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| Author | Stukel, M.R.; Decima, M.; Kelly, T.B. | ||||
| Title | A new approach for incorporating 15N isotopic data into linear inverse ecosystem models with Markov Chain Monte Carlo sampling | Type | $loc['typeJournal Article'] | ||
| Year | 2018 | Publication | PloS one | Abbreviated Journal | PLoS One |
| Volume | 13 | Issue | 6 | Pages | e0199123 |
| Keywords | Isotopic data; Nitrogen-based ecosystem models; Phytoplankton; Defecation by grazers; Mortality by phytoplankton | ||||
| Abstract | Oceanographic field programs often use delta15N biogeochemical measurements and in situ rate measurements to investigate nitrogen cycling and planktonic ecosystem structure. However, integrative modeling approaches capable of synthesizing these distinct measurement types are lacking. We develop a novel approach for incorporating delta15N isotopic data into existing Markov Chain Monte Carlo (MCMC) random walk methods for solving linear inverse ecosystem models. We test the ability of this approach to recover food web indices (nitrate uptake, nitrogen fixation, zooplankton trophic level, and secondary production) derived from forward models simulating the planktonic ecosystems of the California Current and Amazon River Plume. We show that the MCMC with delta15N approach typically does a better job of recovering ecosystem structure than the standard MCMC or L2 minimum norm (L2MN) approaches, and also outperforms an L2MN with delta15N approach. Furthermore, we find that the MCMC with delta15N approach is robust to the removal of input equations and hence is well suited to typical pelagic ecosystem studies for which the system is usually vastly under-constrained. Our approach is easily extendable for use with delta13C isotopic measurements or variable carbon:nitrogen stoichiometry. | ||||
| Address | Department of Earth, Ocean, and Atmospheric Science, Florida State University, Tallahassee, FL, United States of America | ||||
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| Language | English | Summary Language | Original Title | ||
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| Series Volume | Series Issue | Edition | |||
| ISSN | 1932-6203 | ISBN | Medium | ||
| Area | Expedition | Conference | |||
| Funding | strtoupper('2').strtolower('9912928'); strtoupper('P').strtolower('MC6005467') | Approved | $loc['no'] | ||
| Call Number | COAPS @ user @ | Serial | 975 | ||
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| Author | Stukel, M.R.; Ohman, M.D.; Kelly, T.B.; Biard, T. | ||||
| Title | The Roles of Suspension-Feeding and Flux-Feeding Zooplankton as Gatekeepers of Particle Flux Into the Mesopelagic Ocean in the Northeast Pacific | Type | $loc['typeJournal Article'] | ||
| Year | 2019 | Publication | Frontiers in Marine Science | Abbreviated Journal | Front. Mar. Sci. |
| Volume | 6 | Issue | Pages | ||
| Keywords | biological pump; carbon export; remineralization length scale; mesozooplankton ecology; pteropods; marine biogeochemistry; sinking particles; marine snow | ||||
| Abstract | Zooplankton are important consumers of sinking particles in the ocean's twilight zone. However, the impact of different taxa depends on their feeding mode. In contrast to typical suspension-feeding zooplankton, flux-feeding taxa preferentially consume rapidly sinking particles that would otherwise penetrate into the deep ocean. To quantify the potential impact of two flux-feeding zooplankton taxa [Aulosphaeridae (Rhizaria), and Limacina helicina (euthecosome pteropod)] and the total suspension-feeding zooplankton community, we measured depth-stratified abundances of these organisms during six cruises in the California Current Ecosystem. Using allometric-scaling relationships, we computed the percentage of carbon flux intercepted by flux feeders and suspension feeders. These estimates were compared to direct measurements of carbon flux attenuation (CFA) made using drifting sediment traps and U-238-Th-234 disequilibrium. We found that CFA in the shallow twilight zone typically ranged from 500 to 1000 m mol organic C flux remineralized per 10-m vertical depth bin. This equated to approximately 6-10% of carbon flux remineralized/10 