Refining patterns of melt with forward stratigraphic models of stable Pleistocene coastlines

The 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

Hydrothermal areas, microbial mats and sea grass in Paleochori Bay, Milos, Greece

The study presents a 1:3300 scale map, encompassing an area of 1.05 km2, depicting the first detailed map of the shallow-water water hydrothermal system in Paleochori Bay, Milos, Greece. The seafloor was mapped using orthophotos acquired by a drone survey and processed using ArcGIS. The map shows the distribution of white microbial mats, former microbial mats, sea grass and ‘normal’ sand down to a depth of 15 m. Generation of a comprehensive map with native shapefiles and layer files, where any GPS coordinate in Paleochori Bay can be obtained, allows to target specific locations for data collection, rather than resorting to vague site descriptions, as has been the practice in the past. Sea floor temperature measurements carried out by Scuba divers in conjunction with GPS coordinates were mapped and interpolated to evaluate the temperature distribution in Paleochori Bay, which in turn supports the overall understanding of the hydrothermal system

Last Interglacial sea-level proxies in the western Mediterranean

We 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)

MEDFLOOD project: MEDiterranean sea-level change and projection for future FLOODing

MEDFLOOD is a four-year interdisciplinary project recently launched by a team of scientists working in fields concerned with Mediterranean sea-level change. The project has the timely and ambitious aim to build a spatially explicit database of relative sea levels for the Mediterranean and to use this resource to model risk and help project future flooding in and around the Mediterranean basin

Detection of a dynamic topography signal in last interglacial sea-level records

Estimating minimum ice volume during the last interglacial based on local sea-level indicators requires that these indicators are corrected for processes that alter local sea level relative to the global average. Although glacial isostatic adjustment is generally accounted for, global scale dynamic changes in topography driven by convective mantle flow are generally not considered. We use numerical models of mantle flow to quantify vertical deflections caused by dynamic topography and compare predictions at passive margins to a globally distributed set of last interglacial sea-level markers. The deflections predicted as a result of dynamic topography are significantly correlated with marker elevations (>95% probability) and are consistent with construction and preservation attributes across marker types. We conclude that a dynamic topography signal is present in the elevation of last interglacial sea-level records and that the signal must be accounted for in any effort to determine peak global mean sea level during the last interglacial to within an accuracy of several meters

Last interglacial sea level along the Patagonian coast

As part of the World Atlas of Last Interglacial Shorelines (WALIS), we critically review existing chronologically constrained last interglacial sea level indicators along the coast of Patagonia in Argentina, South America. Since Charles Darwin's voyages on the Beagle in the 1830s, the staircase-like shoreline platforms along the Patagonian coast have been used as evidence that it has been subject to uplift. Paleo-sea level indicators, ranging between about 7 and 24 m have been attributed to the Last Interglacial on the basis of electron spin resonance and U/Th dating on mollusc shells, and shows remarkable continuity along the entire coast. If the age of these indicators are accurate, then it would indicate that there is a significant uplift rate during the past 120,000 years, since these values exceed the generally accepted peak globally averaged sea level for the last interglacial. However, the Patagonian coast is close enough to the Antarctic and Patagonian ice sheets that there could be a signal from glacial-isostatic adjustment (GIA). This might be an alternative explanation for these higher than average paleo-sea level values. We test the magnitude of the effect of GIA on the coast of Patagonia using a simple ice reconstruction spanning the past two glacial cycles, using a variety of Earth models

