wave transformation and wave driven flow across a steep coral reef observations of waves setup and wave driven mean flows were made on a steep coral forereef and its associated lagoonal system on the north shore of moorea french polynesia despite the steep and complex geometry of the forereef and wave amplitudes that are nearly equal to the mean water depth linear wave theory showed very good agreement with data measurements across the reef illustrate the importance of including both wave transport owing tostokes drift as well as the eulerianmean transportwhen computing the fluxes over the reef finally the observed setup closely follows the theoretical relationship derived from classic radiation stress theory although the two parameters that appear in the model one reflecting wave breaking the other the effective depth over the reef crest must be chosen to match theory to data

numerical modeling of low frequency wave dynamics over a fringing coral reef abstract low frequency infragravity wave dynamics on a fringing coral reef were investigated using the numerical model xbeach roelvink et al 2009 first the skill of the model was evaluated in one and two dimensions based on its predictions of short waves 0 04 0 2 hz infragravity waves 0 004 0 04 hz and water level measurements tidal and wave setup obtained during a 2009 field study at ningaloo reef in western australia the model calibration was sensitive to friction coefficients for short waves and current infragravity bed friction which were assumed independent in this model study although the one dimensional cross shore model captured the gradients in the dominant hydrodynamic processes at the site a high current ig bed friction coefficient was required this resulted in an overestimation and a phase lag between the observed and predicted wave setup signal in the two dimensional model a lower more realistic current infragravity wave friction coefficient was required to achieve optimum performance due to the presence of significant reef and lagoon mean flows in the model which led to reduced setup across the reef the infragravity waves were found to propagate from the surf zone across the reef in a dominantly cross shore direction towards the shore but with substantial frictional damping the infragravity waves were strongly modulated also over the reef by tidal depth variations primarily due to the variability in frictional dissipation rates when the total water depth over the reef varied two mean wave driven circulation cells were observed in the study area with cross shore flow becoming more alongshore dominated before exiting the system via the two channels in the reef the results reveal that short waves dominated bottom stresses on the forereef and near the reef crest however inside the lagoon infragravity waves become increasingly dominant accounting up to 50 of the combined bottom stresses

forcing of resonant modes on a fringing reef during tropical storm man yi 1 open basin resonant modes have been observed at tidal frequencies on coastal shelves but their excitation on coral reef platforms has only been suggested the topography of and water depth over most fringing reefs correspond to resonant periods that are the order of tens of minutes and fall outside of the energetic part of the wave spectrum during tropical storm man yi low frequency near resonant oscillations dominated the variance of the sea surface elevation at the shoreline of ipan reef guam the excitation of the resonant modes resulted both from a large increase in water level over the reef due to wave setup which increased the resonant frequencies and the occurrence of wave group forcing with time scales commensurate with these increased resonant frequencies

swash oscillations on a natural beach run up swash oscillations were measured on a gently sloping beach face for a variety of incident wave conditions run up energy spectra at wind wave frequencies show an 3 dependence and energy levels that are independent of incident wave height this suggests saturation in contrast run up energy at surf beat periods increase approximately linearly with increasing incident wave energy thus in the inner surf zone where wave breaking limits the energy at wind wave frequencies the principal manifestation of large incident wind waves is energetic surf beat

the dynamics of infragravity wave transformation over a fringing reef a 3 week field study was conducted to investigate the dynamics of low frequency infragravity wave motions over a fringing reef at ningaloo reef western australia short period wave motions 0 04 0 2 hz were observed to dissipate on the reef crest beyond which infragravity wave motions 0 004 0 04 hz gradually dominated toward the lagoon however both the short waves and the infragravity waves were relatively small both 0 3 m on the reef flat owing to the shallow water depth 2 m the results revealed that the surf zone generation of free infragravity wave motions on the steep 1 20 fore reef slope was dominated by breakpoint forcing as opposed to shoaling bound waves which was also supported by detailed numerical simulations of the generation process this is consistent with theory suggesting the efficiency of the breakpoint forcing mechanism should be high in this steep slope regime shoreward propagating infragravity waves traveled across the reef but were damped by bottom friction dissipation however this was at a rate much smaller than experienced by the residual short waves with these rates of frictional dissipation also strongly dependent on the water depth over the reef the infragravity wave heights increased at higher water levels and hence were strongly modulated by the tide due to the strong dissipation of infragravity waves over this wide and shallow reef that is hydraulically rough any seaward propagating infragravity waves that reflected at the shoreline were small leading to the dominance of progressive shoreward propagating infragravity wave motions throughout the reef and lagoon

comment on the neoproterozoic 1000 540 ma glacial intervals no more snowball earth by joseph g meert and rob van der voo

