Soil Atlas of the Northern Circumpolar Region

Edited by:
  • A. Jones,
  • V. Stolbovoy,
  • C. Tarnocai,
  • G. Broll,
  • O. Spaargaren &
  • L. Montanarella
European Commission, Office for Official Publications of the European Communities: 2010. 144 pp. €25

In an era when we can access maps of anywhere in the world on our mobile phones, the skin of our planet seems to have lost its mystery. But the European Commission's Soil Atlas of the Northern Circumpolar Region is worthy of attention. The fragile soils of northern latitudes, especially the Arctic, hold the key to the future of Earth's climate.

Soil sampling requires extensive fieldwork. The Soil Atlas combines data from thousands of pits, dug across the circumpolar region by researchers from different countries each summer for more than 50 years. Experts from Canada, Russia, the United States and northern Europe came together to share these data to mark the International Polar Year in 2007–09 by raising public awareness of northern soils. The Joint Research Centre of the European Commission shows vision by publishing the results so lavishly.

In the past two decades, the northern circumpolar region has experienced faster warming than elsewhere in the world, a trend that climate models predict will continue. How soils respond to this thawing will decide whether the area will be a source or sink of carbon. In warmer future conditions, northern plants would grow better and sequester atmospheric carbon. But carbon would also be lost to the atmosphere through increased microbial decomposition. The land biota exerts further feedback on climate through its albedo and energy exchange, and through methane emissions by the wetlands that carpet flood plains. Unfortunately, we do not know how all these effects will combine.

The high northern latitudes are also of geopolitical and economic interest because of their huge stores of oil, natural gas and gas hydrate. These resources are likely to be exploited for energy as the polar ice retreats. The price could be high, in terms of both damage to the local environments and threats to global climate through increased carbon dioxide emissions.

Mapping carbon-rich northern soils will help track their response to future warming. Credit: JRC, EUROPEAN COMMISSION

The Soil Atlas opens with a reminder that 90% of Alaskan soils, 60% of Russian soils and 50% of Canadian soils are frozen. The presence of ice greatly affects the characteristics of soil, with frost mixing the layers into chaotic patterns. These structures remain after warming — the testimony of former ice ages is still recognizable in thawed soils. The formation of ice wedges, frost cracking and frost heave also affect the physical properties, hydrology and biogeochemical cycles of northern soils.

Freezing conditions below the surface prevent roots from going deep, affecting plant growth. The frigid temperatures also preserve dead roots, which form carbon-rich deposits over time, such as in the Yedoma loess soils of northeastern Siberia. These contain organic matter up to 50 metres deep, intermixed with giant ice wedges. Altogether, frozen soils contain more than twice the mass of carbon in the atmosphere, and the release of even a fraction of this could amplify global warming. However, few studies so far have addressed this problem quantitatively. The book highlights the potential danger but does not address how soil mapping should be improved to monitor it.

The atlas overcomes the contentious issue of how to classify soils objectively by adopting an international standard: the World Reference Base for Soil Resources, produced by the Food Administration Organization of the United Nations. The result is the first unified presentation of the circumpolar landscape. A drawback is the bias caused by reclassification. The arbitrary lumping together of different nationally defined soil categories means that whereas the map of soil types in some regions of Siberia looks extremely detailed, large areas of northern Canada are all mapped in the same colour, labelled cryosol. Readers could conclude that Canadian soils are more uniform or less densely sampled than in Siberia, which is not the case.

The book does not include information about sampling dates and locations, or the interpolation technique used to make maps from field observations. Such explanations would have increased the volume's scientific impact. This omission reflects some reticence of Arctic countries to divulge detailed geo-referenced data about their soils and forestry to their neighbours. Now that climate researchers are, quite rightly, under pressure to be transparent about their source data and models, inventory agencies in each country should follow suit. It is a step in the right direction that the Soil Atlas maps are openly accessible online (see http://go.nature.com/TaMdZR).

Knowledge of the northern soils could benefit many disciplines, from studies of landscape formation to meteorology, climatology, ecology, biogeochemistry and hydrology. To allow further analyses, these data will need to be translated into a form that is amenable to computer modelling — for instance, tabulated soil depths, hydraulic properties, conductivity, and carbon and nutrient content. This can be done if researchers combine their efforts, so let's hope that the collaborative spirit of the International Polar Year lives on.