UMass Dartmouth researchers recently received a total of $1 million in National Science Foundation funding to examine the effects of climate change on marine ecosystems and the environmentally sensitive area where rivers mix with the ocean.
$450,000 for study of atmospheric phenomenon
Oceanographers Drs. Avijit Gangopadhyay and James Bisagni have been awarded $450,000 by the National Science Foundation to investigate the effects of climate change on marine ecosystems.
The two scientists, who hold joint appointments in the Physics Department and the School for Marine Science and Technology (SMAST), will use computer models and ocean observations to study the effects of the North Atlantic Oscillation (NAO) on marine life. The NAO is an atmospheric phenomenon that is responsible for much of the weather and climate variation over the North Atlantic and surrounding continents.
"Everybody has heard of El Niño and how it affects weather around the globe," said Gangopadhyay, who is leading the project. "The North Atlantic Oscillation also has far-reaching effects on weather and climate, from eastern North America to eastern Asia, but it hasn't received the same degree of press coverage."
The NAO is a kind of atmospheric "seesaw" between two pressure centers over the North Atlantic--one over Iceland and the other over the Azores. Each pressure center is the center of a wind system, and changes in the pressure centers modulate winds as well as the intensity, frequency, and pathways of storms.
Year-to-year variations in the NAO explain much of the year-to-year variation in weather both here and in Europe--for example, why we may face a cold, dry winter one year, and a warm, wet winter the next. Longer-term NAO variation is responsible for more enduring phenomena, such as the so-called "cold 1960s" and "warm 1980s," memorable stretches that are well documented in weather records as well as in personal anecdotes.
"Our family dentist told me that he actually moved from Massachusetts to California in the 1960s because it was too cold here," Gangopadhyay recalls. "Then he came back in the 80s, when he heard it had warmed up."
These fluctuations affect not only the lives of dentists, but also the lives of marine species. Gangopadhyay and Bisagni are targeting a type of small crustacean called a copepod to model the NAO's effects on marine ecosystems.
Copepods are the most numerous multi-celled creatures in the oceans, and a large part of the marine food web. Their response to climate change will, in turn, affect the response of the other forms of marine life that depend on them, directly or indirectly, including species of commercially important finfish.
"Understanding long-term variability in the oceans is crucial to sound ecosystem-based fisheries management," Gangopadhyay said. "Management strategies that work well under one NAO regime may fail under a different regime."
The project is part of the GLOBEC (Global Ocean Ecosystems Dynamics) program, a decade-long study of marine ecosystems and how they respond to changes in their physical environment. GLOBEC was launched in response to accumulating evidence of climate shifts in Earth's history and the possibility of a coming climate shift caused at least in part by human activities.
$550,000 for study of river/ocean intersection
Prof. Daniel MacDonald of the UMass Dartmouth School for Marine Science and Technology (SMAST) and Prof. Robert Hetland of Texas A&M University have received $550,000 from the NSF to support their three-year investigation of the little understood "near-field" region of a river plume.
"Ultimately, all river water is mixed completely into the ocean," MacDonald said. "It's how and where that mixing occurs that has implications for the forcing of coastal currents, as well as for the ultimate fate of all the things carried by river water that we might care about, such as pollutants, nutrients, and sediments."
There is evidence of as much mixing in the first few kilometers from the river's mouth as occurs along the whole rest of the plume. This zone, known as the "near field," is "where the action is, but that's also where our physics is the least developed," MacDonald said.
Enhanced understanding of river plumes, particularly the near field region, has the potential for big payoffs. "Much of what happens in the coastal ocean is driven by river input," explains MacDonald, "so coastal modelers have to account for what's happening in the near field."
MacDonald describes a river flowing into the ocean as delivering not only fresh water, but also energy, related to the velocity of the river water at its mouth. Evidence of the fresh water input can often be seen hundreds of kilometers or more from the mouth of the river, but evidence of the enhanced velocities associated with a river plume is typically erased within five kilometers of the mouth.
MacDonald points to potential benefits in harbor management and environmental assessment and remediation. "Quantifying the turbulence in a river plume," he said, "can help us predict how and where the sediment particles will settle out, which also has a great impact on our understanding of pollutant transport, since pollutants like to attach themselves to sediment particles."
From an economic standpoint, "understanding more about the physics in these regions could help to prevent the mislocation of dredging projects as well as the placement of spoils, a potentially huge economic benefit."
MacDonald and Hetland seek to measure and model the mixing, spreading and overall evolution of the river plume within the near field. With MacDonald's expertise in overseeing field programs, he will be responsible for the field component of the study, which will focus on the mouth of the Merrimack River, in Newburyport. Hetland will manage the numerical modeling component of the study.
The turbulence that is ultimately responsible for mixing the fresh water into the background ocean waters is an elusive process, and one that is notoriously difficult to measure. Bringing various methods for measuring turbulence to the field program will be Andone Lavery of the Woods Hole Oceanographic Institution, Philip Orton of Lamont-Doherty Earth Observatory, and Lou Goodman of SMAST with his unmanned submersible vehicle T-REMUS.
Most of MacDonald's previous research on river plumes has been conducted at the mouth of the Fraser River in British Columbia. He has also been involved with field work at the mouth of the Hudson River in New York City.
He is now excited about working on a site closer to his New England roots. "I grew up in New Hampshire, and I spent a lot of time hiking along the east branch of the Pemigawasett River, which is actually the headwaters of the Merrimack," he said. "I even got engaged on the banks of the Pemi. Now, more than a decade later, I find myself at the river's mouth. There's got to be a metaphor about life in there somewhere."