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 (~ 13C, ~ 15N), 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, ~ 13C, and ~ 15N 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 ~4280km 2, suggest that carbon accumulation may account for between 2.3 and 7.8×10 4tonCyr -1. This represents a storage capacity of marine-derived carbon between 1.8 and 6.2×10 4tonyr -1, which corresponds to an assimilation rate of CO 2 by marine photosynthesis between 0.06 and 0.23×10 6tonyr -1. This rate suggests that the entire fjord system of Patagonia, which covers an area of ~240,000km 2, may represent a potentially important region for the global burial of marine organic matter and the sequestration of atmospheric CO 2. © 2010 Elsevier Ltd.