The atmospheric pattern that has shaped Greenland’s climate for thousands of years
Sediments from southern Greenland reveal a persistent link between the North Atlantic Oscillation, precipitation and regional ice-sheet behaviour
image:
The Northern lights (aurora borealis) shines down of the deck of the research vessel MARIA S. MERIAN during expedition MSM111 as it sails towards Greenland, where the sediment core from Narsaq Sound was recovered. Photo: MARUM, University of Bremen; J. Faust
view moreCredit: MARUM, University of Bremen; J. Faust
In high-latitude coastal areas specifically, Arctic Amplification means that temperatures are rising quicker than the global mean. This combination of rising temperatures and changing precipitation patterns driven by the North Atlantic Oscillation (NAO; see info box) has huge impacts on regions with a ‘cryosphere’ – areas that host ice sheets and glaciers, such as southern Greenland. Present day measurements demonstrate a clear relationship between the positive NAO phases, increasing precipitation and cooler temperatures in southern Greenland. Beyond the time measurements began however, the impact of the large- scale atmospheric circulation patterns on the Greenland Ice Sheet is poorly understood.
The aim of a new study led by MARUM scientists, recently published in the journal Nature Communications, was to create such a precipitation record extending back through the Holocene; our planet’s current warm epoch that spans the last ca. 12,000 years. The international research team used a sediment core collected in 2022 from Narsaq Sound, in south western Greenland. The core was collected during the research expedition MSM 111 BAFFDEEP, funded by the MARUM Cluster of Excellence “The Ocean Floor – Earth’s Uncharted Interface”.
Measuring rainfall or snowfall over millennia in marine mud may sound challenging, but the researchers found the clue to this by looking at the distinct geology surrounding Narsaq Sound. The rocks that surround Narsaq Sound are unique in that they are rich in Niobium, a rare Earth element. Niobium concentrations are generally low in the ocean and the element remains stable in the environment. Using X-ray fluorescence scanning (XRF), the researchers searched for changes in Niobium concentrations in the sediments as a fingerprint, or tracer, of past precipitation. Elevated Niobium concentrations found in the core sediments result from increased transport of Niobium-bearing sediment to the fjord by local glaciers or by the river draining the surrounding region. This is the first time Niobium sources, usually commercially exploited for steel and electronics industries, have been used as a tracer for past precipitation.
A clear climate-driven pattern in Niobium concentrations was found throughout the Narsaq Sound sediment record. Concentrations were high following retreat of the Greenland Ice Sheet in the early Holocene (around 11,600 years ago). After comparing the Narsaq Sound record with other records containing a signal of the NAO, the authors found the only explanation for this was that over south western Greenland, precipitation was higher but temperatures lower when the NAO was in a positive phase. “What surprised us most,” says lead author Dr. Johan Faust, “was the persistence of the signal: we can trace the influence of the North Atlantic Oscillation on southern Greenland’s hydroclimate over the thousands of years.”
If this relationship holds in the future this has important implications for the future dynamics of the Greenland Ice Sheet. Some models predict more consistently NAO positive phases under a warming climate. This may increase precipitation in southwestern Greenland, potentially promoting growth of local glaciers despite ongoing climate warming
Journal
Nature Communications
Article Title
Persistent influence of the North Atlantic Oscillation on Late Holocene hydroclimate in southwestern Greenland
No comments:
Post a Comment