@article { ISI:000301669200001,
	title = {Radiocarbon and stable-isotope geochemistry of organic and inorganic carbon in Lake Superior},
	journal = {GLOBAL BIOGEOCHEMICAL CYCLES},
	volume = {26},
	year = {2012},
	month = {MAR 14},
	type = {Article},
	abstract = {We present a lake-wide investigation of Lake Superior carbon and organic matter biogeochemistry using radiocarbon, stable isotope, and carbon concentrations. Dissolved inorganic carbon (DIC) abundance in the lake was 121-122 Tg C, with offshore concentration and delta C-13 values being laterally homogenous and tightly coupled to the physical and thermal regime and biochemical processes. Offshore Delta C-14 of DIC (50-65\%) exhibited lateral homogeneity and was more C-14 enriched than co-occurring atmospheric CO2 (similar to 38\%); nearshore Delta C-14 of DIC (36-38\%) was similar to atmospheric CO2. Dissolved organic carbon (DOC) abundance was 14.2-16.4 Tg C. DOC{\textquoteright}s concentration and delta C-13 were homogenous in June (mixed lake), but varied laterally during August (stratification) possibly due to spatial differences in lake productivity. Throughout sampling, DOC had modern radiocarbon values (14-58\%) indicating a semilabile nature with a turnover time of <= 60 years. Lake particulate organic carbon (POC, 0.9-1.3 Tg C) was consistently C-13 depleted relative to DOC. The delta N-15 of epilimnetic particulate organic nitrogen shifted to more negative values during stratification possibly indicating greater use of nitrate (rather than ammonium) by phytoplankton in August. POC{\textquoteright}s radiocarbon was spatially heterogeneous (Delta C-14 range: 58\% to - 303\%), and generally C-14 depleted relative to DOC and DIC. POC C-14 depletion could not be accounted for by black carbon in the lake but, because of its spatial and temporal distribution, is attributed to sediment resuspension. The presence of old POC within the epilimnion of the open lake indicates possible benthic-pelagic coupling in the lake{\textquoteright}s organic carbon cycle; the ultimate fate of this old POC bears further investigation.},
	issn = {0886-6236},
	doi = {10.1029/2011GB004132},
	author = {Zigah, Prosper K. and Minor, Elizabeth C. and Werne, Josef P.}
}
@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}
}
