Oceanography 3

Causes of Coral Bleaching: Global Warming

-BIGGEST threat -Due to human activities, primarily the burning of fossil fuels (coal, oil, and gas). -Coal is by far the worst of these fuels, producing the most carbon dioxide. Burning natural gas produces 50-60% less CO2 compared to burning coal.

Geographical Consequences

-Because the algae living within the corals need sunlight to photosynthesize, the corals continue to grow the reef upwards towards the surface to compensate for the sinking of the land -Inactive volcanic islands sink as the ocean crust they are sitting on sinks as its ages and moves away from the ocean ridges. -Passive continental margins gradually sink as the ocean crust that they are attached to slowly sinks and pulls the edge of the continent down with it.

Struggles

-Bleaching is common on most of the world's coral reefs. Sometimes the reefs recover and the algae return, and sometimes they don't. -Even well-protected reefs, such as the Great Barrier Reef, are experiencing significant bleaching events, although overfishing and dangerous fishing practices discussed previously do not occur on this reef, and pollution from continental run-off is minimal because Australia can enforce local pollution laws.

Corals

-Coral animals are typically very small. -Many coral species have individuals that are the size of ants. In a reef, millions of corals live in and build the calcium carbonate structure.

Importance of Coral Reefs

-Coral reefs have the greatest biodiversity in the marine environment. Their diversity rivals tropical rain forests on land. Biodiversity refers to the number of different species, rather than the number of individuals. This biodiversity does not mean just the different species of coral, but all of the other species that live in or are part of the coral reef ecosystem. This includes other invertebrates, fish, and sea turtles.

Protection

-Coral reefs protect the mainland coastline from erosion by waves. Wave energy breaks on a reef, and the water behind the reef (if a barrier reef) is relatively calm. -Waves can cause erosion and damage to corals, including breaking off coral pieces, but a healthy reef can repair the damage. Healthy corals can quickly secrete new CaCO3 like cement to re-attach the broken pieces back onto the reef structure

Cyanide Fishing cont.

-Cyanide is a poison that prevents oxygen from reaching the cells. -This fishing practice kills many animals, including up to 75% of the target species, but many fish flee the area and are caught in the nets.

2 Visitors

-In 2012, the film director James Cameron financed the building of his own submersible and visited the trench alone. -In 2019, an American investor, Victor Vescovo, also visited the bottom of the Mariana Trench twice, as well as the trenches in other ocean basins. The most notable thing that he discovered in the bottom of the trench was plastic garbage.

Coral Reef Information in Tropics

-Largest reefs are found in the tropics -Composed of CaCo3 (calcium carbonate) -Tropical reef building corals require shallow clear water for maximum sunlight penetration. -Tropical water, generally, is the clearest water because it has fewer micro-organisms in the water.

Cyanide Fishing

-Most fisherman who use the practice claim it is only used to catch tropical fish for the aquarium trade, and not for human consumption, but this is uncertain. -In cyanide fishing, fisherman squirt a cyanide solution into crevices in the reef structure.

Why coral needs sunlight

-Most reef-building corals have a symbiotic relationship with photosynthetic algae called zooxanthellae. These algae live in the tissues of the coral. -These algae create the vibrant colors of living corals.

Natural Events that cause coral bleaching

-Natural changes in water temperature -Hurricanes -Tsunamis -Volcanic eruptions -Landslides -Earthquakes -Coral Diseases

ocean acidification

-Ocean acidification is due to excess carbon dioxide emissions, so it is also attributed primarily to fossil fuel burning, but it is a separate issue from global warming. -When carbon dioxide is released into the atmosphere, 31% of it is then absorbed by the oceans. -When CO2 is absorbed by the ocean, it converts to carbonic acid. This is a weak acid (it's the same acid in carbonated beverages), but it is enough to cause a significant problem for organisms which create calcium carbonate shells (CaCO3), including corals. -When seawater is even slightly acidic, it causes CaCO3 shells to dissolve, and it makes it more difficult for the organism to produce new CaCO3.

Overfishing

-Overfishing is a problem because it can change the balance of species in the coral reef ecosystem, and this can have a detrimental impact on the coral. -The Giant Triton Snail is one of the few predators of the Crown of Thorns sea star. -The Crown of Thorns sea star eats coral. -When the Giant Triton Snail is removed from the ecosystem, the Crown of Thorns sea stars reproduce rapidly and eat much of the coral.

Boat Strikes

-Reefs are shallow, and sometimes ships run aground on reefs. -The ship to the right is the USS Guardian which ran aground on a reef in the Philippines in 2013. -The CO and 3 officers were relieved of duty for using outdated, inaccurate maps of the region.

Seamounts

-Seamounts are submerged volcanic cones, that in most cases were once inactive islands that have sunk beneath the surface. -Occasionally they can be very young active volcanoes that have not yet reached the surface, such as Loihi off of the Big Island of Hawaii.

