stratigraphy and radiocarbon chronology of a subaerially exposed holocene coral reef dominican republic a subaerially exposed coral reef records a period of marine conditions following earliest holocene transgression into the technically active subsea level enriquillo valley dominican republic field mapping detailed leveling of reef elevations and i4c dating of fossil corals and mollusks reveal the following chronology of reef development in an unusual geologic and tectonic environment 1 earliest holocene 9760 pm 100 yr b p marine transgression and growth of oysters on an alluvial fan surface approximately 33 m below sea level bsl 2 colonization of reef corals at approximately 34 m bsl on the oyster shell deposits 8990 pm 60 yr b p 3 middle holocene development of a typical caribbean fringing reef in a protected environment 6200 pm 80 to 4760 pm 90 yr b p 4 late holocene sedimentation over the reef with fossil bivalves 5710 pm 90 to 2820 pm 40 yr b p that record a gradual change from marine to brackish water that accompanied growth of shoreline th

vertical mixing in the ocean the thermohaline circulation of the ocean results primarily from downwelling at sites in the nordic and labrador seas and upwelling throughout the rest of the ocean the latter is often described as being due to breaking internal waves here we reconcile the difference between theoretical and observed estimates of vertical mixing in the deep ocean by presenting a revised view of the thermohaline circulation which allows for additional upwelling in the southern ocean and the separation of the north atlantic deep water cell from the antarctic bottom water cell the changes also mean that much less wind and tidal energy needs to be dissipated in the deep ocean than was originally thought

flow hydrography turbulent mixing and dissipation at fieberling guyot examined with a primitive equation model 1 the extensive set of measurements previously taken at fieberling guyot provides a backdrop for model results on flow hydrography turbulent mixing and derivative variables a z level primitive equation model driven at subinertial and superinertial tidal frequencies allows the nonlinear interaction of free and topographically trapped motions to jointly determine model outcomes model residual flows mean hydrographic features topographic amplification of oscillatory currents turbulent dissipation and vertical diffusivity kv profiles are all examined in the light of the observations azimuthal residual flows are toroidal above the summit with maximum speed 20 cm s 1 diurnal flow over the summit is intensified by a factor 20 downward vertical flow as a time mean w t occurs from 150 m above the summit apex to summit rim depth with radially inward flow above the apex and radial outward flow below upward w t rings the summit at larger r the existence of the observed cold dome is shown to depend on w t in the summit circulation cell vertical current shear is concentrated in a 150 m thick cap above the summit accounting for a domed distribution of and kv with maxima of 10 7 w kg 1 and 30 cm2 s 1 respectively profiles most like the observations of kv are obtained with a subgrid scale parameterization in which the turbulent prandtl number pr depends on the shear richardson number ri

tropical atlantic coral oxygen isotopes glacial interglacial sea surface temperatures and climate change abstract we have generated a detailed oxygen isotope time series from the fossil coral reefs from offshore barbados the barbados coral based record is a unique paleoceanographic data set with an equivalent sedimentation rate in excess of 600 cm kyr where not only is the annual signal uniquely preserved but seasonality as well oxygen isotope values during the late glacial and lgm 16 20 14c kyrs 19 24 calendar kyrs are 2 3 heavier than corresponding living specimens and indicate a regional cooling on the order of 4 5 c there is also an isotopic expression of the bolling pre boreal climate oscillation with values reflecting a cooling during the younger dryas seasonality a key diagnostic of the state of the climate system remained the same or slightly less than present and indicates that the observed coolings were a change in the mean state of the western tropical atlantic pan tropic cooling during the last glaciation is best explained by a change in the radiative balance of the tropics variable tropical sea surface temperatures during climate oscillations such as the younger dryas challenge the paradigm that climate change only cascades from variations in north atlantic deep water production

ocean current and temperature time series at brothers volcano 1 time series of currents and temperatures were acquired near surface and at depth on three moorings above brothers volcano 34 52 25 s 179 04 e 25 km west of the kermadec ridge and 300 km northeast of the north island new zealand from september 2004 to may 2005 ocean current time series were previously unavailable within 300 km of this site and few such measurements exist anywhere near magmatically or hydrothermally active volcanoes such as brothers energy in near surface currents 163 527 m depth was primarily subtidal 64 subtidal motions to 527 m depth are shown to be reasonably well correlated with geostrophic currents derived from satellite sea level anomalies although the moorings were separated laterally by only 11 km the upper current meters also recorded significant differences in m2 tidal currents indicating the presence of significant internal tides at this site below volcano summit depth 1220 m the kinetic energy of currents was primarily tidal 54 longer period currents at depth evidenced the influence of volcano topography temperature time series showed a 3 month period of sharply decreased temperature that extended in depth from 163 m to at least 1260 m advanced very high resolution radiometer avhrr sea surface temperature data show colder surface water immediately above and north of brothers over the same time period these data together with the velocity records suggest an anomalous deep cold water mass arrived and lingered over brothers for 3 months in the austral late spring and early summer of 2004 2005

