Periodic Reporting for period 2 - ICICLES (Iron and Carbon Interactions and Biogeochemical CycLing in Subglacial EcosystemS)
Okres sprawozdawczy: 2020-09-15 do 2021-09-14
Glaciers have been conventionally viewed as lifeless bodies that have little impact on biogeochemical cycles. It is now known that liquid water is present under all large ice masses. In Antarctica, subglacial lakes and rivers have been discovered, while in Greenland subglacial water channels and interconnected isolated hydrological systems exist. Two subglacial lakes, Whillans Subglacial Lake and Mercer Subglacial Lake, were accessed in 2013 and 2018, and support diverse and metabolically active microbial ecosystems, while microbial communities are also known to be exist under the Greenland Ice Sheet. This raises questions about biogeochemical cycling within these ecosystems. Specifically, the sources, concentrations, flows, modifications and interactions between life essential nutrients. The nutrients sourced from these environments might have an impact on downstream ecosystem productivity. This is of particular importance as the Southern Ocean, which surrounds Antarctica, where iron is the primary limiting element for life. Organic matter is thought to play a major role in regulating the flux and bioavailability of iron, and may also be an important source of bioavailable carbon.
The main objective of ICICLES was to investigate the cycling and interactions between iron and carbon (as organic matter) in glacial environments. Iron, organic matter and associated trace elements in waters and sediment samples from three sites beneath the Antarctic Ice Sheet and from large rivers emerging from the Greenland Ice Sheet and the Patagonian Ice Fields have been characterised using state-of-the-art spectroscopic and microscopic techniques. The fate of these glacier-derived elements in downstream near-coastal systems has been ascertained by sampling coastal marine environments fed by glacial meltwaters. A new budget of trace element and organic matter export from these ice sheet and ice field environments has been constructed and is available for use in regional and global ocean models to help assess the impact of subglacial meltwaters on marine productivity. This data provides unprecedented insight into elemental cycling in subglacial ecosystems and helps evaluate the role of ice sheets in global biogeochemical cycles. The results of this fellowship emphasise the complex societal implications of climate warming induced melting of the cryosphere, via alteration of both essential and toxic elemental fluxes from ice-to-ocean and raises more questions about the associated impacts of ice melt on ecosystem services.
The main objective of ICICLES was to investigate the cycling and interactions between iron and carbon (as organic matter) in glacial environments. Iron, organic matter and associated trace elements in waters and sediment samples from three sites beneath the Antarctic Ice Sheet and from large rivers emerging from the Greenland Ice Sheet and the Patagonian Ice Fields have been characterised using state-of-the-art spectroscopic and microscopic techniques. The fate of these glacier-derived elements in downstream near-coastal systems has been ascertained by sampling coastal marine environments fed by glacial meltwaters. A new budget of trace element and organic matter export from these ice sheet and ice field environments has been constructed and is available for use in regional and global ocean models to help assess the impact of subglacial meltwaters on marine productivity. This data provides unprecedented insight into elemental cycling in subglacial ecosystems and helps evaluate the role of ice sheets in global biogeochemical cycles. The results of this fellowship emphasise the complex societal implications of climate warming induced melting of the cryosphere, via alteration of both essential and toxic elemental fluxes from ice-to-ocean and raises more questions about the associated impacts of ice melt on ecosystem services.
The work performed can be divided into two areas: (i) the chemical characterisation of subglacial meltwaters from the Antarctic and Greenland ice sheets and from Chilean Patagonian, and (ii) the fate of iron, dissolved organic matter and associated trace elements exported from ice sheets and glaciers in near-coastal marine environments. Two initial publications reviewed the state of the art (Raiswell, Hawkings et al., 2018; Wadham, Hawkings et al., 2019) providing context and agenda for the the project. Three further publications (Pryer, Hawkings et al., 2020 a and b, Marshall, Hawkings et al., 2021) detail the first data on iron, silicon and DOM speciation in rivers/fjords draining regions of variable glacier cover in Patagonia. Catchments with high glacier cover produced rivers with higher concentrations of dissolved and particulate iron, with implications for future retreat of glacial cover on the cycling of this element. These studies produced the first budgets of iron export from rivers to fjord systems in Patagonia, and demonstrated the importance of sampling methodology in elemental concentrations from rivers. Hawkings et al. (2020), published in PNAS, provides the first data on trace element concentrations in Greenland and Antarctic meltwaters, with large implications for how we understand these systems as part of global elemental cycles, particularly natural mining of micronutrients from rock. A further publication, Hawkings et al. (2021), in Nature Geosciences, documents the first mercury concentrations and association with organic matter (as methylmercury) from the Greenland Ice Sheet. Multiple other papers (including 7 so far in 2021) further detail the role of glaciers in elemental cycling. The work from this fellowship has cumulated in an invited commentary for the American Geophysical Union journal JGR: Biogeosciences, summarising the role of glaciers in coastal elemental cycling and pointing the way forward for future research (Hawkings, in press).
A growing interest in the role of ice sheets in the global carbon cycle and the sensitivity of glaciated regions to climatic change necessitate an assessment of their role in element mobilization. This project addresses cross-cutting areas of research (ice to ocean) to produce unique first-of-a-kind results. Hawkings et al. (2020) is the first to show that subglacial environments have high concentrations of a range of trace elements and presents the first trace element data from a subglacial lake situated >1000 m under the surface of the Antarctic Ice Sheet. Pryer et al. (2020 a and b) produced the first nutrient datasets for pristine and remote rivers in Chilean Patagonia, demonstrating the importance of glacial cover in catchment elemental cycling, particularly in generation an abundance of reactive microparticles and in elevated filterable iron concentrations. Further publications have used novel high-resolution mass spectrometry techniques to help detail the organic matter composition of subglacial environments in Greenland and Antarctica, and the impacts of ice melt on organic matter cycling in a range of coastal ecosystems from pole-to-pole for the first time (e.g. Kellerman et al., 2021; Marshall et al., 2021). Work from this fellowship has also addressed the role of subglacial ecosystems in cycling of iron (a micronutrient), and the implications for in situ and downstream ecosystems (Hawkings et al., in prep). Furthermore, high impact work has demonstrate that ice sheets have been overlooked in the cycling of toxic elements, such as mercury, with adverse consequences for coastal marine ecosystems that receive larger volumes of meltwater (Hawkings et al., 2021). This project therefore has strong links to interests of high profile organisations such as the Arctic Monitoring and Assessment Programme (e.g. changing nutrient fluxes from ice sheets and implications for regional carbon cycling), the Intergovernmental Panel on Climate Change (e.g. the 2019 IPCC Special Report on “Ocean and Cryosphere in a Changing Climate”) and the United Nations (e.g. Minamata Convention on Mercury), especially regarding the potential impacts on ecosystem services of wasting ice (e.g. changes in fisheries and/or the delivery of toxic Hg to marine ecosystems).