The morphology of a coral reef terrace (CRT) is a key parameter in the interpretation and quantification of past sea-level changes, but it is directly influenced by local morphodynamic and hydrodynamic conditions. Spatial differences in terrace morphology may therefore result in over- or underestimation of paleorelative sea levels and their associated uncertainties. To investigate this, we integrate high-precision field surveys from the island of Aruba (Leeward Antilles, Caribbean Sea) with a stratigraphic forward model (DionisosFlow (R)) to quantify the intra-island variability of the Quaternary coral reef sequence. We establish that a possible slight North-South tectonic tilt of the island may drive differences in the elevation of CRTs and the number of emerged fossil coral reefs imprinted on the coastal landscape. However, terrace geometry is primarily defined by the basement slope and wave exposure. All together, our results show that even small-scale environmental and hydrodynamic variability can introduce meter-scale errors in sea-level reconstructions derived from CRTs.

The Last Interglacial (∼125,000 years ago) experienced global temperatures warmer than today, making it a natural analog for future climate scenarios. Contemporary coral reefs preserve ecological signals that offer valuable insights into past climate dynamics. Here, we examine the fossil reefs of Aruba, Bonaire, and Curaçao to reconstruct wind and wave conditions during this period. While modern reefs across all three islands are confined predominantly to leeward coasts, paleo reefs flourished on both windward and leeward coasts during the Last Interglacial—raising questions as to what mechanisms underlie the spatial asymmetry in reef development through time. Using quantitative analyses of hard coral cover and changes in coral community composition across the Last Interglacial, we document a transition from a well-developed reef dominated by large colonies of Orbicella spp. and Acropora palmata to a less structurally complex system characterized by smaller Orbicella spp. and Diploria spp. colonies, mirroring a ∼20% reduction in hard coral cover by the end of the Last Interglacial. Despite this decline, coral cover remained substantial and did not resemble the Sargassum-dominated nearshore environment observed today. Atmospheric circulation and hydrodynamic models indicate that substantially weaker easterly trade winds and reduced significant wave height at 127 ka initiated robust reef development, which still persisted despite a dramatic increase in wave energy at 124 ka. By highlighting how variations in wave and wind regimes have shaped coral reef growth and resilience in the past, these findings underscore the value of integrating paleoecology and hydrodynamics to advance our understanding of reef stability under future climate change.

Coral reefs have experienced widespread and accelerated decline, driven by a combination of global and local anthropogenic stressors. To contextualize these changes, we compared the composition of coral reef communities on Curaçao between 1973 and 2023 with that of corals preserved in fossil reefs from the Last Interglacial period (128–116 ka). These fossil reefs, exposed along the island’s leeward coast, provide a multi-millennial baseline of ecological variability. Here we show that the ecological transformation observed on modern reefs over the past five decades is unmatched when compared to the relatively stable community structure maintained for more than 12,000 years during the Last Interglacial. We propose that the global, rapid, and well-documented collapse of tropical coral reef ecosystems since the mid-20th century represents a stratigraphically relevant signal of anthropogenic change. We surmise that a well-characterized reef site—such as Curaçao—could, in principle, serve as the Global Boundary Stratotype Section and Point (GSSP) marking the onset of the Anthropocene.

The Last Interglacial (125 ka) was the most recent period in Earth’s history when global temperatures were approximately 1°C higher than pre-industrial levels, with polar regions experiencing a warming of 3–5°C. This warmer climate led to smaller ice sheets, higher sea levels, and significant shifts in atmospheric and oceanic patterns, including changes in temperature and seasonality. Such changes likely influenced coastal dynamics, altering prevailing winds, wave regimes, and coastal ecosystems like coral reefs. These transformations are preserved in the geological record, providing valuable insights into the potential future of our coasts in a warming world. Proper interpretation of these records can offer invaluable insights for policymakers and stakeholders seeking to address the challenges of coastal adaptation to modern climate change.This presentation is a contribution to the WARMCOASTS project, which has received funding from the European Research Council under the European Union's Horizon 2020 research and innovation programme (grant agreement n. 802414) and to the project “Frozen in time: ecology of paleo reefs”, funded by the Deutsche Forschungsgemeinschaft (DFG) - Project number 4685895

