ferromanganese oxide deposits from the central pacific ocean i encrustations from the line islands archipelago abstract chemical and mineralogical analyses of a well controlled suite of ferromanganese encrustations from the line islands archipelago central pacific suggest that they represent purely hydrogenous deposits i e they have formed through the slow accumulation of trace metal enriched oxides directly from the water column mineralogically they consist predominantly of mno2 and amorphous feoohxh2o compositionally they are similar to mno2 nodules from adjoining basinal areas but are enriched in both mn mean 20 4 max 29 3 and co mean 0 55 max 1 57 mno2 is the most important trace metal bearing phase strong associations are noted between it and co mo ni zn and cd whilst only be is associated specifically with feooh v sr and pb are partitioned between the authigenic oxide phases whilst ti most probably occurs as tio2xh2o cu is contained in both aluminosilicate contaminant phases and fe oxide phases these relations are considered to reflect the differing scavenging behaviour of mn and fe oxides in the water column crusts from 1 2 km are enriched in mn and the mn related elements and exhibit higher mn fe ratios than deeper crusts which are compositionally constant the higher mn fe ratios may result from a supply of mn from continental borderland sediments at these depths which is transported horizontally by advective diffusive processes since manganophile elements are enriched relative to mn in the 1 2 km crusts it is considered that the supply of mn is scavenged by existing oxides is oxidised and effectively occludes them a higher proportion of oxide particles thus exhibit mn oxide scavenging properties in the 1 2 km depth zone the increased vertical flux of mn resulting from the supply at 1 2 km is not reflected by higher mn fe ratios in deeper crusts so that the vertical flux of oxides is not simply related to the standing crop the mn fe ratios of the crusts thus reflect the composition of suspended oxides at similar depths

higher order eccentricity cycles of the middle and late miocene climatic variations although there is evidence for milankovitch cycles in deep sea sediments from the pleistocene1 4 and upper miocene5 the origin of orbital eccentricity cycles in these records is controversial5 14 recent spectral analyses15 16 of non glacial climatic records of mid cretaceous and early mesozoic exhibit the dominance of 100 and 400 kyr eccentricity cycles and exclude the possibility that the above periodicities originate from the internal variability of ice sheets here i present the walsh spectrum analyses of 10 myr oxygen 18o and carbonate 13c isotope variations spanning the middle and late miocene which reveal statistically significant periodicities of approximately 2 0 and 1 25 myr 800 400 115 and 93 kyr and harmonics of the higher order terms with remarkable resolution higher order periodicities hitherto unexplained in the spectrum of deep sea records match quite well with predicted large eccentricity cycles in the earth s orbital variations17 indicating that eccentricity forcing induced by orbital variations exerts a major influence on the earth s climate

the influence of strongly varying topography on coastal trapped waves at the southern great barrier reef coastal trapped waves ctws that propagate into a region of strongly varying topography are investigated using 6 months of moored current meter observations at the southern great barrier reef sgbr the dominant topographic variations in this region include a large sand island that extends from the coast to the shelf break and an abrupt doubling in shelf width over an alongshelf distance of approximately 100 km previous observational and numerical studies indicate that the sgbr topography scatters mode 1 ctw energy into higher wave modes in the present study a spatially coherent ctw signal is found in a narrow frequency band near 0 1 cpd adjusted sea level and wind stress measurements from south of fraser island show that the similar alongshelf propagation speeds of coastal winds at 10 day timescales and mode 1 ctws lead to the narrow banded ctw signal a proxy for the incident ctw signal is derived to estimate the wave amplitude and phase in the alongshelf current records the observed northward phase progression of the wave response is consistent with the scattering of mode 1 into mode 2 ctw energy by the sgbr topography the strongest observed wave amplitudes are observed over the shelf slope at 300 m depth below the east australia current and near the shelf break at fraser island the strong current response over the slope at the n line suggests a significant outgoing mode 2 wave

