holocene sedimentary evolution of a mid ocean atoll lagoon maldives indian ocean based on detailed analyses of cores covering the lagoon of rasdhoo atoll maldives six carbonate facies one soil and one peat facies have been identified the abundance of carbonate and rare opaque grains was quantified with a point counter x ray diffractometry was used to measure mineralogical composition of samples the statistical delineation of facies using cluster analysis was based on point count mineralogical and textural analyses in decreasing abundance the six carbonate facies are classified as mollusk coral algal floatstone to rudstone 30 mollusk coral red algae rudstone 23 mollusk coral algal wackestone to floatstone 23 mollusk coral wackestone 13 mollusk coral mudstone to wackestone 9 and mollusk mudstone 2 the carbonate facies represent lagoonal background sedimentation mostly consisting of fine sediments and event sedimentation depositing transported coarse grained reefal components fifty seven carbonate samples and one peat sample were dated radiometrically covering the holocene transgression from 10 kyrs bp until today comparing the sediment accumulation data of the lagoon with two local sea level curves three systems tracts can be identified 1 a lowstand systems tract characterized by karst and soil deposition 10 kyrs bp 2 a transgressive systems tract with peat and carbonate separated by hiatus 10 6 5 kyrs bp and 3 a highstand systems tract dominated by carbonate sedimentation 6 5 0 kyrs bp and further divided into three stages 6 5 3 3 1 and 1 0 kyrs bp during the holocene transgression sedimentation rates increased continuously to a maximum of 1 4 m kyr during 3 1 kyrs bp modern 1 0 kyrs bp mean sedimentation rates average 0 6 m kyr a simple calculation suggests that two processes background sedimentation and sand apron progradation will probably fill up the accommodation space of the lagoon during the holocene highstand but these processes will not suffice to fill the larger atoll lagoons of the archipelago

banktop responses to quaternary fluctuations in sea level recorded in periplatform sediments periplatform sediment from a 12 m core recovered from northwest providence channel bahamas contains a geochemical and paleontological record of sea surface temperatures ice volumes and the response of banktops to highstands of sea level a comparison of these data suggests that fluctuations of carbonate mineralogy in periplatform sediments result from fluctuations of sea level and from patterns of banktop sedimentation highstands of sea level that flood carbonate platforms are recorded in periplatfonn sediments as abrupt increases of exported sr rich aragonite derived from banktop orgiuiisms superposed on a background of sr poor aragonite pteropods and calcite foraminifera and coccoliths derived from planktonic sources the pulses of banktop sediment coincide with increases of water temperature determined from foraminiferal assemblages and with decreases in ratios of oxygen isotopes indicating decreased ice volume and rising sea level following these abrupt changes is a more gradual decline in bank derived sediment although paleotemperatures from foraminiferal assemblages and oxygen isotopic data clearly show that warm conditions and a highstand of sea level persist we suggest that this decrease of offbank transport is part of autocyclic sedimentation patterns of shallow water carbonate environments offbank transport is restricted as reefs sand shoals and islands reach sea level also green algal production may decline because progradation of tidal flats decreases lagoon area and the hydrologic and ecologic conditions change as lagoons are filled

late quaternary reef growth and sea level in the maldives indian ocean abstract based on rotary drilling and radiometric and u series dating we present the first comprehensive data on holocene reef anatomy and sea level rise as well as nature and age of underlying pleistocene limestone in the maldives holocene reefs in rasdhoo atoll central maldives are composed of four facies including 1 robust branching coral facies 2 coralline algal facies 3 domal coral facies and 4 detrital sand and rubble facies branching coral and coralline algal facies predominate the marginal reefs and domal corals and detrital facies preferentially occur in a lagoon reef in addition microbialite crusts are found in lower core sections of marginal reefs microbialites formed during the early holocene in reef cavities holocene reef thickness ranges from 14 5 m to 22 m reef growth started as early as 8 5 kyr bp marginal reefs accreted in the keep up mode with rates of 15 m kyr rate of sea level rise significantly slowed down from 7 6 kyr bp and subsequently gradually rose with rates

global positioning system phase fluctuations and ultraviolet images from the polar satellite in a study designed to determine the temporal development of ionospheric irregularities in the auroral region in magnetic storm periods different types of simultaneous observations were compared for the storms of january 10 april 10 11 and may 15 1997 the data sets consisted of ultraviolet images uvi from the polar satellite phase fluctuations and total electron content tec from global positioning system gps recordings at a large number of sites magnetometer observations and hemispheric power precipitation the large scale global or macroscale picture of the magnetic storm showed the importance of universal time in the development of irregularities the hemispheric total power picture and the global indices such as kp show this macroscale picture of the entire storm period however individual sites show differences in localized magnetic field variations and the development of irregularities this we term the microscale the storms of january 10 and may 15 show the importance of local magnetic time and local magnetic variations at the sites while the storm of april 10 11 was dominated by the ut storm development during the intense activity of the storms total electron content shows minute by minute increases with the satellite moving to positions 6 km apart in the minute the structured precipitation either directly produces irregularities or indirectly sets instability conditions for irregularity development in the auroral region good correlation was established for the three storms between uvi intensity and phase fluctuation development the uvi lyman birge hopfield long 170 nm emission is sensitive to 100 200 km precipitation phase fluctuation development undoubtedly arises from perturbations in the f region as well topside and bottomside soundings have shown the high occurrence of spread f in the auroral region the comparison of the data sets from these storms and from other studies indicates that the creation of irregularities develops from conditions existing over a large range of bottomside heights i e at altitudes from 100 km to the f layer

seismic stratigraphy and depositional signatures of the maldive carbonate system indian ocean abstract as documented by industrial seismic reflection profiles and well data the cenozoic stratigraphic evolution of the maldive carbonate system shows three distinct intervals characterized by their own specific depositional signatures late palaeocene volcanics generated by the reunion hotspot filled deeper pull apart structures and created a flat topography that promoted the onset of the maldive carbonate system in the early eocene some of the initial structural depressions remained as deep internal seaways surrounded by reefal margins until the late oligocene the eocene early oligocene stratigraphic signature is essentially aggradational and corresponds to a transgressive cycle associated with a second order sea level rise in the mid oligocene a major sea level fall exposed the neritic carbonate system and restricted sedimentation to the former deep internal basins during the next transgression a neritic carbonate system re established itself on the newly flooded platform and was finally drowned near the oligocene miocene boundary the main effect of this second order transgressive cycle was the transformation of the central troughs into one single deep basin in the neogene the palaeo maldive inner sea when a reef framework was established in the early miocene near the present location of the platform edge systematic bank margin progradation toward the central inner sea basin became enhanced this neogene progradational phase is explained as the response to a long term sea level fall associated with a second order regressive cycle finally the late pliocene pleistocene depositional signature is mainly aggradational and corresponds to the regional modification from flat topped carbonate banks to atoll physiographies the antecedent karst theory suggests that increased karstification was triggered by high frequency eustatic and climatic changes in the last 3 0 ma

glacial versus interglacial sedimentation rates and turbidite frequency in the bahamas the southern tongue of the ocean is a 1300 m deep flat floored basin in the bahamas that receives large amounts of sediment from the carbonate platforms surrounding it on three sides we have examined five 8 13 m long piston cores and determined bulk sedimentation rates turbidite frequency and turbidite accumulation rates for the past two glacial and interglacial periods the mean of bulk sedimentation rates is four to six times higher in interglacial periods average accumulation rates of recognizable turbidites are higher by a factor of 21 to 45 and interglacial turbidite frequency is higher by a factor of 6 to 14 sediment composition indicates that increased interglacial rates are due to higher accumulation of platform derived material additional data from other bahamian basins as well as published material from the caribbean strongly suggest that highstand shedding is a general trend in pure carbonate depositional systems carbonate platforms without a siliciclastic component export more material during highstands of sea level when the platform tops are flooded and produce sediment the response of carbonate platforms to quaternary sea level cycles is opposed to that of siliciclastic ocean margins where sediment is stored on the inner shelf during highstands and passed on to continental rises and abyssal plains during lowstands of sea level

gps phase scintillation at high latitudes during the geomagnetic storm of 17 18 march 2015 the geomagnetic storm of 17 18 march 2015 was caused by the impacts of a coronal mass ejection and a high speed plasma stream from a coronal hole the high latitude ionosphere dynamics is studied using arrays of ground based instruments including gps receivers hf radars ionosondes riometers and magnetometers the phase scintillation index is computed for signals sampled at a rate of up to 100 hz by specialized gps scintillation receivers supplemented by the phase scintillation proxy index obtained from geodetic quality gps data sampled at 1 hz in the context of solar wind coupling to the magnetosphere ionosphere system it is shown that gps phase scintillation is primarily enhanced in the cusp the tongue of ionization that is broken into patches drawn into the polar cap from the dayside storm enhanced plasma density and in the auroral oval in this paper we examine the relation between the scintillation and auroral electrojet currents observed by arrays of ground based magnetometers as well as energetic particle precipitation observed by the dmsp satellites equivalent ionospheric currents are obtained from ground magnetometer data using the spherical elementary currents systems technique that has been applied over the ground magnetometer networks in north america and north europe the gps phase scintillation is mapped to the poleward side of strong westward electrojet and to the edge of the eastward electrojet region also the scintillation was generally collocated with fluxes of energetic electron precipitation observed by dmsp satellites with the exception of a period of pulsating aurora when only very weak currents were observed

