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  • 1
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    Using Lagrangian-based process studies to test satellite algorithms of vertical carbon flux in the eastern North Pacific Ocean (2015)
    Wiley
    Details
    Publication Date: 2015-10-20
    Description: The biological carbon pump is responsible for the transport of ∼5-20 Pg C yr −1 from the surface into the deep ocean but its variability is poorly understood due to an incomplete mechanistic understanding of the complex underlying planktonic processes. In fact, algorithms designed to estimate carbon export from satellite products incorporate fundamentally different assumptions about the relationships between plankton biomass, productivity, and export efficiency. To test the alternate formulations of export efficiency in remote-sensing algorithms formulated by Dunne et al . [2005], Laws et al . [2011], Henson et al . [2011], and Siegel et al . [2014], we have compiled in situ measurements (temperature, chlorophyll, primary production, phytoplankton biomass and size structure, grazing rates, net chlorophyll change, and carbon export) made during Lagrangian process studies on 7 cruises in the California Current Ecosystem and Costa Rica Dome. A food-web based approach formulated by Siegel et al . [2014] performs as well or better than other empirical formulations, while simultaneously providing reasonable estimates of protozoan and mesozooplankton grazing rates. By tuning the Siegel et al . [2014] algorithm to match in situ grazing rates more accurately, we also obtain better in situ carbon export measurements. Adequate representations of food-web relationships and grazing dynamics are therefore crucial to improving the accuracy of export predictions made from satellite–derived products. Nevertheless, considerable unexplained variance in export remains and must be explored before we can reliably use remote sensing products to assess the impact of climate change on biologically-mediated carbon sequestration. This article is protected by copyright. All rights reserved.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    The biological pump in the Costa Rica Dome: an open-ocean upwelling system with high new production and low export (2016)
    Oxford University Press
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    Publication Date: 2016-03-19
    Description: The Costa Rica Dome is a picophytoplankton-dominated, open-ocean upwelling system in the Eastern Tropical Pacific that overlies the ocean's largest oxygen minimum zone. To investigate the efficiency of the biological pump in this unique area, we used shallow (90–150 m) drifting sediment traps and 234 Th: 238 U deficiency measurements to determine export fluxes of carbon, nitrogen and phosphorus in sinking particles. Simultaneous measurements of nitrate uptake and shallow water nitrification allowed us to assess the equilibrium balance of new and export production over a monthly timescale. While f -ratios (new:total production) were reasonably high (0.36 ± 0.12, mean ± standard deviation), export efficiencies were considerably lower. Sediment traps suggested e- ratios (export/ 14 C-primary production) at 90–100 m ranging from 0.053 to 0.067. ThE-ratios ( 234 Th disequilibrium-derived export) ranged from 0.038 to 0.088. C:N and N:P stoichiometries of sinking material were both greater than canonical (Redfield) ratios or measured C:N of suspended particulates, and they increased with depth, suggesting that both nitrogen and phosphorus were preferentially remineralized from sinking particles. Our results are consistent with an ecosystem in which mesozooplankton play a major role in energy transfer to higher trophic levels but are relatively inefficient in mediating vertical carbon flux to depth, leading to an imbalance between new production and sinking flux.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 3
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    Net biogenic silica production and the contribution of diatoms to new production and organic matter export in the Costa Rica Dome ecosystem (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-19
    Description: We determined the net rate of biogenic silica (bSiO 2 ) production and estimated the diatom contribution to new production and organic matter export in the Costa Rica Dome during summer 2010. The shallow thermocline significantly reduces bSiO 2 dissolution rates below the mixed layer, leading to significant enhancement of bSiO 2 relative to organic matter (silicate-pump condition). This may explain why deep export of bSiO 2 in this region is elevated by an order of magnitude relative to comparable systems. Diatom carbon, relative to autotrophic carbon, was low (〈3%); however, the contribution of diatoms to new production averaged 3 and 13% using independent approaches. The 4-old discrepancy between methods may be explained by a low average C:Si ratio (~1.4) for the net produced diatom C relative to the net produced bSiO 2 . We speculate that this low production ratio is not the result of reduced C, but may arise from a significant contribution of non-diatom silicifying organisms to bSiO 2 production. The contribution of diatoms to organic matter export was minor (5.7%). These results, and those of the broader project, suggest substantial food-web transformation of diatom organic matter in the euphotic zone, which creates enriched bSiO 2 relative to organic matter within the exported material.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 4
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    Phytoplankton production and grazing balances in the Costa Rica Dome (2016)
    Oxford University Press
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    Publication Date: 2016-03-19
