Clark Suzanna

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Clark
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Suzanna
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  • Article
    Pseudo-nitzschia bloom dynamics in the Gulf of Maine: 2012-2016
    (Elsevier, 2019-08-19) Clark, Suzanna ; Hubbard, Katherine A. ; Anderson, Donald M. ; McGillicuddy, Dennis J. ; Ralston, David K. ; Townsend, David W.
    The toxic diatom genus Pseudo-nitzschia is a growing presence in the Gulf of Maine (GOM), where regionally unprecedented levels of domoic acid (DA) in 2016 led to the first Amnesic Shellfish Poisoning closures in the region. However, factors driving GOM Pseudo-nitzschia dynamics, DA concentrations, and the 2016 event are unclear. Water samples were collected at the surface and at depth in offshore transects in summer 2012, 2014, and 2015, and fall 2016, and a weekly time series of surface water samples was collected in 2013. Temperature and salinity data were obtained from NERACOOS buoys and measurements during sample collection. Samples were processed for particulate DA (pDA), dissolved nutrients (nitrate, ammonium, silicic acid, and phosphate), and cellular abundance. Species composition was estimated via Automated Ribosomal Intergenic Spacer Analysis (ARISA), a semi-quantitative DNA finger-printing tool. Pseudo-nitzschia biogeography was consistent in the years 2012, 2014, and 2015, with greater Pseudo-nitzschia cell abundance and P. plurisecta dominance in low-salinity inshore samples, and lower Pseudo-nitzschia cell abundance and P. delicatissima and P. seriata dominance in high-salinity offshore samples. During the 2016 event, pDA concentrations were an order of magnitude higher than in previous years, and inshore-offshore contrasts in biogeography were weak, with P. australis present in every sample. Patterns in temporal and spatial variability confirm that pDA increases with the abundance and the cellular DA of Pseudo-nitzschia species, but was not correlated with any one environmental factor. The greater pDA in 2016 was caused by P. australis – the observation of which is unprecedented in the region – and may have been exacerbated by low residual silicic acid. The novel presence of P. australis may be due to local growth conditions, the introduction of a population with an anomalous water mass, or both factors. A definitive cause of the 2016 bloom remains unknown, and continued DA monitoring in the GOM is warranted.
  • Article
    Projected effects of climate change on Pseudo-nitzschia bloom dynamics in the Gulf of Maine
    (Elsevier, 2022-03-24) Clark, Suzanna ; Hubbard, Katherine A. ; Ralston, David K. ; McGillicuddy, Dennis J. ; Stock, Charles A. ; Alexander, Michael A. ; Curchitser, Enrique N.
    Worldwide, warming ocean temperatures have contributed to extreme harmful algal bloom events and shifts in phytoplankton species composition. In 2016 in the Gulf of Maine (GOM), an unprecedented Pseudo-nitzschia bloom led to the first domoic-acid induced shellfishery closures in the region. Potential links between climate change, warming temperatures, and the GOM Pseudo-nitzschia assemblage, however, remain unexplored. In this study, a global climate change projection previously downscaled to 7-km resolution for the Northwest Atlantic was further refined with a 1–3-km resolution simulation of the GOM to investigate the effects of climate change on HAB dynamics. A 25-year time slice of projected conditions at the end of the 21st century (2073–2097) was compared to a 25-year hindcast of contemporary ocean conditions (1994–2018) and analyzed for changes to GOM inflows, transport, and Pseudo-nitzschia australis growth potential. On average, climate change is predicted to lead to increased temperatures, decreased salinity, and increased stratification in the GOM, with the largest changes occurring in the late summer. Inflows from the Scotian Shelf are projected to increase, and alongshore transport in the Eastern Maine Coastal Current is projected to intensify. Increasing ocean temperatures will likely make P. australis growth conditions less favorable in the southern and western GOM but improve P. australis growth conditions in the eastern GOM, including a later growing season in the fall, and a longer growing season in the spring. Combined, these changes suggest that P. australis blooms in the eastern GOM could intensify in the 21st century, and that the overall Pseudo-nitzschia species assemblage might shift to warmer-adapted species such as P. plurisecta or other Pseudo-nitzschia species that may be introduced.
