Geochemical approaches to the quantification of dispersed volcanic ash in marine sediment

Abstract

Volcanic ash has long been recognized in marine sediment, and given the prevalence of oceanic and continental arc volcanism around the globe in regard to widespread transport of ash, its presence is nearly ubiquitous. However, the presence/absence of very fine-grained ash material, and identification of its composition in particular, is challenging given its broad classification as an "aluminosilicate" component in sediment. Given this challenge, many studies of ash have focused on discrete layers (that is, layers of ash that are of millimeter-to-centimeter or greater thickness, and their respective glass shards) found in sequences at a variety of locations and timescales and how to link their presence with a number of Earth processes. The ash that has been mixed into the bulk sediment, known as dispersed ash, has been relatively unstudied, yet represents a large fraction of the total ash in a given sequence. The application of a combined geochemical and statistical technique has allowed identification of this dispersed ash as part of the original ash contribution to the sediment. In this paper, we summarize the development of these geochemical/statistical techniques and provide case studies from the quantification of dispersed ash in the Caribbean Sea, equatorial Pacific Ocean, and northwest Pacific Ocean. These geochemical studies (and their sedimentological precursors of smear slides) collectively demonstrate that local and regional arc-related ash can be an important component of sedimentary sequences throughout large regions of the ocean.

Sedimentary inputs to the Nankai subduction zone: The importance of dispersed ash

“…Specifically, for the northwest Pacific, geochemical and quantitative statistical analysis has identified multiple dispersed ash components that together comprise ~30-35 weight percent (wt%) of the sediment mass entering the Izu-Bonin-Mariana subduction system (Scudder et al, 2009(Scudder et al, , 2016. These high values are consistent with smear slide data and petrographic studies showing that dispersed glass shards and pumice can comprise as much as 30-40 wt% of the bulk sediment (Straub and Schmincke, 1998;Peters et al, 2000;Scudder et al, 2009Scudder et al, , 2014Scudder et al, , 2016.…”

“…Historically, dispersed ash is an under-utilized repository of information regarding geochemical budgets and tectonic history (Scudder et al, 2009(Scudder et al, , 2016and references therein), and can result from bioturbation of pre-existing discrete ash layers, the settling of airborne or subaqueous ash through the water column, transport by rivers and currents from terrestrially exposed ash deposits, and other processes (e.g., gravity flows). Specifically, for the northwest Pacific, geochemical and quantitative statistical analysis has identified multiple dispersed ash components that together comprise ~30-35 weight percent (wt%) of the sediment mass entering the Izu-Bonin-Mariana subduction system (Scudder et al, 2009(Scudder et al, , 2016.…”

“…Specifically, for the northwest Pacific, geochemical and quantitative statistical analysis has identified multiple dispersed ash components that together comprise ~30-35 weight percent (wt%) of the sediment mass entering the Izu-Bonin-Mariana subduction system (Scudder et al, 2009(Scudder et al, , 2016. These high values are consistent with smear slide data and petrographic studies showing that dispersed glass shards and pumice can comprise as much as 30-40 wt% of the bulk sediment (Straub and Schmincke, 1998;Peters et al, 2000;Scudder et al, 2009Scudder et al, , 2014Scudder et al, , 2016. Here we present geochemical records from Integrated Ocean Drilling Program (IODP) Sites C0011 and C0012 (Expeditions 322 and 333) to determine the composition of the multiple aluminosilicate sources, including dispersed ash, that compose the hemipelagic sediment entering the Nankai Trough.…”

Preface for the article collection “Land–Ocean Linkages under the Influence of the Asian Monsoon”

“…Consequently, the contribution of volcanic ash to pelagic sediments in open oceans, as well as to hemipelagic sediments in marginal areas, is uncertain and probably significantly underestimated. Scudder et al (2016) summarize the geochemical and statistical techniques that can be used to determine the composition of dispersed ashes and quantify their contribution to such ocean sediments. Combined with the results provided by He et al (2015), their method is particularly useful for evaluating the origins and relative contributions of finegrained siliciclastic sediments to the hemipelagic sediments of the East China and Japan seas.…”

“…Twelve oral and four poster presentations were given at the special JpGU session, and the papers presented in this issue include three research articles and six reviews based on presentations from that session. These nine papers cover the evolution and variability of the Asian monsoon , the evolution of surface water and deep-water circulation in East Asian marginal seas (Gallagher et al 2015;Kim et al 2015;Itaki 2016), the impact of the East Asian summer monsoon on the composition of sediment discharged from the Yangtze River, surface water salinity in the East China Sea, flood records and typhoon tracks in southern Japan (He et al 2015;Horikawa et al 2015;Suzuki et al 2016), and volcanic ash as a useful tool for land-ocean correlation and as a significant source of sedimentary material in the northwest Pacific Ocean (Ikehara 2015;Scudder et al 2016).…”