seismicity and subterranean sounds in the northwest deccan volcanic province of india abstract the northwestern deccan volcanic province in india is one of the most seismically active intraplate regions of the world in addition the region is associated with episodic swarm activity and reports of sounds whose linkage hitherto remains elusive during the month of january 2016 a swarm activity occurred in the kachchh and saurashtra regions and continued for about two months many of the events were accompanied by audible sounds like blasting that caused severe panic among local residents prompting us to investigate the causative mechanism the events were recorded by our seismic stations and an additional five stations that we were able to deploy at the onset of the swarm the activity produced sounds with good energy in the audible frequency range of humans spectrogram analysis of the events with associated sounds revealed frequencies 20 hz in contrast to the lower frequencies for those that did not generate the sounds in addition to the higher frequencies we observed horizontal particle motion that was dominated by retrograde elliptical motion consistent with rayleigh waves these observations were not recorded from any of the events that did not generate sounds audible sounds generated by earthquakes are consistently reported from shallow earthquakes that generate high frequency surface waves

increased productivity in the eastern equatorial pacific during the last glacial maximum 19 000 to 14 000 yr b p a widespread pronounced enrichment in the organic carbon content occurs at shallow depths in eastern equatorial pacific sediments the c org peak is shown by radiocarbon dating to be temporally coincident with the last stage 2 or wisconsin glacial maximum in contrast caco 3 profiles show less overall variation which appears to be partly a function of the location of the sediments relative to the lysocline consideration of the iodine c org ratio in the sediments rules out enhanced preservation as a cause of the stage 2 organic carbon enrichment the peak instead must have resulted from a significant increase in productivity during the glacial maximum

production and destruction control of biogenous sedimentation in the tropical atlantic 0 300 000 years b p late pleistocene signals of calcium carbonate organic carbon and opaline silica concentration and accumulation are documented in a series of cores from a zonal meridional depth transect in the equatorial atlantic ocean to reconstruct the regional sedimentary history spectral analysis reveals that maxima and minima in biogenous sedimentation occur with glacial interglacial cyclicity as a function of both 1 primary production at the sea surface modulated by orbitally forced variation in trade wind zonality and 2 destruction at the seafloor by variation in the chemical character of advected intermediate and deep water from high latitudes modulated by high latitude ice volume from these results a pattern emerges in which the relative proportion of signal variance from the productivity signal centered on the precessional 23 kyr band decreases while that of the destruction signal centered on the obliquity 41 kyr and eccentricity 100 kyr periods increases below 3600 m ocean depth

anomalous infrasound generated by the alaskan earthquake of 28 march 1964 in this paper we present and analyze data recorded at three microphone arrays boulder colorado boston massachusetts and washington dc associated with the alaskan earthquake of 03 h 36 min 13 s ut 28 march 1964 61 05n 147 50w we show that the recordings from all three stations contain not only the epicentral and locally generated air waves reported by other authors but also contain evidence of atmospheric radiation apparently generated from seismic surface waves along the rocky mountains the latter became decoupled from the surface wave and traveled at about 314 m s through the air to the arrays

carbon isotopic changes in benthic foraminifera from the western south atlantic reconstruction of glacial abyssal circulation patterns oxygen and carbon isotopic analyses have been performed on the benthic foraminifer planulina wuellerstorfi in seven late quaternary cores from the vema channel rio grande rise region the cores are distributed over the water depth interval of 2340 to 3939 m which includes the present transition from north atlantic deep water nadw to antarctic bottom water aabw the carbon isotopic records in the cores vary as a function of water depth the shallowest and deepest cores show no significant glacial interglacial difference in 13c four of the five cores presently located in the nadw have benthic foraminiferal 13c that is lower during glacial isotopic stages based on bathymetric gradients in 13c we conclude that like today there were two water masses present in the vema channel during glacial intervals a water mass enriched in 13c overlying another water mass depleted in 13c the largest gradient of change of 13c with depth however occurred at 2 7 km 1 km shallower than the present position of this gradient on the basis of paleontologic and sedimentologic evidence we consider it unlikely that the nadw aabw transition shallowed to this level reduced carbon isotopic gradients between the deep basins of the north atlantic and pacific oceans during the last glaciation suggest that production of nadw was reduced lower production of nadw may have modified the local abyssal circulation pattern in the vema channel region

reduced north atlantic deep water flux to the glacial southern ocean inferred from neodymium isotope ratios the global circulation of the oceans and the atmosphere transports heat around the earth broecker and denton1 suggested that changes in the global ocean circulation might have triggered or enhanced the glacial interglacial cycles but proxy data for past circulation taken from sediment cores in the south atlantic ocean have yielded conflicting interpretations of ocean circulation in glacial times 13c variations in benthic foraminifera2 3 4 5 6 support the idea of a glacial weakening or shutdown of north atlantic deep water production whereas other proxies such as cd ca ba ca and 231pa 230th ratios show little change from the last glacial maximum to the holocene epoch7 8 9 here we report neodymium isotope ratios from the dispersed fe mn oxide component of two southeast atlantic sediment cores both cores show variations that tend towards north atlantic signatures during the warm marine isotope stages 1 and 3 whereas for the full glacial stages 2 and 4 they are closer to pacific ocean signatures we conclude that the export of north atlantic deep water to the southern ocean has resembled present day conditions during the warm climate intervals but was reduced during the cold stages an increase in biological productivity may explain the various proxy data during the times of reduced north atlantic deep water export