deep sea fluid and sediment dynamics influence of hill to seamount scale seafloor topography abstract deep sea sediments play a central role in a wide range of subject areas a number of important controls on the formation of sedimentary deposits have been studied however to date the impact of submarine landscape geometry as a possible control has received comparatively little attention this seems to be particularly true for intermediate scale topographic features such as abyssal hills knolls and seamounts that can be found in many regions of the global seafloor recent estimates suggest that in the deep open oceans away from continental margins there might be as many as 25 106 abyssal hills knolls and seamounts despite this large number very little is known about how they influence environmental complexity and patchiness biogeochemical fluxes and the formation of sedimentary records this paper reviews the currently known types of fluid flow interactions with abyssal hills knolls and seamounts that could potentially influence the way sediments are formed the main types of relevant flow components are quasi steady to eddying background flow internal lee and near inertial waves barotropic and baroclinic tides and seamount trapped waves previous studies looking into systematic links between fluid dynamics and sediments at hills knolls and seamounts are reviewed finally a case study is presented which aims to combine our current knowledge and investigate whether a given combination of recent fluid flow components leaves a detectable imprint in the recent sediments on and around a short seamount the main conclusions and implications are as follows 1 topographically generated flow field geometries that are composed of a number of different prevailing fluid flow components can be reflected and detected in properties of the underlying sediments 2 tidal and other higher frequency lee wave near inertial components of deep ocean currents can be essential for locally driving total current velocities across threshold values for non deposition erosion resuspension of freshly deposited deep sea sediments moreover there is evidence suggesting that not only maximum current speeds but also intensities of higher frequency tidal and or near inertial current direction variability might control sediment dynamics and sediment formation this relativises the view that current speed is the main or even only controlling factor for sediment dynamics and sediment formation 3 when it comes to the reconstruction of paleo flows these findings imply that certain sedimentary records may well reveal more about variability in the higher frequency flow components than about variability in the basin scale net flow component that often is the focus of paleoceanographic studies 4 single core paleo records from hill seamount or similarly controlled sediment deposits may be biased due to the asymmetry of flow fields around these topographic features to arrive at unbiased paleo records for non fluid dynamic parameters the influence of the flow field geometry would have to be removed from the record first 5 it seems the mechanistic understanding of hill and seamount related flow topography interactions and their links to sediment dynamics is approaching a level that may a facilitate improved interpretation of topographically controlled sedimentary paleo records b help fill in the knowledge gap that exists for functional deep sea biodiversity at intermediate space scales and c improve predictive capabilities for exploration of economically relevant iron manganese fe mn crusts on seamounts

quaternary reef response to sea level and environmental change in the western atlantic the tropical subtropical western atlantic realm harbours abundant fringing reefs two major barrier reefs belize florida several atolls and large reef fringed carbonate platforms bahamas data from belize and south florida indicate that major barrier reefs were established during the high sea levels of the long and warm marine isotope stage 11 reefs formed during pleistocene sea level highstands whereas erosion non deposition and the formation of subaerial exposure surfaces prevailed during lowstands of sea level florida bahamas exposed reefs and platforms with siliciclastic hinterlands were characterized by deposition of clays and sands on fluvial plains belize elevated terraces and outcrops of reefs of the last interglacial of marine isotope stage 5e are evidence of higher than present sea level and temperature that sustained large reef fringed carbonate platforms and ramps in the florida bahamas region and central america belize mexico including ooid deposition in warm and shallow waters during the highstands of marine isotope stages 5c and 5a at sea levels several metres lower than today fringing reefs developed in parts of the caribbean for example in south florida outlier reefs data from the island of barbados support the contention that the postglacial sea level rise from about 120 m was rapid and punctuated by two meltwater pulses ia and ib which bracket the beginning and end of the younger dryas respectively after reflooding of shelves in the early holocene reefs developed preferentially on highs of the underlying karstified pleistocene limestone surface and on former river channel bars many reefs in the western atlantic region kept pace with holocene sea level rise whereas some were drowned reasons for reef drowning are debated and include sea level rise elevation of antecedent topography and deterioration of environmental conditions such as high nutrient input apart from sea level and antecedent topography factors such as exposure to waves and currents storms and sedimentation have controlled reef development the historical decline of acroporid corals in the caribbean realm has been attributed to cooling following the holocene thermal optimum however historical die offs of reef building corals and other reef organisms suggest that some if not all recent declines were unprecedented during the holocene rising temperatures decreasing carbonate saturation increased frequency of major storms high nutrient concentrations and sedimentation overfishing and disease certainly played a role in decline but systematic studies relating these environmental factors to holocene reef building are only in the early stages

