Ice cores on the Antarctic Peninsula

Ice coring on the Antarcti Peninsula | The James Ross Island ice core | Dyler Plateau ice core | Gomez ice core | Antarctic Peninsula temperature change | Antarctic Peninsula accumulation change | The future outlook | Further Reading | References | Comments |

Ice coring on the Antarctic Peninsula

Instrumental climate records are sparse on the Antarctic Peninsula, and extend back to only 1903 (from the South Orkney Islands). Upper air measurements began only in 1956. Ice cores allow scientists to reconstruct air temperature and snowfall over a longer timescale. This means that they can put modern change into context, understanding the ‘normal’ range of climate. They are better able to understand modern glacier behaviour, which is a response to climate over timescales of several decades or more (see Glacier Response Time). Ultimately, study of past climate helps scientists to make better predictions about future climate and glacier behaviour.

The Antarctic Peninsula has a number of ice cores, the longest of which extends back to 14,000 years ago¹. However, most are very short and it is difficult to compile a ‘representative’ ice-core stack, due to the different techniques and proxies used and measured, the disparate nature of the ice cores, the variance in length, and the widely different climatic regimes either side of the Peninsula². What we can do is reconstruct the climate over the Antarctic Peninsula in different places and over different periods, using the ice-core record in conjunction with other climate proxies, such as lake and marine sediment cores³, glacier fluctuations⁴, and soil and moss banks⁵.

A few key Antarctic Peninsula ice-core records extend at least back into the last century. They are the James Ross Island (14,000 years ago to present)^{1, 6}, Dolleman Island (1795 AD to present)⁷, Dyer Plateau (1505 AD to present)⁸ and Gomez (1850 AD to present)^{5, 7} ice cores. What do these ice cores tell us about temperature, surface melt and snowfall change across the Antarctic Peninsula?

The James Ross Island ice core

Holocene climate change

Ice cores across the Antarctic Peninsula show a consistent story of warming during the Twentieth Century. The James Ross Island ice core extends the longest, back to 14,000 years ago. Deuterium isotopes (an isotope of hydrogen, ²H) were used to reconstruct temperatures from this 363.9 m-long ice core from the Mount Haddington ice cap.

The Holocene period occupies all but the bottom 5 m of the ice core; the basal ice may be as much as 50,000 years old¹. The figure below shows the dramatic warming at the end of the last glaciation, followed by stability for much of the Holocene. There was a slight warming of around 0.5°C during the mid-Holocene (6000 to 2000 years ago), followed by pronounced cooling from 2500 to 600 years ago (which was synchronous with ice-shelf development in the northern Antarctic Peninsula^{9, 10}). Finally, the last 100 years of the ice core indicates strong, but not unprecedented, warming during the Twentieth Century.

The last millennium: increased surface melt

Zooming in on the last 1000 years from the James Ross Island ice core, we see cool conditions from AD 1410 to 1460, followed by warming. This warming has resulted in strong intensification of surface melting, with melt increasing dramatically in the twentieth century⁶. Summer melt is now above any that has occurred in the last 1000 years⁶. This increased surface melting is consistent with observed thinning of the lower parts of glaciers¹¹, glacier recession^{12, 13} and glacier acceleration¹⁴. Twentieth Century warming means that the glaciers on the Antarctic Peninsula are now above a threshold that makes them particularly sensitive to summer melting, and this threatens their long-term viability and stability.

Dyler Plateau ice core

A shorter 480 year ice core record from the Dyer Plateau showed strong warming from 1980-1990 AD, with these last two decades being the warmest in the last five centuries⁷. Conditions were stable here from 1500 AD to 1850 AD, it was slightly cooler from 1850-1930, and strong warming began in 1930. Increasing annual layer thicknesses indicate that accumulation began to increase in the early 19^th Century, following increases in air temperatures.

Gomez ice core

The Gomez ice core is a high resolution, 150 year stable isotope record (δ¹⁸) of climate from the Gomez Plateau^{8, 15}. This 136 m long ice core was drilled in 2007 by a team of scientists from the British Antarctic Survey. The oxygen isotope record is plotted in the figure above (decadal average). This record shows cooling from 1857-1900 and pronounced warming after 1900. The warming over the last 50 years is exceptional, outside the bounds of normal variability, and far higher than pre-industrial temperature ranges¹⁵.

The Gomez ice core records a doubling of snow accumulation high on the Antarctic Peninsula spine since 1850, with the decadal average increasing from 0.49 m water equivalent per year from 1855-1864 to 1.10 m water equivalent per year from 1997-2006⁸. This increase in accumulation is larger than that observed in other ice cores and at Esperanza research station (northern Antarctic Peninsula), highlighting the spatial variability in climate across the Antarctic Peninsula.

Antarctic Peninsula temperature change

Despite the wide distances between the study sites and the strong precipitation and temperature gradients across the Antarctic Peninsula mountain spine, a general trend is emerging. Looking at the record since 1850, which is covered by all three ice cores, there are cooler temperatures from 1800 AD to the early Twentieth Century. Warming consistently begins in the early Twentieth Century, around 1930, with the warming being particularly strong in the summer and autumn. This is significant, as it results in strong summer melting, recorded in the increasing number of melt layers in the James Ross Island ice core⁶.

Antarctic Peninsula accumulation change

While glaciers on the Antarctic Peninsula are thinning in their ablation areas and their fronts are receding, many are thickening in their upper reaches. This is because accumulation (snowfall) is increasing across the Antarctic Peninsula. Warmer air holds more moisture, leading to increased snowfall. Snowfall is forecast to continue into the future^{16, 17}, which may offset increased surface melting from warmer summer air temperatures. However, Barrand et al.¹⁶ found that ice-shelf collapse and grounding line recession still resulted in widespread glacier recession over the next 200 years¹⁶.

What can the ice-core record tell us about accumulation? A Holocene accumulation record is yet to be derived from the James Ross Island ice core, but the shallow ice core from Gomez indicates a doubling in snow accumulation since 1850⁸. This is mirrored by the Dyler Plateau ice core⁷, and by instrumental measurements at Esperanza station (northern tip of the Antarctic Peninsula)⁸. This increase in accumulation may be driving the slightly slower land-terminating glacier recession observed over parts of the northern Antarctic Peninsula over the last 10 years^{12, 18}.

The future outlook

Glaciers are currently receding rapidly all across the Antarctic Peninsula, largely in response to greater surface melting in the ablation zone during the summer and ice-shelf collapse. However, future surface melting may be offset by increased snowfall as warmer air masses can hold more moisture. Whether or not extensive glacier recession will continue on the Antarctic Peninsula over the coming decades depends principally on the threshold for summer melting, and whether precipitation or ablation is the primary control on glacier mass balance, and also on dynamic non-linear glacier responses to events such as ice-shelf collapse¹⁹ and melting from below by incursions of warmer upwelling deeper ocean currents (such as Circumpolar Deep Water)^{20, 21}. It is clearly critical for scientists to investigate past glacier response to Holocene temperature and precipitation changes, in order to better predict likely future glacier behaviour.

Further reading

• Ice core records
• Ice core drilling
• Antarctic Peninsula glacier change
• Ice-shelf collapse
• Glacier Response Time
• Climate change