Major Shifts in North Atlantic Ecosystems Driven by 'Unprecedented' Climate Change in Last Half-Century

The last half-century has witnessed the most dramatic climate-induced ecosystem-level shifts since the advent of human civilization, almost 5,000 years ago, posits a new study published in the November issue of Ecology. Charles Greene, its lead author and an oceanographer at Cornell University, says that current and projected rates of global warming are "unprecedented" in human history and that we could very well see very rapid periods of intense warming in the near future -- rivaling the episodes of rapid cooling, during which temperatures dropped by up to 18°F (10°C) over a period of years to decades. (These drastic shifts, or "abrupt" climate changes, could be precipitated by tipping points, such as the mass release of methane from thawing permafrost regions, according to some researchers.)Large slugs of cold Arctic water drove the shifts
The release of large amounts of cold, low-salinity water into the North Atlantic from melting Arctic ice sheets and glaciers may have caused the most dramatic changes, Greene believes. One example is the introduction of a microscopic algal species from the Pacific Ocean (which has not been seen in the North Atlantic for more than 800,000 years); though it only crossed over the Arctic Ocean a little over a decade ago, it has already spread throughout the North Atlantic region. (Algae are notorious invasive species, and this is probably one of many similar examples.)

Greene and his colleagues did discover that their findings ran counter to many previously widely accepted assumptions. For instance, ecologists had assumed that most species would move northward to seek refuge in cooler areas as the climate warmed; instead, as the colder Arctic waters flowed south all the way to North Carolina, they observed that many northern species actually moved southward.

Ecosystem changes created new "winners" and "losers"
The presence of cooler waters also extended the growth periods of phytoplankton (cooler waters are typically rich in nutrients), which could sometimes alter trophic level dynamics (resulting in new "losers" and "winners") by introducing a more durable food source. Atlantic cod stocks, which had already been overfished, may have failed to recover in part because of the introduction of colder Arctic waters, which inhibited their growth and reproduction cycles. That, coupled with the arrival of more resilient crustacean species, like the snow crab and shrimp, likely did them in, Greene says.

Is this only the beginning?
Reading this study, I couldn't help but think of the larger potential threat posed by the mass melting of ice sheets and glaciers in Greenland and the Arctic Ocean: namely, the shutdown of the ocean conveyor belt (which could effectively precipitate another ice age). While it is certainly premature to consider this a possibility -- most scientists seem to think it is unlikely to happen -- Greene's study, and others in the same mold, make me worry about all of the climate's intangibles.

Via: ScienceDaily: 'Unprecedented' Warming Drives Dramatic Ecosystem Shifts In North Atlantic, Study Finds
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Tags: Oceans