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Climate models suggest major changes in coastal marine ecosystems

by Greg St. Martin

Cli­mate change over the 21st cen­tury will sig­nif­i­cantly alter an impor­tant oceano­graphic process that reg­u­lates the pro­duc­tivity of fish­eries and marine ecosys­tems, according to an inter­dis­ci­pli­nary research team led by North­eastern University.

The researchers’ analysis of an ensemble of models indi­cates that by the end of the cen­tury, coastal upwelling—a process by which deep, cold and nutrient-​​rich water rises to the surface—will begin ear­lier, end later, and increase in inten­sity at higher lat­i­tudes. This will result in a sig­nif­i­cant decrease in the existing lat­i­tu­dinal vari­a­tion in coastal upwelling, which is likely to influ­ence the geo­graph­ical dis­tri­b­u­tion of marine bio­di­ver­sity on a global scale.

The team’s find­ings are reported in a paper to be pub­lished in the Feb. 19 issue of the journal Nature. The paper was pub­lished online Wednesday.

It’s crit­i­cally impor­tant to under­stand how coastal upwelling might change in a warming cli­mate,” said co-​​author Auroop Gan­guly, a cli­mate change expert at North­eastern. He noted that this study is the first to iden­tify a con­sis­tent pat­tern of inten­si­fi­ca­tion and spa­tial homog­e­niza­tion of coastal upwelling under green­house warming in the latest gen­er­a­tion of cli­mate models.

Tarik Gouhier

Asst. Professor Tarik Gouhier

The North­eastern research team com­prised Gan­guly, an asso­ciate pro­fessor in the Depart­ment of Civil and Envi­ron­mental Engi­neering; Tarik Gouhier, an assis­tant pro­fessor in the Depart­ment of Marine and Envi­ron­mental Sci­ences at Northeastern’s Marine Sci­ence Center; and Daiwei Wang, a post­doc­toral researcher in Ganguly’s lab. Bruce A. Menge, a pro­fessor in the Depart­ment of Inte­gra­tive Biology at Oregon State Uni­ver­sity, also col­lab­o­rated on this research and co-​​authored the paper.

We focused on these upwelling changes that are robust and con­sis­tent across models and geo­graph­ical regions because they are most likely a con­se­quence of global cli­mate change,” said Wang, the study’s lead author.

This work dove­tails with Northeastern’s com­mit­ment to inter­dis­ci­pli­nary research that addresses global chal­lenges in sus­tain­ability by bringing together two research labs whose pur­suits are inter­twined. Gan­guly directs Northeastern’s Sus­tain­ability and Data Sci­ences Lab­o­ra­tory, which studies weather extremes, water sus­tain­ability, and marine or urban ecology under cli­mate change as well as the resilience of crit­ical infra­struc­tures and life­lines under nat­ural or man-​​made haz­ards. Gouhier’s lab focuses on devel­oping dynam­ical models to under­stand how eco­log­ical and envi­ron­mental processes occur­ring at dif­ferent scales and levels of orga­ni­za­tion interact to shape the spa­tiotem­poral dis­tri­b­u­tion of marine bio­di­ver­sity in an era of global change.

This crossover research in cli­mate and marine processes clearly demon­strates the power of the inter­dis­ci­pli­nary research occur­ring here at North­eastern,” said Nadine Aubry, dean of the Col­lege of Engi­neering. “Drs. Gan­guly, Wang, and Gouhier are pro­viding key insights into the chal­lenges and adap­ta­tion of our planet’s ecosys­tems, and I look for­ward to Northeastern’s con­tinued impact in this crit­i­cally impor­tant area.”

The col­lab­o­ra­tion between Auroop, Tarik, and their col­leagues epit­o­mizes the inter­dis­ci­pli­nary approach needed to address the major issues facing our envi­ron­ment,” added Geoff Trussell, director of the Marine Sci­ence Center and pro­fessor and chair of the Depart­ment of Marine and Envi­ron­mental Sci­ences. “The Urban Coastal Sus­tain­ability Ini­tia­tive at North­eastern Uni­ver­sity embraces and pro­motes this type of col­lab­o­ra­tion and is what brought this team together. By bringing both unique and over­lap­ping per­spec­tives to these issues, these sci­en­tists have pro­duced key insights.”

Wang, whose back­ground is in cli­mate dynamics and phys­ical oceanog­raphy, found his sci­en­tific and com­pu­ta­tional exper­tise put to good use in this inter­dis­ci­pli­nary study. “The lead­er­ship and ability to bridge cli­mate and marine sci­ences demon­strated by Daiwei in this research have been exem­plary, showing what can be accom­plished through inter­dis­ci­pli­nary training,” added Ganguly.

The researchers exam­ined four upwelling cur­rent sys­tems found in the Atlantic and Pacific oceans. While these four sys­tems cover less than 2 per­cent of the ocean’s sur­face, they con­tribute more than 20 per­cent of the global fish catches. Citing their analysis of cli­mate models, the researchers pro­jected the upwelling season would expand by sev­eral days per decade between 1950 and 2099 at high lat­i­tudes in all four systems.

What’s more, they found notice­able dif­fer­ences between the Northern and Southern hemi­spheres. The two Southern Hemi­sphere sys­tems showed larger and more con­sis­tent trends than the two Northern Hemi­sphere sys­tems. Still, “despite regional dif­fer­ences, the length­ening of the upwelling season at high lat­i­tudes in [the four sys­tems] is a robust global response to green­house warming,” they wrote.

Upwelling, Gouhier explained, is an impor­tant process that drives the avail­ability of nutri­ents in the marine food web. Upwelling pro­motes nutrient avail­ability, which makes phy­to­plankton more abun­dant. Zoo­plankton then feed off phy­to­plankton, and fish feed off zoo­plankton. Increased upwelling in higher lat­i­tudes would pro­mote more pro­duc­tive fish­eries and marine ecosys­tems. How­ever, the researchers warned that having too many nutri­ents cycling through a marine ecosystem could lead to hypoxic con­di­tions, or “dead zones,” over large swaths of the coastal ocean. These are regions where the over­abun­dance of nutri­ents thrust bac­teria into hyper-​​drive and the resulting meta­bolic activity causes a reduc­tion of the con­cen­tra­tion of oxygen in the water, which can lead to mass die-​​offs.

Simply put, too much of a good thing can be really bad,” Gouhier said.

Coastal upwelling hap­pens year-​​round at loca­tions closer to the equator, but its dura­tion and inten­sity is reduced at higher lat­i­tudes. How­ever, if coastal upwelling becomes stronger and more per­sis­tent at higher lat­i­tudes, as the models sug­gest, then there will be a reduc­tion in the existing lat­i­tu­dinal vari­a­tion in coastal upwelling, which may gen­erate a con­comi­tant reduc­tion in of marine bio­di­ver­sity. In other words, the com­po­si­tion of marine com­mu­ni­ties at high and low lat­i­tudes will become more similar.

This could put species in greater com­pe­ti­tion with each other and create more species turnover in the coastal ocean, the researchers said. As a result, hotspots where upwelling changes are occur­ring should be closely mon­i­tored to ensure the sta­bility and pro­duc­tivity of fish­eries and coastal ecosystems.

The research team’s work was funded by grants from North­eastern University’s Inter­dis­ci­pli­nary Research Pro­gram and the National Sci­ence Foundation’s Expe­di­tions in Com­puting program.

Originally posted in news@Northeastern on February 18, 2015.

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