[PDF] Ice Shelf Ocean Interactions In A General Circulation Model eBook

Author : Véronique Dansereau
Publisher :
Page : 123 pages
File Size : 39,67 MB
Release : 2012
Category : Ocean circulation
ISBN :

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Interactions between the ocean circulation in sub-ice shelf cavities and the overlying ice shelf have received considerable attention in the context of observed changes in flow speeds of marine ice sheets around Antarctica. Modeling these interactions requires parameterizing the turbulent boundary layer processes to infer melt rates from the oceanic state at the ice-ocean interface. Here we explore two such parameterizations in the context of the MIT ocean general circulation model coupled to the z-coordinates ice shelf cavity model of Losch (2008). We investigate both idealized ice shelf cavity geometries as well as a realistic cavity under Pine Island Ice Shelf (PIIS), West Antarctica. Our starting point is a three-equation melt rate parameterization implemented by Losch (2008), which is based on the work of Hellmer and Olbers (1989). In this form, the transfer coefficients for calculating heat and freshwater fluxes are independent of frictional turbulence induced by the proximity of the moving ocean to the fixed ice interface. More recently, Holland and Jenkins (1999) have proposed a parameterization in which the transfer coefficients do depend on the ocean-induced turbulence and are directly coupled to the speed of currents in the ocean mixed layer underneath the ice shelf through a quadratic drag formulation and a bulk drag coefficient. The melt rate parameterization in the MITgcm is augmented to account for this velocity dependence. First, the effect of the augmented formulation is investigated in terms of its impact on melt rates as well as on its feedback on the wider sub-ice shelf circulation. We find that, over a wide range of drag coefficients, velocity-dependent melt rates are more strongly constrained by the distribution of mixed layer currents than by the temperature gradient between the shelf base and underlying ocean, as opposed to velocity-independent melt rates. This leads to large differences in melt rate patterns under PIIS when including versus not including the velocity dependence. In a second time, the modulating effects of tidal currents on melting at the base of PIIS are examined. We find that the temporal variability of velocity-dependent melt rates under tidal forcing is greater than that of velocity-independent melt rates. Our experiments suggest that because tidal currents under PIIS are weak and buoyancy fluxes are strong, tidal mixing is negligible and tidal rectification is restricted to very steep bathymetric features, such as the ice shelf front. Nonetheless, strong tidally-rectified currents at the ice shelf front significantly increase ablation rates there when the formulation of the transfer coefficients includes the velocity dependence. The enhanced melting then feedbacks positively on the rectified currents, which are susceptible to insulate the cavity interior from changes in open ocean conditions.

Author : David M. Holland
Publisher : Elsevier Inc. Chapters
Page : 79 pages
File Size : 38,1 MB
Release : 2013-10-22
Category : Science
ISBN : 012805865X

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The polar oceans interact with both sea ice, formed in situ at the ocean surface, and land ice, flowing under gravity from the land onto the ocean surface. This ice–ocean interaction has profound consequences for the ocean and climate in a number of ways: a change in ocean surface albedo and surface energy balance where there is ice cover compared with open ocean, a change in global sea level when land ice flows into the ocean, and a transformation of water masses through melting or freezing of ice which subsequently influences the global conveyor belt. Another type of ice–ocean interaction, less well understood, is that between marine permafrost at the seafloor and the overlying ocean waters. Collectively, we refer to sea ice, land ice, and marine permafrost as the marine cryosphere. In this chapter, we review current understanding of the interaction of the marine cryosphere with the global ocean and discuss emerging technologies to improve observations and numerical modeling of these interactions. Projections for the state of the marine cryosphere into the current century and beyond are reviewed.

