sea level change and superstorms geologic evidence from the last interglacial mis 5e in the bahamas and bermuda offers ominous prospects for a warming earth abstract geological observations from last interglacial lig mis 5e eemian carbonate landscapes in the bahamas and bermuda reveal a turbulent climate transition at the close of the peak interglacial the interval is associated with rapid multi meter shifts in sea level as major ice sheets melted and or collapsed sedimentary evidence from the eastern bahamas includes wave transported megaboulders lowland chevron storm ridges and hillside runup deposits this trilogy collectively provides direct geological evidence of frequent intense storms generating sustained long period waves from the northeast atlantic ocean penecontemporaneous with wave deposits is the subtidal production and flux of a massive volume of ooid sediments associated with amplified winds and storminess during the latter half of mis 5e that resulted in exponential island growth steeper temperature and pressure gradients were evident in the north atlantic ocean while the southern ocean appears to have had a major role in affecting atmospheric co2 as warming of the southern ocean drives ventilation of the deep ocean co2 in turn acts as a tight control knob on global climate the dramatic oceanographic and island building events of late mis 5e are unique among other interglacial periods of the past half million years the lig record reveals that strong climate forcing is not required to yield major impacts on the ocean and ice caps antarctic ice cores document that lig atmospheric co2 was 275 ppm while global temperature was in terms of lyellian uniformitarian principles the trilogy of coeval deposits of mis 5e described herein do not translate to our modern climate parameters and further cannot be explained by coincidental megatsunami in our industrial world rapidly increasing atmospheric co2 rates 2 ppm yr have surpassed 408 ppm levels not achieved since the pliocene 3 ma ago while global temperature increased 1 c since the 1870s with greatly increased co2 forcing at unmatched rates except perhaps during global extinction events dramatic change is certain in the interest of our future world we must seek to understand the complex set of linked natural events and field observations that are revealed in the geology of past warmer climates

revision of the late pleistocene stratigraphy of bermuda the quaternary stratigraphy of bermuda is one of the world s most complete sedimentary records of interglacial highstands representing at least the past million years yet in terms of the last interglacial rocky bay formation marine isotope substage mis 5e only scanty deposits are preserved in contrast mis 7 generally regarded as a diminutive interglaciation exposes widespread emergent subtidal deposits of the belmont formation indicating a prolonged sea level highstand at ca 2 5 0 3 m this belmont paradox has prompted a reexamination of the geology of key sites along the south shore of bermuda this revision of the late quaternary stratigraphy of bermuda is based on geological field observations primarily the questionable origin of red soil like deposits it is concluded here that there is no physical evidence of the exposure of the upper belmont surface for a full glacial cycle 70 100 ka and that interbedded reddish soil like lenticular deposits are the result of colluvial activity during mid mis 5e reexamination of previously published uranium series u th ages indicates that several 3 m notches contain a mix of ca 125 ka and older coral ages contrary to previous works this study favors an early mis 5e interpretation of the coral ages from the 2 5 m belmont shoreline which is further supported by amino acid racemization aar ratios on whole rock poecilozonites glycymeris and brachiodontes samples from shore and notch deposits an updated aar kinetic model demonstrates that the bulk of epimerization occurred during warm interglacial intervals between 130 and 80 ka and the last 10 ka of the holocene this revised stratigraphy of bermuda now falls into accordance with a more general view of middle and late pleistocene sea level history

chevron ridges and runup deposits in the bahamas from storms late in oxygen isotope substage 5e abstract landward pointing v shaped sand ridges several kilometers long are common along the windward margin of the bahama islands their axes share a northeast southwest trend internally the ridges contain low angle oolitic beds with few erosional truncations commonly interbedded are tabular fenestrae rich beds such as those formed by the sheet flow of water over dry sand defined here as chevron ridges these landforms appear to have originated in the rapid remobilization of bank margin ooid bodies by the action of long period waves from a northeasterly source deposits along adjacent coastlines also preserve evidence of the impact of large waves reworked eolian sand bodies preserve beach fenestrae and hydraulic scour traces up to 40 m on older ridges on cliffed coasts 1000 ton boulders have been thrown well inland recording the impact of large waves amino acid ratios confirm a correlation of the ridges across the archipelago while stratigraphy spacing and cross cutting relationships indicate emplacement as sea level fell rapidly from the substage 5e maximum at or above 6 m

