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Author Topic: Southern Ocean Venting of CO2  (Read 18938 times)

AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #50 on: July 08, 2014, 03:23:33 AM »
While the linked article is about increased venting of CO2 from ocean areas other than the Southern Ocean; nevertheless, the article does say that the venting increases with increasing latitude, and all CO2 venting from the ocean contributes to global warming:


W. J. Sydeman, M. García-Reyes, D. S. Schoeman, R. R. Rykaczewski, S. A. Thompson, B. A. Black, S. J. Bograd, (2014), "Climate change and wind intensification in coastal upwelling ecosystems", Science, Vol. 345 no. 6192 pp. 77-80, DOI: 10.1126/science.1251635

http://www.sciencemag.org/content/345/6192/77

Abstract: "In 1990, Andrew Bakun proposed that increasing greenhouse gas concentrations would force intensification of upwelling-favorable winds in eastern boundary current systems that contribute substantial services to society. Because there is considerable disagreement about whether contemporary wind trends support Bakun’s hypothesis, we performed a meta-analysis of the literature on upwelling-favorable wind intensification. The preponderance of published analyses suggests that winds have intensified in the California, Benguela, and Humboldt upwelling systems and weakened in the Iberian system over time scales ranging up to 60 years; wind change is equivocal in the Canary system. Stronger intensification signals are observed at higher latitudes, consistent with the warming pattern associated with climate change. Overall, reported changes in coastal winds, although subtle and spatially variable, support Bakun’s hypothesis of upwelling intensification in eastern boundary current systems."
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #51 on: July 11, 2014, 12:48:53 AM »
The linked reference (with a free access pdf) provides additional information on CO2 absorption and venting from the ocean in general:

Long Cao et al 2014, "Sensitivity of ocean acidification and oxygen to the uncertainty in climate change", Environ. Res. Lett. 9 064005, doi:10.1088/1748-9326/9/6/064005


http://iopscience.iop.org/1748-9326/9/6/064005/pdf/1748-9326_9_6_064005.pdf

Abstract: "Due to increasing atmospheric CO2 concentrations and associated climate change, the global ocean is undergoing substantial physical and biogeochemical changes. Among these, changes in ocean oxygen and carbonate chemistry have great implication for marine biota. There is considerable uncertainty in the projections of future climate change, and it is unclear how the uncertainty in climate change would also affect the projection of oxygen and carbonate chemistry. To investigate this issue, we use an Earth system model of intermediate complexity to perform a set of simulations, including that which involves no radiative effect of atmospheric CO2 and those which involve CO2-induced climate change with climate sensitivity varying from 0.5 °C to 4.5 °C. Atmospheric CO2 concentration is prescribed to follow RCP 8.5 pathway and its extensions. Climate change affects carbonate chemistry and oxygen mainly through its impact on ocean temperature, ocean ventilation, and concentration of dissolved inorganic carbon and alkalinity. It is found that climate change mitigates the decrease of carbonate ions at the ocean surface but has negligible effect on surface ocean pH. Averaged over the whole ocean, climate change acts to decrease oxygen concentration but mitigates the CO2-induced reduction of carbonate ion and pH. In our simulations, by year 2500, every degree increase of climate sensitivity warms the ocean by 0.8 °C and reduces ocean-mean dissolved oxygen concentration by 5.0%. Meanwhile, every degree increase of climate sensitivity buffers CO2-induced reduction in ocean-mean carbonate ion concentration and pH by 3.4% and 0.02 units, respectively. Our study demonstrates different sensitivities of ocean temperature, carbonate chemistry, and oxygen, in terms of both the sign and magnitude to the amount of climate change, which have great implications for understanding the response of ocean biota to climate change."
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #52 on: July 11, 2014, 01:01:49 AM »
The linked reference (with free pdf, images and supplemental data) provides paleo-evidence that CO2 ventilation from the Southern Ocean can contribute significantly to global warming:

