Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin...
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Transcript of Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin...
![Page 1: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/1.jpg)
Frost flowers – implications for tropospheric chemistry and ice
core interpretation
Andrew Rankin1, Eric Wolff1 and Seelye Martin2
(1) British Antarctic Survey, Cambridge, UK.
(2) University of Washington, Seattle, USA.
![Page 2: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/2.jpg)
Thanks
• Victoria Lytle, U. Tasmania – collection of frost flowers near Mertz Glacier
• BAS Halley wintering staff – collection of frost flowers near Halley
• David G. Long, Brigham Young University, NASA-scatterometer images
• Mark Drinkwater, ESA, interpretation of scatterometer images
![Page 3: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/3.jpg)
Outline
• What are frost flowers?
• Importance as source for sea salt aerosol and ice cores
• Importance as surface for Br-related chemistry
![Page 4: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/4.jpg)
What are frost flowers?
Widespread, whenever new sea ice forms
Important part of sea-air interface
Until now, no chemical studies
![Page 5: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/5.jpg)
![Page 6: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/6.jpg)
Source of sea salt aerosol?
• Numerous studies show that winter aerosol and snow, at least in coastal Antarctica, are significantly depleted in sulfate relative to sea water, ie nss SO4
2- is negative
• Ratio of SO42-:Na in sea salt aerosol closer to 0.1 cf 0.25
for seawater
• Sea salt maximum in winter despite much greater sea ice extent
Hypothesis: Sea ice surface (esp. frost flowers) is main source of sea salt, which assumes this surface is highly saline and depleted in sulfate
![Page 7: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/7.jpg)
Frost flowers and brine are highly saline, diluted only when mixed with fresh snow
M ertz g lac ier
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W ed d ell1999
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BrineFro st flo we rs
Se a Ic eSe a wa te rSta nd a rd M e a n O c e a n Wa te r
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Frost flowers and some brine are highly depleted in SO42-
relative to Na, with ratios similar to those seen in Halley aerosol and coastal snow (precipitation of mirabilite)
W eddell1998
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BrineFro st flo we rs
Se a Ic eSe a wa te rSta nd a rd M e a n O c e a n Wa te r Sta nd a rd M e a n O c e a n Wa te r Ha lle y Winte r Ae ro so l
![Page 9: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/9.jpg)
At Halley, all episodes of salty aerosol, depleted in sulfate, are associated with frost flowers; but this is not a sufficient condition
Each vertical bar represents one aerosol filter; grey ones are significantly depleted in sulfate. Black horizontal bars are periods of frost flowers near Halley.
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Frost flower bloom seen on scatterometer (NASA QSCAT)
Back trajectories from Halley (ECMWF) pass over frost flower area
Halley aerosol filter shows high salt, depleted in sulfate
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Back trajectories not over frost flowers, then flowers area decays
Halley aerosol is now low in salt and not obviously depleted in sulfate
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Majority of Na in the core comes from the fractionated mode
Dolleman Island ice core
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Conclusions for ice cores
• Beyond reasonable doubt, frost flowers and sea ice surface are main source of sea salt aerosol in coastal Antarctica
• This conclusion may be extendable to inland sites
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Frost flowers contain high concentrations of bromide, though only in line with their increased salinity. Br- is likely to be on the surface however cold the ice
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BrineFro st flo we rs
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Surfaces for Br-related chemistry
![Page 15: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/15.jpg)
Surfaces and sources for Br-related chemistry
• Frost flowers vs sea water– Surface areas likely to be greater than that of fresh snow (~2 m2 g-
1);
– Where flowers present, estimate ~ 0.05 g cm-2 (Perovich & Richter-Menge 1994)
Surface areas of order 1000 m2 m-2
Concentrations higher than in sea water or old sea ice, both of which have relatively flat surface areas
Likely that at least in winter half-year, frost flowers present a greater Br-laden surface than sea water around Antarctica
![Page 16: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/16.jpg)
Surfaces and sources for Br-related chemistry
• Frost flowers versus snowpack– Surface areas of snowpack to a few cm depth
are very large– But concentration of Br- in snowpack at most a
few ng g-1, compared to 200 000 ng g-1Br- in frost flowers
Frost flowers are expected to provide much more Br than snowpack can in coastal Antarctica
![Page 17: Frost flowers – implications for tropospheric chemistry and ice core interpretation Andrew Rankin 1, Eric Wolff 1 and Seelye Martin 2 (1)British Antarctic.](https://reader036.fdocuments.us/reader036/viewer/2022062620/551a507c550346cb358b5be0/html5/thumbnails/17.jpg)
• Further study is needed but it seems probable that frost flowers provide by far the biggest surface area of available Br-
• Enhanced filterable Br and low-level tropospheric ozone loss episodes are compatible with the episodic (few days) nature of frost flowers
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Conclusions• Sea ice surface (esp. frost flowers) is the main
source of sea salt aerosol in coastal Antarctica• Frost flowers are probably the greatest surface
area of Br-rich material available for reactionsObvious next steps• Relating Br/ozone events with QSCAT frost
flower events• And determining source of sea salt in central
Antarctica