Biogeochemistry of the Ross Sea

354 Pages·2003·29.04 MB·English

ANTARCTIC
American Geophysical Union RESEARCH
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54 Marine Geological and Geophysical Atlas of the and Subantarctic Pycnogonida: Nymphonidae,
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Island, Antarctic Peninsula J. D. Stilwell, 70 Foundations for Ecological Research West of the
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56 The Antarctic Paleoenvironment: A Perspective L. B. Quetin (Eds.)
on Global Change, Part One J. P. Kennett, 71 Geology and Seismic Stratigraphy of the
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59 Physical and Biogeochemical Processes in 73 Antarctic Sea Ice: Biological Processes,
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Measurements and Biological Effects Rocks, McMurdo Sound, East Antarctica
C. S. Weiler, P. A. Penhale (Eds.) Jeffrey D. Stilwell, Rodney M. Feldmann (Eds.)
63 Biology of the Antarctic Seas XXIV, Antarctic 11 The West Antarctic Ice Sheet: Behavior and
and Subantarctic Pycnogonida: Ammotheidae Environment Richard B. Alley and
and Austrodecidae S. D. Cairns (Ed.) Robert A. Bindschadler (Eds.)
64 Atmospheric Halos W. Tape
65 Fossil Scleractinian Corals From James Ross
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ANTARCTIC
Volume 78 RESEARCH
SERIES
Biogeochemistry of the Ross Sea
Giacomo R. DiTullio and Robert B. Dunbar
Editors
88 American Geophysical Union
Washington, D.C.
2003
BIOGEOCHEMISTRY OF THE ROSS SEA
Giacomo R. DiTullio and Robert B. Dunbar, Editors
Published under the aegis of the Board of Associate Directors, Antarctic Research Series
Library of Congress Cataloging-in-Publication Data
Biogeochemistry of the Ross Sea / Giacomo R. DiTullio and Robert B. Dunbar, editors.
p. cm.—(Antarctic research series ; v. 78)
Includes bibliographical references.
ISBN 0-87590-972-8
1. Biogeochemistry—Antarctica—Ross Sea. I. DiTullio, Giacomo R. 1954- II. Dunbar, Robert B., 1954- III. Series.
QH95.58.B54 2003
577.7'74—dc22
2003045120
ISBN 0-87590-972-8
ISSN 0066-4634
ABOUT THE COVER
Front cover images
Large background image: The northern edge of B-15A, the giant iceberg near Ross Island, Antarctica. Photo by Josh Landis
of the National Science Foundation.
Left inset: Emperor penguin tracks in snow on first year sea ice of McMurdo Sound, Ross Sea. Photo by Rob Dunbar.
Center inset: Summer melt starts with a few trickles sliding down glacier slides and icicles. This photo was taken at the Suess
Glacier in the Transantarctic Mountains, by Kristan Hutchison of the National Science Foundation.
Right inset: Actively opening sea ice crack; McMurdo Sound, Ross Sea. Photo by Rob Dunbar.
Back cover image
Chlorophyll-a concentrations in the Ross Sea during the austral summers of 1998-2002 (climatological average). Photo courtesy
of the SeaWiFS Project, NASA Goddard Space Flight Center, and ORBIMAGE.
