While some scientists have pointed to the decline of cod from overfishing as the main reason for the shifting ecosystems, the article emphasizes that climate changes are also playing a big role.
"It is becoming increasingly clear that Northwest Atlantic shelf ecosystems are being tested by climate forcing from the bottom up and overfishing from the top down," said Charles Greene, director of the Ocean Resources and Ecosystems Program in Cornell's Department of Earth and Atmospheric Sciences. "Predicting the fate of these ecosystems will be one of oceanography's grand challenges for the 21st century."
Most scientists believe the planet is being warmed by greenhouse gases emitted in the burning of fossil fuels, and by changing land surfaces. Early signs of this warming have appeared in the Arctic: Since the late 1980s, scientists have noticed that pulses of fresh water from increased precipitation and melting of ice on land and sea in the Arctic have flowed into the North Atlantic Ocean and made the water less salty.
At the same time, climate-driven shifts in Arctic wind patterns have redirected ocean currents. The combination of these processes has led to a freshening of seawater along most of the Northwest Atlantic shelf.
In the past, during summer months, a wind-mixed layer of warmer, less salty water (which is less dense and lighter) floated on the ocean surface. When the air temperature cooled during autumn, temperature and density differences lessened between the surface mixed layer and the cooler, saltier waters below. Similar to the flow of heating and cooling wax in a lava lamp, as the density differences became smaller, mixing between the layers typically increased and the surface mixed layer deepened.
But, Greene cites recent scientific studies that reveal the influx of fresh water from Arctic climate change is keeping the surface mixed layer relatively shallow, curbing its rapid deepening during autumn. A gradual rather than rapid deepening of the surface mixed layer has led to changes in the seasonal cycles of phytoplankton (tiny free-floating plants like algae), zooplankton (tiny free-floating animals like copepods) and fish populations that live near the surface, according to the report.
Without the fall deepening of the surface mixed layer, phytoplankton populations have continued access to daylight needed for growth, and their numbers have stayed abundant throughout the fall. In turn, zooplankton, which feed on the phytoplankton, have increased in number during the fall through the early winter. Herring populations also rose during the 1990s, which some scientists suspect may be because of the abundance of zooplankton to feed on.
At the same time, Greene's article cites how the collapse of the cod populations in the early 1990s has led to increases in bottom-living species such as snow crab and shrimp that cod feed on. Without cod preying on them, other animals that live in the water column and feed on zooplankton, including herring, may have increased in numbers. But, while the story with herring is still unclear, the authors contend that the crash of cod populations does not fully explain why phytoplankton and zooplankton populations at the base of the food chain have risen during autumn.
"We suggest that, with or without the collapse of cod, a bottom-up, climate driven regime shift would have taken place in the Northwest Atlantic during the 1990s," Greene said.
Andrew Pershing, an oceanographer who recently moved from Cornell to the University of Maine and Gulf of Maine Research Institute, co-authored the article.
Press Relations Office | EurekAlert!
Value from wastewater
16.08.2017 | Hochschule Landshut
Species Richness – a false friend? Scientists want to improve biodiversity assessments
01.08.2017 | Carl von Ossietzky-Universität Oldenburg
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
18.08.2017 | Life Sciences
18.08.2017 | Physics and Astronomy
18.08.2017 | Materials Sciences