m. The two flux-feeding taxa considered in this study could account for a substantial proportion of this flux near the base of the euphotic zone. The mean flux attenuation attributable to Aulosphaeridae was 0.69%/10 m (median = 0.21%/10 m, interquartile range = 0.04-0.81%) at their depth of maximum abundance (similar to 100 m), which would equate to similar to 10% of total flux attenuation in this depth range. The maximum flux attenuation attributable to Aulosphaeridae reached 4.2%/10 m when these protists were most abundant. L. helicina, meanwhile, could intercept 0.45-1.6% of carbon flux/10 m, which was slightly greater (on average) than the Aulosphaeridae. In contrast, suspension-feeding zooplankton in the mesopelagic (including copepods, euphausiids, appendicularians, and ostracods) had combined clearance rates of 2-81 L m(-3) day(-1) (mean of 19.6 L m(-3) day(-1)). This implies a substantial impact on slowly sinking particles, but a negligible impact on the presumably rapidly sinking fecal pellets that comprised the majority of the material collected in sediment traps. Our results highlight the need for a greater research focus on the many taxa that potentially act as flux feeders in the oceanic twilight zone. | ||||
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| ISSN | 2296-7745 | ISBN | Medium | ||
| Area | Expedition | Conference | |||
| Funding | Approved | $loc['no'] | |||
| Call Number | COAPS @ user @ | Serial | 1066 | ||
| Permanent link to this record | |||||
| Author | Wang, S.; Kranz, S.A.; Kelly, T.B.; Song, H.; Stukel, M.R.; Cassar, N. | ||||
| Title | Lagrangian Studies of Net Community Production: The Effect of Diel and Multiday Nonsteady State Factors and Vertical Fluxes on O2/Ar in a Dynamic Upwelling Region | Type | $loc['typeJournal Article'] | ||
| Year | 2020 | Publication | Journal of Geophysical Research: Biogeosciences | Abbreviated Journal | J. Geophys. Res. Biogeosci. |
| Volume | 125 | Issue | 6 | Pages | e2019JG005569 |
| Keywords | net community production; O2/Ar; California Current Ecosystem; Lagrangian measurements; vertical fluxes; nonsteady state | ||||
| Abstract | The ratio of dissolved oxygen to argon in seawater is frequently employed to estimate rates of net community production (NCP) in the oceanic mixed layer. The in situ O2/Ar‐based method accounts for many physical factors that influence oxygen concentrations, permitting isolation of the biological oxygen signal produced by the balance of photosynthesis and respiration. However, this technique traditionally relies upon several assumptions when calculating the mixed‐layer O2/Ar budget, most notably the absence of vertical fluxes of O2/Ar and the principle that the air‐sea gas exchange of biological oxygen closely approximates net productivity rates. Employing a Lagrangian study design and leveraging data outputs from a regional physical oceanographic model, we conducted in situ measurements of O2/Ar in the California Current Ecosystem in spring 2016 and summer 2017 to evaluate these assumptions within a �worst‐case� field environment. Quantifying vertical fluxes, incorporating nonsteady state changes in O2/Ar, and comparing NCP estimates evaluated over several day versus longer timescales, we find differences in NCP metrics calculated over different time intervals to be considerable, also observing significant potential effects from vertical fluxes, particularly advection. Additionally, we observe strong diel variability in O2/Ar and NCP rates at multiple stations. Our results reemphasize the importance of accounting for vertical fluxes when interpreting O2/Ar‐derived NCP data and the potentially large effect of nonsteady state conditions on NCP evaluated over shorter timescales. In addition, diel cycles in surface O2/Ar can also bias interpretation of NCP data based on local productivity and the time of day when measurements were made. | ||||
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| ISSN | 2169-8953 | ISBN | Medium | ||
| Area | Expedition | Conference | |||
| Funding | Approved | $loc['no'] | |||
| Call Number | COAPS @ user @ | Serial | 1114 | ||
| Permanent link to this record | |||||
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