the heppner maynard boundary measured by superdarn as a proxy for the latitude of the auroral oval 1 we present a statistical study relating the latitude of the auroral oval measured by the imager for magnetopause to aurora global exploration image si 12 proton auroral camera to that of the heppner maynard boundary hmb determined from super dual auroral radar network superdarn data during the period 2000 2002 the hmb represents the latitudinal extent of the ionospheric convection pattern the oval latitude from the proton auroral images is determined using the method of milan et al 2009a which fits a circle centered on a point 2 duskward and 5 antisunward of the magnetic pole the auroral latitude at midnight is determined for those images where the concurrent superdarn northern hemisphere maps contain more than 200 data points such that the hmb is well defined the statistical study comprises over 198 000 two minute intervals and we find that the hmb is located on average 2 2 equatorward of the proton auroral latitude a superposed epoch analysis of over 2500 substorms suggests that the separation between the hmb and the oval latitude increases slightly during periods of high geomagnetic activity we suggest that during intervals where there are no auroral images available the hmb latitude and motion could be used as a proxy for that of the aurora and therefore provide information about motions of the open closed field line boundary

the paradox of drowned reefs and carbonate platforms shallow water carbonate platforms and reefs are drowned when tectonic subsidence or rising sea level outpaces carbonate accumulation and benthonic carbonate production ceases drowned platforms are common in the geologic record but they present a paradox if one considers rates of processes involved during the early holocene when sea level rose at rates of 6 000 to 10 000 m yr mm 1 000 yr most reefs and platforms were outpaced by the rising sea during the late holocene with sea level rising 500 to 3 000 m yr in the atlantic caribbean area reefs and platforms started to recover built to sea level and prograded seaward 1 000 m yr is thus a conservative estimate of the average growth potential of modern reefs and platforms independently accumulation rates of prograding platforms in the geologic record suggest growth potential in excess of several hundred microns per year the growth potential of 1 000 m yr exceeds any relative rise of sea level caused by long term processes in the geologic record newly formed ocean crust subsides at a maximum of 250 m yr basin subsidence averages 10 to 100 m yr and sea level rises due to increased sea floor spreading amount to less than 10 m yr rapid pulses of relative rise of sea level or reduction of benthic growth by deterioration of the environment remain the only plausible explanations of drowning the geologic record shows examples of both of these processes global mass extinctions of reefs and platforms occurred in the middle cretaceous eustatic rise due to submarine volcanism or desiccation of a small ocean basin and the late devonian global crisis of ocean environment extraterrestrial cause drowning controlled by regional tectonics prevailed in the jurassic and early cretaceous of the tethyan realm and the drowning of mesozoic platforms in the western north atlantic seems to have been dictated by plate tectonic drift to higher latitudes

monsoon induced partial carbonate platform drowning maldives indian ocean multibeam maps and high resolution seismic images from the maldives reveal that a late miocene to early pliocene partial drowning of the platform was linked to strong sea bottom currents in the upper miocene to holocene currents shaped the drowned banks the current moats along the bank edges and the submarine dune fields bottom currents in the maldives are driven by the monsoon it is proposed that the onset and the intensification of the monsoon during the neogene provoked platform drowning through injection of nutrients into surface waters since the late miocene topographically triggered nutrient upwelling and vigorous currents switched the maldives atolls into an aggradational to backstepping mode which is a growth pattern usually attributed to episodes of rising sea level

shallow subsurface diagenesis of pleistocene periplatform ooze northern bahamas previous studies on early submarine diagenesis of periplatform carbonates have implied that these originally polymineralic aragonite magnesian calcite calcite sediments are susceptible to early diagenesis only in current swept open seaways or where surficially exposed by erosion on the seafloor it has also been proposed that while in the shallow subsurface periplatform oozes retain their original mineralogy for at least 200 000 400 000 yr and remain unlithified for tens of millions of years evidence is reported here for extensive calcitization and selective lithification of periplatform oozes of late pleistocene age in two piston cores collected from water depths of 1 000 m north of little bahama bank it is shown that shallow 30 m subsurface diagenesis can significantly alter the original mineralogy of periplatform oozes to predominantly calcite in less than 440 000 yr and that cementation by calcite can produce chalk ooze sequences within the same time frame periplatform oozes that originally contain a high percentage of bank derived magnesian calcite appear to have a higher diagenetic potential than those originally low in magnesian calcite shallow subsurface calcitization and fithification greatly reduce the diagenetic potential of periplatform carbonates and chalk ooze sequences apparently can persist for tens of millions of years and to burial depths of at least 300 m shallow subsurface diagenesis at water depths 1 000 m proceeds via dissolution of magnesian calcite and aragonite and reprecipitation of calcite as allochem fillings exterior overgrowths and cement it is speculated that density driven kohout convection where seawaters under saturated with respect to magnesian calcite and aragonite and saturated supersaturated with respect to calcite flow through the margins of carbonate platforms is the primary driving mechanism for shallow subsurface diagenesis removal of mg during early stages of deep seafloor and shallow subsurface diagenesis should increase the mg content of interstitial waters which is likely to increase the dolomitizing potential of kohout convection fluid flow

quaternary slope development of the western leeward margin of the great bahama bank abstract to date work on the great bahama bank s western leeward margin has centred chiefly on seismic scale expressions of carbonate sequences and systems tracts however periplatform slope sediments also exhibit very well developed cyclicity on scales of decimetres to several metres it is these small scale high frequency cycles within the larger scale facies successions of the quaternary which form the main topic of this paper previous studies have shown that the small scale cycles correlate to the orbitally forced high frequency sea level changes therefore these cycles should indicate how sea level has affected the slope development and thus platform margin evolution during this period through detailed high resolution sequence stratigraphy of the great bahama bank s leeward margin obtained via 18o isotope and mineralogical xrd analyses confined by u th dating and nannofossil bioevents a greater understanding of the bedding geometries within the pleistocene holocene seismic sequences and clues as to the nature of the slope development has been achieved the high resolution seismic profiles indicate that since the plio pleistocene change in geometry in which the great bahama bank developed into a rimmed platform continued steepening and subsequent progradation of the leeward margin has typified slope development during the quaternary which is described as an accretionary slope however on the basis of our observations we conclude that only the early to lower middle pleistocene section isotope stages 45 20 and the holocene isotope stage 1 of the leeward margin is accretionary this indicates that a degree of erosion and or by passing has occurred on the leeward margin since the lower middle pleistocene isotope stage 19 during the first part of this period isotope stages 19 12 erosion and or by passing occurred in the middle to lower slope regions and toe of slope by the end of the upper middle to late pleistocene phase isotope stages 11 2 erosion also occurred on the upper slope this erosion by currents at the toe of slope and oversteepening of the upper and middle slopes have led to back cutting upslope and resulted in the progressive retreat of the toe of slope towards the platform to the east however the rise in sea level since the last glacial maximum to its present day level has allowed high productivity on the platform top during the holocene and the deposition of a thick sediment wedge on the slope and sedimentation across the entire leeward flanks this has led to the redevelopment of an accretionary slope and continued westward progradation of the great bahama bank s western leeward margin

late glacial to post glacial sea levels in the western indian ocean late glacial to post glacial sea level changes provide direct evidence of the progress of melting of large ice sheets during the last deglaciation but although the correlation between ice and ocean volumes is incontrovertible the causal link is commonly obscured local effects including tectonics isostatic and hydroisostatic responses and equatorial ocean syphoning impose additional signals that hide the true picture a detailed regional study of the western indian ocean based on the analysis of drill cores carried out through modern reefs in combination with observations and sampling of reef foreslopes and investigations of outcrops provides a comprehensive data base sites from a range of tectonic settings include the microcontinental margins of madagascar the granitic seychelles and the isolated volcanic islands of reunion mauritius and the comoros in which the effects of subsidence can be shown to be small these cover a range of latitudes and comparisons with adjacent sites on continental margins allow the construction of sea level curves that closely reflect the eustatic response and disengage this from the effects of other mechanisms the mayotte foreslope in the comoro islands provides the first coral reef record of sea level change during the early deglaciation in the indian ocean 110 115 m below present sea level between 18 000 and 17 000 yr bp two distinctive reef terraces at 90 and 60 m water depth are dated at 13 600 yr bp and partly attributed to the younger dryas period 12 700 11 600 cal yr bp reef drowning at around 13 500 yr bp may correspond to meltwater pulse 1a and although there were surges in the rate of sea level rise most notably between 11 950 and 11 350 yr bp there is little evidence to support a well defined meltwater pulse 1b reconstructed holocene sea level curves are in good agreement and reflect a rapid sea level rise of about 6 mm yr 1 between 10 000 and 7500 yr bp followed by a clear inflection around 7500 yr bp when the rate fell to 1 1 mm yr 1 modern reefs started to grow 8000 9000 years ago in the post glacial period the rate of sea level rise was 1 1 5 mm yr 1 before stabilization at its present level 3000 2500 years ago curves for the 10 000 6000 yr 1 bp interval correspond closely with those predicted by theoretical models but lie below these in the subsequent period in particular and with the exception of the margins of the madagascar microcontinent influenced by hydroisostatic processes they do not reflect predicted higher sea level stands during the late holocene

