1,721,151 research outputs found
Hydrothermal areas, microbial mats and sea grass in Paleochori Bay, Milos, Greece
Full text linkWe collected orthophotos of Paleochori Bay, Milos, Greece in 2018 by drone (Orthophotos.zip) and stitched those images together to obtain a high-resolution, georeferenced photographic image (Paleochori_Composite_Photo.tif). This image was used for further processing in ArcGIS to generate a 1:3300 scale map of the seafloor in Paleochori Bay (tjom_a_1748131_sm0990.pdf) with native shapefiles and layer files (Shapefiles.zip), showing the distribution of white microbial mats, former microbial mats, sea grass and “normal” sand down to a depth of 15 m. The georeferenced photographic image allows to obtain GPS coordinates for any point of interest in Paleochori Bay and thus, allows to target specific locations for data collection, rather than resorting to vague site descriptions, as has been the practice in the past. With aid from the georeferenced photo of Paleochori Bay, 150 sea floor temperatures were measurements by Scuba divers (Temperature_measurments.xlsx) to evaluate the temperature distribution in the bay, in order to further the overall understanding of the hydrothermal system
The indicative meaning calculator – quantification of paleo sea-level relationships by using global wave and tide datasets
Full text linkThe study of past sea levels relies largely on the interpretation and quantification of sea-level indicators. These are fossil coastal landforms, bioconstructions or deposits that have a quantifiable relation to paleo sea level (called the indicative meaning) and can be assigned an age of formation. The calculation of the indicative meaning should always rely on the quantitative comparison between the paleo sea-level indicator and the elevational range of the same feature in the modern environment with respect to modern sea level. This may prove difficult to quantify when no site-specific data is available, for example when compiling databases with large geographic scope. In this paper, we provide a method to quantify the indicative meaning of sea-level indicators using simple hydro- and morphodynamic equations with inputs from global wave and tide datasets. We apply and compare our approach exemplary to data published in a relative sea-level database on the Marine Isotope Stage 5e highstand and show how this approach can help in estimating the indicative meaning if no site-specific data on the modern analog is available. For the easier usability of the described approach in this paper, we also present a stand-alone Java-app (IMCalc), which can be used as a calculator of the indicative meaning
Refining patterns of melt with forward stratigraphic models of stable Pleistocene coastlines
Full text linkThe warmest peak of the Last Interglacial (ca. 128–116 ka) is considered a process analogue and is often studied to better understand the effects of a future warmer climate on the Earth's system. In particular, significant efforts have been made to better constrain ice sheet contributions to the peak Last Interglacial sea level through field observation of paleo relative sea level indicators. Along tropical coastal margins, these observations are predominantly based on fossil shallow coral reef sequences, which also provide the possibility of gathering reliable U-series chronological constraints. However, the preservation of many Pleistocene reef sequences is often limited to a series of discrete relative sea level positions within the interglacial, where corals suitable for dating were preserved. This, in turn, limits our ability to understand the continuous evolution of paleo relative sea level through an entire interglacial, also affecting the possibility of unraveling the existence and pattern of sub-stadial sea level oscillations. While the interpretation of lithostratigraphic and geomorphologic properties is often used to overcome this hurdle, geological interpretation may present issues related to subjectivity when dealing with missing facies or incomplete sequences. In this study, we try to step back from a conventional approach, generating a spectrum of synthetic Quaternary subtropical fringing reefs for a site in southwestern Madagascar (Indian Ocean). We use the Dionisos forward stratigraphic model (from Beicip-Franlab) to build a fossil reef at this location. In each model run, we use distinct Greenland and Antarctica ice sheet melt scenarios produced by a coupled ANICE–SELEN glacial isostatic adjustment model. The resulting synthetic reef sequences are then used test these melt scenarios against the stratigraphic record. We propose that this sort of stratigraphic modeling may provide further quantitative control when interpreting Last Interglacial reef sequences
WALIS dashboard: An online tool to explore a global paleo sea-level database
Full text linkIn this paper, we present WALIS Dashboard, an open-access interface to the World Atlas of Last Interglacial Shorelines (WALIS), which was developed and compiled thanks to funding from the European Research Council. WALIS is a database that includes thousands of samples (dated with different radiometric methods) and sea-level indicators formed during the Last Interglacial (~80 to 130 ka). The WALIS Dashboard was coded in R (shiny app), and allows querying a simplified version of WALIS by either geographic extent or by attributes. The user can then download the queried data and perform simple and reproducible data analysis. The WALIS Dashboard can be used both online and offline
Scuba scientific diving and beach monitoring: examples from the Ligurian (NW Mediterranean)
No full textLast Interglacial sea-level proxies in the western Mediterranean
