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  • 1
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    Biological and physical influences on marine snowfall at the equator (2017)
    Nature Research
    In:  Nature Geoscience, 10 (11). pp. 852-858.
    Details
    Publication Date: 2020-06-18
    Description: High primary productivity in the equatorial Atlantic and Pacific oceans is one of the key features of tropical ocean biogeochemistry and fuels a substantial flux of particulate matter towards the abyssal ocean. How biological processes and equatorial current dynamics shape the particle size distribution and flux, however, is poorly understood. Here we use high-resolution size-resolved particle imaging and Acoustic Doppler Current Profiler data to assess these influences in equatorial oceans. We find an increase in particle abundance and flux at depths of 300 to 600 m at the Atlantic and Pacific equator, a depth range to which zooplankton and nekton migrate vertically in a daily cycle. We attribute this particle maximum to faecal pellet production by these organisms. At depths of 1,000 to 4,000 m, we find that the particulate organic carbon flux is up to three times greater in the equatorial belt (1° S–1° N) than in off-equatorial regions. At 3,000 m, the flux is dominated by small particles less than 0.53 mm in diameter. The dominance of small particles seems to be caused by enhanced active and passive particle export in this region, as well as by the focusing of particles by deep eastward jets found at 2° N and 2° S. We thus suggest that zooplankton movements and ocean currents modulate the transfer of particulate carbon from the surface to the deep ocean.
    Type: Article , PeerReviewed
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    DOI: 10.1038/ngeo3042
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Taking action against ocean acidification: A review of management and policy options (2013)
    Springer
    In:  Environmental Management, 52 (4). pp. 761-779.
    Details
    Publication Date: 2018-09-12
    Description: Ocean acidification has emerged over the last two decades as one of the largest threats to marine organisms and ecosystems. However, most research efforts on ocean acidification have so far neglected management and related policy issues to focus instead on understanding its ecological and biogeochemical implications. This shortfall is addressed here with a systematic, international and critical review of management and policy options. In particular, we investigate the assumption that fighting acidification is mainly, but not only, about reducing CO2 emissions, and explore the leeway that this emerging problem may open in old environmental issues. We review nine types of management responses, initially grouped under four categories: preventing ocean acidification; strengthening ecosystem resilience; adapting human activities; and repairing damages. Connecting and comparing options leads to classifying them, in a qualitative way, according to their potential and feasibility. While reducing CO2 emissions is confirmed as the key action that must be taken against acidification, some of the other options appear to have the potential to buy time, e.g. by relieving the pressure of other stressors, and help marine life face unavoidable acidification. Although the existing legal basis to take action shows few gaps, policy challenges are significant: tackling them will mean succeeding in various areas of environmental management where we failed to a large extent so far.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1007/s00267-013-0132-7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Decadal fingerprints of freshwater discharge around Greenland in a multi-model ensemble (2013)
    Springer
    In:  Climate Dynamics, 41 (3-4). pp. 695-720.