Skinner, Luke C. and Waelbroeck, Claire and Scrivner, Adam E. and Fallon, Stewart J. (2014) "Radiocarbon evidence for alternating northern and southern sources of ventilation of the deep Atlantic carbon pool during the last deglaciation," Proceedings of the National Academy of Sciences, 111 (15). pp. 5480-5484. ISSN 0027-8424, 1091-6490, doi: 10.1073/pnas.1400668111

http://eprints.esc.cam.ac.uk/3046/

Abstract: "Recent theories for glacial–interglacial climate transitions call on millennial climate perturbations that purged the deep sea of sequestered carbon dioxide via a “bipolar ventilation seesaw.” However, the viability of this hypothesis has been contested, and robust evidence in its support is lacking. Here we present a record of North Atlantic deep-water radiocarbon ventilation, which we compare with similar data from the Southern Ocean. A striking coherence in ventilation changes is found, with extremely high ventilation ages prevailing across the deep Atlantic during the last glacial period. The data also reveal two reversals in the ventilation gradient between the deep North Atlantic and Southern Ocean during Heinrich Stadial 1 and the Younger Dryas. These coincided with periods of sustained atmospheric CO2 rise and appear to have been driven by enhanced ocean–atmosphere exchange, primarily in the Southern Ocean. These results confirm the operation of a bipolar ventilation seesaw during deglaciation and underline the contribution of abrupt regional climate anomalies to longer-term global climate transitions."
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #53 on: July 11, 2014, 01:45:52 AM »
For more serious investigators, the following link leads to a reference on how to estimate ventilation from the ocean using overturning stream functions:

Thompson, B., Nycander, J., Nilsson, J., Jakobsson, M., and Döös, K., (2014), "Estimating ventilation time scales using overturning stream functions", Ocean Dynamics, Vol 64, Issue 6, Doi: 10.1007/s10236-014-0726-5

http://link.springer.com/article/10.1007%2Fs10236-014-0726-5

Abstract: "A simple method for estimating ventilation time scales from overturning stream functions is proposed. The stream function may be computed using either geometric coordinates or a generalized vertical coordinate, such as potential density (salinity in our study). The method is tested with a three-dimensional circulation model describing an idealized semi-enclosed ocean basin ventilated through a narrow strait over a sill, and the result is compared to age estimates obtained from a passive numerical age tracer. The best result is obtained when using the stream function in salinity coordinates. In this case, the reservoir-averaged advection time obtained from the overturning stream function in salinity coordinates agrees rather well with the mean age of the age tracer, and the corresponding maximum ages agree very well."
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #54 on: July 21, 2014, 04:04:04 PM »
morganism in the "Trends for the Southern Ocean" thread in the "Antarctic" folder provided the following links to references about the DIMES program that provides physically measured parameters supporting the position that increases in the wind velocities of the Southern Hemisphere Westerlies, will result in increased venting of CO₂ from the Southern Ocean:

K. L. Sheen, A. C. Naveira Garabato, J. A. Brearley, M. P. Meredith, K. L. Polzin, D. A. Smeed, A. Forryan, B. A. King, J-B. Sallée, L. St. Laurent, A. M. Thurnherr, J. M. Toole, S. N. Waterman & A. J. Watson, (2014), "Eddy-induced variability in Southern Ocean abyssal mixing on climatic timescales", Nature Geoscience, doi:10.1038/ngeo2200

http://www.nature.com/ngeo/journal/vaop/ncurrent/full/ngeo2200.html

Abstract: "The Southern Ocean plays a pivotal role in the global ocean circulation and climate. There, the deep water masses of the world ocean upwell to the surface and subsequently sink to intermediate and abyssal depths, forming two overturning cells that exchange substantial quantities of heat and carbon with the atmosphere. The sensitivity of the upper cell to climatic changes in forcing is relatively well established. However, little is known about how the lower cell responds, and in particular whether small-scale mixing in the abyssal Southern Ocean, an important controlling process of the lower cell, is influenced by atmospheric forcing. Here, we present observational evidence that relates changes in abyssal mixing to oceanic eddy variability on timescales of months to decades. Observational estimates of mixing rates, obtained along a repeat hydrographic transect across Drake Passage, are shown to be dependent on local oceanic eddy energy, derived from moored current meter and altimetric measurements. As the intensity of the regional eddy field is regulated by the Southern Hemisphere westerly winds, our findings suggest that Southern Ocean abyssal mixing and overturning are sensitive to climatic perturbations in wind forcing."

