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SACRAMENTO BRANCH MEETING
2020 Birdsall-Dreiss Distinguished Lecture
High Latitude Hydrology: Water in a Changing World
Dr. Jonathan B. Martin
Professor of Geological Sciences at the University of Florida
PRESENTATION:
Retreat of continental ice sheets has exposed ~15% of Earth’s surface since the Last Glacial Maximum (LGM) and deposited fine-grained sediments in “deglaciated” watersheds. These sediments are susceptible to enhanced chemical weathering, which may vary in intensity and reaction mechanisms depending on exposure times and precipitation. Thus, ice retreat should alter solute fluxes to the ocean and gas exchange with the atmosphere as reflected by the rise in seawater Pb isotopes following the LGM. Solute and gas fluxes will depend on both riverine concentrations and discharges. Although discharge may be orders of magnitude greater for individual proglacial than non-glacial streams, their specific discharge (normalized to drainage area) is similar in western and southern Greenland. However, chemical compositions are distinct between proglacial and deglaciated watersheds and among deglaciated watersheds depending on their exposure ages and precipitation. Newly deglaciated watersheds have dissolved 87Sr/86Sr ratios that are 0.003 greater than bedload values but this difference decreases to near zero in watersheds with longer exposure ages, reflecting greater chemical weathering. The dominant weathering reactions shift with exposure age from carbonic acid weathering of carbonate minerals to sulfuric acid weathering of silicate minerals, thereby altering CO2 consumption and production. Compared to proglacial watersheds, deglaciated watersheds have enhanced dissolved organic carbon (DOC) specific yields but the DOC is more recalcitrant than proglacial DOC. Among proglacial watersheds CO2 and CH4 fluxes vary, depending on magnitudes of subglacial mineral weathering and organic matter contents. These results indicate ice retreat is an important control on mass fluxes from periglacial environments. Understanding causes of these differences could improve analyses of how past ice retreat altered ocean and atmospheric chemistry and provide predictive capability for changes in fluxes with continued ice retreat in a future warmer world.
SPEAKER BIO:
Jonathan B. Martin is Professor of Geological Sciences at the University of Florida, where he has worked since 1994. He received a BA in Environmental Science at Wesleyan University in 1980, an MS in Geology from Duke University in 1987, and a PhD in Earth Sciences from UC San Diego, Scripps Institution of Oceanography in 1993. His research evaluates water chemistry in a range of environments to understand interactions between flow and biogeochemical and inorganic reactions. His dissertation research focused on discharge and chemical processes at cold methane-rich seeps on the seafloor at convergent margins. Following his move to Florida, his research expanded to include studies of chemical reactions in carbonate aquifers based on variations in spring water compositions. He also developed an interest in nearshore marine settings where he assesses impacts of sea level rise on freshwater-saltwater mixing in coastal aquifers and the chemistry of submarine groundwater discharge. His interests in flow through karstic systems and effects of sea level rise led to studies of glacial hydrology. This research examines how chemical and isotopic compositions of streams draining the Greenland Ice Sheet differ from those draining watersheds exposed during ice sheet retreat. Martin was selected as a GSA Fellow in 2006. He is an emeritus member of the Karst Waters Institute Board of Directors, has been associate editor of Groundwater since 2005, and was a visiting professor at the University of Montpellier, France (2007), and University of Bristol, UK (2017).
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MEETING COSTS AND RSVP:
This meeting will be provided to members at no cost but registration is necessary to receive call-in information.
Member Price: FREE
Non-Member Price: $10.00
Student Price: FREE
CONTACT INFORMATION:
If you have any questions, please call Mike Bombard at (916) 865-5301 or email him at michael.bombard@GHD.com.