Polar Science Station: The Case of the Elusive Element

Week 3
17 July 2006

Searching for the Elusive Element Using Chemical Oceanography

Part I – Section I of II
The University of Hawaii Group

Most people think of oceanography as the study of marine mammals, birds, and fish, that is, the biological aspects of the ocean. In Week 2 of Science in the Spotlight, Meng Zhou described how physical processes initiate change in ocean environments. This week, Chris Measures describes chemical oceanography and its importance in understanding changes not only in the ocean, but also in the earth’s climate

1. What is chemical oceanography?

It is the study of how chemicals get into, move around in, and leave the ocean. The overall quantity of the elements in the ocean does not change over long periods of time. The elements arrive in the ocean by means of physical processes (e.g. wind) and get moved around by biological processes (e.g. consumption by organisms). Chemical oceanographers are the “Sherlock Holmes” of the sea. They track the movement of various elements and want to find out what caused it.


Bill Hiscock processes samples to measure trace metals. Biography

2. What is your project?

On this cruise we measure trace elements in order to find out where the iron east of the Shackleton fracture and around the South Shetland Islands comes from.

Look up 3 different trace elements either on-line or in another resource.

3. Why do you want to do this?

We want to study how the ocean has changed through time and how it has affected the climate.


Mariko Hatta: will defend her dissertation next month! Biography

4. How can you get a record of the past?

In order to understand the climate on earth, we need to understand the processes that take place in the ocean. Animals ingest chemicals, and some of their skeletons get buried in the sediment in the sea floor. These skeletons buried in the sediment provide a record of the distribution of specific types of elements. Trace elements, those found in parts per billion, are the ones that provide clues to changes in the ocean.

Question: What are some ways to get information about the past other than from a written record?

5. Why are you interested in looking at the Ice Age (other than for general information)?

Periodically, there is a “wobble” in the tilt of the Earth. This “wobble” occurs every 100,000 years and can lead to an ice age. During the ice ages, the changes in the amount of sunlight are actually very small. Yet the planet changed in the space of a few thousand years from pleasant to very cool.
The ocean “over-reacts” and amplifies some of these changes. One way to understand the ocean under amplification is to measure iron. To understand climate changes in the future, we need to look at the past. (Referrals to the Ice Age in this section refer to the last ice age.)

This image compares 18,000 years before present and modern day glacial and estimated sea ice coverage of the southern hemisphere.
Photo Credits:
Mark McCaffrey
Paleoclimate Program/NOAA

Link

Question: Why would sea level go down during an ice-age? When was the last ice age? If the next one is 100,000 years from the last one, when would that be?

6. Why are you interested in iron?

All plants need iron, including phytoplankton. When you see plants in your yard that have yellowed leaves, that may be a sign that they are lacking iron. (Adding a Flintstone vitamin with iron is not recommended.) However, it is hard to dissolve iron in the presence of oxygen. Some areas of the ocean are nutrient rich in other elements, but where there is no iron there is no phytoplankton.

7. How do phytoplankton get iron?

Plankton remove iron and carbon dioxide from their environment. When they die, they fall through the deep water into the sediment below. When upwelling occurs, these nutrients rise to the surface where they are again consumed by phytoplankton. In many areas, dust comes out over the ocean. The dust usually contains both iron and aluminum. If scientists find the presence of aluminum with the iron, they know that the iron came from the continent as dust.


Silt and plankton bloom off Elephant Island, Antarctica. 13th of September 2003. Image courtesy of MODIS Rapid Response Project at NASA/GSFC. Link	Link

8. What are you looking at in the waters off Antarctica?

All around Antarctica and the North Pacific, there are high nutrient ocean waters that have low chlorophyll growth. However, east of the Shackleton Fracture zone is an area of high phytoplankton growth. (See illustration – Chlorophyll Concentrations: Antarctic Circumpolar Current.) We want to be able to show that iron is added and also where the iron is coming from.

