discovery of new hydrothermal vent sites in bransfield strait antarctica we carried out a search for hydrothermal vents in the central basin of bransfield strait antarctica the zaps zero angle photon spectrometer chemical sensor and instrument package oregon state university ofos ocean floor observation system camera sled and tvg tv grab geomar were used to explore the water column and underlying seafloor these operations were supplemented with a series of dredges hydrothermal plumes over hook ridge at the eastern end of the basin are confined to the e ridge crest and se flank the plumes are complex and sometimes contain two turbidity maxima one widespread feature centered at 1150 m and a smaller more localized but broad maximum at 600 800 m we traced the source of the shallower plume to a sunken crater near the ridge crest using sensors on the zaps instrument package subsequently two tv grabs from the crater brought back hot soupy sediment 42 49 c overlain by hard siliceous crusts and underlain by a thick layer of volcanic ash we also recovered chimney fragments whose texture and mineralogy indicate venting temperatures in excess of 250 c native sulfur and fe sulfides occur in fractures and porous layers in sediment from throughout the area pore water data from the crater site are consistent with venting into a thin sediment layer and indicate phase separation of fluids beneath hook ridge the source of the deeper plumes at hook ridge has yet to be located we also explored a series of three parallel volcanic ridges west of hook ridge called three sisters we detected water column anomalies indicative of venting with the zaps package and recovered hydrothermal barites and sulfides from middle sister we spent considerable time photographing middle sister and hook ridge but did not identify classic vent fauna at either location we either missed small areas with our photography or typical mor vent fauna are absent at these sites

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

dissolved iron in the southern ocean atlantic sector abstract we report a comprehensive dataset of dissolved iron fe comprising 482 values at 22 complete vertical profiles along a 1 latitudinal section at the zero meridian in addition a shorter high resolution 00 09 surface section of the southernmost part of the transect 66 00 69 35 s is presented within the upper surface mixed layer the concentrations of dissolved fe vary between 0 1 and 0 3 nm an inverse trend versus fluorescence suggests significant fe removal by plankton blooms vertical mixing and upwelling are the most important supply mechanisms of iron from deep waters to the upper surface mixed layer at lower latitude 42 s there is a distinct maximum of 0 6 0 7 nm in the 2000 3000 m depth range due to inflow of north atlantic deep water in one region 55 s elevated dissolved fe found in the surface mixed layer is ascribed to the recent deposition of aeolian dust originating from south america close to the antarctic continent there is an indication of fe supply in surface waters from icebergs in the deep waters there is a strong indication of a hydrothermal plume of dissolved fe and mn over the ridge in the bouvet region 52 56 s in the weddell gyre basin the dissolved fe in the deep water is 0 47 0 16 nm in the eastward flow at 56 62 s and is lower with a value of 0 34 0 14 nm in the westward flow at high 62 69 s latitude at the edge of the continental ice sheet on the prime meridian the continental margin of the antarctic continent appears to be lesser source of dissolved fe than in any other place in the world this is likely because it is unique in being overlain by the extending continental ice sheet that largely prevents biogeochemical cycling

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

facies and geometry of drowning steps in a miocene carbonate platform maldives abstract the study of the miocene carbonate platform of the maldives allows understanding the controlling factors triggering the stepwise drowning of carbonate platforms this research presents high resolution seismic profiles and sediment cores retrieved from sites u1465 u1469 and u1470 drilled during international ocean discovery program iodp expedition 359 a microfacies analysis of the platform deposits was conducted and correlated with a sequence stratigraphic analysis of seismic reflection data the neogene evolution of the maldives encompasses a series of drowning steps two of these steps are compared with regard to the carbonate factory type to unravel if fossil assemblage surviving the first drowning step are different from younger assemblages in both cases the shallow water carbonate facies are formed by coral coralline algal boundstone and foralgal floatstone that change basinwards into slope facies dominated by large benthic foraminifera grainstone to packstone locally floatstone and rudstone the red algae and large benthic foraminifera assemblages are similar before and after the first drowning step after this first drowning the carbonate platform developed under enhanced bottom current conditions as deduced by the coeval drift deposits the carbonate platform and the drift deposits were balanced for circa 2 myr until a global sea level fall at 10 6 ma and later reflooding of the platform which destroyed the equilibrium between both depositional systems favouring the current controlled deposits the drowning of the miocene carbonate platform of the maldives was the result of the combined effect of the fluctuating sea level during the neogene and the intensification of oceanic currents due to the invigoration of the south asian monsoon during the middle miocene

