Key Processes in the Holocene Evolution of Tropical Coasts - Evaluating the Role of Hurricanes and Tsunamis
Final Report Abstract
The interdisciplinary 3-year-project “Key Processes in the Holocene Evolution of Tropical Coasts – Evaluating the Role of Hurricanes and Tsunamis” (now on extended term) was jointly carried out by coastal geomorphologists, sedimentologists, coral reef ecologists and geochronologists with the aim to unravel the Late Holocene history of the coastal evolution of Bonaire Island (Neth-erlands Antilles, Caribbean, at 12°N). The island was chosen as a prototype for a tropical coastal environment as it has been affected by different extreme event types (hurricanes and tsunamis) in the past and since it exhibits typical habitats such as fringing coral reefs (modern and fossil), mangrove wetlands and lagoon systems which potentially preserve the fingerprints of such events. The objective was to distinguish between the event processes in the geologic record, search for tempestites and tsunamites and establish a high resolution geochronological frame-work for the overall coastal evolution, the impact frequency of hurricanes and tsunamis and possibly the response of the ecosystems. A key milestone in this project was the first systematic comparison between surface deposits (boulder ridges, ramparts, overwash fans) and fine sediments within the stratigraphic context of sediment cores and the overall quality, suitability and “completeness” of these different geologic archives. We could show that it is crucial for any future study of such marine natural hazards to investigate both archive types and apply a tightly constrained age control in order to be able to identify events in the prehistoric record. The extreme event deposits have been numerically dated using three different methods (ESR, Radiocarbon and U-series) – partly as a mutual age control, but with the main objective to extend the applicability of the ESR method as a comparably inexpensive method for Late Holocene carbonate samples. We could show that in general the ESR method is applicable to Late Holocene samples; however, the uncertainties are larger as compared to modern U-series and radiocarbon ages. Overall, the research project produced 400 numerical data which represents the densest data set and geochronological framework for studies of coastal evolution and marine hazards worldwide. The data clearly show significant differences (ages and frequency) for hurricane and tsunami impacts, congruent with the different depositional character in facies, landform features and position in respect to the modern shoreline and the reef foreshore as a sediment source. A milestone outcome of this research is the development of physical formula for boulder transport energy of different wave types to discriminate coarse hurricane and tsunami deposits and define thresholds for boulder transport by both processes. A large-scale geomorphologic and sedimentologic survey led to the production of a geomorphic map which formed the base for a discussion of the onshore deposits along the leeward and windward coasts. The sedimentary record of coastal morphological depressions should distinct correlations in candidate tsunami deposits. They seem to represent events shortly after 3300 BP and c. 2000-1700 BP. Further high-energy wave deposits were dated to c. 3600 BP and post-1300 BP, though their appearance is locally only. A mapping and survey program of the status of the adjacent fringing reefs and coral communities in response to the impact of recent hurricanes and changes in reef composition (both short and long term) produced a detailed overview of the health status of Bonaire’s coral reefs and led to new strategies in marine coastal management by the local authority STINAPA. First climate reconstructions could be established by the analyses of pollen from sediment samples from the lagoon and adjacent alluvial fans. A considerable amount of taxa from mangrove forest was only found on the eastern shore of Bonaire. Preliminary results suggest that the area of indicator plants for a drier climate were reduced during the younger Holocene, while Rhizophora sp. enlarges their habitat. At the present stage of knowledge we interpret these findings as a consequence of the increasing human impact and/or the influence of the ongoing sea-level rise.
Publications
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2009. Die Entwicklung der Tsunamiforschung nach der Katastrophe vom 26.12.2004. Geographische Rundschau, Vol. 61. 2009, no. 12, pp. 12-18.
Scheffers, A., Kelletat, D., Engel, M.
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2009. Reading the chapter of extreme wave events in nearshore geo-bio-archieves of Bonaire (Netherlands Antilles) – initial results from Lagun and Boka Bartol. Marburger Geographische Schriften, Bd. 145. 2009, S. 157-178.
Engel, M., Bolten, A., Brückner, H., Daut, G., Kelletat, D., Schäbitz, F., Scheffers, A., Scheffers, S.R., Vött, A., Wille, M., Willershäuser, T.
