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  • 1
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    DEEPEN, Western DAS Branch (2024)
    GFZ Data Services
    Details
    Publication Date: 2024-05-28
    Description: Abstract
    Description: From June to August 2021 the DEEPEN project deployed a dense seismic network across the Hengill geothermal area in southwest Iceland to image and characterize faults and high-temperature zones at high resolution. The nodal network comprised 498 geophone nodes spread across the northern Nesjavellir and southern Hverahlíð geothermal fields and was complemented by an existing permanent and temporary backbone seismic network of a total of 44 short-period and broadband stations. In addition, two fiber optic telecommunication cables near the Nesjavellir geothermal power plant were interrogated with commercial DAS-interrogators. The here published dataset contains a subset of the downsampled DAS-recordings from the western fiber optic array. The original data were downsampled from 2000Hz to 250 Hz using the das-convert tool (https://doi.org/10.5880/GFZ.2.1.2021.005). Note that there was a problem with the GNSS timing in the original recorded data which caused significant temporal drift. This has mostly been corrected in the downsampled data, but some residual timing error may exist. Waveform data is available from the GEOFON data centre, under network code 1D, and is fully open.
    Keywords: EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 EARTHQUAKES ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 VOLCANIC ACTIVITY ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS ; In Situ Land-based Platforms 〉 GEOPHYSICAL STATIONS/NETWORKS 〉 SEISMOLOGICAL STATIONS ; Passive seismic ; Seismometers ; Velocity ; MiniSEED ; DAS
    Type: Dataset , Seismic Network
    Format: 1700GB
    Format: .mseed
    Format: XML
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    DATA GFZ
  • 2
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    Site amplifications for European stations obtained by a spectral decomposition approach (2024)
    GFZ Data Services
    Details
    Publication Date: 2024-05-28
    Description: Abstract
    Description: This repository contains the site amplification functions obtained by Bindi et al. (2023). The site amplifications were obtained through a Generalized Inversion Technique (GIT) applied to seismic recordings downloaded from EIDA (Strollo et al., 2021) and EarthScope (https://service.iris.edu/) using stream2segment software (Zaccarelli, 2018). We computed the Fourier spectra of S-waves windows considering the square root of the sum of the two horizontal components squared. The site amplifications are relative to the station CH.LSS (station Linth-Limmern of the Swiss network, https://stations.seismo.ethz.ch/en/station-information/station-details/station-given-networkcode-and-stationcode/index.html?networkcode=CH&stationcode=LLS), installed on rock with shear wave velocity averaged over the top 30 m equal to vs30=2925 m/s (Fäh et al. 2009). The site amplification at the reference station LLS is constrained to be equal to 1 for frequencies f below 10 Hz and to the function exp[−0.015π(f−10)] above 10 Hz, to account for near-surface attenuation effects at high frequencies. Details about the decomposition can be found in Bindi et al (2023). The file siteAmp_repo.csv uses as field separator the semicolon (;). It contains: - column freq: values of frequency between 0.5 and 20 Hz; - columns with site amplifications: 3001 columns with column name given by network_station_channel (e.g. GR_MOX_HH indicated station MOX of network GR, channel HH). The R script (R Core Team, 2024) plotRepo.R shows how to read and plot the site amplification for a given station.
    Keywords: Site amplification ; Europe ; EARTH SCIENCE 〉 SOLID EARTH 〉 TECTONICS 〉 EARTHQUAKES ; geological process 〉 seismic activity 〉 earthquake
    Type: Dataset , Dataset
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    DATA GFZ
  • 3
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    Pollen analyses of sediment core GeoB9508-5 (2012)
    PANGAEA
    In:  Supplement to: Bouimetarhan, Ilham; Prange, Matthias; Schefuß, Enno; Dupont, Lydie M; Lippold, Jörg; Mulitza, Stefan; Zonneveld, Karin A F (2012): Sahel megadrought during Heinrich Stadial 1: evidence for a three-phase evolution of the low- and mid-level West African wind system. Quaternary Science Reviews, 58, 66-76, https://doi.org/10.1016/j.quascirev.2012.10.015
    Details
    Publication Date: 2024-05-27
    Description: Millennial-scale dry events in the Northern Hemisphere monsoon regions during the last Glacial period are commonly attributed to southward shifts of the Intertropical Convergence Zone (ITCZ) associated with an intensification of the northeasterly (NE) trade wind system during intervals of reduced Atlantic meridional overturning circulation (AMOC). Through the use of high-resolution last deglaciation pollen records from the continental slope off Senegal, our data show that one of the longest and most extreme droughts in the western Sahel history, which occurred during the North Atlantic Heinrich Stadial 1 (HS1), displayed a succession of three major phases. These phases progressed from an interval of maximum pollen representation of Saharan elements between ~19 and 17.4 kyr BP indicating the onset of aridity and intensified NE trade winds, followed by a millennial interlude of reduced input of Saharan pollen and increased input of Sahelian pollen, to a final phase between ~16.2 and 15 kyr BP that was characterized by a second maximum of Saharan pollen abundances. This change in the pollen assemblage indicates a mid-HS1 interlude of NE trade wind relaxation, occurring between two distinct trade wind maxima, along with an intensified mid-tropospheric African Easterly Jet (AEJ) indicating a substantial change in West African atmospheric processes. The pollen data thus suggest that although the NE trades have weakened, the Sahel drought remained severe during this time interval. Therefore, a simple strengthening of trade winds and a southward shift of the West African monsoon trough alone cannot fully explain millennial-scale Sahel droughts during periods of AMOC weakening. Instead, we suggest that an intensification of the AEJ is needed to explain the persistence of the drought during HS1. Simulations with the Community Climate System Model indicate that an intensified AEJ during periods of reduced AMOC affected the North African climate by enhancing moisture divergence over the West African realm, thereby extending the Sahel drought for about 4000 years.
