scholarly journals Anthropogenic carbon dynamics in the changing ocean

Ocean Science ◽  
2010 ◽  
Vol 6 (3) ◽  
pp. 605-614 ◽  
Author(s):  
J. F. Tjiputra ◽  
K. Assmann ◽  
C. Heinze
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
High Latitude ◽  
Meridional Overturning Circulation ◽  
Future Climate Change ◽  
Carbon Uptake ◽  
Overturning Circulation ◽  
Anthropogenic Carbon ◽  
Natural Carbon

Abstract. The long-term response of CO2 fluxes to climate change at the ocean surface and within the ocean interior is investigated using a coupled climate-carbon cycle model. This study also presents the first attempt to quantify the evolution of lateral transport of anthropogenic carbon under future climate change. Additionally, its impact on regional carbon storage and uptake is also evaluated. For the 1850–2099 period, our climate change simulation predicts oceanic uptake of anthropogenic carbon of about 538±23 Pg C. Another simulation indicates that changes in physical climate and its associated biogeochemical feedbacks result in a release of natural carbon of about 22±30 Pg C. The natural carbon outgassing is attributed to the reduction in solubility and change in wind pattern in the Southern Hemisphere. After the anthropogenic carbon passes through the air-sea interface, it is predominantly transported along the large scale overturning circulation below the surface layer. The spatial variations in the transport patterns in turn influence the evolution of future regional carbon uptake. In the North Atlantic, a slow down in the Atlantic Meridional Overturning Circulation weakens the penetration strength of anthropogenic carbon into the deeper ocean, which leads to a reduced uptake rate in this region. In contrast, more than half of the anthropogenic carbon taken up in the high latitude Southern Ocean region (south of 58° S) is efficiently and continuously exported northward, predominantly into intermediate waters. This transport mechanism allows continuous increase in future carbon uptake in the high latitude Southern Ocean, where the annual uptake strength could reach 39.3±0.9 g C m−2 yr−1, more than twice the global mean of 16.0±0.3 g C m−2 yr−1 by the end of the 21st century. Our study further underlines the key role of the Southern Ocean in controlling long-term future carbon uptake.

scholarly journals Anthropogenic carbon dynamics in the changing ocean

2010 ◽  
Vol 7 (2) ◽  
pp. 391-415
Author(s):  
J. F. Tjiputra ◽  
K. Assmann ◽  
C. Heinze
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
High Latitude ◽  
Future Climate Change ◽  
Carbon Uptake ◽  
Continuous Increase ◽  
Carbon Cycle Model ◽  
Anthropogenic Carbon ◽  
Natural Carbon

Abstract. Long-term response of CO2 fluxes to climate change at the ocean surface and the ocean interior are investigated using a coupled climate-carbon cycle model. This study also presents the first attempt in quantifying the evolution of lateral transport of anthropogenic carbon under future climate change. Additionally, its impact on regional carbon storage and uptake are also evaluated. For the 1850–2100 period, our climate change simulation predicts oceanic uptake of anthropogenic carbon of about 538 Pg C. Another simulation indicates that changes in physical climate alone results in a release of natural carbon of about 22 Pg C. The natural carbon outgassing is attributed to the reduction in solubility and change in wind pattern in the Southern Hemisphere. After the anthropogenic carbon passes through the air-sea interface, it is predominantly transported along the large scale overturning circulation below the surface layer. The spatial variations in the transport patterns in turn influence the evolution of future regional carbon uptake. In the North Atlantic, a slow down in Atlantic Meridional Overturnning Circulation weakens the penetration strength of anthropogenic carbon into the deeper ocean, which leads to the reduced uptake rate in this region. In contrast, more than half of the anthropogenic carbon taken up in the high latitude Southern Ocean region (south of 58° S) are efficiently and continuously exported northward, predominantly into intermediate waters. This peculiar transport mechanism allow continuous increase in future carbon uptake in the high latitude Southern Ocean, where the annual uptake strength could reach 3.5 g C m−2 yr−1, nearly triple the global mean of 1.3 g C m−2 yr−1 by the end of the 21st century. Our study further underlines the key role of the Southern Ocean in controlling long-term future carbon uptake.

