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Anner Paldor, Einat Aharonov , Oded Katz GSA annual meeting 2018, Indianapolis

Thermo- haline circulation in confined coastal aquifers and resulting deep submarine groundwater discharge. Anner Paldor, Einat Aharonov , Oded Katz GSA annual meeting 2018, Indianapolis. In unconfined aquifers, Deep SGD of pure seawater arises from geothermal convection ( Wilson, 2005). Z.

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Anner Paldor, Einat Aharonov , Oded Katz GSA annual meeting 2018, Indianapolis

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  1. Thermo-haline circulation in confined coastal aquifers and resulting deep submarine groundwater discharge Anner Paldor, EinatAharonov, Oded Katz GSA annual meeting 2018, Indianapolis

  2. In unconfined aquifers, Deep SGD of pure seawater arises from geothermal convection (Wilson, 2005)

  3. Z Y X Following Phillips (2009): Theory: tilted isopycnals in a confined aquifer provoke circulation. Flow velocity is linearly related to temperatureandsalinity horizontal gradients

  4. Case study for DSGD: Achziv Canyon

  5. Two key features of the geological section: (1) Flexural structure; (2) Outcropping of JG aquifer in the Aczhiv Canyon

  6. FEFLOW model based on the geological section

  7. Confinement End-member 1: Freshwater DSGD 50 0 100 Z [m] 0 Salinity [%] -600 -1200 -1800 33000 27000 21000 15000 9000 3000 X [m] Isotherms Streamlines

  8. Confinement End-member 2: Saltwater DSGD 50 0 100 Z [m] 0 Salinity [%] -600 -1200 -1800 33000 27000 21000 15000 9000 3000 X [m] Isotherms Streamlines

  9. Confinement Intermediate case: Saline DSGD 50 0 100 Z [m] 0 Salinity [%] -600 -1200 -1800 33000 27000 21000 15000 9000 3000 X [m] Isotherms Streamlines

  10. Seepage velocity is expected to increase w. increasing temperature &salinity horizontal differences

  11. Instead - Increasing global gradients in T&S decreases seepage.

  12. Increased global salinity difference between ocean and land causes decreased local salinity gradients. Z [m] 0 -600 -1200 50 0 100 Seawater salinity = 30 g/l Salinity [%] -1800 33000 27000 21000 15000 9000 3000 X [m] Z [m] 0 -600 -1200 Seawater salinity = 39 g/l -1800 33000 27000 21000 15000 9000 3000 X [m]

  13. TAKE HOME MESSAGES • at the nearshore scale SGD in unconfined aquifers results from elevated heads and dispersive mixing of fresh groundwater and seawater along the interface. • deep SGD in unconfined aquifers, occurs purely from geothermal convection, in which case seeping water is 100% SW. • In confined aquifers that outcrop several km offshore, the two mechanisms combine to produce saline deep SGD from thermo-haline convection. • It is not the general salinity/temperature differences in the system that dictate seepage velocity, but rather the local gradients that drive circulation.

  14. Thank you! Taken from Moosdorf and Oehler[2017]

  15. References • Moosdorf, N., & Oehler, T. (2017). Societal use of fresh submarine groundwater discharge: An overlooked water resource. Earth-Science Reviews, 171(April), 338–348. https://doi.org/10.1016/j.earscirev.2017.06.006 • Phillips, O. M. (2009). Geological fluid dynamics: Sub-surface flow and reactions. Geological Fluid Dynamics: Sub-Surface Flow and Reactions. https://doi.org/10.1017/CBO9780511807473 • Wilson, A. M. (2005). Fresh and saline groundwater discharge to the ocean: A regional perspective. Water Resources Research, 41(2), 1–11. https://doi.org/10.1029/2004WR003399

  16. Density [Kg m-3]

  17. Increasing land temperature makes the land water lighter  the interface is pushed landwards local gradients decrease Land temperature = 17o Land temperature = 30o (Seawater Temperature = 14o)

  18. Hydrographic surveying of seawater where DSGD is predicted by the modeling Area of predicted DSGD

  19. Salinity anomaly profile along the canyon shows low-salinity plume Winter 16

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