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2009. Tsunamis, hurricanes, the demise of coral reefs and shifts in prehistoric human populations in the Caribbean. Quaternary International, Vol. 195. 2009, Issues 1–2, pp. 69–87.
Scheffers, S.R., Scheffers, A., Browne, T., Haviser, J.
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2010. Aggressive colonial ascidian impacting deep coral reefs at Bonaire, Netherlands Antilles. Coral Reefs, Vol. 29. 2010, Issue 1, pp. 245-245.
Sommer, B., Harrison, P.L., Scheffers, S.R.
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2010. Assessing the potential of Southern Caribbean corals for reconstructions of Holocene temperature variability. –
IOP Conference Series: Earth and Environmental Science, Vol. 9. 2010: 012021.
Giry, C., Felis, T., Scheffers, S., Fensterer, C.
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2010. Assessment of extreme wave flooding from geomorphologic evidence in Bonaire (Netherlands Antilles). Zeitschrift für Geomorphologie, Supplementary Issues, Vol. 54. 2010, Number 3, pp. 219-245.
Pignatelli, C., Scheffers, A., Scheffers, S.R., Mastronuzzi, G.
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2010. Boulder transport by waves: Progress in physical modelling.
Zeitschrift für Geomorphologie, Supplementary Issues, Volume 54. 2010, Number 3, pp. 127-146.
Benner, R., Browne, T., Brückner, H., Kelletat, D., Scheffers, A.
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2010. Coastal stratigraphies of eastern Bonaire (Netherlands Antilles): New insights into the palaeo-tsunami history of the southern Caribbean. Sedimentary Geology, Vol. 231. 2010, Issues 1–2, pp. 14–30.
Engel, M., Brückner, H., Wennrich, V., Scheffers, A., Kelletat, D., Vött, A., Schäbitz, F., Daut, G., Willershäuser, T., May, S.M.
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2010. Geochemistry and skeletal structure of Diploria strigosa, implications for coral-based climate reconstruction. Palaeogeography, Palaeoclimatology, Palaeoecology, Vol. 298. 2010, Issues 3–4, pp. 378–387.
Giry, C., Felis, T., Kölling, M., Scheffers, S.
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2011. Coral community decline at Bonaire, Southern Caribbean. –
Bulletin of Marine Science, Vol. 87. 2011, Number 3, pp. 541-565.
Sommer, B., Harrison, P.L., Brooks, L., Scheffers, S.R.
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2011. The identification of palaeo-tsunami deposits – a major chal-lenge in coastal sedimentary research. – In: Karius, V., Hadler, H., Deicke, M., Von Eynatten, H., Brückner, H., Vött, A. (eds.): Dynamische Küsten – Grundlagen, Zusammenhänge und Auswirkungen im Spiegel angewandter Küstenforschung. Proceedings of the 28th Annual Meeting of the German Working Group on Geography of Oceans and Coasts, 22-25 Apr. 2010, Hallig Hooge, Coastline Reports 17, pp. 65-80.
Engel, M., Brückner, H.
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2012. Beach ridge sys-tems – archives for Holocene coastal change? Progress in Physical Geography, vol. 36. 2012, no. 1, pp. 5-37.
Scheffers, A., et al.
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2012. Bonaire's boulder fields revisited: evidence for Holocene tsunami impact on the Leeward Antilles. Quaternary Science Reviews,
Vol. 54. 2012, pp. 126–141.
Engel, M., May, S.M.
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2012. Mid- to late Holocene changes in tropical Atlantic temperature seasonality and interannual to multidecadal variability documented in southern Caribbean corals. Earth and Planetary Science Letters, Vol. 331–332. 2012, pp. 187–200.
Giry, C., Felis, T., Kölling, M., Scholz, D., Fensterer, C., Lohmann, G., Wei, W., Scheffers, S.R.
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2012. Shoreline changes and high-energy wave impacts at the leeward coast of Bonaire (Netherlands Antilles). Earth, Planets and Space, Vol. 64. 2012, Issue 10, pp 905-921.
Engel, M., Brückner, H., et al.
