basal platinum group element mineralization in the federov pansky layered mafic intrusion kola peninsula russia the 2501 to 2446 ma federov pansky layered mafic intrusion in the central part of the kola peninsula russia is situated along the northern contact of the early proterozoic imandra varzuga rift and archean granite gneiss the federov pansky intrusion has eight major zones from bottom to top 1 marginal zone mafic schists 50 to 100 m 2 taxitic gabbronorite zone bpca 150 to 300 m 3 norite zone bcpa pbc 200 m 4 main gabbronorite zone pacb 1 000 m 5 lower layered horizon zone bc pc pbac 100 m 6 gabbro zone pacb pbac 1 500 m 7 upper layered horizon zone pocab 250 m 8 upper gabbro zone pacb 400 m the taxitic gabbronorite zone is restricted to the federov and east lastjavr blocks this zone is distinctive due to its pegmatitic taxitic textures and abundant norite xenoliths concentrated near its upper contact with the norite zone chemically the taxitic gabbronorite is more feldspathic and iron enriched than the overlying mgo and cr 2 o 3 rich norite zone and norite xenoliths the zone hosts cu ni pge mineralization with disseminated sulfides which is continuous for over 2 5 km along strike and 150 to 200 m downdip 98 percent of the sulfides consist of varying amounts of pyrrhotite chalcopyrite and pentlandite the mineralization is divided into an upper mineralized section with two higher grade lenses a and b and the restricted lower mineralized section with six narrower lenses the lower mineralized section is less continuous and less uniform in terms of cu ni pge distribution the norite xenoliths and blocks occurring within the taxitic gabbronorite zone are practically barren of sulfide and can dilute higher pge and base metal grades in the gabbronorite matrix average total pge grades in rocks do not exceed a few grams per tonne the mineralization is palladium rich with a pd pt ratio from 4 22 to 4 34 rh and au grades are 0 1 to 0 5 g t os and ir grades are the most common pge bearing minerals are merenskyite moncheite kotulskite sobolevskite and michenerite less common are sperrylite and vysotskite braggite the cu ni pge sulfides are primarily magmatic in origin this is supported by s isotope compositions with a narrow range of 34 s of 0 2 to 1 4 percent and s se ratios of 1 050 to 3 300 a three stage process is postulated for the genesis of the federov mineralization this involves the intrusion of a more fractionated and sulfur saturated gabbronorite magma and its brecciation and mixing with a residual primitive magma forming immiscible sulfides that scavenged cu ni pge the federov resembles other contact type mineralization such as in the portimo intrusion in finland and the lac des iles and east bull lake intrusions in ontario canada

upb geochronology of layered mafic intrusions in the eastern baltic shield implications for the timing and duration of paleoproterozoic continental rifting abstract paleoproterozoic layered mafic ultramafic intrusions are widespread in the eastern baltic fennoscandian shield and mark the initial stages of continental rifting and outpouring of voluminous flood basalts u pb zircon baddeleyite ages have been determined for seven layered mafic intrusions and a subvolcanic felsic unit associated with two paleoproterozoic volcanic sedimentary belts the pechenga imandra varzuga belt in the kola peninsula and the sumi sariola belt in karelia the layered intrusions in the sumi sariola belt show an age progression from 2449 0 1 1 ma for the burakovka complex located at the southeastern edge of the belt to 2442 1 1 4 ma and 2441 3 1 2 ma for the lukkulaisvaara and tsipringa intrusions of the olanga complex in northern karelia northeastern part of the belt these age results indicate a total duration of mafic magmatism along the ca 800 km belt in karelia to be less than 10 m y the pechenga imandra varzuga belt kola peninsula contains two distinct age groups of layered mafic intrusions and related rocks the younger of these overlaps with the ages obtained for the olanga intrusions and includes the 2441 0 1 6 ma imandra lopolith and a spatially associated felsic subvolcanic unit dated at 2442 2 1 7 ma the older group of mafic layered intrusions in the kola peninsula includes the 2501 5 1 7 ma pana tundra intrusion the 2504 4 1 5 ma monche pluton and the 2505 1 1 6 ma general skaya mountain intrusion the temporal and spatial distribution of the 2 50 2 44 ga rift related igneous activity in the baltic shield is consistent both with the model of starting mantle plume and with the model of passive rifting controlled by pre existing lithospheric weaknesses

organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

high resolution stalagmite climate record from the yucatan peninsula spanning the maya terminal classic period the decline of the classic maya civilization was complex and geographically variable and occurred over a 150 year interval known as the terminal classic period tcp c e 800 950 paleoclimate studies based on lake sediments from the yucatan peninsula lowlands suggested that drought prevailed during the tcp and was likely an important factor in the disintegration of the classic maya civilization the lacustrine evidence for decades of severe drought in the yucatan peninsula however does not readily explain the long 150 year socio political decline of the classic maya civilization here we present a new absolute dated highresolution stalagmite 18o record from the northwest yucatan peninsula that provides a much more detailed picture of climate variability during the last 1500 years direct calibration between stalagmite 18o and rainfall amount offers the first quantitative estimation of rainfall variability during the terminal classic period our results show that eight severe droughts lasting from 3 to 18 years occurred during major depopulation events of classic maya city states during these droughts rainfall was reduced by 52 to 36 the number and short duration of the dry intervals help explain why the tcp collapse of the mayan civilization occurred over 150 years

the j m platinum palladium reef of the stillwater complex montana ii origin by double diffusive convective magma mixing and implications for the bushveld complex sequences of cumulates form concurrently by downdip accretion from a column of liquid layers that are primarily separated by diffusive interfaces the low cumulates grow in advance of the upper cumulates in accord with their higher crystallization temperatures an important observation is that mixing of the two parent liquids lowers their crystallization temperatures and consequently should produce unsaturated hybrids that could dissolve earlier cumulates the repetition of cyclic units above the j m reef is explained by having periodic additional injections of dense magma beneath the subsiding column of crystallizing liquid layers neither the j m reef nor the bushveld ore zones should ever have been continuous across the floor of their respective magma chambers and for bushveld the circumstances resulted in zones that are actually minable modified journal abstract

