Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 2 The Sea Floor What does geology have to do with marine biology? A portion of the mid-Atlantic ridge above the sea surface in Iceland.

Before we start: Marine biology = Geology = Geo-, Latin for__________ The study of earth's physical structure and substance, its history, and the processes that act on it. Ex:

The Water Planet The Geography of the Ocean Basins  The oceans cover ____of the planet and regulate its ___________ and ___________  There are four ocean basins  Pacific -  Atlantic  Indian  Arctic –  Connected to the main ocean basins are shallow seas Ex: Mediterranean Sea, Gulf of Mexico, South China Sea

The Geography of the Ocean Basins They all connect to form a world ocean where seawater, materials, and organisms can move about. Continuous body of water surrounding Antarctica is the Southern Ocean Fig. 2.1

The Structure of Earth Big Bang Theory Universe created 13.7 billion years ago. Earth formed 4.5 billion years ago. Fig

The Structure of Earth In the early molten Earth, lighter materials floated toward the surface because of varying densities. They cooled to form the crust The atmosphere and oceans then formed Earth is the right distance from the sun for liquid water, and life, to exist Fig. 2.2 naturenplanet.com

Water Exists only on Earth, due to marrow temp. range required for liquid water. Earth is in prime position/size for liquid water Any closer-too hot, water evaporates Any further-too cold, all water freezes Any smaller (~30%) then not enough gravitational pull to keep water on surface, all moves to atmosphere. Any bigger, then too many clouds -Importance of clouds? Greenhouse Effect -more clouds = warmer surface (Ex: Venus)

How did the water form? As Earth cooled, water vapor in atmosphere condensed, fell to surface, filled up low parts first.

Fig. 2.3

The Structure of Earth Internal Structure The dense CORE is mostly iron Solid inner core and liquid outer core Believed the swirling motions produce the Earth’s magnetic field The mantle is outside the core and under the crust Near molten rock slowly flows like a liquid The crust is the outer layer, comparatively thin Like a skin floating on the mantle composition differs between oceans and continents

The Structure of Earth Continental and Oceanic Crusts Oceanic Crust Continental Crust Made of basalt – a dark mineral More dense Thinner Younger rock; 200 mil years Made of granite – lighter color Less dense Thicker Older rock; ~4 bil years ago

Tab. 2.2

The Structure of Earth Continental and Oceanic Crusts Continental crust floats higher on the mantle and ocean crust floats lower. That’s why ocean crust is covered by water

The Origin and Structure of the Ocean Basins Earth today: still dynamic Not static and unchanging Continents still moving! Size/Shape of ocean basins defined by continental margins Fig. 2.2 You should be asking, where is your evidence that continents move!? www3.bc.sympatico.ca

Alfred Wegener Looked at a map of Earth, continents look like puzzle pieces.

Alfred Wegener 1 st to come up with theory about continental drift Suggested that all the continents had once been a supercontinent, named Pangea He thought, started breaking up ~180 mil years ago tower.com

Continents as puzzle pieces, S. America and Africa Other evidence: Similar rock formations Fossil records

The Theory of Plate Tectonics The Theory of Plate Tectonics explains it all Continents do drift slowly around the world This process involves surface of the entire planet tower.com

The Theory of Plate Tectonics Discovery of Mid-Ocean Ridge After WWII sonar allowed detailed maps of the sea floor SONAR = sound navigation ranging They discovered the mid-ocean ridge system! Chains of ridges in the middle of the oceans, like seams on a baseball The largest geological feature on Earth tower.com

Mid-Ocean Ridge System Some of the mountains rise above sea level to form islands, e.g. Iceland The Mid-Atlantic ridge runs down the center of the Atlantic Ocean and follows the curve of the opposing coastline Sonar also discovered deep trenches = deep depressions in the sea floor. Fig. 2.5

Fig. 2.6

Significance of the Mid-Ocean Ridge Rock near the ridge is young and gets older moving away from the ridge

Significance of the Mid-Ocean Ridge There is little sediment near the ridge, but it gets thicker moving away Sediment = loose material like sand and mud that settles on bottom of sea floor. Found symmetric magnetic bands parallel to the ridge where magnetic field flip-flopped

Magnetic Anomalies Earth’s magnetic field, occasionally reverses direction Magnetic parts in molten rock, free to move. When cool, these particles are “frozen” and keep their orientation, even if magnetic field changes. Sea floor rocks have these bands, or magnetic anomalies. ****Sea floor NOT formed all at once**** Offered a mechanism for movement of continents

Fig. 2.9 Cross section of the sea floor at a mid-ocean ridge. The rocks of the sea floor show the earth’s magnetism at the time of their cooling. Creation of Sea Floor: Sea Floor Spreading

Creation of Sea Floor: Sea-Floor Spreading Huge pieces of oceanic crust are separating at the mid- ocean ridges Magma from the mantle rises through the rift (a crack) forming the ridge The sea floor moves away from the ridge Continuous process, called sea-floor spreading New sea floor is created! This explains why rocks are older and sediment is thicker as you move away from the ridge This also explains the magnetic stripes found in the sea floor ALL EVIDENCE for PLATE TECTONICS

Sea-Floor Spreading and Plate Tectonics The crust and part of the upper mantle form the lithosphere 100 km (60 mi) thick, rigid Broken into plates May be ocean crust, continent crust, or both The plates float on a fluid layer of the upper mantle called the asthenosphere.

