Ackley Stephen

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Ackley
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Stephen
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  • Article
    Overview of the Arctic Sea state and boundary layer physics program
    (American Geophysical Union, 2018-04-16) Thomson, Jim ; Ackley, Stephen ; Girard-Ardhuin, Fanny ; Ardhuin, Fabrice ; Babanin, Alexander ; Boutin, Guillaume ; Brozena, John ; Cheng, Sukun ; Collins, Clarence ; Doble, Martin ; Fairall, Christopher W. ; Guest, Peter ; Gebhardt, Claus ; Gemmrich, Johannes ; Graber, Hans C. ; Holt, Benjamin ; Lehner, Susanne ; Lund, Björn ; Meylan, Michael ; Maksym, Ted ; Montiel, Fabien ; Perrie, Will ; Persson, Ola ; Rainville, Luc ; Rogers, W. Erick ; Shen, Hui ; Shen, Hayley ; Squire, Vernon ; Stammerjohn, Sharon E. ; Stopa, Justin ; Smith, Madison M. ; Sutherland, Peter ; Wadhams, Peter
    A large collaborative program has studied the coupled air‐ice‐ocean‐wave processes occurring in the Arctic during the autumn ice advance. The program included a field campaign in the western Arctic during the autumn of 2015, with in situ data collection and both aerial and satellite remote sensing. Many of the analyses have focused on using and improving forecast models. Summarizing and synthesizing the results from a series of separate papers, the overall view is of an Arctic shifting to a more seasonal system. The dramatic increase in open water extent and duration in the autumn means that large surface waves and significant surface heat fluxes are now common. When refreezing finally does occur, it is a highly variable process in space and time. Wind and wave events drive episodic advances and retreats of the ice edge, with associated variations in sea ice formation types (e.g., pancakes, nilas). This variability becomes imprinted on the winter ice cover, which in turn affects the melt season the following year.
  • Article
    Stable Isotope clues to the formation and evolution of refrozen melt ponds on Arctic Sea ice.
    (American Geophysical Union, 2018-11-15) Tian, Lijun ; Gao, Yongli ; Ackley, Stephen ; Stammerjohn, Sharon E. ; Maksym, Ted ; Weissling, Blake
    Sea ice is one of the determining parameters of the climate system. The presence of melt ponds on the surface of Arctic sea ice plays a critical role in the mass balance of sea ice. A total of nine cores was collected from multiyear ice refrozen melt ponds and adjacent hummocks during the 2015 Arctic Sea State research cruise. The depth profiles of water isotopes, salinity, and ice texture for these sea ice cores were examined to provide information about the development of refrozen melt ponds and water balance generation processes, which are otherwise difficult to acquire. The presence of meteoric water with low oxygen isotope values as relatively thin layers indicates melt pond water stability and little mixing during formation and refreezing. The hydrochemical characteristics of refrozen melt pond and seawater depth profiles indicate little snowmelt enters the upper ocean during melt pond refreezing. Due to the seasonal characters of deuterium excess for Arctic precipitation, water balance calculations utilizing two isotopic tracers (oxygen isotope and deuterium excess) suggest that besides the melt of snow cover, the precipitation input in the melt season may also play a role in the evolution of melt ponds. The dual‐isotope mixing model developed here may become more valuable in a future scenario of increasing Arctic precipitation. The layers of meteoric origin were found at different depths in the refrozen melt pond ice cores. Surface topography information collected at several core sites was examined for possible explanations of different structures of refrozen melt ponds.