Extreme marine events determine different landform imprints, such as out-of-size deposits like coastal boulders with several tons in weight. These extreme marine events are usually connected to storms and tsunamis. Storms and tsunamis are characterized by a high-energy content, which is reflected in wave flow and wave height able to move the boulders. Several coastal boulders have been detected in Aruba, Bonaire, and Curacao (ABC) islands, overlying the marine terrace deposits that surround the seaward side of these islands. In this work, morpho-topographical surveys were performed on these coastal boulders in order to simulate the most probable events that caused their displacements. Unmanned Aerial Vehicle and close-range photogrammetry were used to reconstruct the volume and shape of boulders with their immersive scenario. Volume and shape of coastal boulders have been used to estimate the energy content able to determine their displacement. Furthermore, boulder samples were collected in order to assess their density and to obtain chronological constraints of the extreme marine events by applying U/Th and radiocarbon dating. Numerical models in Delft3D were applied to simulate the scenarios that could be responsible for the boulder movements. The results showed that the biggest boulders are located on Bonaire Island, located in the eastern part of the ABC archipelago, and were influenced by higher energy content than the Aruba and Curacao islands. This energy content could be related to three possible scenarios simulated in Delft3D: 1) a tsunami scenario connected to Venezuela earthquakes, 2) a Hurricane scenario impacting from the western side of the ABC archipelago, 3) a combination of multiple events (tsunami and storms) that caused differential boulders movement in the past.

Large coastal boulders are ubiquitous geomorphological features that are emplaced along coasts by extreme marine events such as storms, hurricanes, and tsunamis. Many large coastal boulders have been identified on emergent fossil coral reefs on the windward sides of the Aruba, Bonaire, and Cura & ccedil;ao (ABC) islands in the Leeward Antilles of the Caribbean. Here, structure-from-motion/multi-view stereo techniques were used to map boulder sizes at several coastal sites in the ABC Islands as well as construct digital terrain models of the surrounding areas. Chronological constraints on boulder transport were established through the radiocarbon dating of the vermetids and coral colonies that comprised boulders located along a ridge on Aruba Island. A suite of hydrodynamic models was used to empirically derive the required flow thresholds for boulder displacement to determine whether tsunamis or hurricanes were responsible for detaching and transporting these boulders. Our results suggest that multiple tsunamis, most likely triggered by the El Pilar fault, located near the Venezuelan coast, were the cause of boulder detachment and transport in this region during the Holocene, between 4000 and 500 years BP.

This zipped repository accompanies the paper, "Refining patterns of melt with forward stratigraphic models on stable Pleistocene coastlines" (submitted to Earth Surface Dynamics, 2023). Within the file are two sub-folders. "Model_Input" and "SELEN". "Model_Input" contains the parameters needed to re-run the model runs described in the manuscript in the model environement "OpenFlowSuit" (Beicip Franlab). The "SELEN" sub-folder contains three additional sub-folders: "Background", "Full", and "G2A5". Each of these sub-folders has three .csv files containing the GIA driven sea level curve under three different mantel viscosities, MV1, MV2, and MV3.

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.