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

ground coupled air waves and diffracted infrasound from the arequipa earthquake of june 23 2001 1 on june 23 2001 a strong earthquake measuring mw 8 4 occurred along the coast of south central peru coherent infrasonic waves were detected over a period of one hour by the is08 infrasound station in bolivia analysis of the ground coupled air waves shows that the rupture propagated from the northwestern to the southeastern part of the fault with a rupture velocity of 3 3 km s the azimuth variation of the infrasonic waves is attributed to a distribution of secondary sources along the highest mountain ranges which excite infrasonic waves that are diffracted to the ground the predominant source of infrasound is likely distributed along the andean cordillera using the azimuth and arrival time determination the horizontal scale size of the distant source regions of infrasonic waves is reconstructed over distances greater than 400 km

evolution of atlantic pacific δ13c gradients over the last 2 5 m y the evolution of interocean carbon isotopic gradients over the last 2 5 m y is examined using high resolution 13c records from deep sea cores in the atlantic and pacific oceans over much of the northern hemisphere ice ages relative reductions in north atlantic deep water production occur during ice maxima from 2 5 to 1 5 ma glacial reductions in nadw are less than those observed in the late pleistocene glacial suppression of nadw intensified after 1 5 ma earlier than the transition to larger ice sheets around 0 7 ma at a number of times during the pleistocene 13c values at dsdp site 607 in the north atlantic were indistinguishable from eastern equatorial pacific 13c values from approximately the same depth odp site 677 indicating significant incursions of low 13c water into the deep north atlantic atlantic pacific 13c values converge during glaciations between 1 13 1 05 m y 0 83 0 70 m y and 0 46 0 43 m y this represents a pseudo periodicity of approximately 300 kyr which cannot easily be ascribed to global ice volume or orbital forcing this partial decoupling at low frequencies of the 18o and 13c signals at site 607 indicates that variations in north atlantic deep water circulation cannot be viewed simply as a linear response to ice sheet forcing

pleistocene δ13c variability of north atlantic intermediate water variations in the stable isotopic composition of benthic foraminifera from deep sea drilling project dsdp site 502b in the caribbean sea are used to reconstruct atlantic intermediate water circulation variability over the last 1 2 m y comparison of this record with other north atlantic benthic isotope records indicates that atlantic intermediate water circulation was relatively enhanced during glacial maxima when north atlantic deep water nadw production was reduced however a simple compensatory relationship between intermediate and deepwater circulation is not apparent geochemical models have shown that such changes in ocean circulation can affect atmospheric co2 levels by changing vertical nutrient and alkalinity profiles the 13c difference between caribbean site 502b and deep equatorial pacific site 677 is highly coherent and in phase with ice volume like the 18o record there is an increase in amplitude 40 and a large increase in 100 kyr power after 0 7 ma the 1 2 13c amplitude scales to 70 ppm v in atmospheric co2 using boyle s 1986 box model result the implied increase in co2 amplitude after 0 7 ma may suggest a positive feedback role in effecting the higher amplitude climatic fluctuations which characterize the last 0 7 m y

biogenic carbonate and ice rafted debris heinrich layer accumulation in deep sea sediments from a northeast atlantic piston core abstract biogenic carbonate mass accumulation rates show distinct quaternary glacial interglacial changes in a mid latitude northeast atlantic deep sea core during the last 208 kyr these were generally higher during interglacials averaging 2 2 g cm 2 kyr than during glacial periods with a maximum average of 1 2 g cm 2 kyr intervals containing high ice rafted debris have very low biogenic carbonate accumulation rates paleo primary productivity estimates based on biogenic carbonate accumulation rates are generally higher during interglacials averaging 80 gc m 2 yr than during glacials which average 49 gc m 2 yr maximum estimate short intervals with possibly reduced primary productivity correspond to heinrich layers which are the result of pulses of massive iceberg production and rapid melting in the north atlantic we identified thirteen heinrich layers in isotopic stages 7 to 2 they have calendar ages of about 201 189 182 183 164 167 146 149 142 128 131 64 67 52 54 40 43 29 31 21 and 15 kyr these heinrich layers contain large amounts of ice rafted debris including detrital carbonate low amounts of coccoliths and planktic foraminifera mainly neogloboquadrina pachyderma sinistral the upper five heinrich layers are almost barren of coccoliths and the fourth layer is also free of foraminifera the virtual absence of coccoliths is interpreted to reflect reduced coccolithophorid productivity in the photic zone due to low salinity of surface waters and to blockage of light by ice and suspended materials shed off by melting icebergs considering the limited use of other proxies such as organic carbon diatom and benthic foraminifera due to their very low content abundance in the sediments biogenic carbonate mass accumulation rates offer a workable paleo primary productivity proxy in open ocean sediments of the carbonate dominated northeast atlantic

