PII S0016-7037(01)00795-5

A tribute to Hal Helgeson on his 70th birthday

EVERETT L. SHOCK and JAN P. AMEND

Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, USA

This issue of Geochimica et Cosmochimica Acta is dedicated toHarold Helgeson on the occasion of his 70th birthday. Togetherwith Dimitri Sverjensky, Eric Oelkers, and all who contributedto this special issue of Geochimica, we wish to acknowledgethe great difference it has made to us to know Hal, to work withhim, or to have been inspired by his example over the years.

Those who meet Hal rarely forget the experience. He iswidely known to the geochemical community for his innova-tion, rigor, farsightedness, and tenacity in the application ofthermodynamics and kinetics to the study of geochemical pro-cesses. He is known to his friends and close colleagues for hisgreat generosity, honesty, fierce loyalty, diverse opinions, andunconventional sense of humor. Hal can also be a formidablechallenge. Once, after a presentation at an international meet-ing, he asked the speaker, “Do you actually expect any of us tobelieve any of this?” Over the years, this speaker has been innoteworthy company. Evidently, there is no dilute version ofHal. He tackles research and life with an enthusiasm and at anenergy level that can exhaust all but a few full-time fellowcontestants. As a result, his influence on the development oftheoretical geochemistry is profound, unique, and monumental.

In the 1960’s, Hal pioneered the use of computers to calcu-late the speciation of major, minor, and trace elements inhydrothermal ore-forming fluids at high pressures and temper-atures, and to predict the consequences of water-rock reactions.Progress in the ability to test thermodynamic models of geo-chemical processes led to the need for internally-consistentdatabases, pragmatic equations of state for aqueous solutions,and new approaches for estimating rates of mineral dissolutionand precipitation. Filling that need has spawned numerousthesis projects at Berkeley, and generated several series ofpapers. Over the years, organic compounds, microorganisms,and biomolecules have been integrated into the same frame-work that first included minerals and electrolyte solutions. As aresult, it is increasingly possible to test ideas about the inter-action of organic and inorganic constituents of geologic mate-rials, as well as the biotic and abiotic mechanisms of geochemi-cal processes. Simply put, Hal has continued to build andexpand on his previous work rather than retracing his steps.This approach acknowledges the reality that new experimentalwork and theoretical breakthroughs will always supersede thecurrent version of a database or equation of state, while keepingthe emphasis on developing the tools of theory that can be usedto solve practical problems. Many of those applications arepursued by Hal and his students, but many more are tackled byother researchers working in cosmochemistry, metallurgy, mi-crobiology and other fields, using the tools developed at Hal’slab: Prediction Central.

It is highly improbable for Hal to take a shortcut. The path ofresearch at Prediction Central can be long, convoluted, andfilled with obstacles that must be overcome. But, as Hal wouldsay, “Once you get to New York City nobody cares how you

got there!” So, although the minutia must be vanquished, thegoal is always in sight. For Hal, the challenge is the motivation,and his persistence, perseverance, and tenacity when attackingresearch problems seems boundless. Students often have longtenures with Hal, but they produce fundamental contributionsto theoretical geochemistry. Other projects take on lives of theirown, with longevities that exceed any graduate career. Thework culminating in the Helgeson-Kirkham-Flowers equationof state began at least a dozen years earlier. Research towardthe internally-consistent thermodynamic data for organic com-pounds published in 1998 began in 1986, work began in 1981on the comprehensive approach to inorganic complexes pub-lished in 1997, and ongoing work on the thermodynamics ofprotein folding began in 1992.

Meanwhile, as bandwagons rattle along, Hal persists in do-ing exactly what he is interested in, and following his convic-tions. Typically, the pay-off is assumed to be in the long term.Some contributions from Prediction Central are immediatelysnapped up by those striving to understand geochemical pro-cesses. Others await discovery, aging like fine wines; a fewstand sequoia-like in the churning forest of the literature, pa-tiently waiting to shed their fruits of insight should someoneaccidently encounter them. Through it all, Hal reminds hisstudents that they are writing papers for posterity, and that theyhave a duty to get it right.

A remarkable feature of Hal’s career is his decision, early on,to freely distribute copies of computer codes and databasesgenerated over the course of research in his lab. Hundreds ofresearchers around the world fire-up a version of SUPCRT, andmany others use software that is derived from products ofPrediction Central, perhaps unknowingly. Hal may say, “it’sfree energy, how could I charge for it?” but the fact is thatresults from Prediction Central easily permeate the theoreticalmethods used by researchers everywhere. This facilitates theuse by others of results from Hal’s research group, creates alegacy beyond the publication record, and encourages a senseof community for those who work on building up the theoret-ical tools.

Rather than restricting submissions to this issue to any par-ticular topic, friends and colleagues were invited to choose theirown personal tribute to Hal. As a result, the diverse topicscovered in this issue reflect many of the geochemical directionsHal has pursued throughout his remarkable career: from min-eral dissolution and growth kinetics to phase equilibria andsolid solutions, from reactive transport to speciation and com-plex formation, and from the stability of organic compounds atgeochemically relevant conditions to fundamental derivationsof thermodynamic relations. Papers on Hal’s current scientificpassion, the reactivity of complex biomolecules such as pro-teins and nucleic acids, are underrepresented in this issue, but,as most of us know first hand, it is nearly impossible to keeppace with Hal.

Pergamon

Geochimica et Cosmochimica Acta, Vol. 65, No. 21, p. 3613, 2001Copyright © 2001 Elsevier Science LtdPrinted in the USA. All rights reserved

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