holocene vegetation change in the northern peten and its implications for maya prehistory an 8400 cal yr record of vegetation change from the northern peten guatemala provides new insights into the environmental history of the archaeological area known as the mirador basin pollen loss on ignition and magnetic susceptibility analyses indicate warm and humid conditions in the early to mid holocene evidence for a decrease in forest cover around 4600 cal yr b p coincides with the first appearance of zea mays pollen suggesting that human activity was responsible the period between 3450 cal yr b p and 1000 cal yr b p is characterized by a further decline in forest pollen types includes an abrupt increase in weedy taxa and exhibits the highest magnetic susceptibility values since the early holocene all of which suggest further agricultural disturbance in the watershed a brief drop in disturbance indicators around 1800 cal yr b p may represent the preclassic abandonment of the area changing pollen frequencies around 1000 cal yr b p indicate a cessation of human disturbance which represents the late classic collapse of the southern maya lowlands

a 3400 year paleolimnological record of prehispanic human environment interactions in the holmul region of the southern maya lowlands abstract the timing magnitude and drivers of late holocene environmental change in the holmul region of the southern maya lowlands are examined by combining paleoenvironmental and archeological data environmental proxy analyses on a 3350 cal yr lacustrine sediment record include pollen charcoal loss on ignition magnetic susceptibility and elemental geochemistry archeological evidence is derived from extensive settlement surveys conducted near the study site results indicate nearby settlement and agricultural activity taking place in an environment characterized by open forest from around 3350 to 950 cal yr bp the fire history shows a dramatic increase in burning during the classic period possibly reflecting changing agricultural strategies a distinct band of carbonate deposited from 1270 to 1040 cal yr bp suggests decreased hydrologic input associated with drier conditions abrupt changes in proxy data around 940 cal yr bp indicate a cessation of human disturbance and local abandonment of the area

a 4000 year lacustrine record of environmental change in the southern maya lowlands peten guatemala a 4000 yr sediment core record from lake salpeten guatemala provides evidence for maya induced forest clearance and consequent soil erosion between 1700 cal yr b c and 850 cal yr a d radiocarbon ages of wood seeds and charcoal support an age depth model with average errors of 110 cal yr relatively low carbonate 18o values between 1300 and 400 cal yr b c coincide with pollen evidence for forest loss consistent with increased surface and groundwater flow to the lake minimum 18o values between 400 cal yr b c and 150 cal yr a d suggest a high lake level as do 14c dated aquatic gastropods as much as 7 5 m above the present lake stage high lake levels resulted from reduced evaporation to precipitation ratios increased hydrologic input caused by anthropogenic deforestation or both the preclassic abandonment 150 a d and early classic late classic boundary 550 a d are marked by relatively high 18o values indicating reduced lake levels oxygen isotope composition increased further coincident with the terminal classic maya demographic decline between 800 and 900 a d this period of high 18o may have been caused by the greater aridity that has been documented in northern yucatan lakes or by decreased hydrologic input to the lake as a consequence of forest recovery reduced soil erosion after 850 cal yr a d coincided with the terminal classic maya demographic decline and permitted forest recovery and resumption of organic sedimentation

oceanic mesoscale eddies as revealed by lagrangian coherent structures 1 we demonstrate the feasibility of using dynamical systems tools to unambiguously identify mesoscale oceanic eddies from surface ocean currents derived using climatological hydrography and altimetry specifically our analysis is based on extracting lagrangian coherent structures lcss from finite time lyapunov exponent ftle fields the ftle fields reveal with unprecedented detail an intricate tangle of lcss which are hidden in ocean surface topography maps but sometimes are apparent in ocean color images these lcss delineate fluid domains with very different advective properties and thus their detection provides an objective i e frame independent means of identifying eddy boundaries the importance of considering lcss in quantifying transport by eddies is highlighted such a quantification does not rely on the common assumption which is shown to be generally not valid that transport is largely effected by the trapping and subsequent translation of water slugs inside eddies defined as the regions enclosed by sea height streamfunction contours within which rotation dominates over strain lcss are calculated for the whole globe and compared with satellite tracked drogue drifter trajectories within a selected region of the south atlantic

climate change on the yucatan peninsula during the little ice age we studied a 5 1 m sediment core from aguada x caamal 20 36 6 n 89 42 9 w a small sinkhole lake in northwest yucatan mexico between 1400 and 1500 a d oxygen isotope ratios of ostracod and gastropod carbonate increased by an average of 2 2 and the benthic foraminifer ammonia beccarii parkinsoniana appeared in the sediment profile indicating a hydrologic change that included increased lake water salinity pollen from a core in nearby cenote san jose chulchaca showed a decrease in mesic forest taxa during the same period oxygen isotopes of shell carbonate in sediment cores from lakes chichancanab 19 53 0 n 88 46 0 w and salpeten 16 58 6 n 89 40 5 w to the south also increased in the mid 15th century but less so than in aguada x caamal climate change in the 15th century is also supported by historical accounts of cold and famine described in maya and aztec chronicles we conclude that climate became drier on the yucatan peninsula in the 15th century a d near the onset of the little ice age lia comparison of results from the yucatan peninsula with other circum caribbean paleoclimate records indicates a coherent climate response for this region at the beginning of the lia at that time sea surface temperatures cooled and aridity in the circum caribbean region increased

climate drying and associated forest decline in the lowlands of northern guatemala during the late holocene abstract palynological studies document forest disappearance during the late holocene in the tropical maya lowlands of northern guatemala the question remains as to whether this vegetation change was driven exclusively by anthropogenic deforestation as previously suggested or whether it was partly attributable to climate changes we report multiple palaeoclimate and palaeoenvironment proxies pollen geochemical sedimentological from sediment cores collected in lake peten itza northern guatemala our data indicate that the earliest phase of late holocene tropical forest reduction in this area started at 4500 cal yr bp simultaneous with the onset of a circum caribbean drying trend that lasted for 1500 yr this forest decline preceded the appearance of anthropogenically associated zea mays pollen we conclude that vegetation changes in peten during the period from 4500 to 3000 cal yr bp were largely a consequence of dry climate conditions furthermore palaeoclimate data from low latitudes in north africa point to teleconnective linkages of this drying trend on both sides of the atlantic ocean