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

spatial patterns of earthquake sounds and seismic source geometry earthquake sounds are heard during or immediately before an event up to several kilometres around the epicentral area sound data as heard by people have been collected by way of macroseismic questionnaires showing that sound audibility does not follow isotropic patterns the explanation of this effect is found in the behaviour of the particular radiation pattern of the p waves for each earthquake in connection with its focal mechanism this result opens the possibility to get more information about the earthquake source parameters in the future and past events making use of non instrumental observations

deep water circulation in the northeast atlantic and climatic changes during the late neogene dsdp site 141 abstract oxygen and carbon stable isotope data of pyrgo murrhina and flux rates of calcium carbonate in the bio and magnetostratigraphically dated sediment sequence at dsdp site 141 were used for a reconstruction of the deep water circulation in the northeast atlantic during late miocene and pliocene times a distinct change towards reduced advection of deep water recorded near 5 4 ma is contemporaneous with the cessation of the outflow of the saline mediterranean water into the atlantic during the pliocene between 4 5 and 2 75 ma and between 2 1 and 1 8 ma north atlantic deep water nadw circulation was sluggish and site 141 possibly influenced by antarctic bottom water aabw near 2 75 ma the advection of well oxidized nadw was strongly intensified this change is related to an onset of major arctic ice growth and or a major cooling of nadw

porewater cadmium geochemistry and the porewater cadmium δ13c relationship results from two continental margin cores collected off pt sur california make possible a direct determination of the relationship between dissolved cadmium and the carbon isotopic composition of dissolved inorganic carbon in the interstitial water of suboxic marine sediments the 13c values of dissolved inorganic carbon decrease nearly 1 in the top 0 5 cm of the sediments and display a more gradual decrease through the top 20 cm of the sediments dissolved cadmium concentrations increase by 0 6 to 1 5 nmol kg in the top 0 5 cm of the sediments and then rapidly decrease to values of approximately 0 12 nmol kg between 5 and 10 cm into the sediments apparently as a result of scavenging onto iron oxide surfaces this pattern contrasts with porewater cadmium profiles previously reported for pelagic sediments which show no evidence of cadmium scavenging by the sediments however porewater cadmium concentrations are poorly correlated with porewater 13c values in both oxic and suboxic sediments these results suggest that the cadmiumcalcium ratios and 13c values of infaunal benthic foraminifera need not be tightly linked and that the relationship between these two aspects of foraminiferal shell chemistry may vary in response to changes in sediment geochemistry

a tectono geomorphological perspective of micro earthquake swarm activity prone areas around bhavnagar and jamnagar in saurashtra western india abstract areas around bhavnagar and jamnagar in eastern and northern parts of saurashtra respectively are identified previously as prone to recurrent earthquake swarm activity sparse seismotectonic studies so far have not revealed any linkage with known faults in bhavnagar area while no structures are known to occur in the area around jamnagar we carried out detailed tectono geomorphic studies with contrasting geomorphic settings with a view to provide an insight into the swarm activity from a geomorphological perspective the study is based on extensive field studies and quantitative geomorphic analysis of landscape and drainage the area around bhavnagar is divisible into two tectono geomorphic domains the e w trending sihor fault zone located to the west of bhavnagar domain i and the terrain to its south which shows undulating landscape controlled by n s trending structural trends domain ii the quadrant in the sw between these two domains consists of southward titled trappean hills which form source area for drainages flowing northward through sihor fault zone and those flowing eastward through domain ii late quaternary possibly holocene tectonic activity along the sihor fault is indicated by the northward tilt of alluvial plain surface knickpoint in rivers and small scale minor faults along the fault zone prominent decrease in depth of fluvial incision away from the fault zone and youthful landscape indicated by drainage basin analysis domain ii comprises the largely erosional pediplain developed over trappean and tertiary rocks to the south of bhavnagar the drainages show an early stage of landscape development due to ongoing tectonic activity the area around jamnagar is dominantly a peneplain formed over subhorizontal trappean lava flows the peneplain is a manifestation of the prolonged period of non erosion and deposition during the cenozoic the rivers show youthful landscape in the central part of the peneplain which includes large knickpoints rapids anomalous river bends steepening of channel gradient and large potholes this ene wsw trending zone of anomalous fluvial geomorphic anomalies points to the existence of a fault or fold in the subsurface the structure appears to be active as indicated by the denser cluster of earthquake swarm along this zone we infer that the generation of earthquake swarm activity comprising low to moderate magnitude shocks is caused by the sheared rocks along the sihor fault near bhavnagar and the ene wsw trending subsurface structure near lalpur which provide avenues for downward percolation of rainwater to deeper levels causing loss the frictional resistance along the weak planes

late glacial and holocene palaeocurrents around rockall bank ne atlantic ocean core samples and hydrographic data from 50 to 60 n and 15 to 25 w in the northeast atlantic ocean are used to study changes in current activity from the last glacial to present we establish a new method to distinguish between the effects of changing bottom current speed and varying size input by drawing upon sediment flux data and detailed grain size analysis changes in current speed are recorded by the mean size of the sortable coarse noncarbonate silt component which increases with current vigor by winnowing away of fines our method involves the definition of an ideal sortable silt input function recorded at a site accumulating unmodified pelagic flux only the ideal profile is then compared with records from other sites to determine the history of current speed at a range of water depths the upper surface of southern source water ssw probably shoaled during the glacial as indicated by the covariation of sortable silt records from sites presently covered by ssw and lower north atlantic deep water lnadw the data suggest that production of lnadw was suppressed during the glacial increased following the last glacial maximum and declined at the start of termination 1a a second pulse of production occurred immediately before the younger dryas event intermediate waters were generally faster flowing during the glacial and may have expanded their depth domain such that a single glacial intermediate water mass covered depths from 1100 to more than 2000 m

