©1996, West Publishing Company (Modified by Asper, 2006) Slide 1 Lesson #5 How did the ocean get...

©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 11

Lesson #5

How did the ocean get that way?Where did all the mud come from?

Paul PinetPrepared by Nancy Marcus,

Florida State University

modified by Vernon Asper

revised by Steven Lohrenz and Charlotte Brunner

University of Southern Mississippi


Learning to Love Mud

• Yes, the bottom of the ocean is covered by mud

• But, believe it or not, mud can be cool

• If you understand it, you can learn a lot from mud.– No, really, you can!

Sea lily

Sponge

Brittle stars

Beer can


Learning to Love Mud

• To love mud, you have to get to know it

• We can classify (name) mud several different ways:

• Size

• Chemistry

• source

Sedimentologists onboard the drilling ship, Resolution.


Sediment Size

• Size matters!• It’s hard to get a

2mm piece of dirt out to the middle of the ocean– You usually find them

only near shore

• Really small stuff (0.01mm or so) can be carried by the wind

• Grade Limits Name• Above 256 mm Boulder• 256-64 mm Cobble• 64-4 mm Pebble• 4-2 mm Granule• 2-1 mm Very coarse

sand• 1- 1/2 mm Coarse sand• 1/2-1/4 mm Medium sand• 1/4--1/8 mm Fine sand• 1/8-1/16 mm Very fine sand• 1/16-1/256 mm Silt• Below 1/256 mm Clay

“Gravel”

“Mud”


Origins / Sources

• Sediments in the ocean originate from one of 5 sources.– From the earth: Terrigenous– From living things: Biogenic– Self made mud: Authigenic– From volcanoes: Volcanogenic– From space: Cosmogenous


The Rock Cycle• The origin of a rock determines its properties

and composition

These 3 These 3 are most are most important important in the in the oceanocean


Origins / Sources (cont).• Terrigenous sediments are derived from the land (terra)

– Rocks weather to small particles

– These particles are transported to the ocean by both wind and rivers

– Weathering and transport are called erosion.

• Much of it is deposited in river deltas like this one (the Atchafalaya subdelta of the Mississippi delta)

Atchafalaya River delta, LA.


Origins / Sources (cont).• Biogenic

sediments are the skeletal remains of living organisms.– Only the “hard

parts” are preserved.

– This is a small fraction of what’s living out there.

• These skeletons dominate the sediment in many places.

Foraminifer:Calcium carbonate

Radiolarian: silica


Biogenic Sediment

• Four of the most common are:

Coccolithophorids

foraminiferaforaminifera

Radiolarians

Diatoms

Foraminifera


Origins / Sources (cont).• Authigenic

sediments are formed in place– The most

common are manganese nodules.

– These have large potential economic value (Manganese, copper, nickel, cobalt and other trace metals)

These are normally fist-sized


The Glomar Explorer Story• Built by Glomar Marine– Howard

Hughs’ company

• Intended for recovering manganese nodules

• Really?


The true story:

• Intended to recover a sunken Soviet submarine

http://www.eaglespeak.us/2007/07/http://www.eaglespeak.us/2007/07/sunday-ship-history-glomar-sunday-ship-history-glomar-explorer.htmlexplorer.html


http://www.tommcmahon.net/2010/05/video-recording-of-the-burial-at-sea-of-http://www.tommcmahon.net/2010/05/video-recording-of-the-burial-at-sea-of-soviet-submariners-recovered-during-the-cia-project-jennifer.htmlsoviet-submariners-recovered-during-the-cia-project-jennifer.html

©1996, West Publishing Company (Modified by Asper, 2006)©1996, West Publishing Company (Modified by Asper, 2006) Slide Slide 1414http://www.shipspotting.com/gallery/photo.php?lid=1340743http://www.shipspotting.com/gallery/photo.php?lid=1340743


Authigenic Sediments• Hydrothermal deposits are formed at midocean ridges as

part of the spreading process.

• Water circulates though cracks in the crust, dissolving minerals and bringing them to the surface.


Authigenic Sediments• When this water mixes with

the cold ocean water,– The water cools.– The minerals precipitate out.

• These precipitates form mineral-rich sediments.


Origins / Sources (cont).

• Volcanogenic particles are produced by most volcanic eruptions– Mostly found near volcanoes (no surprise there!)

