I became an ocean person after moving to Texada Island in 1971. The waters of the Pacific Ocean surrounding Texada Island provided me with access to the ocean world, full of life – some exotic creatures and some intelligent marine mammals – seals, otters, sea lions, porpoises and whales. I developed a scuba meditation sitting on the sandy bottom of Gillies Bay as the tide came in. As an alternative to swimming underwater to see sea life, I sat and watched sea creatures pass by. An early discovery was zooplankton that had interesting shapes and some displayed orbiting bodies that suggested alien spaceships. At night bioluminescence was a delight. Since 1971 I have enjoyed a succession of boats and spent as much time as I could exploring local waters. I travelled with a microscope, centrifuge and containers to sample seawater. I followed red tide blooms caused by dinoflagellates that contained a powerful neurotoxin, saxitoxin, that causes paralytic shellfish poisoning. When red tides appear, the harvesting of shellfish is prohibited.
Life began in oceans and all life continues to depend on a healthy ocean environment. Oceans are important players in the carbon cycle and are major determinants of climate and weather patterns. 230,000 known species live in oceans. Two million marine species are estimated to exist. Oceans contain 97% of Earth's water covering 71% of Earth's surface. Climate change is raising ocean temperatures. Rising levels of carbon dioxide are acidifying the oceans with adverse changes in aquatic ecosystems, threatening, for example, fisheries an important source of human food.
Plankton supply oxygen through photosynthesis which occurs in the photic zone to a depth of 200 m, Life found deeper relies on material sinking from above. Hydrothermal vents are also a source of energy in depths exceeding 200 m (aphotic zone). Three water density zones have been identified: the surface zone, the pycnocline, and the deep zone. The surface zone( 500 to 3,300 feet deep) is in contact with the atmosphere and the temperature and salinity are relatively constant. The pycnocline is characterized by increased water density and decreased temperature. The deep zone begins at depths below 3,300 feet in mid-latitudes occupied by 80% of the total volume of ocean water. The deep zone contains relatively colder and stable water. Vertical movement of water( thermoclines) transfer heat and salinity between the ocean zones.
Ocean currents determine Earth's climate by transferring heat from the tropics to the polar regions.. Surface heat and freshwater fluxes create global density gradients that drive the thermohaline circulation. The thermohaline circulation (THC) governs the transfer of deep waters to the surface which influences atmospheric carbon dioxide concentrations. THC is the ocean conveyor belt part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. Wind-driven surface currents such as the Gulf Stream travel pole wards from the equatorial Atlantic Ocean, cooling en route and eventually sinking at high latitudes forming the North Atlantic Deep Water. This dense water then flows into the ocean basins. Extensive mixing between the ocean basins makes the Earth's oceans a global system. Water masses transport heat, solids,, dissolved substances and gases around the globe. Pelagic ocean fish and mammals use ocean current to travel long distances.
Warming of ocean water is having a worldwide negative impact on ocean life. The world’s largest reef system, which stretches for over 1,400 miles off the coast of Australia, has been severely affected by rising water temperatures. In May 2016, researchers found more than a third of corals in central and northern parts of the reef had been killed and 93 per cent of individual reefs had been affected by a condition known as coral bleaching. Warmer water causes corals to expel algae living in their tissue, turning completely white. Corals depend on a symbiotic relationship with algae-like single cell protozoa. When these are expelled they stop growing and often die. Coral reefs are an important habitat for many fish species who die when the coral dies.
Ocean TidesI look out to a beach with a wide intertidal zone. The beach is changing continuously as the ocean level rises and falls. The intertidal zone attracts many birds who feed on beach life exposed when the tide is low. Gulls, geese, herons and crows are regulars on the beach sometimes in great numbers. Humans have often depended on harvesting the intertidal zone for food – clams, oysters, crab, seaweeds. They would know that there was a rhythmic interval between high and low tide, and that that rhythm was related to the moon’s phases, the lowest tides occurred during new and full moon, an opportunity to harvest abalone and urchins, which are normally inaccessible.
The tides where I live rise and fall twice a day caused by the combined effects of the gravitational forces exerted by the Moon and the Sun and the rotation of the Earth. The ocean water enters the local region from the north and south. Currents are created when large volumes of moving water are squeezed into narrow channels. To reach my boat moorage in the Sechelt Inlet you have to navigate the Skookumchuck narrows at slack tide. With a tide change of 3 meters, 200 billion gallons of water flow through the narrows with each tide change. Current velocity can exceed 16 knots (30km/h), a danger to boats attempting passage. The times and amplitude of tides are determined by the alignment of the Sun and Moon, by the pattern of tides in the deep oceans and the shape of the coastline. Sea levels are also effected by forces such as wind, barometric pressure changes and storm surges, especially in shallow seas and near coasts. Tide and current charts are essential for safe marine navigation.
WavesRipples appear on smooth water when the wind blows. Sea waves are larger-scale, often irregular motions that form under sustained winds. These waves tend to last much longer, even after the wind has died. The restoring force is gravity. As waves propagate away from their area of origin, they form groups of common direction and wavelength. These sets of waves are known as swells. The largest wind waves are up 32.3 m (106 ft) high ( recorded during the 2007 typhoon Krosa near Taiwan.)
Ocean waves can be classified by their amplitude, wavelength or period. Tsunami waves have a period of more than 20 minutes, and speeds of 760 km/h (470 mph). Wind waves have a period of about 20 seconds. The speed of all ocean waves is controlled by gravity, wavelength and water depth. Although the wave moves forward the water molecules affected by the wave move up and down in orbital patterns staying more or less in the same location. Wavelength determines the size of the orbits of water molecules within a wave and water depth determines the shape of the orbits. The paths of water molecules in a wind wave are circular only when the wave is traveling in deep water. The orbits of water molecules in waves moving through shallow water are flattened by the proximity of the sea surface bottom.
As waves travel from deep to shallow water, their shape alters , wave height increases, speed decreases, and length decreases as wave orbits become asymmetrical. If a wave meets an adverse current its wave height increases while the wave length decreases, similar to the shoaling when the water depth decreases.
A tsunami is a series of waves caused by the displacement of a large volume of water. Earthquakes, volcanic eruptions, landslides and underwater explosions, glacier calvings, meteorite impacts all generate tsunamis. A Tsunami is generated when the sea floor vertically displaces the overlying water. Tsunami waves do not resemble normal undersea currents or sea waves, because their wavelength is far longer. A tsunami resembles a rapidly rising tide and are often referred to as tidal waves. Tsunamis are a series of waves with periods ranging from minutes to hours with wave heights of tens of meters. The impact of tsunamis is greatest on coasts where the waves break and flood the land with incredible destructive force. The 2004 Indian Ocean tsunami was among the deadliest of natural disasters in human history with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean. The Fukushima Daiichi nuclear disaster was directly triggered by the 2011 Tōhoku earthquake and tsunami, when waves exceeded the height of the plant's sea wall. Iwate Prefecture, which is an area at high risk from tsunami, had tsunami barriers walls totaling 25 kilometers (16mi) long at coastal towns. The 2011 tsunami toppled more than 50% of the walls and caused catastrophic damage.
(BBC News Asia. Indian Ocean tsunami anniversary: Memorial events held. BBC 26 December 2014
Environmental Information. Tsunamis Interactive Map.