arctic front shifts in the subpolar north atlantic during the mid pleistocene 800 400ka and their implications for ocean circulation abstract surface water conditions at the integrated ocean drilling program iodp site u1314 southern gardar drift 56 21 8 n 27 53 3 w 2820 m depth were inferred using planktic foraminifer assemblages between marine isotope stage mis 19 and 11 ca 800 400 ka factor analysis of the planktic foraminifer assemblages suggests that the assemblage was controlled by three factors the first factor which explained 49 of the variance is dominated by transitional and subpolar species and points to warm and salty surface water conditions atlantic water the second factor 37 is dominated by neogloboquadrina pachyderma sin and has been associated with the presence of cold and low saline surface waters arctic water finally the third factor 9 linked to a significant presence of turborotalita quinqueloba reflects the closeness of the arctic front the boundary between atlantic and arctic water the position of the arctic and polar fronts has been estimated across the glacial interglacial cycles studied according to planktic foraminifer abundances from site u1314 and their factor analysis combined with a synthesis of planktic foraminifer and diatom data from other north atlantic sites regarding at the migrations of the arctic front and the surface water masses distribution across each climatic cycle we determined five phases of development furthermore deep ocean circulation changes observed in glacial interglacial cycles have been associated with each phase the high abundance of transitional subpolar foraminifers above 65 at site u1314 during the early interglacial phase indicated that the arctic front position and surface water masses distribution were similar to present conditions during the late interglacial phase n pachyderma sin and t quinqueloba slightly increased indicating that winter sea ice slightly expanded southwestwards whereas the ice volume remained stable or was still decreasing n pachyderma sin increased rapidly above 65 at site u1314 at the first phase of glacial periods indicating the expansion of the arctic waters in the western subpolar north atlantic during the second phase of glacial periods the transitional subpolar assemblage throve again in the central subpolar north atlantic associated with strong warming events that followed ice rafting events the third phase of glacial periods corresponds to full glacial conditions in which n pachyderma sin dominated the assemblage for the whole subpolar north atlantic this division in phases may be applied to the last four climatic cycles

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

atlantic mediterranean water exchange during the late neocene the nature of water exchange between the mediterranean and the atlantic is examined for three time periods during the late neogene in order to assess the impact of flow patterns between these basins on bottom water conditions in the oceans the large volume of carbonates and evaporites deposited in the mediterranean during the messinian salinity crisis appears to have caused the open ocean to become more undersaturated in calcium carbonate resulting in increased dissolution of deep sea carbonates during the latest miocene during the earliest pliocene an estuarine type of flow existed between the atlantic and mediterranean waters entered the mediterranean at depth and flowed out at the surface benthic foraminiferal stable isotopic evidence from the north atlantic indicates that north atlantic deep water nadw was produced throughout the early pliocene and that the absence of saline mediterranean outflow did not have a significant effect on bottom water production eustatic lowering of sea level during the last glacial maximum 18 000 years b p reduced water exchange between the atlantic and the mediterranean as a result salinities in the mediterranean increased substantially but it seems unlikely that diminished nadw production during the last glacial episode can be attributed to a reduction in mediterranean outflow

glacial interglacial changes in global deepwater circulation variations in the areal extent of the cryosphere appear to exert an important control over glacial interglacial changes in the mode of formation and source areas for deepwater and bottom water masses during interglacials when ice extents are minimal these water masses form by mechanisms which are well documented for the present interglacial climatically related advances and retreats of sea ice in the northern hemisphere during glacials probably resulted in shifting loci of formation for each of the three types of north atlantic deep water nadw probable glacial advances of grounded ice sheets to the continental shelf margins in antarctica precluded formation of antarctic bottom water aabw at the presently active continental shelf sites because these shifts in source areas for aabw and nadw probably involved source waters with salinity temperature oxygen content and nutrient levels that differed from modern values deep and bottom waters are likely to have had different characteristics in glacials than they do during interglacials

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

regional and global benthic δ18o stacks for the last glacial cycle although detailed age models exist for some marine sediment records of the last glacial cycle 0 150 ka age models for many cores rely on the stratigraphic correlation of benthic 18o which measures ice volume and deep ocean temperature change the large amount of data available for the last glacial cycle offers the opportunity to improve upon previous benthic 18o compilations such as the lr04 global stack not only are the age constraints for the lr04 stack now outdated but a single global alignment target neglects regional differences of several thousand years in the timing of benthic 18o change during glacial terminations here we present regional stacks that characterize mean benthic 18o change for 8 ocean regions and a volume weighted global stack of data from 263 cores age models for these stacks are based on radiocarbon data from 0 to 40 ka correlation to a layer counted greenland ice core from 40 to 56 ka and correlation to radiometrically dated speleothems from 56 to 150 ka the regional 18o stacks offer better stratigraphic alignment targets than the lr04 global stack and furthermore suggest that the lr04 stack is biased 1 2 kyr too young throughout the pleistocene finally we compare global and regional benthic 18o responses with sea level estimates for the last glacial cycle

