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Goldschmidt 2015
 Author: Andy Bray

The Global Weathering Thermostat

Yesterday in Terrace 1 was an absolute delight. I sat there for most of the day listening to some fantastic biogeochemistry. From weathering of rock to soil and sediment, to the profound influence of one man on global biogeochemistry.

 

After the conclusion of 5C (From Rock to Soil and Sediment), Sue Brantley took the stage as part of the 25 Anniversary lectures, to give a great overview of the progression and development in the field of weathering science over the last 25 years. It was great to see how experimental setups, conceptual models, reactive transport models, and field measurements have changed as the field has grown and innovated. The testament to this growth was the sheer number of people in the room as Sue spoke. Sue finished the talk by providing a list of things she thought we would discover in the weathering community in the coming years. Sadly, my pen was scribbling too quickly for me to legibly note them! (If anyone has a copy, please let me know)

 

It seemed too good, with room full, that the session then switched to 5A – the session I have been most looking forward to this year. Session 5A The Global Weathering Thermostat, celebrating Bob Berner’s contribution to geochemistry, started with Dave Beerling’s keynote. Dave reminded us all of Bob’s ideas around silicate weathering and the global carbon cycle, and proposed a geoengineering plan to sequester atmospheric CO2, preventing catastrophic global change. Dave’s proposal, to fertilise the terrestrial tropics with 3-5 kg/m-2 of silicates (basalt or harzburgite) and the subsequent mineral weathering would draw down 100 or 260 ppm of CO2 for basalt and harzburgite, respectively, over the next century. The benefits of this would be the improvement of ocean water quality (combating the dangers presented by Peter Sale on Monday), enhancement of agricultural yields through the stimulation of mycorrhizal fungi, and the protection of plants against destructive bugs by the inclusion of additional Si in leaves. Dave admitted that the concept of geoengineering is fraught with ethical dilemmas, but finished by emphasising how viable and promising studies have shown this to be.

 

Following on, Tim Lyons gave a brief history of Bob’s chemical career, highlighting in particular Bob’s chemical autobiography “From Black Mud to Earth System Science: A Scientific Autobiography”. Tim Described how Bob and Rob Raiswell developed ideas on the relationships between iron, sulfur, and carbon. It was this work that led to studies by the FOAM group (Friends of Anoxic Mud), now giving us detailed information on Fe biogeochemistry in modern systems. Tim rounded up his presentation by describing how Bob’s work with many people on iron, sulfur, and carbon has led to the current work on oceanic Fe, S, and C cycling through time.

 

Sue Brantley then highlighted Bob’s work on the trends of atmospheric O2 and CO2 through time. Sue described how rock and mineral weathering is driven by 2 chemical systems, acid/base and reduction/oxidation reactions. The drivers of these two reactions in the regolith being CO2 and O2, respectively. Sue presented evidence from recent studies that the susceptibility of a rock to preferential acid/base or reduction/oxidation reactions is due to the rock’s Fe content, specifically Fe(II). This link between O2, CO2, and weathering rate being very much Bernerite in concept.

 

The last talk of the day was given by Christian März, which he started with a Berner quote about how, after studying the carbon cycle, he had realised that phosphorus is the most important element. Christian noted 4 of the leading phosphorus geochemists that had worked with Bob, van Cappellen, Krom, Ingall, and Ruttenberg, 2 of which I could see in the room, highlighting Bob’s impact on the field. Christian summarised his presentation by describing revisions to the oceanic P cycle, emphasising the role of, in particular, Fe and C on the fate and availability of phosphorous.

 

This was only around ¼ of the session in tribute to Bob. I dare say that today’s contributions in Terrace 1 will further present Bob’s wide reaching, and positively influential addition to this community. Christian finished his presentation by saying the following:

 

“If you think you’ve discovered something new, go back and very carefully read Bob’s papers. He probably did it 30 years ago!”

 

As this quote suggests Bob Berner has had, and continues to have, an incredible impact on the geochemical community. It might be many years until we can truly appreciate this.

Robert A. Berner (1935-2015)

 

Highlights of the day…

Medal citations:

 

25th Anniversary talks:

Today’s plenary talk will be given by Barbara Sherwood Lollar, President of the Geochemical Society

 

From Cohen Geochemistry and the Earth Surface Science Institute at the university of Leeds we have the following presentations:

Not forgetting…

 

Andy’s Pick of the Day is, of course, my very own, highly anticipated presentation at 15:30 in Terrace 1. However, today I can recommend a second pick…the second half of session 5A, in Terrace 1 all morning will be a great continuation of the celebration of, and tributes to the Bob Berner and his work.