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  • ELSEVIER SCIENCE BV
  • 2020-2020
  • 2015-2019  (223)
  • 1
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    The spectrum of persistent volcanic flank instability: A review and proposed framework based on Kīlauea, Piton de la Fournaise, and Etna (2018)
    ELSEVIER SCIENCE BV
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    Publication Date: 2021-03-19
    Description: Persistent motion of the south flank of Kilauea Volcano, Hawai'i, has been known for several decades, but has only recently been identified at other large basaltic volcanoes-namely Piton de la Fournaise (La Reunion) and Etna (Sicily)-thanks to the advent of space geodetic techniques. Nevertheless, understanding of long-term flank instability is based largely on the example of Kilauea, despite the large differences in the manifestations and mechanisms of the process when viewed through a comparative lens. For example, the rate of flank motion at Kilauea is several times that of Etna and Piton de la Fournaise and is accommodated on a slip plane several km deeper than is probably present at the other two volcanoes. Gravitational spreading also appears to be the dominant driving force at Kilauea, given the long-term steady motion of the volcano's south flank regardless of eruptive/intrusive activity, whereas magmatic activity plays a larger role in flank deformation at Etna and Piton de la Fournaise. Kilauea and Etna, however, are both characterized by heavily faulted flanks, while Piton de la Fournaise shows little evidence for flank faulting. A helpful means of understanding the spectrum of persistent flank motion at large basaltic edifices may be through a framework defined on one hand by magmatic activity (which encompasses both magma supply and edifice size), and on the other hand by the structural setting of the volcano (especially the characteristics of the subvolcanic basement or subhorizontal intravolcanic weak zones). A volcano's size and magmatic activity will dictate the extent to which gravitational and magmatic forces can drive motion of an unstable flank (and possibly the level of faulting of that flank), while the volcano's structural setting governs whether or not a plane of weakness exists beneath or within the edifice and can facilitate flank slip. Considering persistent flank instability using this conceptual model is an alternative to using a single volcano as a "type example"-especially given that the example is usually Kilauea, which defines an extreme end of the spectrum-and can provide a basis for understanding why flank motion may or may not exist on other large basaltic volcanoes worldwide.
    Description: U.S. Geological Survey, Agence Nationale de la Recherche ANR-16-CE04-0004-01, European MEDSUV project
    Description: Published
    Description: 63-80
    Description: 2V. Struttura e sistema di alimentazione dei vulcani
    Description: JCR Journal
    Keywords: Flank instability ; Deformation ; Basaltic volcanism ; Kīlauea ; Etna ; Piton de la Fournaise ; 04.08. Volcanology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 2
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    Relationships between biodiversity and the stability of marine ecosystems: comparisons at a European scale using meta-analysis. (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 98, pp. 5-14, ISSN: 1385-1101
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    Publication Date: 2015-06-16
    Description: The relationship between biodiversity and stability of marine benthic assemblages was investigated through meta-analyses using existing data sets (n = 28) covering various spatial (m-km) and temporal (1973-2006; ranging from 5 to 〉250 months) scales in different benthic habitats (emergent rock, rock pools and sedimentary habitats) over different European marine systems (North Atlantic and western Mediterranean). Stability was measured by a lower variability in time, and variability was estimated as temporal variance of species richness, total abundance (density or % cover) and community structure (using Bray-Curtis dissimilarities on species composition and abundance). Stability generally decreased with species richness. Temporal variability in species richness increased with the number of species at both quadrat (〈1 m2) and site (100 m2) scales, while no relationship was observed by multivariate analyses. Positive relationships were also observed at the scale of site between temporal variability in species richness and variability in community structure with evenness estimates. This implies that the relationship between species richness or evenness and species richness variability is slightly positive and depends on the scale of observation. Thus, species richness does not stabilize temporal fluctuations in species number, rather species rich assemblages are those most likely to undergo the largest fluctuations in species numbers and abundance from time to time. Changes within community assemblages in terms of structure are, however, generally independent of biodiversity. Except for sedimentary and rock pool habitats, no relationship was observed between temporal variation of total abundances and diversity at either scale. Overall, our results emphasise that the relation between species richness and species-level measures of temporal variability depend on scale of measurements, type of habitats and the marine system (North Atlantic and Mediterranean) considered.
    Repository Name: EPIC Alfred Wegener Institut
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  • 3
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    Taxonomy and toxicity of Prorocentrum from Perhentian Islands (Malaysia), with a description of a non-toxigenic species Prorocentrum malayense sp. nov. (Dinophyceae) (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 83, pp. 95-108, ISSN: 1568-9883
    Details
    Publication Date: 2020-03-01
    Description: Thirteen isolates of Prorocentrum species were established from the coral reefs of Perhentian Islands Marine Park, Malaysia and underwent morphological observations and molecular characterization. Six species were found: P. caipirignum, P. concavum, P. cf. emarginatum, P. lima, P. mexicanum and a new morphotype, herein designated as P. malayense sp. nov. Prorocentrum malayense, a species closely related to P. leve, P. cf. foraminosum, P. sp. aff. foraminossum, and P. concavum (Clade A sensu Chomérat et al. 2018), is distinguished from its congeners as having larger thecal pore size and a more deeply excavated V-shaped periflagellar area. Platelet arrangement in the periflagellar area of P. malayense is unique, with the presence of platelet 1a and 1b, platelet 2 being the most anterior platelet, and a broad calabash-shaped platelet 3. The species exhibits consistent genetic sequence divergences for the nuclear-encoded large subunit ribosomal RNA gene (LSU rDNA) and the second internal transcribed spacer (ITS2). The phylogenetic inferences further confirmed that it represents an independent lineage, closely related to species in Clade A sensu Chomérat et al. Pairwise comparison of ITS2 transcripts with its closest relatives revealed the presence of compensatory base changes (CBCs). Toxicity analysis showed detectable levels of okadaic acid in P. lima (1.0–1.6 pg cell˗1) and P. caipirignum (3.1 pg cell˗1); this is the first report of toxigenic P. caipirignum in the Southeast Asian region. Other Prorocentrum species tested, including the new species, however, were below the detection limit.
    Repository Name: EPIC Alfred Wegener Institut
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  • 4
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    Distribution of carbon and nitrogen along hillslopes in three valleys on Herschel Island, Yukon Territory, Canada (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3CATENA, ELSEVIER SCIENCE BV, 178, pp. 132-140, ISSN: 0341-8162
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    Publication Date: 2019-03-28
    Description: Thermokarst results from the thawing of ice-rich permafrost and alters the biogeochemical cycling in the Arctic by reworking soil material and redistributing soil organic carbon (SOC) and total nitrogen (TN) along uplands, hillslopes, and lowlands. Understanding the impact of this redistribution is key to better estimating the storage of SOC in permafrost terrains. However, there are insufficient studies quantifying long-term impacts of thaw processes on the distribution of SOC and TN along hillslopes. We address this issue by providing estimates of SOC and TN stocks along the hillslopes of three valleys located on Herschel Island (Yukon, Canada), and by discussing the impact of hillslope thermokarst on the variability of SOC and TN stocks. We found that the average SOC and TN 0–100 cm stocks in the valleys were 26.4 ± 8.9 kg C m-2 and 2.1 ± 0.6 kg N m-2. We highlight the strong variability in the soils physical and geochemical properties within hillslope positions. High SOC stocks were found at the summits, essentially due to burial of organic matter by cryoturbation, and at the toeslopes due to impeded drainage which favored peat formation and SOC accumulation. The average carbon-to‑nitrogen ratio in the valleys was 12.9, ranging from 9.7 to 18.9, and was significantly higher at the summits compared to the backslopes and footslopes (p 〈 0.05), suggesting a degradation of SOC downhill. Carbon and nitrogen contents and stocks were significantly lower on 16% of the sites that were previously affected by hillslope thermokarst (p 〈 0.05). Our results showed that lateral redistribution of SOC and TN due to hillslope thermokarst has a strong impact on the SOC storage in ice-rich permafrost terrains.
    Repository Name: EPIC Alfred Wegener Institut
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  • 5
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    Was the Arctic Ocean ice free during the latest Cretaceous? The role of CO2 and gateway configurations (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 177, pp. 201-212, ISSN: 0921-8181
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    Publication Date: 2021-02-16
    Repository Name: EPIC Alfred Wegener Institut
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  • 6
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    Interactions of trace elements and organic ligands in seawater and implications for quantifying biogeochemical dynamics: A review (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth-Science Reviews, ELSEVIER SCIENCE BV, 192, pp. 631-649, ISSN: 0012-8252
    Details
    Publication Date: 2019-05-03
    Description: Interactions between dissolved trace elements and organic ligands in seawater play an important role in ocean biogeochemistry, ranging from regulating primary production in surface waters to element cycling on basin-wide scale, with strong feedbacks to climate variability. In this study, we review different aspects in the field of marine trace elements and their organic ligands: recent instrumental innovation, factors that affect the fate of trace element complexes at the molecular level, spatial distribution of organic matter – trace element complexes in the ocean, modeling approaches as well as prospect in the scenarios of climate variability. We also assess the critical issues of parameterization in the numerical simulation that incorporate the trace elements – organic ligands interactions. Given the predicted climate changes, we examine the potential of exchange between inorganic and organic complexes for trace elements in different oceanic provinces.
    Repository Name: EPIC Alfred Wegener Institut
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  • 7
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    The Falkland Plateau in the context of Gondwana breakup (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Gondwana Research, ELSEVIER SCIENCE BV, 68, pp. 108-115, ISSN: 1342-937X
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    Publication Date: 2019-05-05
    Description: During the Jurassic, the Falkland Plateau was part of Gondwana and occupied a position between the African and Antarctic plates. Several contrasting models exist for the breakup of Gondwana that depend on assumptions about the currently unknown crustal structure of the Falkland Plateau. Here, we present the results of recently acquired wide-angle seismic data along the entire plateau that provide sound constraints on its role in geodynamic reconstructions. In contrast to published crustal models, the new data show that the Falkland Plateau Basin consists of up to 20 km thick oceanic crust, which is bounded to the east by a continental fragment, the Maurice Ewing Bank. In a refined geodynamic model, rifting started between the Falkland Islands and the Maurice Ewing Bank at ~178 Ma and ceased at around ~154 Ma. The plateau's exceptionally thick oceanic crust likely results from its position in an extensional back-arc-regime situated over a mantle thermal anomaly that was also responsible for the extensive onshore Karoo-Ferrar and Chon Aike volcanic provinces.
    Repository Name: EPIC Alfred Wegener Institut
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  • 8
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    Does ecosystem variability explain phytoplankton diversity? Solving an ecological puzzle with long-term data sets (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 135, pp. 11-17, ISSN: 1385-1101
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    Publication Date: 2018-11-09
    Description: Explaining species diversity as a function of ecosystem variability is a long-term discussion in community-ecology research. Here, we aimed to establish a causal relationship between ecosystem variability and phytoplankton diversity in a shallow-sea ecosystem. We used long-term data on biotic and abiotic factors from Helgoland Roads, along with climate data to assess the effect of ecosystem variability on phytoplankton diversity. A point cumulative semi-variogram method was used to estimate the long-term ecosystem variability. A Markov chain model was used to estimate dynamical processes of species i.e. occurrence, absence and outcompete probability. We identified that the 1980s was a period of high ecosystem variability while the last two decades were comparatively less variable. Ecosystem variability was found as an important predictor of phytoplankton diversity at Helgoland Roads. High diversity was related to low ecosystem variability due to non-significant relationship between probability of a species occurrence and absence, significant negative relationship between probability of a species occurrence and probability of a species to be outcompeted by others, and high species occurrence at low ecosystem variability. Using an exceptional marine long-term data set, this study established a causal relationship between ecosystem variability and phytoplankton diversity.
    Repository Name: EPIC Alfred Wegener Institut
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  • 9
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    The initial Gondwana break-up: A synthesis based on new potential field data of the Africa-Antarctica Corridor (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 750, pp. 301-328, ISSN: 0040-1951
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    Publication Date: 2018-12-21
    Description: The initial opening of the Africa-Antarctica Corridor, in the heart of Gondwana, is still enigmatic due to missing information on the origin of major crustal features and the exact timing of the onset of the first oceanic crust in the Jurassic. Therefore, in 2014, new ship-borne magnetic data were systematically acquired in the northern Mozambique Basin and across Beira High, which we merged with all accessible magnetic data in the Mozambique Basin. Herein, distinct magnetic lineations are observed, which allow a refined identification of a whole set of Jurassic magnetic spreading anomalies, constraining the timing of the onset of oceanization, beginning at M38n.2n (164.1 Ma). In combination with high-resolution potential field data from the conjugate Antarctic margin, well-expressed fracture zones can be traced throughout the Africa-Antarctica Corridor and allow the precise rotation of Antarctica back to Africa. The initial fit depicts striking continuations of onshore tectonic features across the plate boundaries taking onshore aeromagnetic data of both margins into account. Within a tight Gondwana fit, the Beira High can be restored along the major sinistral Namama-Orvin Shear Zone of the East African-Antarctic Orogen. The Beira High represents a continental block, which was detached from Antarctica, by 157 Ma at the latest. Simultaneously, the Antarctic plate cleared the area of the MCP. However, the crustal nature of the southern MCP remains ambiguous. The Northern Natal Valley and the Mozambique Ridge consist of thick oceanic crust, being emplaced between M26r-M18n (157.1–144 Ma) and M18n-M6n (144–131.7 Ma), respectively. About the half of this crust was won from the Antarctic plate by a series of southwards directed ridge jumps to the northern boundary of the Explora Wedge. A refined kinematic break-up model constrained by the most extensive magnetic dataset is presented describing consistently the initial opening of the Africa-Antarctica Corridor and the Somali Basin.
    Repository Name: EPIC Alfred Wegener Institut
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  • 10
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    Can domoic acid affect escape response in copepods? (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 79, pp. 50-52, ISSN: 1568-9883
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    Publication Date: 2019-10-01
    Description: Copepods are important grazers on toxic phytoplankton and serve as vectors for algal toxins up the marine food web. Success of phytoplankton depends among other factors on protection against grazers like copepods, and same way copepod survival and population resilience relies on their ability to escape predators. Little is, however, known about the effect of toxins on the escape response of copepods. In this study we experimentally tested the hypothesis that the neurotoxin domoic acid (DA) produced by the diatom Pseudo-nitzschia affects escape responses of planktonic copepods. We found that the arctic copepods Calanus hyperboreus and C. glacialis reduced their escape response after feeding on a DA-producing diatom. The two species were not affected the same way; C. hyperboreus was affected after shorter exposure and less intake of DA. The negative effect on escape response was not related to the amount of DA accumulated in the copepods. Our results suggest that further research on the effects of DA on copepod behavior and DA toxicity mechanisms is required to evaluate the anti-grazing function of DA.
    Repository Name: EPIC Alfred Wegener Institut
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  • 11
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    The Zambezi Channel: a new perspective on submarine channel evolution at low latitudes (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Geomorphology, ELSEVIER SCIENCE BV, 286, pp. 121-132, ISSN: 0169-555X
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    Publication Date: 2017-04-09
    Description: The submarine Zambezi Channel is the deep, stable, north-south orientated, lower portion of a channel system draining the continental slope of central Mozambique; transporting material southwards into the Mozambique Channel and Basin, southwest Indian Ocean. Using recently collected Multi Beam Echo Sounder and PARASOUND data we discuss the geomorphology of the Zambezi Channel. This system is enigmatic in that the main channel is stable, with low sinuosity despite being at a low latitude where rivers seasonally deliver fine grained sediment. A further enigma is that system does not now continue upslope to the Zambezi River, the largest river in southern Africa. Instead this river flows into the northern Mozambique basin to the south-west of the small channels. The Zambezi Channel is compared to small-scale physical models in an attempt to better understand the geomorphology of the channel. The geomorphological features of the main channel show a quite remarkable resemblance to an analogue model produced within a purely erosive environment. To explain these enigmas, it is proposed that geomorphology of the main Zambezi Channel was produced by periodic, high-volume pulses of flood water, and associated sediment, from the Zambezi River, the second largest river in Africa. These events are considered to be due to minor tectonic movements along the Chobe Fault in the Kalahari that permitted the draining of several palaeo-lake systems between the Early Pleistocene through to the early Mid-Pleistocene. Such repetitive draining of palaeo-lakes would have produced flooding comparable to glacial dam bursts. Such events would deliver significantly more sediment laden flood water to the region than “normal” flow conditions. We hypothesise that these significant flood events have influenced the geomorphology of the Zambezi River to the extent that it is no longer comparable to other low-latitude systems, and exhibits characteristics akin to high-latitude systems with highly variable sediment input.
    Repository Name: EPIC Alfred Wegener Institut
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  • 12
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    Full-field predictions of ice dynamic recrystallisation under simple shear conditions (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 450, pp. 233-242, ISSN: 0012-821X
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    Publication Date: 2019-07-17
    Description: Understanding the flow of ice on the microstructural scale is essential for improving our knowledge of large-scale ice dynamics, and thus our ability to predict future changes of ice sheets. Polar ice behaves anisotropically during flow, which can lead to strain localisation. In order to study how dynamic recrystallisation affects to strain localisation in deep levels of polar ice sheets, we present a series of numerical simulations of ice polycrystals deformed under simple-shear conditions. The models explicitly simulate the evolution of microstructures using a full-field approach, based on the coupling of a viscoplastic deformation code (VPFFT) with dynamic recrystallisation codes. The simulations provide new insights into the distribution of stress, strain rate and lattice orientation fields with progressive strain, up to a shear strain of three. Our simulations show how the recrystallisation processes have a strong influence on the resulting microstructure (grain size and shape), while the development of lattice preferred orientations (LPO) appears to be less affected. Activation of non-basal slip systems is enhanced by recrystallisation and induces a strain hardening behaviour up to the onset of strain localisation and strain weakening behaviour. Simulations demonstrate that the strong intrinsic anisotropy of ice crystals is transferred to the polycrystalline scale and results in the development of strain localisation bands than can be masked by grain boundary migration. Therefore, the finite-strain history is non-directly reflected by the final microstructure. Masked strain localisation can be recognised in ice cores, such as the EDML, from the presence of stepped boundaries, microshear and grains with zig-zag geometries.
