Work Package 1:
All field samples were collected from 2017-2019. In 2017, the PI led a oceanographic expedition on the RRS Discovery (DY081) from St Johns, Canada, to the UK via Orphan Knoll and the Southwest coast of Greenland. In 2018, samples were collected from two fjords near Nuuk, Greenland, with more fjord samples collected in June-September 2019 in collaboration with the Greenland Institute of Natural Resources and the Royal Society.
Further glacial meltwater samples were collected, and analysed for chemical constituents, including silicon and silicon isotopes. We have shown that there is significant inputs of silicon to downstream ecosystems from glacial meltwaters, both in dissolved and reactive particulate form. This silicon is also isotopically light, both in the Arctic and Antarctic, and its isotopic signature can be traced downstream. Our work represents the first seasonally resolved record of silicon and silicon isotopes in glacial meltwaters, and the first measurements of glacial silicon from Antarctica. Other fjord and seawater analysis is well underway, of both dissolved and particulate samples, including contaminants (e.g. showing elevated mercury levels in glacial meltwaters), trace metals, and isotopes. Rock crushing experiments were carried out to investigate sub-glacial silicate weathering processes, showing that physical grinding under glaciers is likely a key source of the isotopically light and reactive silica.
Marine pore water samples were analysed for chemical constituents, including silicon and trace metals. We have revealed the complexities and importance of benthic silicon cycling in glaciated regions, showing for the first time that benthic fluxes are spatially variable, unexpectedly linked with reactive iron availability, but can contribute significantly to deep-water dissolved silicon concentrations.
Ocean gliders were deployed during the 2017 expedition, which collected high-resolution data that reveal the complex physical interaction between meltwaters and seawater in coastal regions, and that particles and coloured dissolved organic matter associated with meltwaters extend out into the strong boundary currents and into the Labrador Sea. Bathymetric data are presented in a paper published in Frontiers in Marine Science, showing enigmatic seamounts off Orphan Knoll that had not been mapped previously.
Work Package 2:
Samples of pelagic and benthic organisms, focusing on silicifiers, were collected during the 2017 expedition. Sponge taxonomic and biogeographic work reveal several new species and extended geographic ranges of existing species. Sponge ground habitat modelling work shows that sponge assemblages strongly impact bottom water flow, with implications for their survival. Sponge samples were also collected for, and are now stored at, the Bristol Sponge Collection in the School of Biochemistry for future natural product research.
Further work was carried out to understand the role of biomineralization in silicon isotope fractionation, including in benthic silicifiers i.e. sponges, and pelagic silicifiers such as diatoms and choanoflagellates. The results show that sponges and choanoflagellates have similarly strong fractionation, there is considerable variation even within monospecific sponge grounds.
Habitat mapping work, using remotely operated vehicles, contributed to two MSc student projects at the University of Southampton, including new methodology for mapping vertical cliff marine habitats.
