Mires and Climat Change: Salinity, Siberia and the Gulf Stream

by John Couwenberg & Hans Joosten

The oceans are a global reservoir and redistribution agent for several important constituents of the Earth’s climate system, among them heat, fresh water and carbon dioxide. Whereas these constituents are actively exchanged with the atmosphere, salt is a component that is approximately conserved in the ocean. The distribution of salinity in the ocean is widely measured, and can therefore be used to diagnose rates of surface freshwater fluxes, freshwater transport and local ocean mixing – important components of climate dynamics. Comparison of salinities on a long transect (50° S to 60° N) through the western basins of the Atlantic Ocean between the 1950s and the 1990s revealed a systematic freshening at both poleward ends contrasted with large increases of salinity pervading the upper water column at low latitudes (Curry et al. 2003).

Shifts in the oceanic distribution of fresh and saline waters seem to be occurring worldwide in ways that suggest links to global warming and possible changes in the hydrologic cycle of the Earth. As a result of these shifts, the Gulf Stream may be “turned off” or reversed and thus plunge western Europe into the same climate conditions as Alaska. The Gulfstream relies on its extreme saltiness to sink off the coast of Norway and re-circulate back to the Caribbean in a continuous loop. If the saltiness is diluted, the water does not sink and the circulation system ceases (Toggweiler & Key 2001).There are two things that dilute the Gulfstream water in the North Atlantic. One is the freshwater melting from Greenland. This has doubled (or more) during the last 5 years (Clarke 2002). The other fresh water source consists of the major Siberian rivers – like Lena, Ob, etc. With increased global warming encouraging both increased melting of Greenland as well as increased rainfall over Russia, the concern is that these two sources will ilute the Gulfstream sufficiently to halt it.

Lake peatland landscape in Central-West-Siberia (photo: M. Succow)

The majority of the Russian rivers arise in peat-dominated landscapes. As these peatlands grow, they not only store Carbon but they also store water. To prevent wild assumptions on the effect of these vast peatland areas on the Gulfstream, we carried out calculations on the quantities of water involved. To make calculations easier we used rounded off figures that, however, approach the real figures sufficiently to make reliable estimates. The total amount of sweet (river) water flowing into the Arctic Ocean is 5000 cubic km per year. The total amount of sweet (river) water flowing into the Arctic Ocean through the major Siberian rivers amounts to 2000 cubic km per year. This amount may – depending on weather conditions – vary over the years with 15% (Shiklomanov 1999).

What is the effect of peat growth on the amount of water reaching the Arctic Ocean? The total area of peatlands in Siberia is 1.200.000 square km (Joosten 2004). With a yearly increase of 0,5 mm peat (a very generous estimate, because many peatlands are slowly accummulating permafrost peatlands) with close to 100% of water, this means an annual increase of the water storage in peatlands of 0,6 cubic km. This 0,6 cubic km is only 0,3 ‰ of the total amount of water flowing into the Arctic Ocean through the Siberian rivers or 2 ‰ of the variation in that amount. 0,6 cubic km is only 0,12 ‰ of the total amount of sweet (river) water flowing into the Arctic Ocean.

What is the effect of draining peatlands? With an estimated mean peat depth of 1,5 m, there is 1.800 cubic km of water stored in Siberian peatlands. It took some 10.000 years to accumulate this water. Successful drainage may perhaps remove 30% of the water of the total peat the most, i.e. 500 cubic km (here we departed from a maximum removal of 20 % of the water from the peat by gravitation drainage – keep in mind that “dry peat” in trade still contains 50% water and that this 50% is only reached by forced drying by evaporation – and an additonal 10 % when the large peatland lakes in the middle part of Western Siberia are drained).

This 500 cubic km is 25% of the total amount of water flowing into the Arctic Sea through the Siberian rivers per year and 10% of the total amount of sweet (river) water flowing into the Arctic Ocean. Even draining all Siberian peatlands would therefore “only” result in a change of 10% of the total amount of sweet (river) water flowing into the Arctic Ocean. This is within the variation of 15% of the annual river discharge. (Of course two “bads” may co-occur, causing a change of 25%). But all the drainage water has to reach the Arctic Ocean in the same year to arrive at this effect, which is virtually impossible.

We may conclude that the quantitative hydrological effects of Siberian peatlands on the water balance of the Arctic Ocean and therewith on the Gulf Stream are extremely small, if not negligible. This, however, does not preclude that there might be some effect in a qualitative way, by changing the inflow of humus particles into the Ocean. But this is another question…

Clarke, T. 2002. Record melt in Arctic and Greenland. Nature Science Update. http://www.nature.com/ nsu/021209/021209-2.html

Curry, R., Dickson, B. & I. Yashayaev (2003) A change in the freshwater balance of the Atlantic Ocean over the past four decades. Nature 426, 826 – 829

Joosten, H. 2004. The IMCG global peatland database. www.img.net

Toggweiler, J.R. & R.M. Key. 2001. Ocean Circulation: Thermohaline circulation. In: J.R. Holton, J. Pyle and J.A. Curry, Encyclopedia of Atmospheric Sciences, Academic Press, London pp. 1549-1555.

Shiklomanov, I. A. 1999. World water resources and their use. http://webworld.unesco.org/water/ihp/db/ shiklomanov/summary/html/summary.html