Oceanography
Lecture 6
Defining Boundaries: 3) Marine Sediments
1. Review
2. Marine Sediments:
a. Introduction
b. Classification: Size vs. Origin
c. Factors that control sedimentation
d. Sedimentation in the Oceans
i. Shelf Sedimentation
ii. Deep-Sea Sedimentation
e. Global distribution
f. A Case Study: Puget Sound (WA)
Review
Defining Boundaries: 3) Plate Tectonics
1. Plate Tectonics
! Paleomagnetic signatures of oceanic crust.
! Increased thickness (and age) of sediments away from midocean ridges.
! Heat flow from the Earth interior to the crust decreases as
the distance from the ridge center and crustal age increase.
! Age of the oceanic crust.
! Shallow earthquakes (linked to ridges and faults)
! Deep earthquakes (linked to subduction zones and trenches).
! Balance of Earth volume!
2. Formation of Oceans: From embryonic to suturing
! Pacific: Old Ocean (shrinking, 200 Ma)
! Atlantic, Indian, Arctic: New Oceans (growing, really?)
Defining Boundaries: 3) Marine Sediments
A. Introduction
• Sediments are produced by the weathering (chemical and
mechanical-physical break down) of rocks such as granite
and basalt into particles that are then moved by air, water,
and ice.
• Sediments can also be formed from the accumulation of
shells or micro- and macro-debris of organisms.
• They can also come as a result of chemical precipitation
reactions
! Sediments can therefore consist of
" Mineral particles
" Fossil particles
Defining Boundaries: 3) Marine Sediments
A. Introduction
! Most erosion of rock occurs on land and most deposition of
sediments occur in the Oceans.
# Net balance (erosion/deposition) would be to even out
Earth’
Earth’s surface
# Tends towards equilibrium (i.e. thermodynamics)
# Plate tectonics! (i.e. kinetics)
Marine Sediments
B. Classification
Sediments can be subdivided on the basis of:
! The size of the particles (grain
(grain size)
size)
Sediment
Gravel
Type
Boulder
Cobble
Pebble
Granule
Diameter (mm)
>256.0
64.0-256.0
4.0-64.0
2.0-4.0
Sand
Very coarse
Coarse
Medium
Fine
Very fine
1.0-2.0
0.5-1.0
0.25-0.50
0.125-0.250
0.0625-0.125
Silt
0.0039-0.0625
Clay
0.0002-0.0039
Mud
Colloids
Marine Sediments
B. Classification
!Their mode of formation (origin
(origin))
• Terrigenous sediments: Fine and coarse grains produced by
weathering and erosion of rocks on land (sands & muds).
muds).
• Biogenous sediments: Fine and coarse grains that are derived
from the hard parts of organisms (shells, skeletal debris –
carbonates and silica)
• Authigenic sediments: Particles that are precipitated by chemical
reactions (diagenesis
(diagenesis)) in seawater near the sea floor or within
sediments (phosphorites
(phosphorites,, ferromanganese nodules)
• Volcanic sediments: Particles that are ejected from volcanoes (i.e.
ash)
• Cosmogenous sediments: Very tiny grains that originate from
meteorite shower and outer space material (mixed with
terrigenous and biogenic sediments)
<0.0002
Marine Sediments
B. Classification
! Both classifications are interrelated.
! Sand & Mud, which are separated on basis of grain size, can be
terrigenous,
terrigenous, biogenic, authigenic,
authigenic, cosmogenous,
cosmogenous, etc…
etc…
C. Factors that control
sedimentation
! Relationship between average
grain size and energy of
bottom currents
! Erosion, Transport and
Deposition (sedimentation)
depend on velocity of current
and grain size
! Settling rate of suspended
particles varies with diameter
(Stokes Law)
Hujlstrom’s diagram. Adapted from Pinet 2000
Marine Sediments
C. Factors that control sedimentation
Stokes Law:
Law: Settling speed of (spherical) particles is
proportional to the size of the particle (Appendix, p. 495)
!s = 0.222 [g("
[g("1 – "2)/µ
)/µ] r2
Where:
!s = Settling velocity (cm/s)
0.222 = constant for all spheres
g = acceleration due to Earth’
Earth’s gravity (981 cm/s2)
"1 = quartz particle density (2.5 g/cm3)
"2 = fluid density (seawater: 1.03 g/cm3)
µ = viscosity of fluid (seawater 10-20#
10-20#10-3 g/cm.s)
r = radius of particle (cm)
Marine Sediments
D. Sedimentation in the Oceans
Two areas of sediment deposition on the basis of water depth
i. Shelf sedimentation:
sedimentation: Shallow, close to terrigenous sources
ii. Deep sea sedimentation:
sedimentation: Deep abyssal plains
Two main sources:
- External (terrigenous
(terrigenous mud and sand)
- Internal (biogenic particles, authigenic particles)
!s = (2.62#104) r2
Settling velocity depends on the shape of the particles!
