the sistan basin se iran as a transition zone between the monsoon summer precipitation zone of south asia and the mediterranean winter precipitation zone of the iranian plateau during the holocene data revealed that during the late glacial to early holocene the lake and its catchment area western hindu kush were under a more prominent influence of the indian ocean monsoon and formed a moist and productive environment with less wind action as shown by the provenance of high organic matter lacustrine sediments together with the lack of an aeolian fraction due to southward migration of the inter tropical convergence zone during the mid holocene arid climate manifested by an interplay of seasonal aeolian and fluvial deposition became dominant these conditions were due to reinforcement of subtropical anticyclones on the iranian plateau the presence of green to brownish green moderate organic matter lacustrine sediments showed that during the late holocene mediterranean type winter precipitation dominated in the area during the initial part of this period the shahr i sukhteh civilization was close to the lake the environment was relatively similar with that of today some palaeostorms can also be detected during this time interval shown by occurrences of high aeolian inputs in the basin

a less humid climate since ca 3500 yr b p from marine cores off karwar western india abstract a marked change in the vegetation of the western ghats at ca 3500 yr b p has been observed from a study of two marine cores taken from the inner shelf off karwar karnataka western india at the mouth of the kalinadi river this change is indicated by a decrease in forest pollen particularly from evergreen forests and by a corresponding increase in savanna pollen as well as by a reduction in mangrove pollen at the same time the values of the stable isotope 13 c of sedimentary organic matter increased suddenly due to a higher contribution of organic matter of margine origin all these modifications were probably induced by a less humid climate the term drier can hardly be used for an area where the annual rainfall still attains 6 m in the hills above this clear limit the same trends steady but considerably weaker also resulting a reduction in the humid conditions were recorded up to ca 2200 yr b p reduction in forest vs increase in savannas decrease in the mangrove vegetation higher 13 c values from there onwards the pollen assemblages have remained uniform up to the present day it may be deduced that a climate quite similar to the present conditions was established about 2200 yr ago and still prevails the curves representing the percentages of marine microfossils dinoflagellates organic tests of foraminifera eggs of copepods show little variation at the 3500 yr b p boundary the marine assemblages were modified drastically only at about 2200 yr b p these sharp modifications are probably due to an increase in the marine influence as a result of a reduction in the fresh water supply from the kalinadi the stability in the representation of marine assemblages which has persisted from about 2200 yr b p to the present confirms the establishment of the present day climate around that date this paleoclimatic reconstruction is in conformity with the evidence for the beginning of drier conditions recorded at about the same time in the low latitudes in many parts of the world india northern arabian sea africa sahara tropical forest east african lakes australia and the carribbean

deterioration mechanisms of tuffs in midas monument slightly weathered white and pink tuffs of the midas monument have deterioration problems in this study depths and characteristics of the weathering zones developed within the tuffs are investigated through optical microscopy x ray diffractometry xrd chemical analyses scanning electron microscopy sem and some index parameters accelerated weathering tests including wetting drying freezing thawing and salt crystallization are performed and durability assessment methods are used to predict the durabilities of the tuffs the findings are compared with field observations by examining quantitative weathering indices and comparing them with thin section studies it is found that thin section analyses of the crystals loi and wpi are good indicators to quantify the depth of weathering for the tuffs however thin section studies have limited value for fine grained tuffaceous matrix the chemical weathering of the tuffs produces weathered zones that are 4 5 cm thick within the white tuff and 2 5 cm thick within the pink tuff physical weathering causes scaling of outer layers of the tuffs and fracturing of feldspars along their cleavage planes however variations of the index properties of the tuffs due to weathering are not so significant to quantify the weathering depths in the tuffs among the accelerated weathering tests salt crystallization is found to be the most destructive environmental condition pigeon droppings rich in no3 are found to be the main source of soluble salt at the midas monument the salt transported up by capillary rise due to surface water causes spalling of the tuffs in the capillary zone surface water and salt of any kind in the close vicinity of the monument should be totally eliminated for the purpose of conservation field observations and the durability equations reveal that the white tuff is less durable than the pink tuff wet to dry strength ratio yields a better stone durability assessment among various durability methods used in this study d 2002 elsevier science b v all rights reserved

middle to late holocene environmental changes in the depositional system of the tropical brackish bolgoda lake coastal southwest sri lanka abstract the tropical bolgoda lake is one of the largest lagoonal estuaries in sri lanka organic constituents in this lake were investigated using 28 surface sediments three cores from the lake and four short cores from mangrove mud elemental and molecular compositions of sediments and living organic matter om were determined using cns elemental analysis and gas chromatography mass spectrometry respectively chronology of events was determined using accelerated mass spectrometry ams 14 c data for bulk oms woods and mollusk shells the history of bolgoda lake can be divided into two major chrono stratigraphic divisions namely a lower sedimentary succession from ca 7 0 cal ky b p to 2 5 cal ky b p and an upper sedimentary succession from ca 2 5 cal ky b p to the recent according to the sapropelic depositional system concentrations of the mangrove biomarker taraxone increased significantly at ca 7 0 cal ky b p the lower part of the sediment sequence had moderate productivity and was mainly deposited under marine terrestrial influence in oxygen poor anoxic conditions during mid holocene sea level highstands a drastic increase in total organic carbon toc content reaching 29 was found in one of the bolgoda cores this increase occurred because of sea level regression at about 2 5 cal ky b p this change was probably caused by development of a beach rock sandbar and the estuary system changed to a semi closed lake due to the sea level regression as a result aquatic vascular plants predominate in this depositional system after ca 2 5 cal ky b p toc content decreased slightly but relatively high toc contents were maintained in the muddy sediments in moderately sized and shallow 1 2 m tropical estuaries lagoons such as bolgoda lake drastic changes in toc contents may be the most sensitive indicator of sea level variations increase in higher plant om with higher n c 29 n c all and n c 37 n c all alkane ratios also suggest a climatic transition from wetter to somewhat drier after the middle holocene accumulations of pyrogenic polycyclic aromatic hydrocarbons pahs in the modern sediments record anthropogenic activity after european settlement in the 15th century

the north pacific climatology of winter mixed layer and mode waters abstract a climatology of the winter mixed layer in the north pacific ocean was constructed using hydrographic data from historical archives and recent observational programs including the world ocean circulation experiment the main aim was to provide better knowledge about source areas of upper water masses the authors have endeavored to preserve water properties near the frontal regions by keeping the smoothing scale as small as possible the resulting climatology shows considerable differences in the mixed layer depth and its water properties from those derived from the world ocean atlas woa maps of the potential vorticity field of the north pacific pycnocline are presented using the isopycnally averaged climatology hydrobase three distinct lateral minima of potential vorticity are identified as subtropical mode water stmw central mode water cmw and eastern subtropical mode water estmw in the western central and eastern parts of the subtropical gyre respectively the hydrobase isopy

the influence of net community production and phytoplankton community structure on co2 uptake in the gulf of alaska 1 biological productivity is a key factor controlling the ocean s ability to take up carbon dioxide from the atmosphere however the ecological dynamics that drive regions of intense productivity and carbon export are poorly understood in this study we present high spatial resolution estimates of air sea co2 flux net community production ncp rates calculated from o2 ar ratios and phytoplankton population abundances determined by continuous underway measurements on a cruise across the gulf of alaska in may 2010 the highest rates of ncp 79 2 13 mmol c m 2 d 1 and oceanic co2 uptake air sea flux of 14 7 2 4 mmol c m 2 d 1 were observed across a transition zone between the high nitrate low chlorophyll hnlc waters of the alaskan gyre and the coastal waters off the aleutian islands while the transition zone comprises 20 of the total area covered in crossing the gulf of alaska it contributed 49 of the total ncp and 48 of the total co2 uptake observed along the cruise track a corresponding transition zone phytoplankton bloom was dominated by two small celled 20 m phytoplankton communities which were distinct from the phytoplankton communities in the surrounding alaskan gyre and coastal waters we hypothesize that mixing between iron rich coastal waters and iron limited alaskan gyre waters stimulated this bloom and fueled the high ncp and co2 export observed in the region

submesoscale features and turbulent mixing of an oblique anticyclonic eddy in the gulf of alaska investigated by marine seismic survey data

multi year meanders and eddies in the alaskan stream as observed by topex poseidon altimeter the birth life and decay of long lived anticyclonic eddies or meanders in the alaskan stream are observed from topex poseidon t p satellite their surface height anomalies approach 72 cm average diameter is about 160km and they live for 1 to 3 years propagating along the stream with mean speed of 2 5 km d 1 of the six observed the last three were formed after the first t p observations in september 1992 of these two evolved from eddies near alaskan panhandle in winter drifting across the northern gulf of alaska before entering the alaskan stream while another formed in the stream west of shelikof strait

