scholarly journals The devil's in the disequilibrium: sensitivity of ocean carbon storage to climate state and iron fertilization in a general circulation model

2017 ◽  
Author(s):  
Sarah Eggleston ◽  
Eric D. Galbraith
Keyword(s):  
Sea Ice ◽  
Carbon Storage ◽  
General Circulation ◽  
Dissolved Inorganic Carbon ◽  
Circulation Model ◽  
Deep Ocean ◽  
Inverse Correlation ◽  
Biogeochemical Model ◽  
Iron Fertilization ◽  
Ocean Carbon

Abstract. Ocean dissolved inorganic carbon (DIC) storage can be conceptualized as the sum of four components: saturation (DICsat), disequilibrium (DICdis), carbonate (DICcarb) and soft tissue (DICsoft). Among these, DICdis and DICsoft have the potential for large changes that are relatively difficult to predict. Here we explore changes in DICsoft and DICdis in a large suite of simulations with a complex coupled climate-biogeochemical model, driven by changes in orbital forcing, ice sheets and the radiative effect of CO2. Both DICdis and DICsoft vary over a range of 40 μmol kg−1 in response to the climate forcing, equivalent to changes in atmospheric CO2 on the order of 50 ppm for each. We find that, despite the broad range of climate states represented, changes in global DICsoft can be well-approximated by the product of deep ocean ideal age and the global export production flux, while global DICdis is dominantly controlled by the fraction of the ocean filled by Antarctic Bottom Water (AABW). Because the AABW fraction and ideal age are inversely correlated between the simulations, DICdis and DICsoft are also inversely correlated. This inverse correlation could be decoupled if changes in deep ocean mixing were to alter ideal age independently of AABW fraction, or if independent ecosystem changes were to alter export and remineralization, thereby modifying DICsoft. As an example of the latter, iron fertilization causes DICsoft to increase, and causes DICdis to also increase by a similar or greater amount, to a degree that depends on climate state. We propose a simple framework to consider the global contribution of DICsoft + DICdis to ocean carbon storage as a function of the surface preformed nitrate and DICdis of dense water formation regions, the global volume fractions ventilated by these regions, and the global nitrate inventory. More extensive sea ice increases DICdis, and when sea ice becomes very extensive it also causes significant O2 disequilibrium, which may have contributed to reconstructions of low O2 in the Southern Ocean during the glacial. Global DICdis reaches a minimum near modern CO2 because the AABW fraction reaches a minimum, which may have contributed to preventing further CO2 rise during interglacial periods.

scholarly journals The devil's in the disequilibrium: multi-component analysis of dissolved carbon and oxygen changes under a broad range of forcings in a general circulation model

2018 ◽  
Vol 15 (12) ◽  
pp. 3761-3777 ◽  
Author(s):  
Sarah Eggleston ◽  
Eric D. Galbraith
Keyword(s):  
Carbon Storage ◽  
Radiative Forcing ◽  
General Circulation ◽  
Extreme Values ◽  
Circulation Model ◽  
Deep Ocean ◽  
Cold Climate ◽  
Biogeochemical Model ◽  
Dissolved Carbon ◽  
Ocean Carbon

Abstract. The complexity of dissolved gas cycling in the ocean presents a challenge for mechanistic understanding and can hinder model intercomparison. One helpful approach is the conceptualization of dissolved gases as the sum of multiple, strictly defined components. Here we decompose dissolved inorganic carbon (DIC) into four components: saturation (DICsat), disequilibrium (DICdis), carbonate (DICcarb), and soft tissue (DICsoft). The cycling of dissolved oxygen is simpler, but can still be aided by considering O2, O2sat, and O2dis. We explore changes in these components within a large suite of simulations with a complex coupled climate–biogeochemical model, driven by changes in astronomical parameters, ice sheets, and radiative forcing, in order to explore the potential importance of the different components to ocean carbon storage on long timescales. We find that both DICsoft and DICdis vary over a range of 40 µmol kg−1 in response to the climate forcing, equivalent to changes in atmospheric pCO2 on the order of 50 ppm for each. The most extreme values occur at the coldest and intermediate climate states. We also find significant changes in O2 disequilibrium, with large increases under cold climate states. We find that, despite the broad range of climate states represented, changes in global DICsoft can be quantitatively approximated by the product of deep ocean ideal age and the global export production flux. In contrast, global DICdis is dominantly controlled by the fraction of the ocean filled by Antarctic Bottom Water (AABW). Because the AABW fraction and ideal age are inversely correlated among the simulations, DICdis and DICsoft are also inversely correlated, dampening the overall changes in DIC. This inverse correlation could be decoupled if changes in deep ocean mixing were to alter ideal age independently of AABW fraction, or if independent ecosystem changes were to alter export and remineralization, thereby modifying DICsoft. As an example of the latter, we show that iron fertilization causes both DICsoft and DICdis to increase and that the relationship between these two components depends on the climate state. We propose a simple framework to consider the global contribution of DICsoft+DICdis to ocean carbon storage as a function of the surface preformed nitrate and DICdis of dense water formation regions, the global volume fractions ventilated by these regions, and the global nitrate inventory.