back to the future the history of acroporid corals at the flower garden banks gulf of mexico usa fossil elkhorn corals acropora palmata were discovered at the flower garden banks fgb on the shelf margin off the texas coast in 2006 radiocarbon dating revealed an a palmata dominated community aged 10 157 6838 cal bp the acropora reefs correspond in time to an interval of warmer than present sea surface temperatures ssts during the holocene thermal maximum htm the subsequent demise of a palmata in the middle holocene was a consequence of the inability of the shallowest reef facies to keep pace with rising sea level following complete submergence of the banks possibly coupled with decreasing ssts following the htm in 2007 the first fossil staghorn corals acropora cervicornis were discovered at the fgb based on radiocar bon dating of these corals to 1027 211 cal bp it appears that populations of a cervicornis flourished in deeper waters 25 32 m depth on the edges of the banks until the peak of the little ice age lia when they died pre sumably from cold water exposure the recent return of a palmata to reefs of the fgb associated with increasing sea temperatures appears to be both an echo of the past and a harbinger of the future 2013 published by elsevier b v

storms modify baroclinic energy fluxes in a seasonally stratified shelf sea inertial tidal interaction observations made near the celtic sea shelf edge are used to investigate the interaction between wind generated near inertial oscillations and the semidiurnal internal tide linear baroclinic energy fluxes within the near inertial f and semidiurnal m2 wave bands are calculated from measurements of velocity and density structure at two moorings located 40 km from the internal tidal generation zone over the 2 week deployment period the semidiurnal tide drove 28 48 w m 1 of energy directly on shelf little spring neap variability could be detected horizontal near inertial energy fluxes were an order of magnitude weaker but nonlinear interaction between the vertical shear of inertial oscillations and the vertical velocity associated with the semidiurnal internal tide led to a 25 43 increase in positive on shelf energy flux the phase relationship between f and m2 determines whether this nonlinear interaction enhances or dampens the linear tidal component of the flux and introduces a 2 day counter clockwise beating to the energy transport two very clear contrasting regimes of a tidally and b inertially driven shear and energy flux are captured in the observations

surface manifestation of internal tides in the deep ocean observations from altimetry and island gauges the sea surface height signatures of internal tides in the deep ocean amounting to a few centimeters or less are studied using two complementary measurement types satellite altimetry and island tide gauges altimetry can detect internal tides that maintain coherence with the astronomical forcing island gauges can monitor temporal variability which in some circumstances is due to internal tides varying in response to changes in the oceanic medium this latter mechanism is at work at hilo and other stations on the northern coasts of the hawaiian islands by detecting spatially coherent low frequency internal tide modulations the tide gauges along with inverted echo sounders at sea suggest that the mean internal tide is also spatially coherent satellite altimetry confirms this at hawaii and in many other places topex poseidon altimetry detects mean surface waves spatially coherent and propagating great distances 1000 km before decaying below background noise when temporal variability is small the altimetry plus information on ocean density sets useful constraints on energy fluxes into internal tides at the hawaiian ridge 15 gw of tidal power is being converted from barotropic to first mode baroclinic motion examples elsewhere warn that a simplistic interpretation of the altimetry without regard to variability noise or in situ information may be highly misleading with such uncertainties extension of the hawaiian results into a usefully realistic estimate of the global internal tide energy balance appears premature at this time

