scholarly journals Reframing the carbon cycle of the subpolar Southern Ocean

2019 ◽  
Vol 5 (8) ◽  
pp. eaav6410 ◽  
Author(s):  
Graeme A. MacGilchrist ◽  
Alberto C. Naveira Garabato ◽  
Peter J. Brown ◽  
Loïc Jullion ◽  
Sheldon Bacon ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Global Climate ◽  
Dominant Role ◽  
World Ocean ◽  
Future Climate Change ◽  
Carbon Uptake ◽  
Shelf Sea ◽  
Horizontal Circulation ◽  
Ocean Carbon

Global climate is critically sensitive to physical and biogeochemical dynamics in the subpolar Southern Ocean, since it is here that deep, carbon-rich layers of the world ocean outcrop and exchange carbon with the atmosphere. Here, we present evidence that the conventional framework for the subpolar Southern Ocean carbon cycle, which attributes a dominant role to the vertical overturning circulation and shelf-sea processes, fundamentally misrepresents the drivers of regional carbon uptake. Observations in the Weddell Gyre—a key representative region of the subpolar Southern Ocean—show that the rate of carbon uptake is set by an interplay between the Gyre’s horizontal circulation and the remineralization at mid-depths of organic carbon sourced from biological production in the central gyre. These results demonstrate that reframing the carbon cycle of the subpolar Southern Ocean is an essential step to better define its role in past and future climate change.

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 Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

2013 ◽  
Vol 10 (9) ◽  
pp. 15033-15076 ◽  
Author(s):  
K. B. Rodgers ◽  
O. Aumont ◽  
S. E. Mikaloff Fletcher ◽  
Y. Plancherel ◽  
L. Bopp ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ad Hoc ◽  
Global Ocean ◽  
Nutrient Concentrations ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model. The objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with differences of order 0.9 Pg C yr−1 over the region south of 45° S. Wind stirring impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other species associated with ocean biogeochemistry. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong sensitivity of nutrient concentrations exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry, through its impact over the Southern Ocean.

scholarly journals Strong sensitivity of Southern Ocean carbon uptake and nutrient cycling to wind stirring

2014 ◽  
Vol 11 (15) ◽  
pp. 4077-4098 ◽  
Author(s):  
K. B. Rodgers ◽  
O. Aumont ◽  
S. E. Mikaloff Fletcher ◽  
Y. Plancherel ◽  
L. Bopp ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Ad Hoc ◽  
Global Ocean ◽  
Relative Reduction ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
The Impact

Abstract. Here we test the hypothesis that winds have an important role in determining the rate of exchange of CO2 between the atmosphere and ocean through wind stirring over the Southern Ocean. This is tested with a sensitivity study using an ad hoc parameterization of wind stirring in an ocean carbon cycle model, where the objective is to identify the way in which perturbations to the vertical density structure of the planetary boundary in the ocean impacts the carbon cycle and ocean biogeochemistry. Wind stirring leads to reduced uptake of CO2 by the Southern Ocean over the period 2000–2006, with a relative reduction with wind stirring on the order of 0.9 Pg C yr−1 over the region south of 45° S. This impacts not only the mean carbon uptake, but also the phasing of the seasonal cycle of carbon and other ocean biogeochemical tracers. Enhanced wind stirring delays the seasonal onset of stratification, and this has large impacts on both entrainment and the biological pump. It is also found that there is a strong reduction on the order of 25–30% in the concentrations of NO3 exported in Subantarctic Mode Water (SAMW) to wind stirring. This finds expression not only locally over the Southern Ocean, but also over larger scales through the impact on advected nutrients. In summary, the large sensitivity identified with the ad hoc wind stirring parameterization offers support for the importance of wind stirring for global ocean biogeochemistry through its impact over the Southern Ocean.

scholarly journals Analytically tractable climate–carbon cycle feedbacks under 21st century anthropogenic forcing

2018 ◽  
Vol 9 (2) ◽  
pp. 507-523 ◽  
Author(s):  
Steven J. Lade ◽  
Jonathan F. Donges ◽  
Ingo Fetzer ◽  
John M. Anderies ◽  
Christian Beer ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Global Climate ◽  
Future Climate Change ◽  
Earth System ◽  
Co2 Solubility ◽  
Carbon Cycle Model ◽  
Ocean Climate ◽  
System Models ◽  
Analytical Expressions ◽  
Earth System Models

