Abstract. 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 Eastern 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 by 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 tidal notches in luminescence limited aeolian deposits in Mozambique. Our database has been compiled using the World Atlas of Last Interglacial Shorelines (WALIS) interface and contains 57 sea-level indicators and 2 terrestrial limiting data points. The database is available open access at https://doi.org/10.5281/zenodo.4043366 (Version 1.02) (Boyden et al., 2020).

Abstract. 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).

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.

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.

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