Fig. 4: Schematic representation of the atmospheric and oceanic processes for different large-scale climate conditions that affect LLWBC transport.
From: Increased tropical South Pacific western boundary current transport over the past century
a, The STCs (blue arrows), Walker circulation (black arrows), Hadley circulation (orange arrows) and the LLWBC in the South Pacific (red arrow) are coupled processes. Green shadings represent the amount of nutrient upwelled and remaining at the surface of the CEP and EEP. b, The positive phase of the PDO is associated with a weaker Walker circulation, reduced equatorial winds and accompanied by weaker oceanic overturning circulation, flattened thermocline tilt and weaker upwelling in the CEP and EEP. The weaker trade winds, if not accompanied by changes in the subtropics, generate negative wind stress curl in the South Pacific, strengthening the LLWBC by Sverdrup transport. c, Schematic representation of projected changes associated with anthropogenic warming. Although the projected weakening in the Walker circulation and slowdown of the STCs are evident in most climate models, confidence in these projections is low (as indicated by dashed arrows) because of inconsistent signals in observations and model biases. Observations and models show a southward expansion of the Hadley cell and strengthening in the Southeasterly trade winds in the South Pacific39, which would work to intensify the LLWBC transport40 as suggested by the long-term decline in the Solomon Sea CS-δ15N. Maps are generated with Ocean Data View50.
