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Title: Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model

Abstract

The Southern Ocean surface has freshened in recent decades, increasing water column stability and reducing upwelling of warmer subsurface waters. The majority of CMIP5 models underestimate or fail to capture this historical surface freshening, yet little is known about the impact of this model bias on regional ocean circulation and hydrography. Here experiments are performed using a global coupled climate model with additional freshwater applied to the Southern Ocean to assess the influence of recent surface freshening. The simulations explore the impact of persistent and long-term broad-scale freshening as a result of processes including precipitation minus evaporation changes. Thus, unlike previous studies, the freshening is applied as far north as 55°S, beyond the Antarctic ice margin. It is found that imposing a large-scale surface freshening causes a surface cooling and sea ice increase under preindustrial conditions, because of a reduction in ocean convection and weakened entrainment of warm subsurface waters into the surface ocean. This is consistent with intermodel relationships between CMIP5 models and the simulations, suggesting that models with larger surface freshening also exhibit stronger surface cooling and increased sea ice. Additional experiments are conducted with surface salinity restoration applied to capture observed regional salinity trends. Remarkably, without anymore » mechanical wind trend forcing, these simulations accurately represent the spatial pattern of observed surface temperature and sea ice trends around Antarctica. This study highlights the importance of accurately simulating changes in Southern Ocean salinity to capture changes in ocean circulation, sea surface temperature, and sea ice.« less

Authors:
 [1];  [2];  [3];  [3];  [4]
+ Show Author Affiliations
  1. Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Aspendale, Victoria, and Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales, Australia
  2. Climate Change Research Centre and ARC Centre of Excellence for Climate System Science, University of New South Wales, Sydney, New South Wales, Australia
  3. Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Aspendale, Victoria, Australia
  4. Program for Climate Model Diagnosis and Intercomparison, Lawrence Livermore National Laboratory, Livermore, California
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1423729
Alternate Identifier(s):
OSTI ID: 1491637
Report Number(s):
LLNL-JRNL-723879
Journal ID: ISSN 0894-8755
Grant/Contract Number:  
AC52-07NA27344
Resource Type:
Published Article
Journal Name:
Journal of Climate
Additional Journal Information:
Journal Name: Journal of Climate Journal Volume: 31 Journal Issue: 7; Journal ID: ISSN 0894-8755
Publisher:
American Meteorological Society
Country of Publication:
United States
Language:
English
Subject:
54 ENVIRONMENTAL SCIENCES; Antarctica; Southern Ocean; Precipitation; Coupled models

Citation Formats

Purich, Ariaan, England, Matthew H., Cai, Wenju, Sullivan, Arnold, and Durack, Paul J. Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model. United States: N. p., 2018. Web. doi:10.1175/JCLI-D-17-0092.1.
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Purich, Ariaan, England, Matthew H., Cai, Wenju, Sullivan, Arnold, & Durack, Paul J. Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model. United States. https://doi.org/10.1175/JCLI-D-17-0092.1
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Purich, Ariaan, England, Matthew H., Cai, Wenju, Sullivan, Arnold, and Durack, Paul J. Sun . "Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model". United States. https://doi.org/10.1175/JCLI-D-17-0092.1.
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@article{osti_1423729,
title = {Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model},
author = {Purich, Ariaan and England, Matthew H. and Cai, Wenju and Sullivan, Arnold and Durack, Paul J.},
abstractNote = {The Southern Ocean surface has freshened in recent decades, increasing water column stability and reducing upwelling of warmer subsurface waters. The majority of CMIP5 models underestimate or fail to capture this historical surface freshening, yet little is known about the impact of this model bias on regional ocean circulation and hydrography. Here experiments are performed using a global coupled climate model with additional freshwater applied to the Southern Ocean to assess the influence of recent surface freshening. The simulations explore the impact of persistent and long-term broad-scale freshening as a result of processes including precipitation minus evaporation changes. Thus, unlike previous studies, the freshening is applied as far north as 55°S, beyond the Antarctic ice margin. It is found that imposing a large-scale surface freshening causes a surface cooling and sea ice increase under preindustrial conditions, because of a reduction in ocean convection and weakened entrainment of warm subsurface waters into the surface ocean. This is consistent with intermodel relationships between CMIP5 models and the simulations, suggesting that models with larger surface freshening also exhibit stronger surface cooling and increased sea ice. Additional experiments are conducted with surface salinity restoration applied to capture observed regional salinity trends. Remarkably, without any mechanical wind trend forcing, these simulations accurately represent the spatial pattern of observed surface temperature and sea ice trends around Antarctica. This study highlights the importance of accurately simulating changes in Southern Ocean salinity to capture changes in ocean circulation, sea surface temperature, and sea ice.},
doi = {10.1175/JCLI-D-17-0092.1},
journal = {Journal of Climate},
number = 7,
volume = 31,
place = {United States},
year = {Sun Apr 01 00:00:00 EDT 2018},
month = {Sun Apr 01 00:00:00 EDT 2018}
}
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Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
https://doi.org/10.1175/JCLI-D-17-0092.1
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Citation Metrics:
Cited by: 32 works
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Figures / Tables:

Figure 1 Figure 1: Trends over 1950–2000. (a) Observed SSS trends from Durack and Wijffels (2010); (b) zonal-mean SSS trends for observations (Durack and Wijffels 2010) and CMIP5 models; (c) zonal-mean precipitation trends for observations (ERA-Interim, COREv2, GPCPv2.2, CMAP standard, CMAP enhanced) and CMIP5 models; and (d) zonal-mean P–E trends for observationsmore » (ERA-Interim, COREv2) and CMIP5 models. In (a), stippling indicates significance at the 95% level. In (b) observations are shown in dashed black. In (c)–(d) observations are shown in colors, and vary in the time periods they cover (refer to the data and methods section). In (b)–(d) CMIP5 models are shown in grey, and the ACCESS1.0 CMIP5 run is shown in dark blue.« less
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Works referenced in this record:

Argo float data and metadata from Global Data Assembly Centre (Argo GDAC)
dataset, January 2018

  • Fumihiko, Akazawa; Turki, Alraddadi; Pascual, Ananda
  • DOI: 10.17882/42182

Argo float data and metadata from Global Data Assembly Centre (Argo GDAC)
dataset, January 2018

  • Fumihiko, Akazawa; Turki, Alraddadi; Pascual, Ananda
  • DOI: 10.17882/42182
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    Works referencing / citing this record:

    Argo float data and metadata from Global Data Assembly Centre (Argo GDAC)
    dataset, January 2018

    • Fumihiko, Akazawa; Turki, Alraddadi; Pascual, Ananda
    • DOI: 10.17882/42182

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    journal, November 2018

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    • Journal of Geophysical Research: Oceans, Vol. 123, Issue 11
    • DOI: 10.1029/2018jc014528

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    • DOI: 10.1038/s41467-018-07865-9

    The Open-Ocean Side of the Malvinas Current in Argo Floats and 24 Years of Mercator Ocean High-Resolution (1/12) Physical Reanalysis
    journal, November 2018

    • Artana, Camila; Lellouche, Jean-Michel; Sennéchael, Nathalie
    • Journal of Geophysical Research: Oceans, Vol. 123, Issue 11
    • DOI: 10.1029/2018jc014528

    Sustained ocean changes contributed to sudden Antarctic sea ice retreat in late 2016
    journal, January 2019

    • Meehl, Gerald A.; Arblaster, Julie M.; Chung, Christine T. Y.
    • Nature Communications, Vol. 10, Issue 1
    • DOI: 10.1038/s41467-018-07865-9

    The Antarctic Slope Current in a Changing Climate
    journal, December 2018

    • Thompson, Andrew F.; Stewart, Andrew L.; Spence, Paul
    • Reviews of Geophysics, Vol. 56, Issue 4
    • DOI: 10.1029/2018rg000624

    Tropical Teleconnections to Antarctic Sea Ice During Austral Spring 2016 in Coupled Pacemaker Experiments
    journal, June 2019

    • Purich, Ariaan; England, Matthew H.
    • Geophysical Research Letters, Vol. 46, Issue 12
    • DOI: 10.1029/2019gl082671

    The Malvinas Current at the Confluence With the Brazil Current: Inferences From 25 Years of Mercator Ocean Reanalysis
    journal, October 2019

    • Artana, Camila; Provost, Christine; Lellouche, Jean‐Michel
    • Journal of Geophysical Research: Oceans, Vol. 124, Issue 10
    • DOI: 10.1029/2019jc015289

    Compounding tropical and stratospheric forcing of the record low Antarctic sea-ice in 2016
    journal, January 2019

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