whitings a sedimentologic dilemma whitings drifting clouds of water milky because of suspended carbonate have been claimed to originate from either the action of bottom feeding fish or direct precipitation of calcium carbonate five cruises during different seasons were made to the great bahama bank to collect data pertinent to the controversy measurements of particulate concentrations average 10 mg liter with a maximum of 20 mg liter of carbonate sediment suspended in whiting water compared with an average of 1 5 mg liter for clear water outside the whitings the particles are dominantly acicular aragonite but mg calcite composes as much as 20 percent of some whitings sedimentation rates measured with fixed and drifting sediment traps were as great as 34 g m 2 hr sediment suspended in whitings aggregated into silt and sand size fioccules and settled to the bottom of settling tanks within six hours even on a rocking ship sediment in artificial whitings created by stirring sediment from the bottom with a shrimp trawl settled to the bottom in about the same time natural whitings on the other hand were never observed to dissipate because sedimentation from whitings occurs at rates sufficient to cause dissipation of the whitings within six hours we conclude that the natural whitings are continually replenished by direct precipitation the search for fish in whitings utilized sidescan sonar and fathometer imaging shrimp trawls rotenone remote video and direct scuba observation these methods and 25 years of casual observations leading to this study indicate that fish are not involved in the formation of most bahamian whitings several whitings were found over rocky or sandy bottoms where there was no mud available for fish to suspend the distance of these whitings from areas of muddy bottom precluded their having been made elsewhere by fish stable carbon and oxygen isotopic analyses and delta 14 c activity are interpreted to indicate that the suspended sediment in whitings contains some precipitated calcium carbonate and is not merely bottom sediment stirred into suspension estimates indicate that the amount of new carbonate produced in whitings on the great bahama bank is substantially higher than that arising from algal production consequently the amount of sediment transported to deep water may be much greater than previously thought

wind variability over the northern indian ocean during the past 4 million years insights from coarse aeolian dust iodp exp 359 site u1467 maldives abstract the lithogenic fraction of carbonate drift sediments from iodp exp 359 site u1467 maldives provides a unique record of atmospheric dust transport over the northern indian ocean during the past 4 myr grain size data provide proxies for dust flux controlled by source area aridity as well as wind transport capacity wind speed entrainment and long range transport of dust in the medium to coarse silt size range is linked to the strength of the arabian shamal winds and the occurrence of convective storms which prolong dust transport dust flux and the size of dust particles increased between 4 0 and 3 3 ma corresponding to the closure of the indonesian seaway and the intensification of the south asian monsoon there is no clear trend in dust flux between 3 3 and 1 6 ma whereas wind transport capacity decreased between 1 6 ma and the recent dust flux increased and shows higher variability especially during the last 500 kyr transport capacity increased between 1 2 and 0 5 ma and slightly decreased since then frequency analysis shows that dust transport varies on orbital timescales with eccentricity control being the most prominent 400 kyr throughout the record 100 kyr between 2 0 and 1 3 ma and since 1 0 ma higher frequency cycles obliquity and precession are more pronounced in wind transport capacity than in the amount of dust this indicates that the amount of coarse dust in sediments from the maldives as a far field site is more prone to changes in transport mechanisms than to changes in dust source area aridity

controls on grain size patterns in periplatform carbonates marginal setting versus glacio eustacy the importance of grain size as a fundamental property controlling other physically derived properties is well known recent grain size studies on periplatform sediments of the caribbean and western north atlantic have shown that grain size variability is coupled with changes in carbonate platform productivity and export in response to pleistocene holocene glacio eustacy these findings showed that periplatform sediments are dominated by fine grained material during sea level highstands and coarser material during sea level lowstands this paper addresses the question of grain size patterns in periplatform settings and their relationship to glacio eustacy furthermore it considers whether these patterns are applicable to different types of margin settings accretionary erosional here existing data pleistocene holocene from the accretionary western leeward margin of great bahama bank odp leg 166 and new data from the erosional eastern windward margin odp leg 101 are used the results show that the grain size patterns of both margins are controlled by late neogene sea level fluctuations the accretionary leeward margin sediments indicate the same grain size pattern as previously described in the literature however the erosional windward margin shows a reverse pattern with coarser sediments in interglacials and finer deposits in glacials this proposes that the leeward margin grain size pattern is controlled by the productivity export mode of the platform this is indicated by the platform top derived fine muds transported off bank to form a thick sediment wedge on the low angled slope during interglacials in contrast on the windward margin the sediment flux pattern is controlled by the impact of mass transport processes this is indicated by the increased occurrence of turbidites during interglacials that might be more frequent at this time because the steep angled erosional slope is less apt for the deposition of excess fine material this material is eroded and or bypasses the slopes and is redeposited in the periplatform basin setting

late pleistocene and holocene cool water carbonates of the western mediterranean sea post glacial neritic cool water carbonates of the western mediterranean sea were examined by means of hydroacoustic data sediment surface sampling and vibrocoring to unravel geometries and to reconstruct sedimentary evolution in response to the last sea level rise the analysed areas located on the alboran ridge in the bay of oran and at the southern shelf of the island of mallorca are microtidal and bathed by oligotrophic to weakly mesotrophic waters seasonal water temperature varies between 13 c and 27 c echosounder profiles show that the bay of oran and the southern shelf of mallorca are distally steepened ramps while the alboran ridge forms a steep flanked rugged plateau around the alboran island in the three areas an up to 10 m thick post glacial sediment cover overlies an unconformity in oran and mallorca stacked lowstand wedges occur in water depths of 120 to 130 m on the alboran ridge and in the bay of oran highstand wedges occur at 35 to 40 m up to 5 m long cores of upper pleistocene to holocene successions were recovered in water depths between 40 and 81 m deposits contain more than 80 carbonate with mixed carbonate volcaniclastics in the lower part of some cores in alboran the carbonates consist of up to 53 of aragonite and up to 83 of high magnesium calcite radiocarbon dating of bivalve shells coralline algae and serpulid tubes indicates that deposits are as old as 12 400 cal yr bp the carbonate factories in the three areas are dominated mostly by red algae but some intervals in the cores are richer in bivalves a facies rich in the gastropod turritella reflecting elevated surface productivity is restricted to the mallorca shelf rhodoliths occur at the sediment surface in most areas at water depths shallower than 70 m they form a 10 to 20 cm thick veneer overlying rhodolith poor bioclastic sediments which nonetheless contain abundant red algal debris this rhodolith layer has been developing for the past 800 to 1000 years similar layers at different positions in the cores are interpreted as reflecting in situ growth of rhodoliths at times of reduced net sedimentation sedimentary successions in the cores record the post glacial sea level rise and the degree of sediment exposure to bottom currents deepening upward trends in the successions are either reflected by shallow to deep facies transitions or by a corresponding change of depth indicative red algae there are only weak downcore variations of carbonate mineralogy which indicate that no dissolution or high magnesium to low magnesium calcite neomorphism occurs in the shallow subsurface these new data support the approach of using the recent facies distribution for interpretation of past cool water low energy microtidal carbonate depositional systems hydroacoustic data show that previous pleistocene transgressive and highstand inner ramp deposits and wedges were removed during sea level lowstands and accumulated downslope as stacked lowstand wedges this suggests that under conditions of high amplitude sea level fluctuations the stratigraphic record of similar cool water carbonates may be biased

relationship between late pleistocene sea level variations carbonate platform morphology and aragonite production maldives indian ocean a piston core from the maldives carbonate platform was investigated for carbonate mineralogy grain size distributions calcium carbonate content and organic carbon the sedimentary record was linked to late pleistocene sea level variations using an age model based on oxygen isotopes obtained from planktonic foramanifera nannofossil biostratigraphy and 14c age determinations the correlation between the sedimentary record and late pleistocene sea level showed that variations in aragonite and mud during the past 150 000 years were clearly related to flooding and sea floor exposure of the main lagoons of the atolls of the maldives carbonate platform platform flooding events were characterized by strongly increased deposition of aragonite and mud within the inner sea of the maldives exposure events in contrast can be recognized by rapid decreases in the values of both proxy records the results show that sediments on the maldives carbonate platform contain a continuous record of pleistocene sea level variations these sediments may therefore contribute to a better understanding of regional and even global sea level changes and yield new insights into the interplay between ocean currents and carbonate platform morphology

