Search publications of the members of the Royal Belgian institute of natural Sciences
-
A surprisingly short early Holocene humid spell inferred from remnant shorelines and palaeolake deposits in northern Arabia
- Early Holocene greening of the Sahara has been inferred from many sedimentary archives (e.g. Hoelzmann et al., 2001). Likewise, over the last two decades similar reconstructions of lakes and a more humid climate have been established for the southern Arabian Peninsula (e.g. Fleitmann et al., 2007; Engel et al., 2017) and the Levant (Bar-Matthews et al., 2003). Such evidence also exists for northern Arabia (Schulz and Whitney, 1986; Crassard et al., 2013; Zielhofer et al., 2018), but is limited in sufficiently robust proxy data and chronological resolution, hampering our understanding of the scarce archaeological record of that time (Hilbert et al., 2014). In this paper, we present latest results of the ongoing DFG-funded project CLEAR, which explores the highly resolved palaeolake record of the sabkha basin in the oasis of Tayma, northern Arabia. Today only flooded episodically after rainfall events, the endorheic basin is encircled by a ring of isolated shoreline deposits in an altitudinal corridor of only a few metres, consisting almost entirely of Melanoides tuberculatus and Hydrobia sp. shells, Amphibalanus amphitrite carapaces, foraminifers, and ostracods, with minor amounts of siliciclastic sand (Engel et al., 2012; Pint et al., 2017). These deposits have recently been mapped and dated by 14C and OSL, and indicate the presence of an early Holocene lake with a depth of up to 17 m and an area of up to 22 km². They correlate with partly varved lake sediments of the central basin according to the 14C-(pollen concentrates), varve- and cryptotephra-based chronology (Dinies et al., 2015; Neugebauer et al., 2017). In the framework of CLEAR, the palaeolake sequence was subjected to detailed sedimentological, geochemical and micropalaeontological analyses (grain-size distribution, XRD, µXRF, thin- section studies, foraminifera, ostracods, diatoms, pollen, stable isotopes, C/N, lipid biomarkers). Current results indicate increasing moisture at Tayma from c. 9300 cal. yrs. BP with pronounced humid conditions only over the second half of the 9th millennium BP, represented by an annually varved sequence of aragonite-, diatom-, and clastic silt- dominated laminae. After 7950 cal. yrs. BP, aridification set in, leading to sabkha development at c. 4200 cal. yrs. BP and the accumulation of aeolian sand. The rather short period of increased moisture availability contrasts with adjacent records from southern Arabia and the Levantine region (Bar-Matthews et al., 2003; Fleitmann et al., 2007), which reflect more humid conditions over several millennia during the early to mid-Holocene. This is a contribution to the research project “CLEAR – Holocene Climatic Events of Northern Arabia” (DFG PL 535/2-1; FR 1489/5-1; EN 977/2-1); see also contribution Pint et al. (this conference) and project website https://clear2018.wordpress.com. References: Bar-Matthews, M, et al., Geochim. Cosmochim. Acta 67, 3181–3199 (2003); Crassard, R., et al., PLOS ONE 8, e68061 (2013); Dinies, M., et al., Quat. Int. 382, 293–302 (2015); Engel, M., et al., 2012, Quat. Int. 266, 131–141 (2012); Engel, M., et al., Global Planet. Change 148, 258–267 (2017); Fleitmann, D., et al., Quat. Sci. Rev. 26, 170–188 (2007); Hilbert, Y.H., et al., J. Archaeol. Sci. 50, 460–474 (2014); Hoelzmann, P., et al., Palaeogeogr. Palaeocl. 169, 193–217 (2001); Neugebauer, I., et al., Quat. Sci. Rev. 170 269–275 (2017); Pint, A., et al., J. Foram. Res. 42, 175–187 (2017); Schulz, E., Whitney, Hydrobiologia 143, 175–190 (1986); Zielhofer, C., et al., Quat. Int. 473, 120–140 (2018).