    Repository Name: EPIC Alfred Wegener Institut
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  • 13
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    Ecology and evolution of marine parasites and diseases: International NIOZ-AWI symposium, 10-14 March 2014, Texel, The Netherlands (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 113, pp. 1-3, ISSN: 1385-1101
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    Publication Date: 2016-07-20
    Repository Name: EPIC Alfred Wegener Institut
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  • 14
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    Oxygen isotope composition of diatoms from sediments of Lake Kotokel (Buryatia). (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Russian Geology and Geophysics, ELSEVIER SCIENCE BV, 57, pp. 1213-1221, ISSN: 1068-7971
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    Publication Date: 2016-08-14
    Description: This is a summary of new oxygen isotope data for diatoms from Lake Kotokel sediments, with implications for responses of the lake system and its environment to global change over the past 46 kyr. Fossil diatoms in all samples are free from visible contamination signatures and contain no more than 2.5% Al2O3, which ensures reliable reconstructions. The δ18O values in diatoms vary between +23.7 and +31.2‰ over the record. The results mainly represent diatom assemblages of summer blooming periods, except for the time span between 36 and 32 kyr, when the isotopic signal rather records a shift from summer to spring blooming conditions. Possible water temperature changes only partly explain the changes in the isotopic record. The observed isotopic patterns are produced mainly by isotope changes in lake water in response to variations in air temperature, hydrology, and atmospheric circulation in the region. During Marine Isotope Stage (MIS) 2 (Last Glacial maximum), high δ18Odiatom resulted from rapid evaporation and low fluvial inputs. The high δ18O values of about +29 to +30‰ during the first half of MIS 1 (Holocene interglacial) suggest an increased share of summer rainfalls associated with southern/southeastern air transport. The δ18O decrease to +24‰ during the second half of MIS 1 is due to the overall hemispheric cooling and increased moisture supply to the area by the Atlantic transport. The record of Lake Kotokel sediments provides an example of complex interplay among several climatic controls of δ18Odiatom in the Late Pleistocene and the Holocene.
    Repository Name: EPIC Alfred Wegener Institut
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  • 15
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    Seasonal variation in parasite infection patterns of marine fish species from the Northern Wadden Sea in relation to inter annual temperature fluctuations (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 113, pp. 73-84, ISSN: 1385-1101
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    Publication Date: 2018-02-15
    Repository Name: EPIC Alfred Wegener Institut
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  • 16
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    Last glacial-interglacial productivity and associated changes in the eastern Arabian Sea (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 483, pp. 147-156, ISSN: 0031-0182
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    Publication Date: 2017-09-01
    Repository Name: EPIC Alfred Wegener Institut
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  • 17
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    Parasites and marine invasions: Ecological and evolutionary perspectives (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 113, pp. 11-27, ISSN: 1385-1101
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    Publication Date: 2016-07-20
    Repository Name: EPIC Alfred Wegener Institut
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  • 18
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    Selective byssus attachment behavior of mytilid mussels from hard- and soft-bottom coastal systems (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, ELSEVIER SCIENCE BV, 497, pp. 61-70, ISSN: 0022-0981
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    Publication Date: 2017-10-03
    Repository Name: EPIC Alfred Wegener Institut
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  • 19
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    Identification of Azadinium species and a new azaspiracid from Azadinium poporum in Puget Sound, Washington State, USA (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 68, pp. 152-167, ISSN: 1568-9883
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    Publication Date: 2019-07-17
    Description: The identification of a new suite of toxins, called azaspiracids (AZA), as the cause of human illnesses after the consumption of shellfish from the Irish west coast in 1995, resulted in interest in understanding the global distribution of these toxins and of species of the small dinoflagellate genus Azadinium, known to produce them. Clonal isolates of four species of Azadinium, A. poporum, A. cuneatum, A. obesum and A. dalianense were obtained from incubated sediment samples collected from Puget Sound, Washington State in 2016. These Azadinium species were identified using morphological characteristics confirmed by molecular phylogeny. Whereas AZA could not be detected in any strains of A. obesum, A. cuneatum and A. dalianense, all four strains of A. poporum produced a new azaspiracid toxin, based on LC–MS analysis, named AZA-59. The presence of AZA-59 was confirmed at low levels in situ using a solid phase resin deployed at several stations along the coastlines of Puget Sound. Using a combination of molecular methods for species detection and solid phase resin deployment to target shellfish monitoring of toxin at high-risk sites, the risk of azaspiracid shellfish poisoning can be minimized.
    Repository Name: EPIC Alfred Wegener Institut
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  • 20
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    Seasonal sea ice cover during the warm Pliocene: Evidence from the Iceland Sea (ODP Site 907) (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 481, pp. 61-72, ISSN: 0012-821X
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    Publication Date: 2017-10-22
    Description: Sea ice is a critical component in the Arctic and global climate system, yet little is known about its extent and variability during past warm intervals, such as the Pliocene (5.33–2.58Ma). Here, we present the first multi-proxy (IP25, sterols, alkenones, palynology) sea ice reconstructions for the Late Pliocene Iceland Sea (ODP Site 907). Our interpretation of a seasonal sea ice cover with occasional ice-free intervals between 3.50–3.00Ma is supported by reconstructed alkenone-based summer sea surface temperatures. As evidenced from brassicasterol and dinosterol, primary productivity was low between 3.50 and 3.00Ma and the site experienced generally oligotrophic conditions. The East Greenland Current (and East Icelandic Current) may have transported sea ice into the Iceland Sea and/or brought cooler and fresher waters favoring local sea ice formation. Between 3.00 and 2.40Ma, the Iceland Sea is mainly sea ice-free, but seasonal sea ice occurred between 2.81 and 2.74Ma. Sea ice extending into the Iceland Sea at this time may have acted as a positive feedback for the build-up of the Greenland Ice Sheet (GIS), which underwent a major expansion ∼2.75Ma. Thereafter, most likely a stable sea ice edge developed close to Greenland, possibly changing together with the expansion and retreat of the GIS and affecting the productivity in the Iceland Sea.
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    Astronomically paced changes in deep-water circulation in the western North Atlantic during the middle Eocene (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 484, pp. 329-340, ISSN: 0012-821X
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    Publication Date: 2018-01-09
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  • 22
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    Boron isotope-based seasonal paleo-pH reconstruction for the Southeast Atlantic - A multispecies approach using habitat preference of planktonic foraminifera (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 487, pp. 138-150, ISSN: 0012-821X
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    Publication Date: 2020-07-15
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  • 23
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    The continental margin east of the Falkland Islands (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 724-72, pp. 234-253, ISSN: 0040-1951
    Details
    Publication Date: 2018-07-15
    Description: The 1500 km long Falkland Plateau is the most prominent morphological structure in the southern South Atlantic Ocean, which crustal composition and development is mainly unknown. At the westernmost boundary of the plateau, the Falkland Islands' Precambrian geology provides the only insight into basement structure and age. The question of whether continental basement of a similar age and origin underlies the Falkland Plateau further east is strongly disputed. We present new high quality constraints on the crustal fabric of the plateau east of the Falkland Islands, based on wide-angle seismic and potential field data acquired in 2013. The P-wave velocity model, supported by amplitude and density modelling, shows that the Falkland Plateau Basin is filled with 8 km of sediments. Continental crust of 34 km thickness underlies the Falkland Islands. The eastern continental margin of the Falkland Islands can be classified as a volcanic rifted margin. The Falkland Plateau Basin is floored by up to 20 km thick oceanic crust. The exceptionally thick igneous crust and its high lower crustal velocities (up to 7.4 km/s) indicate the influence of a regional thermal mantle anomaly during its formation, which provided extra melt material. The wide-angle model revises published crustal models, which predicted thin oceanic or thick extended continental crust below the Falkland Plateau Basin. Our results provide a sound basis for future tectonic interpretations of the area.
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  • 24
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    Effects of salinity variation on growth and yessotoxin composition in the marine dinoflagellate Lingulodinium polyedra from a Skagerrak fjord system (western Sweden) (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 78, pp. 9-17, ISSN: 1568-9883
    Details
    Publication Date: 2019-08-01
    Description: The marine dinoflagellate Lingulodinium polyedra is a toxigenic species capable of forming high magnitude and occasionally harmful algal blooms (HABs), particularly in temperate coastal waters throughout the world. Three cultured isolates of L. polyedra from a fjord system on the Skagerrak coast of Sweden were analyzed for their growth characteristics and to determine the effects of a strong salinity gradient on toxin cell quotas and composition. The cell quota of yessotoxin (YTX) analogs, as determined by liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS), ranged widely among strains. For two strains, the total toxin content remained constant over time in culture, but for the third strain, the YTX cell quota significantly decreased (by 32%) during stationary growth phase. The toxin profiles of the three strains differed markedly and none produced YTX. The analog 41a-homo-YTX (m/z 1155), its putative methylated derivative 9-Me-41a-homo-YTX (m/z 1169) and an unspecified keto-YTX (m/z 1047) were detected in strain LP29-10H, whereas strain LP30-7B contained nor-YTX (m/z 1101), and two unspecified YTX analogs at m/z 1159 and m/z 1061. The toxin profile of strain LP30-8D comprised two unspecified YTX analogs at m/z 1061 and m/z 991 and carboxy-YTX (m/z 1173). Strain LP30-7B cultured at multiple salinities (10, 16, 22, 28 and 34) did not tolerate the lowest salinity (10), but there was a statistically significant decrease (by 21%) in toxin cell quota between growth at the highest versus lower permissible salinities. The toxin profile for strain LP30-7B remained constant over time for a given salinity. At lower salinities, however, the proportion of the unspecified YTX analog (m/z 1061) was significantly higher, especially with respect to nor-YTX (m/z 1101). This study shows high intra-specific variability in yessotoxin composition among strains from the same geographical region and inconsistency in toxin cell quota under different environmental regimes and growth stages in culture. This variation has important implications for the kinetics of YTX production and food web transfer in natural bloom populations from diverse geographical regions.
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  • 25
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    Nutrient optimization of tree growth alters structure and function of boreal soil food webs (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Forest Ecology and Management, ELSEVIER SCIENCE BV, 428, pp. 46-56, ISSN: 0378-1127
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    Publication Date: 2018-09-25
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  • 26
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    Late Quaternary environments in the Gobi Desert of Mongolia: Vegetation, hydrological, and palaeoclimate evolution. (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 514, pp. 77-91, ISSN: 0031-0182
    Details
    Publication Date: 2018-11-11
    Description: Considerable efforts have been devoted to decipher the late Quaternary moisture and thermal evolution of arid central Asia. However, disparate interpretations still exist concerning different proxies. The spatial and temporal heterogeneities have inhibited a holistic understanding of general patterns and underlying mechanisms. To address these issues, two parallel cores (ONW I, 6.00 m; ONW II, 13.35 m) were retrieved in the Gobi Desert of Mongolia from lake Orog Nuur. Multidisciplinary investigations including geomorphological mapping, radiocarbon dating, sedimentological, palynological and ostracod analyses enabled us to gain a comprehensive dataset for vegetation development and hydrological variability over the last ~45 kyr. Higher lake levels during the Marine Isotope Stage (MIS) 3 and early MIS 2 (~35–~24 kyr) were probably caused by increased precipitation. The sharp transition of Termination I (~11 kyr) is indicated by sedimentological, palynological, and ostracod data. During the late Pleistocene, the lower area of the Orog Nuur catchment was dominated by Artemisia steppe and gradually altered to Chenopodiaceae desert steppe in the Holocene. The early Holocene is also characterized by a relatively humid environment. The humid pulses during the MIS 3 and the early Holocene were also recorded in other archives and are possibly the trait of a larger scale phenomenon in arid central Asia. Four major harsh climatic periods were documented in the core at ~43 kyr, ~36 kyr, during the global Last Glacial Maximum, and the Younger Dryas as playa phases. Reduced westerlies' moisture transport and a retreated East Asian Summer Monsoon influence probably caused those dry phases in the Gobi Desert of Mongolia.
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  • 27
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    Two novel azaspiracids from Azadinium poporum, and a comprehensive compilation of azaspiracids produced by Amphidomataceae, (Dinophyceae) (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 82, pp. 1-8, ISSN: 1568-9883
    Details
    Publication Date: 2020-01-01
    Description: Two novel azaspiracids (AZA) with a molecular mass of 869 Da were found in Pacific strains of Azadinium poporum and characterized by tandem mass spectrometry and high resolution mass spectrometry (HRMS). One compound, AZA-42, was found in Az. poporum strains AZFC25 and AZFC26, both isolated from the South China Sea. AZA-42 belongs to the 360-type AZA that in comparison to AZA-1 has an additional double bond in the F–I ring system of AZA comprising C28-C40. The other compound, AZA-62, was detected in Az. poporum strain 1D5 isolated off Chañaral, Northern Chile. Mass spectral data indicate that AZA-62 is a variant of AZA-11 with an additional double bond in the C1-C9 region of AZA. In addition to the description of the two novel AZA, a comprehensive list of all AZA known to be produced by species of the genera Azadinium and Amphidoma comprising 26 AZA variants is presented.
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  • 28
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    Genetic variability of the striped venus Chamelea gallina in the northern Adriatic Sea (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Fisheries Research, ELSEVIER SCIENCE BV, 201, pp. 68-78, ISSN: 0165-7836
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    Publication Date: 2019-03-04
    Description: Chamelea gallina is a valuable commercial species in the Mediterranean Sea. The strong fishing pressure on C. gallina in the northern and central Adriatic Sea has paralleled a clear-cut decrease in clam population density and the occurrence of several irregular mortality events. Despite the commercial interest in this species, nothing is known about its genetic sub-structuring at the geographic and/or temporal scale, nor its levels of genetic variability. Analyzing microsatellite genotypes for samples collected in the Adriatic Sea, we detected large geographic genetic homogeneity with gene flow guided by broad scale circulation in the north-south direction. Our results also indicate weak genetic differentiation among size classes at the local and temporal scale. These small genetic differences might be determined by variability of local circulation and reproductive success, partial overlapping generations and high larval mortality rates as suggested by our estimates of the effective number of breeders. In fact, global effective population size estimates over multiple generations are medium-high, but a low number of breeders are responsible for the small clams size class recruitment. Notwithstanding, it was not possible to detect signatures of bottleneck. Future efforts in fishery management should aim to maintain genetic diversity – essential to the long-term sustainability of the resource – and limit effective population size fluctuations while considering the need to improve water quality to avoid mass mortality events. Keywords: Microsatellite; Clam fishery; Bivalvia; Adriatic Sea; Effective population size; Gene flow
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  • 29
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    On the influence of marine biogeochemical processes over CO2 exchange between the atmosphere and ocean (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Chemistry, ELSEVIER SCIENCE BV, 199, pp. 1-11, ISSN: 0304-4203
    Details
    Publication Date: 2019-01-23
    Description: The ocean holds a large reservoir of carbon dioxide (CO2), and mitigates climate change through uptake of anthropogenic CO2. Fluxes of CO2 between the atmosphere and surface ocean are regulated by a number of physical and biogeochemical processes, resulting in a spatiotemporally heterogeneous CO2 distribution. Determining the influence of each individual process is useful for interpreting marine carbonate system ob- servations, and is also necessary to investigate how changes in these drivers could affect air-sea CO2 exchange. Biogeochemical processes exert an influence primarily through modifying seawater dissolved inorganic carbon (CT) and total alkalinity (AT), thus changing the seawater partial pressure of CO2 (psw). Here, we propose a novel conceptual framework through which the size of the CO2 source or sink generated by any biogeochemical process, denoted Φ, can be evaluated. This is based on the ‘isocapnic quotient’ (Q), which defines the trajectory through (AT,CT) phase space for which there is no change in psw. We discuss the limitations and uncertainties inherent in this technique, which are negligible for most practical purposes, and its links with existing, related approaches. We investigate the effect on Φ of spatiotemporal heterogeneity in Q in the present day surface ocean for several key biogeochemical processes. This leads the magnitude of the CO2 source or sink generated by processes that modify AT to vary spatiotemporally. Finally, we consider how the strength of each process as a CO2 source or sink may change in a warmer, higher-CO2 future ocean.
