Quarter 3 2021

Both the East and West Antarctic Ice Sheets thickened during the first quarter of 2021. In East Antarctica the average thickening was 1 cm – identical to the same period in the previous year (2020). However, in West Antarctica the average thickening was only 2 cm - less than half that of the previous year. The effects of ice dynamical imbalance in the Amundsen Sea sector of West Antarctica were still masked by the wider ice sheet thickening during this quarter, in keeping with previous years, owing to the relatively heavy snowfall that occurs during Austral winter. Indeed the Austral winter of 2021 was the coldest ever recorded in Antarctica, with an a average temperature of -61 °C at the Amundsen-Scott South Pole Station, as a result of a strong polar vortex circulating the continent. The rate of thinning at Pine Island glacier was 37 cm this quarter, similar to the signal recorded in the same quarter of 2020. In total, the glacier has thinned by more than 13 metres since CryoSat-2 was launched. In contrast, the Totten glacier in East Antarctica thinned by just 2 cm. However, this is significantly different to the same quarter in 2020 when the glacier had thickened by 16 cm. Although Austral winter snowfall typically masks some of the dynamic thickening, the effect was less pronounced this year.

During the third quarter of 2021 the Greenland ice sheet thickened by 6 cm, on average. By comparison, the ice sheet saw no overall change in elevation during the same period in the previous year (2020). This year saw incredibly changeable meteorological conditions across much of the ice sheet, which likely explains the difference. Although a cool, wet beginning to the summer led to a delayed onset to the melting season in 2021, this was followed by two separate heatwaves in late July and mid-August. Each of these events led to extensive melting at the ice sheet margins, and this is most prominent as a thinning signal in the southwest. Conditions were so warm during the second rainfall event that rainfall was also recorded at the ice sheet summit for the first time on record [1]. Despite the melting, Hurricane Larry travelled across the southeast of the ice sheet in September and deposited unusually large amounts of snow [2]. This sector (basin 4) recorded an average height change of +37 cm during the quarter. The net effect of these opposing weather events was overall thickening during the third quarter of 2021. The increased snowfall did not, however, have a marked impact on Jakobshavn Isbrae which thinned by 169 cm this quarter as a result of melting throughout the course of the summer.

There are no reported issues related to data availability, with over 90 % and 87 % of the Antarctic and Greenland Ice Sheets surveyed during the quarter. There were 1009 monthly users of the data portal this quarter, down from 1062 monthly users over the past year but up from 688 monthly users over the entire mission.

References

[1] Langen et al., 2017 Liquid Water Flow and Retention on the Greenland Ice Sheet in the Regional Climate Model HIRHAM5: Local and Large-Scale Impacts , Frontiers in Earth Science.

[2] Cohen, J. (2010, June 2). NASA Center for Climate Simulations: Data supporting science. NASA.

Quarter 2 2021

During the second quarter of 2021, East and West Antarctica have exhibited opposing elevation trends. On average, the West Antarctic Ice Sheet thinned by 2 cm, whereas the much larger East Antarctic Ice Sheet thickened by 1 cm. West Antarctica has continued to thin because of the rapid dynamical imbalance of glaciers in the Amundsen Sea sector - notably the Pine Island Glacier which thinned by 39 cm during the quarter. By comparison, increased snowfall during the second quarter of 2020 (the previous year) masked some of the dynamical imbalance in this region. In East Antarctica, thickening was strongest inland of the Amery Ice Shelf. In contrast, Wilkes Land – which has tended to exhibit thickening – shows little overall change as a result of warmer conditions which likely led to lower snowfall than is typical for the region [1]. Nevertheless, the Totten glacier has continued to exhibit signals of ice dynamical imbalance with a further 28 cm of thinning this quarter and 5 metres of thinning overall since CryoSat measurements began.

At the same time, the Greenland Ice Sheet has continued to thin overall. In total, the ice sheet thinned by 9 cm on average during the second quarter of 2021. This amount of thinning is relatively modest by comparison to other quarters as the ice sheet moves through spring and into the melt season, but is nevertheless three times larger than the same quarter in the previous year (2020). The largest thinning was in the southwest (basin 6) where surface temperatures are typically highest and the most surface melting occurs. On average, this sector thinned by 15 cm, almost double the rate for the ice sheet as a whole. During this quarter, Jakobshavn Isbrae thinned by 137 cm – almost three times the rate during the equivalent period in the previous year (2020). This is likely the result of the onset of the melt season towards the end of the spring, though it may also indicate a return to ice dynamical imbalance (analysis of ice velocity data are required to settle this matter).