-
Simulation of boulder transport in a flume comparing cuboid and complex-shaped boulder models
- Coasts around the world are affected by high-energy wave events like storm surges or tsunamis depending on their regional climatological and geological settings. Coarse clasts (boulders to fine blocks) deposited on the shore can provide evidence for hazard-prone areas and physical characteristics of the flooding event. In order to better understand the process of boulder transport by tsunamis and to calibrate numerical hydrodynamic models, we conducted physical boulder transport experiments in a Froude-Scale of 1:50 utilizing idealized boulder shapes (cuboids) as well as realistic, complex boulder shapes based on real-world data. Comparing the behaviour of natural shaped with idealized boulders, allows identifying how the boulder shape influences the transport process in terms of transport mode (sliding, shifting, saltation), path and distance. Experiments are conducted in a 33 m long and 1 m wide flat wave flume ending on an ascending coastal profile. The gradient angle of the ramp changes from 11◦ to 4◦ ending on a flat elevated platform resulting in a total length of 4.5 m. The complex shaped boulder model (17.4x9.6x7.6 cm3) is constructed from photogrammetric data of a coastal boulder on Bonaire in the Dutch Caribbean (BOL2 in Engel and May, 2012), which is assumed to be transported by a tsunami. A cuboid boulder model of equivalent volume and weight (14x8x6 cm3) is created for comparison. The tsunami is modelled as a broken bore generated by two computer-controlled pumps. Each experimental run set-up was repeated for at least three times. The results show a significant influence of the boulder shape, in particular regarding the area of the contact surface when the bore approaches the boulder. With increasing contact surface higher transport distances occur. Due to the shape of the complex boulder tends slightly towards a rough ovoid, which is more streamlined than the idealized shape, the effectively acting drag force decreases and leads to reduced transport distances. The predominant transport mode during the experiments was sliding combined with gentle rotating around the vertical axis. However, in several experimental cases the complex boulder significantly rotates while the idealized does not. Recognizing that the transport distance, presumably due to decreasing ground contact and therefore less friction, increases during rotational transport, it is remarkable that the complex boulder still does not reach the transport distances of the idealized one. Experiments for boulder-boulder interactions generally show reduced transport distances. The bore-facing boulder generates a “flow shield” preserving the latter boulder from movement. In consequence, the bore-facing boulder hits its neighbour and stops moving. Within the range of our experiments, this boulder-boulder impact does not exceed a necessary energy-threshold for dislocating the second boulder. Beside further results regarding the influence of the initial water level, increased bottom friction and exper- iment sensitivity, insights into a numerical model based on these experiments will be presented. Engel, M.; May, S.M.: Bonaire’s boulder fields revisited: evidence for Holocene tsunami impact on the Leeward, Antilles. Quaternary Science Reviews 54, 126–141, 2012.
-
The Early Holocene Humid Period in N Arabia – proxy evidence from a unique varved lake record
- There is growing interest in deciphering the hydroclimatic dynamics on the Northern Arabian Peninsula during and after the Early Holocene Humid Period (EHHP) as a key for better understanding the role of climate in driving neolithisation and the evolution of new lifestyles in the poorly studied Arabian Desert. However, our knowledge about the magnitude, timeframe and sources of increased moisture in Northern Arabia during the EHHP is limited due to a lack of robust proxy data. Here we provide the first high-resolution and precisely dated multi-proxy reconstruction of the hydroclimatic variability during the EHHP for northern Arabia, retrieved from annually laminated (varved) sediments of the Tayma palaeolake record. We found pronounced seasonal variability during the lake’s evolution, which we reconstructed through micro-facies analyses of the varved sediments. Changing lake water evaporation and the lake-internal productivity was inferred using stable oxygen and carbon isotope compositions (δ18O and δ13C) of carbonates. The compound-specific hydrogen isotope composition of plant-wax n-alkanes (δDwax) was used as a proxy for changing moisture supply. Our robust age model is well constrained by a floating varve chronology anchored through 14C dating of pollen concentrates and the well-dated ‘S1’ cryptotephra. Our results show that slightly wetter conditions started at Tayma at ca. 9300 yrs BP. The highest moisture availability was only achieved during a ca. 600 years lasting deep-lake phase from ca. 8500 to 7900 yrs BP, when varves formed in the lake. This implies that the EHHP was comparably short in northern Arabia. Furthermore, we found a complex regional hydrological pattern during the EHHP on centennial time-scales, which we discuss with respect to alternative moisture sources and mechanisms that led to the observed hydroclimatic signature at Tayma. This study is a contribution to the research project “CLEAR – Holocene Climatic Events of Northern Ara- bia” (https://clear2018.wordpress.com/).
