scholarly journals Southern Ocean Deep Circulation and Heat Uptake in a High-Resolution Climate Model

2016 ◽  
Vol 29 (7) ◽  
pp. 2597-2619 ◽  
Author(s):  
Emily R. Newsom ◽  
Cecilia M. Bitz ◽  
Frank O. Bryan ◽  
Ryan Abernathey ◽  
Peter R. Gent
Keyword(s):  
High Resolution ◽  
Southern Ocean ◽  
Sea Ice ◽  
Climate Model ◽  
Water Mass ◽  
Global Climate Model ◽  
Substantial Reduction ◽  
Meridional Overturning Circulation ◽  
Heat Uptake ◽  
Water Mass Transformation

Abstract The dynamics of the lower cell of the meridional overturning circulation (MOC) in the Southern Ocean are compared in two versions of a global climate model: one with high-resolution (0.1°) ocean and sea ice and the other a lower-resolution (1.0°) counterpart. In the high-resolution version, the lower cell circulation is stronger and extends farther northward into the abyssal ocean. Using the water-mass-transformation framework, it is shown that the differences in the lower cell circulation between resolutions are explained by greater rates of surface water-mass transformation within the higher-resolution Antarctic sea ice pack and by differences in diapycnal-mixing-induced transformation in the abyssal ocean. While both surface and interior transformation processes work in tandem to sustain the lower cell in the control climate, the circulation is far more sensitive to changes in surface transformation in response to atmospheric warming from raising carbon dioxide levels. The substantial reduction in overturning is primarily attributed to reduced surface heat loss. At high resolution, the circulation slows more dramatically, with an anomaly that reaches deeper into the abyssal ocean and alters the distribution of Southern Ocean warming. The resolution dependence of associated heat uptake is particularly pronounced in the abyssal ocean (below 4000 m), where the higher-resolution version of the model warms 4.5 times more than its lower-resolution counterpart.

Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning

2016 ◽  
Vol 9 (8) ◽  
pp. 596-601 ◽  
Author(s):  
Ryan P. Abernathey ◽  
Ivana Cerovecki ◽  
Paul R. Holland ◽  
Emily Newsom ◽  
Matt Mazloff ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Water Mass ◽  
Water Mass Transformation

scholarly journals Sea-ice retreat suggests re-organization of water mass transformation in the Nordic and Barents Seas

2022 ◽  
Vol 13 (1) ◽  
Author(s):  
G. W. K. Moore ◽  
K. Våge ◽  
I. A. Renfrew ◽  
R. S. Pickart
Keyword(s):  
Sea Ice ◽  
Water Mass ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Spatiotemporal Variability ◽  
Warming Climate ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Sea Ice Retreat ◽  
Water Mass Transformation

AbstractWater mass transformation in the Nordic and Barents Seas, triggered by air-sea heat fluxes, is an integral component of the Atlantic Meridional Overturning Circulation (AMOC). These regions are undergoing rapid warming, associated with a retreat in ice cover. Here we present an analysis covering 1950−2020 of the spatiotemporal variability of the air-sea heat fluxes along the region’s boundary currents, where water mass transformation impacts are large. We find there is an increase in the air-sea heat fluxes along these currents that is a function of the currents’ orientation relative to the axis of sea-ice change suggesting enhanced water mass transformation is occurring. Previous work has shown a reduction in heat fluxes in the interior of the Nordic Seas. As a result, a reorganization seems to be underway in where water mass transformation occurs, that needs to be considered when ascertaining how the AMOC will respond to a warming climate.

The Southern Ocean Overturning: Parameterized versus Permitted Eddies

2009 ◽  
Vol 39 (7) ◽  
pp. 1634-1651 ◽  
Author(s):  
Paul Spence ◽  
Oleg A. Saenko ◽  
Michael Eby ◽  
Andrew J. Weaver
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Climate Model ◽  
Global Climate Model ◽  
Horizontal Resolution ◽  
Meridional Overturning Circulation ◽  
Transformation Rate ◽  
Intermediate Water ◽  
Meridional Transport ◽  
Overturning Circulation