scholarly journals Impact of Historical Climate Change on the Southern Ocean Carbon Cycle

2008 ◽  
Vol 21 (22) ◽  
pp. 5820-5834 ◽  
Author(s):  
R. J. Matear ◽  
A. Lenton
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Carbon Uptake ◽  
Saturation State ◽  
Aragonite Saturation ◽  
Freshwater Fluxes ◽  
Anthropogenic Carbon ◽  
Natural Carbon ◽  
Ocean Carbon

Abstract Climate change over the last several decades is suggested to cause a decrease in the magnitude of the uptake of CO2 by the Southern Ocean (Le Quere et al.). In this study, the atmospheric fields from NCEP R1 for the years 1948–2003 are used to drive an ocean biogeochemical model to probe how changes in the heat and freshwater fluxes and in the winds affect the Southern Ocean’s uptake of carbon. Over this period, the model simulations herein show that the increases in heat and freshwater fluxes drive a net increase in Southern Ocean uptake (south of 40°S) while the increases in wind stresses drive a net decrease in uptake. The total Southern Ocean response is nearly identical with the simulation without climate change because the heat and freshwater flux response is approximately both equal and opposite to the wind stress response. It is also shown that any change in the Southern Ocean anthropogenic carbon uptake is always opposed by a much larger change in the natural carbon air–sea exchange. For the 1948–2003 period, the changes in the natural carbon cycle dominate the Southern Ocean carbon uptake response to climate change. However, it is shown with a simple box model that when atmospheric CO2 levels exceed the partial pressure of carbon dioxide (pCO2) of the upwelled Circumpolar Deep Water (≈450 μatm) the Southern Ocean uptake response will be dominated by the changes in anthropogenic carbon uptake. Therefore, the suggestion that the Southern Ocean carbon uptake is a positive feedback to global warming is only a transient response that will change to a negative feedback in the near future if the present climate trend continues. Associated with the increased outgassing of carbon from the natural carbon cycle was a reduction in the aragonite saturation state of the high-latitude Southern Ocean (south of 60°S). In the simulation with just wind stress changes, the reduction in the high-latitude Southern Ocean aragonite saturation state (≈0.2) was comparable to the magnitude of the decline in the aragonite saturation state over the last 4 decades because of rising atmospheric CO2 levels (≈0.2). The simulation showed that climate change could significantly impact aragonite saturation state in the Southern Ocean.

scholarly journals Simulating natural carbon sequestration in the Southern Ocean: on uncertainties associated with eddy parameterizations and iron deposition

2017 ◽  
Vol 14 (6) ◽  
pp. 1561-1576 ◽  
Author(s):  
Heiner Dietze ◽  
Julia Getzlaff ◽  
Ulrike Löptien
Keyword(s):  
Carbon Sequestration ◽  
Southern Ocean ◽  
Ocean Circulation ◽  
Spatial Scales ◽  
Carbon Uptake ◽  
Comprehensive Understanding ◽  
Biogeochemical Models ◽  
Anthropogenic Carbon ◽  
Natural Carbon ◽  
Oceanic Carbon

Abstract. The Southern Ocean is a major sink for anthropogenic carbon. Yet, there is no quantitative consensus about how this sink will change when surface winds increase (as they are anticipated to do). Among the tools employed to quantify carbon uptake are global coupled ocean-circulation–biogeochemical models. Because of computational limitations these models still fail to resolve potentially important spatial scales. Instead, processes on these scales are parameterized. There is concern that deficiencies in these so-called eddy parameterizations might imprint incorrect sensitivities of projected oceanic carbon uptake. Here, we compare natural carbon uptake in the Southern Ocean simulated with contemporary eddy parameterizations. We find that very differing parameterizations yield surprisingly similar oceanic carbon in response to strengthening winds. In contrast, we find (in an additional simulation) that the carbon uptake does differ substantially when the supply of bioavailable iron is altered within its envelope of uncertainty. We conclude that a more comprehensive understanding of bioavailable iron dynamics will substantially reduce the uncertainty of model-based projections of oceanic carbon uptake.

