Processes Influencing Carbon Cycling: Observations of the Lower Limb of the Antarctic Overturning (PICCOLO)
Scientific contacts: Dr Simon Ussher, Dr Angela Milne, University of Plymouth, UK
Links: PICCOLO is funded by the Natural Environment Research Council (NERC) with links to the British Antarctic Survey (BAS). It is one of five programmes under the umbrella project ‘Role of the Southern Ocean in the Earth System’ (RoSES) that investigates the importance of this ocean in the global carbon cycle.
Expedition contribution: sampling of snowpack
The global carbon cycle is important for the Earth’s climate regulation, because carbon dioxide (CO2) in the atmosphere is a main contributor to the natural greenhouse effect that ensures temperatures on our planet are hospitable to life as we know it. Before the age of industrialisation, the atmospheric concentration of CO2 had been constant at 280 parts per million (ppm) for several thousand years. Since the 18th century, it has risen above 400 ppm CO2, mainly as a result of fossil fuel burning . These elevated CO2 levels amplify the natural greenhouse effect, leading to changes in climate and more frequent and severe, extreme weather events.
All systems on Earth are linked: atmosphere, hydrosphere, cryosphere and biosphere. The oceans, covering 70% of the planet’s surface, are particularly important in climate regulation through absorption of excess heat, regulating temperature through global ocean currents and dissolution of atmospheric CO2 in surface waters. There, it becomes the carbon source for phytoplankton, the primary producers that utilise sunlight to photosynthesise and carbon to form their cells structures and multiply. As on land, primary producers are the base of the food web, upon which all other organisms, such as grazers and predators, depend.
The Southern Ocean is particularly interesting for climate regulation, having been identified as a major sink for atmospheric carbon dioxide . The main Antarctic deep water branch of the global ocean circulation system forms in the Weddell Sea, where surface water cools on the continental shelf and sinks. The sinking water ‘exports’ the decay products and faeces of a myriad of organisms into the deep ocean and with it, exports the carbon originally captured by the phytoplankton.
The fresh supply of nutrients, other than carbon, in the Southern Ocean is limited by its remoteness and scarcity of exposed land and river, which, at lower latitudes, provide nutrients to the seas surrounding the continents. As a result, primary producers rely more heavily on nutrients available through recycling within the water column . The potential scarcity of essential elements, such as iron and manganese, may limit the productivity of the Southern Ocean, and with it, the effectiveness of the carbon pump that supports climate regulation.
Weather systems transport air masses and moisture across great distances and entrained with these, particles and nutrients that are deposited on ice sheets, ice shelves and the ocean surface. This atmospheric deposition is an important pathway, by which essential element are transported. As plants on land, phytoplankton require macro-nutrients, such as nitrogen and phosphorous, and micro-nutrients, including iron, cobalt, nickel and manganese . Drs Simon Ussher and Angela Milne investigate the processes that determine the carbon export in that region and consider that increased surface melting of snow and ice on the Antarctic Peninsula, one of the most rapidly warming regions on the planet , could make a significant difference to the fluxes of nutrients and the productivity of the Southern Ocean.
The expedition team will take snow-pack samples from cores up to a depth of 10 m along their route.
The analysis of these samples at the University of Plymouth will provide insights into the magnitude of atmospheric deposition of essential elements, their concentration in melt water and any recent changes that may have occurred. The data will be included in models of processes that influence biomass production. A better understanding of this system will help to improve Earth system models of contemporary climate change and predictions of its future evolution.
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