Atlantic Ocean Heat Transport Enabled by Indo‐Pacific Heat Uptake and Mixing

Holmes, R. M.; Zika, Jan D.; Ferrari, Raffaele; Thompson, Andrew F.; Newsom, E. R.; England, Matthew H.

doi:10.1029/2019gl085160

Cited by 22 publications

(33 citation statements)

References 50 publications

(87 reference statements)

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“…11 (cf. Jansen et al 2018;Thompson et al 2019). This deepening of the isopycnals is consistent with the reduced gravity model and could contribute substantially to the warming in these two basins, particularly in the intermediate depths (Figs.…”

Section: B Transient Response Of the Amoc In A Warming Climatesupporting

confidence: 82%

“…For example, as T NADW weakens, the interface deepens, and the Southern Ocean isopycnal slope steepens. This strengthens the eddy component of the Southern Ocean overturning, which implies less dense water is transformed into lighter (upper layer) waters (Thompson et al 2019). This change in the transformation rate relieves the burden on the Indo-Pacific to accommodate changes in the Atlantic overturning.…”

Section: A Summary Of Response Mechanismsmentioning

confidence: 92%

“…However, previous studies have suggested that the surface buoyancy forcing is dominated by surface freshwater flux in the Southern Ocean (e.g., Abernathey et al 2016;Sun et al 2016), which may be better represented as a surface buoyancy flux boundary condition. With a fixed surface buoyancy flux in the Southern Ocean, the outcropping position of isopycnals have more freedom to migrate meridionally (Thompson et al 2019). This might suggest a different response time scale for the Southern Ocean transport from Eq.…”

Section: Impact Of Surface Buoyancy Conditionsmentioning

confidence: 99%

“…(27) also assumes a constant outcropping position of the interface in the Southern Ocean. Thompson et al (2019) used a box model with fixed Southern Ocean surface buoyancy fluxes, which allows the outcropping position to move meridionally, and they found a shorter but still multicentennial time scale for adjustment of the isopycnal depth. The impact of having a fixed surface buoyancy is discussed in section 5.…”

Section: A Transient Response To a Step Change In Nadw Formationmentioning

confidence: 99%

“…Interbasin exchange between the Atlantic Ocean and the Indo-Pacific Ocean has increasingly been identified as a critical component in determining deep ocean stratification and watermass transformation rates (e.g., Jones and Cessi 2016;Thompson et al 2016;Ferrari et al 2017). Recent studies have also highlighted the importance of interbasin exchange in closing heat and buoyancy budgets between the Atlantic and Indo-Pacific basins (Newsom and Thompson 2018;Holmes et al 2019). However, to our knowledge, the role of this interbasin exchange in the transient evolution of the global ocean overturning circulation has not previously been investigated.…”

Section: Introductionmentioning

confidence: 99%

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Transient Overturning Compensation between Atlantic and Indo-Pacific Basins

Sun

Thompson

Eisenman

2020

Journal of Physical Oceanography

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Climate models consistently project (i) a decline in the formation of North Atlantic Deep Water (NADW) and (ii) a strengthening of the Southern Hemisphere westerly winds in response to anthropogenic greenhouse gas forcing. These two processes suggest potentially conflicting tendencies of the Atlantic meridional overturning circulation (AMOC): a weakening AMOC due to changes in the North Atlantic but a strengthening AMOC due to changes in the Southern Ocean. Here we focus on the transient evolution of the global ocean overturning circulation in response to a perturbation to the NADW formation rate. We propose that the adjustment of the Indo-Pacific overturning circulation is a critical component in mediating AMOC changes. Using a hierarchy of ocean and climate models, we show that the Indo-Pacific overturning circulation provides the first response to AMOC changes through wave processes, whereas the Southern Ocean overturning circulation responds on longer (centennial to millennial) time scales that are determined by eddy diffusion processes. Changes in the Indo-Pacific overturning circulation compensate AMOC changes, which allows the Southern Ocean overturning circulation to evolve independently of the AMOC, at least over time scales up to many decades. In a warming climate, the Indo-Pacific develops an overturning circulation anomaly associated with the weakening AMOC that is characterized by a northward transport close to the surface and a southward transport in the deep ocean, which could effectively redistribute heat between the basins. Our results highlight the importance of interbasin exchange in the response of the global ocean overturning circulation to a changing climate.

