MAST382 Exam 2

Coast

from where the water meets the land inland to where there is no longer ocean influence on land

Shelf water depth

~20-50m

What is the coastal ocean?

The region between the land and the open ocean.

What processes dominate the coastal ocean?

Processes resulting from land-ocean boundary interaction.

What geographical features are included in the coastal ocean?

The continental shelf and part of the slope.

Estuary

partially enclosed body of water where freshwater from rivers mix with oceanic salt water

Erosional Coasts

Net loss of land - Eroded by wave action, river or glacier-induced erosion (ex: cliffs, rocky shores)

Depositional Coasts

Net Accumulation of Land - Accumulation after being transported to the area in rivers and glaciers or by ocean currents and waves (e.g., deltas, mangroves, salt marshes, barrier islands, sand dunes)

Coastlines are formed/modified when..

1. Sea level rises (coast added) or landmass subsides (coast loss)

2. Land is added or removed - (deposition/erosion)

What are eustatic sea-level changes?

Changes in volume of water (thermal expansion of water, melting glaciers) or volume of the basin itself (divergent margins).

How do eustatic sea-level changes occur globally?

They occur relatively uniformly worldwide.

What are isostatic sea-level changes?

Local changes in sea level due to processes such as glacial rebound or sediment compaction.

What is the nature of tectonic processes?

Slow (>10^6 year time scales), but constant.

How do volcanic eruptions in magmatic arcs at convergent plate boundaries affect landforms?

They can create island chains, such as Hawai'i.

What geological events can create or destroy coastlines?

Earthquakes that raise or lower sections of the land and seafloor.

What do divergent continental margins create?

Seas or oceans.

What is an example of a geological feature formed by divergent tectonic activity?

Mid-Atlantic spreading ridge.

What is an example of a geological feature formed by rifting?

African Rift Valley.

Landslides

-occur often on volcanic islands (Hawaii) with steep underwater flanks

-Relatively "Common" occurrence in volcanic island history (every 100,000 years in Hawaii)

Tsunamis

-may result from landslides (or other events)

-Canary Islands landslide could impact US via a tsunami

What has been happening to glaciers over the last 15,000 years?

They have been melting since the last ice age.

What type of valleys do glaciers create as they retreat?

Narrow, steep valleys.

What are fjords characterized by?

Submerged sills.

What are fjords made of?

Glacially deposited sediments and rocks, also known as moraines.

How are coasts formed or modified?

Coasts are formed/modified as rivers deposit sediments.

What type of area do most rivers flow across before reaching the sea?

Most rivers flow across a gradually sloping coastal plain.

What happens to rivers as they reach a flatter area near the sea?

Rivers slow down, and sediments fall out in this flatter area.

What landform is created after a river valley fills in with sediments?

A delta is formed.

What are delta soils known for?

Rich in nutrients and organics, making them great for agriculture.

What are the challenges of river deltas?

They are easily flooded and subject to drastic modifications to river courses.

Why are river deltas not ideal for human civilization?

They are easily flooded and have unstable land due to river modifications.

What is the effect of levees on delta soils?

Levees control flooding but reduce soil quality.

What characterizes a river-dominated delta?

It has a 'birdsfoot' shape, expanding into the estuary due to river flow and sediment deposition.

What is a tide-dominated delta?

A delta with small deltas and characteristic sand bars parallel to river flow.

What defines a wave-dominated delta?

It features a narrow river and an arcuate shoreline subject to longshore drift.

What is the principal coast-modifying process?

Breaking waves

How do breaking waves affect rocky coasts?

They progressively erode the rock away.

Which type of rock erodes faster: soft, sedimentary rocks or hard, volcanic rocks?

Soft, sedimentary rocks erode much faster.

What factors increase the rate of coastal erosion?

High wave action, wind, and weather events.

What role does sand composition play in coastal erosion?

It is affected by abrasion from waves and wind.

Where does erosion occur fastest on an indented coastline?

At headlands.

What happens to sand formed via erosion in intervening bays?

It accumulates within the bays.

How does preferential erosion of headlands affect the coastline over time?

It straightens the coast by removing the headlands.

What has happened to former headlands along New Jersey's northern shore?

They have been eroded, moving sand downshore.

How do waves affect coastal cliffs and headlands?

They preferentially erode soft, less resistant rocks.

What happens to land as waves cut into coastal cliffs?

It becomes unstable and breaks away, leaving cliffs.

What forms at the base of cliffs where harder rocks persist?

Sea caves.

What can happen to sea caves in headlands as they continue to erode?

They can meet and form a sea arch.

What occurs when sea arches collapse?

Remaining pinnacles of rock are called stacks.

What eventually happens to stacks?

They also eventually erode away.

Tide range

Tidal range determines the height range over which wave erosion occurs - and the width of the shore

Vegetation

-The type and extent of vegetation on the coast affects the rate at which winds, streams, and storm waves erode the land

-Grasses are important in protecting sand dunes from erosion

-Rooted plants (sea grasses, salt marsh plants, mangroves) that grow in the water help prevent erosion by waves and currents

-Plants dissipate wave energy that would otherwise erode land

-Tree roots (on land) and animal activities such as burrowing, can also contribute to continuous erosion of rocks and soils

Biogenic Construction

Volcanic island: creates a shallow water zone where corals can attach to rock substrate and grow towards the sea surface

Eventually the volcanic island erodes away, while at the same time the coral continues to grow up to the surface, even as its base support subsides.

