Eos,Vol. **, No. **, * November ****

models is to embed coastal models with finer processes. Remote sensing is also showing us we can explore mechanisms of current vari-

that major rivers have a strong influence on ability and predict future change.

resolutions (temporal and spatial) into the

biological processes far into the ocean basins. The University Corporation for Atmospheric

larger-scale models.

There is clearly a strong need to better con-

We know that many biogeochemical aspects Research (UCAR)/NCAR Junior Faculty Forum

strain the role of the coastal zones in biogeo-

of the coastal zones are globally significant on Future Scientific Directions was held 23 25

chemical cycles and feedbacks. Observations

and directly relevant to human activity, but June 2004, at NCAR in Boulder, Colorado.

and models both will contribute to improving

there is much more to be learned.We need to

our understanding of the coastal zone with

understand the influence of the coastal zone

respect to the carbon budget, trace gas emis-

on the global carbon cycle.We need to better

sions, and influence on atmospheric chemistry

constrain the physical and biological processes RONALD L. SIEFERT, Chesapeake Biological Lab-

and aerosols. New observation systems with

that control trace gas exchange.The role of oratory, University of Maryland Center for Environ-

better spatial and temporal resolution will

anthropogenic nutrient inputs in trace gas mental Science, Solomons, Md.; E-mail: siefert@cbl.

help us to understand the heterogeneity of

emissions is particularly important.There are umces.edu; and GIAN-KASPER PLATTNER,Biogeochem-

the coastal zone, define their various types,

also regions in the coastal zones, such as salt istry Group, Institute of Geophysics and Planetary

and parameterize their functions in global

marshes and mangrove swamps, that are still Physics, University of California, Los Angeles; E-mail:

models.With improved prognostic modeling,

relatively understudied with respect to these abqc7i@r.postjobfree.com

Future Applications of Thorium-234 of deep particle layers, such as those produced

from hydrothermal systems,may cause 234Th:238U

in Aquatic Ecosystems disequilibria in some instances. Small disequi-

libria in surface waters are common, and

uncertainties in calibration assumptions can

PAGE 471 tion in Woods Hole, Massachusetts, for a work-

result in large errors in the 234Th flux.

shop on the Future Applications of 234Th in

A fundamental and outstanding issue in Given the wide range of procedures currently

Aquatic Ecosystems (FATE).The purpose of

marine biogeochemistry is understanding the in use for the measurement of 234Th activity, the

the workshop was to bring together a number

mechanisms that control and enhance the flux community should strive to rigorously define

of international experts in the collection,

of material from the surface ocean to depth. analytical procedures that can be compared

analysis, and interpretation of 234Th in aquatic

Sinking particles are the ultimate removal using standardized materials, such as aged

ecosystems with diverse opinions and back-

mechanism of many biologically and particle seawater rather than deep seawaters.This

grounds. Geochemists not directly involved in

reactive elements from the ocean.This includes includes the calibration of equipment for spe-

Th measurements were also present to pro-

234

atmospheric carbon, which is converted from cific sample types, i.e., particles, and geometries

vide outside perspective into the current status

CO2 to particulate phases during biological being measured.

and future directions of 234Th research.A num-

production and sequestered to deep waters ber of students also attended the meeting and

via particle sinking. Unfortunately, the temporal acted as scribes to record comments and Collection and Application of Particulate

and spatial magnitude of the sinking particle ideas put forward during the working group Organic Carbon/234Th Ratios

flux remains an elusive and difficult process sessions.

to study. In order to convert 234Th fluxes into export of

The participants were asked to discuss and

Over the past decade,thorium-234 has increas- a particular element of interest, it is necessary

define current issues in the use of 234Th as well

ingly been used to quantify particle fluxes from to quantify the elemental to 234Th ratios of sink-

as a coherent strategy for future endeavors.

surface waters in both open-ocean and coastal ing particles at a given reference depth.The

Invited talks (available at http://www.geol.sc.edu/

environments.Thorium-234 (t1/2 = 24.1 days) is most common application is in determining

cbnelson/Thmeeting/Index.htm) focused on

a particle reactive radionuclide that is produced the export of POC. POC/234Th ratios may vary

four main areas (see below) and set the stage

in seawater by radioactive decay of its dissolved widely depending on the geographical loca-

for in-depth discussions.A brief overview of

conservative parent, 238U. In principle, the dis- tion, bloom versus nonbloom conditions, and

the working group discussions is presented

equilibrium between 238U and the measured collection technique (i.e., in situ pumps versus

here.

total 234Th activity reflects the net rate of particle sediment traps).

export from the surface ocean on timescales While POC/234Th ratios may vary greatly within