    Description: We investigated phytoplankton production rates and grazing fates in the Costa Rica Dome (CRD) during summer 2010 based on dilution depth profiles analyzed by flow cytometry and pigments and mesozooplankton grazing assessed by gut fluorescence. Three community production estimates, from 14 C uptake (1025 ± 113 mg C m –2 day –1 ) and from dilution experiments analyzed for total Chl a (990 ± 106 mg C m –2 day –1 ) and flow cytometry populations (862 ± 71 mg C m –2 day –1 ), exceeded regional ship-based values by 2–3-fold. Picophytoplankton accounted for 56% of community biomass and 39% of production. Production profiles extended deeper for Prochlorococcus (PRO) and picoeukaryotes than for Synechococcus (SYN) and larger eukaryotes, but 93% of total production occurred above 40 m. Microzooplankton consumed all PRO and SYN growth and two-third of total production. Positive net growth of larger eukaryotes in the upper 40 m was balanced by independently measured consumption by mesozooplankton. Among larger eukaryotes, diatoms contributed ~3% to production. On the basis of this analysis, the CRD region is characterized by high production and grazing turnover, comparable with or higher than estimates for the eastern equatorial Pacific. The region nonetheless displays characteristics atypical of high productivity, such as picophytoplankton dominance and suppressed diatom roles.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 5
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    Phytoplankton production and taxon-specific growth rates in the Costa Rica Dome (2016)
    Oxford University Press
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    Publication Date: 2016-03-19
    Description: During summer 2010, we investigated phytoplankton production and growth rates at 19 stations in the eastern tropical Pacific, where winds and strong opposing currents generate the Costa Rica Dome (CRD), an open-ocean upwelling feature. Primary production ( 14 C-incorporation) and group-specific growth and net growth rates (two-treatment seawater dilution method) were estimated from samples incubated in situ at eight depths. Our cruise coincided with a mild El Niño event, and only weak upwelling was observed in the CRD. Nevertheless, the highest phytoplankton abundances were found near the dome center. However, mixed-layer growth rates were lowest in the dome center (~0.5–0.9 day –1 ), but higher on the edge of the dome (~0.9–1.0 day –1 ) and in adjacent coastal waters (0.9–1.3 day –1 ). We found good agreement between independent methods to estimate growth rates. Mixed-layer growth rates of Prochlorococcus and Synechococcus were largely balanced by mortality, whereas eukaryotic phytoplankton showed positive net growth (~0.5–0.6 day –1 ), that is, growth available to support larger (mesozooplankton) consumer biomass. These are the first group-specific phytoplankton rate estimates in this region, and they demonstrate that integrated primary production is high, exceeding 1 g C m –2 day –1 on average, even during a period of reduced upwelling.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 6
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    Mesozooplankton biomass and grazing in the Costa Rica Dome: amplifying variability through the plankton food web (2016)
    Oxford University Press
    Details
    Publication Date: 2016-03-19
    Description: We investigated standing stocks and grazing rates of mesozooplankton assemblages in the Costa Rica Dome (CRD), an open-ocean upwelling ecosystem in the eastern tropical Pacific. While phytoplankton biomass in the CRD is dominated by picophytoplankton (〈2-µm cells) with especially high concentrations of Synechococcus spp . , we found high mesozooplankton biomass (~5 g dry weight m –2 ) and grazing impact (12–50% integrated water column chlorophyll a ), indicative of efficient food web transfer from primary producers to higher levels. In contrast to the relative uniformity in water-column chlorophyll a and mesozooplankton biomass, variability in herbivory was substantial, with lower rates in the central dome region and higher rates in areas offset from the dome center. While grazing rates were unrelated to total phytoplankton, correlations with cyanobacteria (negative) and biogenic SiO 2 production (positive) suggest that partitioning of primary production among phytoplankton sizes contributes to the variability observed in mesozooplankton metrics. We propose that advection of upwelled waters away from the dome center is accompanied by changes in mesozooplankton composition and grazing rates, reflecting small changes within the primary producers. Small changes within the phytoplankton community resulting in large changes in the mesozooplankton suggest that the variability in lower trophic level dynamics was effectively amplified through the food web.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 7
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    Ocean biogeochemistry modeled with emergent trait-based genomics (2017)
    American Association for the Advancement of Science (AAAS)
    In: Science
    Details
    Publication Date: 2017-12-01
    Description: Marine ecosystem models have advanced to incorporate metabolic pathways discovered with genomic sequencing, but direct comparisons between models and "omics" data are lacking. We developed a model that directly simulates metagenomes and metatranscriptomes for comparison with observations. Model microbes were randomly assigned genes for specialized functions, and communities of 68 species were simulated in the Atlantic Ocean. Unfit organisms were replaced, and the model self-organized to develop community genomes and transcriptomes. Emergent communities from simulations that were initialized with different cohorts of randomly generated microbes all produced realistic vertical and horizontal ocean nutrient, genome, and transcriptome gradients. Thus, the library of gene functions available to the community, rather than the distribution of functions among specific organisms, drove community assembly and biogeochemical gradients in the model ocean.
