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Bdwo
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"The Central Arctic is less relevant, since that's where the MYI hangs out" Not exactly - https://www.climate.gov/news-features/videos/old-ice-arctic-vanishingly-rare or - http://polarportal.dk/en/havisen-i-arktis/nbsp/sea-ice-extent/ Sometimes what appears to be a multiyear ice shelf - https://worldview.earthdata.nasa.gov/?p=arctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2017-03-15&z=3&v=355341.8684741816,-1099815.355097055,692493.8684741816,-936999.355097055 is likely a mix of small chunks & thinly frozen leads. smoothed over with snow - https://worldview.earthdata.nasa.gov/?p=arctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2016-09-15&z=3&v=355341.8684741816,-1099815.355097055,692493.8684741816,-936999.355097055
Toggle Commented Mar 16, 2017 on PIOMAS February 2017 at Arctic Sea Ice
according to http://www.legacy.com/obituaries/dailycamera/obituary.aspx?n=andrew-slater&pid=181701841 Dr Slater " passed away unexpectedly of natural causes at his home in Boulder in the beginning of September."
Toggle Commented Oct 4, 2016 on In memoriam: Andrew Slater at Arctic Sea Ice
Natural marine seepage blowout: Contribution to atmospheric methane; Ira Leifer, Bruce P. Luyendyk, Jim Boles, and Jordan F. Clark doi:10.1029/2005GB002668. http://www.geol.ucsb.edu/faculty/luyendyk/Luyendyk_pdf/Leifer_etal_GBC_06_SeepBoom.pdf - cool pictures; I think "SeepBoom" in the URL indicates the authors position on the wisdom of poking clathrates with rising CO2 emissions. "On 8 March 2002, SCUBA divers were at Shane Seep to measure the bubble plume’s upwelling flow velocity, Vup, the velocity water moves vertically owing to the rising bubbles, by introducing fluorescein dye into the bubble stream at the seabed and measuring its time of arrival at the sea surface [Clark et al., 2003]. Video cameras were situated at the seabed and 5 m above, at the sea surface, and in an airplane. A test dye release at 0845 Local Time (LT) yielded a 50-s transit time, Vup 44 cm s1, comparable to previous values [Clark et al., 2003]. Ten minutes before the airplane’s arrival, divers reported that seabed seepage at the main HC volcano had virtually ceased (Figure 2a). At 0936 LT a large gas ejection occurred at the seabed (Figures 2b and 2c). Suddenly, three separate gas streams arose from the seabed, described by the divers as sounding like a freight train. The leading bubbles expanded very rapidly to several meters in diameter by 5 m above the seabed. Dye introduced into the bubble flow at the seabed a few seconds after the blowout (Figure 2d) first was observed at the sea surface 7 s later (Figure 2e), peak Vup  300 cm s1, while the main mass of dye arrived 10 s after dye injection, Vup  200 cm s1. Bubble plumes lift deeper, cooler water that forms a divergent outward flow of water at the sea surface. During the blowout, the area of outward flow expanded rapidly (Figure 2f). Overflight images showed the dyed bubble stream transversing the water column, tilted by the currents (Figures 2g and 2h)." Note that the dye arrives with the entrained water, not the first gas bubbles. My back of envelope calculations using 40 cm/sec indicate that a 100 meter diameter methane "fountain" entraining water 1 degree above melting(e.g., from the layer of Atlantic Water that penetrates the arctic below the fresher surface layer) could carry enough heat to melt an ~ 1 km diameter hole in 1 meter thick ice per month. Of course, what goes up must come down, and the turnover could transfer heat from solar warmed surface water back to the bottom as the melt season progresses. Warming the fuel for the fire: Evidence for the thermal dissociation of methane hydrate during the Paleocene-Eocene thermal maximum; Thomas et al - doi: 10.1130/0091-7613(2002)​030<1067:WTFFTF>​2.0.CO;2 Geology, v. 30 no. 12 p. 1067-1070 http://geology.gsapubs.org/content/30/12/1067.abstract "We present new high-resolution stable isotope records based on analyses of single planktonic and benthic foraminiferal shells from Ocean Drilling Program Site 690 (Weddell Sea, Southern Ocean), demonstrating that the initial carbon isotope excursion was geologically instantaneous and was preceded by a brief period of gradual surface-water warming. Both of these findings support the thermal dissociation of methane hydrate as the cause of the Paleocene-Eocene thermal maximum carbon isotope