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  • 1
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    Low-latitude expressions of high-latitude forcing during Heinrich Stadial 1 and the Younger Dryas in northern South America (2018)
    Elsevier
    In:  Global and Planetary Change, 160 . pp. 1-9.
    Details
    Publication Date: 2021-02-08
    Description: Changes in Atlantic Meridional Overturning Circulation (AMOC) strength exert a major influence on global atmospheric circulation patterns. However, the pacing and mechanisms of low-latitude responses to high-latitude forcing are insufficiently constrained so far. To elucidate the interaction of atmospheric and oceanic forcing in tropical South America during periods of major AMOC reductions (Heinrich Stadial 1 and the Younger Dryas) we generated a high-resolution foraminiferal multi-proxy record from off the Orinoco River based on Ba/Ca and Mg/Ca ratios, as well as stable isotope measurements. The data clearly indicate a three-phased structure of HS1 based on the reconfiguration of ocean currents in the tropical Atlantic Ocean. The initial phase (HS1a) is characterized by a diminished North Brazil Current, a southward displacement of the ITCZ, and moist conditions dominating northeastern Brazil. During subsequent HS1b, the NBC was even more diminished or yet reversed and the ITCZ shifted to its southernmost position. Hence, dryer conditions prevailed in northern South America, while eastern Brazil experienced maximally wet conditions. During the final stage, HS1c, conditions are similar to HS1a. The YD represents a smaller amplitude version of HS1 with a southward-shifted ITCZ. Our findings imply that the low-latitude continental climate response to high-latitude forcing is mediated by reconfigurations of surface ocean currents in low latitudes. Our new records demonstrate the extreme sensitivity of the terrestrial realm in tropical South America to abrupt perturbations in oceanic circulation during periods of unstable climate conditions.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    Format: other
    DOI: 10.1016/j.gloplacha.2017.11.008
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Subtropical W-Atlantic subsurface warming during deglacial times of reduced Atlantic Meridional Overturning Circulation (2016)
    In:  [Poster] In: 12. International Conference on Paleoceanography (ICP12), 28.08.-02.09.2016, Utrecht, The Netherlands .
    Details
    Publication Date: 2016-09-13
    Description: The Atlantic Meridional Overturning Circulation (AMOC) is intimately linked to abrupt North Atlantic climate change and is a key player for the transport of tropical heat to high northern latitudes. A deglacially reduced AMOC resulted in surface cooling in wide areas of the tropical North Atlantic, while the subsurface ocean experienced regional warming by several degrees due to the reorganization of ocean circulation at intermediate depths (Schmidt et al., 2012). The S-Caribbean (Tobago Basin) is crucial in this respect as several modelling studies predicted substantial subsurface warming during periods of reduced AMOC (Schmidt et al., 2012).We here reconstruct surface and subsurface temperature and salinity changes during the past 30 kyr, based on stable isotope (δ13C, δ18O) and elemental (Mg/Ca) ratios of planktonic surface dwelling (G. ruber) and deep dwelling foraminiferal species, (G. truncatulinoides). The studied sediment core is influenced by cooler and fresher tropical waters during modern circulation conditions. During deglacial times of AMOC slowdowns subsurface waters warmed and became more saline, as the weakened thermohaline circulation allowed Subtropical Gyre waters to enter the tropical W-Atlantic (Chang et al. 2008). Our high resolution data further imply that the inflow of Subtropical Gyre waters into the tropical Atlantic led to the abrupt increase of subsurface temperatures by ~6°C. Such subsurface warming is much higher than the 2.5°C warming proposed by modeling studies. Furthermore, subsurface salinity rose simultaneously with temperatures, pointing to the replacement of cooler/fresher tropical waters by warmer/saltier Subtropical Gyre waters.
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Poster
  • 3
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    Tectonically restricted deep-ocean circulation at the end of the Cretaceous greenhouse (2013)
    Elsevier
    In:  Earth and Planetary Science Letters, 369-370 . pp. 169-177.
