Bullock
Emma J.
Bullock
Emma J.
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DatasetDesorbed Radium from Kolyma (Russia), Ellice (Canada), and Kodiak Island (USA) Rivers(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-17) Charette, Matthew A. ; Bullock, Emma J.This dataset reports concentrations of desorbed Radium from Kolyma (Russia), Ellice (Canada), and Kodiak Island (USA) Rivers from sediment samples collected from July 2018 to September 2019. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/878663
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ArticleRadium inputs into the Arctic Ocean from rivers a basin‐wide estimate(American Geophysical Union, 2022-09-08) Bullock, Emma J. ; Kipp, Lauren ; Moore, Willard S. ; Brown, Kristina A. ; Mann, Paul J. ; Vonk, Jorien E. ; Zimov, Nikita S. ; Charette, Matthew A.Radium isotopes have been used to trace nutrient, carbon, and trace metal fluxes inputs from ocean margins. However, these approaches require a full accounting of radium sources to the coastal ocean including rivers. Here, we aim to quantify river radium inputs into the Arctic Ocean for the first time for 226Ra and to refine the estimates for 228Ra. Using new and existing data, we find that the estimated combined (dissolved plus desorbed) annual 226Ra and 228Ra fluxes to the Arctic Ocean are [7.0–9.4] × 1014 dpm y−1 and [15–18] × 1014 dpm y−1, respectively. Of these totals, 44% and 60% of the river 226Ra and 228Ra, respectively are from suspended sediment desorption, which were estimated from laboratory incubation experiments. Using Ra isotope data from 20 major rivers around the world, we derived global annual 226Ra and 228Ra fluxes of [7.4–17] × 1015 and [15–27] × 1015 dpm y−1, respectively. As climate change spurs rapid Arctic warming, hydrological cycles are intensifying and coastal ice cover and permafrost are diminishing. These river radium inputs to the Arctic Ocean will serve as a valuable baseline as we attempt to understand the changes that warming temperatures are having on fluxes of biogeochemically important elements to the Arctic coastal zone.
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DatasetDissolved Radium from Kolyma (Russia), Ellice (Canada), and Kodiak Island (USA) Rivers(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-17) Charette, Matthew A. ; Bullock, Emma J.This dataset reports concentrations of dissolved Radium from Kolyma (Russia), Ellice (Canada), and Kodiak Island (USA) Rivers from samples collected from June to September 2019. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/878527
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ArticleSeasonality of submarine groundwater discharge to an Arctic coastal lagoon(Association for the Sciences of Limnology and Oceanography (ASLO), 2024-05-12) Bullock, Emma J. ; Schaal, Isabel V. ; Cardenas, M. Bayani ; McClelland, James W. ; Henderson, Paul B. ; Charette, Matthew A.Supra-permafrost submarine groundwater discharge (SGD) in the Arctic is potentially important for coastal biogeochemistry and will likely increase over the coming decades owing to climate change. Despite this, land-to-ocean material fluxes via SGD in Arctic environments have seldom been quantified. This study used radium (Ra) isotopes to quantify SGD fluxes to an Arctic coastal lagoon (Simpson Lagoon, Alaska) during five sampling periods between 2021 and 2023. Using a Ra mass balance model, we found that the SGD water flux was substantial and dependent on environmental conditions. No measurable SGD was detected during the spring sampling period (June 2022), when the lagoon was partially ice-covered. During ice-free periods, the main driver of SGD in this location is wind-driven lagoon water level changes, not tides, which control surface water recirculation through sediments along the lagoon boundary. A combination of wind strength and direction led to low SGD fluxes in July 2022, with an SGD flux of (6 ± 3) × 106 m3 d−1, moderate fluxes in August 2021 and July 2023, which had an average flux of (17 ± 9) × 106 m3 d−1, and high fluxes in October 2022, at (79 ± 16) × 106 m3 d−1. This work demonstrates how soil and environmental conditions in the Arctic impact Ra mobilization, laying a foundation for future SGD studies in the Arctic and shedding light on the major processes driving Ra fluxes in this important environment.
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ArticleDiverse methylotrophic methanogenic archaea cause high methane emissions from seagrass meadows(National Academy of Sciences, 2022-02-14) Schorn, Sina ; Ahmerkamp, Soeren ; Bullock, Emma J. ; Weber, Miriam ; Lott, Christian ; Liebeke, Manuel ; Lavik, Gauke ; Kuypers, Marcel M. M. ; Graf, Jon S. ; Milucka, JanaMarine coastlines colonized by seagrasses are a net source of methane to the atmosphere. However, methane emissions from these environments are still poorly constrained, and the underlying processes and responsible microorganisms remain largely unknown. Here, we investigated methane turnover in seagrass meadows of Posidonia oceanica in the Mediterranean Sea. The underlying sediments exhibited median net fluxes of methane into the water column of ca. 106 µmol CH4 ⋅ m−2 ⋅ d−1. Our data show that this methane production was sustained by methylated compounds produced by the plant, rather than by fermentation of buried organic carbon. Interestingly, methane production was maintained long after the living plant died off, likely due to the persistence of methylated compounds, such as choline, betaines, and dimethylsulfoniopropionate, in detached plant leaves and rhizomes. We recovered multiple mcrA gene sequences, encoding for methyl-coenzyme M reductase (Mcr), the key methanogenic enzyme, from the seagrass sediments. Most retrieved mcrA gene sequences were affiliated with a clade of divergent Mcr and belonged to the uncultured Candidatus Helarchaeota of the Asgard superphylum, suggesting a possible involvement of these divergent Mcr in methane metabolism. Taken together, our findings identify the mechanisms controlling methane emissions from these important blue carbon ecosystems.