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    Decadal variability of north-eastern Atlantic storminess at the mid-Holocene: New inferences from a record of wind-blown sand, western Denmark (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 180, pp. 16-32, ISSN: 0921-8181
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    Publication Date: 2019-06-17
    Description: Disentangling the external and internal forcing responsible for the variability of the Earth's climate and associated extreme events over the Holocene is crucial for producing reliable scenarios of adaptation to the effects of ongoing climate change. At mid-latitudes, significant relationships between westerly storminess, solar activity and internal atmospheric and oceanic modes of variability have been repeatedly evidenced to exist over millennial and centennial time scales. However, at shorter (decadal) scale, it is still challenging to establish clear control links between the forcing mechanisms and the spatio-temporal variability of past extra-tropical storms. This probably owes to the existence of complex multi-scale relationships and feedback loops, as well as to the difficulty of producing proxy-records of sufficiently high-resolution and wide spatial significance. Here we present a reconstruction of westerly storminess in western Denmark between 4840 and 2300 yrs. cal. B·P. Past-storminess is retrieved from an organic-rich sedimentary succession by combining markers of aeolian sand influx, μ-XRF geochemistry and plant macrofossils. Particular focus is paid to the c. 4840–4350 yrs. cal. B·P. period for which our record is characterized by a pluri-annual resolution. We evidence concurrent pluri-decadal shifts in storminess and humidity regime at our site that we interpret as relocations of the mean westerly storm-track over the North-Atlantic. The signal is dominated by ≈ 90, ≈ 50–80 and ≈ 35-yr periods, evoking possible links with solar activity, the North-Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC) modes of variability, respectively. The ≈ 35-yr periodicity found in our record is especially strong and stationary, suggesting that storminess could have been closely linked with the AMOC over the study period. Our records of storminess indeed show some great similarities with a record of deep overflow of a branch of the AMOC. Opposite to some model outputs, the strength of the AMOC seems to have often co-varied with storminess at pluri-decadal scales over the study period. We also find periods of high storminess activity to be significantly correlated with solar minima and relative pluri-decadal lows in the NAO. We suggest that small lowering in the strength of the NAO in an otherwise positive NAO context may have caused southward relocations of the mean westerly storm-track from subpolar latitudes to northern Europe. This invites to reconsider the importance given to using the NAO as a binary index. Finally, an attempt is made to explore the temporal lead-lag relationships between storminess and different potential forcing agents such as the Total Solar Irradiance, the NAO and the AMOC. Unfortunately, the insufficient chronological precision of the proxy-records available for the TSI, the NAO and the AMOC over the study period prevents us from deriving any robust interpretations regarding potential teleconnections at a decadal-scale between past north-Atlantic westerly storminess activity, solar forcing, the NAO and north-Atlantic surface and deep oceanic circulation.
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    Air-sea interactive forcing on phytoplankton productivity and community structure changes in the East China Sea during the Holocene (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 179, pp. 80-91, ISSN: 0921-8181
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    Publication Date: 2019-06-17
    Description: Phytoplankton productivity and community structure in the East China Sea (ECS) play an important role in marine ecology and carbon cycle, but both have been changing rapidly in response to recent oceanic and atmospheric circulation changes. However, the lack of long-term records of phytoplankton productivity and community structure variability in the region hinders our understanding of natural forcing mechanisms. Here, we use the phytoplankton biomarker (brassicasterol, dinosterol and alkenones) contents as well as the ratios between these biomarkers in three sediment cores from the ECS shelf to reconstruct the spatiotemporal variations of productivity and community of diatoms, dinoflagellates and coccolithophores during the Holocene, respectively. During 9–7 ka, the ECS shelf was characterized by low phytoplankton productivity with low coccolithophore contribution, caused by the oligotrophic condition mainly owing to the restricted Kuroshio Current (KC) intrusion under low sea-level conditions, thus the lack of nutrient input. Phytoplankton productivity generally increased during 7–4.6 ka, in response to the initial intrusion of the Yellow Sea Warm Current (YSWC, a branch of the KC), bringing nutrient from the subsurface KC to the upper layer of the ECS for phytoplankton growth. Phytoplankton productivity continuously increased during 4.6–1 ka, due to an enhanced circulation system (YSWC and Yellow Sea Coastal Current (YSCC)) driven by strong East Asia Winter Monsoon (EAWM). Significantly, high alkenone contents and coccolithophore contribution in the eastern core F11A was associated with its location closer to the warm and saline YSWC, which was suitable for coccolithophore growth. Beyond diagenetic processes which could partly account for higher biomarker contents near core tops, elevated phytoplankton productivity during the last 1 ka might be induced by more nutrient supply from the intensified circulation system driven by enhanced KC and anthropogenic activities. The latter also resulted in high dinoflagellate proportions in all three cores. These temporal and spatial changes of phytoplankton productivity and community structure in the ECS during the Holocene corresponded to different mechanisms by the air-sea interaction, providing insights into distinguishing natural forcing and anthropogenic influences on marine ecology.
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    Aerosol optical properties in the Arctic: The role of aerosol chemistry and dust composition in a closure experiment between Lidar and tethered balloon vertical profiles (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Science of The Total Environment, ELSEVIER SCIENCE BV, ISSN: 0048-9697
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    Publication Date: 2020-03-05
    Description: A closure experiment was conducted over Svalbard by comparing Lidar measurements and optical aerosol properties calculated from aerosol vertical profiles measured using a tethered balloon. Arctic Haze was present together with Icelandic dust. Chemical analysis of filter samples, aerosol size distribution and a full set of meteorological parameters were determined at ground. Moreover, scanning electron microscopy coupled with energy-dispersive X-ray (SEM-EDS) data were at disposal showing the presence of several mineralogical phases (i.e., sheet silicates, gypsum, quartz, rutile, hematite). The closure experiment was set up by calculating the backscattering coefficients from tethered balloon data and comparing them with the corresponding lidar profiles. This was preformed in three subsequent steps aimed at determining the importance of a complete aerosol speciation: (i) a simple, columnar refractive index was obtained by the closest Aerosol Robotic Network (AERONET) station, (ii) the role of water-soluble components, elemental carbon and organic matter (EC/OM) was addressed, (iii) the dust composition was included. When considering the AERONET data, or only the ionic water-soluble components and the EC/OM fraction, results showed an underestimation of the backscattering lidar signal up to 76, 53 and 45% (355, 532 and 1064 nm). Instead, when the dust contribution was included, the underestimation disappeared and the vertically-averaged, backscattering coefficients (1.45±0.30, 0.69±0.15 and 0.34±0.08 Mm-1 sr-1, at 355, 532 and 1064 nm) were found in keeping with the lidar ones (1.60±0.22, 0.75±0.16 and 0.31±0.08 Mm-1 sr-1). Final results were characterized by low RMSE (0.36, 0.08 and 0.04 Mm-1 sr-1) and a high linear correlation (R2 of 0.992, 0.992 and 0.994) with slopes close to one (1.368, 0.931 and 0.977, respectively). This work highlighted the importance of all the aerosol components and of the synergy between single particle and bulk chemical analysis for the optical property characterization in the Arctic .
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    Quantification, extractability and stability of dissolved domoic acid within marine dissolved organic matter (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Chemistry, ELSEVIER SCIENCE BV, 215, pp. 103669, ISSN: 0304-4203
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    Publication Date: 2021-01-01
    Description: The widespread diatom Pseudo-nitzschia can produce domoic acid (DA). DA is a compound with well described neurotoxic effects on vertebrates including humans known as amnesic shellfish poisoning (ASP) syndrome. It has also been suggested to serve as an organic ligand that binds to iron and copper. By binding these trace elements, DA may increase their solubility and bioavailability. In order to serve this function, DA has to be excreted and reabsorbed by the cells. Only few records of dissolved domoic acid (dDA) concentrations in the ocean exist. To accomplish quantification by ultra performance liquid chromatography (UPLC), samples have to be pre-concentrated and desalted using solid-phase extraction, a procedure commonly applied for dissolved organic matter. Our major goals were to quantify dDA in a basin-wide assessment in the East Atlantic Ocean, to determine extraction efficiencies for complexed and uncomplexed dDA, and to assess whether domoic acid is represented by its molecular formula in direct-infusion high resolution mass spectrometry. Our results showed that dDA was extracted almost quantitatively and occurred ubiquitously in the ocean surface but also in deeper (and older) water, indicating surprisingly high stability in seawater. The maximum concentration measured was 173 pmol L−1 and the average molar dDA carbon yield was 7.7 ppm. Both carbon yield and dDA concentration decreased with increasing water depth. Providing quantification of dDA in the water column, we seek to improve our understanding of toxic bloom dynamics and the mechanistic understanding of DA production.
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  • 34
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    Distributions of three Alexandrium species and their toxins across a salinity gradient suggest an increasing impact of GDA producing A. pseudogonyaulax in shallow brackish waters of Northern Europe (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 87, pp. 101622, ISSN: 1568-9883
    Details
    Publication Date: 2020-07-01
    Description: Blooms of Alexandrium spp. are a well-known phenomenon in Northern European waters. While A. tamarense/catenella, and A. pseudogonyaulax have been reported from marine waters, high densities of A. ostenfeldii are mainly observed at lower salinities in North Sea estuaries and the Baltic Sea, suggesting salinity as a driver of Alexandrium species composition and toxin distribution. To investigate this relationship, an oceanographic expedition through a natural salinity gradient was conducted in June 2016 along the coasts of Denmark. Besides hydrographic data, phytoplankton and sediment samples were collected for analyses of Alexandrium spp. cell and cyst abundances, for toxin measurement and cell isolation. Plankton data revealed the predominance of A. pseudogonyaulax at all transect stations while A. ostenfeldii and A. catenella generally contributed a minor fraction to the Alexandrium community. High abundances of A. pseudogonyaulax in the shallow enclosed Limfjord were accompanied by high amounts of goniodomin A (GDA). This toxin was also detected at low abundances along with A. pseudogonyaulax in the North Sea and the Kattegat. Genetic and morphological characterization of established strains showed high similarity of the Northern European population to distant geographic populations. Despite low cell abundances of A. ostenfeldii, different profiles of cycloimines were measured in the North Sea and in the Limfjord. This field survey revealed that salinity alone does not determine Alexandrium species and toxin distribution, but emphasizes the importance of habitat conditions such as proximity to seed banks, shelter, and high nutrient concentrations. The results show that A. pseudogonyaulax has become a prominent member of the Alexandrium spp. community over the past decade in the study area. Analyses of long term monitoring data from the Limfjord confirmed a recent shift to A. pseudogonyaulax dominance. Cyst and toxin records of the species in Kiel Bight suggest a spreading potential into the brackish Baltic Sea, which might lead to an expansion of blooms under future climate conditions.
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  • 35
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    Importance of the advection scheme for the simulation of water isotopes over Antarctica by atmospheric general circulation models: A case study for present-day and Last Glacial Maximum with LMDZ-iso (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 524, ISSN: 0012-821X
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    Publication Date: 2019-08-12
    Description: Atmospheric general circulation models (AGCMs) are known to have a warm and isotopically enriched bias over Antarctica. We test here the hypothesis that these biases are partly consequences of a too diffusive advection. Exploiting the LMDZ-iso model, we show that a less diffusive representation of the advection, especially on the horizontal, is very important to reduce the bias in the isotopic contents of precipitation above this area. The choice of an appropriate representation of the advection is thus essential when using GCMs for paleoclimate applications based on polar water isotopes. Too much diffusive mixing along the poleward transport leads to overestimated isotopic contents in water vapor because dehydration by mixing follows a more enriched path than dehydration by Rayleigh distillation. The near-air surface temperature is also influenced, to a lesser extent, by the diffusive properties of the advection scheme directly via the advection of the air and indirectly via the radiative effects of changes in high cloud fraction and water vapor. A too diffusive horizontal advection increases the temperature and so also contributes to enrich the isotopic contents of water vapor over Antarctica through a reduction of the distillation. The temporal relationship, from Last Glacial Maximum (LGM) to present-day conditions, between the mean annual near-air surface temperature and the water isotopic contents of precipitation for a specific location can also be impacted, with significant consequences on the paleo-temperature reconstruction from observed changes in water isotopes.
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  • 36
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    Trend analysis of climate time series: A review of methods (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth-Science Reviews, ELSEVIER SCIENCE BV, 190, pp. 310-322, ISSN: 0012-8252
    Details
    Publication Date: 2019-10-07
    Description: The increasing trend curve of global surface temperature against time since the 19th century is the icon for the considerable influence humans have on the climate since the industrialization. The discourse about the curve has spread from climate science to the public and political arenas in the 1990s and may be characterized by terms such as “hockey stick” or “global warming hiatus”. Despite its discussion in the public and the searches for the impact of the warming in climate science, it is statistical science that puts numbers to the warming. Statistics has developed methods to quantify the warming trend and detect change points. Statistics serves to place error bars and other measures of uncertainty to the estimated trend parameters. Uncertainties are ubiquitous in all natural and life sciences, and error bars are an indispensable guide for the interpretation of any estimated curve—to assess, for example, whether global temperature really made a pause after the year 1998. Statistical trend estimation methods are well developed and include not only linear curves, but also changepoints, accelerated increases, other nonlinear behavior, and nonparametric descriptions. State-of-the-art, computing- intensive simulation algorithms take into account the peculiar aspects of climate data, namely non- Gaussian distributional shape and autocorrelation. The reliability of such computer age statistical methods has been testified by Monte Carlo simulation methods using artificial data. The application of the state-of-the-art statistical methods to the GISTEMP time series of global surface temperature reveals an accelerated warming since the year 1974. It shows that a relative peak in warming for the years around World War II may not be a real feature but a product of inferior data quality for that time interval. Statistics also reveals that there is no basis to infer a global warming hiatus after the year 1998. The post-1998 hiatus only seems to exist, hidden behind large error bars, when considering data up to the year 2013. If the fit interval is extended to the year 2017, there is no significant hiatus. The researcher has the power to select the fit interval, which allows her or him to suppress certain fit solutions and favor other solutions. Power necessitates responsibility. The recommendation therefore is that interval selection should be objective and oriented on general principles. The application of statistical methods to data has also a moral aspect.
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  • 37
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    Cryptic speciation in Protoceratium reticulatum (Dinophyceae): Evidence from morphological, molecular and ecophysiological data (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 88, pp. 101610, ISSN: 1568-9883
    Details
    Publication Date: 2020-09-30
    Description: The cosmopolitan, potentially toxic dinoflagellate Protoceratium reticulatum possesses a fossilizable cyst stage which is an important paleoenvironmental indicator. Slight differences in the internal transcribed spacer ribosomal DNA (ITS rDNA) sequences of P. reticulatum have been reported, and both the motile stage and cyst morphology of P. reticulatum display phenotypic plasticity, but how these morpho-molecular variations are related with ecophysiological preferences is unknown. Here, 55 single cysts or cells were isolated from localities in the Northern (Arctic to subtropics) and Southern Hemispheres (Chile and New Zealand), and in total 34 strains were established. Cysts and/or cells were examined with light microscopy and/or scanning electron microscopy. Large subunit ribosomal DNA (LSU rDNA) and/or ITS rDNA sequences were obtained for all strains/isolates. All strains/isolates of P. reticulatum shared identical LSU sequences except for one strain from the Mediterranean Sea that differs in one position, however ITS rDNA sequences displayed differences at eight positions. Molecular phylogeny was inferred using maximum likelihood and Bayesian inference based on ITS rDNA sequences. The results showed that P. reticulatum comprises at least three ribotypes (designated as A, B, and C). Ribotype A included strains from the Arctic and temperate areas, ribotype B included strains from temperate regions only, and ribotype C included strains from the subtropical and temperate areas. The average ratios of process length to cyst diameter of P. reticulatum ranged from 15% in ribotype A, 22% in ribotype B and 17% in ribotype C but cyst size could overlap. Theca morphology was indistinguishable among ribotypes. The ITS-2 secondary structures of ribotype A displayed one CBC (compensatory change on two sides of a helix pairing) compared to ribotypes B and C. Growth response of one strain from each ribotype to various temperatures was examined. The strains of ribotypes A, B and C exhibited optimum growth at 15 °C, 20 °C and 20–25 °C, respectively, thus corresponding to cold, moderate and warm ecotypes. The profiles of yessotoxins (YTXs) were examined for 25 strains using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). The parent compound yessotoxin (YTX) was produced by strains of ribotypes A and B, but not by ribotype C strains, which only produced the structural variant homoyessotoxin (homoYTX). Our results support the notion that there is significant intra-specific variability in Protoceratium reticulatum and the biogeography of the different ribotypes is consistent with specific ecological preferences.
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  • 38
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    Biodegradability of hydrothermally altered deep-sea dissolved organic matter (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Chemistry, ELSEVIER SCIENCE BV, 217, ISSN: 0304-4203
    Details
    Publication Date: 2020-10-07
    Description: Deep-sea dissolved organic matter (DOM) constitutes a huge carbon reservoir in the worlds' oceans that – despite its abundance – is virtually unused as a substrate by marine heterotrophs. Heating within hydrothermal systems induces major molecular modifications of deep-sea DOM. Here, we tested the hypothesis that hydrothermal heating of deep-sea DOM enhances bioavailability. Aliquots of DOM extracted from the deep North Pacific (North Equatorial Pacific Intermediate Water; NEqPIW) were re-dissolved in artificial seawater and subjected to temperatures of 100 and 200 °C (40 MPa) using Dickson-type reactors. In agreement with earlier findings we observed a temperature-related drop in dissolved organic carbon (DOC) concentration (−6.1% at 100 °C, −21.0% at 200 °C) that predominantly affected the solid-phase extractable (SPE-DOC) fraction (−18.2% at 100 °C, −51.4% at 200 °C). Fourier-transform ion cyclotron resonance mass spectrometric (FT-ICR-MS) analysis confirmed a temperature-related reduction of average molecular mass, O/C ratios, double bond equivalents (DBE) and a relative increase in aromaticity (AImod). This thermally altered DOM was added (25 μmol L−1 DOC) to deep-water samples from the South West Pacific (Kermadec Arc, RV Sonne / SO253, 32° 37.706′ S | 179° 38.728′ W) and incubated with the prevailing natural microbial community. After 16 days at 4 °C in the dark, prokaryotic cell counts in incubations containing the full spectrum of thermally-degraded DOM (extractable and non-extractable compounds) had increased considerably (on average 21× for DOM100°C and 27× for DOM200°C). In contrast, prokaryotic growth in incubations to which only solid-phase extractable thermally-altered DOM was added was not enhanced compared to control incubations. The experiments demonstrate that temperature-driven degradation of deep-sea recalcitrant DOM within hydrothermal systems turns fractions of it accessible to microbes. The thermally-produced DOM compounds that stimulate microbial growth are not retained on reversed-phase resins (SPE-DOM) and are likely low-molecular mass organic acids. Despite the comprehensive compositional modifications of the solid-phase extractable (SPE-DOM) fraction through heating, it remains inaccessible to microbes at the investigated concentration levels. The microbial incubation resulted in only minor and mostly insignificant overall changes in SPE-DOM molecular composition and concentration.
