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Difficulty: MediumAligning Data and Predictions with Viewpoints

### Younger Dryas Debate

The Younger Dryas was a period of abrupt cooling that occurred approximately 12,90012,900 years ago. Two viewpoints discuss the potential cause of this event.

Meltwater Flood Model
A sudden influx of freshwater from the melting Laurentide Ice Sheet entered the North Atlantic Ocean. This freshwater cap was less dense than the saline ocean water, preventing the sinking of cold water and shutting down the Atlantic Meridional Overturning Circulation (AMOC). Without this ocean conveyor belt, heat transport to the high northern latitudes ceased, causing rapid cooling. This model predicts that cooling was localized to the North Atlantic region, and that North Atlantic sea surface salinity dropped abruptly.

Cosmic Impact Model
A fragmenting comet or asteroid collided with or exploded over the Laurentide Ice Sheet. The impact triggered widespread biomass burning and threw massive amounts of dust, soot, and sulfur aerosols into the upper atmosphere, blocking incoming sunlight. This model predicts that the cooling was global, occurring simultaneously in both the Northern and Southern Hemispheres, and that a distinct layer containing impact indicators (such as platinum anomalies) and soot was deposited globally at the start of the event.

Suppose researchers analyze marine sediment cores from the Southern Ocean, located in the Southern Hemisphere, and find that sea surface temperatures in this region did not decrease during the Younger Dryas, but instead continued a gradual warming trend. This finding is consistent with which model(s)?

  1. The Meltwater Flood Model only, because that model predicts cooling would be localized to the North Atlantic region rather than global.Answer
  2. B
    The Cosmic Impact Model only, because that model predicts that soot in the upper atmosphere would insulate the Southern Hemisphere, causing it to warm.
  3. C
    Both models, because both models predict that global temperatures would remain stable while regional temperatures fluctuated.
  4. D
    Neither model, because both models predict that the entire planet, including the Southern Ocean, would experience synchronous cooling.

Answer

The Meltwater Flood Model only, because that model predicts cooling would be localized to the North Atlantic region rather than global.
The finding that the Southern Ocean did not experience cooling is consistent only with the Meltwater Flood Model. According to that model's description, the cooling was regional and localized to the North Atlantic. Conversely, the Cosmic Impact Model predicts that the cooling was global and occurred simultaneously in both the Northern and Southern Hemispheres. Therefore, a lack of cooling in the Southern Hemisphere contradicts the Cosmic Impact Model but is consistent with the Meltwater Flood Model.

Step-by-Step Solution

1
Identify the prediction of the Meltwater Flood Model regarding the geographic distribution of cooling.
The Meltwater Flood Model predicts that cooling was localized to the North Atlantic region.
This is needed to determine if a lack of cooling in the Southern Ocean is consistent with the Meltwater Flood Model.
2
Identify the prediction of the Cosmic Impact Model regarding the geographic distribution of cooling.
The Cosmic Impact Model predicts that cooling was global and occurred simultaneously in both hemispheres.
This is needed to determine if a lack of cooling in the Southern Ocean is consistent with the Cosmic Impact Model.
3
Evaluate the southern hemisphere temperature data against the predictions of both models.
Since temperatures in the Southern Ocean did not decrease, this contradicts the Cosmic Impact Model's prediction of global cooling but is consistent with the Meltwater Flood Model's prediction of localized Northern Hemisphere cooling.
This comparison allows us to identify the correct model alignment.

Key Concept

Aligning Data and Predictions with Viewpoints
Estimated Time:1m 30s
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Topics

Aligning Data and Predictions with Viewpoints

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