  • Article
    Investigating Pseudo-nitzschia australis introduction to the Gulf of Maine with observations and models
    (Elsevier, 2021-07-08) Clark, Suzanna ; Hubbard, Katherine A. ; McGillicuddy, Dennis J. ; Ralston, David K. ; Shankar, Sugandha
    In 2016, an unprecedented Pseudo-nitzschia australis bloom in the Gulf of Maine led to the first shellfishery closures due to domoic acid in the region's history. In this paper, potential introduction routes of P. australis are explored through observations, a hydrodynamic model, and a Lagrangian particle tracking model. Based on particle tracking experiments, the most likely source of P. australis to the Gulf of Maine was the Scotian Shelf. However, in 2016, connectivity between the Scotian Shelf and the bloom region was not significantly different from the other years between 2012 and 2019, nor were temperature conditions more favorable for P. australis growth. Observations indicated changes on the Scotian Shelf in 2016 preceded the introduction of P. australis: increased bottom salinity and decreased surface salinity. The increased bottom salinity on the shelf may be linked to anomalously saline water observed near the coast of Maine in 2016 via transport through Northeast Channel. The changes in upstream water mass properties may be related to the introduction of P. australis, and could be the result of either increased influence of the Labrador Current or increased outflow from the Gulf of St. Lawrence. The ultimate source of P. australis remains unknown, although the species has previously been observed in the eastern North Atlantic, and connectivity across the ocean is possible via a subpolar route. Continued and increased monitoring is warranted to track interannual Pseudo-nitzschia persistence in the Gulf of Maine, and sampling on the Scotian Shelf should be conducted to map upstream P. australis populations.
  • Article
    Potential impacts of offshore wind farms on North Sea stratification
    (Public Library of Science, 2016-08-11) Carpenter, Jeffrey R. ; Merckelbach, Lucas ; Callies, Ulrich ; Clark, Suzanna ; Gaslikova, Lidia ; Baschek, Burkard
    Advances in offshore wind farm (OWF) technology have recently led to their construction in coastal waters that are deep enough to be seasonally stratified. As tidal currents move past the OWF foundation structures they generate a turbulent wake that will contribute to a mixing of the stratified water column. In this study we show that the mixing generated in this way may have a significant impact on the large-scale stratification of the German Bight region of the North Sea. This region is chosen as the focus of this study since the planning of OWFs is particularly widespread. Using a combination of idealised modelling and in situ measurements, we provide order-of-magnitude estimates of two important time scales that are key to understanding the impacts of OWFs: (i) a mixing time scale, describing how long a complete mixing of the stratification takes, and (ii) an advective time scale, quantifying for how long a water parcel is expected to undergo enhanced wind farm mixing. The results are especially sensitive to both the drag coefficient and type of foundation structure, as well as the evolution of the pycnocline under enhanced mixing conditions—both of which are not well known. With these limitations in mind, the results show that OWFs could impact the large-scale stratification, but only when they occupy extensive shelf regions. They are expected to have very little impact on large-scale stratification at the current capacity in the North Sea, but the impact could be significant in future large-scale development scenarios.
  • Thesis
    Pseudo-nitzschia in the Gulf of Maine: investigating bloom dynamics, species introduction, and climate change implications with observations and models
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 2021-01) Clark, Suzanna ; McGillicuddy, Dennis J.
    The apparent global increase in harmful algal blooms (HABs) includes Pseudo-nitzschia blooms in the Gulf of Maine, where shellfishery closures can cost millions of dollars. Temperatures in the gulf are warming, which can affect the severity of some HABs. Yet Pseudo-nitzschia in the region are understudied. Pseudo-nitzschia bloom dynamics, P. australis introduction, and potential future changes thereof were investigated in the Gulf of Maine. Data from ship surveys and moorings were used, as well as hydrodynamic, climate, and Lagrangian particle tracking models. Pseudonitzschia bloom toxicity was driven primarily by species composition, not environmental factors. P. australis was introduced to the region in 2016 via a coastal current from the Scotian Shelf. Climate change might intensify Pseudo-nitzschia blooms, shift bloom timing 1–2 weeks earlier in the spring or 4–6 weeks later in the fall, or lengthen the growing season by 3 weeks. It might also affect species composition and connectivity within the gulf. This work has implications for the monitoring of current and future blooms in the Gulf of Maine and for our understanding of HAB introduction to the region. It can also be used to develop predictive models for Pseudo-nitzschia, which could be applied to other HABs.