Estimation of the Role of Natural Climatic Trends and Local Depositional Conditions on Peat Formation in the Sacramento-San Joaquin Delta, Based on Palynological and Paleomagnetic Data

Abstract:

The Sacramento-San Joaquin Delta of California is a critical ecosystem for reconstructing natural and anthropogenic impacts on environmental conditions, understanding stream development, and assessing the fate of artificial levees. Peat formation is influenced by all these processes and represents the combined effects of climatic and hydrographic evolution.

In the framework of Project REPEAT, we studied three peat cores using palynological and paleomagnetic methods, focusing on the influence of the general climatic setting and postglacial sea-level changes during the last 6500 years on the process of peat formation and the interplay of local environmental and hydrological conditions. In this report we consider the hypothesis that peat accretion was closely related to general climatic trends, as reflected in atmospheric carbon storage in the Delta sediments, and to general sea-level fluctuation.

Based on the fact that the bulk density of the peat is closely correlated with organic carbon content, we examine: 1) whether the pollen concentration is highest when the organic carbon content in the cores is a maximum and corresponds to the warmest episodes; 2) whether organic content is inversely related to the lithic content as determined by paleomagnetic measurements; 3) whether a salinity index based on pollen criteria is highest during the highest stands of sea level; 4) and whether the C3/C4 plant index is a good measure of the carbon content of the peat.