210Pb-Derived Bioturbation Rates in Sediments Around Seamounts in the Tropical Northwest Pacific

Feng Lin,Hui Lin,Cai Lin,Li Lin,Xiuwu Sun

doi:10.3389/fmars.2021.701897

Abstract

To evaluate bioturbation coefficients (DB) and mixing depths (L), 210Pb and 226Ra activity was measured in two sediments cores (from water depths of 5,398 m and 4,428 m), which were collected from seamount areas in the Northwest Pacific. Using a steady-state diffusion mode, we estimated DB values of 16.8 and 24.1 cm2/a, higher than those in abyssal sediments and those predicted by traditional empirical equations. Corresponding L values varied between 19.3 and 23.1 cm. These high values indicate that seamounts are the area of active bioturbation. A one-dimensional model for the transport of total organic carbon (TOC) from the surface layer of sediments to the deep layer was developed using the distribution pattern of the specific activity of excess 210Pb (210Pbex) and its relationship with TOC. The model showed that the TOC flux transmitted downward by bioturbation was 0.09 mmol/(cm2⋅a) and 0.12 mmol/(cm2⋅a).

Highlights

Biological mixing of marine sediments can substantially modify the physical, chemical, and biological properties of the sediment record (Trauth et al, 1997)
Our results showed that the specific activities of 226Ra calculated from peak areas under the 295.2 keV were consistent with those under 609.3 keV, but the activities via 351.9 and 1,120.3 keV were inconsistent
There are many factors influencing the bioturbation of sediments, such as deposition rate, organic carbon deposition flux at the sediment–water interface, abundance of benthic organisms, community structure, living habits and disturbance mode, water depth, oxygen solubility in bottom water or penetration of dissolved oxygen in sediments, sediment type, and hydrodynamic conditions

Summary

Introduction

Biological mixing of marine sediments (bioturbation) can substantially modify the physical, chemical, and biological properties of the sediment record (Trauth et al, 1997). These alterations are reflected in any high-resolution sedimentary record as an attenuation of the short-term variability and major phase shifts between various paleoclimatic tracers (Rodríguez-Tovar and Uchman, 2008). Bioturbation by benthic organisms can affect early diagenesis in surface sediments and the sedimentary record. The process of bioturbation, which involves both the dispersal of sediment particles (i.e., sediment reworking) and the transport of interstitial porewater (i.e., bioirrigation) by benthic organisms, occurs in the most oxic sediments and is of global importance

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Discussion

Conclusion