The study of geological sea-level proxies formed during previous interglacials is a common approach to assess how global sea level will evolve under warmer climate conditions. Over the last decades, technical advancements in both survey and geochronology have allowed improving our knowledge of past sea-level highstands. This is of prime importance to refine our understanding of processes contributing to sea-level changes, and ultimately to improve both local and global sea-level projections. Last Interglacial sea-level proxies in the Western Indian Ocean (and more specifically the island nation of Madagascar), have been less investigated than in other intertropical oceans over the last decades. As a result, paleo sea-level data in this region are less abundant and less precise than elsewhere. Here, we report the results of two field campaigns aimed at studying the site of Lembetabe, southwest Madagascar, where a fossil reef was first described by the researcher Rene ⠁ Battistini more than 50 years ago. We estimate paleo relative sea level history in space and time from 15 new U-series ages from a fossil reef platform mapped with differential GNSS and drone photogrammetry. Our data suggest that, between 129 ka and 115 ka, paleo relative sea level at this location was about 3.4 & PLUSMN; 1.4 m above modern. Once corrected for glacial isostatic adjustment, we find that paleo global mean sea level did not exceed 3 m above modern. Only slight crustal subsidence would reconcile the peak Last Interglacial sea level measured at Lembetabe with the 5 e10 m range reported in the literature.& COPY; 2023 Published by Elsevier Ltd.

The study of paleo shorelines, particularly of those formed during the late Quaternary, provides robust insights into past climate variability. Advances in surveying techniques and chronological methodologies have dramatically improved the inter-comparability of regional and basin-wide paleo shoreline surveys. However, these advances have been applied unevenly across the globe. This is especially true in southwestern Madagascar, where, in the 1960s and 1970s, emerged Pleistocene beach and reef facies were first described in detail and dated to Marine Isotope Stage (MIS) 5a using U–Th alpha activity counting by french geologist René Battistini. Now, 50 years on, no further analysis of the coastal sequence has been made. In this study, we present an updated late Pleistocene coastal evolution model for the southwestern Madagascar coast. Utilizing a combination of Structure-from-Motion/Multi-View Stereo techniques and differential Global Navigation Satellite System surveys, we have created five high-resolution 3D outcrop reconstructions that have, in turn, been chronologically constrained using 10 U-series ages from both in situ and reworked coral samples. Our data suggest that the emerged reef was deposited during MIS 5e (∼125 ka), then was covered by intertidal and beach sediment (including redeposited coral clasts of MIS 5e age), and finally capped off by thick eolianites. This sequence would suggest that the local sea level must have remained stable throughout MIS 5e in order to allow for the progradation of both the beach and reef environments.

The last interglacial (LIG), ca. 128-116 ka, is widely considered a process analogue in understanding Earth’s systems in a future warmer climate. In particular, significant effort has been made to better constrain ice sheet contributions to sea level rise through direct field observation of relative sea level (RSL) indicators. In order to extract the RSL, a series of corrections for formational parameters and post-depositional processes need to be applied. Along tropical coastal margins, LIG RSL observations are predominately based on exposed shallow coral reef sequences due to their relatively narrow indicative range and reliable U-series chronological constraints. However, the often-limited sub-stadial temporal preservation of many Pleistocene reef sequences on stable coastlines restrict many reported RSLs to a series of distinct points in within the LIG. This in turn, limits ability to elucidate different commonly reported meter-scale sub-stadial sea level peak patterns and their associated uncertainties. In order to address this shortcoming, lithostratigraphic and geomorphologic traces are often used to place RSLs into a broader context. Unfortunately, this is often subjective, with significant reliance on field observations where missing facies and incomplete sequences can distort interpretations. Stepping back from a conventional approach, in this study we generate a spectrum of synthetic Quaternary subtropical fringing reefs in southwestern Madagascar within the DIONISOS forward stratigraphic model environment. Each reef sequence has been subjected to distinct Greenland and Antarctica melt scenarios produced by a coupled ANICE-SELEN global isostatic adjustment model, matching previously hypothesized LIG sea level curves in the Indo-Pacific Basin. The resulting suite of synthetic reef sequences provides the ability to probabilistically test any number of melt scenarios against the sensitivity of the stratigraphic record. We propose this accessible additional quantitative quality control during the final interpretation phase of establishing emergent reef sequence based LIG RSL indicators can assist in narrowing down the wide uncertainty surrounding inter-stadial ice sheet behaviors.