the development of antarctic glaciation and the neogene paleoenvironment of the maurice ewing bank abstract a micropaleontologic magnetostratigraphic and sedimentologic analysis of 56 piston cores provides the basis of a geologic study of the late miocene to holocene depositional and erosional history of the intermediate depth maurice ewing bank meb located at the eastern extremity of the falkland malvinas plateau southwest atlantic ocean sedimentation on the meb is controlled presently by the position of the polar front and strong bottom currents beneath the axis of the antarctic circumpolar current acc fluctuations in the position of the polar front and in the intensity of the acc are inferred to have largely controlled deposition on the meb since the initiation of acc flow over the bank in the miocene the sedimentary record of the meb is used to infer the late miocene to holocene oceanographic and climatic conditions in the south atlantic sector of the southern ocean the meb suffered major erosion by intense acc flow during late miocene time which exposed cretaceous miocene sediment near the surface and shaped the present configuration of the bank this erosional event is inferred to have occurred during late miocene to early pliocene time 7 2 4 7 m y b p with the major phase of erosion occurring between middle magnetostratigraphic chron 7 and late chron 6 7 2 6 2 m y b p we suggest that the miocene sedimentary record of the meb and other paleoenvironmental evidence from the circum antarctic region precludes the existence of a west antarctic ice sheet or extensive ice shelves along the antarctic margin prior to the late miocene during the late miocene a west antarctic ice shelf formed in the former west antarctic sea and rapidly thickened until it grounded below sea level to form the west antarctic ice sheet formation of this ice sheet with floating and partially grounded extensions ice shelves in the ross and weddell embayments led to the first major production of true antarctic bottom water formed in a manner similar to today which permanently altered global abyssal circulation late miocene changes in oceanic ccd levels and a permanent shift in the oceanic 13 c 12 c composition may be attributed to this major change in abyssal circulation a decrease in acc velocity during an early pliocene amelioration of climate led to resumption of deposition on the bank from 4 7 to 3 9 m y b p intensification of the acc during the late gilbert and early gauss chrons again resulted in limited deposition and widespread erosion and or non deposition over most of the meb from 4 0 to 3 2 m y b p acc velocity apparently began to wane during the middle of the gauss chron and allowed widespread deposition on the bank during late gauss time 2 9 2 48 m y b p and over more limited areas during earliest matuyama time 2 48 to about 2 2 m y b p during middle to late matuyama time bottom current intensity reached its greatest post miocene level forming a regional disconformity between sediments of about 2 0 and 1 0 m y in age this increased circumpolar circulation and associated erosion is inferred to have peaked during the late matuyama chron 1 2 1 0 m y b p and is approximately the same age as the tentatively dated greatest patagonian glaciation in nearby southern argentina between 1 0 and 0 7 m y b p the bank was blanketed with a coarse erosion resistant layer of ice rafted detritus which armored the older sediment thereby protecting it from major subsequent erosion sedimentation on the meb during the bruhnes chron 720 000 yr b p present was intermittent and finally culminated with the deposition of a veneer of carbonate ooze during or since latest pleistocene time

equatorial pacific seismic reflectors as indicators of global oceanographic events the origin of a series of regionally correlatable seismic horizons in the neogene sediments of the central equatorial pacific is examined through seismic modeling and the detailed analyses of stratigraphic and physical property relationships in deep sea drilling project cores these regionally traceable reflectors are synchronous the younger reflectors are the direct result of carbonate dissolution events the older ones of stratigraphically selective diagenetic processes the changes in ocean chemistry associated with these events appear to be linked to global reorganizations of surface and bottom water circulation patterns the most dramatic of which are associated with reorganizations of north atlantic bottom waters these deepwater seismic horizons appear to correlate with the major events on the relative sea level curve of vail et al for the neogene

variations in the fine scale composition of a central pacific ferromanganese crust paleoceanographic implications a 47 to 60 mm thick fe mn crust from horizon guyot water depth 1800 1780 m central pacific was used to evaluate the potential of crusts as recorders of neogene paleoceanographic and paleoclimatic conditions the chemical composition was determined by microprobe for 16 elements from a polished thin section three analyses were made per millimeter and averaged to give the composition of each millimeter the age of the crust was determined by measuring the strontium isotope composition of the crust and comparing it with the tertiary seawater curve the crust represents 18 5 m y of growth of fe and mn oxyhydroxides the crust is composed of alternating botryoidal and laminated layers the botryoidal layers formed during the same time intervals that widespread neogene deep sea hiatuses were forming in bottom sediments the botryoidal layers represent growth during times of intensified deepwater flow whereas the laminated intervals represent more quiescent conditions the correspondence between the botryoidal layers and the neogene hiatuses is so strong that we were able to choose a variable growth rate model over a constant growth rate model for the crust chemical changes in the crust take two forms the first is represented by broad changes in the composition defined chiefly by fourth order polynomial fits to the chemical profiles of each element with depth in the crust the second is high frequency changes in composition the broader changes occurred primarily at about 15 11 5 7 4 6 4 5 2 and 4 6 ma which may correlate with major changes in paleoceanographic circulation and development of ice caps at the poles the periods of the high frequency changes may reflect climatic changes that resulted from orbital forcing these high frequency changes may correspond to the high order eccentricity periods of 3 47 2 04 and 1 31 m y

