Periodic Reporting for period 4 - ICY-LAB (Isotope CYcling in the LABrador Sea)
Berichtszeitraum: 2021-01-01 bis 2021-12-31
The high-latitude regions are experiencing some of the most rapid changes observed in recent decades: polar temperatures are rising twice as fast as the global mean and there are concerns about the impact of sea-ice and glacier retreat on global oceans and climate. The high-latitude North Atlantic is also a key region for ecologically and economically important natural resources such as fisheries. How these resources will change in the future depends strongly on the response of marine biogeochemical cycling of essential nutrients to increasing anthropogenic stress.
Diatoms are photosynthetic algae that are responsible for nearly half of the export of carbon from the sea surface to the seafloor, and they are a sensitive indication of the state of nutrient cycling. Diatoms are one of many organisms that precipitate biogenic opal, an amorphous glass made of silica, to form protective skeletons, and one of the essential nutrients is therefore dissolved silicon. The response of the silicon cycle to changing environmental conditions is critical for both carbon and nutrient cycling and it can now be addressed through high precision silicon isotopes, which is the focus of ICY-LAB.
The approach will be to capture the whole silicon cycle system in areas of marked environmental change using careful field sampling strategies - with research expeditions to coastal Greenland and the open ocean Labrador Sea - coupled with cutting-edge analytical methods. The results will lead to an unprecedented and cross-disciplinary view of nutrient cycling, biomineralisation, and the taxonomy and biogeography of siliceous organisms in an ecologically important region of the North Atlantic.
The overarching theme of ICY-LAB is to understand nutrient and isotope cycling in the climatically critical but understudied regions of the Labrador Sea and Greenland fjords, in two major Work Packages (WP) investigating: (WP1) the impact of glaciers and fjord processes, and the role of ocean circulation and marine biology, on nutrient cycling in the region, using systematically collected samples that will fully capture the Si cycle; (WP2) the biogeographical controls on sponge and diatom distribution in the Labrador Sea and Greenland fjords.
The specific objectives of WP1 are to:
1) Collect water samples in order to constrain the relative inputs of Si from glacial meltwater and different water masses in the study area;
2) Collect biological and particulate samples in order to constrain the role of particulate silica precipitation and dissolution on the silicon (Si) cycle in the study area;
3) Link the silicon cycle to high-latitude North Atlantic biogeochemistry using water and sedimentary column modelling.
The specific objectives of WP2 are to:
1) Collect and identify benthic organisms (focussing primarily on sponges) in order to carry out biogeographical analyses, and isolate suitable specimens for biomineralisation and natural product research;
2) Collect and identify planktonic organisms in order to carry out biogeographical and geochemical analyses.
Diatoms are photosynthetic algae that are responsible for nearly half of the export of carbon from the sea surface to the seafloor, and they are a sensitive indication of the state of nutrient cycling. Diatoms are one of many organisms that precipitate biogenic opal, an amorphous glass made of silica, to form protective skeletons, and one of the essential nutrients is therefore dissolved silicon. The response of the silicon cycle to changing environmental conditions is critical for both carbon and nutrient cycling and it can now be addressed through high precision silicon isotopes, which is the focus of ICY-LAB.
The approach will be to capture the whole silicon cycle system in areas of marked environmental change using careful field sampling strategies - with research expeditions to coastal Greenland and the open ocean Labrador Sea - coupled with cutting-edge analytical methods. The results will lead to an unprecedented and cross-disciplinary view of nutrient cycling, biomineralisation, and the taxonomy and biogeography of siliceous organisms in an ecologically important region of the North Atlantic.
The overarching theme of ICY-LAB is to understand nutrient and isotope cycling in the climatically critical but understudied regions of the Labrador Sea and Greenland fjords, in two major Work Packages (WP) investigating: (WP1) the impact of glaciers and fjord processes, and the role of ocean circulation and marine biology, on nutrient cycling in the region, using systematically collected samples that will fully capture the Si cycle; (WP2) the biogeographical controls on sponge and diatom distribution in the Labrador Sea and Greenland fjords.
The specific objectives of WP1 are to:
1) Collect water samples in order to constrain the relative inputs of Si from glacial meltwater and different water masses in the study area;
2) Collect biological and particulate samples in order to constrain the role of particulate silica precipitation and dissolution on the silicon (Si) cycle in the study area;
3) Link the silicon cycle to high-latitude North Atlantic biogeochemistry using water and sedimentary column modelling.
The specific objectives of WP2 are to:
1) Collect and identify benthic organisms (focussing primarily on sponges) in order to carry out biogeographical analyses, and isolate suitable specimens for biomineralisation and natural product research;
2) Collect and identify planktonic organisms in order to carry out biogeographical and geochemical analyses.
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.
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.
The results shown above highlight the step changes that ICY-LAB have made to the state of the art, in our understanding of biogeochemical cycling and ecosystems in glaciated margins. Future research will focus on analysing the fjord and coastal waters for additional trace metals, nutrients, and their isotopes, with the expectation that glacial meltwaters will have similarly significant impacts on other elemental cycles in these climatically sensitive regions.