There are no reported issues related to data availability this quarter, with 89 % and 84 % of the Antarctic and Greenland Ice Sheets surveyed, respectively. There were 837 monthly users of the data portal this quarter, down from 1043 monthly users over the past year but up from 675 monthly users over the entire mission.

References

[1] Clem, K.R., Fogt, R.L., Turner, J. et al. Record warming at the South Pole during the past three decades. Nat. Clim. Chang. 10, 762–770 (2020). https://doi.org/10.1038/s41558-020-0815-z

Quarter 1 2021

There was modest thinning across both the West and East Antarctic Ice Sheets during the first quarter of 2021. On average, West Antarctica thinned by 7 cm and East Antarctica thinned by 1 cm. Key outlet glaciers of West Antarctica draining into the Amundsen Sea continued to exhibit signs of ice dynamical imbalance; the Pine Island glacier, for example, has thinned by a further 35 cm this quarter, raising its total thinning to 1.3 metres during the previous 12 months. In addition, the interior sectors of both the East and West Antarctic ice sheets have thinned during the first quarter of 2021, and this is likely related to reduced snowfall during the Austral Summer. Overall, the West Antarctic ice sheet has now thinned by 60 cm since the start of the CryoSat mission.

In this quarter the Greenland Ice Sheet also thinned, by 1 cm on average. The average rate of Greenland ice sheet thinning was five times lower than during the same quarter in 2020. This is because snowfall levels in winter 2021 were close to the climatological mean, whereas in winter 2020 there was very little precipitation. While the southwest sector of Greenland (basin 6) thickened by 6 cm on average during this quarter, the eastern sector (basin 3) thinned by 7 cm on average – well below the long term mean [1]. Jakobshavn Isbrae in west central Greenland has continued to thicken at its terminus, by 55 cm on average this quarter. However, this thickening is still more than offset by melting during the summer of the previous year, and the glacier has thinned by almost 1 metre over the past 12 months. Overall, the Greenland Ice Sheet has thinned by 79 cm, on average, since CryoSat observations began.

Data availability remains high, with 89 % and 84 % of the Antarctic and Greenland Ice Sheets surveyed during the first quarter of 2021. There were 1347 user downloads from the data portal per month this quarter, up from 1140 per month over the past year and up from 668 per month for the entire mission.

References

[1] Langen et al., 2017 Liquid Water Flow and Retention on the Greenland Ice Sheet in the Regional Climate Model HIRHAM5: Local and Large-Scale Impacts , Frontiers in Earth Science

Quarter 4 2020

The West Antarctic Ice Sheet thinned by 2 cm, on average, during the fourth and final quarter of 2020. This thinning reflects the combined effects of ice dynamical imbalance in coastal sectors of the Amundsen Sea and trends in surface mass balance elsewhere. The East Antarctic ice sheet showed no overall change in height during the same period. The thinning in West Antarctica follows tow two consecutive quarters of thickening in this sector, and reflects the shift towards Austral summer when snowfall is relatively low. As a consequence, the rapid thinning of outlet glaciers such as the Pine Island Glacier are once again dominating the overall signal of imbalance. Altogether, the Pine Island Glacier has thinned by 53 cm during quarter 3 2020 and by over 12 metres, on average, since the launch of CryoSat in 2011. The Totten Glacier in East Antarctica has thinned by 13 cm during the reporting period after thickening by a similar amount in the previous quarter.

The Greenland Ice Sheet is in contrast starting to experience the effects of northern hemisphere autumn and winter snowfall, and has thickened by 1 cm during the fourth quarter of 2020. The greatest change has been in the southwest of the ice sheet, which thickened by 9 cm, on average, during the period. Although the Jakobshavn Isbrae has thinned by over 20 metres since CryoSat records began in 2011, its thickening has resumed during the third quarter of 2020. Altogether the glacier thickened by 41 cm after summer melting ceased, indicating that its slowdown is continuing [1].

There are no reported issues related to data availability, with over 87 % and 82 % of the Antarctic and Greenland Ice Sheets surveyed during the fourth quarter of 2020, respectively. There were 1053 monthly users of the data portal, down from 1122 over the past year but up from 637 for the entire mission.

Quarter 3 2020

Both the East and West Antarctic ice sheets thickened during the third quarter of 2020. On average, West Antarctica thickened by 5 cm and the East Antarctica thickened by 1 cm. Although the glaciers draining the Amundsen Sea sector of West Antarctica continue to exhibit ice dynamical imbalance, their thinning is offset during the reporting period by the effects of Austral winter snowfall across the ice sheet as a whole. In general the pattern of ice sheet thickening during quarter 3 2020 is similar to that seen in previous Austral winters The heavy snowfall is a result of moisture transport across West Antarctica by “atmospheric rivers” which lead to large deposits of snowfall [1]. The biggest signal of change is at the Pine Island Glacier in the Amundsen Sea sector of West Antarctica, which has thinnied by 11.7 metres since CryoSat-2 records began including an additional 38 cm during the third quarter of 2020. In East Antarctica, the most significant signal of imbalance is at the Totten Glacier which has thinned by 4.6 m since 2011 and by 53 cm over the past 12 months.