    Details
    Publication Date: 2019-09-23
    Description: The evolution of global ocean circulation toward deep-water production in the high southern latitudes is thought to have been closely linked to the transition from extreme mid-Cretaceous warmth to the cooler Cenozoic climate. The relative influences of climate cooling and the opening and closure of oceanic gateways on the mode of deep-ocean circulation are, however, still unresolved. Here we reconstruct intermediate- to deep-water circulation for the latest Cretaceous based on new high-resolution radiogenic neodymium (Nd) isotope data from several sites and for different water depths in the South Atlantic, Southern Ocean, and proto-Indian Ocean. Our data document the presence of markedly different intermediate water Nd-isotopic compositions in the South Atlantic and Southern Ocean. In particular, a water mass with a highly radiogenic Nd isotope signature most likely originating from intense hotspot-related volcanic activity bathed the crest of Walvis Ridge between 71 and 69 Ma, which formed a barrier that prevented deep-water exchange between the Southern Ocean and the North Atlantic basins. We suggest that the Cenozoic mode of global deep-ocean circulation was still suppressed by tectonic barriers in the latest Cretaceous, and that numerous, mostly regionally-formed and sourced intermediate to deep waters supplied the deep ocean prior to 68 million yr ago.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2013.03.019
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Comparison of Ba/Ca and as freshwater proxies: A multi-species core-top study on planktonic foraminifera from the vicinity of the Orinoco River mouth (2013)
    Elsevier
    In:  Earth and Planetary Science Letters, 383 . pp. 45-57.
    Details
    Publication Date: 2019-09-23
    Description: Past river run-off is an important measure for the continental hydrological cycle and the assessment of freshwater input into the ocean. However, paleosalinity reconstructions applying different proxies in parallel often show offsets between the respective methods. Here, we compare the established foraminiferal Ba/Ca and View the MathML source salinity proxies for their capability to record the highly seasonal Orinoco freshwater plume in the eastern Caribbean. For this purpose we obtained a data set comprising Ba/Ca and View the MathML source determined on multiple species of planktonic foraminifera from core tops distributed around the Orinoco River mouth. Our findings indicate that interpretations based on either proxy could lead to different conclusions. In particular, Ba/Ca and View the MathML source diverge in their spatial distribution due to different governing factors. Apparently, the Orinoco freshwater plume is best tracked by Ba/Ca ratios of G. ruber (pink and sensu lato morphotypes), while View the MathML source based on the same species is more related to the local precipitation-evaporation balance overprinting the riverine freshwater contribution. Other shallow dwelling species (G. sacculifer, O. universa) show a muted response to the freshwater discharge, most likely due to their ecological and habitat preferences. Extremely high Ba/Ca ratios recorded by G. ruber are attributed to Ba2+-desorption from suspended matter derived from the Orinoco. Samples taken most proximal to the freshwater source do not show pronounced Ba/Ca or View the MathML source anomalies. Here, the suspension loaded freshwater lid developing during maximum discharge suppresses foraminiferal populations. Both proxies are therefore biased towards dry season conditions at these sites, when surface salinity is only minimally reduced.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.epsl.2013.09.036
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Indicators for Monitoring Sustainable Development Goals: An Application to Oceanic Development in the European Union (2016)
    Wiley
    In:  Earth's Future, 4 (5). pp. 252-267.
    Details
    Publication Date: 2019-09-23
    Description: The 2030 Agenda for Sustainable Development includes a set of 17 Sustainable Development Goals (SDG) with 169 specific targets. As such, it could be a step forward in achieving efficient governance and policies for global sustainable development. However, the current indicator framework with its broad set of individual indicators prevents straightforward assessment of synergies and trade-offs between the various indicators, targets, and goals thus heightening the significance of policy guidance in achieving sustainable development. With our detailed analysis of SDG 14 (Ocean) for European Union coastal states, we demonstrate how the (complementary) inclusion of composite indicators that aggregate the individual indicators by applying a generalized mean can provide important additional information and facilitate the assessment of sustainable development in general and in the SDG context in particular. Embedded in the context of social choice theory, the generalized mean varies the specification of substitution elasticity and thus allows a) for a straightforward distinction between a concept of weak and strong sustainability and b) for straightforward sensitivity analysis. We show that while in general the EU coastal states have a fairly balanced record at the SDG 14 level, certain countries like Slovenia and Portugal with a fairly balanced and a fairly unbalanced showing, respectively, rank very differently in terms of the two concepts of strong sustainability.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1002/2016EF000353
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Assessment of MSC-certified fish stocks in the Northeast Atlantic (2016)
    Elsevier
    In:  Marine Policy, 71 . pp. 10-14.