living foraminiferal assemblages in two submarine canyons polcevera and bisagno of the ligurian basin mediterranean sea abstract living rose bengal stained benthic foraminifera were investigated in eleven stations sampled along transects following a depth gradient from polcevera and bisagno canyons and the adjacent open slope ligurian sea in a depth interval ranging from 200 to 2000 m in order to understand which environmental factors influence the abundance and taxonomical composition of the foraminiferal assemblages in these two domains canyon and open slope qualitative and quantitative foraminiferal data were correlated to the sediment biochemical composition in terms of phytopigments proteins lipids carbohydrates and biopolymeric carbon grain size and the main hydrological characteristics salinity temperature dissolved oxygen the cluster analysis and canonical correspondence analysis allowed us to detect two sectors coastal and offshore characterized by contrasting trophic conditions the coastal sector reflects spread meso eutrophic conditions in both physiographic domains being possibly more impacted by the river inputs and sediment transport processes from land in fact the narrow continental shelf of the ligurian sea favors the deposition of sediment transported by riverine processes on the immediately adjacent coastal areas as a result homogenization of sea bottom conditions occurs leading to an unclear differentiation between open slope and canyon foraminiferal assemblages conversely the offshore sector is less affected by physical disturbance due to the sedimentary flows decreasing in relation to the larger distance from the coastline consequently the lower organic matter content and lower food quality expressed in terms of contribution of the primary material to the biopolymeric carbon pool lead to a more oligotrophic condition which favors the development of peculiar assemblages dominated by glomospira charoides ammolagena clavata and epifaunal taxa the first finding ever of a warm tropical species amphistegina lessonii in the ligurian sea sediments at 500 m depth can be considered the first evidence of upward expansion of tropical species to the northern portion of the mediterranean sea which is experiencing an evident water warming linked to the ongoing global climate change

mesoscale circulation features of the great barrier reef region inferred from noaa satellite imagery abstract the commissioning of a noaa satellite receiving station at townsville in north queensland in 1988 greatly expanded the a vhrr coverage of the northeast australian region to include the entire great barrier reef system and marginal seas selected imagery from this and a southern station installed previously at aspendale victoria provide a valuable new perspective on oceanographic phenomena occurring in this ecologically significant region this perspective could not be attained using conventional ship board and in situ oceanographic sampling techniques a rich spectrum of mesoscale oceanographic features is revealed in the analyzed imagery and various features such as western boundary current meanders frontal shear waves eddies and jets are described the temporal and spatial variability of these features appears strongly linked to that of the larger scale coral sea current circulation several of the features identified are unique to the region others resemble features observed in other western boundary current systems but are significantly modified by the complex regional topography and by the presence of the great barrier reef gbr evidence has been found for a number of processes which have significant implications for the origin and maintenance of gbr ecosystems including shelf edge exchange processes stratified slope water intrusions onto the shelf and boundary layer mixing around reefs such processes provide a mechanism for injection of cool nutrient rich waters into the reef matrix the imagery provides a clear picture of a well organized but spatially complex frontal system existing in the southern coral sea which is associated with enhanced commercial and recreational fishing activity in the region the avhrr imagery has thus proven to be a valuable tool for spatial mapping of oceanographic features throughout the gbr region for hypothesis formation in dynamical and modeling studies and for ship board reconnaissance operations