scholarly journals Simulating natural carbon sequestration in the Southern Ocean: on uncertainties associated with eddy parameterizations and iron deposition

2016 ◽  
Author(s):  
Heiner Dietze ◽  
Julia Getzlaff ◽  
Ulrike Löptien
Keyword(s):  
Carbon Sequestration ◽  
Southern Ocean ◽  
Ocean Circulation ◽  
Spatial Scales ◽  
Carbon Uptake ◽  
Comprehensive Understanding ◽  
Biogeochemical Models ◽  
Anthropogenic Carbon ◽  
Natural Carbon ◽  
Oceanic Carbon

Abstract. The Southern Ocean is a major sink for anthropogenic carbon. Yet, there is no quantitative consensus about how this sink will change when surface winds increase (as they are anticipated to do). Among the tools employed to quantify carbon uptake are global coupled ocean-circulation biogeochemical models. Because of computational limitations these models still fail to resolve potentially-important spatial scales. Instead, processes on these scales are parameterized. There is concern that deficiencies in these so-called eddy-parameterizations might imprint wrong sensitivities of projected oceanic carbon uptake. Here, we compare natural carbon uptake in the Southern Ocean simulated with contemporary eddy-parameterizations. We find that very differing parameterizations yield surprisingly similar oceanic carbon in response to strengthening winds. In contrast, we find (in an additional simulation) that the carbon uptake does differ substantially when the supply of bioavailable iron is altered within its envelope of uncertainty. We conclude that a more comprehensive understanding of bioavailable iron dynamics will substantially reduce the uncertainty of model-based projections of oceanic carbon uptake.

scholarly journals Influence of the Southern Annular Mode on Projected Weakening of the Atlantic Meridional Overturning Circulation

2013 ◽  
Vol 26 (20) ◽  
pp. 8017-8036 ◽  
Author(s):  
Peter T. Spooner ◽  
Helen L. Johnson ◽  
Tim J. Woollings
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Greenhouse Gas ◽  
Climate Models ◽  
Atlantic Meridional Overturning Circulation ◽  
Southern Annular Mode ◽  
Meridional Overturning Circulation ◽  
Overturning Circulation ◽  
Annular Mode ◽  
Meridional Overturning

Abstract Coupled climate models predict density-driven weakening of the Atlantic meridional overturning circulation (AMOC) under greenhouse gas forcing, with considerable spread in the response between models. There is also a large spread in the predicted increase of the southern annular mode (SAM) index across these models. Regression analysis across model space using 11 non-eddy-resolving models suggests that up to 35% of the intermodel spread in the AMOC response may be associated with uncertainty in the magnitude of the increase in the SAM. Models with a large, positive SAM index response generally display a smaller weakening of the AMOC under greenhouse gas forcing. The initial AMOC strength is also a major cause of intermodel spread in its response to climate change. The increase in the SAM acts to reduce the weakening of the AMOC over the next century by around ⅓, through increases in wind stress over the Southern Ocean, northward Ekman transport, and upwelling around Antarctica. The SAM response is also related to an increase in the northward salt flux across 30°S and to salinity anomalies in the high-latitude North Atlantic. These provide a positive feedback by further reinforcement of the AMOC. The results suggest that, compared with the real ocean where eddies oppose wind-driven changes in Southern Ocean circulation, climate models underestimate the effects of anthropogenic climate change on the AMOC.