late pleistocene holocene paleoclimatic history of the southern kerala basin southwest india abstract the south kerala sedimentary basin sksb constitutes one of the most significant landward extensions of the southwest offshore sedimentary basins of india and is situated between 8o45 and 10o15 n latitudes with a maximum width of about 20 km and incorporating a 700 m thick sedimentary succession ranging in age from early miocene to holocene this belt lies almost entirely under water or alluvium covered coastal plains in this study we use two continuously cored bore holes at eruva 7 25m deep and muthukulam 3m deep separated by a distance of about 7km to investigate the depositional environment as well as paleo ecology of the depocentre and climatic aspects during the late pleistocene and holocene results from c14 dating of shell fragments from eruva depth zone 2 10 6 64m yielded ages in the range of 36 2 to 42 5 kybp corresponding to the late pleistocene wood fragments in the muthukulam core sample depth zone 1 27 3 00m gave c14 ages in the range of 3 7 to 7 2 kybp indicating a holocene history the lower half of the eruva bore hole indicates a marginal marine environment with an abundant supply of terrestrial carbonaceous debris probably corresponding to a period of abnormally high rainfall recorded in many parts of the globe covered by the asian summer monsoon the sediments in the upper part of this bore hole indicate a continuation of this environment but with much less input of terrestrial organic carbon the lower part of the bore hole from this locality corresponding to the holocene transgression is similar to the lower part of eruva bore hole in the case of toc deposition took place in water bodies with considerable marine influence but receiving high amounts of terrestrial plant debris mostly in the form of finely divided particles mixed with mud this transgressive sequence was also deposited during a time when the asian summer monsoon was abnormally high in intensity as indicated by many examples in india africa madagascar and elsewhere it is significant that during the deposition of this part the sea level was probably the same as present or higher suggesting possible lowering of the stream velocities and resultant deposition of only muddy sediments laden with terrestrial organic material along the coast the upper part of the section shows a progressively reduced rainfall pattern culminating in a period of very low precipitation with the development of a paleosol which is traceable all over the sksb where late holocene sediments are available this period also witnessed aeolian activity modifying the sand ridges in the ridge runnel systems formed by the holocene regression

impact of haida eddies on chlorophyll distribution in the eastern gulf of alaska mesoscale haida eddies influence the distribution of surface phytoplankton in the eastern gulf of alaska through two processes enhanced productivity in central eddy water and seaward advection of highly productive coastal waters in the outer rings of eddies these two processes were observed in a sequence of monthly images over five years for which images of seawifs derived chlorophyll distributions were overlaid by contours of mesoscale sea surface height anomaly derived from topex and ers 2 satellite observations satellite measurements were supplemented with ship based chlorophyll observations through one of the eddies haida eddies are deep anticyclonic mesoscale vortices that normally form in winter and early spring near the southwest coast of the queen charlotte islands high levels of chlorophyll observed in eddy centres indicated that they supported phytoplankton blooms in spring of their natal years with timing of these blooms varying from year to year and exceeding in magnitude the chlorophyll concentrations of surrounding water elevated chlorophyll levels also were observed in eddy centres in late summer and early autumn of their natal year enhanced chlorophyll biomass is attributed to higher levels of macro nutrients and higher levels of iron enclosed within eddies than in surface deep ocean water by late spring and summer when coastal water supported higher chlorophyll biomass than did oceanic offshore regions eddies that straddled the continental margin entrained high chlorophyll coastal water into their outer rings and carried it several hundred kilometres into the gulf of alaska along their southern sides on some occasions a deep ocean eddy would entrain chlorophyll from an adjacent eddy located closer to the coast forming a conveyor belt transport process to inject coastal biota into the deep sea region of the gulf this process extended the coastal region of high chlorophyll surface water and therefore phytoplankton rich water several hundred kilometres seaward and dominated the shelf to deep ocean exchange of chlorophyll from late winter to the following autumn

variability of technical properties and durability in volcanic tuffs from the same quarry region examples from northern hungary abstract volcanic tuffs are notoriously very heterogeneous materials exhibiting a recurrent lithological diversity which in turn can be associated with changing petrophysical and mechanical properties this variability was investigated on a small scale in different miocene acid tuffs extracted in the same quarry region within just a few km radius from the town of eger in northern hungary they have been exploited since the middle ages and used for common construction and historical monuments castles churches ottoman architectures or excavated and carved for creating wine cellars cave houses ritual sites etc these pyroclastic rocks are compositionally analogue but turn out to show unexpected major differences in texture and technical properties which affect their resistance to decay the rate and intensity of weathering examined in laboratory conditions by freeze thaw and salt attack tests is governed mainly by the following properties open porosity relative abundance of pumice crystals and groundmass pore size distribution and tensile strength nevertheless open porosity proportional to water absorption and indirectly related to mechanical performance is considerably different among the tuff varieties and this seems to be the most significant factor marking the diverse durability that is questionable in case of unpredicted textural diversities e g enrichment in pumice and higher concentration of groundmass therefore without rejecting the importance of complementary tests a basic and fast study involving thin section examination and open porosity measurement would be sufficient for providing many indications on the quality of these materials and for the selection of dimension stones for restoration of historical heritage and construction

anisotropic features of geometry and permeability in fractured rock masses abstract a geometric anisotropy factor a f of two dimensional natural fracture systems has been defined according to fracture spacing and orientation in a given direction geometric anisotropy of fracture systems has a major effect on the percolation threshold the critical fracture density of fracture systems below which the overall permeability is zero a two dimensional distinct element code udec has been used to calculate directional flow rates of fracture systems simulated and natural fracture patterns sampled on outcrops in the lake district england have been tested to examine the relation between geometric anisotropy and permeability anisotropy which is demonstrated to have a power law form also the differential anisotropy factor a f results in different universal exponents which govern the relation between fracture density and flow rates

constituent material properties and clast size distribution of volcanic breccia abstract volcanic breccia is a representative heterogeneous rock as a preliminary study for determining its mechanical properties in laboratory and field experiments its material properties and structural features were described three dimensional clast size distribution was also estimated for the study site using the theory of stereology with this distribution determined a numerical simulation was performed to investigate the relationship between the volumetric proportion of clasts in a sample and the areal proportion and maximum length of clasts on a lateral surface of the sample the following observations were made 1 coefficients of variation for volumetric proportion are dependent on the size of the sample and became large when the size of the sample is small 2 samples with a small coefficient of variation can be selected at any size if a restriction is placed on the ratio dmax d0 of the maximum length of clasts to the size of the sample and 3 the volumetric proportion of clasts in each sample can be estimated from the observed areal proportions within an error range that depends on the whole volumetric proportion

the influence of petrophysical properties on the salt weathering of porous building rocks the influence of pore structure water transport properties and rock strength on salt weathering is evaluated by means of a thorough rock characterisation and a statistical analysis the pore structure was described in terms of its porosity pore size distribution quantified by mean pore radius and specific surface area density and water transport was characterised by means of water permeability saturated flow and capillary imbibition unsaturated flow whilst the rock strength test was carried out using uniaxial compressive strength compressional and shear wave velocities dynamic elastic constants and waveform energy and attenuation were obtained from the digital analysis of the transmitted signal a principal component analysis and a stepwise multiple regression model was carried out in order to examine the direct relationships between salt weathering and petrophysical properties from the principal component analysis two main components were obtained and assigned a petrophysical meaning the first component is mostly linked to mechanical properties porosity and density whereas the second component is associated with the water transport and pore structure salt weathering quantified by the percentage of weight loss after salt crystallisation was included in both principal components showing its dependence on their petrophysical properties the stepwise multiple regression analysis found that rock strength has a predominant statistical weight in the prediction of salt weathering with a minor contribution of water transport and pore structure parameters

geochemistry of calcretes calcic palaeosols and hardpan coimbatore southern india formation and paleoenvironment abstract there is no major chemical variation in the late quaternary calcic nodules formed within vertisols in the foot hill regions and hardpan calcretes greater than 200 ka formed over the precambrian substrate that occur as duricrust horizons in the plains around coimbatore region tamil nadu india the bulk chemistry of calcic nodules and the hardpan calcretes show very little variability in cao sio2 al2o3 and fe2o3 content the trend of trace metal content in calcic nodules and in the hardpan calcrete is mn zn ni cr pb co cu and zn mn ni co pb cu cr respectively paas normalised ree data of the calcretes calcic nodules and the hardpan demonstrate a positive euanomaly this could be attributed to feldspar apatite mineral alteration and soil digenetic processes differential weathering leaving behind plagioclase phenocrysts and apatite grains which are enriched in eu the stable isotope values of the calcic nodules do not exhibit a wide range 18o 3 39 to 5 84 and 13c 3 01 to 6 64 compared to the hardpan calcretes 18o 2 91 to 12 98 and 13c 0 05 to 7 4 the palaeoenvironment during the formation of the calcretes nodules was dominated by the c4 plants with sparse vegetation cover and that the parent material bedrock supported a thin veneer of soil column with sparse vegetation cover as present day calcic nodule accumulations in the soils has resulted from differential weathering and chemical histories within the soil profiles while the hardpan calcretes formed by complex pedogenic and chemical groundwater processes in arid semi arid conditions over along geological period during the late mis3 to the lgm period the south west monsoon was weak with mean annual rainfall mar between 300 and 500 mm yr the sea level was low and the rainfall at the time of carbonate formation would have remained damp enough to allow silicate weathering of the soil sediments

northeast monsoon variations during the holocene inferred from palaeochannels and active channels of the palar river basin southern peninsular india the present day palar river and its palaeochannel located in the southern peninsular india were investigated with a multidisciplinary approach the main aim of the study was to reconstruct the palaeoenvironment history of the palar river basin and to delineate the role of holocene fluctuations that played a major role in the geomorphological evolution of the region since the holocene period the results obtained based on sedimentary facies analysis supported by elemental concentrations and optically stimulated luminescence osl dates reveal distinct seven climatic phases since the past 10 ka phase 1 signifies a very high precipitation as attested by the low cwi with high rb sr ratio subsequent to phase 1 a decreasing trend in the northeast monsoon rainfall nemr is observed phase 2 phase 3 4 83 3 59 ka reflects a decrease in nemr further supported by low mn al mg al and chemical index of alteration cia values phase 4 3 59 ka is marked by high sand flux higher k al ti al rb sr and ba