fluid flow through carbonate platforms as evidence for deep seated reservoirs in northwest australia fluid flow features in carbonate platforms of the outer browse basin northwest australia are investigated using 3d seismic and borehole data during the cenozoic the study area evolved from a carbonate ramp to a rimmed platform with isolated carbonate build ups as such it played a key role in focusing fluid on their buoyant flow to the surface statistical analyses of direct hydrocarbon indicators show fluid flow to be focused in elevated areas i e the greater is the focusing of fluid the larger is the carbonate platform or isolated build up locally karst systems created regions of enhanced permeability through the evolving carbonate stratigraphy karstified horizons are located on the top of carbonate build ups and platform clinoforms as fluid buoyantly concentrates and diffuses up into topographic highs in turn the putative migration of gas and fluid generated hypogenic karst systems enhancing permeability in otherwise lower permeability rock based on the interpreted data we suggest a pivotal relationship between the presence of carbonate build ups and karsts in the browse basin and hydrocarbon accumulations at depth areas of elevated topography focus sub surface fluid enhancing the permeability of carbonate successions in turn focused fluid flow can lead to the generation of methanogenic carbonates promoting the growth of isolated build ups and leading to further generation of elevated features this grants the identification of similar features on seismic data from northwest australia and other equatorial margins in the world as a valid proxy for the recognition of hydrocarbon accumulations below thick carbonate successions

response of a late miocene mediterranean reef platform to high frequency eustasy the upper miocene reef complex of mallorca a third order depositional sequence shows how carbonate deposition responds to high frequency sea level cycles this reef complex displays a fractal architecture of hierarchically stacked high frequency units from fourth to seventh order the building blocks are sigmoidal units bounded by unconformities not parasequences these sigmodds are stacked in sets of sigmoids the sets are stacked in cosets and these in turn are stacked in sets of cosets all these accretionary units have characteristics of depositional sequences but differ from the model developed by exxon and from other carbonate sequence stratigraphy models these departures result from changes in carbonate production in relation to sea level fluctuations which determined the changes in accommodation in the absence of significant subsidence all these high frequency sequences are composed of four systems tracts 1 a lowstand systems tract formed during the early rise of a sea level cycle and composed of progradational reef to open shelf facies thinning toward the basin 2 an aggrading systems tract formed during sea level rise and composed of thick lagoon to open shelf deposits without landward shift of facies 3 a highstand systems tract formed during the high part of a sea level cycle and composed of progradational reef to open shelf facies thinning toward the basin with lagoon beds thin or absent and 4 an offlapping systems tract formed during sea level fall and composed of thin downlapping reef facies passing into a condensed open shelf section which correlates with an erosion surface on the platform top two bounding surfaces can be recognized by lithofacies changes between these systems tracts the erosion surface on top of the offlapping systems tract and the downlap surface at its base both surfaces merge basinward into a condensed section the sequence boundary which corresponds to the lowest point of the sea level cycle is the erosion surface landward and within the correlative condensed section basinward

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

krill as a central node for iron cycling in the southern ocean 1 in order to establish the potential role of antarctic krill euphausia superba in the recycling of bioactive elements we have quantified the release of iron phosphate and ammonia by these organisms along the antarctic peninsula sector of the southern ocean the experimental results suggested that the presence of krill has a significant impact on ambient iron concentrations as large amounts of this trace element were released by the krill 22 689 nmol fe g dry weight 1 h 1 equivalent to 0 2 to 4 3 nmol fe l 1 d 1 half of this iron release occurred within the first hour of the experiment and differences in iron and phosphate release rates 3 1 to 14 0 mol po43 g dw 1 h 1 seemed to reflect differences in food availability these results identify krill as a major node in iron cycling in the southern ocean potentially influencing iron residence time in the upper water column of this region

carbonate delta drift a new sediment drift type based on high resolution reflection seismic and core data from iodp expedition 359 we present a new channel related drift type attached to a carbonate platform slope which we termed delta drift like a river delta it is comprised of several stacked lobes and connected to a point source the delta drifts were deposited at the exit of two gateways that connect the inner sea of the maldives carbonate platform with the open ocean the channels served as conduits focusing and accelerating the water flow entrained material was deposited at their mouth where the flows relaxed the lobe shaped calcareous sediment drifts must have formed under persistent water through flow sediment supply was relatively high and continuous resulting in an average sedimentation rate of 17 cm ka 1 the two delta drifts occupy 342 and 384 km2 respectively with a depositional relief of approximately 500 m they have a sigmoidal clinoform reflection pattern with a particular convex upward bending of the foresets in the maldives the drift onset marks the transition from a sea level controlled to a progressively current dominated depositional regime this major event occurred in the serravallian about 13 ma ago leading to the partial drowning of the carbonate platform and the creation of shallow seaways the initial bank enclosed topography resembles an empty bucket geometry which is rapidly filled by the drift sediments that aggrade and prograde into the basin thereby the depositional environment of the delta drifts changes from deep water 500 to shallow water conditions at their topsets indicated by the overall coarsening upward trend in grain size and the presence of shallow water large benthic foraminifers at their top

