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Riverine Transport of Dissolved Organic Carbon to the Arctic Ocean
Reference
Benner, R., Benitez-Nelson, B., Kaiser, K. and Amon, R.M.W.  2004.  Export of young terrigenous dissolved organic carbon from rivers to the Arctic Ocean.  Geophysical Research Letters 31: 10.1029/2003GL019251.

Background
The authors set the stage for their study by stating that "the fate of soil carbon in high latitude soils is uncertain, as the effects of global warming and climate change are predicted to be magnified in the Arctic (Serreze et al., 2000)."  They also note that "thawing of the permafrost which underlies a substantial fraction of the Arctic could accelerate carbon losses from soils (Goulden et al., 1998)."  In addition, they report that "freshwater discharge to the Arctic Ocean is expected to increase with increasing temperatures (Peterson et al., 2002), potentially resulting in greater riverine export of terrigenous organic carbon to the ocean."

What was done
Since the organic carbon in Arctic soils, in the words of the authors, "is typically old, with average radiocarbon ages ranging from centuries to millennia (Schell, 1983; Schirrmeister et al., 2002)," they set about to measure the ages of dissolved organic carbon (DOC) in Arctic rivers.  Specifically, they sampled two of the largest Eurasian rivers, the Yenisey and Ob' (which drain vast areas of boreal forest and extensive peat bogs, accounting for about a third of all riverine DOC discharge to the Arctic Ocean), as well as two relatively small rivers on the north slope of Alaska, the Ikpikpuk and Kokolik, whose watersheds are dominated by Arctic tundra.  All four of these rivers were sampled within about three months of their peak discharges, when most DOC is exported to the ocean.

What was learned
Benner et al. report they found modern radiocarbon ages for all samples taken from all rivers, which indicates, in their words, that Arctic riverine DOC "is derived primarily from recently-fixed plant litter and near-surface soil horizons."  In contrast, radiocarbon ages of DOC in tropical and temperate rivers range from modern to over 1300 years (Hedges et al., 1986; Raymond and Bauer, 2001).  Whereas these latter temperate and tropical region data indicate what Benner et al. call "variable retention and aging in soil," their high-latitude data indicate almost complete retention of old soil carbon in the Arctic.

What it means
Benner et al. note that warming should cause the average radiocarbon age of the DOC in Artic rivers to increase, which - if it happened - would, in their words, "provide strong evidence of the mobilization of the vast and relatively old carbon stored in [Arctic] soils," in harmony with the climate-alarmist claim that catastrophic carbon loss from Arctic soils would be one of the major consequences of rising temperatures in that part of the world.  This being the case, the total absence of any aging of Arctic riverine DOC implied by Benner et al.'s measurements provides "strong evidence" of the exact opposite, i.e., the total absence of any recent large-scale warming there, as is also indicated by the region-wide temperature data we discuss in our Editorials of 10 Mar 2004, 17 Mar 2004 and 24 Mar 2004.  Hence, we can safely conclude, as this enormous body of evidence clearly indicates, that one of the most basic of all climate-alarmist claims is just plain wrong.

References
Goulden, M.L., Wofsy, S. C., Harden, J.W., Trumbore, S.E., Crill, P.M., Gower, S.T., Fries, T., Daube, B.C., Fan, S., Sutton, D.J., Bazzaz, A. and Munger, J.W.  1998.  Sensitivity of boreal forest carbon balance to soil thaw.  Science 279: 214-217.

Hedges, J.I., Ertel, J.R., Quay, P.D., Grootes, P.M., Richey, J.E., Devol, A.H., Farwell, G.W., Schmidt, F.W. and Salati, E.  1986.  Organic carbon-14 in the Amazon river system.  Science 231: 1129-1131.

Peterson, B.J., Holmes, R.M., McClelland, J.W., Vorosmarty, C.J., Lammers, R.B., Shiklomanov, A.I., Shiklomanov, I.A. and Rahmstorf, S.  2002.  Increasing river discharge in the Arctic Ocean.  Science 298: 2171-2173.

Raymond, P.A. and Bauer, J.E.  2001.  Riverine export of aged terrestrial organic matter to the North Atlantic Ocean.  Nature 409: 497-500.

Schell, D.M.  1983.  Carbon-13 and carbon-14 abundances in Alaskan aquatic organisms: Delayed production from peat in Arctic food webs.  Science 219: 1068-1071.

Schirrmeister, L., Siegert, C., Kuznetsova, T., Kuzmina, S., Andreev, A., Kienast, F., Meyer, H. and Bobrov, A.  2002.  Paleoenvironmental and paleoclimatic records from permafrost deposits in the Arctic region of northern Siberia.  Quaternary International 89: 97-118.

Serreze, M., Walsh, J.E., Chapin III, F.S., Osterkamp, T., Dyurgerov, M., Romanovsky, V., Oechel, W.C., Morison, J., Zhang, T. and Barry, R.G.  2000.  Observational evidence of recent change in the northern high-latitude environment.  Climatic Change 46: 159-207.


Reviewed 12 May 2004