SEA LEVEL CHANGE ALONG THE TYRRHENIAN COAST FROM EARLY HOLOCENE TO THE PRESENT

In any discussion of the evolution of a river basin, the history of sealevel change is important since river gradients and delta developments are strongly influenced by local sea level. Also, sea level provides a reference for inferring past vertical tectonic stability from the geological record. Hence it is appropriate that the discussion on the Tiber basin starts with sea level change along the Tyrrhenian coast during the Holocene. The past evidence for sea level comes from inferences of the position of the sea surface with respect to the present. Hence it is a relative measure; a function of both the changing position of the ocean surface and of the land surface or an integrated measure of changes in ocean volume, land movement and redistribution of water within the ocean basins. The observation therefore contains information on all the processes that change these surfaces: on geophysical, glaciological and oceanographic processes

Holocene relative sea-level changes in the Qaqortoq area, southern Greenland

We present results from an investigation of relative sea-level changes in the Qaqortoq area in south Greenland from c. 11 000 cal. yr BP to the present. Isolation and transgression sequences from six lakes and two tidal basins have been identified using stratigraphical analyses, magnetic susceptibility, XRF and macrofossil analyses. Macrofossils and bulk sediments have been dated by AMS radiocarbon dating. Maximum and minimum altitudes for relative sea level are provided from two deglaciation and marine lagoon sequences. Initially, relative sea level fell rapidly and reached present-day level at ∼9000 cal. yr BP and continued falling until at least 8800 cal. yr BP. Between 8000 and 6000 cal. yr BP, sea level reached its lowest level of around 6-8m below highest astronomical tide (h.a.t.). At around 3750 cal. yr BP, sea level has reached above 2.7m below h.a.t. and continued to rise slowly, reaching the present-day level between ∼2000 cal. yr BP and the present. As in the Nanortalik area further south, initial isostatic rebound caused rapid isolation of low elevation basins in the Qaqortoq area. Distinct isolation contacts in the sediments are observed. The late Holocene transgression is less well defined and occurred over a longer time interval. The late Holocene sea-level rise implies reloading by advancing glaciers superimposed on the isostatic signal from the North American Ice Sheet. One consequence of this transgression is that settlements of Palaeo-Eskimo cultures from ∼4000 cal. yr BP may have been transgressed by the sea

Sea level and global ice volumes from the Last Glacial Maximum to the Holocene

The major cause of sea-level change during ice ages is the exchange of water between ice and ocean and the planet's dynamic response to the changing surface load. Inversion of ∼1,000 observations for the past 35,000 y from localities far from former ic

Pacific plate-motion change at the time of the Hawaiian-Emperor bend constrains the viscosity of Earth's asthenosphere

Important constraints on asthenospheric viscosity come primarily from modeling the glacial rebound of the past 20 kyr, but remain somewhat loose because of the intrinsic resolving power of these models. We obtain narrower bounds by building on the notio

Relationship between glacial isostatic adjustment and gravity perturbations observed by GRACE

The Gravity Recovery and Climate Experiment space gravity mission provides one of the principal means of estimating present-day mass loss occurring in polar regions. Extraction of the mass loss signal from the observed gravity changes is complicated by the need to first remove the signal of ongoing glacial isostatic adjustment (GIA) since the Last Glacial Maximum. This can be problematic in regions such as Antarctica where the GIA models are poorly constrained by observation and their accuracy is not well known. We present a new methodology that permits the GIA component to be represented mathematically by a simple, linear expression of the ratio of viscoelastic Love numbers that is valid for a broad range of Earth and ice-load models. The expression is shown to reproduce rigorous computations of surface uplift rates to within 0.3 mm/yr, thus providing a means of inverting simultaneously for present-day mass loss and ongoing GIA with all the accuracy of a fully detailed forward model

Continental Island Formation and the Archaeology of Defaunation on Zanzibar, Eastern Africa

With rising sea levels at the end of the Pleistocene, land-bridge or continental islands were formed around the world. Many of these islands have been extensively studied from a biogeographical perspective, particularly in terms of impacts of island creation on terrestrial vertebrates. However, a majority of studies rely on contemporary faunal distributions rather than fossil data. Here, we present archaeological findings from the island of Zanzibar (also known as Unguja) off the eastern African coast, to provide a temporal perspective on island biogeography. The site of Kuumbi Cave, excavated by multiple teams since 2005, has revealed the longest cultural and faunal record for any eastern African island. This record extends to the Late Pleistocene, when Zanzibar was part of the mainland, and attests to the extirpation of large mainland mammals in the millennia after the island became separated. We draw on modeling and sedimentary data to examine the process by which Zanzibar was most recently separated from the mainland, providing the first systematic insights into the nature and chronology of this process. We subsequently investigate the cultural and faunal record from Kuumbi Cave, which provides at least five key temporal windows into human activities and faunal presence: two at the end of the Last Glacial Maximum (LGM), one during the period of post-LGM rapid sea level rise and island formation, and two in the late Holocene (Middle Iron Age and Late Iron Age). This record demonstrates the presence of large mammals during the period of island formation, and their severe reduction or disappearance in the Kuumbi Cave sequence by the late Holocene. While various limitations, including discontinuity in the sequence, problematize attempts to clearly attribute defaunation to anthropogenic or island biogeographic processes, Kuumbi Cave offers an unprecedented opportunity to examine post-Pleistocene island formation and its long-term consequences for human and animal communities

Fossil Java Sea corals record Laurentide ice sheet disappearance

The Laurentide ice sheet was the largest late Pleistocene ice mass and the largest contributor to Holocene pre-industrial sea-level rise. While glaciological dates suggest final ice sheet melting between 8 and 6 ka, inversion of sea-level data indicates deglaciation at ca. 7 ka. Here, we present new chronostratigraphic constraints on Laurentide ice sheet disappearance based on Holocene relative sea-level observations from the tectonically stable north coast of Java, Indonesia. Age-elevation data from the flat upper surfaces of 13 fossil intertidal corals (i.e., microatolls) indicate that the Java Sea experienced a relative sea level of 1.3 ± 0.7 m above present between 6.9 and 5.3 ka. To determine uncaptured relative sea-level trends within the observational uncertainties of this apparently constant highstand, we analyzed the internal structure of three sliced microatolls from the same site to produce a high-resolution data set. These data were used to statistically model relative sea-level rates and trends. Employing the data with the model provided evidence for a short-lived rise of relative sea level from 1.0 ± 0.3 m above present at 6.7 ± 0.1 ka to 1.9 ± 0.3 m above present at 6.4 ± 0.1 ka. The end of this rise likely represents the last input of meltwater from the vast Laurentide ice sheet, which, consequently, collapsed at least 400 yr later than assumed by some widely used models of glacial isostatic adjustment. Incorporating these new results into such predictive models will help to better understand the geographical variability of future sea-level rise as a result of global warming