Abstract. Changes to climate–carbon cycle feedbacks may significantly affect the Earth system's response to greenhouse gas emissions. These feedbacks are usually analysed from numerical output of complex and arguably opaque Earth system models. Here, we construct a stylised global climate–carbon cycle model, test its output against comprehensive Earth system models, and investigate the strengths of its climate–carbon cycle feedbacks analytically. The analytical expressions we obtain aid understanding of carbon cycle feedbacks and the operation of the carbon cycle. Specific results include that different feedback formalisms measure fundamentally the same climate–carbon cycle processes; temperature dependence of the solubility pump, biological pump, and CO2 solubility all contribute approximately equally to the ocean climate–carbon feedback; and concentration–carbon feedbacks may be more sensitive to future climate change than climate–carbon feedbacks. Simple models such as that developed here also provide workbenches for simple but mechanistically based explorations of Earth system processes, such as interactions and feedbacks between the planetary boundaries, that are currently too uncertain to be included in comprehensive Earth system models.

scholarly journals Role of volcanic forcing on future global carbon cycle

2011 ◽  
Vol 2 (1) ◽  
pp. 133-159
Author(s):  
J. F. Tjiputra ◽  
O. H. Otterå
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
21St Century ◽  
Volcanic Eruptions ◽  
Future Climate Change ◽  
Small Scale ◽  
Carbon Uptake ◽  
Carbon Cycle Model ◽  
Large Volcanic Eruptions

Abstract. Using a fully coupled global climate-carbon cycle model, we assess the potential role of volcanic eruptions on future projection of climate change and its associated carbon cycle feedback. The volcanic-like forcings are applied together with business-as-usual IPCC-A2 carbon emissions scenario. We show that very large volcanic eruptions similar to Tambora lead to short-term substantial global cooling. However, over a long period, smaller but more frequent eruptions, such as Pinatubo, would have a stronger impact on future climate change. In a scenario where the volcanic external forcings are prescribed with a five-year frequency, the induced cooling immediately lower the global temperature by more than one degree before return to the warming trend. Therefore, the climate change is approximately delayed by several decades and by the end of the 21st century, the warming is still below two degrees when compared to the present day period. The cooler climate reduces the terrestrial heterotrophic respiration in the northern high latitude and increases net primary production in the tropics, which contributes to more than 45% increase in accumulated carbon uptake over land. The increased solubility of CO2 gas in seawater associated with cooler SST is offset by reduced CO2 partial pressure gradient between ocean and atmosphere, which results in small changes in net ocean carbon uptake. Similarly, there is nearly no change in the seawater buffer capacity simulated between the different volcanic scenarios. Our study shows that even in the relatively extreme scenario where large volcanic eruptions occur every five-years period, the induced cooling only leads to a reduction of 46 ppmv atmospheric CO2 concentration as compared to the reference projection of 878 ppmv, at the end of the 21st century. With respect to sulphur injection geoengineering method, our study suggest that small scale but frequent mitigation is more efficient than the opposite. Moreover, the longer we delay, the more difficult it would be to counteract climate change.

The palaeoceanographic history of the Celtic Sea since the last deglaciation and its potential for carbon storage

2021 ◽  
Author(s):  
Jacob Noble ◽  
Alix Cage ◽  
Olivia Beavers ◽  
Bradley Sparks ◽  
Mark Furze ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Sea Level ◽  
Carbon Storage ◽  
Benthic Foraminifera ◽  
Future Climate Change ◽  
The Holocene ◽  
Shelf Sea ◽  
Celtic Sea ◽  
The Uk ◽  
Seasonal Stratification

