@article { ISI:000310472600012,
	title = {An isotopic (Delta C-14, delta C-13, and delta N-15) investigation of the composition of particulate organic matter and zooplankton food sources in Lake Superior and across a size-gradient of aquatic systems},
	journal = {BIOGEOSCIENCES},
	volume = {9},
	number = {{9}},
	year = {2012},
	pages = {3663-3678},
	type = {Article},
	abstract = {Food webs in aquatic systems can be supported both by carbon from recent local primary productivity and by carbon subsidies, such as material from terrestrial ecosystems, or past in situ primary productivity. The importance of these subsidies to respiration and biomass production remains a topic of debate. While some studies have reported that terrigenous organic carbon supports disproportionately high zooplankton production, others have suggested that phytoplankton preferentially support zooplankton production in aquatic ecosystems. Here we apply natural abundance radiocarbon (Delta C-14) and stable isotope (delta C-13, delta N-15) analyses to show that zooplankton in Lake Superior selectively incorporate recently fixed, locally produced (autochthonous) organic carbon even though other carbon sources are readily available. Estimates from Bayesian isotopic modeling based on Delta C-14 and delta C-13 values show that the average lake-wide median contributions of recent in-lake primary production and terrestrial, sedimentary, and bacterial organic carbon to the bulk POM in Lake Superior were 58\%, 5\%, 33\%, and 3\%, respectively. However, isotopic modeling estimates also show that recent in situ production contributed a disproportionately large amount (median, 91\%) of the carbon in mesozooplankton biomass in Lake Superior. Although terrigenous organic carbon and old organic carbon from resuspended sediments were significant portions (median, 38\%) of the available basal food resources, these contributed only a small amount to mesozooplankton biomass. Comparison of zooplankton food sources based on their radiocarbon composition showed that terrigenous organic carbon was relatively more important in rivers and small lakes, and the proportion of terrestrially derived material used by zooplankton correlated with the hydrologic residence time and the ratio of basin area to water surface area.},
	issn = {1726-4170},
	doi = {10.5194/bg-9-3663-2012},
	author = {Zigah, P. K. and Minor, E. C. and Werne, J. P. and McCallister, S. Leigh}
}
@article { ISI:000290678100009,
	title = {Radiocarbon and stable carbon isotopic insights into provenance and cycling of carbon in Lake Superior},
	journal = {LIMNOLOGY AND OCEANOGRAPHY},
	volume = {56},
	number = {{3}},
	year = {2011},
	month = {MAY},
	pages = {867-886},
	type = {Article},
	abstract = {This study applies radiocarbon and stable carbon isotopic distributions to investigate carbon sources and cycling within Lake Superior. We report the radiocarbon (Delta C-14) and stable carbon isotope (delta C-13) values and the carbon concentrations within dissolved organic carbon (DOC), particulate organic carbon (POC), and dissolved inorganic carbon (DIC) in the lake{\textquoteright}s western basin water column. Samples were taken during spring mixing and late-summer thermal stratification over a 2-yr period (2007-2009). Distinct processes operating in the surface (photosynthesis) and deep waters (sediment resuspension and pore-water intrusion) control the relative contribution of modern and ancient DOC and POC in the water column. The terrigenous carbon input to the open lake POC varied from 13\% +/- 4\% during late summer stratification to 9\% +/- 3\% during spring mixing, with most of the terrestrial carbon being C-14-enriched (modern). The DIC reservoir cycles rapidly, with a bulk Delta C-14(DIC) value that records atmospheric radiocarbon levels from 3 yr prior to sampling. The DOC pool recycles on a longer time scale than does the DIC, with a DOC residence time of <= 60 yr. The suspended POC was in most cases older than co-occurring DOC, most likely as a result of resuspension of lake sediments.},
	issn = {0024-3590},
	doi = {10.4319/lo.2011.56.3.0867},
	author = {Zigah, Prosper K. and Minor, Elizabeth C. and Werne, Josef P. and McCallister, S. Leigh}
}
