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

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 (δ13C, δ15N), 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, δ13C, and δ15N 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‰, and 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 13–96% (average 61%) of the organic carbon pool of surface sediments. Integrated regional calculations for the inner fjord system of northern Patagonia covered in this study, which encompasses an area of ∼4280 km2, suggest that carbon accumulation may account for between 2.3 and 7.8×104 ton C yr−1. This represents a storage capacity of marine-derived carbon between 1.8 and 6.2×104 ton yr−1, which corresponds to an assimilation rate of CO2 by marine photosynthesis between 0.06 and 0.23×106 ton yr−1. This rate suggests that the entire fjord system of Patagonia, which covers an area of ∼240,000 km2, may represent a potentially important region for the global burial of marine organic matter and the sequestration of atmospheric CO2.