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  • Copernicus  (49,228)
  • National Academy of Sciences  (47,314)
  • 2010-2014  (87,825)
  • 1980-1984  (8,717)
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  • 1
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    River flooding as a driver of polygon dynamics: modern vegetation data and a millennial peat record from the Anabar River lowlands (Arctic Siberia) (2013)
    Copernicus
    In:  EPIC3Biogeosciences, Copernicus, 10(3), pp. 5703-5728, ISSN: 1726-4189
    Details
    Publication Date: 2024-04-23
    Description: 〈jats:p〉Abstract. The spatial and temporal variability of a low-centred polygon on the eastern floodplain area of the lower Anabar River (72.070° N, 113.921° E, northern Yakutia, Siberia) has been investigated using a multi-method approach. The present-day vegetation in each square metre was analysed revealing a community of Larix shrubby Betula and Salix on the polygon rim, a dominance of Carex and Andromeda polifolia in the rim-to-pond transition zone, and a predominantly monospecific Scorpidium scorpioides coverage within the pond. The TOC content, TOC/TN ratio, grain-size, vascular plant macrofossils, moss remains, diatoms, and pollen were analysed for two vertical sections and a sediment core from a transect across the polygon. Radiocarbon dating indicates that the formation of the polygon started at least 1500 yr ago; the general positions of the pond and rim have not changed since that time. Two types of pond vegetation were identified, indicating two contrasting development stages of the polygon. The first was a well-established moss association dominated by submerged or floating Scorpidium scorpioides and/or Drepanocladus spp. and overgrown by epiphytic diatoms such as Tabellaria flocculosa and Eunotia taxa. This stage coincides temporally with a period in which the polygon was only drained by lateral subsurface water flow, as indicated by mixed grain sizes. A different moss association occurred during times of repeated river flooding (indicated by homogeneous medium-grained sand that probably accumulated during the annual spring snow melt), characterized by an abundance of Meesia triquetra and a dominance of benthic diatoms (e.g. Navicula vulpina), indicative of a relatively high pH and a high tolerance of disturbance. A comparison of the local polygon vegetation (inferred from moss and macrofossil spectra) with the regional vegetation (inferred from pollen spectra) indicated that the moss association with Scorpidium scorpioides became established during relatively favourable climatic conditions while the association dominated by Meesia triquetra occurred during periods of harsh climatic conditions. Our study revealed a strong riverine influence (in addition to climatic influences) on polygon development and the type of peat accumulated. 〈/jats:p〉
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , isiRev
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  • 2
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    Fertilization success of an arctic sea urchin species, Strongylocentrotus droebachiensis (O. F. Mueller, 1776) under CO2-induced ocean acidification (2013)
    Copernicus
    In:  EPIC3Biogeosciences Discuss, Copernicus, 10, pp. 8027-8064
    Details
    Publication Date: 2024-04-11
    Description: Sea urchins as broadcasting spawners, release their gametes into open water for fertilization, thus being particularly vulnerable to ocean acidification. In this study, we assessed the effects of different pH scenarios on fertilization success of Strongylocen- 5 trotus droebachiensis, collected at Spitsbergen, Arctic. We achieved acidification by bubbling CO2 into filtered seawater using partial pressures (pCO2) of 180, 380, 980, 1400 and 3000 μatm. Untreated filtered seawater was used as control. We recorded fertilization rates and diagnosed morphological aberrations after post-fertilization periods of 1 h and 3 h under different exposure conditions in experiments with and without 10 pre-incubation of the eggs prior to fertilization. In parallel, we conducted measurements of intracellular pH changes using BCECF/AM in unfertilized eggs exposed to a range of acidified seawater. We observed increasing rates of polyspermy in relation to higher seawater pCO2, which might be due to failures in the formation of the fertilization envelope. In addition, our experiments showed anomalies in fertilized eggs: incomplete 15 lifting-off of the fertilization envelope and blebs of the hyaline layer. Other drastic malformations consisted of constriction, extrusion, vacuolization or degeneration (observed as a gradient from the cortex to the central region of the cell) of the egg cytoplasm, and irregular cell divisions until 2- to 4-cell stages. The intracellular pH (pHi) decreased significantly from 1400 μatm on. All results indicate a decreasing fertilization success 20 at CO2 concentrations from 1400 μatm upwards. Exposure time to low pH might be a threatening factor for the cellular buffer capacity, viability, and development after fertilization.
