Figure F18. Downhole temperature measurements at all sites. Although temperature gradients are probably known to be better than 0.005°C/m, postcruise calibration of downhole temperature tools is needed to determine absolute temperature. Scatter in the data is greater at sites near the summit, perhaps because of the effect of gas hydrate on in situ thermal conductivity and/or to dissociation of gas hydrate as a result of insertion of the probe.