high mountain region of the northern romanian carpathians responded sensitively to holocene climate and land use changes a multi proxy analysis a high altitude lake sediment sequence buh iescu mare 1918 m a s l in the subalpine zone of the rodna mountains was analysed through a multi proxy approach to determine the sensitivity of high mountain habitats to climate fire and land use changes the early holocene regional forests were dominated by pinus sylvestris and mugo and replaced by picea abies from 9800 cal yr bp after an extended hiatus in the profile c 9800 4200 cal yr bp probably because of the physical removal of sediments through avalanche or high flow events p abies abies alba and fagus sylvatica forests developed after 4200 cal yr bp the timberline and treeline reacted sensitively to past changes in climate and human impact the site was probably situated above the treeline throughout most of the investigated period however a treeline ecotone or krummholz zone may have sporadically reached the lake s elevation in the early holocene a decline in timberline and treeline elevation was noted during the last 1200 years and more evidently over the past 200 years with replacement by subalpine shrubs alnus viridis and alpine herbaceous communities because these vegetation changes were associated with an increased prevalence of pollen based anthropogenic indicators charcoal particles and abiotic indicators human induced fires and clearance and resultant erosion inputs to the lake are implied effects of current warming on the altitude range of trees are not yet visible probably because land use has more strongly contributed to changes in land cover than the climate fluctuations of the last millennium in the rodna mountains

chronological framework for the lateglacial pollen and macrofossil sequence in the pirin mountains bulgaria lake besbog and lake kremensko 5 the sediments of numerous cirque lakes in the pirin mountains have yielded several generalized pollen diagrams but low stratigraphic and temporal resolution has hampered detailed reconstruction of the vegetational history especially for the lateglacial new pollen and macrofossil analyses of high stratigraphic resolution combined with well controlled timedepth curves for lake besbog and lake kremensko 5 now permit the firm identification of the lateglacial interstadial interval bollingallerod dated at 13 8 12 6 ka cal bp at besbog and 14 1 12 8 ka cal bp at kremensko 5 and correlated with the greenland interstadial gi 1 14 5 12 6 ka cal bp macrofossil analyses indicate that during the bolling allerod period betula and juniperus occurred around the lakes at 2124 2250 m a s l following the younger dryas a betula woodland covered the mountains between 1900 and 2250 m in the early holocene because of higher summer insolation at this time the temperate deciduous forest reached up to 1900 m or 800 m above their present limit producing a regional pollen rain that dominated pollen deposition in the cirque lakes after about 7000 cal yr bp conifer forests replaced the birch woodland at middle and high elevations

observations and predictions of run up for a significant range of offshore wave conditions and foreshore slopes run up observations are compared to semiempirical formulations and predictions of an existing numerical model based on the depth averaged one dimensional nonlinear shallow water equations with bore like breaking wave dissipation and quadratic bottom friction the numerical model is initialized with time series of sea surface elevation and cross shore velocity observed in 80 cm mean water depth approximately 50 m offshore of the mean shoreline on a gently sloping beach and in 175 cm water depth 100 m offshore of the shoreline on a steep concave beach run up was measured with a stack of resistance wires at elevations 5 10 15 20 and 25 cm above and parallel to the beach face at sea swell frequencies nominally 0 05 f 0 18 hz run up energy is limited by surf zone dissipation of shoreward propagating waves so that increasing the offshore wave height above a threshold value does not substantially increase the predicted or observed sea swell run up excursions e g run up is saturated existing semiempirical saturation formulations are most consistent with the observations and numerical model predictions of run up excursions nearest the bed in contrast at infragravity frequencies 0 004 f 0 05 hz where surf zone dissipation is relatively weak and reflection from the beach face is strong e g saturation formulas are not applicable the run up excursions increase approximately linearly with increasing offshore wave height the numerical model also accurately predicts that the tongue like shape of the run up results in sensitivity of run up measurements to wire elevation for instance run up excursions and mean vertical superelevation above the offshore still water level increase with decreasing wire elevation and continuous thinning of the run up tongue during the wave uprush can result in large phase differences between run up excursions measured at different wire elevations numerical model simulations suggest that run up measured more than a few centimeters above the bed cannot be used to infer even the sign of the fluid velocities in the run up tongue

an estimate of average lower mantle conductivity by wavelet analysis of geomagnetic jerks it has recently been proposed that geomagnetic jerks observed at the earth s surface could be viewed as singularities in the time behavior of the geomagnetic field with a regularity of about 1 5 when wavelet analyzed such a signal should have suffered some distortion when diffusing from the core mantle boundary cmb through the conducting mantle assuming that the upper mantle is an insulator and given the electromagnetic time constant of the mantle we compute the distortion that a pure singularity introduced at the cmb suffers as it traverses the mantle we compute this distortion through its effects on the so called ridge functions extracted from the wavelet transform of the signal this distortion is very similar to the small but significant one that we observe in real data we therefore speculate that jerks must have been pure singularities at the base of the mantle and infer an average estimate for the mantle electromagnetic time constant from the way the signal is distorted by fitting the synthetic ridge functions to the experimental ones assuming for example a thickness of 2000 km for a uniform lower conducting mantle we find an electrical conductivity smaller than 10 s m 1 this value is in reasonable agreement with values derived from high pressure experiments for a silicate mantle