    Repository Name: EPIC Alfred Wegener Institut
    Type: Article , peerRev
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  • 3
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    Geochemistry of volcanic rocks from the Woodlark Basin (2011)
    Copernicus
    Details
    Publication Date: 2023-11-08
    Description: EGU2011-12864 The Woodlark Basin east of Papua New Guinea represents one of the few places on Earth where a spreading axis propagates into continental crust. This special tectonic setting allows insights into the evolution of magma composition as continental extension and break-up changes to the formation of ocean crust. We report here geochemical results on samples collected in 2009 from the four segments closest to the continental breakup, from segment 1 which abuts the detachment fault responsible for continental extension on Moresby Seamount in the West, to segment 4, representing mature oceanic crust in the East. A total of 208 glass samples have been analyzed for their major (EMPA) and trace element (LA-ICPMS) compositions. The data show strong E-W variations. Samples ranging from tholeiitic basalt and basaltic andesite to andesite and rhyolite are found on Segment 1. They have generally high alkali values and a wide range of trace element contents and ratios. Segments 2 to 4 magmas in contrast only comprise tholeiitic basalt with lower alkali contents and a more restricted range of trace element chemistry. The geochemical differences between the segments cannot be attributed to differentiation processes alone, and different sources are required. High Ba/La, (La/Sm)N, Rb/Sr, and Th/La on Segment 1 suggest a derivation from an enriched mantle source, while low Nd/Pb and Nb/U suggest that some of the enrichment may also reflect the influence of continental crust during magma genesis. Whether this continental signature is present in the form of recycled material in the mantle or as rafted continental blocks in the axial region is at present unclear. In contrast to rocks from segment 1, trace element compositions of volcanic glasses from segments 2 to 4 show a stronger MORB signature, presumably reflecting more mature spreading in this part of the basin. The influence of continental material appears to be minimal, suggesting that uncontaminated asthenosphere quickly flows into the rift and/or that continental blocks are not retained in the axial region for long time periods following the rifting-spreading transition.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 4
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    Volcanic ash layers illuminate the resilience of Neanderthals and early modern humans to natural hazards (2012)
    National Academy of Sciences
    Details
    Publication Date: 2021-12-06
    Description: Marked changes in human dispersal and development during the Middle to Upper Paleolithic transition have been attributed to massive volcanic eruption and/or severe climatic deterioration. We test this concept using records of volcanic ash layers of the Campanian Ignimbrite eruption dated to ca. 40,000 y ago (40 ka B.P.). The distribution of the Campanian Ignimbrite has been enhanced by the discovery of cryptotephra deposits (volcanic ash layers that are not visible to the naked eye) in archaeological cave sequences. They enable us to synchronize archaeological and paleoclimatic records through the period of transition from Neanderthal to the earliest anatomically modern human populations in Europe. Our results con!rm that the combined effects of a major volcanic eruption and severe climatic cooling failed to have lasting impacts on Neanderthals or early modern humans in Europe. We infer that modern humans proved a greater competitive threat to indigenous populations than natural disasters.
    Description: funded by the United Kingdom Natural Environment Research Council through a Response of Humans to Abrupt Environmental Transitions (RESET) Consortium Grant
    Description: Published
    Description: 13532–13537
    Description: 3.5. Geologia e storia dei vulcani ed evoluzione dei magmi
    Description: JCR Journal
    Description: restricted
    Keywords: Neanderthals ; modern humans ; cryptotephra deposits ; 01. Atmosphere::01.01. Atmosphere::01.01.07. Volcanic effects
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    Seasonal ITCZ migration dynamically controls the location of the (sub)tropical Atlantic biogeochemical divide (2014)
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 111 (4). pp. 1438-1442.
    Details
    Publication Date: 2021-04-23
    Description: Inorganic nitrogen depletion restricts productivity in much of the low-latitude oceans, generating a selective advantage for diazotrophic organisms capable of fixing atmospheric dinitrogen (N2). However, the abundance and activity of diazotrophs can in turn be controlled by the availability of other potentially limiting nutrients, including phosphorus (P) and iron (Fe). Here we present high-resolution data (∼0.3°) for dissolved iron, aluminum, and inorganic phosphorus that confirm the existence of a sharp north–south biogeochemical boundary in the surface nutrient concentrations of the (sub)tropical Atlantic Ocean. Combining satellite-based precipitation data with results from a previous study, we here demonstrate that wet deposition in the region of the intertropical convergence zone acts as the major dissolved iron source to surface waters. Moreover, corresponding observations of N2 fixation and the distribution of diazotrophic Trichodesmium spp. indicate that movement in the region of elevated dissolved iron as a result of the seasonal migration of the intertropical convergence zone drives a shift in the latitudinal distribution of diazotrophy and corresponding dissolved inorganic phosphorus depletion. These conclusions are consistent with the results of an idealized numerical model of the system. The boundary between the distinct biogeochemical systems of the (sub)tropical Atlantic thus appears to be defined by the diazotrophic response to spatial–temporal variability in external Fe inputs. Consequently, in addition to demonstrating a unique seasonal cycle forced by atmospheric nutrient inputs, we suggest that the underlying biogeochemical mechanisms would likely characterize the response of oligotrophic systems to altered environmental forcing over longer timescales.
