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Most of the worlds’ population relies on the processes and ecosystems in the coastal zone. Understanding the long-term change of coastlines is critical for the effective management of these complex, and heavily utilised regions. There has been a recent increase of studies focused on large-scale shoreline change mapping. However, most current methods are optimized for extracting shorelines of wave-dominated sandy beaches, which are only 30% of the global coasts, resulting in uncertainty for other environments such as tidal flats and bedrock. Here, we propose a new shoreline change mapping workflow, using the Landsat archive and Google Earth Engine, which increases compute efficiency and is suitable for retrieving shoreline changes for various coastal landforms at high tide instead of mean sea level. By validating against regional and continental datasets in Australia, we found the approach here produced high mapping accuracy and showed particularly better performance at tide-dominated coasts, where tidal flats and intertidal bars and ridges are present, when compared to past approaches. This is an important step forward since tide-dominated and tide-modified coasts are widely distributed at tropical low latitudes. We also explored the global application of the proposed method and derived hotspots of shoreline erosion and accretion that agreed with multiple regional studies across the world. Most of these hotspots were related to river sediment discharge and human intervention on the coast, as expected. Although it requires further validation, the global application of our method demonstrates the significance of this approach in identifying potential threats to coastal zones, especially in complex tide-dominated environments, which can facilitate effective coastal management.

Protection of coastal ecosystems from deforestation may be the best way to protect coral reefs from sediment runoff. However, given the importance of generating economic activities for coastal livelihoods, the prohibition of development is often not feasible. In light of this, logging codes of practice have been developed to mitigate the impacts of logging on downstream ecosystems. However, no studies have assessed whether managed land‐clearing can occur in tandem with coral reef conservation goals. This study quantifies the impacts of current land use and the risk of potential logging activities on downstream coral reef condition and fisheries using a novel suite of linked land‐sea models, using Kolombangara Island in the Solomon Islands as a case study. Further, we examine the ability of erosion reduction strategies stipulated in logging codes of practice to reduce these impacts as clearing extent increases. We found that with present‐day land use, reductions in live and branching coral cover and increases in turf algae were associated with exposure to sediment runoff from catchments and log ponds. Critically, reductions in fish grazer abundance and biomass were associated with increasing sediment runoff, a functional group that accounts for ~25% of subsistence fishing. At low clearing extents, although best management practices minimize the exposure of coral reefs to increased runoff, it would still result in 32% of the reef experiencing an increase in sediment exposure. If clearing extent increased, best management practices would have no impact, with a staggering 89% of coral reef area at risk compared to logging with no management. Synthesis and applications. Assessing trade‐offs between coastal development and protection of marine resources is a challenge for decision makers globally. Although development activities requiring clearing can be important for livelihoods, our results demonstrate that new logging in intact forest risks downstream resources important for both food and livelihood security. Importantly, our approach allows for spatially explicit recommendations for where terrestrial management might best complement marine management. Finally, given the critical degradation feedback loops that increased sediment runoff can reinforce on coral reefs, minimizing sediment runoff could play an important role in helping coral reefs recover from climate‐related disturbances.

This paper describes a novel image processing technique that detects wave breaking and tracks waves in the surf zone using machine learning procedures. Using time-space images (timestacks), the algorithm detects white pixel intensity peaks generated by breaking waves, confirms these peaks as true wave breaking events by learning from the data's true colour representation, clusters individual waves, and obtains optimal wave paths. The method was developed and tested using data from four sandy Australian beaches under different incident wave and light conditions. Results are a representation of the position of the wave front through time, i.e., space-time data, which when shown overlaid on the original timestack shows the high degree of accuracy of the method developed here. The utility of the method is demonstrated in two ways: 1) through a comparison between the instantaneous wave speed calculated from the wave paths with the theoretical shallow water wave speed, and 2) by obtaining optical intensities that could be translated into wave roller lengths. The algorithm developed here has the potential to improve understanding numerous nearshore process such as bore propagation and capture in the surf zone, surf zone energy dissipation, surf beat and infragravity waves, and as a direct speed input for depth inversion methods.

Evaluating shoreline retreat rate on different spatial-temporal scales is critical for effective coastal management. Large-scale evaluations typically rely on data-driven methods such as Discrete Bayesian networks (BNs). However, these BNs require discretization of continuous variables which can lead to information loss. Here, we propose a new method, the Hybrid Bayesian network to incorporate continuous variables without discretization. Both Discrete and Hybrid BNs were developed and compared to evaluate large-scale (continental scale) shoreline retreat rate in Australia, using Digital Earth Australia dataset. These BNs used forcing parameters (e.g. waves, tide, sediment sink/source, and sea level rise) and geomorphic settings (e.g. geomorphology, backshore profile and surfzone slope) to predict shoreline retreat rate. Validation of the BNs showed that Hybrid BNs, which provide a more realistic assessment of the range of shoreline retreat rate, outperform in predicting continuous variables, when compared with Discrete BNs. However, Discrete and Hybrid BNs provide consistent qualitative findings for the shoreline retreat rate of Australia. Among forcing parameters, the sediment sink/source was found to be the most informative variable to indicate the shoreline retreat, followed by tide, sea level rise rate and wave processes. In the scenario of an increased sea level rise rate, tropical tidal flats were predicted as the most at risk coasts in Australia. We found that BNs can reflect the impact of different factors on coastal evolution, and predict future shoreline change by exploring historical data. The performance of these models can be further improved when more datasets become available.

