Lesson 4: The Biogeochemical Cycle Chemical Oceanography

Last class we learned about CO 2 in the oceans What is the average pH in the ocean? How can increases in CO 2 affect: – Ocean pH? – Calcium carbonate? What substance do marine organisms use to make exoskeletons? 2

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 3

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 Atmosphere Biosphere Hydrosphere 4

How do elements move through the biogeochemical cycle? Elements Organisms use elements as nutrients and put nutrients back into the environment Elements Elements travel among air, land and sea through physical processes 5

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 6

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. 7

Phytoplankton use CO 2 for photosynthesis CO 2 Some CO 2 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 CO 2 Respiration Decomposition As phytoplankton die and decompose, carbon settles to the deep ocean 8

Student activity In today’s activity, we will read an example of modern scientists’ studies of biogeochemical cycles 9