<p>Shelf seas account for around 10-30% of ocean productivity, 30-50% of inorganic carbon burial and up to 80% of organic carbon storage (Sharples et al., 2019); as such, shelf-sea sediments are a potential store of carbon and could play an important role in the ‘blue’ carbon cycle, and thus global climate. UK shelf-sea hydrography is dominated by seasonal stratification which drives productivity; however, stratification evolved with sea-level and tidal dynamic changes over the Holocene epoch on the UK shelf, and thus carbon stores will have changed over time. These shallow marine environments are typically seen as erosional environments and have therefore been somewhat overlooked in terms of palaeoenvironments with only a few studies from the UK continental shelf (e.g. Austin and Scourse, 1997). Here we use a core collected from the Celtic Deep, on the UK shelf, to explore environmental change, and the evolution of stratification in this setting and the potential role it plays in the global carbon cycle.</p><p>JC106-052PC, a 7.5m long marine sediment core, was recovered in 2018 at a water-depth of 116 m from the Celtic Deep (a relatively deep trough in the Celtic Sea between Britain and Ireland) as part of the BRITICE project. A radiocarbon date of 10,435 ±127 years cal BP at 4.1m suggests the core covers the Holocene epoch and preceding deglacial period. Preliminary multiproxy data from this expanded archive (ITRAX XRF, organic content, benthic foraminifera assemblages) points to changing environmental conditions and productivity potentially reflecting the evolution of seasonal stratification in the Celtic Sea over the Holocene. Work currently focuses on increasing the resolution of the benthic foraminifera record of JC106-052PC, extending the record into the deglacial period, and applying a benthic foraminifera transfer function approach to estimate sea-surface temperature of the Celtic Sea during the Holocene and deglacial period.  </p><p>This study aims to increase our understanding of the shelf-sea dynamics and productivity of the Celtic Sea over the last deglacial to Holocene period. By elucidating the response of the Celtic Sea to changing sea level and oceanographic conditions, and its capacity to act as a carbon store, we can better understand the role of other shelf environments, potentially benefiting global studies of palaeoclimate and future climate change. </p>

scholarly journals Effect of increasing CO2 on the terrestrial carbon cycle

2014 ◽  
Vol 112 (2) ◽  
pp. 436-441 ◽  
Author(s):  
David Schimel ◽  
Britton B. Stephens ◽  
Joshua B. Fisher
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Terrestrial Ecosystems ◽  
Future Climate Change ◽  
Carbon Uptake ◽  
Model Diagnostics ◽  
Terrestrial Carbon ◽  
Terrestrial Carbon Cycle ◽  
New Space ◽  
Improved Model

Feedbacks from the terrestrial carbon cycle significantly affect future climate change. The CO2 concentration dependence of global terrestrial carbon storage is one of the largest and most uncertain feedbacks. Theory predicts the CO2 effect should have a tropical maximum, but a large terrestrial sink has been contradicted by analyses of atmospheric CO2 that do not show large tropical uptake. Our results, however, show significant tropical uptake and, combining tropical and extratropical fluxes, suggest that up to 60% of the present-day terrestrial sink is caused by increasing atmospheric CO2. This conclusion is consistent with a validated subset of atmospheric analyses, but uncertainty remains. Improved model diagnostics and new space-based observations can reduce the uncertainty of tropical and temperate zone carbon flux estimates. This analysis supports a significant feedback to future atmospheric CO2 concentrations from carbon uptake in terrestrial ecosystems caused by rising atmospheric CO2 concentrations. This feedback will have substantial tropical contributions, but the magnitude of future carbon uptake by tropical forests also depends on how they respond to climate change and requires their protection from deforestation.

scholarly journals Evaluating CMIP5 ocean biogeochemistry and Southern Ocean carbon uptake using atmospheric potential oxygen: Present-day performance and future projection

2016 ◽  
Vol 43 (5) ◽  
pp. 2077-2085 ◽  
Author(s):  
C. D. Nevison ◽  
M. Manizza ◽  
R. F. Keeling ◽  
B. B. Stephens ◽  
J. D. Bent ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Uptake ◽  
Future Projection ◽  
Ocean Biogeochemistry ◽  
Ocean Carbon ◽  
Potential Oxygen

scholarly journals The Role of the Southern Ocean in Global Processes

2004 ◽  
Vol 16 (4) ◽  
pp. 361-361
Author(s):  
EBERHARD FAHRBACH
Keyword(s):  
Carbon Cycle ◽  
Southern Ocean ◽  
Global Climate ◽  
Global Carbon Cycle ◽  
Climate System ◽  
Antarctic Water ◽  
Biogeochemical Processes ◽  
Long Time ◽  
Global Carbon

The limits of the Southern Ocean and its importance have been under debate for a long time. However, with growing knowledge, it has become obvious that the circum-Antarctic water belt is the defining limit and that the Southern Ocean plays an active and important role in the physical part of the global climate system, the global carbon cycle and biogeochemical processes.

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