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Author Topic: Trends for the Southern Ocean  (Read 50849 times)

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #100 on: September 01, 2016, 04:56:45 AM »
The linked reference indicates that the recent expansion of Antarctic sea ice extent is contributing to the recently observed salinity driven (surface freshening) stratification of the Southern Ocean; which by theory should be making a bigger contribution to Hansen et al (2016)'s positive ice-climate feedback mechanism, than previously thought:

F. Alexander Haumann, Nicolas Gruber, Matthias Münnich, Ivy Frenger & Stefan Kern (01 September 2016), "Sea-ice transport driving Southern Ocean salinity and its recent trends", Nature, Volume: 537, Pages: 89–92, doi:10.1038/nature19101


http://www.nature.com/nature/journal/v537/n7618/full/nature19101.html

Abstract: "Recent salinity changes in the Southern Ocean are among the most prominent signals of climate change in the global ocean, yet their underlying causes have not been firmly established. Here we propose that trends in the northward transport of Antarctic sea ice are a major contributor to these changes. Using satellite observations supplemented by sea-ice reconstructions, we estimate that wind-driven northward freshwater transport by sea ice increased by 20 ± 10 per cent between 1982 and 2008. The strongest and most robust increase occurred in the Pacific sector, coinciding with the largest observed salinity changes4, 5. We estimate that the additional freshwater for the entire northern sea-ice edge entails a freshening rate of −0.02 ± 0.01 grams per kilogram per decade in the surface and intermediate waters of the open ocean, similar to the observed freshening. The enhanced rejection of salt near the coast of Antarctica associated with stronger sea-ice export counteracts the freshening of both continental shelf and newly formed bottom waters due to increases in glacial meltwater. Although the data sources underlying our results have substantial uncertainties, regional analyses and independent data from an atmospheric reanalysis support our conclusions. Our finding that northward sea-ice freshwater transport is also a key determinant of the mean salinity distribution in the Southern Ocean further underpins the importance of the sea-ice-induced freshwater flux. Through its influence on the density structure of the ocean, this process has critical consequences for the global climate by affecting the exchange of heat, carbon and nutrients between the deep ocean and surface waters."


See also:

https://www.washingtonpost.com/news/energy-environment/wp/2016/08/31/how-sea-ice-is-making-the-southern-ocean-less-salty-and-what-that-might-mean-for-the-rest-of-the-world/?utm_term=.0b003dd35a67

Extract: "Now, a new study, published Wednesday in Nature, suggests that sea ice may be one of the major culprits. Using satellite data and models, the authors have shown that Antarctic sea ice has been moving farther and farther away from the continental coastline by strengthening winds in recent years, pouring fresh water farther out into the ocean as it melts. 

A recent paper, led by Columbia professor and former NASA scientist James Hansen, suggested the stratification could help force the trapped warm water right up to the bases of marine-terminating glaciers on the Antarctic continent, melting them from the bottom up and leading to an even faster influx of fresh water into the ocean.

“Haumann and colleagues’ findings emphasize that Antarctic sea ice is not merely a passive indicator of climate change and variability, but also a driver of changes in the climate system,” wrote Maksym wrote in his comment. “…ea ice might have a bigger role than previously thought.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #101 on: September 23, 2016, 11:01:26 PM »
The linked reference associates the Tropical Pacific SST & the PDO to Antarctic sea ice trends; due to an interconnection through the Amundsen Sea Low:

Ariaan Purich, Matthew H. England, Wenju Cai, Yoshimitsu Chikamoto, Axel Timmermann, John C. Fyfe, Leela Frankcombe, Gerald A. Meehl and Julie M. Arblaster (21 September 2016), "Tropical Pacific SST drivers of recent Antarctic sea ice trends", Journal of Climate, DOI: http://dx.doi.org/10.1175/JCLI-D-16-0440.1

