An operational overview of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) Northeast Pacific field deployment

The goal of the EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) field campaign is to develop a predictive understanding of the export, fate, and carbon cycle impacts of global ocean net primary production. To accomplish this goal, observations of export flux pathways, plankton community composition, food web processes, and optical, physical, and biogeochemical (BGC) properties are needed over a range of ecosystem states. Here we introduce the first EXPORTS field deployment to Ocean Station Papa in the Northeast Pacific Ocean during summer of 2018, providing context for other papers in this special collection. The experiment was conducted with two ships: a Process Ship, focused on ecological rates, BGC fluxes, temporal changes in food web, and BGC and optical properties, that followed an instrumented Lagrangian float; and a Survey Ship that sampled BGC and optical properties in spatial patterns around the Process Ship. An array of autonomous underwater assets provided measurements over a range of spatial and temporal scales, and partnering programs and remote sensing observations provided additional observational context. The oceanographic setting was typical of late-summer conditions at Ocean Station Papa: a shallow mixed layer, strong vertical and weak horizontal gradients in hydrographic properties, sluggish sub-inertial currents, elevated macronutrient concentrations and low phytoplankton abundances. Although nutrient concentrations were consistent with previous observations, mixed layer chlorophyll was lower than typically observed, resulting in a deeper euphotic zone. Analyses of surface layer temperature and salinity found three distinct surface water types, allowing for diagnosis of whether observed changes were spatial or temporal. The 2018 EXPORTS field deployment is among the most comprehensive biological pump studies ever conducted. A second deployment to the North Atlantic Ocean occurred in spring 2021, which will be followed by focused work on data synthesis and modeling using the entire EXPORTS data set

EXPORTS Measurements and Protocols for the NE Pacific Campaign

EXport Processes in the Ocean from Remote Sensing (EXPORTS) is a large-scale NASA-led and NSF co-funded field campaign that will provide critical information for quantifying the export and fate of upper ocean net primary production (NPP) using satellite information and state of the art technology

International genome-wide meta-analysis identifies new primary biliary cirrhosis risk loci and targetable pathogenic pathways.

Primary biliary cirrhosis (PBC) is a classical autoimmune liver disease for which effective immunomodulatory therapy is lacking. Here we perform meta-analyses of discovery data sets from genome-wide association studies of European subjects (n=2,764 cases and 10,475 controls) followed by validation genotyping in an independent cohort (n=3,716 cases and 4,261 controls). We discover and validate six previously unknown risk loci for PBC (Pcombined<5 × 10(-8)) and used pathway analysis to identify JAK-STAT/IL12/IL27 signalling and cytokine-cytokine pathways, for which relevant therapies exist

Protist grazing contributes to microbial food web at the upper boundary of the twilight zone in the subarctic Pacific

Grazing by herbivorous protists (microzooplankton) is a major loss pathway of primary production in the surface ocean, yet its impact below the well-lit surface ocean is largely unknown. The upper boundary of the twilight zone is critically important to understanding carbon cycling and is often the depth of highest attenuation of particulate carbon flux. Available measurements of primary production and grazing below the well-lit surface ocean suggest that the upper boundary of the twilight zone may harbor active but poorly constrained food web processes. Previous grazing rates from the base of the euphotic zone were measured in subtropical and tropical environments. Thus, the impact of protist grazing on prey populations remains unknown in colder conditions at higher latitudes. To advance understanding and provide mechanistic insight into processes occurring at the base of the euphotic zone (0.4−0.7% PAR), we measured predation rates on both phytoplankton and heterotrophic prokaryotes in the North Pacific, using a novel method that amplified the grazing signal by concentrating the predator community, enabling detection of grazing rates far below previous limits. Protists consumed 0.6% of the phytoplankton population daily and 12% of daily heterotrophic prokaryote growth. These conservative rate measurements document marginal removal of phytoplankton even in these colder regimes, implying flows of energy from single-cell primary producers and prokaryotes to single-cell protists at rates far below previous detection limits in this twilight region of a low-productivity system

Microzooplankton grazing constrains pathways of carbon export in the subarctic North Pacific

To identify the effect of microzooplankton grazing on phytoplankton abundance and size structure, we quantified phytoplankton growth and herbivorous grazing rates throughout the euphotic zone and across a light gradient on the North Pacific EXport Processes in the Ocean from RemoTe Sensing (EXPORTS) cruise near Ocean Station Papa. During 30 days of continuous, Lagrangian observation in August and September of 2018, depth integrated chlorophyll a (Chl a) concentrations were stable and averaged 20 ± 2 mg m−2. Bottle-incubation experiments revealed that phytoplankton growth was balanced by microzooplankton grazing even when phytoplankton growth rates varied from 0 to 0.4 d−1 in response to light manipulation. Microzooplankton grazing caused a decline in phytoplankton abundance that was balanced by increased phytoplankton cell size resulting in consistent phytoplankton biomass over time. Microzooplankton grazed phytoplankton at an average rate of 0.11 ± 0.17 d−1 which lead to an intrinsic phytoplankton growth rate of −0.07 ± 0.26 d−1. Predicted stocks from grazing experiments aligned closely (within 16%) with in situ Chl a dynamics and phytoplankton abundance, suggesting that the dominant loss process of phytoplankton was grazing by microzooplankton rather than physical mixing or sinking of phytoplankton. Consequently, microzooplankton played a critical role in regulating primary producer biomass and in transferring particulate organic carbon through the food web where a fraction could then be exported as byproducts of food web processes

Relationship between calculated and estimated Ω_Arag.

<p>The latter was approximated from measured pH_T and either TA_est (blue points and line, r² = 0.996, y = 0.998x + 0.0271) or a regional average TA (red points and line, r² = 0.996, y = 0.983x-0.0049). See text for details.</p

Relationship between measured and estimated DIC.

<p>DIC is estimated either from pH_T and TA_est (blue points) or pH_T and regional average TA (red points). The black line denotes the theoretical 1:1 relationship, the blue and red lines the respective correlations with the grey shading marking the 95% intervals. See text for details.</p