Rubble islands are dynamic sedimentary features present on reef platforms that evolve under a variety of morphodynamic processes and controlling mechanisms. They provide valuable inhabitable land for small island nations, critical habitat for numerous species, and are threatened by climate change. Aiming to investigate the controlling mechanisms dictating the evolution of One Tree Island (OTI), a rubble island in the Southern Great Barrier Reef, we combined different remotely-sensed data across varying timescales with wave data extracted from satellite altimetry and cyclone activity. Our findings show that (1) OTI had expanded by 7% between 1978 and 2019, (2) significant gross planform decadal adjustments were governed by the amount, intensity, proximity, and relative position of cyclones as well as El Niño Southern Oscillation (ENSO) phases, and (3) the mechanisms of island growth involve rubble spits delivering and redistributing rubble to the island through alongshore sediment transport and wave overtopping. Frequent short-term monitoring of the island and further research coupling variations in the different factors driving island change (i.e., sediment availability, reef-wave interactions, and extreme events) are needed to shed light on the future trajectory of OTI and other rubble islands under a climate change scenario.

Aim To investigate some of the environmental variables underpinning the past and present distribution of an ecosystem engineer near its poleward range edge. Location >500 locations spanning >7,400 km around Ireland. Methods We collated past and present distribution records on a known climate change indicator, the reef‐forming worm Sabellaria alveolata (Linnaeus, 1767) in a biogeographic boundary region over 182 years (1836–2018). This included repeat sampling of 60 locations in the cooler 1950s and again in the warmer 2000s and 2010s. Using species distribution modelling, we identified some of the environmental drivers that likely underpin S. alveolata distribution towards the leading edge of its biogeographical range in Ireland. Results Through plotting 981 records of presence and absence, we revealed a discontinuous distribution with discretely bounded sub‐populations, and edges that coincide with the locations of tidal fronts. Repeat surveys of 60 locations across three time periods showed evidence of population increases, declines, local extirpation and recolonization events within the range, but no evidence of extensions beyond the previously identified distribution limits, despite decades of warming. At a regional scale, populations were relatively stable through time, but local populations in the cold Irish Sea appear highly dynamic and vulnerable to local extirpation risk. Contemporary distribution data (2013–2018) computed with modelled environmental data identified specific niche requirements which can explain the many distribution gaps, namely wave height, tidal amplitude, stratification index, then substrate type. Main conclusions In the face of climate warming, such specific niche requirements can create environmental barriers that may prevent species from extending beyond their leading edges. These boundaries may limit a species’ capacity to redistribute in response to global environmental change.

Coral reefs provide critical ecological and geomorphic (e.g. sediment production for reef-fronted shoreline maintenance) services, which interact in complex and dynamic ways. These services are under threat from climate change, requiring dynamic modelling approaches that predict how reef systems will respond to different future climate scenarios. Carbonate budgets, which estimate net reef calcium carbonate production, provide a comprehensive ‘snap-shot’ assessment of reef accretionary potential and reef stability. These budgets, however, were not intended to account for the full suite of processes that maintain coral reef services or to provide predictive capacity on longer timescales (decadal to centennial). To respond to the dual challenges of enhancing carbonate budget assessments and advancing their predictive capacity, we applied a novel model elicitation and review method to create a qualitative geo-ecological carbonate reef system model that links geomorphic, ecological and physical processes. Our approach conceptualizes relationships between net carbonate production, sediment transport and landform stability, and rates knowledge confidence to reveal major knowledge gaps and critical future research pathways. The model provides a blueprint for future coral reef research that aims to quantify net carbonate production and sediment dynamics, improving our capacity to predict responses of reefs and reef-fronted shorelines to future climate change.

Coral reefs are among the most diverse and iconic ecosystems on Earth, but a range of anthropogenic pressures are threatening their persistence. Owing to their remoteness, broad spatial coverage and cross‐jurisdictional locations, there are no high‐resolution remotely sensed maps available at the global scale. Here we present a framework that is capable of mapping coral reef habitats from individual reefs (~200 km²) to entire barrier reef systems (200 000 km²) and across vast ocean extents (>6 000 000 km²). This is the first time this has been demonstrated using a consistent and transparent remote sensing mapping framework. The ten maps that we present achieved good accuracy (78% mean overall accuracy) from multiple input image datasets and training data sources, and our framework was shown to be adaptable to either benthic or geomorphic reef features and across diverse coral reef environments. These new generation high‐resolution map data will be useful for supporting ecosystem risk assessments, detecting change in ecosystem dynamics and targeting efforts to monitor local‐scale changes in coral cover and reef health.

Wave breaking and transformation on coral reef flats is an important process protecting tropical coastlines and regulating the energy regimes of coral reefs. However, the high hydraulic roughness, shallow water, and steep bathymetries of coral reefs may confound common surf zone assumptions, such as a depth-limited and saturated surf zone with a constant wave height to water depth ratio (γ). Here, we examine wave transformation across a coral reef flat, during three separate swell events, on both a time-averaged and a wave-by-wave basis. We use the relationship between significant wave height and water depth (γ) to examine the change in surf saturation across the reef flat and compare the measured wave height decay to results of modelled wave energy dissipation in the surf zone. Our results show that γ was not cross-reef constant and varied according to location on the reef flat and local water depth. On average, γ was greatest at the outer reef flat, near the reef crest, and progressively reduced towards the inner reef flat, near the reef lagoon. This was most pronounced in shallow water with large γ values (γ > 0.85) at the outer reef flat and small γ values (γ < 0.1) at the inner reef flat. This indicates that there is an increase in wave energy dissipation in shallow water, most likely due to increased breaker and bed frictional dissipation. The measured wave energy dissipation across the entire reef flat could, on average, be modelled accurately; however, this required location specific calibration of the free parameters, the wave friction factor (f) and γ, and further suggests that there is no value for either parameter that is universally applicable to coral reef flats. Despite model calibration inaccuracies were still observed, primarily at the outer reef flat. These inaccuracies reflected the observed cross-reef variation of γ on the reef flat and potentially the limitations of random wave breaker dissipation models in complex surf zones. Our results have implications for the use of wave energy dissipation models in predicting breaker dissipation and subsequent benthic community change on coral reef flats, and suggest that careful consideration of the free parameters in such models (such as f and γ) is required.

