Two systematic biases have been discovered in the ocean temperature data used in “Recent cooling of the upper ocean” by John M. Lyman, Josh K. Willis, and Gregory C. Johnson (Geophysical Research Letters, 33, L18604, doi:10.1029/2006GL027033). These biases are both substantially larger than sampling errors estimated by Lyman et al. , and appear to be the cause of the rapid cooling reported in that work.
 Most of the rapid decrease in globally integrated upper (0–750 m) ocean heat content anomalies (OHCA) between 2003 and 2005 reported by Lyman et al.  appears to be an artifact resulting from the combination of two different instrument biases recently discovered in the in situ profile data. Although Lyman et al.  carefully estimated sampling errors, they did not investigate potential biases among different instrument types. One such bias has been identified in a subset of Argo float profiles. This error will ultimately be corrected. However, until corrections have been made these data can be easily excluded from OHCA estimates (see http://www.argo.ucsd.edu/ for more details). Another bias was caused by eXpendable BathyThermograph (XBT) data that are systematically warm compared to other instruments [Gouretski and Koltermann, 2007]. Both biases appear to have contributed equally to the spurious cooling.