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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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