@article {Zigah2017,
	title = {Constraining the sources and cycling of dissolved organic carbon in a large oligotrophic lake using radiocarbon analyses},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {208},
	year = {2017},
	pages = {102-118},
	abstract = {Abstract We measured the concentrations and isotopic compositions of solid phase extracted (SPE) dissolved organic carbon (DOC) and high molecular weight (HMW) \{DOC\} and their constituent organic components in order to better constrain the sources and cycling of \{DOC\} in a large oligotrophic lacustrine system (Lake Superior, North America). \{SPE\} \{DOC\} constituted a significant proportion (41-71\%) of the lake \{DOC\} relative to \{HMW\} \{DOC\} (10-13\%). Substantial contribution of 14C-depleted components to both \{SPE\} \{DOC\} (Δ14C = 25 to 43{\textperthousand}) and \{HMW\} \{DOC\} (Δ14C = 22 to 32{\textperthousand}) was evident during spring mixing, and depressed their radiocarbon values relative to the lake dissolved inorganic carbon (DIC; Δ14C \~{} 59{\textperthousand}). There was preferential removal of 14C-depleted (older) and thermally recalcitrant components from \{HMW\} \{DOC\} and \{SPE\} \{DOC\} in the summer. Contemporary photoautotrophic addition to \{HMW\} \{DOC\} was observed during summer stratification in contrast to \{SPE\} DOC, which decreased in concentration during stratification. Serial thermal oxidation radiocarbon analysis revealed a diversity of sources (both contemporary and older) within the \{SPE\} DOC, and also showed distinct components within the \{HMW\} DOC. The thermally labile components of \{HMW\} \{DOC\} were 14C-enriched and are attributed to heteropolysaccharides (HPS), peptides/amide and amino sugars (AMS) relative to the thermally recalcitrant components reflecting the presence of older material, perhaps carboxylic-rich alicyclic molecules (CRAM). The solvent extractable lipid-like fraction of \{HMW\} \{DOC\} was very 14C-depleted (as old as 1270-2320 14C years) relative to the substances isolated by acid hydrolysis of \{HMW\} DOC. Our data constrain relative influences of contemporary \{DOC\} and old DOC, and \{DOC\} cycling in a modern freshwater ecosystem.},
	keywords = {atmospheric co2, Carbohydrate-like substance, Carboxylic-rich alicyclic molecules (CRAM), Contemporary DOC, dissolved inorganic carbon, dissolved organic carbon, Freshwater carbon cycling, Heteropolysaccharides (HPS), High molecular weight DOC, Lake Superior, Lipid-like fraction, Old DOC, Oligotrophic lake, Protein-like substance, radiocarbon, Serial thermal oxidation, Solid phase extracted DOC, Stable isotope, Unhydrolysable material},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2017.03.021},
	url = {http://www.sciencedirect.com/science/article/pii/S0016703717301722},
	author = {Prosper K. Zigah and Elizabeth C. Minor and Ann P. McNichol and Li Xu and Josef P. Werne}
}
@article {2086,
	title = {Accumulation of biogenic and lithogenic material in the Pacific sector of the Southern Ocean during the past 40,000 years},
	journal = {Deep-Sea Research Part Ii-Topical Studies in Oceanography},
	volume = {50},
	year = {2003},
	note = {662agTimes Cited:82
Cited References Count:86
},
	month = {2003},
	pages = {799-832},
	abstract = {The (230)Th-normalization technique was applied to surface sediments and down-core records from the Pacific sector of the Southern Ocean between 120degreesW and 170degreesW in order to reconstruct vertical rain rates, corrected for lateral redistribution of sediment. Preserved rain rates of opal, organic carbon and biogenic Ba all indicate that biological productivity south of the Antarctic Polar Front (APF) was much lower than today during the Last Glacial Maximum (LGM), probably in response to increased ice cover. However, by analogy with modern opal fluxes south of the ACC, we show that year-round ice cover is not a prerequisite for very low rates of opal accumulation. Available records from north of the APF indicate little to no change in opal export, in contrast to records from the Indian and Atlantic sectors, which show enhanced opal export north of the APF during the LGM. Glacial records from north of 66degreesS in the Pacific all show lithogenic fluxes that were greater than today, but significantly lower than lithogenic fluxes in the glacial Atlantic and Indian sectors. Together, these new records from the Pacific sector show that during the LGM the three basins of the Southern Ocean were significantly more differentiated than today. The observed inter-basin distribution of lithogenic fluxes and opal burial, and the presumed geographical distribution of increased dust input to the Southern Ocean during the LGM, are consistent with an Atlantic-Indian-Pacific gradient in the degree of iron-stimulated diatom productivity within the zone lying between the APF and the Subantarctic Front. Previous studies, which focused primarily on the Atlantic sector, may have overestimated the glacial increase in the strength of the biological pump in the Southern Ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.},
	keywords = {antarctic circumpolar current, atmospheric co2, biological productivity, Deep-sea, interglacial changes, Last glacial maximum, marine-sediments, organic-carbon, pa-231/th-230 ratio, terrigenous sediment},
	isbn = {0967-0645},
	author = {Chase, Z. and Anderson, R. F. and Fleisher, M. Q. and Kubik, P. W.}
}
@article {2116,
	title = {Possible biological or physical explanations for decadal scale trends in North Pacific nutrient concentrations and oxygen utilization},
	journal = {Deep-Sea Research Part Ii-Topical Studies in Oceanography},
	volume = {49},
	year = {2002},
	note = {507ceTimes Cited:24
Cited References Count:71
},
	month = {2002},
	pages = {345-362},
	abstract = {We analyze North Pacific GEOSECS (1970s) and WOCE (1990s) observations to examine potential decadal trends of the marine biological carbon pump. Nitrate concentrations ([NO3]) and apparent oxygen utilization (AOU) decreased significantly in intermediate waters (by -0.6 and -2.9 mu mol kg(-1) respectively, at sigma (theta) = 27.4 kg m(-3), corresponding to approximate to 1050 m). In shallow waters (above roughly 750 m) [NO3-] and AOU increased, though the changes were not statistically significant. A sensitivity study with an ocean general circulation model indicates that reasonable perturbations of the biological carbon pump due to changes in export production or remineralization. efficiency are insufficient to account for the intermediate water tracer trends. However, changes in water ventilation rates could explain the intermediate water tracer trends and would be consistent with trends of water age derived from radiocarbon. Trends in AOU and [NO3-] provide relatively poor constraints on decadal scale trends in the marine biological carbon pump for two reasons. First, most of the expected changes due to decadal scale perturbations of the marine biota occur in shallow waters, where the available data are typically too sparse to account for the strong spatial and temporal variability. Second, alternative explanations for the observed tracer trends (e.g., changes in the water ventilation rates) cannot be firmly rejected. Our data analysis does not disprove the null-hypothesis of an unchanged biological carbon pump in the North Pacific. (C) 2001 Published by Elsevier Science Ltd.},
	keywords = {anthropogenic co2 invasion, atmospheric co2, carbon-cycle, el-nino, hydrographic data, organic-matter, redfield ratios, sargasso-sea, subtropical gyre, vertical fluxes},
	isbn = {0967-0645},
	url = {http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2\&amp;SrcAuth=Alerting\&amp;SrcApp=Alerting\&amp;DestApp=WOS\&amp;DestLinkType=FullRecord;UT=WOS:000173008600015},
	author = {Keller, K. and Slater, R. D. and Bender, M. and Key, R. M.}
}
