Posted: November 15th, 2022

Describe what is meant by Residence Time

1. a). Describe what is meant by Residence Time
Residence time (otherwise called evacuation time) is the average measure of time that a particle spends in a specific system. This estimation varies directly with the measure of substance that is available in the system.
The residence time is a representation of the extent of time it takes for the concentration to effectively change in the sediments.

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b). Describe the difference between conservative, nutrient-like, and scavenged elements
Conservative elements: Are elements with long residence times in the sea and have a tendency to be very soluble in ocean water and to be uniformly mixed throughout the sea. Examples include Na, Cl, Mo, Re, TI, N and Ar. They occur in the same proportion to each other all through the ocean regardless of the aggregate salinity.
Nutrients-like elements: Are elements with short residence time in the ocean because of their very high reactivity for example Cd, Fe, Ni, Ag, Y, SE and Zn. They are recyclable and this makes nutrient-like trace elements concentration higher at ocean depth and lower at the surface with the shape of the profile depending on its recycling rate. They are controlled mainly by salinity variations in the sea.
Scavenged elements: Are majorly transition metals and heavy metals such as Mn, Co, Ga, In, Pb, Te, Bi and Ce. They are very reactive with short mean oceanic residence time (10^2 to 10^3 years) and low concentrations. Removals from the sea are dominated by adsorption onto particles surfaces and are transported to the sediments through interactions with large but rapidly settling particles.
2. A) The composition of sea water has been argued to be the end product of an intricate interweaving of physical, chemical and biological processes. Carefully draw a vertical profile of dissolved oxygen in the North Pacific (include approximate units on axis). Label major physical features of the water column. Explain the major physical, chemical, and biological processes that lead to the profile that you’ve drawn.

Physical process: Surface sea waters basically have oxygen concentration near equilibrium with the Earth’s atmosphere. Generally, colder waters hold more oxygen than warmer waters. As this water moves out of the mixed layer into the thermocline it is exposed to a rain of organic matter from above.
Biological process: Aerobic microbes eat this natural matter; oxygen is utilized as a major aspect of the bacterial metabolic procedure bringing down its concentration inside of the water. In this manner, the concentration of oxygen in profound water is subject to the measure of oxygen it had when it was at the surface less depletion by deep ocean organisms.

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