Moreover, the formation of particle aggregates increases their size
and thus their settling velocities!
Marine Sediments
D. Sedimentation in the Oceans
Two major areas of sediment deposition on the basis of
water depth
i.
Source: Pinet 2000
(source: USGC)
Marine Sediments
i. Shelf Sedimentation
Sea level change # Oscillation due to geological changes in
the hydrological cycle
Shelf sedimentation:
sedimentation: theoretical “equilibrium”
equilibrium”
Adapted from Pinet 2000
Adapted from Garrison 2002
Sea level change
Marine Sediments
i. Shelf Sedimentation
Sea level change # Oscillation due to geological changes in
the hydrological cycle
Robert A. Rohde: Global Warming Art project
Adapted from Pinet 2000
Adapted from Pinet 2000
Marine Sediments
i. Shelf Sedimentation
Sea level change # transfer of terrigenous sediments back and
forth between continental shelf and shelf break
Modern deposits occur only on the 1st third of shelves and most
deposits are relict in nature
Marine Sediments
i. Ice Rafting
Heterogeneous mix of terrigenous materials
Present material not in equilibrium with present-day conditions!
Adapted from Pinet 2000
Adapted from Pinet 2000
Marine Sediments
i. Worldwide distribution of Shelf sediments
A regular pattern of sediment types occur based on latitude and
climate (30-40% of sediments are recent - 70-60% are relict)
Marine Sediments
ii. Deep-Sea Sedimentation
Two main sources:
- External (terrigenous
(terrigenous mud and sand)
- Internal (biogenic particles, authigenic particles)
Three categories:
- Bulk emplacement
- Pelagic sediments
- Authigenic sediments
Adapted from Pinet 2000
Adapted from Pinet 2000
Marine Sediments
ii. Deep-Sea Sedimentation
External sources (terrigenous
(terrigenous mud and sand): variable inputs
Marine Sediments
ii. Deep-Sea Sedimentation
Red clays.
clays. Very fine-grained particles of brownish color
(oxidized), composed of clay minerals such as Kaolinite,
Kaolinite,
chlorite, Illite and Montmorillonite.
Montmorillonite. Dominant only when other
sources are less abundant!
Some clay minerals show
strong susceptibility to
weathering and are
altered due to chemical
weathering:
Kaolinite # (formed in
warm moist climate)
Chlorite # (formed in
temperate and subpolar
latitudes)
Adapted from Pinet 2000
Adapted from Pinet 2000
Marine Sediments
ii. Deep-Sea Sedimentation
Biogenic particles.
particles. Usually hard parts, shells, or macro- and microdebris. Two main minerals: CaCO3 and SiO2
- CaCO3 # Foraminifera, Pteropods,
Pteropods, Coccolithophores
2HCO3- (d) + Ca2+ (d) # CaCO3 (s) + CO2 (g) + H2O
- SiO2 # Diatoms & Radiolarian
Marine Sediments
ii. Deep-Sea Sedimentation
Authigenic particles.
particles. Chemical precipitates that form at or near
the sediment/water interface or precipitate from seawater:
- Ferromanganese nodules # metals oxides (Fe and Mn,
Mn, &
more) that grow concentrically around nuclei: 1-4 mm/Ma
- Phosphorites # precipitation of P205 (up to 30%) on
continental shelves with very high primary productivity.
Biogenic oozes consist of 30% or more of skeletal debris of
organisms (70% composed of inorganic mud particles)
Marine Sediments
Ferromanganese Nodules
Adapted from Pinet 2000
Marine Sediments
E. Global distribution of deep-sea sediments
Adapted from Pinet 2000
Marine Sediments
Historical reconstruction of reduced O2
levels in deep waters of Puget Sound:
biogeochemical and Physical
constraints on hypoxia conditions
F. Sedimentation Rates
Patrick Louchouarn
Texas A&M University
Depts.
Depts. Marine Sciences & Oceanography
Jill Brandenberger and Dr. Eric Crecelius (Battelle, Marine
Science Laboratory)
Coastal Hypoxia Research Program (CHRP)
Adapted from Pinet 2000
Average Dissolved Oxygen
Measurements (below 20m) – 1950s - 2004
Average Dissolved Oxygen
Southern Hood Canal (Dabob Bay to Great Bend)
8.000
Low oxygen conditions appear to be getting worse. The
2004 inventory of the oxygen is the lowest on record.
