Lesson 4: The Biogeochemical Cycle

Chemical Oceanography

Last class we learned about CO2 in the oceans

What is the average pH in the ocean? How can increases in CO2 affect:

– Ocean pH?– Calcium carbonate?

What substance do marine organisms use to make exoskeletons?

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Today we will learn more about organic ocean chemistry

1. The biogeochemical cycle is the continuous flow of elements and compounds between organisms and the earth

2. The ocean plays a role in the biogeochemical cycle for elements including carbon and nitrogen

3. As part of the carbon cycle, carbon dissolves into the surface ocean from the atmosphere and is used for photosynthesis

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The biogeochemical cycle

The biogeochemical cycle involves the movement of elements and compounds among the land (lithosphere), organisms, air (atmosphere) and the oceans (hydrosphere).

Human activities can affect these cycles

Lithosphere

AtmosphereBiosphere

Hydrosphere

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How do elements move through the biogeochemical cycle?

Elem

ents

Organisms use elements as

nutrients and put

nutrients back into the

environment

Elements

Elements travel among air, land and sea

through physical processes

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What elements are important to marine life?

Carbon (C) Nitrogen (N) Phosphorus (P) Silicon (Si) Iron (Fe) Trace metals

A trace element exists at LESS THAN 100ppm

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Carbon cycling in the ocean: The “biological pump”

Today we will focus on carbon cycling. We’ll examine the processes that transfer carbon from

the ocean surface to the deep ocean and throughout the food chain.

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Phytoplankton useCO2 for photosynthesis

CO2SomeCO2 is given back off through respiration

Carbon moves up the food chain as primary consumers like zooplankton eat phytoplankton

Carbon moves further up to secondary and tertiary consumers

CO2

Respiration

Decomposition

As phytoplanktondie and decompose,carbon settles to the deep ocean

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Student activity

In today’s activity, we will read an example of modern scientists’ studies of biogeochemical cycles

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