-
Metagenomics of tsunami deposits
- Onshore deposits of tsunamis provide information on the long-term frequency-magnitude patterns of events, which may not be covered by historical or instrumental records. Such information is crucial to assess coastal hazards and mitigation measures against the loss of life and assets. The identification of tsunami deposits in the coastal sedimentary record and the reconstruction of flooding processes requires reliable proxies, which are based on studies of recent tsunami deposits. Microfossils (e.g. foraminifera, ostracods, diatoms) are often applied to recognize tsunami deposits and differentiate them from storm deposits. In terms of foraminifera, tsunami deposits mostly contain allochthonous associations dominated by benthic intertidal to inner shelf taxa. Specimens may originate from outer shelf to bathyal depths; even planktonic forms may occur. Furthermore, changes in test numbers, taphonomy, size or adult/juvenile ratios compared to background sedimentation are common (Engel et al., 2016). However, dissolution of microfossils often prevents identification and reduces their value as a proxy (e.g. Yawsangratt et al., 2012). We address the problem of post-depositional dissolution of foraminiferal tests in tsunami deposits by applying high- throughput metagenomic sequencing techniques to identify foraminiferal associations based on DNA remains. Metagenomics (or environmental genomics) is related to sequencing DNA directly from the sediment record, where the genetic material may persist for tens of thousands of years. Among the broad range of organisms tackled in metagenomic studies so far, foraminifera (single-celled protists) were chosen as they show a water depth-related zonation in subtidal environments and were the first group to have been identified successfully in palaeo-tsunami deposits by their DNA (Szczuciński et al., 2016). The core study area are the Shetland Islands, exposed to the mega-tsunami triggered by the early Holocene Storegga submarine slide off the coast of Norway. Tsunami run-up of more than 25 m left a distinct landward-thinning sand layer with an erosive lower contact, locally large rip- up clasts, fining-upward sequences and marine diatoms in coastal lakes and peat lowlands. In addition to Storegga tsunami deposits, two younger tsunami deposits dated to c. 5 and 1.5 ka (Bondevik et al., 2005) were sampled during a field campaign in March 2018. Preliminary microscope analysis reveals rich foraminiferal associations in the shallow subtidal muddy sands of protected fjords, which represent the main source area for tsunami deposits. The onshore tsunami deposits, however, vertically confined by ubiquitous dystrophic peat, are void of any carbonate, which seems to have quickly dissolved after deposition in the low-pH environment. This setting paves the way for developing a new eDNA-based proxy to support the identification of tsunamis in the sedimentary record. Funding by a BELSPO BRAIN-be pioneer grant (BR/175/PI/GEN-EX) is gratefully acknowledged. References: Bondevik, S., Mangerud, J., Dawson, S., Dawson, A., Lohne, Ø., 2005. Evidence for three North Sea tsunamis at the Shetland Islands between 8000 and 1500 years ago. Quat. Sci. Rev. 24, 1757–1775. Engel, M., Oetjen, J., May, S.M., Brückner, H., 2016. Tsunami deposits of the Caribbean – Towards an improved coastal hazard assessment. Earth Sci. Rev. 163, 260–296. Szczuciński, W., Pawłowska, J., Lejzerowicz, F., Nishimura, Y., Kokociński, M., Majewski, W., Nakamura, Y., Pawlowski, J., 2016. Ancient sedimentary DNA reveals past tsunami deposits. Mar. Geol. 381, 29–33. Yawsangratt, S., Szczuciński, W., Chaimanee, N., Chatprasert, S., Majewski, W., Lorenc, S., 2012. Evidence of probable paleotsunami deposits on Kho Khao Island, Phang Nga Province, Thailand. Nat. Hazards 63, 151–163.
