The Influences of Riverine Dissolved Organic Matter in the Gulf of Maine

Wednesday, 17 December 2014
George Aiken, USGS, Boulder, CO, United States, Xiaoyan Cao, Old Dominion University, Gloucester, VA, United States, Jingdong Mao, Old Dominion University, Norfolk, VA, United States, Robert G Spencer, Woods Hole Research Center, Falmouth, MA, United States, William M Balch, Bigelow Lab for Ocean Sciences, East Boothbay, ME, United States and Thomas Gordon Huntington, USGS Maine Water Science Center, Augusta, ME, United States
Dissolved organic matter (DOM) exported from the Gulf of St. Lawrence and by rivers in Maine, Nova Scotia, and New Brunswick is being studied to quantify and characterize optical proxies in the receiving waters of the Gulf of Maine (GoM). Measurements of DOC concentrations, absorption coefficients (254nm, 350 nm and 412 nm), specific ultraviolet absorbance (SUVA254), spectral slope, and fluorescence, and DOC fractionation and isotopic analyses were used to determine the amount and nature of DOM from major inflowing rivers, marine waters, and the GoM. In addition, lignin phenols, 14C-age, 13C-NMR and FTICR-MS analyses were performed on the hydrophobic (HPOA) and transphilic organic acid fractions of the DOM isolated using XAD resins for a smaller subset of samples from the Penobscot River, Penobscot Bay, GoM waters in the Eastern Maine Coastal Current (EMCC), a sample from the eastern portion of the GoM (Scotian Shelf waters), and the Pacific Ocean. These samples provide detailed DOM compositional data in support of the more easily collected concentration and optical data obtained from discrete samples, optical data obtained by in situ glider, and remotely sensed satellite observations. Optical measurements, 13C-NMR, and lignin phenol analyses showed that DOM associated with inflowing rivers to the GoM is rich in aromatic compounds resulting in a large flux of terrestrially derived chromophoric DOM (CDOM). As a result, GoM DOM is more aromatic and younger than open ocean samples collected from the Sargasso Sea and from the Pacific Ocean near Hawaii. This observation is consistent with isotopic data that indicated δ 13C values for the HPOA fractions from the Gulf samples (δ 13C= -27‰ and -25‰) were considerably depleted in comparison to the whole DOM sample (δ 13C = -19‰; which also includes algal-produced DOM) and are more similar to those from the terrestrial sources. Samples from the EMCC were the most heavily influenced by terrestrial sources. While NMR analyses indicated decreases in the aromaticity of the HPOA fractions moving from the rivers to the open ocean, NMR signals associated with carboxyl-rich alicyclic organic matter were observed for all samples. Results from this study are being used to develop relationships for predicting DOC concentration in the GoM from remotely sensed, satellite optical data.