Water visibility record robust after 3 centuries



Gieskes et al.1 encountered very clear water on October 13, 1986, in a coastal polynya in the eastern Weddell Sea; they recorded a Secchi disc visibility of 79 m at 14.45 UT at 71°23.63'S, 15°02.52'W. They claimed to have “shattered” the “world record” of Berman et al.2 of 53 m in the Mediterranean Sea. They postulated that Secchi disk values in distilled water would be close to 80 m, suggesting that their observation would be the ultimate record. We wish to comment on the record and on maximum Secchi disk values that are possible.