Rovere, Alessio
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Rovere, Alessio
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Rovere, Alessio
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Item type:Publication, Holocene sea-level changes in Southeast Asia(2020-06-25); ; ; Sea-level changes are dynamic processes and changes in relative sea-level (RSL) are common occurrences in the history of Earth, with different rates over time. Since the beginning of the industrial revolution (ca. 1880 AD) greenhouse gas emissions increased and the related climate change accelerated the modern sea-level rise. This became an increasingly important threat within the last century, in particular for global societies where people are living on low-lying coastlines only a few meters above mean sea level (MSL). The study of Holocene (~11.5 ka BP) sea levels is an important tool to understand the natural processes affecting coastal regions, as paleo RSL positions can help assess long-term vertical land motion and , hence, the risk of local flooding and land loss. In the Holocene, sea-level rise was initiated by increasing temperatures of the Last Glacial Maximum (LGM) ~21 ka BP. Land-ice melt caused the eustatic sea level to rise, triggering processes related to glacial isostatic adjustments (GIA), such as, for example, ocean syphoning, land leveling and changes in the gravitational attraction and Earth rotation. Due to these processes, water masses migrated from the poles to equatorial regions, affecting many far-field areas that experienced a sea-level highstand. In fact, after ice-melting slowed down and stopped (~6 to 4 ka BP), water masses migrated back to the poles, generating RSL highstand patterns, which can be seen in the geological record above present sea level in many far-field (i.e., located away from the ice sheets) areas. At these places, different RSL indicators such as coral reefs, salt marshes or beachrocks, were deposited or developed above modern MSL. Today, they provide important benchmarks on local paleo sea-level histories, once post-depositional processes affecting their elevations are taking into account. In general, there are two types of RSL indicators: index points and limiting indicators. Index points are documenting the paleo sea-level position, and marine or terrestrial limiting points, were formed above or below the local tidal ranges. These latter indicate that the paleo RSL was surely above (marine limiting point) or surely below (terrestrial limiting points) the measured elevation of the indicator. According to well-established protocols, all RSL indicators need to have an age, obtained with radiometric dating, coordinates and elevation of the sample. RSL index points also need to have and associated indicative meaning (IM), composed of the indicative range (IR) and the reference water level (RWL). Additional to geological field data, Holocene sea-level studies must include the result of geophysical models that calculate the intensity and timing of GIA, taking into account different ice and earth model combinations. In this thesis, I worked to refine Holocene sea-level histories in Southeast Asia. First, I present a Holocene sea-level database, compiled from published literature. The database includes 546 data points of the broader region of South and Southeast Asia. Within different sample sets, we highlight that some problems such as data inconsistencies, general lack of data, or insufficient data information from literature complicate the analysis of the general sea-level history for the broader study region. Further, besides GIA, the main driver for the RSL highstand at many regions, we identify the need to better constrain syn- and post-depositional processes causing further departures from Eustasy. I then present the results of original fieldwork in the Spermonde Archipelago (SW Sulawesi). Here, we surveyed and dated 24 new RSL index points for the mid to Late-Holocene. Our data, based on highly accurate measurements of fossil microatolls, were supposed to help solving data inconsistencies within the rarely studied region. This study shows that the new data support previous results based on fossil microatolls but cannot completely solve local data inconsistencies derived from two older studies, comprising mainly marine and terrestrial limiting indicators. Using our data in combination with a large suite of GIA models, we discuss possible tectonic rates in our study area. In combination with previous studies, our data show the possibility that one populated island is subject to relevant subsidence. This should be evaluated by further studies, and opens up relevant questions regarding the fate of small, low-lying, heavily populated, tropical islands in face of climate change. As understanding RSL histories is essential, another approach to gauge the relevance and importance of missing RSL information from our large database was developed within this thesis. We use a statistical analysis to better evaluate how GIA models fit geological field data. The results of this exercise can help to highlight if deviating RSL histories predicted by GIA models and observations are based on major data inconsistencies, a lack of data points or if post-depositional processes could be the reason for conflicts between RSL observations and model predictions in the related regions. Therefore, 16 study areas were compared to 54 GIA models providing positive or negative mismatches between model and data RSL predictions. The results are divided into two analyses, calculating the probability for the mismatch between the entire dataset and all GIA models and between each single index point and the models. The results show, that in three cases the results of both analyses differ significantly with each other, five regions indicate only low probability results implying that GIA is not the only driving factor and post-depositional processes cannot be excluded, and eight regions provide high probability results indicating GIA as the main driver for the paleo RSL