decay of an internal tide due to random topography in the ocean we present a theoretical and numerical study of the decay of an internal wave caused by scattering at undulating sea floor topography with an eye towards building a simple model in which the decay of internal tides in the ocean can be estimated as is well known the interactions of internal waves with irregular boundary shapes lead to a mathematically ill posed problem so care needs to be taken to extract meaningful information from this problem here we restrict the problem to two spatial dimensions and build a numerical tool that combines a real space computation based on the characteristics of the underlying partial differential equation with a spectral computation that satisfies the relevant radiation conditions our tool works for finite amplitude topography but is restricted to subcritical topography slopes detailed results are presented for the decay of the gravest vertical internal wave mode as it encounters finite stretches of either sinusoidal topography or random topography defined as a gaussian random process with a simple power spectrum a number of scaling laws are identified and a simple expression for the decay rate in terms of the power spectrum is given finally the resulting formulae are applied to an idealized model of sea floor topography in the ocean which seems to indicate that this scattering process can provide a rapid decay mechanism for internal tides however the present results are restricted to linear fluid dynamics in two spatial dimensions and to uniform stratification which restricts their direct application to the real ocean

spatial variability of turbulent mixing in the abyssal ocean ocean microstructure data show that turbulent mixing in the deep brazil basin of the south atlantic ocean is weak at all depths above smooth abyssal plains and the south american continental rise the diapycnal diffusivity there was estimated to be less than or approximately equal to 0 1 x 10 4 meters squared per second in contrast mixing rates are large throughout the water column above the rough mid atlantic ridge and the diffusivity deduced for the bottom most 150 meters exceeds 5 x 10 4 meters squared per second such patterns in vertical mixing imply that abyssal circulations have complex spatial structures that are linked to the underlying bathymetry

decadal cyclicity of regional mid holocene precipitation evidence from dominican coral proxies 1 the stable carbon 13c and oxygen 18o isotopic compositions of four holocene specimens of montastraea sp and siderastrea sp coral skeletons from the dominican republic were analyzed to examine decadal scale fluctuations in regional precipitation the specimens range in length from 47 to 197 years individually and range in age from 7 2 to 5 2 kyr oscillations in the 13c and 18o of coral skeletons from the holocene enriquillo valley occur with a seemingly consistent frequency of 15 20 years for one coral 6 ka this decadal to multidecadal mode of variability is statistically significant the decadal to multidecadal mode of stable isotopic variability may represent cyclic fluctuations in mid holocene migration of the intertropical convergence zone itcz or in the hydrogeology of the region as governed by fluctuations in the passage of tropical storms and hurricanes regional temperature is believed to act as only a secondary control on the 18o values of these corals however itcz migration and or oscillations in storm frequency at this site may ultimately reflect decadal scale patterns in greater tropical north atlantic sea surface temperatures the length and resolution of climate variability represented in this study indicate a persistent decadal to multidecadal mode of atlantic climate fluctuation throughout the mid holocene that is indistinguishable from observed historical climate

a fluid inclusion study of the porphyry greisen tungsten molybdenum deposit at mount pleasant new brunswick canada homogenization temperatures and salinity data are presented for fluid inclusions from hydrothermal gangue minerals quartz and fluorite associated with porphyry wolframite molybdenite arsenopyrite sphaleritebismuth chalcopyrite cassiterite mineralization within the fire tower ore zone mt pleasant new brunswick the data indicate that ore mineral precipitation occurred within a temperature range of 260 to 490 c from moderate to high salinity 10 42 wt nacl equivalent aqueous fluids two stages of hydrothermal activity characterized by high 30 wt nacl equivalent salinity fluids are recognized one which occurred at relatively high temperature 350 490 c and one which took place at lower temperature 180 250 c the high salinity high temperature stage is interpreted to be the result of resurgent boiling dilution of these early fluids by convecting meteoric water resulted in low to moderate salinity fluids which dominate the inclusion population the low temperature high salinity fluid inclusions are interpreted to represent late residual fluids derived from boiling which occurred as a result of a change in the pressure regime from dominantly lithostatic to hydrostatic conditions

observations of internal tides off the coast of shandong peninsula china abstract bottom mounted platforms equipped with current profilers meters temperature salinity and turbidity sensors were deployed for about 10 days in august 2017 over an elongated deposit off the coast of shandong peninsula in order to monitor the hydrodynamics and sediment processes in the bottom boundary layer in total semidiurnal barotropic tides dominate the measured currents accounting for 90 of total variance however in the cross shore direction greater variance is associated with the semidiurnal internal tidal currents than the semidiurnal barotropic currents both the empirical orthogonal functions and normal mode analysis demonstrate that the baroclinic velocity is dominated by the mode 1 internal tides i e the current has a vertical shear with strong opposite flows near the surface and bottom while weak in the middle although the bottom slope is subcritical in most area of the deposit the ratio between the bottom slope and the slope of internal tide characteristics is greater than 0 5 suitable for local internal tide generation the internal tides generated from the deposit are especially significant considering that the shelf of the yellow sea is usually broad and flat the quantitative estimation of the water column mixing indicate that the bottom dissipation induced by the barotropic tides 6 44 10 4 m3 s 3 is greater than the internal tides 0 95 10 4 m3 s 3 and the total dissipation rate due to bottom drag is 5 49 10 4 m3 s 3 which is much greater than the interior one due to internal tides 2 69 10 4 m3 s 3 the internal tidal current alone is not energetic enough to resuspend the local fine grained sediments however in the cross shore direction the sediment flux due to internal tides is twice as much as the barotropic component resulting in a net onshore sediment flux thus highlighting the advection effect of internal tides in the coastal mass transport