http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-16-0440.1

Abstract: "A strengthening of the Amundsen Sea Low from 1979-2013 has been shown to largely explain the observed increase in Antarctic sea ice concentration in the eastern Ross Sea and decrease in the Bellingshausen Sea. Here we show that while these changes are not generally seen in freely-running coupled climate model simulations, they are reproduced in simulations of two independent coupled climate models; one constrained by observed sea surface temperature anomalies in the tropical Pacific, and the other by observed surface wind-stress in the tropics. Our analysis confirms previous results and strengthens the conclusion that the phase change in the Interdecadal Pacific Oscillation from positive to negative over 1979-2013 contributed to the observed strengthening of the Amundsen Sea Low and associated pattern of Antarctic sea ice change during this period. New support for this conclusion is provided by simulated trends in spatial patterns of sea ice concentrations that are similar to those observed. Our results highlight the importance of accounting for teleconnections from low to high latitudes in both model simulations and observations of Antarctic sea ice variability and change."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #102 on: October 01, 2016, 01:31:40 AM »
The linked reference confirms that the observed increase in the speed of westerly winds over the Southern Ocean was human-induced & I note that this increased in wind speed is believed to have induced warm CDW to accelerate ice melt along the grounding lines of key marine glaciers in Antarctica:

Julie M. Jones et al. Assessing recent trends in high-latitude Southern Hemisphere surface climate, Nature Climate Change (2016). DOI: 10.1038/nclimate3103


http://www.nature.com/nclimate/journal/v6/n10/full/nclimate3103.html

Abstract: "Understanding the causes of recent climatic trends and variability in the high-latitude Southern Hemisphere is hampered by a short instrumental record. Here, we analyse recent atmosphere, surface ocean and sea-ice observations in this region and assess their trends in the context of palaeoclimate records and climate model simulations. Over the 36-year satellite era, significant linear trends in annual mean sea-ice extent, surface temperature and sea-level pressure are superimposed on large interannual to decadal variability. Most observed trends, however, are not unusual when compared with Antarctic palaeoclimate records of the past two centuries. With the exception of the positive trend in the Southern Annular Mode, climate model simulations that include anthropogenic forcing are not compatible with the observed trends. This suggests that natural variability overwhelms the forced response in the observations, but the models may not fully represent this natural variability or may overestimate the magnitude of the forced response."

See also:

http://phys.org/news/2016-09-shift-westerly-climate-impacts-human-induced.html

Extract: "To gain a longer view of recent changes, Dr Jones and her international team of scientists used a compilation of climate records from natural archives, such as ice cores from the Antarctic ice sheet, which give indications of how the region's climate has changed over the last 200 years. They also studied how these recent changes compared to those in experiments with climate models.
They confirmed that human-induced changes have caused the belt of prevailing westerly winds over the Southern Ocean to shift towards Antarctica."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #103 on: December 30, 2016, 10:28:30 PM »
The linked physical research indicates that the ACC is 30% stronger than scientists previously assumed.


K. A. Donohue, K. L. Tracey, D. R. Watts, M. P. Chidichimo & T. K. Chereskin (21 November 2016), "Mean Antarctic Circumpolar Current transport measured in Drake Passage", Geophysical Research Letters, DOI: 10.1002/2016GL070319


http://onlinelibrary.wiley.com/doi/10.1002/2016GL070319/abstract?systemMessage=Wiley+Online+Library+will+be+unavailable+on+Saturday+26th+November+2016+from+07:00-11:00+GMT+/+02:00-06:00+EST+/+15:00-19:00+SGT+for+essential+maintenan

Abstract: "The Antarctic Circumpolar Current is an important component of the global climate system connecting the major ocean basins as it flows eastward around Antarctica, yet due to the paucity of data, it remains unclear how much water is transported by the current. Between 2007 and 2011 flow through Drake Passage was continuously monitored with a line of moored instrumentation with unprecedented horizontal and temporal resolution. Annual mean near-bottom currents are remarkably stable from year to year. The mean depth-independent or barotropic transport, determined from the near-bottom current meter records, was 45.6 sverdrup (Sv) with an uncertainty of 8.9 Sv. Summing the mean barotropic transport with the mean baroclinic transport relative to zero at the seafloor of 127.7 Sv gives a total transport through Drake Passage of 173.3 Sv. This new measurement is 30% larger than the canonical value often used as the benchmark for global circulation and climate models."


