Summary Global Environment - Geochemische cycli (GEO2-1207)
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Course
Geochemische cycli (GEO21207)
Institution
Universiteit Utrecht (UU)
Book
Global Environment
Summary for the course Geochemical cycli (GEO2-1207) of Earth Science. For the first exam. Covers the following chapters: Chapter 1 (Global environment), Chapter 2 (Air Chemistry part 1), Chapter 3 (Air Chemistry part 2), Chapter 4 (Chemical weathering), Chapter 5 (Rivers).
Samenvatting Global Environment - Geochemische cycli (GEO2-1207), Final exam (figures)
Samenvatting Global Environment - Geochemische cycli (GEO2-1207), Final exam
Summary of the figures, Geochemical cycli (GEO2-1207), first exam
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CHAPTER 1 – INTRODUCTION TO GLOBAL
ENVIRONMENT
SECTION 1 - GEOCHEMISTRY
Geochemistry
The geochemistry focuses on the principal constituents of rocks, water, and
life as they circulate through the land, the sea and the air picture 1.
The water moves from the atmosphere to the land surface as rain
containing pollutants, the air flows while distribution pollutants over areas,
the plants on land circulate elements between the atmosphere and soils
The most important constituents are sodium, potassium, calcium,
magnesium, silicon, carbon, nitrogen, sulfur, phosphorus, chlorine, hydrogen
and oxygen.
o Gases & liquids: N2, O2, H2O, Ar, CO2 CH4
o Rocks: Na, K, Ca, Mg, Al, Fe, Si, C, P, S, Cl, organic compounds
o Organisms: C, O, H, S, P, N, K, Ca, Si
SECTION 2 – THE WATER CYCLE
The basic hydrological cycle
Because of the combinations of temperature and pressure on Earth, water can
exist in three states: water vapor, liquid water and as ice.
The water is divided into reservoirs; 97% as seawater in the oceans and
3% on continents or in the atmosphere picture 2. !!!!! Reservoirs in 10^6
km^3 and fluxes in 10^6 km^3 per year
o In the atmosphere - 0.001% of the global water content. On the continents
- two-thirds of the freshwater is in the form of ice in ice sheets, polar ice
caps and glaciers, the rest as subsurface groundwater or in lakes and
rivers
Water is continually moving from one reservoirs to another in the hydrologic
cycle picture 3. Between reservoirs, the sizes of uncertainty are very
different
o For well-known reservoirs an uncertainty between 10 and 20%, for lesser
known reservoirs an uncertainty up to 70%
o Big uncertainty for reservoirs groundwater, permafrost and soil moisture
picture 4
o !!!!! Important pathway from geochemical point are volcanos; the stream
between groundwater and the deepwater streams
Influence of humans picture 5: 50% of river discharge to oceans is impacted
by humans
In order to conserve total water, evaporation must balance precipitation for
the Earth as a whole. The hydrological cycle is in steady state – the total flux
into the reservoirs is equal to the total flux out of the reservoir.
On the continental parts: the precipitation rate exceeds the evaporation
rate. On the ocean parts: the evaporation exceeds the precipitation picture
3
, The differences are rectified by atmospheric water vapor (ocean –
continent) and river runoff and groundwater discharge (continent –
ocean) picture 3
The residence time
The residence time is the average time a water molecule spends in a given
reservoir.
This is defined as the volume of water in a reservoir divided by the rate of
addition (or loss) of water to (from) it (=flux).
The residence times difference between reservoirs: 11 days for the
atmosphere, up top 38000 years for the ocean.
Residence time (y) = mass reservoir / flux
For example: RT ocean (years) = reservoir ocean / riverine influx
Geographic variations
In the water cycle on earth there is latitudinal variability; the net
precipitation (precipitation minus evaporation) difference with the latitudes.
This creates excess (wet) areas and deficit (dry) areas on the Earth’s surface
picture 6.
Important excess areas are the tropics (10N to 10S) and subpoles (35 to
60 N and S). Important deficit areas are the subtropics (15 to 30N and S)
and poles (60 to 90N and S)
!!!!! Form net evaporation to happen, we need a heat source, low moisture
content and water availability. In such areas there are formations of desert
and oceans with a high(er) salinity.
SECTION 3 – THE ENERGY CYCLE
The energy cycle - Solar radiation
The energy cycle drives the circulations of the atmosphere and oceans. The
primary energy source for the Earth is the short-wave sun radiation (99.98%)
and when travelled through the atmosphere it is reflected, absorbed and
converted into other forms of energy picture 7
The reflection of short-wave solar energy by land and by clouds in the
atmosphere
The absorption by the Earth’s surface and clouds
The reradiation as long-wave infrared radiation (IR) by the Earth’s surface
and various components of the atmosphere.
The incoming short-wave radiation is separated into 50% reaching Earth’s
surface, 25% reflection by clouds and 25% absorption by clouds. Of this 50%,
45% is absorbed by the Earth’s surface and 5% is reflected back to the
atmosphere picture 7b.