a review of calcareous nannofossil astrobiochronology encompassing the past 25 million years this paper presents a review of astrobiochronological calibration of recent to late oligocene calcareous nannofossil datum events biohorizons included in the paper are those of the widely used standard nannofossil zonations of martini e 1971 standard tertiary and quaternary calcareous nannoplankton zonation in farinacci a ed proceedings of the second international conference on planktonic microfossils roma rome ed tecnosci vol 2 pp 739 785 and okada h and bukry d 1980 supplementary modification and introduction of code numbers to the low latitude coccolith biostratigraphy zonation bukry 1973 1975 marine micropaleontology 51 321 325 as well as supplementary biohorizons proposed in the literature the biohorizons have been selected on the basis of the unambiguous taxonomy of the index taxa and their biostratigraphic usefulness we emphasise the application of rigorous methodology in nannofossil studies which permits an evaluation of biohorizons in terms of reliability and calibrates their potential correlatability astrochronological age estimates rely on the geologic timescale developed by the ics in 2004 with some new calibrations included we provide an overview of the relative position of biohorizons versus the astronomically calibrated ages of magnetic reversals and reference isotope stratigraphies surprisingly there are still few high resolution quantitative biostratigraphic studies of astrochronologically tuned sections in spite of the central role of such studies in addressing fundamental problems such as the tempo and mode of plankton evolution

holocene millennial to centennial carbonate cyclicity recorded in slope sediments of the great bahama bank and its climatic implications a 38 m long sediment core md992201 retrieved from a water depth of 290 m from the leeward margin of the great bahama bank gbb 25 53 49 n 79 16 34 w has been investigated for changes in aragonite content the core covers the mid to late holocene the past 7230 yr sediment lightness l values was used as a proxy for aragonite content based on a high linear correlation r 0 93 between the x ray diffraction derived aragonite content and l values the resulting time resolution of the l values derived aragonite content ranges from 1 yr at the base of the core to 4 yr at the top detailed time series analysis using monte carlo singular spectrum analysis and spectral analysis lomb scargle fourier transform identifies the presence of seven signals with varying amplitudes and wavelengths that could be traced throughout the past 5500 yr during the first 1600 yr of sedimentation the aragonite record is dominated by the initial flooding of the flat topped gbb superimposed on a multimillennial signal related to holocene sea level changes a millennial scale fluctuation and five quasi periodic oscillations were detected 1 3 2 kyr 500 600 yr 380 yr 260 yr 200 yr and 100 yr period comparisons with other proxies e g tree ring 14c 10be and 18o in ice cores provides information on the origin and dynamics of the individual signals the analysis shows that the 200 yr and 100 yr signals can be attributed to solar forcing the 260 yr 380 yr and the 500 600 yr quasi periodic signals are found to be of climatic origin whereas the millennial scale fluctuations remain enigmatic although solar forcing mechanisms seem likely the data show that variability of solar output as well as past oceanographic and atmospheric changes have modulated the mid to late holocene climate which in turn controlled sediment input variations found in the holocene wedge leeward of the gbb although these periplatform sediments have a rather uniform appearance they still contain a large variety of subtle sedimentary variations

source shifts to periplatform deposits during the early to middle miocene in response to climatic and oceanographic forcing maldives western indian ocean abstract periplatform carbonate ooze records a composite signal reflecting both the regional oceanographic state and the development of the adjacent carbonate platform deconvolving these signals offers the possibility to obtain a holistic perspective on the factors governing the evolution of the platform especially when the platform itself is not accessible here we examine a case study from periplatform deposition in site u1468 on the margins of the kardiva platform maldives this site has a well constrained record with seismic control of the geometric evolution of adjacent carbonate platforms here we integrate geochemistry sedimentology and external constraints to address the relationship between local platform evolution regional nutrient regime and global temperature sea level effects the lower to middle miocene succession at site u1468 is comprised of a wackestone to packstone sequence that hosts foraminifera and other bioclastic grains derived from neritic and pelagic sources as well as biogenic siliceous material such as sponge spicules the sequence records an increase in neritic supply to the periplatform from the late burdigalian to the early serravallian as recorded in sr ca and 13c values the increase in neritic material coincided with a stepwise intensification of the regional oxygen minimum zone omz recorded by mn ca ratios during these trends short lived oscillations in local carbonate production and omz intensity were superimposed on the larger trend the expansion of the omz was driven by periods of cooling while the increase in neritic production was driven by warming and sea level rise these results reinforce existing models of the evolution of the kardiva platform with respect to sea level and add to it a refined understanding of the relation to regional nutrient patterns

sea level related resedimentation processes on the northern slope of little bahama bank middle pleistocene to holocene middle pleistocene to holocene sediment variations observed in a 26 metre long core taken during a cruise of the rv marion dufresne are presented core md992202 was retrieved from the northern slope of little bahama bank and provides an excellent example for sedimentation processes in a mid slope depositional environment the sediment composition indicates sea level related deposition processes for the past 375 000 years marine isotope stages 1 to 11 the sediments consist of i periplatform ooze fine grained particles of shallow water and pelagic origin with moderate variations in carbonate content carbonate mineralogy and grain size and ii coarser intervals with cemented debris consisting of massive poorly sorted mud supported or clast supported deposits with an increased high magnesium calcite content during interglacial stages marine isotope stages 1 5 7 9 and 11 periplatform oozes i are characterized by higher aragonite contents finer grain size and higher organic contents whereas during glacial stages marine isotope stages 2 to 4 6 8 and 10 increased low magnesium and high magnesium calcite values coarser grain size and lower organic contents are recorded these glacial to interglacial differences in mineralogy grain size distribution and organic content clearly show the impact of climatically controlled sea level fluctuations on the sedimentation patterns of the northern slope of little bahama bank the coarser deposits ii occur mainly at the transitions from glacial to interglacial and interglacial to glacial stages and are interpreted as redeposition events indicating a direct link between sediment properties changes in mineralogy grain size distribution variations in organic contents and sea level fluctuations changes in hydrostatic pressure and the wave base position during sea level changes are proposed to have triggered these large scale sediment redepositions

direct observations of the role of convection electric field in the formation of a polar tongue of ionization from storm enhanced density 1 we examine the relationship of convection electric fields to the formation of a polar cap tongue of ionization toi from midlatitude plumes of storm enhanced density sed observations from the geomagnetic storm on 26 27 september 2011 are presented for two distinct sed events during an hour long period of geomagnetic activity driven by a coronal mass ejection a channel of high density f region plasma was transported from the dayside subauroral ionosphere and into the polar cap by enhanced convection electric fields extending to middle latitudes this toi feature was associated with enhanced hf backscatter indicating that it was the seat of active formation of small scale irregularities after the solar wind interplanetary magnetic field conditions quieted and the dayside convection electric fields retreated to higher latitudes an sed plume was observed extending to but not entering the dayside cusp region this prominent feature in the distribution of total electron content tec persisted for several hours and elongated in magnetic local time with the rotation of the earth no ionospheric scatter from superdarn radars was observed within this sed region the source mechanism enhanced electric fields previously drawing the plasma from midlatitudes and into the polar cap as a toi was no longer active resulting in a fossil feature we thus demonstrate the controlling role exercised by the convection electric field in generating a toi from midlatitude sed

westward electric field penetration to the dayside equatorial ionosphere during the main phase of the geomagnetic storm on 22 july 2009 1 the moderate geomagnetic storm minimum sym h 89 nt that occurred during the period from 21 to 25 july 2009 is anomalous because the storm main phase developed during northward interplanetary magnetic field imf a reduction for 4 h in the daytime e region westward drift eastward electric field over the magnetic equatorial location of trivandrum 8 5 n 77 e dip latitude 0 5 n in india is observed during the storm main phase this reduction in the drift is also indicated by the disappearance of the equatorial sporadic e region esq echoes on the ionograms it is suggested that an additional westward prompt penetration electric field characterized by the northward imf bz is superposed on the ionosphere during the storm main phase which contributed to the observed reduction in the drift these are the first observations which indicate the effects of the dusk to dawn penetration electric fields on the east west drifts during northward imf