local and remote wind forcing of new south wales inner shelf currents and sea level abstract linear multiple regression analysis is used to identify the locally and remotely wind driven components of the nearshore current and adjusted sea level asl variability at sydney new south wales the data analyzed comprise a one year time series of current meter records acquired 3 km offshore in 60 80 m of water together with coastal sea level and wind date from one local and 12 remote stations in nsw bass strait and the great australian bight approximately 60 to 70 of the weather band 40 h to 20 d period current and asl variance at sydney appears to be wind driven with the major contributors to the variance being the southern new south wales and bass strait winds both lagged by intervals corresponding to the propagation speed of the first coastal trapped wave ctw mode the multipath nature of wind energy transmission by at least two ctw modes is evident but the energy flux at sydney of the freely propagating second mode from bass strait appears to be only one fifth to one third of

cobalt and platinum rich ferromanganese crusts and associated substrate rocks from the marshall islands abstract ferromanganese crusts cover most hard substrates on seafloor edifices in the central pacific basin crust samples and their associated substrates from seven volcanic edifices of cretaceous age along the ratak chain of the marshall islands are discussed the two most abundant substrate lithologies recovered were limestone dominantly fore reef slope deposits and volcanic breccia composed primarily of differentiated alkalic basalt and hawaiite clasts in a phosphatized carbonate matrix the degree of mass wasting on the slopes of these seamounts is inversely correlated with the thickness of crusts crusts are generally thin on limestone substrate away from areas of active mass wasting processes and large atolls crusts may be as thick as 10 cm maximum the dominant crystalline phase in the marshall islands crusts is mno 2 vernadite high concentrations of cobalt platinum and rhodium strongly suggest that the marshall islands crusts are a viable source for these important metals many metals and the rare earth elements vary significantly on a fine scale through most crusts thus reflecting the abundances of different host mineral phases in the crusts and changes in seawater composition with time high concentrations of cobalt nickel titanium zinc lead cerium and platinum result from a combination of their substitution in the iron and manganese phases and their oxidation potential

observations of strong mid pacific internal tides above horizon guyot abstract large semidiurnal current and isotherm oscillations were observed by one current meter continuously for 9 months in the waters above horizon guyot a seamount located in the central pacific the m2 tides dominated the current meter record the m2 current ellipse was oriented along 142 the semi major amplitude was 7 6 cm s 1 and the currents rotated in a clockwise direction the m2 isotherm deflection amplitude was 20 m the m2 currents observed above the guyot were two to three times larger than m2 currents either observed in or predicted for this region of the mid pacific evidence suggests that the semidiurnal tide was predominantly an internal tide that was generated at the guyot the observed internal tide had a narrow bandwidth and a constant amplitude and phase for 9 months and had characteristics similar to a vertically propagating rather than a vertically standing internal wave

numerical models for diagenesis and the neogene sr isotopic evolution of seawater from dsdp site 590b abstract a numerical model for the diagenetic exchange of sr between carbonates and their pore fluids during sedimentation and compaction has been developed the model has been applied to data from dsdp site 590b in order to assess the accuracy with which the sr isotope record in the carbonate sediment reflects that of seawater the most important process affecting the sr in the solid carbonate is exchange with the pore fluid due to solution reprecipitation but the concentration or isotopic composition of sr in the solid itself gives little or no information as to the magnitude of this exchange the key to determining the rate of exchange is the pore fluid where the variations of sr2 and87sr 86sr with depth are very sensitive indicators the logical structure of applying the model to data from dsdp 590b is to find by successive iteration an ocean history i e the initial87sr 86sr and sr concentration of each increment of carbonate deposited and a rate of sr exchange between pore water and solid carbonate such that the model matches the present sr concentration and87sr 86sr of both pore water and solid carbonate once all the data are matched the model provides an estimate of the rate of sr exchange due to solution reprecipitation and the evolution of87sr 86sr in seawater over the past 20 million years for dsdp 590b we find that solution reprecipitation decreases rapidly with depth from a near surface value of about 10 per million years to about 1 per million years below 200 m this rate of exchange of sr results in the carbonates of dsdp 590b preserving an accurate record of the sr isotopic evolution of the ocean over the past 5 million years but for ages greater than 5 million years the87sr 86sr ratio of the carbonate is systematically displaced from that of the seawater in which it was deposited the maximum difference is of order 5 10 5

