This blog was written by Giulia Magnarini, Birkbeck graduate in Planetary Sciences with Astronomy and PhD candidate in Earth Sciences at UCL.‘To understand current climate changes, we need to understand past events. However, using our existing climate model is really difficult.’ This is how Professor Andrew Carter began his talk on Earth’s long-term climate. Professor Carter’s research focuses on studying Antarctica in terms of climate changes.
Despite some persistent denial, evidence for an increasingly warm climate is clear. To provide a visual idea of the impact that the total melt of ice in Antarctica could have, Professor Carter asked the audience to imagine Big Ben under water up to the clock. Thames barriers would be ineffective and it is increasingly obvious how important research on climate change to tackle its consequential threats is.
Geological evidence for the first appearance of the ice sheet in Antarctica resides in sediments that date from 33 million years ago. The question is: why did Antarctica freeze over? Two hypotheses are proposed. The first one involved plate tectonics; as Antarctica separated from Australia and South America (circa 50 million years ago), ocean circulation changed and the strong Antarctic Circumpolar Current emerged, causing thermal isolation of the continent.
The second one takes reduction of atmospheric carbon dioxide into account. Historic data collected for ice volume, deep sea temperature and sea level all follow the same trend of the reconstructed amount of carbon dioxide in the atmosphere.
However, there are problems with both hypotheses. For instance, at the moment of the break, Antarctica was in a northern position and, although carbon dioxide was lower, overall temperature was warmer.
There are many difficulties in modelling over geological time. Nowadays, different models running for Antarctica show completely different results. Improving the quality of data is crucial because uncertainties are very high. On this point, Professor Carter has been conducting what is called ‘provenance analysis.’ This involves studying sand grains to locate their sources to better constrain past tectonic events and past environmental conditions. The grains that Professor Carter studies have typical shape due to ice erosion. Detrital zircons (very resistant minerals) are used to conduct U-Pb geochronological assessments to reconstruct the age distribution of the sediments. These ages are then compared with rocks from different areas for which age is known.
Oceanic drilling programs have been conducted within the ‘Iceberg Alley’. This is an area where icebergs are transported by currents and during the journey they deposit sediments. Results from sediment cores have shown that the grains come from other areas, meaning that they had been transported by icebergs, therefore implying that ice was already present on the continent at that time.
This new set of information can help improving tectonic models related to the opening of oceanic passages. Sampling the ‘Shag Rocks’, which are the only exposed part of the continental block within the Iceberg Alley, would be of benefit for this. Unfortunately, due to strong currents, this can be very difficult and dangerous.
Professor Carter concluded by pointing out the importance of better understanding the geology of this area because it was here that the Antarctic Circumpolar Current originated. This in turn had a significant implication on the global cooling of the planet. In fact, its influence reaches up to the northern hemisphere.
Therefore, more geological data can greatly improve the quality of climatic models. Better and more reliable climatic models will be fundamental to help future governments make important decisions.. .