fluid substitution in rocks saturated with viscoelastic fluids heavyoilshavehighdensitiesandextremelyhighviscosities and they exhibit viscoelastic behavior traditional rock physics based on gassmann theory does not apply to materials saturated with viscoelastic fluids we use an effective medium approach known as coherent potential approximation cpa as an alternativefluid substitutionschemeforrockssaturatedwithviscoelasticfluids suchrocksaremodeledassolidswithellipticalfluidinclusions when fluid concentration is small and as suspensions of solid particles in the fluid when the solid concentration is small thisapproachisconsistentwithconceptsofpercolationandcritical porosity and it allows one to model sandstones and unconsolidated sands we model the viscoelastic properties of a heavyoil saturated rock sample using cpaand a measured frequencydependent complex shear modulus of the heavy oil comparison of modeled results with measured properties of the heavy oil rock reveals a large discrepancy over a range of frequencies and temperatures we modify the cpascheme to account for the effect of binary pore structure by introducing a compliant porosity term this dramatically improves the predictions the predicted values of the effective shear modulus of the rock are in good agreement with laboratory data for the range of frequencies and temperatures this confirms that our scheme realistically estimates the frequency and temperature dependent properties of heavy oil rocks and can be used as an approximate fluid substitutionapproachforrockssaturatedwithviscoelasticfluids

high rates of sea level rise during the last interglacial period sea level during the last interglacial stood at least 4 m higher than at present with evidence of short term fluctuations of up to 10 m a new continuous sea level record from the red sea and coral ages suggest that during these fluctuations sea level changes were on the order of 1 6 m per century

gps scintillation and irregularities at the front of an ionization tongue in the nightside polar ionosphere in this paper we study a tongue of ionization toi on 31 october 2011 which stretched across the polar cap from the canadian dayside sector to svalbard in the nightside ionosphere the toi front arrived over svalbard around 1930 ut we have investigated gps scintillation and irregularities in relation to this toi front this is the first study presenting such detailed multi instrument data of scintillation and irregularities in relation to a toi front combining data from an all sky imager the european incoherent scatter svalbard radar the super dual auroral radar network hankasalmi radar and three gps scintillation and total electron content tec monitors in longyearbyen and ny alesund we observe bursts of phase scintillation and no amplitude scintillation in relation to the leading gradient of the toi spectrograms of 50hz phase measurements show highly localized and variable structuring of the toi leading gradient with no structuring or scintillation within the toi or ahead of the toi

controls and development of late quaternary periplatform carbonate stratigraphy in walton basin northeastern nicaragua rise caribbean sea the late quaternary sedimentary record in periplatform oozes and muds deposited on the northern nicaragua rise results from the interplay of four main controls 1 input of pelagic carbonates and bank derived fine aragonite and magnesian calcite 2 input of siliciclastic sediments 3 dispersal and removal of sediments by the caribbean current and 4 partial seafloor dissolution of metastable carbonates high accumulation rates of the calcite coarse sediment fraction throughout the study area demonstrate that planktonic foraminiferal productivity peaked during interglacial stages neritic carbonate productivity also peaked during interglacial stages when bank and shelf tops along the nicaragua rise were submerged within the photic zone because the bank and shelf tops remained mostly exposed during glacial stages the surface area available for the neritic carbonate productivity was drastically reduced to a narrow band along the margins of pedro bank and the southern shelf of jamaica a large volume of siliciclastic sediments transported from the coastal area of south america and the eastern and western regions of jamaica were deposited during glacial stages within the eastern and western deep extensions of walton basin this finding contrasts with the input pattern of siliciclastic sediments in walton basin itself where the largest input of siliciclastic sediments occurred at each of the interglacial climatic optima corresponding to intervals of maximum sea level transgression finally cores in water depths exceeding 1100 m display during interglacial stages aragonite accumulation rates systematically lower than rates in cores from water depths shallower than 1100 m this indicates that some bank derived aragonite and magnesian calcite has been partially removed by seafloor dissolution in areas from water depths exceeding 1100 m results from this study on the northeastern nicaragua rise indicate that not only do offbank transport and water column saturation state influence the late quaternary record but also that the variable strength of the caribbean current and the proximity of sources for siliciclastic sediments have played a major role in the development of the late quaternary periplatform high resolution stratigraphy

sub milankovitch cycles in periplatform carbonates from the early pliocene great bahama bank high resolution bulk sediment magnetic susceptibility and aragonite content and 18o records from two different planktonic foraminifera species were analyzed in an early pliocene core interval from the straits of florida ocean drilling program site 1006 the 18o record of the shallow dwelling foraminifera g sacculifer and the aragonite content are dominated by sub milankovitch variability in contrast magnetic susceptibility and the 18o record of the deeper dwelling foraminifera g menardii show precession cycles the relationship between the aragonite and the paleoproxy data suggests that the export of sediment from the adjacent great bahama bank was triggered directly by atmospheric processes rather than by sea level change we propose a climate mechanism that bears similarities with the semiannual cycle component of eastern equatorial pacific sea surface temperatures under present day conditions

calciturbidites and calcidebrites sea level variations or tectonic processes abstract the compositional variation of pleistocene carbonate gravity deposits from the exuma sound basin bahamas and of turonian conacian deposits from the southern provence basin france was determined the bahamian carbonate platform is located in a tectonically stable passive margin setting and the gravity deposits were deposited in an environment controlled by eustatic sea level fluctuations in contrast the southern provence basin sediments were deposited in a tectonic active regime two types of gravity deposits were present in the cores of odp leg 101 site 632a i e calciturbidites and calcidebrites in analogy with earlier studies haak and schlager 1989 the compositional variations in the calciturbidites could be linked to different sources on the carbonate margin i e platform interior platform edge platform slope interglacial sea level highstands calciturbidites show a dominance of non skeletal grains derived from the platform interior while glacial sea level lowstands calciturbidites show a dominance of skeletal platform edge to platform slope derived grains hence the calciturbidite composition can be used to reconstruct the position in relative sea level in contrast the composition of the calcidebrites remained unaltered through time and showed a clear dominance of platform edge derived sediments in addition it was shown that the calcidebrites were deposited during regressions in the southern provence basin spb the gravity deposits were deposited during episodes of sea level rise coinciding with a series of earthquakes associated with the opening of the spb the spb megabreccias show a mix of sediment grains derived from the platform interior the platform edge and the upper slope thus in contrast to the exuma sound calcidebrites with their platform margin domain specific composition the spb megabreccias have a composition that could not be assigned to a single domain on the platform margin and comprise a total mix of platform margin domains in conclusion this study shows that the composition of calciturbidites calcidebrites and megabreccias can be used to determine which processes eustatic variations or tectonic events triggered the redeposition of these gravity deposits

quaternary aragonite cycles and oxygen isotope record in bahamian carbonate ooze carbonate ooze in bahamian troughs displays cyclic variation in the content of aragonite a 10 m core devoid of turbidites shows 3 5 cycles each defined by a sharp increase followed by a gradual decrease of aragonite the aragonite curve matches closely the oxygen isotope curve of planktic foraminifera from the same core aragonite highs correspond to light oxygen isotope values and thus to interglacial stages content of terrigenous material is low during interglacials and higher during glacial periods intermittent flooding and exposure of the bahama banks is most probably not the cause of the cycles because the latest increase in aragonite precedes bank flooding by 8 000 yr and because the cycles are distinctly asymmetric with rapid increase and gradual decrease of aragonitic content carbonate dissolution cycles tied to the glacial rhythm of earth9s climate are a more likely explanation of the variations in aragonite content

misuse of fischer plots as sea level curves fischer plots are graphic representations of cyclic carbonate deposits showing cumulative departure from average cycle thickness plotted against cycle number and corrected for assumed subsidence during each cycle observed cycle thicknesses in excess of subsidence have been interpreted to represent depositional accommodation space formed by eustatic sea level rise however implicit in this interpretation is the assumption that preserved cycle thickness is a proxy for accommodation to test this assumption a survey of carbonate sediment accumulation patterns i e cycle thicknesses developing during a single transgressive event the holocene postglacial sea level rise was conducted on a shallow carbonate platform great bahama bank where accommodation was created primarily by sea level rise over the platform margin i e subsidence was minimal this survey demonstrates that holocene sediment cycle thickness and accommodation are uncorrelated r 2 0 03 consequently fischer plots constructed by using holocene cycle thicknesses are poor representations of the holocene transgression in extreme examples holocene fischer plots would be interpreted to show relative sea level fall during the holocene on great bahama bank because holocene subsidence currently exceeds sediment thickness in addition a simple sensitivity test shows that eustatic sea level interpretations based on interbasinal correlation of fischer plots are equivocal the gross form of fischer plots appears so overly robust as to be insensitive to broad variations in stratigraphic completeness cycle duration or subsidence because cycle thickness apparently is uncorrelated with accommodation and the gross form of fischer plots is relatively invariant it seems prudent to reevaluate the practice of interpreting fischer plots as sea level curves per se in the analysis of ancient carbonate cycles

