Introduction to the marine environment from a physical and chemical perspective

PRATOLONGO, PAULA D.; PAN, JERÓNIMO

Marine Biology: a functional approach to the oceans and their organisms

CRC Press/Taylor & Francis Group

Lugar: Boca Ratón, FL; Año: 2022; p. 21 - 39

1. Most of the solar radiation reaches the Earth in the form of visible light; about 70% is absorbed and heats up the atmosphere and Earth?s surface, producing a latitudinal pattern of the long-term average sea surface temperature. In addition to this latitudinal pattern, water stratification is the process by which water is segregated into vertical layers based on differences in temperature and salinity.2. The drag of trade winds on the ocean surface along the equator creates the Equatorial currents that flow east to west. When these currents meet the east coast of continents, they are deflected away from the equator and become western boundary currents. At higher latitudes, the westerlies push surface water from west to east and continents deflect the currents creating eastern boundary currents. These currents combine to produce gyres that rotate clockwise in the Northern Hemisphere and counterclockwise in the Southern Hemisphere.3. Tides are the rise and fall of sea levels that result from the gravitational attraction of the sun and moon. During new and full moons, the sun, Earth, and moon are aligned producing higher tidal ranges called spring tides. Waves are another important component of the near-shore circulation. Most ocean waves are created by wind blowing across the surface. When wind waves travel from deep to shallow water, they break near the shoreline and generate currents.4. Ocean primary productivity refers to the production of organic matter by photosynthesis. Phytoplankton fixes inorganic CO2 into organic carbon and makes it available to heterotrophs. Within the euphotic zone, primary production by photosynthesis exceeds the loss of carbon by autotrophic respiration. Thus, there is an annual surplus of organic carbon that is exported out of the surface layer. By the sinking of organic matter, marine organisms are responsible for the largest carbon sequestration on Earth, and the process is often referred to as the biological pump.5. Ocean acidification is the ongoing decrease in the pH of seawater, caused by the increasing dissolution of atmospheric CO2 into the oceans. Dissolved CO2 can react with seawater to form carbonic acid and some of the resulting carbonic acid molecules dissociate into a bicarbonate ion and a hydrogen ion (H+), thus lowering pH. This decrease in pH may have a wide range of impact upon marine life, especially on calcifying organisms.6. Those elements required for phytoplankton growth, that may be scarce, and even limit growth and reproduction are typically identified as nutrients. Those elements required by phytoplankton in high concentrations are considered macronutrients. Other elements called micronutrients are needed in much minor quantities. In general, micronutrients act as enzyme co-factors. More recently, organic molecules such as vitamins have been identified as limiting factors for phytoplankton growth, and thus may be considered essential micronutrients too.