Sea Ice: An Introduction to Its Physics, Chemistry, Biology and Geology

Sea Ice: An Introduction to Its Physics, Chemistry, Biology and Geology. Edited by D. N. Thomas and G. Dieckmann. London: Blackwell Science, 2003. 416 pp. (??) 89. ISBN 0-632-05808-0.

Sea ice covers about 7% of our planet, making it one of the largest biomes on earth. The book Sea Ice: An Introduction to Its Physics, Chemistry, Biology and Geology, edited by Drs. David Thomas and Gerhard Dieckmann, provides the scientific community with an excellent source of reference on the biology of sea ice from micro- to macroscale as well as on physical models, large-scale characteristics as derived from satellite observations, and paleo reconstructions. The book includes contributions from a host of international authors who thoroughly discuss state-of-the-art techniques and insights related to sea ice. The varied contributions make the individual chapters demanding, and in some cases provide more detail than necessary. However, a comprehensive glossary and abundant illustrations help to overcome these difficulties.

The book contains a wealth of interesting facts. It is absolutely fascinating to learn about high-latitude species adaptations. Tiny sea-ice organisms survive at temperatures down to –20°C by forming cysts or maintain metabolism by adjusting the proportion of unsaturated fatty acids to retain membrane fluidity at extremely low temperatures. Polar seals have very small flippers to retard heat loss in the cold water, but this makes them less agile on beaches and consequently dependent on pack ice for breeding.

A very useful comparison summarizes the major differences between arctic and antarctic sea ice in all its aspects, from physical properties, such as average extent and heat flux, to biological curiosities, such as species of fish and nematodes associated with the ice.

The different authors convincingly show the importance of understanding the mechanisms that control sea-ice formation and the impact the vast frozen world has on the global climate system.

Sea ice strongly affects the atmosphere because it acts as insulating material and limits energy flux between the ocean and atmosphere. The high albedo of the ice surface keeps solar radiation from being absorbed by the surface and is instead reflected back into the atmosphere. This feedback mechanism is the main reason that scientist expects that climate signals may be amplified in polar regions.

Equally significant is the impact of sea ice on the ocean. When the ice is formed, brines are rejected, increasing the salinity of the upper ocean layer as such by initiating convection. Or the other way around: when ice is melting, fresh meltwater floats as a very stable layer on top of the ocean.

Whereas these processes are understood in broad outline, complex feedback loops are increasingly recognized. Current dynamic sea-ice models are included in global circulation models, but several authors point out the fundamental problems that still prevent accurate predictions.

Recent large ice breakups in both the Arctic (Ward-Hunt Ice Shelf in September 2003) and the Antarctic (Larsen B Ice Shelf in February–March 2002) focused media attention on retreat and decay of polar ice. Both breakups are interpreted as signs of global warming. In this perspective it is interesting to look at results of a survey, “Public Attitudes towards Global Warming,” that the American Geophysical Union (AGU) has conducted (Immerwahr 1999). The survey states that although most Americans (74%) believe the atmosphere is gradually warming, personal concern for global warming has dropped from 35% of the people interviewed in 1989 to 24% in 1997. According to the survey, this decrease is mainly caused by the fact that people are confused about the causes and effects of global warming. In addition, a large part of the public (44%) thinks that scientists are still divided about the issue. Apparently, in 1999 the scientific community had not yet conveyed a sense of unanimity.

This conclusion is still true for the issues concerning melting of sea ice. Although two decades of satellite data show declining sea-ice extent in the Arctic (–2% per decade), the trend for the Antarctic sea ice appears insignificant (+0.4% per decade). It is still under discussion whether 22 years of data is sufficient to delineate a trend or whether the decline could be attributed to natural variability. Comiso in Chapter 4 inclines toward interpreting the data as a negative trend since he found a strong correlation between Northern Hemisphere ice extent changes and temperature changes. However, Haas in Chapter 3 shows that actually one would need to know ice volume changes instead of only area changes. Despite reported dramatic thinning of Arctic ice (e.g., Rothrock et al. 1999), he concludes that scientists are still having tremendous trouble with measuring ice thickness on a regional scale and over longer time spans. Complete new insights are expected from the upcoming CryoSat satellite mission, which is aimed at providing monthly fields of Arctic-wide mean sea-ice thickness. It appears that the general public will need to wait for further conclusive evidence, but earth scientists interested in the complexities and ongoing discussion have a great source of information in this book.