scholarly journals Climate and Ocean Circulation in the Aftermath of a Marinoan Snowball Earth

2021 ◽  
Author(s):  
Lennart Ramme ◽  
Jochem Marotzke
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Co2 Concentration ◽  
Ocean General Circulation Model ◽  
Atmospheric Co2 ◽  
Snowball Earth ◽  
Freshwater Environment ◽  
Atmospheric Co2 Concentration

Abstract. When a snowball Earth deglaciates through a very high atmospheric CO2 concentration, the resulting inflow of freshwater leads to a stably stratified ocean, and the strong greenhouse conditions drive the climate into a very warm state. Here, we use a coupled atmosphere-ocean general circulation model, applying different scenarios for the evolution of atmospheric CO2, to conduct the first simulation of the climate and the three-dimensional ocean circulation in the aftermath of the Marinoan snowball Earth. The simulations show that the strong freshwater stratification breaks up on a timescale in the order of 103 years, mostly independent of the applied CO2 scenario. This is driven by the upwelling of salty waters in high latitudes, mainly the northern hemisphere, where a strong circumpolar current dominates the circulation. In the warmest CO2 scenario, the simulated Marinoan supergreenhouse climate reaches a global mean surface temperature of about 30 °C under an atmospheric CO2 concentration of 15 × 103 parts per million by volume, which is a moderate temperature compared to previous estimates. Consequently, the thermal expansion of seawater causes a sea-level rise of only 8 m, with most of it occurring during the first 3000 years. Our results imply that the surface temperatures of that time were potentially not as threatening for early metazoa as previously assumed. Furthermore, the short destratification timescale found in this study implies a very rapid accumulation of Marinoan cap dolostones, given that they were deposited in a freshwater environment.

scholarly journals Sensitivity of the ocean circulation model to the k–omega vertical turbulence parametrization

2019 ◽  
Vol 55 (5) ◽  
pp. 103-113
Author(s):  
V. B. Zalesny ◽  
S. N. Moshonkin
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Splitting Method ◽  
Three Dimensional ◽  
Numerical Algorithms ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Turbulence Parametrization ◽  
Vertical Turbulence ◽  
Model Equations

Ocean general circulation model (OGCM) of the INM RAS with embedded k turbulent model is developed. The solution of the k model equations depends on the frequencies of buoyancy and velocity shift which are generated by the OGCM. The coefficients of vertical turbulence in OGCM depend on k and omega. The numerical algorithms of both models are based on the splitting method for physical processes. The model equations are split into two stages, describing the three-dimensional transport-diffusion of the kinetic energy of turbulence and frequency and their local generation-dissipation. The system of ordinary differential equations arising at the second stage is solved analytically, which ensures the efficiency of the algorithm. Analytical solution also written for the vertical turbulence coefficient equation. The model is used to study the sensitivity of the model circulation of the North AtlanticArctic Ocean to variations in the parameters of vertical turbulence. Experiments show that varying the coefficients of the analytical model solution can improve the adequacy of the simulation.

scholarly journals Adjoint sensitivities of sub-ice-shelf melt rates to ocean circulation under the Pine Island Ice Shelf, West Antarctica

2012 ◽  
Vol 53 (60) ◽  
pp. 59-69 ◽  
Author(s):  
Patrick Heimbach ◽  
Martin Losch
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Three Dimensional ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Ocean Model ◽  
West Antarctica ◽  
Ice Shelf ◽  
Algorithmic Differentiation ◽  
Freshwater Fluxes

AbstractWe investigate the sensitivity of sub-ice-shelf melt rates under Pine Island Ice Shelf, West Antarctica, to changes in the oceanic state using an adjoint ocean model that is capable of representing the flow in sub-ice-shelf cavities. The adjoint code is based on algorithmic differentiation (AD) of the Massachusetts Institute of Technology’s ocean general circulation model (MITgcm). The adjoint model was extended by adding into the AD process the corresponding sub-ice-shelf cavity code, which implements a three-equation thermodynamic melt-rate parameterization to infer heat and freshwater fluxes at the ice-shelf/ocean boundary. The inferred sensitivities reveal dominant timescales of 30–60 days over which the shelf exit is connected to the deep interior via advective processes. They exhibit rich three-dimensional time-evolving patterns that can be understood in terms of a combination of the buoyancy forcing by inflowing water masses, the cavity geometry and the effect of rotation and topography in steering the flow in the presence of prominent features in the bedrock bathymetry. Dominant sensitivity pathways are found over a sill, as well as ‘shadow regions’ of very low sensitivities. To the extent that these transient patterns are robust they carry important information for decision-making in observation deployment and monitoring.

