The Gulf Stream control of the North Atlantic carbon sink

Lead Research Organisation: NATIONAL OCEANOGRAPHY CENTRE
Department Name: Science and Technology

Abstract

We are all aware that atmospheric CO2 has risen over our lifetimes leading to global warming. The ocean has played an important role in moderating that atmospheric rise by taking up and storing 25% of the emitted carbon. However, the extent to which the ocean will continue to act in this manner as the ocean warms and becomes more acidic is unclear, as is the response in the future as we reduce carbon emissions to net zero in the next 20-30 years. A key region in addressing this question is the North Atlantic, which is disproportionately important for ocean carbon uptake. This carbon sink involves both the uptake of natural carbon (due to surface cooling and biological uptake) and of anthropogenic carbon (due to the rise in atmospheric CO2). A prevailing view is that this carbon sink will weaken in the future as surface warming decreases solubility and increases stratification, which inhibits the supply of nutrients and carbon to the surface ocean. However, this viewpoint takes a local perspective and does not account for the effect of the circulation in redistributing nutrients and carbon over the global ocean.

We wish to propose and test the alternative viewpoint that the circulation plays a central role in determining the carbon sink, by setting the supply of nutrients and carbon to the surface waters of the North Atlantic. In particular, there is a phenomenon - the western boundary current or Gulf Stream - that is crucial for this problem. We know that the Gulf Stream is important for supplying heat to higher latitudes, leading to a warmer European climate. However, its role in driving carbon uptake remains little explored. Surface observations show that there are elevated rates of carbon uptake downstream of the Gulf Stream. This uptake occurs as older waters carried below the surface by the Gulf Stream are transferred downstream to the surface. These older waters are rich in nutrients and depleted in anthropogenic carbon. When these waters outcrop to the surface, they determine the surface nutrient and carbon concentrations, and so control the carbon uptake from the atmosphere. How much carbon uptake is driven by this nutrient and carbon 'stream' in the North Atlantic depends on multiple climate-sensitive processes, including the density range of the stream, the Gulf Stream transport, and a suite of physical and biogeochemical processes occurring along its path.

We will use observations and models to comprehensively understand this pivotal phenomenon, distinguishing between several different mechanisms that transform the fluxes of properties at the beginning of the Gulf Stream to those entering the North Atlantic. We will make new measurements of how the Gulf Stream supply of nutrients and carbon varies all the way from Florida Straits to a carbon uptake hotspot downstream, a distance of over 2000 miles. We will employ moorings in Florida Straits to determine the nutrient and carbon properties at the start of the Gulf Stream. We will deploy a fleet of BioArgo floats and gliders to reveal how nutrients and carbon are conveyed from low to high latitudes, documenting their downstream evolution through the effects of physical transport, mixing and biological cycling. Our work programme sits between two ongoing observing arrays of the Atlantic meridional overturning circulation, RAPID at 26N and OSNAP between Labrador and Scotland, and these arrays place our observations in a wider context. We will test our ideas using experiments in circulation models, including assessing the sensitivity of the North Atlantic carbon sink to physical processes. Finally, we will evaluate how the carbon sink varies in climate model projections and establish whether the models' responses occur for the right reasons.

Unravelling these controls of the ocean carbon sink is crucial if we are to understand and credibly predict the future evolution of the carbon sink, especially given the uncertain ocean response to net zero emissions.

Publications

10 25 50
 
Description C-Streams (The Gulf Stream control of the North Atlantic carbon sink) - 2025 and 2026 glider extension
Amount £327,928 (GBP)
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 06/2024 
End 01/2027
 
Description ROCCA - The Role of the Overturning Circulation in Carbon Accumulation
Amount £1,138,708 (GBP)
Funding ID NE/Y005287/1 
Organisation Natural Environment Research Council 
Sector Public
Country United Kingdom
Start 11/2023 
End 03/2026
 
Description 2023 July - US CLIVAR AMOC Task Team workshop on Meeting AMOC Observation Needs in a Changing Climate 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Hosted by the University of Hamburg, Germany, the goal of this workshop was to inform on the design of a future-focused, sustainable AMOC observing system, providing first a retrospective look at the value of the observational methods and their validation, before discussing questions (in method or scientific) that have not yet been addressed (e.g. the integration of biogeochemistry). The workshop looked at how to bring models and observations together, and how to coordinate an international AMOC observational approach to monitor variability over multiple decades. C-Streams work was presented here.
https://www.clivar.org/events/workshop-meeting-amoc-observation-needs-changing-climate
https://www.conferences.uni-hamburg.de/event/316/
Year(s) Of Engagement Activity 2023
URL https://www.clivar.org/events/workshop-meeting-amoc-observation-needs-changing-climate
 
Description 2024 - February - Subpolar North Atlantic Ocean Biogeochemistry and OSNAP Workshop 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Held alongside the Ocean Sciences conference in New Orleans, USA, on February 20th, 2024 0830-1330,the objectives of the workshop were to:
1) identify and strengthen synergies between the different international physical and biogeochemical programs focused on the high-latitude North Atlantic (both observational, analysis and modelling based)
2) and to develop strategies to leverage OSNAP as an observational and analysis platform to address ocean biogeochemistry questions
C-Streams work and plans were presented here and led to multiple conversations and potential new collaborations
Year(s) Of Engagement Activity 2024
 
Description C-Streams project website 
Form Of Engagement Activity Engagement focused website, blog or social media channel
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Website for C-Streams project created and multiple news items written (http://c-streams.uk). Accessed by more than 200 unique visitors from >10 countries
Year(s) Of Engagement Activity 2023,2024
URL https://c-streams.uk
 
Description DeepWater buoyancy feature on the C-Streams project Nov 2023 
Form Of Engagement Activity A magazine, newsletter or online publication
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact The online industry website DeepWater Buoyancy published a piece on the C-Streams project, and the use of novel technological products in our deployed moorings. It is read by a large number of industry professionals
Year(s) Of Engagement Activity 2023
URL https://deepwaterbuoyancy.com/mooring-matters-the-c-streams-project/
 
Description Press release for C-Streams mooring deployment cruise - August 2023 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Media (as a channel to the public)
Results and Impact Members of the C-Streams project undertook fieldwork to the Florida Straits to deploy a number of deep ocean biogeochemical sensors to track the parameter variability over multiple timescales at the beginning of the Gulf Stream. A press release was made to publicise this fact. Th release was part of the NOC's weekly news outputs, which has an international reach of multiple thousands of people. A similar release was made by colleagues at the University of Liverpool
Year(s) Of Engagement Activity 2023
URL https://c-streams.uk/news/observational-deployment-cruise-august-2023