Size sorting in marine muds: Processes, pitfalls, and prospects for paleoflow‐speed proxies

Abstract

[1] The basis for, and use of, fine grain size parameters for inference of paleoflow speeds is reviewed here. The basis resides in data on deposited sediment taken in conjunction with flow speed measurements in the field, experimental data on suspended sediment transport and deposition, and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed. In the deep sea, sorting events occur under resuspension/deposition events in benthic storms. At flow speeds below 10-15 cm s À1 , size in the noncohesive ''sortable silt'' (10-63 mm) range is controlled by selective deposition, whereas above that range, removal of finer material by winnowing also plays a role. The best particle size instruments to measure a flow speed-related grain size employ the settling velocity method, while laser diffraction sizers can yield misleading results because of particle shape effects. Potential problems, including source effects, downslope supply on continental margins, spatial variability of flow over bedforms, and influence of ice-rafted detritus, are examined. A number of studies using the sortable silt flow speed proxy are reviewed, and inverse modeling of grain size distributions is examined. Outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed.

Tracking climate variability in the western Mediterranean during the Late Holocene: a multiproxy approach

“…McCave et al, 1995;McCave and Hall, 2006). This proxy has been successfully applied in the western Iberian margin, showing that high SS values correlate with faster flows and better oxygenated deep waters (e.g.…”

Can sparse proxy data constrain the strength of the Atlantic meridional overturning circulation?

“…In contrast, a stronger AMOC is hypothesized by Yu et al (1996) and Lippold et al (2012) also based on 231 Pa/ 230 Th isotope ratios; by McCave et al (1995), Manighetti and McCave (1995), and McCave and Hall (2006) based on the grain-size analysis of ocean sediments; and by Curry and Oppo (2005) based on the stable carbon isotope ratios ( 13 C/ 12 C, often expressed as δ 13 C 2 ) of the dissolved inorganic carbon (DIC) in seawater, and cadmium/calcium trace element ratios (Cd/Ca). Finally, Rutberg and Peacock (2006) interpret glacial δ 13 C of DIC as consistent with a circulation regime similar to today.…”

Antarctic link to deep flow speed variation during Marine Isotope Stage 3 in the western North Atlantic

“…The fraction finer than 10 μm should be left out of the calculation of the mean silt size because clay and fine silt are deposited as aggregates and not sorted by primary particle size. The 'sortable silt' mean grain size ( P SS), which varies independently of sediment supply in current-sorted and deposited muds, has been used as an established proxy for flow speed in many studies (see review by McCave and Hall [26]). …”

“…Here we present a high-resolution (average sample interval 100 yr) bottom flow vigour record for ODP Site 1060 (Blake Outer Ridge, 3481 m water depth) during MIS 3, using the mean grain size of the sortable silt size range (10-63 μm) as a physical flow speed proxy [25,26].…”