Podcast
Questions and Answers
What is the depth range of the mesopelagic zone?
What is the depth range of the mesopelagic zone?
- 1000 to 2000 meters
- 2000 to 3000 meters
- 0 to 200 meters
- 200 to 1000 meters (correct)
The mesopelagic zone is completely devoid of light.
The mesopelagic zone is completely devoid of light.
False (B)
What is the name of the region in the mesopelagic zone where sharp changes in temperature occur?
What is the name of the region in the mesopelagic zone where sharp changes in temperature occur?
Thermocline
The mesopelagic zone is also known as the ______ zone.
The mesopelagic zone is also known as the ______ zone.
What organisms are adapted to live in the mesopelagic zone?
What organisms are adapted to live in the mesopelagic zone?
What is the primary role of the biological pump in the mesopelagic zone?
What is the primary role of the biological pump in the mesopelagic zone?
Match the following features with their descriptions:
Match the following features with their descriptions:
What is the approximate temperature at the upper layers of the mesopelagic zone?
What is the approximate temperature at the upper layers of the mesopelagic zone?
How do certain fish in the mesopelagic zone contribute to organic matter export?
How do certain fish in the mesopelagic zone contribute to organic matter export?
Name one of the key processes occurring in the mesopelagic zone.
Name one of the key processes occurring in the mesopelagic zone.
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Study Notes
Mesopelagic Zone Overview
- The mesopelagic zone, or middle pelagic/twilight zone, lies between the epipelagic (photic) and bathypelagic (aphotic) zones.
- Depth ranges from approximately 200 to 1000 meters (660 to 3300 feet) where only 1% of surface light penetrates.
- Home to diverse life forms including bristlemouths, blobfish, bioluminescent jellyfish, and giant squid.
Sharp Environmental Changes
- Characterized by significant changes in temperature, salinity, and density, leading to the formation of thermocline, halocline, and pycnocline.
- Temperature varies drastically from over 20 °C (68 °F) at the surface to around 4 °C (39 °F) near the bathyal zone.
- Salinity remains relatively stable between 34.5 and 35 psu.
- Density ranges from 1023 to 1027 g/kg, impacting stratification and nutrient mixing within the water column.
Unique Acoustic Characteristics
- Features the Sound Fixing and Ranging (SOFAR) channel where sound travels slowly; located at depths of 600-1200 meters.
- Sound waves in this channel can travel long distances due to refraction.
- The channel was historically explored for locating shipwreck survivors and monitoring submarine movements via the Sound Surveillance System (SOSUS) by the US Navy.
Water Mass Formation
- The zone is significant for the formation of mode water, which has vertically mixed properties and long residency times.
- Mode water forms at the thermocline, experiencing residence times on decadal or century scales, contrasting with shorter vertical movements of various marine life.
Role in Ocean's Biological Pump
- Essential to the ocean’s carbon cycle via the biological pump, which sequesters organic carbon from the surface euphotic zone.
- Particles produced through photosynthesis sink into the mesopelagic zone, where they are remineralized.
- Approximately 90% of particulate organic carbon (POC) exported to this zone is respired, aiding in nutrient cycling.
Diel Vertical Migration
- Certain species engage in diel vertical migration, moving between the euphotic zone and mesopelagic zone, effectively transporting organic matter to deeper areas.
- Myctophids in studies transport approximately 15-28% of passive POC sinking to the ocean depths.
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