Quarter 3 2020 is the second reporting period in a row during which no significant change in the average thickness of the Greenland ice sheet thickness has been recorded. This situation is a consequence of moderately intense summer melting being balanced by subsequently above-average snowfall. For example, in the southwestern (basin 6) and northern (basin 1) sectors the average summer thinning was 11 cm while the east (basin 3) and southeast (basin 4) experienced snowfall-driven thickening of 4 and 18 cm, respectively. Although melting was above average in July, unusually intense storms brought record levels of precipitation in mid-August, reducing the net loss of ice and inhibiting further melting by increasing the ice sheet albedo [3]. Jakobshavn Isbrae has thinned by over 20 m since 2011 and by over 1 m during this quarter alone, likely due to intense surface melting during the summer.

There are no reported issues related to data availability, with over 87 % and 83 % of the Antarctic and Greenland Ice Sheets surveyed during the third quarter of 2020. There were 933 users of the data portal per month during the third quarter of 2020, down from 1190 over the past year but up from 617 for the entire mission.

Quarter 2 2020

During the second quarter of 2020, the West Antarctic Ice Sheet thickened by 1 cm, on average, and the East Antarctic Ice Sheet thickened by 2 cm, on average (Middle). The thickening is likely to have resulted from short-term increases in snow accumulation affecting the majority of the ice sheet moving into Austral winter. Overall, the West Antarctic Ice Sheet has thinned by 23 cm since 2011 and the East Antarctic ice sheet has shown little change (+3 cm)(Top). The accumulation appears to have masked rapid thinning of Pine Island and Thwaites Glaciers in West Antarctica, which have thinned by 4 and 11 cm, respectively, over the quarter – a small fraction of their overall change (527 and 227 cm, respectively). In Greenland, there have been no significant changes in the ice sheet thickness over the second quarter of 2020 (bottom right). The ice sheet thinned by 3 cm, on average, and has now thinned by 37 cm on average since the mission launch. There is some indication of thickening in coastal sectors of central East and West Greenland, likely as a result of snowfall. The start of the melt season towards the end of this quarter saw melt induced surface lowering across the ice sheet margins, particularly in the eastern (basin 3), western (basin 7) and northwestern (basin 8) regions, which thinned by 11 cm, 10 cm and 8 cm on average, respectively. This was balanced in part by fresh snowfalls towards the end of this quarter, particularly in the south and southeast of the ice sheet (basins 5 and 4), which thickened by 23 cm and 6 cm, respectively.

Quarter 1 2020

During the first quarter of 2020, the West Antarctic Ice Sheet thinned by 3 cm, on average, and the East Antarctic Ice Sheet thinned by 1 cm, on aver age (middle). The pattern of thickness change is a mixture of thickening in the interior and thinning in coastal areas. The latter signal is itself a mixture of continued thinning of outlet glaciers that have exhibited long-term dynamical imbalance (top) and short-term effects likely related to re duced snowfall during Austral summer. Pine Island glacier has thinned by 44 cm during the reporting period and by 533 cm since the mission launch. In the first quarter of 2020 the Greenland Ice Sheet thinned by 5 cm, on average (bottom right), and the total change since 2011 amounts to a 34 cm red uction in mean thickness (bottom left). The winter of 2019/2020, including Q4 2019 and this quarter, was drier than average, with snowfall below the long term (1981-2010) mean across the southern half of the ice sheet in particular [1]. These conditions led to limited snowfall driven growth across the ice sheet in 2020 compared to previous first quarters, which has typically thickened by 2 cm on average between 2011-2020 during winter months. The terminus of Jakobshavn Isbrae has continued to thicken as a consequence of its slowdown [2], with an average 50 cm increase in thickness across its downstream 50km section. Nevertheless, the glacier continues to thin inland, and has thinned by almost 8 metres overall during the lifetime of Cr yoSat-2.

References

[1] Langen et al., 2017 Liquid Water Flow and Retention on the Greenland Ice Sheet in the Regional Climate Model HIRHAM5: Local and Large-Scale Impacts , Frontiers in Earth Science

[2] Khazendar, A., et al. Interruption of two decades of Jakobshavn Isbrae acceleration and thinning as regional ocean cools. Nat. Geosci. 12, 277–283 (2019). https://doi.org/10.1038/s41561-019-0329-3