– Can be transported LARGE distances by wind.

– Major eruptions can affect sediments on a global scale.

Mt. St. Helens, 1989


Origins / Sources

• Some ash arrives directly via “pyroclastic flows”

• These are extremely hot gasses plus suspended ash particles

• Very deadly

• These are responsible for many volcano-related deaths.

• (mudslides are also very deadly)


Origins / Sources (cont).• Locally, the

effects of volcanic ash can be devastating


Origins / Sources (cont).

• Cosmogenous particles come from “outer space”.– Produced from

fragmented meteorites and products of their impacts.

– Very small amount.

– Important tracers of “events”

Tektites


Moving mud

• Sediment grains can be moved from one place to another if there is enough energy

• This is determined by:– Particle size, and – Energy conditions at the site of deposition.

Ripples on the deep ocean basin

inferPattern Process


Sediments

• It takes more energy to move a larger grain of sediment

• So: – High energy beaches are

composed of coarse sands.

– Quiet lagoons are composed of muds.

• You can see this somewhat on our barrier islands Barrier island, near

Cape Lookout, NC

Sandy beach

Muddy lagoon


More on Sediments

• Grain size and current velocity determine whether a particle will be:– Eroded– Transported– Deposited

• The type ofbeach you getdepends on the energy and the particles available Sandy beach at Assateague Island, MD


Sediments in shallow water

• Sedimentation on the shelf is different from in the deep sea– Shallow water

– More energy


Continental Shelf Sedimentation

• The major source of energy for eroding and transporting sediments on the shelf is energy from breaking waves.

California coast


Continental Shelf Sedimentation

• Wave energy decreases with depth below the surface

• In deep water, no energy reaches the seafloor


Continental Shelf Sedimentation• In shallow water:

– Wave motion at the bottom increases and is maximum when waves break near the beach

– Large grains sizes stay there

– Small grains are taken offshore where energy at the bottom is low

– That’s why the beach is sandy and the bottom in deep water is muddy.


Continental Shelf Sedimentation (Cont.)

In the ideal case, grain size across the continental shelf would vary like this:


• All of this assumes a “steady state condition”, that sea level hasn’t changed• But it has!!!!• Sea level has risen so rapidly over the last 16,000 years that conditions have

not had a chance to equilibrate.• More about this in later lessons!

Curve of sea level


Deep-sea Sedimentation (Cont.)

• Sediment can enter the deep sea directly from the coast– Input from rivers– Chunks fall off of the slope and slide down to

the deep sea

• When this

happens, the

result can be

significant.

http://scicom.ucsc.edu/scinotes/9901/kill/images/slidefinal.jpghttp://scicom.ucsc.edu/scinotes/9901/kill/images/slidefinal.jpg


It’s easy to see this process on land

• A piece of hillside breaks loose and slides down hill.

• The block may remain internally intact or it may break up

Incipient slump

Slump blockSlump scar


Slumping takes place occasionally underwater as well.

Slump Block

Slump scar


– Slurries are mixes of sediment and water.

– Big ones can sweep even boulder-sized particles down slope.

– Turbidity currents are large slurries which move rapidly downslope.



• Turbidity Currents:– Are propelled by gravity

– Water + sediment weighs more than just plain water

– Once started, they can go for miles and miles



• Turbidity currents are often triggered by earthquakes– this quake triggered a flow which

broke 4 communications cables– from the timing of the breaks, we can

measure the speed of the flow

25m/s=56mph

124 miles124 miles 496 miles496 miles


Deep-sea Sedimentation(Cont.)

• Turbidity currents often flow through submarine canyons.

– may have created them

– definitely help maintain them


Deep-sea Sedimentation(Cont.)

• Turbidite beds are– Formed at the bottom

of the slope as the turbidity current slows.

– An example of graded bedding.

– Many turbidites build up a deep sea fan, which is similar to a river delta.



• Ice rafting is another way particles can be transported from the coast to the deep sea.– Only at polar latitudes

(obviously).

– Carries large amounts of terrigenous sediment from the land to the sea .

– The material is dropped as the ice melts.

– Sediments are typically poorly sorted with a wide range of grain sizes.

Erodeddirt!



Deep-sea sediments around Antarctica include ice-rafted (glacial-marine) sediment near the coast.



