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SCOPE data collected during HOT cruises

E. Virginia Armbrust (University of Washington)

The Armbrust lab has developed a novel flow cytometer dubbed the SeaFlow. This instrument allows for continuous underway monitoring and analysis of cell populations in the surface waters. SCOPE field personnel will maintain and ensure proper alignment of this machine on every HOT trip, generating real-time data available to all SCOPE collaborators. The high precision of the SeaFlow system will enable scientists to view daily, in-situ growth rates of Prochlorococcus and other picophytoplankton smaller than 100 µm, generating data sets that will better relate the activity of these organisms to nutrient cycling and community structure.

David A. Caron (University of Southern California)

Despite the fact that heterotrophic and mixotrophic protists are diverse and important members of marine foodwebs, the study of such organisms has lagged far behind that of photosynthetic eukaryotes, bacteria, archaea and viruses. Part of the SCOPE work done by the Caron lab will focus on exploring protest diversity and lifecycles. Monthly HOT trips will enable collection (via filtration) of genetic data for metatranscriptome sequencing of the <80µm size fraction of the Station Aloha water column down to 1000m, augmenting the long term HOT DNA data and further exploring the ecosystem function of these diverse and adaptive protists.

Matthew J. Church (University of Montana, Flathead Lake Biological Station)

Variability in the pathways and supply of nitrogen to the upper ocean exert a major influence on ocean productivity and material export to the deep sea. While the vast majority of ocean productivity is sustained through active recycling, net synthesis of organic matter must be fueled by nutrient sources delivered to the upper ocean vertically from below, deposited onto the surface ocean from the atmosphere, or introduced by the process of N2 fixation. Hence constraining rates of N2 fixation in the open sea is critical to our understanding of biogeochemistry and ecology. In collaboration with Drs. David Karl, Sam Wilson, and Jon Zehr, the Church lab oversees near-monthly measurements of N2 fixation at Station ALOHA. Rates are measured at 6 discrete depths in the upper ocean (0-125 m) on HOT cruises. Samples are collected in the pre-dawn hours, amended with 15N2 enriched seawater, and incubated in situ on a free-drifting array for 24 hours. At the end of the incubation period, samples are filtered for subsequent analyses of rates of 15N assimilation. These measurements are complemented by analyses of selected diazotroph gene abundances (based on quantitative PCR amplification of nifH genes), providing information on how time-varying changes in N2 fixing microorganism population abundances influence rates of N2 fixation in this ecosystem.

Edward F. DeLong (University of Hawai'i)

Microbial communities are responsible for the majority of matter and energy flux in the oceans, but despite this, relatively little is known about either the fine scale temporal and spatial variability or the metagenomic compilation of these diverse assemblages. Thanks to rapid advances in sequencing technologies, the DeLong lab will be able to explore the metagenomics and metatranscriptomics of Station ALOHA like never before, creating a database of gene inventories over nearly the entire depth (down to 4000m) of the water column. Work on HOT cruises will collect the field data for this database, filtering whole water samples of >0.22µm for DNA sequencing, and 0.22µm - 0.02µm for viral DNA. In addition to this, sediment traps containing "dead" (i.e. preserved) particulate (a long standing measurement of HOT) will be augmented with "live" (fixed with RNAlater) sediment traps to add a new dimension in the time-series work.

Daniel J. Repeta (Woods Hole Oceanographic Institution)

The oligotrophic waters of Station ALOHA present a challenge to microbes attempting to gather the requisite macro-nutrients (carbon, nitrogen, phosphorous) and metals (iron, cobalt, zinc, nickel) to sustain themselves. This paucity of nutrients in surface waters has lead to most of these nutrients being predominantly available as dissolved organic matter (DOM), a general term for a wide variety of organic compounds. In order to better understand types, cycling, and degradation of DOM at Station ALOHA, monthly HOT cruises will see the collection of DOM in the upper 200m of the water column.

Angelicque White (Oregon State University)

Primary production (PP) in the surface ocean is of fundamental importance to the global carbon cycle, oceanic biogeochemical cycles, and ecological dynamics. However, the rate of primary production throughout the ocean is not well bounded. In the hopes of ameliorating this lack of information, the White lab will be assessing PP in a novel in situ way, using beam attenuation and a measure of particulate organic carbon (POC). Part of SCOPE fieldwork for the White lab will be maintaining the transmissometer aboard the R/V Kilo Moana to ensure the correct and real-time reporting of beam attenuation. Additionally, SCOPE field personnel will be performing filtrations to create slides for microscopy and enumeration of large diazotrophs in the upper 50m of the water column. These counts will perform a second measurement seasonal changes in large nitrogen fixers at Station ALOHA, augmenting the current qPCR work being done by the HOT program.