Scannell Hillary A.

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Scannell
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Hillary A.
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  • Article
    Drivers and impacts of the most extreme marine heatwaves events
    (Nature Research, 2020-11-09) Sen Gupta, Alexander ; Thomsen, Mads ; Benthuysen, Jessica A. ; Hobday, Alistair J. ; Oliver, Eric ; Alexander, Lisa V. ; Burrows, Michael T. ; Donat, Markus G. ; Feng, Ming ; Holbrook, Neil J. ; Perkins-Kirkpatrick, Sarah ; Moore, Pippa J. ; Rodrigues, Regina ; Scannell, Hillary A. ; Taschetto, Andrea S. ; Ummenhofer, Caroline C. ; Wernberg, Thomas ; Smale, Dan A.
    Prolonged high-temperature extreme events in the ocean, marine heatwaves, can have severe and long-lasting impacts on marine ecosystems, fisheries and associated services. This study applies a marine heatwave framework to analyse a global sea surface temperature product and identify the most extreme events, based on their intensity, duration and spatial extent. Many of these events have yet to be described in terms of their physical attributes, generation mechanisms, or ecological impacts. Our synthesis identifies commonalities between marine heatwave characteristics and seasonality, links to the El Niño-Southern Oscillation, triggering processes and impacts on ocean productivity. The most intense events preferentially occur in summer, when climatological oceanic mixed layers are shallow and winds are weak, but at a time preceding climatological maximum sea surface temperatures. Most subtropical extreme marine heatwaves were triggered by persistent atmospheric high-pressure systems and anomalously weak wind speeds, associated with increased insolation, and reduced ocean heat losses. Furthermore, the most extreme events tended to coincide with reduced chlorophyll-a concentration at low and mid-latitudes. Understanding the importance of the oceanic background state, local and remote drivers and the ocean productivity response from past events are critical steps toward improving predictions of future marine heatwaves and their impacts.
  • Book chapter
    Global Oceans [in “State of the Climate in 2020”]
    (American Meteorological Society, 2021-08-01) Johnson, Gregory C. ; Lumpkin, Rick ; Alin, Simone R. ; Amaya, Dillon J. ; Baringer, Molly O. ; Boyer, Tim ; Brandt, Peter ; Carter, Brendan ; Cetinić, Ivona ; Chambers, Don P. ; Cheng, Lijing ; Collins, Andrew U. ; Cosca, Cathy ; Domingues, Ricardo ; Dong, Shenfu ; Feely, Richard A. ; Frajka-Williams, Eleanor E. ; Franz, Bryan A. ; Gilson, John ; Goni, Gustavo J. ; Hamlington, Benjamin D. ; Herrford, Josefine ; Hu, Zeng-Zhen ; Huang, Boyin ; Ishii, Masayoshi ; Jevrejeva, Svetlana ; Kennedy, John J. ; Kersalé, Marion ; Killick, Rachel E. ; Landschützer, Peter ; Lankhorst, Matthias ; Leuliette, Eric ; Locarnini, Ricardo ; Lyman, John ; Marra, John F. ; Meinen, Christopher S. ; Merrifield, Mark ; Mitchum, Gary ; Moat, Bengamin I. ; Nerem, R. Steven ; Perez, Renellys ; Purkey, Sarah G. ; Reagan, James ; Sanchez-Franks, Alejandra ; Scannell, Hillary A. ; Schmid, Claudia ; Scott, Joel P. ; Siegel, David A. ; Smeed, David A. ; Stackhouse, Paul W. ; Sweet, William V. ; Thompson, Philip R. ; Trinanes, Joaquin ; Volkov, Denis L. ; Wanninkhof, Rik ; Weller, Robert A. ; Wen, Caihong ; Westberry, Toby K. ; Widlansky, Matthew J. ; Wilber, Anne C. ; Yu, Lisan ; Zhang, Huai-Min
    This chapter details 2020 global patterns in select observed oceanic physical, chemical, and biological variables relative to long-term climatologies, their differences between 2020 and 2019, and puts 2020 observations in the context of the historical record. In this overview we address a few of the highlights, first in haiku, then paragraph form: La Niña arrives, shifts winds, rain, heat, salt, carbon: Pacific—beyond. Global ocean conditions in 2020 reflected a transition from an El Niño in 2018–19 to a La Niña in late 2020. Pacific trade winds strengthened in 2020 relative to 2019, driving anomalously westward Pacific equatorial surface currents. Sea surface temperatures (SSTs), upper ocean heat content, and sea surface height all fell in the eastern tropical Pacific and rose in the western tropical Pacific. Efflux of carbon dioxide from ocean to atmosphere was larger than average across much of the equatorial Pacific, and both chlorophyll-a and phytoplankton carbon concentrations were elevated across the tropical Pacific. Less rain fell and more water evaporated in the western equatorial Pacific, consonant with increased sea surface salinity (SSS) there. SSS may also have increased as a result of anomalously westward surface currents advecting salty water from the east. El Niño–Southern Oscillation conditions have global ramifications that reverberate throughout the report.