Modelling the ocean circulation beneath the Ross Ice Shelf

2003 ◽  
Vol 15 (1) ◽  
pp. 13-23 ◽  
Author(s):  
DAVID M. HOLLAND ◽  
STANLEY S. JACOBS ◽  
ADRIAN JENKINS
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Ross Sea ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Shelf Water ◽  
Ice Shelf ◽  
Ross Ice Shelf ◽  
The North ◽  
Ice Shelf Water

We applied a modified version of the Miami isopycnic coordinate ocean general circulation model (MICOM) to the ocean cavity beneath the Ross Ice Shelf to investigate the circulation of ocean waters in the sub-ice shelf cavity, along with the melting and freezing regimes at the base of the ice shelf. Model passive tracers are utilized to highlight the pathways of waters entering and exiting the cavity, and output is compared with data taken in the cavity and along the ice shelf front. High Salinity Shelf Water on the western Ross Sea continental shelf flows into the cavity along the sea floor and is transformed into Ice Shelf Water upon contact with the ice shelf base. Ice Shelf Water flows out of the cavity mainly around 180°, but also further east and on the western side of McMurdo Sound, as observed. Active ventilation of the region near the ice shelf front is forced by seasonal variations in the density structure of the water column to the north, driving rapid melting. Circulation in the more isolated interior is weaker, leading to melting at deeper ice and refreezing beneath shallower ice. Net melting over the whole ice shelf base is lower than other estimates, but is likely to increase as additional forcings are added to the model.

scholarly journals Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model

2011 ◽  
Vol 7 (1) ◽  
pp. 249-263 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot ◽  
R. T. Pierrehumbert ◽  
J. Marotzke
Keyword(s):  
Sea Ice ◽  
Bifurcation Point ◽  
General Circulation ◽  
State Of The Art ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Surface Boundary ◽  
Surface Boundary Conditions ◽  
Global Mean

Abstract. We study the initiation of a Marinoan Snowball Earth (~635 million years before present) with the state-of-the-art atmosphere-ocean general circulation model ECHAM5/MPI-OM. This is the most sophisticated model ever applied to Snowball initiation. A comparison with a pre-industrial control climate shows that the change of surface boundary conditions from present-day to Marinoan, including a shift of continents to low latitudes, induces a global-mean cooling of 4.6 K. Two thirds of this cooling can be attributed to increased planetary albedo, the remaining one third to a weaker greenhouse effect. The Marinoan Snowball Earth bifurcation point for pre-industrial atmospheric carbon dioxide is between 95.5 and 96% of the present-day total solar irradiance (TSI), whereas a previous study with the same model found that it was between 91 and 94% for present-day surface boundary conditions. A Snowball Earth for TSI set to its Marinoan value (94% of the present-day TSI) is prevented by doubling carbon dioxide with respect to its pre-industrial level. A zero-dimensional energy balance model is used to predict the Snowball Earth bifurcation point from only the equilibrium global-mean ocean potential temperature for present-day TSI. We do not find stable states with sea-ice cover above 55%, and land conditions are such that glaciers could not grow with sea-ice cover of 55%. Therefore, none of our simulations qualifies as a "slushball" solution. While uncertainties in important processes and parameters such as clouds and sea-ice albedo suggest that the Snowball Earth bifurcation point differs between climate models, our results contradict previous findings that Snowball Earth initiation would require much stronger forcings.

scholarly journals The Three-Dimensional Steady Circulation in a Homogenous Ocean Induced by a Stationary Hurricane

2010 ◽  
Vol 40 (7) ◽  
pp. 1441-1457 ◽  
Author(s):  
Zhu Min Lu ◽  
Rui Xin Huang
Keyword(s):  
Analytical Solution ◽  
General Circulation ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Coriolis Parameter ◽  
Middle Latitudes ◽  
Oceanic Response ◽  
Stratified Ocean

Abstract Based on the classical Ekman layer theory, a simple analytical solution of the steady flow induced by a stationary hurricane in a homogenous ocean is discussed. The model consists of flow converging in an inward spiral in the deeper layer and diverging in the upper layer. The simple analytical model indicates that both the upwelling flux and the horizontal transport increase linearly with increasing radius of maximum winds. Furthermore, they both have a parabolic relationship with the maximum wind speed. The Coriolis parameter also affects the upwelling flux: the response to a hurricane is stronger at low latitudes than that at middle latitudes. Numerical solutions based on a regional version of an ocean general circulation model are similar to the primary results obtained through the analytical solution. Thus, the simplifications made in formulating the analytical solution are reasonable. Although the analytical solution in this paper is sought for a rather idealized ocean, it can help to make results from the more complicated numerical model understandable. These conceptual models provide a theoretical limit structure of the oceanic response to a moving hurricane over a stratified ocean.