  • Article
    Surface flooding of Antarctic summer sea ice
    (Cambridge University Press, 2020-06-11) Ackley, Stephen ; Perovich, Donald K. ; Maksym, Ted ; Weissling, Blake ; Xie, Hongjie
    The surface flooding of Antarctic sea ice in summer covers 50% or more of the sea-ice area in the major summer ice packs, the western Weddell and the Bellingshausen-Amundsen Seas. Two CRREL ice mass-balance buoys were deployed on the Amundsen Sea pack in late December 2010 from the icebreaker Oden, bridging the summer period (January–February 2011). Temperature records from thermistors embedded vertically in the snow and ice showed progressive increases in the depth of the flooded layer (up to 0.3–0.35 m) on the ice cover during January and February. While the snow depth was relatively unchanged from accumulation (<10 cm), ice thickness decreased by up to a meter from bottom melting during this period. Contemporaneous with the high bottom melting, under-ice water temperatures up to 1°C above the freezing point were found. The high temperature arises from solar heating of the upper mixed layer which can occur when ice concentration in the local area falls and lower albedo ocean water is exposed to radiative heating. The higher proportion of snow ice found in the Amundsen Sea pack ice therefore results from both winter snowfall and summer ice bottom melt found here that can lead to extensive surface flooding.
  • Article
    Antarctic sea ice—A polar opposite?
    (The Oceanography Society, 2012-09) Maksym, Ted ; Stammerjohn, Sharon E. ; Ackley, Stephen ; Massom, Robert A.
    As the world's ice diminishes in the face of climate change—from the dramatic decline in Arctic sea ice, to thinning at the margins of both the Greenland and Antarctic ice sheets, to retreating mountain glaciers the world over—Antarctic sea ice presents something of a paradox. The trend in total sea ice extent in the Antarctic has remained steady, or even increased slightly, over the past three decades, confounding climate model predictions showing moderate to strong declines. This apparent intransigence masks dramatic regional trends; declines in sea ice in the Bellingshausen Sea region that rival the high-profile decline in the Arctic have been matched by opposing increases in the Ross Sea. Much of the explanation lies in the unique nature of the Antarctic sea ice zone. Its position surrounding the continent and exposure to the high-energy wind and wave fields of the open Southern Ocean shape both its properties and its connection to the atmosphere and ocean in ways very different from the Arctic. Sea ice extent and variability are strongly driven by large-scale climate variability patterns such as the El Niño-Southern Oscillation and the Southern Annular Mode. Because many of these patterns have opposing effects in different regions around the continent, decreases in one region are often accompanied by similar, opposing increases in another. Yet, the failure of climate models to capture either the overall or regional behavior also reflects, in part, a poor understanding of sea ice processes. Considerable insight has been gained into the nature of these processes over the past several decades through field expeditions aboard icebreakers. However, much remains to be discovered about the nature of Antarctic sea ice; its connections with the ocean, atmosphere, and ecosystem; and its complex response to present and future climate change.
  • Article
    Sea-ice production and air/ice/ocean/biogeochemistry interactions in the Ross Sea during the PIPERS 2017 autumn field campaign
    (Cambridge University Press, 2020-06-11) Ackley, Stephen ; Stammerjohn, Sharon E. ; Maksym, Ted ; Smith, Madison M. ; Cassano, John ; Guest, Peter ; Tison, Jean-Louis ; Delille, Bruno ; Loose, Brice ; Sedwick, Peter N. ; De Pace, Lisa ; Roach, Lettie ; Parno, Julie
    The Ross Sea is known for showing the greatest sea-ice increase, as observed globally, particularly from 1979 to 2015. However, corresponding changes in sea-ice thickness and production in the Ross Sea are not known, nor how these changes have impacted water masses, carbon fluxes, biogeochemical processes and availability of micronutrients. The PIPERS project sought to address these questions during an autumn ship campaign in 2017 and two spring airborne campaigns in 2016 and 2017. PIPERS used a multidisciplinary approach of manned and autonomous platforms to study the coupled air/ice/ocean/biogeochemical interactions during autumn and related those to spring conditions. Unexpectedly, the Ross Sea experienced record low sea ice in spring 2016 and autumn 2017. The delayed ice advance in 2017 contributed to (1) increased ice production and export in coastal polynyas, (2) thinner snow and ice cover in the central pack, (3) lower sea-ice Chl-a burdens and differences in sympagic communities, (4) sustained ocean heat flux delaying ice thickening and (5) a melting, anomalously southward ice edge persisting into winter. Despite these impacts, airborne observations in spring 2017 suggest that winter ice production over the continental shelf was likely not anomalous.