Abstract Four versions of the same global climate model, with horizontal resolution ranging from 1.8° × 3.6° to 0.2° × 0.4°, are employed to evaluate the resolution dependence of the Southern Ocean meridional overturning circulation. At coarse resolutions North Atlantic Deep Water tends to upwell diabatically at low latitudes, so that the Southern Ocean is weakly coupled with the rest of the ocean. As resolution increases and eddy effects become less parameterized the interior circulation becomes more adiabatic and deep water increasingly upwells by flowing along isopycnals in the Southern Ocean, despite each model having the same vertical diffusivity profile. Separating the overturning circulation into mean and eddy-induced components demonstrates that both the permitted and the parameterized eddies induce overturning cells in the Southern Ocean with mass fluxes across mean isopycnals. It is found that for some density classes the transformation rate derived from surface buoyancy fluxes can provide a proxy for the net meridional transport in the upper Southern Ocean. Changes in the Southern Ocean overturning in response to poleward-intensifying Southern Hemisphere winds concomitant with increasing atmospheric CO2 through the twenty-first century are also investigated. Results suggest that the circulation associated with the formation of Antarctic Intermediate Water is likely to strengthen, or stay essentially unchanged, rather than to slow down.

Evolving air-sea interaction due to sea-ice retreat points to a re-organisation of water mass transformation in the Nordic and Barents Seas

2021 ◽  
Author(s):  
Kent Moore ◽  
Kjetil Våge ◽  
Ian Renfrew ◽  
Bob Pickart
Keyword(s):  
Sea Ice ◽  
Water Mass ◽  
Critical Role ◽  
Heat Fluxes ◽  
Meridional Overturning Circulation ◽  
Spatiotemporal Variability ◽  
Ice Retreat ◽  
Meridional Overturning ◽  
Sea Ice Retreat ◽  
Water Mass Transformation

<p>The Nordic and Barents Seas play a critical role in the climate system resulting from water mass transformation, triggered by intense air-sea heat fluxes, that is an integral component of the Atlantic Meridional Overturning Circulation (AMOC). These seas are undergoing rapid warming, associated with a retreat in ice cover. Here we present a novel analysis, covering the period 1950-2020, of the spatiotemporal variability of the air-sea heat fluxes along the region’s boundary currents, where the impacts on the water mass transformation are large.  We find that the variability is a function of the relative orientation of the current and the axis of sea-ice change that can result in up to a doubling of the heat fluxes over the period of interest. This implies enhanced water mass transformation is occurring along these currents. In contrast, previous work has shown a reduction in fluxes in the interior sites of the Nordic Seas, where ocean convection is also observed, suggesting that a reorganization may be underway in the nature of the water mass transformation, that needs to be considered when ascertaining how the AMOC will respond to a warming climate.</p>

scholarly journals Impact of Southern Ocean surface conditions on deep ocean circulation during the LGM: a model analysis

2021 ◽  
Vol 17 (3) ◽  
pp. 1139-1159
Author(s):  
Fanny Lhardy ◽  
Nathaëlle Bouttes ◽  
Didier M. Roche ◽  
Xavier Crosta ◽  
Claire Waelbroeck ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Boundary Conditions ◽  
Mass Distribution ◽  
Bottom Water ◽  
Water Mass ◽  
Meridional Overturning Circulation ◽  
Surface Conditions ◽  
Proxy Records ◽  
The Impact

Abstract. Changes in water mass distribution are considered to be a significant contributor to the atmospheric CO2 concentration drop to around 186 ppm recorded during the Last Glacial Maximum (LGM). Yet simulating a glacial Atlantic Meridional Overturning Circulation (AMOC) in agreement with paleotracer data remains a challenge, with most models from previous Paleoclimate Modelling Intercomparison Project (PMIP) phases showing a tendency to simulate a strong and deep North Atlantic Deep Water (NADW) instead of the shoaling inferred from proxy records of water mass distribution. Conversely, the simulated Antarctic Bottom Water (AABW) is often reduced compared to its pre-industrial volume, and the Atlantic Ocean stratification is underestimated with respect to paleoproxy data. Inadequate representation of surface conditions, driving deep convection around Antarctica, may explain inaccurately simulated bottom water properties in the Southern Ocean. We investigate here the impact of a range of surface conditions in the Southern Ocean in the iLOVECLIM model using nine simulations obtained with different LGM boundary conditions associated with the ice sheet reconstruction (e.g., changes of elevation, bathymetry, and land–sea mask) and/or modeling choices related to sea-ice export, formation of salty brines, and freshwater input. Based on model–data comparison of sea-surface temperatures and sea ice, we find that only simulations with a cold Southern Ocean and a quite extensive sea-ice cover show an improved agreement with proxy records of sea ice, despite systematic model biases in the seasonal and regional patterns. We then show that the only simulation which does not display a much deeper NADW is obtained by parameterizing the sinking of brines along Antarctica, a modeling choice reducing the open-ocean convection in the Southern Ocean. These results highlight the importance of the representation of convection processes, which have a large impact on the water mass properties, while the choice of boundary conditions appears secondary for the model resolution and variables considered in this study.