    Keywords: 293; Center for Marine Environmental Sciences; GeoB9508-5; Gravity corer (Kiel type); M65/1; MARUM; Meteor (1986); SL
    Type: Dataset
    Format: application/zip, 5 datasets
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    DATA PANGAEA
  • 4
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    Dinoflagellate cysts and pollen distribution of marine surface sediments off West Africa (2009)
    PANGAEA
    In:  Supplement to: Bouimetarhan, Ilham; Marret, Fabienne; Dupont, Lydie M; Zonneveld, Karin A F (2009): Dinoflagellate cyst distribution in marine surface sediments off West Africa (6-17°N) in relation to sea-surface conditions, freshwater input and seasonal coastal upwelling. Marine Micropaleontology, 71(3-4), 113-130, https://doi.org/10.1016/j.marmicro.2009.02.001
    Details
    Publication Date: 2024-05-27
    Description: An organic-walled dinoflagellate cyst analysis was carried out on 53 surface sediment samples from West Africa (17-6°N) to obtain insight in the relationship between their spatial distribution and hydrological conditions in the upper water column as well as marine productivity in the study area. Multivariate analysis of the dinoflagellate cyst relative abundances and environmental parameters of the water column shows that sea-surface temperature, salinity, marine productivity and bottom water oxygen are the factors that relate significantly to the distribution patterns of individual species in the region. The composition of cyst assemblages and dinoflagellate cyst concentrations allows the identification of four hydrographic regimes; 1) the northern regime between 17 and 14°N characterized by high productivity associated with seasonal coastal upwelling, 2) the southern regime between 12 and 6°N associated with high-nutrient waters influenced by river discharge 3) the intermediate regime between 14 and 12°N influenced mainly by seasonal coastal upwelling additionally associated with fluvial input of terrestrial nutrients and 4) the offshore regime characterized by low chlorophyll-a concentrations in upper waters and high bottom water oxygen concentrations. Our data show that cysts of Polykrikos kofoidii, Selenopemphix quanta, Dubridinium spp., Echinidinium species, cysts of Protoperidinium monospinum and Spiniferites pachydermus are the best proxies to reconstruct the boundary between the NE trade winds and the monsoon winds in the subtropical eastern Atlantic Ocean. The association of Bitectatodinium spongium, Lejeunecysta oliva, Quinquecuspis concreta, Selenopemphix nephroides, Trinovantedinium applanatum can be used to reconstruct past river outflow variations within this region.
