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 Southern Ocean Heat Uptake, Redistribution, and Storage in a Warming Climate: The Role of Meridional Overturning Circulation

2018 ◽  
Vol 31 (12) ◽  
pp. 4727-4743 ◽  
Author(s):  
Wei Liu ◽  
Jian Lu ◽  
Shang-Ping Xie ◽  
Alexey Fedorov
Keyword(s):  
Southern Ocean ◽  
Heat Transport ◽  
Climate Models ◽  
Climate Model ◽  
Meridional Overturning Circulation ◽  
The Other ◽  
Anthropogenic Heat ◽  
Overturning Circulation ◽  
Ocean Heat Uptake ◽  
Meridional Overturning

Climate models show that most of the anthropogenic heat resulting from increased atmospheric CO2 enters the Southern Ocean near 60°S and is stored around 45°S. This heat is transported to the ocean interior by the meridional overturning circulation (MOC) with wind changes playing an important role in the process. To isolate and quantify the latter effect, we apply an overriding technique to a climate model and decompose the total ocean response to CO2 increase into two major components: one due to wind changes and the other due to direct CO2 effect. We find that the poleward-intensified zonal surface winds tend to shift and strengthen the ocean Deacon cell and hence the residual MOC, leading to anomalous divergence of ocean meridional heat transport around 60°S coupled to a surface heat flux increase. In contrast, at 45°S we see anomalous convergence of ocean heat transport and heat loss at the surface. As a result, the wind-induced ocean heat storage (OHS) peaks at 46°S at a rate of 0.07 ZJ yr−1 (° lat)−1 (1 ZJ = 1021 J), contributing 20% to the total OHS maximum. The direct CO2 effect, on the other hand, very slightly alters the residual MOC but primarily warms the ocean. It induces a small but nonnegligible change in eddy heat transport and causes OHS to peak at 42°S at a rate of 0.30 ZJ yr−1 (° lat)−1, accounting for 80% of the OHS maximum. We also find that the eddy-induced MOC weakens, primarily caused by a buoyancy flux change as a result of the direct CO2 effect, and does not compensate the intensified Deacon cell.

Evolving Relative Importance of the Southern Ocean and North Atlantic in Anthropogenic Ocean Heat Uptake

2018 ◽  
Vol 31 (18) ◽  
pp. 7459-7479 ◽  
Author(s):  
Jia-Rui Shi ◽  
Shang-Ping Xie ◽  
Lynne D. Talley
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Radiative Forcing ◽  
Meridional Overturning Circulation ◽  
Anthropogenic Heat ◽  
Anthropogenic Aerosols ◽  
Ocean Heat Uptake ◽  
The North ◽  
Heat Uptake ◽  
The North Atlantic

Ocean uptake of anthropogenic heat over the past 15 years has mostly occurred in the Southern Ocean, based on Argo float observations. This agrees with historical simulations from phase 5 of the Coupled Model Intercomparison Project (CMIP5), where the Southern Ocean (south of 30°S) accounts for 72% ± 28% of global heat uptake, while the contribution from the North Atlantic north of 30°N is only 6%. Aerosols preferentially cool the Northern Hemisphere, and the effect on surface heat flux over the subpolar North Atlantic opposes the greenhouse gas (GHG) effect in nearly equal magnitude. This heat uptake compensation is associated with weakening (strengthening) of the Atlantic meridional overturning circulation (AMOC) in response to GHG (aerosol) radiative forcing. Aerosols are projected to decline in the near future, reinforcing the greenhouse effect on the North Atlantic heat uptake. As a result, the Southern Ocean, which will continue to take up anthropogenic heat largely through the mean upwelling of water from depth, will be joined by increased relative contribution from the North Atlantic because of substantial AMOC slowdown in the twenty-first century. In the RCP8.5 scenario, the percentage contribution to global uptake is projected to decrease to 48% ± 8% in the Southern Ocean and increase to 26% ± 6% in the northern North Atlantic. Despite the large uncertainty in the magnitude of projected aerosol forcing, our results suggest that anthropogenic aerosols, given their geographic distributions and temporal trajectories, strongly influence the high-latitude ocean heat uptake and interhemispheric asymmetry through AMOC change.