on the mechanisms for low sulfide high platinum group element and high sulfide low platinum group element mineralization in the eastern gabbro coldwell complex canada evidence from textural associations s se values and platinum group element concentrations of base metal sulfides

stratigraphy petrology and platinum group element mineralization of the early proterozoic penikat layered intrusion northern finland the penikat layered intrusion is part of an early proterozoic belt of layered intrusions 2 440 m y in age which extends across northern finland the intrusion is located between late archean granitoids and early proterozoic supracrustal rocks the marginal series with slightly contaminated chilled margin separates the penikat intrusion from the underlying basement complex the layered series is divided into five megacyclic units i to v from bottom to top each unit comprising an ultramafic lower part and a gabbroic upper part three major mineralized zones enriched in platinum group elements pge the sompujaervi sj ala penikka ap and paasivaara pv mineralizations have been delineated along almost 23 km of strike and occur in megacyclic unit iv the sompujaervi mineralization about 1 m thick is mostly associated with pyroxenitic rocks at the lower contact of the unit whereas the ala penikka zone about 0 35 m thick is associated with gabbronorite and poikilitic textured anorthosite in the middle part and the paasivaara zone about 1 m thick with leucogabbro and anorthosite very close to the upper contact the ratios of platinum group elements are relatively constant for each mineralization the paasivaara mineralization represents the most platinum rich variety and the ala penikka the most palladium rich one the ratio of pd to pt being typically about 2 for the sulfide free type and 1 5 3 5 and 0 7 for the sulfide bearing type for the sompujaervi ala penikka and paasivaara mineralizations respectively the sulfur free platinum group minerals pgm sperrylite and isomertieite are the dominant species encountered in the sompujaervi mineralization whereas sulfur bearing platinum group minerals together with sperrylite dominate in the ala penikka and paasivaara mineralizations these are represented by braggite and vysotskite in the ala penikka one and by braggite and cooperite in the more platinum rich paasivaara mineralization according to the new classification of platinum group element deposits proposed by cabri and naldrett 1984 the typically sulfide free sompujaervi mineralization may be included in the oxide silicate association as a possible new type whereas the ala penikka and paasivaara mineralizations may be classified as merensky reef type of the sulfide associations

southern ocean eddy phenomenology mesoscale eddies are ubiquitous features in the southern ocean yet their phenomenology is not well quantified to tackle this task we use satellite observations of sea level anomalies and sea surface temperature sst as well as in situ temperature and salinity measurements from profiling floats over the period 1997 2010 we identified over a million mesoscale eddy instances and were able to track about 105 of them over 1 month or more the antarctic circumpolar current acc the boundary current systems and the regions where they interact are hot spots of eddy presence representing also the birth places and graveyards of most eddies these hot spots contrast strongly to areas shallower than about 2000 m where mesoscale eddies are essentially absent likely due to topographical steering anticyclones tend to dominate the southern subtropical gyres and cyclones the northern flank of the acc major causes of regional polarity dominance are larger formation numbers and lifespans with a contribution of differential propagation pathways of long lived eddies areas of dominance of one polarity are generally congruent with the same polarity being longer lived bigger of larger amplitude and more intense eddies extend down to at least 2000 m in the acc eddies show near surface temperature and salinity maxima whereas eddies in the subtropical areas generally have deeper anomaly maxima presumably inherited from their origin in the boundary currents the temperature and salinity signatures of the average eddy suggest that their tracer anomalies are a result of both trapping in the eddy core and stirring

terminal classic drought in the northern maya lowlands inferred from multiple sediment cores in lake chichancanab mexico we present new density records from sediment cores taken along a depth transect in lake chichancanab mexico the data reveal in great detail the climatic events that comprised the terminal classic drought tcd and coincided with the demise of classic maya civilization between ca 750 and 1050 ad in shallow water cores the tcd is marked by a condensed gypsum horizon in deeper water sections it is expanded and represented by numerous interbedded gypsum and organic rich strata the tcd was not a single two century long megadrought but rather consisted of a series of dry events separated by intervening periods of relatively moister conditions we estimate the tcd occurred between ca 770 and 1100 ad and included an early phase ca 770 870 ad and late phase ca 920 1100 ad the intervening 50 year period ca 870 920 ad was relatively moister each dry phase is represented by multiple gypsum density bands interbedded with organic rich sediment that indicate alternating dry and wet conditions spectral analysis revealed significant periods around 213 50 and 27 years despite uncertainty regarding the ages of these events their pattern is robust and generally consistent with other proxy records under the same climate regime such as the marine cariaco basin off northern venezuela science 299 2003 1731

quantifying eulerian eddy leakiness in an idealized model an idealized eddy resolving ocean basin closely resembling the north pacific ocean is simulated using mitgcm we identify rotationally coherent lagrangian vortices rclvs and sea surface height ssh eddies based on the lagrangian and eulerian framework respectively general statistical results show that rclvs have a much smaller coherent core than ssh eddies with the ratio of radius is about 0 5 rclvs are often enclosed by ssh anomaly contours but ssh eddy identification method fails to detect more than half of rclvs based on their locations two types of eddies are classified into three categories overlapping rclvs and ssh eddies nonoverlapping ssh eddies and nonoverlapping rclvs using lagrangian particles we examine the processes of leakage and intrusion around ssh eddies for overlapping ssh eddies over the lifetime the material coherent core only accounts for about 25 and about 50 of initial water leak from eddy interior the remaining 25 of water can still remain inside the boundary but only in the form of filaments outside the coherent core for nonoverlapping ssh eddies more water leakage about 60 occurs at a faster rate guided by the number and radius of ssh eddies fixed circles and moving circles are randomly selected to diagnose the material flux around these circles we find that the leakage and intrusion trends of moving circles are quite similar to that of nonoverlapping ssh eddies suggesting that the material coherence properties of nonoverlapping ssh eddies are not significantly different from random pieces of ocean with the same size

