rivers, sometimes huge tropics, organic matter reaches the sea, but at what
speed? And what happens to this carbonaceous material? A French team has been
measured by traversing the Himalayas, instruments in hand, backpack and shoes
on your feet. Conclusion: The highest mountain in the world makes very little
carbon to the living world.
We knew but she has never been measured: the mountain ranges involved in
the carbon cycle according to a simple mechanism. The massive sloping reared
and expose the soil moisture. The significant rainfall generates streams,
rivers and rivers which powerfully erode the surface. Organic matter is so
driven to the ocean where it is, in part, taken up by living organisms while
the rest sediments to the bottom, trapping the carbon for millions of years.
In this game, the most massive assets are those in tropical regions, because
of the significant rainfall, and the youngest, whose slopes are stronger.
In theory, then, no problem. But, specifically, how much organic matter is
transported? To find out, it is sufficient to measure how rivers carry
sediment… But the specific steps that are in desperate need transportation,
as they are difficult. The Brahmaputra, which water down the harvest of
thousands of Himalayan streams, is ten kilometers off near his mouth and
nobody knows exactly how it carries material.
We need to go see on the spot
So, to find out, a team of geologists, armed with samplers sediments and
equipment of the perfect hikers, is a party to conquer the Himalayas, a mass
of both young and tropical, so big recycling organic matter. These brave
scientists working at the Research Center petrography and geochemical and
laboratory Geology and Resource Management (CNRS-Insu,
Nancy-University),
as well as geology laboratory at the Ecole Normale Superieure in Paris
(CNRS-Insu). They returned and the results have just been published in the
journal Nature.
Valier Galy, Christian France-Lanord and their colleagues determined sediment
in rivers since Nepal to the Bay of Bengal via India and Bangladesh. A team of
oceanographers Germans took over on the ship RV-Sonne for further action at
sea.
In total, sends the Himalayas to the sea about one billion tons of material
per year. But if we want to gauge the effect of this erosion on the
balance of the carbon cycle, it is necessary to subtract the amount of fossil
carbon material, which comes from the rock itself, and who will return in the
deep sediments. The differentiation between the two was carried out by
determining carbon 14 with the spectrometer accelerator Artemis Saclay.
The researchers found that sequestration of organic matter depends heavily
on the nature of the sediment and its size. For example, the fine materials
with a base of clay that hold much more coarse sands. For example, the fine
materials with a base of clay that hold much more coarse sands. At the
Himalayas, a misunderstanding of this detail leads in the end to a huge
error on the amounts of organic material sent offshore… It was therefore a
lot to see on the spot!
The analysis of organic matter has led to trace its origin (primarily of
plant debris). The study showed a strong resemblance between the organic
load Brahmaputra (just east of the Himalayas) and the Ganges (which recovers
the waters of western mass). In these comparisons is the largest discovery
of these teams: the sediments deposited in the sea at the bottom of the Bay
of Bengal have the same organic matter content as rivers and lakes.
In other words, almost all the organic sediments taken from the mountain is
deposited on the sea floor and is not for the living world. This substance
carbonaceous s'enfouira rapidly in the geological strata and remain there
for millions of years.
The result has surprised because this operation is very different from that
seen at the mouth of the Amazon where 70% of the organic matter is returned
to the ocean and its plankton.
The scale of geological time, the Himalayas is a huge enfouisseur carbon and
hence a reducer of greenhouse effect, so much so that researchers are wondering
if the erection of this massive does not have a responsibility the Ice Age
started at the beginning of the Oligocene, there are about 34 million years…
Note for Sediment
Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. Sedimentation is the deposition by settling of a suspended material.
Sediments are also transported by wind (eolian) and glaciers. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice transported sediments. Simple gravitational collapse also creates sediments such as talus and mountainslide deposits as well as karst collapse features. Each sediment type has different settling velocities, depending on size, volume, density, and shape.
Seas, oceans, and lakes accumulate sediment over time. These materials can be terrestrial (deposited on the land) or marine (deposited in the ocean); terrigenous deposits originate on land, but may be deposited in either terrestrial, marine, or lacustrine (lake) environments. Deposited sediments are the source of sedimentary rocks, which can contain fossils of the inhabitants of the body of water that were, upon death, covered by accumulating sediment. Lake bed sediments that have not solidified into rock can be used to determine past climatic conditions.
Note for Carbon cycle
The carbon cycle is the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth.
The cycle is usually thought of as four major reservoirs of carbon interconnected by pathways of exchange. The reservoirs are the atmosphere, the terrestrial biosphere (which usually includes freshwater systems and non-living organic material, such as soil carbon), the oceans (which includes dissolved inorganic carbon and living and non-living marine biota), and the sediments (which includes fossil fuels). The annual movements of carbon, the carbon exchanges between reservoirs, occur because of various chemical, physical, geological, and biological processes. The ocean contains the largest active pool of carbon near the surface of the Earth, but the deep ocean part of this pool does not rapidly exchange with the atmosphere.
Note for Clay
Clay is a naturally occurring material, composed primarily of fine-grained minerals, which show plasticity through a variable range of water content, and which can be hardened when dried or fired. Clay deposits are mostly composed of clay minerals (phyllosilicate minerals), minerals which impart plasticity and harden when fired or dried, and variable amounts of water trapped in the mineral structure by polar attraction. Organic matter and materials which do not impart plasticity may also be a part of clay
deposits.
Clay minerals are typically formed over long periods of time by the gradual chemical weathering of rocks (usually silicate-bearing) by low concentrations of carbonic acid and other diluted solvents. These solvents (usually acidic) migrate through the weathering rock after leaching through upper weathered layers. In addition to the weathering process, some clay minerals are formed by hydrothermal activity. Clay deposits may be formed in place as residual deposits, but thick deposits usually are formed as the result of a secondary sedimentary deposition process after they have been eroded and transported from their original location of formation. Clay deposits are typically associated with very low energy depositional environments such as large lake and marine deposits.
Pictures overview
In figure 1, Problem of Geology practice: how to measure the quantity and quality of organic sediment carried by a river tumultuous ten kilometers wide?
Here, the Brahmaputra in Bangladesh.
In figure 2, Valier Galy, geologist and amateur mountaineering, became hikers to analyze the Himalayan rivers.
We see here in action with a sampler of sediment.
In figure 3, Diagram of the carbon cycle. The black numbers indicate how much
carbon is stored in various reservoirs, in billions of tons ("GtC"
stands for GigaTons of Carbon and figures are circa 2004). The purple numbers
indicate how much carbon moves between reservoirs each year. The sediments, as
defined in this diagram, do not include the ~70 million GtC of carbonate rock
and kerogen.
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