Northern High-Latitude Heat Budget Decomposition and Transient Warming

2013 ◽  
Vol 26 (2) ◽  
pp. 609-621 ◽  
Author(s):  
Maria A. A. Rugenstein ◽  
Michael Winton ◽  
Ronald J. Stouffer ◽  
Stephen M. Griffies ◽  
Robert Hallberg
Keyword(s):  
Heat Transport ◽  
High Latitude ◽  
Climate Models ◽  
Heat Budget ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Ocean Heat Uptake ◽  
Control Climate ◽  
Wide Range ◽  
Heat Uptake

Abstract Climate models simulate a wide range of climate changes at high northern latitudes in response to increased CO2. They also have substantial disagreement on projected changes of the Atlantic meridional overturning circulation (AMOC). Here, two pairs of closely related climate models are used, with each containing members with large and small AMOC declines to explore the influence of AMOC decline on the high-latitude response to increased CO2. The models with larger AMOC decline have less high-latitude warming and sea ice decline than their small AMOC decline counterpart. By examining differences in the perturbation heat budget of the 40°–90°N region, it is shown that AMOC decline diminishes the warming by weakening poleward ocean heat transport and increasing the ocean heat uptake. The cooling impact of this AMOC-forced surface heat flux perturbation difference is enhanced by shortwave feedback and diminished by longwave feedback and atmospheric heat transport differences. The magnitude of the AMOC decline within model pairs is positively related to the magnitudes of control climate AMOC and Labrador and Nordic Seas convection. Because the 40°–90°N region accounts for up to 40% of the simulated global ocean heat uptake over 100 yr, the process described here influences the global heat uptake efficiency.

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.

scholarly journals Dependence of regional ocean heat uptake on anthropogenic warming scenarios

2020 ◽  
Vol 6 (45) ◽  
pp. eabc0303
Author(s):  
Xiaofan Ma ◽  
Wei Liu ◽  
Robert J. Allen ◽  
Gang Huang ◽  
Xichen Li
Keyword(s):  
Southern Ocean ◽  
North Atlantic ◽  
Meridional Overturning Circulation ◽  
Anthropogenic Aerosols ◽  
Ocean Heat Uptake ◽  
The North ◽  
Heat Uptake ◽  
The North Atlantic ◽  
Aerosol Effects ◽  
Business As Usual

The North Atlantic and Southern Ocean exhibit enhanced ocean heat uptake (OHU) during recent decades while their future OHU changes are subject to great uncertainty. Here, we show that regional OHU patterns in these two basins are highly dependent on the trajectories of aerosols and greenhouse gases (GHGs) in future scenarios. During the 21st century, North Atlantic and Southern Ocean OHU exhibit similarly positive trends under a business-as-usual scenario but respectively positive and negative trends under a mitigation scenario. The opposite centurial OHU trends in the Southern Ocean can be attributed partially to distinct GHG trajectories under the two scenarios while the common positive centurial OHU trends in the North Atlantic are mainly due to aerosol effects. Under both scenarios, projected decline of anthropogenic aerosols potentially induces a weakening of the Atlantic Meridional Overturning Circulation and a divergence of meridional oceanic heat transport, which leads to enhanced OHU in the subpolar North Atlantic.

Recent trajectory of ocean heat uptake estimated from novel 1972-2017 ocean sea-ice model hindcast simulations

2021 ◽  
Author(s):  
Maurice Huguenin ◽  
Ryan Holmes ◽  
Matthew England
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Heat Content ◽  
Anthropogenic Heat ◽  
Global Ocean ◽  
Ocean Heat Uptake ◽  
Heat Uptake ◽  
The Tropics ◽  
And Storage ◽  
Ice Model

<p>Uptake and storage of heat by the ocean plays a critical role in modulating the Earth's climate system. In the last 50 years, the ocean has absorbed over 90% of the additional energy accumulating in the Earth system due to radiative imbalance. However, our knowledge about ocean heat uptake (OHU), transport and storage is strongly constrained by the sparse observational record with large uncertainties. In this study, we conduct a suite of historical 1972–2017 hindcast simulations using a global ocean-sea ice model that are specifically designed to account for a cold start climate and model drift. The hindcast simulations are initialised from an equilibrated control simulation that uses repeat decade forcing over the period 1962-1971. This repeat decade forcing approach is a compromise between an early unobserved period (where our confidence in the forcing is low) and later periods (which would result in a shorter experiment period and a smaller fraction of the total OHU). The simulations are aimed at giving a good estimate of the trajectory of OHU in the tropics, the extratropics and individual ocean basins in recent decades. Many modelling studies that look at recent OHU rates so far use a simpler approach for the forcing. For example, they use repeating cycles of 1950-2010 Coordinated Ocean Reference Experiment (CORE) forcing that is consistent with the Ocean Model Intercomparison Project 2 (OMIP-2). However, this approach cannot account for model drift. The new simulations here highlight the dominant role of the extratropics, and in particular the Southern Ocean in OHU. In contrast, little heat is absorbed in the tropics and simulations forced with only tropical trends in atmospheric forcing show only weak global ocean heat content trends. Almost 50% of the heat taken up from the atmosphere in the Southern Ocean is transported into the Atlantic Ocean. Two-thirds of this Southern Ocean-sourced heat is then subsequently lost to the atmosphere in the North Atlantic but nevertheless this basin gains heat overall. Our results help to estimate the large-scale cycling of anthropogenic heat within the ocean today and have implications for heat content trends under a changing climate.</p>

