Max Engel

Beach ridge systems: archives for Holocene coastal events?

Holocene coastal evolution has been extensively studied by workers from various earth science disciplines, particularly sedimentologists and geomorphologists. Some of these studies have focused on the history of regional sea-level changes in various ocean basins and the mechanisms – such as eustasy, glacio-isostasy, sediment compaction, neotectonics and climatic forces – involved in such changes. Although beach ridges have been used to identify steps in coastal evolution, only in a few cases have beach ridge systems been investigated with respect to event histories (for example, cyclones and tsunamis). Beach ridge systems, however, belong to the most promising geo-archives for the study of climate change and sea-level variations over the Holocene, as well as for deciphering event histories. This paper presents examples of some studies in this field, in relation to a global overview of beach ridge systems and their morphological characteristics.

Coastal hazards from tropical cyclones and extratropical winter storms based on holocene storm chronologies

Aware of past and future climate changes, the question arose whether modern instrumental data adequately reflect the chronology of tropical cyclones and extratropical winter storms for the period of the present eustatic sea level highstand (approx. the past 6,000 years). For pre-instrumental times, geological and sedimentological methods have been applied at geo- and bioarchives such as coastal marshes, lagoons, washover features or beach ridges, showing a frequency of strong cyclones roughly every 100–300 years, which is in contrast to the high number of major cyclones recorded recently. Many of these palaeotempestological records are discontinuous or contain hiatuses and it may be difficult to evaluate whether these sections of the record represent quiet phases without major cyclones or simply erosion or fluctuations in the ability of an archive to record the signature of cyclones. Manifold questions are still unanswered: as the potential number of former cyclones may be stored in landforms and sediments, how can the intensity of these cyclones be identified? Is the crest height of beach ridges a good indicator for storm surge heights, air pressure, and cyclone categories? This paper reviews important achievements in palaeotempestology and discusses open questions of cyclone distribution, frequency and energy (i.e., hazard potential) in the last few decades and reconstructions of these parameters back into Mid-Holocene times.

Shoreline changes and high-energy wave impacts at the leeward coast of Bonaire (Netherlands Antilles)

Supralittoral coarse-clast deposits along the shores of Bonaire (Netherlands Antilles) as well as increased hurricane frequency during the past decade testify to the major hazard of high-energy wave impacts in the southern Caribbean. Since deducing certain events from the subaerial coarse-clast record involves major uncertainties and historical reports are restricted to the past 500 years, we use a new set of vibracore and push core data (i) to contribute to a more reliable Holocene history of regional extreme-wave events and (ii) to evaluate their impact on shoreline evolution. Multi-proxy palaeoenvironmental analyses (XRF, XRD, grain size distribution, carbonate, LOI, microfossils) were carried out using nearshore sedimentary archives from the sheltered western (leeward) side of Bonaire and its small neighbour Klein Bonaire. In combination with 14C-AMS age estimates the stratigraphy reflects a long-term coastal evolution controlled by relative sea level rise, longshore sediment transport, and short-term morphodynamic impulses by extreme wave action, all three of which may have significantly influenced the development of polyhaline lagoons and the demise of mangrove populations. Extreme wave events may be categorized into major episodic incidents (c. 3.6 ka [?] BP; 3.2–3.0 ka BP; 2.0–1.8 ka BP; post-1.3 ka [?] BP), which may correspond to tsunamis and periodic events recurring on the order of decades to centuries, which we interpret as severe tropical cyclones. Extreme wave events seem to control to a certain extent the formation of coastal ridges on Bonaire and, thus, to cause abrupt shifts in the long-term morphodynamic and ecological boundary conditions of the circumlittoral inland bays.

Potential and limits of combining studies of coarse- and fine-grained sediments for the coastal event history of a Caribbean carbonate environment

Abstract The coastal deposits of Bonaire, Leeward Antilles, are among the most studied archives for extreme-wave events (EWEs) in the Caribbean. Here we present more than 400 electron spin resonance (ESR) and radiocarbon data on coarse-clast deposits from Bonaire’s eastern and western coasts. The chronological data are compared to the occurrence and age of fine-grained extreme-wave deposits detected in lagoons and floodplains. Both approaches are aimed at the identification of EWEs, the differentiation between extraordinary storms and tsunamis, improving reconstructions of the coastal evolution, and establishing a geochronological framework for the events. Although the combination of different methods and archives contributes to a better understanding of the interplay of coastal and archive-related processes, insufficient separation, superimposition or burying of coarse-clast deposits and restricted dating accuracy limit the use of both fine-grained and coarse-clast geoarchives to unravel decadal- to centennial-scale events. At several locations, distinct landforms are attributed to different coastal flooding events interpreted to be of tsunamigenic origin. Coastal landforms on the western coast have significantly been influenced by (sub)-recent hurricanes, indicating that formation of the coarse-clast deposits on the eastern coast is likely to be related to past events of higher energy. Supplementary material: The entire dataset of ESR and 14C dating results used in this paper is available at http://www.geolsoc.org.uk/SUP18637.

