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 (similar to 44-47 degrees S), by studying the elemental (organic carbon, total nitrogen), isotopic (delta C-13, delta N-15), 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, delta C-13, and delta N-15 from organic matter were 0.127 +/- 0.010, -19.8 +/- 0.3 parts per thousand, and 9.9 +/- 0.5 parts per thousand A for autochthonous (marine) sources and 0.040 +/- 0.018, -29.3 +/- 2.1 parts per thousand, and 0.2 +/- 3.0 parts per thousand 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 similar to 4280 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) ton yr(-1), which corresponds to an assimilation rate of CO2 by marine photosynthesis between 0.06 and 0.23 x 10(6) ton yr(-1). This rate suggests that the entire fjord system of Patagonia, which covers an area of similar to 240,000 km(2), may represent a potentially important region for the global burial of marine organic matter and the sequestration of atmospheric CO2. (C) 2010 Elsevier Ltd. All rights reserved.