from tides to mixing along the hawaiian ridge the cascade from tides to turbulence has been hypothesized to serve as a major energy pathway for ocean mixing we investigated this cascade along the hawaiian ridge using observations and numerical models a divergence of internal tidal energy flux observed at the ridge agrees with the predictions of internal tide models large internal tidal waves with peak to peak amplitudes of up to 300 meters occur on the ridge internal wave energy is enhanced and turbulent dissipation in the region near the ridge is 10 times larger than open ocean values given these major elements in the tides to turbulence cascade an energy budget approaches closure

internal tides and ocean mixing recent satellite and in situ observations have shown that at ocean ridges and other seafloor topographic features a substantial amount of energy is transferred from the main ocean tides into internal tides in his perspective garrett explains how these internal waves with tidal periods propagate through the density stratified deep ocean and eventually break down into turbulence the resulting mixing affects ocean stratification and ocean circulation it thus influences climate as well as biological production the energy for the internal tides is derived from the rotational energy of the earth moon system changes of the length of the day and the distance to the moon

the role of internal tides in mixing the deep ocean abstract internal wave theory is used to examine the generation radiation and energy dissipation of internal tides in the deep ocean estimates of vertical energy flux based on a previously developed model are adjusted to account for the influence of finite depth varying stratification and two dimensional topography specific estimates of energy flux are made for midocean ridge topography weakly nonlinear theory is applied to the wave generation at idealized topography to examine finite amplitude corrections to the linear theory most internal tide energy is generated at low modes associated with spatial scales from roughly 20 to 100 km the richardson number of the radiated internal tide typically exceeds unity for these motions and so direct shear instability of the generated waves is not the dominant energy transfer mechanism it also seems that wave wave interactions are ineffective at transferring energy from the large wavelengths that dominate the energy flux instead it appears that most of

tides and the climate some speculations abstract the important role of tides in the mixing of the pelagic oceans has been established by recent experiments and analyses the tide potential is modulated by long period orbital modulations previously loder and garrett found evidence for the 18 6 yr lunar nodal cycle in the sea surface temperatures of shallow seas in this paper the possible role of the 41 000 yr variation of the obliquity of the ecliptic is considered the obliquity modulation of tidal mixing by a few percent and the associated modulation in the meridional overturning circulation moc may play a role comparable to the obliquity modulation of the incoming solar radiation insolation a cornerstone of the milankovic theory of ice ages this speculation involves even more than the usual number of uncertainties found in climate speculations

subaerially exposed holocene coral reef enriquillo valley dominican republic an extremely well preserved holocene fringing coral reef occurs at an average elevation of 5 m below sea level around the margins of the central enriquillo valley dominican republic the reef records the latest marine incursion from the east into an 85 km long 12 km wide tectonic depression and appears to represent a unique preservation excellent cross sections of the reef exposed in erosional gullies reveal a composition and zonation typical of modern caribbean reefs that are found in offshore low energy environments radiocarbon age determinations 2 indicate that reef growth coincided with sea level rise following the last ice age 5 930 100 to 4 760 90 yr b p deltaic deposition and possible vertical movements on active fault scarps dammed the eastern mouth of the valley and created lago enriquillo the level of which was then rapidly lowered by evaporation in an arid climate to produce a saline lake 40 m below sea level stratigraphic studies of rocks along the valley edge and data from drill holes in the basin center indicate that there were earlier post miocene marine incursions similar to that described here

