Oceanography and Hydrology

• Sea-waves continuously strike at the rocks. Cracks develop. Over time they become larger and wider. Thus, hollow like caves are formed on the rocks. They are called sea caves.
•  As these cavities become bigger and bigger only the roof of the caves remains, thus forming sea arches.
•  Further, erosion breaks the roof and only walls are left. These wall-like features are called stacks.
• The steep rocky coast rising almost vertically above seawater is called sea cliff. 

Currents and Tides is not conducive to the formation of deltas. When a river reaches a lake or the sea the water slows down and loses the power to carry sediment . The sediment is dropped at the mouth of the river. Some rivers drop so much sediment that waves and tides can't carry it all away. It builds up in layers forming a delta.

Rain gauge can accurately measure the rainfall without any loss due to evaporation. It is an instrument used for determining the depth of precipitation that occurs over a unit area. Thus, it measures rainfall. One liter of rainfall per meter squared is equivalent to one millimeter of measured precipitation. A funneled aperture of 150-170 cm is found in standard rain gauges. They are designed as a simple passive collector. A graduated measuring glass is used for determining the amount of precipitation. For the measurement of rainfall, the rain gauze should be placed 30 cm above the ground to prevent the splashing of rainwater.

There are reserves of a variety of natural resources in seawater, at the bottom of the sea and beneath the seabed, too. These resources available from seas and oceans are called marine resources.

The upper flow leaves the Black Sea and carries surface water out of it. Meanwhile a bottom flow carries salt water, about 35‰ from the Mediterranean to the Black Sea. The salty water mixes with the waters of the basin proper and that results in a comparatively low salinity at the surface, about 17%.

The prefix 'iso' is a greek word meaning equal, so an isoline must be a line joining equal points. For example, a line drawn on a map to join up all the places that are the same height above sea level is called a contour.

It is possible to separate seawater to obtain pure substances like salt and waters. For this various physical and chemical processes are used.

Fishing grounds are rich where the continental shelf is wide (1) and where warm and cold currents mix (3), as this promotes plankton growth. Statement 2 is incorrect because cold waters are generally more productive than warm tropical waters. Statement 4 is incorrect as marine fisheries are more significant than inland fisheries in India.

Tropical fishing is hindered by the lack of broad continental shelves, the mixing of many species (making large-scale netting of a single species difficult), and lower levels of mechanization. Tropical fish are not inherently oily or less popular; in fact, many are highly prized.

Continental shelves are shallow, sunlit areas that support high primary productivity, making them the most productive regions for marine life and commercial fisheries.

Coastal areas experience less contrasts in temperature conditions due to moderating effect of the seas.  The large water bodies helps in moderating temperature. Water has a higher heat capacity than soil and rock, so the ocean takes much longer to heat and to cool than the land.

The most abundant ions in seawater are chloride (Cl-), sodium (Na+), and magnesium (Mg2+). Together with sulfate, calcium, and potassium, they make up the vast majority of dissolved salts.

Plants that thrive in salty environments, such as sea shore wetlands, are classified as halophytes.

Guano, which is the excrement of sea birds, is rich in phosphorus. When sea birds deposit this on land, it returns phosphorus from the marine food chain back to terrestrial ecosystems.