observations from a yakutat eddy in the northern gulf of alaska 1 the impingement of deep basin eddies on the shelf in the gulf of alaska has been implicated as an important mechanism for cross shelf exchange the influence of eddies on biological processes has been confirmed with data from the sea viewing wide field of view sensor showing elevated chlorophyll associated with eddies altimetry data suggest that an eddy formed in the winter of 2003 near yakutat alaska and propagated along the shelf break reaching the head of the gulf by spring this eddy was sampled during may and september of 2003 the eddy core water was warm salty and high in nitrate relative to basin water of the same density but was similar to historical water properties from the shelf near yakutat this suggests a shelf origin for the eddy core water

the dynamics of mangrove ecosystems changes in sea level and the strategies of neolithic settlements along the coast of oman 6000 3000 cal bc abstract this paper focus on the holocene palaeogeography of the ja alan coast from the 6th to the 4th millennium cal bc integrating the dynamics of mangroves lagoons khors estuaries and deltas with sea level change and the evidence from neolithic shell middens the distribution and maturation of mangrove ecosystems along the arabian coasts has varied considerably affected by physical forces such as sea level changes climate tidal amplitude and duration as well as the quantity of fresh water inflow associated with the monsoon systems along the arabian coast palaeo mangroves and lagoons today replaced by large sabkhas appear to be correlated to mid holocene fossil deltas and estuaries that currently function episodically depending on the rhythm of winter rains all these parameters have determined and impacted the location of settlement networks and the economic strategies of the first arabian farmers along the eastern arabian coast the mid holocene sea level highstand stability 5th millennium bc can be considered to be an optimum period for mangrove development and can be correlated with neolithic sites around the mangroves the decline of mangroves since 3000 2500 cal bc and further degradation is mainly attributed to the prevailing arid climate that reduced summer monsoon effects in the tropical area by favouring the extension of sabkhas we discuss these aspects based on new archaeological surveys excavations and geoarchaeological studies

mineral magnetic proxies of erosion oxidation cycles in tropical maar lake sediments lake tritrivakely madagascar paleoenvironmental implications abstract mineral magnetic measurements were performed on the upper 16 m of five piston cored sedimentary sequences from lake tritrivakely madagascar ams 14 c dating and correlation of the five magnetic susceptibility records allowed establishment of a composite sedimentary record of the last 46 kyr our data suggest that mineral magnetic changes result from changes in concentration of strongly ferrimagnetic terrigenous minerals and from preservation dissolution cycles of detrital iron oxides primarily high coercivity fe iii phases such as hematite in alternately oxic and anoxic depositional environments high coercivity iron oxide phases are restricted to stratigraphic intervals that are interpreted to represent dry periods with oxic conditions comparison with other paleoenvironmental proxies pollen total organic carbon lithology suggests that the sediments record relatively humid conditions before 22 kyr bp and relatively dry conditions during the last glacial maximum lgm and the early holocene such results contrast with the previous observations of relatively dry glacial conditions and humid mid holocene conditions in the summer rainfall area of east and se africa

vegetation response to south asian monsoon variations in konkan western india during the late quaternary evidence from fluvio lacustrine archives the palaeobotanical and palynological data along with physical proxies obtained from konkan western india have been addressed while ascertaining the vegetation response to monsoon variations since late pleistocene 53 000 yrs bp the retrieved plant fossil assemblage being a sensitive indicator of climate changes has important implications in palaeoclimate study of the late pleistocene as it is the first of its kind in the entire 7500 km long coastline of india the plant fossil assemblage of the lacustrine sediments forms potential evidence for the prevalence of wet evergreen forest in the late pleistocene 44 000 yrs bp this scenario was attributed to prevalence of an extended period of rainfall of both the southwest sw and northeast ne monsoon in konkan although the indian subcontinent was under the influence of active tectonic processes numerous fossil plant taxa are now confined to freshwater myristica swamps of southeast asia in general and that of southwestern india in particular suggesting that these areas maintain a similar monsoon trend to that existing prior to 44 000 yrs bp on the other hand the ne monsoon did not reappear during the early holocene when the sw monsoon became strong along the konkan coast many of the plant species of the fossil assemblage have been displaced from konkan as a response to weakening of the monsoons since the late pleistocene and towards the last glacial maximum lgm the aridity reduced rainfall since late pleistocene including the lgm and limited terrestrial accumulation in the early holocene suggests an ecological shift and subsequent replacement of evergreen forest cover and a possible break in sedimentation palynological evidence of the late holocene 3000 yrs bp fluvio lacustrine sediments reveals that the evergreen forest could not reappear rejuvenate in konkan due to such climatic stress in contrast to southwestern india and sri lanka where extended rainfall was still prevalent the hypothesis of an extended period of monsoonal rains prior to 44 000 yrs bp in the present humid tropical parts of konkan holds significance as data on paleosols and vertebrate fossils from the semi arid arid parts of western india indicate relatively wet climate and wetland flood plains

salt and ice crystallisation in porous sandstones salt and ice crystallisation in the pore spaces causes major physical damage to natural building stones the damaging effect of these processes can be traced back to physically induced stress inside of the rock while crystallizing the increasing scientific research done during the past century has shown that there are numerous parameters that have an influence on the weathering resulting from these processes however the working mechanisms of the stress development within the rock and its material dependency are still subject to discussion this article gives an overview of salt and ice weathering additionally laboratory results of various sandstones examined are presented salt crystallisation tests and freeze thaw tests were done to obtain information about how crystallisation weathering depends on material characteristics such as pore space water transportation and mechanical features simultaneous measuring of the length alternating during the salt and ice crystallisation has revealed detailed information on the development of crystal in the pore spaces as well as the development of stress these findings can help to understand the damaging mechanisms

physical deterioration of sedimentary rocks subjected to experimental freeze thaw weathering ten types of sedimentary rock were subjected to repeated cycles of freezing and thawing in addition to monitoring sample weight loss throughout testing a detailed graphic record was made of deterioration mode and its relationship to pre existing rock flaws results suggest that the presence or absence of rock flaws alone does not control deterioration mode but rather that it is the coupled relationship between these flaws and rock strength and textural properties which exerts greatest influence while some pre existing flaws such as syndepositional deformation structures do not appear to influence breakdown others such as incipient fractures cavities and minor lithological boundaries frequently coincide with concentrations of deterioration a characteristic mode of deterioration which is independent of pre existing flaws tends to develop in sandstones indicating the influence in this case of rock texture particularly strong rocks such as crystalline limestone and metasediment tend to fracture preferentially along distinct linear weaknesses such as mineral veins stylolites and incipient fractures particularly weak rocks such as low density chalk break down in a random fashion without regard to pre existing flaws in addition to providing some insight into the role of pre existing flaws in rock deterioration this work also has practical implications for i the study of landform development due to weathering and ii the selection of representative rock samples in durability testing for building stone copyright 2000 john wiley sons ltd

currents and transport on the eastern bering sea shelf an integration of over 20 years of data abstract more than 20 years of data from moorings satellite tracked drifters and hydrographic surveys are integrated to provide a comprehensive view of currents and transport on the eastern bering sea shelf the major sources of water onto the eastern bering sea shelf are north pacific water flowing through unimak pass and bering slope water flowing onto the shelf usually via the canyons that intersect the shelf break absolute geostrophic transport through unimak pass varies from an average of 0 25 106 m3 s 1 sv in the warm months to 0 43 sv in the cold months flow along the 50 m isobath is weak with a transport of 13 months and from amukta pass to bering strait via the bering slope current is 8 months consequently the source of most of the heat transported into the arctic through bering strait is a result of air sea interactions local to the northern bering sea analysis of the currents and water properties on the southern shelf indicates that 50 of the shelf water is exchanged with slope water during october january each year this exchange elevates the october mid shelf average nitrate level from 6 m to 14 16 m by the end of january

iron transport by mesoscale haida eddies in the gulf of alaska abstract a two year study of the iron distributions in anticyclonic mesoscale haida eddies of the eastern north pacific ocean has shown that such eddies are a major source of iron to the high nitrate low chlorophyll hnlc waters of the central gulf of alaska basin these eddies which are typically about 100 km in diameter form off the west coast of canada in winter and then track roughly westward into the open ocean therefore they carry large quantities of iron rich coastal waters into iron limited waters of the oligotrophic gyre when the eddies had first formed their dissolved iron concentrations were nearly two orders of magnitude higher than is typically observed at station papa 50 n 145 w 3 n m versus less than 0 05 n m and the total iron in the eddies surface waters 10 40 m was more than 13 n m higher than open ocean waters of the alaska gyre 14 n m versus 0 5 n m while the overall iron content of the eddies decreased rapidly during the first year after they formed the eddy we were able to track the longest still contained 1 5 2 times more iron than the surrounding waters 16 months after its formation therefore although iron concentrations in the surface mixed layers of the eddies drop to levels observed outside very rapidly within 4 months upward transport along isopycnals and upwelling due to eddy decay as well as vertical advective and diffusive transports typical of north pacific waters probably provide steady fluxes of iron into the euphotic zone from the still iron rich eddy core waters throughout the lifetime of the eddy

