Maximum sinking velocities of suspended particulate matter in a coastal transition zone

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Maerz, J.; Hofmeister, R.; Van Der Lee, E.M.; Gräwe, Ulf; Riethmüller, R. et al.: Maximum sinking velocities of suspended particulate matter in a coastal transition zone. In: Biogeosciences 13 (2016), Nr. 17, S, 4863-4876. DOI:

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Marine coastal ecosystem functioning is crucially linked to the transport and fate of suspended particulate matter (SPM). Transport of SPM is controlled by, amongst other factors, sinking velocity ws. Since the ws of cohesive SPM aggregates varies significantly with size and composition of the mineral and organic origin, ws exhibits large spatial variability along gradients of turbulence, SPM concentration (SPMC) and SPM composition. In this study, we retrieved ws for the German Bight, North Sea, by combining measured vertical turbidity profiles with simulation results for turbulent eddy diffusivity. We analyzed ws with respect to modeled prevailing dissipation rates ϵ and found that mean ws were significantly enhanced around log10(ϵ (m2 s−3)) ≈ −5.5. This ϵ region is typically found at water depths of approximately 15 to 20 m along cross-shore transects. Across this zone, SPMC declines towards the offshore waters and a change in particle composition occurs. This characterizes a transition zone with potentially enhanced vertical fluxes. Our findings contribute to the conceptual understanding of nutrient cycling in the coastal region which is as follows. Previous studies identified an estuarine circulation. Its residual landward-oriented bottom currents are loaded with SPM, particularly within the transition zone. This retains and traps fine sediments and particulate-bound nutrients in coastal waters where organic components of SPM become remineralized. Residual surface currents transport dissolved nutrients offshore, where they are again consumed by phytoplankton. Algae excrete extracellular polymeric substances which are known to mediate mineral aggregation and thus sedimentation. This probably takes place particularly in the transition zone and completes the coastal nutrient cycle. The efficiency of the transition zone for retention is thus suggested as an important mechanism that underlies the often observed nutrient gradients towards the coast.
License of this version: CC BY 3.0
Document Type: article
Publishing status: publishedVersion
Issue Date: 2016
Appears in Collections:Fakultät für Mathematik und Physik

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pos. country downloads
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1 image of flag of Germany Germany 115 79.86%
2 image of flag of Denmark Denmark 7 4.86%
3 image of flag of China China 5 3.47%
4 image of flag of United States United States 3 2.08%
5 image of flag of France France 3 2.08%
6 image of flag of Korea, Republic of Korea, Republic of 2 1.39%
7 image of flag of Canada Canada 2 1.39%
8 image of flag of Vietnam Vietnam 1 0.69%
9 image of flag of United Kingdom United Kingdom 1 0.69%
10 image of flag of Colombia Colombia 1 0.69%
    other countries 4 2.78%

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