McGillicuddy
Dennis J.
McGillicuddy
Dennis J.
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ArticleEphemeral surface chlorophyll enhancement at the New England shelf break driven by Ekman restratification(American Geophysical Union, 2021-12-28) Oliver, Hilde ; Zhang, Weifeng G. ; Archibald, Kevin M. ; Hirzel, Andrew ; Smith, Walker O. ; Sosik, Heidi M. ; Stanley, Rachel H. R. ; McGillicuddy, Dennis J.The Mid-Atlantic Bight (MAB) hosts a large and productive marine ecosystem supported by high phytoplankton concentrations. Enhanced surface chlorophyll concentrations at the MAB shelf-break front have been detected in synoptic measurements, yet this feature is not present in seasonal means. To understand why, we assess the conditions associated with enhanced surface chlorophyll at the shelf break. We employ in-situ and remote sensing data, and a 2-dimensional model to show that Ekman restratification driven by upfront winds drives ephemerally enhanced chlorophyll concentrations at the shelf-break front in spring. Using 8-day composite satellite-measured surface chlorophyll concentration data from 2003–2020, we constructed a daily running mean (DRM) climatology of the cross-shelf chlorophyll distribution for the northern MAB region. While the frontal enhancement of chlorophyll is apparent in the DRM climatology, it is not captured in the seasonal climatology due to its short duration of less than a week. In-situ measurements of the frontal chlorophyll enhancement reveal that chlorophyll is highest in spring when the shelf-break front slumps offshore from its steep wintertime position causing restratification in the upper part of the water column. Several restratification mechanisms are possible, but the first day of enhanced chlorophyll at the shelf break corresponds to increasing upfront winds, suggesting that the frontal restratification is driven by offshore Ekman transport of the shelf water over the denser slope water. The 2-dimensional model shows that upfront winds can indeed drive Ekman restratification and alleviate light limitation of phytoplankton growth at the shelf-break front.
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PreprintMesoscale variability in intact and ghost colonies of Phaeocystis antarctica in the Ross Sea : distribution and abundance( 2016-05) Smith, Walker O. ; McGillicuddy, Dennis J. ; Olson, Elise M. B. ; Kosnyrev, Valery ; Peacock, Emily E. ; Sosik, Heidi M.Phaeocystis, a genus with a cosmopolitan distribution and a polymorphic life cycle, was observed during summer in the Ross Sea, Antarctica, where large blooms of this haptophyte regularly occur. The mesoscale vertical and horizontal distributions of colonies of P. antarctica were assessed using a towed Video Plankton Recorder (VPR). The mean size of colonies was 1.20 mm, and mean abundances within the three VPR surveys were 4.86, 1.96, and 11.5 mL-1. In addition to the typical spherical, transparent colonies, the VPR quantified an optically dissimilar form of colony that had a distinctive translucent appearance. It also measured the abundance of collapsed colonies, similar to those observed previously from cultures and mesocosms, which we called “ghost colonies”. The translucent colonial form had a different distribution than the more common colonial form, and at times was more abundant. Relative to intact colonies, the ghost colonies occurred less frequently, with mean abundances in the three surveys being 0.01, 0.08, and 0.0004 mL-1. Ghost colonies generally were found below the euphotic zone, where they often were in greater abundance than intact colonies. However, the relationship of ghost colonies to intact P. antarctica colonies was not direct or consistent, suggesting that the formation of ghost colonies from living colonies and their appearance within the water column were not tightly coupled. Given their relative scarcity and low carbon content, it is unlikely that ghost colonies contribute substantially to vertical flux; however, it is possible that we did not sample periods of major flux events, and as a result minimized the importance of ghost colonies to vertical flux. They do, however, represent a poorly documented feature of polar haptophyte life cycles.
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PreprintTemporal progression of photosynthetic-strategy in phytoplankton in the Ross Sea, Antarctica( 2015-12) Ryan-Keogh, Thomas J. ; DeLizo, Liza M. ; Smith, Walker O. ; Sedwick, Peter N. ; McGillicuddy, Dennis J. ; Moore, C. Mark ; Bibby, Thomas S.The bioavailability of iron influences the distribution, biomass and productivity of phytoplankton in the Ross Sea, one of the most productive regions in the Southern Ocean. We mapped the spatial and temporal extent and severity of iron-limitation of the native phytoplankton assemblage using long- (>24 h) and short-term (24 h) iron- addition experiments along with physiological and molecular characterisations during a cruise to the Ross Sea in December-February 2012. Phytoplankton increased their photosynthetic efficiency in response to iron addition, suggesting proximal iron limitation throughout most of the Ross Sea during summer. Molecular and physiological data further indicate that as nitrate is removed from the surface ocean the phytoplankton community transitions to one displaying an iron-efficient photosynthetic strategy characterised by an increase in the size of photosystem II (PSII) photochemical cross section (σPSII) and a decrease in the chlorophyll-normalised PSII abundance. These results suggest that phytoplankton with the ability to reduce their photosynthetic iron requirements are selected as the growing season progresses, which may drive the well-documented progression from Phaeocystis antarctica- assemblages to diatom-dominated phytoplankton. Such a shift in the assemblage-level photosynthetic strategy potentially mediates further drawdown of nitrate following the development of iron deficient conditions in the Ross Sea.
