Submarine (or Sublacustrine) Ground-Water Discharge changes during Last Glacial Maximum along PEP III
by
Hugues Faure
INQUA Carbon Comm., IGCP-459/CHANGES, Université de la Méditerranée, Marseille, France
Coauthors: Louis Francois (LPAP, Université de Liège, Belgium), Jean-Luc Probst (LMTG, CNRS/Université Paul Sabatier, Toulouse, France), Robert C. Walter (CICESE/Geologia, San Diego, CA, USA), Richard T. Buffler (IG, University of Texas at Austin, USA), Mireille Guillaume (LBIMM, MNHN, Paris, France), Henrich Bruggemann (DMB, University of Groningen, The Netherlands), Douglas R. Grant (TGI, Ottawa, Canada), Liliane Faure (CEREGE, CNRS, Aix-en-Provence, France), Jonathan M. Adams (University of Rhode Island, USA)

Submarine Ground-Water Discharge (SGWD) is an interesting component of the global water cycle that may or may not change with climate variability. The quantification of the SGWD is difficult and still poorly monitored, though rapidly progressing (Burnet et al., 2000). Here we propose to use Darcy's law to compare the effect of glacial/interglacial lake-level or sea-level changes on SGWD along PEP-III. In the case of vast aquifers, residence times and rates of water flow are such that the SGWD depends more on base level changes than on climatic recharge of the aquifer. The present-day springs that appear in Sahara oases when Holocene lakes dried-up, demonstrate the independence of sublacustrine groundwater discharge (SGWD) from present-day climate and its plurimillenium persistence. For each latitudinal position the SGWD depends on several local or regional hydrological parameters related to lithology, topography-bathymetry, tectonics. Most of these factors are relatively unchanged at the glacial/interglacial-time scale, while the base level, as lake-level or sea-level suffers rapid changes related to local or global water balance (evaporation/rainfall water budget or global ice/ocean water budget). For these reasons we can consider (as a first approximation) that all parameters acting in Darcy's law are unchanged (transmissivity , hydraulic conductivity, porosity), and that the only variable introduced by lake or sea-level changes are hydraulic head and flow path length (sea water depth and distance from initial shoreline). The main controlling factor of the SGWD flow change will be the slope of the new emerged lake or sea bottom. In the case of continental shelves during glacial sea-level fall, emerged submarine springs and seapage flow will be enhanced when the new slope increases the water head. A main parameter of the glacial SGWD change at LGM is the width of the continental shelf from present shore to the 120 m isobath representing the approximative glacial shoreline.

The glacial/interglacial SGWD changes has many implications: for geochemical budget, nutrients and ecology, as well as for human migration out of Africa during Pleistocene and for water availability on the coastal zone for human needs in the future.

References Burnett R., Kontar E., Buddemeier R. (2000). Magnitude of Submarine Groundwater Discharge and its Influence on Coastal Oceanographic Processes. SCOR Working-Group 112: Annual Report (September, 2000) Faure H., Walter R. C. and Grant D. R. . The coastal oasis : Ice Age springs on emerged continental shelves, Global and Planetary Change, Elsevier, (in press, 2001).

Date received: May 30, 2001

Copyright © 2001 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # cahr-26.