Chappell Phoebe Dreux

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Chappell

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Phoebe Dreux

ORCID

0000-0001-5212-6228

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High rates of N-2 fixation in temperate, western North Atlantic coastal waters expand the realm of marine diazotrophy

(American Geophysical Union, 2019-06-10) Mulholland, Margaret R. ; Bernhardt, Peter W. ; Widner, Brittany ; Selden, Corday ; Chappell, Phoebe Dreux ; Clayton, Sophie A. ; Mannino, Antonio ; Hyde, Kimberly J. W.

Dinitrogen (N2) fixation can alleviate N limitation of primary productivity by introducing fixed nitrogen (N) to the world's oceans. Although measurements of pelagic marine N2 fixation are predominantly from oligotrophic oceanic regions, where N limitation is thought to favor growth of diazotrophic microbes, here we report high rates of N2 fixation from seven cruises spanning four seasons in temperate, western North Atlantic coastal waters along the North American continental shelf between Cape Hatteras and Nova Scotia, an area representing 6.4% of the North Atlantic continental shelf area. Integrating average areal rates of N2 fixation during each season and for each domain in the study area, the estimated N input from N2 fixation to this temperate shelf system is 0.02 Tmol N/year, an amount equivalent to that previously estimated for the entire North Atlantic continental shelf. Unicellular group A cyanobacteria (UCYN‐A) were most often the dominant diazotrophic group expressing nifH, a gene encoding the nitrogenase enzyme, throughout the study area during all seasons. This expands the domain of these diazotrophs to include coastal waters where dissolved N concentrations are not always depleted. Further, the high rates of N2 fixation and diazotroph diversity along the western North Atlantic continental shelf underscore the need to reexamine the biogeography and the activity of diazotrophs along continental margins. Accounting for this substantial but previously overlooked source of new N to marine systems necessitates revisions to global marine N budgets.
Coastal upwelling enhances abundance of a symbiotic diazotroph (UCYN-A) and its haptophyte host in the Arctic Ocean

(Frontiers Media, 2022-09-05) Selden, Corday R. ; Einarsson, Sveinn V. ; Lowry, Kate E. ; Crider, Katherine E. ; Pickart, Robert S. ; Lin, Peigen ; Ashjian, Carin J. ; Chappell, P. Dreux

The apparently obligate symbiosis between the diazotroph Candidatus Atelocyanobacterium thalassa (UCYN-A) and its haptophyte host,Braarudosphaera bigelowii , has recently been found to fix dinitrogen (N2) in polar waters at rates (per cell) comparable to those observed in the tropical/subtropical oligotrophic ocean basins. This study presents the novel observation that this symbiosis increased in abundance during a wind-driven upwelling event along the Alaskan Beaufort shelfbreak. As upwelling relaxed, the relative abundance of B. bigelowii among eukaryotic phytoplankton increased most significantly in waters over the upper slope. As the host’s nitrogen demands are believed to be supplied primarily by UCYN-A, this response suggests that upwelling may enhance N2 fixation as displaced coastal waters are advected offshore, potentially extending the duration of upwelling-induced phytoplankton blooms. Given that such events are projected to increase in intensity and number with ocean warming, upwelling-driven N2 fixation as a feedback on climate merits investigation.
Underway dissolved macronutrient concentrations collected on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-01-03) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

Underway dissolved macronutrient concentrations collected on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016. 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/742549
Dissolved trace metal concentrations for Incubation 3, initiated September 27th, 2016 on RVIB Nathaniel B. Palmer cruise NBP16-08 in the Southern Ocean

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-01-24) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

Dissolved trace metal concentrations for Incubation 3, initiated September 27th, 2016 on RVIB Nathaniel B. Palmer cruise NBP16-08 in the Southern Ocean. 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/781841
Chlorophyll and phaeopigment concentrations from incubation experiments performed with amended Southern Drake Passage on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-03-18) Chappell, Phoebe Dreux ; Buck, Kristen ; Jenkins, Bethany D.

This dataset includes chlorophyll and phaeopigment concentrations from incubation experiments performed with amended Southern Drake Passage on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016. 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/742206
Diatom hotspots driven by western boundary current instability

(American Geophysical Union, 2021-05-11) Oliver, Hilde ; Zhang, Weifeng G. ; Smith, Walker O. ; Alatalo, Philip ; Chappell, Phoebe Dreux ; Hirzel, Andrew ; Selden, Corday ; Sosik, Heidi M. ; Stanley, Rachel H. R. ; Zhu, Yifan ; McGillicuddy, Dennis J.

Climatic changes have decreased the stability of the Gulf Stream (GS), increasing the frequency at which its meanders interact with the Mid-Atlantic Bight (MAB) continental shelf and slope region. These intrusions are thought to suppress biological productivity by transporting low-nutrient water to the otherwise productive shelf edge region. Here we present evidence of widespread, anomalously intense subsurface diatom hotspots in the MAB slope sea that likely resulted from a GS intrusion in July 2019. The hotspots (at ∼50 m) were associated with water mass properties characteristic of GS water (∼100 m); it is probable that the hotspots resulted from the upwelling of GS water during its transport into the slope sea, likely by a GS meander directly intruding onto the continental slope east of where the hotspots were observed. Further work is required to unravel how increasingly frequent direct GS intrusions could influence MAB marine ecosystems.
Dissolved trace metal concentrations from depth profiles during RVIB Nathaniel B. Palmer cruise NBP16-08 in the Southern Ocean from 2016-09-11 to 2016-10-10

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-12-19) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

Dissolved trace metal concentrations from depth profiles during RVIB Nathaniel B. Palmer cruise NBP16-08 in the Southern Ocean from 2016-09-11 to 2016-10-10. 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/781773
Dissolved trace metal concentrations for Incubation 2, initiated September 24th, 2016 on RVIB Nathaniel B. Palmer cruise NBP16-08 in the Southern Ocean

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-01-24) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

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/781827
Biological, physical, and chemical data from surface Transect 5 on MV1405 (IRN-BRU)

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-07-06) Chappell, Phoebe Dreux ; Till, Claire P. ; Coale, Tyler ; Bruland, Kenneth W.

