Postglacial variations in the level of the sea: Implications for climate dynamics and solid‐Earth geophysics

Abstract

Abstract. Throughout the latter half of the Pleistocene epoch of Earth history, beginning --•900 kyr ago, the climate system has been dominated by an intense oscillation between full glacial and interglacial conditions. During each glacial stage, global sea level fell by --•120 rn on average, as extensive ice sheets formed and thickened on the surfaces of the continents at high northern (primarily) and southern latitudes. Within each cycle this glaciation phase lasted --•90 kyr and was followed by a much more rapid deglaciation event which terminated after --•10 kyr and which returned the system to the interglacial state. The period of the canonical glacial cycle has remained very close to 100 kyr since its inception in mid-Pleistocene time. Because of the magnitude of the mass that was redistributed over the surface of the Earth during each such glacial cycle and because of the viscoelastic nature of the rheology of the planetary mantle, these shifts in surface mass load induced variations in the shape of the planet that have been indelibly transcribed into the geological record of sea level variability. Indeed, the geological, geophysical, and even astronomical signatures of this process, which is continuing today, are now being measured with unprecedented precision using the methods of space geodesy and have thereby begun to provide important new scientific insight and understanding, both of the interior of the solid Earth and of the climate system variability with which the ice ages themselves are associated. In this article my purpose is to bring together, in a single review, an assessment of where we currently stand scientifically with regard to understanding both of these aspects of the ice ages. Although the discussion will not address in any detail the fascinating issue of ice age climate, since this topic is sufficiently complex of itself to require a detailed review of its own, I will nevertheless attempt to briefly summarize the current state of understanding of the physical processes that are responsible for the occurrence of the ice age cycle, by way of providing a more complete context in which to appreciate the main lines of argument that will be developed.

On the origins of Earth rotation anomalies: New insights on the basis of both “paleogeodetic” data and Gravity Recovery and Climate Experiment (GRACE) data

“…However, there does appear to be sufficient latitude in the model to allow the rotational observables to be employed as an additional constraint on the modern distribution and rates of land ice melting as previously investigated by Peltier [1998Peltier [ , 2007b. Further refinement of such analyses should prove interesting and will be reported elsewhere.…”

The rotational feedback on linear-momentum balance in glacial isostatic adjustment

“…We do not deal with this effect in this paper, since it has already been studied intensively in literature (e.g. Milne & Mitrovica 1996;Peltier 1998).…”

“…Since the sea level equation describes the spatial and temporal distribution of the ocean-water load, the additional term modifies the loading and subsequently induces additional crustal deformation and gravity-field perturbations. Due to the reason that follows, we refine the notion introduced by Peltier (1998) and will refer to this effect as the rotational feedback on the sea level equation. As this feedback mechanism has been intensively studied in the literature, we will not deal with it in this paper.…”

“…Chambers et al 2010Chambers et al , 2012Métivier et al 2012;Peltier et al 2012). The rotational feedback on sea level is mathematically described by adding an extra term into the sea level equation that is proportional to the GIA-induced perturbations in the centrifugal potential and the second-degree tidal Love number (Milne & Mitrovica 1996, 1998Peltier 1998Peltier , 1999Mitrovica et al 2001). Since the sea level equation describes the spatial and temporal distribution of the ocean-water load, the additional term modifies the loading and subsequently induces additional crustal deformation and gravity-field perturbations.…”

“…Milne & Mitrovica 1996;Mitrovica et al 2001), and is known as the rotational feedback (Peltier 1998).…”