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.

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.

Auroop Ganguly is an associate professor in the Department of Civil and Environmental Engineering, and he directs the directs Northeastern’s Sustainability and Data Sciences Laboratory. Northeastern University photo.

Auroop Gan­guly is an asso­ciate pro­fessor in the Depart­ment of Civil and Envi­ron­mental Engi­neering, and he directs the directs Northeastern’s Sus­tain­ability and Data Sci­ences Lab­o­ra­tory. North­eastern Uni­ver­sity photo.

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.

Tarik Gouhier is an assistant professor in the Department of Marine and Environmental Sciences at Northeastern’s Marine Science Center. Photo by Brooks Canaday/Northeastern University.

Tarik Gouhier is an assis­tant pro­fessor in the Depart­ment of Marine and Envi­ron­mental Sci­ences at Northeastern’s Marine Sci­ence Center. Photo by Brooks Canaday/​Northeastern University.

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.