Dimensions of biodiversity of oceanic nitrogen cycling: nutrient co-limitation, nitrogen substrate preferences and more.

Jonathan P Zehr1, Matthew M Mills2, Irina N Shilova3, Kendra Turk-Kubo3, Julie Robidart4, Gert van Dijken2, Karin M Bjorkman5, Daniel B Whitt6, Brenner Wai5, Joaquin Pampin Baro7, Mary Hogan3, Insa Rapp8, Emily Zakem9, A Fredrickson3, Brian Leahy10, Morgan Linney11, Alessandra Santiago10, Michael J Follows12, Eric P Achterberg13, Zbigniew Kolber14, Matthew J Church15 and Kevin R Arrigo2, (1)University of California, Santa Cruz, Ocean Sciences, Santa Cruz, CA, United States, (2)Stanford University, Earth System Science, Stanford, United States, (3)University of California Santa Cruz, Ocean Sciences, Santa Cruz, CA, United States, (4)National Oceanographic Centre, Southampton, United Kingdom, (5)University of Hawai'i, SOEST, Honolulu, HI, United States, (6)University of Cambridge, Cambridge, United Kingdom, (7)GEOMAR, Germany, (8)GEOMAR Helmholtz Centre for Ocean Research Kiel, Chemical Oceanography, Kiel, Germany, (9)Carnegie Institution for Science, Biosphere Sciences & Engineering, Pasadena, United States, (10)Stanford University, Earth System Science, Stanford, CA, United States, (11)Daniel K. Inouye Center for Microbial Oceanography: Research and Education, University of Hawaii at Manoa, Honolulu, HI, United States, (12)Massachusetts Institute of Technology, Department of Earth, Atmospheric and Planetary Sciences, Cambridge, United States, (13)Geomar - Hemholtz Centre for Ocean Research, Chemical Oceanography, Kiel, Germany, (14)University of California, Institute of Marine Sciences, Santa Cruz, CA, United States, (15)University of Hawaii at Manoa, Honolulu, HI, United States
Abstract:
We conducted the research cruise: Nutrient Effects on Marine microOrganisms (NEMO) onboard the R/V New Horizon (NH1417: August 18 to September 16, 2014) between the ports of San Diego, CA and Honolulu, HI. The three major objectives of the cruise were to: 1) evaluate genetic, physiological and phylogenetic responses of marine phytoplankton communities in the North Pacific Subtropical Gyre to different nitrogen (N) substrates and to determine how other nutrients (iron, phosphorus) impact N utilization; 2) characterize the physical processes and dynamics in support of the biological processes; and 3) characterize the diversity and activities of microbial communities in the upper water column in relation to the nutrient availability. Several incubation experiments were conducted along the cruise transect to assess the effect of nutrients on microbial communities. The results showed that N addition resulted in increased chlorophyll a (chl a) and rates of CO2 fixation at most sites, but Prochlorococcus, Synechococcus and picoekaryotic phytoplankton had different responses to urea, ammonium and nitrate. In contrast, chl a and CO2 fixation did not respond to additions of single nutrient (e.g. N, P or Fe alone) at the westernmost experiment (151°W), where the simultaneous addition of N and P was required for stimulation. The physical dynamics were studied through high-resolution surveys of eddy dipole features as well as diel sampling at two locations. Additionally, we characterized an extensive bloom that occurred near the critical latitude (29°N, 140°W) from mid July to the end of September; a typical but still enigmatic event. Here, we present a summary of the initial observations and findings from the NEMO cruise with data including physics, nutrient concentrations, chl a, primary productivity and microbial community composition. The results of this research cruise will help in assessing how ocean N cycling and ecosystem functions will respond to global climate change.
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