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  • 39
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    Tracing processes and sources of Si release during weathering in two small catchments in the Black Forest by using Si isotopes (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Chemical Geology, ELSEVIER SCIENCE BV, 466, pp. 389-402, ISSN: 0009-2541
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    Publication Date: 2020-07-15
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  • 40
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    Occurrence and distribution of Amphidomataceae (Dinophyceae) in Danish coastal waters of the North Sea, the Limfjord and the Kattegat/Belt area (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 88, pp. 101637, ISSN: 1568-9883
    Details
    Publication Date: 2020-12-08
    Description: Some species of the dinophytes Azadinium and Amphidoma (Amphidomataceae) produce azaspiracids (AZA), lipophilic polyether compounds responsible for Azaspiracid Shellfish Poisoning (AZP) in humans after consumption of contaminated seafood. Toxigenic Amphidomataceae are known to occur in the North Atlantic and the North Sea area, but little is known about their importance in Danish coastal waters. In 2016, 44 Stations were sampled on a survey along the Danish coastline, covering the German Bight, Limfjord, the Kattegat area, Great Belt and Kiel Bight. Samples were analysed by live microscopy, liquid chromatography-tandem mass spectrometry (LC–MS/MS) and quantitative polymerase-chain-reaction (qPCR) on the presence of Amphidomataceae and AZA. Amphidomataceae were widely distributed in the area, but were below detection limit on most of the inner Limfjord stations. Cell abundances of the three toxigenic species, determined with species-specific qPCR assays on Azadinium spinosum, Az. poporum and Amphidoma languida, were generally low and restricted to the North Sea and the northern Kattegat, which was in agreement with the distribution of the generally low AZA abundances in plankton samples. Among the toxigenic species, Amphidoma languida was dominant with highest cell densities up to 3×103 cells L−1 on North Sea stations and at the western entrance of the Limfjord. Azaspiracids detected in plankton samples include low levels of AZA-1 at one station of the North Sea, and higher levels of AZA-38 and -39 (up to 1.5 ng L−1) in the North Sea and the Limfjord entrance. Furthermore, one new AZA (named AZA-63) was discovered in plankton of two North Sea stations. Morphological, molecular, and toxinological characterisation of 26 newly established strains from the area confirmed the presence of four amphidomatacean species (Az. obesum, Az. dalianense, Az. poporum and Am. languida). The single new strain of Az. poporum turned out as a member of Ribotype A2, which was previously only known from the Mediterranean. Consistent with some of these Mediterranean A2 strains, but different to the previously established AZA-37 producing Az. poporum Ribotype A1 strains from Denmark, the new strain did not contain any AZA. Azaspiracids were also absent in all Az. obesum and Az. dalianense strains, but AZA-38 and -39 were found in all Am. languida strains with total AZA cell quotas ranging from 0.08 up to 94 fg cell−1. In conclusion, AZA-producing microalgae and their respective toxins were low in abundance but widely present in the area, and thus might be considered in local monitoring programs to preserve seafood safety in Danish coastal waters.
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  • 41
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    Jurassic failed rift system below the Filchner-Ronne-Shelf, Antarctica: New evidence from geophysical data (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 688, pp. 65-83, ISSN: 0040-1951
    Details
    Publication Date: 2016-09-28
    Description: During the austral summer of 1994/95, reasonable ice conditions in the Weddell Sea allowed the acquisition of new high quality seismic refraction data parallel to the Filchner-Ronne Ice Shelf (FRS), Antarctica. Although pack ice conditions resulted in some data gaps, the final velocity-depth/2D-density models cover the entire FRS in E-W direction using all available deep seismic data/picks from this remote area. The velocity-depth model shows a sedimentary basin with a thickness up to 12 km and a large velocity inversion in the lowermost sedimentary unit. The crustal thickness reaches a maximum of 40 km along the basin’s margins in the Antarctic Peninsula and East Antarctica. In the central shelf area, numerous interfering seismic phases occur from the crust-mantle boundary at decreasing distances indicating a thinning of the crust. Here, the modelled velocities and densities reveal a thickness of 20 km for the igneous crust. This corridor of overthickened oceanic or close to oceanic crust is 160 km wide. The corridor is characterized by weak, but in general continuous magnetic anomalies, which we interpret as isochrons developed during the rifting or the initial formation of oceanic crust. If the crustal composition represents an old stripe of oceanic crust, a minimum estimate for the early formation of the oceanic crust is 145/148 Ma (Late Jurassic). However, based on the velocity of rift propagation during the initial opening of the adjacent Weddell Sea the oceanic crust is likely to have formed around 160 Ma. The onset of rifting and development of a thick igneous crust can be related to stresses developed between the interior and the southwestern paleo-Pacific subduction margin of the fragmenting Gondwana supercontinent in combination with additional melt supply from a deeper mantle source that arrived and spread in the period 183-155 Ma.
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  • 42
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    Seasonal variability of stable carbon isotopes (〈delta〉13CDIC) in the Skagerrak and the Baltic Sea: Distinguishing between mixing and biological productivity (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 483, pp. 15-30, ISSN: 0031-0182
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    Publication Date: 2017-09-01
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  • 43
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    Microhabitat preferences of live benthic foraminifera and stable carbon isotopes off SW Svalbard in the presence of widespread methane seepage (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Micropaleontology, ELSEVIER SCIENCE BV, 132, pp. 1-17, ISSN: 0377-8398
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    Publication Date: 2017-05-08
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  • 44
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    Upper mantle structure across the Trans-European Suture Zone imaged by S-receiver functions (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 458, pp. 429-441, ISSN: 0012-821X
    Details
    Publication Date: 2016-12-11
    Description: We present a high-resolution study of the upper mantle structure of Central Europe, including the western part of the East European Platform, based on S-receiver functions of 345 stations. A distinct contrast is found between Phanerozoic Europe and the East European Craton across the Trans-European Suture Zone. To the west, a pronounced velocity reduction with depth interpreted as lithosphere–asthenosphere boundary (LAB) is found at an average depth of 90 km. Beneath the craton, no strong and continuous LAB conversion is observed. Instead we find a distinct velocity reduction within the lithosphere, at 80–120 km depth. This mid-lithospheric discontinuity (MLD) is attributed to a compositional boundary between depleted and more fertile lithosphere created by late Proterozoic metasomatism. A potential LAB phase beneath the craton is very weak and varies in depth between 180 and 250 km, consistent with a reduced velocity contrast between the lower lithosphere and the asthenosphere. Within the Trans-European Suture Zone, lithospheric structure is characterized by strong heterogeneity. A dipping or step-wise increase to LAB depth of 150 km is imaged from Phanerozoic Europe to 20–22° E, whereas no direct connection to the cratonic LAB or MLD to the east is apparent. At larger depths, a positive conversion associated with the lower boundary of the asthenosphere is imaged at 210–250 km depth beneath Phanerozoic Europe, continuing down to 300 km depth beneath the craton. Conversions from both 410 km and 660 km discontinuities are found at their nominal depth beneath Phanerozoic Europe, and the discontinuity at 410 km depth can also be traced into the craton. A potential negative conversion on top of the 410 km discontinuity found in migrated images is analyzed by modeling and attributed to interference with other converted phases.
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  • 45
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    Deeply hidden inside introduced biogenic structures – Pacific oyster reefs reduce detrimental barnacle overgrowth on native blue mussels (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 117, pp. 20-26, ISSN: 1385-1101
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    Publication Date: 2016-12-20
    Description: In sedimentary coastal ecosystems shells of epibenthic organisms such as blue mussels (Mytilus edulis) provide the only major attachment surface for barnacle epibionts, which may cause detrimental effects on their mussel basibionts by e.g. reducing growth rate. In the European Wadden Sea, beds of native blue mussels have been invaded by Pacific oysters Crassostrea gigas, which transformed these beds into mixed reefs of oysters with mussels. In this study, we determined the spatial distribution of M. edulis and their barnacle epibionts (Semibalanus balanoides) within the reef matrix. Mean mussel density near the bottom was about twice as high compared to the mussel density near the top of an oyster reef, whereas barnacles on mussels showed a reversed pattern. Barnacle dry weight per mussel was on average 14 times higher near the top than at the bottom. This patternwas confirmed by experimentally placing clean M. edulis at the top and on the bottomof oyster reefs at two sites in the Wadden Sea (island of Texel, The Netherlands; island of Sylt, Germany). After an experimental period of fiveweeks (April and May 2015, the main settlement period of S. balanoides), the number of barnacles per mussel was at both sites significantly higher on mussels near the top compared to near the bottom. We conclude that the oyster reef matrix offers a refuge for M. edulis: inside reefs they are not only better protected against predators but also against detrimental barnacle overgrowth. This study shows that alien species can cause beneficial effects for native organisms and should not be generally considered as a risk for the recipientmarine ecosystems.
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  • 46
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    Biogeochemical and hydrological drivers of the dynamics of Vibrio species in two Patagonian estuaries (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Science of The Total Environment, ELSEVIER SCIENCE BV, 579, pp. 646-656, ISSN: 0048-9697
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    Publication Date: 2017-01-30
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  • 47
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    Species occurrence of the potentially toxigenic diatom genus Pseudo-nitzschia and the associated neurotoxin domoic acid in the Argentine Sea (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 63, pp. 45-55, ISSN: 1568-9883
    Details
    Publication Date: 2019-07-17
    Description: The marine diatom genus Pseudo-nitzschia, the major known producer of the neurotoxin domoic acid (DA) responsible for the amnesic shellfish poisoning (ASP) syndrome in humans and marine mammals, is globally distributed. The genus presents high species richness in the Argentine Sea and DA has been frequently detected in the last few years in plankton and shellfish samples, but the species identity of the producers remains unclear. In the present work, the distribution and abundance of Pseudo-nitzschia species and DA were determined from samples collected on two oceanographic cruises carried out through the Argentine Sea (∼39–47°S) during summer and spring 2013. Phytoplankton composition was analysed by light and electron microscopy while DA was determined by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was recorded in 71 and 86% of samples collected in summer and spring, respectively, whereas DA was detected in only 42 and 21% of samples, respectively. Microscopic analyses revealed at least five potentially toxic species (P. australis, P. brasiliana, P. fraudulenta, P. pungens, P. turgidula), plus putatively non-toxigenic P. dolorosa, P. lineola, P. turgiduloides and unidentified specimens of the P. pseudodelicatissima complex. The species P. australis showed the highest correlation with DA occurrence (r = 0.55; p 〈 0.05), suggesting its importance as a major DA producer in the Argentine Sea. In the northern area and during summer, DA was associated with the presence of P. brasiliana, a species recorded for the first time in the Argentine Sea. By contrast, high concentrations of P. fraudulenta, P. pungens and P. turgidula did not correspond with DA occurrence. This study represents the first successful attempt to link toxigenicity with Pseudo-nitzschia diversity and cell abundance in field plankton populations in the south-western Atlantic.
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  • 48
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    Synchronicity of Kuroshio Current and climate system variability since the Last Glacial Maximum (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 452, pp. 247-257, ISSN: 0012-821X
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    Publication Date: 2018-08-10
    Description: The Kuroshio Current (KC) is the northward branch of the North Pacific subtropical gyre (NPG) and exerts influence on the exchange of physical, chemical, and biological properties of downstream regions in the Pacific Ocean. Resolving long-term changes in the flow of the KC water masses is, therefore, crucial for advancing our understanding of the Pacific's role in global ocean and climate variability. Here, we reconstruct changes in KC dynamics over the past 20 ka based on grain-size spectra, clay mineral, and Sr–Nd isotope constraints of sediments from the northern Okinawa Trough. Combined with published sediment records surrounding the NPG, we suggest that the KC remained in the Okinawa Trough throughout the Last Glacial Maximum. Together with Earth-System-Model simulations, our results additionally indicate that KC intensified considerably during the early Holocene (EH). The synchronous establishment of the KC “water barrier” and the modern circulation pattern during the EH highstand shaped the sediment transport patterns. This is ascribed to the precession-induced increase in the occurrence of La Niña-like state and the strength of the East Asian summer monsoon. The synchronicity of the shifts in the intensity of the KC, Kuroshio extension, and El Niño/La Niña-Southern Oscillation (ENSO) variability may further indicate that the western branch of the NPG has been subject to basin-scale changes in wind stress curl over the North Pacific in response to low-latitude insolation. Superimposed on this long-term trend are high-amplitude, large century, and millennial-scale variations during last 5 ka, which are ascribed to the advent of modern ENSO when the equatorial oceans experienced stronger insolation during the boreal winter.
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  • 49
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    Constraining foraminiferal calcification depths in the western Pacific warm pool (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Micropaleontology, ELSEVIER SCIENCE BV, 128, pp. 14-27, ISSN: 0377-8398
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    Publication Date: 2016-12-16
    Description: Insight into past changes of upper ocean stratification, circulation, and nutrient signatures rely on our knowledge of the apparent calcification depth (ACD) and ecology of planktonic foraminifera, which serve as archives for paleoceanographic relevant geochemical signals. The ACD of different species varies strongly between ocean basins, but also regionally. We constrained foraminiferal ACDs in the Western Pacific Warm Pool (Manihiki Plateau) by comparing stable oxygen and carbon isotopes (δ18Ocalite, δ13Ccalcite) as well as Mg/Ca ratios from living planktonic foraminifera to in-situ physical and chemical water mass properties (temperature, salinity, δ18Oseawater, δ13CDIC). Our analyses point to Globigerinoides ruber as the shallowest dweller, followed by Globigerinoides sacculifer, Neogloboquadrina dutertrei, Pulleniatina obliquiloculata and Globorotaloides hexagonus inhabiting increasing greater depths. These findings are consistent with other ocean basins; however, absolute ACDs differ from other studies. The uppermost mixed-layer species G. ruber and G. sacculifer denote mean calcification depths of ~95mand ~120 m, respectively. These Western Pacific ACDs are much deeper than in most other studies and most likely relate to the thick surface mixed layer and the deep chlorophyll maximum in this region. Our results indicate that N. dutertrei appears to be influenced by mixing waters from the Pacific equatorial divergence, while P. obliquiloculata with an ACD of ~160 m is more suitable for thermocline reconstructions. ACDs of G. hexagonus reveal a deep calcification depth of ~450 m in oxygen-depleted, but nutrient-rich water masses, consistent to other studies. As the δ13C of G. hexagonus is in near-equilibrium with ambient seawater, we suggest this species is suitable for tracing nutrient conditions in equatorial water masses originating in extra-topical regions.
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  • 50
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    Marine magnetotellurics imaged no distinct plume beneath the Tristan da Cunha hotspot in the southern Atlantic Ocean (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 716, pp. 52-63, ISSN: 0040-1951
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    Publication Date: 2017-11-04
    Description: The Tristan da Cunha (TDC) is a volcanic island located above a prominent hotspot in the Atlantic Ocean. Many geological and geochemical evidences support a deep origin of the mantle material feeding the hotspot. However, the existence of a plume has not been confirmed as an anomalous structure in the mantle resolved by geophysical data because of lack of the observations in the area. Marine magnetotelluric and seismological observations were conducted in 2012–2013 to examine the upper mantle structure adjacent to TDC. The electrical conductivity structure of the upper mantle beneath the area was investigated in this study. Three-dimensional inversion analysis depicted a high conductive layer at ~ 120 km depth but no distinct plume-like vertical structure. The conductive layer is mostly flat independently on seafloor age and bulges upward beneath the lithospheric segment where the TDC islands are located compared to younger segment south of the TDC Fracture Zone, while the bathymetry is rather deeper than prediction for the northern segment. The apparent inconsistency between the absence of vertical structure in this study and geochemical evidences on deep origin materials suggests that either the upwelling is too small and/or weak to be resolved by the current data set or that the upwelling takes place elsewhere outside of the study area. Other observations suggest that 1) the conductivity of the upper mantle can be explained by the fact that the mantle above the high conductivity layer is depleted in volatiles as the result of partial melting beneath the spreading ridge, 2) the potential temperature of the segments north of the TDC Fracture Zone is lower than that of the southern segment at least during the past ~ 30 Myr.
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  • 51
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    Response of Central European SST to atmospheric pCO2 forcing during the Oligocene - A combined proxy data and numerical climate model approach (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Palaeogeography Palaeoclimatology Palaeoecology, ELSEVIER SCIENCE BV, 459, pp. 552-569, ISSN: 0031-0182
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    Publication Date: 2018-03-06
    Description: CO2-induced global warming will affect seasonal to decadal temperature patterns. Expected changes will be particularly strong in extratropical regions where temperatures will increase at faster rates than at lower latitudes. Despite that, it is still poorly constrained how precisely short-term climate dynamics will change in a generally warmer world, particularly in nearshore surface waters in the extratropics, i.e., the ecologically most productive regions of the ocean on which many human societies depend. Specifically, a detailed knowledge of the relationship between pCO2 and seasonal SST is crucial to understand interactions between the ocean and the atmosphere. In the present investigation, we have studied for the first time how rising atmospheric pCO2 levels forced surface temperature changes in Central Europe (paleolatitude ~45 °N) during the mid-Oligocene (fromca. 31 to 25Ma), a time interval of Earth history during which global conditions were comparable to those predicted for the next few centuries. For this purpose, we computed numerical climate models for the Oligocene (winter, summer, annual average) assuming an atmospheric carbon dioxide rise from 400 to 560 ppm (current level to two times pre-industrial levels, PAL) and from 400 to 840 ppm (= three times PAL), respectively. These models were compared to seasonally resolved sea surface temperatures (SST) reconstructed from δ18O values of fossil bivalve shells (Glycymeris planicostalis, G. obovata, Palliolum pictum, Arctica islandica and Isognomon maxillata sandbergeri) and shark teeth (Carcharias cuspidata, C. acutissimaand Physogaleus latus) collected fromthe shallow water deposits of the Mainz and Kassel Basins (Germany). Multi-taxon oxygen isotope-based reconstructions suggest a gradual rise of temperatures in surface waters (upper 30 to 40m), on average, by asmuch as 4 °C during the Rupelian stage followed by a 4 °C cooling during the Chattian stage. Seasonal temperature amplitudes increased by ca. 2 °C during the warmest time interval of the Rupelian stage,withwarming beingmore pronounced during summer (5 °C) than during winter (3 °C). According to numerical climate simulations, the warming of surface waters during the early Oligocene required a CO2 increase by at least 160 ppm, i.e., 400 ppm to 560 ppm. Given that atmospheric carbon dioxide levels predicted for the near future will likely exceed this value significantly, the Early Oligocene warming gives a hint of the possible future climate in Central Europe under elevated CO2 levels.
