Atlantic weather patterns shaped southern Greenland’s rain and snow for millennia, a new study shows. Scientists used a sediment core collected in 2022 from Narsaq Sound to track past precipitation. Lead author Dr. Johan Faust said, "What surprised us most was the persistence of the signal." This record spans 12,000 years.
In high-latitude coastal areas, Arctic amplification means that temperatures are rising faster than the global average. This combination of rising temperatures and changing precipitation patterns driven by the North Atlantic Oscillation has major 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 positive NAO phases, increasing precipitation and cooler temperatures in southern Greenland. However, the impact of large-scale atmospheric circulation patterns on the Greenland Ice Sheet before measurements began remains poorly understood.
The aim of a new study led by MARUM scientists, recently published in the journal Nature Communications, was to create a precipitation record extending back through the Holocene, our planet's current warm epoch that spans approximately the past 12,000 years.
Niobium traces ancient precipitation
The international research team used a sediment core collected in 2022 from Narsaq Sound in southwestern Greenland. The core was collected during the research expedition MSM 111 BAFFDEEP.
Measuring rainfall or snowfall over millennia in marine mud may sound challenging, but the researchers found a clue in the distinct geology surrounding Narsaq Sound. The rocks that surround Narsaq Sound are unusual in that they are rich in niobium, a transition metal. 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 the steel and electronics industries, have been used as a tracer for past precipitation.
A persistent link to Atlantic circulation
A clear climate-driven pattern in niobium concentrations was found throughout the Narsaq Sound sediment record. Concentrations were high following the 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 southwestern Greenland, precipitation was higher but temperatures were 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 thousands of years."
If this relationship holds in the future, it has important implications for the future dynamics of the Greenland Ice Sheet. Some models predict more consistent positive NAO phases under a warming climate. This may increase precipitation in southwestern Greenland, potentially promoting growth of local glaciers despite ongoing climate warming.