Comment on “Equatorial Pacific coral geochemical records show recent weakening of the Walker circulation” by J. Carilli et al.

Carilli et al. [2014] present new geochemical proxy records of sea surface temperature (SST) and salinity spanning 1959–2010 from coral cores collected from Butaritari Atoll, Gilbert Islands, Republic of Kiribati (3.07°N, 172.75°E). The continuous measurement of SST by in situ and satellite platforms generally began in the early 1980s (e.g., the Tropical Atmosphere-Ocean array of moorings [McPhaden et al., 1998] and the Advanced Very High Resolution Radiometer infrared satellite [Reynolds et al., 2002]), and instrumental reconstructions extending back to the midnineteenth century [e.g., Smith et al., 2008] rely on sparse observational sampling both in space in time. The Carilli et al.’s [2014] records thus represent a potentially valuable addition to estimates of past climate variability in the important western tropical Pacific region, confirming the dominant role of El Niño–Southern Oscillation (ENSO). However, the conclusion that the Walker circulation has exhibited a long-term weakening trend over the last several decades is based on an interpretation of the proxy record that does not consider well-documented natural interdecadal variability and is based on trends in a proxy record that are opposite from trends in the observational record over the overlapping portion of the satellite era. In addition, Carilli et al. [2014] misinterpret the relationship between their proxy record of SST and trends in ocean circulation due to incorrect assumptions about the physical oceanographic context of Butaritari. These two issues are addressed below.