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

magma mixing and constitution zone refining in the lac des iles complex ontario genesis of platinum group element mineralization the lac des iles complex is a 2 74 ga old composite intrusion emplaced into a granite and or granite gneiss terrane of the wabigoon subprovince northwestern ontario the complex consists of a gabbroic and ultramafic part the latter has been subdivided into northern and southern intrusive phases both the gabbroic and ultramafic parts contain platinum group element bearing ni cu sulfide mineralization although only the roby zone in the gabbro is of economic importance the southern ultramafic complex consists of a wehrlite to olivine clinopyroxenite core which is surrounded by websterite and gabbronorite cumulates petrographic and geochemical studies suggest that the northern ultramafic complex consists of at least eight cyclic units which ideally are composed of dunite and wehrlite to olivine clinopyroxenite cumulates at the base followed by clinopyroxenite and websterite locally grading into gabbronorite this indicates similar crystallization sequences in both ultramafic centers olivine olivine clinopyroxene clinopyroxene clinopyroxene orthopyroxene or plagioclase in the ultramafic complex platinum group element bearing sulfide mineralization occurs at the top of cyclic units in websterite and orthopyroxenite cumulates sulfide bearing samples up to 1 wt sulfide are enriched in au pd pt and cu relative to ni ir os and ru with pd ir ratios on the order of 250 sulfide immiscibility probably was caused by mixing of fractionated residual melt with more primitive liquid which periodically intruded the magma chamber evidence of mixing is seen in gradational chemical variations across the interface of cyclic units and in the occurrence of inclusions of olivine crystals and crystal aggregates in websterite and gabbronorite cumulates these inclusions are not in equilibrium with their present host rock and presumably formed before mixing in the more primitive magma a mineralized orthopyroxenite cumulate at the top of cyclic unit 2 could not have been produced by the normal crystallization sequence consideration of the phase relationships in the ternary system olivine clinopyroxene plagioclase quartz suggests that these cumulates are the crystallization product of a hybrid magma formed during magma mixing at the interface of cyclic units the gabbroic complex consists mainly of largely altered gabbro and gabbronorite cumulates and is intruded by mafic ultramafic dikes the center of the gabbroic complex contains the economically important roby zone with its platinum group element bearing cu ni sulfide mineralization this is a lithologically and texturally very complex zone in which high grade platinum group element mineralization is associated with pegmatite and mafic ultramaflc dikes the roby zone is characterized by strong enrichments of au pd and pt relative to ir and os and by variable but extremely high pd ir ratios of greater than 10 000 high au pt and pd pt ratios indicate a fractionation of pt from au and pd it is suggested that the high volatile content of the residual magma of the gabbroic complex triggered partial remelting of surrounding gabbro cumulates a process called constitutional zone refining by mcbirney 1987 during the partial melting event compatible elements such as ir and os are buffered by the residual silicate and oxide mineralogy whereas incompatible elements such as au pd and pt as well as volatile components such as h 2 o and h 2 s become highly concentrated in the partial melt phase eventually this newly formed magma may become sulfide saturated either by cooling and fractional crystallization or due to the continuous dissolution of sulfides when the zone of melting proceeds through the gabbro cumulates ratios such as pd ir and pd pt would strongly depend on the degree of remelting and fractional crystallization until the time of sulfide saturation the matrix of the varitextured zone is interpreted as the residuum of this melting process whereas pegmatoids and pegmatites segregationlike gabbro phases and quartz bearing plagioclase and incompatible element rich dikes are regarded as the final crystallization products of the partial melting

using the high mobility of palladium in surface media in exploration for platinum group element deposits evidence from the lac des iles region northwestern ontario platinium group element pge mineralization is commonly accompanied by large amounts of ni fe sulfides which are explored for using a variety of geophysical and geochemical methods appreciation of a new type of pge mineralization is emerging hosted by gabbroic rocks with low concentrations 5 vol of disseminated sulfides the host rocks commonly display textural complexity such as brecciation pods and veins of pegmatite and magma mingling of different lithological units examples include the lac des iles deposit in northwestern ontario the east bull lake suite in eastern ontario and several intrusions in the kola peninsula and northern finland such mineralization does not result in prominent geophysical and geochemical anomalies thus posing a challenge for exploration we initiated a project to develop new geochemical exploration approaches for such pge deposits with low sulfides and selected the lac des iles district northern ontario canada which contains one producing mine and many pd showings mineralization is hosted by gabbroic rocks with low concentrations 5 vol of sulfides enriched elements include pd pt au ni cu and co in separate sulfide rich mineralization base metals can be abundant up to 1 wt percent but pd is insignificant 200 ppb this reduces the relevance of ni cu and co as possible pathfinders for sulfide poor pge mineralization leaving pd pt and au a detailed study in the baker zone at the lac des iles mine and the legris lake property indicates the essentially immobile nature of pt in these surface environments by contrast pd is depleted in b horizon soil suggesting its removal during the conversion of c to b horizon soils the loss of pd in b horizon soil reflects the transport of pd as neutral and anionic complexes probably with oh and possibly with organic ligands which are not adsorbed by fe oxyhydroxides in the soils instead pd migrates in solution to accumulate in humus in swamps and organic rich lake sediments downslope from mineralization the distribution of pd in humus therefore provides a distal indicator of nearby mineralization total digestion of humus using fire assay or aqua regia yielded up to 160 ppb pd whereas a variety of commercially available leaching methods extracted few ppb pd the results indicate that pd is tightly held in organic matter this behavior of pd contrasts with many metallic elements such as cu and ni that are enriched in b horizon soil and may be extracted by a variety of leaching techniques palladium arsenides tellurides antimonides and sulfides are unstable in weathering environments and their dissolution releases pd to surface waters therefore pd can be used to indicate other pge mineralization as it is always abundant among pge where pge mineralization is associated with high concentrations of fe sulfides their oxidation produces acidic waters which further promotes pd dispersion thus the findings of this study are applicable to exploration for both sulfide rich and poor pge mineralization

