Papers by Claudia Benitez-Nelson
Asexual Reproduction in the Planktic Foraminifer Neogloboquadrina Pachyderma and Morphological and Trace Element Variability in the Resulting Offspring
Estuaries and Coasts, Jun 14, 2018
Across the coastal zone, rates of carbon and nutrient exchange are defined by the spatiotemporal ... more Across the coastal zone, rates of carbon and nutrient exchange are defined by the spatiotemporal heterogeneity of individual estuarine systems. Elemental stoichiometry provides a mechanism for simplifying overlapping physical, chemical, and biological drivers into proxies that can be used to compare and monitor estuarine biogeochemistry. To this end, the seasonal and tidal variability of estuarine stoichiometry was examined over an annual cycle in North Inlet (NI), South Carolina. Surface samples for dissolved and particulate carbon (C), nitrogen (N), and phosphorus (P) were collected every 20 days (August 2014 to August 2015) over a semidiurnal tidal cycle. Dissolved nutrient flux estimates of an individual tidal creek were also made. Overall, the results demonstrated the dominance of seasonal versus tidal forcing on water column C:N:P stoichiometry. This seasonal behavior mediated the relative exchange of N and P into and out of the tidal creek and influenced the nutrient status index (NSI) of NI plankton communities. These communities were largely N deficient with the magnitude of this deficiency impacted by assumptions of inorganic versus organic plankton P demand and nutrient supply. Persistent N deficiency appeared to help drive the net import of N, while temporary P surplus likely drives its seasonal export. Combined, these results indicate that material delivery must be considered on seasonal time frames, as net annual fluxes do not reflect the short-term deliveries of C and nutrients into nearshore ecosystems. Keywords Stoichiometry . Tidal exchange . Nutrient status . Salt marsh tidal creek . NERRS * Douglas W. Bell
Decoupling between particulate carbon, nitrogen and biogenic silica export mediated by cyclonic eddies in the North Pacific Subtropical Gyre
Influence of stormwater management on organic matter dynamics and oxygen demand in urbanizing headwater catchments of a coastal plain river
AGU Fall Meeting Abstracts, Dec 1, 2019
Characterizing seasonal contribution of particles from the surface ocean to the mesopelagic food web through amino acid compound specific isotopic analysis and 234 Thorium measurements
American Geophysical Union eBooks, Feb 1, 2016
Estimating relative flux of phytodetritus, fecal pellets, and bacterial biomass using compound-specific isotope analysis of amino acids at Station Papa (EXPORTS)
Ocean Sciences Meeting 2020, Feb 17, 2020
Mercury Stable Isotopes Reveal Deep Methylation of Mercury and its Uptake into the Open Ocean Food Web
American Geophysical Union eBooks, Feb 1, 2016
Ecosystems, Jan 16, 2018
Stormwater detention ponds are widely utilized as control structures to manage runoff during stor... more Stormwater detention ponds are widely utilized as control structures to manage runoff during storm events. These ponds also represent biogeochemical hotspots, where carbon (C) and nutrients can be processed and buried in sediments. This study quantified C and nutrient [nitrogen (N) and phosphorus (P)] sources and burial rates in 14 stormwater detention ponds representative of typical residential development in coastal South Carolina. Bulk sediment accumulation was directly correlated with catchment impervious surface coverage (R 2 = 0.90) with sediment accumulation rates ranging from 0.06 to 0.50 cm y -1 . These rates of sediment accumulation and consequent pond volume loss were lower than anticipated based on maintenance guidelines provided by the State. Nalkanes were used as biomarkers of sediment source; the derived terrestrial aquatic ratio (TAR HC ) index was strongly correlated with sediment accumulation rate (R 2 = 0.71) which, in conjunction with high C/N ratios (16-33), suggests that terrestrial biomass drives this sediment accumulation, with relatively minimal contributions from algal derived material. This is counter to expectations that were based on the high algal productivity generally observed in stormwater ponds and previous studies of natural lakes. Sediment C and nutrient concentrations were consistent among ponds, such that differences in burial rates were a simple function of bulk sediment accumulation rate. These burial rates (C: 8.7-161 g m -2 y -1 , N: 0.65-6.4 g m -2 y -1 , P: 0.238-4.13 g m -2 y -1 ) were similar to those observed in natural lake systems, but lower than those observed in reservoirs or impoundments. Though individual ponds were small in area (930-41,000 m 2 ), they are regionally abundant and, when mean burial rates are extrapolated to the regional scale (% 21,000 ponds), ultimately sequester 2.0 9 10 9 g C y -1 ,
Journal Of Geophysical Research: Oceans, Nov 1, 2015
The biological carbon pump is responsible for the transport of 5-20 Pg C yr 21 from the surface i... more The biological carbon pump is responsible for the transport of 5-20 Pg C yr 21 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 remotesensing algorithms formulated by Dunne et al. ( ), Laws et al. (2011), Henson et al. (2011), and Siegel et al. ( ), 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 seven cruises in the California Current Ecosystem and Costa Rica Dome. A food-web based approach formulated by Siegel et al. ( ) 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. ( ) 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 satellitederived 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.
