EGU2020-9395, updated on 12 Feb 2021
https://doi.org/10.5194/egusphere-egu2020-9395
EGU General Assembly 2020
© Author(s) 2021. This work is distributed under
the Creative Commons Attribution 4.0 License.

Unravelling the North Alantic ‘nutrient stream’ variability

Lidia I. Carracedo1,2, Elaine McDonagh2,3, Richard Sanders2,3, Edward Mawji2, Sinhué Torres-Valdés4, Molly Baringer5, Herlé Mercier6, and Virginie Thierry1
Lidia I. Carracedo et al.
  • 1IFREMER, Laboratoire d'Océanographie Physique et Spatiale, Plouzané, France (lcarrace@ifremer.fr)
  • 2National Oceanography Centre (NOC), Southampton SO14 3ZH, UK
  • 3NORCE, Norwegian Research Centre, Bjerknes Centre for Climate Research, Nygårdsgaten 112, 5008 Bergen, Norway
  • 4Alfred Wegener Institute, Am Handelshafen 12, 27570 Bremerhaven, Germany
  • 5NOAA/AOML/PHOD, 4301 Rickenbacker Causeway, Miami, FL 33149, USA
  • 6Centre National de la Recherche Scientifique (CNRS), Ifremer, Université de Brest, Institut de Recherche pour le Développement (IRD), LOPS, Centre Ifremer de Bretagne, 29280, Plouzané, France

The Florida Current (FC), upstream extension of the Gulf Stream, is a very intense current (~32 Sv) confined to a 800-m depth narrow passage off the east coast of Florida. Associated with an intense poleward (subsurface maximum) transport of nutrients, this current has earned the name of North Atlantic ‘nutrient stream’. Since the biological sequestration of carbon (namely the Biological Carbon pump, BCP) is limited by the presence of nutrients in the upper ocean (euphotic zone), the FC can be seen as precursor of the nutrient induction process downstream feeding the subtropical gyre productivity. However, the relevance of this current is not only limited to its interplay with the subtropical gyre. The FC also comprises the bulk of the warm upper limb of the meridional overturning circulation reaching subpolar latitudes. Therefore, disentangling the range of intra-annual variability of the nutrient transport by the FC is crucial to better understand its linkage to and influence on the BCP magnitude and efficiency at higher latitudes. Based on a high-quality nutrient and velocity dataset from repeated hydrography between May 2015 and Oct 2018, we present an analysis of the nutrient transport by the FC in its 3 main water masses (the surface water, upper thermocline water and lower thermocline water). Our results show that the transport of inorganic nutrients is dominated by the upper and lower thermocline waters, whose transport-weighted nutrient concentration reaches a maximum in winter. Conversely, the transport of organic nutrients is dominated by the surface and upper thermocline waters, peaking in spring and autumn. Inorganic transport-weighted nutrient concentrations strongly correlate with volume transport. The correlation is positive in the surface water and the lower thermocline water (of South Atlantic origin), whereas it correlates negatively in the lower thermocline water (North Atlantic recirculated water). This indicates a southern remote source for the inorganic nutrient supply, which is mainly driven by advection. Organic nutrients, however, do not show a clear correlation with volume transport. Only the upper thermocline water shows a certain positive correlation, confirming the North Atlantic subtropical gyre as a main source of organic nutrients, ultimately driven not only -nor mainly- by circulation, but also by biological activity upstream.

How to cite: Carracedo, L. I., McDonagh, E., Sanders, R., Mawji, E., Torres-Valdés, S., Baringer, M., Mercier, H., and Thierry, V.: Unravelling the North Alantic ‘nutrient stream’ variability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9395, https://doi.org/10.5194/egusphere-egu2020-9395, 2020

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