Crowdsourcing in the Quaternary sea level community: insights from the Pliocene

In order to establish the ‘fingerprint’ of past sea level changes, many field measurements of paleo sea level from globally distributed locations are needed. It is because this problem requires a geographically expansive database that it becomes an ideal candidate for crowdsourcing techniques. In order to crowdsource sea level data from the Mid-Pliocene Warm Period, we developed three tools: PlioWiki, RSLcalc and RSLmap. PlioWiki is a web portal, open to contributions, where investigators can share knowledge on Pliocene to Quaternary relative sea levels. RSLcalc is a standardized, ready-to-use tool for field geologists to log their own sea level field observations and, if they desire, submit new data to an open access database of relative sea level markers. RSLmap allows one to visualize and query the database built with RSLcalc on a Google Map interface. Here we describe these tools and discuss the advantages of crowdsourcing, relative to traditional approaches, for the creation of sea level databases for any time period

Determining last interglacial ice sheet configuration using glacial isostatic adjustment modelling

The last interglacial (MIS 5e) was a period characterized by sea level that was up to 6-9 m above present day level, due in part to the partial collapse of the Greenland and West Antarctic Ice Sheets. Assessing the pattern of sea level change for this period is complicated due to the uncertainties in the relative contributions of these two ice sheets. In addition, past sea level is the integrated history of water load changes and associated glacial isostatic adjustment before and after the period of interest. We present a the initial results of a global ice sheet reconstruction that seeks to untangle the last interglacial ice sheet configuration. The ice sheets are reconstructed by using the program ICESHEET, which uses ice sheet margin reconstructions and estimates of basal shear stress to produce realistic ice sheet configurations. We calibrate this model by modelling glacial-isostatic adjustment with relative sea level indicators. We also investigate the role of different Earth rheology models on the global pattern of sea level change during this period. We make an assessment of how much uncertainty in the last interglacial sea level is due to the ice sheet configuration during the last glacial cycle

Tides in the Last Interglacial: insights from notch geometry and palaeo tidal models in Bonaire, Netherland Antilles

The study of past sea levels relies largely on the interpretation of sea-level indicators. Palaeo tidal notches are considered as one of the most precise sea-level indicators as their formation is closely tied to the local tidal range. We present geometric measurements of modern and palaeo (Marine Isotope Stage (MIS) 5e) tidal notches on Bonaire (southern Caribbean Sea) and results from two tidal simulations, using the present-day bathymetry and a palaeo-bathymetry. We use these two tools to investigate changes in the tidal range since MIS 5e. Our models show that the tidal range changes most significantly in shallow areas, whereas both, notch geometry and models results, suggest that steeper continental shelves, such as the ones bordering the island of Bonaire, are less affected to changes in tidal range in conditions of MIS 5e sea levels. We use our data and results to discuss the importance of considering changes in tidal range while reconstructing MIS 5e sea level histories, and we remark that it is possible to use hydrodynamic modelling and notch geometry as first-order proxies to assess whether, in a particular area, tidal range might have been different in MIS 5e with respect to today

Structure-from-Motion on shallow reefs and beaches: potential and limitations of consumer-grade drones to reconstruct topography and bathymetry

Reconstructing the topography of shallow underwater environments using Structure-from-Motion—Multi View Stereo (SfM-MVS) techniques applied to aerial imagery from Unmanned Aerial Vehicles (UAVs) is challenging, as it involves nonlinear distortions caused by water refraction. This study presents an experiment with aerial photographs collected with a consumer-grade UAV on the shallow-water reef of Fuvahmulah, the Maldives. Under conditions of rising tide, we surveyed the same portion of the reef in ten successive flights. For each flight, we used SfM-MVS to reconstruct the Digital Elevation Model (DEM) of the reef and used the flight at low tide (where the reef is almost entirely dry) to compare the performance of DEM reconstruction under increasing water levels. Our results show that differences with the reference DEM increase with increasing depth, but are substantially larger if no underwater ground control points are taken into account in the processing. Correcting our imagery with algorithms that account for refraction did not improve the overall accuracy of reconstruction. We conclude that reconstructing shallow-water reefs (less than 1 m depth) with consumer-grade UAVs and SfM-MVS is possible, but its precision is limited and strongly correlated with water depth. In our case, the best results are achieved when ground control points were placed underwater and no refraction correction is used