    Keywords: 286; 287; 288; 289; 290; 291; 293; 295; 297; 298; 300; 301; 302; 303; 304; 305; 306; 307; 310; 311; 312; 313; 314; 316; 317; 318; 319; 320; 321; 322; 323; 324; 326; 327; 329; 330; 331; 371; 376; 388; Atlantic Ocean; Center for Marine Environmental Sciences; Eckernfoerder Bay; GeoB9501-4; GeoB9502-5; GeoB9503-3; GeoB9503-5; GeoB9504-4; GeoB9505-3; GeoB9506-3; GeoB9508-4; GeoB9510-3; GeoB9512-4; GeoB9513-5; GeoB9515-2; GeoB9516-4; GeoB9517-5; GeoB9518-4; GeoB9519-6; GeoB9520-4; GeoB9521-3; GeoB9522-2; GeoB9525-5; GeoB9526-4; GeoB9527-6; GeoB9528-1; GeoB9529-1; GeoB9531-2; GeoB9532-1; GeoB9533-3; GeoB9534-4; GeoB9535-5; GeoB9536-4; GeoB9537-4; GeoB9538-5; GeoB9539-1; GeoB9541-1; GeoB9542-1; GeoB9544-1; GeoB9545-1; GeoB9546-1; GEOTROPEX 83, NOAMP I; Giant box corer; GIK16402-1; GIK16404-1; GIK16405-1; GIK16407-1; GIK16414-1; GIK16421-1; GIK16425-1; GIK16437-3; GIK16558-1; GIK16755-1; GIK16764-1; GIK16765-1; GIK16766-1; GIK16767-1; GIK16768-1; GIK16769-1; GKG; Gravity corer (Kiel type); LI198x; Littorina; M6/5; M65; M65/1; MARUM; Mauritania Canyon; Meteor (1964); Meteor (1986); MUC; MultiCorer; off Guinea; SL; van Veen Grab; VGRAB
    Type: Dataset
    Format: application/zip, 2 datasets
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    DATA PANGAEA
  • 5
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    Pollen and organic-walled dinoflagellate cyst assemblages of sediment core GeoB9503-5 (2009)
    PANGAEA
    In:  Supplement to: Bouimetarhan, Ilham; Dupont, Lydie M; Schefuß, Enno; Mollenhauer, Gesine; Mulitza, Stefan; Zonneveld, Karin A F (2009): Palynological evidence for climatic and oceanic variability off NW Africa during the late Holocene. Quaternary Research, 72(2), 188-197, https://doi.org/10.1016/j.yqres.2009.05.003
    Details
    Publication Date: 2024-05-27
    Description: Pollen and organic-walled dinoflagellate cyst assemblages from core GeoB 9503-5 retrieved from the mud-belt ( 50 m water depth) off the Senegal River mouth have been analyzed to reconstruct short-term palaeoceanographic and palaeoenvironmental changes in subtropical NW Africa during the time interval from ca. 4200 to 1200 cal yr BP. Our study emphasizes significant coeval changes in continental and oceanic environments in and off Senegal and shows that initial dry conditions were followed by a strong and rapid increase in humidity between ca. 2900 and 2500 cal yr BP. After ca. 2500 cal yr BP, the environment slowly became drier again as indicated by slight increases in Sahelian savannah and desert elements in the pollen record. Around ca. 2200 cal yr BP, this relatively dry period ended with periodic pulses of high terrigenous contributions and strong fluctuations in fern spore and river plume dinoflagellate cyst percentages as well as in the fluxes of pollen, dinoflagellate cysts, fresh-water algae and plant cuticles, suggesting "episodic flash flood" events of the Senegal River. The driest phase developed after about 2100 cal yr BP.
    Keywords: 288; Center for Marine Environmental Sciences; GeoB9503-5; Gravity corer (Kiel type); M65/1; MARUM; Meteor (1986); SL
    Type: Dataset
    Format: application/zip, 3 datasets
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    DATA PANGAEA
  • 6
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    Microcharcoal concentration and elongation, and age model of sediment core MD96-2098 (2015)
    PANGAEA
    In:  Supplement to: Daniau, Anne-Laure; Sanchez Goñi, Maria Fernanda; Martinez, Philippe; Urrego, Dunia H; Bout-Roumazeilles, Viviane; Desprat, Stéphanie; Marlon, Jennifer R (2013): Orbital-scale climate forcing of grassland burning in southern Africa. Proceedings of the National Academy of Sciences, 110(13), 5069-5073, https://doi.org/10.1073/pnas.1214292110
    Details
    Publication Date: 2024-05-27
    Description: Although grassland and savanna occupy only a quarter of the world's vegetation, burning in these ecosystems accounts for roughly half the global carbon emissions from fire. However, the processes that govern changes in grassland burning are poorly understood, particularly on time scales beyond satellite records. We analyzed microcharcoal, sediments, and geochemistry in a high-resolution marine sediment core off Namibia to identify the processes that have controlled biomass burning in southern African grassland ecosystems under large, multimillennial-scale climate changes. Six fire cycles occurred during the past 170,000 y in southern Africa that correspond both in timing and magnitude to the precessional forcing of north-south shifts in the Intertropical Convergence Zone. Contrary to the conventional expectation that fire increases with higher temperatures and increased drought, we found that wetter and cooler climates cause increased burning in the study region, owing to a shift in rainfall amount and seasonality (and thus vegetation flammability). We also show that charcoal morphology (i.e., the particle's length-to-width ratio) can be used to reconstruct changes in fire activity as well as biome shifts over time. Our results provide essential context for understanding current and future grassland-fire dynamics and their associated carbon emissions.
