Southern Ocean carbon trends: Sensitivity to methods

2014 ◽  
Vol 41 (19) ◽  
pp. 6833-6840 ◽  
Author(s):  
Amanda R. Fay ◽  
Galen A. McKinley ◽  
Nicole S. Lovenduski
Keyword(s):  
Southern Ocean ◽  
Ocean Carbon

Detecting Climate Fingerprints in Southern Ocean Carbon using a Biogeochemical Ocean Model

2021 ◽  
Author(s):  
Rebecca Wright ◽  
Corinne Le Quéré ◽  
Erik Buitenhuis ◽  
Dorothee Bakker
Keyword(s):  
Climate Change ◽  
Climate Variability ◽  
Southern Ocean ◽  
Observational Data ◽  
Ecosystem Dynamics ◽  
Global Ocean ◽  
Subsurface Waters ◽  
Climatic Drivers ◽  
Ocean Carbon ◽  
And Storage

<p>The Southern Ocean plays an important role in the uptake, transport and storage of carbon by the global oceans. These properties are dominated by the response to the rise in anthropogenic CO<sub>2</sub> in the atmosphere, but they are modulated by climate variability and climate change. Here we explore the effect of climate variability and climate change on ocean carbon uptake and storage in the Southern Ocean. We assess the extent to which climate change may be distinguishable from the anthropogenic CO<sub>2</sub> signal and from the natural background variability. We use a combination of biogeochemical ocean modelling and observations from the GLODAPv2020 database to detect climate fingerprints in dissolved inorganic carbon (DIC).</p><p>We conduct an ensemble of hindcast model simulations of the period 1920-2019, using a global ocean biogeochemical model which incorporates plankton ecosystem dynamics based on twelve plankton functional types. We use the model ensemble to isolate the changes in DIC due to rising anthropogenic CO<sub>2</sub> alone and the changes due to climatic drivers (both climate variability and climate change), to determine their relative roles in the emerging total DIC trends and patterns. We analyse these DIC trends for a climate fingerprint over the past four decades, across spatial scales from the Southern Ocean, to basin level and down to regional ship transects. Highly sampled ship transects were extracted from GLODAPv2020 to obtain locations with the maximum spatiotemporal coverage, to reduce the inherent biases in patchy observational data. Model results were sampled to the ship transects to compare the climate fingerprints directly to the observational data.</p><p>Model results show a substantial change in DIC over a 35-year period, with a range of more than +/- 30 µmol/L. In the surface ocean, both anthropogenic CO<sub>2</sub> and climatic drivers act to increase DIC concentration, with the influence of anthropogenic CO<sub>2</sub> dominating at lower latitudes and the influence of climatic drivers dominating at higher latitudes. In the deep ocean, the anthropogenic CO<sub>2</sub> generally acts to increase DIC except in the subsurface waters at lower latitudes, while climatic drivers act to decrease DIC concentration. The combined fingerprint of anthropogenic CO<sub>2</sub> and climatic drivers on DIC concentration is for an increasing trend at the surface and decreasing trends in low latitude subsurface waters. Preliminary comparison of the model fingerprints to observational ship transects will also be presented.</p>

scholarly journals Diagnosing CO2 emission-induced feedbacks between the Southern Ocean carbon cycle and the climate system: A multiple Earth System Model analysis using a water mass tracking approach

2021 ◽  
pp. 1-62
Author(s):  
Tilla Roy ◽  
Jean Baptiste Sallée ◽  
Laurent Bopp ◽  
Nicolas Metzl
Keyword(s):  
Climate Change ◽  
Southern Ocean ◽  
Water Mass ◽  
Buffering Capacity ◽  
Climate Impacts ◽  
System Model ◽  
Earth System ◽  
Local Climate ◽  
Mode Waters ◽  
Ocean Carbon