excursion. Furthermore, the data reveal that the methane-derived carbon was mixed from the surface ocean downward, suggesting that a significant fraction of the initial dissociated hydrate methane reached the atmosphere prior to oxidation." An Ancient Carbon Mystery, Mark Pagani, Ken Caldeira, David Archer, James C. Zachos Science 8 December 2006: Vol. 314 no. 5805 pp. 1556-1557 DOI: 10.1126/science.1136110 http://www.sciencemag.org/content/314/5805/1556.full "According to one hypothesis, the PETM was caused by the release of ∼2000 PgC from the destabilization of methane hydrates (which would subsequently oxidize to form CO2) (10). However, it is unlikely that methane was the sole source of warming. For example, the size of the methane hydrate reservoir at the end of the Paleocene was probably much smaller than it is today (11), and the magnitude of the sustained warming and the change in the carbonate compensation depth are compatible with a much greater mass of carbon than originally estimated (6). To account for larger carbon inputs, other sources have been invoked, including the oxidation of terrestrial (12) and marine (13) organic carbon and/or volcanic outgassing and thermal decomposition of organic matter (14). There is no single satisfactory explanation." Will the current rapid warming as opposed to gradual PETM surface-water warming have a lower or higher threshold for triggering a "geologically instantaneous" release of CH4? Do the differences in seafloor configuration, ocean circulation, methane hydrate amounts, background CO2 levels, and other unknown unknowns raise or lower the threshold for triggering the clathrate gun? If you keep pushing on a trigger to find the force required, eventually you will reach it. Given the unknowns and uncertainty, we could get lucky. Being as this is a 1400 Gt Magnum, the most powerful GHGgun in the world, and would blow most everybodies head clean off, you've got to ask yourself one question: Do I feel lucky? Well, do ya, punks? (apologies to Clint Eastwood as Dirty Harry) Dietary controls on extinction versus survival among avian megafauna in the late Pleistocene Geology, Kena Fox-Dobbs, Thomas A. Stidham, Gabriel J. Bowen, Steven D. Emslie, and Paul L. Koch August, 2006, v. 34, p. 685-688, doi:10.1130/G22571.1 http://geology.gsapubs.org/content/34/8/685.abstract "The late Pleistocene extinction decimated terrestrial megafaunal communities in North America, but did not affect marine mammal populations. In coastal regions, marine megafauna may have provided a buffer that allowed some large predators or scavengers, such as California condors (Gymnogyps californianus), to survive into the Holocene." Are homo (notso)sapiens megafauna? Will we come to regret so many seals were killed(reducing or eliminating populations) just to make fur coats instead of keeping them around for food? What are we prepared to do if the scientists tell us "X was the clathrate gun trigger threshold that we have already passed"?
@ A-Team | July 08, 2013 at 01:49 "If well-mixed, the heat content of the deeper waters would overwhelm surface ice..." I've noticed what seem to be curveiinear early melt features in the ice over the East Siberian Shelf which roughly follow ocean depth contours. The pressure/temperature response of methane hydrate decomposition means that at a constant temperature, there is a pressure(depth) below which the hydrate decomposes, and above which it is stable; the upper edge of a hydrate layer would therefore follow a depth contour. As the temperature increases, the hydrate stability depth increases - so the hydrate between the original edge of the hydrate layer and the new stability contour would decompose, causing the "bubble fountains" (observed by Semilotev and others) to align approximately along depth contours. These rising bubbles of methane will entrain bottom water, which is saltier, denser, but warmer - which could contribute to bottom melt of the ice. Higher resolution ice maps and on site observations would confirm this theory(SWAG?) According to http://www.hindawi.com/journals/ace/2010/789547/, "Experimental Investigation of a Rectangular Airlift Pump", the mass flow ratio of gas to liquid is on the order of 100:1. This is ducted, not free flow, and working against a head created by raising the top of the duct above the surface of the entrained liquid, so the mass of sea water lifted versus methane evolved from hydrate decomposition is likely larger.