The characteristics of a reef-top boulder field created by a local submarine landslide tsunami are presented for the first time. Our examination of large reef-derived boulders deposited by the 1953 tsunami near Suva City, Fiji, revealed that shorter-than-normal-period tsunami waves generated by submarine landslides can create a boulder field resembling a storm boulder field due to relatively short boulder transport distances. The boulder-inferred 1953 tsunami flow velocity is estimated at over 9 m s(-1) at the reef edge. Subsequent events, for example Cyclone Kina (1993), appear to have remobilised some large boulders. While prior research has demonstrated headward retreat of Suva Canyon in response to the repeated occurrence of earthquakes over the past few millennia, our results highlight the lingering vulnerability of the Fijian coastlines to high-energy waves generated both in the presence (tsunami) and absence (storm) of submarine failures and/or earthquakes. To explain the age discrepancies of U-Th dated coral comprising the deposited boulders, we introduce a conceptual model showing the role of repeated episodes of tsunamigenic submarine landslides in removing reef front sections through collapse. Subsequent high-energy wave events transport boulders from exposed older sections of the reef front onto the reef where they are deposited as 'new' boulders, alongside freshly detached sections of the living reef. In similar situations where anachronistic deposits complicate the deposition signal, age-dating of the coral boulders should not be used as a proxy for determining the timing of the submarine landslides or the tsunamis that generated them. (C) 2017 Elsevier B.V. All rights reserved.

Colonisation of Sahul 70-60 thousand years ago (kya) represents the first great maritime migration undertaken by anatomically modern humans in one of the final phases of the Out of Africa dispersal. Visual connectivity network analyses, agent-based simulations and ocean current modelling reveal that modern humans could follow numerous northern and southern migration pathways into Sahul. Our results support a southern route out of Africa through South Asia with entry into ISEA through the Banda Arc, culminating in an early colonisation of Sahul on the northwest shelf. Our results show multiple colonisation events through other entry points were also probable, and raise interesting possibilities for complex regional migration and population histories.

Sediment transport is a key driver of reef zonation and biodiversity, where an understanding of sediment dynamics gives insights into past reef processes and allows the prediction of geomorphic responses to changing environmental conditions. However, modal conditions within the back-reef seldom promote sediment transport, hence direct observation is inherently difficult. Large benthic foraminifera (LBF) have previously been employed as ‘tracers’ to infer sediment transport pathways on coral reefs, as their habitat is largely restricted to the algal flat and post-mortem, their calcium carbonate test is susceptible to sediment transport forces into the back-reef. Foraminiferal test abundance and post-depositional test alteration have been used as proxies for sediment transport, although the resolution of these measures becomes limited by low test abundance and the lack of variation within test alteration. Here we propose the novel use of elemental ratios as a proxy for sediment transport. Two species, Baculogypsina sphaerulata and Calcarina capricornia, were analysed using a taphonomic index within One Tree and Lady Musgrave reefs, Great Barrier Reef (Australia). Inductively coupled plasma-atomic emission spectrometry (ICP-AES) was used to determine Mg/Ca and Sr/Ca and these ratios were compared with taphonomic data. Decreases in test Mg/Ca accompany increases in Sr/Ca in specimens from algal-flat to lagoonal samples in both species, mirroring trends indicated by taphonomic values, therefore indicating a relationship with test alteration. To delineate mechanisms driving changes in elemental ratios, back-scattered electron (BSE) images, elemental mapping and in situ quantitative spot analyses by electron microprobe microanalysis (EPMA) using wavelength dispersive X-ray spectrometers (WDS) were performed on un-altered algal flat and heavily abraded tests for both species. EPMA analyses reveal heterogeneity in Mg/Ca between spines and the test wall, implying the loss of appendages results in a decrease in Mg/Ca. BSE imaging and WDS elemental mapping provided evidence for cementation, facilitated by microbial-boring as the primary cause of increasing Sr/Ca. These novel proxies hold advantages over taphonomic measures and further provide a rapid method to infer sediment transport pathways within back-reef environments.

Fellowes, T.E.; Gacutan, J.; Harris, D.L.; Vila-Concejo, A.; Webster, J.M., and Byrne, M., 2017. Patterns of sediment transport using foraminifera tracers across sand aprons on the Great Barrier Reef. Sediment dynamics exert large control over coral reef geomorphological evolution and are vital to understanding past and present geomorphic responses. Large benthic foraminifera (LBF) live in the algal reef flats, and their tests (shells) are transported post-mortem by waves and currents onto back-reef environments, including sand aprons. This study investigated the patterns of transport linking surficial and downcore sediments in samples from three sand aprons with different wave exposures at One Tree Reef on the southern Great Barrier Reef (Australia). Six LBF genera represented up to 32% of the sediments analysed. Lagoonward transport increased LBF test abrasion and sediment bulk density. Sediment grain size and LBF abundance in sediments also decreased with lagoonward transport. Sediment transpo...