Methodologies and Techniques

of days to weeks.Thus, 234Th should serve as an the upper 100 m and within coastal areas,

integrative tracer that is relatively forgiving in evidence presented at the meeting provided

There are currently a number of techniques

terms of biological patchiness and temporal convincing arguments that there is much less

available for the measurement of 234Th.These

heterogeneity. Furthermore, it enables multiple variability in open-ocean settings at depths

techniques have inherent strengths and weak-

sample collection at a suite of depths throughout just below the euphotic zone.The group agreed

nesses that are not necessarily clear to those

the water column, enabling a closer examina- that at these depths POC/234Th ratios are often

outside the 234Th community. Guidance and a

tion of particle flux and remineralization within a factor of 2 3. At least some of this

consensus on where and when each method

patterns. range in the ratio of POC/234Th at depth is due

should or should not be used is needed,

In spite of advances in sample collection, to natural variability, but there are also differ-

including specific recommendations regarding

analytical methods, and technology, there ences in the POC/234Th ratio depending on the

sample size and collection methods, precon-

remain a number of important questions con- method of collection that needs to be further

centration techniques,the use of yield monitors,

cerning 234Th speciation, reactivity, sample col- evaluated.

counting procedures, and error analysis.

lection and analysis, and modeling strategies In essence, the thorium community has

In addition, there are currently no specific

that affect our interpretation of 234Th disequi- inherited the same issues encountered by the

Th standards available for intermethod and

234

librium.The uncertainties and debate regard- sediment trap community; there is no unbiased

interlaboratory comparisons.This is due in

ing these issues need to be resolved if 234Th is part to the fact that 234Th has a very short half- mechanism for collecting a representative

going to continue to be successfully applied life and is therefore not amenable to being sinking particle. The group suggested that

as an in situ tracer for the export of particulate distributed as a standard reference material. following specific protocols in the collection

organic carbon (POC) and associated biogenic Many laboratories calibrate 234Th to deep-water of particulate 234Th will reduce the range and

and other particle reactive elements. samples and assume equilibrium with 238U uncertainty of POC/234Th measurements and

In August 2004, over 40 researchers from the (which is in turn derived from salinity). allow for better intercomparisons between

United States,Europe,India, Australia,and China However, sediment resuspension, deep-sea data sets. Further characterization of samples

met at the Woods Hole Oceanographic Institu- migrating zooplankton,and even the abundance using simultaneous particle collection by

Eos,Vol. 85, No. 45, 9 November 2004

various techniques is needed to clarify why Th:238U disequilibria and the ratio of a specif- in coastal areas, estuaries, ice-covered regions,

234

ic element to 234Th on sinking particles with- and even freshwater ecosystems. Furthermore,

methodological differences occur, such as dif-

out any inherent understanding of the there may be specific scavenging processes,

ferences in POC concentrations from bottles

relationships between them,i.e.,an empirical such as those involving marine snow and other

versus pumps. Many examples were given

approach.While it may not be requisite to constituents, such as iron, other radionuclides

where such studies are already under way.As

understand the speciation of 234Th to constrain (210Po/210Pb), and metal and organic contami-

better collection techniques are developed,

particle flux, the group concluded that a nants, that may be better used in combination

natural variability in POC/234Th ratios versus

mechanistic understanding of particle interac- with 234Th for understanding surface export.

methodological differences will become more

tions of Th is highly desirable. It was argued A series of five papers in a special volume of

apparent.

that at least some of the variability associated Marine Chemistry regarding 234Th are scheduled

with changes in POC/234Th ratios is related to to appear in summer 2005.An important

Modeling and Synthesis

Th speciation within different regimes. objective of these papers is to help clarify the

234

Historically, measurements of 234Th have most Understanding why the POC/234Th ratio varies mystique of the 234Th technique to the larger

often been treated with a simple one-dimen- should clarify the sample collection issues aquatic community, provide a summary of our

sional, one-box model of 234Th:238U disequilibria discussed here. current understanding of 234Th applications,

for the determination of particle flux. Multiple However,dissolved organic matter and organic and set the stage for future endeavors of 234Th

particle box models for elucidating particle ligand speciation in natural waters is a com- in aquatic ecosystems.

residence times, and particle aggregation/dis- plex issue unto itself. Combined laboratory, Future Applications of Thorium-234 in Aquatic

aggregation dynamics have also been applied. mesocosm, and field-based studies that char- Ecosystems (FATE) was held 16 19 August

The advent of new analytical techniques, however, acterize the speciation of the dissolved,colloidal, 2004 at the Woods Hole Oceanographic Institu-

has enabled the collection of multiple profiles and particulate 234Th pool are recommended. tion,in Woods Hole,Massachusetts.

