Natural carbon release compensates for anthropogenic carbon uptake when Southern Hemispheric westerlies strengthen

The Southern Ocean is one of today's largest sink of carbon, having absorbed about 10\% of the anthropogenic carbon emissions. Southern Ocean's dynamics are principally modulated by the strength of the Southern Hemispheric westerlies, &#160;which are projected to increase over the coming century. Here, using a high-resolution ocean-sea-ice-carbon cycle model, we explore the impact of idealized changes in Southern Hemispheric westerlies on the ocean carbon storage . We find that a 20\% strengthening of the Southern Hemispheric westerlies leads to a $\sim$25 Gt loss of natural carbon, while an additional 13 Gt of anthropogenic carbon is absorbed compared to the control run, thus resulting in a net loss of $\sim$12 GtC from the ocean over a period of 42 years. This tendency is enhanced if the westerlies are also shifted polewards, with a total natural carbon loss of almost 37 GtC, and an additional anthropogenic carbon uptake of 18 GtC. While both experiments display a large natural carbon loss south of 10$^\circ$S, the amplitude is three times greater in the poleward strengthening case, which is &#160;not fully compensated by the increase in anthropogenic carbon content. However, the poleward wind shift leads to significant differences in the pattern of DIC change due to a weakening of the upper overturning cell, &#160;which leads to an increase in natural and total carbon north of 35$^\circ$S in the upper 2000 m.

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Natural carbon release compensates for anthropogenic carbon uptake when Southern Hemispheric westerlies strengthen

10.1002/essoar.10504120.1 ◽

2020 ◽

Author(s):

Laurie Menviel ◽

Darryn W. Waugh ◽

Paul Spence ◽

Matthew A Chamberlain ◽

Veronique Lago ◽

...

Keyword(s):

Carbon Uptake ◽

Anthropogenic Carbon ◽

Carbon Release ◽

Natural Carbon

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

Biogeosciences ◽

10.5194/bg-14-1561-2017 ◽

2017 ◽

Vol 14 (6) ◽

pp. 1561-1576 ◽

Cited By ~ 3

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.

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

10.5194/bg-2016-460 ◽

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.

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Anthropogenic carbon dynamics in the changing ocean

Ocean Science ◽

10.5194/os-6-605-2010 ◽

2010 ◽

Vol 6 (3) ◽

pp. 605-614 ◽

Cited By ~ 21

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.

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Quantifying the ocean carbon sink for 1994-2007: Combined evidence from multiple methods

10.5194/egusphere-egu21-6704 ◽

2021 ◽

Author(s):

Galen A. McKinley ◽

Jessica Cross ◽

Timothy DeVries ◽

Judith Hauck ◽

Amanda Fay ◽

...

Keyword(s):

Steady State ◽

Working Group ◽

Carbon Sink ◽

Carbon Fluxes ◽

Carbon Uptake ◽

Best Estimate ◽

Anthropogenic Carbon ◽

Natural Carbon ◽

Ocean Models ◽

Ocean Carbon

By means of a variety of international observing and modeling efforts, the ocean carbon community has developed numerous estimates for ocean carbon uptake. In this presentation, we report on the synthesis effort we are undertaking under the auspices of an Ocean Carbon and Biogeochemistry Working Group. &#160;Our initial goal for this working group is to determine the best estimate for the net and anthropogenic carbon sink from 1994-2007 based on three approaches that independently use interior data, surface data or hindcast ocean models. Combining two approaches that use interior ocean data to estimate anthropogenic carbon, Fant = -2.40+-0.21 PgC/yr (2 sigma uncertainty). Estimates for the net, or contemporary, ocean carbon uptake come from 6 products that interpolate surface ocean pCO2 data to global coverage: Fnet = -1.58+-0.19 &#160;PgC/yr for 1994-2007. Uncertain closure terms for naturally-outgassed river-derived carbon and non-steady state natural carbon fluxes in the open ocean are then added to derive Fant from surface observation-based Fnet. Ocean models do not include river-derived carbon, but do include non-steady state natural carbon fluxes, and thus a third estimate for Fant is derived. The combined best-estimate is Fant = -2.35+-0.53 PgC/yr.&#160; We detail the uncertainties and assumptions made in deriving these estimates, and suggest paths forward to further reduce uncertainties.

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Anthropogenic carbon dynamics in the changing ocean

Ocean Science Discussions ◽

10.5194/osd-7-391-2010 ◽

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.

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Impact of Historical Climate Change on the Southern Ocean Carbon Cycle

Journal of Climate ◽

10.1175/2008jcli2194.1 ◽

2008 ◽

Vol 21 (22) ◽

pp. 5820-5834 ◽

Cited By ~ 40

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.

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Light Modulates the Physiology of NonphototrophicActinobacteria

Journal of Bacteriology ◽

10.1128/jb.00740-18 ◽

2019 ◽

Vol 201 (10) ◽

Cited By ~ 5

Author(s):

Julia A. Maresca ◽

Jessica L. Keffer ◽

Priscilla P. Hempel ◽

Shawn W. Polson ◽

Olga Shevchenko ◽

...

