Stable Water Isotopes
The fundamental control on the isotopic composition of precipitation is
temperature. With increasing temperature, precipitation becomes enriched
in the heavier isotopes,18O and 2H, in a linear relationship. Temperature
affects fractionation at a rate of approximately 0.5‰ for every C° for
oxygen. Similar effects are shown with increasing elevation and increased
distance from the equator (both of which correspond to lower
temperature). Because precipitation becomes progressively enriched in
light oxygen as it moves toward the cold polar regions, polar ice
constitutes a reservoir of 16O enriched water as compared to sea water.
F. Hydraulic Conductiv ity (m/s)
0
0
2 E-0 4
4 E-0 4
-200
-100
0
100
200
300
4.7E-05
8.2E-05
2.5E-04
20
3.6E-04
?
M ay- 0 1
1.2E-04
1.8E-04
40
Dec- 0 1
2.2E-04
Jan - 0 2
3.9E-04
60
Fe b - 0 2
May-01
M ar- 0 2
2.4E-04
Ap r- 0 2
Depth 80
(m)
100
7.2E-05
-10
120
Clay
140
160
3.9E-05
H. δ18 O (per thousand)
G . Relative Head (mm difference from 19m value)
8
-6
-4
-2
0 2
0. 0
-1. 0
-2. 0
-3. 0
-4. 0
Tritium and Helium
⎡⎣ H ⎤⎦ = ⎡⎣ H 0 ⎤⎦ e
3
3
− λt
⎡⎣ 3 H 0 ⎤⎦ = ⎡⎣ 3 Hetrit ⎤⎦ + ⎡⎣ 3 H ⎤⎦
t 3 H / 3 He
3
⎛
[
Hetrit ] ⎞
1
= ln ⎜ 3
+ 1⎟
λ ⎝ [ H]
⎠
Tr
0
1
2
3
4
5
0
0
1
Tr
2
3
4
0
As
As
20
20
40
40
60
60
80
80
100
100
depth
0
100 200 300 400 500 600
As
0
100 200 300 400 500 600
As
Carbon Isotopes
Dissolved Carbon
Dissolved Organic Carbon (DOC) (mM)
0
0.4
.
0.8
.
1.2
.
1.6
.
2
Methane
20
40
60
Depth
(m )
80
DIC
100
DOC
120
401
601
180
0
2
4
6
8
Inorganic (DIC) and Methane (mM)
10
Carbon Isotopes
1000
• Inflow of young
carbon
Surface Water Carbon
(Atmospheric values
over last 50 years)
500
• Young carbon
drives biochemistry
Inorganic
Carbon
C0/00
0
Methanogenesis
Methane
3m
19m
0
700
30m
60m
2000
4000
Organic
Carbon
-500
CaCO3
-1000
-70
-30
-25 -20 -15 -10
13
C0/00
-5
0
Radiocarbon Age
14
• Mixture of young
and old carbon is
not the result of
pore water mixing,
but mobilization of
old organic carbon
At Waquoit Bay
Waquoit Bay,
MA
Saline Circulation Mechanisms
dh
k ρ g dh
q = −K
=−
dz
µ dz
k ⎛ dP
⎞
q=− ⎜
− ρg⎟
⎠
µ ⎝ dz
Initial Salinity
Elapsed
TimeProfile
2:20
21:00
33:00
47:46
67:30
76:00
80:00