scholarly journals Understanding why the volume of suboxic waters does not increase over centuries of global warming in an Earth System Model

2012 ◽  
Vol 9 (3) ◽  
pp. 1159-1172 ◽  
Author(s):  
A. Gnanadesikan ◽  
J. P. Dunne ◽  
J. John
Keyword(s):  
Global Warming ◽  
Dissolved Oxygen ◽  
Lateral Diffusion ◽  
Earth System Model ◽  
System Model ◽  
Oxygen Solubility ◽  
Earth System ◽  
Eddy Transport ◽  
Term Analysis ◽  
The Tropical Pacific

Abstract. Global warming is expected to reduce oxygen solubility and vertical exchange in the ocean, changes which would be expected to result in an increase in the volume of hypoxic waters. A simulation made with a full Earth System model with dynamical atmosphere, ocean, sea ice and biogeochemical cycling (the Geophysical Fluid Dynamics Laboratory's Earth System Model 2.1) shows that this holds true if the condition for hypoxia is set relatively high. However, the volume of the most hypoxic (i.e., suboxic) waters does not increase under global warming, as these waters actually become more oxygenated. We show that the rise in dissolved oxygen in the tropical Pacific is associated with a drop in ventilation time. A term-by-term analysis within the least oxygenated waters shows an increased supply of dissolved oxygen due to lateral diffusion compensating an increase in remineralization within these highly hypoxic waters. This lateral diffusive flux is the result of an increase of ventilation along the Chilean coast, as a drying of the region under global warming opens up a region of wintertime convection in our model. The results highlight the potential sensitivity of suboxic waters to changes in subtropical ventilation as well as the importance of constraining lateral eddy transport of dissolved oxygen in such waters.

scholarly journals Will open ocean oxygen stress intensify under climate change?

2011 ◽  
Vol 8 (4) ◽  
pp. 7007-7032
Author(s):  
A. Gnanadesikan ◽  
J. P. Dunne ◽  
J. John
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Sea Ice ◽  
Lateral Diffusion ◽  
System Model ◽  
Oxygen Solubility ◽  
Diffusive Flux ◽  
Earth System ◽  
Oxygen Stress ◽  
Term Analysis

Abstract. Global warming is expected to reduce oxygen solubility and vertical exchange in the ocean, changes which would be expected to result in an increase in the volume of hypoxic waters. A simulation made with a full earth system model with dynamical atmosphere, ocean, sea ice and biogeochemical cycling shows that this holds true if the condition for hypoxia is set relatively high. However, the volume of the most hypoxic waters does not increase under global warming, as these waters actually become more oxygenated. We show that the rise in oxygen is associated with a drop in ventilation time. A term-by-term analysis within the least oxygenated waters shows an increased supply of oxygen due to lateral diffusion. compensating an increase in remineralization within these highly hypoxic waters. This lateral diffusive flux is the result of an increase of ventilation along the Chilean coast, as a drying of the region under global warming opens up a region of wintertime convection in our model.

scholarly journals Implementation of methane cycling for deep time, global warming simulations with the DCESS Earth System Model (Version 1.2)

2017 ◽  
Author(s):  
Gary Shaffer ◽  
Esteban Fernández Villanueva ◽  
Roberto Rondanelli ◽  
Jens Olaf Pepke Pedersen ◽  
Steffen Malskær Olsen ◽  
...  
Keyword(s):  
Global Warming ◽  
Time Scales ◽  
Sediment Cores ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Deep Time ◽  
Methane Cycling ◽  
Model Version ◽  
Ocean Atmosphere

Abstract. Geological records reveal a number of ancient, large and rapid negative excursions of carbon-13 isotope. Such excursions can only be explained by massive injections of depleted carbon to the Earth System over a short duration. These injections may have forced strong global warming events, sometimes accompanied by mass extinctions, for example the Triassic-Jurassic and End-Permian extinctions, 201 and 252 million years ago. In many cases evidence points to methane as the dominant form of injected carbon, whether as thermogenic methane, formed by magma intrusions through overlying carbon-rich sediment, or from warming-induced dissociation of methane hydrate, a solid compound of methane and water found in ocean sediments. As a consequence of the ubiquity and importance of methane in major Earth events, Earth System models should include a comprehensive treatment of methane cycling but such a treatment has often been lacking. Here we implement methane cycling in the Danish Center for Earth System Science (DCESS) model, a simplified but well-tested Earth System Model of Intermediate Complexity. We use a generic methane input function that allows variation of input type, size, time scale and ocean-atmosphere partition. To be able to treat such massive inputs more correctly, we extend the model to deal with ocean suboxic/anoxic conditions and with radiative forcing and methane lifetimes appropriate for high atmospheric methane concentrations. With this new model version, we carried out an extensive set of simulations for methane inputs of various sizes, time scales and ocean-atmosphere partitions to probe model behaviour. We find that larger methane inputs over shorter time scales with more methane dissolving in the ocean lead to ever-increasing ocean anoxia with consequences for ocean life and global carbon cycling. Greater methane input directly to the atmosphere leads to more warming and, for example, greater carbon dioxide release from land soils. Analysis of synthetic sediment cores from the simulations provides guidelines for the interpretation of real sediment cores spanning the warming events. With this improved DCESS model version and paleo-reconstructions, we are now better armed to gauge the amounts, types, time scales and locations of methane injections driving specific, observed deep time, global warming events.

