The First Iceberg

Guest Blog from Dr Amber Annett a NERC Independent Research Fellow within Ocean and Earth Science, National Oceanography Centre Southampton at the University of Southampton.

Every expedition is full of firsts. First cruise with these colleagues, first time on this ship, first time in that location, first time collecting this type of sample or running that analysis on board. Even when it’s not new for me, it’s always new for someone, like the group of people rushing outside at the news of the first iceberg. I’ve seen hundreds, but still I grabbed my jacket and ran outside with them, infected by the excitement. It was a big, tabular iceberg, but it was miles way, just on the horizon against the cloudy-bright sky. Hundreds of photos later everyone went back inside to warm up with some tea, grinning like fools and reluctantly admitting that it didn’t show up very well in the pictures, but we had definitely, probably seen it.

The following day we sailed past a bright white iceberg, irregularly shaped and smooth in some places where it had rolled to expose the areas that had been melting below the waterline. Even from our safe distance, we could tell it dwarfed the ship, this time the excitement was mixed with awe. You can imagine the squeals when we saw penguins swimming around it. Although we like to joke that these “charismatic megafauna” steal the show, seeing marine animals in the wild is always special.

A friend in my oceanography class once told me, “If it’s too small to see, I don’t care about it.”  I am the exact opposite: it’s the tiny things, from plankton to molecules, that fascinate me, because these tiny things have the power to change the world. The reason our planet has an atmosphere with oxygen is a result of cyanobacteria, the photosynthetic bacteria that are still ubiquitous in the oceans. Today, about half of the oxygen we breathe comes from phytoplankton, even though most of us think only of forests when we hear the phrase “the lungs of the planet.”

Along with this generation of oxygen, photosynthesis also draws carbon out of the atmosphere, forming organic matter that can sink. Any carbon not decomposed on the way down can be buried in the seafloor, effectively removing it from the climate system, which is a natural carbon sink that is becoming increasingly important as human carbon emissions rise. Models suggest that if this biological sink in the ocean was turned off, CO₂ in the atmosphere would rise by ~200ppm [Parekh et al., 2006] (for context, current levels are 417 (https://www.esrl.noaa.gov/gmd/ccgg/trends/) and the last glacial maximum was 190ppm (Sigman and Boyle, 2000).

However, in some areas of the ocean, phytoplankton aren’t reaching their full potential, and the Southern Ocean is one such region. Here, phytoplankton are limited by lack of iron [Tagliabue et al., 2017]. My research focuses on understanding the supply of iron from the Antarctic Peninsula, as the seafloor sediments and melting glaciers can provide iron to stimulate phytoplankton growth. We don’t yet know exactly how much iron is coming from these processes, and the Antarctic Peninsula is the fastest warming region of the Southern Hemisphere [Henley et al., 2019], so measuring the supply of iron and understanding how it might change with continued warming is crucial to understanding how carbon will cycle through this region in the future, and subsequently affect global climate.

There are many factors at play in how carbon cycling will respond to future warming, and many are interconnected. For example, as ice shelves melt this brings deep, iron-rich seawater to the surface. The melt water from the ice itself also contains iron. As this water moves offshore and out into the Southern Ocean, it can transport the iron to where it’s needed to promote phytoplankton growth and carbon uptake. Independent of any iron supply, as glaciers retreat this exposes new area of ocean where phytoplankton can grow – and new seafloor where this blue carbon can be buried.

This process is a small but significant carbon sink that we are only just starting to measure  – an early result from the project that myself and three colleagues joined in January [Barnes et al., 2020]. The project, aptly named ICEBERGS, aims to understand how glacial retreat along the Antarctic Peninsula impacts benthic ecosystems. My team’s goal was to sample the seafloor as well as glacial meltwater to constrain how much iron is supplied by these sources.

Studying how our planet is changing is how I ended up spending 28 months of my life in the Antarctic, surrounded by stunningly beautiful landscapes and incredibly smelly wildlife. It’s cold, it’s remote, and it can be very isolated; many of my expeditions have been four weeks away from home and family, but I’ve also spent 12 consecutive months there. The conditions can make routine tasks very challenging, but the sense of community and passion on the research ships and bases makes it even more rewarding. Whether it’s running outside together to see an iceberg, someone unexpectedly stopping in to help after their shift ends, or celebrating packing up the last of the cargo after a successful expedition.

Even after the science work ended, we had some firsts. We had crossed the Antarctic circle into 24h daylight, and heading back north we were looking forward to seeing darkness again. The first cloudless night we spent a long time lying on the deck above the bridge, enjoying our first glimpse of stars for weeks. One of the little things we don’t appreciate until it’s gone, like so many of the things we all miss during the pandemic as we maintain our distance to keep ourselves and our communities safe.

One aspect of the Antarctic that surprised me, and that I love sharing with people, is the variety of sounds that ice can make. The low clinking as brash ice washes against a rocky beach like oversized ice cubes. The muted whooshing of soft, thin sea ice tearing like paper as a small boat pushes through it. The crunch and groan of thick sea ice breaking apart around the bow of a research ship, and the constant scrape of that ice down the sides of the ship as we head toward our next sampling site. The lumps of glacial ice washed up on the beach, made from snow that’s so densely packed and compressed that it would be perfectly clear if not for the millions of tiny bubbles frozen throughout – walking past these in the bright sunshine sounds like being inside a popcorn machine, I think this is my favourite. Perhaps the most impressive though is the loud, deep cracking of an ice shelf, like a not-too-distant canon, the boom echoing off the surrounding mountains as everyone rushes to see where the noise came from, and if we can see any ice tumbling into the sea. When I make an iced coffee or G&T on a hot day, I always add the ice at the end, to hear the sharp crack of the ice cubes as I drop them in. Next time you find yourself with an ice cube tray, close your eyes and try to imagine how it would feel and sound if that ice cube was the size of a block of flats.