two dimensional modelling of wave dynamics and wave forces on fringing coral reefs abstract two dimensional numerical modelling of swell wave dynamics on idealized fringing reefs is performed using swan covering a wide range of bathymetries climate forcing conditions and water depths over the reefs the results illustrate the impact of reef geometry and bathymetry coral species and sea level rise on key hydrodynamic parameters on the reef and on forces on corals the modelling demonstrates that one dimensional models underestimate the wave action on the reef flat wide short reefs and narrow long reefs have similar wave heights at the centre of the reef flat for a given reef length the wave height first decreases with increasing reef width then increases to a local maximum when reef width is approximately equal to the reef length and then decreases for further increases in width this pattern is a result of combined dissipation and refraction processes which combine to lead to different zones of cross reef wave transformation provided that a reef retains its hydrodynamic functions in breaking and refracting the waves sea level rise enhances the wave heights and wave orbital velocities on the reef flat if vertical coral growth does not keep pace with sea level rise loss of the hydrodynamic functions of the reef may occur on deeper reefs and result in a reduction of near bed velocities with sea level rise hydrodynamic forces on corals vary by coral species and slr changes the magnitude of the forces on different species in different ways which may lead to less favourable conditions for certain coral species for long period swell the intermediate size corals are drag dominated and behave similarly to branching corals whereas for short period swell their behavior is similar to that of the inertia dominated massive corals for intermediate corals different responses to slr may therefore be expected for different overall regional wave climates over time this process may contribute to changes in the structural complexity of reefs the influence of sea level rise on the forces on corals on the reef flat is different under swell and cyclonic wind conditions since wind influences wave period in the latter case

observations of wave energy fluxes and swash motions on a low sloping dissipative beach 1 field observations of swash and ocean waves show that runup saturation at infragravity frequencies 0 025 0 035 hz infragravity waves where typically less than 5 of the linear energy flux was reflected from the beach and where similar to the sea swell band the swash energy was independent of offshore wave energy the infragravity frequency range of saturation was determined by the tide with saturation extending to lower frequencies at low tide when the local beach face slope over the concave shaped profile was gentler runup was strongly dominated by infragravity frequencies which accounted on average for 96 of the runup variance and its energy levels were entirely consistent with strong infragravity wave dissipation observed in the surfzone particularly when including the nonlinear contributions to the wave energy fluxes the infragravity wave dissipation was strongly associated with breaking of sea swell waves which abruptly decreased nonlinear transfers to infragravity frequencies and made infragravity dissipation prevail over forcing within the breaking region our observations show evidence of nonlinear interactions involving infragravity and high frequency harmonic waves and suggest that these harmonics could play a role in the wave energy balance near the shoreline on low sloping dissipative beaches

modeling of nonlinear wave propagation over fringing reefs abstract the applicability of existing nonlinear triad spectral models for steep slopes 0 1 0 2 characteristic of reef environments was investigated using both deterministic phase resolving and stochastic phased averaged formulations model performance was tested using laboratory observations of unidirectional wave transformation over steep and smooth bathymetry profiles the models developed for mild slopes were implemented with minimal modifications the inclusion of breaking parametrizations and linear steep slope corrections required by laboratory data the deterministic model produced typically more accurate predictions than the stochastic one but the phase averaged formulation proved fast enough to allow for an inverse modeling search for the optimal breaking parametrization the effects of the additional assumptions of the stochastic approach resulted in a slower than observed evolution of the infragravity band despite the challenge posed by the fast wave evolution and energetic breaking characteristic to the steep reef slopes both formulations performed overall well and should be considered as good provisional candidates for use in numerical investigation of wave current interaction processes on steep reefs

spectral wave dissipation over a barrier reef 1 a 2 week field experiment was conducted to measure surface wave dissipation on a barrier reef at kaneohe bay oahu hawaii wave heights and velocities were measured at several locations on the fore reef and the reef flat which were used to estimate rates of dissipation by wave breaking and bottom friction dissipation on the reef flat was found to be dominated by friction at rates that are significantly larger than those typically observed at sandy beach sites this is attributed to the rough surface generated by the reef organisms which makes the reef highly efficient at dissipating energy by bottom friction results were compared to a spectral wave friction model which showed that the variation in frictional dissipation among the different frequency components could be described using a single hydraulic roughness length scale surveys of the bottom roughness conducted on the reef flat showed that this hydraulic roughness length was comparable to the physical roughness measured at this site on the fore reef dissipation was due to the combined effect of frictional dissipation and wave breaking however in this region the magnitude of dissipation by bottom friction was comparable to wave breaking despite the existence of a well defined surf zone there under typical wave conditions the bulk of the total wave energy incident on kaneohe bay is dissipated by bottom friction not wave breaking as is often assumed for sandy beach sites and other coral reefs

holocene vegetation history in the upper forest belt of the eastern romanian carpathians abstract pollen analysis supported by nine ams 14 c dates from the poiana tiol peat sequence 1540 m in the rodnei mountains eastern romanian carpathians romania is used to reconstruct the holocene vegetation history in this mountain region the results are then compared with other sequences from romania and eastern europe in order to better understand the past dynamics of the main forest constituents the vegetation record at poiana tiol starts at ca 11 000 cal yr bp with the occurrence of rather closed woodlands composed of betula pinus picea abies alnus a viridis and ulmus picea abies was the dominant tree species for almost the entire period however during the last 3000 years p abies forests were largely replaced by pinus in the area temperate tree taxa fraxinus quercus acer tilia and corylus avellana were also common but likely at lower elevation c avellana expanded around 10 300 cal yr bp and reached maximum values after 9000 cal yr bp pollen of carpinus betulus and fagus sylvatica was already recorded around 7000 cal yr bp however the spread of c betulus occurred at ca 6000 cal yr bp with maximum values between 4800 cal yr bp and 3000 cal yr bp while f sylvatica spread from ca 3200 cal yr bp and attained maximum values between 2000 and 200 cal yr bp the first indications of human activities appeared around 3200 cal yr bp and intensified within the last 200 years comparison with other sequences from romania and surrounding countries reveals both similarity and great differences related to the location of glacial refugia climate change and human impact