Characterization of Mercury Particle Flux Using 238 U: 234 Th Disequilibria in the North Pacific Subtropical Gyre
AGUOS, Feb 1, 2016
Deep zooplankton rely on small particles in response to low fluxes
Ocean Sciences Meeting 2020, Feb 17, 2020
Ha estat un camí llarg però finalment aquesta tesi doctoral és una realitat. Avui escric aquestes... more Ha estat un camí llarg però finalment aquesta tesi doctoral és una realitat. Avui escric aquestes línies recordant la multitud de bons moments viscuts al costat de persones que han fet que no només aquesta tesi hagi arribat a bon port, sinó que també han fet que gaudís del camí fent que el trajecte fos d'allò més excitant, divertit i gratificant. First of all I want to thank my PhD supervisors, Pere and Claudia. I started to work with both of you when I was still doing my Bachelors. I was sent to participate on my first research cruise and I instantaneously fell in love with the world of oceanographic research. Since then, there have been many more expeditions, but I am still passionate about going to sea; no matter what regions, there is always something new to explore. I think part of that enthusiasm is due to having you as supervisors, since both of you are extremely active and exited about a wide variety of topics. You have fed my passion of going to sea and always supported me, even when you probably thought it was not the smartest decision if one was planning to finish a PhD thesis, and for that I will be eternally grateful. I know the academic world is competitive and papers seem to be the only thing that matters nowadays, but you have always been patient and supportive, clearly valuing other aspects of research that had a much deeper impact on me as a person. Thanks for giving me the opportunity to work with you, for all the support, knowledge and advice provided. It has been a great pleasure and hopefully it will not finish here. Em sento extremadament afortunada per haver tingut els companys de grup que he tingut. Heu estat una peça clau del meu dia a dia, heu fet de tots aquests anys un record inoblidable. Gràcies a vosaltres he tirat endavant quan el que em venien ganes de fer era plegar veles i triar l'opció cocotero. Moltes gràcies pel recolzament, per tots els moments fantàstics compartits i per la vostra amistat. Sé que acabar el doctorat no implicarà perdre el contacte amb vosaltres perquè sou molt més que companys de laboratori. Vull començar donant les gràcies al Jordi perquè tu vas ser el que em vas iniciar en el món de la radioactivitat ambiental i ets el culpable que els radioisòtops es convertissin en la meva passió aquell curs 2005/06 (si si, ara fa 10 anys!!!). Sempre has estat disponible i ajudant quan ha fet falta, amb la millor de les actituds i amb bon humor. Gràcies per ser un jefe que aporta tan bon ambient al grup, amb tanta motivació i tan involucrat en tot, fins i tot quan ja no queden més minuts lliures per res. Moltes gràcies Joan Manuel per tot el suport que m'has donat durant tots aquests anys, en el lab (amb les depos i mesurant discs de Pb-Po del dret i del revés tantes vegades com ha fet falta amb molta paciència), com preparant campanyes com fins i tot participant-ne en una. Saps que sense tu donant un cop de mà quan fes falta, arribar fins aquí microphytoplankton. Thus, and although different food web regimes led to similar export of carbon, the sinking particle pools differed in their composition north and south of the Antarctic Polar Front (aggregates of small particles in the north vs fast-sinking large particles in the south), resulting in two different scenarios regarding the amount of exported carbon that reached greater depths. Finally, estimates of particle flux and export efficiency were examined in a semi-enclosed basin (Gulf of California and the surrounding waters of the Eastern Tropical North Pacific), with a strong seasonality that leads to changes in the planktonic community. Export estimates were assessed using the 234 Th approach in combination with surface-tethered sediment traps. Data on size fractionation and high vertical resolution of in situ pump deployments allowed a comparison of the C/ 234 Th ratios attenuation with depth between small (1-53 μm) and large (>53 μm) particles. Results indicate that, under dominance of pico-and nanoplankton and with presence of diazotrophs, small particles play and important role in carbon export and that this export might be more efficient than that resulting from a diatom dominated planktonic community in the study area.