9. What could be possible sources of iron? We know that no dust is coming from Antarctica, therefore that continent cannot be the source of iron.

Is it possible that the dust is from South America? Possible sources might be the Atacama Desert or Patagonia. (Look at a map of Chile to find the Atacama Desert in the north and Patagonia in the southern part of both Chile and Argentina.)
Is the source of iron the upwelling that brings up sediment from the bottom of the ocean?
Could the source be the continental shelf of Antarctica or the shelves of southern islands like King George or Elephant?

Rick bravely holds an XBT canXBT launcher and canisterister

Figure showing CO2 levels in the atmosphere over the last 400,000 years

Vivid colors belie the arid landscape of northern Chile where the Atacama Desert, one of the world’s driest, meets the foothills of the Andes. Here salt pans and gorges choked with mineral-streaked sediments give way to white-capped volcanoes. This scene was acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra satellite on Oct. 28, 2001.
Image Credit: NASA/USGS
Link

10. Why would the shelves be a good source of iron?

In the deeper waters, when the plankton die, the particles fall several thousand meters. The iron is no longer easily accessible. The water in the coastal areas is shallow. When the phytoplankton die, their remains don’t fall far and they reach the sediments. Water does not circulate through the sediments. The iron and other chemicals are released by bacteria. A trace mineral that occurs with iron in shelf water sediments is manganese. The shelves around the Antarctic islands are good sources of manganese. Thus, the occurrence of high levels of manganese with high levels of iron in the waters east of the Shackelton Fracture Zone, indicates that the iron there comes from the coastal shelf rather than from dust blown over the ocean.

Antarctica satellite image.
This file is in the public domain because it was created by NASA. NASA copyright policy states that "NASA material is not protected by copyright unless noted". (NASA copyright policy page or JPL Image Use Policy)..
Link

11. How do you know where the shelf ends?

As you move seaward away from the continent the shelf is a fairly flat region about 120m deep. At the shelf edge the bottom suddenly gets much deeper as you go out into the open ocean. The shelf is where the edge of the land was during lower sea level during the last ice age.

Possible question: Why would sea level go down during an ice-age?

12. How do quantities of phytoplankton relate to climate change?

Phytoplankton remove carbon dioxide from the air. During the Ice Age, quantities of CO2 dropped 100ppm which equates to approximately a 30% reduction. The quantity of CO2 is only one factor in climate change.

13. How does a change in the amount of sunlight affect CO2?

We think part of the explanation is that during the colder period of ice age the climate was much driuer and windier which increased the amount of dust in the atmosphere.

http://earthobservatory.nasa.gov/Library/CarbonCycle/carbon_cycle4.html

In any given year, tens of billions of tons of carbon move between the atmosphere, hydrosphere, and geosphere. Human activities add about 5.5 billion tons per year of carbon dioxide to the atmosphere. The illustration above shows total amounts of stored carbon in black, and annual carbon fluxes in purple. (Illustration courtesy NASA Earth Science Enterprise)

Link

14. How did dust play a role in the Ice Age?

Ice cores taken from Vostok, Antarctica show that there was from 15-50 times more dust during that period. This dust contains a lot of iron and when some of it is deposited on the surface of the ocean, around places like Antarctica, it would have provided more iron for the phytoplankton. More iron means more plankton removing more CO2.

Question: If there is less CO2 , will temperatures be warmer or colder? Why?

15. Why should I care about all this?

Because we have only one planet. With increased population and increased emissions of CO2 into the environment, we are affecting planetary systems including climate. “The planet is an angry beast. Don’t go poking the angry beast with a stick.” The result would be highly unpleasant for all of us.

Question: What can individuals, businesses, and governments do to make life on this planet sustainable?

Week 3 17 July 2006

Searching for the Elusive Element Using Chemical Oceanography

Part I – Section I of II The University of Hawaii Group

Week 3
17 July 2006

Part I – Section I of II
The University of Hawaii Group