Correction for Stein et al., Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks

Abstract. During the last termination (from ~18 000 yr ago to ~9000 yr ago) the climate significantly warmed and the ice sheets melted. Simultaneously, atmospheric CO2 increased from ~190 ppm to ~260 ppm. Although this CO2 rise plays an important role in the deglacial warming, the reasons for its evolution are difficult to explain. Only box models have been used to run transient simulations of this carbon cycle transition, but by forcing the model with data constrained scenarios of the evolution of temperature, sea level, sea ice, NADW formation, Southern Ocean vertical mixing and biological carbon pump. More complex models (including GCMs) have investigated some of these mechanisms but they have only been used to try and explain LGM versus present day steady-state climates. In this study we use a climate-carbon coupled model of intermediate complexity to explore the role of three oceanic processes in transient simulations: the sinking of brines, stratification-dependant diffusion and iron fertilization. Carbonate compensation is accounted for in these simulations. We show that neither iron fertilization nor the sinking of brines alone can account for the evolution of CO2, and that only the combination of the sinking of brines and interactive diffusion can simultaneously simulate the increase in deep Southern Ocean δ13C. The scenario that agrees best with the data takes into account all mechanisms and favours a rapid cessation of the sinking of brines around 18 000 yr ago, when the Antarctic ice sheet extent was at its maximum. Sea ice formation was then shifted to the open ocean where the salty water is quickly mixed with fresher water, which prevents deep sinking of salty water and therefore breaks down the deep stratification and releases carbon from the abyss. Based on this scenario it is possible to simulate both the amplitude and timing of the CO2 increase during the last termination in agreement with data. The atmospheric δ13C appears to be highly sensitive to changes in the terrestrial biosphere, underlining the need to better constrain the vegetation evolution during the termination.

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Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1908670117 ◽

2020 ◽

Vol 117 (9) ◽

pp. 4498-4504 ◽

Cited By ~ 4

Author(s):

Karl Stein ◽

Axel Timmermann ◽

Eun Young Kwon ◽

Tobias Friedrich

Keyword(s):

Carbon Cycle ◽

Southern Ocean ◽

Sea Ice ◽

General Circulation ◽

Deep Ocean ◽

General Circulation Models ◽

Ice Dynamics ◽

Carbon Cycle Model ◽

Ocean Stratification ◽

Ocean Ventilation

The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here, we use a transient run of an intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of 10. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared with the current climate. Sensitivity tests with a steady-state carbon cycle model indicate that the two mechanisms combined can reduce atmospheric carbon by 40 ppm, with ocean stratification acting early within a glacial cycle to amplify the carbon cycle response.

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Timing and magnitude of Southern Ocean sea ice/carbon cycle feedbacks over the last eight glacial cycles

10.5194/egusphere-egu2020-1755 ◽

2020 ◽

Author(s):

Karl Stein ◽

Axel Timmermann ◽

Eun Young Kwon ◽

Tobias Friedrich

Keyword(s):

Carbon Sequestration ◽

Carbon Cycle ◽

Southern Ocean ◽

Sea Ice ◽

Deep Ocean ◽

Glacial Cycles ◽

Ice Dynamics ◽

Ocean Stratification ◽

Ocean Ventilation ◽

The Impact

<p class="p1"><span class="s1">The Southern Ocean (SO) played a prominent role in the exchange of carbon between ocean and atmosphere on glacial timescales through its regulation of deep ocean ventilation. Previous studies indicated that SO sea ice could dynamically link several processes of carbon sequestration, but these studies relied on models with simplified ocean and sea ice dynamics or snapshot simulations with general circulation models. Here we use a transient run of the LOVECLIM intermediate complexity climate model, covering the past eight glacial cycles, to investigate the orbital-scale dynamics of deep ocean ventilation changes due to SO sea ice. Cold climates increase sea ice cover, sea-ice export, and Antarctic Bottom Water formation, which are accompanied by increased SO upwelling, stronger poleward export of Circumpolar Deep Water, and a reduction of the atmospheric exposure time of surface waters by a factor of ten. Moreover, increased brine formation around Antarctica enhances deep ocean stratification, which could act to decrease vertical mixing by a factor of four compared to the current climate. The impact of the two mechanisms on carbon sequestration was then tested within a steady-state carbon cycle. The two mechanisms combined can reduce atmospheric carbon by 40 ppm, of which approximately 30 ppm is due to ocean stratification. Moreover, ocean stratification from increased SO sea ice production acts early within glacial cycles to amplify the carbon cycle response.</span></p>

