On the climate impacts of atolls in the central equatorial Pacific

摘要

Contrary to the above title, a more typical question might be 'How does climate variability and change impact atolls (and associated ecosystems and civilizations)?' While several studies have focused on the effects of island topography on local circulation, equatorial currents and their dynamics play a vital role in the tropical heat balance and therefore global climate through atmospheric teleconnections. The Gilbert Islands, which straddle the equator in the western Pacific, block 55% of the corridor between 2 degrees S and 2 degrees N. Here we explore the potential role of relatively small open-ocean topographic features, in particular equatorial atolls such as the Gilbert Islands, on the large-scale climate system. Observations and high-resolution ocean model simulations spanning the full width of the Pacific basin indicate that, whereas the Gilbert Islands have only a local impact on the Equatorial Undercurrent (EUC), the South Equatorial Current (SEC) is substantially reduced downstream of the islands, resulting in a surface warming and freshening over a similar to 1000-km wide region along the sharp temperature and salinity front defining the eastern edge of the Indo-Pacific warm pool (IPWP), the heat engine that is a critical player in global climate processes. The simulated mean thermohaline structure in the central and western Pacific, which has previously been shown to be crucial for El Nino-Southern Oscillation (ENSO) dynamics, is improved by including the Gilbert Islands. Implications for coupled model biases, ENSO simulation and paleoclimate are discussed.