Sources and distribution of organic matter in northern Patagonia fjords, Chile (∼44–47°S): A multi-tracer approach for carbon cycling assessment

Abstract

We investigated the provenance of organic matter in the inner fjord area of northern Patagonia, Chile (~44-47° S), by studying the elemental (organic carbon, total nitrogen), isotopic (δ 13 C, δ 15 N), and biomarker (n-alkanoic acids from vascular plant waxes) composition of surface sediments as well as local marine and terrestrial organic matter.Average end-member values of N/C, δ 13 C, and δ 15 N from organic matter were 0.127 ± 0.010, -19.8 ± 0.3‰, and 9.9 ± 0.5‰ for autochthonous (marine) sources and 0.040 ± 0.018, -29.3 ± 2.1‰, 0.2 ± 3.0‰ for allochthonous (terrestrial) sources. Using a mixing equation based on these two end-members, we calculated the relative contribution of marine and terrestrial organic carbon from the open ocean to the heads of fjords close to river outlets. The input of marine-derived organic carbon varied widely and accounted for 13 to 96% (average 61%) of the organic carbon pool of surface sediments. Integrated regional calculations for the inner fjord system of northern Patagonia, which encompasses an area of ~ 4,280 km 2 , suggest that carbon accumulation may account for between 2.3 and 7.8 x 10 4 ton C yr -1 . This represents a storage capacity of marine-derived carbon between 1.8 and 6.2 x 10 4 tons yr -1 , which corresponds to an assimilation rate of CO 2 by marine photosynthesis between 0.06 and 0.23 x 10 6 tons yr -1 . This rate suggests that the entire fjord system of Patagonia, which covers an area of ~ 240,000 km 2 , may represent a potentially important region for the global burial of marine organic matter and the sequestration of atmospheric CO 2 .

Geochemistry of surface sediments from the fjords of Northern Chilean Patagonia (44–47°S): Spatial variability and implications for paleoclimate reconstructions

“…The precision, calculated by replicate analysis of the internal standard, is 0.03 ‰ for δ 13 C and 0.08 ‰ for δ 15 N. Some of the bulk organic geochemical results used in this study were previously reported in Sepúlveda et al (2011). …”

“…The N/C value obtained on the river samples is very similar to the average of the seven soil samples (N/C = 0.0680) but it is preferred because it is known that N/C ratios are affected by transport in rivers and by weathering in soil profiles (Bertrand et al, 2010). Although bulk sedimentary δ 13 C data can also be used to calculate F terr (e.g., Sepúlveda et al, 2011), we prefer using the N/C data because δ 13 C values of marine organic matter are affected by several processes such as changes in productivity (e.g., Bickert, 2006). The values of F terr obtained using the two methods are highly positively correlated (r=0.94, p<0.0001).…”

“…In the modern environment, terrestrial input/river discharge clearly affects (1) surface salinities (Dávila et al 2002) and (2) the proportion of terrestrial organic carbon in surface sediments (Sepúlveda et al, 2011, Silva et al, 2011. These two variables were therefore used to define a Terrestrial Index (TI), which serves as a reference to evaluate relations between inorganic geochemical results and the energy of the terrestrial river supply.…”

Geochemical characterisation of northern Norwegian fjord surface sediments: A baseline for further paleo-environmental investigations

“…Studies from fjords in Chile (Bertrand et al, 2012;Sepúlveda et al, 2011;Silva et al, 2011), New Zealand (Hinojosa et al, 2014;Knudson et al, 2011;Smith et al, 2015), east Greenland (Andrews and Vogt, 2014) and Svalbard (Winkelmann and Knies, 2005) reported a significant influence of freshwater inflow on their geochemical composition and suggest a common decreasing gradient of terrigenous-derived organic-and inorganic material from the inner fjords towards the open ocean. In contrast to these findings, Munoz and Wellner (2016) found terrigenous deposits to occur predominantly in the outer bay of an Antarctic fjord.…”

“…Fjords comprise a substantial part of the coastal environments and are important sites for carbon burial due to their high inorganic and organic sedimentation rates (Hedges et al, 1997;Knies, 2005;Knudson et al, 2011;Ludwig et al, 1996;Raymond and Bauer, 2001;Sepúlveda et al, 2011;Smith et al, 2015;St-Onge and Hillaire-Marcel, 2001;Syvitski et al, 1987) but only a very few studies exist using surface sediments to investigate modern fjord environmental settings. Studies from fjords in Chile (Bertrand et al, 2012;Sepúlveda et al, 2011;Silva et al, 2011), New Zealand (Hinojosa et al, 2014;Knudson et al, 2011;Smith et al, 2015), east Greenland (Andrews and Vogt, 2014) and Svalbard (Winkelmann and Knies, 2005) reported a significant influence of freshwater inflow on their geochemical composition and suggest a common decreasing gradient of terrigenous-derived organic-and inorganic material from the inner fjords towards the open ocean.…”