The importance of tides for sediment dynamics in the deep sea-Evidence from the particulate-matter tracer Th-234 in deep-sea environments with different tidal forcing
Key aspects of deep-ocean fluid dynamics such as basin-scale (residual) and tidal flow are believed to have changed over glacial/interglacial cycles, with potential relevance for climatic change. To constrain the mechanistic links, magnitudes and temporal succession of events analyses of sedimentary...
| Published in: | Deep Sea Research Part I: Oceanographic Research Papers |
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| Main Authors: | , , , , , |
| Format: | Article in Journal/Newspaper |
| Language: | English |
| Published: |
2009
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| Subjects: | |
| Online Access: | https://pure.uhi.ac.uk/en/publications/cb6b02a5-d3ae-4aff-bb20-bf9417944f4c https://doi.org/10.1016/j.dsr.2009.03.009 |
| Summary: | Key aspects of deep-ocean fluid dynamics such as basin-scale (residual) and tidal flow are believed to have changed over glacial/interglacial cycles, with potential relevance for climatic change. To constrain the mechanistic links, magnitudes and temporal succession of events analyses of sedimentary paleo-records are of great importance. Efforts have been underway for some time to reconstruct residual-flow patterns from sedimentary records. Attempts to reconstruct tidal flow characteristics from deep-sea sediment deposits, however, are at a very early stage and first require a better understanding of the reflection of modern tides in sediment dynamics. In this context internal (baroclinic) tides, which are formed by the surface (barotropic) tide interacting with seafloor obstacles, are believed to play a particularly important role. Here we compare two modern deep-sea environments with respect to the effect of tides on sediment dynamics. Both environments are influenced by kilometre-scale topographic features but with vastly different tidal forcing: (1) two sites in the Northeast Atlantic (NEA) being surrounded by, or located downstream of, fields of short seamounts (maximum barotropic tidal current velocities similar to 5cm s(-1)); and (2) a site next to the Anaximenes seamount in the Eastern Mediterranean (EMed) (maximum barotropic tidal current velocities similar to 0.5 cm s(-1)). With respect to other key fluid-dynamical parameters both environments are very similar. Signals of sedimentary particle dynamics, as influenced by processes taking place in the bottom boundary layer, were traced by the vertical water-column distribution of radioactive disequilibria (daughter/parent activity ratios not equal 1) between the naturally occurring, short-lived (half-life: 24.1 d) particulate-matter tracer Th-234 relative to its very long-lived and non-particle-reactive parent nuclide U-238. Activity ratios of Th-234/U-2381). The results of this study, therefore, add to the evidence suggesting that tides in the deep sea ... |
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