Late Quaternary Antarctic cryosphere interactions

Our international team aims to answer how sea ice and Antarctic ice shelves interact and vary through geological time. Ice shelves are a crucial tipping element of the West Antarctic Ice Sheet, and sea ice protects those ice shelves from disintegration. Currently we know very little about sea ice, ice shelves and their interaction on both short and longer time scales. This can be attributed to the lack of suitable sediment records and the limited availability of tools (or proxies) for sea ice and ice shelf reconstructions. We now access to a unique set of sea floor sediment samples and a 9-m long sediment core from the Weddell Sea. The sediment core contains a ca. 160,000 year record of Antarctic climate, ocean, sea ice and ice shelf variations. We have collected samples for investigating diatoms, biomarkers, palynology and paleogenomics. Following detailed testing of several DNA extraction methods, we have now identified the best method for extraction DNA from seafloor sediment as well as a sediment core. Forty-five seafloor sediments have been characterised for sedimentology, diatoms and palynology and DNA. Our results so far show a clear influence from ice shelfs in the southern Weddell Sea, and from open water, more productive conditions around the Antarctic Peninsula. All seafloor sediments have yielded DNA, and are currently being prepared for sequencing. Also, 25 pilot samples from the gravity core have revealed the presence of DNA in the sediment back to ca. 160,000 years. We detected diatoms, radiolaria, cercozoans, bacteria and fungi and their abundance changes throughout time. Diatom analysis and the first palynological results clearly identify the Holocene and Last Interglacial (ca. 125,000 years ago). Additional samples will be analysed for DNA across the Last Interglacial, a period that was warmer than today, and the last deglaciation climate transition to the Holocene. We have also designed an assay, a genetic fingerprinting tool, for the open ocean coccolithophore Emiliania huxleyi and are in the process of designing one for Berkelya adeliensis, a diatom described from sea ice that forms in front of an ice shelf. We already have an in-house working assay for the sea ice dinoflagellate Polarella glacialis. All three assays will be tested on all our seafloor and sediment core samples in order to assist with the (paleo-)environmental interpretation. Our work happens in close collaboration with the international partners in Australia, Germany and the UK. Our aim is to produce the first multi-proxy data from sea floor data by spring 2023, which can subsequently be used to determine the role of sea ice in Antarctic ice shelf (in)stability and Southern Ocean circulation over the past ca. 160,000 years.

In this project, we gather a cross-disciplinary, international team to provide for the first time essential knowledge on Antarctic sea ice–ice shelf variability and interaction on (sub)millenial time scales. Sea ice plays a key role in the global climate system and in the Southern Ocean it protects ice shelves from disintegration, a crucial tipping element of the West Antarctic Ice Sheet. Despite the pivotal role in the climate system, there is limited knowledge on sea ice–ice shelf interaction in the geological past. This knowledge gap exists due to the limited availability of (sea ice) proxy methods and the lack of suitable sediment records for reconstructing sea ice–ice shelf interactions. Using a unique set of sediment samples, we will evaluate existing geochemical and paleontological methods as well as a novel sedimentary ancient DNA approach for reconstructing sea ice–ice shelf variability and interactions. Subsequently, we will apply our new methodology to a Weddell Sea sediment core to generate the first (sub)millennial biomarker and sedimentary ancient DNA record back to >130,000 years ago. We will focus on the Last Interglacial, where we will compare our proxy records and climate model experiments to obtain a dynamical insight into sea ice–ice shelf variability during a critical time in Earth’s history where global climate was warmer than today. As such, the project is highly relevant for understanding the natural variability of Antarctic sea ice–ice shelves, their impact on ocean circulation and the Antarctic Ice Sheet, and ultimately on global sea level. Within the project, we commit to train a young researcher in the emerging field of paleogenomics and aim to establish Norway at the forefront of paleogenomics in the marine environment.