a review of human and natural changes in maya lowland wetlands over the holocene abstract in the maya lowlands of mexico belize and guatemala two main types of wetlands have played important roles in human history bajos or intermittently wet environments of the upland interior yucatan and perennial wetlands of the coastal plains many of the most important maya sites encircle the bajos though our growing evidence for human wetland interactions is still sparse the deposits of these wetlands record two main eras of slope instability and wetland aggradation the pleistocene holocene transition as rainfall increased and forests eclipsed savannas and the maya preclassic to classic as deforestation land use intensity and drying increased the ancient maya adapted with terraces around these bajo margins but retracted in the late preclassic in some areas the perennial wetlands of the coastal plains have different histories and the first conceptual model of human wetland interaction described intensive wetland agriculture in the preclassic through classic based on raised fields and canals but a second model arose that interpreted the wetland stratigraphy and canals as more indicative of natural aggradation by accelerated erosion and gypsum precipitation that buried archaic and preclassic fields and there was little classic era use we present new data on a third and fourth model in this study the third is a hybrid of the models one and two including the archaic to preclassic aggradation of the second model and the first model s classic period fields and canals as piecemeal attempts by the maya to adapt to these and other environmental changes the fourth conceptual model describes a very late terminal classic preplanned project on a floodplain these wetland fields were short lived aggraded rapidly but with some reoccupation in the postclassic all of these new models display the burgeoning evidence for intricate maya interactions with wetlands and the diversity of evidence from the relatively few studies underscores the infancy of our understanding of maya interaction with tropical wetlands

controls on the formation of contact type platinum group element mineralization in the east bull lake intrusion the east bull lake intrusion is the type example of a series of 2 48 to 2 49 ga layered mafic intrusions that developed within the rifted southern margin of the superior craton central ontario the east bull lake intrusion contains contact type pge mineralization e g strata bound pge rich disseminated sulfide mineralization occurring within 200 to 300 m of the contact with footwall and sidewall units although the mineralization locally occurs in massive plagioclase cumulates anorthosite zone most of the sulfides are concentrated within an underlying heterolithic inclusion rich unit inclusion bearing zone that grades into an intrusive breccia disseminated sulfides also occur in fine grained gabbroic veins within brecciated footwall rocks border zone geochemical characteristics of the contact type sulfide mineralization and its host rocks include 1 high average pd abundances throughout the east bull lake intrusion including an average of ca 200 ppb in the lower series 2 low average s contents typically contact type pge mineralization in the east bull lake intrusion reflects flow enhanced gravitational settling of a cu rich sulfide liquid followed by local fractionation of ni rich monosulfide solid solution to produce minor amounts of cu and pt rich residual sulfide liquid most of the observed compositional variation in the sulfides can be modeled using variable silicate liquid sulfide liquid mass ratios field and geochemical observations suggest that the parental magmas to the mineralized parts of the east bull lake intrusion were s saturated and pge rich at the time of their emplacement these fertile parent magmas most likely originated as buoyant feldspathic residual magmas that escaped from a deeper more primitive subchamber although first described from the east bull lake intrusion contact type pge mineralization is now recognized in all of the major east bull lake suite intrusions similar styles of magmatic sulfide mineralization are developed in the contact environments of the bushveld igneous complex platreef deposits and the duluth complex minnesota e g dunka road deposit these contact type deposits are part of the family of basal accumulation magmatic sulfide deposits the economics of low sulfide tenor contact type pge cu ni mineralization such as that developed in the east bull lake intrusion will be most favorable in systems in which 1 the parent magmas possessed high initial pge tenors and reached s saturation prior to emplacement 2 the parent magmas experienced vigorous convection in the early stages of chamber development and 3 segregated sulfide was not diluted by coprecipitating silicate minerals a scenario that is most likely to occur in feldspathic magmas in which plagioclase is the principal high temperature liquidus mineral

the kemi stratiform chromitite deposit northern finland the kemi chromite deposit is hosted by an early proterozoic 2 44 ga layered intrusion the lower part of the intrusion is composed of peridotitic and pyroxenitic cumulates and chromitite layers olivine and chromite have not been observed in the upper part where plagioclase is the predominant cumulus phase occurring either alone or together with pyroxenes the intrusion was metamorphosed during the svecokarelidic orogeny mafic minerals of the lower and upper parts of the complex are completely altered to chlorite serpentine talc amphiboles and carbonates whereas the middle part is well preserved the chromite grains too suffered from alteration but the cores of the grains still exhibit primary compositions a continuous chromitite layer can be traced for the entire length of 15 km of the intrusion it varies in thickness from a few millimeters to as much as 90 m in the central part of the intrusion the mineable thicker part of the main chromitite layer is about 4 5 km long the main chromitite layer is overlain by a sequence of thin chromite rich layers which continues upward to the stratigraphic level of 500 m above the basal contact of the intrusion the upper part of the main chromitite is layered but the lower part is more massive and brecciated the ore reserves for open pit mining are ca 40 million metric tons with an average grade of 26 6 percent cr 2 o 3 and a cr fe ratio of 1 53 the whole area has additional reserves of about 110 million metric tons of ore the ore zone is intensely fractured the host rocks have undergone alteration which has degraded the quality of the ore the present surface section of the kemi intrusion is interpreted as a cross section typical of a funnel shaped intrusion and plunging about 70 degrees to the northwest the cumulate sequence especially the main chromitite layer is at its thickest in the middle of the intrusion and the magmatic conduit which fed the intrusion is also thought to have been located just below this thickening it is suggested that the chromitite was deposited when the input of magma into the kemi intrusion was contaminated by salic material from the underlying basement complex this magma mixed with the fresh input of primitive magma resulting in chromite saturation the chromite crystals formed during mixing in a plume according to the model of huppert et al 1986 and accumulated preferentially around the magmatic conduit evidence of contamination is found in chromite grains in the form of small inclusions rich in alkalies which are thought to represent trapped droplets of the contaminant salic melt

cultural and climatic history of coba a lowland maya city in quintana roo mexico abstract lake coba within the archaeological site of coba provides evidence bearing on lowland maya development palynological and geochemical data record multidecadal precipitation cycles from a 8 80 m 8370 yr lake sediment sequence terminating on bedrock late classic sedimentation rates are rapid but an anthropogenically derived colluvium layer is lacking initial vegetation was medium semi deciduous and swamp forest forest clearance began 1650 b c early preclassic and maize first occurred at 850 b c middle preclassic lakeside milpas existed until a d 720 late classic and then were moved from the city center as urbanization intensified and lake coba was diked as a reservoir coba was at most briefly vacated during the classic collapse and was abandoned after a d 1240 although some habitation persisted the paleoecological record matches the archaeological history for coba but pervasive disturbance muted the climatic signal as the late classic drought is barely evident the question whether economic trees were maintained within the city is unresolved maize cultivation allowed the maya to develop a complex society and support a large population but dependence on maize was ultimately doomed by variable rainfall precipitation in extreme years was insufficient to support crops while native vegetation was not directly affected by drought that devastated maya agriculture

