OS1 The Oceans
Seawater
Name: _______________________
Fall 2009
Section/ TA: ____________________
TAKE HOME- due at beginning of next section
Work Independently. Show all work.
Activity 3: World Ocean Salt/Residence Time
1. Calculate the amount of salt in the oceans today (in grams) using the following
information and steps:
Assume that the oceans of the world can be approximated by a basin with totally vertical
sides – like a bathtub whose bottom has a constant area.
Seawater density  1.026 g
cm 3
Mean ocean salinity  35 g kg
Mean depth of the ocean  3.8 km
Surface area of the Earth  5.0 1014 m 2
Area  side  side (or side 2 )
Volume  side  side  side (or side 3 )

a. The global ocean covers 71% of earth’s surface area. Using the mean depth of the ocean,
calculate the volume of the ocean. (5 points)
b. What is the mass of the ocean (in kg)? (5 points)
c. Calculate the amount of salt in the ocean (in kg). (5 points)
Seawater- 1
OS1 The Oceans
Seawater
Fall 2009
d. Cl-(chloride) and SO42-(sulfate) are 2 major anions in seawater. Cl - makes up 55% of the
salt in seawater, while SO42- makes up 7.7%. What is the weight of each anion in the
ocean (in kg)? (5 points)
The mean residence time of a seawater constituent is defined as the amount of time it
takes for the total mass of the seawater constituent to be replaced in the ocean. When
the constituent sources to the ocean are equal to the sinks, the ocean is said to be at
steady state, and the residence time of the constituent can be calculated by the
following equation:

Inventory
Flux (in or out)
τ
In the equation above, , is the residence time, inventory is the total mass of the
constituent in the ocean, and the flux in (or out) is the rate of input (or removal) to the

oceans. The major sources
of material to the oceans include rivers and winds, which
carry dissolved and particulate materials form the continents to the ocean. The major
removal process is the formation of marine sediments both by settling of particles
through the water column and by precipitation of insoluble phases.
Continue using the information from the previous questions to complete the next set of
questions.
e. The flux of Cl- from the rivers to the oceans is about 220 Tg/yr (1 Tg = 1012 g). For
SO42-, the flux is 87 Tg/yr. What is the residence time of each anion in My? (10 points)
f. If the input of Cl- and SO42- were to stop today, in 50 My which ion would you still find in
the ocean? (10 points)
Seawater- 2
OS1 The Oceans
Seawater
Fall 2009
Activity 4: Sedimentation
In July, NOAA announced the arrival of El Nino, a climate phenomenon with significant
influence on the ocean-atmosphere system with anomalies expressed as distinct
weather patterns and ocean conditions across the globe. Consequences of the
atmospheric and oceanographic anomalies during an El Nino event result in limited
ocean productivity, especially in the Eastern Equatorial Pacific, which is usually
characterized by a vibrant marine food web during normal, non-El Nino conditions.
During normal conditions, ocean productivity is fueled by upwelling of cold-nutrient rich
waters brought to the surface along the Eastern Pacific.
For more info visit:
http://www.noaanews.noaa.gov/stories2009/20090709_elnino.html
http://www.sciencemag.org/cgi/content/full/309/5735/758
Oceanographic and atmospheric conditions of the past are recorded and often well
preserved in marine sediments that deposit on the seafloor. Suppose you are given the
opportunity to investigate the frequency and duration of El Nino events in the past by
collecting marine sediment samples from the Eastern Pacific.
1. If the East Pacific Rise (EPR), a mid-ocean ridge in the East Pacific Ocean, is 52 My
old at its Eastern edge, and mean sedimentation rates in this equatorial upwelling
region can approach 20 cm/kyr, what is the mean sediment thickness (in km) at the
Eastern edge of the Pacific Ocean Basin? (10 points)
2. You decide that you only want to study samples from the late Miocene,
approximately 5 My ago. Remember that the EPR has a ½ spreading rate of roughly
4 cm/yr. How many nautical miles from the ridge axis of the EPR would you have to
sample to make sure you get 5 My old sediment? (10 points)
3. How deep would you have to drill to get your sample (meters)? (10 points)
Seawater- 3