(Non-TEP) Abiotic Particle Formation From Dissolved Organic Matter in Marine Environments: Possible Shunt to the Microbial Loop

University Of Hawaii, Honolulu

Investigators

Abstract

In the ocean autotrophs are the principle particle vector converting dissolved inorganic carbon (DIC) to particulate organic matter (POM). Exudates, principally derived from phytoplankton as dissolved organic matter (DOM), exist in the ocean as labile, semi-labile and refractory DOM. As an alternate particulate pathway the microbial loop represents a process where bacteria are able to metabolize a portion of this DOM and therefore convert DOM to POM. This conversion of DOM to POM has been found to be substantial, providing significant energy for higher trophic levels. Recently, a process has been described where 0.2 um filtered and poisoned river water produced particles abiotically in dark incubations. The analysis of particles and source waters showed that the particles are distinctly different from TEP (transparent exopolymers particles) and were derived from DOM and contained organic components found in living organisms (i.e., DNA, carbohydrates, lipids, proteins). Over the incubation period the rate and magnitude of formation, as well as size, of these abiotic microparticles were similar to bacteria, and carbon-nitrogen ratios suggest they could be nutritionally important. If a similar process occurs in the marine environment it would by-pass the traditional biotic microbial loop in terms of transforming DOM to POM and may constitute an important alternate pathway, especially if labile DOM comprise major components of the abiotic particle formation pathway. However, if the source material of the microparticles are composed primarily of the refractory fraction of the DOM pool then they may provide a poor nutritional source, but may still make a significant contribution to the deep sea carbon flux. The proposed study will examine the abiotic formation of organic particles in two major contrasting ocean environments: the oligotrophic North Pacific near Station ALOHA and the highly productive upwelling zone off the Pacific coast of N. America (cruise of opportunity). Carefully controlled time-series experimental incubations will be conducted with filtered and poisoned surface (1% light level) and deep (~1000 m) seawater to elucidate the formation rate, size, quantity, composition and nutritional quality of abiotically formed particles as well as a determination of source material. Intellectual Merit: The results of this research will provide a first-order global estimate of the magnitude of this process in the sea and its significance relative to the traditional microbial loop pathway. If the abiotic formation of organic particles is a significant process in the sea, then this process could be a significant shunt to the microbial loop and would expand our understanding of particle dynamics in the sea. Broader Impacts: There is a strong educational benefit to these studies. Undergraduate students will be intimately involved in the planning and implementation of this project, and will benefit from exposure to interdisciplinary faculty from UH and other institutions involved with HOTs and other cruises (informal education in the form of dissemination of ideas, techniques and field experience). Project PI Cowen is a faculty member of the Global Environmental Sciences, a rigorous undergraduate science major administered through the Department of Oceanography; it is anticipated that undergraduate participation in this project will lead to at least one student Senior Thesis. Cowen is also involved in Science-Teacher outreach projects and will continue the very successful .Teacher at Sea. outreach program initiated by Cowen as part of another NSF project; this program integrates local teachers and their classrooms into all phases of the research project; in this project we will involve teachers in the local sample collections, incubation experiments and analyses. Teachers. students will be invited to UH ships and to analytical facilities for examination of project samples.