scholarly journals <sup>14</sup>C-age tracers in global ocean circulation models

2014 ◽  
Vol 7 (5) ◽  
pp. 7033-7074 ◽  
Author(s):  
W. Koeve ◽  
H. Wagner ◽  
P. Kähler ◽  
A. Oschlies
Keyword(s):  
Gas Exchange ◽  
Ocean Circulation ◽  
Model Evaluation ◽  
Global Ocean ◽  
Exchange Constant ◽  
Model Parameters ◽  
Water Age ◽  
14C Age ◽  
Ocean Models ◽  
Global Ocean Circulation

Abstract. The natural abundance of 14C in total CO2 dissolved in seawater is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, the time elapsed since a body of water had contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with aging, i.e. the time component of circulation and one associated with a "preformed 14C-age". This latter quantity exists because of the slow and incomplete atmosphere/ocean equilibration of 14C in particular in high latitudes where many water masses form. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability, e.g. in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. In the Atlantic, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age alone. Between models the variability of age can also be considerable (factor of 2), related to the combinations of physical model parameters, which influence circulation dynamics, and gas exchange in the models. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation exercise, the choice of the gas exchange constant from within the current range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age it could easily impair the evaluation and tuning of a models circulation on global and regional scales. Based on the results of this study, we propose that considering preformed 14C-age is critical for a correct assessment of circulation in ocean models.

scholarly journals <sup>14</sup>C-age tracers in global ocean circulation models

2015 ◽  
Vol 8 (7) ◽  
pp. 2079-2094 ◽  
Author(s):  
W. Koeve ◽  
H. Wagner ◽  
P. Kähler ◽  
A. Oschlies
Keyword(s):  
Gas Exchange ◽  
Ocean Circulation ◽  
Model Evaluation ◽  
Global Ocean ◽  
Exchange Constant ◽  
Model Parameters ◽  
Water Age ◽  
14C Age ◽  
Ocean Models ◽  
Global Ocean Circulation

Abstract. The natural abundance of 14C in total CO2 dissolved in seawater (DIC) is a property applied to evaluate the water age structure and circulation in the ocean and in ocean models. In this study we use three different representations of the global ocean circulation augmented with a suite of idealised tracers to study the potential and limitations of using natural 14C to determine water age, which is the time elapsed since a body of water has been in contact with the atmosphere. We find that, globally, bulk 14C-age is dominated by two equally important components, one associated with ageing, i.e. the time component of circulation, and one associated with a "preformed 14C-age". The latter quantity exists because of the slow and incomplete atmosphere–ocean equilibration of 14C particularly in high latitudes where many water masses form. In the ocean's interior, preformed 14C-age behaves like a passive tracer. The relative contribution of the preformed component to bulk 14C-age varies regionally within a given model, but also between models. Regional variability in the Atlantic Ocean is associated with the mixing of waters with very different end members of preformed 14C-age. Here, variations in the preformed component over space and time mask the circulation component to an extent that its patterns are not detectable from bulk 14C-age. Between models, the variability of preformed 14C-age can also be considerable (factor of 2), related to the combination of physical model parameters, which influence circulation dynamics or gas exchange. The preformed component was found to be very sensitive to gas exchange and moderately sensitive to ice cover. In our model evaluation, the choice of the gas-exchange constant from within the currently accepted range of uncertainty had such a strong influence on preformed and bulk 14C-age that if model evaluation would be based on bulk 14C-age, it could easily impair the evaluation and tuning of a model's circulation on global and regional scales. Based on the results of this study, we propose that considering preformed 14C-age is critical for a correct assessment of circulation in ocean models.

scholarly journals Double-diffusive mixing makes a small contribution to the global ocean circulation

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Carine G. van der Boog ◽  
Henk A. Dijkstra ◽  
Julie D. Pietrzak ◽  
Caroline A. Katsman
Keyword(s):  
Ocean Circulation ◽  
Mechanical Energy ◽  
Global Ocean ◽  
Small Contribution ◽  
Global Ocean Circulation ◽  
Diffusive Fluxes ◽  
Diffusive Mixing ◽  
Diffusive Processes ◽  
Flowing Waters ◽  
Double Diffusive