boulder deposits from large waves during the last interglaciation on north eleuthera island bahamas abstract seven boulders measuring 100 to 1000 m 3 are scattered along the coastal ridge of north eleuthera some are situated on ridge crests up to 20 m above present sea level the boulders were probably deposited during oxygen isotope substage 5e or 5d as shown by their stratigraphic setting and by amino acid racemization ratios d alloisoleucine l isoleucine ratios were determined for land snails and oolite of both marine and eolian origin was associated with the boulders like the boulders the probable source rocks exposed in the adjacent cliffs are composed of marine and eolian limestone of oolitic and peloidal composition the source beds are correlated with stage 9 or 11 the largest boulder is about 10 times the size of the largest holocene ones moved by waves in the area tsunamis are a reasonable possibility as a transporting mechanism of the pleistocene boulders however if deposited instead by storms during the last interglaciation the storms were of much greater intensity than those occurring in the region during the late holocene

cliff top megaclast deposits of ireland a record of extreme waves in the north atlantic storms or tsunamis past occurrences of major tsunami in the global record have often been inferred from the presence of megaclast accumulations at significant heights above sea level which sometimes exhibit a pronounced seaward directed imbricate fabric the aran islands off the west coast of ireland exist in a marine environment which is totally unprotected from the most extreme sea states encountered in the north atlantic spectacular megaclast accumulations are found along the tops of vertical cliffs on these islands the elevation of these deposits varies from 0 m to 50 m above mean sea level and they include clasts weighing 250 tonnes at sea level over 117 tonnes at 12 m and 2 9 tonnes at 50 m above sea level imbrication measurements on these megaclasts indicate a well defined and consistent mean direction from the southwest for the emplacing waves one that is consistent with the prevalent storm wind direction for the area the megaclast accumulations are subject to episodic and on going erosion by cliff retreat but the existing accumulations are estimated to record events since at least 1839 recent emplacement and reworking is evidenced by trapped plastic detritus within the deposits and eyewitness accounts of large storms during which clasts have been emplaced similar deposits are found on the exposed coasts of the shetland and orkney islands off scotland there is at present no evidence of any tsunami in recorded history affecting the western irish and scottish coasts other than those generated by the lisbon earthquake of 1755 where the wave effects were slight thus the presence of megaclast accumulations at significant heights above sea level on exposed coasts and exhibiting imbrication should not be used as a definitive criterion for the past occurrence of tsunami these deposits attest to extreme wave conditions occasionally encountered in the north atlantic and act as a record of such events extending back at least 160 years such data on extreme wave conditions are essential for the prediction of the effects of deepwater waves on structures such as offshore drilling platforms

palaeoclimatic significance of co occurring wind and water induced sedimentary structures in the last interglacial coastal deposits from bermuda and the bahamas abstract the late pleistocene stratigraphic record from the bahamas and bermuda archipelagoes includes peculiar v shaped coastal ridges and wedges of seaward dipping planar beds showing fenestral porosity up to 40 m above present sea level judging from this porosity these landforms were till now interpreted as resulting from the action of giant waves during a period of climatic instability at the end of the last interglacial period the occurrence of widespread mm thick laminae of aeolian origin subcritically climbing translatent stratification throughout these deposits does not agree with this hypothesis it rather suggests that the v shaped ridges and seaward dipping beds represent fossil parabolic and climbing aeolian dunes respectively the occurrence of fenestrae high above the intertidal zone could be related to both wave splashing and rainfall action parabolic dunes are restricted to the nw bahamas they were probably formed during a time interval ca 500 5000 yr when regional climatic conditions were dryer than today and characterized by persistently blowing ne trade winds

