Bioturbation in the hadal zone.

Area of Science:

• Marine Geology
• Deep-Sea Ecology
• Ichnology

Background:

• The hadal zone (>6 km deep) is a poorly understood marine ecosystem.
• Sediment cores from the Japan Trench (IODP Expedition 386) provide insights into deep-sea environments.
• Bioturbation, the disturbance of sediment by organisms, is a key process in marine environments.

Purpose of the Study:

• To investigate bioturbational structures and trace fossils in hadal sediments (>7.5 km depth).
• To understand the colonization successions and feeding strategies of endobenthic organisms in the Japan Trench.
• To identify factors controlling bioturbation in extreme deep-sea environments.

Main Methods:

• Analysis of sediment cores collected during IODP Expedition 386.
• Micro-CT imaging of 20 core sections to visualize sedimentary structures.
• Identification and interpretation of biogenic sedimentary structures (trace fossils).

Main Results:

• Identified incipient trace fossils and colonization successions within gravity flow deposits.
• Observed recurring bioturbation successions, from deposit-feeding (Phycosiphon, Nereites, Artichnus) to microbe-dependent feeding (Gyrolithes, Pilichnus, Trichichnus).
• Soupy substrate, oxygenation, and organic matter availability were identified as key factors controlling colonization.

Conclusions:

• Hadal bioturbation is characterized by distinct colonization stages and feeding strategies.
• Environmental factors like substrate consistency and oxygen levels significantly impact endobenthic life.
• The study reveals adaptations of deep-sea organisms to extreme conditions, including chemosymbiosis.