The solid Earth's influence on sea level

Abstract

Because it lies at the intersection of Earth's solid, liquid, and gaseous components, sea level links the dynamics of the fl uid part of the planet with those of the solid part of the planet. Here, I review the past quarter century of sea-level research and show that the solid components of Earth exert a controlling infl uence on the amplitudes and patterns of sea-level change across time scales ranging from years to billions of years. On the shortest time scales (10 0 -10 2 yr), elastic deformation causes the ground surface to uplift instantaneously near deglaciating areas while the sea surface depresses due to diminished gravitational attraction. This produces spatial variations in rates of relative sea-level change (measured relative to the ground surface), with amplitudes of several millimeters per year. These sea-level "fi ngerprints" are characteristic of (and may help identify) the deglaciation source, and they can have signifi cant societal importance because they will control rates of coastal inundation in the coming century. On time scales of 10 3 -10 5 yr, the solid Earth's time-dependent viscous response to deglaciation also produces spatially varying patterns of relative sea-level change, with centimeters-per-year amplitude, that depend on the time-history of deglaciation. These variations, on average, cause net seafl oor subsidence and therefore global sea-level drop. On time scales of 10 6 -10 8 yr, convection of Earth's mantle also supports long-wavelength topographic relief that changes as continents migrate and mantle fl ow patterns evolve. This changing "dynamic topography" causes meters per millions of years of relative sea-level change, even along seemingly "stable" continental margins, which affects all stratigraphic records of Phanerozoic sea level. Nevertheless, several such records indicate sea-level drop of ~230 m since a mid-Cretaceous highstand, when continental transgressions were occurring worldwide. This global drop results from several factors that combine to expand the "container" volume of the ocean basins. Most importantly, ridge volume decrease since the mid-Cretaceous, caused by an ~50% slowdown in seafl oor spreading rate documented by tectonic reconstructions, explains ~250 m of sea-level fall. These tectonic changes have been accompanied by a decline in the volume of volcanic edifi ces on Pacifi c seafl oor, continental convergence above the former Tethys Ocean, and the onset of glaciation, which dropped sea level by ~40, ~20, and ~60 m, respectively. These drops were approximately offset by an increase in the volume of Atlantic sediments and net seafl oor uplift by dynamic topography, which each elevated sea level by ~60 m. Across supercontinental cycles, expected variations in ridge volume, dynamic topography, and continental compression together roughly explain observed sea-level variations throughout Pangean assembly and dispersal. On the longest time scales (10 9 yr), sea level may change as ocean water is exchanged with reservoirs stored by hydrous minerals within the...

Jurassic Sea-Level Variations: A Reappraisal

“…A variety of solid-Earth tectonic influences can affect sea-level changes (see, e.g., Conrad, 2013;Haq, 2014). But these influences can only provide some explanations for the local, very short time-scale changes of hundreds of years to 100 k.y.…”

Depositional characteristics and constraints on the mid-Valanginian demise of a carbonate platform in the intra-Tethyan domain, Circum-Rhodope Belt, northern Greece

“…5, 16, 17). Therefore, the early Valanginian shallowing and subsequent mid-Valanginian demise of the Circum-Rhodope carbonate platform resulted from a major sealevel fall which was possibly linked to glacioeustacy (Gr eselle and Pittet, 2010), increased water storage on the continents as an effect of climate humidification (F€ ollmi, 2012), or various solid-earth factors such as dynamic topography and ridge-volume changes (Conrad, 2013;Haq, 2014). For comparison, it is noteworthy that occurrences of lower Valanginian regressive trend, midValanginian unconformity with locally manifested evidence for subaerial exposure, and/or upper Valanginian stratigraphic gap are particularly well documented in earliest Cretaceous intra-Tethyan platform carbonates from adjacent regions, including Italy, Croatia, Albania, Serbia, Romania, Bulgaria and Turkey (Mati cec et al, 1996;Rojay and Altiner, 1998;Bosellini et al, 1999;Altiner et al, 1999;Bucur and S as aran, 2005;Dragastan et al, 2005;Radoi ci c, 2005;Husinec and Jelaska, 2006;Gawlick et al, 2008;Ivanova et al, 2008;Mircescu et al, 2013;Bucur et al, 2014;Polavder, 2014).…”

Mantle dynamics, isostasy, and the support of high terrain

“…Both the global map of isostatic anomalies ( Figure 2c) and regional maps of such anomalies [Conrad, 2013], and >1200 m [Flament et al, 2013[Flament et al, , 2014. These amounts differ in part because different authors have used different convection codes with different assumed viscosity structures [e.g., Thoraval and Richards, 1997] and because they have employed different scaling relationships between wave speed anomalies and density anomalies.…”

“…This analysis exploiting Morgan's [1965a] formulas and isostatic anomalies casts doubt on suggestions that even as much as~300 m of the mean elevation of southern Africa results from convection associated with a deep upwelling plume of low-density material [e.g., Conrad, 2013;Flament et al, 2013Flament et al, , 2014Gurnis et al, 2000;Lithgow-Bertelloni and Silver, 1998]. It seems likely to us that most of southern Africa's anomalously high elevation arises from isostatically compensated density contrasts within the crust and mantle lithosphere, which may be thermal or compositional in origin [e.g., Janney et al, 2010;Nyblade and Robinson, 1994;Stanley et al, 2013].…”