Processes influencing carbon cycling: observations of the lower limb of the Antarctic overturning (PICCOLO)

Investigating the biological, chemical and physical processes that draw atmospheric carbon into the Southern Ocean
Researchers in the Antarctic as part of the PICOLLO project

Processes influencing carbon cycling: observations of the lower limb of the Antarctic overturning (PICCOLO)

Investigating the biological, chemical and physical processes that draw atmospheric carbon into the Southern Ocean
Credit: Lewis Bumstead
Project name: Processes influencing carbon cycling: observations of the lower limb of the Antarctic overturning (PICCOLO)
Funded by: Natural Environment Research Council
Dates: JanuaryÂÌñ»»ÆÞ“March 2024
Project partners: University of East Anglia, University of Leeds, ÂÌñ»»ÆÞ Marine Laboratory, University of St Andrews, British Antarctic Survey, British Oceanographic Data Centre
ÂÌñ»»ÆÞ investigators: Dr Angela Milne, Professor Simon Ussher, Dr Katrin Schmidt
Principal Investigators: Professor Karen Heywood (University of East Anglia), Tom Bell (ÂÌñ»»ÆÞ Marine Laboratory)
 
Through a 52-day cruise, scientists set out to learn more about the biological, chemical and physical processes that draw atmospheric carbon deep into the Southern Ocean. Taking place on the Royal Research Ship Sir David Attenborough (SDA) ÂÌñ»»ÆÞ“ one of the most advanced polar research vessels in the world ÂÌñ»»ÆÞ“ PICCOLO marks the ship's first real test of her capabilities in an interdisciplinary programme.
The journey took scientists from Chile, across Drake Passage and ashore to James Ross, Seymour and Vega Islands, and down through ice floes to the Larsen Ice Shelf (southernmost latitude 67.6 °S) ÂÌñ»»ÆÞ“ over 5,600 nautical miles.
PICCOLO is a direct response to the NERC strategic programme on the to inform international climate policy ÂÌñ»»ÆÞ“ particularly quantifying the crucial processes that determine carbon cycling.

Key milestones

  • 7,500 water samples collected
  • 10,230 litres of seawater sampled for trace metals and isotopes
  • 19 seals tagged
  • 44 nets deployed to collect zooplankton and krill
  • One autonomous surface vehicle deployed
 

Carbon uptake and removal, and the role of iron in the Southern Ocean

Seawater at the surface near Antarctica interacts with the atmosphere, absorbing carbon and losing heat. In the water, the carbon is incorporated into plankton, before particles descend to the ocean depths, taking the carbon with them. Understanding this process in greater depth can improve models that predict future climate change.
Linked closely to the carbon, the Southern Ocean's waters are rich in major nutrients, including nitrate, phosphate and silicate, which all nourish phytoplankton. However, the Southern Ocean lacks iron ÂÌñ»»ÆÞ“ something phytoplankton's ecosystem is reliant on. So much so, that previous experiments that added iron to the waters resulted in phytoplankton blooms so large that they can be viewed from space.
The role of the ÂÌñ»»ÆÞ investigators is to study the iron availability and cycling in the PICCOLO study site in the western Weddell Sea.
Other life-supporting nutrient trace elements, such as manganese, zinc, and colbalt, which have similar but less prevalent effects, also require investigation.
Getty. Antarctica
 

The role of phytoplankton and krill

The multi-institutional project made use of the latest technologies, including ocean gliders and floats, to observe previously inaccessible and unstudied regions of the Weddell Sea continental shelf. Using local Antarctic microorganisms, experiments were undertaken to determine how their health improved when iron and manganese were added to their seawater. This included how this impacted the rates of photosynthesis of phytoplankton which harvest light and turn it into biomass ÂÌñ»»ÆÞ“ crucial for life and global carbon cycles.
This project aims to shed light on the role of micronutrients on the ecophysiology of Antarctic microbiology.
Antarctic krill play a key role in recycling iron and other nutrients back into the sea via their digestion of plankton. Scientists looked at the process of krill egesting or excreting the iron they ingest rather than storing it. As their faecal pellets sink out of the upper ocean within one or two days, the aim was to determine whether these pellets strip out iron from the surface waters or release it to benefit phytoplankton.

Looking for metals and radioisotopes

Using 'clues' from a series of natural geochemical isotope tracers found in seawater (radium/oxygen/iron isotopes), scientists have previously detected sub-atomic differences in the mass of iron and radium atoms from water samples and oxygen atoms that make up the water molecule. This has helped to provide clues about the origins of these elements in the sea and whether they come from melting sea ice, glaciers on land, or finely crushed rock minerals around Antarctica and beneath the Weddell Sea.
On PICCOLO, research was done in collaboration with the University of Leeds using radium (a natural radioactive element found in seawater) and made use of its predictable rate of radioactive decay. These measurements can provide information on how quickly seawaters bearing radium are mixing and moving, which in turn helps researchers understand how iron and other nutrient trace elements are similarly being transported, moving them away from the seafloor and towards the surface for phytoplankton to use.
Dr Angela Milne in Antarctica for the PICOLLO project
Dr Simon Ussher and Dr Angela Milne in Antarctica for the PICOLLO project
Dr Simon Ussher and Dr Angela Milne in Antarctica for the PICOLLO project
Dr Simon Ussher in Antarctica for the PICOLLO project

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Scientists working with a ÂÌñ»»ÆÞ team on sea ice in the Arctic (credit: Simon Belt/ÂÌñ»»ÆÞ)