Cyclonic eddies modulate temporal and spatial decoupling of particulate carbon, nitrogen, and biogenic silica export in the North Pacific Subtropical Gyre
Limnology and Oceanography, Jul 23, 2021
Mesoscale eddies may enhance nutrient injection into the photic zone and ultimately the magnitude... more Mesoscale eddies may enhance nutrient injection into the photic zone and ultimately the magnitude and composition of particle export to depth. Using satellite altimetry, we identified 38 cyclonic eddies that passed in close proximity to the Hawaii Ocean Time‐series (HOT) Station ALOHA, located in the North Pacific Subtropical Gyre, from 1993 to 2018. Particulate carbon (C), nitrogen (N), and biogenic silica (Si) export rates, measured using free floating sediment traps deployed at 150 m as part of HOT, were then associated with either the eddy core or edge based on distance to the eddy center and time of eddy evolution. Elemental fluxes varied significantly within and among individual eddies depending on season and eddy age. Spatially, biogenic Si fluxes were enhanced relative to particulate C and N fluxes at both the cores and edges, with temporally highest particulate C, N and biogenic Si fluxes occurring during the mature stage (3–8 weeks). On average, biogenic Si fluxes were 200 ± 80% (30–270% increase) higher relative to non‐eddy and during non‐bloom periods, with modest enhanced particulate C (10–30% increase) and N (10–20% increase) fluxes. In contrast, during the bloom season (July and August), elemental fluxes were all reduced by 20% relative to non‐eddy references, suggesting that cyclonic eddies depress export during the bloom period. Our results indicate that cyclonic eddies not only increase, but differentially impact the sinking export of critical biological elements, thereby contributing to long term ecological changes in foodwebs that rely on silica as well as carbon for growth.
Global and Planetary Change, Sep 1, 2017
Few long-term environmental records are available for southern Africa where shifts in atmospheric... more Few long-term environmental records are available for southern Africa where shifts in atmospheric circulation and changes in sea surface temperatures interact to influence regional climate dynamics. We present downcore grain size and inorganic geochemistry data covering the last ~23,000 years from a peatland on the east coast of South Africa and examine links between shifts in regional wind activity and palaeoclimatic variability. Our record documents substantial variations in aeolian flux associated with changes in regional climate and wind patterns that reflect larger scale atmospheric circulation patterns. Substantially higher fluxes observed during the Last Glacial Maximum (LGM) are linked to widespread aridification and an expansion in local source areas brought about by a clear shift to dry and cool conditions. Variations in grain size distribution reveal that the aeolian record from Mfabeni comprises two dominant end-members; locally-derived coarse-grained material and a more fine-grained dust component. Marked changes in composition and modal grain size suggest that hydrological shifts in the region during the LGM were accompanied by an increase in storm frequency and wind strength that we link to a northward displacement in the westerly wind belt and a strengthening in wind intensity.
