scholarly journals Efficiency of small scale carbon mitigation by patch iron fertilization

2010 ◽  
Vol 7 (11) ◽  
pp. 3593-3624 ◽  
Author(s):  
J. L. Sarmiento ◽  
R. D. Slater ◽  
J. Dunne ◽  
A. Gnanadesikan ◽  
M. R. Hiscock
Keyword(s):  
Southern Ocean ◽  
General Circulation ◽  
Ross Sea ◽  
Equatorial Pacific ◽  
Global Ocean ◽  
Small Scale ◽  
Co2 Uptake ◽  
The North ◽  
Biogeochemical Models ◽  
Iron Fertilization

Abstract. While nutrient depletion scenarios have long shown that the high-latitude High Nutrient Low Chlorophyll (HNLC) regions are the most effective for sequestering atmospheric carbon dioxide, recent simulations with prognostic biogeochemical models have suggested that only a fraction of the potential drawdown can be realized. We use a global ocean biogeochemical general circulation model developed at GFDL and Princeton to examine this and related issues. We fertilize two patches in the North and Equatorial Pacific, and two additional patches in the Southern Ocean HNLC region north of the biogeochemical divide and in the Ross Sea south of the biogeochemical divide. We evaluate the simulations using observations from both artificial and natural iron fertilization experiments at nearby locations. We obtain by far the greatest response to iron fertilization at the Ross Sea site, where sea ice prevents escape of sequestered CO2 during the wintertime, and the CO2 removed from the surface ocean by the biological pump is carried into the deep ocean by the circulation. As a consequence, CO2 remains sequestered on century time-scales and the efficiency of fertilization remains almost constant no matter how frequently iron is applied as long as it is confined to the growing season. The second most efficient site is in the Southern Ocean. The North Pacific site has lower initial nutrients and thus a lower efficiency. Fertilization of the Equatorial Pacific leads to an expansion of the suboxic zone and a striking increase in denitrification that causes a sharp reduction in overall surface biological export production and CO2 uptake. The impacts on the oxygen distribution and surface biological export are less prominent at other sites, but nevertheless still a source of concern. The century time scale retention of iron in this model greatly increases the long-term biological response to iron addition as compared with simulations in which the added iron is rapidly scavenged from the ocean.

scholarly journals Efficiency of small scale carbon mitigation by patch iron fertilization

2009 ◽  
Vol 6 (6) ◽  
pp. 10381-10446 ◽  
Author(s):  
J. L. Sarmiento ◽  
R. D. Slater ◽  
J. Dunne ◽  
A. Gnanadesikan ◽  
M. R. Hiscock
Keyword(s):  
Southern Ocean ◽  
Ross Sea ◽  
Biological Response ◽  
Equatorial Pacific ◽  
Global Ocean ◽  
Small Scale ◽  
Co2 Uptake ◽  
The North ◽  
Biogeochemical Models ◽  
Iron Fertilization

Abstract. While nutrient depletion scenarios have long shown that the high-latitude High Nutrient Low Chlorophyll (HNLC) regions are the most effective for sequestering atmospheric carbon dioxide, recent simulations with prognostic biogeochemical models have suggested that only a fraction of the potential drawdown can be realized. We use a global ocean biogeochemical general circulation model developed at GFDL and Princeton to examine this and related issues. We fertilize two patches in the North and Equatorial Pacific, and two additional patches in the Southern Ocean HNLC region north of the biogeochemical divide and in the Ross Sea south of the biogeochemical divide. We obtain by far the greatest response to iron fertilization at the Ross Sea site. Here the CO2 remains sequestered on century time-scales and the efficiency of fertilization remains almost constant no matter how frequently iron is applied as long as it is confined to the growing season. The second most efficient site is in the Southern Ocean. Here the biological response to iron fertilization is comparable to the Ross Sea, but the enhanced biological uptake of CO2 is more spread out in the vertical and thus less effective at leading to removal of CO2 from the atmosphere. The North Pacific site has lower initial nutrients and thus a lower efficiency. Fertilization of the Equatorial Pacific leads to an expansion of the suboxic zone and a striking increase in denitrification that causes a sharp reduction in overall surface biological export production and CO2 uptake. The impacts on the oxygen distribution and surface biological export are less prominent at other sites, but nevertheless still a source of concern. The century time scale retention of iron in these models greatly increases the long-term biological response to iron addition as compared with models in which the added iron is rapidly scavenged from the ocean.