Keyword(s):

Organic Carbon ◽

Cellular Response ◽

Action Spectrum ◽

Sugar Transport ◽

Growth Effect ◽

Carbon Uptake ◽

Aquatic Environments ◽

Primary Producers ◽

Carbon And Nitrogen ◽

Carbon Release

ABSTRACTLight is a source of energy and an environmental cue that is available in excess in most surface environments. In prokaryotic systems, conversion of light to energy by photoautotrophs and photoheterotrophs is well understood, but the conversion of light to information and the cellular response to that information have been characterized in only a few species. Our goal was to explore the response of freshwaterActinobacteria, which are ubiquitous in illuminated aquatic environments, to light. We found thatActinobacteriawithout functional photosystems grow faster in the light, likely because sugar transport and metabolism are upregulated in the light. Based on the action spectrum of the growth effect and comparisons of the genomes of threeActinobacteriawith this growth rate phenotype, we propose that the photosensor in these strains is a putative CryB-type cryptochrome. The ability to sense light and upregulate carbohydrate transport during the day could allow these cells to coordinate their time of maximum organic carbon uptake with the time of maximum organic carbon release by primary producers.IMPORTANCESunlight provides information about both place and time. In sunlit aquatic environments, primary producers release organic carbon and nitrogen along with other growth factors during the day. The ability ofActinobacteriato coordinate organic carbon uptake and utilization with production of photosynthate enables them to grow more efficiently in the daytime, and it potentially gives them a competitive advantage over heterotrophs that constitutively produce carbohydrate transporters, which is energetically costly, or produce transporters only after detection of the substrate(s), which delays their response. Understanding how light cues the transport of organic carbon and its conversion to biomass is key to understanding biochemical mechanisms within the carbon cycle, the fluxes through it, and the variety of mechanisms by which light enhances growth.

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TREE RING RECONSTRUCTION OF MODERN RADIOCARBON DIOXIDE VARIABILITY OVER THE SOUTHERN OCEAN

10.26686/wgtn.14703831 ◽

2021 ◽

Author(s):

Rachel Corran

Keyword(s):

Southern Ocean ◽

Southern Hemisphere ◽

Tree Ring ◽

Deep Water ◽

Latitudinal Gradient ◽

Carbon Sink ◽

Carbon Uptake ◽

Co2 Uptake ◽

Anthropogenic Carbon ◽

Ocean Carbon

The Southern Ocean is the largest ocean carbon sink region. However, its trend of increasing carbon uptake has shown variability over recent decades. It is important to understand the underlying mechanisms of anthropogenic carbon uptake such that the future response of the Southern Ocean carbon sink under climate forcing can be predicted. The carbon uptake of the Southern Ocean is characterised by the balance of outgassing of CO2 from carbon-rich deep water and sequestration of anthropogenic carbon into surface waters. Atmospheric radiocarbon dioxide (Del14CO2) in the Southern Hemisphere is sensitive to the release of CO2 from the upwelling of ‘old’ 14C-depleted carbon-rich deep water at high southern latitudes, but is insensitive to CO2 uptake into the ocean. Thus Del14CO2 has the potential to be used as a tracer of the upwelling observed, thereby isolating the outgassing carbon component. The Southern Ocean Region has limited atmospheric Del14CO2 measurements, with sparse long-term sampling sites and few shipboard flask measurements. Therefore in this PhD project I exploit annual growth tree rings, which record the Del14C content of atmospheric CO2, to reconstruct Del14CO2 back in time. Within tree ring sample pretreatment for 14C measurement I automate the organic solvent wash method at the Rafter Radiocarbon Laboratory. I present new annual-resolution reconstructions of atmospheric Del14CO2 from tree rings, from coastal sites in New Zealand and Chile, spanning a latitudinal range of 44 S to 55 S, for the period of interest, 1985 – 2015. Data quality analysis using a range of replicate 14C measurements conducted within this project leads to assignment of apx 1.9 ‰ uncertainties for all results, in line with atmospheric measurements. In this project I also develop a harmonised dataset of atmospheric Del14CO2 measurements in the Southern Hemisphere for this period from different research groups, including the new tree ring Del14CO2 records alongside existing data. The harmonised atmospheric Del14CO2 dataset has a wide range of applications, but specifically here allows investigation of temporal and spatial variability of atmospheric Del14CO2 over the Southern Ocean over recent decades, thereby also considering the role of upwelling in recent Southern Ocean carbon sink variability. Backward trajectories are produced for the tree ring sites from an atmospheric transport model, to help inform interpretation of results. Over recent decades a latitudinal gradient of 3.7 ‰ is observed between 41 S and 53 S in the New Zealand sector, with a smaller gradient of 1.6 ‰ between 48 S and 55S in the Chile sector. This is consistent with other studies, with the spatial variability of atmospheric Del14CO2 attributed to air-sea 14C disequilibrium associated with carbon outgassing from 14C-depleted carbon-rich deep water upwelling at around 60 S, driving a latitudinal gradient of atmospheric Del14CO2 in the Southern Hemisphere, with longitudinal variability also observed. A stronger atmospheric Del14CO2 latitudinal gradient is observed in the 1980s/1990s relative to later 1990s/2000s. Stronger atmospheric Del14CO2 latitudinal gradients observed in 1980s/1990s suggest stronger deep water upwelling thereby greater associated outgassing of 14C-depleted CO2. These Del14CO2-based observations are consistent with modelling studies that predict changes in deep-water upwelling have controlled decadal variability in CO2 uptake, and are consistent with observation-based studies of decadal changes in rate of CO2 uptake of the Southern Ocean. The results presented in this thesis present the first observation-based confirmation that decadal changes in the strength of deep-water upwelling can explain decadal changes in the rate of CO2 uptake.

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