
Sea level rises relative to land
Sea levels have been rising for the last 10 thousand years around the coast of southern England. Near me in London, for example, water has risen relative to land by about 4.1 metres since Roman times. However, all around the south and east coast of England one can find areas where land has grown at the expense of sea since Roman times. In other words, material has been positively deposited there. Precisely how erosion and sedimentation balance out in any particular area depends on a lot of factors, notably including sea currents and silt being washed down from inland, both of which can be heavily influenced by human activity. However, as a general rule, marshy coastal estuaries tend to remain in balance at about high tide level. I have no idea how far Pacific islands are affected by the other big variable -- vertical movement in the earth's crust -- but it seems entirely plausible that some of them could be net traps for sediment and therefore net growers not shrinkers.