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Impact of oceanic processes on the carbon cycle during the last termination

Climate of the Past ◽

10.5194/cp-8-149-2012 ◽

2012 ◽

Vol 8 (1) ◽

pp. 149-170 ◽

Cited By ~ 21

Author(s):

N. Bouttes ◽

D. Paillard ◽

D. M. Roche ◽

C. Waelbroeck ◽

M. Kageyama ◽

...

Keyword(s):

Carbon Cycle ◽

Southern Ocean ◽

Sea Ice ◽

Ice Core ◽

Vertical Mixing ◽

Salty Water ◽

Iron Fertilization ◽

Transient Simulations ◽

Carbon Pump ◽

Complex Models

Abstract. During the last termination (from ~18 000 years ago to ~9000 years ago), the climate significantly warmed and the ice sheets melted. Simultaneously, atmospheric CO2 increased from ~190 ppm to ~260 ppm. Although this CO2 rise plays an important role in the deglacial warming, the reasons for its evolution are difficult to explain. Only box models have been used to run transient simulations of this carbon cycle transition, but by forcing the model with data constrained scenarios of the evolution of temperature, sea level, sea ice, NADW formation, Southern Ocean vertical mixing and biological carbon pump. More complex models (including GCMs) have investigated some of these mechanisms but they have only been used to try and explain LGM versus present day steady-state climates. In this study we use a coupled climate-carbon model of intermediate complexity to explore the role of three oceanic processes in transient simulations: the sinking of brines, stratification-dependent diffusion and iron fertilization. Carbonate compensation is accounted for in these simulations. We show that neither iron fertilization nor the sinking of brines alone can account for the evolution of CO2, and that only the combination of the sinking of brines and interactive diffusion can simultaneously simulate the increase in deep Southern Ocean δ13C. The scenario that agrees best with the data takes into account all mechanisms and favours a rapid cessation of the sinking of brines around 18 000 years ago, when the Antarctic ice sheet extent was at its maximum. In this scenario, we make the hypothesis that sea ice formation was then shifted to the open ocean where the salty water is quickly mixed with fresher water, which prevents deep sinking of salty water and therefore breaks down the deep stratification and releases carbon from the abyss. Based on this scenario, it is possible to simulate both the amplitude and timing of the long-term CO2 increase during the last termination in agreement with ice core data. The atmospheric δ13C appears to be highly sensitive to changes in the terrestrial biosphere, underlining the need to better constrain the vegetation evolution during the termination.

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

Annals of Glaciology ◽

10.3189/s0260305500013884 ◽

1997 ◽

Vol 25 ◽

pp. 111-115 ◽

Cited By ~ 3

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.

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DASSO: a data assimilation system for the Southern Ocean that utilizes both sea-ice concentration and thickness observations

Journal of Glaciology ◽

10.1017/jog.2021.57 ◽

2021 ◽

pp. 1-6

Author(s):

Hao Luo ◽

Qinghua Yang ◽

Longjiang Mu ◽

Xiangshan Tian-Kunze ◽

Lars Nerger ◽

...

Keyword(s):

Data Assimilation ◽

Southern Ocean ◽

Sea Ice ◽

Coupled Model ◽

Sea Ice Concentration ◽

Model Free ◽

Antarctic Sea Ice ◽

Ice Concentration ◽

Data Assimilation System ◽

Assimilation System

Abstract To improve Antarctic sea-ice simulations and estimations, an ensemble-based Data Assimilation System for the Southern Ocean (DASSO) was developed based on a regional sea ice–ocean coupled model, which assimilates sea-ice thickness (SIT) together with sea-ice concentration (SIC) derived from satellites. To validate the performance of DASSO, experiments were conducted from 15 April to 14 October 2016. Generally, assimilating SIC and SIT can suppress the overestimation of sea ice in the model-free run. Besides considering uncertainties in the operational atmospheric forcing data, a covariance inflation procedure in data assimilation further improves the simulation of Antarctic sea ice, especially SIT. The results demonstrate the effectiveness of assimilating sea-ice observations in reconstructing the state of Antarctic sea ice, but also highlight the necessity of more reasonable error estimation for the background as well as the observation.

