Abstract
Abstract A data-constrained ocean circulation model is used to characterize the distribution of water masses and their ages in the global ocean. The model is constrained by the time-averaged temperature, salinity, and radiocarbon distributions in the ocean, as well as independent estimates of the mean sea surface height and sea surface heat and freshwater fluxes. The data-constrained model suggests that the interior ocean is ventilated primarily by water masses forming in the Southern Ocean. Southern Ocean waters, including those waters forming in the Antarctic and subantarctic regions, make up about 55% of the interior ocean volume and an even larger percentage of the deep-ocean volume. In the deep North Pacific, the ratio of Southern Ocean to North Atlantic waters is almost 3:1. Approximately 65% of interior ocean waters make first contact with the atmosphere in the Southern Ocean, further emphasizing the central role played by the Southern Ocean in the regulation of the earth’s climate. Results of the age analysis suggest that the mean ventilation age of deep waters is greater than 1000 yr throughout most of the Indian and Pacific Oceans, reaching a maximum of about 1400–1500 yr in the middepth North Pacific. The mean time for deep waters to be reexposed at the surface also reaches a maximum of about 1400–1500 yr in the deep North Pacific. Together these findings suggest that the deep North Pacific can be characterized as a “holding pen” of stagnant and recirculating waters.
Highlights
[5] Here we present a new finite element, thermomechanical numerical model of ice flow named ISSM (Ice Sheet System Model) that includes higher-order stress components, high spatial resolution capability and relies on a massively parallelized architecture
We describe the equations adopted in ISSM to model ice flow, including its thermal regime, stress regime, boundary conditions and ice rheology
We present an application of ISSM to the modeling of the entire Greenland Ice Sheet (GIS) to illustrate the large scale applicability of ISSM
Summary
[2] Detailed and realistic modeling of the evolution of the Antarctic and Greenland Ice Sheets is needed to improve projections of sea level rise in a warming climate [Intergovernmental Panel on Climate Change (IPCC), 2007]. In case the margin retreats, ISSM assumes a minimum ice thickness of 1 m, which allows for the retreating ice to become dynamically decoupled from the rest of the ice sheet, without introducing instabilities in the ice flow dynamics, and without the need for actively imposing velocity constraints when the ice is fully retreated This scenario will be covered more efficiently when dynamic boundary migration is implemented. [30] our criteria for grounding line migration need to be further refined, using a full-Stokes computation of the stress-balance of the ice sheet/ice shelf system, and migration based on contact and pressure conditions at the grounding line [Nowicki and Wingham, 2008; Durand et al, 2009a, 2009b]. Further work is required to implement a scalable FS solver, similar to what was implemented by Leng et al [2010], but the performance of the MUMPS solver still ensures that reasonable computational times are reached, as shown later on
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