Full text linkWe describe a database of Last Interglacial (Marine Isotopic Stage 5) sea-level proxies for the western Mediterranean region. The database was compiled reviewing the information reported in 199 published studies and contains 396 sea-level data points (sea-level index points and marine- or terrestrial-limiting points) and 401 associated dated samples. The database follows the standardized WALIS template and is available as Cerrone et al. (2021b, 10.5281/zenodo.5341661)
Sea-level oscillations within the last interglacial: Insights from coral reef stratigraphic forward modelling
Full text linkUnderstanding past sea-level variations is essential to constrain future patterns of sea-level rise in response to warmer climate conditions. Due to good preservation and the possibility to use various geochemical methods to date fossil sea-level index points, the Last Interglacial (Marine Isotope Stage, MIS, 5e, 130–116 ka) is often regarded as one of the best climate analogs for a future warmer climate. MIS 5e coastal stratigraphic sequences, such as fossil coral reefs, are characterized by abrupt shifts in their geological facies, steps within the reef topography or backstepped morphologies, which have been often interpreted as proxies for abrupt sea-level fluctuations within the interglacial. However, the observational evidence and magnitude of such abrupt changes are controversial. Here, we run nearly 50 thousand simulations of a 2D kinematic reef model that can reproduce coral reef growth and demise through time. Our aim is to investigate the parameters of space, the sea-level scenarios, and the processes which multiple-stepped MIS 5e fossil reefs form. As inputs to the model, we use both published and synthetic sea-level histories (17 sea-level curves, with different sea-level oscillation patterns), and a wide range of reef growth and marine erosion rates, and bedrock foundation slopes. Our results show that the only sea-level history that could explain the generation of an emerged MIS 5e backstepped reef is a first sea-level peak followed by an abrupt rise in sea level and a second short-term peak. Any other multiple-stepped stratigraphy can be explained by the interplay between reef growth, marine erosion, and bedrock slope
Accuracy of sand beach topography surveying by drones and photogrammetry
Full text linkBeaches are characterized by high morphodynamic activity, and high-frequency measurements are needed to understand their states and rates of change. Ideally, beach survey methods should be at once accurate, rapid and low-cost. Recently, unmanned aerial systems (drones) have been increasingly utilized to measure beach topography. In this paper, we present a review of the state of art in drones and photogrammetry for beach surveys and the respective achieved measurement quality (where reported). We then show how drones with a minimal configuration and a low-cost setup can meet the high accuracy and rapidity required for beach surveys. To test a minimal drone and ground control point configuration, we used consumer-grade equipment to perform the same flight path with different cameras and at different altitudes. We then used photogrammetry to produce digital elevation models of the beach. Using a GNSS-RTK system, we collected 2950 independent control points to evaluate the accuracy of the digital elevation models. Results show that, once a few potential sources of uncertainties in the final digital elevation model are taken into account, the average RMSE(z) of the digital elevation models was ~5 cm, with a survey efficiency of ca. 3 m2 min−1. Digital elevation models taken at different times were used to calculate the before–after sediment budget following a storm that hit a sandy coast in Sylt Island at the German North Sea coast
An updated database of Holocene relative sea level changes in NE Aegean Sea
Full text linkThe reconstruction of Holocene relative sea levels has several implications, ranging from the investigation of coastal vertical movements to the calibration of earth rheology models and ice sheet reconstructions. The North Eastern Aegean Sea is among the tectonically complex sectors of the Eastern Mediterranean, mainly influenced by the activity of the North Anatolian Fault. In this paper, we created a relative sea level (RSL) database by expanding upon the previous compilation with recently published geological and archaeological data. We reconstruct the RSL history in those Aegean coastal sectors located within the South Marmara microplate, a broad shear zone located between western Anatolia and central Greece and affected by dominant strike-slip faulting, at times combined with a normal component. Then, we compared it with the RSL histories obtained for the surrounding coastal sectors. The analysis of the database indicated that it is not possible to define a common Holocene RSL curve for the entire NE Aegean, as RSL history here is majorly influenced by changes in deformation patterns. In addition, data in our database are consistent with a continuous RSL rise in the last 6.0 ka BP in the whole NE Aegean Sea and cannot support the hypothesis of a mid-Holocene RSL highstand in the area. Finally, we present our best estimates of late Holocene rates of RSL prior to any possible acceleration during the twentieth century in the broad area of NE Aegean. Here we identified the fastest rising rate (~0.9 mm a-1) in that sector whose active tectonic deformation is mainly controlled by the North Anatolian Fault activity. © 2013 Elsevier Ltd and INQUA
Fixed biological indicators. In: Handbook of sea-level research (Edited by I. Shennan, A. J. Long, B. P. Horton).
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