See also:
http://phys.org/news/2014-07-insight-southern-ocean-behaviour.html
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #55 on: September 13, 2014, 01:21:51 AM »
The linked reference provides insight about the influence of sea ice in the Southern Ocean on CO₂ absorption and release:

Bruno Delille, Martin Vancoppenolle, Nicolas-Xavier Geilfus, Bronte Tilbrook, Delphine Lannuzel, Véronique Schoemann, Sylvie Becquevort, Gauthier Carnat, Daniel Delille, Christiane Lancelot, Lei Chou, Gerhard S. Dieckmann and Jean-Louis Tison, (2014), "Southern Ocean CO2 sink: The contribution of the sea ice", Journal of Geophysical Research: Oceans, DOI: 10.1002/2014JC009941

http://onlinelibrary.wiley.com/doi/10.1002/2014JC009941/abstract

Abstract: "We report first direct measurements of the partial pressure of CO2 (pCO2) within Antarctic pack sea ice brines and related CO2 fluxes across the air-ice interface. From late winter to summer, brines encased in the ice change from a CO2 large over-saturation, relative to the atmosphere, to a marked under-saturation while the underlying oceanic waters remains slightly oversaturated. The decrease from winter to summer of pCO2 in the brines is driven by dilution with melting ice, dissolution of carbonate crystals and net primary production. As the ice warms, its permeability increases, allowing CO2 transfer at the air-sea ice interface. The sea ice changes from a transient source to a sink for atmospheric CO2. We upscale these observations to the whole Antarctic sea ice cover using the NEMO-LIM3 large-scale sea ice-ocean, and provide first estimates of spring and summer CO2 uptake from the atmosphere by Antarctic sea ice. Over the spring-summer period, the Antarctic sea ice cover is a net sink of atmospheric CO2 of 0.029 PgC, about 58% of the estimated annual uptake from the Southern Ocean. Sea ice then contributes significantly to the sink of CO2 of the Southern Ocean."
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #56 on: August 26, 2015, 01:11:32 AM »
The linked reference provides observational findings that the Subantarctic Zone (SAZ) is important when assess the propensity for the Southern Ocean to vent CO₂:

E. H. Shadwick, T. W. Trull, B. Tilbrook, A. J. Sutton, E. Schulz & C. L. Sabine (2015), "Seasonality of biological and physical controls on surface ocean CO2 from hourly observations at the Southern Ocean Time Series site south of Australia", Global Biochemical Cycles, Volume 29, Issue 2, Pages 223–238, DOI: 10.1002/2014GB004906



http://onlinelibrary.wiley.com/doi/10.1002/2014GB004906/abstract


Abstract: "The Subantarctic Zone (SAZ), which covers the northern half of the Southern Ocean between the Subtropical and Subantarctic Fronts, is important for air-sea CO2 exchange, ventilation of the lower thermocline, and nutrient supply for global ocean productivity. Here we present the first high-resolution autonomous observations of mixed layer CO2 partial pressure (pCO2) and hydrographic properties covering a full annual cycle in the SAZ. The amplitude of the seasonal cycle in pCO2 (∼60 μatm), from near-atmospheric equilibrium in late winter to ∼330 μatm in midsummer, results from opposing physical and biological drivers. Decomposing these contributions demonstrates that the biological control on pCO2 (up to 100 μatm), is 4 times larger than the thermal component and driven by annual net community production of 2.45 ± 1.47 mol C m−2 yr−1. After the summer biological pCO2 depletion, the return to near-atmospheric equilibrium proceeds slowly, driven in part by autumn entrainment into a deepening mixed layer and achieving full equilibration in late winter and early spring as respiration and advection complete the annual cycle. The shutdown of winter convection and associated mixed layer shoaling proceeds intermittently, appearing to frustrate the initiation of production. Horizontal processes, identified from salinity anomalies, are associated with biological pCO2 signatures but with differing impacts in winter (when they reflect far-field variations in dissolved inorganic carbon and/or biomass) and summer (when they suggest promotion of local production by the relief of silicic acid or iron limitation). These results provide clarity on SAZ seasonal carbon cycling and demonstrate that the magnitude of the seasonal pCO2 cycle is twice as large as that in the subarctic high-nutrient, low-chlorophyll waters, which can inform the selection of optimal global models in this region."
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #57 on: November 17, 2016, 06:58:26 PM »
The linked article discusses both the reality and consequences of the changing nature of CO₂ absorption/release and heat uptake by the Southern Ocean.  The extracts below only focus on the risks that the Southern Ocean may soon start venting more CO₂ than it is absorbing.