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals Assessment of the sea-ice carbon pump: Insights from a three-dimensional ocean-sea-ice biogeochemical model (NEMO-LIM-PISCES)

Elem Sci Anth ◽  
2016 ◽  
Vol 4 ◽  
Author(s):  
Sébastien Moreau ◽  
Martin Vancoppenolle ◽  
Laurent Bopp ◽  
Oliver Aumont ◽  
Gurvan Madec ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Total Alkalinity ◽  
The Arctic ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Co2 Fluxes ◽  
Ice Growth

Abstract The role of sea ice in the carbon cycle is minimally represented in current Earth System Models (ESMs). Among potentially important flaws, mentioned by several authors and generally overlooked during ESM design, is the link between sea-ice growth and melt and oceanic dissolved inorganic carbon (DIC) and total alkalinity (TA). Here we investigate whether this link is indeed an important feature of the marine carbon cycle misrepresented in ESMs. We use an ocean general circulation model (NEMO-LIM-PISCES) with sea-ice and marine carbon cycle components, forced by atmospheric reanalyses, adding a first-order representation of DIC and TA storage and release in/from sea ice. Our results suggest that DIC rejection during sea-ice growth releases several hundred Tg C yr−1 to the surface ocean, of which < 2% is exported to depth, leading to a notable but weak redistribution of DIC towards deep polar basins. Active carbon processes (mainly CaCO3 precipitation but also ice-atmosphere CO2 fluxes and net community production) increasing the TA/DIC ratio in sea-ice modified ocean-atmosphere CO2 fluxes by a few Tg C yr−1 in the sea-ice zone, with specific hemispheric effects: DIC content of the Arctic basin decreased but DIC content of the Southern Ocean increased. For the global ocean, DIC content increased by 4 Tg C yr−1 or 2 Pg C after 500 years of model run. The simulated numbers are generally small compared to the present-day global ocean annual CO2 sink (2.6 ± 0.5 Pg C yr−1). However, sea-ice carbon processes seem important at regional scales as they act significantly on DIC redistribution within and outside polar basins. The efficiency of carbon export to depth depends on the representation of surface-subsurface exchanges and their relationship with sea ice, and could differ substantially if a higher resolution or different ocean model were used.

scholarly journals On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals Global cooling linked to increased glacial carbon storage via changes in Antarctic sea ice

2020 ◽  
Author(s):  
Alice Marzocchi ◽  
Malte Jansen
Keyword(s):  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Ice Core ◽  
Circulation Model ◽  
Deep Ocean ◽  
Water Masses ◽  
Global Ocean ◽  
Ocean Water ◽  
Deep Ocean Water

<p>Palaeo-oceanographic reconstructions indicate that the distribution of global ocean water masses has undergone major glacial–interglacial rearrangements over the past ~2.5 million years. Given that the ocean is the largest carbon reservoir, such circulation changes were probably key in driving the variations in atmospheric CO<sub>2</sub> concentrations observed in the ice-core record. However, we still lack a mechanistic understanding of the ocean’s role in regulating CO<sub>2</sub> on these timescales. Here, we show that glacial ocean–sea ice numerical simulations with a single-basin general circulation model, forced solely by atmospheric cooling, can predict ocean circulation patterns associated with increased atmospheric carbon sequestration in the deep ocean. Under such conditions, Antarctic bottom water becomes more isolated from the sea surface as a result of two connected factors: reduced air–sea gas exchange under sea ice around Antarctica and weaker mixing with North Atlantic Deep Water due to a shallower interface between southern- and northern-sourced water masses. These physical changes alone are sufficient to explain ~40 ppm atmospheric CO<sub>2</sub> drawdown—about half of the glacial–interglacial variation. Our results highlight that atmospheric cooling could have directly caused the reorganization of deep ocean water masses and, thus, glacial CO<sub>2</sub> drawdown. This provides an important step towards a consistent picture of glacial climates.</p>