7.000
Major fish kills: 2002-03, 2006
Date of First Documented
Hypoxic event
1970s
1980s
1990s
2000
milligrams/liter
6.000
5.000
4.000
3.000
2.000
0
Source: America’s Oceans: Charting a Course for the Sea Change, Pew Ocean Commission, June 2003
(http://www.pewtrusts.com/pdf/env_pew_oceans_final_report.pdf)
50
100
150
200
250
300
350
Day of Year
1960
1961
1962
1963
1965
1966
1998
1999
2000
2001
Source:
M. Warner
(UW)
analysis;
UW
Collias
& PRISM
data 2002
1952-3
1954
1955
1956
1957
1958
1959
2003
2004
1939 Aerial Photography
Heavy Timber Harvesting Evident in Hood Canal Watershed
Scientific Objectives
1. When did hypoxia begin in Puget Sound and how
has the intensity varied over the last several
hundred years?
2. How have sources of carbon and nitrogen changed
as a function of increased human population,
primary productivity, and alterations in LU/LC?
3. How have assemblages of diatoms and
foraminifera changed as the basins were logged,
river runoff patterns changed, freshwater inflows
increased, and nutrient loading increased?
Core Collection
!
!
2-3 meter long cores were
collected using a Kasten corer
Cores were subsectioned at 2cm
intervals down to 100cm and 2 or
5cm intervals down to the core
catcher.
Original imagery source: US Forest Service, distribution
by UW, Puget Sound River History Project
Puget Sound (PS-1)
Sediment Accumulation Rates
Puget Sound Basins
Pb-210 (dpm/g)
Bangor
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
Main Basin of Puget Sound
! Hood Canal
!
Seattle
Bremerton
10
20
30
" Pb-210 activity used to
determine the sediment
accumulation rate
(g/cm2/yr).
40
50
ln Pb-210xs (dpm/g)
60
-1.5
-1
-0.5
0
70
0
80
10
" Estimated sediment
accumulation rate for
PS-1 is 0.6 g/cm2/yr.
" Estimated sedimentation
rate is 1.2 cm/yr.
Total Solid Accumulation (g/cm2)
Bainbridge
Island
Total Solid Accumulation (g/cm2)
0
0.5
1
20
30
40
y = -18.917x + 41.453
50
2
R = 0.9866
60
70
Tacoma
Geographical Sediment Accumulation
Stable Pb and Previous Studies
!
Stable Pb profiles from 3 coring studies at PS-1.
1.5
2
Burial Rate for PS-1
Stable Pb and Previous Studies (PS-1)
R2 = 0.999
Stable Pb profiles from 3 coring studies at PS-1
confirm estimated ages from sedimentation rates.
" 1991 NOAA Status and
Trends Study
(Lefkovitz et al. 1997)
" 1982 Puget Sound
Coring (Bloom and
Crecelius 1987)
20
Age Dating for the Three Studies
1970s
Environmental
Regulations
1990
1970
1950
Great Depression
1930
1910
Pb smelting began in
Puget Sound in 1890
Northern Hood Canal (HC-5)
Dark
Horizons
30
Depth (cm)
" 2005 Hypoxia Study
• The depth of the max stable Pb in
each of the 3 studies plotted to
estimate the sediment accumulation
rate at PS-1 from 1982 to 2005.
10
1890
1870
Estimated Year
!
0
1991
2005
1982
40
28
• Burial rate of the peak used to
confirm sedimentation rates for the
2005 study.
41
50
60
70
59
80
90
1. Sedimentation rate using stable
Pb peak burial rate = 1.34 cm/year
2. Sedimentation rate using Pb210 = 1.2 ± 0.22 cm/year
100
1982
1991
Year Core Collected
2005
Core PS-1
PS-1
Puget Sound
Core HC-5
HC-5
Hood Canal
% Marine OM vs (C/N)a
(" C
(" C
13
%MOM =
sed
13
TOM
#"13CMOM )
#" CMOM )
13
$13CMOM = -19.7±0.3‰
-19.7±0.3‰
$13CTOM = -26.9±0.5‰
-26.9±0.5‰
TOM inputs vs. Marine productivity
!
Puget Sound
Hood Canal
Pacific Decadal Oscillation
Pacific Decadal Oscillation
warm eras have seen enhanced coastal ocean biological productivity
in Alaska and inhibited productivity off the west coast of the
contiguous United States, while cold PDO eras have seen the
opposite north-south pattern of marine ecosystem productivity.
Warm eras have seen inhibited coastal ocean biological productivity off the west coast
of the contiguous United States, while cold PDO eras have seen the opposite pattern of
marine ecosystem productivity.
For Next Time
# Waves I (Chap. 9)