AbstractDouble-diffusive processes enhance diapycnal mixing of heat and salt in the open ocean. However, observationally based evidence of the effects of double-diffusive mixing on the global ocean circulation is lacking. Here we analyze the occurrence of double-diffusive thermohaline staircases in a dataset containing over 480,000 temperature and salinity profiles from Argo floats and Ice-Tethered Profilers. We show that about 14% of all profiles contains thermohaline staircases that appear clustered in specific regions, with one hitherto unknown cluster overlying the westward flowing waters of the Tasman Leakage. We estimate the combined contribution of double-diffusive fluxes in all thermohaline staircases to the global ocean’s mechanical energy budget as 7.5 GW [0.1 GW; 32.8 GW]. This is small compared to the estimated energy required to maintain the observed ocean stratification of roughly 2 TW. Nevertheless, we suggest that the regional effects, for example near Australia, could be pronounced.

The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation

2020 ◽  
Vol 33 (6) ◽  
pp. 2111-2130
Author(s):  
Woo Geun Cheon ◽  
Jong-Seong Kug
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
North Pacific ◽  
Global Ocean ◽  
The North ◽  
Westerly Winds ◽  
The North Atlantic ◽  
Global Ocean Circulation ◽  
The Antarctic ◽  
The North Pacific

AbstractIn the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circulation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven teleconnection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre). The North Atlantic Deep Water (NADW) formation is controlled by salt advected northward by the North Atlantic WBC.

scholarly journals Impact of partial steps and momentum advection schemes in a global ocean circulation model at eddy-permitting resolution

2006 ◽  
Vol 56 (5-6) ◽  
pp. 543-567 ◽  
Author(s):  
Barnier Bernard ◽  
Gurvan Madec ◽  
Thierry Penduff ◽  
Jean-Marc Molines ◽  
Anne-Marie Treguier ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Ocean Circulation Model ◽  
Advection Schemes ◽  
Global Ocean Circulation

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

2021 ◽  
Author(s):  
Ryan Holmes ◽  
Jan Zika ◽  
Stephen Griffies ◽  
Andrew Hogg ◽  
Andrew Kiss ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Horizontal Resolution ◽  
Global Ocean ◽  
Vertical Diffusivity ◽  
Mixing Parameters ◽  
Ocean Models ◽  
Numerical Mixing ◽  
Comparable Magnitude ◽  
Ice Model

&lt;p&gt;Numerical mixing, the physically spurious diffusion of tracers due to the numerical discretization of advection, is known to contribute to biases in ocean circulation models. However, quantifying numerical mixing is non-trivial, with most studies utilizing specifically targeted experiments in idealized settings. Here, we present a precise method based on water-mass transformation for quantifying numerical mixing, including its spatial structure, that can be applied to any conserved variable in global general circulation ocean models. The method is applied to a suite of global MOM5 ocean-sea ice model simulations with differing grid spacings and sub-grid scale parameterizations. In all configurations numerical mixing drives across-isotherm heat transport of comparable magnitude to that associated with explicitly-parameterized mixing. Numerical mixing is prominent at warm temperatures 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 much of the numerical mixing in these regions acts as a proxy for neutral diffusion when it is explicitly absent. Comparison of equivalent (with respect to vertical resolution and explicit mixing parameters) 1/4-degree and 1/10-degree horizontal resolution configurations shows only a modest enhancement in numerical mixing at the eddy-permitting 1/4-degree resolution. Our results provide a detailed view of numerical mixing in ocean models and pave the way for future improvements in numerical methods.&lt;/p&gt;

scholarly journals Viscosity and elasticity: a model intercomparison of ice-shelf bending in an Antarctic grounding zone

2017 ◽  
Vol 63 (240) ◽  
pp. 573-580 ◽  
Author(s):  
CHRISTIAN T. WILD ◽  
OLIVER J. MARSH ◽  
WOLFGANG RACK
Keyword(s):  
Young’S Modulus ◽  
Ocean Circulation ◽  
Young's Modulus ◽  
Viscoelastic Model ◽  
Ice Sheet ◽  
Global Ocean ◽  
Elastic Model ◽  
Ice Shelf ◽  
Bending Stresses ◽  
Global Ocean Circulation

