CHARACTERIZING SEDIMENTATION WITHIN A SOUTHERN CALIFORNIA COASTAL WETLAND DURING AN EXTREME EL NIÑO PERIOD

From the late 1970s to through the 1990s California experienced multiple intense El Niño events, the strongest ones occurring in 1977-1978, 1982-1983, and 1997-1998. In total, this resulted in a multi-decadal period where extreme El Niño events dominated in contrast to the decades before and after this period. This study looked to determine whether estuarine sediments preserved a record of this extreme period and to characterize how sedimentation varied relative to the more quiescent decades before and after this period of extreme events. Our focus was on the Tijuana River Estuary (TRE) a wetland system in Southern California located proximal to the US-Mexico border where extreme sedimentation has been documented for this period. We collected multiple sediment cores from different marsh habitats throughout the estuary. Sediment from cores were analyzed for grain size, organic matter, and elemental composition with ages determined through lead-210 and cesium-137 chronologies. The data suggest temporal changes in sedimentation are characterized by multi-decadal shifts in response to these climatic cycles. The most notable shifts did occur in the 1980s and 1990s during the period where the strong and frequent El Niño events impacted the region. This extreme event period is contrasted with a shift to prolonged drought conditions in the 2000s and 2010s. These data demonstrate that sedimentation in coastal estuaries in southern California were impacted by the extreme El Niño events in the late 1970s, 1980s, and 1990s demonstrating that estuarine sediments serve as a valuable archive to preserve evidence of these events. Further, these results highlight the importance of multiple extreme events compounding to make a prolonged period of extreme sedimentation in an estuary.