sediment dynamics driven by contour currents and mesoscale eddies along continental slope a case study of the northern south china sea abstract based upon 3 d seismic reflection data published drill core studies oceanographic observations and numerical modelling this study identifies a small scale contourite depositional system that is locally confined by canyons slope failures erosional terraces and erosional slopes on the jianfeng slope northern south china sea 1500 to 2300 m water depth possible oceanic driving mechanisms for the spatial heterogeneity in sedimentation and erosion within the quaternary deposits in this complex slope system are investigated numerical simulations show that the quasi steady south china sea deep water circulation which affects the study area is characterised by low velocities maximum 4 cm s with a slight modulation by tides 1 cm s this quasi steady deep water thermohaline circulation is able to keep sediment particles in suspension rather than to erode seafloor sediment the bottom hydrodynamic regime becomes energetic when mesoscale eddies horizontal scale of 10 to 100 km approach our modelling study indicates that both surface and bottom mesoscale eddies are essential to account for the spatial heterogeneity in sedimentation pattern along the northern south china sea continental slope according to simulation the eddy front contains the highest flow velocity over a mesoscale eddy cycle 45 days exceeding the threshold for resuspension of unconsolidated sediment 15 cm s as a consequence massive resuspension is produced at various sites and redistributed by sub mesoscale horizontal scale of 1 to 10 km circulations originated from an eddy topography interaction in contrast to the surrounding areas which are subject to erosional forcing for a relatively long part 7 of an eddy cycle both the locally confined drift and a further upstream large elongated mounded drift experience little erosion

estimates of m2 tidal energy dissipation from topex poseidon altimeter data most of the tidal energy dissipation in the ocean occurs in shallow seas as has long been recognized however recent work has suggested that a significant fraction of the dissipation perhaps 1 tw or more occurs in the deep ocean this paper builds further evidence for that conclusion more than 6 years of data from the topex poseidon satellite altimeter are used to map the tidal dissipation rate throughout the world ocean the dissipation rate is estimated as a balance between the rate of working by tidal forces and the energy flux divergence computed using currents derived by least squares fitting of the altimeter data and the shallow water equations such calculations require dynamical assumptions in particular about the nature of dissipation to assess sensitivity of dissipation estimates to input assumptions a large suite of tidal inversions based on a wide range of drag parameterizations and employing both real and synthetic altimeter data are compared these experiments and monte carlo error fields from a generalized inverse model are used to establish error uncertainties for the dissipation estimates owing to the tight constraints on tidal elevation fields provided by the altimeter area integrals of the energy balance are remarkably insensitive to required dynamical assumptions tidal energy dissipation is estimated for all major shallow seas excluding individual polar seas and compared with previous model and data based estimates dissipation in the open ocean is significantly enhanced around major bathymetric features in a manner consistent with simple theories for the generation of baroclinic tides

geoarchaeological evidence from peru for a 5000 years b p onset of el nino for the tropical west coast of south america where el nino southern oscillation enso is most pronounced archaeological and associated paleontological deposits in northern peru revealed a major climate change at about 5000 years before the present yr b p the data implied the presence of stable warm tropical water as far south as 10 s during the early mid holocene about 8000 to 5000 yr b p these data suggest that enso did not occur for some millennia preceding 5000 yr b p when global and regional climate was warmer than today

how vulnerable is acropora cervicornis to environmental change lessons from the early to middle holocene the coral acropora cervicornis is considered a modern environmental indicator species vulnerable to anthropogenic stress and rapidly disappearing throughout the caribbean causes for its decline have been attributed to both natural and anthropogenic factors physical and geochemical data are used to explore conditions under which this species thrived in early to middle holocene reef deposits ca 9 4 5 4 ka of the enriquillo valley southwestern dominican republic this study shows that a cervicornis fl ourished during a 4000 yr period spanning the holocene thermal maximum and high resolution radiocarbon dating reveals continuous growth for at least 2000 yr holocene a cervicornis survived large scale climate and environmental changes that included high temperatures variable salinity hurricanes and rapid sea level rise with remarkable resilience our data suggest that the recent decline in a cervicornis is anomalous and likely tied to ecosystem change beyond natural causes

spatial and temporal variations in sediment accumulation and their impacts on coral communities in the sanya coral reef reserve hainan china this study investigated the spatial and temporal variations of sediment accumulation and their impacts on coral communities in four sites at two or three depths 3 m 6 m and 9 m at the sanya coral reef reserve by deploying sediment traps on the sea floor during 2007 2009 rainfall and typhoon events which appeared to control sediment accumulation in the sea floor of the coral reef were positively correlated with total sediment and sand sized i e 63 2000 mu m sediment accumulation sediment accumulation rate significantly decreased with the distance far away from the coast in sanya the mean sediment accumulation rates in ximaozhou luhuitou and xiaodonghai during 2007 to 2009 were close to 20 mg cm 2 d 1 and they were significantly higher than that in yalongwan probably as a result of terrestrial soil erosion caused by strong coast human activities e g coastal construction dredging and hillside clearing correlation analysis revealed that silt clay sized sediment accumulation rate was highly negatively correlated with total live coral cover and coral cover in some taxa such as montipora and branching porites whereas diploastrea heliopora was positively correlated with silt clay sized sediment accumulation correlation analysis also suggested that silt clay sized sediment accumulation had a higher efficiency in predicting the spatial variation of total live coral cover in sanya than did the total sediment accumulation based on this investigation we conclude that high rates of sediment accumulation pose a severe threat to the sanya coral reef reserve highlighting the importance of integrated watershed management practices in the sanya coral reef reserve c 2013 elsevier ltd all rights reserved

