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Theme 12

Global Geochemical Cycles: Past Record and Future Impact

Kirk Cochran, SUNY-Stony Brook,
Yair Rosenthal, Rutgers,

Co-hosted sessions

SESSIONS

12a. Peatlands and lakes as dynamic geochemical systems

Co-convenors:
François De Vleeschouwer (EcoLab-Toulouse) – fdevleeschouwer gmail.com
Richard Bindler (Umeå University, Sweden) - richard.bindleremg.umu.se
Gaël Le Roux (EcoLab, UMR-CNRS 5245, Toulouse) - gael.lerouxensat.fr

Investigating peatland and lake geochemistry is crucial to better understand environmental changes induced either by natural or anthropogenic forcings. Peatlands are very efficient geochemical traps. Accumulating since the very early Holocene in temperate zones and longer in the Tropics, peatlands are environmental archives of inorganic and organic compounds. Therefore, they record ancient and recent fluxes of natural and anthropogenic compounds (e.g. REE, Ti, halogens, Pb, Sb, Hg, POPs, radionuclides). Whereas lake sediments are not directly recording atmospheric signals, they can effectively be used to trace past environmental changes occurring at a local (watershed) or global scale, regardless if those changes are forced by natural or anthropogenic factors. Moreover, as dynamic geochemical systems, peatlands and lakes can store and/or release toxic elements (e.g. As, U) to the watershed as a result of climate change and human disturbances (e.g. drainage, pastures).

This session welcomes contributions dealing mainly with these aspects of geochemical peatland and lake research. We also invite contributions about new geochemical proxies (e.g. PGE's, non-traditional stable isotopes) as well as interdisciplinary studies. New researchers are also warmly welcome to present their work.

Keynote speakers:
William Shotyk (University of Alberta), shotykualberta.ca
Alain Véron (CEREGE-CNRS, France), veroncerege.fr

12b. Pa and Th distributions in the ocean: controlling mechanisms

(co-hosted by Themes 12 and 13)

Co-convenors:
Abel Guihou (SUNY-Stony Brook) - abel.guihoustonybrook.edu
Robert F Anderson (LDEO of Columbia University) - bobaldeo.columbia.edu

231Pa and long-lived Th isotopes are naturally occurring radionuclides. Their potential to provide quantitative information of modern and past oceanographic processes (such as large scale ocean circulation and particle fluxes and dissolution) has been acknowledged for decades. However, some uncertainties still remain regarding what actually controls their distribution in the ocean. This session invites contributions aimed to better understand these mechanisms such has new dissolved and particulate water column profiles, new views on the distribution of these radionuclides onto particles from natural samples or from laboratory experiments as well as modeling studies.

Keynote speaker:
Michiel Rutgers van der Loeff (Alfred Wegener Institute for Polar and Marine Research) -  Michiel.Rutgers.v.d.Loeffawi.de

12c. Low-temperature Si isotope geochemistry: a proxy for environmental conditions?

Co-convenors:
Karen Ziegler (UC-Los Angeles) - kziegleress.ucla.edu
Johanna Marin-Carbonne (UC-Los Angeles) - jmarincarbonnegmail.com

Si is one of the most abundant elements on Earth, and with improved analytical precision with MC-ICPMS and SIMS analyses, we expect a better understanding of the role of Si in terrestrial surface and near-surface processes. These include, amongst others, weathering, soil-plant-interactions, early diagenesis, and transport pathways and mechanisms of Si from land to ocean. Despite improved precision, there is still incomplete and controversial information on Si isotope fractionations in low-temperature environments. In order to better determine this fractionation, more experiments are required.

This session invites contributions on the latest insights from experimental and empirical (natural) Si isotope studies that elucidate the nature and mechanisms of isotopic fractionation. These will be invaluable for the comprehension of the fundamental systematics of Si isotope geochemistry. An additional key point of this session is to seek out known or anticipated issues that need to be addressed regarding the possibility of Si isotopes as a new proxy for climate and paleoclimate conditions.

