Author: nc56@duke.edu (Page 3 of 4)

Hot off the press paper by Seaver Wang in The ISME Journal

Marine net community production (NCP) tracks uptake of carbon by plankton communities and its potential transport to depth. Relationships between marine microbial community composition and NCP currently remain unclear despite their importance for assessing how different taxa impact carbon export. We conducted 16 and 18S rRNA gene (rDNA) sequencing on samples collected across the Western North Atlantic in parallel with high-resolution O₂/Ar-derived NCP measurements. Using an internal standard technique to estimate in-situ prokaryotic and eukaryotic rDNA abundances per liter, we employed statistical approaches to relate patterns of microbial diversity to NCP. Taxonomic abundances calculated using internal standards provided valuable context to traditional relative abundance metrics. A bloom in the Mid-Atlantic Bight featured high eukaryote abundances with low eukaryotic diversity and was associated with the harmful algal bloom-forming Aureococcus anophagefferens, phagotrophic algae, heterotrophic flagellates, and particle-associated bacteria. These results show that coastal Aureococcus blooms host a distinct community associated with regionally significant peaks in NCP. Meanwhile, weak relationships between taxonomy and NCP in less-productive waters suggest that productivity across much of this region is not linked to specific microplankton taxa.

FARACAS Concept

Because of the difficulty in resolving the large variability of N₂ fixation with current methods which rely on discrete sampling, the development of new methods for high resolution measurements is highly desirable. We present a new method for high-frequency measurements of aquatic N₂ fixation by continuous flow-through incubations and spectral monitoring of the acetylene (C₂H_2, a substrate analog for N₂) reduction to ethylene (C₂H₄). In this method, named “Flow-through incubation Acetylene Reduction Assays by Cavity ring-down laser Absorption Spectroscopy” (FARACAS), dissolved C₂H₂ is continuously admixed with seawater upstream of a continuous-flow stirred-tank reactor (CFSR) in which C₂H₂ reduction takes place. Downstream of the flow-through incubator, the C₂H₄ gas is stripped using a bubble column contactor and circulated with a diaphragm pump into a wavelength-scanned Cavity Ring Down laser absorption Spectrometer (CRDS). Our method provides high-resolution and precise mapping of aquatic N₂ fixation, its diel cycle, and its response to environmental gradients, and can be adapted to measure other biological processes. The short-duration of the flow-through incubations without preconcentration of cells minimizes potential artefacts such as bottle containment effects while providing near real-time estimates for adaptive sampling. We expect that our new method will improve the characterization of the biogeography and kinetics of aquatic N₂ fixation rates. See Cassar et al. 2018.

EXPORTS is a NASA large-scale field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) from satellite observations. The overarching goal of EXPORTS is to develop a predictive understanding of the export and fate of global ocean primary production and its implications for the Earth’s carbon cycle in present and future climates.

Siegel et al. 2016

Lin, Y., Cassar, N., Marchetti, A., Ducklow, H., Li, Z. Specific eukaryotic plankton are good predictors of net community production in the Southern Ocean. Nature Scientific Reports, doi:10.1038/s41598-017-14109-1.

Where in the world is our TARA Mass Spec ?

Monaco Explorations

Monaco Explorations cruise track

ACE Antarctic Circumnavigation Expedition

ACE cruise track

TARA Oceans Expeditions

Cassar begins LabexMer Chair International d’Excellence at Université de Bretagne Occidentale

Seaver Wang awarded a Chateaubriand Fellowship. Way to go Seaver!

Postdoc Hugo Berthelot and Graduate Student Seaver Wang recently participated in the “Sea to Sky Particle Investigation” research cruise from Honolulu to Seattle.

Li, Z. & Cassar, N. 2017. A mechanistic model of an upper bound on oceanic carbon export as a function of mixed layer depth and temperature. Biogeosciences, 14, 5015-5027.