Fringing reef

A reef attached to the shore of a continent or island.

Barrier Reef

a long coral reef near and parallel to the shore

Atoll

an island consisting of a circular coral reef surrounding a lagoon

Where are many coral reefs located?

Around islands or submerged pinnacles that are sinking isostatically.

What effect does isostatic sinking and sea-level rise have on coral reefs?

It increases water depth, decreasing the amount of light reaching the corals for photosynthesis.

How is coral reef growth expected to be affected by ocean acidification?

Coral reef growth is expected to decline due to increased CO2 in water and the dissolution of calcium carbonate.

Where do tidal wetlands grow?

On shores protected from wave action

What do tidal wetlands rely on to provide their physical environment?

Soil/sediment accumulation

What type of areas are tidal wetlands?

Flat, muddy or vegetated areas covered by water during only part of the tidal cycle

What type of plants characterize salt marshes?

March grasses

What type of plants characterize mangrove swamps?

Mangroves

What is the ecological value of wetlands?

-Supply organic matter, protection from predators

-Attractive places for marine animals to feed

-Habitat for juvenile marine organisms which then migrate to the sea at maturity

-Important feeding area for waterfowl

-Trap sediments/preserve coastlines

-Filter nutrients which reduces eutrophication in estuaries

-Provide gorgeous vistas

-Sequester 'blue' carbon

-Often conflict with human interests: Water front properties

Offshore

seaward of the breaker zone

Near-shore

below the low tide line in the breaker zone (may contain longshore bars)

Foreshore

between high and low tide lines

Backshore

area between high tide line and point reached by highest storm wave (often cliffs, sand dunes)

Littoral Zone - Berms

Berms - created by storm wave erosion of sand

• Identified where the beach slope steepens abruptly, top of berm is usually flat and the seaward side slopes downward relatively steeply

• Higher berms are caused by earlier storms

• Highest berm is called winter berm

Littoral

-Scarps are steep slopes or miniature cliffs formed by normal wave action (analogous to berms)

-Located on beach where wave normally reach during high tides

-If two scraps are present the highest one was formed when the tidal range was larger (spring tides)

What is longshore transport?

The movement of sediments along a coastline due to wave action.

How do waves approach shorelines in longshore transport?

Waves approach shorelines at oblique angles.

In which direction is the net transport of sediments during longshore transport?

The net transport of sediments is in the direction to which waves are angled.

What is the effect of longshore transport on coastlines and beaches?

Exposed coastlines and beaches are naturally altered, which is not good for human use.

What is a groin?

A groin is a wall built perpendicular to the beach from the backshore out to beyond the surf zone.

What is the purpose of a groin?

To block the longshore drift so that sand accumulates on the upcurrent side of the groin.

What effect do groins have on the downcurrent side of the beach?

They deplete the sand supply, which can lead to severe erosion.

How is a barrier island coastline stabilized in developed areas?

Through erosion control and sand replenishment.

What happens to the adjoining area of the island that is down current of a groin?

It continues to migrate in an inshore direction.

What is taxonomy?

All living things are arranged into formal groups according to their anatomy, physiology, and genetic differences

Species are classified into 1 of 3 domains:

Bacteria, Archaea, and Eukarya

Protists

• mostly single-celled

• Diatoms, dinoflagellates, foraminifera, seaweeds, algae

• Brown, red algae can be multicellular

Plantae:

Sea grasses, mangroves, salt marsh grasses

Autotrophic synthesizing:

organisms synthesize organic matter using light or chemical energy (primary production: plants, protists, some bacteria, archaea)

Heterotrophic production:

organisms consume autotrophic production to gain energy and make more cells (secondary production: animals, fungi, some bacteria, archaea)

Photosynthesis in organisms

-carried out by phytoplankton and cyanobacteria

Photosynthetic requirements:

1) carbon dioxide, 2) water, 3) nutrients, and 4) energy (sunlight)

Primary Production in organisms

can be light-, nutrient-, C-limited (rarely C-limited)

Chemosynthesis in organisms

phytoplankton, bacteria, and cyanobacteria

• Typically occurs in extreme environments (deep ocean, anoxic waters, no light)

Energy to synthesize organic matter is obtained from:

-Oxidation of hydrogen sulfide to sulfate

-Transformation of metals (Mn, Fe) from a reduced to an oxidized form

-Oxidation of hydrogen to water

-Oxidation of methane to carbon dioxide and water

What moves through a food web?

Mass and energy stored in molecules

What is the microbial loop

process by which microbe decomposers recycle nutrients and organic matter in the euphotic and aphotic zones

Compensation Depth

The depth at which photosynthetic organisms can produce only as much organic matter as they need for respiration (Production = Rate)

Biological Pump

the removal of atmospheric carbon dioxide with storage in the deep ocean, essentially removing it for centuries

What happens to nutrients in the photic zone?

Nutrients are consumed to depletion by photosynthesizers.

How are nutrients released below the thermocline?

Nutrients are released via respiration and decomposition.

What is the trend of dissolved oxygen levels in surface waters?

Dissolved oxygen levels are high in surface waters.

How does dissolved oxygen change below the thermocline?

Dissolved oxygen decreases as it is used in respiration and decomposition.

What happens to dissolved oxygen levels with depth below the thermocline?

Dissolved oxygen levels increase with depth below the thermocline.