scholarly journals The Role of Rough Topography in Mediating Impacts of Bottom Drag in Eddying Ocean Circulation Models

2017 ◽  
Vol 47 (8) ◽  
pp. 1941-1959 ◽  
Author(s):  
David S. Trossman ◽  
Brian K. Arbic ◽  
David N. Straub ◽  
James G. Richman ◽  
Eric P. Chassignet ◽  
...  
Keyword(s):  
Ocean Circulation ◽  
General Circulation ◽  
Turbulence Models ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Wave Drag ◽  
Flat Bottom ◽  
Length Scales ◽  
Barotropic Flow ◽  
Horizontal Length

AbstractMotivated by the substantial sensitivity of eddies in two-layer quasigeostrophic (QG) turbulence models to the strength of bottom drag, this study explores the sensitivity of eddies in more realistic ocean general circulation model (OGCM) simulations to bottom drag strength. The OGCM results are interpreted using previous results from horizontally homogeneous, two-layer, flat-bottom, f-plane, doubly periodic QG turbulence simulations and new results from two-layer, β-plane QG turbulence simulations run in a basin geometry with both flat and rough bottoms. Baroclinicity in all of the simulations varies greatly with drag strength, with weak drag corresponding to more barotropic flow and strong drag corresponding to more baroclinic flow. The sensitivity of the baroclinicity in the QG basin simulations to bottom drag is considerably reduced, however, when rough topography is used in lieu of a flat bottom. Rough topography reduces the sensitivity of the eddy kinetic energy amplitude and horizontal length scales in the QG basin simulations to bottom drag to an even greater degree. The OGCM simulation behavior is qualitatively similar to that in the QG rough-bottom basin simulations, in that baroclinicity is more sensitive to bottom drag strength than are eddy amplitudes or horizontal length scales. Rough topography therefore appears to mediate the sensitivity of eddies in models to the strength of bottom drag. The sensitivity of eddies to parameterized topographic internal lee wave drag, which has recently been introduced into some OGCMs, is also briefly discussed. Wave drag acts like a strong bottom drag in that it increases the baroclinicity of the flow, without strongly affecting eddy horizontal length scales.

scholarly journals Initiation of a Marinoan Snowball Earth in a state-of-the-art atmosphere-ocean general circulation model

2010 ◽  
Vol 6 (5) ◽  
pp. 1853-1894 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot ◽  
R. T. Pierrehumbert ◽  
J. Marotzke
Keyword(s):  
Carbon Dioxide ◽  
Bifurcation Point ◽  
General Circulation ◽  
Circulation Model ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Surface Boundary ◽  
Surface Boundary Conditions ◽  
Ocean General Circulation ◽  
Global Mean

Abstract. We study the initiation of a Marinoan Snowball Earth (635 million years before present) with the most sophisticated atmosphere-ocean general circulation model ever used for this purpose, ECHAM5/MPI-OM. A comparison with a pre-industrial control climate shows that the change of surface boundary conditions from present-day to Marinoan, including a shift of continents to low latitudes, induces a global mean cooling of 4.6 K. Two thirds of this cooling can be attributed to increased planetary albedo, the remaining one third to a weaker greenhouse effect. The Marinoan Snowball Earth bifurcation point for pre-industrial atmospheric carbon dioxide is between 95.5 and 96% of the present-day total solar irradiance (TSI), whereas a previous study with the same model found that it was between 91 and 94% for present-day surface boundary conditions. A Snowball Earth for TSI set to its Marinoan value (94% of the present-day TSI) is prevented by quadrupling carbon dioxide with respect to its pre-industrial level. A zero-dimensional energy balance model is used to predict the Snowball Earth bifurcation point from only the equilibrium global mean ocean potential temperature for present-day TSI. We do not find stable states with sea-ice cover above 55%, and land conditions are such that glaciers could not grow with sea-ice cover of 55%. Therefore, none of our simulations qualifies as a "slushball" solution. In summary, our results contradict previous claims that Snowball Earth initiation would require "extreme" forcings.

scholarly journals Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

2012 ◽  
Vol 8 (4) ◽  
pp. 2445-2475 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Ice Cover ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Ice Dynamics ◽  
Sea Ice Dynamics

Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare sea ice albedo is assumed because bare sea ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare sea-ice albedo and disabling sea-ice dynamics increase the critical sea-ice cover in ECHAM5/MPI-OM, but sea-ice dynamics have a much larger influence on the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude sea-ice margins. Our results indicate that differences in sea-ice dynamics schemes can be as important as sea ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.

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