buoyancy forcing by turbulence above rough topography in the abyssal brazil basin abstract observations of turbulent dissipation above rough bathymetry in the abyssal brazil basin are presented relative to regions with smooth bathymetry dissipation is markedly enhanced above rough topography of the mid atlantic ridge with levels above bathymetric slopes exceeding levels observed over crests and canyon floors furthermore mixing levels in rough areas are modulated by the spring neap tidal cycle internal waves generated by barotropic tidal flow over topography are the likely mechanism for supplying the energy needed to support the observed turbulent dissipation a model of the spatial and temporal patterns in the turbulent dissipation rate is used to constrain the diapycnal advection in an inverse calculation for the circulation in an area of rough bathymetry this inverse model uses both beta spiral and integrated forms of the advective budgets for heat mass and vorticity and contains sufficient information to resolve the full three dimensional flow the inverse model solution re

the generation of internal tides at the hawaiian ridge previous analyses of altimeter and acoustic data indicate that the hawaiian ridge is a significant generation site for semidiurnal m2 period internal waves owing to tidal flow over topography such waves likely play an important role connecting the dissipation of tidal energy to ocean mixing here a primitive equation numerical model with realistic stratification bathymetry and tidal forcing is used to simulate the generation of these waves in a manner consistent with altimeter sea surface observations the highest amplitude waves originate at three generation sites located at both the island and seamount portions of the chain these sites have in common both enhanced flows across ridge shaped topography and maxima in model calculated body force which couples barotropic and baroclinic motions the model vertical structure suggests the presence of multiple dynamical modes within 100 km of the ridge and not just the lowest modes that have been detected at the sea surface

an introduction to the physical oceanography of six seamounts in the southwest indian ocean exploratory surveys of six seamounts in the southwest indian ocean provide a description of physical processes induced by seamounts along the southwest indian ridge mean currents 15 25 cm s 1 in the vicinity of each seamount were dominated by mesoscale eddies the dominant seamount driven process was the generation of internal tides by the barotropic tide interacting with the seamount crests this led to enhanced shear in the vicinity of the crests resulting in mixing where stratification was weak for example in the core of an anticyclonic mesoscale eddy or where there had been a winter mixed layer tidally driven up and downwelling was observed at the seabed with associated variability in bottom temperature of up to 3 c over a tidal cycle vertical displacement of isopycnals by internal tidal waves reached 200 m peak to trough fluorescence in the surface eutrophic layer could thus extend down to the seamount crest on each tidal cycle apparently spatial variations in short conductivity temperature depth sections across each seamount were probably aliased temporal variations from the strong tidal signal evidence for taylor caps or other potential trapped circulations at the seamount crest was weak most likely because currents associated with mesoscale eddies were too strong to allow their formation

latitudinal distribution of mixing rate caused by the m2 internal tide abstract ten years of ocean topography experiment topex poseidon tidal data and an energy balance relation are used to estimate the mixing rate caused by m2 internal tides in the upper ocean the results indicate that latitudinal distribution of the mixing rate has a generally symmetrical structure with respect to the equator the maxima are distributed around 28 9 n and 28 9 s and can be as high as 3 8 10 5 m2 s 1 in the pacific 5 10 5 m2 s 1 in the atlantic and 3 7 10 5 m2 s 1 in the indian oceans the minimum which is only 10 of those at 28 9 is located near the equator the data imply that midlatitudes are the key regions for internal tide mixing