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

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

contour current imprints and contourite drifts in the bahamian archipelago new data collected along the slopes of little and great bahama bank and the abyssal plain of the bahama escarpment provides new insights about contour current related erosive structures and associated deposits the bahamian slope shows abundant evidence of bottom current activity such as furrows comet like structures sediment waves and drifts at a seismic scale large erosion surfaces and main periods of drift growth resulted from current acceleration related to plate tectonic processes and progressive opening and closure of gateways and long term palaeoclimate evolution at present day erosion features and contourite drifts are either related to relatively shallow currents 2500 m water depth it appears that the carbonate nature of the drifts does not impact the drift morphology at the resolution addressed in the present study classical drift morphologies defined in siliciclastic environments are found such as mounded plastered and separated drifts in core contourite sequences show a bi gradational trend that resembles classical contourite sequences in siliciclastic deposits showing a direct relationship with a change in current velocity at the sea floor however in a carbonate system the peak in grain size is associated with increased winnowing rather than increased sediment supply as in siliciclastic environments in addition the carbonate contourite sequence is usually thinner than in siliciclastics because of lower sediment supply rates little bahama bank and great bahama bank contourites contain open ocean input and slope derived debris from glacial episodes inner platform platform edge and open ocean pelagic input characterize the classical periplatform ooze during interglacials in all studied examples the drift composition depends on the sea floor topography surrounding the drift location and the type of sediment supply carbonate particles are derived from either the slope or the platform in slope and toe of slope drifts very deep contourites have distant siliciclastic sources of sediment supply the recent discovery of the importance of a large downslope gravitary system along bahamian slopes suggests frequent interactions between downslope and along slope contour currents processes the interlayering of mass flow deposits and contourites at a seismic scale or the presence of surface structures associated with both contour currents and mass flow processes shows that both processes act at the same location finally contour currents have an important impact on the repartition of deep water coral mounds currents can actively interact with mounds as a nutrient and oxygen supplier or have a passive interaction with mounds solely being obstacles orienting erosion and deposition

giant pockmarks in a carbonate platform maldives indian ocean abstract circular structures and depressions in carbonate platforms are known to represent karst chimneys or sinkholes which form as a response to rock solution this formation mechanism is plausible for shallow water carbonates which lie in the reach of meteoric diagenesis or fresh water lenses circular structures which occur in deeper waters however need an alternative interpretation such an example of sea floor depressions in more than 300 m deep waters occurs in the inner sea of the maldives carbonate platform in the indian ocean the structures were mapped with multibeam and parasound multi channel seismics were used to link the depressions with structures at depth the circular depressions have diameters of up to 3000 m and depths of up to 180 m the craters are interpreted as pockmarks formed through the venting of gas and fluids gas and fluid lenses below the pockmarks are reflected by bright spots in the seismic sections as well as a reduction of the instantaneous frequency these areas at depth are linked to chimneys connected to faults and drowned oligocene carbonate banks a model is presented that relates the different forms and sizes of the structures to distinct development stages of sea floor deformation to one process early stages of gas and fluid migration into the shallow part of the sedimentary succession induce formation of dome shaped bodies initial gas and fluid escape to the sea floor is reflected by the formation of sand volcanoes and aligned small pockmarks active pockmarks are the deepest and have the shape of truncated cones in cross section mature pockmarks are characterized by erosion of the flanks of the structure by bottom currents late stage pockmarks are bowl shaped in cross section and are to different degrees filled by drift sediments packages of strata revealing high reflection amplitudes and high interval velocities interpreted as microbially mediated carbonate precipitates underlie some of the pockmarks the pockmarks in the maldives show that circular structures other than solution related features can be abundant in carbonate platform deposits and that such structures may be more abundant in the geological record of carbonate platforms as previously thought pockmarks in the maldives indicate that the archipelago is an example of a hydrocarbon system which consists of an isolated oceanic carbonate platform overlying a volcanic basement and lacustrine source rocks