of 234Th:238U disequilibria with depth. In principle, These studies must examine the relationships

data can be acquired that can address steady between particulate 234Th, number, and type of Acknowledgments

state versus non-steady-state assumptions and surface sites, biophysical ligand properties,

The FATE workshop was supported by the

include the role of physical mixing processes. and chemical composition as well as how

U.S. National Science Foundation, Chemical

It appears that physical transport processes these interactions are modified by biological

Oceanography Program (grant #OCE 0354757)

may influence the budget of 234Th, particularly activity over time.This undertaking will require

and the Scientific Committee on Oceanographic

in coastal and upwelling areas, and hence the a paradigm shift in the quest for a better under-

Research (SCOR Working Group 116).

measured 234Th:238U disequilibrium from which standing of a family of highly surface reactive

The 234Th-Group: David Amiel, Bob Anderson,

fluxes are derived. macromolecular Th binding ligands that neces-

Robert Armstrong, Mike Bacon, Mark Baskaran,

Non-steady-state processes, such as bloom sitates a larger investment in marine biophysical

Ken Buesseler,Adrian Burd, Matt Charette, Kirk

events in open-ocean oligotrophic settings, and analytical chemical research.

Cochran, Laurent Coppola, Minhan Dai,Timo-

can also be important.

thy Eglinton, Kelly Falkner, Nicholas Fisher, Scott

The group suggested that simple guidelines Conclusions and Future Work

Fowler,Wilford Gardner, Laodong Guo, Orjan

be developed that detail the complexity, uncer-

Gustafsson, Kate Hagstrom, Chin-Chang Hung,

The meeting was successful in delineating

tainty and assumptions inherent in 234Th-derived,

George Jackson, Carl Lamborg, Kanchan Maiti,

the community s current knowledge and use

particle fluxes. For example, errors associated

Pere Masque,Juan Carlos Miquel,Bradley Moran,

of 234Th as a tracer of POC export, and in iden-

with non-steady-state models become increas-

Paul Morris, James W. Murray, Kent Orlandini,

tifying issues that need to be resolved for future

ingly large when 234Th:238U disequilibria is small

Uta Passow, Kim Roberts,Alessia Rodriguez y

work.Throughout the course of discussions,

due to propagation of analytical uncertainties.

Baena, Matthieu Roy-Barman, Michiel Rutgers

however, it became apparent that 234Th may be

Such guidelines would help focus current

van der Loeff, Peter Santschi, Manmohan Sarin,

underutilized for examining particle-related

sampling efforts and in the derivation of more

Nicolas Savoye, Sabine Schmidt, Jennifer

processes beyond POC export. Advances in

accurate 234Th particle export estimates.

Szlosek, Gillian Stewart,Tom Trull, James Waples,

technology have now made it possible for 234Th

Sarah Weinstein, and Jianhong Xue.

to be used as a tracer of particle formation

Thorium 234 Speciation

and remineralization well below the depth of

CLAUDIA BENITEZ-NELSON, University of South

the euphotic zone.Thorium-234 may also be

To date, the application of 234Th for deriving

Carolina, Columbia; and THE 234TH-GROUP

applied to help quantify particle scavenging

particle export has involved a measure of

Saied Mostaghimi has received the 2004

G E O P H Y S I C I S T S Alumni Award for Excellence in Undergraduate

Advising, which is presented annually by the

Virginia Polytechnic Institute and State Univer-

Honors

PAGE 472

sity to a faculty member who has demonstrated

In Memoriam outstanding advisement of graduate

Patricia Manley has received the 2004 Asso-

students.

ciation for Women Geoscientists Foundation

William Bandeen, 77, 2004,AGU Fellow, Outstanding Educator Award,which is presented Veerabhadran Ramanathan has been

Atmospheric Sciences, 1961. to well-established college or university teach- appointed by Pope John Paul II to be an aca-

ers who have played a significant role in the demician of the Pontifical Academy of Sciences.

Raymond A. Lewandowski, 82, September education and support of women geoscientists He will contribute by attending scientific

2004, Volcanology, Geochemistry, and both within and outside the classroom. During meetings, including the academy s plenary

Petrology, 1965. her 15-year stint at Middlebury College in Ver- sessions, proposing subjects for scientific

mont, Manley has supervised numerous senior meetings, and nominating outstanding scien-

Tsuneji Rikitake, 83,August 2004,AGU theses, with many of these students presenting tists for membership as well as young scien-

Fellow, Retired Life Member, Geomagnetism their work at regional and national scientific tists of international reputation for the Pius XI

and Paleomagnetism, 1964. meetings. Medal.

Contact this candidate