discussion of palaeoclimatic significance of co occurring wind and water induced sedimentary structures in the last interglacial coastal deposits from bermuda and the bahamas kindler and strasser 2000 sedimentary geology 131 1 7 kindler and strasser sediment geol 131 2000 1 have identified sedimentary structures of possible aeolian origin within the chevron ridges of north eleuthera thereby proposing that they are migrating parabolic dunes formed by wind rather than the impact of giant waves as postulated by hearty et al quat res 50 1998 309 however the abundance of beach fenestrae and the conspicuous absence of foreset bedding throughout the chevron structures invalidate their conclusions in addition enormous megaboulders situated between the two kindler and strasser 2000 study sites in north eleuthera confirm the occurrence of giant waves at the end of marine isotope substage mis 5e and argue strongly the same genesis for the chevron ridges and runup deposits

irregular fenestrae in bahamian eolianites a rainstorm induced origin abstract fenestrae are primary or penecontemporaneous pores in the sediment framework that are larger than grain supported interstices these features have long been used to characterize peritidal environments and as a sea level indicator in ancient successions we report the occurrence of irregular i e equidimensional fenestrae in pleistocene eolianites on san salvador and eleuthera bahamas as much as 35 m above the coeval sea level a rainstorm induced origin is proposed as the mechanism for production of such voids in eolian deposits we suggest that fenestrae should be used as a sea level indicator only when they are associated with other intertidal or peritidal characteristics

coastal staircase sequences reflecting sea level oscillations and tectonic uplift during the quaternary and neogene many coasts feature sequences of quaternary and neogene shorelines that are shaped by a combination of sea level oscillations and tectonics we compiled a global synthesis of sea level changes for the following highstands mis 1 mis 3 mis 5e and mis 11 also we date the apparent onset of sequences of paleoshorelines either from published data or tentatively extrapolating an age for the uppermost purported oldest shoreline in each sequence including the most documented mis 5e benchmark we identify 926 sequences out of which 185 also feature holocene shorelines six areas are identified where elevations of the mis 3 shorelines are known and 31 feature elevation data for mis 11 shorelines genetic relationships to regional geodynamics are further explored based on the elevations of the mis 5e benchmark mean apparent uplift rates range from 0 01 0 01 mm yr hotspots to 1 47 0 08 mm yr continental collision passive margins appear as ubiquitously uplifting while tectonic segmentation is more important on active margins from the literature and our extrapolations we infer ages for the onset of formation for 180 coastal sequences sea level fingerprinting on coastal sequences started at least during mid miocene and locally as early as eocene whether due to the changes in the bulk volume of seawater or to the temporal variations in the shape of ocean basins estimates of eustasy fail to explain the magnitude of the apparent sea level drop thus vertical ground motion is invoked and we interpret the long lasting development of those paleoshore sequences as the imprint of glacial cycles on globally uplifted margins in response to continental compression the geomorphological expression of the sequences matches the amplitude and frequency of glacial cyclicity from middle pleistocene to present day moderately fast 100 000 yrs oscillating sea levels favor the development of well identified strandlines that are distinct from one another pliocene and lower pleistocene strandlines associated with faster cyclicity 40 000 yrs are more compact and easily merge into rasas whereas older cenozoic low frequency eustatic changes generally led to widespread flat lying coastal plains

