Antarctica's Larsen C ice shelf is undergoing extensive melting from above; Marine life threatened.

The Independent writes on the intensification of melting on the Antarctic peninsula. Last year's melt season was the highest in forty years of satellite records.

Antarctica’s Larsen C Ice Shelf experienced its highest rate of melting since records began 40 years ago from 2019-2020, a new study has found.

The unprecedented melt at Larsen C, which is Antarctica’s fourth-largest ice shelf, coincided with record-breaking summer temperatures at a weather station in the Antarctic Peninsula, the research says.

The melting was primarily driven by a series of rare weather events that brought additional heat towards the ice shelf, causing it to melt from above, the study says.

The effects of such meteorological events can combine with human-caused global heating to create a “perfect storm” for Antarctica’s ice shelves, a climate scientist told The Independent.

NASA’s Earth Observatory covers the early melting of Larsen C.
In mid-November, about a month before the start of summer in the southern hemisphere, the Antarctic melting season is usually just starting. By that time this year, vast areas along the Antarctic Peninsula were already painted blue with meltwater.

By the end of November 2020, much of the meltwater on the ice had refrozen. But scientists want to know if this event was similar to a strong early season melt that launched the 2019-2020 melt season. Last year, unusually warm air and water led to record-breaking melting across the Larsen C Ice Shelf. It is the largest remaining ice shelf along the Antarctic Peninsula, even though it lost a Delaware-sized iceberg in 2017.

Widespread melting on Larsen C, located just south of this image, was not apparent in natural-color satellite images. But scientists are watching how this season progresses. The ice shelf surface on the Larsen A was full of ponded meltwater just before its complete collapse in 1995; the same thing occurred before the near-complete collapse of Larsen B in 2002.

From the Study.

Surface melt and ponding on Antarctic Peninsula (AP) ice shelves has been linked to firn densification (Holland et al., 2011), surface lowering (Paolo et al., 2015), hydrofracture (Banwell et al., 2013), and eventual collapse (Scambos et al., 2000; van den Broeke, 2005). Following collapse the glaciers that feed the ice shelves have been observed to speed up (Gudmundsson, 2013), discharging more land ice to the oceans and increasing the rate of sea-level rise. Larsen C Ice Shelf (LCIS, Fig. 1) is the largest remaining ice shelf on the AP, and surface melt and ponding have led to surface lowering, concentrated in the inlets and the northern parts of the shelf, and to the formation of a large subsurface mass of ice (Hubbard et al., 2016). If LCIS were to disintegrate, in the same way as Prince Gustav and Larsen A ice shelves in 1995 (Rott et al., 1996) and Larsen B ice shelf in 2002 (Rott et al., 2002), modelling studies suggest that the dynamic response of the inland ice might be limited owing to the small amount of buttressing generated by LCIS (Furst et al., 2016). The potential sea-level contribution might only be of the order of millimetres over the next two centuries (Schannwell et al., 2018). However, removal of ice shelves has consequences other than sea-level rise with potential impacts on ocean circulation and biodiversity (Siegert et al., 2019).

St. Andrews Bay on South Georgia Island.
St. Andrews Bay on South Georgia Island.

Iceberg A68 was twelve percent of the marine extension of land ice on the Antarctic Peninsula before the calving from the Larsen C ice shelf in 2017. The iceberg will reach the South Atlantic islands of S Sandwich and South Georgia, also known as the iceberg graveyard, within a couple of weeks.

CNN writes on how the iceberg collision will impact the small island's food web. Be sure to visit the CNN map in the link illustrating the scale of A68 compared to South Georgia — it is nothing short of jaw-dropping.

Adrian Luckman, a glaciologist and professor of geology at  Swansea University told CNN that the “area-to-thickness ratio of A68a is approximately the same as a few sheets of copier paper stuck together, so it is remarkable that it has stayed pretty much intact despite over three years of drifting in the Southern Ocean.”
It has only been in the last year that the iceberg has picked up considerable pace, even acting as a positive fertilizing force as it makes its way through the ocean.
In open water, the iceberg is accumulating significant amounts of dust from the atmosphere that act as essential nutrients that open waters lack. But as soon as that mass hits the island's shallow waters, it will have the opposite effect.
Shallow waters are already heavily fertilized and the iceberg's excess fresh water and shading will prevent the growth of marine algae — the fuel that so much of that biodiverse marine life depends on.
Marine animals will have a difficult time finding food. Penguins and seals can not swim around the block of ice; they would die of exhaustion before locating a significant food source. Krill populations will struggle as well, disrupting migratory patterns. 

Robot footage of the colorful sea bottom.
Robot footage of the colorful sea bottom.

  • December 11, 2020