Skip to main content

Sea level and extreme waves in the Last Interglacial

Periodic Reporting for period 1 - WARMCOASTS (Sea level and extreme waves in the Last Interglacial)

Reporting period: 2019-04-01 to 2020-09-30

"The ERC StG ""WARMCOASTS"" aims at improving our knowledge of the Last Interglacial, a period of the Earth's history characterized by a slightly warmer climate than today. During the Last Interglacial (here intended as MIS 5e, peaking 125 thousand years ago), polar and global temperatures were slightly higher than pre-industrial, ice sheets were smaller and sea level was higher than today.
While today’s warming climate is led by an increase of carbon dioxide in the atmosphere to levels well above 400 ppm (part per million), the Last Interglacial warmth was driven by orbital forcing. This means that the tilt of the Earth's axis and shape of the Earth's orbit around the sun was different than today, causing more insolation to reach the Earth. For this reason, the Last Interglacial is often referred to as an “imperfect analog” or a “process-analog” of a future warmer world. In short, regardless of the causes of warming, it provides a past analog of the consequences that a warmer climate might have on many Earth processes, such as ice sheets.
While we have a broad understanding of the Last Interglacial climate, some important details are still uncertain and highly debated. In WARMCOASTS, we tackle the three most relevant open issues regarding sea level and coastal changes in the Last Interglacial.
First, it is often stated that sea level during the Last Interglacial was 6-10m higher than today. Recent work demonstrated that this estimate is bounded by significant uncertainties, that need to be addressed before we can confidently use the Last Interglacial sea level as a proxy for the upper bounds of ice sheet melting in a warmer climate.
Second, some studies suggest that there were, during a period of substantial climatic stability within the Last Interglacial, relevant sea-level oscillations. Other studies reject this hypothesis. These sea-level oscillations are attributed to rapid ice-sheet melting. Understanding whether there were important sea-level oscillations in the Last Interglacial is paramount to gauge the sensitivity of ice sheets to even small changes in ocean and atmospheric polar temperatures.
Third, some studies suggest that the Last Interglacial was characterized, in some coastal regions, by stronger sea storms/hurricanes than today. The geological proofs for this hypothesis are heavily debated and limited to a small geographic context in the Bahamas and Bermuda. Finding new proofs related to the “stronger storms” hypothesis is crucial to gauge whether we can expect more coastal damage (caused by larger waves) under future climate conditions.
These three open issues have one common thread: improving our knowledge on the Last Interglacial will enable us to better understand the extent of impacts that our coastal areas will experience as we approach a Last Interglacial-like world. A better understanding of these processes has direct relevance to society at large, which is preparing to face the consequences of climate change."
In WARMCOASTS, we plan to tackle the issues above merging the approaches of geosciences and earth process modeling.
We plan to enable the compilation of a global Last Interglacial sea-level database to provide a full account of the available information on Last Interglacial coastal stratigraphies globally. We called this database “The World Atlas of Last Interglacial Shorelines” (WALIS).
At the same time, we are working with earth modelers towards obtaining a large array of models to predict vertical land motions caused by glacial isostatic adjustment and dynamic topography. Analyzing the database in light of these models will allow us to give a more precise answer to the question: “how high was sea level in the Last Interglacial?”.
While working on the database, we are also collecting our field data, aiming at obtaining highly accurate information on coastal stratigraphy at a selected pool of locations globally. For example, we use high-precision Global Navigation Satellite System tools to measure the elevation of features above present sea level within a few centimeters. To obtain accurate “virtual outcrops” we analyze drone and land photography with Structure-from-Motion/Multi-View Stereo techniques. We couple these relatively new technologies with classic geological interpretation and radiometric dating (Uranium-series, Optically Stimulated Luminescence) to unravel the Last Interglacial history recorded in the rocks.
To go beyond the simple stratigraphic interpretation, we plan to use a set of models, called stratigraphic forward models, to help us understand how coastal systems might evolve through an entire interglacial. With these models, we can model how a coastal system evolves through time tuning the environmental conditions (such as hydrodynamics and sea level) to match what we observe in the field. The challenge in using these models is in the small temporal and spatial scales at which we are working.
As of November 2020, the compilation of WALIS is well underway. A large part of the paleo sea-level community is currently involved in compiling standardized data into the database and writing up summary review articles in a special issue on the open-access journal Earth System Science Data. We are setting up model/data analysis tools that will be applied once the database is complete. We already collected field data at three locations in the Atlantic/Indopacific, and we are now postprocessing the information collected.
We expect that the WALIS database, our new field data, and model results will contribute to advance the state of the art on Last Interglacial sea-level studies. As a preliminary example of the significance of WARMCOASTS activities, as of November 2020 the number of sea-level data points contained in WALIS already surpassed the number of data points contained in previous global compilations. WALIS is also characterized by a more complete structure, allowing (and in some case requesting) the insertion of more data and metadata than previous compilations. We expect that WALIS will represent a milestone for paleo sea-level studies, and we are confident that the results of our field investigations and modeling will have the same impact.