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    A shell regeneration assay to identify biomineralization candidate genes in mytilid mussels (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, 27, pp. 57-67, ISSN: 1874-7787
    Details
    Publication Date: 2017-01-06
    Description: Biomineralization processes in bivalve molluscs are still poorly understood. Here we provide an analysis of specifically expressed sequences from a mantle transcriptome of the blue mussel, Mytilus edulis. We then developed a novel, integrative shell injury assay to test, whether biomineralization candidate genes highly expressed in marginal and pallial mantle could be induced in central mantle tissue underlying the damaged shell areas. This experimental approach makes it possible to identify gene products that control the chemical micro-environment during calcification as well as organic matrix components. This is unlike existing methodological approaches that work retroactively to characterize calcification relevant molecules and are just able to examine organic matrix components that are present in completed shells. In our assay an orthogonal array of nine 1 mm holes was drilled into the left valve, and mussels were suspended in net cages for 20, 29 and 36 days to regenerate. Structural observations using stereo-microscopy, SEM and Raman spectroscopy revealed organic sheet synthesis (day 20) as the first step of shell-repair followed by the deposition of calcite crystals (days 20 and 29) and aragonite tablets (day 36). The regeneration period was characterized by time-dependent shifts in gene expression in left central mantle tissue underlying the injured shell, (i) increased expression of two tyrosinase isoforms (TYR3: 29-fold and TYR6: 5-fold) at day 20 with a decline thereafter, (ii) an increase in expression of a gene encoding a nacrein-like protein (max. 100-fold) on day 29. The expression of an acidic Asp-Ser-rich protein was enhanced during the entire regeneration process. This proof-of-principle study demonstrates that genes that are specifically expressed in pallial and marginal mantle tissue can be induced (4 out of 10 genes) in central mantle following experimental injury of the overlying shell. Our findings suggest that regeneration assays can be used systematically to better characterize gene products that are essential for distinct phases of the shell formation process, particularly those that are not incorporated into the organic shell matrix.
    Repository Name: EPIC Alfred Wegener Institut
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    Non-Antarctic notothenioids: Past phylogenetic history and contemporary phylogeographic implications in the face of environmental changes (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, 25, pp. 1-9, ISSN: 1874-7787
    Details
    Publication Date: 2017-01-06
    Description: The non-Antarctic Notothenioidei families, Bovichtidae, Pseudaphritidae and Eleginopsidae, diverged early from the main notothenioid lineage. They are important in clarifying the early evolutionary processes that triggered notothenioid evolution in the Antarctic. The early-diverged group represents 8% of all notothenioid species and never established themselves on the Antarctic shelf. Most attention has been paid to the Antarctic notothenioids and their limited physiological tolerance to climate change and increased temperatures. In this review, we discuss key life history traits that are characteristic of the non-Antarctic early-diverged notothenioid taxa as well as the genetic resources and population differentiation information available for this group. We emphasise the population fitness and dynamics of these species and indicate how resource management and conservation of the group can be strengthened through an integrative approach. Both Antarctic waters and the non-Antarctic regions face rapid temperature rises combined with strong anthropogenic exploitation. While it is expected that early-diverged notothenioid species may have physiological advantages over high Antarctic species, it is difficult to predict how climate changes might alter the geographic range, behaviour, phenology and ultimately genetic variability of these species. It is possible, however, that their high degree of endemism and dependence on local environmental specificities to complete their life cycles might enhance their vulnerability.
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    Empirical model to estimate permeability of surface sediments in the German Bight (North Sea) (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, ISSN: 1385-1101
    Details
    Publication Date: 2017-02-02
    Description: As the determinant of solute and particle fluxes through sediments, quantifying sediment permeability is vital step in understanding of the exchange phenomena between the water column and sediment as permeability determines the mode and intensity of solute and particle fluxes. Reliable estimates of sediment permeability are therefore a constraint on the accurate implementation of benthic biogeochemical models. This is particularly true for the North Sea, as field data are scarce and available grain-size-based models fail to represent the full range of sediment types. In this study, we combine measurements of sediment permeability and grain size analysis with a generic permeability model to establish a high-resolution permeability map of the sediment in the German Bight (North Sea). Our results show a good agreement between model-based prediction and measurements of permeability, even for a wide range of permeability values.
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    Origin and fate of sedimentary organic matter in the northern Bay of Bengal during the last 18 ka (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 146, pp. 53-66, ISSN: 0921-8181
    Details
    Publication Date: 2016-10-19
    Description: The Northern Bay of Bengal (NBoB) is a globally important region for deep-sea organic matter (OM) deposition due to massive fluvial discharge from the Ganges-Brahmaputra-Meghna (G-B-M) rivers and moderate to high surface productivity. Previous studies have focused on carbon burial in turbiditic sediments of the Bengal Fan. However, little is known about the storage of carbon in pelagic and hemipelagic sediments of the Bay of Bengal over millennial time scales. This study presents a comprehensive history of OM origin and fate as well as a quantification of carbon sediment storage in the Eastern Bengal Slope (EBS) during the last 18 ka. Bulk organic proxies (TOC, TIC, TN, δ13CTOC, δ15NTN) and content and composition of total hydrolysable amino acids (THAA) in a sediment core (SO188-342KL) from the EBS were analyzed. Three periods of high OM accumulation were identified: the Late Glacial (LG), the Bölling/Alleröd (B/A), and the Early Holocene Climatic Optimum (EHCO). Lower eustatic sea level before 15 ka BP allowed a closer connection between the EBS and the fluvial debouch, favoring high terrestrial OM input to the core site. This connection was progressively lost between 15 and 7 ka BP as sea level rose to its present height and terrestrial OM input decreased considerably. Export and preservation of marine OM was stimulated during periods of summer monsoon intensification (B/A and EHCO) as a consequence of higher surface productivity enhanced by cyclonic-eddy nutrient pumping and fluvial nutrient delivery into the photic zone. Changes in the THAA composition indicate that the marine plankton community structure shifted from calcareous-dominated before 13 ka BP to siliceous-dominated afterwards. They also indicate that the relative proportion of marine versus terrestrial OM deposited at site 342KL was primarily driven by relative sea level and enlarged during the Holocene. The ballasting effect of lithogenic particles during periods of high coastal proximity and/or enhanced fluvial discharge promoted the export and preservation of OM. The high organic carbon accumulation rates in the EBS during the LG (18–17 ka BP) were 5-fold higher than at present and comparable to those of glacial upwelling areas. Despite the differences in sediment and OM transport and storage among the Western and Eastern sectors of the NBoB, this region remains important for global carbon sequestration during sea level low-stands. In addition, the summer monsoon was a key promotor of terrestrial and marine OM export to the deep-ocean, highlighting its relevance as regulator of the global carbon budget.
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    Distribution of Dinophysis species and their association with lipophilic phycotoxins in plankton from the Argentine Sea (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 59, pp. 31-41, ISSN: 1568-9883
    Details
    Publication Date: 2019-07-17
    Description: Dinophysis is a cosmopolitan genus of marine dinoflagellates, considered as the major proximal source of diarrheic shellfish toxins and the only producer of pectenotoxins (PTX). From three oceanographic expeditions carried out during autumn, spring and late summer along the Argentine Sea (∼38–56°S), lipophilic phycotoxins were determined by liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS) in size-fractionated plankton samples. Lipophilic toxin profiles were associated with species composition by microscopic analyses of toxigenic phytoplankton. Pectenotoxin-2 and PTX-11 were frequently found together with the presence of Dinophysis acuminata and Dinophysis tripos. By contrast, okadaic acid was rarely detected and only in trace concentrations, and dinophysistoxins were not found. The clear predominance of PTX over other lipophilic toxins in Dinophysis species from the Argentine Sea is in accordance with previous results obtained from north Patagonian Gulfs of the Argentine Sea, and from coastal waters of New Zealand, Chile, Denmark and United States. Dinophysis caudata was rarely found and it was confined to the north of the sampling area. Because of low cell densities, neither D. caudata nor Dinophysis norvegica could be biogeographically related to lipophilic toxins in this study. Nevertheless, the current identification of D. norvegica in the southern Argentine Sea is the first record for the southwestern Atlantic Ocean. Given the typical toxigenicity of this species on a global scale, this represents an important finding for future surveillance of plankton-toxin associations.
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    Oxygen isotope composition of diatoms as Late Holocene climate proxy at Two-Yurts-Lake, Central Kamchatka, Russia (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 134, pp. 118-128, ISSN: 0921-8181
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    Publication Date: 2016-10-22
    Repository Name: EPIC Alfred Wegener Institut
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    Holocene environmental history of a small coastal lake from north-eastern Kamchatka Peninsula. (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 134, pp. 55-66, ISSN: 0921-8181
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    Publication Date: 2016-10-22
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    Do drivers of biodiversity change differ in importance across marine and terrestrial systems—Or is it just different research communities' perspectives? (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Science of The Total Environment, ELSEVIER SCIENCE BV, 574, pp. 193-203, ISSN: 0048-9697
    Details
    Publication Date: 2019-02-15
    Repository Name: EPIC Alfred Wegener Institut
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    Mid Holocene climate and vegetation in the Northern Altay mountains recorded in Lake Teletskoe. (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 141, pp. 12-24, ISSN: 0921-8181
    Details
    Publication Date: 2016-10-22
    Description: Wereport the first high-resolution (20–50 years) mid- to late Holocene pollen records fromLake Teletskoye, the largest lake in the Altai Mountains, in south-eastern West Siberia. Generally, the mid- to late Holocene (the last 4250 years) vegetation of the north-eastern Altai, as recorded in two studied sediment cores, is characterised by Siberian pine–spruce–fir forests that are similar to those of the present day. A relatively cool and dry intervalwith July temperatures lower than those of today occurred between 3.9 and 3.6 ka BP. The widespread distribution of open, steppe-like communitieswith Artemisia, Chenopodiaceae and Cyperaceae reflects maximumdeforestation during this interval. After ca. 3.5 ka BP, the coniferous mountain taiga spread significantly,withmaximumwoody coverage and taiga biome scores between ca. 2.7 and 1.6 ka BP. This coincides wellwith the highest July temperature (approximately 1 °C higher than today) intervals. A short period of cooling about 1.3–1.4 ka BP could have been triggered by the increased volcanic activity recorded across the Northern Hemisphere. A new period of cooling started around 1100–1150 CE, with the minimum July temperatures occurring between 1450 and 1800 CE.
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    Northern Russian chironomid-based modern summer temperature data set and inference models (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 134, pp. 10-25, ISSN: 0921-8181
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    Publication Date: 2016-10-22
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    The Pacific-Atlantic connection: Biogeochemical signals in the southern end of the Argentine shelf (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Marine Systems, ELSEVIER SCIENCE BV, 163, pp. 95-101, ISSN: 0924-7963
    Details
    Publication Date: 2017-01-30
    Repository Name: EPIC Alfred Wegener Institut
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    Distinctly different behavioral responses of a copepod, Temora longicornis, to different strains of toxic dinoflagellates, Alexandrium spp. (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 62, pp. 1-9, ISSN: 1568-9883
    Details
    Publication Date: 2017-12-15
    Description: Zooplankton responses to toxic algae are highly variable, even towards taxonomically closely related species or different strains of the same species. Here, the individual level feeding behavior of a copepod, Temora longicornis, was examined which offered 4 similarly sized strains of toxic dinoflagellate Alexandrium spp. and a non-toxic control strain of the dinoflagellate Protoceratium reticulatum. The strains varied in their cellular toxin concentration and composition and in lytic activity. High-speed video observations revealed four distinctly different strain-specific feeding responses of the copepod during 4 h incubations: (i) the ‘normal’ feeding behavior, in which the feeding appendages were beating almost constantly to produce a feeding current and most (90%) of the captured algae were ingested; (ii) the beating activity of the feeding appendages was reduced by ca. 80% during the initial 60 min of exposure, after which very few algae were captured and ingested; (iii) capture and ingestion rates remained high, but ingested cells were regurgitated; and (iv) the copepod continued beating its appendages and captured cells at a high rate, but after 60 min, most captured cells were rejected. The various prey aversion responses observed may have very different implications to the prey and their ability to form blooms: consumed but regurgitated cells are dead, captured but rejected cells survive and may give the prey a competitive advantage, while reduced feeding activity of the grazer may be equally beneficial to the prey and its competitors. These behaviors were not related to lytic activity or overall paralytic shellfish toxins (PSTs) content and composition and suggest that other cues are responsible for the responses.
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    Spatio-temporal pattern of detrital clay-mineral supply to a lake system on the north-eastern Tibetan Plateau, and its relationship to late Quaternary paleoenvironmental changes (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3CATENA, ELSEVIER SCIENCE BV, 137, pp. 203-218, ISSN: 0341-8162
    Details
    Publication Date: 2017-01-20
    Description: Clay-mineral fingerprints from modern and fossil lake sediments from Lake Donggi Cona, situated on the northeastern Tibetan Plateauwere studied to determine changes in sediment provenance and environmental development since the late Glacial. To infer the source areas of the lake sediments, characteristic facies units (cover sediments and soils) from the catchment of the lake were studied concerning their clay-mineral compositions and through statistical analyses using the Fuzzy C-Means algorithm. Sediment contributions from the various geological provinces in the catchment of the lake are reflected in a systematic spatial pattern of variable clay-mineral assemblages, which is most pronounced in modern fluvial and lake sediments. Downcore changes in the clay-mineral fingerprints of lake sediments provide information on the spatio-temporal variability of detrital sediment supplies, related to climate-influenced changes in environmental boundary conditions. Since the late Glacial, water-level fluctuations driven by glacier melt appear to have exerted the greatest control over the transport paths of detrital sediments. Probably glacial melt-waters carried mainly illitic rich pre-Cenozoic debris into the lake fromthe northern and north-western catchment areas. During the Holocene the detrital clay mineral supply was mainly controlled from pre-Cenozoic and Neogene sources. However, because of the increased summer monsoon precipitation the lake level rose dramatically to at least modern levels, resulting in a relative increase in the supply frompedogenic karsticweathering sources mainly fromthe east,which during the Holocene was possibly flooded morewidely than today. During the late Holocene a decreasing input of smectite suggests a relative reduction in the supply of far-traveled aquatic suspensions into the lake. In contrast, during the sameinterval kaolinite concentrations increased,which suggests a relatively strong sediment supply from the east, possibly triggered by a current flowing from east to west.
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    Amphidoma languida (Amphidomatacea, Dinophyceae) with a novel azaspiracid toxin profile identified as the cause of molluscan contamination at the Atlantic coast of southern Spain (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 62, pp. 113-126, ISSN: 1568-9883
    Details
    Publication Date: 2018-01-16
    Description: Azaspiracids (AZA) are a group of food poisoning phycotoxins that are known to accumulate in shellfish. They are produced by some species of the planktonic dinophycean taxon Amphidomataceae. Azaspiracids have been first discovered in Ireland but are now reported in shellfish from numerous global sites thus showing a wide distribution. In shellfish samples collected in 2009 near Huelva (Spain),AZA was also found along the Andalusian Atlantic coast for the first time. Analysis using LC–MS/MS revealed the presence of two different AZA analogues in different bivalve shellfish species (Chamelea gallina, Cerastoderma edule, Donax trunculus, and Solen vagina). In a number of samples, AZA levels exceeded the EU regulatory level of 160 mg AZA-1 eq. kg�1 (reaching maximum levels of 〉500 mg AZA- 1 eq. kg�1 in Chamelea gallina and 〉250 mg AZA-1 eq. kg�1 in Donax trunculus) causing closures of some local shellfish production areas. One dinophyte strain established from the local plankton during the AZA contamination period and determined as Amphidoma languida was in fact toxigenic, and its AZA profile disclosed it as the causative species: it contained AZA-2 as the main compound and the new compound AZA-43 initially detected in the shellfish. AZA-43 had the same mass as AZA-3, but produced different collision induced dissociation (CID) spectra. High resolution mass spectrometric easurements indicated that there is an unsaturation in the H, I ring system of AZA-43 distinguishing it from the classical AZA such as AZA-1, -2, and -3. Furthermore, the Spanish strain was different from the previously reported AZA profile of the species that consist of AZA-38 and AZ-39. In molecular phylogenetics, the Andalusian strain formed a monophyletic group together with other strains of Am. languida, but ITS sequences data revealed surprisingly high intragenomic variability. The first Andalusian case of AZA contamination of shellfish above the EU regulatory limit reported here clearly revealed the risk of azaspiracid poisoning (AZP) for this area and also for the Atlantic coast of Iberia and North Africa. The present study underlines the need for continuous monitoring of AZA and the organisms producing such toxins.