late quaternary sea level position evidence from bahamian carbonate deposition and dissolution cycles abstract the bahama islands offer a unique opportunity to examine late quaternary sea level position as the island group places significant constraints on the time and space boundary conditions for climatic events recorded there the bahamian archipelago extends as a series of large and small islands on shallow carbonate banks of various sizes for 1400 km across a climatic gradient wet in the northwest to dry in the southeast the entire island group is tectonically stable and consists solely of quaternary carbonate sediments with interspersed paleosols the islands reflect glacioeustatic sea level highstand positions in their eolian and subtidal suite of limestones a depositional record of platform flooding and carbonate sediment production a coeval record of phreatic cave development in the island s fresh water lenses also documents sea level highstand positions absolute dating of late pleistocene fossil corals and cave stalagmites by u th methods has produced an excellent record of the last interglacial marine isotope substage mis 5e holocene eolianites have been dated by 14 c to reveal platform flooding at 5000 ybp and sea level stabilization at 3000 ybp pleistocene eolianites have been dated by amino acid racemization analysis but subdivisons of the eolianites into separate mis 5a 5c and 5e deposits are controversial paleosols representing integrated aerosol dust deposition of 100 ka long platform exposure events during glaciations have been differentiated by paleomagnetic secular variation measurements previous interpretations of a beach unit to indicate a 20 m mis stage 11 sea level highstand and of large boulders to represent a mega tsunami appear to be incorrect phreatic caves in today s subaerial environment have been ascribed to mis 5e but some may have formed earlier carbonate deposition and dissolution cycles create a mass flux of co 2 sufficient to explain the atmospheric co 2 excursions of the quaternary

giant boulders and last interglacial storm intensity in the north atlantic as global climate warms and sea level rises coastal areas will be subject to more frequent extreme flooding and hurricanes geologic evidence for extreme coastal storms during past warm periods has the potential to provide fundamental insights into their future intensity recent studies argue that during the last interglacial mis 5e 128 116 ka tropical and extratropical north atlantic cyclones may have been more intense than at present and may have produced waves larger than those observed historically such strong swells are inferred to have created a number of geologic features that can be observed today along the coastlines of bermuda and the bahamas in this paper we investigate the most iconic among these features massive boulders atop a cliff in north eleuthera bahamas we combine geologic field surveys wave models and boulder transport equations to test the hypothesis that such boulders must have been emplaced by storms of greater than historical intensity by contrast our results suggest that with the higher relative sea level rsl estimated for the bahamas during mis 5e boulders of this size could have been transported by waves generated by storms of historical intensity thus while the megaboulders of eleuthera cannot be used as geologic proof for past superstorms they do show that with rising sea levels cliffs and coastal barriers will be subject to significantly greater erosional energy even without changes in storm intensity

boulder ridges on the aran islands ireland recent movements caused by storm waves not tsunamis abstractireland s aran islands are an excellent place to test whether coastal boulder deposits including individual rocks weighing several tens of tonnes near sea level and clasts weighing several tonnes transported at tens of meters above sea level require a tsunami for emplacement or whether storm waves can do this work elongate deposits of cobbles boulders and megagravel are strung along the atlantic coasts of the aran islands no tsunamis have affected this region in recent centuries so if these deposits are forming or migrating at the present time they must be storm activated we find a diverse range of evidence for recent ridge activity first shells of hiatella arctica subtidal rock boring bivalves preserved in life position within ridge boulders yield radiocarbon ages from 200 ad to modern post 1950 ad second recent motion is attested to by eyewitness accounts that pin the movement of several individual 40 80 t blocks to a specific 1991 storm and by repeat photography over the last fe

boulder transport by the 2011 great east japan tsunami comprehensive field observations and whither model predictions abstract predicting the local size of a historic high energy event from its boulders using numerical models is a challenging research topic modern high energy events and their deposits are useful to validate these models however validating the accuracy of the results is difficult due to the scarcity of good datasets or the ambiguity of existing field data data on boulders transported by the 2011 great east japan tsunami at coastal sites settai taro and karakuwa on the northeast coast of japan were compiled pre tsunami locations and settings and transport distances were found from evidence such as photographs aerial images and the testimony of survivors the estimated weight of the boulders analyzed ranged from 11 to as much as 167 t while the transport distance varied from a few to up to 600 m modeling results predicted that the minimum limit of maximum flow velocity of the tsunami at the pre tsunami locations of the boulders varied from 4 2 to 6 8 m s the measured maximum flow depths at settai 17 18 m and taro 14 m were within the predicted range of flow depth when the froude number 1 0 1 5 numerical model estimates for an older boulder 285 t in settai indicate that it was probably transported by a historical tsunami 1611 keicho sanriku event which may have been similar to or bigger than that of the 2011 event in the area the maximum flow velocity could not have been less than 6 1 m s and if the boulder was transported to the present location by rolling the flow velocity must have been within 7 5 23 7 m s following systematic validation the numerical modeling of boulder transport is proving promising for reconstructing the local magnitude of historical high energy events further improvements can be made with additional high quality field data from modern high energy events