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CONTENTS
Preface
Giacomo R. DiTullio and Robert B. Dunbar
Biogeochemistry of the Ross Sea—An Introduction
Giacomo R. DiTullio and Robert B. Dunbar
Section 1: Physics and Hydrography of the Ross Sea
The Ross Sea Circulation During the 1990s
Michael L. Van Woert, Eric S. Johnson, Leonardo Langone, Denise L. Worthen, Andy Monaghan,
David H Bromwich, Roberto Meloni, and Robert B. Dunbar
Section 2: Phytoplankton Biomass and Primary Production in the Ross Sea
Algal Pigment Ratios in the Ross Sea: Implications for CHEMTAX Analysis of Southern Ocean Data
Giacomo R. DiTullio, Mark E. Geesey, Amy R. Leventer, and Michael R Lizotte
The Ross Sea Polynya Project: Diatom- and Phaeocystis-dommated Phytoplankton Assemblages in the
Ross Sea, Antarctica, 1994 and 1995
David L. Garrison, Angela Gibson, Holly Kunze, Marcia M. Gowing, Chrystal L. Vickers,
Sylvie Mathot, and Ross C. Bayre
Evaluating Photosynthetic Carbon Fixation During Phaeocystis antarctica Blooms
Dale H Robinson, Kevin R. Arrigo, Giacomo R. DiTullio, and Michael P. Lizotte
A Coupled Ocean-Ecosystem Model of the Ross Sea. Part 1: Interannual Variability of Primary Production
and Phytoplankton Community Structure
Denise L. Worthen and Kevin R. Arrigo
The Influence of Sea Ice on Ross Sea Biogeochemical Processes
Michael P. Lizotte
Section 3: Dissolved Organic Matter and Microbial Dynamics in the Ross Sea
The Contribution of Dissolved Organic Carbon and Nitrogen to the Biogeochemistry of the Ross Sea
Craig A. Carlson and Dennis A. Hansell
Seasonal Production and Bacterial Utilization of DOC in the Ross Sea, Antarctica
Hugh W Ducklow
Section 4: Nutrient Dynamics
Effects of Ammonium on Nitrate Utilization in the Ross Sea, Antarctica: Implications for
/-ratio Estimates
William P. Cochlan and Deborah A. Bronk
Non-Redfield Production and Export of Marine Organic Matter: A Recurrent Part of the Annual Cycle in
the Ross Sea, Antarctica
Robert B. Dunbar, Kevin R. Arrigo, Michael Lutz, Giacomo R. DiTullio, Amy R. Leventer,
Michael P. Lizotte, Michael P. Van Woert, and Dale H. Robinson 179
Effects of Assemblage Composition on the Temporal Dynamics of Carbon and Nitrogen Uptake
in the Ross Sea
Walker O. Smith, Jr. and Christina M. van Hilst 197
Flavodoxin as a Diagnostic Indicator of Chronic Iron Limitation in the Ross Sea and
New Zealand Sector of the Southern Ocean
Jennifer M. Maucher and Giacomo R. DiTullio 209
Section 5: Particulate Fluxes in the Ross Sea
Rapid Sinking of Biogenic Material During the Late Austral Summer in the Ross Sea, Antarctica
Leonardo Langone, Robert B. Dunbar, David A. Mucciarone, Mariangela Ravaioli, Roberto Meloni,
and Charles A. Nittrouer 221
The Distribution of Particulate Organic Carbon and Its Dynamics in the Southern Ross Sea
Vernon L. Asper and Walker O. Smith, Jr. 235
Larger Microplankton in the Ross Sea: Abundance, Biomass and Flux in the Austral Summer
Marcia M. Gowing and David L. Garrison 243
Annual Sedimentation Pattern of Zooplankton Fecal Pellets in the Southern Ross Sea: What Food Webs and
Processes Does the Record Imply?
Alessandra Accornero and Marcia M. Gowing 261
Section 6: Non-conservative Tracers and Biogenic Gases
Dimethylsulfide Dynamics in the Ross Sea During Austral Summer
Giacomo R. DiTullio, David R. Jones, and Mark E. Geesey 279
The Annual Cycle of Surface Water C0 and 0 in the Ross Sea: A Model for Gas Exchange on the
2 2
Continental Shelves of Antarctica
Colm Sweeney 295
Section 7: Benthic-Pelagic Coupling in the Ross Sea
Benthic Carbon Cycling in the Ross Sea Polynya, Antarctica: Benthic Community Metabolism
and Sediment Tracers
Jacqueline M. Grebmeier, Giacomo R. DiTullio, James P. Barry, and Lee W. Cooper 313
Oceanographic Versus Seafloor-Habitat Control of Benthic Megafaunal Communities in the S.W. Ross Sea,
Antarctica
James P. Barry, Jacqueline M. Grebmeier, James Smith, and Robert B. Dunbar 327
Biogeochemistry of the Ross Sea—A Summary
Giacomo R. DiTullio and Robert B. Dunbar 355
PREFACE
The seas surrounding Antarctica are the least-studied posed of microzooplankton, phytoplankton, bacteria, and
on Earth, yet they figure prominently in both the global viruses. In many areas, phytoplankton cells frozen into
climate system and the biogeochemical cycling of such the developing sea ice during autumn act as "seeds" for
key elements as C, N, Si, and P. The Southern Ocean large algal blooms the following summer when the ice
affects climate directly through the sinking of surface melts. During the brief Antarctic summer, rapid sea ice
waters via cooling and changes in salt content. Such melting also enhances primary production by stabilizing
water near Antarctica moves slowly northward through the upper water column with a slightly fresher and less
all major ocean basins. In doing so, it retains a long-lived dense meltwater layer. Algae within this layer are less
signature of the physical and biological processes that likely to be mixed into the darker deep waters by strong
occurred in Antarctic surface waters lasting many hun­ winds and are therefore more productive.