    Keywords: Geochemistry, Geophysics, Microbiology
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Geosciences , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 8
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    Pelagic community responses to a deep-water front in the California Current Ecosystem: overview of the A-Front Study (2012)
    Oxford University Press
    Details
    Publication Date: 2012-08-02
    Description: In October 2008, we investigated pelagic community composition and biomass, from bacteria to fish, across a sharp frontal gradient overlying deep waters south of Point Conception, California. This north–south gradient, which we called A-Front, was formed by the eastward flow of the California Current and separated cooler mesotrophic waters of coastal upwelling origin to the north, from warm oligotrophic waters of likely mixed subarctic–subtropical origin to the south. Plankton biomass and phytoplankton growth rates were two to three times greater on the northern side, and primary production rates were elevated 5-fold to the north. Compared with either of the adjacent waters, the frontal interface was strongly enriched and uniquely defined by a subsurface bloom of large diatoms, elevated concentrations of suspension-feeding zooplankton, high bioacoustical estimates of pelagic fish and enhanced bacterial production and phytoplankton biomass and photosynthetic potential. Such habitats, though small in areal extent, may contribute disproportionately and importantly to regional productivity, nutrient cycling, carbon fluxes and trophic ecology. As a general introduction to the A-Front study, we provide an overview of its design and implementation, a brief summary of major findings and a discussion of potential mechanisms of plankton enrichment at the front.
    Print ISSN: 0142-7873
    Electronic ISSN: 1464-3774
    Topics: Biology
    Published by Oxford University Press
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  • 9
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    Processes driving seasonal variability in DMS, DMSP, and DMSO concentrations and turnover in coastal Antarctic waters (2016)
    Wiley
    Details
    Publication Date: 2016-10-11
    Description: This study presents new measurements of the concentrations and turnover rates of dimethyl sulfide (DMS), dimethylsulfoniopropionate (DMSP), and dimethyl sulfoxide (DMSO) in coastal waters near Palmer Station, Antarctica, during the spring and summer of 2012–2013. Using several novel analytical and experimental techniques, we document variability in DMS, DMSP, and DMSO (DMS/P/O) concentrations and quantify dominant production and removal terms in the mixed layer DMS budget. Our results demonstrate considerable seasonal variability in the concentration of DMS (range 0–20 nM), total DMSP (8–160 nM), and total DMSO (4–160 nM). Over the seasonal cycle, dissolved DMSP concentrations were well correlated with total DMSP concentrations and the abundance of Phaeocystis antarctica , while DMSO concentrations (total and dissolved) were well correlated with DMS concentrations. DMSP cleavage from the dissolved pool (mean rate = 5.5 nM d −1 ) and release from microzooplankton grazing (mean 5.6 nM d −1 ) were the dominant sources of DMS, with smaller DMS production rates associated with DMSO reduction from the dissolved pool (mean 2.6 nM d −1 ) and krill grazing (mean 0.82 nM d −1 ). Specific rate constants for DMSP cleavage were inversely related to net primary production. Bacterial uptake was a primary contributor to DMS removal (mean −12 nM d −1 ), and we observed a significant correlation between bacterial production and gross DMS loss rate constants. Estimated sea-air flux and photo-oxidation constituted secondary DMS sinks. Our experimental and analytical methods provide insight into the DMS/P/O cycle at Palmer Station, and a starting point for future studies examining inter-annual DMS/P/O variability in coastal Antarctic waters.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
    Published by Wiley on behalf of The Association for the Sciences of Limnology and Oceanography (ASLO).
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  • 10
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    The KDK (potassium decay) experiment (2020)
    Institute of Physics
    Details
    Publication Date: 2020-01-01
    Print ISSN: 1742-6588
    Electronic ISSN: 1742-6596
    Topics: Physics
    Published by Institute of Physics
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