Jeff Tollefson (17 November 2016), "How much longer can Antarctica’s hostile ocean delay global warming?", Nature, Volume: 539, Pages: 346–348, doi:10.1038/539346a

http://www.nature.com/news/how-much-longer-can-antarctica-s-hostile-ocean-delay-global-warming-1.20978

The waters of the Southern Ocean have absorbed much of the excess heat and carbon generated by humanity.

Although controversial when she encountered it back in 1994, this powerful upwelling is now recognized as a hallmark of the Southern Ocean, a mysterious beast that swirls around Antarctica, driven by the world’s strongest sustained winds. The Southern Ocean absorbs copious amounts of carbon dioxide and heat from the atmosphere, which has slowed the rate of global warming. And its powerful currents drive much of the global ocean circulation.

Already, initial data from an array of ocean floats suggest that upwelling waters could be limiting how much CO2 the Southern Ocean absorbs each year. This raises new questions about how effective these waters will be as a brake on global warming in decades to come.

“The Southern Ocean is doing us a big climate favour at the moment, but it’s not necessarily the case that it will continue doing so in the future,” says Michael Meredith …

Indirect evidence suggests that the Southern Ocean is a net carbon sink and has absorbed as much as 15% of the carbon emissions emitted by humanity since the industrial revolution. But at some times of year and in specific places in this region, carbon-rich surface waters release CO2 into the atmosphere.

Now, researchers are getting some of their first glimpses in near-real time of what happens in the Southern Ocean, particularly in winter. “Right off the bat, we are seeing CO2 fluxes into the atmosphere that are much greater than we had estimated before,” Sarmiento says. “It’s just revolutionary.”

The unpublished analysis is based on just 13 floats that have been in the water for at least a year, so the question now is whether the higher CO2 emissions during winter represent larger trends across the entire Southern Ocean.

“It’s pretty tantalizing,” says Alison Gray, a postdoctoral researcher at Princeton who is leading the study. “It would imply that potentially there is a much weaker carbon sink in the Southern Ocean than has been estimated.”

Hints of something similar have been seen before. In 2007, a team led by Corinne Le Quéré, now director of the Tyndall Centre for Climate Change Research in Norwich, UK, published a study in Science indicating that the rate of carbon uptake by the Southern Ocean decreased between 1981 and 2004. The authors blamed the changes on the winds that encircle the Antarctic continent. The speed of those winds had increased during that time, probably as a result of the hole in the stratospheric ozone layer over Antarctica and possibly because of global warming. Stronger winds are better able to pull up deep, ancient water, which releases CO2 when it reaches the surface. That would have caused a net weakening of the carbon sink.

If that trend were to continue, atmospheric CO2 levels would rise even faster in the future. However, a study in Science last year found that the carbon sink started to strengthen in the early 2000s (see ‘The unreliable sink’).

Le Quéré says it’s unclear whether that rise in CO2 absorption is a return to normal or a deviation from the long-term weakening of the sink. Regardless, she says, it’s now clear that the Southern Ocean might be much more fickle than scientists thought."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #58 on: January 23, 2017, 07:20:48 PM »
The linked reference indicate that current models likely do not accurately represent CO₂ ventilation from the equatorial Pacific (& Atlantic) Ocean(s) during periods of deglaciation.  The reference states: "In addition, both gradual and rapid deglacial radiocarbon changes in these Pacific records are coeval with changes in the Atlantic records.  This in-phase behavior suggest that the Southern Ocean overturning was the dominant driver of changes in the Atlantic and Pacific ventilation during deglacitions."  This does not bode well for our future.

Natalie E. Umling & Robert C. Thunell (2017), "Synchronous deglacial thermocline and deep-water ventilation in the eastern equatorial Pacific", Nature Communications, doi:10.1038/ncomms14203

http://www.nature.com/articles/ncomms14203
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jai mitchell

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Re: Southern Ocean Venting of CO2
« Reply #59 on: January 23, 2017, 09:21:13 PM »
the paleoclimate analog is not accurate for the current system.  They are looking at warming and venting from the ocean that is at saturation with the current atmosphere.  These deeper ocean currents are much undersaturated as we continue to (rapidly) increase our atmospheric CO2 abundance.  So they won't vent according to the paleoclimate history, at least not the deeper, older currents that are not in contact with the atmosphere.
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AbruptSLR

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Re: Southern Ocean Venting of CO2
« Reply #60 on: January 24, 2017, 12:38:11 AM »
the paleoclimate analog is not accurate for the current system.  They are looking at warming and venting from the ocean that is at saturation with the current atmosphere.  These deeper ocean currents are much undersaturated as we continue to (rapidly) increase our atmospheric CO2 abundance.  So they won't vent according to the paleoclimate history, at least not the deeper, older currents that are not in contact with the atmosphere.


