The Beginnings of Ocean Acidification Studies in Mexican Waters

The 2016 West Coast Ocean Acidification (WCOA) cruise is the fifth of its kind, and the research we are performing aboard the NOAA Ship Ronald H. Brown has been over a decade in the making. It has been eleven years since NOAA PMEL scientists Dr. Richard Feely and Dr. Chris Sabine organized the first planning meeting in 2005 for the 2007 West Coast Ocean Acidification cruise. Before this, U.S., Canadian, and Mexican researchers, led by Richard Feely, had noticed that large changes in carbonate chemistry data had taken place between 1994 and 2004 on a regularly-sampled transect line that runs from Japan to San Diego, California. The researchers found that the aragonite saturation horizon, the depth below which seawater becomes corrosive to aragonite-shelled creatures, was getting shallower in the North Pacific basin, and that these corrosive waters could be transported to the shelf during upwelling events, leaving calcifying organisms vulnerable to shell destruction.

arag saturation horizon
The aragonite saturation horizon is the depth below which shells made of aragonite, a calcium carbonate mineral, become vulnerable to weakening and dissolution.  Above the saturation horizon, there is enough carbonate in the seawater for aragonite-building organisms to maintain their shells.  Illustration: Katie Douglas

Following these results, Dr. Feely and Dr. Sabine organized the June 2007 cruise as part of the North American Carbon Project (NACP), which I participated in as a representative of Mexico. During the 2007 west coast cruise, three transect lines were sampled along Mexico’s coast: one located in the Southern California Bight; a second, located off Punta Eugenia, which several studies identify as the transition area between the California Current and subtropical waters; and the third, located in San Lazaro Bay, where sub-tropical waters are predominant. These are the same transect lines that we just resampled during the first leg of the 2016 WCOA cruise.

map_southernmost
Map showing the three transect lines sampled off the west coast of Mexico during the first leg of the cruise.  These lines are noted with numbers 1-3 on the map.  Figure: Dana Greeley

During the 2007 cruise, we observed aragonite-undersaturated seawater upwelling onto large portions of the continental shelf, reaching depths as shallow as 40–120 m (130–390 ft) along most transect lines and all the way to the surface off northern California. The results from the first line of our cruise off Mexico supported the idea that upwelling processes transport corrosive water onto the continental shelf in this region. These results also represented the first evidence that the continental shelf in Mexico is being seasonally impacted by ocean acidification.

In Baja California over the last decade, scientists have reported changes in physical conditions within the California Current System. These regional changes have been associated with larger-scale, basin-wide events, and have included the warming caused by the 1997–1998 El Niño, the 2000 La Niña event, the limited influence of a weak El Niño in 2002–2003, and a freshening (i.e., decreased salinity or “saltiness”) of the upper 100 m of the water column in 2002 and 2006. This year’s 2015–2016 El Niño is considered to be nearly as strong as the 1997–1998 El Niño event. The current El Niño event is predicted to end this summer according to NOAA’s most recent report, but we may see the “residual” effects from these El Niño conditions in our waters over the months to come.

We expect future changes in the chemistry of upwelled seawater to affect the biology of the west coast. In Mexico, Baja California’s coastal area alone contributes to as much as 20% of the nation’s commercial fishing per year. When the areas of Sonora and Sinaloa are included in this figure, the total is about 70%. Thus, the possible impact of ocean acidification on marine fisheries on the Pacific coast of Mexico may have a large economic impact on coastal fishing communities.

2007 Cruise Participants.png
Group photo of the 2007 WCOA cruise scientific party. I am in the back row, second from the left. Next to me are my friends Chris Sabine (on my left) and Richard Feely (sunglasses, no hat). Photo: Richard Feely

The 2007 west coast cruise was the beginning of ocean acidification research in Mexican waters, and that research continues today. I would like to thank the great team of researchers from NOAA PMEL – especially Richard Feely, Dr. Dr. Simone Alin, Chris Sabine, and Mr. Mr. Dana Greeley – for their great friendship and collaboration.

Written by Jose Martin Hernandez-Ayon

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