high resolution stratigraphy with strontium isotopes the isotopic ratio of strontium 87 to strontium 86 shows no detectable variation in present day ocean water but changes slowly over millions of years the strontium contained in carbonate shells of marine organisms records the ratio of strontium 87 to strontium 86 of the oceans at the time that the shells form sedimentary rocks composed of accumulated fossil carbonate shells can be dated and correlated with the use of high precision measurements of the ratio of strontium 87 to strontium 86 with a resolution that is similar to that of other techniques used in age correlation this method may prove valuable for many geological paleontological paleooceanographic and geochemical problems

coastal trapped waves behind a large continental shelf island southern great barrier reef abstract the salient features of subinertial frequency fluctuations of current sea level temperature and wind stress observed within the capricornia section of the great barrier reef are interpreted by comparison with coastal trapped wave ctw theories near coastal currents and sea levels are modeled with some success by a theory of first mode wind forced barotropic continental shelf waves with geographical origin at fraser island the southern across shelf boundary of the study region however current and temperature variations of period 8 10 days on the continental slope are observed to have energy far in excess of that generated by the local wind decomposition of the observed alongshore velocity field in terms of baroclinic ctw modes indicates the signal is predominantly a second or third mode wave propagating equatorward at 0 4 0 6 m s 1 these modes have most of their energy flux propagating along the continental slope and the energy levels indicate that the source region lies to the south of

late cenozoic changes in atmospheric circulation deduced from north pacific eolian sediments abstract isolation and analysis of the eolian component of late cenozoic pelagic sediments from the north pacific provides direct information concerning changes in atmospheric circulation a 50 increase in intensity of both the prevailing westerlies and the tradewinds coincides with increasing pole to equator temperature gradients resulting from the onset of northern hemisphere glaciation at the same time the mass flux of dust from continents to the north pacific increased by a factor of 4 5 apparently reflecting significantly increased continental aridity associated with the late cenozoic glacial ages

ferromanganese crusts from necker ridge horizon guyot and s p lee guyot geological considerations abstract necker ridge horizon guyot and s p lee guyot in the central pacific were sampled seismically surveyed and photographed by bottom cameras in order to better understand the distribution origin and evolution of ferromanganese crusts necker ridge is over 600 km long with a rugged crest pods of sediment to 146 m thick slopes that average 12 to 20 and debris aprons that cover some of the lower flanks substrate lithologies are mostly hyaloclastite volcaniclastic breccia and minor alkalic basalt horizon guyot 300 km long and 75 km wide is capped by at least 160 m of sediment which buries stepped terraces substrate lithologies are similar to those on necker ridge although previous workers sampled much tholeiitic basalt on horizon s p lee guyot 125 km long and 80 km wide is capped by at least 300 m of sediment and contains talus aprons along its lower flanks ferromanganese encrusted rocks were recovered in every dredge and are thickest on necker ridge crust thicknesses average about 2 5 1 5 and 0 8 cm for necker horizon and s p lee respectively crusts range from smooth or porous surfaces to knobby and botryoidal the entire crust is laminated however two distinct layers commonly exist separated by a paper thin layer of phosphorite the dominant mineral of all crusts is vernadite mno 2 while quartz feldspar apatite and in three rocks todorokite are minor phases quartz and feldspar decrease with decreasing latitude of occurrence and is suggested to be related to eolian input on the average apatite also increases within the crusts with decreasing latitude of occurrence which may be related to high biological productivity in the zone of equatorial upwelling phosphorite substrates are more abundant on necker ridge and s p lee guyot than they are on horizon guyot seamount ferromanganese nodules are distinct from abyssal nodules in their chemistry and internal structure

sr and nd isotopic variations in ferromanganese crusts from the central pacific implications for age and source provenance abstract isotopic analyses of two hydrogenetic ferromanganese fe mn crusts from volcanic edifices in the central pacific ocean reveal systematic variations in 87 sr 86 sr and 143 nd 144 nd with both ratios decreasing as a function of depth into the fe mn crusts leaching experiments suggest that sr in the crusts is contained in at least two discrete sites a loosely bound sr dominated by modern marine sr is removed by leaching with a 10 percent acetic acid solution the 87 sr 86 sr ratio of the residue is significantly less than the 87 sr 86 sr ratio of the unleached material the sr isotope ratios of leached samples are compared with the temporal variation in seawater to provide ages for layers within the fe mn crusts these data suggest that the oldest crust layers began to accrete in the early to middle miocene correlated to the 87 sr 86 sr variations 143 nd 144 nd ratios suggest that the nd isotope composition of central pacific ocean seawater also changed systematically over this time interval or that the fe mn crusts simply incorporated nd from various parts of an isotopieally heterogeneous ocean as the crusts were carried along with the oceanic plate in contrast to the layered ferromanganese crust the phosphatized volcaniclastic substrates have sr and nd isotope compositions that are consistent with their volcanic origin