    Details
    Publication Date: 2019-09-23
    Description: The recent increase in the rate of the Greenland ice sheet melting has raised with urgency the question of the impact of such a melting on the climate. As former model projections, based on a coarse representation of the melting, show very different sensitivity to this melting, it seems necessary to consider a multi-model ensemble to tackle this question. Here we use five coupled climate models and one ocean-only model to evaluate the impact of 0.1 Sv (1 Sv = 106 m3/s) of freshwater equally distributed around the coast of Greenland during the historical era 1965–2004. The ocean-only model helps to discriminate between oceanic and coupled responses. In this idealized framework, we find similar fingerprints in the fourth decade of hosing among the models, with a general weakening of the Atlantic Meridional Overturning Circulation (AMOC). Initially, the additional freshwater spreads along the main currents of the subpolar gyre. Part of the anomaly crosses the Atlantic eastward and enters into the Canary Current constituting a freshwater leakage tapping the subpolar gyre system. As a consequence, we show that the AMOC weakening is smaller if the leakage is larger. We argue that the magnitude of the freshwater leakage is related to the asymmetry between the subpolar-subtropical gyres in the control simulations, which may ultimately be a primary cause for the diversity of AMOC responses to the hosing in the multi-model ensemble. Another important fingerprint concerns a warming in the Nordic Seas in response to the re-emergence of Atlantic subsurface waters capped by the freshwater in the subpolar gyre. This subsurface heat anomaly reaches the Arctic where it emerges and induces a positive upper ocean salinity anomaly by introducing more Atlantic waters. We found similar climatic impacts in all the coupled ocean–atmosphere models with an atmospheric cooling of the North Atlantic except in the region around the Nordic Seas and a slight warming south of the equator in the Atlantic. This meridional gradient of temperature is associated with a southward shift of the tropical rains. The free surface models also show similar sea-level fingerprints notably with a comma-shape of high sea-level rise following the Canary Current.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1007/s00382-012-1479-9
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Simulations of a Line W-based observing system for the Atlantic meridional overturning circulation (2013)
    Springer
    In:  Ocean Dynamics, 63 (8). pp. 865-880.
    Details
    Publication Date: 2019-09-23
    Description: In a series of observing system simulations, we test whether the Atlantic meridional overturning circulation (AMOC) can be observed based on the existing Line W deep western boundary array. We simulate a Line W array, which is extended to the surface and to the east to cover the basin to the Bermuda Rise. In the analyzed ocean circulation model ORCA025, such an extended Line W array captures the main characteristics of the western boundary current. Potential trans-basin observing systems for the AMOC are tested by combining the extended Line W array with a mid-ocean transport estimate obtained from thermal wind "measurements" and Ekman transport to the total AMOC (similarly to Hirschi et al., Geophys Res Lett 30(7):1413, 2003). First, we close Line W zonally supplementing the western boundary array with several "moorings" in the basin (Line W-32A degrees N). Second, we supplement the western boundary array with a combination of observations at Bermuda and the eastern part of the RAPID array at 26A degrees N (Line W-B-RAPID). Both, a small number of density profiles across the basin and also only sampling the eastern and western boundary, capture the variability of the AMOC at Line W-32A degrees N and Line W-B-RAPID. In the analyzed model, the AMOC variability at both Line W-32A degrees N and Line W-B-RAPID is dominated by the western boundary current variability. Away from the western boundary, the mid-ocean transport (east of Bermuda) shows no significant relation between the two Line W-based sections and 26A degrees N. Hence, a Line W-based AMOC estimate could yield an estimate of the meridional transport that is independent of the 26A degrees N RAPID estimate. The model-based observing system simulations presented here provide support for the use of Line W as a cornerstone for a trans-basin AMOC observing system.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1007/s10236-013-0632-2
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    The Agulhas System in a Global Context (2013)
    Springer
    In:  In: High Performance Computing in Science and Engineering '13. , ed. by Nagel, W. E., Kröner, D. B. and Resch, M. M. Springer, Heidelberg u.a., pp. 569-576. ISBN 978-3-319-02164-5
    Details
    Publication Date: 2014-05-12
    Description: The Agulhas is a convoluted and multifarious system [1]. It consists of a western boundary current, the Agulhas Current, which is arguably one of the most prominent current systems of the Southern Hemisphere (Fig.1). The Agulhas Current, roughly on par with its Northern Hemisphere counterpart, the Gulf Stream, carries vast amount of heat and salt towards the pole [2].