spatial attenuation the most sensitive ultrasonic parameter for detecting petrographic features and decay processes in carbonate rocks abstract the evaluation of stone quality by means of non destructive tests is of vital importance especially when rock is used as a building material usually however only vp p wave velocity is considered when rock properties such as strength durability or decay level are assessed in this paper we propose a novel ultrasonic estimator based on wave energy spatial attenuation s the benefits of this estimator were evaluated by comparison with five other ultrasonic parameters compressional v p and shear v s wave velocities velocity ratio v p v s waveform energy and temporal attenuation the sensitivity of each ultrasonic parameter was compared by measuring 300 samples from ten different types of rock each type was selected according to its mineralogy calcite and or dolomite rock and structural complexity homogeneous fractured brecciated foliated or laminated samples were subjected to weathering tests thermal shock and salt crystallisation tests in order to study the sensitivity of both ultrasonic parameters during fracture initiation fracture growth and rock fabric disintegration results show that although vp is the most widely used parameter the information it yields is extremely imprecise however the new parameter s is highly sensitive to the petrographic characteristics of rocks as well as to the presence of individual defects fractures vugs or disintegrated areas moreover the most significant aspect of s is that its values fall between two fixed limits 0 db cm and 20 db cm a rock with a s value close to 0 db cm is an unweathered homogeneous and good quality rock whilst a s value higher than 12 db cm indicates extreme decay i e open fractures developed vugs and or disintegrated areas

petrographic quantification of brecciated rocks by image analysis application to the interpretation of elastic wave velocities abstract this paper presents a new procedure to quantify the petrology of materials with complex and heterogenic rock fabric features the classical methodologies for petrographic quantification by image analysis are not appropriate for this kind of rock due to both the high chromatic complexity of these materials and the scale with which the samples are studied the proposed process is particularly interesting for materials with complex chromatic characteristics such as highly fractured rocks concrete etc two commercial varieties of highly fractured brecciated dolostones were selected for this study in order to test the designed methodology this new procedure is based on the analysis process of colour images obtained from mesoscopic sample scanning six petrographic parameters and diagrams have been designed in order to quantify the most influential aspects in compressional v p and shear v s ultrasonic wave propagation these petrographic parameters and diagrams are brecciation density brecciation density map clast size distribution fine grained matrix content shape preferred orientation and rose diagrams the results demonstrate that the proposed methodology is suitable for quantifying the petrography of these kinds of materials furthermore the variations measured in v p and v s are fully explained by the values measured for the following parameters brecciation density fine grained matrix content clast size distribution and preferred orientation of clasts

3 d water properties and geostrophic circulation on the eastern bering sea shelf abstract the national oceanic and atmospheric administration s noaa alaska fisheries science center bottom trawl survey samples demersal fish at over 350 sites on the eastern bering sea continental shelf each summer on a 37 37 km 2 grid rugged conductivity temperature depth sensors ctds were added to the net hauls to obtain gridded data sets of temperature and salinity measurements for 2008 2010 results reveal the three dimensional thermohaline structure of the shelf including the cold pool and areas of fresher water around st matthew island and in bristol bay horizontal gradients are often strongest roughly along the 50 m and 100 m isobaths that traditionally separate the inner and outer shelf from the middle shelf centered along the 70 m isobath the summer mixed layer depth is less than 30 m over much of the region it reaches the bottom along the alaska peninsula in water depths greater than 70 m showing that the boundary of the well mixed inner shelf is not always at the 50 m isobath the greatest upper to lower layer density difference is found across the shelf north of 59 n the salinity difference is the main contributor to this density difference over most of the region in 2008 and 2010 but the temperature difference dominates in 2009 due to decreased ice melt and reduced freshening near st matthew island the geostrophic velocity relative to the bottom shows northwestward flow seaward of the 100 m isobath and northwestward transports integrated across the shelf of 0 10 0 25 10 6 m 3 s in 2008 and 2010 there was clockwise circulation in a region of less saline water around st matthew island in 2009 that fresher lens did not exist and flow was more concentrated along the 100 m isobath bringing saltier water across the shelf

dynamics and energetics of trapped diurnal internal kelvin waves around a midlatitude island abstractthe generation of trapped and radiating internal tides around izu oshima island located off sagami bay japan is investigated using the three dimensional stanford unstructured nonhydrostatic terrain following adaptive navier stokes simulator suntans that is validated with observations of isotherm displacements in shallow water the model is forced by barotropic tides which generate strong baroclinic internal tides in the study region model results showed that when diurnal k1 barotropic tides dominate resonance of a trapped internal kelvin wave leads to large amplitude internal tides in shallow waters on the coast this resonance produces diurnal motions that are much stronger than the semidiurnal motions the weaker freely propagating semidiurnal internal tides are generated on the western side of the island where the m2 internal tide beam angle matches the topographic slope the internal wave energy flux due to the diurnal internal tides is much higher than that of the semidiurnal tides

correlation between rock fabrics and physical properties of carbonate reservoir rocks three carbonate core samples from an oil and gas reservoir of the nw german basin were chosen to study the correlation between rock fabrics and physical properties of reservoir rocks detailed fabric analyses and texture investigations were carried out as well as laboratory measurements of different physical properties e g density porosity permeability electrical conductivity seismic compressional and shear wave velocities although the three core samples come from a similar depositional facies they show great differences in the occurrence and three dimensional distribution of the rock fabric elements these heterogeneities are the result of various diagenetic and tectonic processes for the correlation between the rock fabrics and the physical properties four main rock fabric types have to be considered a major constituents e g fossils ooides peloides and crystals b pore space with different pore types c fractures and d stylolites the results of the correlation clearly show that the values and anisotropies of the petrophysical properties are fairly related to the observed fabric elements with their different arrangements spatial distributions and preferred orientations these results also provide a fundamental understanding of the petrophysical responses such as seismics to the different geological features e g fractures and their dynamic changes with pressure which can be converted to different depths the knowledge gained from such correlations may lead to an improved interpretation of geophysical data for hydrocarbon exploration and production and therefore to an advanced reservoir characterization

a regression modeling approach for studying carbonate system variability in the northern gulf of alaska 1 the northern gulf of alaska goa shelf experiences carbonate system variability on seasonal and annual time scales but little information exists to resolve higher frequency variability in this region to resolve this variability using platforms of opportunity we present multiple linear regression mlr models constructed from hydrographic data collected along the northeast pacific global ocean ecosystems dynamics globec seward line the empirical algorithms predict dissolved inorganic carbon dic and total alkalinity ta using observations of nitrate no3 temperature salinity and pressure from the surface to 500 m with r2s 0 97 and rmse values of 11 mol kg 1 for dic and 9 mol kg 1 for ta we applied these relationships to high resolution no3 data sets collected during a novel 20 h glider flight and a globec mesoscale seasoar survey results from the glider flight demonstrated time space along isopycnal variability of aragonite saturations arag associated with a dicothermal layer a cold near surface layer found in high latitude oceans that rivaled changes seen vertically through the thermocline the seasoar survey captured the uplift to 100 m of dense high pco2 waters at the shelf break that had been forced by the passage of a yakutat eddy during this event the aragonite saturation horizon depth where arag 1 shoaled to a previously unseen depth in the northern goa this work is similar to recent studies aimed at predicting the carbonate system in continental margin settings albeit demonstrates that a no3 based approach can be applied to high latitude data collected from platforms capable of high frequency measurements

stratification on the eastern bering sea shelf revisited abstract the timing and magnitude of stratification can have profound influences on the marine ecosystem on the eastern bering sea shelf in the absence of strong wind mixing stratification can be initiated by the melting of seasonal sea ice or by springtime warming of the surface temperature and salinity both influence the stratification of the eastern bering sea shelf with their relative importance varying spatially and temporally in the northern middle shelf domain north of 60 n salinity stratification is often as important as temperature stratification on the southern middle shelf while the influence of temperature on stratification dominates during summer the influence of salinity stratification plays a role in the interannual variability mooring 2 m2 56 9 n 164 1 w has been deployed at 70 m depth in the southern middle shelf domain since 1995 data from this mooring show that stratification typically begins to set up in may and to break down in september october but these dates can vary by 30 d while no trend is found in the timing of the spring setup the fall stratification breakdown exhibited a trend toward later breakdown 2 d later per year from 1996 to 2009 results suggest that it may be difficult to forecast stratification on the eastern bering sea shelf from climate models as simple indices of wind mixing or heat fluxes are not correlated with stratification contrary to intuition the strength of summer stratification is not correlated with depth averaged temperature warm years such as 2000 and 2001 can have low stratification and cold years such as 2007 can have very high stratification this decoupling of stratification and temperature has implications for forecasting the ecosystem in the face of climate change as we cannot assume that projections of a warmer climate simply imply higher stratification in the future

low frequency isopycnal variability in the alaska gyre from argo abstract the deployment of a large number of argo floats in the northeast pacific ocean since 2001 has led to a great increase in the volume of data available to study the regional variability on interannual to decadal time scales in this paper gridded fields of hydrographic data from argo are used to examine the low frequency variability of representative isopycnal surfaces over the alaska gyre in the eastern subpolar north pacific anomalies in the depth of isopycnal surfaces and spice anomalies on these surfaces are considered over the 14 year period 2004 2017 an eof analysis is used to characterize the variability occurring at large scales over the region the leading mode of isopycnal depth anomalies through the upper 1000 m of the water column is found to be related to the pacific decadal oscillation the response of a stochastic climate model driven by local ekman pumping is shown to give a reasonable account of variability in the depth of the shallow main pycnocline over the alaska gyre although ocean dynamics must play a role in shaping the spatial response to the wind forcing evidence is presented for counter propagating isopycnal depth anomalies in the subarctic current at the depth of the main pycnocline propagation is dominated by disturbances that are advected eastward by the mean flow at greater depths isopycnal depth anomalies propagate westward at approximately twice the speed of first mode long baroclinic rossby waves consistent with the propagation of rossby waves seen in altimetric observations of sea surface height variability the eastward advection of spice anomalies is also evident in the upper ocean however the dominant signal in the record is a large scale positive spice anomaly that forms locally on subsurface isopycnals evidence is presented that this anomaly arises mainly from the downward diffusion across the pycnocline of heat associated with the marine heatwave of 2013 14 over the northeast pacific the extent to which anomalies are generated locally may limit the potential for decadal prediction of upper ocean conditions over the region