The associated linked article is entitled: "Notorious Ocean Current Is Far Stronger Than Previously Thought".
https://eos.org/research-spotlights/notorious-ocean-current-is-far-stronger-than-previously-thought?utm_source=eos&utm_medium=email&utm_campaign=EosBuzz123016


Extract: "The Antarctic Circumpolar Current is the only ocean current to circle the planet and the largest wind-driven current on Earth. It's also 30% more powerful than scientists realized."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #104 on: February 05, 2017, 12:51:48 PM »
The linked reference indicates that the rate of freshening of the AABW is accelerating rapidly, thus supporting Hansen's ice-climate feedback mechanism:

Viviane V. Menezes, Alison M. Macdonald and Courtney Schatzman (25 Jan 2017), "Accelerated freshening of Antarctic Bottom Water over the last decade in the Southern Indian Ocean", Science Advances, Vol. 3, no. 1, e1601426, DOI: 10.1126/sciadv.1601426

http://advances.sciencemag.org/content/3/1/e1601426

Extract: "Southern Ocean abyssal waters, in contact with the atmosphere at their formation sites around Antarctica, not only bring signals of a changing climate with them as they move around the globe but also contribute to that change through heat uptake and sea level rise. A repeat hydrographic line in the Indian sector of the Southern Ocean, occupied three times in the last two decades (1994, 2007, and, most recently, 2016), reveals that Antarctic Bottom Water (AABW) continues to become fresher (0.004 ± 0.001 kg/g decade−1), warmer (0.06° ± 0.01°C decade−1), and less dense (0.011 ± 0.002 kg/m3 decade−1). The most recent observations in the Australian-Antarctic Basin show a particularly striking acceleration in AABW freshening between 2007 and 2016 (0.008 ± 0.001 kg/g decade−1) compared to the 0.002 ± 0.001 kg/g decade−1 seen between 1994 and 2007. Freshening is, in part, responsible for an overall shift of the mean temperature-salinity curve toward lower densities. The marked freshening may be linked to an abrupt iceberg-glacier collision and calving event that occurred in 2010 on the George V/Adélie Land Coast, the main source region of bottom waters for the Australian-Antarctic Basin. Because AABW is a key component of the global overturning circulation, the persistent decrease in bottom water density and the associated increase in steric height that result from continued warming and freshening have important consequences beyond the Southern Indian Ocean."

See also the associated article entitled: "Antarctic Bottom Waters Freshening at Unexpected Rate".

https://scripps.ucsd.edu/news/antarctic-bottom-waters-freshening-unexpected-rate

Extract: "Shift could disturb ocean circulation and hasten sea level rise, researchers say.

The team found that the previously detected warming trend has continued, though at a somewhat slower pace. The biggest surprise, however, was its lack of saltiness: AABW in the  region off East Antarctica’s Adélie Land has grown fresher four times faster in the past decade than it did between 1994 and 2007."
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #105 on: February 05, 2017, 01:09:58 PM »
The linked reference helps to explain why the Antarctic deep water is freshening unexpectedly quickly; which likely will accelerate the slowing of the thermohaline circulation.  This research also indicates that the Antarctic sea ice extent will likely retreat faster than previously expected.

Alberto C. Naveira Garabato, Alexander Forryan, Pierre Dutrieux, Liam Brannigan, Louise C. Biddle, Karen J. Heywood, Adrian Jenkins, Yvonne L. Firing & Satoshi Kimura (2017), "Vigorous lateral export of the meltwater outflow from beneath an Antarctic ice shelf", Nature; doi:10.1038/nature20825

http://www.nature.com/articles/nature20825.epdf?author_access_token=DF62yOZXCaJUnJISA1g1PNRgN0jAjWel9jnR3ZoTv0MR1tk45gxKLxa6eT2BdeuvYwxU8paCVQ2zahPfQktn7LRlJScf53AShbsmYwaBPWLsy2X11W9kCUj_9XPaD8Mz

Abstract: "The instability and accelerated melting of the Antarctic Ice Sheet are among the foremost elements of contemporary global climate change. The increased freshwater output from Antarctica is important in determining sea level rise, the fate of Antarctic sea ice and its effect on the Earth’s albedo, ongoing changes in global deep-ocean ventilation, and the evolution of Southern Ocean ecosystems and carbon cycling. A key uncertainty in assessing and predicting the impacts of Antarctic Ice Sheet melting concerns the vertical distribution of the exported meltwater. This is usually represented by climate-scale models as a near-surface freshwater input to the ocean, yet measurements around Antarctica reveal the meltwater to be concentrated at deeper levels. Here we use observations of the turbulent properties of the meltwater outflows from beneath a rapidly melting Antarctic ice shelf to identify the mechanism responsible for the depth of the meltwater. We show that the initial ascent of the meltwater outflow from the ice shelf cavity triggers a centrifugal overturning instability that grows by extracting kinetic energy from the lateral shear of the background oceanic flow. The instability promotes vigorous lateral export, rapid dilution by turbulent mixing, and finally settling of meltwater at depth. We use an idealized ocean circulation model to show that this mechanism is relevant to a broad spectrum of Antarctic ice shelves. Our findings demonstrate that the mechanism producing meltwater at depth is a dynamically robust feature of Antarctic melting that should be incorporated into climate-scale models."

