Sander Scheffers

Documentation of the Impact of Hurricane Ivan on the Coastline of Bonaire (Netherlands Antilles)

Abstract Situated just north of the Venezuelan coast around 12° to 13° N, the Netherlands Antilles are normally well outside the hurricane belt. Nevertheless, some of these powerful storms sent waves and swell of significant size to these islands, strong enough for impacts on the coastal geomorphology. Hurricane Ivan of September 2004, with Saffir–Simpson category 5 and around 250 km/h sustained winds less than 150 km north of Bonaire, was the most recent and one of the strongest of these events in history. Waves along the rocky eastern coastline reached heights of >12 m. Our observations during the days of Hurricane Ivan on Bonaire Island include impacts on exposed and sheltered shorelines, transformation of beaches and cliffs, sediment movement on higher terraces, as well as boulder transport. The latter is important to distinguish storm wave-induced boulder movement from boulder movement by tsunami, which have affected Bonaire several times during the Younger Holocene.

Paleo-Tsunami Relics on the Southern and Central Antillean Island Arc

Abstract Three Holocene tsunami events that struck the islands of Aruba, Curaçao, and Bonaire around 450–500 YBP, 1,500 YBP, and 3,500 YBP resulted in extensive deposits of coarse sediments and boulders along the coastal zone. The tsunami waves approached the islands from an easterly direction. We investigated paleo-tsunami imprints on the islands of Grenada, St. Lucia, and Guadeloupe to locate the source area of those three events. However, along the Caribbean coastlines of the islands, no evidence for Holocene tsunami impacts have been found. Instead, tsunami relics of Middle Pleistocene age are incorporated into tephra depositions of these volcanic islands. At least one Holocene tsunami event is preserved in the form of bimodal accumulations and boulder deposits along the east coast of Guadeloupe, indicating that the tsunami hit the island from the open Atlantic ocean. Radiocarbon dating yielded an age of about 2,400–2,700 years YBP for the event.

Wave‐Emplaced Coarse Debris and Megaclasts in Ireland and Scotland: Boulder Transport in a High‐Energy Littoral Environment

Many coastlines of the world, particularly those at higher latitudes and those located in tropical cyclone belts, are regularly battered by strong storm waves. Drowning of low‐lying areas by storm surges and storm floods has been thoroughly recorded; however, storm deposits at rocky shorelines or on cliffs have been underrepresented in the literature. This article presents observations of extraordinary wave deposits along the high–wave energy coastlines of western Ireland and the northern Scottish isles and discusses possible wave event types and time windows of the processes responsible. We used archaeological, geomorphological, and geochronological disciplines to compare our findings with earlier results published for these areas and to contribute to the debate on whether large clasts found well above sea level and/or a considerable distance inland were deposited by storms or by tsunamis.

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.

Tropical Atlantic temperature seasonality at the end of the last interglacial

The end of the last interglacial period, ~118 kyr ago, was characterized by substantial ocean circulation and climate perturbations resulting from instabilities of polar ice sheets. These perturbations are crucial for a better understanding of future climate change. The seasonal temperature changes of the tropical ocean, however, which play an important role in seasonal climate extremes such as hurricanes, floods and droughts at the present day, are not well known for this period that led into the last glacial. Here we present a monthly resolved snapshot of reconstructed sea surface temperature in the tropical North Atlantic Ocean for 117.7±0.8 kyr ago, using coral Sr/Ca and δ18O records. We find that temperature seasonality was similar to today, which is consistent with the orbital insolation forcing. Our coral and climate model results suggest that temperature seasonality of the tropical surface ocean is controlled mainly by orbital insolation changes during interglacials.

Island outlook : warm and swampy

In his In Depth News story “Warming may not swamp islands” (1 August, p. 496), C. Pala argues that “coral reefs supporting sandy atoll islands will grow and rise in tandem with the sea,” based largely on studies that showed stable Pacific-island area over recent decades (1–4). He suggests that recent land losses are driven mostly by bad choices and that islanders are being affected “for the same reason as millions of people on the continents: because they live too close to shore.” We disagree with these conclusions.

