Particle Fluxes at the Australian Southern Ocean Time Series (SOTS) Achieve Organic Carbon Sequestration at Rates Close to the Global Median, Are Dominated by Biogenic Carbonates, and Show No Temporal Trends Over 20-Years

Abstract

Particle fluxes at the Southern Ocean time series (SOTS) site in the Subantarctic Zone (SAZ) south of Australia (∼47 • S, ∼142 • E, 4600 m water depth) were collected from 1997-2017 using moored sediment traps at nominal depths of 1000, 2000, and 3800 m. Annually integrated mass fluxes showed moderate variability of 14 ± 6 g m −2 yr −1 at 1000 m, 20 ± 6 g m −2 yr −1 at 2000 m and 21 ± 4 g m −2 yr −1 at 3800 m. Particulate organic carbon (POC) fluxes were similar to the global median, indicating that the Subantarctic Southern Ocean exports considerable amounts of carbon to the deep sea despite its high-nutrient, low chlorophyll characteristics. The interannual flux variations were larger than those of net primary productivity as estimated from satellite observations. Particle compositions were dominated by carbonate minerals (>60% at all depths), opal (∼10% at all depths), and particulate organic matter (∼17% at 1000 m, decreasing to ∼10% at 3800 m), with seasonal and interannual variability much smaller than for their flux magnitudes. The carbonate counter-pump effect reduced carbon sequestration by ∼8 ± 2%. The average seasonal cycle at 1000 m had a two-peak structure, with a larger early spring peak (October/November) and a smaller late summer (January/February) peak. At the two deeper traps, these peaks became less distinct with a greater proportion of the fluxes arriving in autumn. Singular value decomposition (SVD) shows that this temperate seasonal structure accounts for ∼80% of the total variance (SVD Mode 1), but also that its influence varies significantly relative to Modes 2 and 3 which describe changes in seasonal timings. This occurrence of significant interannual variability in seasonality yet relatively constant annual fluxes, is likely to be useful in selecting appropriate models for the simulation of environmental-ecological

Lithogenic Particle Flux to the Subantarctic Southern Ocean: A Multi‐Tracer Estimate Using Sediment Trap Samples

“…While TMF and CaCO 3 , BSiO 2 , and POC fluxes all showed a primary peak in spring, the associated secondary late summer peaks reported by Wynn‐Edwards et al. (2020) were more variable (Figures 5a, 5c, 5e and 5g) than our F LithAv summer peak, with magnitudes similar or higher than the initial spring‐summer peak for the 2010–2011, 2011–2012, and 2017–2018 seasons (Figures 4b–4e).…”

“…To examine a potential link between the lithogenic particle flux at 1,000 m depth and export production at SOTS, our estimates of F LithAv were compared to TMF and major biogenic flux components (CaCO 3 , BSiO 2 , and POC) reported by Wynn‐Edwards et al. (2020) (Table 2, Figures 4 and 5). F LithAv showed a slightly different seasonal pattern compared with major biogenic components.…”

“…The sediment trap sampling and sample processing methods used in this study are briefly described and further detailed in Wynn‐Edwards et al. (2020). Sediment traps were McLane PARFLUX Mark 78H 21‐cup traps, with a baffled 0.5 m 2 funnel area (2.5 cm baffle cell diameter).…”

Release from biogenic particles, benthic fluxes, and deep water circulation control Cr and δ 53 Cr distributions in the ocean interior

“…Chromium redox transformations are accompanied by isotopic fractionation. While fractionation patterns during Cr oxidation are variable (Zink et al, 2010;Miletto et al, 2021), reduction consistently enriches light isotopes in Cr(III) (e.g. Wanner and Sonnenthal, 2013).…”

Recommendations for Plankton Measurements on OceanSITES Moorings With Relevance to Other Observing Sites

“…Examples of scientific results from the SAZ mooring deep sediment traps include quantification of bulk fluxes of organic and inorganic carbon, nitrogen, and silicon and their contribution to the global carbon cycle [Trull et al (2001);Wynn-Edwards et al (2020)], and examination of seasonal and interannual variations in the abundance of specific taxa [e.g., Roberts et al (2014); Kloster et al (2019); Rigual Hernández et al (2020)]. The SOFS mooring has supported a broad range of sensor-based studies, including quantification of air-sea fluxes of heat, moisture, and CO 2 [Schulz et al (2012); Shadwick et al (2015)], estimates of net community production obtained by separating physical and biological contributions to oxygen budgets [Weeding and Trull (2014)], and seasonal variations in bio-optical properties, phytoplankton, and the abundance and diel migration of zooplankton and fish [Schallenberg et al (2019);Trull et al (2019)].…”