Author : Carl Wunsch
Publisher : Elsevier Inc. Chapters
Page : 68 pages
File Size : 22,47 MB
Release : 2013-10-22
Category : Science
ISBN : 0128058706

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The World Ocean Circulation Experiment drove the development of estimates of the decadal scale time evolving general circulation that are dynamically and kinematically consistent. A long timescale, and a goal of estimation rather than prediction, preclude the use of meteorological methods called “data assimilation (DA).” Instead, “state estimation” methods are reviewed here and distinguished from DA. Results from the dynamically consistent family of solutions from the project Estimating the Circulation and Climate of the Ocean based upon least-squares Lagrange multipliers (adjoints) are used to discuss the determination of the dominant elements of the circulation in the period since 1992—which marked the beginning of the satellite altimetric record. Significant changes documented in the Arctic in recent decades now mandate consideration of the coupled ocean-cryospheric state.

Author : Yidongfang Si
Publisher :
Page : 0 pages
File Size : 50,42 MB
Release : 2023
Category :
ISBN :

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The Antarctic Slope Current (ASC) is a narrow and westward circulation feature that surrounds the Antarctic continental shelves. It regulates onshore ocean heat transport toward the Antarctic ice shelves and dense water outflow, playing an important role in global meridional overturning circulation, glacier melt, and sea level rise. Despite its significance to Earth's climate system, the circulation and heat transport around the Antarctic margins remain poorly understood due to the difficulties and expense in observation and modeling. In this work, the dynamics of the ASC and the ice-ocean interactions around the Antarctic margins are investigated using high-resolution process-oriented simulations. The key results are summarized as follows: (i) Due to topographic eddy suppression, almost no wind-input momentum is transferred vertically over the continental slope; as a result, sea ice horizontally redistributes the wind-input momentum away from the continental slope, playing a critical role in the momentum balance of the ASC. (ii) Melt-induced freshening of the coastal waters that are buoyant compared with the open ocean leads to increased eddy-driven shoreward heat flux, which implies a positive feedback in a warming climate that may cause further melt of ice shelves. (iii) The West Antarctic slope undercurrent originates from the cyclonic vorticity input by meltwater upwelling in the cavities of West Antarctic ice shelves, which drives warm Circumpolar Deep Water toward the glaciers; increased basal melt therefore strengthens the slope undercurrent and enhances onshore heat transport, which indicates another positive feedback that may accelerate future melt, potentially further destabilizing the West Antarctic Ice Sheet. The work in this dissertation advances the understanding of the ice-ocean system near the Antarctic margins and highlights previously unrecognized climate feedbacks that may be key to projecting future changes in Antarctic ice sheets and thus sea level rise. In addition, our results help guide future climate model development and future observations of near-Antarctic ocean heat flux and glacier melt.

Author : Timothy Andrew Smith (Ph. D.)
Publisher :
Page : 0 pages
File Size : 33,22 MB
Release : 2021
Category :
ISBN :

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Along the Antarctic coastline, ice shelves extend over the ocean, forming where glacial ice streams flow from the land to the sea. Ice shelves are important structures for the climate system, as they hold back land ice from reaching the ocean and contributing to sea level rise. In the Amundsen Sea region of Antarctica, ice shelves are in contact with warm, subsurface ocean waters, which is likely a key driver of high meltrates, thinning, and glacial mass loss. Numerical models of the ocean circulation in the Amundsen Sea have been essential for building our understanding of the mechanisms responsible for heat delivery and meltrate response. However, these computational models are subject to a host of uncertainties stemming from the representation of external forcing and unresolved physical processes. The primary goal of this work is to address this issue. We develop a numerical model of the ocean circulation in the cavity formed by the Pine Island ice shelf, which is fed by one of the fastest flowing glaciers in Antarctica. We then formulate a two-stage Bayesian inverse problem in which we constrain the open boundary conditions of the model to the sparsely available observations of the ocean state in Pine Island Bay. In the inference problem we specify our prior uncertainty according to Gaussian statistics. We build off of previous work to develop a general covariance model that is appropriate for applications with complex boundaries, multivariate control parameters, and highly anisotropic length scales - a common scenario in oceanography. In the first stage of the inference problem we solve an optimal interpolation problem to inform an initial estimate of the mean and posterior uncertainty of the open boundary conditions. We use this initial estimate to refine the nonlinear forward model configuration. We evaluate the sub ice shelf cavity circulation and meltrate response to parameterizations of (1) subgrid-scale ocean turbulence and (2) ice-ocean interactions. We find that a recently developed parameterization scheme based on quasi-geostrophic dynamics together with a velocity dependent meltwater flux provides a reasonable representation of the circulation, and serves as our baseline numerical model. In the second stage of the inverse problem, we condition the open boundary conditions on mooring data, subject to the dynamics of this numerical model. We then use an adjoint-based method to propagate uncertainty onto the simulated sub ice shelf meltrate. We find that most of the information gained in the temperature and salinity fields is achieved during the optimal interpolation problem. In the second stage of the inverse problem, however, we further reduce our uncertainty stemming from the velocity field. We emphasize that no direct observations of the velocity field are considered during this stage, highlighting the success of the numerical model in transferring information from observed to unobserved quantities