Data that can be used to monitor biodiversity through time are essential for conservation and management. The reef-forming worm, Sabellaria alveolata (L. 1767) is currently classed as ‘Data Deficient’ due to an imbalance in the spread of data on its distribution. Little is known about the distribution of this species around Ireland. Using data archaeology, we collated past and present distribution records and discovered that S. alveolata has a discontinuous distribution with large gaps between populations. Many regions lack data and should be targeted for sampling. Biodiversity surveys revealed that S. alveolata supported diverse epibiotic algal communities. Retrograding (declining) reefs supported greater infaunal diversity than prograding (growing) reefs or sand, suggesting that S. alveolata is a dynamic ecosystem engineer that has a lasting legacy effect. Similar research should be carried out for other Data Deficient species, habitats and regions. Such data are invaluable resources for management and conservation.

Measurements of geomorphic change in the intertidal zones of coral reefs are made using a variety of remote sensing and in-situ techniques, where variations in the coverage and spatial-temporal precision achieved are directly related to the cost of data acquisition. We present a novel, low-cost technique for measuring high-resolution changes in reef environments based on Kite Aerial Photography (KAP) and photogrammetry/structure-from-motion post-processing. KAP images are used to measure fine-scale changes in intertidal topography and sediment texture characteristics, including rubble particle size, of a coral shingle cay at One Tree Island, Great Barrier Reef in the context of storm activity. Validation using Real Time Kinematic DGPS demonstrates the ability to measure topographic elevation with an error of 5.53 cm (RMSE) and a spatial resolution of 5 cm per point, an accuracy/resolution that is superior to airborne LiDAR and equivalent to terrestrial LiDAR, but at a fraction of the equipment cost.

Subtropical reefs are important habitats for many marine species and for tourism and recreation. Yet, subtropical reefs are understudied, and detailed habitat maps are seldom available. Citizen science can help fill this gap, while fostering community engagement and education. In this study, 44 trained volunteers conducted an ecological assessment of subtropical Flinders Reef using established Reef Check and CoralWatch protocols. In 2017, 10 sites were monitored to provide comprehensive information on reef communities and to estimate potential local drivers of coral community structure. A detailed habitat map was produced by integrating underwater photos, depth measurements, wave-exposure modelling and satellite imagery. Surveys showed that coral cover ranged from 14% to 67%. Site location and wave exposure explained 47% and 16% respectively, of the variability in coral community composition. Butterflyfishes were the most abundant fish group, with few invertebrates being observed during the surveys. Reef impacts were three times lower than on other nearby subtropical reefs. These findings can be used to provide local information to spatial management and Marine Park planning. To increase the conservation benefits and to maintain the health of Flinders Reef, we recommend expanding the current protection zone from 500- to a 1000-m radius.

Estuarine beaches are ubiquitous, yet understudied, coastal systems. The mixed hydrodynamic processes – such as combined tidal and wave forcing – and the influence of adjacent sedimentary features – such as flood-tide deltas (FTDs) – leads to complex morphodynamic processes. As such, the dynamics and evolution of these important coastal systems are poorly understood. This study synthesises a set of analyses conducted on an estuarine beach, in southeast Australia, over multiple temporal scales. Nearshore waves and currents were measured and used to determine the processes driving seasonal to yearly beach change between 2007 and 2010. These results were compared to decadal scale beach change determined from aerial photos between 1963 and 2006. We found the westward transport of sediment towards the inner estuary was the dominant nearshore process leading to erosion in the eastern regions of the beach (near the estuary entrance) and accretion in the west over yearly time scales. Cross-shore sediment transport occurred during winter storm swell conditions leading to erosion in more exposed sites and some limited accretion in sheltered zones, most likely due to sediment input from the flood-tide delta. However, severe storm swell events that propagated into the estuary led to a loss of sediment and erosion across the entire beach which was not recovered during the study period. It is likely that the erosion processes observed in the short- to medium-term (days to years) analyses are the conditions that led to the long-term shoreline retreat observed in the aerial photograph record. The long-term shoreline retreat since 1963 is likely a result of a negative sediment balance due to movement of the FTD and a lack of sediment input in the eastern regions of Shoal Bay. Shoreline retreat will likely continue unless increased sediment input occurs from marine sources or shoreline interventions are maintained.

A refined description of local wave conditions along the eastern coastline of Queensland is necessary for improved construction of regional models. A nearshore wave climate is constructed to provide boundary conditions for further modelling of wave action in both the open coast of South East Queensland (SEQ) and the sheltered coasts of Central to North Queensland (CNQ). Long term wave data collected from 13 Wave Rider buoys along the inner shelf of the Queensland coast have been analysed to provide representative wave height, period and directional conditions on a seasonal to interannual scale. Interannual to decadal conditions are determined through the distribution of wave energy flux over directional segments, while mean daily wave parameters are investigated over a smaller time scale to determine representative seasonal conditions.