scholarly journals Contribution of ocean physics and dynamics at different scales to heat uptake in low-resolution AOGCMs

2020 ◽  
pp. 1-62
Author(s):  
Oleg A. Saenko ◽  
Jonathan M. Gregory ◽  
Stephen M. Griffies ◽  
Matthew P. Couldrey ◽  
Fabio Boeira Dias
Keyword(s):  
Climate Change ◽  
General Circulation ◽  
Large Scale ◽  
Heat Budget ◽  
Heat Content ◽  
Ocean Dynamics ◽  
Small Scale ◽  
Upper Ocean ◽  
Ocean Heat Uptake ◽  
Heat Uptake

AbstractUsing an ensemble of atmosphere-ocean general circulation models (AOGCMs) in an idealized climate change experiment, this study quantifies the contributions to ocean heat uptake (OHU) from ocean physical parameterizations and resolved dynamical processes operating at different scales. Analysis of heat budget diagnostics reveals a leading-order global heat balance in the sub-surface upper ocean in a steady state between the large-scale circulation warming it and mesoscale processes cooling it, and shows that there are positive contributions from processes on all scales to the subsurface OHU during climate change. There is better agreement among the AOGCMs in the net OHU than in the individual scales/processes contributing to it. In the upper ocean and at high latitudes, OHU is dominated by small-scale diapycnal processes. Below 400 m, OHU is dominated by the super-residual transport, representing large-scale ocean dynamics combined with all parameterized mesoscale and submesoscale eddy effects. Weakening of the AMOC leads to less heat convergence in the subpolar North Atlantic and less heat divergence at lower latitudes, with a small overall effect on the net Atlantic heat content. At low latitudes, the dominance of advective heat redistribution is contrary to the diffusive OHU mechanism assumed by the commonly used upwelling-diffusion model. Using a density watermass framework, it is found that most of the OHU occurs along isopycnal directions. This feature of OHU is used to accurately reconstruct the global vertical ocean warming profile from the surface heat flux anomalies, supporting advective (rather than diffusive) models of OHU and sea-level rise.

scholarly journals Surging of Global Surface Temperature due to Decadal Legacy of Ocean Heat Uptake

2020 ◽  
Vol 33 (18) ◽  
pp. 8025-8045
Author(s):  
Bablu Sinha ◽  
Florian Sévellec ◽  
Jon Robson ◽  
A. J. George Nurser
Keyword(s):  
Thermal Gradient ◽  
Climate Model ◽  
Heat Budget ◽  
Global Climate ◽  
Global Climate Model ◽  
Vertical Mixing ◽  
Base Layer ◽  
Ocean Heat Uptake ◽  
Surface Warming ◽  
Global Surface

AbstractGlobal surface warming since 1850 has consisted of a series of slowdowns (hiatus) followed by surges. Knowledge of a mechanism to explain how this occurs would aid development and testing of interannual to decadal climate forecasts. In this paper a global climate model is forced to adopt an ocean state corresponding to a hiatus [with negative interdecadal Pacific oscillation (IPO) and other surface features typical of a hiatus] by artificially increasing the background diffusivity for a decade before restoring it to its normal value and allowing the model to evolve freely. This causes the model to develop a decadal surge that overshoots equilibrium (resulting in a positive IPO state), leaving behind a modified, warmer climate for decades. Water-mass transformation diagnostics indicate that the heat budget of the tropical Pacific Ocean is a balance between large opposite-signed terms: surface heating/cooling resulting from air–sea heat flux is balanced by vertical mixing and ocean heat transport divergence. During the artificial hiatus, excess heat becomes trapped just above the thermocline and there is a weak vertical thermal gradient (due to the high artificial background mixing). When the hiatus is terminated, by returning the background diffusivity to normal, the thermal gradient strengthens to prehiatus values so that the mixing (diffusivity × thermal gradient) remains roughly constant. However, since the base layer just above the thermocline remains anomalously warm, this implies a warming of the entire water column above the trapped heat, which results in a surge followed by a prolonged period of elevated surface temperatures.