a late pleistocene time series of bottom current speed in the vema channel abstract a coarsening of the mean particle size of the carbonate free silt fraction from sea floor samples below 4000 m in the vema channel has been used to separate high velocity antarctic bottom water aabw from the overlying slower north atlantic deep water nadw a time series of fluctuations in bottom current speed within the modern aabw nadw transition zone was examined by determining the particle size distribution of sediments from eight gravity cores with a high resolution stratigraphy for the past 250 kyrs the bottom current paleospeed was inferred from a correlation of particle size in seafloor samples with mean current speed from nearby current meters the mean bottom current speed at depths comparable to modern aabw was highest 7 10 cm s during interglacial to glacial transitions corresponding to the oxygen isotopic stage 6 7 and 4 5 boundaries and at present the mean bottom current speed at depths comparable to modern nadw was nearly uniform for most of the past 250 kyrs except during glacial oxygen isotopic stage 2 when the speed dropped to 2 cm s or one half of the present speed the application of the calibrated particle size method to examine bottom current paleospeed allows testing of paleoceanographic models which rely on assumptions or inferences of changes in bottom water production rate during the late pleistocene paleoclimatic fluctuations

the role of vertical chemical fractionation in controlling late quaternary atmospheric carbon dioxide the 30 decrease in atmospheric carbon dioxide during glacial maxima must be driven by some change in the chemical circulation of the ocean here a new model for late quaternary co2 variability is presented which resolves some problems occurring in previous models including the timing of carbon dioxide response and changes in the oxygen content of the deep ocean the primary driving factor in this model is a rearrangement of chemical distributions in the ocean whereby labile nutrients and metabolic co2 are concentrated in deep waters rather than in intermediate waters as observed in the modern ocean this new bottom heavy chemical structure does not affect atmospheric carbon dioxide directly instead co2 induced acidity lowers the deep ocean carbonate ion concentration and temporarily increases carbonate dissolution rates oceanic alkalinity then rises until the deep ocean carbonate ion is restored to its steady state value the resulting increase in oceanic alkalinity draws co2 out of the atmosphere into the ocean alkalinity and atmospheric co2 lag several thousand years behind the change in oceanic chemical structure this delayed response is determined by the limited rate of continental weathering and deep ocean carbonate dissolution relative to the oceanic alkalinity inventory it is proposed that characteristic deglacial and preglacial states of the ocean are leading factors driving glacial interglacial climate changes this concept reinterprets the carbon isotope contrast between surface water and deep waters 13c p b as due to a shift of light metabolic carbon from intermediate waters into deep waters the process is illustrated here by a simple equilibrium five box ocean model the observed intermediate depth nutrient depletion is not sufficient in itself to determine which of several possible mechanisms are operating and some mechanisms are not as effective in changing atmospheric co2 as others the largest response is seen from deepening the regeneration cycle of organic carbon the least response is seen from converting north atlantic deep water into intermediate water

orbital forcing of bottom current enhanced sedimentation on feni drift ne atlantic during the mid pleistocene feni ridge is a plastered sediment drift deposited along the northwestern flank of rockall trough ne atlantic under the influence of deep geostrophic currents formed by intermittent overflows of arctic intermediate water from the norwegian sea across the iceland scotland ridge nsow lower deep water ldw a derivative of antarctic bottom water from the south atlantic mixed with old north atlantic deep water nadw also bathes the lower flanks of the drift below 2500 m deep sea drilling project site 610 was drilled in a sediment wave field on the surface of feni drift 2417 m though the sediments recovered proved to be typically pelagic preserving a high resolution 5 cm kyr 1 quaternary record of orbitally modulated ice rafting and biogenic productivity cycles but showing little evidence of current affected deposition from particle size and compositional analyses of the biogenic and lithogenic 10 m silt which we then compared with records of the percentage and flux of ice rafted detrital ird sand foraminifera and coccoliths for the same interval cross spectral comparisons were then made between these records and variations in a model of northern hemisphere ice volume ice sheet growth and decay in response to orbitally forced insolation changes at 65 n variations in the relative proportions and fluxes of ird sand foraminifera and coccoliths all covary closely with orbitally forced ice volume fluctuations but with differing amplitude coherency and phase relationships at each milankovitch frequency however there is a significant component of variance in pelagic and ice rafted sedimentation which is controlled by bottom currents and this shows excellent phase and coherency agreement with the ice volume model at all orbital frequencies the relative enrichment coarseness and flux of the contourite silt fraction of feni drift sediments all increase during glacial or cold stages of the mid pleistocene relative to warm stages suggesting that currents were stronger during these periods possible explanations for such changes in current activity include 1 an increased flux of nsow via the wyville thompson ridge into the rockall trough during glacials but not due to increased production of nsow 2 ldw presently lying below 2500 m rises during glacials by at least 50 60 m thereby flooding over the surface of feni ridge at site 610 3 the path of a major recirculation gyre in the lower nadw ldw system presently situated marginally south of site 610 encroaches upon the southern tip of feni ridge during glacials and 4 the rockall trough itself is a site of deep water formation during glacials analogous to labrador sea deep water formation today

