Oceanography Lecture 6 Defining Boundaries: 3) 1. Review 2. : 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 mid- ocean 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) 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) 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 s s surface # Tends towards equilibrium (i.e. thermodynamics) # Plate tectonics! (i.e. kinetics) B. Classification Sediments can be subdivided on the basis of:! The size of the particles (grain( size) Sediment Type Diameter (mm) Gravel Boulder >256.0 Cobble 64.0-256.0 Pebble 4.0-64.0 Granule 2.0-4.0 Sand Very coarse 1.0-2.0 Coarse 0.5-1.0 Medium 0.25-0.50 Fine 0.125-0.250 Very fine 0.0625-0.125 Mud Silt 0.0039-0.0625 Clay 0.0002-0.0039 Colloids <0.0002 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). 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) B. Classification! Both classifications are interrelated.! Sand & Mud, which are separated on basis of grain size, can be terrigenous,, biogenic, authigenic, cosmogenous,, 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.
C. Factors that control sedimentation Stokes Law: : Settling speed of (spherical) particles is proportional to the size of the particle (Appendix, p. 495)! s = 0.222 [g(" 1 " 2 )/µ] ] r 2 Where:! s = Settling velocity (cm/s) 0.222 = constant for all spheres g = acceleration due to Earth s s gravity (981 cm/s 2 ) " 1 = quartz particle density (2.5 g/cm 3 ) " 2 = fluid density (seawater: 1.03 g/cm 3 ) µ = viscosity of fluid (seawater 10-20#10-3 g/cm.s) r = radius of particle (cm) D. Sedimentation in the Oceans Two areas of sediment deposition on the basis of water depth i. Shelf sedimentation: : Shallow, close to terrigenous sources ii. Deep sea sedimentation: : Deep abyssal plains Two main sources: - External (terrigenous( mud and sand) - Internal (biogenic particles, authigenic particles)! s = (2.62#10 4 ) r 2 Settling velocity depends on the shape of the particles! Moreover, the formation of particle aggregates increases their size and thus their settling velocities! Source: Pinet 2000 (source: USGC) D. Sedimentation in the Oceans Two major areas of sediment deposition on the basis of water depth i. Shelf sedimentation: : theoretical equilibrium i. Shelf Sedimentation Sea level change # Oscillation due to geological changes in the hydrological cycle Adapted from Garrison 2002
i. Shelf Sedimentation Sea level change # Oscillation due to geological changes in the hydrological cycle Sea level change Robert A. Rohde: Global Warming Art project 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 1 st third of shelves and most deposits are relict in nature Present material not in equilibrium with present-day conditions! i. Ice Rafting Heterogeneous mix of terrigenous materials
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) ii. Deep-Sea Sedimentation Two main sources: - External (terrigenous( mud and sand) - Internal (biogenic particles, authigenic particles) Three categories: - Bulk emplacement - Pelagic sediments - Authigenic sediments ii. Deep-Sea Sedimentation External sources (terrigenous( mud and sand): variable inputs ii. Deep-Sea Sedimentation Red clays.. Very fine-grained particles of brownish color (oxidized), composed of clay minerals such as Kaolinite, chlorite, Illite and 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)
ii. Deep-Sea Sedimentation Biogenic particles.. Usually hard parts, shells, or macro- and micro- debris. Two main minerals: CaCO 3 and SiO 2 - CaCO 3 # Foraminifera, Pteropods, Coccolithophores 2HCO - 3 (d) + Ca + 2 (d) # CaCO 3 (s) + CO 2 (g) + H 2 O - SiO 2 # Diatoms & Radiolarian ii. Deep-Sea Sedimentation Authigenic particles.. Chemical precipitates that form at or near the sediment/water interface or precipitate from seawater: - Ferromanganese nodules # metals oxides (Fe and Mn,, & more) that grow concentrically around nuclei: 1-4 mm/ma - Phosphorites # precipitation of P 2 0 5 (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) Ferromanganese Nodules E. Global distribution of deep-sea sediments
F. Sedimentation Rates Historical reconstruction of reduced O 2 levels in deep waters of Puget Sound: biogeochemical and Physical constraints on hypoxia conditions Patrick Louchouarn Texas A&M University Depts.. Marine Sciences & Oceanography Jill Brandenberger and Dr. Eric Crecelius (Battelle, Marine Science Laboratory) Coastal Hypoxia Research Program (CHRP) Average Dissolved Oxygen Measurements (below 20m) 1950s - 2004 8.000 7.000 Southern Hood Canal (Dabob Bay to Great Bend) Low oxygen conditions appear to be getting worse. The 2004 inventory of the oxygen is the lowest on record. 6.000 Major fish kills: 2002-03, 2006 Date of First Documented Hypoxic event 1970s 1980s 1990s 2000 milligrams/liter 5.000 4.000 3.000 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) 2.000 0 50 100 150 200 250 300 350 Day of Year 1952-3 1954 1955 1956 1957 1958 1959 1960 1961 1962 Source: M. Warner (UW) analysis; UW Collias & PRISM data
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? 1939 Aerial Photography Heavy Timber Harvesting Evident in Hood Canal Watershed Original imagery source: US Forest Service, distribution by UW, Puget Sound River History Project 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.
Puget Sound Basins Puget Sound (PS-1) Sediment Accumulation Rates! Main Basin of Puget Sound! Hood Canal Bangor Bremerton Bainbridge Island Seattle Total Solid Accumulation (g/cm2) 0 10 20 30 40 50 60 70 Pb-210 (dpm/g) 0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 " Pb-210 activity used to determine the sediment accumulation rate (g/cm 2 /yr). ln Pb-210xs (dpm/g) -1.5-1 -0.5 0 0.5 1 1.5 2 0 80 " Estimated sediment accumulation rate for PS-1 is 0.6 g/cm 2 /yr. " Estimated sedimentation rate is 1.2 cm/yr. Total Solid Accumulation (g/cm2) 10 20 30 40 50 60 70 y = -18.917x + 41.453 R 2 = 0.9866 Tacoma Geographical Sediment Accumulation Stable Pb and Previous Studies! Stable Pb profiles from 3 coring studies at PS-1.
Stable Pb and Previous Studies (PS-1)! Stable Pb profiles from 3 coring studies at PS-1 confirm estimated ages from sedimentation rates. " 2005 Hypoxia Study "1991 NOAA Status and Trends Study (Lefkovitz et al. 1997) "1982 Puget Sound Coring (Bloom and Crecelius 1987) Great Depression Age Dating for the Three Studies Pb smelting began in Puget Sound in 1890 1970s Environmental Regulations 1990 1970 1950 1930 1910 1890 1870 Estimated Year 1991 2005 1982 Depth (cm) 0 10 20 30 40 50 60 70 80 90 100 1982 Burial Rate for PS-1 28 R 2 = 0.999 41 1991 Year Core Collected 59 2005 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. Burial rate of the peak used to confirm sedimentation rates for the 2005 study. 1. Sedimentation rate using stable Pb peak burial rate = 1.34 cm/year 2. Sedimentation rate using Pb- 210 = 1.2 ± 0.22 cm/year Northern Hood Canal (HC-5) Dark Horizons
Core PS-1 PS-1 Core HC-5 HC-5 Puget Sound Hood Canal
%MOM = % Marine OM vs (C/N)a ( "13 C sed #" 13 C MOM ) " 13 C TOM #" 13 C MOM ( ) $ 13 C MOM $ 13 C TOM MOM = -19.7±0.3 TOM = -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. # Waves I (Chap. 9) For Next Time