PrimaryProductivity in The Ocean
Microscopicorganisms called phytoplankton are responsible for the primaryproduction in the ocean. There is low productivity in the North andSouth Atlantic due to the presence of large gyre systems. Productionin the Pacific is relatively high but low in the gyres. There is highproductivity in the southern ocean due to the high phytoplanktondensity.
Shelfareas are responsible for 50% of oceanic primary productivity. Thewaters in these regions are shallow thus facilitating the recyclingof nutrients. Since the regions are close to the land, nutrientsrunoff from the land during the rainy seasons. The other reason isthat the level of light is relatively high in the areas. In anutshell, the high nutrients and light concentration in the inshorewaters is responsible for the high productivity rates.
Theupwelling zones avail the deep waters that are rich in nutrients tothe surface thus facilitating productivity. The winds move the wateralong the coastline causing the coastal upwelling. The CoriolisEffect together with the Ekman transport curls the water from rightto left. Water from 200-300m deep comes up to replace the shiftingsurface water. The Coriolis Effect causes currents along the equatorto flow in the opposite direction. The deeper water is thereforeforced up to take the space left by the surface water. Productivityalong island masses is very high. When the currents encounterislands, deeper water masses that are rich in nutrients are forced upto the surface[ CITATION Mor11 l 1033 ].
Productivityis very high in the photic zone of the ocean. The thickness of thezone is determined by the depth at which light has at least 1% of itssurface value. The layer can, therefore, reach a maximum depth of100m. Near the surface, light is sufficient enough to aid inphotosynthesis. The interaction between the zone and the mixed layerdetermines the net photosynthesis. The mixed layer varies from beingmuch deeper than the photic zone to being shallower. However, at thecritical depth, the growth of the phytoplankton becomes stunted.Therefore, net production takes place when the mixed layer isshallower than the photic zone.
Productivityin the polar oceans blooms during the summer. The favorable lightconditions result in the short term increase in primary productivity.During the summer time, the Antarctic Ocean exhibits the highestproductivity in the globe along its upwelling zones. The other factoraffecting primary productivity is the sea ice formation and meltingprocesses. When frazil ice is mixed with surface water, organisms aretrapped between the ice crystals. During the melting process, theorganisms are released into the ocean water resulting in increasedproductivity.
Warmertemperatures in the water have a negative impact on the growth ofphytoplankton. Mixing between the warmers surface waters and thedeeper water becomes less, leading to a reduction in theconcentration of nutrients in the surface. The scarcity of thenutrients inhibits the growth of the phytoplankton leading to reducedproductivity. The effect is very obvious in the areas of the oceanthat are said to be “permanently stratified”. In such areas,there is a noticeable difference in the density of the water.Furthermore, seasonal stratification can occur in other areas of theocean as well[ CITATION Eld06 l 1033 ].
Primaryproductivity is high in some areas of the ocean and low in others.The upwelling zones exhibit high productivity du3 to a high nutrientconcentration. There is high productivity in the photic zone due tothe presence of sufficient light. Low productivity occurs in theareas of the ocean where the surface water is warm. In such areas,the surface water fails to mix with the deeper water leading tonutrient deficiency.
Elderfield, Harry , Heinrich D Holland and Karl K Turekian. The Oceans and Marine Geochemistry. Boston: Elsevier, 2006.
Morrissey, John and James Sumich. Introduction to the Biology of Marine Life. Sudbury: Jones & Bartlett Publishers, 2011.