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

2018 ◽  
Vol 12 (9) ◽  
pp. 3033-3044 ◽  
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.

scholarly journals Marine productivity response to Heinrich events: a model-data comparison

2012 ◽  
Vol 8 (5) ◽  
pp. 1581-1598 ◽  
Author(s):  
V. Mariotti ◽  
L. Bopp ◽  
A. Tagliabue ◽  
M. Kageyama ◽  
D. Swingedouw
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Circulation Model ◽  
Global Ocean ◽  
Biogeochemical Model ◽  
Heinrich Events ◽  
The North ◽  
Heinrich Event ◽  
The North Atlantic ◽  
Marine Productivity

Abstract. Marine sediments records suggest large changes in marine productivity during glacial periods, with abrupt variations especially during the Heinrich events. Here, we study the response of marine biogeochemistry to such an event by using a biogeochemical model of the global ocean (PISCES) coupled to an ocean-atmosphere general circulation model (IPSL-CM4). We conduct a 400-yr-long transient simulation under glacial climate conditions with a freshwater forcing of 0.1 Sv applied to the North Atlantic to mimic a Heinrich event, alongside a glacial control simulation. To evaluate our numerical results, we have compiled the available marine productivity records covering Heinrich events. We find that simulated primary productivity and organic carbon export decrease globally (by 16% for both) during a Heinrich event, albeit with large regional variations. In our experiments, the North Atlantic displays a significant decrease, whereas the Southern Ocean shows an increase, in agreement with paleo-productivity reconstructions. In the Equatorial Pacific, the model simulates an increase in organic matter export production but decreased biogenic silica export. This antagonistic behaviour results from changes in relative uptake of carbon and silicic acid by diatoms. Reasonable agreement between model and data for the large-scale response to Heinrich events gives confidence in models used to predict future centennial changes in marine production. In addition, our model allows us to investigate the mechanisms behind the observed changes in the response to Heinrich events.

The Southern Ocean carbon sink 1985-2018: first results of the RECCAP2 project

2021 ◽  
Author(s):  
Judith Hauck ◽  
Luke Gregor ◽  
Cara Nissen ◽  
Eric Mortenson ◽  
Seth Bushinsky ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Seasonal Cycle ◽  
Carbon Sink ◽  
Global Ocean ◽  
Biogeochemical Models ◽  
Wide Range ◽  
Data Products ◽  
First Results ◽  
Ocean Carbon ◽  
Indian Sector

<p>The Southern Ocean is the main gateway for anthropogenic CO<sub>2</sub> into the ocean owing to the upwelling of old water masses with low anthropogenic CO<sub>2</sub> concentration, and the transport of the newly equilibrated surface waters into the ocean interior through intermediate, deep and bottom water formation. Here we present first results of the Southern Ocean chapter of RECCAP2, which is the Global Carbon Project’s second systematic study on Regional Carbon Cycle Assessment and Processes. In the Southern Ocean chapter, we aim to assess the Southern Ocean carbon sink 1985-2018 from a wide range of available models and data sets, and to identify patterns of regional and temporal variability, model limitations and future challenges.</p><p>We gathered global and regional estimates of the air-sea CO<sub>2</sub> flux over the period 1985-2018 from global ocean biogeochemical models, surface pCO<sub>2</sub>-based data products, and data-assimilated models. The analysis on the Southern Ocean quantified geographical patterns in the annual mean and seasonal amplitude of air-sea CO<sub>2</sub> flux, with results presented here aggregated to the level of large-scale ocean biomes.</p><p>Considering the suite of observed and modelled estimates, we found that the subtropical seasonally stratified (STSS) biome stands out with the largest air-sea CO<sub>2</sub> flux per area and a seasonal cycle with largest ocean uptake of CO<sub>2</sub> in winter, whereas the ice (ICE) biome is characterized by a large ensemble spread and a pronounced seasonal cycle with the largest ocean uptake of CO<sub>2</sub> in summer. Connecting these two, the subpolar seasonally stratified (SPSS) biome has intermediate flux densities (flux per area), and most models have difficulties simulating the seasonal cycle with strongest uptake during the summer months.</p><p>Our analysis also reveals distinct differences between the Atlantic, Pacific and Indian sectors of the aforementioned biomes. In the STSS, the Indian sector contributes most to the ocean carbon sink, followed by the Atlantic and then Pacific sectors. This hierarchy is less pronounced in the models than in the data-products. In the SPSS, only the Atlantic sector exhibits net CO<sub>2</sub> uptake in all years, likely linked to strong biological production. In the ICE biome, the Atlantic and Pacific sectors take up more CO<sub>2</sub> than the Indian sector, suggesting a potential role of the Weddell and Ross Gyres.</p><p>These first results confirm the global relevance of the Southern Ocean carbon sink and highlight the strong regional and interannual variability of the Southern Ocean carbon uptake in connection to physical and biogeochemical processes.</p>

