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  • 1
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    Agulhas leakage dynamics affects decadal variability in Atlantic overturning circulation (2008)
    Nature Publishing Group
    In:  Nature, 456 . pp. 489-492.
    Details
    Publication Date: 2019-09-23
    Description: Predicting the evolution of climate over decadal timescales requires a quantitative understanding of the dynamics that govern the meridional overturning circulation (MOC)1. Comprehensive ocean measurement programmes aiming to monitor MOC variations have been established in the subtropical North Atlantic2, 3 (RAPID, at latitude 26.5° N, and MOVE, at latitude 16° N) and show strong variability on intraseasonal to interannual timescales. Observational evidence of longer-term changes in MOC transport remains scarce, owing to infrequent sampling of transoceanic sections over past decades4, 5. Inferences based on long-term sea surface temperature records, however, supported by model simulations, suggest a variability with an amplitude of plusminus1.5–3 Sv (1 Sv = 106 m3 s-1) on decadal timescales in the subtropics6. Such variability has been attributed to variations of deep water formation in the sub-arctic Atlantic, particularly the renewal rate of Labrador Sea Water7. Here we present results from a model simulation that suggest an additional influence on decadal MOC variability having a Southern Hemisphere origin: dynamic signals originating in the Agulhas leakage region at the southern tip of Africa. These contribute a MOC signal in the tropical and subtropical North Atlantic that is of the same order of magnitude as the northern source. A complete rationalization of observed MOC changes therefore also requires consideration of signals arriving from the south.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/nature07426
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Water column methanotrophy controlled by a rapid oceanographic switch (2015)
    Nature Publishing Group
    In:  Nature Geoscience, 8 (5). pp. 378-382.
    Details
    Publication Date: 2020-11-23
    Description: Large amounts of the greenhouse gas methane are released from the seabed to the water column1, where it may be consumed by aerobic methanotrophic bacteria2. The size and activity of methanotrophic communities, which determine the amount of methane consumed in the water column, are thought to be mainly controlled by nutrient and redox dynamics3–7. Here, we report repeated measurements of methanotrophic activity and community size at methane seeps west of Svalbard, and relate them to physical water mass properties and modelled ocean currents. We show that cold bottom water, which contained a large number of aerobic methanotrophs, was displaced by warmer water with a considerably smaller methanotrophic community within days. Ocean current simulations using a global ocean/sea-ice model suggest that this water mass exchange is consistent with short-term variations in the meandering West Spitsbergen Current. We conclude that the shift from an offshore to a nearshore position of the current can rapidly and severely reduce methanotrophic activity in the water column. Strong fluctuating currents are common at many methane seep systems globally, and we suggest that they affect methane oxidation in the water column at other sites, too.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/ngeo2420
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Die thermohaline Zirkulation des Atlantischen Ozeans in wirbelauflösenden Modellen (1995)
    Springer
    In:  Deutsche Hydrographische Zeitschrift, Suppl. 2 . pp. 13-20.
    Details
    Publication Date: 2018-06-15
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 4
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    The Agulhas system as a key region of the global oceanic circulation (2009)
    IFM-GEOMAR
    In:  IFM-GEOMAR Annual Report, 2008 . pp. 12-13.
    Details
    Publication Date: 2018-10-16
    Description: The Agulhas system transports warm and salty waters from the Indian to the Atlantic Ocean and therefore acts as a key element in the global oceanic circulation. Studies have shown that mesoscale processes are not only important for the correct description of the circulation around South Africa itself but also for its impact on the Gulf Stream system in the North Atlantic.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
  • 5
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    North Atlantic Deep Water Formation in the Labrador Sea, Recirculation through the Subpolar Gyre, and Discharge to the Subtropics (2008)
    Springer
    In:  In: Arctic-Subarctic Ocean Fluxes, Defining the Role of the Northern Seas in Climate. , ed. by Dicksen, R. R., Meincke, J. and Rhines, P. Springer, Dordrecht, pp. 653-702. ISBN 978-1-4020-6773-0
    Details
    Publication Date: 2012-02-23
    Type: Book chapter , PeerReviewed
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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 response of the Antarctic Circumpolar Current to recent climate change (2008)
    Nature Publishing Group
    In:  Nature Geoscience, 1 . pp. 864-869.
    Details
    Publication Date: 2017-02-22
    Description: Observations show a significant intensification of the Southern Hemisphere westerlies, the prevailing winds between the latitudes of 30° and 60° S, over the past decades. A continuation of this intensification trend is projected by climate scenarios for the twenty-first century. The response of the Antarctic Circumpolar Current and the carbon sink in the Southern Ocean to changes in wind stress and surface buoyancy fluxes is under debate. Here we analyse the Argo network of profiling floats and historical oceanographic data to detect coherent hemispheric-scale warming and freshening trends that extend to depths of more than 1,000 m. The warming and freshening is partly related to changes in the properties of the water masses that make up the Antarctic Circumpolar Current, which are consistent with the anthropogenic changes in heat and freshwater fluxes suggested by climate models. However, we detect no increase in the tilt of the surfaces of equal density across the Antarctic Circumpolar Current, in contrast to coarse-resolution model studies. Our results imply that the transport in the Antarctic Circumpolar Current and meridional overturning in the Southern Ocean are insensitive to decadal changes in wind stress.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1038/ngeo362
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Hindcasting the uptake of anthropogenic trace gases with an eddy-permitting model of the Atlantic Ocean (2001)
    Springer
    In:  In: High Performance Computing in Science and Engineering '01. , ed. by Krause, E. and Jäger, W. Springer, Berlin, Germany, pp. 396-405. ISBN 3-540-42675-2
    Details
    Publication Date: 2020-05-07
    Description: The ocean takes up a large fraction of the pertubation C02 that enters the atmosphere by human activity. A realistic representation of this uptake in numerical models is essential for future climate studies. Uptake of C02 or other atmospheric trace gases is strongly influenced by oceanic physical variability at spatial scales between 20 and 100 km. Our main goal is to study the effect of this mesoscale variability on the cumulative uptake of anthropogenic C02 and chlorofluorocarbons using an existing model of the ocean circulation in the Atlantic that resolves a significant part of that variability explicitly because of its grid spacing of about 20 km. Results are compared with simulated trace gas distribution obtained from a model with coarser resolution.
    Type: Book chapter , NonPeerReviewed
    Format: text
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    OceanRep: Book chapter
  • 9
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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
  • 10
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    Spatial variability of sea level change (2011)
    IFM-GEOMAR
    In:  IFM-GEOMAR Annual Report, 2010 . pp. 22-23.
    Details
    Publication Date: 2018-10-16
    Description: Globally averaged sea level has risen by just under 10 cm during the last 50 years as a consequence of global warming. The rise, however, is not uniform, neither in time nor in space. Natural climate fluctuations and associated changes in the ocean currents have contributed to the inhomogeneity and is an important factor which will determine the pattern of future sea level rise. While research in the past years has focused on the global-mean trend and its attribution to the melting of glaciers and the thermal expansion of sea water under global warming, attention is shifting to the geographical pattern of sea level change. This is essential for coastal impact assessments, but has not been practical yet because ocean projections from current climate models widely diverge. The improvement of regional sea level prediction requires a better understanding of the underlying dynamical causes.
    Type: Article , NonPeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - without review
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