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Section: B Transient Response Of the Amoc In A Warming Climatesupporting

confidence: 82%

Section: A Summary Of Response Mechanismsmentioning

confidence: 92%

Section: Impact Of Surface Buoyancy Conditionsmentioning

confidence: 99%

Section: A Transient Response To a Step Change In Nadw Formationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Transient Overturning Compensation between Atlantic and Indo-Pacific Basins

Sun

Thompson

Eisenman

2020

Journal of Physical Oceanography

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The geography of numerical mixing in a suite of global ocean models

Holmes

Zika

Griffies³

et al. 2020

Preprint

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Numerical ocean general circulation models are useful tools for studying ocean dynamics, interpreting observations and providing predictions of past and future circulation states (Griffies et al., 2009;Fox-Kemper et al., 2019). However, numerical models are necessarily approximate in that they represent continuous physical processes using discrete operators. These discrete representations can impact the accuracy Abstract Numerical mixing, defined here as the physically spurious tracer diffusion due to the numerical discretization of advection, is known to contribute to biases in ocean models. However, quantifying numerical mixing is nontrivial, with most studies utilizing targeted experiments in idealized settings. Here, we present a water mass transformation-based method for quantifying numerical mixing that can be applied to any conserved variable in general circulation models. Furthermore, the method can be applied within individual fluid columns to provide spatial information. We apply the method to a suite of global ocean model simulations with differing grid spacings and subgrid-scale parameterizations. In all configurations numerical mixing drives diathermal heat transport of comparable magnitude to that associated with explicit parameterizations. Numerical mixing is prominent in the tropical thermocline, where it is sensitive to the vertical diffusivity and resolution. At colder temperatures numerical mixing is sensitive to the presence of explicit neutral diffusion, suggesting that it may act as a proxy for neutral diffusion when it is explicitly absent. Comparison of otherwise equivalent 1/4° and 1/10° configurations with grid-scale dependent horizontal viscosity shows only a modest enhancement in numerical mixing at 1/4°. However, if the lateral viscosity is maintained while resolution is increased then numerical mixing is reduced by almost 35%. This result suggests that the common practice of reducing viscosity in order to maximize permitted variability must be considered carefully. Our results provide a detailed view of numerical mixing in ocean models and pave the way for improvements in parameter choices and numerical methods.Plain Language Summary Numerical ocean circulation models are useful tools for studying the ocean's role in climate and providing projections of climate change. However, due to constraints on computational power, numerical models must represent processes that are continuous in the real ocean using discrete approximations. One consequence of such discrete approximations is numerical mixing, whereby seawater transport (a process that should not mix properties such as heat and salt content) results in mixing and exchange of properties with surrounding seawater. Mixing in the ocean interior is weak, and so the presence of additional numerical mixing in ocean models can cause the models to drift away from reality, reducing their accuracy and utility. In this study, we present a new method for quantifying numerical mixing in global ocean models, including its three-dimensional spati...

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The role of mixing in the large-scale ocean circulation

et al. 2022

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Irreversible mixing of tracers and momentum in the ocean occurs via diffusion and friction at the scale of molecules. That such molecular processes profoundly influence basin-scale ocean currents is counter-intuitive. Many successful theories of ocean circulation indeed ignore diffusive and frictional processes. Yet oceanographers have long recognized that turbulence can amplify irreversible mixing and its influence on large-scale flows. In recent years, substantial progress has been made in the mapping of mixing energized by three-dimensional and geostrophic turbulence. This progress not only helps to quantify connections between mixing and observed circulation systems, but also to better characterize these circulation systems. This chapter surveys the rapidly evolving understanding of the impacts of mixing on the strength and structure of major ocean gyres, overturning circulations and the Antarctic Circumpolar Current. Accumulating evidence suggests that global ocean circulation is shaped by energetic mixing near ocean boundaries, while either weak or largely adiabatic away from boundaries.

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Atlantic Ocean Heat Transport Enabled by Indo‐Pacific Heat Uptake and Mixing

Cited by 22 publications

References 50 publications

Transient Overturning Compensation between Atlantic and Indo-Pacific Basins

Transient Overturning Compensation between Atlantic and Indo-Pacific Basins

The geography of numerical mixing in a suite of global ocean models

The role of mixing in the large-scale ocean circulation

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