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    Hunting for the Tristan mantle plume – An upper mantle tomography around the volcanic island of Tristan da Cunha (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 462, pp. 122-131, ISSN: 0012-821X
    Details
    Publication Date: 2017-02-01
    Description: The active volcanic island Tristan da Cunha, located at the southwestern and youngest end of the Walvis Ridge – Tristan/Gough hotspot track, is believed to be the surface expression of a huge thermal mantle anomaly. While several criteria for the diagnosis of a classical hotspot track are met, the Tristan region also shows some peculiarities. Consequently it is vigorously debated if the active volcanism in this region is the expression of a deep mantle plume, or if it is caused by shallow plate tectonics and the interaction with the nearby Mid-Atlantic Ridge. Because of a lack of geophysical data in the study area, no model or assumption has been completely confirmed. We present the first amphibian P-wave finite-frequency travel time tomography of the Tristan da Cunha region, based on cross-correlated travel time residuals of teleseismic earthquakes recorded by 24 ocean-bottom seismometers. The data can be used to image a low velocity structure southwest of the island. The feature is cylindrical with a radius of ∼100km down to a depth of 250km. We relate this structure to the origin of Tristan da Cunha and name it the Tristan conduit. Below 250km the low velocity structure ramifies into narrow veins, each with a radius of ∼50km. Furthermore, we imaged a linkage between young seamounts southeast of Tristan da Cunha and the Tristan conduit.
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    Patterns and rates of riverbank erosion involving ice-rich permafrost (yedoma) in northern Alaska (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Geomorphology, ELSEVIER SCIENCE BV, ISSN: 0169-555X
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    Publication Date: 2015-12-05
    Description: Yedoma, a suite of syngenetically frozen silty ice- and organic-rich deposits with large ice wedges that accumulated during the late Pleistocene, is vulnerable to thermal degradation and erosion because of the extremely high ice contents. This degradation can result in significant surface subsidence and retreat of coastal bluffs and riverbanks with large consequences to landscape evolution, infrastructure damage, and water quality. We used remote sensing and field observations to assess patterns and rates of riverbank erosion at a 35-m-high active yedoma bluff along the Itkillik River in northern Alaska. The total volumetric ground-ice content—including wedge, segregated, and pore ice—was estimated to be ~ 86%. The process of riverbank erosion and stabilization include three main stages typical of the areas with ice-rich permafrost: (1) thermal erosion combined with thermal denudation, (2) thermal denudation, and (3) slope stabilization. Active riverbank erosion at the main study site started in July 1995, when the Itkillik River changed its channel. The total retreat of the riverbank during 1995–2010 within different segments of the bluff varied from 180 to 280 m; the average retreat rate for the most actively eroded part of the riverbank was almost 19 m/y. From August 2007 to August 2011, the total retreat varied from 10 to almost 100 m. The average retreat rate for the whole 680-m-long bluff was 11 m/y. For the most actively eroded central part of the bluff (150 m long) it was 20 m/y, ranging from 16 to 24 m/y. More than 180,000 m3 of ground ice and organic-rich frozen soil, or almost 70,000 metric tons (t) of soil solids including 880 t of organic carbon, were transported to the river from the retreating bank annually. This study reports the highest long-term rates of riverbank erosion ever observed in permafrost regions of Eurasia and North America.
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    Phytoplankton and pigment patterns across frontal zones in the Atlantic sector of the Southern Ocean (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Chemistry, ELSEVIER SCIENCE BV, 177, pp. 510-517, ISSN: 0304-4203
    Details
    Publication Date: 2016-06-09
    Description: Phytoplankton distribution and concentrations of macronutrients and iron were studied in the Polar Frontal Zone (PFZ) and the eastern Weddell Gyre of the Southern Ocean, during austral autumn. HPLC analysis of algal pigments was combined with microscopy observations to assess algal distribution. Patterns of algal distribution were dictated by the frontal systems. Travelling from north to south, four distinctively different algal communities were observed, the composition of which could be explained by variations in nutrients, light climate and grazing pressure. North of the PFZ, low silicate levels (〈3 μM) were limiting diatom growth, and the algal community was dominated by prasinophytes. Silicate concentrations increased over the PFZ, which coincided with the dominance of diatoms. South of the PFZ, the open waters of the Weddell Gyre are characterised as a high nutrient low-chlorophyll area. Low iron concentrations (〈0.4 nM on average) supported an algal community that was dominated by smaller size algae (〈20 μm). Deep wind-mixed layers (〉100 m depth) together with low incident irradiance in autumn were likely limiting algal growth. At the Marginal Ice Zone (MIZ), the phytoplankton community consisted mainly of low numbers of flagellates (Chlorophyceae and haptophytes) and high numbers of microzooplankton, indicating phytoplankton control by grazing. The phytoplankton distribution patterns presented here and the relation with potential growth-controlling factors provides more insight in the mechanisms that control carbon fluxes from the atmosphere into the ocean interior.
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    Bathymetric patterns in standing stock and diversity of deep-sea nematodes at the long-term ecological research observatory HAUSGARTEN (Fram Strait) (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Marine Systems, ELSEVIER SCIENCE BV, 172, pp. 160-177, ISSN: 0924-7963
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    Publication Date: 2017-04-11
    Description: Bathymetric patterns in standing stocks and diversity are a major topic of investigation in deep-sea biology. From the literature, responses of metazoanmeiofauna and nematodes to bathymetric gradients arewell studied, with a general decrease in biomass and abundance with increasing water depth, while bathymetric diversity gradients often, although it is not a rule, show a unimodal pattern. Spatial distribution patterns of nematode communities along bathymetric gradients are coupled with surface-water processes and interacting physical and biological factors within the benthic system. We studied the nematode communities at the Long-TermEcological Research (LTER) observatory HAUSGARTEN, located in the FramStrait at theMarginal Ice Zone, with respect to their standing stocks as well as structural and functional diversity.We evaluated whether nematode density, biomass and diversity indices, such asH0, Hinf, EG(50), Θ−1, are linkedwith environmental conditions along a bathymetric transect spanning from 1200mto 5500mwater depth. Nematode abundance, biomass and diversity, as well as food availability from phytodetritus sedimentation (indicated by chloroplastic pigments in the sediments), were higher at the stations located at upper bathyal depths (1200–2000 m) and tended to decrease with increasing water depth. A faunal shift was found below 3500 m water depth, where genus composition and trophic structure changed significantly and structural diversity indices markedly decreased. A strong dominance of very fewgenera and its high turnover particularly at the abyssal stations (4000–5500 m) suggests that environmental conditions were rather unfavorable for most genera. Despite the high concentrations of sediment-bound chloroplastic pigments and elevated standing stocks found at the deepest station (5500 m), nematode genus diversity remained the lowest compared to all other stations. This study provides a further insight into the knowledge of deep-sea nematodes, their diversity patterns and a deeper understanding of the environmental factors shaping nematodes communities at bathyal and abyssal depths.
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    CO2-dependent carbon isotope fractionation in dinoflagellates relates to their inorganic carbon fluxes (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, ELSEVIER SCIENCE BV, 481, pp. 9-14, ISSN: 0022-0981
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    Publication Date: 2016-05-10
    Repository Name: EPIC Alfred Wegener Institut
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    Insights into the crustal structure of the transition between Nares Strait and Baffin Bay (2016)
    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 691, pp. 31-47, ISSN: 0040-1951
    Details
    Publication Date: 2016-11-19
    Description: The crustal structure and continental margin between southern Nares Strait and northern Baffin Bay were studied based on seismic refraction and gravity data acquired in 2010. We present the resulting P wave velocity, density and geological models of the crustal structure of a profile, which extends from the Greenlandic margin of the Nares Strait into the deep basin of central northern Baffin Bay. For the first time, the crustal structure of the continent-ocean transition of the very northern part of Baffin Bay could be imaged. We divide the profile into three parts: continental, thin oceanic, and transitional crust. On top of the three-layered continental crust, a low-velocity zone characterizes the lowermost layer of the three-layered Thule Supergroup underneath Steensby Basin. The 4.3–6.3 km thick oceanic crust in the southern part of the profile can be divided into a northern and southern section, more or less separated by a fracture zone. The oceanic crust adjacent to the continent-ocean transition is composed of 3 layers and characterized by oceanic layer 3 velocities of 6.7–7.3 km/s. Toward the south only two oceanic crustal layers are necessary to model the travel time curves. Here, the lower oceanic crust has lower seismic velocities (6.4–6.8 km/s) than in the north. Rather low velocities of 7.7 km/s characterize the upper mantle underneath the oceanic crust, which we interpret as an indication for the presence of upper mantle serpentinization. In the continent-ocean transition zone, the velocities are lower than in the adjacent continental and oceanic crustal units. There are no signs for massive magmatism or the existence of a transform margin in our study area.
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    Metatranscriptome of marine bacterioplankton during winter time in the North Sea assessed by total RNA sequencing (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, 19, pp. 45-46, ISSN: 1874-7787
    Details
    Publication Date: 2019-03-08
    Description: Marine metatranscriptome data was generated as part of a study investigating the bacterioplankton communities towards the end of a diatom-dominated spring phytoplankton bloom. This genomic resource article reports a metatranscriptomic dataset from amidst the winter time prior to the occurrence of the spring diatom bloom. Up to 58% of all sequences could be assigned to predicted genes. Taxonomic analysis based on expressed 16S ribosomal RNA genes identified Alphaproteobacteria and Gammaproteobacteria as the most active community members.
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  • 73
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    Life in the sea of plenty: Seasonal and regional comparison of physiological performance of Euphausia hanseni in the northern Benguela upwelling system (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Sea Research, ELSEVIER SCIENCE BV, 103, pp. 103-112, ISSN: 1385-1101
    Details
    Publication Date: 2017-01-26
    Description: Variability in upwelling events may lead to periods of constrained food availability in the northern Benguela upwelling system (NBUS), thereby affecting the physiological state and metabolic activity of euphausiids. Most attention has so far been paid to seasonal effects but little is known about regional variability.Metabolic activity (expressed by respiration and excretion rates) and physiological state (expressed by reproductive effort and moult activity) in Euphausia hanseni were examined at different stations during austral summer (minimum upwelling) and austral winter (maximum upwelling). Overall, regional differences in physiological state, influencing metabolic activity, were greater than seasonal ones, indicating favourable conditions for growth and reproduction year-round. Higher respiration rateswere found for females in more advanced stages of sexual development.Moult stage did not affect oxygen consumption rates, however. The physiological state of E. hanseni at the time of capture may serve as ameaningful indicator of the associated hydrographic conditions in the NBUS,to be further used in eco-system analysis on seasonal or long-term time scales. A latitudinal comparison of species highlights the extraordinary physiological plasticity of euphausiids.
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  • 74
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    Impact of ocean acidification on thermal tolerance and acid-base regulation of Mytilus edulis (L.) from the North Sea (2015)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, ELSEVIER SCIENCE BV, 473, pp. 16-25, ISSN: 0022-0981
    Details
    Publication Date: 2015-12-14
    Description: Anthropogenic climate change confronts marine organisms with rapid trends of concomitant warming and CO2 induced ocean acidification. The survival and distribution of species partly depend on their ability to exploit their physiological plasticity during acclimatization. Therefore, in laboratory studies the effects of simulated future ocean acidification on thermal tolerance, energy metabolism and acid–base regulation capacity of the North Sea population of the blue mussel Mytilus edulis were examined. Following one month of pre-acclimation to 10 °C and control CO2 levels, mussels were exposed for two weeks to control and projected oceanic CO2 levels (390, 750 and 1120 μatm) before being subjected to a stepwise warming protocol between 10 °C and 31 °C (+ 3 °C each night). Oxygen consumption and heart rates, anaerobic metabolite levels and haemolymph acid–base status were determined at each temperature. CO2 exposure left oxygen consumption rate unchanged at acclimation temperature but caused a somewhat stronger increase during acute warming and thus mildly higher Q10-values than seen in controls. Interestingly, the thermally induced limitation of oxygen consumption rate set in earlier in normocapnic than in hypercapnic (1120 μatm CO2) mussels (25.2 °C vs. 28.8 °C), likely due to an onset of metabolic depression in the control group following warming. However, the temperature induced increase in heart rate became limited above 25 °C in both groups indicating an unchanged pejus temperature regardless of CO2 treatment. An upper critical temperature was reached above 28 °C in both treatments indicated by the accumulation of anaerobic metabolites in the mantle tissue, paralleled by a strong increase in haemolymph PCO2 at 31 °C. Ocean acidification caused a decrease in haemolymph pH. The extracellular acidosis remained largely uncompensated despite some bicarbonate accumulation. In all treatments animals developed a progressive warming-induced extracellular acidosis. A stronger pH drop at around 25 °C was followed by stagnating heart rates. However, normocapnic mussels enhanced bicarbonate accumulation at the critical limit, a strategy no longer available to hypercapnic mussels. In conclusion, CO2 has small effects on the response patterns of mussels to warming, leaving thermal thresholds largely unaffected. High resilience of adult North Sea mussels to future ocean acidification indicates that sensitivity to thermal stress is more relevant in shaping the response to future climate change.
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    Micro-seismicity in the Gulf of Cadiz: Is there a link between micro-seismicity, high magnitude earthquakes and active faults? (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Tectonophysics, ELSEVIER SCIENCE BV, 717, pp. 226-241, ISSN: 0040-1951
    Details
    Publication Date: 2017-11-19
    Description: The Gulf of Cadiz seismicity is characterized by persistent low to intermediate magnitude earthquakes, occasionally punctuated by high magnitude events such as the M ~ 8.7 1755 Great Lisbon earthquake and the M = 7.9 event of February 28th, 1969. Micro-seismicity was recorded during 11 months by a temporary network of 25 ocean bottom seismometers (OBSs) in an area of high seismic activity, encompassing the potential source areas of the mentioned large magnitude earthquakes. We combined micro-seismicity analysis with processing and interpretation of deep crustal seismic reflection profiles and available refraction data to investigate the possible tectonic control of the seismicity in the Gulf of Cadiz area. Three controlling mechanisms are explored: i) active tectonic structures, ii) transitions between different lithospheric domains and inherited Mesozoic structures, and iii) fault weakening mechanisms. Our results show that micro-seismicity is mostly located in the upper mantle and is associated with tectonic inversion of extensional rift structures and to the transition between different lithospheric/rheological domains. Even though the crustal structure is well imaged in the seismic profiles and in the bathymetry, crustal faults show low to negligible seismic activity. A possible explanation for this is that the crustal thrusts are thin-skinned structures rooting in relatively shallow sub-horizontal décollements associated with (aseismic) serpentinization levels at the top of the lithospheric mantle. Therefore, co-seismic slip along crustal thrusts may only occur during large magnitude events, while for most of the inter-seismic cycle these thrusts remain locked, or slip aseismically. We further speculate that high magnitude earthquake's ruptures may only nucleate in the lithospheric mantle and then propagate into the crust across the serpentinized layers.
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    Sensitivity of open-water ice growth and ice concentration evolution in a coupled atmosphere-ocean-sea ice model (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Dynamics of Atmospheres and Oceans, ELSEVIER SCIENCE BV, 79, pp. 10-30, ISSN: 0377-0265
    Details
    Publication Date: 2017-11-20
    Description: A coupled atmosphere-ocean-sea ice model is applied to investigate to what degree the area-thickness distribution of new ice formed in open water affects the ice and ocean properties. Two sensitivity experiments are performed which modify the horizontal-to-vertical aspect ratio of open-water ice growth. The resulting changes in the Arctic sea-ice concentration strongly affect the surface albedo, the ocean heat release to the atmosphere, and the sea-ice production. The changes are further amplified through a positive feedback mechanism among the Arctic sea ice, the Atlantic Meridional Overturning Circulation (AMOC), and the surface air temperature in the Arctic, as the Fram Strait sea ice import influences the freshwater budget in the North Atlantic Ocean. Anomalies in sea-ice transport lead to changes in sea surface properties of the North Atlantic and the strength of AMOC. For the Southern Ocean, the most pronounced change is a warming along the Antarctic Circumpolar Current (ACC), owing to the interhemispheric bipolar seasaw linked to AMOC weakening. Another insight of this study lies on the improvement of our climate model. The ocean component FESOM is a newly developed ocean-sea ice model with an unstructured mesh and multi-resolution. We find that the subpolar sea-ice boundary in the Northern Hemisphere can be improved by tuning the process of open-water ice growth, which strongly influences the sea ice concentration in the marginal ice zone, the North Atlantic circulation, salinity and Arctic sea ice volume. Since the distribution of new ice on open water relies on many uncertain parameters and the knowledge of the detailed processes is currently too crude, it is a challenge to implement the processes realistically into models. Based on our sensitivity experiments, we conclude a pronounced uncertainty related to open-water sea ice growth which could significantly affect the climate system sensitivity.
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    Chronology of the Fram Slide Complex offshore NW Svalbard and its implications for local and regional slope stability (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 393, pp. 141-155, ISSN: 0025-3227
    Details
    Publication Date: 2017-11-19
    Description: The best known submarine landslides on the glaciated NW European continental margins are those at the front of cross-shelf troughs, where the alternation of rapidly deposited glycogenic and hemi pelagic material generates sedimentary overpressure. Here, we investigate landslides in two areas built of contourite drifts bounded seaward by a ridge-transform junction. Seismic and bathymetric data from the Fram Slide Complex are compared with the tectonically similar Vastness area ~120km to the south, to analyze the influence of local and regional processes on slope stability. These processes include tectonic activity, changes of climate and oceanography, gas hydrates and fluid migration systems, slope gradient, toe erosion and style of contourite deposition. Two areas within the Fram Slide Complex underwent different phases of slope failures, whereas there is no evidence at all for major slope failures in the Vastness area. The comparison cannot reveal the distinct reason for slope failure but demonstrates the strong impact of variation in the local controls on slope stability. The different failure chronologies suggest that toe erosion, which is dependent on the throw of normal faults, and the different thickness and geometry of contourite deposits can result in a critical slope morphology and exert pronounced effects on slope stability. These results highlight the limitations of regional hazard assessments and the need for multi-disciplinary investigations, as small differences in local controlling factors led to substantially different slope failure histories.