the climate of europe 6000 years ago palaeoclimates across europe for 6000 y bp were estimated from pollen data using the modern pollen analogue technique constrained with lake level data the constraint consists of restricting the set of modern pollen samples considered as analogues of the fossil samples to those locations where the implied change in annual precipitation minus evapotranspiration p e is consistent with the regional change in moisture balance as indicated by lakes an artificial neural network was used for the spatial interpolation of lake level changes to the pollen sites and for mapping palaeoclimate anomalies the climate variables reconstructed were mean temperature of the coldest month tc growing degree days above 5 c gdd moisture availability expressed as the ratio of actual to equilibrium evapotranspiration and p e the constraint improved the spatial coherency of the reconstructed palaeoclimate anomalies especially for p e the reconstructions indicate clear spatial and seasonal patterns of holocene climate change which can provide a quantitative benchmark for the evaluation of palaeoclimate model simulations winter temperatures tc were 1 3 k greater than present in the far n and ne of europe but 2 4 k less than present in the mediterranean region summer warmth gdd was greater than present in nw europe by 400 800 k day at the highest elevations and in the alps but 400 k day less than present at lower elevations in s europe p e was 50 250 mm less than present in nw europe and the alps but was 10 15 greater than present in s europe and p e was 50 200 mm greater than present in s and e europe

edge wave trapping and amplification on barred beaches theoretical predictions show that edge waves may be trapped on bars providing a possible mechanism for bar growth simple solutions to the linear shallow water equations reveal that bar trapping is controlled by the depth of the water over the bar hbar and the geometry of the inshore trough relative to the bar for specific geometries amplification over the bar approaches an order of magnitude or more as the phase speed approaches where amplification is defined as the surface displacement over the bar relative to the surface displacement at the shoreline the amplification increases with the cross shore length scales of the profiles the amplification is somewhat frequency dependent generating stronger currents at the location of the bar in specific frequency ranges previous work showed that particular edge wave modes have the correct length scales to generate beach features such as bars and beach cusps but field observations notably shoreline run up data frequently show no evidence of edge wave energy being concentrated at the appropriate frequencies however for bar trapped modes edge wave energy is concentrated at the location of the bar therefore this edge wave energy will not necessarily be evident in shoreline measurements strong correlation exists between the energy distribution of the longshore component of the orbital velocity observed in data collected at superduck october 11 1986 and the distribution expected for a white edge wave spectrum at the shoreline this suggests that bar trapped edge waves exist in particular at incident wave frequencies

adcp observations of edge waves off oahu in the wake of the november 2006 kuril islands tsunami received 13 september 2007 revised 5 october 2007 accepted 8 november 2007 published 15 december 2007 1 during the 2006 kuril islands tsunami edge waves propagating along oahu s south shore were observed via depth averaged adcp velocity and pressure data acquired in real time by a coastal observatory at 12 m depth and 400 m offshore time varying rotary component velocity spectra obtained via wavelet analysis agree with the phase lag observed between pressure and each cartesian velocity component in indicating the directions of rotation and travel of progressive edge waves furthermore the theoretical ratios between power in the free surface elevation and in each velocity component of edge waves agree with those observed and a nonlinear shallow water model shows edge waves of various modes propagating along the shore near our observation location importantly the maximum surge in sea level occurred at a time when edge waves of all constituent frequencies were superposed citation bricker j d s munger c pequignet j r wells g pawlak and k f cheung 2007 adcp observations of edge waves off oahu in the wake of the november 2006 kuril islands tsunami geophys res lett 34 l23617 doi 10 1029 2007gl032015

numerical experiments on low frequency fluctuations on a submerged coastal reef abstract low frequency fluctuations on a reef coast are studied through a numerical model based on nonlinear conservation equations of mass and momentum the model is used to investigate the long wave generation and propagation phenomena under both breaking and non breaking incident short wave groups the effects of incident wave characteristics and reef topography on the long wave phenomena are discussed the results show that the long wave elevations on reef coasts are substantial which explains the large water level fluctuations observed at certain occasions