Hearty and Tormey (1) challenge our conclusions (2), incorrectly arguing that the megaboulders we discuss were shown to originate from the cliff bottom. A number of mischaracterizations are made by Hearty and Tormey (1) in their letter. First, we do not use a “tsunami wave model.” Second, we do not address the two other Bahamian landforms Hearty and Tormey (1) mention: their “superstorm” genesis interpretation [for which alternative hypotheses have been proposed (3, 4)] has no bearing on our (2) conclusions. Hearty and Tormey’s (1) claim that the boulders have “fingerprints” based on “several physical criteria” and “data from multiple disciplines” is false. Only two mega-boulder “physical properties” were reported by Hearty … [↵][1]1To whom correspondence should be addressed. Email: arovere{at}marum.de. [1]: #xref-corresp-1-1

The response of platform reefs to sea-level stabilization over the past 6 ka is well established for the Great Barrier Reef (GBR), with reefs typically accreting laterally from windward to leeward. However, these observations are based on few cores spread across reef zones and may not accurately reflect a reef's true accretional response to the Holocene stillstand. We present a new record of reef accretion based on 49 U/Th ages from Heron and One Tree reefs in conjunction with re-analyzed data from 14 reefs across the GBR. We demonstrate that hydrodynamic energy is the main driver of accretional direction; exposed reefs accreted primarily lagoon-ward while protected reefs accreted seawards, contrary to the traditional growth model in the GBR. Lateral accretion rates varied from 86.3 m/ka–42.4 m/ka on the exposed One Tree windward reef and 68.35 m/ka–15.7 m/ka on the protected leeward Heron reef, suggesting that wind/wave energy is not a dominant control on lateral accretion rates. This represents the most comprehensive statement of lateral accretion direction and rates from the mid-outer platform reefs of the GBR, confirming great variability in reef flat growth both within and between reef margins over the last 6 ka, and highlighting the need for closely-spaced transects.

Waves are the main hydrodynamic force acting on coral reefs and are crucial in driving the evolution of reef systems. Previous research has mainly focused on wave breaking and transformation on the reef flat but often neglected the spatial variation of reformed wave characteristics once they have propagated into the back-reef environment. This study examines wave conditions on a reef flat and the adjacent back-reef sand apron specifically focusing on the transformation of wave height, period and spectra (including changes to long-period and incident wave height). The ability of reformed waves in the back-reef environment to entrain sediment is also investigated. Wave conditions were found to be distinctly different on the sand apron compared to the reef flat, with the majority of wave energy dissipated during initial breaking and transformation. Almost all incident waves are dissipated on the reef flat under a depth threshold of 0.5 m before reaching the back-reef with long-period motions dominating in the back-reef during these tidal stages. At higher tidal stages incident waves are capable of propagating into the back reef but they are very low energy with under 1% of all waves capable of entraining sediment. This suggests that higher energy events, such as high frequency storms, are required to significantly transport sediment and change reef geomorphology. Smaller scale spatial changes in wave height were observed on the sand apron that shows the influence of both cross- and along-reef attenuation processes. A distance parameter ( X pd ) is introduced that combines the cross-reef distance from the reef crest ( X d ) and the temporally specific along-reef distance from the first point of wave breaking on the reef rim ( X p , where X pd = X d + X p ). X pd is shown to accurately describe the changes in wave height and sediment entrainment if deep water significant wave height, wave direction, and depth over the reef flat are known. The results in this study shows that wave conditions, sediment entrainment, and longer term trends in sediment characteristics can be predicted in back-reef environments from a few simple geomorphic inputs.

Relative sea-level rise has been a major factor driving the evolution of reef systems during the Holocene. Most models of reef evolution suggest that reefs preferentially grow vertically during rising sea level then laterally from windward to leeward, once the reef flat reaches sea level. Continuous lagoonal sedimentation ("bucket fill") and sand apron progradation eventually lead to reef systems with totally filled lagoons. Lagoonal infilling of One Tree Reef (southern Great Barrier Reef) through sand apron accretion was examined in the context of late Holocene relative sea-level change. This analysis was conducted using sedimentological and digital terrain data supported by 50 radiocarbon ages from fossil microatolls, buried patch reefs, foraminifera and shells in sediment cores, and recalibrated previously published radiocarbon ages. This data set challenges the conceptual model of geologically continuous sediment infill during the Holocene through sand apron accretion. Rapid sand apron accretion occurred between 6000 and 3000 calibrated yr before present B.P. (cal. yr B.P.); followed by only small amounts of sedimentation between 3000 cal. yr B.P. and present, with no significant sand apron accretion in the past 2 k.y. This hiatus in sediment infill coincides with a sea-level fall of ~1-1.3 m during the late Holocene (ca. 2000 cal. yr B.P.), which would have caused the turn-off of highly productive live coral growth on the reef flats currently dominated by less productive rubble and algal flats, resulting in a reduced sediment input to backreef environments and the cessation in sand apron accretion. Given that relative sea-level variations of ~1 m were common throughout the Holocene, we suggest that this mode of sand apron development and carbonate production is applicable to most reef systems.

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.

This paper investigates the mechanics of sediment transport on a subtidal sand apron located on a coral reef environment. In this environment 100% of the sediment is carbonate bioclasts generated in situ. The sand apron is located on the back reef and only affected by waves during high tides. It is commonly accepted in the literature that sand aprons are features that prograde lagoonwards and that most of the progradation occurs during high-energy events. Measurements of water depths, waves, currents and near bed suspended sediment concentrations (all at 10. Hz) on the sand apron were undertaken over a nine day intensive field campaign over both spring and neap tides; waves and tides were also measured in the lagoon. The topography and bathymetry of the sand apron were measured and mixing depth was obtained on three transects using depth of disturbance rods. We found that sediment transport on sand aprons is not solely restricted to high-energy events but occurs on a daily basis during spring tides. The main factor controlling the sediment transport was the water depth above the bed, with depths of 2-2.3. m allowing waves to promote the most sediment transport. This corresponds to a depth over the reef crest of 1.6-1.9. m. The second most important control was waves; transport was observed when H on the apron was 0.1. m or greater. In contrast, current magnitude was not a controlling mechanism for sediment entrainment but did affect sediment transport. The morphology of the sand apron was shown to affect the direction of currents with the currents also expected to influence the morphology of the sand apron. The currents measured during this field campaign were aligned with a shallow channel in the sand apron. Mixing depths were small (< 2.5. cm) yet they were larger than the values predicted by empirical formulae for gentle siliciclastic ocean beaches.