growth and demise of cenozoic isolated carbonate platforms new insights from the mozambique channel seamounts sw indian ocean although long term evolutions of isolated shallow water carbonate platforms and demise episodes leading to guyot formation have been the subject of numerous studies during the last decades their driving processes are still the subject of active debates the mozambique channel sw indian ocean is characterized by several flat topped seamounts ranging from 11 s to 21 s in latitudes based on a comprehensive geomorphologic study and on dredged samples analysis we show that these features correspond to tropical isolated shallow water carbonate platforms coupling strontium isotopy and foraminifera biostratigraphy well constrained chronostratigraphy results indicate that shallow water carbonate production started in the mozambique channel during distinct cenozoic periods ranging from paleocene to early miocene our data also demonstrate that these carbonate platforms were subsequently characterized by different evolutions locally marked by tectonic and rejuvenated volcanism while some of them kept developed until present days forming modern carbonate systems some others were drowned during late neogene and subsided to form guyots although different factors can be discussed tectonic and volcanism appear as good potential triggers for demise episodes during late miocene early pliocene times chronology and location of this geodynamical activity tend to emphasize influence of east african rift system until southern mozambique channel

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

evolution of late oligocene early miocene attached and isolated carbonate platforms in a volcanic ridge context maldives type yadana field offshore myanmar this study investigates the stratigraphic evolution of the late oligocene early miocene carbonate platforms of the yadana area offshore myanmar well data regional 2d and local 3d seismic surveys allow the identification of three shallow water carbonate platforms yadana 3df and 3de showing various morphologic and stratigraphic patterns influenced by the presence of a paleohigh the identification of seven seismic sequences in the yadana area constrains the stratigraphic evolution in three stages 1 development of aggrading attached and isolated platforms during the chattian 2 a period of platform emersion during the oligocene miocene transition 3 drowning of the smaller buildup 3de associated with km scale backstepping on the large platforms 3df and yadana during the aquitanian the aquitanian marks the onset of renewed volcanic activity associated with the development of fringing carbonate reefs during the burdigalian the rapid similar to 6 my development of these wide similar to 5 70 km and thick similar to 300 850 m carbonate platforms has been mainly controlled by the subsidence however the results highlight a strong overprint of eustatic fluctuations on the rates of change in accommodation and hence on the stratigraphic architecture of the carbonate platforms based on an alternative model for the cenozoic geodynamic evolution of the yadana area our results suggest that the platforms developed on a volcanic ridge of hotspot origin located in the indian ocean and not on a volcanic arc subduction jump processes are interpreted to have played a key role in the demise of all platforms by drastically changing the paleoenvironmental conditions during the early miocene and led to the present day location of the yadana ridge in a back arc setting the carbonate platforms from the yadana area are thus a representative example of the interplay between global mechanisms and local paleoenvironmental parameters on carbonate platform initiation growth and demise c 2017 elsevier ltd all rights reserved

the sawqirah contourite drift system in the arabian sea nw indian ocean a case study of interactions between margin reactivation and contouritic processes the relationships between oceanic circulation in the arabian sea and late cenozoic climate changes including variations in monsoon intensity at the million year time scale remain poorly investigated using multibeam and seismic data we provide the first description of a contourite drift in the arabian sea along the south eastern oman margin this contourite drift is referred as the sawqirah contourite drift system late miocene reactivation of the south eastern oman margin resulted in the formation of a complex anticline system which shaped the seafloor topography above which the sawqirah drift subsequently developed the drift resulted from the circulation of bottom currents within the north intermediate indian water major seismic unconformities identified within the sawqirah drift were tied to ocean drilling program odp drill holes and allowed defining distinct episodes of drift construction at least two of these unconformities record reorganizations of the oceanic circulation at 4 5 4 8 ma and 2 4 ma the 4 5 4 8 ma old unconformity is coeval with the onset of upwelling of deep and cold waters in the owen basin the 2 4 ma old unconformity records a major episode of indian monsoon intensification at the million year time scale over the arabian sea indicating strong coupling between oceanic and atmospheric circulation processes

imaging tertiary carbonate system the maldives indian ocean insights into carbonate sequence interpretation seismic imaging of carbonate systems is often more complicated than their siliciclastic counterparts carbonates sediments typically get cemented very early and their seismic velocities are normally faster than those of siliciclastic sediments this reduces the resolution of carbonates in comparison to the clastics when using identical acquisition design carbonates are also easily dissoved which may lead to karsting a phenomenon unique to carbonate rocks karst surfaces commonly form highly irregular topography that causes energy dispersion and makes it difficult to image the sediments or rocks below it