control of organic carbon accumulation in the late quaternary equatorial atlantic ocean drilling program sites 664 and 663 productivity versus terrigenous supply organic geochemical records of the last 940 kyr are presented for equatorial atlantic ocean drilling program odp sites 663 and 664 and discussed with regard to the development of ocean productivity and african paleoclimate proportions of marine and terrigenous organic matter om are estimated from elemental pyrolytic isotopic and petrologic data spectral analyses reveal a strong power at the eccentricity and obliquity band indicating a close response of tropical organic sedimentation to the climatic evolution at high latitudes the orbital covariance of organic carbon with biogenous opal and terrigenous records favor that glacially enhanced dust supply and surface water mixing were primary controls for deposition of organic carbon wind borne supply of terrigenous om contributes 26 to 55 and 0 to 39 to the bulk om based on microscopic and isotopic records respectively admixture of c4 plant matter was approximated to contribute up to 16 to the bulk organic fraction during peak glacial conditions

possible role of fluids in the process of earthquake swarm generation in the west bohemia vogtland seismoactive region abstract the west bohemia vogtland region in the western part of the bohemian massif known for periodic occurrence of earthquake swarms is also characterised by 0 2 0 5 ma old quaternary volcanoes rich co2 emissions anomalies of mantle derived he mineral springs and moffets the detailed analysis of the time space pattern of seismicity during the january 1997 swarm demonstrates the gradual and ordered migration of micro seismic activity suggesting the step by step penetration of fluids into a small fractured volume this scenario is supported by the similarity of the source mechanisms of the natural events of the january 1997 swarm with artificial injection induced micro earthquakes during the german deep drilling project ktb in neighbouring ne bavaria also the comparison of the west bohemia vogtland earthquake swarm region with other intraplate earthquake swarm regions and with earthquake swarms induced by current volcanic processes indicates a role of intrusions of magma and related fluids in generation process of earthquake swarms

pleistocene fluctuations in the western boundary undercurrent on the blake outer ridge the mean grain size of the detrital silt fraction was analyzed in two piston cores from the crest of the blake outer ridge using electronic particle analysis the resultant profiles in the two cores are highly correlatable and are interpreted to reflect the paleospeed of the western boundary undercurrent wbuc for the past 90 kyr the record can be divided into three periods the first encompasses the past 12 000 years and begins with an abrupt acceleration marking the transition from slow glacial to more vigorous holocene conditions the later holocene is a period of strong but variable flow the second period extends from 30 to 12 10 years and is characterized by a steady reduction of wbuc strength through the last ice age the current continued to decelerate until 12 10 years when the polar front finally retreated northward past the passages connecting the norwegian sea to the north atlantic the third period from 30 to about 90 10 years was a time of strong and variable flow that was independent of the glacial interglacial signal that is seen in the oxygen isotope record during this time the core of maximum flow appears to have shifted up and down the flank of the blake outer ridge and may have been influenced as much by salinity as by temperature variations in the source areas of the wbuc

deep water temperature carbonate ion and ice volume changes across the eocene oligocene climate transition 1 paired benthic foraminiferal stable isotope and mg ca data are used to estimate bottom water temperature bwt and ice volume changes associated with the eocene oligocene transition eot the largest global climate event of the past 50 myr we utilized odp sites 1090 and 1265 in the south atlantic to assess seawater 18o w antarctic ice volume and sea level changes across the eot 33 8 33 54 ma we also use benthic 13c data to reconstruct the sources of the deep water masses in this region during the eot our data together with previously published records indicate that a pulse of northern component water influenced the south atlantic immediately prior to and following the eot benthic 18o records show a 0 5 increase at 33 8 ma eot 1 that represents a 2 c cooling and a small 10 m eustatic fall that is followed by a 1 0 increase associated with oi 1 the expected cooling of deep waters at oi 1 33 54 ma is not apparent in our mg ca records we suggest the cooling is masked by coeval changes in the carbonate saturation state co32 which affect the mg ca data to account for this the bwt ice volume and w estimates are corrected for a change in the co32 of deep waters on the basis of recently published work corrected bwt at sites 1090 and 1265 show a 1 5 c cooling coincident with oi 1 and an average w increase of 0 75 the increase in ice volume during oi 1 resulted in a 70 m drop in global sea level and the development of an antarctic ice sheet that was near modern size or slightly larger

late pliocene variations in the carbon isotope values of north atlantic benthic foraminifera biotic control of the isotopic record abstract analyses of benthic foraminifera carbon isotope values were made in 172 samples from the late pliocene at dsdp site 548 which is located in the northeast atlantic on the continental slope southwest of ireland 1253 m water depth the carbon isotope record is quite stable from about 3 4 to 2 5 ma and contrasts with the record at site 552a in the north atlantic 2311 m water depth which is much more variable for this time period the carbon record at site 548 is also consistently more negative than that of site 552a after 2 5 ma the benthic carbon isotope record of uvigerina at site 548 becomes extremely variable with large negative deviations these isotopic variations might be associated with paleoceanic circulation changes caused by glaciation between 2 5 and 2 ma however paired analyses of uvigerina and cibicidoides species for 38 samples within the glacial interval yield carbon isotopic records which are quite different from one another the uvigerina record contains larger negative deviations than does the cibicidoides record also the isotopic difference between uvigerina and cibicidoides increases during glaciations and in a long term trend from 2 5 to 2 0 ma the lack of covariance between the uvigerina and cibicidoides carbon isotope records indicates that after 2 5 ma at site 548 biotic factors influenced the benthic isotopic record

