Lab: Ocean Chemistry and Modes of Nutrient Distribution


This lab allows you to use actual observational (chemical) data to investigate the role of ocean biology in redistributing nutrients between the surface and deep ocean (the Biologic Pump) as well as its role in affecting the vertical distribution of oxygen. You will also see that you can use the phosphate concentration in deep waters to observe the effect of deep ocean circulation in "sweeping" deep ocean nutrients from one basin to another. The second part of this lab allows you to examine upwelling and downwelling through the concentration of chemical elements, as well other physical processes. Observing vertical profiles of the ocean, you will be able to determine from what depths upwelled water originates, as well as the relationship existing between surface and deep water circulation and the occurrence of upwelling and downwelling.

As you work through each part of the lab, remember to check your numbers - magnitude as well as units. Do they make sense? Use the lecture notes as a guide.

I. Global Distribution of Phosphate (PO4)

In the first part of this lab you will study the horizontal and vertical distribution of phosphate and oxygen throughout the ocean. The concentration of both are affected by biological activity. Phosphate, in many areas of ocean surface waters is the nutrient that limits biological activity. In other words, the growth of plants in the near surface sun-drenched waters of these areas completely uses up available phosphate. Subsequently the plants containing the phosphate are consumed by other organisms which in turn sink into deeper water where the action of bacteria causes their decay resulting in the release of the phosphate to deeper levels in the ocean. This phosphate, released to the deeper layers of the sea, is returned to the depleted surface waters by upwelling. In this way biological activity "pumps" phosphate from surface waters, where is it rapidly incorporated into organic particles, to deeper layers, where it is oxidized back to phosphate by microbial activity, and ocean circulation subsequently returns the nutrients to selected areas of the oceans surface. The longer a parcel of deep water stays within these deeper layers the more phosphate it will accumulate.

Surface waters are charged with dissolved oxygen from the atmosphere and from the photosynthetic action of plants. Oxygen in general is more soluble in cold water than in warm water. As surface water charged with oxygen sinks, the oxygen is consumed by the respiration of animals and bacteria living on sinking organic matter. Consequently the longer water stays below the surface the more oxygen will be consumed by respiration.

Task 1: View the surface distribution of PO4 (annual mean) in the world's oceans, from the World Ocean Atlas 98 (WOA98) database.

Task 2: Use the viewer's depth bar to replot the map of PO4 for a depth of 2000 meters (also study the maps for 3000 and 1000 meters). Be sure to adjust the upper end of the concentration scale if areas of the ocean appear in grey rather than color. The data "missing" exists in the files, but is being excluded from the view plot because the concentration range displayed on the scale is too narrow.

Task 3: Use the viewer to make a latitude-depth plot through the Atlantic ocean at about 30 degrees west longitude. (Note: depth should be on the y-axis and 0 meters, the ocean's surface, should be at the top of the graph. This may require you to reverse the depth axis values on the viewer.)

Task 4: Make a latitude-depth plot through the Pacific along 160 degrees west longitude.

Task 5: Transfer the Levitus PO4 "Near Hawaii" data to an Excel file.

Task 6: Oxygen is generated by plant life in the surface water of the ocean and also dissolved in ocean water from the overlying atmosphere. Thus surface waters are usually rich in oxygen. At depth oxygen is consumed by the respiration of organisms living on the sinking organic matter.

Task7: If deep/bottom water did not form at the poles, how would the profiles of O2 and PO4 with depth near Hawaii (Part 1 - steps 5 and 6) look different?

II. The Role of Upwelling and Downwelling in Nutrient Distribution

In this section of the lab you will investigate the relationship between upwelling and the distribution of nutrients. This lab is open ended – you can use any of the atmospheric or oceanographic data available to you from our data catalog.

Hints: You will need to look at properties in both plan view (e.g. surface ocean distributions) and sections (latitude vs. depth or longitude vs. depth). To make sections simply click on the graph and all of the parameters to make changes to the viewer should be available to you. Use the zoom function to focus in on specific areas.

Task 1: Review the conditions required for upwelling and downwelling (Text: p. 86-87, 153-160, 226-227, Lecture).

Task 2: Using the databases available to you answer the following questions.

Task 3: Using the databases available to you, locate a region where seasonal upwelling occurs.


Lab Report Instructions

Write lab report (as per the Lab Report Format) synthesizing and summarizing the major findings of your investigation. Consider the relationship between what you observed in lab (nutrient distribution, upwelling, and downwelling) and the surface and deep water circulation and currents which you have learned about in class. Based on your findings, why do you think fishing around Alaska is so productive?

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Updated July 13, 2007
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