EGU2020-13803, updated on 09 Jan 2024
EGU General Assembly 2020
© Author(s) 2024. This work is distributed under
the Creative Commons Attribution 4.0 License.

The modern Northeast Atlantic Radiocarbon Content viewed along a basin transect from 29°- 61°N

Norbert Frank1, Markus Miltner1, Steffen Therre1, Marleen Lausecker1, Nadine Tisnerat-Laborde2, Paolo Montagna3, and Ronny Friedrich4
Norbert Frank et al.
  • 1Heidelberg, Institute of Environmental Physics, Physics, Heidelberg, Germany (
  • 2Laboratoire des Science du Climat et de L'Environnement, CNRS, CEA, UVSQ, 91191 Gif-sur-Yvette
  • 3Institute of Polar Sciences - National Research Council, ISP-CNR Via Gobetti, 101 – 40129 Bologna
  • 4Curt-Engelhorn Centre for Archeometry, Klaus-Tschira-Labor, C4, 8 68159 Mannheim

The Northeast Atlantic is crucial regarding the northward heat and carbon export into the Arctic Ocean. At the surface and at mid-depth (0 -1000 m), however, most of the water re-circulates through two basin scale gyres, with warm and salty waters in the sub-tropical gyre (STG) and significantly fresher and colder waters in the sub-polar gyre (SPG). In addition, the Azores Front (AF) separates the northeastern branch from the southeastern branch of the STG, which is today positioned around 34.5°N in the east Atlantic. Underneath both gyres newly formed deep waters from the Arctic Ocean and Labrador Sea are spread into the Atlantic basin. Here we investigate, whether these water masses and recirculation patterns reveal distinct histories of carbon uptake and advection in the eastern North Atlantic. Therefore, water samples spanning the entire water column have been collected at 6 stations along a north-south transect at 25°W spanning from 42° to 61°N in 2012 (N/O Thalassa ICE-CTD cruise). In 2018 (RV Meteor M151 ATHENA cruise) samples further south were collected spanning until 29.5°N thus including the present day AF.

The radiocarbon content of Dissolved Inorganic Carbon (DIC) from 8 profiles (N>60, 30° to 61°N, 50-3000m depth) were measured at the AMS facility at CEZA facility in Mannheim following CO2 extraction from seawater at Heidelberg University. Δ14C values range from +50 ‰ in the upper layers of the subtropical Atlantic to -100 ‰ in 3000 m depth also in the subtropical Atlantic. Three main feature appear in the radiocarbon distribution. The surface shows a moderate difference between SPG and STG Δ14C values of <15‰ with a decreasing trend towards the North, hence indicating equilibration with the atmosphere. Underneath, between 100-1000 m depth SPG (46° – 61°N) Δ14C values of nearly 0‰ are found identical to the modern Northern Hemisphere atmosphere. In contrast, the STG (30°-43°N) reveals up to 50‰ enriched water reflecting limited carbon uptake from the atmosphere. Thus this layer will act as a source of radiocarbon to the polar seas and atmosphere in the near future. Below, between 1000 and 2000 m water masses north of the AF reveal a nearly homogeneous Δ14C value of -10‰ with a moderate decreasing trend with depth. South of the AF Δ14C values show a strong decrease with depth from 0 to -75‰, hence water masses remain still little affected by the advection of bomb radiocarbon (thus anthropogenic carbon). Thus, as expected the AF and the mid-depth gyre play a crucial role in distributing carbon throughout the east Atlantic.

How to cite: Frank, N., Miltner, M., Therre, S., Lausecker, M., Tisnerat-Laborde, N., Montagna, P., and Friedrich, R.: The modern Northeast Atlantic Radiocarbon Content viewed along a basin transect from 29°- 61°N, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13803,, 2020.