Gases disueltos

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Gases in seawater
-Major atmospheric gases have concentrations in seawater comparable to the major ions -Solubility of all gases increases with pressure, and decreases with temp. and salinity -oversaturated, undersaturated, invasion, evasion

Dissolved Gases & The Carbonate System Chap 6

-Some gases mostly conservative (inert gases…N2, Ar, etc) -concentration proportional to atmosphericconc. and solubility of each gas -Some gases not conservative (e.g. O2, CO2) -proportional to atmospheric conc., solubility of each gas, in-ocean production or consumption, and atmospheric exchange -Biological activity and/or carbonate reactions cause non-conservative gases to be non-conservative.

Relating atmospheric gas conc. to seawater gas conc.

Frequently atmospheric gas concentrations arereported in partial pressures Partial pressure = % abundance divided by 100.

Atmosphere partial pressure = (% / 100)

Seawater

What are ppm and ppb in volume gas units?

log scale

log scale

-Atm conc. -Solubility (N2/Ar) -non-conservativeness

1

Temperature effects on gas solubility

-Colder water holds more gas -Regardless of whether the gas is conservative or not ml L-1= ppt -Implications of downwelling or upwelling water

DISSOLVED OXYGEN (DO)
Most studied gases are CO2 and DO DO measured using Winkler titration 1888 and modified 1965 using Mn, Iodine, & a starch solution to create a concentration standard curve = still used to calibrate instruments

DISSOLVED OXYGEN (DO)
Most studied gases are CO2 and DO DO measured using Winkler titration 1888 andmodified 1965 using Mn, Iodine, & a starch solution to create a concentration standard curve = still used to calibrate instruments

DO in the ocean changes with: Equilibration across the air-sea interface Photosynthesis and respiration in the upper layers Net respiration in the lower layers Net increases in deep water from sinking of cold, DO saturated water

2

DISSOLVED OXYGEN (DO)
Moststudied gases are CO2 and DO DO measured using Winkler titration 1888 and modified 1965 using Mn, Iodine, & a starch solution to create a concentration standard curve = still used to calibrate instruments

Nonconservative gases (e.g. O2) The O2 concentration is determined by the balance between photosynthesis, respiration, and atmospheric exchange Photosynthesis

CO2 + H2O -

O2 + CH2O

DO inthe ocean changes with: Equilibration across the air-sea interface Photosynthesis and respiration in the upper layers Net respiration in the lower layers
Relative DO concentration

Respiration Gas Transfer Photo Photo and GT control in the upper water column

Net increases in deep water from sinking of cold, DO saturated water

O2
Resp Resp., temp, pressure controls in lower water columnDO saturation capacity and concentrations inversely proportional to T

0

10

20 Temperature

30

The CO2 concentration is aslo affected by these reactions, but even more so by the carbonate buffer system and pH.

How about depth profiles…..

Describe why O2 max oxycline

O2 profile surface waters of different temps

O2 min

m te re tu ra pe co l ro nt

Saturation curvepredicts O2 conc. if temp only controlled O2 conc. O2 rebound with depth

Assignment: draw an idealized Argon profile

3

South

North transects – O2 (ml L-1)

western Atlantic

Gas solubility
Henry’s Law relates the dissolved concentration of a gas to its Its overlying partial pressure through the Henry’s Law constant (KH) Ci = Pi KH Partial pressure Concentration

Pacific

Partialpressure = the total pressure x fractional amount of an individual gas

Ex: 1 atm, N2 = 78% of all gases Pi = 0.78 atm KH usually has units of (mol L-1 bar-1) or (mol L-1 atm-1)

Some Henry’s Law constants (they do vary with temp)
* See also the pdf file on the website.
-1 -1 Table 2-1 Henry’s Law constants for gases at 1 bar total pressure in mol L-1 bar-1 *

AIR-SEA GAS EXCHANGE...
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