nonhydrostatic and surfbeat model predictions of extreme wave run up in fringing reef environments abstract the accurate prediction of extreme wave run up is important for effective coastal engineering design and coastal hazard management while run up processes on open sandy coasts have been reasonably well studied very few studies have focused on understanding and predicting wave run up at coral reef fronted coastlines this paper applies the short wave resolving nonhydrostatic xb nh and short wave averaged surfbeat xb sb modes of the xbeach numerical model to validate run up using data from two 1d alongshore uniform fringing reef profiles without roughness elements with two objectives i to provide insight into the physical processes governing run up in such environments and ii to evaluate the performance of both modes in accurately predicting run up over a wide range of conditions xbeach was calibrated by optimizing the maximum wave steepness parameter maxbrsteep in xb nh and the dissipation coefficient alpha in xb sb using the first dataset and then applied to the second dataset for validation xb nh and xb sb predictions of extreme wave run up rmax and r2 and its components infragravity and sea swell band swash sig and sss and shoreline setup were compared to observations xb nh more accurately simulated wave transformation but under predicted shoreline setup due to its exclusion of parameterized wave roller dynamics xb sb under predicted sea swell band swash but overestimated shoreline setup due to an over prediction of wave heights on the reef flat run up swash spectra were dominated by infragravity motions allowing the short wave but not wave group averaged model xb sb to perform comparably well to its more complete short wave resolving xb nh counterpart despite their respective limitations both modes were able to accurately predict rmax and r2

constraints on magnetic energy and mantle conductivity from the forced nutations of the earth observations of the earth s nutations are used to explore the possible presence of a conducting layer at the base of the mantle the existence of such a layer is suggested by recent experiments on iron and silicate mixtures at high pressures and temperatures knittle and jeanloz 1986 1989 which indicate that iron may react with silicate minerals to produce metallic compounds nutations provide an ideal tool for investigating the existence of such a layer because they are sensitive to the electrical properties within a thin magnetic boundary layer along the core mantle boundary cmb evidence in favor of a conducting layer is found in the effects of ohmic dissipation which cause the amplitude of the earth s nutation to be out of phase with tidal forcings although out of phase components in the earth s nutations are conventionally attributed to the dissipative influences of ocean tides and mantle anelasticity these effects appear incapable of explaining nutation amplitudes determined from very long baseline interferometry vlbi observations the additional effects of ohmic dissipation enhanced by the presence of a thin conducting layer at the cmb are sufficient to reconcile theory and observation the largest mismatch between observations and theory taking account of ocean tides and mantle anelasticity is a discrepancy of 0 39 0 04 milliarcseconds in the out of phase component of the retrograde annual nutation this discrepancy can be eliminated if the lowermost 200 m of the mantle has a conductivity of 5 105s m 1 and the magnetic energy in the spherical harmonic components of the field at the cmb in degrees l 12 is approximately 4 times greater than the energy inferred in degrees l 12 from surface observations unfortunately the vlbi observations do not uniquely resolve the mantle conductivity and magnetic energy so that trade offs exist between these two parameters nevertheless a high mantle conductivity is favored on the grounds that the alternative involving high levels of magnetic energy yields an excessive amount of ohmic heating other interpretations of the vlbi discrepancy are also discussed one such alternative involves viscous dissipation at the cmb requiring a kinematic viscosity of 0 1m2s 1

wave setup over a pacific island fringing reef 1 measurements obtained across a shore attached fringing reef on the southeast coast of the island of guam are examined to determine the relationship between incident waves and wave driven setup during storm and nonstorm conditions wave setup on the reef flat correlates well r 0 95 and scales near the shore as approximately 35 of the incident root mean square wave height in 8 m water depth waves generated by tropical storm man yi result in a 1 3 m setup during the peak of the storm predictions based on traditional setup theory steady state inviscid cross shore momentum and depth limited wave breaking and an idealized model of localized wave breaking at the fore reef are in agreement with the observations the reef flat setup is used to estimate a similarity parameter at breaking that is in agreement with observations from a steeply sloping sandy beach a weak 10 increase in setup is observed across the reef flat during wave events the inclusion of bottom stress in the cross shore momentum balance may account for a portion of this signal but this assessment is inconclusive as the reef flat currents in some cases are in the wrong direction to account for the increase an independent check of fringing reef setup dynamics is carried out for measurements at the neighboring island of saipan with good agreement

observations of surf beat forcing and dissipation 1 we used a simple energy balance equation and estimates of the cross shore energy flux carried by progressive surf beat to calculate the rate of net surf beat forcing or dissipation on a beach near duck north carolina far inside the surf zone surf beat dissipation exceeded forcing outside the surf zone surf beat forcing exceeded dissipation when incident waves were large surf beat dissipation inside the surf zone and forcing just outside the surf zone were both very strong the surf beat energy dissipated in the surf zone in a single beat period was of the same order as the total amount of surf beat energy stored in the surf zone during storms shoreward propagation of surf beat maintained surf beat energy in the surf zone net surf beat dissipation in the surf zone scaled as predicted by a simple bottom stress parameterization the inferred dissipation factor for surf beat was 0 08 within the range of wave dissipation factors usually observed in the field and 27 80 times larger than drag coefficients appropriate for the mean longshore current the observed rapid forcing rapid dissipation and shoreward propagation of surf beat are not simulated by existing models of surf beat dynamics

late precambrian paradoxical glaciation and obliquity of the earth a discussion of dynamical constraints abstract g e williams observations on late precambrian glaciogenic sequences pose some major challenges to the understanding of the dynamical evolution of the earth s orbit and spin that have not yet been adequately addressed in this paper we investigate whether dissipative core mantle coupling is an effective mechanism for reducing the obliquity by such a large amount as suggested by williams g e williams earth sci rev 112 1993 1 45 and we examine the relationship between the obliquity and spin rate in the presence of such coupling we show that this mechanism not only cannot explain the rapid and substantial decrease in obliquity but also that such a decrease is in contradiction with existing paleorotation evidence for the same period thus confirming the previous findings of neron de surgy and laskar o neron de surgy j laskar astron astrophys 318 1997 975 989