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.

Overturning Circulation Pathways in a Two-Basin Ocean Model

2020 ◽  
Vol 50 (8) ◽  
pp. 2105-2122
Author(s):  
Louis-Philippe Nadeau ◽  
Malte F. Jansen
Keyword(s):  
Southern Ocean ◽  
General Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Meridional Overturning Circulation ◽  
Global Ocean ◽  
Direct Result ◽  
Diapycnal Mixing ◽  
Overturning Circulation ◽  
Deep Ocean Water

AbstractA toy model for the deep ocean overturning circulation in multiple basins is presented and applied to study the role of buoyancy forcing and basin geometry in the ocean’s global overturning. The model reproduces the results from idealized general circulation model simulations and provides theoretical insights into the mechanisms that govern the structure of the overturning circulation. The results highlight the importance of the diabatic component of the meridional overturning circulation (MOC) for the depth of North Atlantic Deep Water (NADW) and for the interbasin exchange of deep ocean water masses. This diabatic component, which extends the upper cell in the Atlantic below the depth of adiabatic upwelling in the Southern Ocean, is shown to be sensitive to the global area-integrated diapycnal mixing rate and the density contrast between NADW and Antarctic Bottom Water (AABW). The model also shows that the zonally averaged global overturning circulation is to zeroth-order independent of whether the ocean consists of one or multiple connected basins, but depends on the total length of the southern reentrant channel region (representing the Southern Ocean) and the global ocean area integrated diapycnal mixing. Common biases in single-basin simulations can thus be understood as a direct result of the reduced domain size.

scholarly journals Stochastic Subgrid-Scale Ocean Mixing: Impacts on Low-Frequency Variability

2017 ◽  
Vol 30 (13) ◽  
pp. 4997-5019 ◽  
Author(s):  
Stephan Juricke ◽  
Tim N. Palmer ◽  
Laure Zanna
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
High Frequency ◽  
Low Frequency ◽  
Global Ocean ◽  
Small Scale ◽  
Subgrid Scale ◽  
Low Frequency Variability ◽  
Ocean Models

In global ocean models, the representation of small-scale, high-frequency processes considerably influences the large-scale oceanic circulation and its low-frequency variability. This study investigates the impact of stochastic perturbation schemes based on three different subgrid-scale parameterizations in multidecadal ocean-only simulations with the ocean model NEMO at 1° resolution. The three parameterizations are an enhanced vertical diffusion scheme for unstable stratification, the Gent–McWilliams (GM) scheme, and a turbulent kinetic energy mixing scheme, all commonly used in state-of-the-art ocean models. The focus here is on changes in interannual variability caused by the comparatively high-frequency stochastic perturbations with subseasonal decorrelation time scales. These perturbations lead to significant improvements in the representation of low-frequency variability in the ocean, with the stochastic GM scheme showing the strongest impact. Interannual variability of the Southern Ocean eddy and Eulerian streamfunctions is increased by an order of magnitude and by 20%, respectively. Interannual sea surface height variability is increased by about 20%–25% as well, especially in the Southern Ocean and in the Kuroshio region, consistent with a strong underestimation of interannual variability in the model when compared to reanalysis and altimetry observations. These results suggest that enhancing subgrid-scale variability in ocean models can improve model variability and potentially its response to forcing on much longer time scales, while also providing an estimate of model uncertainty.

