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Open Access Publications from the University of California

Scholarly Works (7 results)

  • Thesis
  • Peer Reviewed
UC Irvine Electronic Theses and Dissertations (2018)

The modern contribution of glaciers and ice sheets to sea level rise increases with time and has largely been attributed to anthropogenic sources. The mass losses through the dynamic discharge of ice into the ocean has played a major role in the last two decades with a widespread acceleration of marine terminating glaciers. Recent studies have shown that these changes are closely linked to the ocean conditions, the bedrock and fjord topography. It is therefore crucial to document in details the evolution of glaciers and ice sheets, the bedrock topography and ocean properties to understand how and why the glaciers have been changing recently. Therefore, the aim of this thesis is to improve our understanding of ice dynamics and ice-ocean interaction by using a set of satellite and airborne remote sensing data over key regions. We describe the evolution of glacier dynamics and the detailed partitioning of the mass losses of the Queen Elizabeth Islands, Canada since the 1990s, which are major contributors to recent sea level rise. In Antarctica, we provide the first map of the sub-ice shelf bathymetry of the largest glaciers in the Amundsen Sea Embayment that reveals deep pathways for circumpolar warm water up to the grounding line of the glaciers. Finally, we assembled a comprehensive map of the bedrock and fjord topography of the southeastern coast of Greenland, and interpret the pattern of glacier retreat during the last 80 years, which was not possible before. The work proposed help to understand the recent deglaciation history of key regions in the Arctic, Greenland and Antarctica. The new mapping of sub-ice shelf, bedrock and fjord topography provides invaluable insights for mass balance calculation, ocean and ice-sheet modeling.