Back-reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems. The development of these features influences the evolution and defines the maturity of coral reefs. However, the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport. Current and wave conditions on a back-reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron, reef flats and lagoon. The current and wave processes that may entrain and transport sediment were assessed using second order small amplitude (Stokes) wave theory and Shields equations. The morphodynamic interactions between current flow and geomorphology were also examined. The results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents. A morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel-like areas directing current off the sand apron towards the lagoon or the reef crest. These results show that the short-term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium.

Carbonate mud from reefs and carbonate platforms in six locations of the Atlantic, Indian, and Pacific Oceans (Belize, Bahamas, Florida, the Maldives, French Polynesia, Great Barrier Reef) was systematically and quantitatively analyzed with regard to texture, composition, mineralogy, and geochemistry. Mud composition shows considerable variability, however, the data supports the contention that these muds are largely derived from the breakdown of skeletal grains and codiacean algae. Only mud from the Bahamas and northern Belize, areas which are characterized by common whitings, is interpreted to be mainly inorganically precipitated. Three grain-size fractions (63–20 μm, 20–4 μm

We propose a novel technique to measure the small-scale three-dimensional features of a shallow-water coral reef using a small drone equipped with a consumer-grade camera, a handheld GPS and structure from motion (SfM) algorithms. We used a GoPro HERO4 with a modified lens mounted on a DJI Phantom 2 drone (maximum total take-off weight

Harris, D.L. and Vila-Concejo, A., 2013. Wave transformation on a coral reef rubble platform Wave transformation across coral reef platforms is the primary process affecting changes in coral reef geomorphology. Transformation regulates the amount of wave energy entering reef systems, however there have been relatively few hydrodynamic assessments conducted on coral reefs when compared to siliciclastic environments with the effects of common geomorphic features like rubble platforms on wave transformation never specifically examined. This study focuses on the changes in wave characteristics across a rubble platform in a high energy environment (One Tree Reef, southern Great Barrier Reef). Wave conditions were measured at five locations over two days along a cross-reef transect from the reef rim to lagoon. Most of the wave energy was dissipated during wave breaking with energy attenuation due to bottom friction a secondary process. Wave energy attenuation was between 60–99% of the offshore wave con...

International audience; The Last Interglacial (MIS 5e, 128-116 ka) is among the most studied past periods in Earth's history. The climate at that time was warmer than today, primarily due to different orbital conditions, with smaller ice sheets and higher sea-level. Field evidence for MIS 5e sea-level was reported from thousands of sites, but often paleo shorelines were measured with low-accuracy techniques and, in some cases, there are contrasting interpretations about paleo sea-level reconstructions. For this reason, large uncertainties still surround both the maximum sea-level attained as well as the pattern of sea-level change throughout MIS 5e. Such uncertainties are exacerbated by the lack of a uniform approach to measuring and interpreting the geological evidence of paleo sea-levels. In this review, we discuss the characteristics of MIS 5e field observations, and we set the basis for a standardized approach to MIS 5e paleo sea-level reconstructions, that is already successfully applied in Holocene sea-level research. Application of the standard definitions and methodologies described in this paper will enhance our ability to compare data from different research groups and different areas, in order to gain deeper insights into MIS 5e sea-level changes. Improving estimates of Last Interglacial sea-level is, in turn, a key to understanding the behavior of ice sheets in a warmer world. (C) 2016 Elsevier B.V. All rights reserved.

The Southern Alps field experiment was designed to identify the dominant rainfall processes in intense orographic events in the South Island of New Zealand and included the deployment of a rain gauge network and meteorological radar. Multiscaling statistics, used to characterize the rainfall from a single extreme event, revealed both orographic and temporal changes in the rainfall nature, with significantly more incessant rainfall observed in the higher-altitude regions, Central to this work was physical interpretation of the statistical parameters, which contributes toward forming links between multiscaling analysis and meteorological processes necessary for practical applications of multiscaling statistics. A further step was taken by combining the statistical results with other meteorological data to infer details of the physical processes, hence providing an example of the utility of multiscaling characterization of rainfall for improving our understanding of physical rainfall processes. Evidence is presented of lateral broadening of precipitating elements as the alpine divide is approached and is used, in conjunction with the wind profile, to explain the quasi-incessant rainfall observed near the divide.

A new method for the statistical description and simulation of two-dimensional rainfall radar images is proposed. It is based on the theory of multiaffine random fields and the bounded lognormal cascade model. The model has three free parameters, which are shown to provide a parsimonious and robust statistical description of rainfall images. The parameters retrieved from the analysis of the real rainfall data by fitting the one- and two-point statistics are used for simulation. The simulated rainfall fields are in good statistical and visual agreement with their real counterparts.