Global Biogeochemical Cycles, Jun 1, 2019
The oceans are an important global reservoir for mercury (Hg), and marine fish consumption is the... more The oceans are an important global reservoir for mercury (Hg), and marine fish consumption is the dominant human exposure pathway for its toxic methylated form. A more thorough understanding of the global biogeochemical cycle of Hg requires additional information on the mechanisms that control Hg cycling in pelagic marine waters. In this study, Hg isotope ratios and total Hg concentrations are used to explore Hg biogeochemistry in oligotrophic marine environments north of Hawaii. We present the first measurements of the vertical water column distribution of Hg concentrations and the Hg isotopic composition in precipitation, marine particles, and zooplankton near Station ALOHA (22°45′N, 158°W). Our results reveal production and demethylation of methylmercury in both the euphotic (0-175 m) and mesopelagic zones (200-1,000 m). We document a strong relationship between Hg isotopic composition and depth in particles, zooplankton, and fish in the water column and diurnal variations in Δ 199 Hg values in zooplankton sampled near the surface (25 m). Based on these observations and stable Hg isotope relationships in the marine food web, we suggest that the Hg found in large pelagic fish at Station ALOHA was originally deposited largely by precipitation, transformed into methyl-Hg, and bioaccumulated in situ in the water column. Our results highlight how Hg isotopic compositions reflect abiotic and biotic production and degradation of methyl-Hg throughout the water column and the importance of particles and zooplankton in the vertical transport of Hg.
Marine Chemistry, Nov 1, 2019
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Oceanography, Sep 1, 2006
Mercury isotopic evidence for the importance of particles as a source of mercury to marine organisms
Proceedings of the National Academy of Sciences of the United States of America, Oct 24, 2022
The origin of methylmercury in pelagic fish remains unclear, with many unanswered questions regar... more The origin of methylmercury in pelagic fish remains unclear, with many unanswered questions regarding the production and degradation of this neurotoxin in the water column. We used mercury (Hg) stable isotope ratios of marine particles and biota to elucidate the cycling of methylmercury prior to incorporation into the marine food web. The Hg isotopic composition of particles, zooplankton, and fish reveals preferential methylation of Hg within small (&lt; 53 µm) marine particles in the upper 400 m of the North Pacific Ocean. Mass-dependent Hg isotope ratios (δ 202 Hg) recorded in small particles overlap with previously estimated δ 202 Hg values for methylmercury sources to Pacific and Atlantic Ocean food webs. Particulate compound specific isotope analysis of amino acids (CSIA-AA) yield δ 15 N values that indicate more-significant microbial decomposition in small particles compared to larger particles. CSIA-AA and Hg isotope data also suggest that large particles (&gt; 53 µm) collected in the equatorial ocean are distinct from small particles and resemble fecal pellets. Additional evidence for Hg methylation within small particles is provided by a statistical mixing model of even mass–independent (Δ 200 Hg and Δ 204 Hg) isotope values, which demonstrates that Hg within near-surface marine organisms (0–150 m) originates from a combination of rainfall and marine particles. In contrast, in meso- and upper bathypelagic organisms (200–1,400 m), the majority of Hg originates from marine particles with little input from wet deposition. The occurrence of methylation within marine particles is supported further by a correlation between Δ 200 Hg and Δ 199 Hg values, demonstrating greater overlap in the Hg isotopic composition of marine organisms with marine particles than with total gaseous Hg or wet deposition.
Prediction and Verification of a Strong Pulse of Submarine Groundwater Discharge Onto the South Carolina, Usa, Continental Shelf, and Its Effect on Dissolved Oxygen Concentrations
Geological Society of America Abstracts with Programs
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and mostly mafic oceanic crust in which they remain relatively buoyant, leading to a fast ascent ... more and mostly mafic oceanic crust in which they remain relatively buoyant, leading to a fast ascent directly to the surface (see the figure) and an effusive volcanism domi-nated by basaltic lava flows. Magma ascent through thick continen-tal crust proceeds in more complex ways. Basaltic melts are denser than most of the felsic rocks that make up the upper crust. They therefore tend to stall within the lower or middle crust, where they form magma reservoirs that grow over many thousands or a few millions of years ( 8) by accretion of many individual sills ( 9, 10). Si-licic magmas that are enriched in volatiles
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Papers by Claudia Benitez-Nelson