Award: OCE-1357411

The overall goal of this project was to better understand the source(s) and the structural origin(s) of the optical properties of marine chromophoric dissolved organic matter (CDOM) within the ocean basins, focusing on North Pacific waters (Station Aloha). The importance of CDOM to environmental and biogeochemical processes is widely recognized. However, the source of CDOM and structural origins of its optical properties are still highly debated for offshore marine waters. While some authors have proposed in situ production of CDOM from marine dissolved or particulate organic matter for offshore marine locales based on correlations between absorption or fluorescence (at a few wavelengths) and apparent oxygen utilization (AOU) without additional chemical tests of structure or sources, others have suggested that offshore marine waters contain a significant "humic-like" terrestrial component based on complete optical measurements and chemical tests. Our prior work in the Equatorial Atlantic Ocean (EAO) which combined acquisition of complete absorption and emission spectra with additional chemical tests (C18 extraction and borohydride reduction), provided strong evidence for a major terrestrial CDOM component that absorbs in the UV and visible but emits in the visible, along with marine CDOM components that absorb and emit primarily in the UV. In this project, the EOA work was extended to the North Pacific Ocean (NPO) (Station ALOHA) to probe very different water masses and examine how the CDOM might vary with water mass origin in particular the North Pacific Intermediate Waters, where past studies have provided potentially conflicting evidence concerning the possible source of the CDOM, ie. terrestrial vs. marine in situ production. As in the EAO, our results suggest the presence of a substantial terrestrial "humic-like" component throughout the water column, along with structurally-dissimilar marine CDOM components that primarily absorb and emit in the ultraviolet. To gain further information on the molecular composition of DOM, high resolution mass spectra obtained with electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS) of untreated and reduced DOM from the EAO and NPO were compared to those of riverine and coastal waters from the Middle Atlantic Bight (MAB) and to reference material from IHSS (SRFA and PLFA). Regardless of location, the open ocean samples always represented a subset of the terrestrially-impacted samples for which the CHO species dominated (>80%) relative to the CHON and CHOS species and were the most affected by chemical reduction thus suggesting a common structural basis for this material independent of location. This project has culminated in the publication of 7 papers and 1 book chapter. Another 6 articles are nearing submission. This work has been presented 18 times at national and international meetings. This effort is about to graduate two PhD students with thesis/dissertations and has provided training for a new PhD student. Last Modified: 03/12/2018 Submitted by: Rossana Del Vecchio