Fluctuating sea level

In addition to the man-made environmental problems that have affected the Caspian adversely, the sea has exhibited a curious natural variation in its water level that has created additional problems and has wrought havoc on coastal infrastmcture. Since 1978, the sea level has risen almost 7.5 feet. Flooding in coastal zones has inundated residential areas, transport, telecommunications and energy infrastructure, chemical and petrochemical industries, croplands and hatcheries, forcing thousands of residents to be evacuated from flooded homes. In Turkmenistan, the town of Dervish, which is detached from the western part of the mainland, is turning into an island due to the rise in sea level, and Cheleken and Karakul are sinking into the water as well. 

---

Sources of Sulfur in Coal and Oil. The major coal beds of eastern North America are of Pennsylvanian age. During that time, there was a constantly fluctuating sea level across flat lowlands over the North American interior. Coal was formed just before the onset of marine conditions, so that coal swamp forests occurred on broad lands along or near the sea shore. Thicker sections accumulated on the more rapidly subsiding Illinois and Forest City basins and in the Appalachia fireland basin (14). 

Global warming would also be expected to influence surface waters such as lakes and streams, through changes induced in the hydrologic cycle. However, the last published report of the IPCC states no clear evidence of widespread change in annual streamflows and peak discharges of rivers in the world (IPCC, 1995, p. 158). Wliile lake and inland sea levels have fluctuated, the IPCC also points out that local effects make it difficult to use lake levels to monitor climate variations. 

High and low stands of sea level are directly recorded as sedimentary coastal onlap sequences and as erosional terraces. These records are complicated in regions of crustal instability, and the rate and nature of crustal deformation determines whether evidence of short-term or long-term sea-level fluctuations are preserved and how easily this evidence is interpreted. Because continental basement warps and fractures through time, and because evidence of sea level is erased by erosion, the interpretation of this evidence to produce sea-level curves for the Phanerozoic has been a subject of considerable debate. 

In regions where land is steadily rising relative to mean sea level, the effects of sea-level fluctuations are sometimes recorded as ero-sional features on land. Whenever the rate of sea-level rise matches the rate of uplift, there is an apparent sea level still stand. Both deposition and erosion are controlled by this almost fixed base level, and a terrace may form. If sea level falls and again rises, the terrace will have risen sufficiently so that it is preserved upslope. Epi-... 

This is in part because denudation rates are very low and because sea-level fluctuation may be important to the erosion process. Cratons seem to undergo major episodes of erosion following drops of sea level. When the level drops to a stable stand of several million years, much of the landscape is eroded down to the new level and an erosion surface or a planation surface forms. 

At sea level, atmospheric pressure supports a mercury column approximately 760 mm in height. Changes in altitude and weather cause fluctuations in atmospheric pressure. Nevertheless, at sea level the height of the mercury column seldom varies by more than 10 mm, except under extreme conditions, such as in the eye of a hurricane, when the mercury in a barometer may fall below 740 mm. 

Palaeo-sea (and -water-table) fluctuations. Edwards et al. (2003) describe methods used to obtain valuable information about past sea level elevations and tectonics using U-... 

The continuous availability of trillions of independent microreactors greatly multiplied the initial mixture of extraterrestrial organics and hydrothermal vent-produced chemicals into a rich variety of adsorbed and transformed materials, including lipids, amphiphiles, chiral metal complexes, amino add polymers, and nudeo-tide bases. Production and chiral amplification of polypeptides and other polymeric molecules would be induced by exposure of absorbed amino adds and organics to dehydration/rehydration cydes promoted by heat-flows beneath a sea-level hydro-thermal field or by sporadic subaerial exposure of near-shore vents and surfaces. In this environment the e.e. of chiral amino adds could have provided the ligands required for any metal centers capable of catalyzing enantiomeric dominance. The auto-amplification of a small e.e. of i-amino adds, whether extraterrestrially delivered or fluctuationally induced, thus becomes conceptually reasonable. 

At sea level, Pj is approximately 1 atm, but exhibits some temporal and spatial variability. For example, the annual mean pressure in the northern hemisphere is 0.969 atm and in the southern hemisphere is 0.974 atm, with monthly averages varying by as much as 0.0001 atm, i.e., about 1 mbar (1 atm = 1013.25 mbar). These fluctuations are caused by spatial and temporal variations in atmospheric temperature and water vapor content associated with weather, and seasonal and longer-term climate shifts. Pj is also affected by diurnal atmospheric tides, and it decreases with increasing altitude above sea level. Some gases, such CO2 and O2, exhibit seasonal variability that is caused in part by seasonal variability in plant and animal activity (see Figures 25.4 and 6.7). 

In the event of a decline in sea level, the supratidal zone will move seaward, causing evaporites to deposit on top of old lagoonal sediments. When sea level rises back, it drowns these evaporites. These low-amplitude fluctuations in sea level build up laminated sediments in which layers of biogenic oozes and organic-rich muds alternate with evaporites. 

To convert calciiun carbonate to dolomite, some of the calcium must have been replaced by magnesiiun, requiring the partial dissolution of the carbonate. This process is promoted by contact with acidic pore water, such as occurs in organic-rich sediments because remineralization produces carbon dioxide. This is probably why dolomites are presently forming in detrital algal mats buried beneath sabkhat. The restricted extent of these modern dolomites reflects a kinetic hindrance to precipitation. Apparently dolomite precipitation in this setting is too slow to form substantial deposits when sea level is rapidly fluctuating. 

Pressure. Pressure, defined as force per unit area, can be expressed as an absolute or relative value. Although atmospheric pressure constantly fluctuates, a standard value of 101.3 kPa (14.7 psia) has been assigned as the accepted value at sea level. The MaM in the psia stands for absolute, ie, the pressure is 14.7 psi (101.3 kPa) above zero pressure or a vacuum. Most ordinary pressure-measuring instruments do not measure true pressure, but rather a pressure relative to the barometric or atmospheric pressure. This relative pressure is called gauge pressure. The atmospheric pressure is defined to be 1 psig, in which the "g" indicates that it is relative to atmospheric pressure. Vacuum is the pressure below atmospheric pressure and is, therefore, a relative pressure measurement as well. The relationship between absolute and relative pressure is shown in Figure 3 (see Pressure measurement, Vacuum technology). 

Acharyya, S.K., Lahiri, S., Raymahashay, B.C. and Bhowmik, A. (2000) Arsenic toxicity of groundwater in parts of the Bengal basin in India and Bangladesh the role of Quaternary stratigraphy and Holocene sea-level fluctuation. Environmental Geology, 39(10), 1127-37. 

Consideration of the impact of low-frequency fluctuations of climate on Caspian Sea level showed that the long-term variability of the level is connected mainly with SST anomalies in the eastern part of the tropical Pacific Ocean. It turns out that positive SST anomalies correlate with the growing rain rate in the Volga River watershed basin and vice versa. The main reason for variations in Caspian Sea level is the long-term dynamics of El Nino events, which should be considered as chaotic. 

The location of the mixing zone depends on the river water runoff, the pattern of the nearshore zone (deep, shallow, wide, narrow), the range and phase of tide, wind direction and force, and sea level fluctuations. Therefore, this zone undergoes both seasonal and short-term variations. 

Water levels in the oceans were lower by over 150 m during the ice ages, and similar water level fluctuations occurred in lakes and inland seas due to climatic changes and tectonic events. The sea level changes influenced the near-shore regions in the following ways ... 

This is perhaps the most dramatic sea level fluctuation during the late geological periods, dwarfing in comparison the sea level changes during the glacial periods. The hydrological consequences must have been enormous ... 

---