natural iron fertilization of the atlantic sector of the southern ocean by continental shelf sources of the antarctic peninsula in large parts of the southern ocean primary production is limited due to shortage of iron fe we measured vertical fe profiles in the western weddell sea weddell scotia confluence and antarctic circumpolar current acc showing that fe is derived from benthic fe diffusion and sediment resuspension in areas characterized by high turbulence due to rugged bottom topography our data together with literature data reveal an exponential decrease of dissolved fe dfe concentrations with increasing distance from the continental shelves of the antarctic peninsula and the western weddell sea this decrease can be observed 3500 km eastward of the antarctic peninsula area downstream the acc we estimated dfe summer fluxes into the upper mixed layer of the atlantic sector of the southern ocean and found that horizontal advection dominates dfe supply representing 54 15 of the total flux with significant vertical advection second most important at 29 13 horizontal and vertical diffusion are weak with 1 2 and 1 1 respectively the atmospheric contribution is insignificant close to the antarctic continent but increases to 15 10 in the remotest waters 1500 km offshore of the acc translating southern ocean carbon fixation by primary producers into biogenic fe fixation shows a twofold excess of new dfe input close to the antarctic continent and a one third shortage in the open ocean fe recycling with an estimated fe ratio of 0 59 is the likely pathway to balance new dfe supply and fe fixation

last interglacial reef facies and late quaternary subsidence in the maldives indian ocean abstract to date there is hardly any knowledge of facies and age of pleistocene reef limestone in the maldives likewise there are no robust estimates of quaternary subsidence in this major shallow water carbonate platform and reef area in a core recovered on the windward margin of rasdhoo atoll in the central part of the archipelago pleistocene coralgal grainstone facies belonging to marine isotope stage mis 5e were recovered underlying a holocene reef succession 14 5 m below modern sea level based on the occurrence of shallow water stony corals such as isopora palifera and possibly acropora gr robusta high energy coralline algae including porolithon onkodes in part associated with vermetids and grain supported limestone texture the paleoenvironment is interpreted as a shallow back reef area with a paleo waterdepth of

bucket structure in carbonate accumulations of the maldive chagos and laccadive archipelagos peritidal platforms rimmed by reefs and raised reefs rimming deep lagoons are characteristic morphologies of the tropical carbonate factory their geometry contrasts sharply with the seaward sloping shelves of siliciclastic margins the structure has been compared to a bucket stiff reef rims holding a pile of loose sediment remote sensing data from the maldive chagos and laccadive archipelagos of the indian ocean show that ring reefs with bucket structure are the dominant depositional pattern from patch reefs of tens of meters to archipelagos of hundreds of kilometers in diameter that is over more than 4 orders of magnitude in linear size over 2 5 orders of magnitude the bucket structures qualify as statistical fractals exhibiting self similar patterns and size distributions following power laws however most regional or genetic subsets of the data follow lognormal distributions and small subsets of lagoon reefs exhibit exponential distributions seismic data and boreholes in the maldives indicate that the bucket has been a dominant depositional motif since the oligocene ecological and hydrodynamic studies on modern reefs suggest that the bucket structure is a form of biotic self organization the edge position in a reef is favored over the center position because bottom shear is higher and the diffusive boundary layer between reef and water thinner thus the reef edge has easier access to nutrients and is less likely to be buried by sediment the bucket structure reflects these conditions karst processes have accentuated the surface relief of the buckets particularly in the late quaternary

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

architecture development and geological control of the xisha carbonate platforms northwestern south china sea newly acquired seismic data allow improved understanding of the architecture and evolution of isolated carbonate platforms on the continental slope of the northern south china sea the xisha carbonate platforms were initiated on a basement high the xisha uplift in the early miocene and have remained active up to the present their distribution is limited to pre existing localized fault bounded blocks within the xisha uplift so individual platforms were small in size at the beginning of the miocene however during the middle miocene the platform carbonate factories flourished across an extensive area with 55 900 km 2 the platforms began to backstep in response to a relative sea level rise in the late miocene platform edge reefs patch reefs pinnacle reefs atoll reefs and horseshoe reefs all developed on various platforms the distribution of platform carbonates shrank significantly during pliocene quaternary time to isolated carbonate platforms represented today by xuande atoll and yongle atoll tectonics and eustasy were the two main controls on platform development tectonics controlled both the initial topography for reef growth and the distribution of platforms including those that survived the drowning event associated with the late miocene rapid relative sea level rise eustasy controlled high frequency carbonate sequence development crown copyright c 2014 published by elsevier b v all rights reserved