stratigraphical and palynological appraisal of the late quaternary mangrove deposits of the west coast of india the organic deposits derived from the mangrove swamps form reliable stratigraphic markers within the late quaternary sequence of kerala konkan basin three generations of such deposits have been identified the older one is dated to around 43 000 40 000 14c yr b p with a few dates beyond the range of radiocarbon the younger ones date from the middle holocene to latest pleistocene 10 760 4540 14c yr b p and the late holocene 4000 14c yr b p pollen analyses confirm that the deposits are mostly derived from the mangrove vegetation peat accumulation during the period 40 000 28 000 14c yr b p can be correlated with the excess rainfall 40 100 greater than modern values of the asian summer monsoon the low occurrence of mangrove between 22 000 and 18 000 14c yr b p can be attributed to the prevailing aridity and or reduced precipitation associated worldwide with last glacial maximum because exposure surfaces and ferruginous layers are commonly found in intervals representing this period the high rainfall of 11 000 4000 14c yr b p is found to be the most significant as the mangrove reached an optimum growth around 11 000 14c yr b p but with periods of punctuated weaker monsoons from the present and previous studies it has been observed that after about 5000 or 4000 14c yr b p the monsoons became gradually reduced leading to drying up of many of the marginal marine mangrove ecosystems a case study of hadi profile provided an insight to the relevance of magnetic susceptibility to record the ecological shift in late holocene

the influence of building materials on salt formation in rural environments blocks of limestone and sandstone used in walls of the manasija monastery complex showed damage caused by the efflorescence and subflorescence of different salts in a low pollution rural environment in addition to common salts such as thenardite thermonatrite trona and gypsum a small amount of eugsterite and darapskite was also present although these sodium and sodium calcium salts formed where cement mortar was used for repairs the lithological type and chemical composition of the substrate also had an influence on the development of distinct salts the interaction between limestone and sandstone substrates and a solution rich in sodium without calcium was successfully simulated in the laboratory the presence of gypsum and sodium calcium sulphate as experimental products solely on the limestones indicated that in addition to the cement mortar solution part of the calcium required for the formation of calcium and double sodium calcium salts could occur from this substrate

mid holocene climate and land sea interaction along the southern coast of saurashtra western india abstract the relict mudflat from the southern saurashtra coast of gujarat was investigated using geochemical and palynological analyses supported by radiocarbon dating to understand whether climate fluctuations and sea level operated in tandem during mid holocene the study revealed that the saurashtra coast experienced relatively wet climatic conditions with simultaneous occurrence of marginally high sea level between 4710 and 2825 cal yr bp subsequently a gradual onset of aridity and lowering of the sea level was observed between 2825 and 1835 cal yr bp and further a slight decrease in aridity is observed after 1835 cal yr bp the present day coastal configuration was probably achieved after around 1500 cal yr bp considering the tectonic instability of saurashtra coast land level changes the effective mid holocene sea level was estimated to be 1 m higher than the present the study demonstrates that sea level changes climate variability and land level changes were coupled during the mid holocene

experimental salt weathering of limestones in relation to rock properties a total of 21 different types of british and european mesozoic limestones have been subjected to simulated salt weathering using sodium sulphate na2so4 with the following aims assessment of the relative durabilities of different types of limestone assessment of the importance of modulus of elasticity and other factors in affecting durability and assessment of the use of impulse excitation techniques to monitor changes in rock modulus of elasticity the rocks showed a wide spectrum of durabilities while rocks with high values of modulus of elasticity lower water absorption capacities high densities and low salt uptakes tended to be durable there were anomalies the explanation for which probably lies in their pore structures non destructive testing techniques showed that although the more durable rocks failed to lose weight or to show visual signs of disintegration their modulus of elasticity values did tend to decline indicating a loss in strength copyright 1999 john wiley sons ltd

late pleistocene holocene monsoon variations on climate landforms and vegetation cover in southwestern india an overview abstract signatures of monsoon variability preserved in the late quaternary sediments of southwestern india have been decoded and addressed using biological proxies along with geochronological data barring sediments beyond the threshold for conventional 14c dating late pleistocene sequences have been recognized both in konkan and kerala basins konkan area has only subsurface continental lacustrine late pleistocene whereas kerala coast has mixed facies the landscape as well as the vegetation cover has been substantially modified and the fossil contents and related palaeoenvironment provided ample evidence to demonstrate the landscape and vegetation dynamics since late pleistocene evidence of myristica swamps until late pleistocene and its subsequent replacement by riparian forest towards late holocene in konkan has been a significant impact of monsoon variations on the tropical rain forests the prevalence of such freshwater swamps and a sensitive habitat indicated that konkan had enjoyed an extended period of rainfall due to the combined effects of both sw and ne monsoons until the late pleistocene the tropical rainforest cover along kerala coast has shrunken considerably and pieces of evidence suggest that the entire terrain west of sahyadri western ghats was under dense forest cover during the holocene climatic optimum 9 0 6 0 k yrs bp when the region had witnessed heavy precipitation much higher than that of the present the forest land has been converted into major wetlands and present ecology is unsuitable to support evergreen forests and it can be concluded that coastal plains and associated landforms were covered by thick tropical evergreen forests which got destroyed by flooding towards middle holocene development of a chain of wetland system all along kerala coast loss of sheltered habitat and mangrove cover and loss of sensitive freshwater myristica swamps are some of the significant aspects brought in while addressing the monsoon variability in southwestern india

observation of mesoscale ocean features in the northeast pacific using geosat radar altimetry data in this paper geosat altimetry data from the northeast pacific are examined the data are 1 binned data on 1 latitude by 2 longitude blocks and 2 collinear track data the binned data cover the region from 20 n to 60 n from the north american coast westward to 150 w and span from december 15 1986 to june 1 1989 to examine the data for evidence of westward propagation of sea level anomalies three zonal transects 45 n 49 n and 57 n are made complex empirical orthogonal function analysis of the data transects at these latitudes reveals phase speed and amplitude information the first eigenmode at each latitude has a very strong annual signal two dimensional spectral analysis of the first eigenmode at 45 n and 57 n shows westward propagation of sea level anomalies at 45 n only the propagating features are annual in period and of order 1000 km in length at 57 n westward propagation is evident as at 45 n but there is also an eastward component to examine the variability of the coastal sea level signal collinear track data from three ascending tracks crossing the gulf of alaska are analyzed revealing mesoscale features of the order of 100 km that parallel the canadian and alaskan coast the most notable feature is the sitka eddy westward propagation of several of these features is observed the results from the analysis of both types of geosat data are compared with other observational data

abrupt changes in the asian southwest monsoon during the holocene and their links to the north atlantic ocean during the last ice age the indian ocean southwest monsoon exhibited abrupt changes that were closely correlated with millennial scale climate events in the north atlantic region1 2 3 suggesting a mechanistic link in the holocene epoch which had a more stable climate the amplitude of abrupt changes in north atlantic climate was much smaller and it has been unclear whether these changes are related to monsoon variability here we present a continuous record of centennial scale monsoon variability throughout the holocene from rapidly accumulating and minimally bioturbated sediments in the anoxic arabian sea our monsoon proxy record reveals several intervals of weak summer monsoon that coincide with cold periods documented in the north atlantic region4 including the most recent climate changes from the medieval warm period to the little ice age and then to the present we therefore suggest that the link between north atlantic climate and the asian monsoon is a persistent aspect of global climate

long term observations of alaska coastal current in the northern gulf of alaska abstract the alaska coastal current is a continuous well defined system extending for 1700 km along the coast of alaska from seward alaska to samalga pass in the aleutian islands the currents in this region are examined using data collected at 20 mooring sites and from 400 satellite tracked drifters while not continuous the mooring data span a 30 year period 1984 2014 using current meter data collected at a dozen mooring sites spread over four lines seward gore point kennedy and stevenson entrances and the exit to shelikof strait total transport was calculated transport was significantly correlated with alongshore winds although the correlation at the seward line was weak the largest mean transport in the alaska coastal current occurred at gore point 1 4 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer with the transport at the exit to shelikof strait 1 3 10 6 m 3 s 1 in winter and 0 6 10 6 m 3 s 1 in summer only slightly less the transport was modified at the seward line in late summer and fall by frontal undulations associated with strong river discharge that enters onto the shelf at that time of year the interaction of the alaska coastal current and tidal currents with shallow banks in the vicinity of kodiak archipeligo and in kennedy stevenson entrance results in mixing and prolonged primary production throughout the summer

