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? Teacher’s Note: The average pH of seawater is around 8. Increases in CO2 can decrease ocean pH and cause calcium carbonate (the substance used by marine organisms to make exoskeletons, shells) to break down.

Today we will learn more about organic ocean chemistry The biogeochemical cycle is the continuous flow of elements and compounds between organisms and the earth The ocean plays a role in the biogeochemical cycle for elements including carbon and nitrogen As part of the carbon cycle, carbon dissolves into the surface ocean from the atmosphere and is used for photosynthesis Source: National Marine Educators Association. 2010. Life on an Ocean Planet. Current Publishing Corps, Santa Margarita, CA. 598pp.

The biogeochemical cycle Atmosphere 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 Biosphere Teacher’s note: Arrows indicating biogeochemical cycle movement will appear as you advance the slide. Hydrosphere Lithosphere

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

What elements are important to marine life? Carbon (C) Nitrogen (N) Phosphorus (P) Silicon (Si) Iron (Fe) Trace metals Teacher’s Note: This slide is set up so that you can ask your students to guess first, then each element will “fly” into the screen as you advance. Elements and some of their essential functions to marine life Carbon: Basic building block of marine life Nitrogen and Phosphorus: Nutrients required by plants (phytoplankton) for photosynthesis Silicon: Used by some marine organisms to build shells and skeletons Iron: Required by plants to produce chlorophyll; May limit phytoplankton production in ocean areas far from land where iron is scarce Trace Metals: Essential (in small quantities) to marine organisms for growth, other functions A trace element exists at LESS THAN 100ppm

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. Teacher’s Note: The term “biological pump” is used to refer to the movement of carbon to the deep ocean

CO2 is given back off through respiration Phytoplankton use CO2 for photosynthesis CO2 Some CO2 is given back off through respiration Carbon moves up the food chain as primary consumers like zooplankton eat phytoplankton CO2 Respiration Teacher’s note: When played in slideshow format, this walks students through the biological pump, the biogeochemical process by which CO2 cycles through the ocean. Some of the carbon then settles to the deep ocean, some is respired as CO2 and some moves up to higher order consumers. Carbon moves further up to secondary and tertiary consumers Decomposition As phytoplankton die and decompose, carbon settles to the deep ocean

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