Life and death after super typhoon Haiyan

Super typhoon Haiyan, packing sustained winds >300 kph, wrought immense damage on the Philippines in November 2013. Haiyan displaced large boulders in some areas (Engel et al. 2014) and generated an estimated 5 m surge in the Sagay Marine Reserve (10 58¢57.58†N, 123 27¢50.00†E), central Philippines. Immediately after, a coral boulder and rubble ridge several hundred meters long was exposed at low tide on Carbin Reef within the reserve (Fig. 1a). It was either newly established or heightened by the typhoon, but the presence of at least two different depositional units of rubble suggests the latter may be more likely. We present an exhibition of extremes: a heavily damaged subtidal reef area (Fig. 1b) and a largely untouched intertidal coral community (Fig. 1c) separated only by the 20 m-wide ridge. On Carbin’s western slope, the typhoon displaced boulders, sheared stands of Heliopora, and overturned massive colonies down to 10 m. Landwards of the ridge, in the shallow intertidal, many branching acroporids and massive faviids and poritids remained alive and structurally intact, consistent with observations and model predictions of Hongo et al. (2012). Haiyan maystill take its tollhere, however.ByFebruary 2014, partial mortality was evident on the tips of some branching acroporids where they remain above water at low tide. Future surveys will document if the newly established or significantly heightened ridge wrought physical/ hydrological changes that could cause delayed mortality (HarmelinVivien 1994). However, the observable immediate effects of super typhoon Haiyan on Carbin demonstrate that even a category five storm is not a universal death sentence for corals in shallow habitats. Local geomorphology, exposure, and sediment dynamics merit consideration in assessing storm vulnerability, even in the shallowest of reef areas.

Holocene sea levels of Bonaire (Leeward Antilles) and tectonic implications

Summary. Future relative sea-level (RSL) rise is one of the most serious coastal hazards worldwide, in particular in the Caribbean region. RSL is a function of global (glacioeustasy, steric effect), regional (e.g. glacioisostatic adjustment [GIA], gravitational effects inducing deformation of the earth, upper/lower mantle viscosity, etc.) and local (lithosome compaction, vertical neotectonic movement) factors which are connected via a complex pattern of interference. Information on past RSL supports inferences on upper limits of ice shield ablation, estimates of anthropogenic contribution to historical and future RSL rise and calibration of rheological models of the earth. We present the first RSL curve for the island of Bonaire (S Caribbean). Forty-two 14 C ages from 20 sediment cores taken from nine different sedimentary archives along the coast were used. The sedimentary environment of each index point was linked to a palaeowater depth based on literature and field observations. The index points trace a local RSL history of decelerating rise since 7000-6000 years ago and subsequent asymptotical approximation, similar to existing RSL curves from Curaςao and Venezuela. The results were compared to a simulation of Holocene sea-level history (reference model) which considers global effects and regional GIA (including consequences for geopotential and vertical position of earth surface). Even though the central and NW parts of Bonaire experienced slow tectonic uplift of up to 50 cm since the mid-Holocene and tentative correction for compaction was applied, the new RSL curve for Bonaire runs slightly below the reference model. A further outcome of this study is the detection of an unmapped micro-graben structure with a vertical slip rate of c. 1.5 mm yr -1 at Boka Bartol, which was identified based on depth discrepancies of well-dated isochronous highenergy wave deposits. Zusammenfassung. Der zukunftige relative Meeresspiegelanstieg stellt eines der gravierendsten Kustenrisiken weltweit dar, dies gilt insbesondere fur den karibischen Raum. Der relative Meeresspiegel ist eine Funktion globaler (Glazialeustasie, sterischer Effekt), regionaler (z. B. Glazialisostasie, gravitative Effekte und deren Einfluss auf die Deformation der Asthenosphare, Dynamik der Asthenospharenviskositat) und lokaler (Sedimentkompaktion, vertikale tektonische Bewegungen) Faktoren, die wiederum uber ein komplexes Netzwerk von Wechselwirkungen verbunden sind. Die Rekonstruktion lokaler Meeresspiegelhistorien ermoglicht Ruckschlusse auf maximale postglaziale Ablationswerte der Eisschilde, den anthropogenen Einfluss auf den historischen und zukunftigen relativen Meeresspiegelanstieg, und dient daruber hinaus der Kalibrierung rheologischer Modelle. Diese Studie prasentiert die erste relative Meeresspiegelkurve der Insel Bonaire (Sud-Karibik), deren Basis aus 42 14 C-Altern aus 20 Sedimentkernen von neun unterschiedlichen Sedimentarchiven entlang der Kuste besteht. Der umgebenden Fazies eines jeden datierten Objekts wurde auf Basis von Literaturwerten und Gelandebeobachtungen eine Palao-Wassertiefe zugewiesen. Die Resultate deuten auf einen sich seit 7000-6000 Jahren vor heute verlangsamenden Meeresspiegelanstieg und eine damit verbundende asymptotische Annaherung an das heutige Niveau hin, ahnlich der bereits existierenden relativen