    Details
    Publication Date: 2019-09-23
    Description: This study examines the status and exploitation level of 31 northern European stocks targeted by fisheries certified by the Marine Stewardship Council (MSC) as being sustainable and well managed. In the first year of certification, 11 stocks (52% of stocks with available data) were exploited above the maximum sustainable level and four stocks (16% of stocks with available data) were outside of safe biological limits. MSC states that it certifies sub-standard stocks because they will improve once they are in their program. However, after a duration of certification of one to ten years (average four years), no significant changes in fishing pressure or stock size were detected. In the last certified year with available data, seven stocks (44% of stocks with available data) were subject to overfishing and five stocks (21% of stocks with available data) were outside of safe biological limits. Certification should guarantee that fishing quotas are set correctly and are enforced. However, in 11 stocks quotas were set 20–60% above the level that fishers were taking, whereas in three stocks landings exceeded quotas by 30–50%. The study concludes that MSC should change its rules such that overfishing or unsafe stock sizes lead to immediate suspension of certification and that no certification is issued in the first place for a stock that is already in such a situation.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1016/j.marpol.2016.05.003
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Life-history traits and physiological limits of the alpine fly Drosophila nigrosparsa (Diptera: Drosophilidae): A comparative study (2018)
    Wiley-Blackwell
    Details
    Publication Date: 2018-01-18
    Description: Interspecific variation in life-history traits and physiological limits can be linked to the environmental conditions species experience, including climatic conditions. As alpine environments are particularly vulnerable under climate change, we focus on the montane-alpine fly Drosophila nigrosparsa . Here, we characterized some of its life-history traits and physiological limits and compared these with those of other drosophilids, namely Drosophila hydei , Drosophila melanogaster , and Drosophila obscura . We assayed oviposition rate, longevity, productivity, development time, larval competitiveness, starvation resistance, and heat and cold tolerance. Compared with the other species assayed, D. nigrosparsa is less fecund, relatively long-living, starvation susceptible, cold adapted, and surprisingly well heat adapted. These life-history characteristics provide insights into invertebrate adaptations to alpine conditions which may evolve under ongoing climate change. Life-history traits and physiological limits of the alpine fly Drosophila nigrosparsa were assayed in the laboratory and compared with those of four other Drosophila species. Drosophila nigrosparsa has relatively low fecundity, is long-living, starvation susceptible, cold adapted, and surprisingly heat tolerant.
    Electronic ISSN: 2045-7758
    Topics: Biology
    Published by Wiley-Blackwell
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    PAPER CURRENT
  • 8
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    Geochemistry of Globigerinoides ruber of sediment core M78/1_235-1 (2017)
    PANGAEA
    In:  Supplement to: Bahr, André; Hoffmann, Julia; Schönfeld, Joachim; Schmidt, Matthew W; Nürnberg, Dirk; Batenburg, Sietske J; Voigt, Silke (2018): Low-latitude expressions of high-latitude forcing during Heinrich Stadial 1 and the Younger Dryas in northern South America. Global and Planetary Change, 160, 1-9, https://doi.org/10.1016/j.gloplacha.2017.11.008
    Details
    Publication Date: 2023-03-03
    Description: Changes in Atlantic Meridional Overturning Circulation (AMOC) strength exert a major influence on global atmospheric circulation patterns. However, the pacing and mechanisms of low-latitude responses to high-latitude forcing are insufficiently constrained so far. To elucidate the interaction of atmospheric and oceanic forcing in tropical South America dur-ing periods of major AMOC reductions (Heinrich Stadial 1 and the Younger Dryas) we gen-erated a high-resolution foraminiferal multi-proxy record from off the Orinoco River based on Ba/Ca and Mg/Ca ratios, as well as stable isotope measurements. The data clearly indi-cate a three-phased structure of HS1 based on the reconfiguration of ocean currents in the tropical Atlantic Ocean. The initial phase (HS1a) is characterized by a diminished North Brazil Current, a southward displacement of the ITCZ, and moist conditions dominating northeastern Brazil. During subsequent HS1b, the NBC was even more diminished or yet reversed and the ITCZ shifted to its southernmost position. Hence, dryer conditions pre-vailed in northern South America, while eastern Brazil experienced maximally wet condi-tions. During the final stage, HS1c, conditions are similar to HS1a. The YD represents a smaller amplitude version of HS1 with a southward-shifted ITCZ. Our findings imply that the low-latitude continental climate response to high-latitude forcing is mediated by recon-figurations of surface ocean currents in low latitudes. Our new records demonstrate the ex-treme sensitivity of the terrestrial realm in tropical South America to abrupt perturbations in oceanic circulation during periods of unstable climate conditions.