-
Reef-top platform coral boulders of Eastern Samar demonstrate the long-term coastal hazard of extreme waves
- The Eastern Visayas region in the Philippines experiences some of the most violent tropical cyclones on Earth, exemplified by Typhoon Haiyan (7–9 November 2013) or Typhoon Hagupit (6–8 December 2014). Moreover, strong earthquakes along the Philippine Trench have triggered tsunamis in the past, both implying significant hazards of coastal flooding through extreme waves for the Pacific coast of the island of Samar. Due to the very short and fragmented historical record of the region, not much is known about frequency-magnitude relationships and maximum magnitudes on centennial and millennial scales, which can be derived from geological traces and which should be considered in coastal hazard management. We studied a large boulder field along the north coast of Eastern Samar distributed over an elevated reef platform to understand mechanisms of boulder transport and to derive implications for the maximum spatial extent, depth and velocity of coastal flooding. In this paper, we compare the field observations to physical experiments of boulder transport by extreme waves currently undertaken in a flume of the Methods: (i) Documentation of location, shape, morphological features, length, orientation of main axes of >250 boulders (1.5 m<a-axes<11.9 m) in the field; (ii) UAV-based 2D/3D- mapping; (iii) creation of SfM-based models of prominent boulders; (iv) interviewing elders of the local community for past events; (v) inverse modelling of coastal flooding and comparison with Deft3D-based numerical models of Haiyan and Hagupit; (vi) multi-temporal analyses of Pléiades and Worldview-3 scenes to reconstruct boulder movement during recent events; (vii) estimate the age of the carbonate platform and the timing of transport through 230U/Th dating. Preliminary results: (i) the platform’s age is mid-/late Holocene and formed through relative sea-level fall; boulder transport occurred over the late Holocene; (ii) Haiyan and Hagupit shifted boulders up to 115 t in steps of <32 m only at the seaward margin of the boulder field; (iii) transport during Haiyan and Hagupit clearly reflects the individual approaching angle of waves; (iv) size-distance relationships of the entire boulder field are unclear (r2=0.46 at best) and large clasts are located up to 1.3 km from the platform edge indicating that also major long-period waves (infragravity waves, tsunamis) have occurred in the past; (vi) flow velocities of up to 6–7 m/s were inferred for Hagupit, while largest clasts more inland (up to 11.9x8.1x4.2 m3; 433 t) require minimum values >10 m/s.
-
Anthropogenic and environmental controls of barchan dune dynamics in Qatar
- Barchan dunes are crescentic aeolian landforms of loose, mostly well-sorted sand with a convex side directed upwind and two horns pointing downwind. Their migration is mainly controlled by sand supply, dune size, wind patterns, vegetation cover and human impact. In Qatar, their distribution is limited to the southeastern part of the peninsula, where they play an important role for tourism and camping activities among locals. We investigate the variability of dune migration in Qatar over a time period of 50 years using high-resolution satellite and aerial imagery. We then explore its relation to the regional Shamal wind system (NNW–SSE), teleconnection patterns, and limitations in sand supply associated with the transgression of the Arabian Gulf, which explain the fact that Qatar is gradually being stripped from aeolian landforms with a remaining dune population in the southeast. Strong size-dependent differences in migration rates of individual dunes as well as significant decadal variability on a dune-field scale are detected, the latter closely correlating with summer Shamal activity. The summer Shamal itself is mainly driven by pressure differences between the stationary anticyclone over the eastern Mediterranean and the established summer heat low over Iran and adjacent areas. It seems to be related to the intensity of the North Atlantic Oscillation and the Indian Summer Monsoon, in particular during years of relatively strong (weak) summer Shamals. High uncertainties associated with the extrapolation of migration rates back into the Holocene, however, do not permit further refining of the timing of the loss of sand supply and the onset of the mid-Holocene relative sea-level (RSL) highstand. For the youngest phase considered in this study (2006–2015), human impact has significantly accelerated dune migration under a more or less stable Shamal regime through systematic sand mining and excessive vehicle traffic upwind of the core study area, which started in 2007.