The optimized geometries of the stable ferrous dioxygen and transient reduced ferrous dioxygen forms of a methylmercaptate porphine model of the cytochrome P450 heme system were calculated using nonlocal density functional theoretical (DFT) methods. The optimized geometry of the ferrous dioxygen form is in good agreement with the structure of a model compound of this species and the calculated diamagnetic singlet ground state is consistent with the reported lack of ESR spectrum of this species. The calculated ground state of the reduced ferrous dioxygen species is a low-spin (doublet) state, in agreement with the reported ESR signature of this species in P450cam. The dioxygen ligand in the reduced form is shown to preferentially bind to the heme iron in an asymmetric “end-on” geometry. The most pronounced structural effects of the reduction of the ferrous dioxygen species are the elongation of the Fe−O and Fe−S bonds. This bond lengthening is due to the addition of an electron into a molecular orbital of ...

The theory of self-similar random fields is applied to the statistical description and simulation of rainfall. Fluctuations in rainfields measured by a high resolution weather radar covering a 15 km square are shown to satisfy the condition of self-similarity. The probability density function of the logarithm of the breakdown coefficients (defined as the ratio of two field means, each computed at different resolutions) of the rainfall fluctuation field generally belongs to the class of infinitely divisible distributions. The theoretical framework for scaling self-similar fields is presented and related to results from alternate frameworks, presented in the literature. A simple procedure for the parameterization and modeling of the experimentally measured probability density function is presented. The obtained generator is then used for rainfall simulation by multiplicative cascades. Simulated results exhibit a good statistical and visual agreement with the measured data.

Molecular dynamics simulations have been performed on three phenylimidazole inhibitor complexes of P450cam, utilizing the X-ray structures and the AMBER suite of programs. Compared to their corresponding optimized X-ray structures, very similar features were observed for the 1-phenylimidazole (1-PI) and 2-phenylimidazole (2-PI) complexes during a 100 ps MD simulation. The 1-PI inhibitor binds as a Type II complex with the imidazole nitrogen as a ligand of the heme iron. Analysis of the inhibitor-enzyme interctions during the MD simulations reveals that electrostatic interactions of the imidazole with the heme and van der Waals interactions of the phenyl ring with nearby hydrophobic residues are dominant. By contrast, 2-PI binds as a Type I inhibitor in the substrate binding pocket, but not as a ligand of the iron. The interactions of this inhibitor are qualitatively different from that of the Type II 1-PI, being mainly electrostatic/H-bonding interactions with a bound water and polar residues. Although the third compound, 4-PI, in common with 1-PI, also binds as a Type II inhibitor, with one nitrogen of the imidazole as a ligand to the iron, the MD average binding orientation deviates significantly from the X-ray structure. The most important changes observed include: (1) the rotation of the imidazole ring of this inhibitor by about 90° to enhance electrostatic interactions of the imidazole NH group with the carbonyl group of LEU244, and (2) the rotation of the carbonyl group of ASP251 to form a H-bond with VAL254. An analysis of the H-bonding network surrounding this substrate in the optimized crystal structure revealed that there is no H-bonding partner either for the free polar NH group in the imidazole ring of 4-phenylimidazole or for the polar carbonyl group of the nearby ASP25l residue. The deviation of the dynamically averaged inhibitor-enzyme structure of the 4-PI complex from the optimized crystal structure can therefore be rationalized as a consequence of the optimization of the electrostatic interactions among the polar groups.

Methods for the partial purification of the phosphoprotein phosphatase of the frog egg are described. The enzyme is soluble in distilled water, is heat stable, and is not inactivated by 1 m acetic acid or 0.1 n Na2CO3. The pH optimum (3.0) is unusually low. The enzyme is inhibited competitively by phosphate and molybdate. The enzyme has no activity on the internal pyrophosphates of dinucleotides and similar compounds, on phosphoramidates, or on aliphatic phosphate esters. The enzyme is active on a long series of acyl phosphates: organic and inorganic polyphosphates, both long and short chains and small rings; aromatic phosphates; phosphoenolpyruvate; acetyl phosphate; and carbamyl phosphate. It is less active on phosphoproteins. Evidence is presented which suggests that these activities are all due to one enzyme. The enzyme most closely resembles the phosphoprotein phosphatase of spleen but differs from the latter in several critical respects. The implications of these findings are examined. It is suggested that the enzyme is better classified as a nonspecific phosphoanhydride hydrolase than as a phosphoprotein phosphatase.

Evidence, consisting of analysis of growth requirements and assay of thiamine and precursors accumulated by various strains of Neurospora, strongly suggests that there are two alternative pathways of thiamine biosynthesis in this organism, but that the predominant pathway involves the condensation of pyrimidine with a precursor of thiazole to form a thiamine-like intermediate which is secondarily changed to B1. The reactions are summarized in Eq. (1) (Introduction). These reactions explain the anomalous behavior of those strains which require exogenous pyrimidine and thiazole for growth but synthesize as much of these compounds as does the wild type. The implications of these findings are briefly discussed.

The volume changes of rat liver mitochondria exposed to hypotonic solutions or to solutions of penetrating non-electrolytes were studied by direct estimation of mitochondrial volume from photomicrographs and by changes in optical density of mitochondrial suspensions. The data permit the following conclusions about the osmotic behavior and permeability of these particles. 1. 1. Mitochondria undergo reversible volume changes in anisotonic solutions. 2. 2. Minor secondary changes of undetermined origin also occur. 3. 3. Mitochondria obey osmotic (Boyle-van't Hoff) law. 4. 4. They contain a substantial amount (40–50%) of material which does not participate in volume changes. 5. 5. There appears to be little leakage of osmotically active solute from mitochondria during short exposure to hypotonic solutions. 6. 6. A simple, empirical relation between the optical density of a mitochondrial suspension and mitochondrial volume has been established. 7. 7. Non-electrolytes permeate the mitochondria and thereby induce reversible osmotic volume changes. 8. 8. The rate of penetration is correlated with the olive oil/water partition coefficient of the compound. 9. 9. The permeability constants of the substances studied are quantitatively similar to those found for typical cells. 10. 10. Mitochondria possess a semipermeable membrane which probably contains a high proportion of lipide.

