Tatoosh observations link acidification to a shrinking silicon supply
Long coastal observations around Tatoosh Island connect lower seawater pH with declining dissolved silicon relative to nitrogen and lower chlorophyll concentrations. The peer-reviewed observational study supports a proposed link between acidification, slower silica recycling and the nutrients available to diatoms. Tests of water mixing and river inputs did not explain the pattern, while food-web effects remain harder to separate.
Science··Evening
Coastal nutrients declined alongside pH
A long observational series around Tatoosh Island off Washington in the United States links seawater acidification with a shrinking silicon supply. In the peer-reviewed study, the molar ratio of dissolved silicon to inorganic nitrogen had an average logarithmic value of about 0.28 initially and 0.13 later, a decline of about 56 per cent. Nutrient analysis covered 24 annual means and 1,364 individual measurements. Chlorophyll concentrations also declined in this productive coastal system.[1]
Silica recycling may slow
Diatoms are microscopic organisms that use dissolved silicon to build silica structures around their cells. When dead cells’ shells dissolve, silicon becomes available again. Lower pH can slow this dissolution, leaving more silica to settle out of the water. The researchers interpret the joint declines as support for this proposed silicon-loss mechanism. The observational association in one coastal system does not establish the same causal response throughout the oceans.[1]
Water transport checks left the association intact
The analysis considered wind-based upwelling indices, salinity and nearby river discharge. Adjusting for these factors left both the falling silicon-to-nitrogen ratio and the link to pH in place. Water-source mixing models likewise found that varying the shares of the source waters was insufficient on its own.[1]
Chlorophyll indicates phytoplankton abundance rather than counting all species or measuring all production. Grazing within the food web can also change that abundance. A zooplankton-grazing series spanning the whole study was unavailable, leaving the unequal changes in chlorophyll and nutrient concentrations incompletely explained.[1]