late quaternary record of pteropod preservation from the andaman sea abstract in order to understand the glacial to interglacial fluctuations in pteropod preservation and productivity during the late quaternary 54 ka bp to present we investigated pteropod organic carbon corg and globigerina bulloides abundance in a deep sea core from the western andaman sea pteropod abundance and preservation is similar to the indo pacific carbonate preservation type showing better preservation during glacial and poor preservation during interglacial periods the core site appears to have remained below the aragonite compensation depth acd throughout the holocene indicated by the total absence of pteropods maximum abundance and good preservation of pteropods was observed during stadials such as younger dryas yd heinrich events hes and last glacial maxima lgm indicating weaker oxygen minimum zone omz and deeper acd furthermore the high relative abundance of mesopelagic pteropods over epipelagic forms suggests a well ventilated water column with weak omz particularly during lgm apparently driven by intense winter monsoon increased monsoon driven productivity was observed during 45 40 ka of early marine isotope stage 2 mis 2 24 22 ka bolling allerod b a 15 13 5 ka yd and late holocene as evidenced by corg content and g bulloides enhanced pteropod preservation of h1 associated with low corg content and g bulloides suggests that reduced monsoonal driven productivity might have influenced pteropod preservation deglacial preservation spike in the andaman sea is consistent with other northern indian ocean records and elsewhere outside the indian ocean implying the event is global in nature marked by deepening of acd probably driven by enhancement of winter monsoon on local and changes in intermediate water circulation on regional scale

mixed carbonate siliciclastic sedimentation along the great barrier reef upper slope a challenge to the reciprocal sedimentation model abstract results of studies involving numerous cores and odp holes along the great barrier reef gbr margin and adjacent queensland trough and queensland plateau have challenged the use of a reciprocal sedimentation model to describe the sedimentary response of slope and basin settings to glacioeustatic sea level fluctuations upper slope sedimentation results from the relationships between sea level fluctuations antecedent topography and regional climate that play an important role in the type and amount of sediment deposited on the upper slope during glacial deglacial and interglacial times during the last glacial maximum lgm 20 ka ago upper slope sediments generally lacked siliciclastic material and are characterized by very low accumulation rates whereas early deglacial time termination i ti deposits are dominated by a siliciclastic and neritic carbonate pulse siliciclastic sedimentation was significantly reduced in the holocene while carbonate sedimentation remains elevated a new borehole iodp expedition 325 hole m0058a hole 58a recovered 82 of a 40 4 m hole on the upper slope east of noggin passage on the central gbr margin near cairns australia hole 58a provides a detailed sedimentary record during termination ii tii marine isotope stage 6 5e mis 6 5e deglacial transition and through most of interglacial mis 5 this hole along with two others odp leg 133 holes 820a and 819a from the upper slope east of grafton passage show carbonate siliciclastic cyclicity as the result of glacioeustatic change with the gbr shelf sedimentation at hole 58a is consistent with that of previous studies along the gbr margin focusing on the lgm to present and extends the upper slope sedimentary record back to tii and interglacial mis 5 a siliciclastic pulse similar to the one during ti occurred during the penultimate deglaciation tii however the maximum neritic aragonite export to the upper slope occurred not during peak mis 5e highstand when sea level was a few meters above modern position but subsequently during a time mis 5d to 5a when lowered sea level fluctuated between 30 and 50 m below present sea level siliciclastic sediments were reworked and exported to the upper slope when the lowstand fluvial plain was re flooded whereas neritic carbonate export to the slope reached a maximum when sea level fell and much of the mid to outer shelf re entered the photic zone subsequent to a drowning interval thus this analysis refines the mixed sedimentation models of upper slope sedimentation along the central gbr margin during the penultimate deglacial transgression and subsequent interglacial early and late highstand this study provides further evidence that mixed carbonate siliciclastic margins do not always behave in a predictable manner and that mixed margins both modern and ancient would benefit from detailed study of sediment transport in the context of sea level rise and fall

high production and highstand shedding from deeply submerged carbonate banks northern nicaragua rise abstract because the shallow isolated carbonate banks on the northern nicaragua rise the nicaragua honduras and southern jamaica carbonate shelves and many other modern carbonate banks worldwide are covered by an average of 20 to 30 m of water and by a thin blanket of coarse carbonate sediments other carbonate sedimentologists have considered these banks good examples of incipiently drowned or even drowned carbonate banks however based on recent research on the northern nicaragua rise we can demonstrate that these banks currently are healthy producers of large volumes of periplatform sediments fine aragonite and magnesian calcite which are exported almost entirely to the deep surrounding slopes these sediments which were deposited during the past 9000 10 000 years form peripl tform wedges on the middle and upper slopes which are seen clearly on 3 5 khz seismic profiles radiocarbon ages of the wedge surface sediment range between 230 and 610 ybp and provide clear evidence for the contemporaneous production of sediments on the shallow bank and shelf and their instantaneous export to the upper slopes for the last 5000 years sedimentation rates ranged from 2000 mm ky off pedro bank to 1300 mm ky off jamaica these rates are somewhat lower than but of the same order of magnitude as sedimentation rates on the western leeward slopes of great bahama bank deposition of the metastable carbonate sediments discussed in this paper occurred as soon as sea level rose to flood the bank and shelf which flank walton basin following the last glacial lowstand they com rise a wedge shaped package of transgressive and highstand sediments on the upper and middle slopes of pedro bank and the southern jamaica shelf

timing and distribution of calciturbidites around a deeply submerged carbonate platform in a seismically active setting pedro bank northern nicaragua rise caribbean sea the sedimentological study of thirteen sediment cores from the periplatform setting surrounding pedro bank northern nicaragua rise caribbean sea shows that during the last 300 ka turbidite deposition is controlled by at least four factors 1 late quaternary sea level fluctuations 2 prolific fine grained sediment production and export resulting in oversteepening of the upper slope environment 3 the proximity to the bank margin and 4 local slope and seafloor morphology the most intriguing finding of this study is the paucity of turbidites with only 101 turbidites in 13 cores in this tectonically active setting near the caribbean plate boundary throughout the last 300 ka the frequency of turbidite input during interglacial stages is three times higher than during glacial stages also it is obvious that changes in sea level influence the timing of turbidite deposition this is especially evident during the transgressions resulting in rapid renewed bank top flooding subsequent neritic sediment overproduction and offbank export the flooding event during each transgression is usually recorded by the onset of turbidite deposition at various sites along several platform to basin transects in down and upcurrent slope settings overall however more turbidites are deposited during the regressive rather than the transgressive phases in sea level probably as a result of sediment reorganisation on the slope resulting in slope failure five cores show highstand bundling of calciturbidites i e higher number of turbidites during highstands than during lowstands in sea level

isotopic signature of burial diagenesis and primary lithological contrasts in periplatform carbonates miocene great bahama bank the stable isotope geochemistry of miocene sediments from the leeward margin of the great bahama bank was examined to investigate burial diagenetic processes in periplatform carbonates data indicate that in addition to differences in bulk proportions of neritic and pelagic carbonate along the slope rhythmic variation in primary carbonate content has controlled patterns of burial diagenesis and associated geochemical signatures throughout much of the succession examined the present study focuses on ocean drilling program sites 1006 and 1007 the most distal of five sites drilled from marginal to deep basin environments during leg 166 these miocene sections are characterized by their cyclic appearance manifest as decimeter to meter scale alternations between light colored ooze chalk limestone and dark colored marl marlstone the section at site 1006 contains a high proportion of pelagic carbonate and is unlithified to a subbottom depth of 675 m fluctuations in 18 o and 13 c values at this site are independent of lithological variation and reflect primary conditions at site 1007 located at the toe of slope and composed of a mixture of bank derived and pelagic carbonate limestones are densely cemented show little evidence of compaction and have 18 o values up to 2 higher than coeval sediments at site 1006 marlstones at site 1007 are poorly cemented exhibit an increase in compaction related features with depth and have lower and more variable 18 o values that are similar to those of coeval sediments at site 1006 isotopic and petrographic characteristics of limestone interbeds result from cement precipitation from cold sea water during the first 100 m of burial higher proportions of insoluble materials and pelagic carbonate seem to have inhibited diagenetic alteration in adjacent marlstones in spite of significant compaction and pressure solution during burial original isoto pic compositions appear to be best preserved in these intervals at site 1007 the documented contrasts in petrographic and isotopic patterns illustrate the role of primary sediment composition in controlling lithification processes in periplatform carbonates and stress the importance of consid ering such factors when interpreting geochemical data from ancient shelf and slope limestones

orbital scale variation of primary productivity in the central equatorial indian ocean maldives during the early pliocene abstract we investigate the response of the central equatorial indian ocean odp site 716 maldives upwelling system to orbital forcing between 3 64 and 4 19 ma this time interval in the early pliocene was characterized by global average temperatures considerably warmer than present and reduced zonal and meridional sea surface temperature gradients across the major oceans chlorin a degradation product of chlorophyll and a potential indicator of primary productivity was previously shown to record orbital scale variations at this site to confirm that chlorin records primary productivity and to understand the mechanism controlling the orbital variations we compare changes in the planktic foraminiferal assemblages with the chlorin content of the sediment cross wavelet analysis demonstrates the in phase relationship between the abundance of thermocline species and chlorin content indicating that upwelling and a shallower thermocline drive the productivity changes the aragonite content in periplatform carbonates is known to reflect variations in sea level and or climate with high values generally indicating sea level highstands the aragonite content in the studied interval shows precession and eccentricity astronomical cycles whereas the primary productivity proxies show only precessional cycles the negative correlation between aragonite content and the relative abundance of thermocline species on the precessional band implies that the primary productivity increased during sea level lowstands this phase coupling is consistent with quaternary productivity records from the central indian ocean that were proposed to be controlled by orbital induced variations of the el nino southern oscillation enso we therefore propose that a similar mechanism was active in the early pliocene despite major changes in the global boundary conditions