Toggle Commented Jul 9, 2013 on So, how slow was this start? at Arctic Sea Ice
@ Ulrick Vonbek | September 15, 2012 at 00:34 on the differences between Arctic and Antarctic sea ice dynamics, and correlations Some of the posters over at weatheroutlook have noted the differences imposed by geography - Arctic sea Ice surrounded by land versus thick, high altitude Antarctic ice sheets surrounded by circumpolar current and atmospheric vortex, as well as the freshening, easier to freeze surface water from melt and precipitation. A part of that is from ice shelf collapse; Larsen B was about 220 meters thick. After it collapsed, melted, and spread out/mixed into the surface water around the continent, it would cover a much larger area when it refroze 1-2 m thick. 220 meters thick by 3,250 km^2 yields 400,000 to 600,000 km^2 at typical Antarctic sea ice thickness. This may account for some of the rebound in Antarctic sea ice* from the dip around 2002-2003, but the signal is very noisy - http://www.woodfortrees.org/plot/nsidc-seaice-s/from:1979.6/every:12 - and very dependent on the specific time and way that the remains of Larsen B spread out. As for short term correlations, if one detrends the NH minimum, and the SH maximum, and compares them, one gets the following; Pearson correlation efficient: -0.03768145 95% confidence interval: ( -0.3761304 , 0.30963904 ) Significance: p > 0.05 *my nonexpert blogging SWAG -"scientific wild a$$ guess"
"Heat does not move against a temperature gradient. It always flows from warmer to cooler. As long as the Arctic is cooler than the South, the heat stays put, or is radiated to space..." But a lot of the heat gained in the tropics is transported to the poles before being radiated into space - and with warmer poles, and lower gradient, less gets transported poleward. Jacking up the temperature locally at the poles by decreasing albedo results in less transport of heat poleward and warmer temperatures globally even without any changes elsewhere. I wonder if the larger annual variation in ice freeze/melt will cause large annual cycles in the AMOC, and if more open (esp. summer) water will change the balance between latent and sensible heat transport in the atmosphere - with concomitant changes in the weather.
@: Mdoliner43 | August 26, 2012 at 22:13 "Water, ice, and snow generally have a high emissivity, 0.94 to 0.99, across the thermal infrared region." www.icess.ucsb.edu/modis/EMIS/html/em.html (yes, that MODIS) Ice cover lowers the heat loss by virtue of its lower thermal transport(conduction only) compared to water(conductivity+convection). Snow covered ice allows even lower surface temperatures by virtue of its' high thermal infrared emissivity and low conductivity compared to solid ice, which is why -40 degrees surface temperatures are common with only a meter or two of ice+snow over -2 degree water - but it also means that not much thickness beyond 1-2 meters can freeze in the winter even with such low surface temps. A potential feedback for thinner winter ice(some ice will always form when the sun sets in the arctic) is that so much open water will be a large new source of atmospheric water vapor over the pole, which will result in rapid early accumulation of thick insulating snow cover. Once the ice reaches a thickness that is mechanically stable to wind and wave action, preventing wetting of the snow(0.5 meter?), the insulation will prevent much further growth in thickness even with -40 degree surface temperatures - and it's possible that thicker snow will allow much lower winter temperatures than currently seen in the Arctic. When there are outbreaks of Arctic air in January or February to New York or London, they will be deadly, IMHO.
Toggle Commented Aug 28, 2012 on ASI 2012 update 10: (wh)at a loss at Arctic Sea Ice
wind blowing from open water toward the ice edge will bring warmed surface water to it, and waves will also form, which will tend to break up the ice and expose more surface area to melting conditions. Winds blowing from the ice towards open water will carry melt away from the edge along with near surface water, which will cause upwelling of deeper, saltier, and warmer water. (In the Arctic Ocean, the positive salinity gradient with depth wins out over the positive temperature gradient with depth, maintaining a positive density gradient with depth and stable stratification under permanent ice. With larger ice free areas subject to wind mixing, I will confidently predict this is changing, but I haven't seen any published results on this.) How effective is this Eckmann transport of thermal energy from the depths at melting ice? Cooling ~80 meters of seawater 1 degree C will provide enough energy to melt 1 meter of ice; winds can cause mixing of sea surface to hundreds of meters depth, and the Arctic ocean is thousands of meters deep. I wonder if this could provide an amplifying mechanism when the ice edge is over deep water, compared to shallower continental shelves, where wind driven upwelling wouldn't have a massive heat reservoir to tap?
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Aug 7, 2012