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Progress report: by nfzW895

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									Nitrogen Cycling in the Gulf of Alaska, Past and Present: A Nitrogen Isotope
Approach
SOLAS Project Progress Report

Submitted by:

Tom Pedersen,
Professor and Director, School of Earth and Ocean Sciences, Univ. Victoria
Adjunct Professor, Earth and Ocean Sciences, UBC

Joe Needoba,
PhD candidate, University of British Columbia

Eric Galbraith,
PhD candidate, University of British Columbia

June 17, 2003

        The purpose of this document is to address the outstanding comments and
requested outcomes presented to us on June 17, 2003 (reproduced immediately below) as
a result of the C-SOLAS Board of Directors midterm report.

Project 2.1.4: Pedersen (formerly Harrison)
Comments: A very successful project but more work took place in this project
than is
reported here. What has been done by Price, Pederson[sic], and Dower? They
are not even listed as being part of the research team but they have received a
lot of SOLAS money.
There is concern about the lack of interest by the IOS/UBC/UVic research teams
in the
Atlantic SOLAS efforts even though the spring lagrangian study was planned to
compare
and contrast with SERIES. There was a general concern with the lack of west-
coast
participation in Atlantic fieldwork.
Outcome(s): Please submit a full account (along with Paul Harrison) of the details
of
funding and progress in the subprojects by Price, Dower, and Pederson [sic]. It is
clear that NSERC and CFCAS will require this accountability and funds to
support these
subprojects could be in jeopardy without a full report. Promote efforts of data
exchange
between Pacific and Atlantic fieldwork.
        The following provides an explanation of our results and progress from our
participation in the C-SOLAS program, particularly in light of the above. We have been
directly involved in the SERIES experiment, and in closely related paleoceanographic
research.

        Our mandate during the SOLAS-SERIES experiment was to collect, analyze, and
interpret measurements of the stable isotopic composition of nitrogen during the iron-
induced phytoplankton bloom that resulted during the SERIES experiment in July 2002.
This project presented an outstanding opportunity to address important scientific
questions relating to the biogeochemistry of N cycling in the surface ocean. N isotope
biogeochemistry is rapidly becoming a powerful tool in many areas of oceanographic
research, and important constraints on the distribution of stable isotopes have yet to be
fully understood. This work is being carried out by Joe Needoba under the supervision of
T. Pedersen.

        A second focus, stemming from our original proposal to the Canadian SOLAS
Program, was to explore nutrient cycling and export productivity history in the Gulf of
Alaska region through a detailed investigation of nitrogen isotope variations and
partitioning in sediments from a 750,000 year section recovered from the Patton-Murray
Seamounts, just north of the SERIES experiment field area. This work is being carried
out by Eric Galbraith under the supervision of T. Pedersen.

        Grant funds were expended as follows: Joe Needoba has been employed as a
research assistant since the summer of 2002 to conduct analyses and work up the data, as
described below. He will defend his thesis in late June, and assuming a successful
defense, will continue on the project as a Post-Doctoral Fellow starting July 1, 2003.
TFP’s portion of the C-SOLAS grant supported the stable isotope measurements, as well
as travel expenses to the conferences described below.

       Eric Galbraith’s work, although closely allied to the SOLAS objectives, has been
supported by Pedersen from other sources at no cost to the SOLAS grant.