Can ocean deoxygenation accelerate global warming via enhanced marine N2O production?

2020 ◽  
Author(s):  
Angela Landolfi ◽  
Wolfgang Koeve
Keyword(s):  
Global Warming ◽  
Ocean Circulation ◽  
Positive Feedback ◽  
Emission Scenario ◽  
Earth System Model ◽  
System Model ◽  
Metabolic Rates ◽  
Earth System ◽  
N2o Production ◽  
Ocean Deoxygenation

<p>Ocean warming is projected to cause marine deoxygenation, reduce solubility, affect ocean circulation and enhance metabolic rates over this century. These changes, affecting oceanic N<sub>2</sub>O production and emissions, have been suggested to potentially rise atmospheric N<sub>2</sub>O concentrations and increase the positive feedback to anthropogenic climate change.However, current global model projections all suggest a decline in marine N<sub>2</sub>O emissions under global warming but the processes leading to this decline are poorly constrained. Here, using an Earth system model of intermediate complexity, we disentangle the contribution of ocean deoxygenation and the direct and indirect warming effects on oceanic N<sub>2</sub>O production and emissions changes under RCP8.5 emission scenario. We find that ocean deoxygenation and warming-reduced N<sub>2</sub>O solubility do in fact increase oceanic N<sub>2</sub>O emissions, however this increase is overcompensated by ocean circulation slow-down and reduced export production, suggesting a neglectable N<sub>2</sub>O-emssion feedback to climate on centennial timescales.</p>

scholarly journals Climate and land use change impacts on global terrestrial ecosystems and river flows in the HadGEM2-ES Earth system model using the representative concentration pathways

2015 ◽  
Vol 12 (5) ◽  
pp. 1317-1338 ◽  
Author(s):  
R. A. Betts ◽  
N. Golding ◽  
P. Gonzalez ◽  
J. Gornall ◽  
R. Kahana ◽  
...  
Keyword(s):  
Climate Change ◽  
Global Warming ◽  
Land Cover ◽  
Land Cover Change ◽  
21St Century ◽  
Terrestrial Ecosystems ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Impacts Of Climate Change

Abstract. A new generation of an Earth system model now includes a number of land-surface processes directly relevant to analyzing potential impacts of climate change. This model, HadGEM2-ES, allows us to assess the impacts of climate change, multiple interactions, and feedbacks as the model is run. This paper discusses the results of century-scale HadGEM2-ES simulations from an impacts perspective – specifically, terrestrial ecosystems and water resources – for four different scenarios following the representative concentration pathways (RCPs), used in the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC, 2013, 2014). Over the 21st century, simulated changes in global and continental-scale terrestrial ecosystems due to climate change appear to be very similar in all 4 RCPs, even though the level of global warming by the end of the 21st century ranges from 2 °C in the lowest scenario to 5.5° in the highest. A warming climate generally favours broadleaf trees over needleleaf, needleleaf trees over shrubs, and shrubs over herbaceous vegetation, resulting in a poleward shift of temperate and boreal forests and woody tundra in all scenarios. Although climate related changes are slightly larger in scenarios of greater warming, the largest differences between scenarios arise at regional scales as a consequence of different patterns of anthropogenic land cover change. In the model, the scenario with the lowest global warming results in the most extensive decline in tropical forest cover due to a large expansion of agriculture. Under all four RCPs, fire potential could increase across extensive land areas, particularly tropical and sub-tropical latitudes. River outflows are simulated to increase with higher levels of CO2 and global warming in all projections, with outflow increasing with mean temperature at the end of the 21st century at the global scale and in North America, Asia, and Africa. In South America, Europe, and Australia, the relationship with climate warming and CO2 rise is less clear, probably as a result of land cover change exerting a dominant effect in those regions.

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