Iceberg Killing Fields Threaten Carbon Cycling

The vast, unpopulated landscape of Ryder Bay, West Antarctica gives the impression of complete isolation. However, despite its barren, cold exterior, Antarctica plays an important role in regulating the Earth’s climate system. Located along the southeast coast of Adelaide Island, Ryder Bay is helping mitigate impacts of climate change by removing greenhouse gases from the atmosphere to the ocean, where these gases can remain for centuries. This repurposing is being done by benthos, microorganisms like phytoplankton that bloom during summer months and provide critical food supplies that maintain the marine ecosystem in Ryder Bay. Quietly residing on the floor of the Southern Ocean, benthos are encountering increased risks due to a changing climate. While the potential carbon recycling capacity of local marine ecosystems remains significant, the collapsing glaciers and ice shelves in Ryder Bay may threaten this productivity, according to an article in the journal of Global Change Biology.

West Antarctica during winter. (Source: Ashley Cordingley)
West Antarctica during winter (Source: Ashley Cordingley).

The carbon recycling process in the marine ecosystems is one of the strongest mechanisms helping to reduce the impacts associated with historic carbon emissions. Located along the continental shelf, benthos absorb carbon through photosynthesis; when these organisms die and fall to the ocean floor, this carbon is then stored in sediments. Undisturbed, the ocean can help thwart warming due to an enhanced greenhouse effect by removing carbon from the atmosphere and storing it in the ocean. David Barnes, a Marine Benthic Ecologist with the British Antarctic Survey and an author of the article,  pointed out to GlacierHub, “Trends in carbon accumulation and immobilization, which occur on the seabed, could be considered most important as these involve long-term carbon storage. [These trends] are perhaps the largest negative feedback on climate change.” However, because of shifting land dynamics, the increased frequency of iceberg creation is having a direct impact on the ability of the marine ecosystems to recycle carbon.

Iceberg shape and size is hard to estimate solely from its above sea level figuration. (Source: Ashley Cordingley)
Iceberg shape and size is hard to estimate solely from its above sea level figuration (Source: Ashley Cordingley).

As the Earth continues to warm, ice sheets and glaciers in Antarctica advance and become thinner, causing cracks and crevasses to form. These fissures, in turn, lead to unpredictable, large-scale breaks which create icebergs that discharge into the ocean. At the time of detachment, ice formations hit the ocean floor, obliterating the marine ecosystems below. Icebergs can continue to impact the benthos as they travel on the ocean.

Barnes described this problem to GlacierHub:  “At places like Ryder Bay, it would be very difficult to provide forecasting, because it is very frequent and a bit chaotic. The direction an iceberg travels depends on its shape, how deep its keel is, wind, and current speed. A smaller iceberg with a vertically flat side above water will easily catch wind like a sail, so if the wind is strong it will mainly follow wind direction. Conversely, a bigger iceberg with a deep vertical flat side might more easily catch current.”

According to NOAA, these icebergstypically rising 5 meters above the sea surface and covering 500 square meters in areaare large enough to inflict significant destruction. Dubbed “iceberg killing fields,” these places of impact can cause extensive disruption to the beneficial marine ecosystems along the ocean floor.

Divers assess seabed for ice scour damage (Source: Ashley Cordingley)
A diver assesses the seabed for ice scour damage (Source: Ashley Cordingley).

David Barnes works with the British Antarctic Survey to study the iceberg killing fields and measure the impact of iceberg-seabed collisions on marine ecosystems. The British Antarctic Survey has been monitoring the local marine ecosystems in Ryder Bay due to their sensitivity to environmental change and the surprisingly large role benthos play in removing carbon from the atmosphere. According to the report, “The scour monitoring has probably become the longest continuously running direct measurement of disturbance on the seabed anywhere in the world.” With roughly 93 percent of carbon dioxide being stored in our oceans, it is necessary to monitor how these potential carbon sinks may fluctuate, according to the Worldwatch Institute.  

According to Barnes’ findings, the benthos in Ryder Bay are experiencing high mortality rates due to the frequent and powerful collisions between collapsing ice shelves and the sea floor, often referred to as ice scour. “Since 2003, when it was first measured in Ryder Bay, ice scour has been less predictable and more variable (than many other environmental variables),” according to Barnes and the British Antarctic Survey. The heightened unpredictability of ice scour makes predicting and preventative measures challenging.

Collisions between icebergs and the ocean floor are frequent and damaging, with the “potential to halve the value of benthic immobilized carbon in the Ryder Bay shallows,” says Barnes. These measurements show a very high frequency of scouring in the shallows because of its proximity to the ocean floors in Ryder Bay, according to the article. In fact, on average, ice scour affected 29 percent of the seabed study area yearly, from 5 to 25 meters deep. In the past decade, Barnes found that only seven percent of the shallows had not been hit by icebergs. This scouring accounts for nearly 60 percent of total benthic fatality at a 5m depth. The high frequency and fatality rates associated with iceberg scour make it one of the “most significant natural disturbance events,” according to Barnes.

Extensive research conducted on the sea floor in Ryder Bay helps measure ice scour. (Source: Ashley Cordingley)
Extensive research conducted on the sea floor in Ryder Bay helps measure ice scour (Source: Ashley Cordingley).

Weekly ocean measurements of temperature, salinity and size-fractionated (micro, nano and pico) phytoplankton have been collected since 1997, says Barnes. The field work conducted by the British Antarctic Survey set up 75 ice scour markers gridded at 5, 10 and 25m. These grids are surveyed and replaced by researchers using scuba gear, allowing for the different scour depths to be calculated. Frequency of collisions is then calculated through the recording of disturbances for each meter squared in order to establish a detailed history and provide insight into potential future trends. Annual collection of faunal remains and boulders are integrated into the disturbance data sets. These collections will help further quantify the damages inflicted upon marine ecosystems and their abilities to sequester carbon.

While glaciers in polar regions seem inconsequential to our everyday experiences with climate, they have the ability to significantly influence the biological systems which remove greenhouse gasses from the atmosphere. Continued support of scientific endeavors in the polar regions are critical in order to understand the places and processes that play such a vital role in the Earth’s climate system. As Barnes states, “We have a huge and powerful ally [in the polar regions] in the fight against climate change, so let’s make sure we look after it.”

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