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    Fraction-specific controls on the trace element distribution in iron formations: Implications for trace metal stable isotope proxies (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Chemical Geology, ELSEVIER SCIENCE BV, 474, pp. 17-32, ISSN: 0009-2541
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    Publication Date: 2017-11-19
    Description: Iron formations (IFs) are important geochemical repositories that provide constraints on atmospheric and ocean chemistry, prior to and during the onset of the Great Oxidation Event. Trace metal abundances and their Mo-Cr- U isotopic ratios have been widely used for investigating ocean redox processes through the Archean and Paleoproterozoic. Mineralogically, IFs consist of three main Fe-bearing fractions: (1) Fe-Ca-Mg-Mn carbonates, (2) magnetite and/or hematite and (3) Fe-silicates. These fractions are typically fine-grained on a sub-μm scale and their co-occurrence in varying amounts means that bulk-rock or microanalytical geochemical and stable isotope data can be influenced by cryptic changes in mineralogy. Fraction specific geochemical analysis has the potential to resolve mineralogical controls and reveal diagenetic versus primary precipitative controls on IF mineralogy. Here we adapt an existing sequential extraction scheme for Fe-phases (Poulton and Canfield, 2005) to the high Fe-content in IF and the specific three-fraction mineralogy. We optimized the scheme for magnetite-dominated Archean IFs using samples from the hematite-poor Asbestos Hills Subgroup IF, Transvaal Supergroup, South Africa. Previously commonly-used hydroxylamine-HCl and dithionite leaches were omitted since ferric oxides are quantitatively insignificant in these IF samples. The acetate leach was tested at variable temperatures, reaction times and under different atmospheres in order to ensure that all micro-crystalline Fe-carbonates were effectively dissolved, resulting in an optimum extraction for 48 h at 50 °C under anoxic conditions. The dissolution of magnetite by NH4-oxalate was also tested, resulting in an optimum extraction for 24 h under an ambient atmosphere. Finally, a HF-HClO4-HNO3 leach was used to dissolve the residual silicate fraction which has to date not been considered in detail in IF. Accuracy of the extraction technique was generally excellent, as verified using 1) elemental recoveries, 2) comparison of major and trace element distributions against mineralogy and 3) comparison to results from microanalytical techniques. This study focuses on the distribution of three frequently used geochemical proxies in IF; U, Mo and Cr. Molybdenum abundances in the Kuruman and Griquatown IF are low and show an apparent correlation with mineralogical variability, as determined by the sequential extraction. This suggests that changes in bulk-rock mineralogy, rather than redox chemistry might significantly affect Mo stable isotopes. For Cr, a minor bulk-rock stratigraphic increase can be related to the oxide and silicate fraction. However, a positive relationship with Zr indicates that this was also controlled by detrital or volcanic ash input. Uranium is predominantly bound to the silicate fraction and shows clear correlations with Zr and Sc implying detrital reworking under anoxic conditions. The discrepant behaviour of these three proxies indicate that mineralogy should be taken into account when interpreting heterogeneous bulk-rock samples and that fraction specific techniques will provide new insights into the evolution of atmosphere and ocean chemistry.
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    Reconstruction of Holocene environmental changes in Southern Kurils (North-Western Pacific) based on palaeolake sediment proxies from Shikotan Island (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Global and Planetary Change, ELSEVIER SCIENCE BV, 159, pp. 25-36, ISSN: 0921-8181
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    Publication Date: 2020-06-14
    Description: We investigated a well-dated sediment section of a palaeolake situated in the coastal zone of Shikotan Island (Lesser Kurils) for organic sediment-geochemistry and biotic components (diatoms, chironomids, pollen) inorder to provide a reconstruction of the palaeoenvironmental changes and palaeo-events (tsunamis, sea-level fluctuations and landslides) in Holocene. During the ca 8000 years of sedimentation the changes in organic sediment-geochemistry and in composition of the diatoms and chironomids as well as the shifts in composition of terrestrial vegetation suggest that the period until ca 5800 cal yr BP was characterized by a warm and humid climate (corresponds to middle Holocene optimum) with climate cooling thereafter. A warm period reconstructed from ca 900 to at least ca 580 cal yr BP corresponds to a transition to a Nara-Heian-Kamakura warm stage and can be correlated to a Medieval Warm Period. After 580 cal yr PB, the lake gradually dried out and climatic signals could not be obtained from the declining lacustrine biological communities, but the increasing role of spruce and disappearance of the oak from the vegetation give evidences of the climate cooling that can be correlated with the LIA. The marine regression stages at the investigated site are identified for ca 6200–5900 (at the end of the middle Holocene transgression), ca 5500–5100 (Middle Jomon regression or Kemigawa regression), and ca 1070–360 cal yr BP (at the end of Heian transgression). The lithological structure of sediments and the diatom compositions give evidences for the multiple tsunami events of different strengths in the Island. Most remarkable of them can be dated at around ca 7000, 6460, 5750, 4800, 950 cal yr BP. The new results help to understand the Holocene environmental history of the Southern Kurils as a part of the Kuril-Kamchatka and Aleutian Marginal Sea-Island Arc Systems in the North-Western Pacific region.
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    Stability of marine phytoplankton communities facing stress related to global change: Interactive effects of heat waves and turbidity (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, ELSEVIER SCIENCE BV, 497, pp. 219-229, ISSN: 0022-0981
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    Publication Date: 2017-11-21
    Description: According to climate models, coastal ecosystems will face an increased frequency of heat waves and increased turbidity due to terrestrial sediment run-off induced by increasing precipitation. Several studies have examined the effects of heat waves and turbidity separately, whereas this study analysed the individual effects of both stressors as well as their interaction, because stressors affect communities differently when acting in combination. Using a factorial experimental design, we simulated heat waves (22 °C and 26 °C compared to an 18 °C control) and turbidity (sediment addition). The response of the phytoplankton community was analysed for the aggregate parameters biovolume and diversity index (H′), as well as for community composition. Heat waves had a significant negative effect on biovolume, whereas turbidity tended to affect biovolume positively. Repeated measures ANOVA revealed significant interactions of heat waves and turbidity for H′ and community composition. Strong heat waves (26 °C) alleviated the otherwise positive effect of turbidity on H′, i.e. highest diversity remained in the turbid control. Diatoms gained dominance in the control and the 22 °C heat wave treatment with Cylindrotheca closterium being the successful competitor. At 26 °C this species was lost and small flagellates dominated the experimental communities. Future increases in heat wave intensity and frequency may thus induce major changes in phytoplankton community structure whereas algae might profit from increased turbidity as an additional source of nutrients.
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    Late Cretaceous onset of current controlled sedimentation in the African–Southern Ocean gateway (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 395, pp. 380-396, ISSN: 00253227
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    Publication Date: 2017-12-06
    Description: During the breakup of Gondwana the Mozambique Ridge, a Large Igneous Province emplaced between 140 and 125 Ma, was located in the evolving African–Southern Ocean gateway. Therefore, it represents an archive of the evolving exchange of water masses between the South Atlantic and Indian Ocean via the development of surface, intermediate, and bottom circulation. Two Cretaceous seismic units (S1 and S2a) were deposited on top of magmatic basement separated by a hiatus. Unit S1 mostly shows seismic reflections parallel to the top of the basement and no indications of current activity. The occurrence of several sediment drifts within seismic unit S2a indicates the onset of current controlled sedimentation. Based on our observations we propose deposition under partly euxinic conditions in the area of the Mozambique Ridge until ~ 100 Ma. The onset of a strong shallow circulation affecting deposition at the Mozambique Ridge is inferred by the Late Cretaceous ~ 25 Myr hiatus reported by drilling results and documented in the seismic records, whereas black shales deposited in the nearby deep Transkei Basin indicate a restricted deep circulation at least until ~ 85–80 Ma. We propose that the observed hiatus might be a consequence of a late Early Cretaceous uplift of the Mozambique Ridge and the progressive opening of the Agulhas Passage allowing inflow of surface (Upper Pacific Water, Upper North Atlantic Water) and intermediate water (Intermediate Southern Ocean Water) into the study area. The intense circulation that caused the hiatus seems to have weakened in Campanian times, which is documented by the occurrence of sediment drifts in seismic unit S2a. We suggest that the onset of current controlled sedimentation was caused by palaeogeographic modifications in the Atlantic Ocean along with relocation of circulation pathways. Our results illustrate the crucial role of the African–Southern Ocean gateway in the commencing water mass exchange between the Atlantic and Indian Ocean and highlight the complex interactions that eventually lead to the initiation of a proto–Antarctic Circumpolar Current in Turonian times.
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    Hotspot tracks in the South Atlantic located above bands of fast flowing asthenosphere driven by waning pulsations from the African LLSVP (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Gondwana Research, ELSEVIER SCIENCE BV, 53, pp. 197-208, ISSN: 1342-937X
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    Publication Date: 2017-12-11
    Description: The location and crustal structure of hotspot tracks in the South Atlantic reflectwhere melts related to sluggishly flowing plume material can reach the plate surface. This raises the paradox of how long-lived, age progressive hotspot tracks can arise in the absence of closely spaced, narrow mantle plumes. Here we show that young hotspot trails in the southern South Atlantic are located above bands of seismically slowmaterial in the asthenosphere, which we interpret as channels of fast-flowing asthenosphere fed by a large scale plume upwelling from the African LLSVP. A broad region of seismically slow asthenosphere in the vicinity of Paraná continental flood basalts may be indicative of a long-lived, large scale plume under the South American plate. We propose that hotspot tracks developed above fast flow channels in the asthenosphere that evolved between these largescale plumes as they migrated apart with the African and South American plates, respectively. A progression fromcontinental flood basalts to broad aseismic ridges (e.g.,Walvis Ridge-Rio Grande Rise), to lowvolume intraplate hotspot tracks (e.g., Tristan-Gough; Discovery; Shona and Bouvet) reflects the interplay between tectonic setting and asthenosphere flow channels driven by waning pulsations from these diverging LLSVP plumes. We link the splitting of the Walvis Ridge into isotopically distinct, age-progressive intraplate sub-tracks about 72 Ma to the first sampling of material rising from the African LLSVP plume, perhaps as weak shallow longlived plumes. Faster flowing asthenosphere enables melts related to LLSVP plumes to reach the plate surface via spreading and tectonic boundaries, and as low-volume intraplate hotspot (sub)tracks. The concept that asthenosphere flowchannels and hotspot tracks evolve together between pulsating deep-seated plumes under Africa and South America suggests that LLSVPs might be a significant force in driving continental rifting and (absolute) plate motion.
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    Bedrock morphology reveals drainage network in northeast Baffin Bay (2018)
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    In:  EPIC3Geomorphology, ELSEVIER SCIENCE BV, 303, pp. 133-145, ISSN: 0169-555X
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    Publication Date: 2017-12-10
    Description: A subglacial drainage network underneath the paleo-ice sheet off West Greenland is revealed by a new compilation of high-resolution bathymetry data from Melville Bay, northeast Baffin Bay. This drainage network is an indicator for ice streaming and subglacial meltwater flow toward the outer shelf. Repeated ice sheet advances and retreats across the crystalline basement together with subglacial meltwater drainage had their impact in eroding overdeepened troughs along ice stream pathways. These overdeepenings indicate the location of a former ice sheet margin. The troughs inherit characteristics of glacial and subglacial meltwater erosion. Most of the troughs follow tectonic weakness zones such as faults and fractures in the crystalline bedrock. Many of these tectonic features correspond with the orientations of major fault axes in the Baffin Bay region. The troughs extend from the present (sub) glacial fjord systems at the Greenland coast and parallel modern outlet-glacier pathways. The fast flowing paleo-ice streams were likely accelerated from the meltwater flow as indicated by glacial landforms within and along the troughs. The ice streams flowed along narrow tributary troughs and merged to form large paleo-ice streams bedded in the major cross-shelf troughs of Melville Bay. Apart from the troughs, a rough seabed topography characterises the bedrock, and we see a sharp geomorphic transition where ice flowed onto sedimentary rock and deposits.
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    Bioturbation rates in the deep Fram Strait: Results from long-term in situ experiments at the arctic LTER Observatory HAUSGARTEN (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, ELSEVIER SCIENCE BV, 511, pp. 1-9, ISSN: 0022-0981
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    Publication Date: 2018-11-10
    Description: Benthic fauna constantly modifies their physical, chemical and biological environment. The permanent biological reworking of surface sediments mediates biogeochemical processes at the seafloor and is, therefore, of global importance. There are numerous studies measuring the rate and extent of bioturbation worldwide, however, information on mixing rates in the deep ocean and especially in the Polar Regions are extremely scarce; to our knowledge there is, by now, only a single study providing bioturbation rates from the deep Arctic Ocean. The present study presents mixing rates and mixed layer depths for the deep seafloor at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean. Two stations at similar water depths (2400 m and 2500 m water depth, respectively) but approx. 55 km apart from each other were chosen to carry out long-term (2 and 4 years, respectively) in situ bioturbation experiments using luminophores as a tracer. Biodiffusion-like mixing rates Db at the experimental sites were rather similar (0.26 cm2 a-1 at HG-IV; 0.28 cm2 a-1 at S3); slightly (non-significantly) higher Db values at the southern HAUSGARTEN site S3 could be explained by more favorable environmental conditions and related differences in the faunal composition. Indications for a non-local transport of sediment particles from the surface to deeper parts of the sediment, resulting in higher values for the Non-Local Index (NLI), could only be found for the central HAUSGARTEN site HG-IV. Elevated densities of burrowing megafauna at HG-IV, compared to S3, might be responsible for the subsurface maxima in luminophore distribution and comparably higher NLI values at the central HAUSGARTEN site (5.37 at HG-IV; 3.26 at S3). Mixed layer depths L at the two sites were almost identical; considerable mixing of surface sediments occurred down to max. 6-7 cm sediment depth.
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    Cross-disciplinarity in the advance of Antarctic ecosystem research (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, 37, pp. 1-17, ISSN: 1874-7787
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    Publication Date: 2018-03-06
    Repository Name: EPIC Alfred Wegener Institut
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    Ocean and climate response to North Atlantic seaway changes at the onset of long-term Eocene cooling (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Earth and Planetary Science Letters, ELSEVIER SCIENCE BV, 498, pp. 185-195, ISSN: 0012-821X
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    Publication Date: 2018-07-16
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    Phosphorus dynamics around the sulphate-methane transition in continental margin sedimnts: Authigenic apatite and Fe(II) phosphates (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 404, pp. 84-96, ISSN: 0025-3227
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    Publication Date: 2018-08-08
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  • 88
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    Morphometry of the diatom Fragilariopsis kerguelensis from Southern Ocean sediment: High-throughput measurements show second morphotype occurring during glacials (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Micropaleontology, ELSEVIER SCIENCE BV, 143, pp. 70-79, ISSN: 0377-8398
    Details
    Publication Date: 2018-09-09
    Description: Fragilariopsis kerguelensis is one of the most abundant diatoms in the sediments of the Southern Ocean. Its morphometric features have been proposed as proxies, based on links with, for example, iron availability, sea surface temperature and glacial/interglacial conditions. We investigated morphometric changes in F. kerguelensis valves in a well-studied sediment core record, focusing on transition periods between glacials and interglacials. By applying a high-throughput diatom imaging and morphometry workflow, we found two clearly distinct morphotypes which were differentiated by their rectangularity. One of them occurred preferentially in glacial samples, whilst the other persisted throughout. This indicates that their relative abundances depend on environmental conditions and thereby points to the possibility that paleo-proxies based on F. kerguelensis valve morphometric features might in the future benefit from differentiating these two morphotypes. As an initial exploration of this idea, we show that the abundance ratio of both morphotypes correlates well with paleo-temperatures which had been reconstructed using independent data from the same core. Distinguishing between the two morphotypes only became possible by image analysis for precisely measuring diatom valve outlines and area, highlighting the potential of such methods for diatom analyses.
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  • 89
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    Modeling of intra-annual abundance distributions: Constancy and variation in the phenology of marine phytoplankton species over five decades at Helgoland Roads (North Sea) (2019)
    ELSEVIER SCIENCE BV
    In:  EPIC3Ecological Modelling, ELSEVIER SCIENCE BV, 404C, pp. 46-60, ISSN: 0304-3800
    Details
    Publication Date: 2020-05-15
    Description: Annually recurring environmental processes such as the cycle of temperature and light drive the phenology of marine plankton populations. Improved knowledge about the homogeneity and amplitude of the phenological response of phytoplankton to climate change is essential for an assessment of ecological consequences on the marine ecosystem. We analyzed phenological variability of 21 phytoplankton species monitored work-daily at Helgoland Roads from 1962-2015. We used a function of “Weibull”-type to estimate phenological dates of species-specific abundance peaks. The combination of derived dates and peak abundances formed the basis for the analyses of long-term changes in phenological time slots and associated environmental conditions. Species-specific preferences in combination with seasonally varying environmental trends resulted in a complex pattern of phenological long-term response. Phenological trends showed both constant occurrence and shifts to an earlier or later occurrence. Co-occurring phytoplankton species were shown to exhibit different phenological trends even within identical time slots. Differences in species-specific trends in timing also reflected the seasonally varying shifts in water temperature ranges due to warming. In spring and summer, the main patterns of common variability in timing were associated with different abiotic and biotic drivers. The majority of species showed more narrow time slots related to the occurrence of higher peaks. Considering the variation of species occurrence in their “typical” time window provided insight in terms of assigning the effect of environmental drivers on inter-annual phenological variation. Phytoplankton species with similar long-term trends in timing (days) showed different trends in biomass, i.e. the phenological changes resulted from different ecological responses to environmental change. The local character of environmental trends at Helgoland underpins the limits for comparison of findings between different measuring sites or wider areas, such as the North Sea. The study emphasizes the benefit and necessity of a highly resolved phytoplankton record for a true understanding of long-term ecological changes in a highly dynamic marine environment such as the North Sea.