10 be dating of a manganese crust from central north pacific and implications for ocean palaeocirculation one of the most promising applications of the new 10be detection technique using accelerator mass spectrometry is the determination of growth rates of mn nodules and crusts1 5 because the half life of cosmogenic 10be 1 5 myr is of the same order as the time needed for a few millimetres of nodule material to grow 10be is a useful tool for unravelling such evolution during the late tertiary when most nodules are assumed to have started their growth6 mass spectrometric measurement of a 10be profile across the manganese crust va 13 2 from the central pacific using a tandem van de gr a ff accelerator yields growth rates of 2 7 and 4 8 mm myr 1 for the layers of the crust accumulated between recent and 6 myr bp and between 6 and 11 myr respectively using these measurements as well as 230th dating we have been able to distinguish boundaries between zones in the crust with different structures and chemical compositions and to assign ages to them these ages are 0 12 2 9 3 4 5 7 6 7 7 9 10 12 and 13 16 myr bp all of these boundaries apparently coincide with the times reported for quaternary and late tertiary palaeoclimatic events suggesting that the crust growth has been strongly influenced by palaeoclimate

sedimentary indicators of atmospheric activity in the northern hemisphere during the cenozoic abstract the concentrations and accumulation rates of eolian phases and the mineralogy of sediments from a north pacific core ll44 gpc3 have been used to evaluate changes in eolian sedimentation and atmospheric activity during the cenozoic the quartz content and clay mineralogy of the sediments reflect changing source areas for eolian material whereas the accumulation rates of eolian phases reflect climatic variation and wind intensity eolian sedimentation decreased from 70 to 50 m y ago at the site as it moved north out of the equatorial pacific where it was supplied with eolian debris from north america and africa low rates of eolian sediment accumulation 50 to 25 m y ago reflect the temperate humid environment of the early tertiary and the lack of vigorous atmospheric circulation at that time from 25 to 7 m y ago eolian accumulation increased as the site moved into the influence of the westerlies from 7 to 3 m y ago there was a more rapid increase in accumulation of eolian material at the site which was not accompanied by changes in mineralogy or quartz content and was therefore related to climatic change and more vigorous atmospheric circulation about 2 5 m y ago a dramatic increase in eolian sedimentation accompanied the onset of dry northern hemisphere glaciation

covariance patterns of foraminiferal dgr18o an evaluation of pliocene ice volume changes near 3 2 million years ago oxygen isotope data for a pliocene interval from 3 6 to 2 8 million years ago show a mean increase 0 5 per mil of benthic delta 18 o at about 3 2 million years ago whereas planktic delta 18 o does not increase this lack of covariance indicates that the event at 3 2 million years did not result in a permanent increase in the ice budget of either the northern or the southern hemisphere

detailed record of the neogene sr isotopic evolution of seawater from dsdp site 590b a detailed study of strontium isotope variations in neogene marine carbonate sediments from deep sea drilling project site 590b using techniques that allow the 87sr 86sr ratio to be determined to better than 0 00001 gives a high resolution record of the sr isotopic evolution of seawater the data show that the rate of change of the marine 87sr 86sr ratio has varied significantly even on time scales as short as 1 m y periods of particularly rapid growth appear to follow major marine regressions and probably reflect an increase in the delivery of radiogenic sr from the continents coupled with a decreased submarine carbonate dissolution rate greater carbonate compensation depth periods of relatively slowly changing 87sr 86sr follow major marine transgressions on the basis of correlations with the marine oxygen isotope record and the times of major continental glacier growth it is inferred that the effects of sea level variations are modified by climatic factors that affect the intensity of continental weathering and runoff the effects of sea floor generation rate variations are not discernible for the neogene the maximum attainable stratigraphic resolution using sr isotopes is between 0 1 and 2 m y for this time period