    Type: Article , PeerReviewed
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  • 6
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    Cyclic volcanism at convergent margins: linked to aarth orbital parameters or climate changes? (2010)
    Copernicus
    In:  [Talk] In: EGU General Assembly 2010, 02.05.-07.05.2010, Vienna, Austria . Geophysical Research Abstracts .
    Details
    Publication Date: 2019-09-23
    Description: EGU2010-13373 The frequency of volcanic activity varies on a wide rangeof spatial and temporal scales, from 〈1 yr. periodicities in single volcanic systems to periodicities of 106 yrs. in global volcanism. The causes of these periodicities are poorly understood although the long-term global variations are likely linked to plate-tectonic processes. Here we present evidence for temporal changes in eruption frequencies at an intermediate time scale (104 yrs.) using the Pleistocene to recent records of widespread tephras of sub-Plinian to Plinian, and occasionally co-ignimbrite origin, along the Pacific Ring of Fire, which accounts for about half of the global length of 44,000 km of active subduction. Eruptions at arc volcanoes tend to be highly explosive and the well-preserved tephra records from the ocean floor can be assumed to be representative of how eruption frequencies varied with time. Volcanic activity along the Pacific Ring of Fire evolved through alternating phases of high and low frequency; although there is modulation by local and regional geologic conditions, these variations have a statistically significant periodicity of 43 ka that overlaps with the temporal variation in the obliquity of the Earth’s rotation axis, an orbital parameter that also exerts a strong control on global climate changes. This may suggest that the frequency of volcanic activity is controlled by effects of global climate changes. However, the strongest physical effects of climate change occur at 100 ka periods which are not seen in the volcanic record. We therefore propose that the frequency of volcanic activity is directly influenced by minute changes in the tidal forces induced by the varying obliquity resulting in long-period gravitational disturbances acting on the upper mantle.
    Type: Conference or Workshop Item , NonPeerReviewed
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  • 7
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    Oceanic heat advection to the Arctic in the last Millennium (2011)
    Copernicus
    In:  [Talk] In: EGU General Assembly 2011, 03.04.-08.04.2011, Vienna, Austria ; p. 8738 .
    Details
    Publication Date: 2019-09-23
    Description: EGU2011-8738 At present, the Arctic is responding faster to global warming than most other areas on earth, as indicated by rising air temperatures, melting glaciers and ice sheets and a decline of the sea ice cover. As part of the meridional overturning circulation which connects all ocean basins and influences global climate, northward flowing Atlantic Water is the major means of heat and salt advection towards the Arctic where it strongly affects the sea ice distribution. Records of its natural variability are critical for the understanding of feedback mechanisms and the future of the Arctic climate system, but continuous historical records reach back only ca. 150 years. To reconstruct the history of temperature variations in the Fram Strait Branch of the Atlantic Current we analyzed a marine sediment core from the western Svalbard margin. In multidecadal resolution the Atlantic Water temperature record derived from planktic foraminifer associations and Mg/Ca measurements shows variations corresponding to the well-known climatic periods of the last millennium (Medieval Climate Anomaly, Little Ice Age, Modern/Industrial Period). We find that prior to the beginning of atmospheric CO2 rise at ca. 1850 A.D. average summer temperatures in the uppermost Atlantic Water entering the Arctic Ocean were in the range of 3-4.5°C. Within the 20th century, however, temperatures rose by ca. 2°C and eventually reached the modern level of ca. 6°C. Such values are unprecedented in the 1000 years before and are presumably linked to the Arctic Amplification of global warming. Taking into account the ongoing rise of global temperatures, further warming of inflowing Atlantic Water is expected to have a profound influence on sea ice and air temperatures in the Arctic.
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  • 8
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    Acidified seawater impacts sea urchin larvae pH regulatory systems relevant for calcification (2012)
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 109 (44). pp. 18192-18197.