tracking fin whales in the northeast pacific ocean with a seafloor seismic network ocean bottom seismometer obs networks represent a tool of opportunity to study fin and blue whales a small obs network on the juan de fuca ridge in the northeast pacific ocean in 2 3 km of water recorded an extensive data set of 20 hz fin whale calls an automated method has been developed to identify arrival times based on instantaneous frequency and amplitude and to locate calls using a grid search even in the presence of a few bad arrival times when only one whale is calling near the network tracks can generally be obtained up to distances of 15 km from the network when the calls from multiple whales overlap user supervision is required to identify tracks the absolute and relative amplitudes of arrivals and their three component particle motions provide additional constraints on call location but are not useful for extending the distance to which calls can be located the double difference method inverts for changes in relative call locations using differences in residuals for pairs of nearby calls recorded on a common station the method significantly reduces the unsystematic component of the location error especially when inconsistencies in arrival time observations are minimized by cross correlation

ice volume and sea level during the last interglacial during the last interglacial period 125 000 years ago sea level was at least several meters higher than at present with substantial variability observed for peak sea level at geographically diverse sites speculation that the west antarctic ice sheet collapsed during the last interglacial period has drawn particular interest to understanding climate and ice sheet dynamics during this time interval we provide an internally consistent database of coral u th ages to assess last interglacial sea level observations in the context of isostatic modeling and stratigraphic evidence these data indicate that global eustatic sea level peaked 5 5 to 9 meters above present sea level requiring smaller ice sheets in both greenland and antarctica relative to today and indicating strong sea level sensitivity to small changes in radiative forcing

traditional and multivariate techniques in the interpretation of floodplain sediment grain size variations the vertical and horizontal variation of sedimentary fades is the raw data for the interpretation of flood plain history from which palaeohydrological inferences are frequently drawn mixed and fine floodplain sediments present problems of interpretation because of a large grain size range and frequent polymodality caused by the mixing of process associated grain size components this paper discusses the use of traditional grain size statistics and the use of the mode and multivariate statistics the mode although much neglected is indicative of up profile grain size changes and has practical advantages over the mean for mixed and fine floodplain sediments constrained cluster analysis and principal components analysis are used directly on coulter counter results these techniques can rapidly divide a floodplain profile into grain size units and indicate the principal vectors of grain size variation which will be related to the changing processes of deposition principal components analysis reveals the importance of the medium to fine silt category in accounting for grain size variations suggesting that a critical factor in determining the type of alluvial unit deposited is the degree to which it has received fine suspended material grain size data from the lower severn are used to construct a cm diagram which is compared with a texture triangle from both the cm and multivariate analysis a generalized backswamp profile is constructed which shows the existence of a coarser top unit caused by the addition of a fine to medium sand component to the underlying sediment during the late holocene

