Carbon sources in suspended particles and surface sediments from the Beaufort Sea revealed by molecular lipid biomarkers and compound-specific isotope analysis

Abstract

Molecular lipid biomarkers (hydrocarbons, alcohols, sterols and fatty acids) and compound-specific isotope analysis of suspended particulate organic matter (SPM) and surface sediments of the Mackenzie Shelf and slope (southeast Beaufort Sea, Arctic Ocean) were studied in summer 2009. The concentrations of the molecular lipid markers, characteristic of known organic matter sources, were grouped and used as proxies to evaluate the relative importance of fresh algal, detrital algal, fossil, C₃ terrestrial plants, bacterial and zooplankton material in the organic matter (OM) of this area. Fossil and detrital algal contributions were the major fractions of the freshwater SPM from the Mackenzie River with ~34% each of the total molecular biomarkers. Fresh algal, C₃ terrestrial, bacterial and zooplanktonic components represented much lower percentages, 17, 10, 4 and <1%, respectively. In marine SPM from the Mackenzie slope, the major contributions were fresh and detrital algal components (>80%), with a minor contribution of fossil and C₃ terrestrial biomarkers. Characterization of the sediments revealed a major sink of refractory algal material mixed with some fresh algal material, fossil hydrocarbons and a small input of C₃ terrestrial sources. In particular, the sediments from the shelf and at the mouth of the Amundsen Gulf presented the highest contribution of detrital algal material (60–75%), whereas those from the slope contained the highest proportion of fossil (40%) and C₃ terrestrial plant material (10%). Overall, considering that the detrital algal material is marine derived, autochthonous sources contributed more than allochthonous sources to the OM lipid pool. Using the ratio of an allochthonous biomarker (normalized to total organic carbon, TOC) found in the sediments to those measured at the river mouth water, we estimated that the fraction of terrestrial material preserved in the sediments accounted for 30–40% of the total carbon in the inner shelf sediments, 17% in the outer shelf and Amundsen Gulf and up to 25% in the slope sediments. These estimates are low compared to other studies conducted 5–20 yr earlier, and they support the increase in primary production during the last decade mainly because of the increase in the number of ice-free days and due to the strength and persistence of winds favouring upwelling

Multivariate benthic ecosystem functioning in the Arctic – benthic fluxes explained by environmental parameters in the southeastern Beaufort Sea

“…The lower Mackenzie Shelf sites (site 260 and 680) form the next group, which finally can be separated from the Cape Bathurst polynya sites (110 and 140) and the deeper Beaufort slope sites (235 and 345). This spatial pattern is confirmed by lipid biomarker analyses conducted on sediment samples collected from some of our sites (Rontani et al, 2012;Tolosa et al, 2013). For example, particularly high concentrations of autochthonous fresh material derived from diatom production were found at site 390, with decreasing concentrations farther north from the Mackenzie Delta (Rontani et al, 2012;Tolosa et al, 2013).…”

Seasonal survey of the composition and degradation state of particulate organic matter in the Rhône River using lipid tracers

“…The TAR (AL) in our samples is always above 1, and clearly indicates a strong terrigenous contribution to the suspended particulate matter found in the lower Rhône. The Average Chain Length of nalkanols, a proxy positively correlated to the abundance of higher plant debris (Van Dongen et al, 2008), ranged from 26 to 22 across all samples, also attesting to the strong contribution of terrestrial vascular plants. The long-chain evennumbered n-alkanol profiles show a strong contribution of C 22 and C 28 n-alkanols.…”

“…While autoxidation processes appeared to play only a minor role during the degradation of sitosterol in the cold Mackenzie River (Arctic) (Rontani et al, 2014b), it is worth questioning the role that temperature plays in OM degradation, and wondering if it influences one degradation process over the others: do the temperatures found in the Rhône River, warmer than those of the Mackenzie, favor autoxidation? However, the low autoxidation state in the Mackenzie River could also be attributed to the presence of significant proportions of fresh sitosterol-producing phytoplanktonic species (Tolosa et al, 2013). Due to the lack of specificity of this sterol, it is clear that identification of autoxidation products of more specific tracers (such as betulin or amyrins) is absolutely necessary to monitor the degradation of higher plant material in rivers and oceans more precisely.…”

“…Here we used the TAR (AL) as calculated by Van Dongen et al (2008) for nalkanols: (C 26 +C 28 )/(C 16 +C 18 ). The TAR (AL) in our samples is always above 1, and clearly indicates a strong terrigenous contribution to the suspended particulate matter found in the lower Rhône.…”

“…In comparison with bulk geochemical analyses, where δ 13 C terrestrial end-member determination is precarious, δ 13 C signatures of organic matter at a molecular level can be more specific (Tolosa et al, 2013). Unfortunately, carbon isotopic data in freshwater ecosystems is not always source-specific, because freshwater phytoplankton and terrestrial plants can often produce similar δ 13 C signatures (Cloern et al, 2002).…”