Compositional heterogeneity within oceanic POM : a study using flow cytometry and mass spectrometry

Abstract

This thesis applied direct temperature-resolved mass spectrometry (DT-MS), flow cytometry, and multivariate statistics to the study of marine particulate organic matter (POM) collected from the North Atlantic. DT-MS is an important asset to marine organic geochemistry as a single two minute analysis (with 16 eV, EI+ ionization) provides information on polysaccharides, proteins, and lipids within concentrated and desalted samples. Although the molecularlevel information obtained with DT -MS is less detailed than traditional analyses of specific compound classes, DT-MS can act as a useful molecular-level screening technique (as illustrated in this thesis), indicating what samples and compound classes to investigate more thoroughly. In addition to its rapidity, DT-MS only reqires microgram quantities of sample. This sensitivity permits t..l-J.e coupling of DT -MS and preporative flow cytometry. In this thesis, preparative flow cytometry was used to isolate "phytoplankton" and "detritus" (i.e., non-phytoplankton particles) in 2~53 !liD POM. The molecular-level differences between and within small-particle POM (<53 !liD), large-particle POM (>53 !liD), "phytoplankton" and "detritus" were explored using DT -MS and discriminant analysis. For POM collected from the Mid-Atlantic Bight and from Great Harbor, Woods Hole, MA, small-particle POM contained more phytoplankton chemical characteristics than large-particle POM. In Great Harbor, the molecular-level characteristics of large-particle POM indicated a significant grazer biomass component. On the MAB (in March 1996), the large-particle POM appeared more phytodetrital. "Phytoplankton" was enriched in protein, chlorophyll and lipids as compared to "detritus," which was enriched in selected polysaccharides. As the polysaccharide composition of POM subclasses was a major source of variation, polysaccharides in selected samples were further studied using ammonia and deuterated ammonia CI+ DT-MS. Principal component analysis of the resulting NH3-CI+ spectra indicated that the majority of polysaccharide variation in the selected samples could be explained by a component that appeared related to the degree of degradation of the organic matter. The results from this thesis, coupled with existing work on particulate and dissolved organic matter, were used to support a modified "size-reactivity continuum model" of organic matter cycling.