late proterozoic and paleozoic tides retreat of the moon and rotation of the earth the tidal rhythmites in the proterozoic big cottonwood formation utah united states the neoproterozoic elatina formation of the flinders range southern australia and the lower pennsylvanian pottsville formation alabama united states and mansfield formation indiana united states indicate that the rate of retreat of the lunar orbit is dxi dt approximately k2 sin 2delta where xi is the earth moon radius vector k2 is the tidal love number and delta is the tidal lag angle and that this rate has been approximately constant since the late precambrian when the contribution to tidal friction from the sun is taken into account these data imply that the length of the terrestrial day 900 million years ago was approximately18 hours

field study of wave attenuation on an offshore coral reef a major field experiment was conducted which obtained measurements of the attenuation and transformation of short gravity waves as they cross the windward edge of an offshore coral reef water level data were collected for over 3000 individual time series during a wide range of environmental conditions at the innermost measurement site which is located on the horizontal reef flat after the completion of wave breaking the upper bound of significant and maximum wave heights is limited to less than 40 and 60 of the reef flat water depth respectively as with significant wave height both the shape and energy level of the reef flat spectra are strongly affected by changes in reef flat water depth for higher tide levels the spectra on the reef flat closely mimic the corresponding incident spectra however the attenuation is greater for both lower frequencies and higher energy portions of the spectra this causes the reef flat spectra to be broader than those measured windward of the reef at lower water levels considerable energy losses due to wave breaking and bottom friction occur most of the energy loss comes from the vicinity of the spectral peak and energy shifts to harmonics of the peak of the spectrum can be seen

energy transfer between wind waves and low frequency oscillations on a fringing reef ipan guam field observations from a guam fringing reef are used to examine the cross reef energy exchange between high frequency sea and swell ss and low frequency infragravity ig and far infragravity fig waves energetic ss waves significant wave heights 2 4 m break at the outer reef leading to weak 1 m conditions on the shallow reef flat as ss waves shoal on the reef face before breaking ig and fig energy fluxes both increase through nonlinear energy transfer from the ss waves in contrast through the surf zone the ig energy flux decreases whereas fig flux increases the decrease in ig energy flux through the surf zone is attributed to breaking ss waves working against the incident bound ig wave energy which dominates breakpoint forced ig waves yielding a net flux decrease in contrast fig energy flux increases through the surf zone consistent with breakpoint forcing and the absence of an energetic bound fig component on the reef face ig and fig energy fluxes decay on the shallow reef flat due primarily to frictional dissipation with tidal modulations attributed to nonlinear conversion and friction forcing at fig frequencies may lead to a normal mode response on the reef with comparable incoming and outgoing fig energy fluxes at the outer reef flat depending on water level over the reef flat and the degree of frictional dissipation

lateglacial to holocene vegetation development in the central rila mountains bulgaria the vegetation history of the central rila mountains for the last 14 000 years was reconstructed by means of pollen analysis and radiocarbon chronology of a core retrieved from lake manastirsko 2

wave transformation and shoreline water level on funafuti atoll tuvalu the influence of sea swell ss waves infragravity ig waves and wave setup on maximum runup rmax is investigated across different tidal stages on fatato island funafuti atoll tuvalu field results illustrate that ss waves are tidally modulated at the shoreline with comparatively greater wave attenuation and setup occurring at low tide versus high tide a shoreward increase in ig wave height is observed across the 100 m wide reef flat at all tidal elevations with no tidal modulation of ig wave height at the reef flat or island shoreline a 1 d shock capturing green naghdi solver is used to replicate the field deployment and analyze rmax model outputs for ss wave height ig wave height and setup at the shoreline match field results with model skill 0 96 model outputs for rmax are used to identify the temporal window when geomorphic activity can occur on the beach face during periods of moderate swell energy waves can impact the beach face at spring low tide due to a combination of wave setup and strong ig wave activity under mean wave conditions the combined influence of setup ig waves and ss waves results in interaction with island sediment at midtide at high tide ss and ig waves directly impact the beach face overall wave activity is present on the beach face for 71 of the study period a significantly longer duration than is calculated using mean water level and topographic data

water level effects on breaking wave setup for pacific island fringing reefs the effects of water level variations on breaking wave setup over fringing reefs are assessed using field measurements obtained at three study sites in the republic of the marshall islands and the mariana islands in the western tropical pacific ocean at each site reef flat setup varies over the tidal range with weaker setup at high tide and stronger setup at low tide for a given incident wave height the observed water level dependence is interpreted in the context of radiation stress gradients specified by an idealized point break model generalized for nonnormally incident waves the tidally varying setup is due in part to depth limited wave heights on the reef flat as anticipated from previous reef studies but also to tidally dependent breaking on the reef face the tidal dependence of the breaking is interpreted in the context of the point break model in terms of a tidally varying wave height to water depth ratio at breaking implications for predictions of wave driven setup at reef fringed island shorelines are discussed

