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Analytical Benthic Flux Model Forced by Surface-Gravity Waves

This study explores benthic flux, the flow rate across a water body bed, and its relationship with surface-gravity waves in the South Atlantic Bight. The research features analytical models and conclusions on volume and mass quantities, transient processes, and driving factors. It investigates processes like seepage, ventilation, and submarine groundwater discharge, discussing their independence of direction and location within water bodies. The study presents a generalized analytical model, incorporating factors like wave-induced advection and nearshore processes, with implications for future work in understanding benthic flux dynamics in aquatic environments.

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Analytical Benthic Flux Model Forced by Surface-Gravity Waves

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  1. Analytical Benthic Flux Model Forced by Surface-Gravity Waves Application to the South Atlantic Bight j.n. king U.S. Geological Survey Florida Integrated Science Center Fort Lauderdale, FL, USA Definition ◊ Model ◊ SAB ◊ Conclusions

  2. Benthic flux is the rate of flow of some quantity across the bed of a water body, per unit area of bed. • Benthic flux is a vector quantity, where the vector is oriented normal to the bed. • Benthic flux units are a function of the quantity under consideration: • volume quantity: L3 T-1 L-2 (=LT-1) • mass quantity: M T-1 L-2 • Benthic flux is a transient process. Definition :: Benthic Flux Definition◊ Model ◊ SAB ◊ Conclusions

  3. Benthic flux is the rate of flow of some quantity across the bed of a water body, per unit area of bed. • Benthic flux is a vector quantity, where the vector is oriented normal to the bed. • Benthic flux units are a function of the quantity under consideration: • volume quantity: L3 T-1 L-2 (=LT-1) • mass quantity: M T-1 L-2 • Benthic flux is a transient process. Definition :: Benthic Flux Definition◊ Model ◊ SAB ◊ Conclusions

  4. newer … older • Also known as: • Seepage • Irrigation • Flushing • Ventilation • Percolation • Sub-tidal pump • Submarine ground water discharge (SGD) • Submarine ground water recharge (SGR) • Submarine pore water exchange (SPE) • Related processes: • Deposition & Resuspension • Bio-turbation • Bio-irrigation • Salt fingering • Fluidization of sediment in the surf zone Burnett et. al. (2003) • Benthic flux is independent of direction: • benthic discharge (flux): gw => sw • benthic recharge (flux): sw => gw • Benthic flux is independent of water body: wetland, river, lake, estuary, lagoon, ocean • Benthic flux is independent of location in the water body: surf zone, shelf, deep ocean Definition◊ Model ◊ SAB ◊ Conclusions

  5. Processes that Drive Benthic Flux Definition◊ Model ◊ SAB ◊ Conclusions

  6. Surface-Gravity Wave over Rigid, Porous Media +z 4Unknowns – 4Equations Assume z=0 +x (DFSBC) (KFSBC) (DBBC) z=-h (KBBC) (Bernoulli) (velocity potential) Reid & Kajiura (1957) (Darcy) Definition◊ Model ◊ SAB ◊ Conclusions

  7. Definition◊ Model ◊ SAB ◊ Conclusions

  8. Generalized Analytical Modelfor Benthic Water Flux King, Mehta & Dean (2008?) Definition◊ Model ◊ SAB ◊ Conclusions

  9. Moore (1996) Moore (1999) Definition◊ Model ◊ SAB ◊ Conclusions

  10. Estuaries Ocean 0.08 dpm/L 0.01 dpm/L Moore (1996) A 226Ra= 0.19 dpm/L SAB A 226Ra.Excess= 0.19-0.01-0.08 = 0.10 dpm/L Moore (1999) VSAB.InS = 20km × 320km × 10m = 6.4×1013L Tresidence.226Ra = 30d Å 226Ra.Excess= 0.10×(6.4×1013)÷30 =2.1×1011dpm/d Definition◊ Model ◊ SAB ◊ Conclusions

  11. 7 dpm/L Pore Water Moore (1996) A 226Ra= 0.19 dpm/L SAB Ocean Estuaries 0.08 dpm/L 0.01 dpm/L Å 226Ra.Excess=2.1×1011dpm/d QMoore=2.1×1011÷7 =3×1010L/d =350m3/s qMoore=0.5cm/d Definition◊ Model ◊ SAB ◊ Conclusions

  12. Three (nearshore) processes: Tidal pumping on sloped beach 130m3/s or 37%QMoore Wave set up 190m3/s or 54%QMoore Terrestrial hydraulic gradient (from Younger,1996) 14m3/s or 4%QMoore Linear sum = 14+130+190 = 334m3/s or 95%QMoore Li and others (1999) Definition◊ Model ◊ SAB ◊ Conclusions

  13. bathymetry from Riedl et al. (1972) Riedl et al. (1972) canonical canonical Riedl et al. (1972) Riedl et al. (1972) Application of Case I to SAB shoaled and damped Definition◊ Model ◊ SAB ◊ Conclusions

  14. 1.3dpm/L 0.2dpm/L Martin et. al. (2006) Wave mixed zone Moore & Wilson (2005) 7dpm/L? Moore & Wilson (2005) Definition◊ Model ◊ SAB ◊ Conclusions

  15. Updated Moore (1996) 0.5 dpm/L 7 dpm/L 0.19 dpm/L Pore Water A 226Ra= 0.19 dpm/L SAB Ocean Estuaries 0.08 dpm/L 0.01 dpm/L Pore Water QMoore= 2.1×1011÷0.3 = 7×1011L/d = 8100m3/s qMoore= 11cm/d Definition◊ Model ◊ SAB ◊ Conclusions

  16. Waves matter!Surface gravity waves advect pore water constituents into surface waters. Shelf-wide processes are probably larger contributors than near-shore processes. = 8,100m3/s too large? What about bedform effects? Conclusions Definition◊ Model ◊ SAB ◊ Conclusions

  17. Future Work (?) • Wave mixed-zone: other forcing mechanisms transport pore water constituents onto the wave-mixed zone • Density gradients • Pressure gradients • Concentration gradients • Episodic gradients • Numerical model! Definition◊ Model ◊ SAB ◊ Conclusions

  18. Questions?

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