reconstruction of the 30 40 ka bp enhanced indian monsoon climate based on geological records from the tibetan plateau abstract multi proxy records from ice caps lakes and pollen records from the tibetan plateau are used to reconstruct the palaeoclimate during the period 30 40 ka bp lake geomorphological and lacustrine sedimentological studies show that numerous high lake level stands and or freshwater lakes occurred in large areas of western china at this time including over the tibetan plateau where the area contains mostly shallow water and saline hypersaline water lakes under extremely dry conditions of today pollen based reconstruction of tibetan vegetation shows systematic differences from the present alpine steppe forests were shifted ca 400 km further north and the alpine conifer forest extended ca 400 800 km beyond their present western limits variations in 18 o curves from ice cores from the plateau suggest that the temperature was 2 4 c higher and precipitation was 40 to over 100 higher than today all of the evidence consistently suggests the existence of an exceedingly strong summer monsoon climate over the plateau the vigorous evaporation of the tropical ocean surface would also play an important role in promoting the penetration of moisture rich southwest monsoon over the tibetan plateau these climate patterns with strong summer monsoon circulation during the period 30 40 ka bp reflect the 20 ka earth orbital precessional cycle when the tibetan plateau region received greater solar radiation which thus enlarged the thermodynamical contrast between the plateau and the mid south portion of the indian ocean

holocene climatic vicissitudes and sea level changes in the south western coast of india appraisal of stable isotopes and palynology abstract the southern kerala coast in sw india has experienced dramatic changes in climate and sea level during holocene these changes are apparently well preserved in the sedimentary archives of the estuarine basins that are entrenched on the uplifted neogene deposits here we report the sedimentary processes palaeoclimate and sea level records decoded from two borehole cores puthenthuruthu and munrothuruthu borehole cores retrieved respectively from the marine and fluvial ends of the second largest estuarine basin in sw india the ashtamudi estuary using sedimentology palynology and stable isotopes as the major proxies the heavy rainfall event at the latter half of early holocene 6117 101 bp is reflected well in the isotopic signatures of the puthenthuruthu borehole core the higher level of lighter isotopes of oxygen and carbon at 10 15 m below ground level is a clear indication of freshwater influx from the hinterland due to intensified monsoon activity this in turn was responsible for the development of bay head delta in the fluvial end of the estuary during early middle holocene period palynological contents below the level indicate a facies change as freshwater and terrestrial elements dominate over marine contents further the occurrence of desmids shows the marine facies is being gradually replaced by freshwater to continental facies this was followed by the deposition of littoral sands as flood tide islands within the estuarine basin the palynological investigations of sediments with radiocarbon age of 4350 90 bp in the munrothuruthu borehole core show a dry phase with high saline depositional environment in the beginning which is followed by influx of freshwater as indicated by the higher content of lighter isotopes of carbon and oxygen in the calcareous nodules algal pisolites embedded in the sediments the occurrence of pteridophytic spores and a few pollen of cullenia in the palynological preparations in the upper half of the silt and clay dominated intervening layers reiterate this view

rock fabric pore geometry and mineralogy effects on water transport in fractured dolostones abstract the combined influence of rock fabric pore geometry and mineralogy petrological parameters on transport properties in complex and heterogeneous naturally fractured rocks was studied experimentally as fissure geometry quantification has rarely been addressed in most theoretical studies of transport properties emphasis was placed on the effects of fissure geometry on both non saturated media capillary rise and saturated media permeability we proved that prediction of transport properties in complex rocks is not guaranteed by the estimation of the classic micro structural variables considered in the literature and that accurate prediction can only be attained when petrological parameters are first quantified in depth and then combined principal component analysis and the regression models proposed here clearly demonstrated on the one hand that a meaningful porous network in non saturated media must be modelled with a combination of different geometrical capillary tubes representing the matrix cylindrical and the fissure rectangular prism and on the other hand that in saturated media a well in deep fissure size quantification enabled a more accurate prediction of permeability to be made the experimental data confirm that transport properties and its anisotropy are closely dependent on fissure typology textural characteristics mineralogy and spatial distribution of the whole rock fabric elements enlarged fissures weakly exert capillary suction due to the retarding effect of gravitational forces but they are vital in controlling permeability cracklebreccias with small clasts high dolomite cement content and high inter clast fissure density exhibit strong capillary suction however high calcite cement produces abnormally low rates of capillary rise due to possible pore surface contamination together with a high contact angle effect good agreement between permeability and geometric factors provided a suitable basis for identifying preferred permeable directions additionally we found a critical fissure density which defined the isotropic matrix permeability we also present a new practical and simple linear model relating permeability to capillarity with meaningfully and easily estimated petrological parameters results obtained in the present study demonstrated the correct identification and use of more directly related petrological variables for modelling transport properties moreover the analysis of these results using multivariate analysis is considerably more demanding compared to the conventional approaches

impact of salt and frost weathering on the physical and durability properties of travertines and carbonate tufas used as building material this study was financed by the spanish ministry of education and science mec through the research project cgl2006 05027 bte and community of madrid s2023 mit 2914 a pre doctoral research fellowship was awarded to n cueto by the mec

upwelling and convergence in the middle atlantic bight shelfbreak front convergent and upwelling circulation within the shelfbreak front in the middle atlantic eight are detected using a dye tracer injected into the bottom boundary layer at the foot of the front from the three day displacement and dispersion of two dye injections within the front we infer lagrangian isopycnal diapycnal velocities and diffusivities of 2 x 10 2 m s 4 x 10 6 m s and 9 m 2 s 6 x 10 6 m 2 s these results substantiate model predictions of chapman and lentz 1994 and previous dye tracer observations by houghton 1997

cryogenic powderization of triassic dolostones in the buda hills hungary disintegration of dolostones to dolomite powder powderization was a widespread phenomenon in triassic dolostones of the buda hills where the areal extent of powdered dolostones is large compared to similar occurrences elsewhere in the world in the buda hills dolostone disintegration proceeded in four stages that correspond to a gradual decrease in particle size that is from the parent dolostone to 1 crackle breccia via 2 mosaic breccia diameter 2 cm via 3 mosaic breccia blocks floating in dolomite powder to 4 dolomite powder diameter 100 300 m stable isotope ratios and trace element compositions of dolomite remained constant throughout these stages and there are no indications of dissolution in most locations suggesting that disintegration was predominantly a mechanical process combining these findings with the geological history of the region and supported by a simple freezing thawing experiment and pertinent experimental studies on weathering of building stones it appears that powderization in the buda hills was caused by repeated freeze thaw cycles during and or after the pleistocene glaciations subaerial exposure under cold climate conditions involves multiple freeze thaw cycles that create mechanical stresses in the rock framework related to the opposing thermal expansion of rock and water that freezes and of ice that liquefies this process is herewith called cryogenic powderization our data further suggest that the synergy of four factors promoted dolostone powderization in the buda hills 1 tectonics which created a pervasive fracture network 2 intercrystalline porosity of the dolostone 3 relatively high water saturation and 4 subaerial exposure under cold climate conditions

evolution of the coastal wetland systems of sw india during the holocene evidence from marine and terrestrial archives of kollam coast kerala abstract kerala coast in southwest india is endowed with an interlacing network of wetlands evolved during the late quaternary the wetlands in the southern part of kerala especially around kollam district show antecedent characteristics and are incised on the neogene sediments these wetlands include 20 0 35 0 m thick deposits of holocene sediments containing good archives of landform evolution and climate changes holocene sedimentation was initiated at about 8920 110 bp and is represented mainly by sub fossil wood peat or carbonaceous clays subsequent deposition of brackish water to marine sediments occurred in the middle holocene the proposed evolutionary model reveals that many wetland bodies including sasthamkotta lake chelupola lake chittumalachira lake and kotta lake were evolved from the proto estuarine basins the upper arms of the pre holocene ashtamudi and paravur estuaries were cut off due to progradation of alluvial sediments during the holocene climatic optimum

environmental magnetism past present and future environmental magnetism involves the application of rock and mineral magnetic techniques to situations in which the transport deposition or transformation of magnetic grains is influenced by environmental processes in the atmosphere hydrosphere and lithosphere the first explicit description of environmental magnetism as a distinct field was in 1980 since that time environmental magnetism has become a broad field that is finding application in an ever increasing array of scientific disciplines in this review of the present state of environmental magnetic studies we divide the field into three broad but arbitrary categories the first involves the use of mineral magnetic assemblages in the geological record to study physical processes in depositional environments this category includes the correlation of sediment cores using magnetic susceptibility measurements studies of geomagnetic field behavior the analysis of depositional and postdepositional mechanical processes that affect sediments and the examination of magnetic parameters that might represent proxies for paleoclimatic variation the second category encompasses studies of the processes responsible for variations in the magnetic minerals brought into a sedimentary environment these provenance investigations include studies of changes in catchment derived sediment in lakes fluctuations in contributions from terrigenous aeolian and glaciogenic components in deep sea sediments and the origin of atmospheric particulates the final category addresses in situ changes and transformations of magnetic minerals in sedimentary environments including pedogenesis authigenetic diagenetic formation of ferrimagnetic phases dissolution of magnetic minerals due to reductive diagenesis and contributions of biomagnetism to sedimentary magnetism because environmental magnetism can address problems in so many disciplines and because many of these problems may be inaccessible to other techniques it is likely that the scope of environmental magnetism will continue to expand rapidly environmental magnetism is capable of providing important data for studies of global environmental change climatic processes and the impact of humans on the environment all of which are major research initiatives in the international scientific community these factors suggest that environmental magnetism has a bright and diverse future