See also the linked article entitled: "Scientists Say They Now Know Why Antarctic Meltwater Stays Below Ocean Surface".

http://blogs.ei.columbia.edu/2017/02/02/scientists-say-they-now-know-why-antarctic-meltwater-stays-below-ocean-surface/

Extract: " Scientists believe that the depth at which meltwater enters the ocean can affect global ocean circulation and, in turn, climate. Fresh surface meltwater makes the upper layers of the Southern Ocean lighter. This is thought to slow down the sinking of surface water, and to favor the expansion of Antarctic sea ice. Injecting the same meltwater further down is believed to have the opposite effect, favoring sinking of surface waters and the retreat of Antarctic sea ice.

The potential effects of such processes were taken to the extreme in the 2004 movie The Day After Tomorrow, in which floating meltwater produced by warming climate caused the North Atlantic to freeze over almost instantly, in turn locking much of the United States in ice within days. “While no one expects our climate to change in the space of a few days, like the movie, we do know that fresh water flowing into our seas could dramatically affect sea levels and ocean circulation,” said study coauthor Alexander Forryan of the University of Southampton. “As such, it is vital our models take into account the presence of both surface and deep meltwater to maximize their accuracy.”"
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson

longwalks1

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Re: Trends for the Southern Ocean
« Reply #106 on: February 26, 2017, 07:15:32 PM »
I stumbled over this one via the Carbon Cycle  thread and also the ocean acidification site https://news-oceanacidification-icc.org/

Southern Ocean Phytoplankton in a Changing Climate

Stacy L. Deppeler1* and Andrew T. Davidson2,3

1Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, TAS, Australia
2Australian Antarctic Division, Department of the Environment and Energy, Kingston, TAS, Australia
3Antarctic Climate and Ecosystem Cooperative Research Centre (ACE CRC), University of Tasmania, Hobart, TAS, Australia

http://journal.frontiersin.org/article/10.3389/fmars.2017.00040/full

Predicting the net effect of multiple climate-induced stressors over a range of environments is complex. Yet understanding the response of SO phytoplankton to climate change is vital if we are to predict the future state/s of the ecosystem, estimate the impacts on fisheries and endangered species, and accurately predict the effects of physical and biotic change in the SO on global climate. This review looks at the major environmental factors that define the structure and function of phytoplankton communities in the SO, examines the forecast changes in the SO environment, predicts the likely effect of these changes on phytoplankton, and considers the ramifications for trophodynamics and feedbacks to global climate change. Predictions strongly suggest that all regions of the SO will experience changes in phytoplankton productivity and community composition with climate change. The nature, and even the sign, of these changes varies within and among regions and will depend upon the magnitude and sequence in which these environmental changes are imposed. It is likely that predicted changes to phytoplankton communities will affect SO biogeochemistry, carbon export, and nutrition for higher trophic levels.

It is a review and  not short.  It is not that difficult to read for the most part.  It goes into the major zones of the Southern Ocean - Permanently Open Ocean Zone, Seasonal Sea Ice Zone,  Marginal Ice Zone,  Antarctic Continental Shelf Zone. West Antarctica, East Antarctica and the phytoplankton environment in each..  The conclusions are heavily prefaced by the lack of data and the difficulty in getting ice thickness, and chlorophyll values from under the ice. 

I am still digesting it, but I like it enough that I will probably convert to .epub and import the illustrations.
Shut my mouth, it is already available for download as an .epub. 

Hyperion

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Re: Trends for the Southern Ocean
« Reply #107 on: April 12, 2017, 12:02:53 PM »
And so the southern ocean continues to steal the energy and moisture from the entire tropical pacific. And a close up of us being the meat in the sandwich. :o

They told us the last 2 events in the last month were 500 year floods. This ones already much worse. And the real stuffs coming tomorrow.  ;)
Policy: The diversion of NZ aluminum production to build giant space-mirrors to melt the icecaps and destroy the foolish greed-worshiping cities of man. Thereby returning man to the sea, which he should never have left in the first place.
https://en.wikipedia.org/wiki/McGillicuddy_Serious_Party

steve s

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Re: Trends for the Southern Ocean
« Reply #108 on: April 12, 2017, 08:41:46 PM »
Best of luck, H.