positions.doctoral thesis444 267 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Drivers of Pleistocene to Holocene sea-level changes in the Southwestern AtlanticGlobal mean sea levels have been rising since the last century; this trend is expected to continue as the planet faces a warmer future. However, the rate and magnitude of this rise remain subject to debate, making decisions about land use and coastal management difficult. Sea level changes are not linear. In fact, they are driven by an intricate relationship between eustatic (i.e., global), isostatic, and local factors through time. Therefore, there is a clear need for precise and accurate data covering various spatiotemporal scales. Quaternary sea-level records offer valuable data to improve our understanding of these complex sea-level dynamics and enhance the predictions of future sea-level scenarios. In particular, interglacial records provide sea-level variability data under warm climate conditions. Marine Isotope Stage 5 (~125 to 80 ka) represents the most recent interglacial period when the Earth's climate was warmer than the pre-industrial, and the sea level was higher than today, leaving geological and biological traces of rising sea levels around the world. Especially, the southwestern Atlantic is considered a hot spot for past sea-level dynamics due to the abundance and preservation of sea-level indicators. This dissertation aims to provide an overview of the state-of-the-art of sea-level research in this broad region, provide context on the accuracy of published data from the Pleistocene to the Holocene interglacials, discuss the uncertainties surrounding them, and propose new methodological approaches to improve the interpretations.doctoral thesis258 123 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Last interglacial sea level in the western Indian Ocean: multifaceted approach to paleo relative sea level indicator interpretation and analysis(2022-04-08); ; ; The global population living within low lying coastal zones face significant challenges in the coming century as sea levels rise. Unfortunately, the acceleration and magnitude of the rise is still a subject of debate, leaving coastal communities often paralyzed in the decision whether to mitigate or abandon. In order to better elucidate future sea-level rise, process analogues from the geological record are used to constrain model predictions. The Last Interglacial (LIG, ca. 128–116 ka), represents the most recent period when Earth’s climate was warmer and sea levels were higher than today. Such insights are derived from the global accumulation of geological sea-level proxies, called paleo relative sea level (PRSL) indicators that are comprised of accurate chronological and elevation constraints as well as considerations for post-depositional processes. However, the spatial and temporal coverage of PRSL indicators is uneven, especially within Eastern Africa and the Western Indian Ocean (EAWIO). In order to establish the current understanding of LIG sea-level in the EAWIO, this dissertation compiles a sea-level database using published LIG geological sea-level proxies. The EAWIO comprises of extensive tropical coastlines and coralline islands with many occurrences of well preserved LIG sequences. These LIG sequences vary in form from islands entirely composed of Pleistocene reefs (i.e., Aldabra, the Seychelles) to uplifted marine terraces in the north of Somalia to Marine Isotope Stage (MIS) 5 tidal notches in Mozambique. This effort uses theWALIS interface and contains 58 sea-level indicators and 2 terrestrial limiting data points. Studies within this database stretch from the 1960s until present, with varying degrees of PRSL precision. Taking this into account, this dissertation explores the advantages of applying modern chronological constraints and advanced surveying techniques to a classic Pleistocene site along the southwestern shores of Madagascar. Here, new investigative techniques provide an updated late Pleistocene geomorphological understanding of southwestern Madagascar. Through the use of Structure from Motion / Multi-View Stereo in combination with differential Global Navigation Satellite System surveys, 3D outcrop reconstructions of sequential geomorphologcial zones and their intrinsic facies are presented. This sequence is chronologically constrained using U-series ages from both in situ and reworked coral samples. From this chronologically sequence, the LIG in Lembetabe was initiated by the deposition of a fringing reef that reaches approximately 2 m above mean sea level. This fringing reef environment persisted throughout the LIG, before a combination of slow regression and changes in the sedimentation regime covered the fringing reef with intertidal and beach sediment. A final close-out of the system occurred as sea level fell further and dune fields began to migrate offshore before. This interpretation of the Lembetabe LIG sequence is then examined through the use of Forward Stratigraphic Models (FSMs). Currently, FSMs are commonly deployed within large-scale basinwide characterizations for industry. By scaling-down the FSM DIONISOS, a suite of synthetic Quaternary subtropical fringing reefs in southwestern Madagascar are produced. Through this approach, each reef is subjected to a distinct Greenland Ice-Sheet (GrIS) and Antarctica Ice-Sheet (AIS) melt scenarios produced by a coupled ANICE-SELEN glacial isostatic adjustment (GIA) model. These scenarios match LIG sea-level curves previously hypothesized within the Indo-Pacific Basin. The resulting collection of synthetic reef sequences so dramatic shifts in both sedimentation and preservation regimes along the Lembetabe coast. By establishing a broad compilation of PRSL indicators at a basin scale, the reexamination of a previously described PRSL indicator, and finally the evaluation of outcrop interpretation, this dissertation provides a new PRSL benchmark for the EAWIO and a new workflow for the evaluation of PRSL indicators along carbonate coasts.doctoral thesis321 324