dreds of years through all phases: sinking, northward Through large, multi-year process studies such as the
flow, and mixing or upwelling into the sunlit ocean thou­ U.S. Joint Global Flux Study (JGOFS), Ross Sea
sands of kilometers away. By this process, C0 that dis­ Polynya Project and ROAVERRS (Research on Ocean-
2
solves into the Antarctic seas may be stored in the deep Atmosphere Variability and Ecosystem Response in the
ocean for centuries. In fact, the Southern Ocean is one of Ross Sea), we are now beginning to gain insight into
the most important regions on Earth for the uptake and how the Southern Ocean ecosystem may respond to
subsurface transport of fossil fuel C0. changes in climate. A key prediction of global warming
2
Although the physics of gas uptake is relatively is increasing reduction of sea ice extent in the Southern
straightforward (colder water holds more dissolved Ocean, a prediction borne out by recent satellite, ecolog­
C0), the biological processes associated with ocean C ical as well as anecdotal observations. Given the impor­
2
uptake remain poorly understood. For example, phyto­ tance of sea ice as a regulator of the type, timing, and
plankton take up C0 via primary production in sunlit rate of primary production in the Southern Ocean, many
2
waters, thus reducing the partial pressure of surface process studies have focused on areas of strong sea ice
ocean C0 and increasing the air-to-sea flux. These phy­ seasonality — the best known area being the Ross Sea,
2
toplankton populations also support a complex food web where a large polynya (an area of open water in an ice-
wherein C can be transferred from one organism to covered sea) forms each austral spring and summer.
another, respired, or excreted. Some fixed C is transport­ An intense phytoplankton bloom occurs each summer
ed to the deep sea via the export of cells, aggregates and within the polynya, and some of this material sinks out
fecal pellets; in effect, a biological enhancement of the of the upper layer when sea ice begins to cover the Ross
physical sinking of dissolved forms of C. Thus in this Sea again in March and April. Yet the fate of most of the
volume, we have compiled a series of papers that address material produced in these blooms is unknown. Different
key aspects of the biogeochemical processes related to C methodological approaches have yielded widely con­
in a seasonally ice-covered part of the Southern Ocean. flicting viewpoints. The Ross Sea serves as a rich natur­
We summarize the current state of knowledge on bio­ al laboratory setting for studying the various processes
geochemical processes, so as to draw attention to key of organic matter production, degradation, and transport
outstanding issues. in an area of strong and somewhat predictable physical
Biological processes in the Southern Ocean are forcing. Often, our best indicators of what is occurring in
strongly controlled by the seasonal cycle. Not only does the water column or what has occurred during the previ­
the amount of solar insolation vary dramatically between ous few months are the biogeochemical tracers that
winter and summer, but changes in the radiation budget remain in the water column. In this volume, our authors
also force the seasonal formation and subsequent melt­ elucidate many of the processes that influence the bio­
ing of more than 20 million km2 of annual sea ice. Sea logical cycling of key elements and use this knowledge
ice affects biology by acting as a lid on the ocean, reduc­ to understand the seasonal cycle of production and rem-
ing the penetration of sunlight and the exchange of heat ineralization. Collectively, these papers address such key
and dissolved gases with the atmosphere. Yet it also acts questions as: (1) how do changes in the annual cycle of
as a habitat for a remarkable microbial ecosystem com­ sea ice and wind stress moderate primary production and
ix
our heartfelt appreciation to our oversight editor, Dr.
