Table Of ContentNATO ASI Series
Advanced Science Institutes Series
A series presenting the results of activities sponsored by the NATO Science
Committee, which aims at the dissemination of advanced scientific and
technological knowledge, with a view to strengthening links between
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conjunction with the NATO Scientific Affairs Division
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B Physics London and New York
C Mathematical and Kluwer Academic Publishers
Physical Sciences Dordrecht, Boston and London
o Behayioural and
Social Sciences
E Applied Sciences
F Computer and Springer-Verlag
Systems Sciences Berlin Heidelberg New York
G Ecological Sciences London Paris Tokyo Hong Kong
H Cell Biology Barcelona Budapest
I Global Environmental
Change
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The electronic index to the NATO ASI Series provides full bibliographical
references (with keywords and/or abstracts) to more than 30000
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Series I: Global Environmental Change, Vol. 10
The ASI Series Books Published as a Result of
Activities of the Special Programme on
Global Environmental Change
This book contains the proceedings of a NATO Advanced Research
Workshop held within the activities of the NATO Special Programme on
Global Environmental Change, which started in 1991 under the auspices
of the NATO Science Committee.
The volumes published as a result of the activities of the Special Programme
are:
Vol. 1: Global Environmental Change. Edited by R. W. Corell and P. A.
Anderson. 1991.
Vol. 2: The LaSt Deglaciation: Absolute and Radiocarbon Chronologies.
Edited by E. Bard and W. S. Broecker. 1992.
Vol. 3: Start of a Glacial. Edited by G. J. Kukla and E. Went. 1992.
Vol. 4: Interactions of C, N, P and S Biogeochemical Cycles and Global
Change. Edited by R. Wollast, F. T. Mackenzie and L. Chou. 1993.
Vol. 5: Energy and Water Cycles in the Climate System. Edited by
E. Raschke and D. Jacob. 1993.
Vol. 6: Prediction of Interannual Climate Variations. Edited by J. Shukla.
1993.
Vol. 7: The Tropospheric Chemistry of Ozone in the Polar Regions.
Edited by H. Niki and K. H. Becker. 1993.
Vol. 8: The Role of the Stratosphere in Global Change.
Edited by M.-L. Chanin. 1993.
Vol. 9: High Spectral Resolution Infrared Remote Sensing for Earth's
Weather and Climate Studies. Edited by A. Chedin, M.T. Chahine
and NA Scott. 1993.
Vol.10:Towards a Model of Ocean Biogeochemical Processes. Edited by
G. T. Evans and M.J. R. Fasham. 1993.
Towards a Model of Ocean
Biogeochemical Processes
Edited by
Geoffrey T. Evans
Department of Fisheries and Oceans
St. John's, Newfoundland
CanadaA1C 5X1
Michael J. R. Fasham
James Rennell Centre for Ocean Circulation
Natural Environment Research Council
Chilworth Research Centre
Southampton S01 7NS
U.K.
Springer-Verlag
Berlin Heidelberg New York London Paris Tokyo
Hong Kong Barcelona Budapest
Published in cooperation with NATO Scientific Affairs Division
Proceedings of the NATO Advanced Research Workshop Towards a Model of
Ocean Biogeochemical Processes,
held at Chateau de Bonas, France, May 3-9,1992
ISBN-13 :978-3-642-84604-5 e-ISBN -13 :978-3-642-84602-1
DOl: 10.1007/978-3-642-84602-1
Library of Congress Cataloging-in-Publication Data
Towards a model pf biogeochemical processes / edited by Geoffrey T. Evans. Michael J.R.
Fasham. p. cm. - (NATO ASI series. Series I, Global environmental change; vol. 10)
'Proceedings of the NATO Advanced Research Workshop Towards a Model of Ocean
Biogeochemical Processes, held at Chateau de Bonas, France, May 3-9, 1992" - T. p. verso.
"Published in cooperation with NATO Scientific Affairs Division.'
Includes index.
1. Marine biology ~ Simulation methods - Congresses. 2. Biogeochemical cycles - Simulation
methods - Congresses. I. Evans, Geoffrey T., 1948 -. II. Fasham, M. J. R. III. NATO Advanced
Research Workshop Towards a Model of Ocean Biogeochemical Processes (1992: Chateau de
Bonas, France) IV. North Atlantic Treaty Organization. Scientific Affairs Division. V. Series.
QH91.8.B5T68 1993 574.5'263~c20 93-23008 CIP
This work is subiect to copyright. All rights are reserved, whether the whole or part of the material
is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation,
broadcasting, reproduction on microfilm or in any other way, and storage in data banks.
Duplication of this publication or parts thereof is permitted only under the provisions of the
German Copyright Law of September 9, 1965, in its current version, and permission for use must
always be obtained from Springer-Verlag. Violations are liable for prosecution under the German
Copyright Law.