• Pelagic sedimentation is largely responsible for sediments in the deep-sea.– It consists of mostly very fine particles.– It’s origins are

• Inorganic• Organic


electron micrograph of

red clay

Deep-sea Sedimentation • Inorganic pelagic sediments are mostly red clay

– Aka “brown clay”, “pelagic clay”

• It occurs mostly where nothing else is present to overwhelm it– Background signal

• Consists of terrigenous material blown from the land by winds– The red color is due to oxidized

iron (rust).


Red clay

• It is derived partly from wind transport of dust weathered on land, especially deserts!

Dust storm blow dust from the Sahara to the Atlantic

Amount of dust in the air over the oceans.


Cosmogenic• Particles from

space! – Fallout – “tektites”=

products of a collision

http://www.lbl.gov/Science-Articles/Archive/images5/comet-shower.jpghttp://www.lbl.gov/Science-Articles/Archive/images5/comet-shower.jpg


Authigenic particles

– Self-forming– Spontaneously– Chemical

precipitation like Manganese nodules

http://pubs.usgs.gov/of/2000/of00-006/images/nod_r.gifhttp://pubs.usgs.gov/of/2000/of00-006/images/nod_r.gif


Deep-sea Sedimentation • Biogenic oozes.

– Consist of 30% or more of the skeletal remains – mostly surface dwelling, microscopic,

planktonic organisms.– The shells are either calcareous or siliceous.

Live planktonic foraminifer

Fossil planktonicforaminifers



• Calcareous (calcium carbonate) biogenic oozes are formed by– Zooplankton (“animals”)

• Foraminifera

– Phytoplankton (plants: need light!)• Coccolithophorids - algae



• For some rather complicated reasons, calcareous shells dissolve in the deepest parts of the ocean

• They are only found in shallower places like the mid ocean ridge

• Distribution controlled by depth

“Snow line”



• Siliceous biogenic oozes are derived from– Phytoplankton

• Diatoms

– Zooplankton• Radiolarians


Deep-sea Sedimentation

(Cont.)• Siliceous biogenic particles also dissolve

• Dissolve most in warm water, near the surface

• But high production overcomes dissolution

• Therefore, the distribution of siliceous ooze is controlled by production


Siliceous Sediments• Siliceous sediments are found beneath

areas of high biological production – Equator– Polar fronts– Margins of continents



• Summary:– silica and carbonate are

essentially opposite

– silica dissolves in surface water while carbonate dissolves in deep water

– distribution of siliceous sediment controlled by production

– distribution of carbonate sediment controlled by water depth


Summary – Abyssal sediments - How do they get to the sea floor?

Distribution of deep-sea sediments.Distribution of deep-sea sediments.


The Dynamic Shoreline• The coastal zone is the place where we humans

interact with the sea• So, let’s take a close look at this region so that:

– when we go to the beach, you’ll know what we’re looking at

– we’ll be able to appreciate what we see


Coastal Water Movement

• The shoreline (beach) is the interface where the land meets the sea.

• A beach environment consists of several zones:– Nearshore zone

– Breaker zone

– Surf zone

– Swash zone

– Offshore zone

– Backshore zone


Coastal Water Movement(Cont.)

Here’s the ideal case of what this looks like:Here’s the ideal case of what this looks like:



• In very shallow waters waves oversteepen and form breakers.



• Review: As waves enter shallow water they interact with the sea bottom where their – Speed slows

– Height increases

– Wavelength decreases

• Most waves encounter the shoreline at an angle and are refracted.



• Wave refraction is easy to see: notice the curved waves entering this cove:



• This refraction focuses energy on headlands and disperses energy in coves:


Coastal Water Movement• Here’s how this works; watch the coast become straight:



• Note the sand which accumulated in this small cove because of reduced energy



• This coast is being smoothed:– promontories are being eroded– coves are being filled in


Coastal Water Movement (ont.)

• Longshore currents and rip currents can also be generated by wave setup which forms pressure gradients.



– Where waves are higher, water piles up and flows longshore in the direction of “lower water”

– Longshore currents converge result in water being forced away from the shoreline forming a rip current.


Hanauma Bay

• Volcanic caldera, open on one side• Waves bring water over the reef• Must get out somehow• Cable channel is easiest point• Rip current develops


Coastal Water Movement (Cont.)• Longshore currents flow parallel to the shoreline.

