Episodic deposition and 137Cs immobility in Skan Bay sediments: A ten-year 210Pb and 137Cs time series

Abstract

Sugai, S.F., Alperin, M.J. and Reeburgh, W.S., 1994. Episodic deposition and 137Cs immobility in Skan Bay sediments: A ten-year 2X°pb and 13~Cs time series. In: M.I. Scranton (Editor), Variability in Anoxic Systems. Mar. Geol., A geochronology time series provides a powerful tool for elucidating sedimentary processes such as episodic deposition and diffusive mobility of particle-reactive constituents. Depth distributions of 21°Pb and 137Cs from Skan Bay, Alaska were determined for sediment cores collected in 1980, 1984, 1987, and 1990. Sediment X-radiographs reveal distinct layers indicating that sediments were not continuously mixed by bioturbation. However, the geochronology time series is inconsistent with an undisturbed, steady-state sediment column. Profiles from 1980Profiles from , 1984Profiles from , and 1990 reveal subsurface regions in which 21°pb activity is relatively constant. In addition, the depth of the primary 137Cs maximum (reflecting the 1963 peak in atmospheric bomb testing) does not increase in a regular fashion between 1980 and 1990. The 21°pb and 137Cs geochronologies can be reconciled by removing the effects of an instantaneous depositional event. The average 2X°pb sedimentation rate (corrected for episodic deposition) in cores that were collected over a ten year period (0.241 +0.006 g cm -2 yr-1) is in excellent agreement with the average 137Cs sedimentation rate (0.258 _+ 0.008 gcm-2 yr-1) calculated from three stratigraphic markers [peak fallout (1963), first appearance in the sediment record (1952), and the Chernobyl accident (1986)]. The mobility of bomb-derived 13VCs under in situ conditions was evaluated by a time-dependent numerical model applied to the 137Cs time series. The model indicates that bomb-derived cesium is immobile in Skan Bay sediments with a solid-liquid distribution coefficient (Kd) of/> 105 (ml g-1).

Diversity of Archaea in Marine Sediments from Skan Bay, Alaska, Including Cultivated Methanogens, and Description of Methanogenium boonei sp. nov

“…These microbes may gain energy via an alternative mode of metabolism or may be simply residual from sediment burial. Given the lack of bioturbation at Skan Bay, and a sedimentation rate of 0.9 cm per year (58), the cells present in the deep interval are 10 to 50 years removed from the methane-oxidizing zone. Whether rRNA genes would remain intact for this period of time in inactive cells is not clear.…”

Modeling detailed sedimentary 210Pb and fallout 239,240Pu profiles to allow episodic events: An application in Chesapeake Bay

“…Others have noticed episodic deposition in estuarine sediment (Schubel and Zabawa 1977;Hirschberg and Schubel 1979;Helz et al 1985Helz et al /1986Sugai et al 1994). However, to the best of our knowledge, the effort to distinguish this effect has previously been limited to cutting a certain portion from the tracer profile and modeling the event-corrected profile with a steady-state model (Goldberg et al 1978;Sugai et al 1994). The novel approach described here is an extension of the existing steady-state models and gives the flexibility to simulate episodic deposition or erosion that may have occurred in association with major storm events.…”

Radiometric dating of recent sediments: beyond the boundary conditions

“…This will allow us to explain the often-observed ''penetrating tails'' in 137 Cs profiles and the subsurface maxima in 210 Pb exc profiles (Sugai et al 1994;Baskaran and Naidu 1995;Fuller et al 1999;Belluci et al 2007). Although the main purpose of this paper is not development of a new dating model, the subject has implications for radiometric dating of recent sediments.…”

“…In this example, the values of the parameters describing the non-ideal deposition pattern are comparable to those of the Santa Barbara Basin. Sugai et al (1994) reported depth distributions of 210 Pb and 137 Cs in sediment cores from Skan Bay, Alaska, collected between 1980 and 1990. The sediment porosity was very high ([0.97) near the SWI, and remained *0.88 above a mass depth of 2 g cm -2 .…”