a multi proxy reconstruction of monsoon variability in the late holocene south india abstract pookode lake kerala south india a fresh water lake situated at an altitude of 770 m a s l receives predominantly rains from the south west monsoon a sediment core 125 cm long was investigated for sediment texture dating and geochemical composition radiocarbon dates obtained on the organic carbon rich sediments of the pookode lake range in age from the mid holocene to more recent 6240 565 14 c bp bc 4786 to ad 1434 cal geochemical data of the sediment cores were corroborated with phytolith and pollen studies although phytoliths occur in the entire sediment core pollen assemblages start occurring only since 1500 14 c bp ad 650 cal the sediments older than 1500 14 c bp were not suitable for the preservation of the pollen assemblages there is a major change in the lake hydrology indicating lacustrine conditions subsequent to 1500 bp occurrence of diatoms in the upper sediment layers of the sediment core indicates shallowing of the lake both the medieval warm period mwp and the little ice age lia are represented in the pookode lake sediment core sediment texture chemical weathering intensity cwi values supported by phytolith and pollen assemblages indicate that overall warm and dry conditions prevailed during 6200 420 14 c bp bc 4786 ad 1434 cal but this was interrupted by short intense wet phases between 3900 and 1900 bc 4000 ad 300 cal 1400 760 ad 800 ad 1200 cal and 420 140 14 c bp ad 1570 ad 1860 cal the wet events resulted from the strengthening of south west monsoon swm causing rising water levels and brief expansion of the pookode lake margin

combined effects of salt cyclic wetting and drying cycles on the physical and mechanical properties of sandstone abstract salt weathering has considerable effects and it has recently become the subject of interest among researchers and engineers especially in terms of sandstone heritage buildings and sandstone monuments however the impacts of salt weathering on sandstone after wetting drying cycles have been neglected in the literature under the conditions of the long term or gradual underground seepage of water into sandstone heritage buildings and monuments salt accumulation and recrystallization occur in sandstone when the rate of evaporation is sufficiently high and they reduce rock stability in view of this problem experiments subjecting sandstone to up to 50 wetting drying cycles were conducted using water and solutions containing concentrations of 4 6 or 8 magnesium sulfate mgso4 the physical and mechanical properties were tested after different wetting drying cycles the results show that the wetting drying cycles impacted the sandstone samples soaked in a salt solution more than the samples that were soaked in only water thirty cycles is the threshold number in terms of changes in p wave velocity thermal conductivity and tensile strength a correlation analysis was conducted and it showed that both color lightness and thermal conductivity are good parameters for evaluating tensile strength the results contribute to the evaluation process and protection of sandstone heritage buildings and monuments against salt weathering

differential rates of vertical accretion and elevation change among aerial root types in micronesian mangrove forests abstract root systems in mangrove swamps have captured the attention of scientists for decades among the postulated roles of root structures include a contribution to the geomorphological stability of mangrove soils through sediment trapping and binding in this study we used feldspar marker horizons and sediment pins to investigate the influence of three different functional root types prop roots in rhizophora spp root knees in bruguiera gymnorrhiza and pneumatophores in sonneratia alba on vertical accretion and elevation change in three mangrove forests in the federated states of micronesia prop roots facilitated vertical accretion 11 0 mm year 1 more than pneumatophores or bare soil controls mean 8 3 mm year 1 sediment elevation on the other hand increased at an average rate of only 1 3 mm year 1 across all root types with rate differences by root type ranging from 0 2 to 3 4 mm year 1 being detected within river basins this investigation demonstrates that prop roots can assist in the settling of suspended sediments from estuarine waters yet prop root structures are not as successful as pneumatophores in maintaining sediment elevation over 2 5 years as root densities increase over time an increase in turbulence induced erosion and in shallow subsidence as organic peat layers form is expected in micronesian mangrove forests

high resolution holocene monsoon record from the eastern arabian sea through stable oxygen and carbon analyses of rapidly accumulating sediment cores from the eastern arabian sea we show that the excess of evaporation over precipitation e p steadily appears to have decreased during the last 10 000 to 2000 years most probably due to an increasing trend in the summer monsoon rainfall contrary to the land based paleoclimatic data from this region which indicate onset of aridity around 4000 years ago our results are consistent with the hypothesis that significant spatial variability in the monsoon rainfall observed today was persistent during most of the holocene alternatively the trend can be seen as an adjustment between two phases one between 10 000 and 6000 years ago of increasing precipitation and another between 3500 and 2000 years ago after the arid episode we also report a significant 700 year periodicity similar to that reported recently from the south china sea indicating that the centennial millennial scale response of the indian and chinese monsoons to high latitude forcing may be alike

the anticyclonic baroclinic eddy off sitka alaska in the northeast pacific ocean abstract among the many mesoscale eddies found in the northeast pacific ocean is a well developed anticyclonic baroclinic eddy situated within a few hundred kilometers of sitka alaska 57 n 138 w it has definitely been observed during spring and summer 1958 summer 1960 and summer 1961 observations made at other times show some evidence of its occurrence also the trajectories of three norpax drifting buoys for april may 1977 also indicated the probable presence of an eddy there the eddy whose diameter ranges from 200 to 300 km and whose depth extends to 100 m and probably to as much as 2000 m recurs at the same location the center of the eddy is characterized by the following features the surface water is less saline and only somewhat warmer than at its periphery at depths within and below the halocline it is warmer less saline and contains more dissolved oxygen than at the periphery and a warm core is situated within the halocline the halocline is usually depressed by less than 100 m but

holocene environmental changes and cultural patterns in coastal western india a geoarchaeological perspective abstract geomorphological studies carried out around coastal sites at hazira kanmer padri and sanjan in gujarat and chaul and kelshi in maharashtra indicate human activity throughout the holocene the offshore site at hazira of early holocene age is the only submerged prehistoric site at a depth of 20 40 m below the present sea level in the entire 7000 km long coastline of india protohistoric harappan sites at kanmer and padri are of mid holocene age the sites of sanjan chaul and kelshi represent an early historic cultural phase belonging to the late holocene age the site of hazira was located on the banks of a buried channel adjusted to the low sea level phase of the early holocene cultural development of the harappan site at kanmer in the present semi arid rocky landscape of kachchh was closely related to the existence of 2 5 m deep water in the presently dried up part of rann of kachchh throughout the mid holocene on the other hand the economy of the harappan site of padri depended on salt manufacturing in a stable estuarine environment close to the present sea level of the gulf of cambay sanjan chaul and kelshi appear to have depended on a trading economy these sites are situated in estuarine environments involving lateral transgressive regressive phases more or less within the present intertidal zone of arabian sea in a humid environment

weathering of granitic rocks by chlorides effect of the nature of the solution on weathering morphology five granites from nw spain were subjected to two salt spray weathering tests under controlled atmospheric conditions granite samples were exposed to a sodium chloride solution in the first test and to a complex solution sea water in the second subsequent examination of the rocks by light and petrographic microscopy clearly demonstrated the development of different weathering morphologies in each test the distribution of dissolved ions in samples taken at different depths from the weathered surfaces at the end of the experiments and the changes in weight of the samples during the tests also differed in our opinion these results were determined by the nature of the solution used although sodium chloride is the predominant salt in sea water the presence of other ions modifies its solubility thereby varying the dynamics of mobility and precipitation and thus the weathering morphology that develops copyright 2003 john wiley sons ltd

variability of physical and chemical characteristics along the 70 m isobath of the southeastern bering sea abstract from observations of ice cover temperature salinity currents and nitrate it is evident that along shelf variability was significant over the middle shelf of the eastern bering sea but less distinct than that observed in the cross shelf domains along the 70 m isobath three zones were evident in the summer the southeastern cold pool centered at 57 n an intermediate zone consisting of warmer water with weaker stratification and the northern cold pool extending northward from 58 n small scale 20 km horizontal features that persisted for months were common nutrient concentrations were related to salinity and were replenished more uniformly over the southern shelf than north of the pribilof islands although mean currents were weak 1 cm s 1 short energetic advective events impacted the temperature and salinity structure

sharp decrease in summer monsoon strength 4000 3500 cal yr b p in the central higher himalaya of india based on pollen evidence from alpine peat age constrained pollen data and magnetic susceptibility of an alpine peat profile from the garhwal higher himalaya display a continuous record of climate and monsoon trends for the past 7800 yr about 7800 cal yr b p dominance of evergreen oak quercus semecarpifolia alder alnus and grasses in the pollen record reflect a cold wet climate with moderate monsoon precipitation from 7800 to 5000 cal yr b p vegetation was progressively dominated by conifers indicating ameliorated climate with a stronger monsoon a warm humid climate with highest monsoon intensity from 6000 4500 cal yr b p represents the mid holocene climatic optimum between 4000 and 3500 cal yr b p the abundance of conifers sharply decreased with the greatest increase in evergreen oak this trend suggests progressive cooling with a decrease in the monsoon to its minimum about 3500 cal yr b p two relatively minor cold dry events at ca 3000 and 2000 cal yr b p marked step wise strengthening of the monsoon until ca 1000 cal yr b p after a cold dry episode that culminated ca 800 cal yr b p the monsoon again strengthened and continued until today a sharp decrease in temperature and rainfall at 4000 3500 cal yr b p represents the weakest monsoon event of the holocene record this cold dry event correlates with proxy data from other localities of the indian subcontinent arabian sea and western tibet