    Details
    Publication Date: 2019-09-23
    Description: Calcifying echinoid larvae respond to changes in seawater carbonate chemistry with reduced growth and developmental delay. To date, no information exists on how ocean acidification acts on pH homeostasis in echinoderm larvae. Understanding acid–base regulatory capacities is important because intracellular formation and maintenance of the calcium carbonate skeleton is dependent on pH homeostasis. Using H+-selective microelectrodes and the pH-sensitive fluorescent dye BCECF, we conducted in vivo measurements of extracellular and intracellular pH (pHe and pHi) in echinoderm larvae. We exposed pluteus larvae to a range of seawater CO2 conditions and demonstrated that the extracellular compartment surrounding the calcifying primary mesenchyme cells (PMCs) conforms to the surrounding seawater with respect to pH during exposure to elevated seawater pCO2. Using FITC dextran conjugates, we demonstrate that sea urchin larvae have a leaky integument. PMCs and spicules are therefore directly exposed to strong changes in pHe whenever seawater pH changes. However, measurements of pHi demonstrated that PMCs are able to fully compensate an induced intracellular acidosis. This was highly dependent on Na+ and HCO3−, suggesting a bicarbonate buffer mechanism involving secondary active Na+-dependent membrane transport proteins. We suggest that, under ocean acidification, maintained pHi enables calcification to proceed despite decreased pHe. However, this probably causes enhanced costs. Increased costs for calcification or cellular homeostasis can be one of the main factors leading to modifications in energy partitioning, which then impacts growth and, ultimately, results in increased mortality of echinoid larvae during the pelagic life stage.
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  • 9
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    Transcriptomic resilience to global warming in the seagrass Zostera marina, a marine foundation species (2011)
    National Academy of Sciences
    In:  PNAS Proceedings of the National Academy of Sciences of the United States of America, 108 (48). pp. 19276-19281.
    Details
    Publication Date: 2019-09-23
    Description: Large-scale transcription profiling via direct cDNA sequencing provides important insights as to how foundation species cope with increasing climatic extremes predicted under global warming. Species distributed along a thermal cline, such as the ecologically important seagrass Zostera marina, provide an opportunity to assess temperature effects on gene expression as a function of their long-term adaptation to heat stress. We exposed a southern and northern European population of Zostera marina from contrasting thermal environments to a realistic heat wave in a common-stress garden. In a fully crossed experiment, eight cDNA libraries, each comprising ∼125 000 reads, were obtained during and after a simulated heat wave, along with nonstressed control treatments. Although gene-expression patterns during stress were similar in both populations and were dominated by classical heat-shock proteins, transcription profiles diverged after the heat wave. Gene-expression patterns in southern genotypes returned to control values immediately, but genotypes from the northern site failed to recover and revealed the induction of genes involved in protein degradation, indicating failed metabolic compensation to high sea-surface temperature. We conclude that the return of gene-expression patterns during recovery provides critical information on thermal adaptation in aquatic habitats under climatic stress. As a unifying concept for ecological genomics, we propose transcriptomic resilience, analogous to ecological resilience, as an important measure to predict the tolerance of individuals and hence the fate of local populations in the face of global warming.
    Type: Article , PeerReviewed
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  • 10
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    Targeted metagenomics and ecology of globally important uncultured eukaryotic phytoplankton (2010)
    National Academy of Sciences
    In:  Proceedings of the National Academy of Sciences of the United States of America (PNAS), 107 (33). pp. 14679-14684.
    Details
    Publication Date: 2019-09-23
    Description: Among eukaryotes, four major phytoplankton lineages are responsible for marine photosynthesis; prymnesiophytes, alveolates, stramenopiles, and prasinophytes. Contributions by individual taxa, however, are not well known, and genomes have been analyzed fromonly the latter two lineages. Tiny "picoplanktonic" members of the prymnesiophyte lineage have long been inferred to be ecologically important but remain poorly characterized. Here, we examine pico-prymnesiophyte evolutionary history and ecology using cultivation-independent methods. 18S rRNA gene analysis showed picoprymnesiophytes belonged to broadly distributed uncultivated taxa. Therefore, we used targeted metagenomics to analyze uncultured pico-prymnesiophytes sorted by flow cytometry from subtropical North Atlantic waters. The data reveal a composite nuclear-encoded gene repertoire with strong green-lineage affiliations, which contrasts with the evolutionary history indicated by the plastid genome. Measured pico-prymnesiophyte growth rates were rapid in this region, resulting in primary production contributions similar to the cyanobacterium Prochlorococcus. On average, pico-prymnesiophytes formed 25 of global picophytoplankton biomass, with differing contributions in five biogeographical provinces spanning tropical to subpolar systems. Elements likely contributing to success include high gene density and genes potentially involved in defense and nutrient uptake. Our findings have implications reaching beyond pico-prymnesiophytes, to the prasinophytes and stramenopiles. For example, prevalence of putative Ni-containing superoxide dismutases (SODs), instead of Fe-containing SODs, seems to be a common adaptation among eukaryotic phytoplankton for reducing Fe quotas in low-Fe modern oceans. Moreover, highly mosaic gene repertoires, although compositionally distinct for each major eukaryotic lineage, now seem to be an underlying facet of successful marine phytoplankton.
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