As Earth's glaciers melt, their runoff is helping sea levels rise rise about twice as quickly as a century ago, threatening to push the oceans up to 3 feet higher by 2100. And since nearly half of all humans now live in coastal areas, that's one of many reasons we're uneasy about the pace of climate change.

Yet melting glaciers could make life easier for some Antarctic animals, a new study finds, including icons like penguins, seals and whales. It's one thing when our efforts to curb climate change benefit us as well as wildlife — from pikas and polar bears to sea turtles and coral reefs — but what if our pain is a penguin's gain?

Published in the Journal of Geophysical Research, the study is less about penguins than phytoplankton, a motley mix of seafaring bacteria, protists and single-celled plants that all photosynthesize. They form the base of the marine food web, feeding krill and fish that in turn fall prey to larger animals (like penguins).

Fortunate phytoplankton tend to pay it forward. The tiny creatures off Antarctica may soon turn that continent's meltwater into an ecological gold rush, the study suggests, although it could lose its luster in the big picture of climate change.

types of phytoplanktonPhytoplankton are extremely diverse, with various types adapted to specific water conditions. (Image: Sally Bensusen/NASA)

Sunny outlook

Since they need sunlight, phytoplankton off Antarctica's coasts tend to congregate in "polynyas," or large, long-lasting patches of open water amid sea ice. That means polynyas often become biological hot spots, some livelier than others.

In hopes of understanding that variation, the study's authors used satellite imagery to measure the chlorophyll content of 46 polynyas around Antarctica, and then looked for environmental conditions to help explain the differences.

The conditions included sunlight, polynya size, water temperature and nutrient upwelling. Some had a significant effect on chlorophyll, but most of the variation boiled down to something else: the speed at which nearby glaciers were melting.

polynya off AntarcticaPolynyas can be created by winds or upwelling of warm water from below. (Photo: Jeff Schmaltz/NASA GSFC)

Something in the water

Why would phytoplankton like melting glaciers? The water is spiked with a key ingredient — iron — that accumulated over time as the ancient ice scraped across land and gathered windblown dust. Phytoplankton need iron to grow, and since the nutrient isn't abundant off Antarctica's coasts, glaciers may act as a "food delivery service," the researchers say, dumping iron into nearby polynyas.

This flow of iron into the ocean explains 59 percent of the chlorophyll variation among polynyas, according to the study, making meltwater a major factor in how much life a polynya can support. Polynyas that develop near the outflow of land ice likely get more iron, and those located farther offshore get less.

While Antarctica's ice sheets are not melting as dramatically as those in Greenland, they are in significant decline. After losing about 6 cubic miles of volume annually from 1991 to 2003, their rate of melting jumped in recent years — especially in West Antarctica, which lost 74 cubic miles of ice per year from 2003 to 2012.

(If you've heard people cite Antarctica's growing ice as evidence that climate change isn't real, they mean sea ice, not glaciers. Antarctic sea ice has bucked global trends lately, likely due to low ozone levels and the influx of freshwater from melting land ice. But that isn't enough to offset the decline of Arctic sea ice or global glaciers, it probably won't last, and it doesn't disprove climate change.)

Since Antarctica's glacier loss is expected to continue as Earth warms up, local phytoplankton could be on the brink of a breakthrough. "Coastal Antarctica is likely to become a more productive place in the future," lead author and Stanford University oceanographer Kevin Arrigo says in a statement about the new study.

phytoplankton closeupWhile glacier water might benefit some phytoplankton, the threat of ocean acidification looms large. (Photo: NOAA)

Acid test

That boom could also echo far beyond Antarctica, since phytoplankton sequester CO2 from seawater during photosynthesis. "These polynyas appear to be disproportionately important, for their size, as sinks of carbon," Arrigo says. "And the reality is they really are not included in anyone's carbon budget."

More carbon-storing plankton hordes would be a welcome silver lining to climate change, but as Arrigo and his co-authors point out, any benefit from busier polynyas likely pales in comparison to the overall impact of surging CO2 levels.

"[A]lthough climate change could increase the amount of iron in the polynyas, any positive effects of the additional iron may be offset by other climate change-driven environmental shifts," the American Geophysical Union (AGU) says in a news release.

The extra carbon storage would only slow down climate change at best, and probably couldn't fend off dangers to humans like longer droughts, stronger storms, rising seas and migrating disease. As for penguins, the short-term effects of climate change are muddled and vary by species. Receding land ice may be opening up more habitat for some Adélie penguins, for example, but the eventual decline of Antarctica's sea ice is expected to pose a growing threat for emperor penguins.

And even for phytoplankton itself, the extra iron from glaciers may not be worth other effects of climate change, namely ocean acidification. The pH of Earth's seawater is falling as it absorbs more and more CO2 from the air, creating acidic conditions that threaten an array of sea life. Phytoplankton can't sequester all of it, and some research suggests their carbon storage will diminish in the future anyway, as warmer water reduces the upwelling of nutrients from below.

diatoms and CO2 levelsHigher CO2 levels over the next 140 years are expected to hinder large phytoplankton like diatoms. (Image: NASA)

Ocean acidification is particularly hard on organisms that build their shells or skeletons from calcium carbonate. That includes a wide range of important sea life such as corals, oysters, clams, mussels, snails, zooplankton — and phytoplankton.

As the AGU notes, "most marine organisms will be negatively affected by global increases in ocean temperatures and acidification that are expected to happen as a result of climate change." So even if melting glaciers do enable a feast around Antarctica, it might eventually be ruined by a bad case of acid reflux.