Marine Zoology & Ecosystems: Marine properties

Physiography definition

shape of sea floor- large & small scales features

spatial arrangement of those features: how they're connected/ laid out

Physiography is controlled by

broad geological process

geochemical make up of crust & mantle + heat flow= plate tectonics

Seafloor physiography: First order

underpinning control

Seafloor physiography: Second order

seawater properties and oceanographic processes & substrate properties

Seafloor physiography: Third order

biological interactions

effects of competition, predation, bioturbation, reef building

How does geology control physiography:

Earth crust= geochemically different between continent & ocean

creates different densities

Continental shelf sea:

much shallower than ocean

continent that happens to be flooded due to high sea levels

Reasonable approximation of crust & mantle

Crust= solid, brittle

mantle= viscous fluid

Crust floats on mantle

lighter continental crust floats higher than denser ocean crust

What creates strikingly broad ridges that occur on ocean floor:

results from heat flow from deep in mantel

take form or large-scale convection cells

Where does new oceanic crust originate?

In areas of high mantle heat flow.

Why does the seafloor bulge near mid-ocean ridges?

Because the underlying mantle is warm, causing the crust to expand and rise

What is the rate/type of magma input at mid-ocean ridges?

Relatively slow and steady input of magma.

Where is the youngest and warmest oceanic crust found?

At the mid-ocean ridge.

Where is the oldest and coldest oceanic crust found?

Adjacent to the continents.

How does water depth change with crustal age?

Water depth increases as crust ages because the crust cools, contracts, and becomes denser.

What major seafloor feature is created by hot, buoyant crust at spreading centres?

Ocean ridges

What hydrothermal activity is common at ridges?

Episodic hydrothermal vents.

What covers older seafloor away from the ridge?

Slowly accumulating fine sediment.

What broad, flat seafloor regions are formed by sediment covering old crust?

Abyssal plains.

Subduction:

when subduction occurs between two oceanic plates, string of volcanic islands (island arc) form

Ocean-ocean subduction:

gives rise to deepest ocean trenches

Shallow water hydrothermal environments:

occur on submarine flanks of volcanoes

Shelf sea example: North Sea

can be very shallow, considering area

mean water depth 38m

Seafloor slopes are shallow- steepest along line= 0.4% (2m height change over 500m)

Shelf sea Example: Skagerrak

500m deep channel

Many seafloor habitats in higher temp latitudes are result of global processes

most recent reached peak around 20,000 yrs ago

Shelf Seas:

Shallow but often spatially highly variable & dynamic:

Transition from shelf sea to ocean:

Stark & intricate

Main ocean basins- fundamentally different in terms of depth

Nature of transition between shelf sea (Celtic) and deep ocean (abyssal plain)

Ocean ridges:

Large scale features

Ocean ridges: Example transect from US-Mauritania

ridge flanks not too dissimilar to continental slops- offer a mix of rocks & sediments on sloping topography

sloping topography affects ocean dynamics (potentially transporting nutrients)

Argued= being very long & linear features, provide potential corridor of habitat

The tide: What are intertidal zones?

Coastal areas that are alternately exposed and submerged due to tidal cycles.

The Tide: Why do intertidal zones host diverse communities?

Organisms are specially adapted to repeated wet-dry cycles.

The tide: What types of habitats occur along intertidal coastlines?

Soft-sediment habitats and rocky shores.

The Tide: What coastal environments are strongly influenced by tides in temperate regions?

Estuaries, saltmarshes, and tidal flats.

The tide: Why are flooding and draining important for estuaries and saltmarshes?

They maintain physical structure and ecological balance.

The Tide: How do tidal currents affect larvae?

Strong currents disperse larvae.

The tide: What is the "flushing effect" of tides?

Removal of waste products, pollutants, and excess nutrients.

The tide: When do shorebirds typically feed in tidal environments?

At low tide.

The tide: How do fish and crabs use the tides?

They move in with the rising tide to feed in newly flooded areas.

The tide: How are spawning and larval release timed in many marine organisms?

They are synchronized with tidal cycles.

Spring-Neap Tidal cycle: What causes tides on Earth?

The combined gravitational effects of the Moon and the Sun.

Spring-Neap Tidal cycle: Which body has the stronger effect on tides, the Moon or the Sun?

The Moon.

Spring-Neap Tidal cycle: Why does the Moon have a stronger tidal effect than the Sun?

closer to earth than sun

Spring-Neap Tidal cycle: What is the tidal period associated with the Moon

Approximately 25 hours.

Spring-Neap Tidal cycle: What is the tidal period associated with the Sun

Approximately 24 hours.

Spring-Neap Tidal cycle: How strong is the Sun's tidal influence compared to the Moon's

half as strong

Tide generating force diagrams: black arrow

moon's gravitational attraction

Tide generating force diagrams: blue arrow

Centrifugal force acting on the Earth.

Tide generating force diagrams: Red arrow

net tide-generating force.

How many tides does most of the Earth experience per day

2

Semi-diurnal tide.

a tide with two highs and two lows per day

What happens to point P on Earth during one full rotation

it passes through two tidal bulges, producing two high tides

What produces tidal waves in the ocean

The tide-generating force

Why don't shelf seas directly feel the tide-generating force

They are too small relative to the scale of tidal wavelengths

How does tidal motion appear in shelf seas

Like waves travelling across the shelf, causing the ocean level to rise and fall

Coriolis effect

The effect of Earth's rotation on the direction of winds and currents.

Why does water pile up in the eastern Irish Sea

the Coriolis effect deflects moving water to the right in the Northern Hemisphere

Why is the Coriolis effect important

strongly influences weather systems and ocean circulation

How fast is Earth's surface moving at the equator

1670 km/h

Why don't we feel Earth's rotation in everyday life

the land, atmosphere, and oceans move together

How fast is Earth's surface moving near the North Pole

655 km/h

In which direction does the Coriolis effect deflect motion in the Northern Hemisphere

To the right

Which direction do tidal currents flow?

north

Kelvin Waves

wave like this that is strongly controlled by Coriolis & is bounded by coast

How does tidal range change in embayments

Increases with embayments

Funnel-shaped embayments

produces largest tidal ranges

How does the funnel shape affect tidal range

concentrates tidal energy, increasing tidal height toward the head of the embayment

What role does side-friction play in embayments

slows tidal flow and contributes to the buildup of water, enhancing tidal range

What additional effect can increase tidal range in some gulfs

Resonance between the basin shape and the tidal period

Which well-known location shows strong tidal resonance

The Gulf of Maine

Why are sea floor sediments important

fundamental control on marine habitats

How are seafloor sediments typically classified

grain size

What grain size measures are commonly used to label sediments

Mean or median grain size

Why does grain size matter for benthic organisms

influences burrowing ability, stability, oxygenation, and food availability

Wentworth Scale

the classification of sediments by size; a boulder is the largest grain size and clay is the smallest grain size in this classification system

Folk scale

captures little of range of sizes present