Study reveals causes for freshwater increase in oceans

A new analysis of 50 years of changes in freshwater inputs to the Arctic and North Atlantic oceans may shed light on what’s behind the recently observed increase in freshwater in the North Atlantic. University of Texas at Austin marine scientist Dr. Jim McClelland and his colleagues report their findings in the Aug. 25 issue of the journal Science.

The first-of-its-kind, big-picture effort reveals that freshwater increases from Arctic Ocean sources—rivers, ice melt and precipitation—appear to be highly linked to a fresher North Atlantic.

“Our synthesis shows that the amount of excess freshwater coming into the oceans matches up with the amount of excess freshwater that’s being stored there,” says McClelland, assistant professor at the Marine Science Institute in Port Aransas, Texas. “Normally, oceanographers would think these changes in freshwater storage are associated with changes in ocean circulation and mixing patterns, but this shows that rivers, ice melt and precipitation have a large influence.”

Scientists contend that a significant increase of freshwater flow to the Arctic Ocean could alter global ocean circulation and influence the planet’s climate. One of the potential effects could be a cooling of Northern Europe within this century.

“The high-latitude freshwater cycle is one of the most sensitive barometers of the impact of changes in climate and broad-scale atmospheric dynamics because of the polar amplification of the global warming signal,” says Dr. Bruce Peterson, senior scientist at Marine Biological Laboratory (MBL). “It’s easiest to measure these changes in the Arctic and the better we understand this system, the sooner we will know what is happening to the global hydrologic cycle.”

The multidisciplinary team of scientists led by Peterson calculated annual and cumulative freshwater input for the latter half of the 20th century. The scientists compared the fluxes to measured rates of freshwater accumulation in the North Atlantic during the same time period.

They found that increasing river discharge and excess net precipitation on the ocean contributed the most freshwater (about 20,000 cubic kilometers) to the Arctic and high-latitude North Atlantic. Sea ice reduction provided about 15,000 cubic kilometers of freshwater, followed by about 2,000 cubic kilometers from melting glaciers.

The sum of inputs from all of the freshwater sources analyzed matched the amount and rate at which freshwater accumulated in the North Atlantic during much of the period from 1965 through 1995.

“This synthesis allows us to judge which freshwater sources are the largest, but more important shows how the significance of different sources have changed over the past decades and what has caused the changes,” says Peterson.

In recent years, much attention has been given to the observed freshening of the Arctic Ocean and North Atlantic and the potential impacts it may have on the Earth’s climate. Models predict that a significant increase of freshwater flow to the Arctic Ocean could slow or halt the Atlantic Deep Water formation, a driving factor behind the great “conveyor belt” current that is responsible for redistributing salt and thermal energy around the globe, influencing the planet’s climate.

“We’re observing changes that climate change scientists have been modeling for a while,” adds McClelland, “particularly those scientists that have been modeling increased net precipitation in response to global warming.”

“Theory is meeting reality and that’s a major, exciting aspect to this work.”

Source: University of Texas at Austin

Related stories:

Signals from the Atlantic salmon highway
For years scientists have struggled to understand the decline and slow recovery of Atlantic salmon, a once abundant and highly prized game and food fish native to New England rivers. Biologists agree that poor marine survival is affecting salmon in the U.S. and Canada, but specific causes are difficult to determine in the ocean. Small acoustic tags and associated technology may provide some answers.
Freshwater runoff from the Greenland Ice Sheet will more than double by the end of the century
The Greenland Ice Sheet is melting faster than previously calculated according to a recently released scientific paper by University of Alaska Fairbanks researcher Sebastian H. Mernild.
Changes in Ocean Conditions in Sargasso Sea Potential Cause for Decline in Eel Fishery
American eels are fast disappearing from restaurant menus as stocks have declined sharply across the North Atlantic. While the reasons for the eel decline remain as mysterious as its long migrations, a recent study by a NOAA scientist and colleagues in Japan and the United Kingdom says shifts in ocean-atmosphere conditions may be a primary factor in declining reproduction and survival rates.
Tipping elements in the Earth's climate system
Anthropogenic forcing could push the Earth’s climate system past critical thresholds, so that important components may “tip” into qualitatively different modes of operation. In the renowned magazine Proceedings of the National Academy of Sciences (PNAS) an international team of researchers describes, where small changes can have large long-term consequences on human and ecological systems.
Present-day species of piranha result from a marine incursion into the Amazon Basin
Piranhas inhabit exclusively the fresh waters of South America. Their geographical distribution extends from the Orinoco River basin (Venezuela) to the North, down to that of the Paraná (Argentina) to the South. Over this whole area, which also embraces the entire Amazon Basin, biologists have recorded 28 carnivorous species of these fish. In spite of the evolutionary success of this subfamily of fish, the mechanisms that generated the species richness of this group are still insufficiently known.
The sea ice is getting thinner
Large areas of the Arctic sea-ice are only one metre thick this year, equating to an approximate 50 percent thinning as compared to the year 2001. These are the initial results from the latest Alfred-Wegener-Institute for Polar and Marine Research in the Helmholtz Association lead expedition to the North Polar Sea.
Call for network to monitor Southern Ocean current
The senior science advisor to the World Climate Research Programme (WCRP) has called for the establishment of a Southern Hemisphere network of deep ocean moorings to detect any change in ocean circulation that may adversely influence global climate.

Research shows Australian weather could get worse
Research by University of Queensland climatologists into Australia's past climate has shown just how extreme our weather can be.

News discussion:

Space & Earth science news