Transient Climate Sensitivity Depends on Base Climate Ocean Circulation

2017 ◽  
Vol 30 (4) ◽  
pp. 1493-1504 ◽  
Author(s):  
Jie He ◽  
Michael Winton ◽  
Gabriel Vecchi ◽  
Liwei Jia ◽  
Maria Rugenstein
Keyword(s):  
Climate Change ◽  
Ocean Circulation ◽  
Climate Sensitivity ◽  
High Latitude ◽  
Climate Models ◽  
Meridional Overturning Circulation ◽  
Future Climate Change ◽  
Tropical Ocean ◽  
Ocean Heat Uptake ◽  
Starting Point

Abstract There is large uncertainty in the simulation of transient climate sensitivity. This study aims to understand how such uncertainty is related to the simulation of the base climate by comparing two simulations with the same model but in which CO2 is increased from either a preindustrial (1860) or a present-day (1990) control simulation. This allows different base climate ocean circulations that are representative of those in current climate models to be imposed upon a single model. As a result, the model projects different transient climate sensitivities that are comparable to the multimodel spread. The greater warming in the 1990-start run occurs primarily at high latitudes and particularly over regions of oceanic convection. In the 1990-start run, ocean overturning circulations are initially weaker and weaken less from CO2 forcing. As a consequence, there are smaller reductions in the poleward ocean heat transport, leading to less tropical ocean heat storage and less moderated high-latitude surface warming. This process is evident in both hemispheres, with changes in the Atlantic meridional overturning circulation and the Antarctic Bottom Water formation dominating the warming differences in each hemisphere. The high-latitude warming in the 1990-start run is enhanced through albedo and cloud feedbacks, resulting in a smaller ocean heat uptake efficacy. The results highlight the importance of improving the base climate ocean circulation in order to provide a reasonable starting point for assessments of past climate change and the projection of future climate change.

Are there pre-Quaternary geological analogues for a future greenhouse warming?

2011 ◽  
Vol 369 (1938) ◽  
pp. 933-956 ◽  
Author(s):  
Alan M. Haywood ◽  
Andy Ridgwell ◽  
Daniel J. Lunt ◽  
Daniel J. Hill ◽  
Matthew J. Pound ◽  
...  
Keyword(s):  
Climate Change ◽  
Greenhouse Gases ◽  
Future Climate ◽  
Future Climate Change ◽  
Anthropogenic Emissions ◽  
Earth System ◽  
System Sensitivity ◽  
Earth History ◽  
Scientific Papers

Given the inherent uncertainties in predicting how climate and environments will respond to anthropogenic emissions of greenhouse gases, it would be beneficial to society if science could identify geological analogues to the human race’s current grand climate experiment . This has been a focus of the geological and palaeoclimate communities over the last 30 years, with many scientific papers claiming that intervals in Earth history can be used as an analogue for future climate change. Using a coupled ocean–atmosphere modelling approach, we test this assertion for the most probable pre-Quaternary candidates of the last 100 million years: the Mid- and Late Cretaceous, the Palaeocene–Eocene Thermal Maximum (PETM), the Early Eocene, as well as warm intervals within the Miocene and Pliocene epochs. These intervals fail as true direct analogues since they either represent equilibrium climate states to a long-term CO 2 forcing—whereas anthropogenic emissions of greenhouse gases provide a progressive (transient) forcing on climate—or the sensitivity of the climate system itself to CO 2 was different. While no close geological analogue exists, past warm intervals in Earth history provide a unique opportunity to investigate processes that operated during warm (high CO 2 ) climate states. Palaeoclimate and environmental reconstruction/modelling are facilitating the assessment and calculation of the response of global temperatures to increasing CO 2 concentrations in the longer term (multiple centuries); this is now referred to as the Earth System Sensitivity, which is critical in identifying CO 2 thresholds in the atmosphere that must not be crossed to avoid dangerous levels of climate change in the long term. Palaeoclimatology also provides a unique and independent way to evaluate the qualities of climate and Earth system models used to predict future climate.

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