Beschreibung: The element silicon is everywhere! In fact, silicon is the second most abundant element in Earth’s crust. Silicon in rocks and minerals breaks down and is transported from rivers and streams into the world’s oceans. Many marine organisms need silicon as it is a crucial nutrient to build their skeletons. Silicon eventually reaches the seafloor, but its journey into the abyss is not straightforward due to biological, physical, and chemical processes. All these processes transport and transform silicon, creating a cycle that we call the marine silicon cycle. The silicon cycle is directly connected to the carbon cycle, making silicon a key player in the regulation of Earth’s climate. In this article, we discuss why we need to understand the marine silicon cycle, explain the steps that happen in the ocean, and demonstrate how the marine silicon cycle affects humans.

Beschreibung: The Southern Ocean, the ocean encircling Antarctica, has been described by explorers as cold, empty, and dangerous. Despite this, it is a paradise for tiny algae called diatoms that are crucial players in the regulation of our climate. Why are these tiny organisms so happy in this cold and far away ocean? Diatoms have a solid shell made of a glass-like material called silica, so they need to find silicon in surface waters to build it. The Southern Ocean is the perfect place for diatoms because it is full of silicon compared to the other oceans. This is due to a special phenomenon called the silicon pump, which makes the Southern Ocean a giant trap for silicon. In this article, we point out the central role of the Southern Ocean in the regulation of Earth’s climate and how it controls the distribution of silicon and the wellbeing of diatoms in Antarctic waters.

Beschreibung: The West Antarctic Peninsula (WAP) is a highly productive shelf region during austral summer, supporting a rich ecosystem that has a significant impact on carbon sequestration. This ecosystem is heterogeneous, and characterised by biological "hotspots" fuelled largely by diatom production. The specific mechanisms determining the location and extent of these hotspots are not fully understood. Sedimentary enrichment of silicic acid (DSi) relative to other nutrients along the WAP, suggest that nutrient transfer across the sediment-water interface could have an impact on algal community composition. Here we combine reaction-transport modelling with porewater profiles of DSi concentration and stable silicon isotopic composition, biogenic silica content (BSi) and diatom abundances from sediment cores collected along the WAP, to assess the DSi flux and the processes that release this key nutrient from the WAP sediment into the overlying waters. We estimate a DSi diffusive flux of 2.67- 10**10 ± 2.75- 10**9 mol/yr for the WAP continental shelf area, which is lower than that previously estimated for the open Southern Ocean. Porewater isotopic compositions suggest that DSi concentrations are supplied primarily by BSi dissolution and respond to authigenic phase formation. Reaction-transport modelling highlights the highly dynamic environment of core-top sediments and the strong impact of surface productivity on sedimentary processes and the early diagenetic release of DSi. Both observations and modelling suggest a strong pelagic influence on benthic environment with the silicon benthic fluxes highly variable on different temporal and spatial scales, and thus sensitive to sea ice dynamics and climate change.

Beschreibung: The West Antarctic Peninsula (WAP) is a highly productive shelf region during austral summer, supporting a rich ecosystem that has a significant impact on carbon sequestration. This ecosystem is heterogeneous, and characterised by biological "hotspots" fuelled largely by diatom production. The specific mechanisms determining the location and extent of these hotspots are not fully understood. Sedimentary enrichment of silicic acid (DSi) relative to other nutrients along the WAP, suggest that nutrient transfer across the sediment-water interface could have an impact on algal community composition. Here we combine reaction-transport modelling with porewater profiles of DSi concentration and stable silicon isotopic composition, biogenic silica content (BSi) and diatom abundances from sediment cores collected along the WAP, to assess the DSi flux and the processes that release this key nutrient from the WAP sediment into the overlying waters. We estimate a DSi diffusive flux of 2.67- 10**10 ± 2.75- 10**9 mol/yr for the WAP continental shelf area, which is lower than that previously estimated for the open Southern Ocean. Porewater isotopic compositions suggest that DSi concentrations are supplied primarily by BSi dissolution and respond to authigenic phase formation. Reaction-transport modelling highlights the highly dynamic environment of core-top sediments and the strong impact of surface productivity on sedimentary processes and the early diagenetic release of DSi. Both observations and modelling suggest a strong pelagic influence on benthic environment with the silicon benthic fluxes highly variable on different temporal and spatial scales, and thus sensitive to sea ice dynamics and climate change.

Beschreibung: The West Antarctic Peninsula (WAP) is a highly productive shelf region during austral summer, supporting a rich ecosystem that has a significant impact on carbon sequestration. This ecosystem is heterogeneous, and characterised by biological "hotspots" fuelled largely by diatom production. The specific mechanisms determining the location and extent of these hotspots are not fully understood. Sedimentary enrichment of silicic acid (DSi) relative to other nutrients along the WAP, suggest that nutrient transfer across the sediment-water interface could have an impact on algal community composition. Here we combine reaction-transport modelling with porewater profiles of DSi concentration and stable silicon isotopic composition, biogenic silica content (BSi) and diatom abundances from sediment cores collected along the WAP, to assess the DSi flux and the processes that release this key nutrient from the WAP sediment into the overlying waters. We estimate a DSi diffusive flux of 2.67- 10**10 ± 2.75- 10**9 mol/yr for the WAP continental shelf area, which is lower than that previously estimated for the open Southern Ocean. Porewater isotopic compositions suggest that DSi concentrations are supplied primarily by BSi dissolution and respond to authigenic phase formation. Reaction-transport modelling highlights the highly dynamic environment of core-top sediments and the strong impact of surface productivity on sedimentary processes and the early diagenetic release of DSi. Both observations and modelling suggest a strong pelagic influence on benthic environment with the silicon benthic fluxes highly variable on different temporal and spatial scales, and thus sensitive to sea ice dynamics and climate change.

Beschreibung: Three sediment cores were collected along the West Antarctic Peninsula during RRS James Clark Ross expedition JR15003. Pb-210 analyses of sediment samples were carried out at GAU-Radioanalytical Laboratories, National Oceanography Centre, Southampton. The samples were measured by alpha spectrometry of Po-210, a proxy method that gives the activity of Pb-210, as Po-210 is a granddaughter of Pb-210 (Appleby, 2008; doi:10.1177/0959683607085598). The sediment samples were almost 2 years old, so it was assumed Pb-210 had reached secular equilibrium with Po-210 (half-life = 138 days) within the sediment (Baskaran, 2011; doi:10.1016/j.jenvrad.2010.10.007 and San Miguel et al., 2002; doi:10.1016/S0168-9002(02)01415-8).