a cretaceous carbonate delta drift in the montagna della maiella italy the upper cretaceous campanian maastrichtian bioclastic wedge of the orfento formation in the montagna della maiella italy is compared to newly discovered contourite drifts in the maldives like the drift deposits in the maldives the orfento formation fills a channel and builds a miocene delta shaped and mounded sedimentary body in the basin that is similar in size to the approximately 350 km2 large coarse grained bioclastic miocene delta drifts in the maldives the composition of the bioclastic wedge of the orfento formation is also exclusively bioclastic debris sourced from the shallow water areas and reworked clasts of the orfento formation itself in the near mud free succession age diagnostic fossils are sparse the deposi tional textures vary from wackestone to float rudstone and breccia conglom erates but rocks with grainstone and rudstone textures are the most common facies in the channel lensoid convex upward breccias cross cut ting channelized beds and thick grainstone lobes with abundant scours indi cate alternating erosion and deposition from a high energy current in the basin the mounded sedimentary body contains lobes with a divergent progradational geometry the lobes are built by decametre thick composite megabeds consisting of sigmoidal clinoforms that typically have a channel ized topset a grainy foreset and a fine grained bottomset with abundant irregular angular clasts up to 30 m thick channels filled with intraforma tional breccias and coarse grainstones pinch out downslope between the megabeds in the distal portion of the wedge stacked grainstone beds with foresets and reworked intraclasts document continuous sediment reworking and migration the bioclastic wedge of the orfento formation has been vari ously interpreted as a succession of sea level controlled slope deposits a shoaling shoreface complex or a carbonate tidal delta current controlled delta drifts in the maldives however offer a new interpretation because of their similarity in architecture and composition these similarities include i a feeder channel opening into the basin ii an excavation moat at the exit of the channel iii an overall mounded geometry with an apex that is in shallower water depth than the source channel iv progradation of stacked lobes v channels that pinch out in a basinward direction and vi smaller channelized intervals that are arranged in a radial pattern as a result the upper cretaceous campanian maastrichtian bioclastic wedge of the orfento formation in the montagna della maiella italy is here interpreted as a carbonate delta drift

the maldives a giant isolated carbonate platform dominated by bottom currents abstract the maldives a 900 km north south trending paired chain of atolls that surround a ca 100 km wide central basin the inner sea represent a giant isolated carbonate platform in the indian ocean new reflection seismic multibeam and acoustic doppler current profiler data show that its development exhibits a distinct change from sea level to mainly bottom current controlled sedimentation at the end of the middle miocene the post middle miocene intra basinal fill consists of 9 mega units that have been formed and shaped by strong bottom currents entering the inner sea between the inter atoll passages at the end of the middle miocene the maldives represent a rimmed platform with the inner sea forming an empty bucket a connection to the indian ocean existed only in the northeastern part of the platform namely the kardiva channel probably concomitant with the onset of the indian monsoon the current pattern around the maldives changed significantly resulting in the formation of channels in the rimmed platform margin the latter process was encouraged by local drowning of large platform parts and additionally by bottom current forced submarine erosion that widened the channels to passages disintegrating the platform into separated atolls of different sizes the reworked material was dumped into the inner sea where it formed large contourite fans along slope bottom currents entering the inner sea from the north further redistributed the material leading to a southward shift of these sedimentary bodies in this way the inner sea was filled from west to east mega units 1 5 starting with mega unit 6 the opening of a southern gateway introduced a prominent northward flow of bottom waters in the inner sea it leads to the deposition of giant elongated drifts at the eastern flank of the basin filling it from east to west because the current swept away most of the material around the atolls the system was not able to prograde and the steady subsidence was compensated by aggradation accordingly a fundamental characteristic of a current controlled carbonate system is that aggradation occurs irrespective of platform sediment export or differently worded the rate of change in accommodation is always positive and greater than the rate of sediment supply adcp measurements in the winter monsoon season show two water masses in the inner sea one at the surface 0 150 m and a second below it that reaches its sea floor by the use of the grain size distribution of odp leg 716 located in the inner sea as proxy for the flow intensity of the bottom water we recognized an inverse proportional relationship to the monsoon strength from late upper miocene to present some of the current controlled deposits form sigmoidal prograding clinoforms preferably at the edges of the atolls adjacent to the passages where the velocity of the current entering the inner sea is high the anatomy of these prograding wedges is similar to sea level controlled clinoforms described for large isolated carbonate platforms in the sequence stratigraphic concept however our results document that they are not influenced by sea level fluctuations because of the high current velocities involved in their deposition they predominately consist of coarse sand sized carbonate fragments exhibiting large pore space and high permeability therefore these drift deposits comprise a possible exploration target

