New research suggests short-term decreases in marine animal growth and reproduction could be linked to an increasing variability in the strength of coastal upwelling currents, which work to supply nutrients to a number of crucial ecosystems.
Along North America's west coast winds generally lift nutrient-rich water from the deep ocean to shallower waters, allowing it to promote phytoplankton blooms which feed local birds and animals, the University of Texas at Austin reported.
The study's findings suggest the region has seen winters with extremely low rates of upwelling since as far back as the 1950s, which has led to slower growth in fish and reduced reproduction in seabird populations.
"Our study underscores the fact that California is a place of high coastal upwelling variability," said Bryan Black, assistant professor of marine science and lead author on the study. "You have to keep that in mind if you're managing a fishery - for example, you can't plan for every year being moderate or reliable. There are a lot of ups and downs."
To make their findings the researchers looked at 600 years-worth of tree rings from local blue oak trees; these specimens' growth is highly sensitive to the same climate factors associated with upwelling. Their findings also relied on integrated data on how quickly fish grew every year and the timing of seabird egg laying since the 1970s and the success of their fledglings.
When the researchers compared the tree ring data with various other biological factors they found poor upwelling was linked to drops in biological productivity. Since the affected populations rebounded from years of the poorest upwelling (four out of 10 of which occurred since 1950) their population is not believed to have ultimately declined.
The researchers are unsure if climate change is to blame for this phenomenon, but it does seem to be related to be related to the El Niño-Southern Oscillation (ENSO) which is believed to have been extremely variable over the 20th century.
"This is consistent with what we expect from climate change, but at this point, we can't attribute it to that," Black said. "This is something we need to continue watching to see how climate variability plays out in the coming years."
In the future the researchers hope to gain insight into how upwelling will change in the future,
"We understand the atmospheric drivers behind winter upwelling, so now we plan to use climate models to see what they say about these drivers and whether they forecast change for those in the future," Black said.
The findings were published Sept. 19 in the journal Science.