benthic carbonate factories of the phanerozoic marine carbonate precipitation occurs in three basic modes abiotic or quasi abiotic biotically induced and biotically controlled on a geologic scale these precipitation modes combine to form three carbonate production systems or factories in the benthic environment 1 tropical shallow water factory dominated by biotically controlled mainly photo autotrophic and abiotic precipitates 2 cool water factory dominated by biotically controlled mainly heterotrophic precipitates and 3 mud mound factory dominated by biotically induced mainly microbial and abiotic precipitates sediment accumulations of the factories differ in composition geometry and facies patterns and some of these differences appear prominently in seismic data thus facilitating subsurface prediction the characteristic accumulation of the tropical factory is the flat topped often reef rimmed platform in cool water systems reefs in high energy settings are scarce and hydrodynamic influence dominates producing seaward sloping shelves and deep water sediment drifts often armored by skeletal framework the typical accumulation of the mud mound factory is groups of mounds in deeper water where the mud mound factory expands into shallow water it forms rimmed platforms similar to the tropical factory the tropical factory is most productive the mud mound factory reaches 80 90 and the cool water factory 20 30 of the tropical growth rate the three factories represent end members connected by transitions in space transitions in time are linked to biotic evolution

antarctic temperature and global sea level closely coupled over the past five glacial cycles sea level has varied by over one hundred metres across glacial interglacial cycles over the past 520 000 years an extended sea level reconstruction shows a strong coupling between these sea level changes and antarctic surface temperatures over the past five glacial cycles

biochemical and ultrastructural evidence for the origin of whitings a biologically induced calcium carbonate precipitation mechanism we propose that bahamian whitings floating patches of lime mud are in part the result of biological precipitation of calcium carbonate induced by picoplankton and cellular components the cells may act as nucleation sites for crystallization from seawater supersaturated with caco3 our model represents a new hypothesis concerning bahamian whiting formation and is based on several lines of evidence biochemical data suggest that the macromolecules from carbonate suspended in bahama banks whitings are distinct from those found in the lime mud sediment producer penicillus and from bottom sediment direct ultrastructural evidence indicates that mineralization occurs on the surfaces of picoplankton cells and degrading organic cellular components the organic constituents include but are not restricted to whole and fragmented algal cells and composite structures 20 30 m in diameter the observed calcium carbonate crystals are distinct from skeletal debris because of the magnitude of the whiting phenomenon calculations of carbonate sediment production budgets should include the potential contribution of calcium carbonate produced by epicefular precipitation knowledge of carbonate mud genesis is critical to interpretation of ancient occurrences of lime mud as well as to understanding ancient and global carbon cycles

the leaking bucket of a maldives atoll implications for the understanding of carbonate platform drowning abstract seismic and multibeam data as well as sediment samples were acquired in the south male atoll in the maldives archipelago in 2011 to unravel the stratigraphy and facies of the lagoonal deposits multichannel seismic lines show that the sedimentary succession locally reaches a maximum thickness of 15 20 m above an unconformity interpreted as the emersion surface which developed during the last glacial sea level lowstand such depocenters are located in current protected areas flanking the reef rim of the atoll or in infillings of karst dolinas much of the 50 m deep sea floor in the lagoon interior is current swept and has no or very minor sediment cover erosive current moats line drowned patch reefs whereas other areas are characterized by nondeposition karst sink holes blue holes and karst valleys occur throughout the lagoon from its rim to its center lagoonal sediments are mostly carbonate rubble and coarse grained carbonate sands with frequent large benthic foraminifers halimeda flakes red algal nodules mollusks bioclasts and intraclasts some of them glauconitic as well as very minor ooids finer grained deposits locally are deposited in current protected areas behind elongated faros i e small atolls which are part of the rim of south male atoll the south male atoll is a current flushed atoll where water and sediment export with the open sea is facilitated by the multiple passes dissecting the atoll rim with an elevated reef rim and tower like reefs in the atoll interior it is an example of a leaky bucket atoll which shares characteristics of incipiently drowned carbonate banks or drowning sequences as known from the geological record

glacial to holocene sedimentation on the western slope of great bahama bank abstract thick late quaternary sediment sections were recovered at several sites on the leeward slope of great bahama bank during leg 166 of the ocean drilling program these sections have paleoceanographic records with potentially high temporal resolution to make an initial assessment of the records corresponding to the holocene highstand of sea level we have identified and dated the sediments from the four upper slope sites 1004 1005 1008 and 1009 that were deposited during the period of time which spans the last glaciation through the holocene age identifications are based upon the abundances of the globorotalia menardii complex of planktonic foraminifera the stable oxygen isotopic ratios of bulk sediment and the planktonic foraminifera globogerinoides ruber and ams c 14 dating of bulk sediment comparison of these data with the sediment lithologic and geoacoustic properties shows that consistent stratigraphic relationships exist at each site the uppermost interval of aragonite rich sediments corresponds to the holocene highstand of sea level i e oxygen isotope stage 1 and these sediments are underlain by a relatively thin interval of aragonite poor partially lithified sediments which corresponds to the last glaciation when sea level was significantly lower than today i e oxygen isotope stages 2 4 the leg 166 upper slope sites possess carbonate accumulation and paleoceanographic proxy records with very high temporal resolution with sites 1004 1008 and 1009 appearing to have the greatest stratigraphic integrity comparison of core and high resolution seismic profile data establishes the holocene nature of the uppermost seismic unit in the stratigraphic package of the western slope of great bahama bank

global positioning system phase fluctuations at auroral latitudes using observations of a diversity of propagation paths of global positioning system satellites from each of 11 high latitude stations it was possible to determine the behavior pattern for the development of phase fluctuations in the auroral and subauroral irregularity regions the coverage comprised a large range of longitudes and latitudes with all data measuring the same parameter i e phase fluctuations starting with characteristics of the irregularity development on magnetically quiet days it was noted that the start and stop times of phase fluctuations correlated with the entry and exit into the irregularity oval maximum occurrence of phase fluctuation took place near magnetic midnight during magnetic storms the irregularity oval expands equatorward and poleward and phase fluctuations increase in intensity using the time difference of the development of irregularities between stations considerably separated in longitude the conclusion was reached that during a magnetic storm there is a long time feeding of the turbulent energy that develops irregularities in the oval while the geographic position of the station relevant to the oval is important during storms the dynamics of each storm modifies the simple behavior shown during quiet times observations at corrected geomagnetic latitudes 80 indicate that phase scintillation intensities were lower than those in the oval during both quiet and disturbed conditions in years of low solar flux since the technique yields a measure of total irregularity intensity for the total propagation path it was not possible solely from these data to determine the altitude of the irregularities in case studies it was found that during magnetically quiet periods when irregularities are noted on propagation paths in the irregularity oval f layer critical frequencies and thicknesses were greater than those of the e layer during magnetic storm periods e layer critical frequencies are for various periods of time greater than those of the f layer during storms there are probably contributions from both layers with different mechanisms for the development of irregularities operating as a function of time storm development and latitude

gulf stream s induced sea level rise and variability along the u s mid atlantic coast 1 recent studies indicate that the rates of sea level rise slr along the u s mid atlantic coast have accelerated in recent decades possibly due to a slowdown of the atlantic meridional overturning circulation amoc and its upper branch the gulf stream gs we analyzed the gs elevation gradient obtained from altimeter data the florida current transport obtained from cable measurements the north atlantic oscillation nao index and coastal sea level obtained from 10 tide gauge stations in the chesapeake bay and the mid atlantic coast an empirical mode decomposition hilbert huang transformation emd hht method was used to separate long term trends from oscillating modes the coastal sea level variations were found to be strongly influenced by variations in the gs on timescales ranging from a few months to decades it appears that the gs has shifted from a 6 8 year oscillation cycle to a continuous weakening trend since about 2004 and that this trend may be responsible for recent acceleration in local slr the correlation between long term changes in the coastal sea level and changes in the gs strength was extremely high r 0 85 with more than 99 99 confidence that the correlation is not zero the impact of the gs on slr rates over the past decade seems to be larger in the southern portion of the mid atlantic bight near cape hatteras and is reduced northward along the coast the study suggests that regional coastal sea level rise projections due to climate change must take into account the impact of spatial changes in ocean dynamics

