AbstractThe deep-sea fauna is dependent on the delivery of nutrients from the overlying waters. As data/observations show, benthic fauna is supported under both oligotrophic oceanic conditions and at the greatest (hadal) depths. This can be explained by an additional food source originating from sediment resuspension. However, the mechanisms of resuspension at these depths remain uncertain.
Two diverse environments with intermediate scale topographical features were studied: seamounts in the North Atlantic and Pacific hadal trenches were observed via a radionuclide approach (234Th and 210Pb) in terms of assessing the control mechanism of carbon deposition to the seafloor. It is understood that topographical features alter the path of hydrological flow and these, in return, alter the sedimentary environment, biochemistry and consequently benthic and epibenthic fauna.
The main observations highlight the highly dynamic environment in the whole area of the Ampère Seamount, where more complex hydrodynamic and sedimentary pathways are observed. Similarly, the Senghor Seamount displays winnowing at two opposite slopes, suggesting the influence of internal tides. In contrast, the Eastern Mediterranean seamounts, Eratosthenes and Anaximenes, did not show alternations in sediment accumulation to such a degree. The radionuclides in the water column profiles at Eratosthenes, however, show irregularities connected to the presence nearby of an anticyclonic eddy and/or gyre.
The samples collected from all four Pacific hadal trenches revealed the presence of freshly derived particles in the lower water column and the sediment, presumably originating from re-suspended material. Some characteristics suggest winnowing at hadal depths. This strongly contrasts with the widely accepted image of quiescence in hadal environments. The degree of these observations varies between trenches, but Challenger Deep clearly shows these ‘disturbances’ at their highest.
Lastly, a method of measurement and calculation of sedimentary excess in the deep-sea environment was tested in order to ascertain accurate accretion values. The importance of calculation method choice for a specific type of sample is shown.
|Date of Award||7 Jan 2020|
|Supervisor||Robert Turnewitsch (Supervisor), John Howe (Supervisor) & Ronnie Glud (Supervisor)|