    Keywords: 235-1; AGE; DEPTH, sediment/rock; Globigerinoides ruber, Aluminium/Calcium ratio; Globigerinoides ruber, Barium/Calcium ratio; Globigerinoides ruber, Iron/Calcium ratio; Globigerinoides ruber, Magnesium/Calcium ratio; Globigerinoides ruber, Manganese/Calcium ratio; Globigerinoides ruber, δ13C; Globigerinoides ruber, δ18O; M78/1; M78/1_235-1; Meteor (1986); N. Tobago; PC; Piston corer; Sea surface temperature, annual mean; SST from Mg/Ca ratios; δ18O, water
    Type: Dataset
    Format: text/tab-separated-values, 1818 data points
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    DATA PANGAEA
  • 9
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    Planktic foraminiferal Mg/Ca ratios of Globorotalia truncatulinoides of sediment core M78/1_235-1 recovered during METEOR cruise M78/1 (2019)
    PANGAEA
    Details
    Publication Date: 2023-03-30
    Keywords: 235-1; AGE; DEPTH, sediment/rock; Globorotalia truncatulinoides, Aluminium/Calcium ratio; Globorotalia truncatulinoides, Iron/Calcium ratio; Globorotalia truncatulinoides, Magnesium/Calcium ratio; Globorotalia truncatulinoides, Manganese/Calcium ratio; Globorotalia truncatulinoides, δ18O; M78/1; M78/1_235-1; Meteor (1986); N. Tobago; PC; Piston corer; Sub-surface temperature; δ18O, water
    Type: Dataset
    Format: text/tab-separated-values, 1705 data points
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    DATA PANGAEA
  • 10
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    Planktic foraminiferal Mg/Ca ratios of sediment cores in the tropical Atlantic (2019)
    PANGAEA
    In:  Supplement to: Reissig, Stefan; Nürnberg, Dirk; Bahr, André; Poggemann, David-Willem; Hoffmann, Julia (2019): Southward Displacement of the North Atlantic Subtropical Gyre Circulation System During North Atlantic Cold Spells. Paleoceanography and Paleoclimatology, 34, 866-885, https://doi.org/10.1029/2018PA003376
    Details
    Publication Date: 2023-01-13
    Description: During times of deglacial Atlantic Meridional Overturning Circulation (AMOC) perturbations, the tropical Atlantic experienced considerable warming at subsurface levels. Coupled ocean-atmosphere simulations corroborate the tight teleconnection between the tropical Atlantic and climate change at high northern latitudes, but still underestimate the relevance of the subsurface N Atlantic Subtropical Gyre (STG) for heat and salt storage and its sensitivity to rapid climatic change. Here we reconstruct vertical and lateral temperature and salinity gradients in the tropical W Atlantic and the Caribbean over the last 30 kyrs, based on planktic deep and shallow dwelling foraminiferal Mg/Ca and δ18O-records. The rapid and large amplitude subsurface changes illustrate a dynamic STG associated with abrupt shifts of North Atlantic hydrographic and atmospheric regimes. We infer that during full glacial conditions, the STG has been shifted southward while intensified Ekman-downwelling associated to strengthened trade winds fostered the formation of warm and saline Salinity Maximum Water (SMW). The southward propagation of SMW was facilitated by the glacially eastward deflected North Brazil Current. During periods of significant AMOC perturbations (Heinrich Stadials 2, 1, and the Younger Dryas), extreme subsurface warming by ~6°C led to diminished lateral subsurface temperature gradients. Coevally, a deep thermocline suggests that SMW fully occupied the subsurface tropical W Atlantic and that the STG reached its southernmost position. During the Holocene, modern-like conditions gradually developed with the northward retreat of SMW and the development of a strong thermocline ridge between the Subtropical Gyre and the tropical W Atlantic.
    Type: Dataset
    Format: application/zip, 4 datasets
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    DATA PANGAEA
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