Controls on biogenic silica burial in the Southern Ocean

Abstract

Understanding the controls on opal export in the Southern Ocean can inform both the prediction of how the leakage of silicic acid from the Southern Ocean responds to climate and the interpretation of paleo-proxies. We have compiled a database of 185 230 Thorium-normalized opal burial rates and 493 opal concentration measurements in Southern Ocean sediments and matched these with environmental climatologies. By subdividing the Southern Ocean on the basis of oceanographic regions and interpolating the opal burial rates, we estimate a total biogenic Si burial south of 40°S of 2.3 ± 1.0 Tmol Si yr À1. In both the seasonally ice-covered and permanently ice-free regions we can explain 73% of opal burial variability from surface ocean properties. Where sea ice is present for at least part of the year, the length of the ice-free season determines the upper limit of opal burial in the underlying sediments. In the ice-free regions of the Southern Ocean, the supply of silicic acid through winter mixing is the most important factor. Our results do not support a strong role of iron in controlling opal burial. We do however find that satellite-derived net primary production increases with increasing (modeled) dust delivery. These findings support the decoupling between carbon and opal fluxes in the Southern Ocean. When corrected for opal dissolution, the observed opal fluxes are in reasonable agreement with fluxes simulated using an ocean biogeochemical model. However, the results suggest current preservation algorithms for opal could be improved by incorporating the composition of particle flux, not only its magnitude.

The Missing Silica Sink: Revisiting the Marine Sedimentary Si Cycle Using Cosmogenic 32Si

“…More recently, removal of bSi opal to this region has been reestimated to be 2.0 ± 1.2 Tmol/yr, about one half lower than prior calculations (DeMaster, 1981;Tréguer et al, 1995;Pondaven et al, 2000;Tréguer & De La Rocha, 2013;Chase et al, 2015). Revised budgets, which are still poorly constrained, attribute greater bSi opal burial,~3.3 ± 2.1 Tmol/yr, to continental margins (DeMaster, 2002;Tréguer & De La Rocha, 2013).…”

Temporal variability in the Antarctic Polar Front (2002–2014)

“…While it is generally agreed that changes in sediment composition occurred in the vicinity of the PF during glacial‐interglacial cycles, whether the PF has migrated on these time scales is still an open question [see Kemp et al ., , references therein]. This uncertainty highlights a need to further investigate the relationship between the PF and biogeography in the modern‐day Southern Ocean [e.g., Chase et al ., ].…”

Water Column Stratification in the Antarctic Zone of the Southern Ocean During the Mid‐Pleistocene Climate Transition

“…Variations in sediment movement and relocation on the sea floor (focusing) and silica preservation (diagenesis) may affect interpretation of opal mass accumulation rates (MARs) with respect to diatom productivity (e.g., see review by Chase et al, ). To constrain the former, late Pleistocene opal burial rates are commonly normalized to 230 Th in the sediments (e.g., Francois et al, ).…”