A high resolution study of spatial and temporal variability of natural and anthropogenic compounds in offshore Lake Superior sediments

Johnson, Thomas C.; Alstine, Jon D. Van; Rolfhus, Kristofer R.; Colman, Steven M.; Wattrus, N. J.

doi:10.1016/j.jglr.2012.09.013

Cited by 9 publications

(9 citation statements)

References 37 publications

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“…Johnson et al . [] collected ten sediment cores from an 8 km 2 area representative of deep offshore basins in Lake Superior and reported, among the coring sites, mass accumulation rates varied greatly between 50 g/m 2 yr and 180 g/m 2 yr. They attributed this variability as sediment redistribution by bottom currents over the complex morphology of the Lake Superior basin that is not uniform in space and time.…”

Section: Resultsmentioning

confidence: 99%

Sensitivity of sediment geochemical proxies to coring location and corer type in a large lake: Implications for paleolimnological reconstruction

Meyers

Robbins

et al. 2014

Geochem Geophys Geosyst

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We compared a suite of geochemical proxies in sediment cores collected in 1982, 1988, 1991, and 2003 from sites near the depocenter of Lake Erie to evaluate the reliability of paleoenvironmental reconstructions derived from lacustrine sediments. Our proxies included the concentrations and carbon isotopic compositions of organic and inorganic carbon (TOC, CaCO 3 , d13 C org , and d 13C CaCO3 ), augmented by organic C to total N ratios (C org it difficult to extract consistent environment information from different cores. Our findings suggest that in addition to temporal environmental changes, high-resolution paleolimnological reconstruction is sensitive to many factors that could include spatial sediment heterogeneity, discontinuous sedimentation processes, bioturbation, sediment dating uncertainty, and artifacts associated with analytical and coring procedures. Therefore, multiple-core sampling and analysis are important in reliably reconstructing environmental changes, particularly for large, heterogeneous lacustrine basins.

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Section: Resultsmentioning

confidence: 99%

Sensitivity of sediment geochemical proxies to coring location and corer type in a large lake: Implications for paleolimnological reconstruction

Meyers

Robbins

et al. 2014

Geochem Geophys Geosyst

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“…5). Cores recovered from this unit within the study area (including LS00-3P, location shown in Figures 1 and 2) show that both sub-units are glacial-lacustrine varves (Breckenridge, 2007;Hobbs and Breckenridge, 2011;Johnson et al, 2012), and that the red-gray boundary is approximately at the contact between the Gll and Glu sub-units (see Fig. 5).…”

Section: Seismic-stratigraphic Unitsmentioning

confidence: 96%

“…This unit has been the subject of many coring studies (cf. Dell, 1972;Breckenridge et al, 2004;Johnson et al, 2012) and will not be discussed in detail here. The lake floor and the Holocene lacustrine clay are affected by polygonal faulting and ring structures that are well developed in the study area (Wattrus et al, 2003;Cartwright et al, 2004;Johnson et al, 2012), and whose annular depressions appear in seismic profiles as sharp V-shaped "valleys" in the lake floor (see Figs.…”

Section: Seismic-stratigraphic Unitsmentioning

confidence: 99%

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Moraines and late-glacial stratigraphy in central Lake Superior

et al. 2020

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Seismic-reflection surveys of the Isle Royale sub-basin, central Lake Superior, reveal two large end moraines and associated glacial sediments deposited during the last cycle of the Laurentide Ice Sheet in the basin. The Isle Royale moraines directly overlie bedrock and are cored with dense, acoustically massive till intercalated down-ice with acoustically stratified outwash. Till and outwash are overlain by glacial varves, a lower red unit and an upper gray unit. The maximum extent of late Younger Dryas-age readvance into the western Lake Superior basin is uncertain, but it was probably controlled by both ice dynamics and climate. Our data indicate that during retreat from the maximum, the ice paused just long enough to construct the outer of the two moraines, >100 m high, and then retreated to the inner moraine, during which time most of the lower glacial-lacustrine sequence (red varves) was deposited. Retreat from the inner moraine coincided with a marked flux of icebergs at the calving margin and a change to gray varves. Rapid retreat may be related to both an influx of meltwater from Glacial Lake Agassiz about 10,500 cal yr BP and retreat of the calving margin down an adverse slope into the Isle Royale sub-basin.

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“…Under suitable conditions, MeHg can be produced within lake sediments. Examples include Boston Harbor, Massachusetts, Lake Superior, St. Lawrence River, and Saguenay Fjord in Canada (Benoit et al 2009;Johnson et al 2012;Fathi et al 2013;and Gagnon et al 1997). Yet MeHg requires special conditions for formation: availability of sulfate, suppressed oxygen levels, redox conditions, organic carbon content, low sulfur content, and non-toxic conditions for bacteria (Hollweg et al 2009;Heyes et al 2006;Heyes et al 2004;Sunderland et al 2004).…”

Section: Mining Discharges Into the Keweenaw Waterway As Mentioned Ementioning

confidence: 99%

Legacy mercury releases during copper mining near Lake Superior

Kerfoot

Urban

McDonald

et al. 2016

Journal of Great Lakes Research

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To examine issues of mercury contamination in lake sediments and fish, we require insight into historic sources of mercury and details of watershed methyl mercury (MeHg) cycling. Modern-day National Atmospheric Deposition Program (NADP) estimates of atmospheric mercury deposition in the upper Midwest region range from 4-10 μg/m 2 /y (wet only) to 5-30 μg/m 2 /y (gross deposition). Sedimentary records from scattered Michigan lakes, removed from mining sites, record around 5-24 μg/ m 2 /y modern THg deposition. However, these values are not representative of historic deposition near mining sites. On the Keweenaw Peninsula, mercury occurs naturally in copper ores and was discharged by smelting and stamp mill (tailings) operations. Here we examine mercury fluxes into two lakes (Portage and Torch Lake, portions of the Keweenaw Waterway) off Lake Superior, part of the previous Torch Lake Superfund site. Total mercury fluxes document greatly enhanced mercury loading (mean ca. 1,590 μg/m 2 /y; peaks of 5,120 to 21,300 μg/m 2 /y) during the height of copper mining (1880-1930), followed by a rapid decline once activities ceased. Methylmercury profiles appear to document both current methylation and historic methylation during mining operations. Time differences in MeHg and THg profiles may relate to watershed delivery time lags, toxic effects of copper on methylating bacteria, or to stratigraphic mobility. Whereas rapid sedimentation and lowered copper flux are promoting ecosystem recovery in Portage Lake, slower burial by organic-rich sediments is enhancing metal concentrations in Torch Lake sediments.

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A high resolution study of spatial and temporal variability of natural and anthropogenic compounds in offshore Lake Superior sediments

Cited by 9 publications

References 37 publications

Sensitivity of sediment geochemical proxies to coring location and corer type in a large lake: Implications for paleolimnological reconstruction

Sensitivity of sediment geochemical proxies to coring location and corer type in a large lake: Implications for paleolimnological reconstruction

Moraines and late-glacial stratigraphy in central Lake Superior

Legacy mercury releases during copper mining near Lake Superior

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