ABSTRACTGrounding zones are vital to ice-sheet mass balance and its coupling to the global ocean circulation. Processes here determine the mass discharge from the grounded ice sheet, to the floating ice shelves. The response of this transition zone to tidal forcing has been described by both elastic and viscoelastic models. Here we examine the validity of these models for grounding zone flexure over tidal timescales using field data from the Southern McMurdo Ice Shelf (78° 15′S, 167° 7′E). Observations of tidal movement were carried out by simultaneous tiltmeter and GPS measurements along a profile across the grounding zone. Finite-element simulations covering a 64 d period reveal that the viscoelastic model fits best the observations using a Young's modulus of 1.6 GPa and a viscosity of 1013.7 Pa s (≈ 50.1 TPa s). We conclude that the elastic model is only well-constrained for tidal displacements >35% of the spring-tidal amplitude using a Young's modulus of 1.62 ± 0.69 GPa, but that a viscoelastic model is necessary to adequately capture tidal bending at amplitudes below this threshold. In grounding zones where bending stresses are greater than at the Southern McMurdo Ice Shelf or ice viscosity is lower, the threshold would be even higher.

Electromagnetic fields generated by a three dimensional global ocean circulation

1997 ◽  
Vol 102 (C3) ◽  
pp. 5531-5551 ◽  
Author(s):  
Robert H. Tyler ◽  
Lawrence A. Mysak ◽  
Josef M. Oberhuber
Keyword(s):  
Electromagnetic Fields ◽  
Ocean Circulation ◽  
Three Dimensional ◽  
Global Ocean ◽  
Global Ocean Circulation

Eddy formation by dense flows on slopes in a rotating fluid

1998 ◽  
Vol 363 ◽  
pp. 229-252 ◽  
Author(s):  
GREGORY F. LANE-SERFF ◽  
PETER G. BAINES
Keyword(s):  
Ocean Circulation ◽  
Laboratory Experiments ◽  
Lower Layer ◽  
Ekman Layer ◽  
Global Ocean ◽  
Circulation System ◽  
Geostrophic Adjustment ◽  
Viscous Effects ◽  
Dense Fluid ◽  
Global Ocean Circulation

Properties of the flow generated by a continuous source of dense fluid on a slope in a rotating system are investigated with a variety of laboratory experiments. The dense fluid may initially flow down the slope but it turns (under the influence of rotation) to flow along the slope, and initial geostrophic adjustment gives it an anticyclonic velocity profile. Some of the dense fluid drains downslope in a viscous Ekman layer, which may become unstable to growing waves. Provided that the viscous draining is not too strong, cyclonic vortices form periodically in the upper layer and the dense flow breaks up into a series of domes. Three processes may contribute to the formation of these eddies. First, initial downslope flow of the dense current may stretch columns of ambient fluid by the ‘Taylor column’ process (which we term ‘capture’). Secondly, the initial geostrophic adjustment implies lower-layer collapse which may stretch the fluid column, and thirdly, viscous drainage will progressively stretch and spin up a captured water column. Overall this last process may be the most significant, but viscous drainage has contradictory effects, in that it progressively removes dense lower-layer fluid which terminates the process when the layer thickness approaches that of the Ekman layer. The eddies produced propagate along the slope owing to the combined effects of buoyancy–Coriolis balance and ‘beta-gyres’. This removes fluid from the vicinity of the source and causes the cycle to repeat. The vorticity of the upper-layer cyclones increases linearly with Γ=Lα/D (where L is the Rossby deformation radius, α the bottom slope and D the total depth), reaching approximately 2f in the experiments presented here. The frequency at which the eddy/dome structures are produced also increases with Γ, while the speed at which the structures propagate along the slope is reduced by viscous effects. The flow of dense fluid on slopes is a very important part of the global ocean circulation system and the implications of the laboratory experiments for oceanographic flows are discussed.

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