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ArticleA regional, early spring bloom of Phaeocystis pouchetii on the New England continental shelf(American Geophysical Union, 2021-01-15) Smith, Walker O. ; Zhang, Weifeng G. ; Hirzel, Andrew ; Stanley, Rachel M. ; Meyer, Meredith G. ; Sosik, Heidi M. ; Alatalo, Philip ; Oliver, Hilde ; Sandwith, Zoe O. ; Crockford, E. Taylor ; Peacock, Emily E. ; Mehta, Arshia ; McGillicuddy, Dennis J.The genus Phaeocystis is distributed globally and has considerable ecological, biogeochemical, and societal impacts. Understanding its distribution, growth and ecological impacts has been limited by lack of extensive observations on appropriate scales. In 2018, we investigated the biological dynamics of the New England continental shelf and encountered a substantial bloom of Phaeocystis pouchetii. Based on satellite imagery during January through April, the bloom extended over broad expanses of the shelf; furthermore, our observations demonstrated that it reached high biomass levels, with maximum chlorophyll concentrations exceeding 16 µg L−1 and particulate organic carbon levels > 95 µmol L−1. Initially, the bloom was largely confined to waters with temperatures <6°C, which in turn were mostly restricted to shallow areas near the coast. As the bloom progressed, it appeared to sink into the bottom boundary layer; however, enough light and nutrients were available for growth. The bloom was highly productive (net community production integrated through the mixed layer from stations within the bloom averaged 1.16 g C m−2 d−1) and reduced nutrient concentrations considerably. Long‐term coastal observations suggest that Phaeocystis blooms occur sporadically in spring on Nantucket Shoals and presumably expand onto the continental shelf. Based on the distribution of Phaeocystis during our study, we suggest that it can have a significant impact on the overall productivity and ecology of the New England shelf during the winter/spring transition.
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DatasetBottle sample data from CTD casts from the third cruise of SPIROPA project, R/V Thomas G. Thompson cruise TN368, to the New England Shelfbreak in July of 2019(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-11) McGillicuddy, Dennis J. ; Sosik, Heidi M. ; Zhang, Weifeng Gordon ; Smith, Walker O. ; Stanley, Rachel ; Turner, Jefferson ; Petitpas, ChristianBottle sample data from CTD casts from the third cruise of SPIROPA project, R/V Thomas G. Thompson cruise TN368, to the New England Shelfbreak in July of 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/849340
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ArticleDiatom 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.
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DatasetCTD casts from the SPIROPA project from R/V Neil Armstrong cruise AR29, Ronald H. Brown cruise RB1904 and R/V Thomas G. Thompson cruise TN368 to the New England Shelfbreak in 2018 and 2019(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-11) McGillicuddy, Dennis J. ; Sosik, Heidi M. ; Zhang, Weifeng Gordon ; Smith, Walker O. ; Stanley, Rachel ; Turner, Jefferson ; Petitpas, ChristianCTD casts from the first, second and third cruises of the SPIROPA project. The first cruise (AR29), took place aboard the R/V Neil Armstrong in April 2018, the second cruise (RB1904) on the Ronald H. Brown in May 2019 and the third cruise (TN368) took place on the R/V Thomas G. Thompson cruise in July of 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/807119
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ArticleIron supply and demand in an Antarctic shelf ecosystem(John Wiley & Sons, 2015-10-08) McGillicuddy, Dennis J. ; Sedwick, Peter N. ; Dinniman, M. S. ; Arrigo, Kevin R. ; Bibby, Thomas S. ; Greenan, Blair J. W. ; Hofmann, Eileen E. ; Klinck, John M. ; Smith, Walker O. ; Mack, Stefanie L. ; Marsay, Christopher M. ; Sohst, Bettina M. ; van Dijken, Gert L.The Ross Sea sustains a rich ecosystem and is the most productive sector of the Southern Ocean. Most of this production occurs within a polynya during the November–February period, when the availability of dissolved iron (dFe) is thought to exert the major control on phytoplankton growth. Here we combine new data on the distribution of dFe, high-resolution model simulations of ice melt and regional circulation, and satellite-based estimates of primary production to quantify iron supply and demand over the Ross Sea continental shelf. Our analysis suggests that the largest sources of dFe to the euphotic zone are wintertime mixing and melting sea ice, with a lesser input from intrusions of Circumpolar Deep Water and a small amount from melting glacial ice. Together these sources are in approximate balance with the annual biological dFe demand inferred from satellite-based productivity algorithms, although both the supply and demand estimates have large uncertainties.
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DatasetBottle sample data from CTD casts from the second cruise of SPIROPA project, R/V Ronald H. Brown cruise RB1904, to the New England Shelfbreak in May of 2019.(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-11) McGillicuddy, Dennis J. ; Sosik, Heidi M. ; Zhang, Weifeng Gordon ; Smith, Walker O. ; Stanley, Rachel ; Turner, Jefferson ; Petitpas, ChristianBottle sample data from CTD casts from the second cruise of SPIROPA project, R/V Ronald H. Brown cruise RB1904, to the New England Shelfbreak in May of 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/873854
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DatasetBottle sample data and water processing samples from CTD casts from the first cruise of SPIROPA project, R/V Neil Armstrong cruise AR29, to the New England Shelfbreak in April 2018.(Biological and Chemical Oceanography Data Management Office (BCO-DMO). Contact: bco-dmo-data@whoi.edu, 2022-08-11) McGillicuddy, Dennis J. ; Sosik, Heidi M. ; Zhang, Weifeng Gordon ; Smith, Walker O. ; Stanley, Rachel ; Turner, Jefferson ; Petitpas, ChristianBottle sample data and water processing samples from CTD casts from the first cruise of SPIROPA project, R/V Neil Armstrong cruise AR29, to the New England Shelfbreak in April 2018. 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/863240