Edge of many plates, a mid-ocean ridge The plates move apart here, to create new sea floor If the plate has continental crust it carries the continent with it. Spread 2-18 cm/year Called continental drift, continents moving apart

Plate Boundaries at Trenches If seas floors are spreading, does this mean the Earth is growing bigger? No it means that somewhere else plates get pushed down into the mantle As new lithosphere is created, old lithosphere is destroyed somewhere else Some plate boundaries are trenches where oceanic plates get “pulled down” into the mantle, melts, is recycled This process =Subduction Trenches are also called subduction zones Plate boundaries are violent (if slow) collisions.

The plates colliding can be oceanic   cont. Ocean plates always sink below, denser Produces earthquakes and volcanic mountain ranges; e.x. Andes, Sierra Nevada oceanic   cont

The plates colliding can be oceanic   oceanic Earthquakes and volcanic island arcs = volcanic island chain that follow trench curvature Ex: Aleutian Islands, Mariana Islands oceanic   oceanic Either plate could have dipped below the other, in this case.

The plates colliding can be cont.   cont. Neither plate sinks, instead they buckle Producing huge mountain ranges Ex: Himalayas. continental   continental

Shear boundary Another type is shear boundary or transform fault The plates slide past each other Causes earthquakes Ex: San Andreas Fault, CA Fig. 2.14

Fig Two forces move the plates: 1) Slab-Pull theory - the sinking plate pulls the rest behind it 2) Convection theory – the swirling mantle moves the plate

Geological History of the Earth Continental Drift and the Changing Oceans 200 mil years ago all the continents were joined in Pangea It was surrounded by a single ocean called Panthalassa 180 mil years ago a rift formed splitting it into two large continents Laurasia – North America and Eurasia Gondwana – South America, Africa, Antarctica, India, and Australia

Fig The plates are still moving today. Atlantic Ocean is growing, Pacific is shrinking

C. Geological History of the Earth 2. The Record in the Sediments Studying sediments deposited in past, can learn about the history of the planet 2 types of marine sediments: 1) Lithogenous – 2) Biogenous – Mostly composed of calcium carbonate or silica Microfossils tell what organisms lived in the past

= animal-like Protists

Oceans and Climate in the Past Past climate on Earth can be determined by: Chemical composition of microfossils Measure ratios of Mg and Ca Oxygen isotope ratios Sr and Ca ratios in ancient coral skeletons Ice cores Fossil Agatized Coral is Florida's state stone million years ago

C. Geological History of the Earth 3. Climate and Changes in Sea Level The Earth alternates between interglacial (warm) period and ice age (cold) periods Sea level falls during ice ages because water is trapped in glaciers on the continents Currently in an interglacial period Pleistocene Epoch, 2 mya, began last ice age…Peak was 18,000 yrs. ago Fig. 2.18

The Geological Provinces of the Ocean 2 main regions of the sea floor. 1) 2)

A. Continental Margins = Boundaries between the continental and oceanic crusts Consists of: Shelf Slope Rise

A. Continental Margins 1. The shallowest part Only 8% of the sea floor, but biologically rich and diverse Large submarine canyons can be found here, from past glaciation Ends at the shelf break, where it steeply slopes down Shelf 1km to 460 km (280 m) wide

A. Continental Margins 2. The “edge” of the continent Slopes down from the shelf break to the deep-sea floor Submarine canyons can carry sediments from the shelf to the sea floor. Reaches sea floor at 10,000-16,500 ft underwater A submarine canyon

A. Continental Margins 3. Some, similar to a river delta = deep-sea fan

A. Continental Margins 4. Active and Passive Margins Active margin = the subducting plate creates a trench

A. Continental Margins 4. Active and Passive Margins Passive margin – no plate boundary Ex: see next slide

Passive Margins Example: Atlantic Coast of U.S.A Buildup of sediments Broad coastal plains Estuaries Barrier Islands Salt Marshes

Studying near continents Most of what Marine Biologists study are near continents…why do you think?

B. Deep-Ocean Basins Most of sea floor, 10,000-16,500 ft Abyssal plain - flat region of the sea floor, but has features: A Seamounts – submarine volcanoes Guyots (“gee-oh”) – Trenches, subduction zones, = the deepest part of the ocean Mariana Trench is 36,163 ft deep (11,022 m) the deepest on Earth

C. Mid-Ocean Ridge and Hydrothermal Vents At the center of the ridge, where the plates pull apart = Water seeps down through cracks, gets heated by the mantle Then emerges through hydrothermal vents 350oC (660oF)

C. Mid-Ocean Ridge and Hydrothermal Vents Dissolved minerals from the mantle, like sulfides, are brought up Black smokers form when minerals solidify around a vent Marine life, including chemosynthesizers, exist around hydrothermal vents Fig. 2.26

Fig Chimney-like structures that build up around vents as the minerals solidify.

Hawaiian Islands Part of the Emperor Seamount chain Made from a Hotspot = Pacific plate, slowly moving over the stationary hotspot Much debate still, a stationary hotspot or various cracks in the crust.

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Grattan Seamount In S.Atlantic, following the Mid-Atlantic Ridge between the remote islands of St. Helena and Ascension.

Helpful table for studying Tab. 2.1

Geology and Marine Biology What does geology have to do with marine biology? Profoundly influences habitats= The natural environment where organisms live Sculpts shorelines Determines water depth Controls if muddy, sandy, rocky bottom Creates new islands, ridges, mountains for organisms to colonize