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  • 90
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    Shell disease in Crangon crangon (Linnaeus, 1758): The interaction of temperature and stress response (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Experimental Marine Biology and Ecology, ELSEVIER SCIENCE BV, 500, pp. 105-111
    Details
    Publication Date: 2018-02-14
    Description: The prevalence of black spot shell disease is increasing among marine crustaceans worldwide. Rising seawater temperatures – often stressful for ectothermic species – are assumed to enhance the occurrence of shell disease. In the North Sea 〉 50% of local populations of the brown shrimp (Crangon crangon) are affected by the disease. While fisheries are suffering because diseased crustaceans are barely merchantable, the impact of shell disease on life history traits of crustaceans is little understood. To determine the role of temperature on the development of black spots and its implications for survival and physiology in the brown shrimp, a prolonged (3 months) thermal stress experiment was performed. We measured the increment of shell disease and the effect of molting in shrimps kept at control (15 °C = equivalent to the seafloor temperature in the North Sea during sampling) and increased temperature (20 °C = according to predictions for the end of the century). The resting metabolic rate was analyzed to determine the physiological state of diseased compared to non-diseased animals. In the present study, the warmer temperature in the range of 20 °C did not increase the spot size of shell disease and no differences were observed between the two temperatures. The process of molting thereby seemed to diminish and in most of the cases even completely remove the signs of shell disease. At 15 °C but not at 20 °C, metabolic rate was reduced in diseased in contrast to healthy individuals. This study showed that shell disease might lead to a higher mortality rate and an impairment of the physiological state in C. crangon.
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  • 91
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    Modeling plankton interactions in the meta-omics era. Are we ready? (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, 32, pp. 1-17, ISSN: 1874-7787
    Details
    Publication Date: 2018-02-27
    Description: Recent progress in applying meta-omics approaches to the study of marine ecosystems potentially allows scientists to study the genetic and functional diversity of plankton at an unprecedented depth and with enhanced precision. However, while a range of persistent technical issues still need to be resolved, a much greater obstacle currently preventing a complete and integrated view of the marine ecosystem is the absence of a clear conceptual framework. Herein, we discuss the knowledge that has thus far been derived from conceptual and statistical modelling of marine plankton ecosystems, and illustrate the potential power of integrated meta-omics approaches in the field. We then propose the use of a semantic framework is necessary to support integrative ecological modelling in the meta-omics era, particularly when having to face the increased interdisciplinarity needed to address global issues related to climate change.
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  • 92
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    The North Sea goes viral: Occurrence and distribution of North Sea bacteriophages (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, ISSN: 1874-7787
    Details
    Publication Date: 2019-03-08
    Description: Marine viruses are dominated by phages and have an enormous influence on microbial population dynamics, due to lysis and horizontal gene transfer. The aim of this study is to analyze the occurrence and diversity of phages in the North Sea, considering the virus-host interactions and biogeographic factors. The virus community of four sampling stations were described using virus metagenomics (viromes). The results show that the virus community was not evenly distributed throughout the North Sea. The dominant phage members were identified as unclassified phage group, followed by Caudovirales order. Myoviridae was the dominant phage family in the North Sea, which occurrence decreased from the coast to the open sea. In contrast, the occurrence of Podoviridae increased and the occurrence of Siphoviridae was low throughout the North Sea. The occurrence of other groups such as Phycodnaviridae decreased from the coast to the open sea. The coastal virus community was genetically more diverse than the open sea community. The influence of riverine inflow and currents, for instance the English Channel flow affects the genetic virus diversity with the community carrying genes from a variety of metabolic pathways and other functions. The present study offers the first insights in the virus community in the North Sea using viromes and shows the variation in virus diversity and the genetic information moved from coastal to open sea areas.
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  • 93
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    Carbon diagenesis in different sedimentary environments of the subtropical Beibu Gulf, South China Sea (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Journal of Marine Systems, ELSEVIER SCIENCE BV, 186, pp. 68-84, ISSN: 0924-7963
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    Publication Date: 2018-06-27
    Repository Name: EPIC Alfred Wegener Institut
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  • 94
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    Submarine geomorphology of northeast Baffin Bay and its implications for local paleo-ice sheet dynamics (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Geomorphology, ELSEVIER SCIENCE BV, 318, pp. 88-100, ISSN: 0169-555X
    Details
    Publication Date: 2018-07-15
    Description: High-resolution bathymetric data from close to the northwest Greenland coast in northern Melville Bay, northeast Baffin Bay, reveal a range of glacial and nonglacial landforms. The glacial landforms include crag-and-tails, mega-scale glacial lineations (MSGL), rock drumlins, and roche moutonnées that indicate paleo-ice sheet dynamics. The nonglacial landforms include steep ridges that are interpreted as volcanic dykes (Neoproterozoic Thule dyke swarms and Paleoproterozoic Melville Bugt dyke swarms). These dykes are glacially overprinted and may have channeled ice and subglacial meltwater flow through narrow subglacial cavities. Some of the glacial landforms eroded into bedrock indicate a southward paleo-ice stream orientation; while other glacial landforms, including the sedimentary depositional landforms, indicate a westward paleo-ice stream orientation. The glacial landforms were likely produced during at least two epochs and under changing thickness of the ice streams. The glacial landforms eroded into the bedrock are likely older than the sedimentary glacial landforms and were likely produced by a thin south/southeastward ice stream that allowed cavity formation. The westward-oriented glacial landforms were likely produced by a thick ice stream that was probably active during the Last Glacial Maximum (LGM). The different orientations of the glacial landforms indicate a reorganization of the ice streams that may have occurred during retreat and subsequent readvance. This reorganization likely coincided with a migration of the ice divide from south to north.
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  • 95
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    Chronology of Greenland Scotland Ridge overflow: What do we really know? (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Geology, ELSEVIER SCIENCE BV, 406, pp. 109-118, ISSN: 0025-3227
    Details
    Publication Date: 2018-09-28
    Description: As a sill constricting the exchange of deep water masses between the Nordic Seas and the North Atlantic, which forms an essential part of the Atlantic Meridional Overturning Circulation, the dynamic height of the Greenland Scotland Ridge and thus its overflow have an important influence on global climate. Several DSDP, ODP, and IODP sites have been drilled in the North Atlantic to shed light on the overflow and climate development. Reconstructions of bathymetry and sediment thickness have been put forward as well as calculations of the potential temperature of the conduit feeding the Iceland plume. The available studies have been screened to construct a conceptual model for the evolution of the palaeo-circulation in the North Atlantic and identify possible weaknesses in our knowledge. Details, e.g., timing and location, about the onset of the overflow are unknown, and especially the Paleogene development remains enigmatic. The database for this period is inadequate, and covers only small areas. The discussion centres on the earliest traces of the overflow leading to formation of sediment drifts in the eastern North Atlantic. More data provide a better base to reconstruct variations for the Neogene overflow, but also appears insufficient for in-depth analyses in time and space. Sediment drifts in the Iceland Basin indicate a first Iceland Faroe Ridge overflow for the early Miocene. Denmark Strait overflow appears to have started in mid-Miocene times, but evidence for this still is sparse. Grids of high-resolution seismic reflection data across all sediment drifts and all limbs of the Greenland Scotland Ridge combined with deeper drill sites targeting the complete sedimentary column down to basement are needed to fully understand the chronology of the Greenland Scotland Ridge overflow and its detailed impact on climate.
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  • 96
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    Transcriptome analysis of the midgut gland of the brown shrimp Crangon crangon indicates high polymorphism in digestive enzymes (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Marine Genomics, ELSEVIER SCIENCE BV, ISSN: 1874-7787
    Details
    Publication Date: 2018-10-17
    Description: Tolerance of organisms towards heterogeneous and variable environments is highly related to physiological flexibility. An effective strategy to enhance physiological flexibility is the expression of polymorphic enzymes. This seems to be the case in the brown shrimp Crangon crangon. It shows high reproduction rates, feeds opportunistically on endo- and epibenthic organisms, and is apparently well adapted to variable environmental conditions. Previous electrophoretic studies revealed a high level of polymorphism and no consistent phenotype of digestive enzymes between individuals. In order to understand the underlying biochemical processes, we carried out a transcriptome-based study of digestive enzymes of C. crangon. Detailed sequence analyses of triacylglycerol lipase, phospholipase A2, alpha amylase, chitinase, trypsin and cathepsin L were performed to identify putative isoforms. The number of isoforms, and thus the degree of polymorphism varied among enzymes: lipases and carbohydrases showed higher numbers of isoforms in enzymes that besides their extracellular function also have diverse intracellular functions. Furthermore, cysteine proteinases showed a lower polymorphism than serine proteinases. We suggest that the expression of enzyme isoforms improves the efficiency of C. crangon in gaining energy from different food sources.
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  • 97
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    Diversity, distribution, and azaspiracids of Amphidomataceae (Dinophyceae) along the Norwegian coast (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 80, pp. 15-34, ISSN: 1568-9883
    Details
    Publication Date: 2019-10-11
    Description: Azaspiracids (AZA) are a group of lipophilic polyether compounds which have been implicated in shellfish poisoning incidents around Europe. They are produced by a few species of the dinophycean genera Azadinium and Amphidoma (Amphidomataceae). The presence of AZA toxins in Norway is well documented, but knowledge of the distribution and diversity of Azadinium and other Amphidomataceae along the Norwegian coast is rather limited and poorly documented. On a research survey along the Norwegian coast in 2015 from the Skagerrak in the South to Trondheimsfjorden in the North, plankton samples from 67 stations were analysed for the presence of Azadinium and Amphidoma and their respective AZA by on-board live microscopy, real-time PCR assays specific for Amphidomataceae, and liquid chromatography-tandem mass spectrometry (LC–MS/MS). Microscopy using live samples and positive real-time PCR assays using a general family probe and two species specific probes revealed the presence of Amphidomataceae distributed throughout the sampling area. Overall abundance was low, however, and was in agreement with a lack of detectable AZA in plankton samples. Single cell isolation and morphological and molecular characterisation of established strains revealed the presence of 7 amphidomatacean species (Azadiniun spinosum, Az. poporum, Az. obesum, Az. dalianense, Az. trinitatum, Az. polongum, Amphidoma languida) in the area. Azaspiracids were produced by the known AZA producing species Az. spinosum, Az. poporum and Am. languida only. LC–MS/MS analysis further revealed that Norwegian strains produce previously unreported AZA for Norway (AZA-11 by Az. spinosum, AZA-37 by Az. poporum, AZA-38 and AZA-39 by Am. languida), and also four novel compounds (AZA-50, -51 by Az. spinosum, AZA-52, -53 by Am. languida), whose structural properties are described and which now can be included in existing analytical protocols. A maximum likelihood analysis of concatenated rDNA regions (SSU, ITS1-ITS2, partial LSU) showed that the strains of Az. spinosum fell in two well supported clades, where most but not all new Norwegian strains formed the new Ribotype B. Ribotype differentiation was supported by a minor morphological difference with respect to the presence/absence of a rim around the pore plate, and was consistently reflected by different AZA profiles. Strains of Az. spinosum from ribotype A produce AZA-1, -2 and -33, whereas the new strains of ribotype B produce mainly AZA-11 and AZA-51. Significant sequence differences between both Az. spinosum ribotypes underline the need to redesign the currently used qPCR probes in order to detect all AZA producing Az. spinosum. The results generally underline the conclusion that for the Norwegian coast area it is important that amphidomatacean species are taken into account in future studies and monitoring programs.
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  • 98
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    Domoic acid in a marine pelagic food web: Exposure of southern right whales Eubalaena australis to domoic acid on the Península Valdés calving ground, Argentina (2017)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 68, pp. 248-257, ISSN: 1568-9883
    Details
    Publication Date: 2019-07-17
    Description: The gulfs that surround Península Valdés (PV), Golfo Nuevo and Golfo San José in Argentina, are important calving grounds for the southern right whale Eubalaena australis. However, high calf mortality events in recent years could be associated with phycotoxin exposure. The present study evaluated the transfer of domoic acid (DA) from Pseudo-nitzschia spp., potential producers of DA, to living and dead right whales via zooplanktonic vectors, while the whales are on their calving ground at PV. Phytoplankton and mesozooplankton (primary prey of the right whales at PV and potential grazers of Pseudo-nitzschia cells) were collected during the 2015 whale season and analyzed for species composition and abundance. DA was measured in plankton and fecal whale samples (collected during whale seasons 2013, 2014 and 2015) using liquid chromatography coupled to tandem mass spectrometry (LC–MS/MS). The genus Pseudo-nitzschia was present in both gulfs with abundances ranging from 4.4 x 102 and 4.56 x 105 cell l -1. Pseudo-nitzschia australis had the highest abundance with up to 4.56 x 105 cell l-1. DA in phytoplankton was generally low, with the exception of samples collected during a P. australis bloom. No clear correlation was found between DA in phytoplankton and mesozooplankton samples. The predominance of copepods in mesozooplankton samples indicates that they were the primary vector for the transfer of DA from Pseudo-nitzschia spp. to higher trophic levels. High levels of DA were detected in four whale fecal samples (ranging from 0.30 to 710 mg g-1 dry weight of fecal sample or from 0.05 and 113.6 mg g-1 wet weight assuming a mean water content of 84%). The maximum level of DA detected in fecal samples (710 mg DA g-1 dry weight of fecal sample) is the highest reported in southern right whales to date. The current findings demonstrate for the first time that southern right whales, E. australis, are exposed to DA via copepods as vectors during their calving season in the gulfs of PV.
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  • 99
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    New geophysical data from a key region in East Antarctica: Estimates for the spatial extent of the Tonian Oceanic Arc Super Terrane (TOAST) (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Gondwana Research, ELSEVIER SCIENCE BV, 59, pp. 97-107, ISSN: 1342-937X
    Details
    Publication Date: 2019-04-23
    Description: Within Antarctica, eastern Dronning Maud Land (DML) represents a key region for improving our understanding of crustal fragments that were involved in the amalgamation and breakup histories of Rodinia and Gondwana. An aerogeophysical survey was flown during the austral summers 2013/14 and 2014/15 to explore the largely ice- covered region south and east of Sør Rondane. Here, we present 40,000 new line kilometer of aeromagnetic data gathered across an area of ca. 295,000 km2 with a 10 km line spacing. Magnetic domains, major lineaments, lo- cations, and depths of magnetic source bodies are detected from total field data, their tilt derivative, pseudo- gravity, and analytical signal transformations, and from Euler Deconvolution maps. These data are integrated with exposure information from the Sør Rondane, Belgica and the Yamato mountains in order to identify the eastern spatial extent of a major juvenile Early Neoproterozoic crustal province, the Tonian Oceanic Arc Super Terrane (TOAST). Magnetic data reveal a characteristic pattern with NW-SE trending elongated magnetic anom- alies to the south of Sør Rondane. This area is interpreted as the eastward continuation of the distinct SE DML Province and therefore of the TOAST. Major curvilinear magnetic anomalies of several hundreds of kilometers length dissect the region south and southwest of Sør Rondane. These may represent boundaries of individual oce- anic arc terrane or alternatively major Pan-African shear zones. A significant change of the magnetic anomaly pat- tern ca. 800 km inland of Sør Rondane may indicate the southern minimum extent of the TOAST. Magnetic anomalies of varying size, amplitude, and orientation suggest a complex transitional area between the Belgica and Yamato Mts., which appears to separate the TOAST from an Indo-Antarctic craton to the east. The new data suggest that the TOAST is comparable in size with the Antarctic Peninsula and therefore represents a signif- icant piece of Neoproterozoic crustal addition. It originated at the periphery or outboard of Rodinia and is a rem- nant of the Mozambique Ocean.
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  • 100
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    Morphological, molecular and toxigenic characteristics of Namibian Pseudo-nitzschia species – including Pseudo-nitzschia bucculenta sp. nov (2018)
    ELSEVIER SCIENCE BV
    In:  EPIC3Harmful Algae, ELSEVIER SCIENCE BV, 76, pp. 80-95, ISSN: 1568-9883
    Details
    Publication Date: 2019-07-17
    Description: A field study was undertaken to investigate the occurrence and toxin production of species in the diatom genus Pseudo-nitzschia in Namibian waters, in the extremely productive Benguela upwelling system. From surveys conducted on the R/V Mirabilis and the R/V !Anichab, 52 strains were morphologically determined to species level, supported by nuclear ITS rDNA data. Seven species were identified; P. australis, P. decipiens, P. dolorosa, P. fraudulenta, P. plurisecta, P. pungens var. cingulata, and the new species P. bucculenta F. Gai, C. K. Hedemand, N. Lundholm & Ø. Moestrup sp. nov. Molecular and morphological diversity of the Namibian Pseudo-nitzschia species is discussed. Most importantly, P. bucculenta is both morphologically and phylogenetically most similar to P. dolorosa differing mainly in valve width and densities of striae, poroids and band striae as well as by four hemi-compensatory base changes in the ITS2. Morphological and molecular differences among the strains of P. decipiens suggest a temperate and a warm water subdivision. The geographical and toxigenic characteristics of the identified Pseudo-nitzschia species are described and compared to previous studies. Initial tests of toxin production in all seven species revealed production of domoic acid (DA) in two species: one strain of P. australis (0.074 pg DA cell−1) and two strains of P. plurisecta (0.338 pg DA cell−1 and 0.385 pg DA cell−1).
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