AbstractAnthropogenic CO2 emission-induced feedbacks between the carbon cycle and the climate system perturb the efficiency of atmospheric CO2 uptake by land and ocean carbon reservoirs. The Southern Ocean is a region where these feedbacks can be largest and differ most among Earth System Model projections of 21st century climate change. To improve our mechanistic understanding of these feedbacks, we develop an automated procedure that tracks changes in the positions of Southern Ocean water masses and their carbon uptake. In an idealised ensemble of climate change projections, we diagnose two carbon–concentration feedbacks driven by atmospheric CO2 (due to increasing air-sea CO2 partial pressure difference, dpCO2, and reducing carbonate buffering capacity) and two carbon–climate feedbacks driven by climate change (due to changes in the water mass surface outcrop areas and local climate impacts). Collectively these feedbacks increase the CO2 uptake by the Southern Ocean and account for one-fifth of the global uptake of CO2 emissions. The increase in CO2 uptake is primarily dpCO2-driven, with Antarctic intermediate waters making the largest contribution; the remaining three feedbacks partially offset this increase (by ~25%), with maximum reductions in Subantarctic mode waters. The process dominating the decrease in CO2 uptake is water mass-dependent: reduction in carbonate buffering capacity in Subtropical and Subantarctic mode waters, local climate impacts in Antarctic intermediate waters, and reduction in outcrop areas in circumpolar deep waters and Antarctic bottom waters. Intermodel variability in the feedbacks is predominately dpCO2–driven and should be a focus of efforts to constrain projection uncertainty.

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>

scholarly journals Deep ocean ventilation, carbon isotopes, marine sedimentation and the deglacial CO<sub>2</sub> rise

2011 ◽  
Vol 7 (3) ◽  
pp. 771-800 ◽  
Author(s):  
T. Tschumi ◽  
F. Joos ◽  
M. Gehlen ◽  
C. Heinze
Keyword(s):  
Southern Ocean ◽  
Ocean Circulation ◽  
Isotope Composition ◽  
Deep Ocean ◽  
Atmospheric Co2 ◽  
Carbon Cycle Model ◽  
Ocean Ventilation ◽  
Marine Sedimentation ◽  
Sediment Formation ◽  
Ocean Carbon

Abstract. The link between the atmospheric CO2 level and the ventilation state of the deep ocean is an important building block of the key hypotheses put forth to explain glacial-interglacial CO2 fluctuations. In this study, we systematically examine the sensitivity of atmospheric CO2 and its carbon isotope composition to changes in deep ocean ventilation, the ocean carbon pumps, and sediment formation in a global 3-D ocean-sediment carbon cycle model. Our results provide support for the hypothesis that a break up of Southern Ocean stratification and invigorated deep ocean ventilation were the dominant drivers for the early deglacial CO2 rise of ~35 ppm between the Last Glacial Maximum and 14.6 ka BP. Another rise of 10 ppm until the end of the Holocene is attributed to carbonate compensation responding to the early deglacial change in ocean circulation. Our reasoning is based on a multi-proxy analysis which indicates that an acceleration of deep ocean ventilation during early deglaciation is not only consistent with recorded atmospheric CO2 but also with the reconstructed opal sedimentation peak in the Southern Ocean at around 16 ka BP, the record of atmospheric δ13CCO2, and the reconstructed changes in the Pacific CaCO3 saturation horizon.

scholarly journals Southern Ocean carbon export efficiency in relation to temperature and primary productivity

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Gaojing Fan ◽  
Zhengbing Han ◽  
Wentao Ma ◽  
Shuangling Chen ◽  
Fei Chai ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Primary Productivity ◽  
Carbon Export ◽  
Ocean Carbon

Millennial-scale changes in atmospheric CO2 levels linked to the Southern Ocean carbon isotope gradient and dust flux

2013 ◽  
Vol 6 (6) ◽  
pp. 457-461 ◽  
Author(s):  
Martin Ziegler ◽  
Paula Diz ◽  
Ian R. Hall ◽  
Rainer Zahn
Keyword(s):  
Southern Ocean ◽  
Carbon Isotope ◽  
Atmospheric Co2 ◽  
Dust Flux ◽  
Co2 Levels ◽  
Ocean Carbon ◽  
Millennial Scale

scholarly journals The Effect of Antarctic Sea Ice on Southern Ocean Carbon Outgassing: Capping Versus Light Attenuation

2020 ◽  
Vol 34 (8) ◽  
Author(s):  
Mukund Gupta ◽  
Michael J. Follows ◽  
Jonathan Maitland Lauderdale
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Light Attenuation ◽  
Antarctic Sea Ice ◽  
Ocean Carbon

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

Sustained growth of the Southern Ocean carbon storage in a warming climate

2015 ◽  
Vol 42 (11) ◽  
pp. 4516-4522 ◽  
Author(s):  
Takamitsu Ito ◽  
Annalisa Bracco ◽  
Curtis Deutsch ◽  
Hartmut Frenzel ◽  
Matthew Long ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Carbon Storage ◽  
Sustained Growth ◽  
Warming Climate ◽  
Ocean Carbon

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

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

<p><b>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. </b></p><p>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. </p><p>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. </p><p>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. </p><p>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. </p>

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