mineralization mechanisms in the shangfanggou giant porphyry skarn mo fe deposit of the east qinling china constraints from h o c s pb isotopes abstract the giant shangfanggou skarn porphyry mo fe deposit one of the largest mo deposits in the east qinling orogen is hosted by the neoproterozoic luanchuan group on the southern margin of the north china craton the mineralization occurs mainly as veinlets and in veinlet disseminated form within altered schists skarns hornfelses and or marbles the hydrothermal alteration and mineralization at shangfanggou took place over four stages stage 1 involved potassic alteration and silicification in the porphyry skarnization and magnetization in carbonate strata and hornfelsization in schists quartz molybdenite veins associated with phyllic alteration were produced in the porphyry during stage 2 along with sericitization chloritization serpentinization and silicification in the skarns hornfelses and or marbles quartz polymetallic sulfide veins related to phyllic alteration were produced during stage 3 and ore barren quartz calcite pyrite veins associated with weak carbonatation were produced during stage 4 c o and d isotope compositions of hydrothermal calcite dolomite magnetite phlogopite and quartz from different stages of mineralization during the formation of the shangfanggou deposit range from 12 9 to 8 8 3 2 to 22 7 and 100 to 80 respectively sulfur isotope compositions of sulfides from the ores of the shanfanggou deposit range from 3 6 to 4 4 206 pb 204 pb 207 pb 204 pb and 208 pb 204 pb ratios of 17 648 to 18 742 apart from one magnetite with a value of 20 78 15 526 to 15 690 and 38 197 to 39 823 in the shanfanggou deposit the evolution of the ore forming fluids in the shangfanggou deposit as revealed by 18 o d and 13 c isotope studies was one of progressive modification of the magmatic fluids through fluid wall rock interactions along conduits during fluid ascent and this signifies the involvement of formation strata water during the earlier stages of mineralization and the predominance of meteoric waters over magmatic fluids in the later stages the carbon sulfur and lead isotope compositions suggest mixing took place between the magmas and the host rocks within the region integrating the data obtained from studies of the regional geology ore geology fluid inclusions and c h o s pb isotope geochemistry we conclude that the shangfanggou mo fe deposit is a porphyry skarn type system that formed during a transition from compressional to extensional tectonics during the jurassic early cretaceous continental collision between the north china craton and yangtze craton the ore materials were sourced from magmatic ore forming fluids that mixed with components derived from carbonaceous wall rocks during their ascent and which were gradually mixed with meteoric waters especially in the later stages

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

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

the record of oligocene middle miocene paleoenvironmental changes in a carbonate platform iodp exp 359 maldives indian ocean abstract the carbonate edifice of the maldives has an exceptional record of the global climate and ocean current reconfigurations during the neogene that set the path for the establishment of the present day global climate system the study of seismic profiles sedimentary facies microfacies and ichnofabrics of the oligocene miocene platform slopes allows reconstructing the different stages of basin evolution the focus is on the characterization of paleoenvironmental conditions along the slope at iodp expedition 359 drill sites as well as subtle changes of the slope depositional regime controlled by variations in the frequency and intensity of the platform shedding and the basin oxygenation natural gamma radiation and ichnofabric logs are used as a proxy for sea floor ventilation in the inner sea area which is today surrounded by atolls from the oligocene 25 5 ma to the end of the middle miocene climate optimum 15 ma the maldives carbonate platform slopes were poorly oxygenated the opening of the eastern passages through the maldives carbonate platform at 17 5 ma led to an improvement of the sea floor oxygenation sea level fluctuations controlled the sediment input from the platform onto the slope that resulted in changes of the fossil and trace fossil assemblages after the evolution from a ramp to a flat topped platform with well defined bank edges the platform developed hanging shoulder and more sigmoidal clinoforms this correlates to the global decline of coral reefs during the middle miocene climate transition 15 ma and a general sea level lowering the associated slope deposits show abundant channels and cyclic steps are rich in reworked bioclasts and have ichnofabrics pointing towards a good oxygenation of the sea floor the example of the maldives carbonate platform therefore shows how integrating seismic geometries and compositional changes i e microfacies and ichnofabrics allow identifying changes in sea level and in the current pattern as the main controlling factors on carbonate platform evolution

assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude shallow water drift deposit abstract due to their large heat and moisture storage capabilities the tropics are fundamental in modulating both regional and global climate furthermore their thermal response during past extreme warming periods such as super interglacials is not fully resolved in this regard we present high resolution analytical foraminiferal geochemical 18 o and mg ca records for the last 1800 kyr from the shallow 487 m inner sea drift deposits of the maldives archipelago in the equatorial indian ocean considering the diagenetic susceptibility of these proxies in carbonate rich environments we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets globigerinoides ruber white globigerinita glutinata with bulla pulleniatina obliquiloculata with cortex and cibicides mabahethi and their use for future paleoceanographic reconstructions using a combination of spot secondary ion mass spectrometer electron probe micro analyzer and scanning electron microscope image data it is evident that authigenic overgrowths are present on both the external and internal test shell surfaces yet the degree down core as well as the associated bias is shown to be variable across the investigated species and proxies given the elevated authigenic overgrowth mg ca 12 22 mmol mol and 18 o values closer to the benthic isotopic compositions the whole test planktonic g ruber w geochemical records are notably impacted beyond 627 4 ka 24 7 mcd yet considering the setting i e bottom water location for overgrowth formation the benthic foraminifera 18 o record is markedly less impacted with only minor diagenetic bias beyond 790 0 ka 28 7 mcd even though only the top of the g ruber w and c mabahethi records whole test data would be suitable for paleo reconstructions of absolute values i e sea surface temperature salinity seawater 18 o the long term cycles while dampened appear to be preserved furthermore planktonic species with thicker tests i e p obliquiloculata w c might be better suited in comparison to thinner test counter parts i e g glutinata w b g ruber w for traditional whole test geochemical studies in shallow carbonate rich environments a thicker test equates to a smaller overall bias from the authigenic overgrowth overall if the diagenetic impact is constrained as done in this study these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures latitudinal scale ocean current shifts and south asian monsoon dynamics

sea level changes and carbonate platform evolution of the xisha islands south china sea since the early miocene abstract analyses of the biogeochemical branched and isoprenoid tetraether bit index and elemental geochemistry from well xk1 provide insight into the development of the xisha islands carbonate platform in the south china sea scs since the early miocene bit is the ratio of branched glycerol dialkyl glycerol tetraethers bgdgts to isoprenoid glycerol dialkyl glycerol tetraethers igdgts which are derived from meteoric and marine environments respectively bit serves as a novel proxy for tracking sea level changes the bit curve of well xk1 is characterized by low high low high alternating stages indicating the superposition of sea level changes on carbonate platform evolution in the scs following the rapid expansion of the scs in the early stages of the early miocene biogenic reefs began to form and bit oscillated intensely the scs started to regress after its initial expansion during the middle miocene at which time global sea level was also falling significantly the combination of both tectonic activity and eustatic variation has resulted in the deposition of strata with reef beach facies which are characterized by high bit values relative sea level reached its lowest point in the late stages of the middle miocene 11 6 ma subsequent sea level rise between the late miocene and pliocene induced a negative shift in bit and lagoonal facies formed under optimal warm marine conditions periodic exposure caused the reefs of the xisha islands to suffer from erosion during the pleistocene which is consistent with a second elevation in the bit index however modern trends show increasing regional water depths again major and trace element curves na si p b ga mo zn as well as the associated ratios na2o k2o na2o sio2 b ga ti sr zr sr al sr th u accurately record sea level variations several significant discontinuities correlate with sea level shifts and provide important details about the geomorphology sedimentation patterns and diagenesis types on the scs carbonate platform the agreement between organic and inorganic geochemical data demonstrates that our reconstructions of scs sea level changes and modes of carbonate platform development are robust our findings also demonstrate that carbonate evolution in the xisha islands was shaped by relative sea level changes implying that sea level fluctuations in the scs were controlled by global eustatic factors in addition to regional tectonic subsidence

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

magnetic properties of early pliocene sediments from iodp site u1467 maldives platform reveal changes in the monsoon system we report a study of the magnetic stratigraphy and the anisotropy of isothermal remanent magnetization of pliocene sediments from international ocean discovery program iodp site u1467 drilled in the maldives platform indian ocean during exp 359 magnetic stratigraphy gives a precise record of geomagnetic reversals of the early pliocene from approximately 5 3 ma to 3 1 ma providing a detailed age model in an interval where the biostratigraphic record is scarce we use the anisotropy of isothermal remanent magnetization airm to investigate the statistical orientation of fine magnetic particles and provide data on the strength and direction of bottom currents during the early pliocene the strength of bottom currents recorded by the airm shows a prominent increase at the top of chron c3n 1n about 4 2 ma and the current direction ne sw is consistent with that of modern instrumental measurements since bottom currents in the maldives are driven by the monsoon we speculate that the 4 2 ma increase of bottom currents could mark the onset of the present day setting probably related to the coeval uplift phase of the himalayan plateau