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  • 1
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    Southern Ocean Decadal Variability and Predictability (2017)
    Springer
    In:  Current Climate Change Reports, 3 (3). pp. 163-173.
    Details
    Publication Date: 2020-02-06
    Description: The Southern Ocean featured some remarkable changes during the recent decades. For example, large parts of the Southern Ocean, despite rapidly rising atmospheric greenhouse gas concentrations, depicted a surface cooling since the 1970s, whereas most of the planet has warmed considerably. In contrast, climate models generally simulate Southern Ocean surface warming when driven with observed historical radiative forcing. The mechanisms behind the surface cooling and other prominent changes in the Southern Ocean sector climate during the recent decades, such as expanding sea ice extent, abyssal warming, and CO2 uptake, are still under debate. Observational coverage is sparse, and records are short but rapidly growing, making the Southern Ocean climate system one of the least explored. It is thus difficult to separate current trends from underlying decadal to centennial scale variability. Here, we present the state of the discussion about some of the most perplexing decadal climate trends in the Southern Ocean during the recent decades along with possible mechanisms and contrast these with an internal mode of Southern Ocean variability present in state-of-the art climate models.
    Type: Article , PeerReviewed
    Format: text
    Format: text
    DOI: 10.1007/s40641-017-0068-8
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Multi-Centennial Variability Controlled by Southern Ocean Convection in the Kiel Climate Model (2013)
    Springer
    In:  Climate Dynamics, 40 . pp. 2005-2022.
    Details
    Publication Date: 2019-09-24
    Description: A quasi-oscillatory multi-centennial mode of open ocean deep convection in the Atlantic sector of the Southern Ocean in the Kiel Climate Model is described. The quasi-periodic occurrence of the deep convection causes variations in regional and global surface air temperature, Southern Hemisphere sea ice coverage, Southern Ocean and North Atlantic sea surface height, the Antarctic Circumpolar Current and the Atlantic Meridional Overturning Circulation (AMOC). The deep convection is stimulated by a strong built-up of heat at mid-depth. When the heat reservoir is virtually depleted a coincidental strong freshening event at the sea surface shuts down the convection. The heat originates from relatively warm deep water formed in the North Atlantic. The several decades lasting recharge process of the heat reservoir depends on the AMOC and the Weddell Gyre and sets a minimum delay for the deep convection to recur. While the strength of the AMOC increases, the Weddell Gyre weakens during the non-convective regime. Convection onset and shutdown also depend on the stochastic occurrence of favorable sea surface conditions, which contributes to the multi-centennial period of the phenomenon. The shutdown triggers a century-long deviation in AMOC strength caused by significant reductions in bottom water formation and surface salinity in the Southern Ocean’s Atlantic sector. Additional numerical experimentation reveals that sea ice has an important effect on the frequency of occurrence and intensity of the deep convection. Further, we find intriguing similarities to the Weddell Polynya observed during the 1970s
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1007/s00382-012-1586-7
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Internal Southern Ocean Centennial Variability: Dynamics, Impacts and Implications for Global Warming. Climate Change: Multidecadal and Beyond (2015)
    World Scientific Publishing Company
    In:  In: Climate Change: Multidecadal and Beyond. , ed. by Chang, C. P., Ghil, M., Latif, M. and Wallace, J. M. World Scientific Series on Asia-Pacific Weather and Climate, 6 . World Scientific Publishing Company, Singapore, pp. 109-124. ISBN 978-981-4579-92-6
    Details
    Publication Date: 2017-05-22
    Description: It is well established that centennial climate variability can be externally forced by, e.g., quasi-oscillatory fluctuations of the solar constant or slowly varying atmospheric aerosol concentrations in association with changes of volcanic activity. Climate models recently suggested that substantial centennial variability can be also produced internally, and different competing mechanisms have been proposed. This paper deals with the internal centennial variability originating in the Southern Ocean Sector simulated by the Kiel Climate Model (KCM). In that model, the Southern Ocean centennial variability (SOCV) is linked to Weddell Sea deep convection activity and drives regional as well as global climate variations, as witnessed, for example, by coherent changes in Antarctic sea ice extent and globally averaged surface air temperature (SAT). Furthermore, the SOCV is associated with changes in deep Southern Ocean temperature in the KCM. Interestingly, a warming of the abyssal Southern Ocean has been observed during the recent decades, suggesting a contribution from SOCV. Another important impact of the SOCV in the model concerns the Atlantic Meridional Overturning Circulation (AMOC). The AMOC strengthens and deepens after the cessation of Weddell Sea deep convection and Antarctic Bottom Water (AABW) formation with a time delay of several decades to a century. Internal North Atlantic sea level variations can be as large as ± 15cm/century in the model with a strong contribution from the SOCV. Such regional sea level variations are of the same order of magnitude as the observed globally averaged 20th century sea level rise amounting to about 15-20cm. Finally, the KCM simulation suggests that the SOCV may have contributed to the current hiatus in global warming through an enhanced deep ocean heat uptake.
    Type: Book chapter , NonPeerReviewed
    Format: text
    DOI: 10.1142/9789814579933_0007
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    OceanRep: Book chapter
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