scholarly journals Dominance of the Southern Ocean in Anthropogenic Carbon and Heat Uptake in CMIP5 Models

2015 ◽  
Vol 28 (2) ◽  
pp. 862-886 ◽  
Author(s):  
Thomas L. Frölicher ◽  
Jorge L. Sarmiento ◽  
David J. Paynter ◽  
John P. Dunne ◽  
John P. Krasting ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Storage ◽  
Heat Storage ◽  
Global Ocean ◽  
Cmip5 Models ◽  
Co2 Uptake ◽  
Anthropogenic Co2 ◽  
Recent Climate ◽  
Heat Uptake ◽  
Anthropogenic Carbon

Abstract The authors assess the uptake, transport, and storage of oceanic anthropogenic carbon and heat over the period 1861–2005 in a new set of coupled carbon–climate Earth system models conducted for the fifth phase of the Coupled Model Intercomparison Project (CMIP5), with a particular focus on the Southern Ocean. Simulations show that the Southern Ocean south of 30°S, occupying 30% of global surface ocean area, accounts for 43% ± 3% (42 ± 5 Pg C) of anthropogenic CO2 and 75% ± 22% (23 ± 9 × 1022 J) of heat uptake by the ocean over the historical period. Northward transport out of the Southern Ocean is vigorous, reducing the storage to 33 ± 6 Pg anthropogenic carbon and 12 ± 7 × 1022 J heat in the region. The CMIP5 models, as a class, tend to underestimate the observation-based global anthropogenic carbon storage but simulate trends in global ocean heat storage over the last 50 years within uncertainties of observation-based estimates. CMIP5 models suggest global and Southern Ocean CO2 uptake have been largely unaffected by recent climate variability and change. Anthropogenic carbon and heat storage show a common broad-scale pattern of change, but ocean heat storage is more structured than ocean carbon storage. The results highlight the significance of the Southern Ocean for the global climate and as the region where models differ the most in representation of anthropogenic CO2 and, in particular, heat uptake.

scholarly journals North Atlantic SST Anomalies and the Cold North European Weather Events of Winter 2009/10 and December 2010

2014 ◽  
Vol 142 (2) ◽  
pp. 922-932 ◽  
Author(s):  
Jian Buchan ◽  
Joël J.-M. Hirschi ◽  
Adam T. Blaker ◽  
Bablu Sinha
Keyword(s):  
North Atlantic ◽  
General Circulation ◽  
Cold Weather ◽  
Global Ocean ◽  
Northern Europe ◽  
Significant Shift ◽  
The North ◽  
Extreme Cold ◽  
The North Atlantic ◽  
Sst Anomalies

Abstract Northern Europe experienced consecutive periods of extreme cold weather in the winter of 2009/10 and in late 2010. These periods were characterized by a tripole pattern in North Atlantic sea surface temperature (SST) anomalies and exceptionally negative phases of the North Atlantic Oscillation (NAO). A global ocean–atmosphere general circulation model (OAGCM) is used to investigate the ocean’s role in influencing North Atlantic and European climate. Observed SST anomalies are used to force the atmospheric model and the resultant changes in atmospheric conditions over northern Europe are examined. Different atmospheric responses occur in the winter of 2009/10 and the early winter of 2010. These experiments suggest that North Atlantic SST anomalies did not significantly affect the development of the negative NAO phase in the cold winter of 2009/10. However, in November and December 2010 the large-scale North Atlantic SST anomaly pattern leads to a significant shift in the atmospheric circulation over the North Atlantic toward a NAO negative phase. Therefore, these results indicate that SST anomalies in November/December 2010 were particularly conducive to the development of a negative NAO phase, which culminated in the extreme cold weather conditions experienced over northern Europe in December 2010.

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