U.S. Department of the Interior U.S. Geological Survey Recent Reductions of Subsidence Rates in the Mississippi River Delta Plain Julie C. Bernier 1 and Robert A. Morton 2 1 U.S. Geological Survey, Florida Integrated Science Center, St. Petersburg, FL 2 U.S. Geological Survey, Florida Integrated Science Center, Austin, TX Introduction Historic Wetland Loss Delta plain: ~ 4000 km 2 land loss since 1930s Objective Identify historic trends and most recent subsidence rates through integration of: tide-gauge records (NOS) relative sea-level rise (RSLR) repeat leveling surveys (NGS) decadal elevation change continuous GPS (CORS) short-term elevation change Integrated Datasets Grand Isle Tide Gauge Mid-1960s to early 1990s: accelerated RSLR Bayou Lafourche Leveling Line : accelerated subsidence Integrated Datasets: Temporal Trends : -3.3 mm/yr : mm/yr : -4.1 mm/yr : -9.6 mm/yr : -11 mm/yr : -4.4 mm/yr : -6.3 mm/yr : -3.5 mm/yr : to mm/yr Delta-Plain Subsidence Rates SourcePeriod Rate (mm/yr) Reference Radiocarbon agesHolocene1-5 Penland et al, 1988; Roberts et al, 1994; Morton et al, 2006 Numerical modelHolocene< 5Meckel et al., 2006 NGS leveling Bayou Lafourche Shinkle & Dokka, NGS leveling Bayou Petit Caillou NGS leveling Mississippi River 18.7 NOS tide gauge Grand Isle Morton and Bernier, this study NGS CORS stations Dokka et al, 2006 Subsidence Mechanisms MechanismScaleReference Compaction Holocene sediments < 5 mm/yr Penland & Ramsey, 1990; Roberts et al., 1994; Meckel et al., 2006 Neotectonics salt tectonics, sediment loading, growth faulting geological time scale Dokka et al., 2006; Gagliano et al., 2003 Fluid withdrawal hydrocarbon production decadal time scale Morton et al., 2006; this study Delta-Plain Oil-and-Gas Fields Bayou Lafourche Leveling Line Highest rates occur over nearby producing fields Conclusions and Implications Decadal-scale acceleration and subsequent deceleration of historic subsidence rates was likely induced by deep subsurface hydrocarbon production Most recent subsidence rates are comparable to rates averaged over geological time scales A better understanding of most recent trends and processes causing subsidence needs to be incorporated into coastal restoration efforts and efforts to model expected impacts of increased RSLR