    Type: Book chapter , PeerReviewed
    DOI: 10.1007/978-3-319-02165-2_40
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    OceanRep: Book chapter
  • 6
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    The Agulhas system as a key region of the global oceanic circulation (2006)
    Springer
    In:  In: High Performance Computing on Vector Systems. , ed. by Resch, M. Springer, Berlin, pp. 163-169. ISBN 978-3-540-29124-4
    Details
    Publication Date: 2017-04-06
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 7
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    The Agulhas System as a Prime Example for the Use of Nesting Capabilities in Ocean Modelling (2009)
    Springer
    In:  In: High Performance Computing on Vector Systems 2009. , ed. by Resch, M., Roller, S., Benkert, K., Galle, M., Bez, W. and Kobayashi, H. Springer, Berlin, pp. 191-198. ISBN 978-3642039126
    Details
    Publication Date: 2012-07-05
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 8
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    The Agulhas System as a Key Region of the Global Oceanic Circulation (2012)
    Springer
    In:  In: High Performance Computing in Science and Engineering '12. , ed. by Nagel, W. E., Kröner, D. H. and Resch, M. M. Springer, Heidelberg u.a., pp. 407-414. ISBN 978-3-642-33373-6
    Details
    Publication Date: 2014-05-12
    Description: The oceans around southern Africa form a unique system, impacting the regional and global climate [1]. From the Indian Ocean to the Atlantic Ocean vigorous interoceanic exchange of warm and saline waters takes place that is subject to a complicated interplay between local dynamics and global embedment. Central element of the circulation around South Africa is the Agulhas Current [2] that flows poleward along the east coast, closely bound to the shelf at first, and subsequently overshoots the southern tip of Africa to abruptly turn back into the Indian Ocean. Part of the warm and saline waters with tropical Indian Ocean origin, the “Agulhas leakage” [3], flows into the Atlantic and forms the surface return flow of the global thermohaline circulation towards the North Atlantic [4]. The exchange takes place in a highly nonlinear manner, with mesoscale eddies being separated from the retroflecting Agulhas Current, which then strongly interact in the Cape Basin [5]. West of the Cape Basin, large Agulhas rings that have been formed [6] transport the anomalous warm and saline waters into the South Atlantic. In addition to its own dynamics, the Agulhas Current system is influenced by nonlinearities in the source regions: mesoscale eddies originating from the Mozambique Channel and east of Madagascar [7, 8] drift southward and cause the Agulhas Current to be displaced offshore of its mean position by more than 100 km. These solitary meanders (a.k.a. “Natal Pulses”) [9] rapidly propagate downstream triggering the timing of Agulhas rings [10, 11]
    Type: Book chapter , PeerReviewed
    DOI: 10.1007/978-3-642-33374-3_30
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    OceanRep: Book chapter
  • 9
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    The Agulhas System as a Key Region of the Global Oceanic Circulation (2008)
    Springer
    Details
    Publication Date: 2023-11-08
    Description: The Agulhas system all the interface between the Indian and Atlantic Ocean is an important region in the global oceanic circulation with a recognized key role in global climate and climate change. The simulation of the Agulhas system was performed by a high-resolution regional model nested in a global coarse-resolution ocean model. It is shown that this model simulates all characteristics of the Agulhas regime in a highly realistic manner. Due to the two-way coupling of both models the importance of the Agulhas leakage on the large-scale thermohaline circulation was demonstrated.
    Type: Book chapter , PeerReviewed
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    OceanRep: Book chapter
  • 10
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    Larval behaviour, dispersal and population connectivity in the deep sea (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Ecosystem connectivity is an essential consideration for marine spatial planning of competing interests in the deep sea. Immobile, adult communities are connected through freely floating larvae, depending on new recruits for their health and to adapt to external pressures. We hypothesize that the vertical swimming ability of deep-sea larvae, before they permanently settle at the bottom, is one way larvae can control dispersal. We test this hypothesis with more than 3x108 simulated particles with a range of active swimming behaviours embedded within the currents of a high-resolution ocean model. Despite much stronger horizontal ocean currents, vertical swimming of simulated larvae can have an order of magnitude impact on dispersal. These strong relationships between larval dispersal, pathways, and active swimming demonstrate that lack of data on larval behaviour traits is a serious impediment to modelling deep-sea ecosystem connectivity; this uncertainty greatly limits our ability to develop ecologically coherent marine protected area networks.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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