Ice sheets and biogeochemical cycles
Teeming with life, hydrologically active, ice sheets are hot spots for biogeochemical activity on Earth
The wet-based regions of the Greenland and Antarctic Ice Sheets are now known to be habitable for life. They contain diverse communities of single-celled microorganisms which are involved in the chemical breakdown of rocks and, aided by dynamic sub-ice plumbing systems, export freshwater, nutrients and dissolved organic carbon via runoff to the coastal ocean. This designates ice sheets as important components of Earth’s carbon and nutrient cycles, which affect our climate and the ecosystems on which we rely. Climate warming in the Polar Regions is already accelerating melting on the Greenland Ice Sheet, may amplify iceberg loss from both ice sheets and initiate surface melting for the first time around Antarctica and in the Greenland interior. These physical changes will fundamentally affect the connectivity between ice sheets and their neighbouring ecosystems (e.g. rivers, lakes, fjords, oceans), which are shaped by freshwater, carbon and nutrients delivered by glacial runoff and icebergs or mobilsed from deep ocean waters by upwelling glacial meltwaters at marine glacier margins. These potential shifts include changes to marine food-webs, the viability of fisheries and the release of greenhouse gases such as methane, which is produced in oxygen-starved environments beneath ice sheets. They are all NEW dimensions to glacier change that have only been uncovered in the last 20 years, and urgently warrant study in order to create resilience against accelerating climate warming of our Polar regions.
Research Funding
Funded by the following grants/funders:
Royal Society Wolfson Merit Award to JL Wadham
Leverhulme Trust Research Project grant: Ice Sheets: A missing link in the global silicon cycle
The Engineering and Physical Sciences Research Council Challenging Engineering Grant
The Natural Environment Research Council UK: DELVE: DEveLopment and Validation of first generation chemical sensors for icy Ecosystems, Investigating meltwater flow beneath the Greenland Ice sheet using a multi-tracer approach; Biogenic production of climate amplifiers under ice.
Water flow beneath our ice sheets
25 years ago, we weren’t sure how water flowed within ice sheets or even whether meltwater produced on their surfaces made it to the ice sheet bed, where it could influence glacier flow by lubrication. One of the challenging things about working out how water flows within ice sheets is that meltwater has to be followed deep beneath kilometres of ice. Chemical tracers have been used to trace ocean currents across entire basins. In Greenland, we have used similar tracers to show that beneath the ice sheet lies a complex hydrological system not that dissimilar to beyond the ice. This includes the evolution, by mid summer, of a network of fast flowing sub-ice rivers which shunt meltwater, sediments and their carbon and nutrients to the ice edge.
Ice sheets as methane sources
The basal regions of ice sheets are dark, cold and often contain the fossil remains of organic matter (e.g. ancient soils, marine muds, lake sediments, rock carbon) - all entombed beneath the ice when the glacier grew. Just like a landfill site, these conditions are ideal habitats for an anaerobic microbe called “a methanogen”, which produces the powerful greenhouse gas - methane. Furthermore, some deep parts of ice sheets lie in geothermally active zones where heating of ancient carbon at depth in thick sediments produces a “thermogenic” form of methane. We do not currently know how much methane is locked beneath ice sheets, what form it is in and what its fate might be if ice thins and retreats. Could this be an important positive feedback to climate?
Ice sheets, nutrients and ocean productivity.
The Greenland Ice Sheet annually discharges around 1000 cubic kilometres of water to the oceans as subglacial meltwater and icebergs (in a ratio of about 50/50 at present). The Antarctic Ice Sheet (whose surface only melts at its fringes) releases a similar amount of freshwater via icebergs plus a small amount of subglacial melt produced by slow heating of its sole. Dissolved within this water are important rock-sourced nutrients such as iron, phosphorus and silicon, which are delivered to fjords and oceans. Further nutrient is supplied at marine-terminating glaciers where upwelling subglacial meltwaters entrains nutrient-replete ocean water as they rise to the ocean surface. Understanding these forms of “life support” to ocean food-webs is important in a warming world when freshwater discharge is likely to rise.
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Ice sheet plumbing systems
Chandler, D., J.L. Wadham, G. Lis, T. Cowton, A. Sole, I. Bartholomew, J. Telling, P. Nienow, E.B. Bagshaw, D. Mair, S. Vinen and A. Hubbard. 2013. Evolution of the subglacial drainage system of the Greenland Ice Sheet revealed by tracers, Nature Geoscience, 6(3), 195-198.