Synopsis of Progress, Year 2

The SERIES Experiment
        In order to collect data from dissolved, particulate, and sinking nitrogen pools, we
utilized resources from all three ships that participated in the SERIES experiment.
Collaborative efforts with Adrian Marchetti (UBC), Mike Henry (UBC), and Keith
Johnson (IOS), allowed us to collect material from the water column and sediment traps
during the entire SERIES experiment. This allowed us to give up our berth on the cruise,
and therefore provided other investigators with more ship space, including an additional
berth. It is possible, because we were not on the ship, that our contribution to SERIES has
been somewhat overlooked.
        The post-experimental period has required substantial data workup. For example,
to measure the stable isotope ratio of nitrate, we successfully utilized a teflon-membrane
diffusion technique to capture nitrate in a form suitable for analysis on a mass
spectrometer. As a result, our lab at UBC is now one of four places in the world where
this important technique is being used. This, and the analysis of the phytoplankton and
sediment trap material, represented the main goals of our post-SERIES efforts. However,
we were also able to determine the stable isotope ratio of carbon, which significantly
increases our data contribution to the SERIES program.
        We attended and presented results at the SERIES workshop in March 2003. Our
participation in SERIES was not well appreciated prior to this meeting, possibly due to
the reason given above; however we largely erased these concerns at the meeting, and
have since collaborated with other PI’s in an effort to resolve some of the scientific
concerns that emerged from SERIES. An excellent example of this is our contribution to
the understanding of the fate of the phytoplankton bloom, as we are able to show
conclusive evidence of the bloom material in the sediment traps from our isotope data.
Our data are an important part of the manuscript that is being prepared by Phil Boyd for
submission to Nature, as evidenced by Joe Needoba’s inclusion as one of the primary
authors on the paper.
        Mr. Needoba presented our data at the recent CMOS meeting in Ottawa. The title
of the talk was “Stable Isotope Dynamics of a Phytoplankton Bloom: Results From the
SERIES Experiment in The North Pacific Ocean”, and was presented during the SERIES
talks of the C-SOLAS session. Those in attendance provided a great deal of positive
feedback, and further emphasizes our important role in the SERIES experiment as a
whole.
        We have two objectives for publication of our results. The first is to describe the
stable isotope dynamics of nitrogen and carbon that we observed, in order to provide new
information on biological, physical, and chemical constraints of important processes such
as biological isotope fractionation and nitrate utilization by phytoplankton. The papers
will be directed to the larger scientific community, including biologists and geologists
who seek to use stable isotopes as part of their research program. The second objective is
to use our data to help interpret the nitrogen and phytoplankton dynamics of the SERIES
experiment. We have already substantially contributed to the first manuscript that will
result from SERIES, as described above, and we will follow up the data in the Nature
paper with a more in-depth analysis of the nitrate utilization, phytoplankton nitrogen and
carbon properties, and the sinking material. Mr. Needoba will be pursuing this in
collaboration with Pedersen as an initial part of his PDF research program this summer.
Together, these objectives and subsequent publications will represent a substantial
contribution to the literature that emerges from this phase of the C-SOLAS program.

        The success of our project indicates that natural distribution stable isotope
research should be incorporated by other Canadian scientists, including future projects
under the C-SOLAS program. However, we have not pursued any additional
collaborative efforts with the groups currently working in the Atlantic region. This is not
due to a lack of interest, but rather was never part of our initial research program. We
would enthusiastically contribute to future cruises or data analysis in the Atlantic region
if such an opportunity exists; indeed, we are willing to commit to analysis and
interpretation of samples for 15N (and 13C, where appropriate) that are currently being
collected during the Atlantic field program. Such work could be readily added to Dr.-to-
be Needoba’s PDF research program.
Gulf of Alaska Export Production and Nutrient Cycling History

The second aspect of our C-SOLAS work relates to the determination of productivity
history in the Gulf of Alaska, through a focus on the sedimentary record at ODP Site 887.
Eric Galbraith has been working on the nitrogen isotopic variability in bulk sediments
and extracted diatom-frustule nitrogen in an effort to discern relative nitrate abundance
through time as export production varied (quite markedly, as shown by my previous
student Darcy McDonald; see McDonald, D., T.F. Pedersen, and J. Crusius (1999).
Multiple late Quaternary episodes of exceptional diatom production in the Gulf of
Alaska. Deep-Sea Research, 46, 2993-3017). Galbraith has shown that diatom 15N
differs from bulk sedimentary 15N by a generally constant value of about –1.5 per mil
downcore, suggesting that variable trophic effects cannot account for the light 15N values
observed in the remarkable diatom oozes that episodically punctuate the hemipelagic
sedimentary section at the site. The diatom strata have been interpreted previously to
represent extreme export production events. We do not yet understand what drove these
episodes of high production, but enhanced dust input and the effects of oceanic
circulation changes on nutrient supply remain targets for continuing research.

Galbraith has recently related maxima in 15N at various intervals in the Site 887 section
to similar-amplitude maxima that occur at the same time in cores from the North
American and African continental margins. He attributes this congruent behaviour to
physical control of oxygen supply to zones of water-column denitrification in key areas
of the Pacifica, Atlantic and Indian oceans. This hypothesis is supported by a range of
data, including the Gulf of Alaska results, and is about to be submitted (E. Galbraith et
al., Response of the marine nitrogen cycle to varying high latitude surface ocean
conditions over glacial/interglacial timescales. to be submitted to Nature, June 2003).
This work suggests a new feedback mechanism by which the atmosphere modulates the
marine biosphere, and offers insight as to the flux of N2O to the atmosphere through
time, one of the many objectives of the SOLAS program. Galbraith’s research on the
nitrogen cycle has been supported to date by other funds that have been awarded to
Pedersen.

In a related aspect of Galbraith’s work, diatoms have been cultured in the lab, their
frustule-bound N has been extracted, and the d15N analyzed. Frustule-bound organic
matter is physically protected from alteration during sedimentation and, as such, may
provide a very reliable link between living diatoms in the Gulf of Alaska and their
fossilized progenitors. It is hoped that frustule-bound organic matter will provide a useful
tool in SOLAS studies by improving the constraints on palaeoceanographic proxies for
surface ocean processes, particularly nutrient utilization. This work has been done in
close collaboration with Needoba who is highly skilled in culturing techniques.

								
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