Holocene glacial retreat

For recent (post-Little Ice Age) effects, see Retreat of glaciers since 1850.

Eight records of local temperature variability on multi-centennial scales throughout the course of the Holocene, and an average of these (thick dark line).

Holocene glacial retreat had a profound effect on landscapes in many areas that were covered by ice at the Last Glacial Maximum. The many valleys of the Cairngorms, a mountainous region in the Eastern Scottish Highlands are littered with deposits from this period.

Geographical alterations

Evidences of the retreat of the ice sheets

Changes in sea level during the Holocene.

• Terminal moraine
• Altered river courses

The modern Ohio River was formed when the river was temporarily dammed just southwest of Louisville, Kentucky, creating a large lake until the dam burst. The Ohio River largely supplanted the former Teays River drainage system, which was disrupted by the glaciers.

• Ancient shores

Ancient Lake Chicago, on the southern margin of the Wisconsin Glacier, found successive lower outlets as the glacier retreated, until the Saint Lawrence River route was uncovered. Corresponding to each level, remnant lake shore features may be found in many areas. One prehistoric shoreline is delineated by Bluff Avenue, a north-south street on the La Grange, Illinois east side.

Late Pleistocene - Holocene Marine Transgressions

The retreat and shrinking of Pleistocene ice sheets, ice caps, and mountain glaciers resulted in the addition of enormous quantities of water to the oceans and seas of the world. As result, sea level rose significantly globally resulting in extensive retreat of their shorelines around the world. In some areas, the sea level retreated inland rapidly as a result of rising sea level.

The lower Tigris-Euphrates Valley, reflooding the Persian Gulf (12,000 years ago)

When sea levels were low, the combined Tigris-Euphrates river flowed through a wide flat marshy landscape. The Persian Gulf today has an average depth of only 35 m. During the most recent glaciation, which ended 12,000 years ago, worldwide sea levels dropped 120 to 130 metres (390 to 430 ft), leaving the bed of the Persian Gulf well above sea level during the glacial maximum. It had to have been a swampy freshwater floodplain, where water was retained in all the hollows. High in the Taurus Mountains glaciation would have been extensive.

The drainage of the combined glacial era Tigris-Euphrates made its way down the marshes of this proto-Shatt-al-Arab to the Strait of Hormuz into the Arabian Sea. Reports of the exploration ship "Meteor" have confirmed that the Persian Gulf was an entirely dry basin about 15,000 BC. Close to the steeper Iranian side a deep channel apparently marks the course of the ancient extended Shatt al-Arab, being called the "Ur-Schatt". A continuous shallow shelf across the top (north) of the Persian Gulf and down the west side, at a 20 metres (66 ft) depth, suggests that this section was the last to be inundated. At the Straits of Hormuz the bathymetric profile indicates a division into two main channels which continue across the Bieban Shelf before dropping to a depth of approximately 400 metres (1,300 ft) in the Gulf of Oman; the deeper parts of these channels may be due to delta deposits at the edge of the deep ocean collapsing in a succession of big underwater landslides, causing underwater erosion by the resulting turbidity currents.

There is a theory that there was also a Black-Sea-type sill collapse at the Strait of Hormuz at the outlet of the Persian Gulf.

In a 1981 Journal of Cuneiform Studies article, "The Tangible Evidence for the Earliest Dilmun", Theresa Howard-Carter espoused her theory identifying Dilmun with Qurna, an island at the Strait of Hormuz. Her scenario put the original mouths of the Tigris-Euphrates rivers, which she thought should be the site of the primeval Dilmun, at or even beyond the Straits of Hormuz. Theresa Howard-Carter also wrote: "It is more likely that the original Persian Gulf inhabitants lived along the banks of the lower or extended Shatt al-Arab, ranging some 800 km across the dry Persian Gulf bed. We can thus postulate that the pre-Sumerian cultures had more than ample time to be born and flourish in a riverine setting, encouraged by the agricultural potential and the blessings of a temperate climate. The fact that the body of proof for the existence of these societies must now lie at the bottom of the Persian Gulf furnishes at least a temporary excuse for the archaeologist's failure to produce evidence for their material culture."

In our time, mangrove edge habitat and coral reefs encrustation of fossil dunes characterize the Persian Gulf. Mangroves recolonize easily from established mangrove fringe colonies elsewhere in the Arabian Sea. Artificial reefs are being established today along the coast of Iran. The present-day natural reef developments in the Persian Gulf, corals grow on hardground substrates but have not yet formed the massive calcium carbonate structures familiar from, say, Australia's Great Barrier Reef.

The article Dive conditions described by Eric Bjornstrom found in 1999 in Dubai coral-encrusted sand barrier islands situated 32 km off the coast of the Saudi city of Jubail. There lies a chain of five coral cays, barely above the tide. They appear to be formations called diapirs in which a mobile core containing minerals of low density such as salt, deforms under pressure. The core pushes upwards, deforming overlying rock to form a dome. An ancient diapir at Enorama formed an island in shallow seas, buoyed up by salt. There are similar examples today in the Persian Gulf.

In addition to this large scale flooding of the Persian Gulf there is confirmed evidence of relatively recent extended local flooding in this part of the world. Excavations in Iraq, for example, have shown evidence of a flood at Shuruppak around 2900-2750 BCE which extended nearly as far as the city of Kish (whose king, Etana, supposedly founded the first Sumerian dynasty after the Deluge). Sir C. Leonard Woolley’s excavations at Ur south of Uruk in the 1920s found a more than 2.5 metres (8.2 ft) thick homogeneous silty loam stratum that was void of artifacts, which Woolley in 1931 ascribed to Noah’s Flood.

Persian Gulf (around 8,000 years ago)

An article published in Current Anthropology in 2010 revealed that a fertile landmass now submerged beneath the Persian Gulf may have been home to some of the earliest human populations outside Africa. Jeffrey Rose, an archaeologist and researcher with the University of Birmingham, says that the area in and around this "Persian Gulf Oasis" may have been host to humans for over 100,000 years before it was swallowed up by the Indian Ocean around 8,000 years ago. Archaeological sites in Yemen and Oman have yielded a stone tool style that is distinct from the East African tradition. This raises the possibility that humans were established on the southern part of the Arabian Peninsula beginning as far back as 100,000 years ago. The Persian Gulf links up Iran (ancient Persia), Saudi Arabia and Iraq (the ancient region of Southern Mesopotamia). A map published in the Journal "Current Anthropology" shows regions of the Arabian Peninsula that were exposed as sea levels fell, and hence supposes that people of that region became environmental refugees around 8000 years ago.

The Carpentaria plain (12,000 to 10,000 years ago)

During glacial times, a stretch of level plain joined Australia with New Guinea and enabled humans to walk into Australia. That plain flooded to form the Gulf of Carpentaria around 12,000 to 10,000 years ago. Aboriginal Australian myth of the "dream time" includes a Great Flood which is not ordinarily a recognizable feature of the Australian climate and geography, except for infrequent filling of ordinarily dry lake basins (e.g. Lake Eyre).

See also

• Deglaciation
• Postglacial vegetation
• Meltwater pulse 1B

External links

• The Post-Glacial Period Holocene Epoch