– Often caused by waves striking the beach at an angle.

– Strength depends on the angle of wave approach


Beaches• Beach sand is continually being moved by longshore

currents and rip currents. • To keep track of these movements scientists develop

sand budgets which are estimates of – Sand sources

• River input• Sea cliff erosion• Longshore and onshore

sand transport

– Sand losses• Longshore and offshore

transport• Wind erosion


Sand budgetsSand budgets

-- ==

http://soundwaves.usgs.gov/2009/03/http://soundwaves.usgs.gov/2009/03/


Beaches (Cont.)

• When the input and output of sand are equal the beach is stable and in steady-state equilibrium.

• When input exceeds output the result is deposition and the beach widens.

• When output exceeds input the result is erosion and the beach narrows


Beaches (Cont.)

• Beaches are dynamic environments that expand and contract depending upon wave conditions. Typically sand is moved shoreward during the summer and seaward during the winter.


Barrier Islands• Barrier islands are large deposits of sand

that are separated from the mainland by bodies of water

• They are common along the Atlantic and Gulf coasts of the United States.


Barrier Islands (Cont.)• The barrier island environment consists of several distinct

regions:– Their characteristics are determined by the amount of wave energy.


Storm Effects• Storms have more

effect on shaping the shoreline than “normal” conditions

• Storm surges are extreme high water events

• Caused by high winds that pile water up along the shoreline.


Storm Effects• They lead

to flooding of low lying coastal areas and contribute to the overwash of barrier islands.

Note the missing homesNote the missing homes


Storm Effects• They can contribute to the formation of

temporary tidal inlets due the fragmentation of barrier islands.


Storm Effects

• Here are before and after pictures

• Hurricane Georges (October 1998) removed most of this island.


Estuaries• Estuaries are semi-enclosed bodies of

water where a river meets the sea.

• Estuaries are protected and provide good natural harbors.

• They are highly productive areas and serve as important nursery grounds for fish and other marine organisms.


Estuaries (Cont.)

• Estuaries are influenced by two important factors.– The input of freshwater.– Tidal flow which mixes

the fresh and salt

water.


Estuaries (Cont.)

Origin of estuaries. Bar-built estuaries form when a spit forms across an embayment.


Curve of sea level

Estuaries• In general, the earth’s recent history has

been one of rising sea level.– this resulted in the drowning of river valleys.– these become estuaries


Estuaries (Cont.)

An estuary formed from a drowned river valley.


Estuaries

• The Chesapeake is this nation’s “classic” estuary– input from several

rivers

– definite salinity and habitat gradients

– important fisheries

– population centers


Deltas• Deltas form where the sediment input from rivers exceeds the sediment removed by waves and tidal currents.

• And where the rate of accumulation exceeds both sea level rise and subsidence


DELTAS• Sea level rise inhibits the formation of deltas

– as sediments are deposited at river mouths, the rising sea level keeps them submerged.

– the only way you can form a delta is to have MASSIVE sediment input!

The Missi

ssippi R

iver has it!

The Missi

ssippi R

iver has it!

That’s why we have a delta

That’s why we have a delta

The Chesapeake is The Chesapeake is fed by rivers with fed by rivers with very little very little sediment loadsediment loadThis allows it to This allows it to continue to existcontinue to existIt doesn’t fill in.It doesn’t fill in.


Deltas• Notice that deltas form at river mouths.

• The area in northwestern Mississippi called “the Delta” isn’t.

• This is actually just the flood plain of the Mississippi River


Deltas• As the flood waters recede, they deposit layers of mud

– this builds up the flat, fertile fields of the flood plain

– here in Mississippi, we incorrectly call them a “delta”


Impact of People on the Coastline

• Humans have tried to modify the coastal zone to make it more stable and thus suitable for building homes, hotels, etc.

• Methods of stabilization include:– Jetties– Groins– Breakwaters– Seawalls– Beach nourishment


Impact of People on the Coastline (Cont.)

• Jetties are built to diminish sediment deposition at the mouths of harbors, inlets, etc. They prevent dispersal of sand across the mouth. They cause erosion on the downdrift side.



• These jetties are doing their job:– note the sand building up on the upstream side of the jetty

– AND the erosion taking place downstream!