disconformities and paleoceanography in the southeast indian ocean during the past 5 4 million years biostratigraphy and magnetostratigraphy are used to identify deep sea disconformities in the southeast indian ocean the hiatuses are used to define periods of increased bottom water activity and to indicate deep sea circulation patterns during the pliocene and pleistocene seven zones of hiatus are restricted to areas confined by topographic restrictions or by water depth control on bottom water flow an analysis of hiatus frequency reveals that a water depth of about 4 200 m separates disconformities formed by antarctic bottom water 4 200 m and circumpolar deep water 4 200 m hiatus zones in deep basins occur in the tasman emerald balleny and south indian basins and east of the macquarie ridge shallow water hiatus zones 4 200 m occur at the junction of the southeast indian rise the macquarie ridge and the tasman basin and along the antarctic margin changes in the extent of these regional hiatuses are examined by analysis of hiatus occurrence in seven time slices during the past 5 4 m y although the timing of hiatuses produced by deep and shallow water masses are not synchronous the causes of increased bottom water activity may be correlated with paleoclimatic events southern ocean cooling and the proposed re establishment of the west antarctic ice sheet and its fringing ice shelves in the late gilbert chron t 4 2 to 3 6 m y b p were accompanied by increased antarctic bottom water and circumpolar deep water activity as revealed by the frequency of both shallow and deep disconformities the formation of the northern hemisphere barents ice sheet at 3 5 m y b p however led to a decrease in antarctic bottom water production by inhibiting the formation of saline north atlantic deep water which combines with cold antarctic shelf water to form antarctic bottom water cool southern ocean climatic conditions that culminated in the late matuyama chron t 1 66 to 0 72 m y b p resulted in a widespread disconformity produced by increased circumpolar deep water activity and a more restricted disconformity produced by antarctic bottom water the areal extent of both deep and shallow disconformities was reduced after the late matuyama chron t 0 72 m y b p in response to decreased bottom current activity

a method for estimating wind driven frictional time dependent stratified shelf and slope water flow abstract friction the alongshore pressure gradient and time dependent effects are all of lowest order importance in the dynamics of wind driven fluctuating currents and sea levels on continental shelves previous work has shown that when all these effects are included the ocean response can be described by an infinite sum of coastal trapped waves whose amplitudes satisfy a fully coupled infinite set of forced first order wave equations we present a practical method for solving this coupled set of equations for general low frequency large scale wind stress forcing as input convergence properties of the solution are examined analytically for the same accuracy more modes are required to describe alongshore currents than sea level and fewer modes are required to describe barotropic than depth dependent motion as an example numerical calculations were carried out for a model of the west florida shelf the sea level field was effectively described by one mode but the alongshore velocity field was not

variations in the strontium isotopic composition of seawater during the neogene the authors report 261 strontium isotopic analyses of well preserved planktonic foraminifers from three deep sea drilling project sites 519 588 and 607 these samples cover the period from 24 ma to present with an average of approximately one sample per 100 ka the combination of high sample density and uniformity of analytical procedures has produced a well defined record of changes in the sup 87 sr sup 86 sr of seawater during the neogene the record can be viewed as a series of essentially linear segments with slopes ranging from as high as 6 times 10 sup minus 5 m y to as low as 0 m y the times associated with major inflections in the curve do not appear to correspond to simple geologic phenomena such as eustatic cycles but are probably controlled by a combination of tectonic and climatic factors that influenced the abundance and isotopic composition of terrestrial strontium input to the oceans the strontium isotopic data are consistent with a progressive increase in the chemical weathering rates of the continents during the neogene probably related to repeated glaciations increased exposure of continents by lowered sea level and increased continental relief resulting from high rates of tectonic uplift

