@article {kruger_sediment_2022,
	title = {Sediment organic matter compositional changes in a tropical rift lake as a function of water depth and distance from shore},
	journal = {Organic Geochemistry},
	year = {2022},
	month = {11/2022},
	pages = {104527},
	abstract = {Little is known of modern carbon cycling in East African rift lakes. These large tropical systems with anoxic bottom waters can act as test cases for carbon cycling under future climate change scenarios as well as key sediment repositories for paleolimnology studies and fossil fuel generation. This study is the first to combine stable and radiocarbon isotopic information on bulk sediment and biomarkers (n-alcohols) in an African rift lake by investigating surface sediments collected on a nearshore to offshore transect in northern Lake Malawi. This study is also the first to report radiocarbon content in water column particulate organic, dissolved organic and inorganic carbon from an African rift lake. General surface-sediment trends with increasing water depth were an increase in \%TOC, and decreases in grain size, δ13C and C/N. Carbon radioisotope analyses showed that bulk sedimentary organic matter was modern across the transect. Biomarker data indicated a primarily aquatic origin for sedimentary organic matter at offshore sites; terrestrial material dominated the n-alcohol signature closest to the shore. Protokerogen stable isotope signatures were similar, and radiocarbon was somewhat depleted relative to bulk sediment organic matter. As compared to bulk organic matter, lipids were 13C-depleted throughout the sampling transect and 14C-depleted at the most nearshore location. This indicates an aged lipid carbon source and likely significant diagenetic alteration of modern sources prior to deposition in nearshore sediments, perhaps a combination of soil erosion, in-river processing, sediment resuspension and mobilization, and preferential degradation of younger organic matter in the oxic nearshore region.},
	keywords = {-Alcohols, C/N ratio, carbon isotopes, Lake Malawi, Protokerogen, radiocarbon, Sedimentary organic carbon},
	issn = {0146-6380},
	doi = {10.1016/j.orggeochem.2022.104527},
	url = {https://www.sciencedirect.com/science/article/pii/S0146638022001619},
	author = {Kruger, Brittany R. and Werne, Josef P. and Minor, Elizabeth C.}
}
@article {2663,
	title = {An investigation of size-fractionated organic matter from Lake Superior and a tributary stream using radiocarbon, stable isotopes and NMR},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {127},
	year = {2014},
	month = {Jan-02-2014},
	pages = {264 - 284},
	issn = {00167037},
	doi = {10.1016/j.gca.2013.11.037},
	url = {https://linkinghub.elsevier.com/retrieve/pii/S0016703713006765https://api.elsevier.com/content/article/PII:S0016703713006765?httpAccept=text/xmlhttps://api.elsevier.com/content/article/PII:S0016703713006765?httpAccept=text/plain},
	author = {Zigah, Prosper K. and Minor, Elizabeth C. and Abdulla, Hussain A.N. and Werne, Josef P. and Hatcher, Patrick G.}
}
@article {72,
	title = {An investigation of size-fractionated organic matter from Lake Superior and a tributary stream using radiocarbon, stable isotopes and NMR},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {127},
	year = {2014},
	pages = {264-284},
	abstract = {This study investigated the concentration and isotopic composition of different size fractions of organic matter (OM) in Lake Superior and in one of its many tributary streams and rivers (Amity Creek, Duluth, Minnesota, USA). Structural compositional drivers of the Δ14C of high molecular weight (HMW, >1 kDa) dissolved organic carbon (DOC) in the lake were also evaluated. Low molecular weight (LMW, 0.7 μm) was generally 13C-depleted (-29 {\textpm} 1.2{\textperthousand}) relative to {\textquotedblleft}bulk{\textquotedblright} (<0.7 μm) DOC (-26.4 {\textpm} 0.7{\textperthousand}), {\textquotedblleft}init{\textquotedblright} (<0.2 μm) DOC (-26.6 {\textpm} 0.8{\textperthousand}), HMW DOC (-26.9 {\textpm} 0.3{\textperthousand}) and LMW DOC (-26.5 {\textpm} 0.9{\textperthousand}), and had more variable 14C content (Δ14C of -94{\textperthousand} to 53{\textperthousand}; 735 years BP to modern) than the other size