Lost palaeoenvironments- what can we learn from the past?
Significant palaeoenvironmental changes that occurred during the Quaternary, the most recent geological period, could be the key to the future.
Climate-driven sea-level changes have become a common topic of discussion, and not just among the scientific community. Intergovernmental panels, boards and commissions (e.g. Intergovernmental Panel on Climate Change) are also concerned. The reason for their alarm is the worry that climate and sea-level changes could significantly transform the environments in which we live and therefore everyday life in the future. Human impact on these changes is also apparent. Since the beginning of the 20th century, global sea-levels rose by approximately 0.19 metres. If the sea-level starts to rise even more rapidly, as some estimations suggest they could, by the end of this century many coastal areas will be flooded. This will have serious economic and environmental consequences, so pay attention! Future generations will probably never be able to see the same landscape that we do today. Earth is changing constantly, and it has experienced significant variations in the climate and sea-level before. So if we take a look at the geological past, can we learn from it?
The Quaternary is the youngest geological period in our planet's four-and-a-half billion year existence and spans the most recent 2,588 million years. Many intervals of sea-level rise and fall have occurred during this period as the Earth cycled between glacial and interglacial periods. Glacial intervals were generally cold and accompanied by the expansion of ice-sheets. During these times, large amounts of ocean water were locked up as ice causing sea-levels to fall. During interglacials, on the other hand, the climate was warmer, there was little or no ice in the northern hemisphere, and sea-levels rose as the ice melted.
The transitions between these glacial and interglacial periods were very abrupt and are known as "terminations". At the moment we are living in an interglacial period known as the "Holocene", which began 11,700 years ago. Extensive climate and sea-level changes have led to the development of different environments around the world. The most significant recent drop in the sea-level occurred in the period between 30,000-19,000 years ago, during the last glacial maximum (LGM) when the global sea-level was 120 metres lower than at present. At that time, vast areas that are today submerged by the sea were terrestrial environments. This had a strong impact on the migration of humans via land bridges between land masses. The importance of studying the Quaternary stems from the fact that the aforementioned events could be the key to the future. Only by unravelling climate and sea-level changes during the Quaternary can we hope to estimate and model changes that the future has in store for us. And in order to do that, we need reliable geological evidence!
Evidence of Quaternary changes
Fortunately, Quaternary events left relatively abundant geological records (both marine and land-based) that are preserved and point to the massive environmental changes that must have occurred. When talking about the sea-level oscillations of the past and evaluating the sea-level changes of the future, it is important to distinguish different sea-level indicators. There are sedimentological (e.g. marine sediment cores), geomorphological (e.g. speleothems in submerged caves, tidal notches), but also biological (e.g. algal rims) and archaeological (e.g. fish tanks, salt pans) sea-level indicators, as well as instrumental data (tide gauges, satellites). Every indicator of the former sea-level has its pros and cons, but generally most of them can offer us a really good look into the past oscillations. Many studies have been conducted around the world using different materials and methods.
As a part of the LoLADRIA project (“Lost Lake Landscapes of the Eastern Adriatic Shelf”), funded by the Croatian Science Foundation, an international group of scientist is trying to track sea-level changes and reconstruct environments that existed during the Quaternary along the eastern coast of the Adriatic Sea. This research is based on sediment cores drilled from the seafloor. A small amount of sediment can yield a rich seam of environmental information. Based on different types of analyses (palaeontological, mineralogical, geochemical and sedimentological) the environmental conditions that prevailed during the deposition of those sediments can be distinguished and the timings of marine intrusions can be determined.
The results obtained so far have proved that silled depressions between Croatian islands filled with freshwater during the glacial periods of lower sea-level and became lakes. But as the sea-level rose again with the onset of interglacial conditions, these lakes were invaded by the sea and the present-day coastline of the eastern Adriatic was formed. The timing of sea-water intrusion can be determined, which enables tracking of the sea-level rise along the eastern Adriatic coast since the Last Glacial Maximum.