    Keywords: CALYPSO; Calypso Corer; IMAGES; IMAGES II; International Marine Global Change Study; Lüderitz Transect; Marion Dufresne (1995); MD105; MD962098; MD96-2098
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 7
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    Organic-walled dinoflagellate cyst analysis of sediment core GeoB8331-4 and from surface sediment samples off western South Africa (2017)
    PANGAEA
    In:  Supplement to: Zhao, Xueqin; Dupont, Lydie M; Schefuß, Enno; Bouimetarhan, Ilham; Wefer, Gerold (2017): Palynological evidence for Holocene climatic and oceanographic changes off western South Africa. Quaternary Science Reviews, 165, 88-101, https://doi.org/10.1016/j.quascirev.2017.04.022
    Details
    Publication Date: 2024-05-27
    Description: Atmospheric and oceanographic interactions between the Atlantic and Indian Oceans influence upwelling in the southern Benguela upwelling system. In order to obtain a better knowledge of paleoceanographic and paleoenvironmental changes in the southern Benguela region during the Holocene, 12 marine surface sediment samples and one gravity core GeoB8331-4 from the Namaqualand mudbelt off the west coast of South Africa have been studied for organic-walled dinoflagellate cysts in high temporal resolution. The results are compared with pollen and geochemical records from the same samples. Our study emphasizes significantly distinct histories in upwelling intensity as well as the influence of fluvial input during the Holocene. Three main phases were identified for the Holocene. High percentages of cysts produced by autotrophic taxa like Operculodinium centrocarpum and Spiniferites spp. indicate warmer and stratified conditions during the early Holocene (9900-8400 cal. yr BP), suggesting reduced upwelling likely due to a northward shift of the southern westerlies. In contrast, the middle Holocene (8400-3100 cal. yr BP) is characterized by a strong increase in heterotrophic taxa in particular Lejeunecysta paratenella and Echinidinium spp. at the expense of autotrophic taxa. This indicates cool and nutrient-rich waters with active upwelling probably caused by a southward shift of the southern westerlies. During the late Holocene (3100 cal. yr BP to modern), Brigantedinium spp. and other abundant taxa interpreted to indicate fluvial nutrient input such as cyst of Protoperidinium americanum and Lejeunecysta oliva imply strong river discharge with high nutrient supply between 3100 and 640 cal. yr BP.
    Keywords: Center for Marine Environmental Sciences; MARUM; RAiN; Regional Archives for Integrated iNvestigations
    Type: Dataset
    Format: application/zip, 2 datasets
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    DATA PANGAEA
  • 8
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    Dinoflagellate cyst assemblages, Mg/Ca based reconstructed temperatures, stable carbon isotopes, and geochemical parameters of sediment core GeoB9508-5 (2013)
    PANGAEA
    In:  Supplement to: Bouimetarhan, Ilham; Groeneveld, Jeroen; Dupont, Lydie M; Zonneveld, Karin A F (2013): Low- to high- productivity pattern within Heinrich stadial 1: Inferrences from dinoflagellate cyst records off Senegal. Global and Planetary Change, https://doi.org/10.1016/j.gloplacha.2013.03.007
    Details
    Publication Date: 2024-05-27
    Description: In order to investigate a possible connection between tropical northeast (NE) Atlantic primary productivity, Atlantic meridional overturning circulation (AMOC), and drought in the Sahel region during Heinrich Stadial 1 (HS1), we used dinoflagellate cyst (dinocyst) assemblages, Mg/Ca based reconstructed temperatures, stable carbon isotopes (d13C) and geochemical parameters of a marine sediment core (GeoB 9508-5) from the continental slope offshore Senegal. Our results show a two-phase productivity pattern within HS1 that progressed from an interval of low marine productivity between ~ 19 and 16 kyr BP to a phase with an abrupt and large productivity increase from ~ 16 to 15 kyr BP. The second phase is characterized by distinct heavy planktonic d13C values and high concentrations of heterotrophic dinocysts in addition to a significant cooling signal based on reconstructions of past sea surface temperatures (SST). We conclude that productivity variations within HS1 can be attributed to a substantial shift of West African atmospheric processes. Taken together our results indicate a significant intensification of the North East (NE) trade winds over West Africa leading to more intense upwelling during the last millennium of HS1 between ~ 16 and 15 kyr BP, thus leaving a strong imprint on the dinocyst assemblages and sea surface conditions. Therefore, the two-phase productivity pattern indicates a complex hydrographic setting suggesting that HS1 cannot be regarded as uniform as previously thought.