C uptake in a Southern Ocean polynya; (2) how is C pro­
John Priscu, who was instrumental in helping us develop
duced by algae subsequently partitioned between dis­
solved phases, higher trophic levels, and sinking particu­ and produce this special volume.
late debris; (3) how does ocean circulation and bathyme­
Giacomo R. DiTullio
try affect the accumulation of sinking surface debris at
Hollings Marine Lab
the seabed and therefore control benthic secondary pro­
College of Charleston
duction; and (4) how do different algal groups take up C
Charleston, South Carolina
and nutrients and how might they respond to significant
changes in climate? Robert B. Dunbar
We thank all authors who submitted manuscripts to Department of Geology and Environmental Sciences
this volume, especially for their patience and under­ Stanford University
standing in allowing this volume to come to fruition. Stanford, California
Special thanks are also extended to all the anonymous
Editors
referees who devoted much time and effort to ensure that
a high quality product was produced. Finally, we extend
BIOGEOCHEMISTRY OF THE ROSS SEA
ANTARCTIC RESEARCH SERIES VOLUME 78, PAGES 1-4
BIOGEOCHEMISTRY OF THE ROSS SEA—AN INTRODUCTION
Giacomo R. DiTullio
Hollings Marine Laboratory, College of Charleston, Charleston, South Carolina
Robert B. Dunbar
Geological and Environmental Sciences, Stanford University, Stanford, California
Satellite imagery has confirmed that the Ross Sea typi­ munity structure. As they do in the modern ocean, both
cally exhibits the largest and most predictable phytoplank- bottom-up (Fe-silicate-light interactions) and top-down
ton bloom in the Southern Ocean. Just as evident, howev­ controls (e.g., macro- and micro-grazers) will govern
er, is the large interannual variability associated with the net community production and composition in the
temporal and spatial extent of these phytoplankton blooms future Southern Ocean. Changing oceanic food webs,
within the Ross Sea polynya. We are just now beginning however, will be intimately involved in the biogeo­
to understand how physical and climatic forcing factors chemical cycling of other major elements (e.g., nitro­
affect the interannual distribution of sea ice and the size of gen, phosphorus, silicon and iron), which directly affect
the Ross Sea polynya. A mechanistic understanding of carbon cycling and sequestration in the Southern
how these physical forcing factors impact the opening of Ocean. Factors governing the interrelationships
the polynya and cause the initiation of the spring phyto­ between the oceanic food web and the biogeochemical
plankton bloom (and hence the trophodynamic relation­ cycling of the major elements in the Southern Ocean
ships within the Ross Sea Ecosystem) is a subject of great are not yet well understood. The Ross Sea is an ideal
interest to oceanographers and modelers alike. Recent observational ecosystem that can serve as a small-scale
numerical simulations predict that the Southern Ocean proxy for testing hypotheses for the broader Southern
will respond more sensitively to projected climatic forcing Ocean. The rationale for comparison of these two
relative to other oceanic provinces. It seems almost certain ecosystems is based on the fact that in both the Ross
that the oceanic C system, and the associated nutrient ele­ Sea and the larger Southern Ocean only two groups of
mental cycles, will be significantly affected. One objective phytoplankton (diatoms and the colonial haptophyte
of this volume is to provide a new view of the complex Phaeocystis antarctica) tend to dominate the algal com­
biogeochemical interactions that occur in the Ross Sea, munity assemblage. Whether the modern ecology of the
based on several process studies completed in the 1990's. Southern Ocean operates in a similar manner relative to
We hope that the interpretations of these results will that during the last glacial maximum is the subject of
springboard researchers into developing new testable intense research by paleoceanographers.
hypotheses about the Ross Sea ecosystem. During the past decade, new NSF-funded research pro­
The biogeochemical cycling of carbon in the grams have supported intensive oceanographic field
Southern Ocean is likely to be significantly influenced studies in the Ross Sea. For instance, the commissioning
by increased air-sea fluxes of anthropogenic C0 in the of the RV/IB Nathaniel B. Palmer in 1992 has enabled
2
coming century. Algal community assemblages will early spring, austral autumn, and winter oceanographic
play a major role in determining the efficiency of the investigations to be carried out in the Ross Sea for the
biological pump in the transfer of C0 to intermediate first time. Previously, Ross Sea research was limited to
2
and deep waters. The reverse process has not received a measurements performed during the late spring and
great deal of attention yet, but recent evidence suggests summer seasons. The Ross Sea Flux Experiment
that C0 levels may significantly impact the algal com­ (1990-1992) and Ross Sea Polynya Project (1994-96)
2
Copyright 2003 by the American Geophysical Union
10.1029/078ARS01 1