Laboratory for Environmental and Sedimentary Isotope Geochemistry (LESIG)

San Francisco Bay Marsh Paleohistory

Marshes growing along the shores of the bay also change in response to changing climate and salinity in the bay. In collaboration with Geography Professor Roger Byrne, graduate student Frankie Malamud-Roam and I are analyzing changes in marsh vegetation over the past several millennia using the carbon isotopic composition of sedimentary organic carbon. The carbon isotopic composition of the bulk marsh sediments reflects the relative proportions of C3 and C4 plants growing in the marsh. Plants using the C3 photosynthetic pathway grow in relatively fresh water conditions, while those using the C4 pathway are more adapted to drought and higher salinity conditions. We have cored marshes along a salinity gradient between San Pablo Bay and the Delta. Preliminary results show that over the past 3000 years, there were three general periods of relatively high salinity (low freshwater inflow): 3000 to 2500 years ago, 1700 to 730 years ago, and from about 1930 A.D. to the present. The most recent period of high salinity is primarily due to upstream storage and water diversion within the Sacramento-San Joaquin watershed. These and other records from California indicate that prolonged drought conditions prevailed in California during the Medieval Warm Period (about 1200-800 years ago), and that conditions were on average wetter in California during the Little Ice Age (about 500–100 years ago).

PUBLICATIONS:

Malamud-Roam, K., F. Malamud-Roam, J.Collins, B.L. Ingram and E. Watson (2005) The Historical geography and biogeography of tidal salt marshes in Studies in Avian Biology. Special Volume “Vertebrates of Tidal Marshes: Ecology.Evolution, and Conservation (in press).

Malamud-Roam, F., and Ingram, B.L. (2003) Late Holocene d 13C and pollen records of paleosalinity from Tidal Marshes in the San Francisco Bay Estuary, California . Quaternary Research 62, p. 134-145.

Malamud-Roam, F., and Ingram, B. L. (2001) Developing stable carbon isotopes in the San Francisco estuary marshes as a tool for paleo-ecological reconstructions. J. Coastal Res. V. 17(1), p. 17-29.

Byrne, A.R., Ingram, B. L., Starratt, S., Conrad, M. E., and Malamud-Roam, F. (2001), Carbon isotopes, pollen, and diatom evidence for late Holocene paleoenvironmental change in San Francisco Bay, California, Quaternary Research V. 55, p. 66-76.

Ingram, B. L., De deckker, P., Chivas, A. R., Byrne, A.R., and Conrad, M. E. (1998) Stable isotopes, Sr/Ca and Mg/Ca in biogenic carbonates from Petaluma Marsh, change in Northern California, USA, Geochim. Cosmochim. Acta. V. 62, pp. 3229-3237.