satellite observations of mesoscale eddy induced ekman pumping abstractthree mechanisms for self induced ekman pumping in the interiors of mesoscale ocean eddies are investigated the first arises from the surface stress that occurs because of differences between surface wind and ocean velocities resulting in ekman upwelling and downwelling in the cores of anticyclones and cyclones respectively the second mechanism arises from the interaction of the surface stress with the surface current vorticity gradient resulting in dipoles of ekman upwelling and downwelling the third mechanism arises from eddy induced spatial variability of sea surface temperature sst which generates a curl of the stress and therefore ekman pumping in regions of crosswind sst gradients the spatial structures and relative magnitudes of the three contributions to eddy induced ekman pumping are investigated by collocating satellite based measurements of sst geostrophic velocity and surface winds to the interiors of eddies identified from their sea surface height signatures on average e

climate variability on the yucatan peninsula mexico during the past 3500 years and implications for maya cultural evolution climate variability on the yucatan peninsula during the past 3500 yrs is reconstructed from the measurement of 18o in monospecific ostracods and gastropods in a 6 3 m sediment core from lake punta laguna mexico this late holocene record is divided into three periods based on changes in mean 18o values from 3310 to 178514c yr b p period i low mean 18o values indicate relatively wet conditions i e low evaporation to precipitation ratio e p mean oxygen isotopic values increased 178514c yr b p and the interval between 1785 and 93014c yr b p period ii was distinctly drier than the periods before or after the climate during the latter part of period ii was persistently dry with exceptionally arid events centered at 1171 1019 and 94314c yr b p equivalent to 862 986 and 1051 a d this interval of frequent drought was recorded at several other localities in mexico and central america and coincided with the collapse of classic maya civilization following the last arid event 18o values decreased abruptly at 93014c yr b p beginning of period iii signaling a return to wetter conditions that have generally prevailed to the present with the exception of a dry episode centered at 55914c yr b p 1391 a d the paleoclimatic record from punta laguna provides evidence that multi decadal and millennial scale changes ine poccurred on the yucatan peninsula during the late holocene these wet dry episodes may have influenced cultural evolution in mesoamerica

an eddy resolving numerical model of the ventilated thermocline abstract a three dimensional primitive equation numerical model is used to study the effects of mesoscale eddies within the subtropical thermocline solutions are obtained for an ocean bounded by idealized topography are driven by simple wind and buoyancy forcing at the surface results using an eddy resolving fine grid are compared to those using a noneddy resolving coarser grid relatively little difference is realized in the basic mean flow patterns of the two solutions however more significant differences are seen in the distributions of a passive tracer and the potential vorticity mixing by eddies in the westward flowing sector of the subtropical gyre is quite effective in homogenizing these quantities on isopycnals whereas previous theory has predicted homogenization of potential vorticity on long time scales within recirculating gyres the present model demonstrates homogenization on a much shorter time scale across recirculating ventilating flow boundaries anomalous potential vorticity th

nickel copper occurrences in the belleterre angliers belt of the pontiac subprovince and the use of cu pd ratios in interpreting platinum group element distributions within the belleterre angliers greenstone belt of the pontiac subprovince there are a number of ni cu sulfide occurrences associated with synvolcanic gabbros the stratigraphy and geochemistry of the belt suggest that it is a rifted island arc and that the gabbros which contain the ni cu sulfides were derived from the mantle plume that rifted the island arc the conditions under which the sulfides formed may be modeled either by recalculating the sulfide compositions to 100 percent sulfide or by using the cu pd ratios both approaches suggest that most of the sulfide occurrences formed from an enriched morb magma with r factors of 200 to 1 000 one of the occurrences la force is depleted in platinum group elements pge relative to cu and this depletion may be the result of the removal of sulfides from the magma prior to emplacement at this stratigraphic level the advantage of using the cu pd ratio rather than recalculating to 100 percent sulfide is that it is not necessary to have s analyses to model the conditions of formation of the sulfides further the cu pd ratio may be used as a prospecting tool rocks with ratios greater than mantle values formed from magmas depleted in pd possibly due to removal of sulfide from the magma this implies the potential for a pge bearing sulfide deposit at stratigraphically lower levels such an approach has been applied to pge targets in the eastern abitibi subprovince samples from four ni cu occurrences with cu pd ratios close to mantle ratios have the potential to produce pge as a by product samples from seven ni cu sulfide occurrences and the layered intrusions lac dore bell river and cummings complex have cu pd ratios much greater than mantle ratios indicating that these intrusions and sulfides are not good targets for pge at this stratigraphic level although there may be pge rich sulfides present at depth

recovery of the forest ecosystem in the tropical lowlands of northern guatemala after disintegration of classic maya polities we employed paleolimnological methods to investigate tropical forest recovery and soil stabilization that followed abandonment of agricultural systems associated with disintegration of classic maya polities ca a d 800 1000 we used lithological geochemical magnetic and palynological data from sediment cores of lake peten itza in the maya lowlands of northern guatemala sediment core chronology was developed using radiocarbon dates on terrestrial wood and charcoal fragments our results indicate that in the absence of large human populations and extensive farming activities peten forests recovered under humid climate conditions within a span of 80 260 yr soil stabilization postdates pollen evidence of forest regrowth stratigraphically and required between 120 and 280 yr we conclude that the tropical forest ecosystem in the watershed of lake peten itza had been reestablished by the early postclassic period a d 1000 1200