Keynote speaker:
Bastian Georg (Trent University, Canada), rgeorgtrentu.ca

12d. Ocean deoxygenation and coastal hypoxia: impact on ocean biogeochemistry

(co-hosted by Themes 12 and 13)

Co-convenors:
Samuel L. Jaccard (ETH-Zurich, Switzerland) - samuel.jaccarderdw.ethz.ch
Rebecca S. Robinson (University of Rhode Island) - rebeccargso.uri.edu

Anthropogenic warming is expected to drive oxygen out of the ocean, as the water temperature rises and the upper ocean becomes stratified. Surface-ocean warming will not be uniform, with stronger warming concentrated in tropical and Northern Hemisphere subpolar regions. The largest changes in O₂ will probably occur close to the outcrops of the thermocline and deep ocean, but regions of particular vulnerability will be the low oxygen regions of the low latitudes, where oxygen-depleted waters impinge on continental margins. Widespread deoxygenation will have an impact on shelf habitat as well as on several of the ocean’s major biogeochemical cycles, as O₂ is a key controlling factor for the cycling of carbon, nitrogen, iron and other elements. While recent observations appear to confirm this prediction, the apparent changes remain subtle in the face of natural decadal variability. Paleoceanographic records extend much further back in time, beyond the noise of recent variability, to provide an independent perspective on the links between climate-driven ocean circulation and/or export production changes and hypoxia.

We welcome contributions addressing the volumetric evolution of OMZs since the Pliocene, including the present and near future, and associated effects of deoxygenation on nutrient cycling, in particular on nitrogen and trace metal inventories, based on observations, model simulations or sedimentary reconstructions.

Keynote speaker:
Curtis Deutsch (UCLA), cdeutschatmos.ucla.edu
Invited speakers:
Eric Galbraith (McGill University), eric.galbraithmcgill.ca
Frank Whitney (Dept. Fisheries & Oceans Canada, Victoria), WhitneyFdfo-mpo.gc.ca

12e. Present and past biogeochemical cycling of nutrients and metals in high latitude marine environments

(co-hosted by Themes 12 and 16)

Co-convenors:
Laura Wehrmann (University of California Riverside, USA) - laura.wehrmannucr.edu
Christian März (Newcastle University, UK) - christian.maerznewcastle.ac.uk

This session targets the emerging field of biogeochemical research in Arctic and Antarctic environments, with a focus on understanding the role of the high latitudes for global element cycles (C, N, P, S, Si, transition metals) at present and in the past. We welcome contributions elucidating the cycling of these elements in the water column, at the ice-sediment and sediment-water interface, in shallow as well as in deeply buried marine sediments of high latitude environments. This session aims to gather scientists studying Arctic and Antarctic fjords, estuaries and river mouths, glacial and pro-glacial environments, as well as associated continental shelves, slopes, and the deep oceans. Topics of particular interest include, but are not limited to the (coupled) cycling of carbon, sulphur, phosphorus, iron and manganese in Arctic and Antarctic sediments; the overprint of paleoclimate proxies by biogeochemical processes; the role of microbial processes in shaping the diagenetic characteristics of high latitude environments; biogeochemical interactions between glaciers and the coastal ocean; the role of high latitude environments for global biogeochemical cycles in the past. We especially encourage contributions that apply multidisciplinary approaches, novel analytical techniques, and computer modelling to natural samples and/or in laboratory experiments.

Keynote speaker:
Hein de Baar (NIOZ, The Netherlands), Hein.de.Baarnioz.nl

12f. Processes of mineralization: understanding classical vs. non-classical crystallization and controls on the kinetics and thermodynamics of nucleation and growth

Co-convenors:
Laura Hamm (Virginia Tech) - maehamm6vt.edu
Patricia Dove (Virginia Tech) - dovevt.edu

CANCELLED

12g. Contribution of submarine groundwater discharge to oceanic chemical cycles

(co-hosted by Themes 12 and 22)

Co-convenors:
Aaron Beck (Virginia Institute of Marine Science) - abeckvims.edu
Richard Peterson (Coastal Carolina University) - rpeters2coastal.edu

Submarine groundwater discharge (SGD) comprises all water transported by advection across the permeable sediment-water interface, including both fresh groundwater and recirculated seawater. Biogeochemical reactions such as ion exchange, dissolution and precipitation, and metal redox cycling occur in the subsurface mixing zone of fresh and saline groundwaters (the “subterranean estuary”), resulting in brackish SGD that can be very different in composition from either of the original end-members. Further, the advection of groundwater through the diagenetic zone can mobilize regenerated nutrients, and serve as a transport pathway of these recycled nutrients back to the water column. A growing body of work demonstrates the importance of SGD and subterranean estuaries to marine budgets of nutrients, radionuclides, and trace elements. Understanding current SGD-driven chemical fluxes is critical for predicting how future changes in the hydrologic cycle, coastal margins, and anthropogenic factors may affect chemical cycling in the ocean. This session will explore the role of SGD and the subterranean estuary in controlling chemical fluxes between land and sea. We especially encourage studies that assess the ecological impact of these fluxes, which is yet relatively unrepresented in this field.

