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This chapter describes the physical, chemical, and biotic features of the main types of ice-based aquatic ecosystems. Dark-coloured sediments on and in ice enhance absorption of solar radiation, promote melting, and the formation of habitats of varying sizes and longevity. These range from ‘bubbles’ within glacial and perennial lake ice (~10^-2 m diameter), cryoconite holes (~10^-1 -10⁰ m diameter) on ice surfaces to large melt lakes (~10¹ - 10² m diameter) and rivers on ice shelves and ice sheets. For the most part, the development of ice-based aquatic ecosystems depends on liquid water. Communities are predominantly microbial, with cyanobacteria and algae dominating the phototrophs, while microinvertebrates with stress-tolerate strategies (rotifers, tardigrades, and nematodes) are also present. The chapter argues that ice-based ecosystems represent important biodiversity elements within polar landscapes, and would have been essential refugia from which polar region ecosystems recovered after periods of extended glaciation.

This chapter discusses the marine benthos. Topics covered include the littoral zone, the shallow sublittoral zone, the benthos of deep waters, benthos under ice shelves, and seasonality and dynamics of benthic communities.

This chapter focuses on ice shelves, supraglacial habitats (snow, supraglacial lakes, cryoconites holes), and other debris habitats including the ice margin. It discusses the nature of mat communities, and their photosynthetic and biogeochemical activity; the hydrology of glacier ice surfaces and the biology of supraglacial melt habitats; the formation of cryoconite and cryoconite holes, and their impact on albedo; and cryoconite hole communities, and their biological makeup, photosynthesis, bacterial production, metazoan activity, and viral dynamics for Arctic, Antarctic, and alpine glaciers.

Summarizes the causes of sea-level rise; primarily these are warming and expansion in the upper 2,000 meters of the ocean, and melting of the ice sheets. The ice sheets are the most difficult aspect of sea-level rise to predict. There is a possibility of a catastrophic loss of ice from West Antarctica, leading to a sea-level rise of 10 feet by the end of the century. Although possible, this is highly unlikely. There is a strong tendency for communities to protect properties as the sea level rises. After each storm, cries arise for seawalls or beach replenishment. In the long term, seawalls destroy beaches and replenishment will become increasingly expensive with sea-level rise.

Shallow lakes and ponds form on the surfaces of glaciers and ice shelves. Supraglacial lakes or cryolakes are poorly researched but interest in them is growing. This chapter outlines our current knowledge on the structure, formation, geochemistry and biology of these relatively short-lived lake systems. Much more is known about ice shelf lakes and ponds, particularly those of the McMurdo Ice Shelf that range from freshwater to hypersaline. Some of the ponds have life spans of decades and all freeze to their base in winter. These water bodies are characterised by extensive cyanobacterial mats but also possess a functional plankton community?. The biota and functional dynamics of these systems is outlined as well as the challenges faced by seasonal freezing of the habitat.

Most of the 1°C temperature change since the start of the industrial revolution has occurred in the last six decades (Figure 1.1). The warming is evident in all independently monitored timeseries of global temperature. The general warming trend has been overprinted by variability on a lot of different timescales, largely because of internal (re-) distributions of heat within the atmosphere- ocean system. The world ocean, with an average depth of 3700 m, has more than 1000 times the heat capacity of the atmosphere. Even just the upper 700 m that are in effective exchange with the atmosphere have 200 times the heat capacity of the atmosphere. As a result, even a tiny fraction of a degree centigrade change in just the upper ocean represents an enormous amount of heat. This means two things: first, atmospheric temperature can be substantially affected by almost undetectable changes in the ocean; and second, ocean heat gain calculation requires very precise temperature measurements. Precise measurement series for the ocean only exist since about 1960. Let’s have a look at what atmospheric and oceanic heat gains tell us about the Earth’s energy balance since the industrial revolution. The roughly 1°C rise of Earth’s surface temperature during the indus-trial age, with more than two- thirds of it since about 1960, represents the “realized” response to forcing. Using standard values for global climate sensitivity to radiative forcing, we can determine that this 1° C warming corresponds to a component of climate forcing of roughly 1.1 to 1.3 W/m2. In contrast, the ocean is such a vast reservoir to heat up that it has not yet realized its full warming—ocean warming will therefore continue to develop over many decades to centuries even if we managed to “freeze” all radiative forcing agents at their current levels. Since 1960, the heat content of the upper 2000 m of the ocean has increased by roughly 27 × 1022 joules in about 55 years. This is an enormous number; namely 27 followed by 22 zeroes. For comparison, the most powerful nuclear detonation ever had a yield of about 22 × 1016 joules.

As I briefly mentioned in Chapter 3, the global mean sea level, as deduced from the accumulation of paleo-sea level, tide gauge, and satellite-altimeter data, rose by 0.19 m (range, 0.17–0.21 m) between 1901 and 2010 (see Figure 3.3). Global mean sea level represents the longer-term global changes in sea level, without the short-term variability, and is also commonly called eustatic sea-level change. On an annual basis, global mean sea-level change translates to around 1.5 to 2 mm. During the last century, global sea level rose by 10 to 25 cm. Projections of sea-level rise for the period from 2000 to 2081 indicate that global mean sea-level rise will likely be as high as 0.52 to 0.98 m, or 8 to 16 mm/ yr, depending on the greenhouse gas emission scenarios used in the models. Mean sea-level rise is primarily controlled by ocean thermal expansion. But there is also transfer of water from land to ocean via melting of land ice, primarily in Greenland and Antarctica. Model predictions indicate that thermal expansion will increase with global warming because the contribution from glaciers will decrease as their volume is lost over time. (Take a look at Figure 5.1 if you have doubts about glaciers melting.) And remember our discussion in Chapter 2 about the role of the oceans in absorbing carbon dioxide (CO2) and the resultant ocean acidification in recent years. The global ocean also absorbs about 90% of all the net energy increase from global warming as well, which is why the ocean temperature is increasing, which in turn results in thermal expansion and sea-level rise. To make things even more complicated, the expansion of water will vary with latitude because expansion of seawater is greater with increasing temperature. In any event, sea level is expected to rise by 1 to 3 m per degree of warming over the next few millennia.