scholarly journals Atmospheric Responses and Feedback to the Meridional Ocean Heat Transport in the North Pacific

2017 ◽  
Vol 30 (15) ◽  
pp. 5715-5728 ◽  
Author(s):  
Hiroaki Tatebe ◽  
Masao Kurogi ◽  
Hiroyasu Hasumi
Keyword(s):  
Heat Transport ◽  
North Pacific ◽  
Climate Model ◽  
Global Climate ◽  
Global Climate Model ◽  
Storm Track ◽  
Ocean Heat Transport ◽  
The North ◽  
The Mean ◽  
The North Pacific

Atmospheric responses and feedback to meridional ocean heat transport (OHT) have been investigated using a global climate model that is interactively connected with a high-resolution regional ocean model embedded in the western North Pacific. Compared with a global climate model without the regional model, the net heat supply into the Kuroshio–Oyashio Extension (KOE) region is increased as a result of the increase of the mean northward ocean heat transport (OHT) by the western boundary currents and mesoscale eddies. Resultant sea surface temperature (SST) rise sharpens the meridional SST gradient and reinforces the cross-frontal difference of the surface heat flux and thereby enhances lower-tropospheric baroclinicity. These changes cause northward deflection and strengthening of the wintertime storm track over the North Pacific, which leads to the Pacific–North American (PNA)-like pattern anticyclonic response of the mean westerly jet. The increase of the eddy northward atmospheric heat flux (AHF) associated with the enhanced storm-track activity is compensated by the decrease of the mean northward AHF. The changes of the atmospheric circulations reduce the mean northward OHT in the eastern North Pacific that compensates the increase of the mean northward OHT in the KOE region. The atmospheric responses, which have once been excited by the SST fronts in the KOE region, stabilize the trans–North Pacific OHT. The modeling results herein suggest that basinwide Bjerknes-like compensation works in air–sea coupled processes for the formation of the climatic mean state in the North Pacific.

scholarly journals Impacts on Ocean Heat from Transient Mesoscale Eddies in a Hierarchy of Climate Models

2015 ◽  
Vol 28 (3) ◽  
pp. 952-977 ◽  
Author(s):  
Stephen M. Griffies ◽  
Michael Winton ◽  
Whit G. Anderson ◽  
Rusty Benson ◽  
Thomas L. Delworth ◽  
...  
Keyword(s):  
Heat Transport ◽  
Climate Models ◽  
Climate Model ◽  
Heat Budget ◽  
Mesoscale Eddy ◽  
Mesoscale Eddies ◽  
Temperature Drift ◽  
Coupled Models ◽  
Ocean Heat Uptake ◽  
Ocean Climate

Abstract The authors characterize impacts on heat in the ocean climate system from transient ocean mesoscale eddies. Their tool is a suite of centennial-scale 1990 radiatively forced numerical climate simulations from three GFDL coupled models comprising the Climate Model, version 2.0–Ocean (CM2-O), model suite. CM2-O models differ in their ocean resolution: CM2.6 uses a 0.1° ocean grid, CM2.5 uses an intermediate grid with 0.25° spacing, and CM2-1deg uses a nominal 1.0° grid. Analysis of the ocean heat budget reveals that mesoscale eddies act to transport heat upward in a manner that partially compensates (or offsets) for the downward heat transport from the time-mean currents. Stronger vertical eddy heat transport in CM2.6 relative to CM2.5 accounts for the significantly smaller temperature drift in CM2.6. The mesoscale eddy parameterization used in CM2-1deg also imparts an upward heat transport, yet it differs systematically from that found in CM2.6. This analysis points to the fundamental role that ocean mesoscale features play in transient ocean heat uptake. In general, the more accurate simulation found in CM2.6 provides an argument for either including a rich representation of the ocean mesoscale in model simulations of the mean and transient climate or for employing parameterizations that faithfully reflect the role of eddies in both lateral and vertical heat transport.

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