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Atlantic carbon basics
Roughly half the carbon dioxide released by human activities stays in the atmosphere; the rest is removed by land vegetation or the ocean - in more or less equal measure. The Atlantic plays a pivotal role in ocean uptake. To understand how, we need to look at some marine carbon budget basics.
The biological carbon pump
A crucial mechanism in the ocean's carbon uptake is known as the 'biological carbon pump', because it transfers carbon dioxide fixed by photosynthesis from the surface to the deep ocean. In reality the 'pump' is more like a fall of snow - with 'flakes' of dead organisms, faecal material and bacteria drifting down into the deep, where it may remain for centuries. MORE
Marine carbonate chemistry
Chemical buffering of carbon dioxide is one of the most important reasons for the ocean acting as a carbon sink. The buffer capacity of seawater depends on its alkalinity, and will gradually decrease as CO2 uptake from the atmosphere makes the ocean less alkaline. Alkalinity also depends on the seawater content of calcium carbonate - a mineral found in the hard shells of many marine organisms. MORE
The Atlantic conveyor belt
The North Atlantic plays a key role in the global ocean circulation - the system of surface and deep currents that transport heat, carbon, nutrients, and much else around the ocean. One of the 'engines' driving this 'conveyor belt' is found in the high-latitude North Atlantic. It explains why this region is so important for ocean uptake of carbon dioxide. MORE
Carbon emission uptake and storage. Credit: S.Khatiwala
Larger figure and detailed explanation
Atlantic carbon storage
From recent research we know that the North Atlantic is accumulating human carbon emissions faster than anywhere else in the ocean. This is because of the unique way that warm, salty water from the subtropics reaches further north than in any other ocean. As this salty water cools, its capacity to take up carbon dioxide from the air increases.
The details of this Atlantic "carbon capture" are less clear.
- How do physical properties of the water (temperature, salinity), seawater chemistry and biology interact to transfer carbon from the air into the deep ocean for long-term storage?
- How do the physics, chemistry, biology and geology of the ocean adjust to changes in atmospheric carbon dioxide?
- Can we expect the ocean to continue to "capture" carbon emissions at the same rate?
ABC is one of several projects designed to answer such question. It focuses on carbon fluxes in the North Atlantic subtropical gyre, and how carbon transport in this region contributes to Atlantic carbon uptake storage.
ABC sensors on the array at 26°N. Larger figure
Plans for 2015
|14 Oct:||ABC annual science meeting|
|Oct-Nov:||6-week cruise to deploy new biogeochemical sensors on the RAPID array at 25°N|
ABC deploys new sensors at 26°N
18 Oct 2015: RRS Discovery is leaving Southampton for a 6-week expedition to collect data from on the RAPID array across the Atlantic at 26°N. Onboard is Pete Brown from ABC. He will make measurements of oxygen and carbon, and deploy new biogeochemical sensors and RAS samplers on some of the moorings (left).
Credit: Samar Khatiwala. Source:
Left: Global carbon storage (column inventory) for anthropogenic carbon (Canth) in 2008. The total inventory in that year was about 140 ± 25 Pg carbon. Right: Cumulative uptake of anthropogenic carbon (cumulative flux) up to 2008.
The difference between the cumulative uptake and the storage must be accounted for by horizontal transport of carbon by ocean currents. Calculating this transport is one of the aims of the ABC project.
The research behind these figures are described in two scientific papers:
1. Khatiwala, S. et al., (2009) Nature 462 doi: 10.1038/nature08526, and
2. Khatiwala, S. et al., (2013) Biogeosciences 10 2169-2191. www.biogeosciences.net/10/2169/2013/bg-10-2169-2013.html
Schematic of the Atlantic Meridional Overturning Circulation (ANOC) with concentrations of anthropogenic carbon concentrations at 24.5°N in 2010. ABC will deploy biogeochemical sensors (oxygen, pCO2, pH) and remote access sampling (RAS) on some of the RAPID moorings at 25°N, as indicated in the figure. Credit: NOC/P.Brown & V.Byfield. [Larger version available on request].