-
Micro-and Macrofossils as indicators of Early Holocene palaeoenvironmental changes in the northwestern Saudi Arabia
-
GEN-EX - Metagenomics of Extreme-Wave Events
-
Megaclasts of Eastern Samar (Philippines)–Implications for the long-term hazard of extreme waves
-
CARTS - the database of CARibbean Tsunami depositS
-
Tracing ancient DNA of Foraminifera in tsunami deposits (GEN-EX)
- 1. Background Tsunami deposits provide information on the long-term frequency-magnitude patterns of events, which may not be covered by the historical and instrumental record. Such information is crucial for the assessment of coastal hazards and mitigation measures against the loss of life and assets. In order to identify tsunami deposits in the coastal sedimentary record and to infer tsunami characteristics, a wide range of proxies has been established based on studies of recent tsunami deposits. Microfossils (e.g. foraminifera, ostracods, diatoms) are often used to recognize tsunami deposits, and to differentiate them from those of other processes. In terms of foraminifera, tsunami deposits mostly contain allochthonous associations dominated by benthic intertidal to inner shelf taxa. Specimens may originate from outer shelf to bathyal depths; even planktonic forms may occur. Furthermore, changes in test numbers, taphonomy, size or adult/juvenile ratios compared to background sedimentation are common (Pilarczyk et al., 2014; Engel et al., 2016). However, dissolution of microfossils often prevent identification and diminish their value as a proxy (Yawsangratt et al., 2012). 2. Study goals and concept To address the problem of post-depositional alteration of microfossil associations in tsunami deposits, high-throughput metagenomic sequencing techniques are applied by the GEN-EX project to identify marine organisms in onshore sand layers based on their DNA remains. Metagenomics (or environmental genomics) is related to sequencing DNA directly from the environmental samples, where the genetic material may have been preserved in sedimentary records covering tens of thousands of years. Metagenomics is an emerging technique in environmental research and is used to characterize the diversity of bacterial communities but also higher organisms such as animals, plants and fungi of recent and ancient origin in a variety of settings, including ice, lake sediments, soils, cave deposits, and various types of surface waters. Metagenomics can also be used to detect cryptic diversity, ultimately providing more accurate estimates of biodiversity (Pedersen et al., 2015). Among the broad range of organisms, foraminifera (single-celled protists) show a water depth-related zonation in subtidal environments, and are the first to have been identified successfully in palaeo- tsunami deposits by their DNA (SzczuciĔski et al., 2016). The main objectives of GEN-EX include: quantifying the relationship between water depth and the distribution of different foraminiferal taxa where known tsunami deposits are present, using a comparative classic micropalaeontological and metagenomic approach; assessing the potential (based on both approaches) for identifying key indicator species in tsunami deposits in different coastal settings; and establishing how metagenomic approaches can contribute to the differentiation between storm and tsunami deposits. 