It has been all over the news in the past week that iceberg A76a, an iceberg the size of Greater London, has been drifting closer to shipping lanes in the South Atlantic and causing a range of potential issues. Another iceberg, A81 calved off Antarctica earlier this year and is set to follow the same course, creating further issues. But what exactly are these icebergs and what issues are they causing?
Photo of an iceberg in the Drake Passage in December 2007 from the National Geographic website https://education.nationalgeographic.org/resource/iceberg/
An iceberg is defined by the USA's National Oceanic and Atmospheric Administration (NOAA) as a piece of ice broken off from a glacier or ice shelf that is floating in open water. Icebergs come in a range of sizes but to fit the description they must be over 16 feet (4.8m) above sea level and 98 feet (approx 30m) wide. Smaller ice bodies are classified as either bergy bits (medium sized) or growlers (smaller) depending on their size. Bergy bits and growlers may have calved off a glacier or ice sheet but may also originate from a bigger iceberg breaking up into smaller pieces. Icebergs are much, much bigger than they appear to be above the surface. Ice cliffs on the scale of 10s of metres require 100s of metres of ice underwater to support them.
Icebergs are named very systematically. The US' National Ice Center (NIC), a collaboration between NOAA, The US Navy and The US Coastguard, have a record of all named Antarctic Icebergs including A81 and A76a which can be found here: https://usicecenter.gov/Products/AntarcIcebergs
Icebergs are given a letter (A-D) signifying which part of Antarctica they originated from. A in the context of A81 and A76a refers to the Weddell Sea/Bellingshausen quadrant. The suffix numbers are then sequential in order of calving and a press release is issued by NIC whenever a new iceberg is identified and named. Letter suffixes such as the a in A76a indicate that the iceberg has calved from an already named iceberg, again with the letters being in sequential order. The worlds largest iceberg is currently A32a which is over 4000 sq km and calved from Antarctica's Flichner-Ronne Ice Shelf in 1986. It has spent the last 3 decades grounded in the Weddell Sea, far from shipping lanes hence its lack of media attention.
So why has A76a suddenly made the news?
Iceberg A76a calved from the Flichner-Ronne ice shelf in May 2021 and has been on the move for almost three years now. Carried by winds and currents it is heading north into the South Atlantic, and this is where the issues lie.
Satellite image of A76a from the NIC website archives
A76a is the largest piece of iceberg A76 that has split into three. Being 135km long and 25km wide it has been compared to both the size and shape of Cornwall and is currently located near South Georgia and the Falkland islands about 2,500km off the coast of Argentina, getting disruptively close to international shipping lanes. The British Research Ship RRS Discovery encountered the iceberg as it was leaving the Weddell Sea and entering the South Atlantic resulting in a forced detour to get around it. Circumnavigating the iceberg took the ship 24 hours but did allow for the collection of water samples which can be used for scientific research into the iceberg and its potential impacts.
Other than disrupting shipping routes, the main concern for A76a is that it may become grounded on the shallow continental waters surrounding South Georgia or the nearby Shag Rocks (a group of small islets). Becoming grounded could cause the iceberg to break up into smaller bits, impacting vessel movements in the area affecting both tourism and fishing operations. The break up and melting of the iceberg would release large volumes of freshwater into the surrounding oceans, altering the local ecosystems and potentially having negative impacts on native flora and fauna. Not only this, but the presence of the iceberg could interrupt foraging routes and ocean currents. If the iceberg is to break up over the winter season, coinciding with the end of the tourist season and when animals don't need to keep returning to land to feed their young, its impact may be lesser but nevertheless substantial.
What about A81?
A81 is another iceberg that has recently been in the news after its calving from the Brunt Ice Shelf in January this year. The Brunt Ice Shelf is heavily studied by the British Antarctic Survey (BAS), being the location of its Halley Base. The base was previously located on the part of the shelf that has now broken off as A81 but was moved a few years earlier when it first showed signs of calving. The iceberg calved off from the shelf when the large crack (called chasm-1, first observed in 2012) extended across the whole shelf and is the second major splitting from the shelf in two years. A81 is expected to follow the path of A76a into the South Atlantic ocean, carried westwards by the strong Antarctic Coastal Current, capable of causing similar issues that we are potentially facing with A76a. The BAS are currently monitoring A81, with it first being photographed when scientists were flying overhead, leaving Halley base for the season.
Satellite image of A81 from the NIC website archives
Are the calvings a cause for concern?
As discussed with regard to A76a, there are many potential issues that a grounded iceberg of this size could cause to people, animals and the environment. These impacts though may not be purely harmful. As the icebergs melt the large volumes of freshwater produced may make it hard for some organisms continue their current way of life, requiring some adaptations. However, melting icebergs also release mineral dust that had been previously trapped in the ice due to glacial erosion of the bedrock. This mineral dust can be a powerful source of nutrients to the ocean and can encourage life.
Icebergs take decades to fully melt and the calving of icebergs from this area of the Antarctic is not a current cause of concern for the BAS. Calving is a natural process and even these large calvings are not thought to be a direct impact of climate change. While it is true, some icebergs further north may be breaking off due to warming that is not a major worry for A81 or A76a.
Sources:
British Antarctic Survey (BAS) https://www.bas.ac.uk/
National Ice Center (NIC) https://usicecenter.gov/
National Oceanographic and Atmospheric Administration (NOAA) https://www.noaa.gov/
News articles (ITV, BBC)
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