Gledhill Dwight K.

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Dwight K.

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  • Article
    Projecting ocean acidification impacts for the Gulf of Maine to 2050: new tools and expectations
    (University of California Press, 2021-05-13) Siedlecki, Samantha A. ; Salisbury, Joseph E. ; Gledhill, Dwight K. ; Bastidas, Carolina ; Meseck, Shannon L. ; McGarry, Kelly ; Hunt, Christopher W. ; Alexander, Michael A. ; Lavoie, Diane ; Wang, Zhaohui Aleck ; Scott, James D. ; Brady, Damian C. ; Mlsna, Ivy ; Azetsu-Scott, Kumiko ; Liberti, Catherine M. ; Melrose, D. Christopher ; White, Meredith M. ; Pershing, Andrew J. ; Vandemark, Douglas ; Townsend, David W. ; Chen, Changsheng ; Mook, Bill ; Morrison, J. Ruairidh
    Ocean acidification (OA) is increasing predictably in the global ocean as rising levels of atmospheric carbon dioxide lead to higher oceanic concentrations of inorganic carbon. The Gulf of Maine (GOM) is a seasonally varying region of confluence for many processes that further affect the carbonate system including freshwater influences and high productivity, particularly near the coast where local processes impart a strong influence. Two main regions within the GOM currently experience carbonate conditions that are suboptimal for many organisms—the nearshore and subsurface deep shelf. OA trends over the past 15 years have been masked in the GOM by recent warming and changes to the regional circulation that locally supply more Gulf Stream waters. The region is home to many commercially important shellfish that are vulnerable to OA conditions, as well as to the human populations whose dependence on shellfish species in the fishery has continued to increase over the past decade. Through a review of the sensitivity of the regional marine ecosystem inhabitants, we identified a critical threshold of 1.5 for the aragonite saturation state (Ωa). A combination of regional high-resolution simulations that include coastal processes were used to project OA conditions for the GOM into 2050. By 2050, the Ωa declines everywhere in the GOM with most pronounced impacts near the coast, in subsurface waters, and associated with freshening. Under the RCP 8.5 projected climate scenario, the entire GOM will experience conditions below the critical Ωa threshold of 1.5 for most of the year by 2050. Despite these declines, the projected warming in the GOM imparts a partial compensatory effect to Ωa by elevating saturation states considerably above what would result from acidification alone and preserving some important fisheries locations, including much of Georges Bank, above the critical threshold.
  • Article
    Time of Emergence of surface ocean carbon dioxide trends in the North American coastal margins in support of ocean acidification observing system design.
    (Frontiers Media, 2019-03-08) Turk, Daniela ; Wang, Hongjie ; Hu, Xinping ; Gledhill, Dwight K. ; Wang, Zhaohui Aleck ; Jiang, Liqing ; Cai, Wei-Jun
    Time of Emergence (ToE) is the time when a signal emerges from the noise of natural variability. Commonly used in climate science for the detection of anthropogenic forcing, this concept has recently been applied to geochemical variables, to assess the emerging times of anthropogenic ocean acidification (OA), mostly in the open ocean using global climate and Earth System Models. Yet studies of OA variables are scarce within costal margins, due to limited multidecadal time-series observations of carbon parameters. ToE provides important information for decision making regarding the strategic configuration of observing assets, to ensure they are optimally positioned either for signal detection and/or process elicitation and to identify the most suitable variables in discerning OA-related changes. Herein, we present a short overview of ToE estimates on an OA variable, CO2 fugacity f(CO2,sw), in the North American ocean margins, using coastal data from the Surface Ocean CO2 Atlas (SOCAT) V5. ToE suggests an average theoretical timeframe for an OA signal to emerge, of 23(±13) years, but with considerable spatial variability. Most coastal areas are experiencing additional secular and/or multi-decadal forcing(s) that modifies the OA signal, and such forcing may not be sufficiently resolved by current observations. We provide recommendations, which will help scientists and decision makers design and implement OA monitoring systems in the next decade, to address the objectives of OceanObs19 ( in support of the United Nations Decade of Ocean Science for Sustainable Development (2021–2030) ( and the Sustainable Development Goal (SDG) 14.3 ( target to “Minimize and address the impacts of OA.”
  • Article
    Ocean and coastal acidification off New England and Nova Scotia
    (The Oceanography Society, 2015-06) Gledhill, Dwight K. ; White, Meredith M. ; Salisbury, Joseph E. ; Thomas, Helmuth ; Mlsna, Ivy ; Liebman, Matthew ; Mook, Bill ; Grear, Jason S. ; Candelmo, Allison C. ; Chambers, R. Christopher ; Gobler, Christopher J. ; Hunt, Christopher W. ; King, Andrew L. ; Price, Nichole N. ; Signorini, Sergio R. ; Stancioff, Esperanza ; Stymiest, Cassie ; Wahle, Richard A. ; Waller, Jesica D. ; Rebuck, Nathan D. ; Wang, Zhaohui Aleck ; Capson, Todd L. ; Morrison, J. Ruairidh ; Cooley, Sarah R. ; Doney, Scott C.
    New England coastal and adjacent Nova Scotia shelf waters have a reduced buffering capacity because of significant freshwater input, making the region’s waters potentially more vulnerable to coastal acidification. Nutrient loading and heavy precipitation events further acidify the region’s poorly buffered coastal waters. Despite the apparent vulnerability of these waters, and fisheries’ and mariculture’s significant dependence on calcifying species, the community lacks the ability to confidently predict how the region’s ecosystems will respond to continued ocean and coastal acidification. Here, we discuss ocean and coastal acidification processes specific to New England coastal and Nova Scotia shelf waters and review current understanding of the biological consequences most relevant to the region. We also identify key research and monitoring needs to be addressed and highlight existing capacities that should be leveraged to advance a regional understanding of ocean and coastal acidification.