Biological, physical, and chemical data from surface Transect 5 on MV1405 (IRN-BRU) collected in July 2014 in the California Current System. 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/876590
The relationship between iron and nitrogen fixation in Trichodesmium spp.

(Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2009-06) Chappell, Phoebe Dreux

Trichodesmium spp. are considered the dominant nitrogen (N) fixing cyanobacteria in tropical and subtropical oceans, regimes frequently characterized by low iron (Fe). Limited information exists about what levels of Fe limit Trichodesmium N fixation. I developed a diagnostic for Fe limitation using quantitative reverse transcription PCR (qRT-PCR) of the Fe stress response gene isiB, which encodes for flavodoxin a non-Fe containing substitute for ferredoxin. I determined that high isiB gene expression corresponded to cell-specific reductions in N fixation rates in both phylogenetic clades of Trichodesmium grown on varying levels of Fe. Using these laboratory-determined thresholds, I assessed Fe limitation of Trichodesmium from the Sargasso Sea, equatorial Atlantic Ocean and Western Pacific Warm Pool in conjunction with other analytical measurements (N, phosphorus (P) and dissolved Fe (<0.4μm filtered)). I found widespread Fe limitation in Trichodesmium from the Pacific Ocean and minimal expression in the North Atlantic Ocean. I also found an inverse correlation between isiB expression and dissolved Fe:P ratios in seawater and data suggesting that most dissolved Fe in seawater, including organic ligand-bound Fe, is available to Trichodesmium. These data support and refine previous model predictions and demonstrate, in situ, the importance of Fe to the marine N cycle.
Dissolved macronutrient concentrations from depth profiles from RVIB Nathaniel B. Palmer cruise NBP1608 in the Southern Ocean from September to October 2016

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-01-03) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

Dissolved macronutrient concentrations from depth profiles from RVIB Nathaniel B. Palmer cruise NBP1608 in the Southern Ocean from September to October 2016. 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/742819
Chlorophyll and phaeopigment concentrations from near-surface profiles collected using the conventional CTD in the Southern Drake Passage and Antarctic Peninsular region on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-03-18) Chappell, Phoebe Dreux ; Buck, Kristen ; Jenkins, Bethany D.

This dataset includes chlorophyll and phaeopigment concentrations from near-surface profiles collected using the conventional CTD in the Southern Drake Passage and Antarctic Peninsular region on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016. 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/740939
Dissolved trace metal concentrations for Incubation 1, initiated September 11th, 2016 on RVIB Nathaniel B. Palmer cruise NBP16-08 in the Southern Ocean

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2019-12-20) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

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/781759
Dissolved macronutrient concentrations from incubation experiments performed on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016

(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2020-01-03) Buck, Kristen N. ; Chappell, Phoebe Dreux ; Jenkins, Bethany D.

Dissolved macronutrient concentrations from incubation experiments performed on RVIB Nathaniel B. Palmer cruise NBP 16-08 from September to October 2016. 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/743072
Nitrogen fixation at the Mid‐Atlantic Bight Shelfbreak and transport of newly fixed nitrogen to the Slope Sea

(American Geophysical Union, 2024-04-05) Selden, Corday R. ; Mulholland, Margaret R. ; Crider, Katie E. ; Clayton, Sophie A. ; Macias-Tapia, Alfonso ; Bernhardt, Peter W. ; McGillicuddy, Dennis J. ; Zhang, Weifeng Gordon ; Chappell, Phoebe Dreux

Continental shelves contribute a large fraction of the ocean's new nitrogen (N) via N2 fixation; yet, we know little about how physical processes at the ocean's margins shape diazotroph biogeography and activity. Here, we test the hypothesis that frontal mixing favors N2 fixation at the Mid-Atlantic Bight shelfbreak. Using the 15N2 bubble release method, we measured N2 fixation rates on repeat cross-frontal transects in July 2019. N2 fixation rates in shelf waters (median = 5.42 nmol N L−1 d−1) were higher than offshore (2.48 nmol N L−1 d−1) but did not significantly differ front frontal waters (8.42 nmol N L−1 d−1). However, specific N2 uptake rates, indicative of the relative contribution of diazotroph-derived N to particulate N turnover, were significantly higher in frontal waters, suggesting that diazotroph-derived N is of greater importance in supporting productivity there. This study furthered captured an ephemeral shelf-water streamer, which resulted from the impingement of a warm core ring on the shelf. The streamer transported shelf-water diazotrophs (including UCYN-A and Richelia spp., as assessed by qPCR) offshore with sustained high N2 fixation rates. This feature injected >50 metric tons d−1 of newly fixed N to the Slope Sea—a rate equivalent to ∼4% of the total N flux estimated for the entire Mid-Atlantic Bight. As intrusions of Gulf Stream meanders and eddies onto the shelf are increasing in frequency due to climate change, episodic lateral fluxes of new N into the Slope Sea may become increasingly important to regional budgets and ecosystem productivity.

Chappell Phoebe Dreux

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