scintillation and loss of signal lock from poleward moving auroral forms in the cusp ionosphere we present two examples from the cusp ionosphere over svalbard where poleward moving auroral forms pmafs are causing significant phase scintillation in signals from navigation satellites the data were obtained using a combination of ground based optical instruments and a newly installed multiconstellation navigation signal receiver at longyearbyen both events affected signals from gps and global navigation satellite system glonass when one intense pmaf appeared the signal from one gps spacecraft also experienced a temporary loss of signal lock although several polar cap patches were also observed in the area as enhancements in total electron content the most severe scintillation and loss of signal lock appear to be attributed to very intense pmaf activity this shows that pmafs are locations of strong ionospheric irregularities which at times may cause more severe disturbances in the cusp ionosphere for navigation signals than polar cap patches

aragonite pteropod abundance and preservation records from the maldives equatorial indian ocean inferences on past oceanic carbonate saturation and dissolution events abstract during the international ocean discovery program iodp expedition 359 a long continuous carbonate rich sequence was recovered from the inner sea of maldives we investigated pteropod proxies absolute abundance of pteropods species total pteropods epipelagic to mesopelagic ratio fragmentation ratio limacina dissolution index ldx mean shell size variations of l inflata from sites u1467 water depth 487 m and u1468 water depth 521 m to understand both surface and sub surface paleoceanographic changes in the equatorial indian ocean and to improve our understanding of the factors responsible for pteropod preservation on longer timescales a total of 15 species of pteropods were identified and their downcore variations were documented from the core top to 707 49 mbsf in u1467 and from 447 4 to 846 92 mbsf in u1468 at the site u1467 pteropod shells show high abundances preservation up to a depth of 45 mbsf 1 2 ma which is consistent with the presence of aragonite content in sediments with the top 50 m bearing high aragonite content beyond 45 mbsf only fragmented pteropod shells were seen down to 50 mbsf corresponding to 1 5 ma followed by a total absence of pteropod shells and fragments from 50 mbsf 1 5 ma to the end of the core at 846 92 mbsf 24 ma a decrease in the so42 concentration and alkalinity in the interstitial fluid geochemistry is seen at these depths the presence of dolomite content below 50 mbsf also indicates the alteration of aragonite into dolomite analyses of the carbonate preservation proxies reveal that the pteropods exhibit considerable fluctuation in abundance preservation during the last 1 2 myr a good to moderate preservation ldx 2 to 3 is seen which correlates well with the fragmentation ratio but with an inverse relation with calcification rate the proxies for in life pteropod shell dissolution average size of l inflata and ldx indicate that glacial periods mis 16 14 6 4 and 2 have shown no signs of dissolution pointing better calcification under aragonite saturated water column which is in good correlation with reduced atmospheric co concentration epipelagic mesopelagic ratio indicates that the water column exhibited enhanced ventilation and mixing during glacial to interglacial periods but intervals of intense stratification a sign of poor ventilation or weakened circulation was prevalent beyond mis 14 the longest interval of poorest preservation was marked during mis 11 and 13 which corresponds to the mid brunhes dissolution interval mbdi on a longer time scale the abundances preservation of pteropods in the maldives seems to be controlled by changes in the seawater chemistry associated with monsoon productivity water column ventilation and atmospheric co2 concentration

mineralogy and grain size variations along two carbonate margin to basin transects pedro bank northern nicaragua rise abstract the analysis of nine periplatform cores in the surrounding of the pedro bank carbonate platform showed the presence of characteristic depositional environments during the last 300 ky this subdivision is based on mineralogical and grain size variations in space and time along the leeward downcurrent transect the fine sediment fraction 40 km aragonite is still the most abundant mineral but the percentage decreases while the pelagic carbonate mineral content lmc increases within the subordinate coarse fraction classes 63 m the very fine sand fraction dominates at proximal sites 20 km show a more bimodal distribution pattern in the coarse grain sizes with maximum percentages within the very fine and medium sand fraction indicating a mixed neritic pelagic signal during glacial lowstands in sea level a twofold division in the spatial distribution of the periplatform sediments is evident a proximal environment 28 km showing a strong dominance of the fine fraction 90 the increased coarse fraction percentage during glacials at proximal sites results from various interacting processes 1 lower input of fine neritic sediments 2 increased current winnowing and 3 redepositional processes at the upper slope during lowered sea level and the export of this material to proximal basinal sites at upcurrent sites the mineralogy displays a similar spatial evolution as seen along the downcurrent margin but with overall reduced percentages this is the result of the lower export potential of the platform against the main direction of the caribbean current the most important factor for neritic sediment dispersal in the study area the coarse fraction content is slightly higher during interglacials compared to the downcurrent margin during glacials a similar reduction in the percentage of the coarse fraction is evident in a spatial context this also substantiates the reduced sediment export and redeposition potential at the upcurrent margin

current and sea level signals in periplatform ooze neogene maldives indian ocean abstract periplatform ooze is an admixture of pelagic carbonate and sediment derived from neritic carbonate platforms compositional variations of periplatform ooze allow the reconstruction of past sea level changes periplatform ooze formed during sea level highstands is finer grained and richer in aragonite through the elevated input of material from the flooded platform compared to periplatform ooze formed during the episodes of lowered sea level in many cases however the sea floor around carbonate platforms is subjected to bottom currents which are expected to affect sediment composition i e through winnowing of the fine fraction the interaction of sea level driven highstand shedding and current impact on the formation of periplatform ooze has hitherto not been analyzed to test if a sea level driven input signal in periplatform ooze is influenced or even distorted by changing current activity an integrated study using seismic hydroacoustic and sedimentological data has been performed on periplatform ooze deposited in the inner sea of the maldives the miocene to pleistocene succession of drift deposits is subdivided into nine units limits of seismostratigraphic units correspond to changes or turnarounds in grain size trends in cores recovered at odp site 716 and neoma site 1143 for the pleistocene it can be shown how changes in grain size occur in concert with sea level changes and changes of the monsoonal system which is thought to be a major driver of bottom currents in the maldives a clear highstand shedding pattern only appears in the data at a time of relaxation of monsoonal strength during the last 315 ky results imply 1 that drift sediments provide a potential target for analyzing past changes in oceanic currents and 2 that the ooze composition bears a mixed signal of input and physical winnowing at the sea floor

reef talus a popular misconception reef fronts have traditionally been regarded as comprising debris derived by contemporaneous erosion of the reef however evidence from wave transport indicates that on present day reefs the bulk of the debris generated in this way accumulates in the back reef area with only finer grained sediment carried off reef by retreating flows or by overwash nevertheless in contrast to this observation fore reef debris slopes are commonly considered characteristic of phanerozoic reefs this apparent error reflects the conflation of processes defining contemporary growth and accretion of the reef and the corresponding long term accretion of the carbonate platform on which it rests present day reefs are commonly although not exclusively additions to long lived carbonate platforms growth of the latter is intermittent and has been moderated by changes in sea level that for recent reefs have been on time scales of less than 100 ka during low sea level stands growth ceases or is translated downslope and earlier deposits are subject to lithification and subaerial erosion similar changes are applied on a larger scale to the aggrading growth of carbonate platforms but the bulk accretion of these includes quite different processes and reflects far longer timescales during low sea level stands the margins of platforms commonly become unstable with instability reflected in slope failure and in the shedding of blocks ranging from metres to kilometres in diameter associated with the generation of debris flows and turbidites it is argued that these are the materials that are commonly described as reef talus in ancient structures although their formation is largely independent of any contemporary reef growth difficulties arise where the reef and the platform are treated as a single functional entity it is important to recognize the conceptual distinction between them reef talus is a misleading description of the debris predominantly generated by platform erosion and slope failure

application and validation of the spherical elementary currents systems technique for deriving ionospheric equivalent currents with the north american and greenland ground magnetometer arrays 1 with data from the canadian magnetic observatory system canadian array for real time investigations of magnetic activity geophysical institute magnetometer array greenland time history of events and macroscale interactions during substorms themis and magnetometer array for cusp and cleft studies ground magnetometer arrays we applied the state of art technique on the basis of spherical elementary currents systems secs developed by amm and viljanen 1999 in order to calculate maps of ionospheric equivalent currents over the whole north american auroral region this study is the first to apply the secs technique to a large nonrectangular area with widely separated ground magnetometers 350 km for this study we will first demonstrate the validity of the technique using synthetic data and then examine equivalent ionospheric currents associated with a harang discontinuity for a case study on 10 december 2007 the results show in detail the dynamic evolution of the currents over the entire north american ground magnetometer network equivalent ionospheric current eic maps inferred at the minimum resolution of the database in this case 10 s can thus be analyzed further in conjunction with near simultaneous images of the themis all sky imager mosaics and super dual auroral radar network radar data the eic maps represent a value added product from the raw magnetometer database and can be used for contextual interpretation as well as help with our understanding of magnetosphere ionosphere coupling mechanisms using the ground arrays and the themis spacecraft data