© Springer-Verlag Berlin Heidelberg 1993
Softcover reprint of the hardcover 1s t edition 1993
Typesetting: Camera ready by authors
31/3145-54321 O-Printed on acid-free paper
CONTENTS
Themes in modelling ocean biogeochemical processes
G T Evans and M J R Fasham . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 1
Global extrapolation
E Murphy, J Field, B Kagan, C Lin, V Ryabchenko, J L Sanniento and
J H Steele ........................................... 21
Fluctuations: a task package for the physicists
V C Garcon, H Baumert, W Schrimpf and J D Woods.. . .. ... . . ... 47
Trophic resolution
I J Totterdell, R A Annstrong, H Drange, J S Parslow, T M Powell and
A H Taylor ........................................... 71
Modelling growth and light absorption in the marine diatom Skeletonema
costatum
D A Kiefer. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93
Carbon: a phycocentric view
J A Raven ............................................ 123
Towards a general description of phytoplankton growth for biogeochemical
models
J J Cullen, R J Geider, J Ishizaka, D A Kiefer, J Marra, E Sakshaug and
J A Raven ........................................... 153
Modelling zooplankton
T R Anderson, V Andersen, H G Fransz, B W Frost, 0 Klepper,
F Rassoulzadegan and F Wulff . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 177
Microbial processes and the biological carbon pump
T F Thingstad ......................................... 193
Dissolved organic matter in biogeochemical models of the ocean
D L Kirchman, C Lancelot, M J R Fasham, L Legendre, G Radach and
M Scott .. , ........................................... 209
Modelling particle fluxes
P Tett, G Jackson, F Joos, P Nival, J Rodriguez and U Wolf. . . . . . . .. 227
The significance of interannual variability
J H Steele and E W Henderson .............................. 237
VI
Some parametric and structural simulations with a three-dimensional
ecosystem model of nitrogen cycling in the North Atlantic euphotic zone
R D Slater, J L Sarmiento and M J R Fasham ................... 261
Data assimilation for biogeochemical models
J Ishizaka ............................................ 295
An annotated bibliography of marine biological models
IJTotterdell ......................................... 317
List of participants ..................................... 341
Subject Index .................................... ..... 347
THEMES IN MODELLING OCEAN BIOGEOCHEMICAL
PROCESSES
Geoffrey T. Evans
Department of Fisheries and Oceans
PO Box 5667
St. John's, Newfoundland
Canada, AIC 5XI
MichaelJ. R. Fasham1
1. Introduction
This book is about how to write mechanistic models of marine ecology
that describe and predict how concentrations and fluxes of biologically
important elements (especially carbon) vary in space and time, throughout
the ocean over many years, in response to physical forcing. Such models
are needed because of widespread interest in the global carbon cycle and
the ocean's place in it. The chances of achieving them are improving
because computers are getting better, because satellite remote sensing
offers much more information, and because many scientists worldwide are
cooperating, through the Joint Global Ocean Flux Study (JGOFS), to
collect relevant data and understand relevant processes. As different
research groups undertake modelling projects, comparisons between them
can become as much of an issue as comparisons with observations. It will
help the whole modelling community if common approaches are used
where possible, and if divergent approaches arise from clearly understood
reasons instead of by accident. In the first week of May 1992, a NATO
Advanced Research Workshop (with additional funding from the Scientific
Committee on Oceanic Research) "Towards a Model of Ocean
Biogeochemical Processes" was held at the Chateau de Bonas in Gascony,
lJames Rennell Centre for Ocean Circulation, Natural Environment Research Council,
Chilworth Research Centre, Southampton, SOl 7NS, U.K.
NATO ASI Senes. Vol. 110
Towards a Model of Ocean
BlOgeochclntCal Processes
EdIlcd by G T Evans and M J R. Fasham
IOSpnnger-Verlag Berhn HeIdelberg 1993
2
France. It brought together 45 scientists from 16 countries to discuss the
issues and to explore the extent to which a common approach is possible,
emphasizing the model-building process rather than the results of
particular models. This book is the record of invited lectures and working
group discussions of that meeting.
This introductory chapter presents what the organizers see as the main
themes in developing a model, elaborating most on those themes that
subsequent chapters leave unresolved.
2. Biology in the ocean carbon cycle
To first order, the oceanic carbon cycle consists of water masses
moving and carrying bicarbonate and carbonate ions with them.
Temperature and alkalinity can influence the small fraction of carbon
(-1 %) that is dissolved CO2 gas. If physics and chemistry were acting
alone, then the large-scale circulation and mixing of the ocean would bring
the carbon concentration to much the same value everywhere, with minor
variations in surface waters due to exchange with the atmosphere
modulated by temperature-dependent solubility of CO2•
The distinctive role of biology in global element cycling in the ocean is
to act against this homogenizing tendency: to separate substances and create
particles that move through the water. Photosynthesis converts CO2 to an
organic, non~volatile form; the sinking of biologically-produced material,
both organic tissue and carbonate shells, can induce gradients in the total
carbon concentration. Such processes acting over thousands of years have
led to total carbon concentrations in the deep North Pacific exceeding those
in surface waters by 20%. Changes in these processes are implicated in
large shifts in atmospheric CO between glacial and interglacial periods.
