SEAMUS (v1.20): a Δ<sup>14</sup>C-enabled, single-specimen sediment accumulation simulator

Abstract

Abstract. The systematic bioturbation of single particles (such as foraminifera) within deep-sea sediment archives leads to the apparent smoothing of any temporal signal as recorded by the downcore, discrete-depth mean signal. This smoothing is the result of the systematic mixing of particles from a wide range of depositional ages into the same discrete-depth interval. Previous sediment models that simulate bioturbation have specifically produced an output in the form of a downcore, discrete-depth mean signal. However, palaeoceanographers analysing the distribution of single foraminifera specimens from sediment core intervals would be assisted by a model that specifically evaluates the effect of bioturbation upon single specimens. Taking advantage of advances in computer memory, the single-specimen SEdiment AccuMUlation Simulator (SEAMUS) was created for MATLAB and Octave, allowing for the simulation of large arrays of single specimens. This model allows researchers to analyse the post-bioturbation age heterogeneity of single specimens contained within discrete-depth sediment core intervals and how this heterogeneity is influenced by changes in sediment accumulation rate (SAR), bioturbation depth (BD) and species abundance. The simulation also assigns a realistic 14C activity to each specimen, by considering the dynamic Δ14C history of the Earth and temporal changes in reservoir age. This approach allows for the quantification of possible significant artefacts arising when 14C-dating multi-specimen samples with heterogeneous 14C activity. Users may also assign additional desired carrier signals to single specimens (stable isotopes, trace elements, temperature, etc.) and consider a second species with an independent abundance. Finally, the model can simulate a virtual palaeoceanographer by randomly picking whole specimens (whereby the user can set the percentage of older, “broken” specimens) of a prescribed sample size from discrete depths, after which virtual laboratory 14C dating and 14C calibration is carried out within the model. The SEAMUS bioturbation model can ultimately be combined with other models (proxy and ecological models) to produce a full climate-to-sediment model workflow, thus shedding light on the total uncertainty involved in palaeoclimate reconstructions based on sediment archives.

Re-evaluating <sup>14</sup>C dating accuracy in deep-sea sediment archives

“…3. Furthermore, as has been detailed in previous studies, changes in abundance and bioturbation depth can in themselves also cause additional general age-depth artefacts, no matter what geochronological method is being used (independent of the 14 C method) (Bard, 2001;Löwemark and Grootes, 2004;Löwemark et al, 2008;Lougheed, 2020). Such effects can be seen in age-depth artefacts also visible in the true median age for the dynamic BD scenario (Fig.…”

“…It may also be necessary to revisit existing studies and re-evaluate the magnitude of changes in deep-sea sediment SAR inferred from 14 C-based geochronologies, especially close to periods of dynamic 14 C and/or dynamic foraminiferal abundance. These 14 C-specific artefacts should be considered in addition to previously highlighted general age-depth artefacts that can occur in sedimentary records (Bard, 2001;Löwemark and Grootes, 2004;Löwemark et al, 2008;Lougheed, 2020). One should also consider that paired analysis of multi-specimen samples for both 14 C and another proxy could lead to a signal offset between the two proxies due to the 14 C method, as currently applied within palaeoceanography, being prone to the generation of the types of age artefacts outlined in this study.…”

“…Such best-case conditions do not exist in the field, meaning that a computer modelling environment can uniquely be used to create such a best-case scenario, which is ideal for testing the current state of the art. We use the 14 Cenabled, single-specimen SEdiment AccuMUlation Simulator (SEAMUS) (Lougheed, 2020). This model uses the long-established understanding of bioturbation as included in existing bioturbation models (Trauth, 2013;Dolman and Laepple, 2018), but it differs in that it explicitly simulates the accumulation and bioturbation of single foraminifera, each with individually assigned 14 C activities, to create a synthetic sediment archive history.…”

“…The SEAMUS model (Lougheed, 2020) synthesises n single foraminifera raining down from the water column per simulation time step, whereby n is the capacity of the synthetic sediment archive being simulated (analogous to sediment core radius) scaled to the SAR of the time step as predicted by an inputted age-depth relationship (Lougheed, 2020). To provide good statistics, all simulations use a time step of 5 years and 10 4 synthetic foraminifera per centimetre of core depth.…”

A proxy modelling approach to assess the potential of extracting ENSO signal from tropical Pacific planktonic foraminifera

“…A secondary factor is bioturbation. Systematically bioturbated deep-sea sediment cores can produce discrete sediment intervals with foraminifera that have ages spanning many centuries and/or millennia (Berger and Heath, 1968;Lougheed et al, 2018;Peng et al, 1979). In order to model the effect of bioturbation upon the age distribution of discrete core depths, a number of studies have used a diffusion-style approach that reduces the parameters down to SAR and sediment mixing depth (herein referred to as bioturbation depth, BD), although this may be an artificial division purely driven by mathematical need rather than biological constraints (Boudreau, 1998).…”