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  • 1
    Language: English
    In: Nature, 22 May 2019
    Description: The ocean-the Earth's largest ecosystem-is increasingly affected by anthropogenic climate change. Large and globally consistent shifts have been detected in species phenology, range extension and community composition in marine ecosystems. However, despite evidence for ongoing change, it remains unknown whether marine ecosystems have entered an Anthropocene state beyond the natural decadal to centennial variability. This is because most observational time series lack a long-term baseline, and the few time series that extend back into the pre-industrial era have limited spatial coverage. Here we use the unique potential of the sedimentary record of planktonic foraminifera-ubiquitous marine zooplankton-to provide a global pre-industrial baseline for the composition of modern species communities. We use a global compilation of 3,774 seafloor-derived planktonic foraminifera communities of pre-industrial age and compare these with communities from sediment-trap time series that have sampled plankton flux since AD 1978 (33 sites, 87 observation years). We find that the Anthropocene assemblages differ from their pre-industrial counterparts in proportion to the historical change in temperature. We observe community changes towards warmer or cooler compositions that are consistent with historical changes in temperature in 85% of the cases. These observations not only confirm the existing evidence for changes in marine zooplankton communities in historical times, but also demonstrate that Anthropocene communities of a globally distributed zooplankton group systematically differ from their unperturbed pre-industrial state.
    Keywords: Plankton ; Community Composition ; Zooplankton ; Anthropogenic Factors ; Temperature ; Community Composition ; Anthropogenic Climate Changes ; Environmental Changes ; Marine Ecosystems ; Climate Change ; Sediments ; Communities ; Zooplankton ; Time Series ; Marine Ecosystems ; 20th Century ; Climate Change ; Historic Temperatures ; Climate Change ; Zooplankton ; Zooplankton ; Marine Ecosystems ; Foraminifera ; Plankton ; Range Extension ; Composition ; Time Series ; Time Series ; Ocean Floor ; Ocean Floor;
    ISSN: 00280836
    E-ISSN: 1476-4687
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  • 2
    Language: English
    In: Earth and Planetary Science Letters, August 15, 2013, Vol.376, p.137(8)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.epsl.2013.06.019 Byline: Lukas Jonkers, Patricia Jimenez-Amat, P. Graham Mortyn, Geert-Jan A. Brummer Abstract: Given the importance of high-latitude areas in the ocean-climate system, there is need for a paleothermometer that is reliable at low temperatures. Here we assess the applicability of the Mg/Ca-temperature proxy in colder waters (5-10a[degrees]C) by comparing for the first time the seasonal Mg/Ca and [delta].sup.18O cycles of N. pachyderma (s) and G. bulloides using a sediment trap time-series from the northern North Atlantic. While both species show indistinguishable seasonal [delta].sup.18O patterns that clearly track the near surface temperature cycle, their Mg/Ca are very different. G. bulloides Mg/Ca is high (2.0-3.1 mmol/mol), but varies in concert with the seasonal temperature cycle. The Mg/Ca of N. pachyderma (s), on the other hand, is low (1.1-1.5 mmol/mol) and shows only a very weak seasonal cycle. The [delta].sup.18O patterns indicate that both species calcify in the same depth zone. Consequently, depth habitat differences cannot explain the contrasting Mg/Ca patterns. The elevated Mg/Ca in pristine G. bulloides might be due to the presence of high Mg phases that are not preserved in fossil shells. The contrasting absence of a seasonal trend in the Mg/Ca of N. pachyderma (s) confirms other studies where calcification temperatures were less well constrained. The reason for this absence is not fully known, but may include species-specific vital effects. The very different seasonal patterns of both speciesE1/4 Mg/Ca underscore the importance of parameters other than temperature in controlling planktonic foraminiferal Mg/Ca. Our results therefore lend further caution in the interpretation of Mg/Ca-temperature reconstructions from high northern latitudes. Author Affiliation: (a) Institut de Ciencia i Tecnologia Ambientals (ICTA), Universitat Autonoma de Barcelona, Campus UAB, 08193 Bellaterra (Cerdanyola del Valles), Spain (b) Department of Geography, Universitat Autonoma de Barcelona, Campus UAB, 08193 Bellaterra (Cerdanyola del Valles), Spain (c) Department of Marine Geology, Royal Netherlands Institute for Sea Research, Texel, The Netherlands (d) Cardiff University, School of Earth and Ocean Sciences, Park Place, Cardiff CF10 3AT, Wales, UK Article History: Received 11 January 2013; Revised 10 June 2013; Accepted 12 June 2013 Article Note: (miscellaneous) Editor: J. Lynch-Stieglitz
    Keywords: Seawater
    ISSN: 0012-821X
    Source: Cengage Learning, Inc.