2
(The proximate cause may be changes in physical circulation, but without
the separating effect of biology such changes would have no implications
for CO2) More rapid events, like a spring phytoplankton bloom, can
reduce the local concentration of CO in the surface water by 10% in a
2
week or two. This only represents a reduction in total carbon of 0.1 %, but
it is comparable to the changes in atmospheric CO that human activities
2
have caused. Not that the natural biologically-induced variability has the
potential to absorb the atmospheric increase. It is a local drawdown that
3
will be cancelled, even locally, by events at other times of the year; and it
cannot usefully be compared with a worldwide and unidirectional increase.
We need to consider biogeochemical processes when contemplating a
changed ocean carbon cycle, both because of their feedback potential and
because of the variability they add locally to large-scale surveys.
It may be possible to set an upper bound on the possible effects of
biology. Although biological production needs carbon, it is limited much
more by the availability of other chemical elements (possible 'most
limiting' elements in different circumstances include nitrogen, phos
phorous, silicon and iron) or by light. If biological production goes as far
as its other limiting factors allow - if the water in which there is enough
light (say the top 100 m) is stripped of some essential nutrient (say
nitrogen) and of the corresponding amount of carbon - then we know the
greatest influence biology could possibly have on carbon concentrations.
Shaffer (1993) makes calculations along these lines.
Such calculations would indicate a theoretical upper bound, were it not
that biology acts to separate things. Nitrogen and carbon are combined, in
an almost fixed ratio, into biological particles, some of which sink out of
the well-lit water. Particles don't sink forever: the nitrogen and carbon are
oxidized in deeper water to soluble forms that can be returned to the
surface by physical transport processes. But they are not necessarily
oxidized in the same fixed ratio in which they are combined. There is
evidence that nitrogen is oxidized and dissolved somewhat faster (and
therefore shallower) than carbon, and reaches the surface again sooner.
Each nitrogen atom can only take 6 or 7 carbon atoms down with it on
each trip, but it can possibly make more trips than the carbon it takes
down.
This-differential regeneration affects the rate of cycling; less obviously,
it also affects equilibrium carbon concentrations. Calculating the size of the
effect requires detailed knowledge of differential regeneration and vertical
mixing rates (see Thingstad, this volume); but the principle can be
demonstrated quite simply. Most carbon is regenerated at the same depth as
its associated nitrogen; and so that part of the production and regeneration
cycle is covered by the discussion above. Subtract it out, and consider a
model of only that part of the new production in which nitrogen is
regenerated significantly shallower than carbon. Exaggerate the difference
in regeneration depths by considering that the ocean has three layers: all
the nitrogen that is mixed into the top layer is immediately converted to
4
organic particles that sink; the produced nitrogen sinks to be immediately
regenerated in the middle layer; the produced carbon sinks to be
immediately regenerated in the bottom layer. The nitrogen concentration in
the top layer is thus always zero; and (because there is never any net flux
between the top two layers) mixing will bring nitrogen to the same value,
N say, in the lower two layers. Denote the carbon concentrations in the
top, middle and bottom layers by CT , CM , CB , and the exchange rates
between the layers by KTM and KMB . Nitrogen is mixed into the top layer
at a rate NKTM ; this is therefore also the rate of nitrogen production. The
rate of carbon production is then RNKTM , where R is the Redfield ratio.
The equations that describe the changes in carbon concentrations are:
=
, dCT Idt KTM (CM - CT) - RNKTM (1)
dCM Idt= KTM(CT-CM) + KMB (CB - CM) (2)
dCB Idt = KMB (CM - CB) + RNKTM (3)
=
and at equilibrium, with C T +CM +.C B 3C,
CT = C - (2 + KTMIKMB )RNI3 (4)
CM = C + (1 - KTMIKMB) RNI3 (5)
CB = C + (1 + 2KTMIKMB) RNI3 (6)
The phenomenon of regeneration at different depths thus leads to a
reduction on equilibrium surface carbon concentration. In principle there
is no limit to how far this reduction can go, especially if KMB is very
=
smalL In the extreme case where KMB 0, this is intuitively obvious: the
bottom layer is an unlimited graveyard for carbon, with nitrogen as the
undertaker. Sarmiento et aL (1988) have an identical argument concerning
. ,
the separation of organic carbon and carbonate, and Walsh et aL (1981)
commented on the importance of nitrogen cycling faster than carbon. If
vertical mixing were to change in such a way that the ratio of KTM to KMB
did not change, then there would be no effect on equilibrium carbon levels
despite the change in new production.
In summary, the places where we should seek, and model, a distinctive
role for biological processes in global carbon cycling are (i) the initial
removal of carbon from inorganic, potentially volatile forms: primary
production; (ii) the physical movement of particulate carbon through the
water: sinking and perhaps swimming of organisms - especially vertical
