Climatic trends of the equatorial undercurrent: A backup mechanism for sustaining the equatorial Pacific production

The Equatorial Undercurrent (EUC) is the major source of iron to the equatorial Pacific and it is sensitive to
climatic changes as other components of the tropical Pacific. This work proposes a methodology based on a
Lagrangian approach aimed at understanding the changes in the transport of iron rich waters to the EUC in
a future climate change scenario, using climate model data from an Earth system model. A selected set of
regions from the northern and southern extra-equatorial Pacific has been chosen. These regions are charac-
terized by the presence of iron sources from continental shelf processes like the Papua New Guinea region
and atmospheric deposition like the northern subtropical gyre. The trajectories that reach the EUC during
the 20th and the 21st century departing from these areas have been analyzed using a set of statistics designed
to determine variations in the amount of transport and in the travel times of the water masses. The transport
of waters to the EUC from the north Pacific subtropical gyre and from the Bismarck Sea is projected to
increase during the 21st century. The increase is particularly significant for water masses from the northern
subtropical gyre, with travel times lower than 10 years in the second half of the 21st century. This increased
interaction between the extra-tropics and the EUC may bring additional iron-rich waters in the high-nutrient
low-chlorophyll region of the equatorial Pacific compatibly with the significant increase of the simulated net
primary production found in the biogeochemical model, thus partly offsetting the anticipated decrease of
production implied by the surface warming

This work was funded by the Centro Euro-Mediterraneo per i Cambiamenti Climatici through the GEMINA project.

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