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  • 3
    In: Nature, 2015, Vol.520(7547), p.333
    Description: Abrupt climate change is a ubiquitous feature of the Late Pleistocene epoch (1). In particular, the sequence of Dansgaard--Oeschger events (repeated transitions between warm interstadial and cold stadial conditions), as recorded by ice cores in Greenland (2), are thought to be linked to changes in the mode of overturning circulation in the Atlantic Ocean (3). Moreover, the observed correspondence between North Atlantic cold events and increased iceberg calving and dispersal from ice sheets surrounding the North Atlantic (4) has inspired many ocean and climate modelling studies that make use of freshwater forcing scenarios to simulate abrupt change across the North Atlantic region and beyond (5-7). On the other hand, previous studies (4,8) identified an apparent lag between North Atlantic cooling events and the appearance of ice-rafted debris over the last glacial cycle, leading to the hypothesis that iceberg discharge may be a consequence of stadial conditions rather than the cause (4,9-11). Here we further establish this relationship and demonstrate a systematic delay between pronounced surface cooling and the arrival of ice-rafted debris at a site southwest of Iceland over the past four glacial cycles, implying that in general icebergs arrived too late to have triggered cooling. Instead we suggest that--on the basis of our comparisons of ice-rafted debris and polar planktonic foraminifera--abrupt transitions to stadial conditions should be considered as a nonlinear response to more gradual cooling across the North Atlantic. Although the freshwater derived from melting icebergs may provide a positive feedback for enhancing and or prolonging stadial conditions (10,11), it does not trigger northern stadial events.
    Keywords: Climate Change -- Environmental Aspects ; Icebergs -- Environmental Aspects ; Environmental Impact Analysis -- Methods;
    ISSN: 0028-0836
    E-ISSN: 14764687
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  • 4
    Language: English
    In: Earth and Planetary Science Letters, 01 October 2016, Vol.451, pp.177-184
    Description: Many species of planktonic foraminifera show distinct banding in the intratest distribution of Mg/Ca. This heterogeneity appears biologically controlled and thus poses a challenge to Mg/Ca paleothermometry. The cause of this banding and its relation with chamber formation are poorly constrained and most of what we know about intratest Mg/Ca variability stems from culture studies of tropical, symbiont-bearing foraminifera. Here we present data on the non-spinose, symbiont-barren from the subpolar North Atlantic where wintertime mixing removes vertical gradients in temperature and salinity. This allows investigation of biologically controlled Mg/Ca intratest variability under natural conditions. We find that intratest Mg/Ca varies between 〈0.1 and 7 mmol/mol, even in winter specimens. High Mg/Ca bands occur at the outer edge of the laminae, indicating reduced Mg removal at the end of chamber formation. Our data thus provide new constraints on the timing of the formation of such bands and indicate that their presence is intrinsic to the chamber formation process. Additionally, all specimens are covered with an outer crust consisting of large euhedral crystals. The composition of the crust is similar to the low Mg/Ca bands in the laminar calcite in winter and summer specimens, indicating a tight biological control on crust formation and composition. Nevertheless, despite high intratest variability, the median Mg/Ca of summertime tests is higher than that of wintertime tests. This provides support for Mg/Ca paleothermometry, but to improve the accuracy of paleotemperature estimates biological effects on Mg incorporation need to be better accounted for.