paleodepth distribution of neocene deep sea hiatuses the depth of formation of miocene to middle pliocene deep sea hiatuses nh1 to nh8 has been determined using 152 deep sea drilling project sites in the atlantic pacific and indian oceans megahiatuses representing maxima in deep sea erosion occur at three water depths below 3800 m at intermediate depths between about 2000 and 3000 m and in shallower waters above 1500 m paleodepth both the paleodepths and distribution of these hiatus maxima suggest that flow of antarctic bottom water antarctic intermediate water and north atlantic deep water masses largely caused this erosion correlation of the hiatuses with oxygen isotope carbonate and sea level records indicates that prior to 11 ma brief hiatuses including those resulting from nondeposition in high productivity equatorial regions largely correlate with global cooling episodes high carbonate content and lowstands of sea level during the last 11 m y hiatuses also seem to correlate with cooling episodes but carbonate dissolution is characteristic and sea levels may have been rising or at a lowstand during the nh4 nh7 and nh8 intervals it is possible that a rise in sea level corresponds with polar cooling but there is uncertainty in correlation brief hiatuses during rising sea levels can be explained by basin shelf fractionation of carbonates hiatuses during sea level lowstands and cooling episodes may result from intensified bottom water circulation and increased corrosiveness of bottom water due to higher levels of co2 and increased productivity during increased upwelling supplement appendix 1 is availablewith entire article on microfiche orderfrom american geophysical union 2000florida avenue n w washington dc20009 document p87001 2 50 paymentmust accompany order

coastal trapped waves on the east australian continental shelf part ii model verification abstract the australian coastal experiment ace was designed to test coastal trapped wave ctw theory and the generation of coastal trapped waves by the wind for the ace dataset we use ctw theory to attempt to hindcast the observed alogshelf currents and coastal sea levels at locations remote from the upstream in the ctw sense boundary of the ace region local in the ace region wind forcing is responsible for only about a quarter of the ctw energy flux at stanwell park the center of the ace region and the remainder enters the ace region from the south and propagates northward through the ace region including the second mode ctw improves the correlation between the hindcast and the observed near bottom currents on the upper slope at stanwell park but the use of the third mode ctw cannot be justified a linear bottom drag coefficient of r 2 5 10 4 m s 1 works better than a larger drag coefficient and simplifying the ctw equations by assuming the modes are uncoupled does not detract from th

scattering of coastal trapped waves by irregularities in coastline and topography abstract the scattering of freely propapting coastal trapped waves ctws by large variations in coastline and topography is studied using a numerical model which accomodates arbitrary density stratification bathymetry and coastline particular attention is paid to the role of stratification which in moderate amounts can eliminate backscattered free waves which occur theoretically in a barotropic ocean numerical simulations using widening and narrowing shelf topographies show that the strength of the forward scattering into transmitted ctw modes is proportional to a topographic warp factor which estimates the severity of the topographic irregularities the forward scattering is further amplified by density stratification within the scattering region itself the strengths of the scattered wave induced currents exhibit substantial variation over short spatial scales there is generally a marked intensification of the flow within the scattering region and rapid variations in phase on narrowing shelves

the australian coastal experiment a search for coastal trapped waves abstract the australian coastal experiment ace was conducted in the coastal waters of new south wales from september 1983 to 1984 the data obtained allow a detailed examination of the dynamics of flow on the continental shelf and slope and in particular allow a description of coastal trapped wave modes propagating within the coastal waveguide the trapped wave signal is contaminated by energy from the east australia current eddies approaching the continental slope however the data do allow a clear separation of the first three coastal trapped wave modes over the range of frequencies appropriate to the weather forcing band through that frequency range the phase speed is computed and an empirical dispersion relation determined for each mode the empirical dispersion relations compare well with the theoretical relations indicating that a large fraction of the variance in current velocities on the continental shelf can be accounted for by coastal trapped wave theory wind forcing of trapped waves is als

coastal trapped waves on the east australian continental shelf part i propagation of modes abstract the currents observed over the shelf and slope during the australian coastal experiment ace are used to determine the amplitudes as functions of time of the first three coastal trapped wave ctw modes at three locations along the southeast coast of australia a statistical eddy mode is included to minimize contamination of the coastal trapped wave currents from east australian current eddies the first three ctw modes account for about 65 of the observed variance in the alongshelf currents on the shelf and slope at cape howe about 40 at stanwell park but only about 24 at newcastle currents associated with the east australian current dominate the observations offshore from newcastle ctws account for all but 10 37 and 27 of the currents observed at the most nearshore locations on the shelf at cape howe stanwell park and newcastle the first two coastal trapped wave modes propagate at close to the appropriate theoretical phse speeds but the third coastal trapped wave mode and the