    Cover page: Dynamics of Glaciers and Ice Sheets at the Ocean Margin from Airborne and Satellite Data
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2017)
    We employ airborne gravity data from NASA's Operation IceBridge collected in 2009–2014 to infer the bathymetry of sub–ice shelf cavities in front of Pine Island, Thwaites, Smith, and Kohler glaciers, West Antarctica. We use a three-dimensional inversion constrained by multibeam echo sounding data offshore and bed topography from a mass conservation reconstruction on land. The seamless bed elevation data refine details of the Pine Island sub–ice shelf cavity, a slightly thinner cavity beneath Thwaites, and previously unknown deep (>1200 m) channels beneath the Crosson and Dotson ice shelves that shallow (500 m and 750 m, respectively) near the ice shelf fronts. These sub–ice shelf channels define the natural pathways for warm, circumpolar deep water to reach the glacier grounding lines, melt the ice shelves from below, and constrain the pattern of past and future glacial retreat.
      Cover page: Bathymetry of the Amundsen Sea Embayment sector of West Antarctica from Operation IceBridge gravity and other data
      • Article
      • Peer Reviewed
      UC Irvine Previously Published Works (2019)
      We reconstruct the mass balance of the Greenland Ice Sheet using a comprehensive survey of thickness, surface elevation, velocity, and surface mass balance (SMB) of 260 glaciers from 1972 to 2018. We calculate mass discharge, D, into the ocean directly for 107 glaciers (85% of D) and indirectly for 110 glaciers (15%) using velocity-scaled reference fluxes. The decadal mass balance switched from a mass gain of +47 ± 21 Gt/y in 1972-1980 to a loss of 51 ± 17 Gt/y in 1980-1990. The mass loss increased from 41 ± 17 Gt/y in 1990-2000, to 187 ± 17 Gt/y in 2000-2010, to 286 ± 20 Gt/y in 2010-2018, or sixfold since the 1980s, or 80 ± 6 Gt/y per decade, on average. The acceleration in mass loss switched from positive in 2000-2010 to negative in 2010-2018 due to a series of cold summers, which illustrates the difficulty of extrapolating short records into longer-term trends. Cumulated since 1972, the largest contributions to global sea level rise are from northwest (4.4 ± 0.2 mm), southeast (3.0 ± 0.3 mm), and central west (2.0 ± 0.2 mm) Greenland, with a total 13.7 ± 1.1 mm for the ice sheet. The mass loss is controlled at 66 ± 8% by glacier dynamics (9.1 mm) and 34 ± 8% by SMB (4.6 mm). Even in years of high SMB, enhanced glacier discharge has remained sufficiently high above equilibrium to maintain an annual mass loss every year since 1998.
        Cover page: Forty-six years of Greenland Ice Sheet mass balance from 1972 to 2018Creative Commons 'BY' version 4.0 license
        • Article
        • Peer Reviewed
        UC Irvine Previously Published Works (2022)
        Over the past two decades, ice loss from the Greenland ice sheet (GrIS) has increased owing to enhanced surface melting and ice discharge to the ocean1-5. Whether continuing increased ice loss will accelerate further, and by how much, remains contentious6-9. A main contributor to future ice loss is the Northeast Greenland Ice Stream (NEGIS), Greenland's largest basin and a prominent feature of fast-flowing ice that reaches the interior of the GrIS10-12. Owing to its topographic setting, this sector is vulnerable to rapid retreat, leading to unstable conditions similar to those in the marine-based setting of ice streams in Antarctica13-20. Here we show that extensive speed-up and thinning triggered by frontal changes in 2012 have already propagated more than 200 km inland. We use unique global navigation satellite system (GNSS) observations, combined with surface elevation changes and surface speeds obtained from satellite data, to select the correct basal conditions to be used in ice flow numerical models, which we then use for future simulations. Our model results indicate that this marine-based sector alone will contribute 13.5-15.5 mm sea-level rise by 2100 (equivalent to the contribution of the entire ice sheet over the past 50 years) and will cause precipitous changes in the coming century. This study shows that measurements of subtle changes in the ice speed and elevation inland help to constrain numerical models of the future mass balance and higher-end projections show better agreement with observations.
          Cover page: Extensive inland thinning and speed-up of Northeast Greenland Ice Stream
          • Article
          • Peer Reviewed
          UC Irvine Previously Published Works (2021)
          The retreat and acceleration of Greenland glaciers since the mid-1990s have been attributed to the enhanced intrusion of warm Atlantic Waters (AW) into fjords, but this assertion has not been quantitatively tested on a Greenland-wide basis or included in models. Here, we investigate how AW influenced retreat at 226 marine-terminating glaciers using ocean modeling, remote sensing, and in situ observations. We identify 74 glaciers in deep fjords with AW controlling 49% of the mass loss that retreated when warming increased undercutting by 48%. Conversely, 27 glaciers calving on shallow ridges and 24 in cold, shallow waters retreated little, contributing 15% of the loss, while 10 glaciers retreated substantially following the collapse of several ice shelves. The retreat mechanisms remain undiagnosed at 87 glaciers without ocean and bathymetry data, which controlled 19% of the loss. Ice sheet projections that exclude ocean-induced undercutting may underestimate mass loss by at least a factor of 2.
            Cover page: Ocean forcing drives glacier retreat in Greenland.
            • Article
            • Peer Reviewed
            UC Irvine Previously Published Works (2020)
            Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 × 200 m versus 500 × 500 m) and with individual depth soundings constraining three times more area of the Arctic Ocean (∼19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises ∼14.3% in Ver. 4.0 compared to ∼5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet.
              Cover page: The International Bathymetric Chart of the Arctic Ocean Version 4.0.
              • Article
              • Peer Reviewed
              UC Irvine Previously Published Works (2022)
              The Southern Ocean surrounding Antarctica is a region that is key to a range of climatic and oceanographic processes with worldwide effects, and is characterised by high biological productivity and biodiversity. Since 2013, the International Bathymetric Chart of the Southern Ocean (IBCSO) has represented the most comprehensive compilation of bathymetry for the Southern Ocean south of 60°S. Recently, the IBCSO Project has combined its efforts with the Nippon Foundation - GEBCO Seabed 2030 Project supporting the goal of mapping the world's oceans by 2030. New datasets initiated a second version of IBCSO (IBCSO v2). This version extends to 50°S (covering approximately 2.4 times the area of seafloor of the previous version) including the gateways of the Antarctic Circumpolar Current and the Antarctic circumpolar frontal systems. Due to increased (multibeam) data coverage, IBCSO v2 significantly improves the overall representation of the Southern Ocean seafloor and resolves many submarine landforms in more detail. This makes IBCSO v2 the most authoritative seafloor map of the area south of 50°S.
                Cover page: The International Bathymetric Chart of the Southern Ocean Version 2
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