    Keywords: Mg/Ca Paleothermometry ; Neogloboquadrina Pachyderma ; Planktonic Foraminifera ; Intratest Mg/Ca Variability ; Sediment Trap ; Geology ; Physics
    ISSN: 0012-821X
    E-ISSN: 1385-013X
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  • 5
    Language: English
    In: PLOS ONE, 12/19/2018, Vol.13(12), p.e0208598
    Description: Aragonite (along with calcite) is one of the most common polymorphs of the crystalline calcium carbonate that forms the skeletal structures of organisms, but it has relatively low preservation potential. Under ambient conditions and in the presence of water, aragonite transforms into calcite, the stable polymorph. Aragonite is also more soluble therefore, in water-permeable siliceous limestones (opokas) that are typical of Upper Cretaceous deposits of Poland and Ukraine, the primary aragonitic skeletons are either entirely dissolved and found as moulds and casts or transformed into secondary calcite, whereas the primary calcitic shells remain well preserved. Contrary to the common notion of the lack of aragonite in such porous carbonate deposits, we show that relics of aragonite can be preserved as a nacreous lining on cephalopod moulds or as thin, lenticular structures entrapped in neomorphic calcite. Based on the observed intermediate steps of aragonite alteration, we propose an extended model of nacre diagenesis. Among the originally aragonitic biota, only nautilids and ammonites have retained relics of pristine skeletons. Such selective preservation of only some aragonitic structures (nacre but not the prismatic aragonitic layers) points to the role of microstructural and biochemical differences between cephalopod shell layers that may set a threshold for the dissolution, dissolution/precipitation or preservation of original biomineral structures.
    Keywords: Aragonite – Research ; Cephalopods – Research ; Cephalopods – Environmental Aspects ; Diagenesis (Geology) – Research ; Limestone – Research ; Limestone – Environmental Aspects;
    ISSN: PLOS ONE
    E-ISSN: 1932-6203
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  • 6
    Language: English
    In: Quaternary Science Reviews, August 10, 2012, Vol.48, p.43(11)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.quascirev.2012.06.006 Byline: Lukas Jonkers (a), Maarten A. Prins (b), Matthias Moros (c)(d), Gert Jan Weltje (e), Simon R. Troelstra (b), Geert-Jan A. Brummer (a)(b) Abstract: Rapid climatic switches during marine isotope stage 3 (29-59 ka BP) are often attributed to ocean circulation changes caused by freshwater input into the North Atlantic through the melting of large amounts of icebergs and sea ice. However, recent studies have questioned this direct coupling between factors influencing the ocean-climate system. By combining multiple proxies from two mid depth northern North Atlantic sediment cores we assess temporal offsets and links between freshwater input and response of the near bottom flow as well as between near bottom flow and sea surface temperatures changes. Grain size, mineralogical and magnetic proxies for ice rafting and near-bottom flow speed, interpreted as indicators of freshwater input and deep circulation strength, consistently indicate a delay in the recovery of the deep circulation after freshwater perturbations. Sea surface temperature variability is inferred from foraminiferal assemblages and Mg/Ca and [delta].sup.18O of Neogloboquadrina pachyderma s. The records show rapid switches towards higher temperatures following the ice-rafting events. Interestingly, near sea surface temperatures increased and decreased again during periods of accelerating bottom flow speed, likely reflecting the sudden release of heat from deeper in the water column, rather than circulation changes. Our data thus confirm the impact of freshwater forcing on the Atlantic deep circulation, but suggest that temperature variability at the surface was not directly linked to these circulation changes. Author Affiliation: (a) Royal Netherlands Institute for Sea Research, Dept. Marine Geology, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands (b) VU University Amsterdam, Faculty of Earth and Life Sciences, Dept. Earth Sciences, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands (c) Leibniz Institute for Baltic Sea Research, Warnemunde, Seestra[sz]e 15, D-18119 Rostock, Germany (d) Bjerknes Centre for Climate Research, Allegaten 55, NO-5007 Bergen, Norway (e) Delft University of Technology, Geotechnology Department, PO Box 5048, 2600 GA Delft, The Netherlands Article History: Received 25 June 2011; Revised 3 June 2012; Accepted 8 June 2012
    Keywords: Ocean Circulation -- Analysis ; Proxy -- Analysis ; Sediments (Geology) -- Analysis ; Sea Ice -- Analysis ; Universities And Colleges -- Analysis
    ISSN: 0277-3791
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Climate of the Past Discussions, 09/06/2018, pp.1-19
    ISSN: Climate of the Past Discussions
    E-ISSN: 1814-9359
    Source: CrossRef
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  • 8
    Language: English
    In: Climate of the Past, June 6, 2017, Vol.13(6), p.573