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

earthquake sound perception 1 sound is an effect produced by almost all earthquakes using a web based questionnaire on earthquake effects that included questions relating to seismic sound we collected 77 000 responses for recent shallow italian earthquakes an analysis of audibility attenuation indicated that the decrease of the percentage of respondents hearing the sound was proportional to the logarithm of the epicentral distance and linearly dependent on earthquake magnitude in accordance with the behavior of ground displacement even if this result was based on italian data qualitative agreement with the results of theoretical displacement and of a similar study based on french seismicity suggests wider validity we also found that given earthquake magnitude audibility increased together with the observed macroseismic intensity leading to the possibility of accounting for sound audibility in intensity assessment magnitude influenced this behavior making small events easier to recognize as suggested by their frequency content

the role of deep ocean circulation in setting glacial climates the glacial cycles of the pleistocene involve changes in the circulation of the deep ocean in important ways this review seeks to establish what were the robust patterns of deep sea water mass changes and how they might have influenced important parts of the last glacial cycle after a brief review of how tracers in the modern ocean can be used to understand the distribution of water masses i examine the data for biogeochemical circulation rate and conservative tracers during glacial climates some of the robust results from the literature of the last 30 years include a shoaled version of northern source deep water in the atlantic expanded southern source water in the abyss and deep ocean salt rather than heat stratification of the last glacial maximum lgm deep sea and several lines of evidence for slower overturning circulation in the southern deep cell we combine these observations into a new idea for how the ocean atmosphere system moves from interglacial to glacial periods across a single cycle by virtue of its influence on the melting of land based ice around antarctica cooling north atlantic deep water nadw leads to a cold and salty version of antarctic bottom water aabw this previously underappreciated feedback can lead to a more stratified deep ocean that operates as a more effective carbon trap than the modern helping to lower atmospheric co 2 and providing a mechanism for the deep ocean to synchronize the hemispheres in a positive feedback that drives the system to further cooling

variability in the deep and intermediate water circulation of the atlantic ocean during the past 25 000 years northern hemisphere modulation of the southern ocean the relative flux of north atlantic deep water nadw out of the atlantic can be monitored in the southern ocean where high 13c nadw mixes rapidly with low 13c recirculated pacific water before forming antarctic bottom water aabw by using 13c measured in benthic foraminifera as a water mass tracer it is shown that the southern ocean was dominated by pacific water with little nadw contribution during the last glaciation these tracer results document the direct physical connection between insolation controlled northern hemisphere oscillations and changes in the chemical and physical properties of southern ocean water the 13c records from the deep tropical atlantic document the transition from an atlantic dominated by southern ocean water during the last glaciation to an atlantic dominated by nadw during the holocene with more southern ocean water in the deep atlantic during the last glaciation the boundary between nadw and southern ocean water was north of its modern position allowing more southern ocean water to enter the eastern atlantic through the romanche fracture zone carbon isotope records from the caribbean and mediterranean seas suggest that the influence of mediterranean overflow water mow extended to the caribbean during the last glaciation and therefore was a volumetrically much more important water mass in the intermediate depth atlantic than it is today

pliocene paleoceanography circulation and oceanographic changes associated with the 2 4 ma glacial event high resolution 18o records from the equatorial pacific site 503b equatorial atlantic site 665a and north atlantic site 606a based on the benthic foraminifera cibicidoides wuellerstorfi show the 2 4 ma onset of major northern hemispheric glaciation to be a package of three events occurring at 2 39 2 35 and 2 31 ma in which a periodicity of about 40 kyr is evident the amplitude of the signals at the three sites indicates that these events were 1 2 to 2 3 the size of the latest quaternary glaciation and also indicates cooling of northern source bottom water by 2 7 4 1 c relative to southern source water during glaciations carbon isotopes indicate that southern source waters were less oxygenated than in the quaternary and that there was reduced production of northern source water during glacial intervals the dominant presence of southern source water in the eastern basin of the equatorial atlantic regardless of climatic cycles throughout the late pliocene indicates a greater influence of these waters relative to northern source waters in the late pliocene ocean

cadmium calcium and carbon isotope reconstructions of the glacial northeast atlantic ocean the 13c and cd measurements from benthic foraminifera from biogeochemical ocean flux study bofs northeast atlantic ocean sediment cores are presented the 13c values in glacial foraminifera are consistent with those from elsewhere in the north atlantic ocean for intermediate water 1000 2000 m water depth 13c values were higher at the last glacial maximum than in present north atlantic deep water nadw whereas for deep water 2000 m they were lower during the glacial maximum the cd concentrations of glacial northeast atlantic intermediate water were lower than those of present nadw however deepwater cd concentrations increased to values between nadw and present pacific deep water pdw the 13c and cd data are consistent and show that the northeast atlantic ocean was strongly stratified with 13c enriched low cd intermediate water overlying 13c depleted high cd deep water the glacial water column comprised two different water masses deep water similar in character to present antarctic bottom water aabw and intermediate water different in character from both aabw and nadw and any present intermediate depth north atlantic water the characteristics of glacial intermediate water were however similar to present near surface waters in the north atlantic which suggests rapid ventilation of the glacial ocean to depths of up to 2000 m by cold nutrient depleted young surface waters

