The Antarctic ice sheet is the largest single mass of fresh water in solid form on Earth and could cause a sea level rise of 65 m if it melted.
The Antarctic has been studied intensively since IGY (International Geophysical Year 1957-58) but much remains to be investigated.
Of prime importance is the determination of the detailed surface topography and volume of the Antarctic Ice Sheet, which could be accomplished with high-precision data obtained with advanced instrumental technology.
A second question is, how old is the Antarctic ice? Ice at least seven hundred thousand years old may be expected in Antarctica, formed at a time during the Ice Age when glacial and interglacial conditions alternated every one hundred thousand years. The oldest ice from the Vostok (Russia) and Dome Fuji (Japan) ice cores may exceed three hundred thousand years in age.
The greatest mystery relates to subglacial lakes. Recent observations reveal that they are widespread, but the mechanism of lake formation and water characteristics are unknown.
Water cycle in the Tibet-Himalayan cryosphere has an important role in the global climate through water and heat transportation. Characteristic processes of glaciers, permafrost and river discharge in this region related to the water cycle are reviewed with the effects on the cryosphere variation.
Characteristics of glacier mass balance in this region are that almost all annual accumulation and ablation occur simultaneously in the summer. Mass balance variation of such type of glaciers is sensitive to summer temperature variation; its rising accelerates glacier shrinkage. Refreezing of infiltrated melt water is active in Tibetan glaciers. Thickness of snow cover above the glacier ice has effective roles in the variation of glacier mass balance.
Seasonal melting and refreezing to the deeper layers in the permafrost are faster at a dry unvegetated place than that at a wet vegetated place. Such difference of heat, soil moisture and vegetation causes the difference of evaporation, and affects the exchange of water and heat between ground surface and the atmosphere.
River discharge from the drainage basin of glaciers and permafrost in the Tibetan Plateau concentrates in summer. Glacier shrinkage due to air temperature rising will cause decrease of contribution of glaciers to the discharge which is a stable water resource. Decrease of snow/rain ratio in the precipitation due to air temperature rising affects glaciers, permafrost and river discharge variation effectively.
There are eleven basins of deep-borne groundwater in the great desert region of North Africa and the Arabian Peninsular. The basins are deployed in the Arabo-African basement rock structure, i.e., basin-and-swell structure, and the major aquifer formations are terrestrial sediments of Lower Cretaceous, called Nubian Sandstone. Tremendous amount of water was replenished to the aquifers at the rims of these basins during the palaeo-pluvial periods, dating back some thousands or tens of thousand years ago. The present volume of this palaeo-groundwater was estimated to be 80, 000 km3, accounting for 2% of the world total of the currently circulating groundwater. Excellent quality is often available in the water of this aquifer. The reserve was confirmed of dissipating under the residual hydraulic gradient, which has been in the decaying process since the end of the last Ice Age. The ultimate discharging sites of the palaeo-groundwater are presumably at desert oases, salt swamps (“sabkha” or “chott” in local language) and sub-marine springs. Despite its great recharge age, not all the palaeo-groundwaters are isolated from the present hydrologic cycle. But the modern contribution is negligible in general.
In order to alleviate the environmental burdens, several countries in the region launched large scale projects for developing palaeo-groundwater. In some basins quick declines of the resources have already been observed. Model simulations were challenged by some researchers to forcast the procedure of resource exhaustion. More effort is required in extending exploration and collecting data of these precious resources yet. Human exploitation of the resources will be inevitable and accelerated to a great extent. However, the local people have to be clever enough to exploit the resources at its maximum value and avoid exhaustion by trivial mistakes.
Submarine groundwater discharge (SGD) is thought to be distributed all over the world, especially in volcanic regions and limestone areas. The volume of discharged groundwater amounts to 40 % of total river discharge, recent studies indicate, and its quality is like that of pure groundwater. Lack of drinking and industrial water is a worldwide (including Japan) serious problem, and it is necessary to initiate studies concerning the development of new water resources, like SGD, which prevents a problem such as saline groundwater and subsidence by excess of groundwater use from arising. As the result of choices based on the consideration of cost, technology and performance, it is proposed that we use deep groundwater as a new way of opening up water resources, but research is needed because SGD is located at the end of the continental groundwater flow system and gives us reliable data of waste rate of groundwater.
Thermal waters obtained from deep-seated hydrothermal systems can be classified based on geothermal heat sources and geochemical characteristics of hot spring waters. As it is evident that in several kinds of geothermal heat sources, “volcanic” heat sources can supply the hugest energy for the formation of deep-seated hydrothermal systems, geothermal heat sources are classified into 2 types, i.e. “volcanic; [V]” related to Quaternary volcanic activities younger than 1 Ma, and “sub- or non-volcanic; [!]” not related to Quaternary volcanic activities. From geochemical classification of hot spring waters, it is clarified that thermal waters obtained from deep-seated hydrothermal systems are derived in essence from following four “source waters”, i.e. “meteoric water; [MW]”, “sea water; [SW]”, “volcanic thermal fluid; [VF]” and “waters formed by water-rock interactions; [WR]”.
As the results, it is explained that deep-seated hydrothermal systems can be categorized thermally and geochemically into following 4 types, i.e. “meteoric-water-originated volcanic hydrothermal system; [V, MW (+VF/WR)]”, “sea-water-originated volcanic hydrothermal system; [V, SW+MW (+VF/WR)]”, “meteoric-water-originated sub-or non-volcanic hydrothermal system; [!, MW (+WR)]” and “sea-water-originated sub-or non-volcanic hydrothermal system; [!, SW+MW (+WR)]”.
Volcanic gases that emitted from active volcanoes dominantly composed of water (normally higher than 95%), with minor amounts of CO2, SO2, H2S, HCI, H2 and rare gases. Volcanic gas is a mixture of magmatic water and meteoric water (+seawater), as revealed by stable isotope composition of water. Island arc magmatic water which has a typical hydrogen isotope ratio of about -20‰ primarily originated from dehydrated water at greater depth (1OOkm) from subducting altered basalt in the oceanic crust. Water in the altered basalt is added long time before at oceanic ridges as hydrothermal alteration from circulating seawater. The global water circulation systematics in the solid earth suggested that present mass of seawater may have circulated in 2 Gy.
The average supply rate of magmatic water by dehydration of subducting slab is 300-600 t/d for one island arc volcano. However, some volcano emits magmatic water with fluxes up to 50000 t/d. This large discrepancy is explained if we consider some large reservoirs with long periods of retention time, e. g., magma reservoirs with a volume of over 100 km3. The large amounts of magma and magmatic water are accumulated in the long dormant periods, and magma degas their volatiles in relatively short periods of active stage.
A temporal variation in isotope composition of discharged water from Izu-Oshima volcano during the period from 1988-1990 is shown as an example of relational changes between magmatic activity and local groundwater system. The proportion of groundwater (+seawater) to the summit volcanic gases increased with time as the magma head subsided. The fracture network which formed in the volcanic body during 1986 fissure eruption may have allowed G-H lens waters (groundwater and seawater) incursion from the coast to the central part of the island.