Restoration

-Some severely damaged coral reefs are being "restored" by the growing of coral fragments in protected areas. -These individual healthy coral pieces are then transplanted onto damaged and or severely bleached reefs. -The coral pieces can be secured onto the reef with wires and bolts, or using a type of cement. -In some cases, the corals grown and transplanted are species better able to withstand warmer temperatures or other conditions that harm more sensitive species. Corals have also been transplanted after a major "boat strike" which physically strips off many of the original coral. -In one example, after a tanker hit a pristine reef on a protected island off of Puerto Rico, divers replaced 1500 coral pieces on the reef.

Largest Reef

-The Great Barrier Reef is the largest biological structure on the planet. It is about 2300 km long and up to 150 km wide.

Zooxanthellae

-The algae photosynthesize and provide sugars (food) to the coral. -The corals provide protection from predation and organic waste (as nutrients) to the algae. -Additionally, the corals have stinging tentacles and can catch their own food. -There are coral species that live in deeper, colder water that rely entirely upon catching their own food to survive. They grow very slowly. Occasionally these species can build reefs, but they are less common and not as diverse as tropical reefs.

Sediment Distribution

-The dominant sediment in the deep Pacific (unlike the rest of the global ocean) is primarily windblown continental sediment from the great deserts of the world. This material can be carried for long distances. (Deserts provide most of the windblown sediment because they do not have vegetation and root systems that hold the sediment in place.) -Much of the river deposited sediment that DOES end up in the Pacific is carried down into subduction zones, instead of spreading over the surrounding seafloor. All of continental margins in the Atlantic, however, are passive margins, lacking subduction zones at the edge of the continent.

Mariana Trench

-The location of the deepest trench on earth made from two oceanic crusts converging. -Humans have visited 4 times -Lack of food is the main factor limiting life at the bottom of the trench, not pressure, cold temperatures, or lack of light.

Atlantic versus Pacific

-There are more abyssal hills in the Pacific compared to the Atlantic because the sediment cover is twice as thick in the Atlantic. (There is an average of 1 km of sediment on the deep seafloor of the Atlantic, and 0.5 km on the deep seafloor of the Pacific.) -There are several reasons for this difference. Many more rivers drain into the Atlantic, creating more sediment for turbidity currents to carry onto the seafloor. -The deep Pacific is naturally more acidic (unrelated to fossil fuel burning) and this dissolves most CaCO3 shells from dead organisms before they settle onto the bottom. In every part of the deep ocean except for large regions of the deep Pacific, microscopic CaCO3 shells are the dominant sediment type.

Causes of Coral Bleaching: Greenhouse Effect

-These greenhouse gases allow visible light to pass through the atmosphere (like glass) but that solar radiation which is absorbed by the Earth's surface (or the interior of the greenhouse) is trapped by the gases. -The radiation absorbed is re-radiated as infrared heat, can't pass through the atmosphere (or the glass) and it heats up the surface.

Coral Bleaching continues

-They try to save their energy, The corals will stop secreting any new calcium carbonate (CaCO3). This means that they no longer repair pieces that are broken off in storms, etc. If those living pieces of coral are not quickly re-attached, they are tossed in the surf and the living coral quickly die.

Abyssal Plains and Hills

-This is the final topographic feature of the ocean, and it is the remainder of the seafloor that is not any of the previous features. -Abyssal plains are relatively flat regions of the seafloor, that are buried by sediment. -Abyssal hills are smaller than seamounts (less than 1 km in elevation) and are more likely to be found where the sediment thickness is less.

Coral Bleaching

-When corals are stressed in their environment, their algal symbionts leave -The corals bleach to a white color. -The corals can catch their own food with their tentacles, but this will usually only sustain the corals for a short time. -If the algae do not return to the corals, they will usually die of starvation.

Second Stage- Barrier Reef

A body of water called a lagoon separates the reef from the land, which can also be a volcanic island or a continent. The largest reef in the world is the Great Barrier Reef off of northeast Australia.

First Stage- Fringing Reef

A fringing reef is directly adjacent to the land, either a volcanic island or continent.

Fishing Practices are Harmful: Blast Fishing

One destructive method of catching fish living in a coral reef is called "blast fishing." This is using small homemade "bombs" to explode small portions of the reef. This kills many of the fish (and other animals) in the blast zone (as well as physically damaging the reef structure), but enough fish escape and swim into the nets to make the practice worthwhile.

Pollution

Run-off pollution from the land is a broad category, but all of these can harm coral reefs. This type of pollution includes: -Sewage -Industrial Chemicals -Pesticides and Fertilizers from farmlands -Sediment Run-off due to Logging -Oil Spills

Global Warming Fact

The U.S. and China account for 40% of all CO2 emissions. Historically, until recently, the U.S. was the largest single emitter of fossil fuels and is currently second in emissions after China. India is third and Indonesia is fourth.

Microscopic CaCO3 Shells are often Coccolithophorids

These are microscopic photosynthetic organisms that live everywhere in the ocean. When they die, their shells sink to the bottom and create white mud.

Third Stage- Atoll

This is a ring of reef which surrounds a seamount. This stage is only associated with dormant volcanic islands which have sunk beneath the surface. Continents are far too large to completely submerge.

Trenches

Trenches are the deepest regions of the ocean. In the example here, the Peru-Chile Trench offshore from the west coast of South America is deeper below sea level than the tallest Andes mountains are above sea level.