the offshore boundary condition in surf zone modeling abstract numerical models predicting surfzone waves and shoreline runup in field situations are often initialized with shoreward propagating sea swell and infragravity waves at an offshore boundary in 10 30 m water depth we develop an offshore boundary condition based on fourier analysis of observations with co located current and pressure sensors that accounts for reflection and includes nonlinear phase coupling the performance of additional boundary conditions derived with limited or no infragravity observations are explored with the wave resolving nonlinear model swash 1d in some cases errors in the reduced boundary conditions applied in 11 m depth propagate shoreward whereas in other cases errors are localized near the offshore boundary boundary conditions that can be implemented without infragravity observations e g bound waves do not accurately simulate infragravity waves across the surfzone and could corrupt predictions of morphologic change however the bulk properties of infragravity waves in the inner surfzone and runup are predicted to be largely independent of ig offshore boundary conditions and dominated by ig generation and dissipation

pollen and plant macrofossil analyses of radiocarbon dated mid holocene profiles from two subalpine lakes in the rila mountains bulgaria pollen analysis plant macrofossil determination and radiocarbon dating were performed on profiles of holocene age obtained from two subalpine lakes 2320 2340 m a s l in the central rila mountains bulgaria the palaeovegetational reconstruction dates back to the mid atlantic 6500 6700 cal bp the plant macrofossil record revealed that groups of pinus mugo and juniperus sibirica were distributed in the subalpine zone the treeline was shaped by pinus sylvestris and pinus peuce and was higher up to 2200 2300 m a s l compared with the present day a change to cooler summers and warmer winters after 6700 cal bp characterized by a rise in humidity and precipitation stimulated the formation of a coniferous vegetation belt dominated by pinus sylvestris pinus peuce and abies alba the pollen assemblages also indicated a dominance of deciduous trees quercetum mixtum corylus phase at low altitudes until c 6000 cal bp the sub boreal was characterized by a wider distribution of abies alba in the lower part of the coniferous belt and a gradual enlargement of the areas occupied by fagus sylvatica and picea abies after 3800 3500 cal bp the macrofossil finds of picea abies testify to its expansion after 2800 cal bp when average temperatures dropped and precipitation increased traces of human disturbance in the subalpine area are continuously registered in the pollen and plant macrofossil records since 3770 cal bp indicating livestock grazing burning of dwarf pine pinus mugo for new pasture land and lowering of the treeline

wave run up on a high energy dissipative beach 1 because of highly dissipative conditions and strong alongshore gradients in foreshore beach morphology wave run up data collected along the central oregon coast during february 1996 stand in contrast to run up data currently available in the literature during a single data run lasting approximately 90 min the significant vertical run up elevation varied by a factor of 2 along the 1 6 km study site ranging from 26 to 61 of the offshore significant wave height and was found to be linearly dependent on the local foreshore beach slope that varied by a factor of 5 run up motions on this high energy dissipative beach were dominated by infragravity low frequency energy with peak periods of approximately 230 s incident band energy levels were 2 5 to 3 orders of magnitude lower than the low frequency spectral peaks and typically 96 of the run up variance was in the infragravity band a broad region of the run up spectra exhibited an f 4 roll off typical of saturation extending to frequencies lower than observed in previous studies the run up spectra were dependent on beach slope with spectra for steeper foreshore slopes shifted toward higher frequencies than spectra for shallower foreshore slopes at infragravity frequencies run up motions were coherent over alongshore length scales in excess of 1 km significantly greater than decorrelation length scales on moderate to reflective beaches

precambrian tidal and glacial clastic deposits implications for precambrian earth moon dynamics and palaeoclimate abstract over the past decade the study of precambrian clastic tidal rhythmites stacked laminae of sandstone siltstone and mudstone that display periodic variations in thickness reflecting a strong tidal influence on sedimentation has provided accurate palaeotidal and palaeorotational data palaeotidal records obtained from tidal rhythmites may be systematically abbreviated however and derived periods and frequencies can be misleading the validity of such values including past length of day can be assessed by testing for internal self consistency through application of the laws of celestial mechanics such a test supports the estimated length of day of 21 9 0 4 h derived from the late neoproterozoic 620 ma elatina reynella rhythmites in south australia and the indicated mean rate of lunar retreat of 2 16 0 31 cm year since 620 ma the validity of estimated lengths of day obtained from other precambrian tidal rhythmites remain unverified because the data sets contain only one primary value directly determined from the rhythmites the elatina reynella data militate against significant earth expansion at least since 620 ma and suggest that the free nutation or tipping of the earth s fluid core has undergone a resonance with the earth s annual forced nutation since the neoproterozoic glaciogenic deposits are readily distinguishable from ejecta resulting from impacts with earth crossing bodies palaeomagnetic data based on the geocentric axial dipole model for the geomagnetic field indicate that neoproterozoic and palaeoproterozoic glaciation and cold climate near sea level occurred in low palaeolatitudes this enigmatic finding may imply global glaciation or an increased obliquity of the ecliptic and is relevant to modelling the effect of ice sheet formation on the earth s obliquity history by obliquity oblateness feedback mechanisms through multidisciplinary studies clastic sedimentology and geophysics together can make substantial contributions to understanding precambrian earth moon dynamics and global palaeoenvironments

