Other things related to sealevel data: [[,sealevel-method,
  [[<-,sealevel-method,
  as.sealevel,
  plot,sealevel-method,
  read.sealevel,
  sealevel-class,
  sealevelTuktoyaktuk,
  sealevel,
  summary,sealevel-method
Other functions that subset oce objects: subset,adp-method,
  subset,adv-method,
  subset,amsr-method,
  subset,argo-method,
  subset,cm-method,
  subset,coastline-method,
  subset,ctd-method,
  subset,echosounder-method,
  subset,lobo-method,
  subset,met-method,
  subset,oce-method,
  subset,odf-method,
  subset,rsk-method,
  subset,section-method,
  subset,topo-method