Geophysical Changes: Glacial Oscillations & Geomagnetism

South Georgia Glacial Oscillations

Research in Nature highlights the nature of the glacial changes over the period from the last glacial maximum (LGM; 19–26,000 years ago) to the Holocene (which began around 11,500 years ago until now). South Georgia is an area that is sensitive to regional climate change and will be where future environmental changes will be first identified. Many glaciers on South Georgia are in retreat: there has been significant retreat in more than 90% of its glaciers over the past 60 years or so. The island’s glacier’s behaviour is linked to the Southern Hemisphere (Antarctic) climate variations. The island’s climate is influenced by complex ocean water circulations and the linked Antarctic Polar Front currently situated to the north of the island.

Peripheral ice sheets to the Antarctica can help to provide data for simulations of the Antarctic Peninsula and West Antarctic ice sheets during glacial stages. It also helps to understand the sensitivity to atmospheric and oceanic warming of ice sheets in the Southern Hemisphere. The study uses geophysical data from the sea-floor along with marine sediment cores to contribute to the understanding of offshore glacial history of South Georgia. Sediment logs from moraine, glacial sediments at the margins of glaciers, cores from shallow and deeper basins help to provide a chronology for the glacial history of an area around South Georgia. This has enabled a detailed ancient climate history to be better understood.

A significant sea-floor record of land form and sedimentary past ice-cap change exists on the South Georgia continental block. The stratigraphy highlights several extensive glaciations of the island. South Georgia and the Southern Hemisphere in general are one of the fastest warming places on the Earth. This study highlights the changes to ice that have gone before as well as the susceptibility to the area of changes in temperature. The area has been incredibly sensitive to minor changes in temperature. Over the past few thousand years the glaciers and ice caps retreated and sometimes advanced again. The evidence, from around 12,500 years ago, points towards ocean-led driven by warming seas or rising sea-levels rather than an atmospheric driver in South Georgia.

Full details of the study are on the Nature web site. It highlights some of the spatial extents of the Antarctic Cold Reversal (ACR) which is documented in Antarctic ice cores and in other locations. The extent of this cooling in the Southern Hemisphere was for a period around 14,540 to 12,760 years ago; it interrupted a warming phase that was associated with deglaciation.

Since the 1950s, the great acceleration, the glaciers went into significant retreat. This could have serious implications for South Georgia’s local ecosystems. The changes are brought through very moderate increases in local atmospheric and oceanic temperature. The study can assist in the understanding of ice sheets near their thermal limits and indeed the fastest warming parts of the world such as the Antarctic Peninsula.

This combined dating and geophysical analysis has enabled a better understanding of the Southern Hemisphere’s climate history and will support research into climate change impacts.

Reference: Graham, A. G. C. et al. Major advance of South Georgia glaciers during the Antarctic Cold Reversal following extensive sub-Antarctic glaciation. Nat. Commun. 8, 14798 doi: 10.1038/ncomms14798 (2017). This is available on this link.

Earth’s Magnetic Poles About To Flip?

Research undertaken by the University of Rochester suggest that the Earth maybe about to experience a geomagnetic reversal. The event has occurred many times over hundreds of thousands to millions of years. The magnetic poles swap from south to north and back again.

The last full reversal of the magnetic poles happened about 780,000 years ago. Evidence of the magnetic field weakening has been collected over the past 160 years. It is particularly apparent in a vast area in the Southern Hemisphere. It is known as the South Atlantic Anomaly and it stretches from Zimbabwe to Chile. The magnetic field here is so weak that satellites passing over the region are at high risk from radiation damage that can affect their electronics. An area under South Africa deep in the Earth’s mantle actually shows reversed polarity. In modelled simulations this behaviour is expected before a geomagnetic reversal.

The map below shows the area of the South Atlantic Anomaly:

The South Atlantic Anomaly

A polar reversal is unlikely to be very rapid but a shift would affect navigation systems and orientation. It would have serious consequences for many systems that rely on navigating in the context of magnetic north. It is debated if the changes would take centuries or thousands of years. There is speculation that the “reversed core patches”, such as the South Atlantic Anomaly, may grow rapidly and then wane more slowly. A patch may grow large enough to dominate the magnetic field of the Southern Hemisphere perhaps causing the poles to reverse?

Further details can be reviewed on The Conversation web site. Additional reading is available on the Nature World News web site.


About mappedit

Geographical practitioner with an interest in climate change, open mapping, sustainability, the transition movement, transport and many other things.
This entry was posted in Climate Change, Earth Science, Geography, Islands. Bookmark the permalink.

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