• This is because the flow of sand has been cut off– this region has lots of sand – this region is starved for sand

Normal flow of sandNormal flow of sand



• Groins are built on eroding beaches to trap sand and to promote accretion. Like jetties they also cause erosion on the downdrift side.



• These groins are doing their job, but look at the consequences!

AccumulationAccumulation

Serious erosionSerious erosion

Flow of sand



• Breakwaters are built to redirect wave energy. They are usually built in front of harbors or other expensive property to absorb the impact of waves. Sediment accumulates shoreward.



• This breakwater protects the land behind it, but causes sand to accumulate as well

• Nothing we do to “engineer” the environment is without consequences



• Seawalls are built along the shore to protect beaches, roads, etc. from erosion by storms.

• However, they increase turbulence and promote erosion at their base.

• Seawalls and beaches don’t mix.


Impact of People on the Coastline (Cont.)• seawalls are not very “scenic”……..


• In Bay St. Louis, MS, we are building a “new and improved” seawall

• Note the effect of storm sewer pipes

http://media.gulflive.com/mississippi-press-news/photo/corps-bay-st-louis-seawall-dc1afaadac30d655.jpg


Impact of People on the Coastline (Cont.)• But when we build on the beach, they are often a necessity!

– Look at what happened without them in these cases:

““Move it or lose it!”Move it or lose it!”


• After a storm damaged it, they finally moved the house from the film “Nights in Rodanthe”

http://smugpessimist.blogspot.com/http://smugpessimist.blogspot.com/

http://www.wral.com/news/local/image/7557003/?ref_id=7556863http://www.wral.com/news/local/image/7557003/?ref_id=7556863http://hamptonroads.com/2009/12/nights-http://hamptonroads.com/2009/12/nights-rodanthe-house-sold-bail-bondsmanrodanthe-house-sold-bail-bondsman



• Beach nourishment is the process of adding

sand to beaches.



• This is only a temporary solution because sand will always be removed by waves.



• Money spent on beach nourishment must be spent again and again and again…….


TABLE 8-3 Selected beach-replenishment projects on the U.S. East Coast TABLE 8-3 Selected beach-replenishment projects on the U.S. East Coast

BeachBeach

Ocean CityOcean CityAtlantic BeachAtlantic BeachMyrtle BeachMyrtle BeachTybee IslandTybee IslandCape CanaveralCape Canaveral BeachBeachPompano BeachPompano BeachHollywood-HallandaleHollywood-HallandaleMiami BeachMiami BeachKey BiscayneKey Biscayne

StateState

MDMDNCNCSCSCGAGAFLFL

FLFLFLFLFLFLFLFL

YearYear

19631963198619861986-’871986-’871976197619751975

19701970197919791979-821979-8219871987

Volume of Volume of Sand (ydSand (yd33))

2,300,0002,300,0001,050,0001,050,000

3,6000,0003,6000,000850,000850,000

2,715,0002,715,000

1,076,0001,076,0001,980,0001,980,000

12,000,00012,000,000360,000360,000

Cost at TimeCost at Timeof Constructionof Construction

$ 3,600,000$ 3,600,0001,050,0001,050,000

1,873,4371,873,4377,743,3767,743,376

55,000,00055,000,0002,600,0002,600,0001,517,6001,517,6004,750,0004,750,0004,500,0004,500,000

Source: Adapted from O.H. Pilkey, Jr., and T.D. Clayton, Source: Adapted from O.H. Pilkey, Jr., and T.D. Clayton, Journal of Coastal Research 5 Journal of Coastal Research 5 (1988):(1988):147-159147-159




• In addition to slow erosion, sudden storms can destroy homes built on the beach.

• The city of Cancœn, on Mexico's Yucatan peninsula, was devastated by hurricane Gilbert in September, 1988.



Many of these homes were Many of these homes were destroyed by hurricane destroyed by hurricane HugoHugo

9 Months later, they were 9 Months later, they were rebuilt, bigger and better, rebuilt, bigger and better, using our tax dollars!using our tax dollars!


Impact of People on the Coastline (Cont.)• Still, we put up with the cost and danger, because we

love to be near the water!• Questions?• Anyone?

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©1996, West Publishing Company (Modified by Asper, 2006) Slide 1 Lesson #5 How did the ocean get...

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