Little on the news here, the US, about your extreme weather.

AbruptSLR

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Re: Trends for the Southern Ocean
« Reply #109 on: October 15, 2017, 04:39:54 PM »
The linked article provides some evidence that the stratospheric ozone hole over Antarctica has been slowly (at the lower end of the expected rate) healing itself since 2000.  While it is nice to know that our policies are being effective, we should not forget that since at least 1979 the ozone hole has increased the speed of the circumpolar westerly winds into a 'sweet spot' that has nearly maximized the advection of warm CDW to the grounding lines of many key marine glaciers.  Furthermore, we should remember that at the same time as the ozone hole is healing itself (thus contributing to slowing the westerly wind velocities) the GHG concentration over Antarctica is increasing, which is effectively keeping the westerly wind velocity in the 'sweet spot' for advection of the warm CDW.  You could not ask for a more perfect storm for promoting rapid ice mass loss from key Antarctic marine glaciers.

A. T. J. de Laat, M. van Weele & R. J. van der A (12 October 2017), "Onset of Stratospheric Ozone Recovery in the Antarctic ozone hole in assimilated daily total ozone columns", JGR Atmospheres, DOI: 10.1002/2016JD025723 

http://onlinelibrary.wiley.com/doi/10.1002/2016JD025723/abstract?utm_content=buffer78f11&utm_medium=social&utm_source=twitter.com&utm_campaign=buffer

Abstract

In this paper we evaluate the long-term changes in ozone depletion within the Antarctic ozone hole using a 37 years (1979-2015) of daily Ozone Mass Deficits (OMD) derived from assimilated total ozone column data. For each year an ‘average daily OMD’ is calculated over a 60-day preferential time period DOY (Day of Year) 220-280). Excluding years with a reduced Polar Stratospheric Cloud (PSC) volume (the so-called PSC-limited years), the 1979-2015 time series of spatially-integrated average daily OMD correlates very well with long-term changes in Equivalent Effective Stratospheric Chlorine (EESC; R2 = 0.89). We find a corresponding statistically highly significant post year-2000 decrease in OMD of -0.77 ± 0.17 MegaTon (Mt; trend significance of 9.8σ), with an associated post year-2000 change in OMD of approximately -30%, consistent with the post year-2000 change in EESC relative to 1980 EESC levels of approximately -30%. The post year-2000 trend significance is robust to the choice of start year.

The spatial distribution of the average daily OMD trends reveals a vortex-core region (approximately covering the region [90°W – 0 ° – 90°E / 75°S – 85°S]) largely unaffected by dynamics with a post year-2000 trend significance of > 8σ, and a vortex-edge region in which the trend is locally strongly affected by vortex dynamics though not spatially integrated over the whole vortex-edge region (trend significance > 9σ). For the trend significance we do not find consistent evidence for long-term changes in wave driving, vortex mixing, pre-ozone hole conditions, or the applied assimilation method, playing a role.

Our observation/assimilation-based analysis provides robust evidence of a post year-2000 statistically highly significant decrease in the average daily OMD that is consistent with the long-term decrease in ozone depleting substances since 2000 following international emission regulations.

Plain Language Summary
The Antarctic Ozone hole is a prime example of detrimental effects humanity can have on its environment. Successful implementation of policies to reduce emissions of ozone depleting substances have lead to a stabilization and reduction of these substances in the atmosphere. The identification of recovery of Antarctic ozone has remained difficult because of ambiguities on what is the best method to detect recovery. Yet one would be tempted to think that, with the large amount of observational data available nowadays, recovery of Antarctic ozone should be 'hidden' somewhere in the data. In our paper we discuss different observations-based methods for recovery detection, and identify the best method for doing so (as far as we are concerned). We then show that, using this best method, recovery of Antarctic ozone has actually been slow - consistent with expectations - but also very steady ever since approximately the year 2000. Our results are consistent with expections and provide confidence that the policies that have led to a reduction of the amount of ozone depleting substances in the atmosphere, actually also have the expected effect on Antarctic ozone itself.
“It is not the strongest or the most intelligent who will survive but those who can best manage change.”
― Leon C. Megginson