quantification of rock control in geomorphology abstract rock control the influence of rock properties on landform development has for long been a relatively under researched topic but numerous techniques have been developed especially by geotechnical engineers and stone conservationists that are now being applied to geomorphological issues by geomorphologists these techniques range in scale from the quantification of major discontinuities through to analysis of micro pores rock control studies that have taken place over the last few decades have contributed important insights into our understanding of such diverse phenomena as 1 river terraces bedrock channel forms and gradients pot hole development drainage density and gully badland development 2 slope forms and failures especially with respect to rock mass strength 3 the form of glacial troughs and of subglacial erosional landforms 4 weathering controls on rock durability and the association of weathering with porosity 5 classic karst features including various types of karren 6 sandstone landforms 7 inselbergs and tors and 8 cliffs and shore platforms

satellite and hydrographic observations of eddy induced shelf slope exchange in the northwestern gulf of alaska 1 satellite and hydrographic observations of oceanographic conditions in the northwestern gulf of alaska indicate that anticyclonic eddies propagating adjacent to the continental shelf alter the structure of the shelf break front and in doing so influence the shelf slope exchange of biota and water mass properties eddies typically form in the northern gulf of alaska during fall and winter and propagate southwestward within an 200 km wide corridor along and above the continental slope eddy activity within this corridor diminishes in the downstream direction the trajectories of faster propagating 4 km day eddies tend to lie closer to the shelf break than do the trajectories of slower propagating 1 5 km day eddies the interaction between azimuthal eddy currents and the shelf break frontal jet 1 establishes an upwelling zone associated with the leading flank of the eddy that strengthens cross slope gradients 2 weakens cross slope gradients and promotes shelf slope exchange where the eddy is adjacent to the shelf and 3 reestablishes a weak upwelling zone associated with the trailing flank of the eddy

characteristics and variability of the inner front of the southeastern bering sea the inner front of the southeastern bering sea shows marked spatial variability in frontal characteristics created by regional differences in forcing mechanisms differences in forcing mechanisms sea ice advance retreat and storm strength and timing and early spring water properties result in strong interannual variability in biological chemical and physical features near the front we have developed a simple model based on surface heat flux and water column mixing to explain the existence of cold belts cont shelf res 19 14 1999 1833 associated with such fronts hydrography fluorescence and nutrient observations show that pumping of nutrients into the euphotic zone occurs and this can prolong primary production at the inner front the effectiveness of this process depends on two factors the existence of a reservoir of nutrients in the lower layer on the middle shelf and the occurrence of sufficient wind and tidal energy to mix the water column

mechanisms for vertical nutrient transport within a north atlantic mesoscale eddy abstract prompted by observational evidence for an enhanced source of surface nutrients within an anticyclonic eddy in the ne atlantic we investigate vertical transport processes that may produce such a phenomenon for the eddy investigated the dominant mechanism is found to be ageostrophic circulation resulting from a perturbation of the circular flow of the eddy this can produce upwelling velocities of order 10 m d 1 ekman pumping due to wind stress on the eddy also produces upwelling within but on a smaller scale of 0 5 m d 1 there is no evidence that self propagation of the eddy leads to an enhanced nutrient flux by displacement upwards of nutrient laden deeper isopycnals over the core of the eddy deeper winter mixing within the eddy relative to the surroundings however may contribute to the elevated nutrient levels

mangrove vegetation responses to holocene climate change along konkan coast of south western india abstract the pollen signatures preserved in the mangrove sediments provided records of species variation over a period of time with past climate and sea level changes the airoli profile has a late pleistocene sequence and all the other studied profiles and intervals cover the holocene only the absence of mangrove signatures during the late pleistocene interval is attributed to a relatively low sea level the ideal conditions for mangrove development along konkan prevailed during middle holocene when the first extensive mangrove swamps appeared in sindhudurg dhamapur hadi area particularly between 7220 and 4770 yrs bp this period coincides with the holocene climate optimum hco when monsoon asia witnessed much higher precipitation however the mangroves responded to environmental changes due to relative abundance of fresh water leading to change in species composition two different scenarios of mangrove response during the late holocene one in dhamapur and the other in palm beach are found to be significant the rhizophora sonneratia transition from early mid holocene to late holocene is considered to be the most distinctive feature the decline of mangroves since 3500 yrs bp and further degradation has been attributed to the prevailing arid climate and weakening trends of the monsoon until 1500 yrs bp however there seems to be a positive trend in emergence of mangroves in the least disturbed areas of south konkan attributed to strengthening of summer monsoon in the recent past

methods for measuring rock surface weathering and erosion a critical review studies of rates processes and modes of rock surface and near surface deterioration and also hardening are central to rock weathering and building stone research conservation and management there is a need to measure and monitor weathering at the rock atmosphere interface to facilitate understanding of climatic environmental and lithological controls on the evolution and development of surface weathering features this paper reviews long established and recently developed field and laboratory methods used by geomorphologists to monitor and measure the impact of weathering and erosion on physical and mechanical properties of exposed rock surfaces and their immediate subsurface key advances are highlighted their application to multi scalar understanding and modelling of rock surface weathering in different contexts is discussed and potential future advances to provide new insights into rock weathering durability and materials conservation are identified in highlighting key advantages and disadvantages of a wide range of methods to the broader earth science community the paper aims to contribute to further innovative thinking across disciplines to develop new methods for measuring and monitoring rock weathering

mid holocene indian summer monsoon variability off the andaman islands bay of bengal abstract a sediment core retrieved from the andamans forearc basin afb near landfall island north andaman provides a record of sediment provenance and climate change during the mid to late holocene radiocarbon ages ranging from 6078 to 1658 indicate that the core represents the interval from 6500 bp to the present grain size variation indicates a cyclic variation of wetter and drier conditions corresponding to changes in intensity of the indian summer monsoon ism which was at greatest intensity near 6400 5300 and 3300 3000 bp geochemical parameters including abundance of caco3 end and 18o in globigerinoides ruber are consistent with a long term trend from cooler wetter conditions to the warmer drier conditions at present chemical weathering intensity which lags behind climate changes on land shows a pulse of highly weathered sediment deposited at about 4000 bp during the short duration pulses of intense monsoon activity sandy sediment was supplied from the andaman islands the irrawaddy salween and sittang rivers of myanmar are the secondary sediment sources for the study area

a note on cross shelf exchange in the northern gulf of alaska the continental shelf of the gulf of alaska goa is a complex system characterized by large freshwater runoff and strong winds the goa supports one of the world s richest ecosystems including numerous species of fishes marine mammals and sea birds the mechanisms that provide nutrients to support this ecosystem are not well understood the rivers and streams that provide freshwater to the shelf are low in nitrate and the regional winds favor downwelling high concentrations of nitrate are available in the deep basin of the goa but these must be introduced to the shelf in order to support the high productivity we present evidence for cross shelf exchange due to three different mechanisms episodes of downwelling relaxation result in a flux of saline nutrient rich water onto the shelf at depth eddies formed in the northeastern goa propagate along the shelf break influencing cross shelf exchange by carrying shelf origin water from the formation region into the basin and by interacting with the shelf break circulation bathymetric steering in the many canyons that incise the goa shelf results in flow into the canyons where strong tidal mixing results in cross isobath movement of water properties

a basin scale oceanic instability event in the gulf of alaska a composite noaa 14 satellite advanced very high resolution radiometer image of the gulf of alaska for early march 1995 reveals a sequence of six anticyclonic oceanic eddies spanning more than 1500 km of the continental margin of north america from central british columbia to central alaska although isolated mesoscale eddies have previously been documented for this eastern boundary region the composite image provides the first evidence that trains of such eddies can develop simultaneously along the entire coast the 80 km radius and 250 km spacing of these warm core eddies are consistent with a baroclinic instability event in the poleward coastal current that prevails along the northwest continental margin of north america in winter roughly october through march wind data from offshore meteorological buoys combined with partial cloud free thermal images for january and february suggest that the event was triggered in mid january by an abrupt coast wide reversal in the prevailing poleward wind the instability event disrupted the alongshore transport of relatively warm high salinity water and presumably resulted in a greatly enhanced cross shore flux of brackish nutrient rich coastal water into the open ocean on the basis of its basin scale extent and more than 2 month duration it is feasible that the event had a major impact on the early spring recruitment and survival of zooplankton and pelagic fish within the highly productive fishery zones of coastal british columbia and alaska less extensive eddy sequences found in several earlier satellite images for the region suggest that these instability events are fairly common if so this indicates that the poleward current that forms over the eastern pacific continental slope in late fall herein the northeast pacific coastal current is marginally stable and likely to deform into a series of mesoscale eddies following abrupt basin scale reversals in the seasonally dominant wind provided these wind events occur early enough in the season the coastal current could reform with the onset of poleward winter winds

assessment of rock geomechanical quality by quantitative rock fabric coefficients limitations and possible source of misinterpretations abstract rock microfabrics were quantified by image measurement system petrographic image analysis of thin sections along with common measured parameters grain area and size length of major and minor axes and their orientation some quantitative parameters aspect ratio grain boundary smoothness and fabric coefficients micropetrographic quality index k texture coefficient tc indexes of interlocking t and grain size homogeneity g were determined the reliability of these parameters for the evaluation of geomechanical properties was tested on the set of granitic rocks showing pronounced variability in rock mechanical properties none of the tested rock fabric coefficients or parameters proved a close correlation to rock mechanical properties except grain size based on experimental findings the grain size is along with porosity the controlling factor of rock mechanical properties of genetically and mineralogically similar rocks obliteration of the real effects of rock fabric parameters on the mechanical properties of rocks by application of complex fabric coefficients disables their practical use in petrography applied to geomechanics