fractions. Init DOC (Δ14C of 17{\textendash}59{\textperthousand}), HMW DOC (Δ14C of 23{\textendash}64{\textperthousand}) and LMW DOC (Δ14C of 16{\textendash}62{\textperthousand}) all reflected contemporary (modern) radiocarbon signatures. Bulk DOC (Δ14C of -19{\textperthousand} to 57{\textperthousand}; 90 years BP to modern) had modern radiocarbon values in the offshore sites (Δ14C of 2{\textendash}57{\textperthousand}) with pre-aged samples (Δ14C of -8{\textperthousand} to -19{\textperthousand}) seen at the nearshore site. HMW DOM was relatively N-poor (C:N of 12{\textendash}19) compared to particulate organic matter (POM, C:N of 8{\textendash}10) revealing either a more diagenetically altered state or contrasting sources. 13C NMR data showed that biochemical composition of HMW DOC in Lake Superior was dominated by carbohydrates (53{\textendash}65\%) with only trace aromatic components (2{\textendash}4\%). Structurally complex components such as heteropolysaccharides (HPS), amide/peptides and amino sugars (AMS) constitute 75{\textendash}84\% of HMW DOC whereas carboxylic-rich alicyclic molecules (CRAM) made up 16{\textendash}25\% of HMW DOC in the lake. Combined HPS and AMS, O-alkyl carbohydrate carbon, and total carbohydrate carbon contents were significantly positively correlated to the Δ14C of HMW DOC suggesting they contribute a contemporary 14C-enriched component to the HMW DOC in the lake. In contrast, CRAM and aliphatic carbons were significantly inversely correlated with Δ14C of HMW DOC implying that these represent 14C-depleted (older) components of HMW DOC in the lake. At Amity Creek, storm events led to larger loads of bulk DOC and POC, which were both 14C-enriched (modern). However, in baseflow conditions 14C-depleted bulk DOC and POC were exported. LMW DOC from the creek was considerably 14C-depleted compared to concurrent HMW DOC.},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2013.11.037},
	url = {http://www.sciencedirect.com/science/article/pii/S0016703713006765},
	author = {Zigah, Prosper K. and Minor, Elizabeth C. and Abdulla, Hussain A. N. and Werne, Josef P. and Hatcher, Patrick G.}
}
@article {95,
	title = {Diagenetic changes in Lake Superior sediments as seen from FTIR and 2D correlation spectroscopy},
	journal = {Organic Geochemistry},
	volume = {58},
	year = {2013},
	note = {id: 2319},
	pages = {125-136},
	abstract = {Isotopic and elemental analysis, Fourier transform infrared spectroscopy (FTIR), principal components analysis (PCA) and two dimensional (2D) correlation analysis, where core depth was used as perturbation, were used to study the diagenesis of organic matter (OM) in Lake Superior sediments. Changes in OM composition were examined at five lake stations over a depth range of 0{\textendash}10 cm. PCA results show that depth-related changes among sites are similar, leading to an increased contribution from inorganic (and possibly refractory aromatic organic) components at each site, and a loss of contribution from other organic components. Synchronous spectra reveal that aliphatic esters and carbohydrates are degraded significantly with increasing depth, leading to an increased contribution from clay/biogenic silica/inactive carbohydrates. Asynchronous spectra show that, in general, carboxyl groups, including aliphatic ester and amide in protein, are degraded first, followed by a group of carbohydrates and then aromatic compounds and/or the SiO framework in clay and biogenic silica. Site dependent compositional variation occurs and appears to be influenced by topography and geology, e.g. the delivery of a larger load of terrestrial inorganic silicate minerals to certain sites and re-suspension/re-deposition, leading to less intensive down core variation at mid-lake central and eastern basin sites. The study demonstrates the usefulness of FTIR coupled with PCA and 2D correlation approaches for exploring structural changes in sedimentary material during diagenesis.},
	issn = {0146-6380},
	doi = {10.1016/j.orggeochem.2013.03.002},
	url = {http://www.sciencedirect.com/science/article/pii/S0146638013000533},
	author = {Li, Hongyu and Minor, Elizabeth C. and Zigah, Prosper K.}
}
@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}
}