impacts of the ancient maya on soils and soil erosion in the central maya lowlands abstract many studies across the central and southern maya lowlands of belize guatemala honduras and mexico have produced records of land degradation mostly sedimentation and soil erosion during the ancient maya period from before 1000 bc to the maya collapse of c ad 900 this paper provides new data from two sites blue creek and cancuen synthesizes more than a decade of the authors research in guatemala belize and mexico and synthesizes other findings from this region these research projects analyzed more than 100 excavations in upland and depression sites cored lakes and wetland sediments and studied sediments in the field and laboratory using radiocarbon dating a battery of soil chemistry tests stratigraphic analysis magnetic susceptibility elemental analyses and artifact identification our objective was to date when sedimentation and soil erosion occurred identify stable surfaces and correlate them with the state of knowledge about past land use these findings indicate three general epochs of accelerated soil erosion and identified two major paleosols the three waves of soil erosion occurred in the preclassic period c 1000 bc to ad 250 the late classic ad 550 to 900 and in the last several decades the major paleosol eklu um in these sites is a well developed mollisol or vertisol that started forming in the early holocene and was buried in either the preclassic or classic periods ad 250 to 900 at some sites the eklu um paleosol lies beneath sediments with a fainter paleosol which in turn lies buried below classic period and later sediments this picture shows higher than expected soil erosion linked to the region s first pioneer farmers in the preclassic and less than expected soil erosion in the late classic when population peaked and land use was the most intensive in other regions like cancuen guatemala however most soil erosion occurred during the maya late classic ad 550 830 erosion here was intense but short lived depressions record 1 3 m of aggradation in two centuries a third epoch of accelerated soil loss and aggradation arose with the rapid land use changes brought by new pioneers during the last several decades

particle size evidence for source areas of charcoal accumulation in late holocene sediments of eastern north american lakes abstract two methods of analyzing charcoal in sediment reveal changes in charcoal accumulation across temperate eastern north america during the last several hundred years in one method the analyst counts mostly small particles that reflect regional emissions in the other the analyst counts only larger particles derived mostly from such local sources as catchment fires we used these methods to compare charcoal accumulation at 14 lakes from the prairie forest border in minnesota to eastern maine the two methods gave concordant accumulation rates for sediments of pre 1850 age at each of 4 lakes analyzed by both methods this concordance is consistent with the interpretation that pre 1850 emissions were controlled by broad scale factors such as climatically controlled regional differences in fuels and moisture since 1900 large particles decreased greatly and small particles decreased slightly in minnesota and wisconsin by contrast in the northeast the large particle accumulation has remained at the low values measured in pre 1900 sediments at most sites while small particles increased everywhere east of central new york and pennsylvania the observed patterns suggest that 1 large particles primarily reflect local fires that were common in the midwest before fire suppression became effective 2 large particles were rare in the northeast especially before extensive land clearance 3 small particles reflect regional combustion that increased in the northeast after extensive use of fire for land clearance and wood burning for industrial purposes of the 19th century and 4 small particles remain abundant in the midwest long after effective fire suppression probably because these well dispersed small particles have a large source area that extends beyond the local wildfires that account for large particles before european settlement

the evolution and propagation of quasigeostrophic ocean eddies abstractthe long term evolution of initially gaussian eddies is studied in a reduced gravity shallow water model using both linear and nonlinear quasigeostrophic theory in an attempt to understand westward propagating mesoscale eddies observed and tracked by satellite altimetry by examining both isolated eddies and a large basin seeded with eddies with statistical characteristics consistent with those of observed eddies it is shown that long term eddy coherence and the zonal wavenumber frequency power spectral density are best matched by the nonlinear model individual characteristics of the eddies including amplitude decay horizontal length scale decay and zonal and meridional propagation speed of a previously unrecognized quasi stable state are examined the results show that the meridional deflections from purely westward flow poleward for cyclones and equatorward for anticyclones are consistent with satellite observations examination of the fluid transport properties of the eddies shows that an

isotope data on the age and genesis of layered basic ultrabasic intrusions in the kola peninsula and northern karelia northeastern baltic shield abstract new u pb zircon ages and sm nd data are presented for layered basic ultrabasic intrusions of the kola peninsula and northern karelia in the northeastern part of the baltic shield all ages are in the range between 2 5 and 2 4 ga but there appear to exist three phases of intrusion thus the monchegorsk intrusion and the fedorovy pansky massif have ages between 2493 and 2470 ma the kivakka and lukkulaisvaara massifs of the olanga group of intrusions between 2445 and 2435 ma while the imandra lopolith is 2396 7 ma old a narrow range of negative nd t values between 2 3 and 1 2 suggests formation by partial melting of a semi homogeneous enriched mantle source

mesoscale eddies off peru in altimeter records identification algorithms and eddy spatio temporal patterns relatively little is known about coherent vortices in the eastern south pacific along the peruvian coast even with regard to basic facts about their frequency of occurrence longevity and structure this study addresses these issues with nearly 15 years of relatively high resolution satellite altimetry measurements we first compare two distinct automated methods for eddy identification the objective validation protocol shows that the rarely used geometrical or winding angle method based on the curvature of the streamline functions is more accurate than the commonly used okubo weiss algorithm which defines a vortex as a simple connected region with values of okubo weiss parameter weaker than a given threshold we then investigate vortices off peru using more than 20 000 mesoscale eddies identified by the winding angle method coherent eddies characterized by a high ratio of vorticity to deformation rate are typically formed along the coast and propagate westward at 3 6 cm s 1 the vortices have a mean radius of 80 km increasing northward and are most frequently observed off of chimbote 9s and south of san juan 15s the mean eddy lifetime is about 1 month but if eddies survive at least 2 months the probability for surviving an additional week or month is constant at 90 or 67 anticyclonic eddies tend to propagate northwestward whereas cyclonic vortices migrate southwestward in general cyclones and anticyclones are similar except for eddies surviving at least 6 months in this case after a similar 3 4 months of radius and amplitude growth amplitudes or sizes decay particularly rapidly for anticyclonic or cyclonic eddies in terms of intensity cyclonic eddies show a rapid decay during the first 3 months before arriving at a quasi constant value whereas anticyclones exhibit steady decline finally eddy temporal variations were examined at seasonal and interannual scales in the coastal region favorable to the formation of energetic mesoscale structures on seasonal scales eddy activity is maximal in fall and minimum in spring at interannual scales the eddy activity index was maximal during the strong el nino of 1997 1998 but another strong maximum of eddy activity also occurred late in 2004 these temporal variations are probably associated with the intensification of the upwelling thermal front and with the passage of coastal trapped waves which generate baroclinic instabilities further investigation of the mechanisms involved on the eddy genesis is needed