3. DNA extraction DNA will be analysed in two types of material – modern extant foraminifera and sediments (tsunami deposits and adjacent layers). DNA extracted from single foraminiferal specimens will be followed by whole genome amplification to obtain sufficient DNA concentrations. Either part of the nuclear 18S rRNA region or the mitochondrial genome (mtDNA) will be amplified, before high-throughput sequencing of the amplicons. Sequences will be edited and aligned, and their identity verified by BLAST (Altschul et al., 1990) searches in Genbank and the Forambarcoding project (http://forambarcoding.unige.ch). A project-specific database of 18S and mtDNA data of the identified recent foraminifera will be constructed. Sampling of tsunami deposits and DNA extraction follows the protocol of SzczuciĔski et al. (2016). Suitable primers will be developed from our reference database of recent foraminifera to amplify overlapping short fragments of 18S or mtDNA of the target species. Amplicon concentration will be quantified and prepared for high-throughput sequencing. Sequence data will be analysed with different bioinformatics pipelines (e.g. QIIME), including quality control, removal of barcodes and adaptors, identification and removal of chimeric and redundant sequences, and comparisons with our own and open access databases of 18S data for defining Operational Taxonomic Units with 95% and 97% similarity cut-offs. 4. Study area One of the study areas, where the eDNA approach is applied, are the Shetland Islands, exposed to the mega-tsunami triggered by the early Holocene Storegga submarine slide off the coast of Norway. Sediment run-up of more than 25 m left a distinct landward-thinning sand layer with an erosive lower contact, large rip-up clasts, fining-upward sequences and marine diatoms in near-shore lakes and coastal peat lowlands. In addition to sediments associated with the Storegga tsunami, two younger tsunami deposits dated to c. 5 and 1.5 ka (Bondevik et al., 2005) are investigated. Sampling for the planned foraminiferal analyses and eDNA extraction of the deposits and their source area, comprising along the beach and subtidal area to the central shelf area is scheduled for the second half of March 2018. 5. Acknowledgements Funding is kindly provided by a BELSPO BRAIN-be pioneer grant (BR/175/PI/GEN-EX). 6. References Altschul, S.F., Gish, W., Miller, W., Myers, E.W. & Lipman, D.J., 1990. Basic local alignment search tool. Journal of Molecular Biology, 215, 403–410. Bondevik, S., Mangerud, J., Dawson, S., Dawson, A. & Lohne, Ø., 2005. Evidence for three North Sea tsunamis at the Shetland Islands between 8000 and 1500 years ago. Quaternary Science Reviews, 24, 1757–1775. Engel, M., Oetjen, J., May, S.M. & Brückner, H., 2016. Tsunami deposits of the Caribbean – Towards an improved coastal hazard assessment. Earth-Science Reviews, 163, 260–296. Pedersen, M.W., Overballe-Petersen, S., Ermini, L., Sarkissian, C.D., Haile, J., Hellstrom, M., Spens, J., Thomsen, P.F., Bohmann, K., Cappellini, E., Bærholm Schnell, I., Wales, N.A., Carøe, C., Campos, P.F., Schmidt, A.M.Z., Gilbert, M.T.P., Hansen, A.J., Orlando, L. & Willerslev, E., 2015. Ancient and modern environmental DNA. Philosophical Transactions of the Royal Society B, 370, 20130383. Pilarczyk, J.E., Dura, T., Horton, B.P., Engelhart, S.E., Kemp, A.C. & Sawai, Y., 2014. Microfossils in coastal environments as indicators of paleo-earthquakes, tsunamis and storms. Palaeogeography, Palaeoclimatology, Palaeoecology, 413, 144–157. SzczuciĔski, W., Pawłowska, J., Lejzerowicz, F., Nishimura, Y., KokociĔski, M., Majewski, W., Nakamura, Y. & Pawlowski, J., 2016. Ancient sedimentary DNA reveals past tsunami deposits. Marine Geology, 381, 29–33. Yawsangratt, S., SzczuciĔski, W., Chaimanee, N., Chatprasert, S., Majewski, W. & Lorenc, S., 2012. Evidence of probable paleotsunami deposits on Kho Khao Island, Phang Nga Province, Thailand. Natural Hazards, 63, 151–163.
