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.

4.7E-05

3.6E-042.5E-04

8.2E-05

2.2E-04

1.8E-04

1.2E-04

2.4E-04

3.9E-04

7.2E-05

3.9E-05

0

20

80

60

40

100

160

140

120

Clay

0 2E-04 4E-04

?

0 2-4-6-10 -8

-2

May-01

G. Relative Head (mm difference from 19m value)F. Hydraulic Conductivity (m/s)

-100-200 3002001000

M ay- 0 1

D ec- 0 1

Jan - 0 2

Feb - 0 2

M ar- 0 2

A p r- 0 2

-4.0-3.0-2.0-1.00.0

Depth (m)

H. δ18O (per thousand)

Tritium and Helium

3H⎡⎣ ⎤⎦ = 3H0⎡⎣ ⎤⎦e−λt

3H0⎡⎣ ⎤⎦ = 3Hetrit⎡⎣ ⎤⎦ + 3H⎡⎣ ⎤⎦

3 3

3

3/

[ ]1 ln 1[ ]

tritH He

HetHλ

⎛ ⎞= +⎜ ⎟

⎝ ⎠

0

20

40

60

80

1000 100 200 300 400 500 600

0 1 2 3 4 5

As

Tr

0

20

40

60

80

1000 100 200 300 400 500 600

0 1 2 3 4

As

As As

Tr

depth

Carbon Isotopes

Dissolved Carbon

Dissolved Organic Carbon (DOC) (mM)

0 2 4 6 8 10

20

40

60

80

100

120

401

601

180

0 0.4. 0.8. 1.2. 1.6. 2

Methane

DOC

DICDepth

(m )

Inorganic (DIC) and Methane (mM)

Carbon Isotopes

InorganicCarbon

OrganicCarbon

30m19m3mMethanogenesis

CaCO3

(Atmospheric valuesover last 50 years)

60m

14C0/00

-1000

-500

0

500

1000

-30 -25 -20 -15 -10 -5 0-70

Methane

Surface Water Carbon• Inflow of young

carbon

• Young carbon drives biochemistry

• Mixture of young and old carbon is not the result of pore water mixing, but mobilization of old organic carbon

0700

40002000

Radiocarbon A

ge

13C0/00

At Waquoit Bay

Waquoit Bay, MA

Saline Circulation Mechanisms

q = −K dhdz

= −kρgµ

dhdz

q = −kµ

dPdz

− ρg⎛⎝⎜

⎞⎠⎟

Initial Salinity ProfileElapsed Time 2:20Elapsed Time 21:00Elapsed Time 33:00Elapsed Time 47:46Elapsed Time 67:30Elapsed Time 76:00Elapsed Time 80:00