1.5: Core Connections
Compared with climate indicators such as CO2 levels or global ice volume, what other indicators can tell you about Earth's past climate? How do these indicators relate to the carbon cycle?
In this unit, you have investigated real data. These data are the evidence for variations in Earth's climate in the past. A key part of this climate story is the carbon forms moving in the Earth system. Changes in the climate also connect to the carbon cycle. You will investigate the carbon cycle and climate more in Units 2 and 3.
If someone mentions an ice age, you are likely to think of the great ice sheets in the regions of Earth's poles. The Northern Hemisphere image, for example, emphasizes the changing sizes of continental and sea ice in the Arctic. A broader issue for scientists is testing whether a glacial period is related to the global climate. To find out, you would need to examine other locations on Earth, and perhaps some other proxy records for climate. You will do just that in this lesson as you take two virtual field trips. In general, you will solidify your understandings that:
You have investigated several indicators of climate, such as CO2 levels, ice volume, and Antarctica temperature variations. In this lesson, you will make more connections between carbon and climate with two field trips, where you will analyze some other climate indicators. This is a great way to show what you have learned. Listen to your teacher for what to turn in for this lesson.
Before you start your activity, you may want to review what you've learned so far.
In Lesson 1.4, you investigated a record of the size of ice sheets. The global ice-volume record showed times of large ice sheets (glacial periods, or glacials), and times when ice sheets were small and mostly restricted to Greenland and Antarctica (interglacial periods, or interglacials). These occurred at high latitudes and away from the equator. But is there a record of past climates cycles around the equator? If so, what might that evidence look like at the Equator? Let's explore this with a field trip to the Galápagos Islands.
GALÁPAGOS ISLANDS, ECUADOR, FIELD TRIP
The Galápagos Islands are a cluster of large, volcanic islands in the equatorial Pacific Ocean. The islands are just west of Ecuador, South America. The waters are warm and tropical. Perhaps you have read about these islands in your science class. Animals collected at the Galápagos Islands and South America helped Charles Darwin develop the theory of biological evolution.
The Pacific Ocean around the Galápagos Islands abounds with marine life, including foraminifera (forams). The waters have been that way for millions of years. Geologists have obtained long cores of marine sediments that contain forams from a drilling site called ODP (Ocean Drilling Project) Site 677. This helps the geologists determine the δ18O of ocean water at that locality in the geologic past.
Two Types of Forams
The δ18O data for forams from the Galápagos Islands come from two varieties; each is a key part of marine ecosystems. One type is planktonic foraminifera. Planktonic forams thrive in the photic zone of oceans. This is the upper 100-200 meters, where light penetrates and photosynthesis occurs. In this zone, primary producers (such as diatoms and single-celled algae) transfer carbon in the oceans to organisms of marine food webs. They do this by photosynthesis, the process of using CO2 in the oceans to create their tissues. You will learn more about photosynthesis in Unit 2.
Planktonic foraminifera consume these primary producers. In other words, the planktonic forams are primary consumers because they eat the producers. When the planktonic forams die, or when they themselves are eaten, their carbon-bearing remains sink to the seafloor. Recall that this part is the calcium carbonate test. This is all that remains after the organic tissues of the foram either are digested or decompose in the ocean. The image shows an example of a carbonate test that became part of the seafloor sediments.
Another type is benthicforaminifera. Benthic forams live on the seafloor. By comparison, other types of benthic organisms also live at the bottom of lake ecosystems. Because temperatures are much colder in deeper ocean waters, benthic forams have a different δ18O values than planktonic foraminifera. The key question is whether the pattern of δ18O curves is similar or different for benthic and planktonic forams. What do you see in the data from ODP Site 677 at the Galápagos Islands? Use the interactive to compare these foram data with some other global data sets that you have studied. That's question 2 from the previous section.
Let's take another field trip! This time, we're visiting the open waters of the Pacific Ocean, offshore of northern California and Oregon. This region is the Pacific Northwest. It is at mid-latitudes, about halfway between the equator and the North Pole. On this field trip, you will examine data from a drill core to see whether the sediment keeps a record of climate variation. You will also investigate what the climate indicators tell you about ecosystems and the carbon cycle in the Pacific Northwest. This will help you answer your focus questions.
The cores are from the deep-sea muds at ODP Site 1020. There, large rivers have flushed sediments from the rugged mountains of the Cascades down to the Pacific Ocean. Along with mud and silt, these rivers also contain the pollen of plants and trees that live in the mountains.
By looking at the types of pollen in the core, you can infer the kinds of vegetation that lived in the mountains. This, in turn, gives us key clues about climate. When the climate in the Pacific Northwest was cold and dry, the pollen in the rivers show that the mountains had more plants that lived in a cold, dry climate. In contrast, when the climate in the Pacific Northwest was warm and wet, the pollen in the rivers indicate plant varieties that live in that kind of climate. You will use the data from ODP Site 1020 to see what plants these are. The Pollen Journey video will show you a bit more about rivers and pollen in the Pacific Northwest.
The ocean waters above ODP Site 1020 region are rich with marine life, including forams. Geologists have measured the δ18O of those forams. In addition, another chemical indicator from the forams tells geologists the temperature of the ocean water where the forams lived. You will continue to use these data to make inferences about the climate and ecosystems in the Pacific Northwest.
On your field trip to this site, use the geologic data in the interactive to answer the questions below.
If you are unable to see the interactive, click here to open it in a new tab.
|Pollen type||Regional climate||Evidence for the average regional climate|
|Warm, wet||Cold, dry|
|Redwood||X||Peaks in redwood pollen correlate with peaks in atmospheric CO2 levels, low global ice volume, and interglacial periods like today.|
Spruce is another interesting plant in the Pacific Northwest. See if you can tell whether spruce is relatively more common during glacial or interglacials in the Pacific Northwest. If you are able to graph data in your class, do these steps:
At the end of Unit 1, it is a good time to reflect on some key concepts. Your teacher will tell you which of the following questions to complete and when they are due.