The outcoming long-wave radiation is transmitted, absorbed or reflected
back the Earth’s surface. The highest transmitted radiation when absent of
clouds; for example in the desert of at rain shadow areas picture 7c
!!! Clouds have different functions: reflection of short-wave radiation
causing cooling of the Earth’s surface, absorption of long-wave radiation
causing warming of the Earth.
,In total 30% of the short-wave radiation is reflected by clouds and the
Earth’s surface due to the albedo effect. Generally, the continents reflect
more radiation than the oceans; the oceans has a lower albedo picture 7d
In the summer: > reflection in the North-Hemisphere because of the present
of clouds due to the specific climate. No incoming radiation at the South
pole causing no reflection, present of ice at the North Pole causing extra
reflection.
The energy spectra
Most of the sun radiation on earth is in the form of visible light, almost all
ultraviolet solar radiation is absorbed in the upper atmosphere by ozone
and O2. The long-wave infrared radiation (IR) from the Earth’s surface is
absorbed at certain wavelengths by atmospheric water vapor and CO2, and by
water droplets in clouds (= atmospheric absorption).
See picture 8 – Gaps in spectra where atmospheric absorption occurs
Because of this most of the infrared radiation originating form the Earth’s
surface is absorbed by these gases and little of it escapes directly to space.
The greenhouse effect is the passing through of incoming short-wave
solar radiation to the ground, while absorbing and reradiating most of the
Earth’s outgoing long-wave radiation resulting in the warming of the Earth’s
surface and lower atmosphere
o The enhanced greenhouse effect is the atmospheric build up of
greenhouse gases by mankind, causing a higher absorbing than the
normal amount of the Earth’s outgoing radiation, resulting in an
enhanced greenhouse effect and global warming.
Use of the Stefan – Boltzmann law Radiation flux (I) = σ * T^4
= …. W/m^2
Variations in Solar Radiation
The amount of solar radiation decreases with the latitude, causing a variation
in the Earth’s heating and driving circulations of the ocean and atmosphere
picture 9. These latitudinal variations are due to two factors:
The angle of the sun’s rays varies from 90 degrees at the equator to 0
degrees near the poles. With higher latitudes the same amount of radiation
is spread out over a larger area and the sun must travel through a greater
thickness of atmosphere causing more absorption and reflection.
The tilt of the earth causing seasonal changes in duration of daylight
!!!!! Heat is disturbed evenly by (1) oceans currents, (2) atmospheric
circulation by warm air (3) atmospheric circulation by latent heat in the form
of water vapor.
SECTION 4 – THE ATMOSPHERIC CIRCULATION
The Atmospheric circulation
The atmosphere circulates as a consequence of the latitudinal heat
imbalance and because of the rotation of the earth (Coriolis force) the
circulation consists of three different circulation cells picture 10:
The Hadley cell consists of the circulation of air between the equator and
subtropics
, o Low pressure aera at the equator (ITCZ) where warm and moist air rises
releasing latent heat causing moisture to condense resulting in
precipitation and a wet area --> formation of tropics
o High pressure aera at the subtropics/horse latitudes where cold and dry
air sinks is heated resulting in intense evaporation at the Earth’s surface
and a dry area --> formation of deserts
The Ferrel cell consists of the circulation of air between the subtropics and
subpoles
o Low pressure aera at the subpoles / polar fronts resulting in a wet area
of unstable air, storm activity and precipitation --> occurrence of the polar
jet stream
The Polar Easterlies consists of the circulation of air between the subpoles
and poles
o High pressure area at the poles / polar high
!!!! The Coriolis force causes the winds in the hemispheres to have a specific
rotation: North – Hemisphere has a deflection to the right (clockwise), the
South-Hemisphere has a deflection to the left (counter clockwise) picture 10
!!!!! The atmosphere is a well-mixed reservoir with rapid and long-distance
transport of chemical components
SECTION 5 – THE OCEAN CIRCULATION
The ocean circulation – Depth profile
The oceanic circulation can be divided into two portions: the surface water
or mixed layer and the deep water or thermohaline circulation. In between
you have the thermocline; the ocean region of steeply decreasing
temperature gradient picture 11.
The surface water is a well-mixed layer of the top 50 to 300 meters with
lateral differences in chemical composition. It is driven by wind and in direct
interaction with the atmosphere.
For example the Gulf Stream in the Atlantic and the Kuroshio Current in the
Pacific.
Due to the associated Ekman transport, currents do not move parallel to
the wind, but with a 90 degree to the left (SH) of right (NH) of the wind
direction.
o Coastal upwelling is a special case of wind-driven circulation that effects
the biological productivity in the ocean. For example the supply of deep
water rich in nutrients, creating high planktonic productivity.
Effects west boundaries of continents like Peru, West Africa and
California coast
The wind creates gyres picture 12 and 13: clockwise in the Northern
Hemisphere, counterclockwise in the Southern Hemisphere due to the
Coriolis effect.
o In the Southern Hemisphere currents have a strong western side and a
weak east side.
o Formation of Ocean garbage patches picture 14
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