Sea-level rise represents a severe hazard for populations living within low-elevation coastal zones and is already largely affecting coastal communities worldwide. As sea level continues to rise following unabated greenhouse gas emissions, the exposure of coastal communities to inundation and erosion will increase exponentially. These impacts will be further magnified under extreme storm conditions. In this paper, we focus on one of the most valuable coastal real estate markets globally (Palm Beach, FL). We use XBeach, an open-source hydro and morphodynamic model, to assess the impact of a major tropical cyclone (Hurricane Matthew, 2016) under three different sea-level scenarios. The first scenario (modern sea level) serves as a baseline against which other model runs are evaluated. The other two runs use different 2100 sea-level projections, localized to the study site: (i) IPCC RCP 8.5 (0.83 m by 2100) and (ii) same as (i), but including enhanced Antarctic ice loss (1.62 m by 2100). Our results show that the effective doubling of future sea level under heightened Antarctic ice loss amplifies flow velocity and wave height, leading to a 46% increase in eroded beach volume and the overtopping of coastal protection structures. This further exacerbates the vulnerability of coastal properties on the island, leading to significant increases in parcel inundation.

With global average temperatures 2°C higher than pre-industrial and eustatic sea-level ranging between 5 and 9 m above present, the Last Interglacial is often regarded as a good process-analogue for a future warmer climate. Large uncertainties are associated with Last Interglacial eustatic sea-level estimations. To quantify these uncertainties through standardization of sea-level metadata, the World Atlas of Last Interglacial Shorelines (WALIS) provides a community-wide standard for documenting the geological context of sea-level indicators and their chronology. By applying this standard, WALIS allows for the quantitative cross-comparison between previous studies, often times separated by decades. We use WALIS to review published sea-level indicators for the Last Interglacial within the Western Indian Ocean basin. Located in the far field with respect to past glaciations, the Western Indian Ocean has the potential to provide precisely measured and dated sea level proxies, enabling a reliable estimation of maximum eustatic sea level for the Last Interglacial. This, in turn, would allow to better constrain upper boundaries of melting within ice-sheet models. Furthermore, this review highlights localities that should be revisited based on the presence of geological facies indicative of former highstands where not enough detail has been reported or where advanced dating and geodetic techniques can increase the accuracy of metadata.

This Excel spreadsheet is a complete record of the relative sea level proxies described in "Last Interglacial sea-level proxies in East Africa and the Western Indian Ocean" (Boyden et al., 2020, Earth System Science Data). It has been exported from "The World Atlas of Last Interglacial Shorelines (WALIS) database (https://warmcoasts.eu/world-atlas.html).

In this paper, we describe a sea-level database compiled using published last interglacial, Marine Isotopic Stage 5 (MIS 5), geological sea-level proxies within East Africa and the Western Indian Ocean (EAWIO). Encompassing vast tropical coastlines and coralline islands, this region has many occurrences of well-preserved last interglacial stratigraphies. Most notably, islands almost entirely composed of Pleistocene reefs (such as Aldabra, the Seychelles) have provided reliable paleo relative sea-level indicators and well-preserved samples for U-series chronology. Other sea-level proxies include uplifted marine terraces in the north of Somalia and Pleistocene eolian deposits notched by the MIS 5 sea level in Mozambique to tidal notches in luminescence-limited eolian deposits in Mozambique. Our database has been compiled using the World Atlas of Last Interglacial Shorelines (WALIS) interface and contains 58 sea-level indicators and 2 terrestrial-limiting data points. The open-access database is available at https://doi.org/10.5281/zenodo.4302244 (Version 1.03; Boyden et al., 2020).

The PALSEA (PALeo constraints on SEA level rise; pastglobalchanges.org/palsea)working group convened recently at Trinity College, Dublin.This meeting (pastglobalchanges.