Untangling the influence of El Niño on West Antarctic snow accumulation

New research shows that Central Pacific and Eastern Pacific El Niño have distinct effects on snow accumulation patterns in West Antarctica. The findings, published in Geophysical Research Letters, highlight the importance of understanding how the type, intensity and frequency of El Niño events will influence Antarctic surface mass balance. 

Why changes in Antarctic snow accumulation matter

Antarctica is losing ice, but predictions of the continent’s contribution to future sea level rise are uncertain. Predictions range from estimates of mass gain to multiple metres of mass loss over the coming decades to centuries. 

One reason for this uncertainty is that ocean-driven melting in some regions of West Antarctica is counteracted by mass gain in other regions of Antarctica from increased snow accumulation due to climate variability and extreme events

Since 2021, high snow accumulation events have tipped the scales of Antarctic mass balance towards mass gain, a reversal from the mass loss trend of the previous few decades. For example, over a three-day period during the unprecedented Antarctic heatwave of March 2022, huge amounts (estimated 97 gigatonnes) of snow fell over Antarctica and offset ice loss that year, temporarily reducing Antarctica’s contribution to sea level rise. 

High-magnitude snow accumulation events are expected to increase in the future due to a higher frequency of extreme weather events. Snow accumulation across Antarctica, associated with non-extreme events, is also expected to increase because a warmer atmosphere can contain more water vapour, leading to higher precipitation levels over Antarctica. Under extreme future warming, some models project accumulation increases that could outweigh increases in melting, but this is uncertain.

Snow accumulation in Antarctica is spatially and temporally variable and depends on a complex interplay of tropical and polar climate variability. Understanding how and why snow accumulation varies is essential to accurately predicting Antarctica’s future.

What’s El Niño got to do with it?

In our new research, we untangle how Antarctic snow accumulation varies due to the influence of El Niño events. El Niño describes the warming of ocean surface temperatures in the central and eastern tropical Pacific Ocean, leading to a shift in weather patterns and circulation across the Pacific and in Australia and Antarctica. 

El Niño events can be classified as different types or ‘flavours’, defined by the location of the warmest sea surface temperatures in the tropical Pacific, either in the central equatorial Pacific –called “Central Pacific El Niño” – or the eastern equatorial Pacific — called “Eastern Pacific El Niño”.

Schematic of Central Pacific and Eastern Pacific El Niño idealised sea surface temperature and atmospheric conditions. Figure from Fruend et al (2019) The Conversation

El Niño causes changes in Antarctic temperature and precipitation, driven by changes in atmospheric circulation, which bring warm, moisture-laden air over the continent. El Niño conditions also enhance the ocean-driven melting of glaciers, such as Thwaites Glacier, as more relatively warm water reaches underneath the ice shelf and melts the glacier. Recent research has established that a prolonged extreme El Niño event is likely to have caused the onset of Thwaites glacier retreat, which currently contributes 4% of global sea level rise. 

How Central Pacific El Niño and Eastern Pacific El Niño events impact the Antarctic Ice Sheet differently is a crucial question because El Niño type, frequency and intensity are all projected to change in a warming climate. Importantly, no previous studies have considered how different El Niño types influence Antarctic snow accumulation.  

Our research shows West Antarctic snow accumulation increases are more widespread during Central Pacific El Niño events than during Eastern Pacific El Niño events. We show that Central Pacific El Niño events impact West Antarctica earlier in the yearly cycle than Eastern Pacific El Niño, and these accumulation impacts last longer throughout both austral winter and spring.

Map of Antarctic surface mass gain (accumulation increases) in green, surface mass loss (accumulation decreases) in pink during Central Pacific El Niño (top row) and Eastern Pacific El Niño (bottom row), during austral winter (left column) and spring (right column). Stipples show 5% significance.

Why do we care?

El Niño events have been changing over recent decades. Central Pacific El Niño events’ frequency and intensity are predicted to continue increasing in the future, and if these teleconnections hold, our results suggest that El Niño events will cause enhanced snow accumulation across parts of Antarctica, which could potentially offset some regional melt. Accurate predictions of future changes in El Niño are crucial to better understand Antarctica’s future. 

Future work needs to better understand how climate drivers and extreme events such as atmospheric rivers are expected to change in the future and whether this could facilitate further snow accumulation increases, stabilising the scales of Antarctic mass balance. 

Read more

Macha, J.M.A., Mackintosh, A.N., McCormack, F.S., Henley, B.J., McGregor, H.V., van Dalum, C.T. & Purich, A. (2024). Distinct Central and Eastern Pacific El Niño Influence on Antarctic Surface Mass Balance. Geophysical Research Letters, 51, 11. https://doi.org/10.1029/2024GL109423

About the author

Jessica Macha is a SAEF PhD candidate based at Monash University