Abstracts Biological Sciences

The distribution and partitioning of dissolved organic matter off the Oregon Coast : a first look

by Jon K. Hill

The purpose of this thesis is to provide a first look at the spatial and temporal distributions of dissolved organic material (DOM) off the Oregon coast of North America. While this paper is not a comprehensive examination of these distributions, several patterns are identified as promising candidates for continued research. Most of the data presented was acquired during a strong El Nino event. The DOM data is presented as dissolved organic carbon (DOC) and dissolved organic nitrogen (DON) and is accompanied by temperature, salinity, nitrate plus nitrite (N+N), ammonium, silicate, chlorophyll, total organic carbon (TOC), particulate organic carbon (POC), total nitrogen (TN), total organic nitrogen (TON), and zooplankton biomass measurements. During July 1997, we examined the distribution of DOM in the surface waters off the Oregon and Southern Washington coasts. Eleven east-west transects were sampled from nearshore waters to 190km offshore. DOC concentrations as high as 180 iM were observed in the Columbia River plume. Patterns in the DOC distribution were also associated with upwelling regions, an offshore coastal jet, and an oligotrophic water mass in the northern portion of our study area. Beginning with the July 1997 study and continuing until July 1998, samples were collected on weekly and seasonal time scales at station NH-05, located 9km offshore from Newport, Oregon. Various problems have limited our seasonal comparisons, but we were able to collect high quality data depicting the changes in organic matter partitioning during a phytoplankton bloom and its decline during a two month period from mid-July through mid-September in 1997. During the bloom, POC increased dramatically, but DOC decreased. Possible explanations for this decrease and for changes in the C/N ratio of the DOM during the bloom are explored. Suggestions for future research are presented in the final chapter.