See Replies #1615 & 1616 in the Conservative Scientists ... thread.

http://forum.arctic-sea-ice.net/index.php/topic,1053.msg100292.html#msg100292
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jai mitchell

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Re: Southern Ocean Venting of CO2
« Reply #61 on: February 09, 2017, 04:29:38 AM »
New study models increased CO2 venting from overturning circulation in the southern oceans, with the last paragraph I was thinking of posting this on 'conservative scientists'

https://www.carbonbrief.org/scientists-solve-ocean-carbon-sink-puzzle?utm_content=buffer84290&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

DeVries, T. et al. (2017) Recent increase in oceanic carbon uptake driven by weaker upper-ocean overturning, Nature, doi:10.1038/nature21068 Mikaloff-Fletcher, S.E. (2017) Ocean circulation drove increase in CO2 uptake, Nature

http://nature.com/articles/doi:10.1038/nature21068

“My working hypothesis is that it is natural variability, but only time will tell. I say this because model simulations suggest that the point where the human-caused impact on the ocean carbon sink is clearly separable from natural variability is rather distant in the future.”
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Bruce Steele

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Re: Southern Ocean Venting of CO2
« Reply #62 on: February 09, 2017, 06:25:51 AM »
Jai, I didn't see a retraction of your
These deeper ocean currents are much undersaturated as we continue to (rapidly) increase our atmospheric CO2 abundance. 


You again make some claim that there is an increase in venting when the article you site says
" stronger ocean overturning,as seen in the 1990s, brings more carbon -rich water up from the deeper ocean "
The graphic in the article shows a 3 gigatonne decrease in venting to the atmosphere relative to the 1990s not an increase in venting.

Maybe I am confused with your choice of terms but to me ocean venting implies an ocean to atmosphere CO2 transfer whereas ocean ventilation is a transfer of CO2 from the atmosphere to the ocean. If you might spell out which transfer you intend it might help me to better understand your meaning. At any rate the deep ocean is not undersaturated relative to current atmospheric levels and that is why there was a larger ocean to atmosphere CO2 transfer in the 1990s when upwelling was bringing more deep water to the surface. Again you might better explain your choice of the word undersaturated because it is used as a definition for the solubility of aragonite. I think you mean there is less CO2 at depth but that is incorrect.
I also think you should respect Grubers contention that we don't know whether the more recent conditions represent a longer term trend. I would much consider Gruber an expert and accept his opinion that variability is responsible . He is a top notch biogeochemist . Not a field easily mastered .
I have read his predictions for U.S. West Coast surface water undersaturation and they are Not conservative . Undersaturation is the point that aragonite dissolves and Gruber has predicted months long periods of undersaturation by 2035. I will tract down numbers when I get a chance.

« Last Edit: February 09, 2017, 06:32:49 AM by Bruce Steele »

jai mitchell

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Re: Southern Ocean Venting of CO2
« Reply #63 on: February 10, 2017, 08:25:48 PM »
from the article

If the weak circulation patterns continue, this “may help to enhance the oceanic CO2 sink for some time”, the paper says. But there is also the distinct possibility that the changes we are seeing now are temporary, says DeVries:

“The overturning circulation [could] switch back to a more vigorous state in the next decade. In this case, the changes would be reversed, and we would go back to a weaker ocean CO2 sink (like in the 1990s).”

and yes, I felt that ASLRs response to my statement was more than adequate.  I was incorrect in asserting that deep ocean currents were undersaturated since I was thinking of the atmospheric exchange function only, not the larger chemical processes involved with deep ocean currents. 
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Bruce Steele

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Re: Southern Ocean Venting of CO2
« Reply #64 on: February 11, 2017, 05:24:15 AM »
Jai, yes well it is kinda difficult disagreeing without coming off like a dick. Didn't intend to be rude.
More importantly I too worry that a switch back to the earlier conditions of the 1990s would result in an extra 3GT additional  CO2 moving from the ocean carbon sink back into the atmosphere annually . It is also unnerving that even though the Southern Oceans are currently functioning as a weak sink Mauna Loa is accelerating. If the southern Oceans hadn't become a more effective sink the atmospheric CO2 levels would have grown even faster.