The coastlines of the world with Google Earth: understanding our environment

Introduction: Oceans and Coastlines 1 The Oceans 1.1 Extent, Origin and Topography 1.2 Sediments in the Oceans 1.3 Physics and Chemistry of Ocean Waters 1.4 Life in the Oceans 1.5 Movements in the Ocean: Currents, Waves and Tides 1.6 Changing Sea Levels 2 Coastal Landforms and Landscapes 2.2 Ice Cliffs, Calving Glaciers and Sea Ice 2.3 Structural Dominated Coastlines 2.4 Volcanic Coasts 3 Coastlines Dominated by Ingression of the Sea into older Terrestrial Landforms 3.1 Ingression in Rocky Glacial Landscapes 3.2 Ingression in Sedimentary Glacial Landscapes 3.3 Ingression into Fluvial Landscapes 3.4 Ingression into Karst Landforms 3.5 Ingression into Eolian Landforms 3.6 Permafrost Coastlines with Ingression 4 Destructive Coastline 4.1 Bioerosion 4.2 Tafoni and Tessellated Pavements 4.3 Cliffs and Shore Platforms 5 Sedimentary Coasts 5.1 Introduction - The beach and its features 5.2 Foreshore Features and Tidal Flats 5.3 Spits and Tombolos 5.4 Barriers, Barrier Islands and Lagoons 5.5 Beach Ridge Systems and Cheniers 5.6 Coastal Dunes 5.7 Marine Deltas 6 Coasts Dominated by Organisms 6.1 Marine Plants - Algae and Seagrass 6.2 Marine Plants - Mangroves 6.3 Coral Reefs 6.4 Other organic hardgrounds 7 Coasts as Archives of the Past 7.1 Geologic archives in coastal environments 7.2 Coastal Geoarchaeology 8 Coasts at Risk 8.1 Coastal Natural Hazards - Storms and Tsunamis 8.2 Sea Level Rise - The unavoidable and uncertain future of our coasts 8.3 Man-made Coastlines Epilogue Index 3 Coastlines Dominated by Ingression of the Sea into older Terrestrial Landforms 3.1 Ingression in Rocky Glacial Landscapes 3.2 Ingression in Sedimentary Glacial Landscapes 3.3 Ingression into Fluvial Landscapes 3.4 Ingression into Karst Landforms 3.5 Ingression into Eolian Landforms 3.6 Permafrost Coastlines with Ingression 4 Destructive Coastline 4.1 Bioerosion 4.2 Tafoni and Tessellated Pavements 4.3 Cliffs and Shore Platforms 5 Sedimentary Coasts 5.1 Introduction - The beach and its features 5.2 Foreshore Features and Tidal Flats 5.3 Spits and Tombolos 5.4 Barriers, Barrier Islands and Lagoons 5.5 Beach Ridge Systems and Cheniers 5.6 Coastal Dunes 5.7 Marine Deltas 6 Coasts Dominated by Organisms 6.1 Marine Plants - Algae and Seagrass 6.2 Marine Plants - Mangroves 6.3 Coral Reefs 6.4 Other organic hardgrounds 7 Coasts as Archives of the Past 7.1 Geologic archives in coastal environments 7.2 Coastal Geoarchaeology 8 Coasts at Risk 8.1 Coastal Natural Hazards - Storms and Tsunamis 8.2 Sea Level Rise - The unavoidable and uncertain future of our coasts 8.3 Man-made Coastlines Epilogue Index

The cave-profiler: a simple tool to describe the 3-D structure of inaccessible coral reef cavities

Introduction An important part of the bottom of a coral reef consists of dead coral reef framework cavities, this includes the spaces and surfaces under rubble, the undersides of skeletal organisms such as corals, the shaded undersides of overhanging dead or live coral, and deep framework cavities. Cavities are formed below protruding edges of stony corals, in the coral reef framework and are often enlarged by bioeroding organisms. These cavities make up a major part of the volume of the skeleton of a reef. Estimates of the volume encompass 30-75% of total reef volume (Ginsburg, 1983). Cavities provide a surface area for colonization by organisms that may be greater than the horizontally projected reef surface area (Ginsburg, 1983; Gischler & Ginsburg, 1996; Jackson & Winston, 1982). The species composition of these cryptic habitats has been extensively studied (Kobluk & van Soest, 1989; Meesters et al., 1991). Sessile groups such as sponges, crustose coralline and filamentous algae, ascidians, polychaetes, bryozoans, and foraminiferans, usually dominate cryptofauna. Bioeroding organisms, such as clionid

Aggressive colonial ascidian impacting deep coral reefs at Bonaire, Netherlands Antilles

Large colonies of the ascidian Trididemnum solidum were observed during benthic surveys at Bonaire, Netherlands Antilles, in January 2009. Mean cover of T. solidum was recorded in a total of 72, randomly located, 30 m long by 1.3-m-wide photo transects, in four replicate transects at three depths (5, 10, and 20 m) in each of six locations along the northwest coast of Bonaire. Locations were chosen due to their remoteness from human development. Photographs were analyzed using CPCe. T. solidum occupied 10.4% ± 3.8 (mean ± SE) of available substrata (sensu Bak et al. 1996) at the 20-m site at the Saliña Tern location. Mean T. solidum cover of available substrata (all sites pooled) significantly increased with depth (P £ 0.05) with 0.2% ± 0.1 at 5 m, 3.2% ± 0.6 at 10 m, and 6.3% ± 0.8 at 20 m. While T. solidum colonies occurred on various substrata, aggressive overgrowth of scleractinian corals including Montastraea spp. (Fig. 1a) and Agaricia agaricites (Fig. 1b) and the hydrocoral Millepora spp. (Fig. 1c) were frequently observed. Bak et al. (1996) recorded a 900% increase in the number of T. solidum colonies on neighboring Curaçao between 1978 and 1993. Daily availability of larvae (van Duyl et al. 1981), fast growth rates, and high mobility (Bak et al. 1981) make T. solidum a potentially superior competitor over corals in environments altered by disturbance (Bak et al. 1996). High abundance of the aggressive T. solidum ascidian recorded at deeper reefs in this study is of concern and highlights another threat to Bonaire’s coral reefs, especially as deeper reefs are considered to be relatively undisturbed (Bak et al. 2005).

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.