Question

a) Draw a depth profile of PO4, Cd, Si, Ba, and Pb in the Atlantic and Pacific.

a) Explain the sources and reasons for variation in the profiles that drew

c) Pick two of these elements one with a large and one with a short residence time. What can you say about the relative reactivity for each one of these elements? What process(es) controls the residence time of each element?

Answer 1

Cd is a nutrient type elements and is very active hence has a short residence time. typically have higher concentrations in deep pacific oceans as compared to deep Atlantic oceans. Its distribution is mainly controlled by salinity and temperature variations in the oceans. The major source of Cd is continental, ocean current circulations and black smokers.

Pb (lead ) is a very reactive or scavenged element henceforth have a long residence time. Its highest concentration is the Atlantic ocean and the lowest in the Pacific Ocean. Pb is recycled many times on the surface and is not controlled by salinity variation. The major source is although is the continental source but nowadays are influxes into oceans due to anthropogenic activities.

The concentrations of silica are less on the surface of both the oceans but in the Pacific, it rises with the increase in depth. The reason for this is biogenic silica planktons(opal, shells, radiolarian cherts etc.,)

The residence time of phosphate in ocean water is 69K years. High values of Po4 are found on the surface, deep water circulations (low oxygen content) are the reason for abundance of phosphate in the pacific ocean than Atlantics.