Southern Ocean sea ice and its wider linkages: insights revealed from models and observations

2004 ◽  
Vol 16 (4) ◽  
pp. 387-400 ◽  
Author(s):  
CLAIRE L. PARKINSON
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Polar Region ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Polar Regions ◽  
Sea Ice Extent ◽  
Positive Feedbacks ◽  
Enhanced Sensitivity

Early conceptual models and global climate model (GCM) simulations both indicated the likelihood of an enhanced sensitivity to climate change in the polar regions, derived from the positive feedbacks brought about by snow and ice. As GCMs developed, however, the expected enhanced sensitivity has been more robust in the North Polar Region than the South Polar Region. Some recent increased-CO2 simulations, for instance, show little change in Southern Ocean sea ice extent and thickness and much less warming in the Southern Ocean region than in the sea ice regions of the Northern Hemisphere. Observations show a highly variable Southern Ocean ice cover that decreased significantly in the 1970s but, overall, has increased since the late 1970s. The increases are non-uniform, and in fact decreases occurred in the last three years of the 1979–2002 satellite record highlighted here. Regionally, the positive trends since the late 1970s are strongest in the Ross Sea, while the trends are negative in the Bellingshausen and Amundsen seas, a pattern that appears in greater spatial detail in maps of trends in the length of the sea ice season. These patterns correspond well with patterns of temperature trends, but there is a substantial way to go before they are understood (and can be modelled) in the full context of global change.

scholarly journals Impacts of Ice-Shelf Melting on Water-Mass Transformation in the Southern Ocean from E3SM Simulations

2020 ◽  
Vol 33 (13) ◽  
pp. 5787-5807
Author(s):  
Hyein Jeong ◽  
Xylar S. Asay-Davis ◽  
Adrian K. Turner ◽  
Darin S. Comeau ◽  
Stephen F. Price ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Water Mass ◽  
Dominant Role ◽  
Heat Fluxes ◽  
Ice Formation ◽  
Ice Shelf ◽  
Overturning Circulation ◽  
Antarctic Sea Ice ◽  
Water Mass Transformation

AbstractThe Southern Ocean overturning circulation is driven by winds, heat fluxes, and freshwater sources. Among these sources of freshwater, Antarctic sea ice formation and melting play the dominant role. Even though ice-shelf melt is relatively small in magnitude, it is located close to regions of convection, where it may influence dense water formation. Here, we explore the impacts of ice-shelf melting on Southern Ocean water-mass transformation (WMT) using simulations from the Energy Exascale Earth System Model (E3SM) both with and without the explicit representation of melt fluxes from beneath Antarctic ice shelves. We find that ice-shelf melting enhances transformation of Upper Circumpolar Deep Water, converting it to lower density values. While the overall differences in Southern Ocean WMT between the two simulations are moderate, freshwater fluxes produced by ice-shelf melting have a further, indirect impact on the Southern Ocean overturning circulation through their interaction with sea ice formation and melting, which also cause considerable upwelling. We further find that surface freshening and cooling by ice-shelf melting cause increased Antarctic sea ice production and stronger density stratification near the Antarctic coast. In addition, ice-shelf melting causes decreasing air temperature, which may be directly related to sea ice expansion. The increased stratification reduces vertical heat transport from the deeper ocean. Although the addition of ice-shelf melting processes leads to no significant changes in Southern Ocean WMT, the simulations and analysis conducted here point to a relationship between increased Antarctic ice-shelf melting and the increased role of sea ice in Southern Ocean overturning.

Mechanisms of Southern Ocean Heat Uptake and Transport in a Global Eddying Climate Model

2016 ◽  
Vol 29 (6) ◽  
pp. 2059-2075 ◽  
Author(s):  
Adele K. Morrison ◽  
Stephen M. Griffies ◽  
Michael Winton ◽  
Whit G. Anderson ◽  
Jorge L. Sarmiento
Keyword(s):  
Southern Ocean ◽  
Heat Transport ◽  
Climate Model ◽  
Heat Budget ◽  
Global Climate Model ◽  
Heat Content ◽  
Ocean Heat Uptake ◽  
The North ◽  
Heat Uptake ◽  
Mixed Layers

