For those who might not realize the implications of increased flow from rivers that empty into the Arctic Sea, permit me to provide some background in my usual non-scientific language.
OK, in areas where there is no permafrost, we have "groundwater" under the ground, right? This can be quite close to the surface or even very deep as in an aquifer. It flows somewhere, following gravity and the path of least resistance. Some of it stays underground once it finds its way to a deep area like an aquifer, or it keeps flowing until it reaches streams and rivers.
In areas where there is permafrost, which is usually quite deep, the water is frozen in the ground and doesn't flow anywhere.
But, what can we imagine will occur when the permafrost is no longer "perma"? Hmm...
Indeed, permafrost is warming up in the regions all around the Arctic Sea, to the point that groundwater is now flowing to the rivers.
This has consequences. The surface water in the Artic Sea becomes less saline. And good ol' methane is being released by the permafrost, and as this process continues, the land subsides. It becomes a big mushy mess basically not good for anything. Buildings fall over, roads sink, gas belches out of the thermokarst lakes. The warming in the Arctic amplifies.
River Discharge
A. Shiklomanov
University of New Hampshire, Durham, NH
August 27, 2009
A general increase of river discharge to the Arctic Ocean from Eurasia was observed over the period 1936-2007, with a rate of annual change (defined from the linear trend) of 2.7 ± 0.5 km3/year (Fig. R1). The most pronounced positive (increasing) trend for the six largest Eurasian rivers is observed during the last 21 years (1987-2007), at a rate of 11.8 km3/year. The rate of discharge has continued to increase in the 21st century. The mean 2000-2007 discharge was 171 km3 higher (10%) than the long-term average over the period 1936-1999. A new historical maximum for Eurasian river discharge to the Arctic Ocean was observed in 2007, reaching 2250 km3/year or 30% higher than the long-term mean discharge from 1936-1999, reported in Peterson et al. (2002).
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| Figure R1. Total annual river discharge to the Arctic Ocean from the six largest rivers in the Eurasian Arctic for the observational period 1936-2007 (updated from Peterson et al., 2002) (red line) and from the five large North American pan-Arctic rivers over 1973-2006 (blue line). The least squares linear trend lines are shown as dashed lines. Provisional estimates of annual discharge for the six major Eurasian Arctic rivers based on near real time data from http://RIMS.unh.edu are shown as red diamonds. |
The mean annual discharge to the ocean over 2000-2007 from the 5 large North American Arctic rivers based on data from the Environment Canada and USGS was about 6% (31 km3) greater than the long-term mean from 1973-1999. The river discharge during 2007 was higher than the long-term mean and, taking into account that this year had extremely high fresh water discharge from Greenland (Mernild et al., 2009), we can estimate that 2007 showed record high total freshwater input to the Arctic Ocean from the terrestrial land surface.
Official river discharge data are usually processed and published with some delay, the longest delay often being associated with rivers in cold regions that are ice covered for extended periods (Shiklomanov et al. 2006). To provide for more timely detection and diagnosis of changing conditions, a method to estimate near-real time river discharge from the most important Russian monitoring sites, based on provisional stage measurements and river ice data, has been developed in cooperation with the Arctic and Antarctic Research Institute (AARI) (http://RIMS.unh.edu). The provisional estimates over 2003-2007 show a tendency to underestimate the annual observed values within an error of 5% of the officially released data (Figure R1). The preliminary estimate of annual river discharge to the Arctic Ocean from the major Russian rivers in 2008 was significantly greater than the long-term mean but lower than the historical maximum observed in 2007. The North American annual river discharge to the Arctic Ocean in 2008 was probably close to or slightly higher than the long-term mean. However, this estimate is much less reliable due to gaps in near real time discharge data for major North American rivers.
References
Mernild, S. H., G. E. Liston, C. A. Hiemstra, and K. Steffen, 2009: Record 2007 Greenland Ice Sheet surface melt extent and runoff. Eos, Trans. Amer. Geophys. Union, 90, doi:10.1029/2009EO020002. Peterson, B. J., R. M. Holmes, J. W. McClelland, C. J. Vorosmarty, R. B. Lammers, A. I. Shiklomanov, I. A. Shiklomanov, and S. Rahmstorf, 2002: Increasing river discharge to the Arctic Ocean. Science, 298, 2171-2173.
Shiklomanov A. I., T. I. Yakovleva , R. B. Lammers, I. Ph. Karasev, C. J. Vörösmarty, and E. Linder, 2006: Cold region river discharge uncertainty - estimates from large Russian rivers. J. of Hydrol., 326, 231–256.
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2 comments:
I made some basic research to put these figures in contexte.
- total water inflow from the Eurasian rivers to the Arctic is estimated for 2007 to 2250 km3
- total Arctic sea volume is about 1 million km3 (grossly 500 x more)
- the total volume from all rivers is also about 1 million km3 (1 sverdrup, SV); the total rain volume on the oceans is around 10 SV
- the Agassiz lake was also roughly 1 million km3 - when it suddenly went to Hudson Bay it's thought to have stopped the Thermohaline Circulation (THC)
- the THC carries (carried ? found no date for this figure) around 130 SV in the Great Banks area
So this increase in the Eurasian rivers doesn't seem to be a major risk to the THC until it reaches much higher levels - perhaps 100.000 km3, 50 x more ?
But of course, it really remains a problem about methane release, permafrost, and even carrying more land to the sea (sediments).
I'd say it's rather a (one more) consequence of warming than a factor of warming-related problems - while Arctic Ice rapid reduction is alltogether a consequence AND a cause.
Fred, I think these figures can best be used as a baseline indicator for what is going on with the permafrost in those regions.
Also, it gives confirmation to the research on warming permafrost. Then, since fresh water is not saline, it will stay on the surface of the Arctic Sea and not sink as does the heavier salty water.
Eventually, this fresher water will make its way out of the Arctic Sea and into the north Atlantic Ocean, although, since it has become significantly windier and stormier over the Arctic Ocean, there will be a lot of mixing of layers (also not a good thing for an ecosystem that is not used to this).
Did you see the article on what wind is stirring up on the Canadian side of the Arctic Ocean, bringing up water from the bottom that is not compatible with life in the upper layers?
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