Carbon mineralization and oxygen dynamics in sediments with deep oxygen penetration, Lake Superior

Abstract

To understand carbon and oxygen dynamics in sediments with deep oxygen penetration, we investigated eight locations (160-318-m depth) throughout Lake Superior. Despite the 2-4 weight percent organic carbon content, oxygen penetrated into the sediment by 3.5 to . 12 cm at all locations. Such deep penetration is explained by low sedimentation rates (0.01-0.04 cm yr 21 ), high solubility of oxygen in freshwater, and a shallow (, 2 cm) bioturbation zone. In response mainly to oxygen variations in the bottom waters, the sediment oxygen penetration varied seasonally by as much as several centimeters, suggesting that temporal variability in deeply oxygenated sediments may be greater than previously acknowledged. The oxygen uptake rates (4.4-7.7 mmol m 22 d 21 , average 6.1 mmol m 22 d 21 ) and carbon mineralization efficiency (, 90% of deposited carbon) were similar to those in marine hemipelagic and pelagic sediments of comparable sedimentation rates. The reactivity of organic carbon was found to decrease with age similarly to the power-law documented in marine environments. The burial flux of carbon into the deep sediment (0.7 mmol m 22 d 21 ) was 2.5% of the previously estimated primary production. Maximum volume-specific carbon degradation rates were 0.3-1.5 mmol cm 23 d 21 ; bioturbation coefficient near the sediment surface was 3-8 cm 2 yr 21 . These results indicate that carbon cycling in large freshwater systems conforms to many of the same trends as in marine systems.

Organic carbon mass accumulation rate regulates the flux of reduced substances from the sediments of deep lakes

“…In the oligotrophic lakes Superior and Baikal, TOC-MAR was 4 and 7 gC m −2 yr −1 (see Table S2), respectively, and the resulting F red from the sediment was close to zero (Och et al, 2012;Klump et al, 1989;Remsen et al, 1989;Richardson and Nealson, 1989). In addition to low gross sedimentation of OC, the high sediment O 2 penetration depth (of around 1-3 cm) causes a long exposure time to oxic conditions and thus oxic mineralization of a large fraction of the deposit (Maerki et al, 2006;Martin et al, 1993;Li et al, 2012). In consequence, the TOC buried in lakes like Superior and Baikal is already highly mineralized and therefore does not generate significant amounts of reduced substances.…”

“…TOC-MAR and F red values from Lake Erie (LE) were extracted from Matisoff et al (1977), Adams et al (1982), and Smith and Matisoff (2008). Values for Lake Superior (LS) were compiled from Klump et al (1989), Remsen et al (1989), Richardson and Nealson (1989), Heinen and McManus (2004), and Li et al (2012). but mirror the slower processes of anaerobic degradation of buried OC and F red . Hence, in Fig.…”

Nitrogen cycling in deeply oxygenated sediments: Results in Lake Superior and implications for marine sediments

“…16 cm in water depths between 120 and 300 m; Li et al 2012), typical of oceanic hemipelagic sediments in 2000-3000 m water depth (Glud 2008). The organic carbon mineralization rates and carbon burial efficiencies in these sediments are similar to those in the deep ocean (Li et al 2012). The nitrogen dynamics in Lake Superior have been enigmatic (Sterner et al 2007), as over the last century the lake has experienced an unusual increase in water column nitrate concentrations, leading to an extreme N : P ratio of 10,000 (Guildford and Hecky 2000).…”

“…Lake Superior, the world's largest lake by surface area, provides an opportunity to investigate the nitrogen cycle in a freshwater end member system that in many respects is similar to marine systems. Characterized by relatively low organic carbon (C) content (3-5 wt%; Li et al 2012;Kistner 2013) and slow accumulation rates, the offshore sediments of Lake Superior exhibit an exceptionally deep penetration of oxygen (2 to . 16 cm in water depths between 120 and 300 m; Li et al 2012), typical of oceanic hemipelagic sediments in 2000-3000 m water depth (Glud 2008).…”

“…Characterized by relatively low organic carbon (C) content (3-5 wt%; Li et al 2012;Kistner 2013) and slow accumulation rates, the offshore sediments of Lake Superior exhibit an exceptionally deep penetration of oxygen (2 to . 16 cm in water depths between 120 and 300 m; Li et al 2012), typical of oceanic hemipelagic sediments in 2000-3000 m water depth (Glud 2008). The organic carbon mineralization rates and carbon burial efficiencies in these sediments are similar to those in the deep ocean (Li et al 2012).…”