Keynote speaker:
Peter W. Swarzenski (USGS-Santa Cruz), pswarzenusgs.gov

12h. New frontiers in methane biogeochemistry

(co-hosted by Themes 12 and 16)

Co-convenors:
José M. Mogollón (Alfred Wegener Institute for Polar and Marine Research) - jose.mogollonawi.de
Michael Formolo (University of Tulsa, OK) - michael-formoloutulsa.edu
Laura Lapham (University of Maryland) - laphamumces.edu

Methane is a potent greenhouse gas which constitutes an integral part of the global carbon cycle. Although methane has been extensively studied in the past decades, open questions still linger in terms of the methane cycle across a large range of aquatic and sedimentary environments. In this context, some of the greatest unknowns pertain to our current understanding of methanogenesis, namely rates, timescales, and dominant pathways, as well as to the methanotrophic role of oxidizing agents other than sulfate. Addressing these queries will ultimately aid in pinpointing dominant methane sources and sinks, quantifying how much methane is present in the hydrosphere, and further elucidate on past, contemporary, and future methane turnover rates. In this session, we invite active discussion about state-of-the-art studies of methanogenesis and methanotrophy from the biological, geochemical, geological, paleontological, isotopic and modeling perspectives. Topics include insights into methane provenance, methanogenesis vs. methanotrophy, tools for estimating methanogenic and methanotrophic rates, geochemical signatures of these processes, and behavior/detection of methanogenic and methanotrophic communities.

Keynote speaker:
Marc Alperin (University of South Carolina – Chapel Hill), alperinemail.unc.edu

12i. Combining spectroscopic and isotopic techniques: new insights in trace elements biogeochemical cycles comprehension.

(co-hosted by Themes 12 and 17)

Co-convenors:
Marc Benedetti (Université Paris Diderot) - benedettiipgp.fr
Dominik J. Weiss (Imperial College, London) - d.weissimperial.ac.uk
Farid Juillot (Université Paris Diderot) - Farid.Juillotimpmc.upmc.fr

Whereas major element behavior in biogeochemical cycles can be reasonably well predicted, the fate and behavior of trace metals is still challenging. The major headways obtained during the last decade in the comprehension of trace elements biogeochemical cycles are directly related to the development of both X -Ray absorption Spectroscopy and isotopic techniques. The combination of spectroscopic (EXAFS, XANES...) and non-traditional isotopic fractionation measurements methods allows the elaboration of more comprehensive models of trace-element fate and behavior on the Earth surface. This session will bring together experts of both fields. We welcome contributions dealing with aquatic/solid/biological interfaces either on natural or experimental samples/systems. The contribution can address each approach (XAS vs Isotopic) separately although contributions combining both approaches are favored. Contributions addressing modeling issues are also welcomed, if they can help us to improve our understanding of fractionation processes.

Keynote speaker: TBA

Co-hosted sessions:

Please note that for abstract submission purposes, the following sessions and their respective descriptions appear in their primary Theme assignments (numbers in red or before the title).

7f.- Critical zone processes: their role in ecology and evolution

Co-convenors: Elisabeth Bui/CSIRO, Australia and Martin Goldhaber/USGS
(co-hosted by Themes 7, 12 and 15)

7h.- Weathering of sediments – from natural processes to underground CO₂ storage

Co-convenors: Matthias Haeckel/GEOMAR, Judith Schicks/GFZ, Potsdam and Giovanni Aloisi/UPMC, Paris
(co-hosted by Themes 7, 12 and 19)

13g.- Insights into recent and Cenozoic carbon cycle perturbations using boron based isotopes

Co-convenors: Marcus Gutjahr/Southampton, Gavin Foster/Southampton and Bärbel Hönisch/LDEO
(co-hosted by Themes 13 and 12)

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