Abstract The Southern Ocean plays a dominant role in anthropogenic oceanic heat uptake. Strong northward transport of the heat content anomaly limits warming of the sea surface temperature in the uptake region and allows the heat uptake to be sustained. Using an eddy-rich global climate model, the processes controlling the northward transport and convergence of the heat anomaly in the midlatitude Southern Ocean are investigated in an idealized 1% yr−1 increasing CO2 simulation. Heat budget analyses reveal that different processes dominate to the north and south of the main convergence region. The heat transport northward from the uptake region in the south is driven primarily by passive advection of the heat content anomaly by the existing time mean circulation, with a smaller 20% contribution from enhanced upwelling. The heat anomaly converges in the midlatitude deep mixed layers because there is not a corresponding increase in the mean heat transport out of the deep mixed layers northward into the mode waters. To the north of the deep mixed layers, eddy processes drive the warming and account for nearly 80% of the northward heat transport anomaly. The eddy transport mechanism results from a reduction in both the diffusive and advective southward eddy heat transports, driven by decreasing isopycnal slopes and decreasing along-isopycnal temperature gradients on the northern edge of the peak warming.

scholarly journals Using Eulerian and Lagrangian Approaches to Investigate Wind-Driven Changes in the Southern Ocean Abyssal Circulation

2013 ◽  
Vol 44 (2) ◽  
pp. 662-675 ◽  
Author(s):  
Paul Spence ◽  
Erik van Sebille ◽  
Oleg A. Saenko ◽  
Matthew H. England
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Climate Model ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Lagrangian Particle ◽  
Stress Changes ◽  
Abyssal Circulation ◽  
Flow Pathways ◽  
Ocean Wind

Abstract This study uses a global ocean eddy-permitting climate model to explore the export of abyssal water from the Southern Ocean and its sensitivity to projected twenty-first-century poleward-intensifying Southern Ocean wind stress. The abyssal flow pathways and transport are investigated using a combination of Lagrangian and Eulerian techniques. In an Eulerian format, the equator- and poleward flows within similar abyssal density classes are increased by the wind stress changes, making it difficult to explicitly diagnose changes in the abyssal export in a meridional overturning circulation framework. Lagrangian particle analyses are used to identify the major export pathways of Southern Ocean abyssal waters and reveal an increase in the number of particles exported to the subtropics from source regions around Antarctica in response to the wind forcing. Both the Lagrangian particle and Eulerian analyses identify transients as playing a key role in the abyssal export of water from the Southern Ocean. Wind-driven modifications to the potential energy component of the vorticity balance in the abyss are also found to impact the Southern Ocean barotropic circulation.

High-Resolution Climate Change Impact Analysis on Expected Future Water Availability in the Upper Jordan Catchment and the Middle East

2014 ◽  
Vol 15 (4) ◽  
pp. 1517-1531 ◽  
Author(s):  
Gerhard Smiatek ◽  
Harald Kunstmann ◽  
Andreas Heckl
Keyword(s):  
Climate Change ◽  
High Resolution ◽  
Water Availability ◽  
Impact Analysis ◽  
River Flow ◽  
Climate Model ◽  
Mesoscale Model ◽  
Global Climate Model ◽  
Full Range ◽  
The Impact

Abstract The impact of climate change on the future water availability of the upper Jordan River (UJR) and its tributaries Dan, Snir, and Hermon located in the eastern Mediterranean is evaluated by a highly resolved distributed approach with the fifth-generation Pennsylvania State University–NCAR Mesoscale Model (MM5) run at 18.6- and 6.2-km resolution offline coupled with the Water Flow and Balance Simulation Model (WaSiM). The MM5 was driven with NCEP reanalysis for 1971–2000 and with Hadley Centre Coupled Model, version 3 (HadCM3), GCM forcings for 1971–2099. Because only one regional–global climate model combination was applied, the results may not give the full range of possible future projections. To describe the Dan spring behavior, the hydrological model was extended by a bypass approach to allow the fast discharge components of the Snir to enter the Dan catchment. Simulation results for the period 1976–2000 reveal that the coupled system was able to reproduce the observed discharge rates in the partially karstic complex terrain to a reasonable extent with the high-resolution 6.2-km meteorological input only. The performed future climate simulations show steadily rising temperatures with 2.2 K above the 1976–2000 mean for the period 2031–60 and 3.5 K for the period 2070–99. Precipitation trends are insignificant until the middle of the century, although a decrease of approximately 12% is simulated. For the end of the century, a reduction in rainfall ranging between 10% and 35% can be expected. Discharge in the UJR is simulated to decrease by 12% until 2060 and by 26% until 2099, both related to the 1976–2000 mean. The discharge decrease is associated with a lower number of high river flow years.

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