There may exist proxies for salinity, but to date the main way that salinity has been measured has been by directly measuring chlorinity in pore fluids. Adkins et al. (2002) used pore fluid chlorinity in ODP cores, with the paleo-depth estimated from nearby coral horizons. Chlorinity was measured rather than pure salinity because the major ions in seawater are not constant with depth in the sediment column; for example, sulfate reduction and cation-clay interactions can change overall salinity, whereas chlorinity is not heavily affected.