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Phytoplankton under Southern Ocean Sea Ice

10.1002/essoar.10507491.1 ◽

2021 ◽

Author(s):

Kelsey M Bisson ◽

B. B. Cael

Keyword(s):

Southern Ocean ◽

Sea Ice

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Energy exchange in early spring over sea ice in the Pacific sector of the Southern Ocean

Journal of Geophysical Research Atmospheres ◽

10.1029/1998jd200069 ◽

1999 ◽

Vol 104 (D4) ◽

pp. 3925-3935 ◽

Cited By ~ 5

Author(s):

Adrian Hauser ◽

Gerd Wendler ◽

Ute Adolphs ◽

Martin O. Jeffries

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Energy Exchange ◽

Early Spring ◽

The Pacific

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A Link Between CMIP5 Phytoplankton Phenology and Sea Ice in the Atlantic Southern Ocean

Geophysical Research Letters ◽

10.1029/2018gl078061 ◽

2018 ◽

Vol 45 (13) ◽

pp. 6566-6575 ◽

Cited By ~ 3

Author(s):

Mark Hague ◽

Marcello Vichi

Keyword(s):

Southern Ocean ◽

Sea Ice

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Modeling the effect of Ross Ice Shelf melting on the Southern Ocean in quasi-equilibrium

The Cryosphere ◽

10.5194/tc-12-3033-2018 ◽

2018 ◽

Vol 12 (9) ◽

pp. 3033-3044 ◽

Cited By ~ 1

Author(s):

Xiying Liu

Keyword(s):

Southern Ocean ◽

Sea Ice ◽

Ross Sea ◽

Global Ocean ◽

Freshwater Flux ◽

Quasi Equilibrium ◽

Ice Shelf ◽

Sea Ice Concentration ◽

Ross Ice Shelf ◽

Ice Concentration

Abstract. To study the influence of basal melting of the Ross Ice Shelf (BMRIS) on the Southern Ocean (ocean southward of 35∘ S) in quasi-equilibrium, numerical experiments with and without the BMRIS effect were performed using a global ocean–sea ice–ice shelf coupled model. In both experiments, the model started from a state of quasi-equilibrium ocean and was integrated for 500 years forced by CORE (Coordinated Ocean-ice Reference Experiment) normal-year atmospheric fields. The simulation results of the last 100 years were analyzed. The melt rate averaged over the entire Ross Ice Shelf is 0.25 m a−1, which is associated with a freshwater flux of 3.15 mSv (1 mSv = 103 m3 s−1). The extra freshwater flux decreases the salinity in the region from 1500 m depth to the sea floor in the southern Pacific and Indian oceans, with a maximum difference of nearly 0.005 PSU in the Pacific Ocean. Conversely, the effect of concurrent heat flux is mainly confined to the middle depth layer (approximately 1500 to 3000 m). The decreased density due to the BMRIS effect, together with the influence of ocean topography, creates local differences in circulation in the Ross Sea and nearby waters. Through advection by the Antarctic Circumpolar Current, the flux difference from BMRIS gives rise to an increase of sea ice thickness and sea ice concentration in the Ross Sea adjacent to the coast and ocean water to the east. Warm advection and accumulation of warm water associated with differences in local circulation decrease sea ice concentration on the margins of sea ice cover adjacent to open water in the Ross Sea in September. The decreased water density weakens the subpolar cell as well as the lower cell in the global residual meridional overturning circulation (MOC). Moreover, we observe accompanying reduced southward meridional heat transport at most latitudes of the Southern Ocean.

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