-
Abc Taxa: series of peer-reviewed manuals dedicated to capacity building in taxonomy & collection management
- Today, the so-called taxonomic impediment, i.e., the lack of taxonomic (inclusive of genetic) information, taxonomic and curatorial expertise, and infrastructure in many parts of the world, means that accessing and generating taxonomic information remains extremely difficult. To alter this trend, the Convention on Biological Diversity installed the Global Taxonomy Initiative (GTI) and endorsed it with an operational program of work. Its objectives are to remedy the knowledge gaps in our taxonomic system, increase the number of well-trained taxonomists and curators, optimize the infrastructure needed to do sound taxonomic research, significantly improve access to taxonomic collections, data, and metadata, and, thereby, to improve decision- making in conservation of biodiversity. To speed up taxonomic capacity building the Belgian GTI Focal Point has established the series Abc Taxa (www.abctaxa.be), a toll-free information highway between experts and novices. It is believed that this artery will speed up the construction of taxonomic capacity, as it does not evoke the expensive, long-term teacher-apprentice relationships previously utilized to install operational, high-quality taxonomists and collection managers. Since 2005, 19 volumes have been released with subjects as diverse as taxonomy of sea cucumbers of the Comoros, good practices in collection management of mollusc collections, taxonomy of the amphibians of Cuba and of Guyana, taxonomy of algae of Sri Lanka, bee taxonomy in sub-Saharan Africa, mushroom taxonomy of Central Africa, introduction to the taxonomy of mites, taxonomy of invasive succulents of South Africa, taxonomy of the sawflies of southern Africa, taxonomy of the diatoms of the Congo, taxonomy of fish parasites of African Freshwater fishes and taxonomy of the brittle and basket stars of South Africa. This contribution briefly details the scope and aims of Abc Taxa, demonstrates the value of the series for development, and acts as a call for future manuscripts.
-
Size-effect, asymmetry, and small-scale spatial variation in otolith shape of juvenile sole in the Southern North Sea
-
Zebinidae (Caenogastropoda: Rissooidea) from the islands of St Helena and Ascension, with the description of two new species and a comment on Rissoina decipiens E. A. Smith, 1890
-
Generating affordable protection of high seas biodiversity through cross-sectoral spatial planning
-
Rapid Local Adaptations in an Invasive Frog (Xenopus laevis): the Importance of Functional Trait Measurements to Predict Future Invasions
-
The oldest cereals in the coversand area along the North Sea coast of NW Europe, between ca. 4800 and 3500 cal BC, at the wetland site of ‘Bazel-Sluis’ (Belgium).
-
The use of Scientific Techniques in the Study, Reconstruction of and Human Interaction with Woodlands
-
CoastColour Round Robin data sets: a database to evaluate the performance of algorithms for the retrieval of water quality parameters in coastal waters
- The use of in situ measurements is essential in the validation and evaluation of the algorithms that provide coastal water quality data products from ocean colour satellite remote sensing. Over the past decade, various types of ocean colour algorithms have been developed to deal with the optical complexity of coastal waters. Yet there is a lack of a comprehensive intercomparison due to the availability of quality checked in situ databases. The CoastColour Round Robin (CCRR) project, funded by the European Space Agency (ESA), was designed to bring together three reference data sets using these to test algorithms and to assess their accuracy for retrieving water quality parameters. This paper provides a detailed description of these reference data sets, which include the Medium Resolution Imaging Spectrometer (MERIS) level 2 match-ups, in situ reflectance measurements, and synthetic data generated by a radiative transfer model (HydroLight). These data sets, representing mainly coastal waters, are available from doi:10.1594/PANGAEA.841950. The data sets mainly consist of 6484 marine reflectance (either multispectral or hyperspectral) associated with various geometrical (sensor viewing and solar angles) and sky conditions and water constituents: total suspended matter (TSM) and chlorophyll a (CHL) concentrations, and the absorption of coloured dissolved organic matter (CDOM). Inherent optical properties are also provided in the simulated data sets (5000 simulations) and from 3054 match-up locations. The distributions of reflectance at selected MERIS bands and band ratios, CHL and TSM as a function of reflectance, from the three data sets are compared. Match-up and in situ sites where deviations occur are identified. The distributions of the three reflectance data sets are also compared to the simulated and in situ reflectances used previously by the International Ocean Colour Coordinating Group (IOCCG, 2006) for algorithm testing, showing a clear extension of the CCRR data which covers more turbid waters.
-
Classification of multibeam sonar image using the Weyl transform