interannual variability of the north pacific subtropical countercurrent and its associated mesoscale eddy field interannual changes in the mesoscale eddy field along the subtropical countercurrent stcc band of 188 258n in the western north pacific ocean are investigated with 16 yr of satellite altimeter data enhanced eddy activities were observed in 1996 98 and 2003 08 whereas the eddy activities were below average in 1993 95 and 1999 2002 analysis of repeat hydrographic data along 1378e reveals that the vertical shear between the surface eastward flowing stcc and the subsurface westward flowing north equatorial current nec was larger in the eddy rich years than in the eddy weak years by adopting a 2 layer reduced gravity model it is shown that the increased eddy kinetic energy level in 1996 98 and 2003 08 is because of enhanced baroclinic instability resulting from the larger vertical shear in the stcc nec s background flow the cause for the stcc nec s interannually varying vertical shear can be sought in the forcing by surface ekman

new cnes cls09 global mean dynamic topography computed from the combination of grace data altimetry and in situ measurements 1 an accurate knowledge of the ocean mean dynamic topography mdt is mandatory for the optimal use of altimetric data including their assimilation into operational ocean forecasting systems a new global 1 4 resolution mdt was computed for the 1993 1999 time period with improved data and methodology compared to the previous rio05 mdt field first a large scale mdt is obtained from the cls01 altimetric mean sea surface and a recent geoid model computed from 4 5 years of grace gravity recovery and climate experiment data altimetric sea level anomalies and in situ measurements are then combined to compute synthetic estimates of the mdt and the corresponding mean currents while the rio05 mdt was based on 10 years of in situ dynamic heights and drifting buoy velocities the new field benefits from an enlarged data set of in situ measurements ranging from 1993 to 2008 and includes all hydrological profiles from the argo array moreover the processing of the in situ data has been updated a new ekman model was developed to extract the geostrophic velocity component from the drifting buoy measurements the handling of hydrologic measurements has also been revisited compared to the previous rio05 solution the new global mdt resolves much stronger gradients in western boundary currents with mean velocities being doubled in some places moreover in comparison to several other recent mdt estimates we find that the new cnes cls09 mdt is in better agreement with independent in situ observations

quantitative mineral resource assessment of undiscovered pge resources in finland abstract most of the known platinum group element pge resources in finland are in contact type and reef type deposits in 2 45 ga mafic ultramafic layered intrusions these intrusions are also estimated to contain the majority of possibly existing yet undiscovered pge resources in finland the undiscovered pt pd au ni and cu resources in contact type and reef type deposits were estimated down to 1000 m depth using a three part quantitative assessment method this included the delineation of 19 contact type and 24 reef type permissive tracts the formulation of a grade tonnage model for the contact type deposits and a separate model for each reef type tract estimation of the number of undiscovered deposits for each permissive tract and monte carlo simulation to estimate the frequency distributions of metal tonnages in the undiscovered deposits the expected number of undiscovered contact type deposits is 29 and that of reef type deposits is 23 at the 50 probability level the total undiscovered pge resources of finland are estimated to be at least 5600 t pt 12 000 t pd 430 t au 4 2 mt ni and 5 7 mt cu at the 90 probability level the corresponding tonnages are 720 t pt 1700 t pd 59 t au 0 87 mt ni and 0 91 mt cu more than 80 of the pt pd in the undiscovered resources are estimated to be in reef type deposits the known pge resources in finland are 259 t pt pd in six contact type deposits plus 69 t pt pd in the atypical kevitsa deposit these figures indicate that the presently known deposits account for approximately 2 of the total assessed pge resources in finland they suggest that significant potential exists for the discovery of additional pge resources in the country

particle motion and the theory of charcoal analysis source area transport deposition and sampling principles from particle motion physics were applied to recurring problems of the interpretation of stratigraphic charcoal data 1 fires within catchments of lakes often produce no record in fossil charcoal curves and 2 periods characterized by no local fire e g 20th century fire suppression often display as much charcoal as times when local fire was frequent quantitative theory on source area transport deposition and sampling of charcoal shows the relationship between particle sizes counted by alternative methods of charcoal analysis pollen slides for particles 5 80 m in diameter petrographic thin sections for particles 50 10 000 m diameter and charcoal diagrams the relationship between diameter and critical and deposition velocities results in fundamental aerodynamic differences between the sizes of particles quantified by the two methods charcoal recorded on pollen slides is of a size that is difficult to lift but once entrained it remains in suspension thin section charcoal is lifted at relatively low wind velocities but it is not suspended at normal surface wind speeds thermal buoyancy during fire lofts charcoal above the forest canopy depending on particle size and wind speed pollen slide charcoal sizes are underrepresented near the fire because they remain in suspension and are preferentially exported from the burn area thin section charcoal is convected to lower heights on average and is deposited nearby following fire thin section charcoal is redistributed locally by wind and thus may enter lakes because of cohesive forces and aerodynamics more pollen slide charcoal remains on the ground and less enters lakes source areas for pollen slide charcoal are subcontinental to global and diagrams of pollen slide charcoal are biased toward nonlocal charcoal they can be used to interpret importance of fire for broad spatial and temporal scales thin section charcoal represents the catchment fire regime simulation models that generate charcoal during fire mix sediments and then sample at specified intervals indicate that 1 in the absence of sediment mixing the pollen slide method should consistently resolve individual fires that occur with an expectation of 30 50 yr 2 unless samples are continuous neither method will produce useful estimates of fire frequency and 3 even a modest amount of sediment mixing will obscure the signal

quantifying the source area of macroscopic charcoal with a particle dispersal model abstract to aid interpreting the source area of charcoal in lake sediment records we compare charcoal deposition from an experimental fire to predictions from a particle dispersal model this provides both a theoretical framework for understanding how lake sediments reflect fire history and a foundation for simulating sediment charcoal records the dispersal model captures the two dimensional patterns in the empirical data predicted vs observed r2 0 67 p