• The Antarctic ecosystem is an incredibly fragile one.

• Thermohaline slowing is having a negative impact on phytoplankton productivity.

• Negative feedback loops are becoming more concentrated and are speeding up trends of ice melt and thermohaline slowdown.

• These trends exacerbate issues of food security around the globe, as Antarctic oceanic slowdown has knock-on effects throughout the entire oceanic circulation loop.

Antarctica, a continent with no permanent population, is very much an ecosystem that is influenced by dynamic equilibria and feedback loops. The continent relies on key geographical processes to maintain its fragile environment and is a key indicator of climate change and of the health of oceanic ecosystems as a whole.

It’s not looking like a positive story, as longstanding mechanisms are being altered by the warming planet. 

Oceanic circulation

The key oceanic mechanism at play in the Antarctic is the thermohaline conveyor belt. The rising and sinking of warm and cold ocean currents respectively is a key driver of maintaining water flows and local environments, delivering heat, carbon, oxygen and vital nutrients around the globe. However, melting ice poses a significant threat to this mechanism. Ice is made up of freshwater, with this having a very different saline content to the ocean currents surrounding the Antarctic ice sheet. This influx of freshwater makes Antarctic water less dense and less salt-heavy, acting as an inhibiting factor in the usual sinking of cold Antarctic water. The decrease in the water's sinking capabilities leads to an isolation of thermohaline water circulation systems; the water cannot sink and these feedback loops become more concentrated.

This is problematic. The isolation of the lower part of the thermohaline current leads to increased ice-melt rates as warm water remains close to the surface of Antarctic ice. Furthermore, the shutting off of sinking water traps nutrients that have sunk with the cold water at the bottom of the ocean, leading to reduced nutrient transfer as the deep ocean is stagnated and starved of oxygen. Research also shows that thermohaline disruption could also lead to altered climate patterns, including shifts in precipitation systems, and increasingly volatile temperature extremes.  This has significant consequences for food chains, resulting in increased food insecurity in key areas of the globe, as the ocean is permanently altered.

 Phytoplankton nutrient transfers

The slowing of the thermohaline conveyor belt and the increasingly warm temperatures of Antarctic oceans have a significant impact on oceanic phytoplankton. Phytoplankton, microscopic single-celled organisms are the foundation for a large number of aquatic food webs and play an integral part in taking in carbon dioxide from the atmosphere and releasing oxygen in return. At least 50% of atmospheric oxygen has been produced by phytoplankton, making it a major carbon sink, with phytoplankton blooms being so bright in the Antarctic waters that they can sometimes be seen from space.

As the thermohaline circulation slows, and nutrient webs are interrupted, phytoplankton production becomes increasingly unsupported. Ocean currents are responsible for cultivating over ¾ of global phytoplankton production, with global warming directly impacting the health of these ecosystems so integral to supporting life on Earth. Increasingly intense positive feedback cycles of Antarctic warming may lead to a deep current slowdown of up to 40% in the next three decades, with phytoplankton productivity slowing. The eroding stability of the foundational organism at the base of so many food chains raises stark questions about the sustainability of oceanic food chains, with the potential knock-on effects of this trend being drastic.

Ice melt

Whilst the dangerous consequences of ice melt have been highlighted, it is also important to understand how ice melt in the Antarctic is not a phenomenon that occurs as a constant, and the process is speeding up. As ice sheets melt, the darker surfaces beneath ice such as water are revealed. These surfaces have a higher absorption capacity, leading to a greater amount of heat energy being absorbed and increased warming rates, acting in tandem with the ever-growing concentration of thermohaline mechanisms to increase the rate of Antarctic water heating. Furthermore, the decreasing amount of ice sees less heat reflected into space, leading to more intense heat waves and weather extremities, with research also highlighting the potentially destabilising impacts of warmer air on polar jet stream mechanisms.

The Problem faced by the Antarctic is that all of these destabilising processes are occurring in tandem, and exacerbating the other. The increasing speed of ice melt and water warming is acting as a positive feedback loop of increasing severity, with the impacts of thermohaline circulation disruption being felt around the world. Global warming is not simply caused by the increasing prevalence of greenhouse gases in the atmosphere, it is also a result of changes happening in the most remote regions in the world, and is influenced by a growing range of inputs. The concerning changes in the Antarctic are simply the latest example of the severity of climate change, and how weather ‘extremities’ and temperature extremes are becoming an increasingly permanent part of our society.

These changes will potentially have incredibly destabilising consequences on food chains, and human food security around the world.