The Bottom Of The Ocean Is Sinking
As most of us know, the world’s ice is melting and steadily flowing into the planetary ocean. And based on computer models, this influx of water should raise the overall sea level by several feet above what it currently is.
Nevertheless, one variable seems to have been overlooked, or not anticipated to its realistic degree. And that variable is the fact that the sea bottom is actually sinking due to the increasing weight of the excess water.
“The Earth itself is not a rigid sphere, it’s a deforming ball,” geoscientist Thomas Frederikse from the Delft University of Technology in the Netherlands told Earther. “With climate change, we do not only change temperature.”
According to the science team, this development has an implication that can distort future scientific discoveries about the subject. Sattelite observations can only tell us part of the story, the geocentric sea level rise, to be more exact.
“[B]ecause satellite altimetry observes sea level in a geocentric reference frame, global mean sea-level estimates derived from altimetry will not observe the increase in ocean volume due to ocean-bottom subsidence, and hence, they may underestimate [global mean sea-level] rise,” the researchers explain in a new paper.
To quantify how much the bottom of the sea is deforming under the extra load of meltwater, the researchers used various estimates of mass loss from glaciers, the Greenland and Antarctic ice sheets, and land water storage, including groundwater depletion and dam retention.
According to the calculations, over the past two decades, from 1993 to 2014, the seabed has subsided by about 0.13 mm per year. In total, there has been a 2.5 mm subsidence of the sea floor over this period. Now, even though that doesn’t seem like much, we have to keep in mind that the ocean floor is vast. What’s more, this distortion isn’t uniform either. In some places, such as the Arctic Ocean the depression is of 1 mm per year or the South Pacific with 0.4 mm per year.
“In a future warming climate, the sea-level rise induced by ice sheets will increase, and therefore, the magnitude of the bias due to elastic ocean-bottom deformation will grow,” the team writes.
“To increase the accuracy of sea-level estimates, the effect of ocean-bottom deformation should be taken into account, either based on modeled estimates of ocean mass change, as was done in this study, or using more direct observations.”