the temperature of europe during the holocene reconstructed from pollen data we present the first area average time series reconstructions of warmest month coldest month and mean annual surface air temperatures across europe during the last 12 000 years these series are based on quantitative pollen climate reconstructions from over 500 pollen sites assimilated using an innovative four dimensional gridding procedure this approach combines three dimensional spatial gridding with a fourth dimension represented by time allowing data from irregular time series to be focussed onto a regular time step we provide six regional reconstructed temperature time series as well as summary time series for the whole of europe the results suggest major spatial and seasonal differences in holocene temperature trends within a remarkably balanced regional and annual energy budget the traditional mid holocene thermal maximum is observed only over northern europe and principally during the summer this warming was balanced by a mid holocene cooling over southern europe whilst central europe occupied an intermediary position changes in annual mean temperatures for europe as a whole suggest an almost linear increase in thermal budget up to 7800 bp followed by stable conditions for the remainder of the holocene this early holocene warming and later equilibrium has been mainly modulated by increasing winter temperatures in the west which have continued to rise at a progressively decreasing rate up to the present day

observations of runup and energy flux on a low slope beach with high energy long period ocean swell the transformation of surface gravity waves from 11 m depth to runup was observed on the low sloped 1 80 agate beach oregon with a cross shore transect of current meters pressure sensors and a scanning lidar offshore wave heights h0 ranged from calm 0 5 m to energetic 7 m runup measured with pressure sensors and a scanning lidar increases linearly with h0l0 1 2 with l0 the deep water wavelength of the spectral peak runup saturation in which runup oscillations plateau despite further increases in h0l0 1 2 is not observed infragravity wave shoaling and nonlinear energy exchanges with short waves are included in an infragravity wave energy balance this balance closes for high infragravity frequencies 0 025 0 04 hz but not lower frequencies 0 003 0 025 hz possibly owing to unmodeled infragravity energy losses of wave breaking and or bottom friction dissipative processes limit but do not entirely damp increases in runup excursions in response to increased incident wave forcing

glaciation in the rila mountains bulgaria during the last glacial maximum abstract relict glacial landform complexes have been studied in the mountains of the central balkan peninsula since the end of the 19th century since their existence was proved for the first time by cvijic various authors have debated the number of glacial phases as well as their age at present the problem of age determination is being solved by the application of the new methods for numerical dating this paper is a detailed study of the maximum glaciation in the rila massif which is the highest mountain in bulgaria and in the whole balkan peninsula the application of cosmogenic nuclide dating 10be on moraine samples confirmed that the largest extent of former glaciers that left moraine deposits was around the time of the last glacial maximum most probably the maximum extent occurred in two phases the first around the beginning and the second around the end of the lgm 24 23 ka bp and 18 16 ka bp respectively separated by a retreat phase during the coldest but also driest phase of the glacial stage the gis processed calculations on the basis of field evidence of the former glacier extent and the preliminary calculations of the equilibrium line altitude ela through the accumulation ablation ratio aar method show that the ela during the lgm had quite small differences throughout the rila massif from about 2150 to 2200 m a s l in the nw to about 2250 2290 m in the se despite the considerable differences in terminal moraine depositional altitudes from 1150 to 2000 m a s l this is due to both the complicated pattern in the directions of moisture supply and to the influences of local topography

high obliquity simulations for the archean earth implications for climatic conditions on early mars global climate model simulations using high obliquity 70 higher co 2 and ch 4 but reduced o 3 concentrations produce warm climate conditions for archean boundary conditions reduced solar forcing solar radiation under high obliquity is distribution in such a way as to warm high latitudes and cool low latitudes global mean air temperatures of approximately 280 k are found with a 25 reduction in the solar forcing 4760 ppmv co 2 and 25 ppmv ch 4 high obliquity could also explain why polar oceans on mars may have occurred in its history a substantial increase in the amount of insolation is accounted for if mars had an obliquity of 70

numerical modeling of infragravity wave response during delilah 1 the nearshore circulation model shorecirc is applied to simulate the infragravity wave conditions at two intervals during the 1990 delilah campaign at duck n c the model has been extended to solve the energy equation for random short waves on the timescale of the wave groups which acts as a wave driver for the long wave model to simulate the wave conditions an algorithm has been derived which synthesizes a directional offshore wavefield from measured data including the bound directional low frequency components the model data comparison shows that the mean short wave transformation and mean longshore current are predicted well the structure of the infragravity spectrum as measured in the nearshore array is correctly represented albeit that the energy levels are underpredicted in most locations the 2 d frequency longshore wavenumber spectra show that the infragravity wave energy consists mostly of edge waves and that the computations qualitatively resemble the measurements it is shown that for 1 day bar trapped edge waves are present the model is also used to show that the influence of the longshore variability is small for this particular beach and that the directional spreading in the offshore wave field is critical in predicting the nearshore infragravity wave conditions correctly edge waves which propagate against the current are generated by the directionally broad short wave forcing and to a lesser extent by back scattering the nonlinear terms are relatively unimportant for the prediction of the infragravity wave climate the cross shore gradient of the onshore directed radiation stress is the most important of the forcing terms