How does the oxygen isotope analysis of ocean floor sediments and glacial ice tell us about past temperatures?
How does the oxygen isotope analysis of ocean floor sediments and glacial ice tell us about past temperatures?
On the Earth, most elements like hydrogen and oxygen are present in multiple variants known as isotopes.
Oxygen isotope is a signature for determining the past climatic trends of the Earth. The Earth never had a uniform climate, and there were glacial and interglacial periods where the warming and cooling trends were periodically changing. These events have a role in regulating the hydrological cycles of the Earth. During the warming, evaporation events will be more prominent, and during the cooling period, the precipitation event of the hydrological cycle will be apparent. The hydrological cycle includes different water molecules phases, and each water molecule has oxygen and hydrogen elements. The water molecule has different properties based on the type of oxygen isotope makeup the water molecules, and this forms the basis for climate evidence using oxygen isotopes.
- The water molecules made of heavier oxygen isotope (O-18) are denser and require more time and heat to transform from liquid to vapor and less time to change from vapor to liquid or solid form of water.
- Similarly, the lighter oxygen isotope (O-16) makes up lighter water molecules, which respond quickly to heat and transforms from liquid to vapor state easily.
Based on this background, the historical climate can be evaluated from the analysis of the glacial ice and sediments in the ocean floor because:
- During the period of global warming on the Earth, the high heat transforms the water with heavier isotope into a vapor state, which later moves in the form of a cloud and precipitates near the poles to form a glacial ice sheet. Hence, the warming period's higher temperature depletes the concentration of heavier isotopes of oxygen in the ocean and sediments of the ocean and increases the concentration of heavier isotopes of oxygen in the glacial ice.
- During the cooling period of the Earth, less heat will not promote the evaporation of heavier isotopes of water molecules from the ocean, which results in the predominant evaporation of the lighter water molecules with O-16. The lighter molecule of water forms clouds and precipitates as snow ad rain in poles, making the glacial ice sheet have higher water dominance with the lighter oxygen isotope. Conversely, the ocean system fills with heavier oxygen isotopes that will form part of the ocean sediments.
Hence, the relative proportion of the oxygen isotope present in the water molecules of the glacial ice and the ocean sediments indicates the climatic variations in the past.
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