An eddy-permitting ocean-sea ice general circulation model (E3SMv0-HiLAT03): Description and evaluation

2019 ◽  
Author(s):  
Jiaxu Zhang ◽  
Wilbert Weijer ◽  
Mathew Einar Maltrud ◽  
Carmela Veneziani ◽  
Nicole Jeffery ◽  
...  
Keyword(s):  
Sea Ice ◽  
General Circulation Model ◽  
General Circulation ◽  
Circulation Model

scholarly journals Estimating the Continental Response to Global Warming Using Pattern-Scaled Sea Surface Temperatures and Sea Ice

2016 ◽  
Vol 29 (24) ◽  
pp. 9125-9139 ◽  
Author(s):  
Adeline Bichet ◽  
Paul J. Kushner ◽  
Lawrence Mudryk
Keyword(s):  
Global Warming ◽  
Sea Ice ◽  
General Circulation ◽  
Circulation Model ◽  
Tropical Indian Ocean ◽  
Sea Surface ◽  
Climate Projections ◽  
Western Boundary ◽  
Sea Ice Concentration ◽  
Continental Climate

Abstract Better constraining the continental climate response to anthropogenic forcing is essential to improve climate projections. In this study, pattern scaling is used to extract, from observations, the patterned response of sea surface temperature (SST) and sea ice concentration (SICE) to anthropogenically dominated long-term global warming. The SST response pattern includes a warming of the tropical Indian Ocean, the high northern latitudes, and the western boundary currents. The SICE pattern shows seasonal variations of the main locations of sea ice loss. These SST–SICE response patterns are used to drive an ensemble of an atmospheric general circulation model, the National Center for Atmospheric Research (NCAR) Community Atmosphere Model, version 5 (CAM5), over the period 1980–2010 along with a standard AMIP ensemble using observed SST—SICE. The simulations enable attribution of a variety of observed trends of continental climate to global warming. On the one hand, the warming trends observed in all seasons across the entire Northern Hemisphere extratropics result from global warming, as does the snow loss observed over the northern midlatitudes and northwestern Eurasia. On the other hand, 1980–2010 precipitation trends observed in winter over North America and in summer over Africa result from the recent decreasing phase of the Pacific decadal oscillation and the recent increasing phase of the Atlantic multidecadal oscillation, respectively, which are not part of the global warming signal. The method holds promise for near-term decadal climate prediction but as currently framed cannot distinguish regional signals associated with oceanic internal variability from aerosol forcing and other sources of short-term forcing.

scholarly journals Impact of abrupt sea ice loss on Greenland water isotopes during the last glacial period

2019 ◽  
Vol 116 (10) ◽  
pp. 4099-4104 ◽  
Author(s):  
Louise C. Sime ◽  
Peter O. Hopcroft ◽  
Rachael H. Rhodes
Keyword(s):  
Sea Ice ◽  
Temperature Increase ◽  
General Circulation ◽  
Ice Core ◽  
Circulation Model ◽  
Ice Cores ◽  
Nitrogen Isotope ◽  
Ice Shelf ◽  
Last Glacial Period ◽  
Precipitation Seasonality

Greenland ice cores provide excellent evidence of past abrupt climate changes. However, there is no universally accepted theory of how and why these Dansgaard–Oeschger (DO) events occur. Several mechanisms have been proposed to explain DO events, including sea ice, ice shelf buildup, ice sheets, atmospheric circulation, and meltwater changes. DO event temperature reconstructions depend on the stable water isotope (δ18O) and nitrogen isotope measurements from Greenland ice cores: interpretation of these measurements holds the key to understanding the nature of DO events. Here, we demonstrate the primary importance of sea ice as a control on Greenland ice coreδ18O: 95% of the variability inδ18O in southern Greenland is explained by DO event sea ice changes. Our suite of DO events, simulated using a general circulation model, accurately captures the amplitude ofδ18O enrichment during the abrupt DO event onsets. Simulated geographical variability is broadly consistent with available ice core evidence. We find an hitherto unknown sensitivity of theδ18O paleothermometer to the magnitude of DO event temperature increase: the change inδ18O per Kelvin temperature increase reduces with DO event amplitude. We show that this effect is controlled by precipitation seasonality.

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