In many cells, a large part of the cytoplasm consists of numerous granules of various types. Undoubtedly they have a real functional significance, but little is yet known of the roles which they may play in cellular processes. This lack of knowledge may be due to the fact that, ordinarily, granules are rather inaccessible to experimental treatment. It was therefore thought worth while to attempt to isolate the granules and study them outside the living cell. This method has the advantage that it enables one to add reagents in known concentrations, and to be certain that they are affecting the granules directly and not secondarily through effects upon the cell itself. Although most granules appear as solid particles, many may actually be minute vacuoles. That this is true of the pigment granules of the Arbacia egg was concluded by Chambers (1935) who found that the pigment escapes when these granules are punctured with a micro-needle. In preliminary studies, I was able to confirm this observation and to provide additional evidence that the pigment granules are actually vacuoles. The most cogent part of this evidence is the fact that in the presence of calcium, magnesium, and strontium ions, the pigment granules (and some colorless granules) coalesce with each other to form large fluid vacuoles from which the pigment soon diffuses, revealing small particles inside in active brownian movement. It is difficult to understand how two particles could coalesce in this manner unless they were vacuoles initially. Photomicrographs of this interesting reaction in isotonic CaC12 are shown in Figure 1. Such minute granules or vacuoles should exhibit osmotic activity. That they do was concluded by Lewis and Lewis (1915) who actually observed swelling and shrinking of mitochondria in tissue culture cells placed in anisotonic media, and by Costello (1939) who found that the formed components of the Arbacia egg occupy 41 per cent of the total volume of the egg, while the osmotically

The inhibition by short-chain fatty acids of several metabolic reactions in yeast and cell-free yeast extracts is demonstrated. Some properties of these inhibitions are shown and their similarity to the binding of short-chain fatty acids to proteins is discussed.

In the nutrition of the young, the role of phosphoproteins is, without doubt, an important one. As casein in milk, or as the yellow yolk of many vertebrate and invertebrate eggs, phosphoprotein occurs in substantial quantities. In the frog egg, for example, the yolk platelets occupy almost half the volume of the cell. According to McClendon (5), the yolk of the frog egg consists of phosphoprotein bound to lipide; thus the platelets are a ready source of protein, lipide, and phosphorus. And yet, in spite of the obvious importance of phosphoprotein, little information is available about the manner of its utilization by the developing embryo. It has been assumed that ordinary proteolytic enzymes degrade the protein, and that ordinary phosphomonoesterases split the phosphate from phosphopeptone or from phosphoserine. In the course of an investigation of the distribution of enzymes in the frog egg, a new enzyme (or enzymes) was discovered which is apparently capable of splitting inorganic phosphate from the intact protein molecule. It is the purpose of this paper to present the experiments which led to this conclusion.

All pyridoxineless mutants of Neurospora crassa and Neurospora sitophila grow better if thiamine is also added to the culture medium. On the basis of the evidence which includes ( a ) an analysis of the growth curves; ( b ) the requirement for thiamine at various concentrations of pyridoxine; ( c ) the interrelation of vitamins B 6 , B 1 , and time; and ( d ) assay of the mycelial content of B 6 and B 1 ; it is concluded that B 1 competitively inhibits the destruction of B 6 . B 6 in turn interferes with thiamine biosynthesis, but sufficient endogenous B 1 is present to satisfy normal metabolic requirements, at least so far as growth is concerned. A specific mechanism is suggested which will be further developed in later publications.

It has been shown that pyridoxine inhibits thiamine biosynthesis. This inhibition is overcome efficiently and noncompetitively by thiamine, competitively by pyrimidine, and inefficiently and noncompetitively by thiazole. In view of these findings, the fact that 4-deoxypyridoxine (a known antimetabolite of pyridoxine) can act in an identical fashion, the great structural similarity of these pyridine compounds to pyrimidine, as well as findings published elsewhere (1–3, 6), it is concluded that pyridoxine competitively prevents pyrimidine utilization, probably by acting as a competitive substrate for the enzyme which couples pyrimidine (or pyridoxine) to thiazole.

1. 1. The dependence of the optical density of a mitochondrial suspension on mitochondrial concentration, osmotic pressure, the refractive index of the medium (Fig. 2), and the wavelength of incident light (Fig. 1) have been examined. 2. 2. Empirical equations which describe the observed relation have been deduced and subjected to empirical verification (e.g. eqn. (8)). 3. 3. The measurements necessary for using these equations for calculating mitochondrial volume from photometric data are described. 4. 4. The simplifications resulting from keeping constant the refractive index of experimental and calibrating solutions are pointed out. 5. 5. The application of photometric techniques to a biological problem, the study of permeability, has been discussed. 6. 6. It is pointed out that a number of changes can occur in mitochondria producing changes in optical density which might be spuriously interpreted as volume changes. Techniques for testing whether an observed optical density change is in fact due to osmotic phenomena are described. 7. 7. A rough theoretical basis for the empirical equations is discussed.