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Paleoflooding
The phenomenon of paleoflooding is apparent in the geologic record over various spatial and temporal scales. It often occurred on a large scale, and was the result of either glacial ice melt causing large outbursts of freshwater, or high sea levels breaching bodies of freshwater. If a freshwater outflow event was large enough that the water reached the ocean system, it caused changes in salinity that potentially affected ocean circulation and global climate. Freshwater flows could also accumulate to form continental glacial lakes, and this is another indicator of large-scale flooding. In contrast, periods of high global sea level (often during interglacials) could cause marine water to breach natural dams and flow into bodies of freshwater. Changes in salinity of freshwater and marine bodies can be detected from the analysis of organisms that inhabited those bodies at a given time, as certain organisms are more suited to live in either fresh or saline conditions. Paleoflooding r ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Glacial
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate between glacial periods. The Last Glacial Period ended about 15,000 years ago. The Holocene is the current interglacial. A time with no glaciers on Earth is considered a greenhouse climate state. Quaternary Period Within the Quaternary, which started about 2.6 million years before present, there have been a number of glacials and interglacials. At least eight glacial cycles have occurred in the last 740,000 years alone. Penultimate Glacial Period The Penultimate Glacial Period (PGP) is the glacial period that occurred before the Last Glacial Period. It began about 194,000 years ago and ended 135,000 years ago, with the beginning of the Eemian interglacial. Last Glacial Period The last glacial period was the most recent glacial period ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lake Algonquin
Lake Algonquin was a prehistoric proglacial lake that existed in east-central North America at the time of the last ice age. Parts of the former lake are now Lake Huron, Georgian Bay, Lake Superior, Lake Michigan, Lake Nipigon, and Lake Nipissing. The lake varied in size, but it was at its biggest during the post-glacial period and gradually shrunk to the current Lake Huron and Georgian Bay. About 7,000 years ago, the lake was replaced by Lake Chippewa and Lake Stanley as the glaciers retreated and 3,000 years later by the current Lakes Michigan, Huron, and Superior. Physiography About 11,000 years before present, the Laurentian Glacier had retreated northward, forming a boundary across the northern edges of Lake Superior and Lake Huron. The water level was at above sea level, creating a single body of water in the three basins of Lake Michigan, Lake Huron and Lake Superior.Bulletin 4, The Glacial Lakes around Michigan; William R. Farrand, University of Michigan, Ann Arbor, Mich ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mississippi River Valley
The Mississippi embayment is a physiographic feature in the south-central United States, part of the Mississippi Alluvial Plain. It is essentially a northward continuation of the fluvial sediments of the Mississippi River Delta to its confluence with the Ohio River at Cairo, Illinois. The current sedimentary area was formed in the Cretaceous and early Cenozoic by the filling with sediment of a pre-existing basin. An explanation for the embayment's formation was put forward by Van Arsdale and Cox in 2007: movement of the earth's crust brought this region over a volcanic " hotspot" in the Earth's mantle causing an upthrust of magma which formed the Appalachian-Ouachita range. Subsequent erosion caused a deep trough that was flooded by the Gulf of Mexico and eventually filled with sediment from the Mississippi River. Geography The embayment is a topographically low-lying basin that is filled with Cretaceous to recent sediments. The northern end of the embayment appears as a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Sverdrup
In oceanography, the sverdrup (symbol: Sv) is a non- SI metric unit of volumetric flow rate, with equal to . It is equivalent to the SI derived unit cubic hectometer per second (symbol: hm3/s or hm3⋅s−1): 1 Sv is equal to 1 hm3/s. It is used almost exclusively in oceanography to measure the volumetric rate of transport of ocean currents. It is named after Harald Sverdrup. One sverdrup is about five times what is carried by the world’s largest river, the Amazon. In the context of ocean currents, a volume of one million cubic meters may be imagined as a "slice" of ocean with dimensions × × (width × length × thickness). At this scale, these units can be more easily compared in terms of width of the current (several km), depth (hundreds of meters), and current speed (as meters per second). Thus, a hypothetical current wide, 500 m (0.5 km) deep, and moving at 2 m/s would be transporting of water. The sverdrup is distinct from the SI sievert unit or th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Thermohaline Circulation
Thermohaline circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The adjective ''thermohaline'' derives from '' thermo-'' referring to temperature and ' referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of about 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy (in the form of heat) and mass (dissolved solids and ga ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
North Atlantic Deep Water
