# How much does sea level rise due to sediment deposition?

There has been a lot of noise in the news in the last few days because Congressman Mo Brooks from Alabama claimed that erosion played a role in rising sea levels. Quoting from Science magazine:

Brooks then said that erosion plays a significant role in sea-level rise, which is not an idea embraced by mainstream climate researchers. He said the California coastline and the White Cliffs of Dover tumble into the sea every year, and that contributes to sea-level rise. He also said that silt washing into the ocean from the world's major rivers, including the Mississippi, the Amazon and the Nile, is contributing to sea-level rise.

"Every time you have that soil or rock or whatever it is that is deposited into the seas, that forces the sea levels to rise, because now you have less space in those oceans, because the bottom is moving up," Brooks said.

Duffy responded: "I'm pretty sure that on human time scales, those are minuscule effects."

Everywhere I have read, people just say "that man is an idiot"; but nowhere have I seen an authoritative, fact-based response to prove this.

How much does the sediment carried into the oceans by rivers contribute to the rise in sea level?

• At Cretaceous level rised because of a big activity on oceanic dorsals. I think this is just a convoluted appointment from congressman. Rivers carry sediments yes, but at basins. Basins has his own equillibrium as there is also subsidence. – Universal_learner May 19 '18 at 9:06
• It's a claim comparable to the suggestions made in 2014 that newly identified thermal "hotspots" of 114 milliwatts per square meter were melting the West Antarctic Ice Sheet; it's faintly true, but too small by orders of magnitude to account for what's happening in the modern era. – jeffronicus May 20 '18 at 1:44

In a 1983 Journal of Geology paper by Milliman and Meade, "World-Wide Delivery of River Sediment to the Oceans" (link) it is estimated that the world's rivers carry about $13.5\times 10^9$ tonnes of sediment per year. If we assume an average density of $2.5~\rm{g/cm^3}$, this corresponds to a volume of 8.8 cubic kilometers. The total surface area of the world's oceans is 360 million square kilometers. This means that the sediment of the rivers contributes to a rise in sea level of 15 µm per year, or 1.5 mm per century.

The IPCC estimated in its fifth report that the average rate of sea level rise is about 3.2 mm per year. That means that about 0.5 % of that rise could be attributed to sediment. It is certainly not a major factor, but is non-zero all the same.

• Also you need to consider that putting sediment into the oceans loads the ocean basins and causes subsidence, lowering sea level. – bon May 19 '18 at 6:58
• @bon - that means this is an upper estimate. Do you have any data on the degree to which sediments cause subsidence? The additional mass isn’t very much on a global scale - what is the coefficient of elasticity of the crust? – Floris May 19 '18 at 11:46
• Large piles of sediment can cause many kilometres of subsidence in some cases. It's a pretty common effect that is widely analysed in sedimentary basin analysis. Wikipedia gives a brief introduction to the concept. – bon May 19 '18 at 13:33
• @bon: Also plate tectonics will create areas where ocean rock is uplifted to become land. See e.g. the geology of much of California, or these nice ichthyosaur fossils in central Nevada, at an elevation of 6,975 ft/2,126 m: parks.nv.gov/parks/berlin-ichthyosaur – jamesqf May 19 '18 at 18:29

The total rise in ocean level in cubic miles is 330 cubic miles per year!! By the estimated sediment deposit of 13.5x10*9 tons per year, there is around 169 cubic miles of sediment deposited by rivers each year!! Or over 50% of the ovens rise can be associated with river deposit!! That’s not including what is put in the ocean from coastal corrosion, underwater volcanic eruptions, etc!!!!

• to put things into perspective ten cubic kilometers of ice melted from greenland today,this means ten days like this equals more mass than all the sediment added to the oceans over a whole year. – trond hansen Aug 3 at 18:08
• @trondhansen are you sure of your math? A cubic mile is a lot bigger than a cubic kilometer... – Floris Aug 3 at 18:49
• my math is off but it ilustrates the amount of sediment compared to the amount of meltwater,the melting from greenland on last wednesday was ten bilion metric tons of water. – trond hansen Aug 3 at 20:04