reduced advection into atlantic ocean deep eastern basins during last glaciation maximum causes of change in deep water 13c can be either global or local in extent global causes include 1 climatically induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1 and 2 erosion and deposition of organic rich continental shelf sediments during sea level fluctuations which change the mean oceanic carbon phosphorus ratio2 regional gradients of 13c are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow changes in a single geological record of benthic foraminiferal 13c can result from any combination of these global and abyssal circulation effects by sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity we can assume that each 13c record was equally affected by global causes of 13c variation the differences seen between the 13c records must therefore reflect changes in the distribution of 13c in the deep ocean we interpret these differences in distribution in terms of changes in the ocean s abyssal circulation benthic foraminiferal carbon isotopic evidence from a suite of sierra leone rise cores indicates that the deeper parts of the eastern atlantic basins underwent a reduction in o2 during the maximum of the last glaciation reduced advection of o2 rich deep water through low latitude fracture zones associated with increased delivery of organic matter to the deep ocean lowered the 13c of deep water co2 at all depths below the sill separating the eastern and western atlantic basins 3 this decreased advection into the eastern atlantic ocean coincides with the overall decrease in deep water production in the north atlantic during the last glacial maximum4 7

core top evaluation of benthic foraminiferal isotopic ratios for paleo oceanographic interpretations abstract the benthic foraminifera cibicides wuellerstrofi oridforsalis tener and pyrgo rotalaria from twelve core tops in the norwegian greenland sea and c wuellerstorfi o tener and o umbonatus from four core tops on the rio grande rise were analysed for oxygen and carbon isotopes the norwegian greenland sea data yield statistically discrete means for both 18o and 13c for each species the interregional comparison of our data to published data from the east pacific rise shows that c wuellerstorfi 18o and 13c variations reflect oceanographic differences between sites whereas the data on oridorsalis and pyrgo do not we conclude that c wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility supportive biological studies and the lack of positive covariance of 18o to 13c among deep sea benthic taxa lead us to reject models calling for incorporation of metabolic co2 to explain the isotopic variation among deep sea benthic foraminifera we propose a within sediment microhabitat hypothesis to explain the 13c variations among taxa

late quaternary carbonate sedimentation at the sierra leone rise eastern equatorial atlantic ocean abstract in the eastern equatorial atlantic ocean changes in the concentration of carbonate in late quaternary sediments resulted from reduced production of carbonate in surface waters and increased dilution with non carbonate sediments during glacial maxima during glacial stages production of carbonate in surface water measured as its accumulation rate in shallow undissolved cores decreased by one half the glacial accumulation rate of non carbonate components increased 1 5 to 4 times over holocene values the greatest increases occurred in the deepest cores carbonate dissolution during stages 2 3 and 4 increased the proportion of foraminiferal fragments and decreased the accumulation rate of susceptible species in the deep sites in shallow sites slightly increased dissolution can be detected during stage 3 while greatly increased dissolution occurred during stage 4 bathymetric profiles of foraminiferal fragmentation and accumulation document a shoaling of the foraminiferal lysocline by 1000 m during glacial isotopic stages we present a mass balance model of sediment accumulation for carbonate and insoluble components and from this model we estimate the rate of downslope transport and dissolution of carbonate at the sierra leone rise our results show that during stage 4 the rate of carbonate loss to dissolution was greater than the rate observed today or during other interglacial stages the calculated rates of dissolution for stages 2 and 3 are not significantly different from those calculated for stage 1

diatom record of late quaternary climatic change in the eastern equatorial atlantic and tropical africa over the last 160 000 years diatom productivity in the equatorial atlantic has been high during glacial stages 2 4 and 6 and moderate during parts of substages 5b and 5d approximately 96 000 and 117 000 years b p productivity of diatoms is particularly low in substage 5e and in the middle of stage 1 higher productivity implies more vigorous trade winds during glacial intervals leading to stronger upwelling and enhanced lateral advection of surface waters the influence of the benguela current near the equator was strongest during stage 2 a separate regime of coastal upwelling may have existed in the gulf of guinea at this time upwelling and advection may not always respond to the same forcing as sea surface temperature results support the hypothesis that ethmodiscus rex oozes result from high diatom productivity runoff from the zaire and niger rivers was highest at the stage 2 1 transition and just prior to the stage 6 5 transition due to intensification of the african monsoon several other times of increased runoff are indicated periods of increased surface water circulation in the eastern equatorial atlantic appear to correspond to times of aridity in tropical africa conversely intervals of decreased circulation in the eastern equatorial atlantic coincide with times of humidity in tropical africa precessional forcing of continental climate is suggested however precessional forcing of surface ocean circulation can be neither confirmed nor refuted based on the records examined here influx of antarctic bottom water to the eastern equatorial atlantic has been insignificant throughout the last 160 000 years