Cowton, T., P.W. Nienow, A. Sole, J.L. Wadham, G. Lis, I. Bartholomew, D. Mair and D. Chandler. 2013. Evolution of drainage system morphology at a land-terminating Greenland outlet glacier, Journal of Geophysical Research, Doi:10.1029/2012JF002540.
Bagshaw, E.A, B.S.R. Lishman, J.L. Wadham, J.A. Bowden, S.G. Burrow, L.R. Clare and D.M. Chandler, DM. 2014. Novel wireless sensors for in situ measurement of sub-ice hydrologic systems, Annals of Glaciology, 55(65), Doi:10.3189/2014AoG65A007.
Bagshaw, E.A., N.B. Karlsson, L.B. Lok, B. Lishman, L. Clare, K.W. Nicholls, S. Burrow, J.L. Wadham, O. Eisen, H. Corr, P. Brennan, D. Dahl-Jensen. 2018. Prototype wireless sensors for monitoring sub-surface processes in firn, Journal of Glaciology, 64(248), 887-896.
Linhoff, B., M. Charette, P.W. Nienow, A. Tedstone, J.L. Wadham, T. Cowton. 2017. Utility of Radon as a passive tracer of distributed subglacial drainage, 222Rn, Earth and Planetary Science Letters, 462, 180-188.
Methane & ice sheets
Lamarche-Gagnon, G., J.L. Wadham, B. Sherwood-Loller, S. Arnt, P. Fietzek, G. Lacrampe-Couloume, A.D. Beaton, A.J. Tedstone, J. Telling, E.A. Bagshaw, J.R. Hawkings, T.J. Kohler, J.D. Žárský, M.C. Mowlem and M. Stibal. 2019. Continuous-pulsed methane export from the Greenland Ice Sheet, Nature, 565, 73-77.
Wadham, J.L., S. Arndt, S. Tulaczyk, M, Stibal, M. Tranter, A. Ridgwell, J. Telling, E. Lawson, A. Dubnick, M.J. Sharp, A.M Anesio, C. Butler. 2012. Potential methane reserves beneath Antarctica, Nature, 488, 633–637.
Wadham, J.L., M. Tranter, M. J. Sharp and S. Tulaczyk. 2008. Subglacial methanogenesis: a potential climatic amplifier? Global Biogeochemical Cycles, Doi:10.1029/2007GB002951.
Ice sheets and biogeochemical cycles
Wadham, J.L., J. Hawkings, L. Tarasov, L. Gregoire, A. Ridgwell, R. Spencer and K. Kohfeld. 2019. Why Ice Sheets Matter for the Global Carbon Cycle, Nature Communications, 10(1), Doi:10.1038/s41467-019-11394-4.
Wadham, J.L., M. Tranter, M. Skidmore, A.J. Hodson, J. Priscu, W. B. Lyons, M. Sharp, P. Wynn, M. Jackson. 2010. Biogeochemical weathering under ice: size matters, Global Biogeochemical Cycles, Doi:10.1029/2009GB003642.
Hawkings, J., J. Hatton, K. Hendry, J.L. Wadham, M. Hain, R. Ivanovic, T. Kohler, M. Stibal, A. Beaton, G. Lamarche-Gagnon, A. Tedstone, J. Pike, M. Tranter. 2018. The silicon cycle impacted by past ice sheets, Nature Communications, 9, Doi:10.1038/s41467-018-05689-1.
Hawkings, J., J.L. Wadham, L. Benning, K. Hendry, M. Tranter, A. Tedstone, P.W. Nienow and R. Raiswell. 2017. Ice Sheets as a missing source of silica to the world’s oceans, Nature Communications, 8, Doi:10.1038/ncomms14198.
Hawkings, J. J.L. Wadham, M. Tranter, J. Telling, E.A. Bagshaw, A. Beaton, S.L. Simmons, D.M. Chandler, A. Tedstone and P.W. Nienow. 2016. The Greenland Ice Sheet as a hotspot for phosphorus weathering and export in the Arctic, Global Biogeochemical Cycles, 30(2), 191-210.
Hawkings, J., J.L. Wadham, M. Tranter, E. Lawson, A. Sole, T. Cowton, A.J. Tedstone, I. Bartholomew, P. Nienow, D. Chandler and J. Telling. 2015. The effect of warming climate on nutrient and solute export from the Greenland Ice Sheet, Geochemical Perspectives Letters, 1, 94-104.
De’ath, R., J.L. Wadham, F. Monteiro, A. M. Lebrocq, M. Tranter, A. Ridgwell, S. Dutkiewicz, R. Raiswell. 2014. Antarctic Ice Sheet fertilises the Southern Ocean, Biogeosciences Discussions, 11, 1635-2643.