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

boundary mixing in lakes 2 combined effects of shear and convectively induced turbulence on basin scale mixing a detailed comparison of results from a numerical three dimensional hydrostatic lake model with high resolution observations of the vertical structure of the turbulent bottom boundary layer bbl in a medium size lake lake alpnach switzerland is provided the focus of this study is on the shear induced generation and destruction of stratification in the bbl that may ultimately lead to unstable layers convection the model was shown to provide a reliable description of the internal seiching dynamics as well as the local bbl properties including the generation of shear induced convection in two data sets from 2003 and 2007 basin scale mixing parameters inferred from the simulations are closely connected to the seiching motions with the hypolimnetic mixing reacting almost immediately to the variable wind forcing and seiching activity during upslope flow the bbl becomes convectively turbulent causing low mixing efficiency on a basin scale whereas during downslope flow the bbl is restratifying and shear induced turbulence is weak but leads to a higher mixing efficiency the overall deep water mixing efficiency varied in the range of 5 to 10 in this system dominated by turbulent boundary processes

the maintenance of the subsurface chlorophyll maximum in the stratified western irish sea the diapycnal flux of nitrate from the deep water provides a limit on new production in the subsurface chlorophyll maximum scm during summer in stratified shelf seas here we estimate the diapycnal nitrate flux into the scm in the stratified western irish sea swis sampling took place immediately before neap tides when winds were light so flux estimates reported provide a lower limit to nitrate supply to the scm measurements of turbulent kinetic energy dissipation chlorophyll a and nitrate were used to estimate the flux of nitrate and chlorophyll through the scm turbulent dissipation was low in the scm 10 9 to 10 7 m2 s 3 driving a correspondingly low nitrate flux into the scm 0 31 mmol m 2 d 1 the thermocline was marginally stable throughout sampling and thus the addition of shear would likely result in shear instabilities and mixing we show that although the swis is documented as having an energetic internal tide at this time there was a low level of dissipation within the thermocline we argue that the internal tide sets up background shear which results in marginal stability the addition of extra shear through the passage of nonlinear internal waves and or the wind can trigger instability and mixing we extrapolate our flux estimate over the summer and show that the nitrate flux is insufficient to sustain the documented summer production estimates for the swis this suggests that episodic events are likely to be important for nitrate fluxes or even largely responsible for the nitrate flux that sustains the scm

holocene and deglacial ocean temperature variability in the benguela upwelling region implications for low latitude atmospheric circulation 1 mg ca analyses of g bulloides and abundances of n pachyderma left coiling from ocean drilling program odp leg 175 hole 1084b in the benguela coastal upwelling system document lower sea surface temperatures during the last glacial maximum lgm younger dryas mid holocene and little ice age in the southeastern atlantic taking into consideration the possible effects of differential carbonate dissolution the mg ca data indicate younger dryas temperatures 2 3 c cooler than those of the early holocene and lgm temperatures 4 5 c cooler than those of the early holocene the cool interval during the deglacial period at hole 1084b matches the timing of younger dryas shifts in cariaco basin and greenland ice sheet records and that of a nearby alkenone record comparison of mid holocene cooling at hole odp1084b with other high resolution records of holocene and last deglacial sea surface temperatures from the tropical atlantic implies consistent basin wide changes in atmospheric circulation a brief period of 1 5 2 c cooling between 17 8 and 17 2 ka if related to heinrich event 1 is consistent with a previously hypothesized tropical origin of all heinrich climate change events

orbitally forced sedimentary rhythms in the stratigraphic record is there room for tidal forcing the imprint of orbital cycles which result from the varying eccentricity of the earth s orbit and changes in the orientation of its axis have been recognised throughout the phanerozoic rock record variations in insolation and their effect on climate are generally considered to be the sole transfer mechanism between the orbital variables and cyclic sedimentary successions common oceanographic principles however show that the ocean tide also responds to variations in the orbital parameters the ocean tide has not yet been considered to be a valid additional transfer mechanism for the orbital variations in geological studies of milankovitch cycles in sedimentary successions the insolation paradigm offers satisfying explanations and the role of long term variations of the ocean tide has not yet been appreciated variations in the ocean tide related to changing eccentricity at present 0 0165 theoretical maximum 0 0728 affect a variety of oceanographic and sedimentary processes in addition to the widely accepted paradigm of orbitally forced insolation changes the tidal transfer of orbital signals may explain certain less well understood aspects of orbitally induced cycles in the stratigraphic record related to ocean mixing organic productivity and tidal processes in shallow seas and deep water variations of the ocean tide in relation to the 18 6 year lunar nodal cycle which has no insolation counterpart by which they may be obscured indeed show that these relatively small variations can produce significant effects in sedimentary environments that are sensitive to variations in the strength of the ocean tide in analogy with the 18 6 year lunar nodal cycle orbital variations of the tide on milankovitch time scales are likely to have affected sedimentary systems in the past