North Atlantic Deep Water (NADW) is a deep water mass formed in the North Atlantic Ocean. Thermohaline circulation (properly described as meridional overturning circulation) of the world's oceans involves the flow of warm surface waters from the southern hemisphere into the North Atlantic. Water flowing northward becomes modified through evaporation and mixing with other water masses, leading to increased salinity. When this water reaches the North Atlantic it cools and sinks through convection, due to its decreased temperature and increased salinity resulting in increased density. NADW is the outflow of this thick deep layer, which can be detected by its high salinity, high oxygen content, nutrient minima, high 14C/12C, and chlorofluorocarbons (CFCs). CFCs are anthropogenic substances that enter the surface of the ocean from gas exchange with the atmosphere. This distinct composition allows its path to be traced as it mixes with Circumpolar Deep Water (CDW), which in turn fi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Practical Salinity Unit
Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ‰). Salinity is an important factor in determining many aspects of the chemistry of natural waters and of biological processes within it, and is a thermodynamic state variable that, along with temperature and pressure, governs physical characteristics like the density and heat capacity of the water. A contour line of constant salinity is called an ''isohaline'', or sometimes ''isohale''. Definitions Salinity in rivers, lakes, and the ocean is conceptually simple, but technically challenging to define and measure precisely. Conceptually the salinity is the quantity of dissolved salt content of the water. Salts are compounds like sodium chloride, magnesium sulfate, potassium nitrate, and sodium bicarbonate which dissolve into ions ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Elphidium
''Elphidium'' is an abundant genus of foraminifera. Species can be found from coastal regions out to the continental slope, and in all temperature ranges. Like other forams, fossils from different species are used to date rocks. The taxonomy of the species within this genus is disputed due to the high variability of some species. Description ''Elphidium'' is generally around 1 mm in size. The test is spiral-shaped, and can be red, orange, or brown. This shell is made up of calcium carbonate. Species of this genus have seven to twenty chambers in the final whorl, and may have an umbilical plug on each side. In some species the rim is sharp, while in others it is more rounded. Another distinctive feature is the retral processes (small backward extensions of the chamber walls) that cross the sutures, giving some the appearance of tiny rolled up glass baskets. ''Elphidium'' crawls using a type of pseudopod called reticulopodia. Life cycle ''Elphidium'' shows dimorphism with ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Brackish
Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuaries, or it may occur in brackish fossil aquifers. The word comes from the Middle Dutch root '' brak''. Certain human activities can produce brackish water, in particular civil engineering projects such as dikes and the flooding of coastal marshland to produce brackish water pools for freshwater prawn farming. Brackish water is also the primary waste product of the salinity gradient power process. Because brackish water is hostile to the growth of most terrestrial plant species, without appropriate management it is damaging to the environment (see article on shrimp farms). Technically, brackish water contains between 0.5 and 30 grams of salt per litre—more often expressed as 0.5 to 30 parts per thousand (‰), which is a specific grav ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
δ13C
In geochemistry, paleoclimatology, and paleoceanography ''δ''13C (pronounced "delta c thirteen") is an isotopic signature, a measure of the ratio of stable isotopes 13C : 12C, reported in parts per thousand (per mil, ‰). The measure is also widely used in archaeology for the reconstruction of past diets, particularly to see if marine foods or certain types of plants were consumed The definition is, in per mil: :\delta \ce = \left( \frac - 1 \right) \times 1000 ‰ where the standard is an established reference material. ''δ''13C varies in time as a function of productivity, the signature of the inorganic source, organic carbon burial, and vegetation type. Biological processes preferentially take up the lower mass isotope through kinetic fractionation. However some abiotic processes do the same, methane from hydrothermal vents can be depleted by up to 50%. Reference standard The standard established for carbon-13 work was the Pee Dee Belemnite (PDB) and was based on a Cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Paleosalinity
Paleosalinity (or palaeosalinity) is the salinity of the global ocean or of an ocean basin at a point in geological history. Importance From Bjerrum plots, it is found that a decrease in the salinity of an aqueous fluid will act to increase the value of the carbon dioxide-carbonate system equilibrium constants, (pK*). This means that the relative proportion of carbonate with respect to carbon dioxide is higher in more saline fluids, e.g. seawater, than in fresher waters. Of crucial importance for paleoclimatology is the observation that an increase in salinity will thus reduce the solubility of carbon dioxide in the oceans. Since there is thought to have been a 120 m depression in sea level at the last glacial maximum due to the extensive formation of ice sheets (which are solely freshwater), this represents a significant fractionation towards saltier seas during glacial periods. Correspondingly, this will cause a net outgassing of carbon dioxide into the atmosphere because ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