Author : Jens Bischof
Publisher : Springer Science & Business Media
Page : 254 pages
File Size : 18,50 MB
Release : 2000-11
Category : Nature
ISBN : 9781852336486

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The issue of global warming and climate change is of continuous concern. Since the 1970s, it bas been shown that the pack-ice around the Arctic Ocean is thinning, the margin of permafrost is moving north and the vegetation in the high northern parts of the world is changing (the 'greening' of the Arctic). But are these changes the result of human activity or simply regular variations of the Earth's climate system? Over thousands of years, a continuous archive of iceberg and sea ice drift bas formed in the deep-sea sediments, revealing the place of the ice's origin and allowing a reconstruction of the surface currents and the climate of the past. However, the drift of floating ice from one place to another is not just a passive record of past ocean circulation. It actively influences and changes the surface ocean circulation, thus having a profound effect on climate change. Ice Drift, Ocean Circulation and Climate Change is the first book to focus on the interactions between ice, the ocean and the atmosphere and to describe how these three components of the climate system influence each other. It makes clear the positive contribution of paleoclimatology and paleoceanography and should be read by anyone concerned with global warming and climate change.

Author : Stanley S. Jacobs
Publisher : American Geophysical Union
Page : 400 pages
File Size : 35,69 MB
Release : 1998-02-04
Category : Science
ISBN :

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In this latest oceanology volume of the Antarctic Research Series, polar scientists describe and model air-sea and ice-ocean interactions, the formation and chemistry of deep and bottom waters, regional circulations, tidal heights and currents, ocean bathymetry, interannual variability and the Antarctic Slope Front.

Author : John A. Church
Publisher : Elsevier Inc. Chapters
Page : 82 pages
File Size : 24,24 MB
Release : 2013-10-22
Category : Science
ISBN : 0128058765

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The ocean has the largest heat capacity in the climate system and as a result the ocean plays a critical role in the climate. Changes in ocean heat content dominate the Earth’s energy storage; and the ocean’s thermal expansion has been a major contributor to sea-level rise in the twentieth century and likely to be the largest contributor in the twenty-first century. The agreement between changes in ocean heat storage over recent decades and changes in the Earth’s radiative balance, within uncertainties, provides strong support for current understanding of anthropogenic climate change. As a result of improvements in observations and modeling of sea level and components contributing to sea-level change, there is now an improved explanation for twentieth century sea-level rise. Models project a continuing sea-level rise during the twenty-first century and beyond. However, a number of uncertainties remain in our understanding of the global mean and regional distribution of sea-level rise resulting from changes in ocean circulation and changes in the Earth’s gravitational field. Ocean-ice-sheet interactions are important for quantitatively estimating future ice-sheet contributions to sea-level rise.

Author : Fabio Florindo
Publisher : Elsevier
Page : 606 pages
File Size : 31,71 MB
Release : 2008-10-10
Category : Science
ISBN : 0080931618

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Antarctic Climate Evolution is the first book dedicated to furthering knowledge on the evolution of the world’s largest ice sheet over its ~34 million year history. This volume provides the latest information on subjects ranging from terrestrial and marine geology to sedimentology and glacier geophysics. An overview of Antarctic climate change, analyzing historical, present-day and future developments Contributions from leading experts and scholars from around the world Informs and updates climate change scientists and experts in related areas of study