Spatial and vertical variability of dissolved carbohydrate species in the northern Gulf of Mexico following the Deepwater Horizon oil spill, 2010–2011

Abstract

Seawater samples were collected from the northern Gulf of Mexico during October 2010 and October 2011 to examine the abundance, spatial and vertical distributions, and partitioning of carbohydrates (CHO) among monosaccharides (MCHO), HCl-hydrolysable polysaccharides (HCl-PCHO), and dilute-HCl-resistant polysaccharides (HR-PCHO). Concentrations of total dissolved carbohydrates (TCHO) and other CHO species in surface waters decreased in general from shelf to basin regions, ranging from 4 to 27μM-C for MCHO, 4 to 34μM-C for HCl-PCHO, and from undetectable (<0.8μM-C) to 42μM-C for HR-PCHO. On average, PCHO accounted for up to 72±12% of TCHO in shallow waters, but fell to 59±27% in deeper waters, showing a production of CHO in the upper water column and active transformation between PCHO and MCHO during the transport in the water column. HR-PCHO consisted a considerable fraction (36±23%) of the TCHO and correlated significantly with the percentage of TCHO in the bulk DOC, indicating the need for quantifying the HR-PCHO species and its role in the biogeochemical cycling of dissolved organic matter (DOM) in marine environments. Two types of vertical distributions were found for CHO species in the northern Gulf of Mexico: one showing a decrease in CHO concentrations with depth as also reported in previous studies and the other showing an increase in both CHO concentrations and TCHO/DOC ratios with depth especially at stations influenced by Macondo oil. Elevated deepwater HR-PCHO abundance and TCHO/DOC ratio at some stations likely resulted from enhanced microbial production of exopolysaccharides due to the presence of oil components after the Deepwater Horizon oil spill. Our results here demonstrated the importance of dilute-HCl-resistant PCHO species in marine environments and the influence of oil spill and subsequent microbial processes on the biogeochemical cycling of DOM and CHO species in the northern Gulf of Mexico.