The GRACE (Gravity Recovery and Climate Experiment) mission was a pioneering collaboration between NASA (National Aeronautics and Space Administration) and the GFZ (German Research Centre for Geosciences).
Launched in March 2002, the mission’s pair of identical satellites operated until October 2017. Their primary objective was to detect variations in Earth’s gravity resulting from mass movement on and beneath the planet’s surface. [emphasis, links added]
By producing monthly maps of these gravity anomalies, GRACE provided invaluable insights into several key Earth processes. The data enabled scientists to track changes in ice sheets and glaciers, particularly in regions like Greenland and Antarctica.
Additionally, the mission highlighted shifts in underground water storage and offered critical observations on sea levels, ocean currents, and even the dynamics deep within Earth’s mantle.
Building on the success of GRACE, the GRACE-FO (GRACE Follow-On) mission [pictured above] was launched in May 2018. Its main goal is to ensure continuity in the collection of gravity anomaly data initiated by its predecessor.
As of September 2023, GRACE-FO remains operational, perpetuating its vital role in Earth observation. While GRACE-FO mirrors the core objectives of the original GRACE mission, it boasts advancements in technology.
One notable enhancement is the inclusion of a laser-ranging interferometer, anticipated to refine the precision of measurements between the two satellites.
Through this follow-on mission, scientists continue to deepen their understanding of various Earth processes, spanning climate science, hydrology, oceanography, and geophysics.
Measuring ice mass from space…
The GRACE and GRACE-FO missions utilize a unique approach to monitor changes in ice mass, especially in regions like Antarctica.
Unlike traditional observation methods, these missions don’t directly measure the ice itself. Instead, they focus on detecting gravity anomalies, which serve as indicators of mass changes.
Both missions employ a pair of satellites flying in tandem in a polar orbit. The primary principle behind their operation hinges on gravitational pull.
As the leading satellite approaches an area with a significant mass—be it a mountain range or a dense portion of an ice sheet—it experiences a stronger gravitational attraction.
This causes the satellite to momentarily accelerate, creating a slight increase in the distance between itself and its trailing counterpart. As the second satellite subsequently approaches the same mass, it experiences a similar acceleration.
This delicate dance, with satellites constantly adjusting their relative distances due to Earth’s gravity, allows for precise mapping of gravitational variations. In GRACE-FO, this precision is further enhanced by a laser-ranging interferometer.
The magic lies in the interpretation of this data. Ice, being a substantial mass, exerts its own gravitational pull. When regions like Antarctica lose ice, whether through melting or calving events, there’s a discernible decrease in gravitational pull in that vicinity.
Conversely, significant snowfall or ice accumulation results in an increased gravitational attraction. By processing the raw satellite data into monthly gravitational maps and analyzing these over time, researchers can identify regions undergoing gravitational increase or decrease.
The real-world implications of these findings are profound. By pinpointing areas where gravity has changed over consecutive months or years, scientists can deduce the loss or gain of ice mass in Antarctica.
This not only paints a clearer picture of the state of ice on the continent but also aids in predicting potential future sea-level rise.
GRACE and GRACE-FO data…
In Greenland, the GRACE missions detected pronounced ice mass loss. Since 2002 Greenland’s ice sheet diminished by approximately 270 gigatons annually.
This significant decrease in ice mass underscores the rapid changes that have occurred in the Arctic, however, a significant slowdown in melting since 2020 is evident.
Antarctica presented a more complex picture. While the continent as a whole lost about 130 gigatons of ice each year during a similar timeframe, the loss was most pronounced in West Antarctica, especially around the Amundsen Sea sector.
This accelerated melting in West Antarctica is a matter of particular concern for researchers, as it is claimed to have the potential to destabilize larger sections of the Antarctic ice sheet, leading to more pronounced sea-level rise in the future.
However, since early 2020, nearly 1,000 gigatons of ice have been added to Antarctica. This remarkable ice gain represents nearly one-third of the total ice loss since 2002.
What’s causing the melting of West Antarctica?
While it’s true that CO2 and other greenhouse gases can contribute to an overall increase in global temperatures, the effects of this warming can manifest differently across regions due to various local and regional factors.
A study published in the journal Nature in 2020, titled “Low Antarctic continental climate sensitivity due to high ice sheet orography” concludes:
The Antarctic continent has not warmed in the last seven decades, despite a monotonic increase in the atmospheric concentration of greenhouse gases.
When looking at Antarctica, the continent is vast, diverse, and influenced by a combination of atmospheric, oceanic, and geophysical conditions that contribute to changes in ice dynamics.
One of the biggest drivers of ice melt in West Antarctica is warm ocean water getting underneath the floating ice shelves.
The Circumpolar Deep Water (CDW) is a relatively warm and salty water mass. It’s more pronounced in West Antarctica, especially in the Amundsen Sea sector, where it can get beneath ice shelves and melt them from below.
Changes in atmospheric circulation can affect different parts of the continent differently. For example, the Antarctic Peninsula, which juts out toward South America, has experienced more warming in recent decades, partly because of its unique position and the atmospheric patterns it encounters.
East Antarctica, which is largely comprised of the East Antarctic Ice Sheet, is primarily situated on a continental landmass that’s higher in elevation. In contrast, much of the West Antarctic Ice Sheet rests on bedrock that’s below sea level.
This makes West Antarctica particularly vulnerable to oceanic intrusion and the associated melt.
Finally, West Antarctica is home to a significant number of subglacial volcanoes, primarily concentrated within the West Antarctic Rift System. This region stands out as one of Earth’s most geothermally active areas.
These subglacial volcanoes have the potential to heat the base of the ice sheet, causing what is known as basal melting. This process can form subglacial lakes and potentially lubricate the glaciers’ bases, which might influence their speed as they flow toward the sea.
In conclusion, the complexity of melting in Antarctica, and the recent mass gains reported by GRACE-FO, suggest that atmospheric CO2 plays a minor role in large-scale ice dynamics and future sea-level rise.
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