the geology of eleuthera island bahamas a rosetta stone of quaternary stratigraphy and sea level history abstract a 5 km stretch of coastline in north eleuthera reveals a long and detailed stratigraphy that includes all known surficial limestone units in the bahamas and supplements the record with several previously unrecognized ones eight paleosol bounded limestone parasequences comprise at least six interglacial periods the lithostratigraphy demonstrates cyclicity at several frequencies 10 5 10 4 20 40 ka and 10 3 years and displays a variety of distal to proximal shoreline facies indicative of shifting depocenters associated with changing sea levels stratigraphy petrology pedology and whole rock aminostratigraphy are used to correlate units and subunits among the 12 described sections amino acid ratios are also converted to absolute age estimates which support the lithostratigraphy the parasequences are correlated with marine oxygen isotope stages 1 to 13 or older evidence of middle pleistocene highstands are abundant in the eleutheran stratigraphy including paleo sea levels of decreasing age at 2 m 7 m 20 m associated with stages 11 and or 9 and two near present highstands during stage 7 a complex sea level history is associated with substage 5e while substage 5a is represented by near shore aggradation of coastal dune complexes in eleuthera and throughout the bahamas concordance of sea level deposits between bermuda and the bahamas reinforce their tectonic stability while the abundance of highstand evidence during the middle pleistocene contradicts suggestions that platform subsidence has obscured all evidence of these events below present sea level the high resolution late quaternary stratigraphy of eleuthera is unrivaled among geologic records from stable carbonate coastlines and thereby offers a rosetta stone for interpretation of the quaternary evolution of the bahamas and sea level history over the past 500 ka

boulder accumulations related to storms on the south coast of the reykjanes peninsula iceland coastal boulder accumulations are often mentioned in the literature even though their interpretation remains difficult especially along rock coasts affected both by storms and tsunamis studies on the geomorphic impact of such high energy events are actually of great interest since their intensity and frequency are key issues for the future evolution of coasts in the framework of the global change the southwest coast of iceland faces the powerful storms of the north atlantic ocean with wave heights of more than 15 m the probability for past and present tsunamis to hit this coast is very low in this paper we describe boulder accumulations along the volcanic rock coast of reykjanes southwest iceland they consist of cliff top boulders clusters and ridges beaches and boulder fields large boulders up to 70 t in weight have been transported and deposited up to 65 m inland 6 masl the maximum limit of boulder deposition and driftwood was found respectively 210 m and 550 m inland storms appear to be a predominant factor in the geomorphic evolution of reykjanes coasts our observations also give new insight for the interpretation of coastal boulder accumulations processes of erosion and deposition by tsunamis are a rising topic in the literature and the effects of recurrent and powerful storms are neglected

chevrons are not mega tsunami deposits a sedimentologic assessment since the introduction of the term chevron for large v or u shaped bed forms in egypt and the bahamas others have adopted the term to describe large scale coastal bed forms in australia madagascar and elsewhere these authors interpret chevron bed forms as deposits of mega tsunamis resulting from holocene oceanic asteroid impacts we reason that chevron type bed forms are common and are present far enough from the coast to preclude tsunami genesis moreover we argue that chevrons are not mega tsunami deposits by modeling tsunami behavior and evaluating sediment transport conditions under which such features formed we model the southern madagascar case with an impact source in the indian ocean and show that a modeled wave approach is inconsistent with chevron orientation we then evaluate sediment transport conditions under which these chevron bed forms could persist i e bed load transport in our analysis no conditions specified generate pure bed load transport and most result in pure suspended load transport

contribution of antarctica to past and future sea level rise polar temperatures over the last several million years have at times been slightly warmer than today yet global mean sea level has been 6 9 metres higher as recently as the last interglacial 130 000 to 115 000 years ago and possibly higher during the pliocene epoch about three million years ago in both cases the antarctic ice sheet has been implicated as the primary contributor hinting at its future vulnerability here we use a model coupling ice sheet and climate dynamics including previously underappreciated processes linking atmospheric warming with hydrofracturing of buttressing ice shelves and structural collapse of marine terminating ice cliffs that is calibrated against pliocene and last interglacial sea level estimates and applied to future greenhouse gas emission scenarios antarctica has the potential to contribute more than a metre of sea level rise by 2100 and more than 15 metres by 2500 if emissions continue unabated in this case atmospheric warming will soon become the dominant driver of ice loss but prolonged ocean warming will delay its recovery for thousands of years