    Description: The composition of planktonic foraminiferal (PF) calcite is routinely used to reconstruct climate variability. However, PF ecology leaves a large imprint on the proxy signal: seasonal and vertical habitats of PF species vary spatially, causing variable offsets from annual mean surface conditions recorded by sedimentary assemblages. PF seasonality changes with temperature in a way that minimises the environmental change that individual species experience and it is not unlikely that changes in depth habitat also result from such habitat tracking. While this behaviour could lead to an underestimation of spatial or temporal trends as well as of variability in proxy records, most palaeoceanographic studies are (implicitly) based on the assumption of a constant habitat. Up to now, the effect of habitat tracking on foraminifera proxy records has not yet been formally quantified on a global scale. Here we attempt to characterise this effect on the amplitude of environmental change recorded in sedimentary PF using core top [delta].sup.18 O data from six species. We find that the offset from mean annual near-surface [delta].sup.18 O values varies with temperature, with PF [delta].sup.18 O indicating warmer than mean conditions in colder waters (on average by -0.1 0/00 (equivalent to 0.4 #xB0;C) per #xB0;C), thus providing a first-order quantification of the degree of underestimation due to habitat tracking. We use an empirical model to estimate the contribution of seasonality to the observed difference between PF and annual mean [delta].sup.18 O and use the residual #xCE;#x94;[delta].sup.18 O to assess trends in calcification depth. Our analysis indicates that given an observation-based model parametrisation calcification depth increases with temperature in all species and sensitivity analysis suggests that a temperature-related seasonal habitat adjustment is essential to explain the observed isotope signal. Habitat tracking can thus lead to a significant reduction in the amplitude of recorded environmental change. However, we show that this behaviour is predictable. This allows accounting for habitat tracking, enabling more meaningful reconstructions and improved data-model comparison.
    Keywords: Foraminifera – Research ; Foraminifera – Environmental Aspects ; Plankton – Analysis ; Plankton – Environmental Aspects ; Seasons – Research
    ISSN: 1814-9332
    ISSN: 18149324
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  • 9
    Language: English
    In: Climate of the Past Discussions, 12/05/2016, pp.1-34
    ISSN: Climate of the Past Discussions
    E-ISSN: 1814-9359
    Source: CrossRef
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  • 10
    In: PLoS ONE, 2018, Vol.13(10)
    Description: The unique macroevolutionary dataset of Aze & others has been transferred onto the TimeScale Creator visualisation platform while, as much as practicable, preserving the original unrevised content of its morphospecies and lineage evolutionary trees. This is a “Corrected Version” (not a revision), which can serve as an on-going historical case example because it is now updatable with future time scales. Both macroevolutionary and biostratigraphic communities are now equipped with an enduring phylogenetic database of Cenozoic macroperforate planktonic foraminiferal morphospecies and lineages for which both graphics and content can be visualised together. Key to maintaining the currency of the trees has been specification of time scales for sources of stratigraphic ranges; these scales then locate the range dates within the calibration series. Some ranges or their sources have undergone mostly minor corrections or amendments. Links between lineage and morphospecies trees have been introduced to improve consistency and transparency in timing within the trees. Also, Aze & others’ dual employment of morphospecies and lineage concepts is further elaborated here, given misunderstandings that have ensued. Features displayed on the trees include options for line styles for additional categories for range extensions or degrees of support for ancestor–descendant proposals; these have been applied to a small number of instances as an encouragement to capture more nuanced data in the future. In addition to labeling of eco- and morpho-groups on both trees, genus labels can be attached to the morphospecies tree to warn of polyphyletic morphogenera, and the lineage codes have been decoded to ease their recognition. However, it is the mouse-over pop-ups that provide the greatest opportunity to embed supporting information in the trees. They include details for stratigraphic ranges and their recalibration steps, positions relative to the standard planktonic-foraminiferal zonation, and applications as datums, as well as mutual listings between morphospecies and lineages which ease the tracing of their interrelated contents. The elaboration of the original dataset has been captured in a relational database, which can be considered a resource in itself, and, through queries and programming, serves to generate the TimeScale Creator datapacks.
    Keywords: Research Article ; Biology And Life Sciences ; Biology And Life Sciences ; Computer And Information Sciences ; Earth Sciences ; Biology And Life Sciences ; Biology And Life Sciences ; Computer And Information Sciences ; Earth Sciences ; Biology And Life Sciences ; Earth Sciences ; Biology And Life Sciences ; Computer And Information Sciences ; Social Sciences ; Biology And Life Sciences ; Earth Sciences
    E-ISSN: 1932-6203
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