Investigating Source(s) and Structure of Chromophoric Dissolved Organic Matter (CDOM) in the North Pacific Ocean Using Optical Spectroscopy and Chemical Properties.
Carmen Marie Cartisano, Univeristy of Maryland College Park, Chemistry and Biochemistry, College Park, MD, United States, Marla Bianca, University of Maryland College Park, Chemistry and Biochemistry, College Park, MD, United States, Rossana Del Vecchio, University of Maryland, ESSIC, College Park, MD, United States and Neil V Blough, Univ Maryland, College Park, MD, United States
Abstract:
The source of CDOM in the open ocean remains uncertain. Past research, using different combinations of single wavelength optical measurements and correlations with properties such as apparent oxygen utilization, has led some researchers to conclude that the majority of ocean CDOM is produced in-situ from marine source material. More detailed optical and chemical measurements have instead allowed other researchers to conclude that oceanic CDOM is mainly terrestrial in origin or a combination of terrestrial and marine material. This research aims to more fully investigate the source(s) and structure of CDOM in the open oceans though the use of optical properties and chemical tests, including reduction with NaBH4, which is used to selectively reduce carbonyl containing groups, and pH titrations, which can test for the presence of phenolic and carboxylic acid moieties. The primary area of focus is on samples from Station ALOHA encompassing depths from the surface to 4500 meters. Preliminary optical properties (including the spectral dependence of absorption, fluorescence emission and apparent fluorescence quantum yields) along the entire water column indicate that there are some minor differences with depth, and no unique peaks or bands present at any depth. In addition, CDOM optical properties are very similar to reference humic substances and terrigenous CDOM. The changes in optical properties upon NaBH4 reduction and pH titration are also similar to those observed in humic and fulvic acid standards. Combining optical properties and chemical tests can provide more reliable insights into the source(s) and structure of CDOM in the North Pacific Ocean. Further results and their possible implications will be discussed.
