Biogeochemistry of near-bottom suspended particulate matter of the Beaufort Sea shelf (Arctic Ocean): C, N, P, δ 13C and fatty acids

The influence of the Mackenzie River on the source, composition, and distribution of dissolved nutrients and suspended particulate matter (SPM) in near-bottom waters on the Beaufort Sea shelf was determined by measuring particulate organic carbon (POC), particulate nitrogen (PN), particulate phosphorus (PP), elemental ratios (C:N, C:P, N:P), chlorophyll a, bulk δ 13C, and fatty acids. The Mackenzie River had a strong influence on the composition of SPM in near-bottom waters across the entire Canadian Beaufort Sea shelf, including the Amundsen Gulf. This influence was strongest at stations near the river mouth and decreased offshore and northeastward towards the Amundsen Gulf, as seen in SPM elemental concentrations, δ 13C, and terrestrial plant fatty acid markers. Low C:N ratios and high relative levels of odd-numbered carbon and branched-chained fatty acids (bacterial fatty acid markers) indicated that bacteria were an important contributor to organic matter at stations near the river and on the Mackenzie shelf. Fatty acid analysis allowed detection of a phytoplankton sinking event in the Amundsen Gulf in which polyunsaturated fatty acid (PUFA) levels in near-bottom waters significantly increased from June to July. However, this change in PUFA was not associated with any observed temporal change in chlorophyll a, δ 13C, or C:N ratios. These results show that a multiple biomarker approach is necessary in ecosystem studies of dynamic environments such as near-bottom waters or river-influenced shelves.

► Sources of suspended particulate matter in bottom waters of the Beaufort Sea shelf.
► We used multiple-biomarkers: fatty acids, stable isotopes, and elemental ratios.
► Mackenzie River influences the chemistry of bottom waters across the entire shelf.
► Bacteria contribute to organic matter near the river and on the Mackenzie shelf.
► PUFA levels in near-bottom waters of the Amundsen Gulf increased from June to July.