    Keywords: Center for Marine Environmental Sciences; MARUM
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 9
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    Charcoal records of two sediment cores off SW Africa (2012)
    PANGAEA
    In:  Supplement to: Daniau, Anne-Laure; Bartlein, Patrick J; Harrison, S P; Prentice, Iain Colin; Brewer, Simon; Friedlingstein, Pierre; Harrison-Prentice, T I; Inoue, J; Izumi, K; Marlon, Jennifer R; Mooney, Scott D; Power, Mitchell J; Stevenson, J; Tinner, Willy; Andric, M; Atanassova, J; Behling, Hermann; Black, M; Blarquez, O; Brown, K J; Carcaillet, C; Colhoun, Eric A; Colombaroli, Daniele; Davis, Basil A S; D'Costa, D; Dodson, John; Dupont, Lydie M; Eshetu, Z; Gavin, D G; Genries, A; Haberle, Simon G; Hallett, D J; Hope, Geoffrey; Horn, S P; Kassa, T G; Katamura, F; Kennedy, L M; Kershaw, A Peter; Krivonogov, S; Long, C; Magri, Donatella; Marinova, E; McKenzie, G Merna; Moreno, P I; Moss, Patrick T; Neumann, F H; Norstrom, E; Paitre, C; Rius, D; Roberts, Neil; Robinson, G S; Sasaki, N; Scott, Louis; Takahara, H; Terwilliger, V; Thevenon, Florian; Turner, R; Valsecchi, V G; Vannière, Boris; Walsh, M; Williams, N; Zhang, Yancheng (2012): Predictability of biomass burning in response to climate changes. Global Biogeochemical Cycles, 26(4), https://doi.org/10.1029/2011GB004249
    Details
    Publication Date: 2024-05-27
    Description: We analyze sedimentary charcoal records to show that the changes in fire regime over the past 21,000 yrs are predictable from changes in regional climates. Analyses of paleo- fire data show that fire increases monotonically with changes in temperature and peaks at intermediate moisture levels, and that temperature is quantitatively the most important driver of changes in biomass burning over the past 21,000 yrs. Given that a similar relationship between climate drivers and fire emerges from analyses of the interannual variability in biomass burning shown by remote-sensing observations of month-by-month burnt area between 1996 and 2008, our results signal a serious cause for concern in the face of continuing global warming.
    Keywords: Center for Marine Environmental Sciences; MARUM
    Type: Dataset
    Format: application/zip, 2 datasets
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  • 10
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    Southeast African provenance study (2017)
    PANGAEA
    In:  Supplement to: Hahn, Annette; Miller, Charlotte; Andó, Sergio; Bouimetarhan, Ilham; Cawthra, Hayley C; Garzanti, Eduardo; Green, Andrew N; Radeff, Giuditta; Schefuß, Enno; Zabel, Matthias (2018): The provenance of terrigenous components in marine sediments along the east coast of southern Africa. Geochemistry, Geophysics, Geosystems, 19(7), 1946-1962, https://doi.org/10.1029/2017GC007228
    Details
    Publication Date: 2024-05-27
    Description: Terrestrial signals in marine sediment archives are often used for paleoclimatic reconstructions. It is therefore important to know the origin of the different terrestrial sedimentary components. The proximity to a river mouth is often the key location to determine the source. Especially in regions with strong ocean currents, such an assumption might,however, lead to considerable misinterpretations. To investigate the source of various terrigenous sediment fractions in southeastern Africa, a region with strong sediment redistribution, we have performed an extensive comparison between terrestrial material (pollen, plant lipids, detrital modes and heavy minerals as well as bulk inorganic geochemical composition) from potential source regions and the same components in the adjacent coastal and continental shelf sediments. Onshore the proxy‐indicators reflect small‐scale diversity in sampling locations and associated environments (riverbank sediments, flood deposits, suspension loads and soils). Nevertheless, the overall trends reflect significant environmental gradients along a SW to NE transect. We note a general comparability of the studied parameters between the continental and marine sediments regardless of their specific differences in transport and depositional characteristics. We propose that the influence of the Agulhas Current affects sediment deposition and distribution only seaward of the mid‐shelf and that pockets of sediment remain preserved in the lee of coastal protrusions where they are protected from erosion. This study provides the essential prerequisite to allow the attribution of temporal variations of compositional changes in marine sediment cores to environmental changes in southeastern Africa.
    Keywords: Center for Marine Environmental Sciences; MARUM
    Type: Dataset
    Format: application/zip, 6 datasets
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