CHAPTER #10 -- Ocean Waters & The Ocean Floor
Earth -- “water planet”, since 71% of surface is covered by the global ocean Oceanography-- involves the application of all the sciences in a comprehensive and interrelated study of the oceans in all of their aspects and relationships Physical Oceanography -- concerned with energy transmission through ocean water; e.g., waves, tides, currents, etc. Chemical Oceanography -- study of the chemical properties of seawater Biological Oceanography -- study of the interrelationship of marine life with its oceanic environment Geological Oceanography -- deals with the ocean floor and shore The Seven Seas? Sea is often used interchangeably with ocean, referring to bodies of salt water. Technically, a sea is considered to be part of an ocean or a body of water substantially smaller than an ocean. The Seven Seas refers to the seas known to the Moslems prior to the 15th century . . . Mediterranean Sea China Sea Red Sea Persian Gulf East African Sea Indian Ocean West African Sea Since Kipling’s Book of Poetry called The Seven Seas, there has been a tendency to divide the world ocean into seven parts . . . North Atlantic South Atlantic North Pacific South Pacific Indian Arctic Antarctic Extent of the Oceans “Land” Hemisphere “Water” Hemisphere 61% water & 39% land (North) 81% water & 19% land (South)
The Pacific is the largest ocean and has the greatest average depth (12,900 ft), so it contains the most water. The Atlantic connects the polar regions and has the shallowest average depth(10,860 ft) because of the continental shelves & shallow seas.
Composition of Sea Water 3.5% dissolved salts; mostly NaCl, smaller amounts of MgCl2, Na2SO4, CaCl2, and others high evaporation rates high salinity Persian Gulf, Red Sea high rainfall or freshwater flow low salinity Baltic Sea Source of Salinity products of chemical weathering out-gassing by volcanic action - - Cl, Br, S, & B are more abundant in the oceans than in the crust Salinity over time is essentially constant . . . removed when chemically precipitated as sediment. withdrawn by plants and animals as they build shells and skeletons. Resources from Sea Water Commercial Extraction (1) NaCl 30% of the world’s salt (2) *Mg (late 60’s) 61% (3) *Br (late 60’s) 70% *2 & *3 now are extracted primarily from . . . Utah’s Great Salt Lake Brine Wells Evaporite Deposits Desalination -- removal of salt from sea water to produce fresh water Ocean’s Layered Structure Temperature and Salinity vary with depth (1) a shallow surface mixed zone (2) a transition zone (3) a deep zone high T high S thermocline halocline low T low S *Temperature(T) & Salinity(S) generally decrease with depth.
Earth Beneath the Sea (1) Continental margins which include the . . . (a) continental shelf (b) continental slope (c) continental rise Continental shelf -- gently sloping submerged surface extending from the shoreline toward the deep-ocean basin; a flooded extension of the continents; essentially flat (plateau-like). Contains important mineral deposits (including oil & gas) plus sand and gravel deposits; several are also important fishing grounds Continental slope -- seaward edge of the continental shelf which leads to deep water and has a steep gradient; represents the true edge of the continent Continental Rise -- the gently sloping surface at the base of the continental slope; consists of a thick accumulation of sediments that moved downslope from the continental shelf to the deep ocean floor; does not coexist with ocean trenches The turbidity currents that carry these sediments emerge from submerged canyons to form deep-sea fans; analogous to alluvial fans; these fans coalesce to produce the continuous apron of sediment at the base of the continental slope. (2) Ocean Basin Floor which includes . . . (a) Submarine canyons -- deep, steep-sided valleys that originate on the continental slope; evidence indicates that these canyons were not formed by glaciers or stream erosion but by some process that operates far below the ocean surface (b) turbidity currents -- the downslope movement of dense, sedimentladen water; gravity, sediment, and these currents are thought to be the major force in the excavation of most submarine canyons Evidence for the Existence of Turbidity Currents . . . (1) Newfoundland Earthquake of 1929 which caused damage to transatlantic telephone and telegraph cables; damage occurred far from the epicenter and at successive time intervals indicating an avalanche of sediment
(2) examination of deep-sea sediment samples which contain graded beds of sand, silt, clay, fragments of plants and animals that live only on the continental shelves (3) direct measurement in the Bute inlet, a deep fiord along the coast of British Columbia Features of the Ocean Basin Floor (1) Deep Ocean Trenches (2) Abyssal Plains -- incredibly flat regions consisting of thick accumulations of sediment that were deposited atop the low, rough portion of the ocean floor (3) Seamounts -- isolated volcanic peaks that rise from the ocean floors; rise far enough to become islands; can erode to submerged, flat-topped seamounts called guyots (4) Mid-ocean Ridges -- sites of sea-floor spreading; characterized by elevated position, extensive faulting, and numerous volcanic structures (5) Coral Reefs and Atolls coral reefs -- constructed primarily from the calcite-rich skeletal remains and secretions of corals and certain algae; confined largely to the warm waters of Pacific & Indian Oceans atolls -- islands built from coral that form on the flanks of sinking volcanic islands; proved by extensive studies of Eniwetok & Bikini Islands in the South Pacific (6) Sea-Floor Sediments -- consist mostly of mud with a significant portion of sand Types of Sea-Floor Sediments (a) lithogenous -- “derived from rocks” (b) biogenous -- “derived from organisms” (c) hydrogenous -- “derived from water”; includes Mn nodules