Decline in Oceans' Phytoplankton Alarms Scientists

Experts pondering whether reduction of 
marine plant life is linked to warming of the seas 

DAVID PERLMAN / SF Chronicle 6oct03

[Abstracts below / Also see C-19: Huge Antarctic Iceberg Makes a BIG Splash on Sea Life]

Plant life covering the surface of the world's oceans, a vital resource that helps absorb the worst of the "greenhouse gases" involved in global warming, is disappearing at a dangerous rate, scientists have discovered.

Satellites and seagoing ships have confirmed the diminishing productivity of the microscopic plants, which oceanographers say is most striking in the waters of the North Pacific—ranging as far up as the high Arctic.

Whether the lost productivity of the plants, called phytoplankton, is directly due to increased ocean temperatures that have been recorded for at least the past 20 years remains part of an extremely complex puzzle, says Watson W. Gregg, a NASA biologist at the Goddard Space Flight Center in Greenbelt, Md., but it surely offers a fresh clue to the controversy over climate change.

According to Gregg, the greatest loss of phytoplankton has occurred where ocean temperatures have risen most significantly between the early 1980s and the late 1990s. In the North Atlantic summertime, sea surface temperatures rose about 1.3 degrees Fahrenheit during that period, Gregg said, while in the North Pacific the ocean's surface temperatures rose about 7/10ths of a degree.

While the link between ocean temperatures and the productivity of plankton is striking, other factors can also affect the health of the plants. They need iron as nourishment, for example, and much of it reaches them in powerful winds that sweep iron-containing dust across the oceans from continental deserts. When those winds diminish or fail, plankton can suffer. There have been small but measurable decreases in the amount of iron deposited over the oceans in recent years, according to Gregg and his colleagues.

PRODUCTIVITY OFF 6% GLOBALLY

The significant decline in plankton productivity has a direct effect on the world's carbon cycle, Gregg said. Normally, he noted, the ocean plants take up about half of all the carbon dioxide in the world's environment because they use the carbon, along with sunlight, for growth, and release oxygen into the atmosphere in a process known as photosynthesis.

Primary production of plankton in the North Pacific decreased by more than 9 percent during the past 20 years, and by nearly 7 percent in the North Atlantic, Gregg and his colleagues determined from their satellite observations and shipboard surveys. Combining all the major ocean basins of the world, Gregg and his colleagues found the decline in plankton productivity more than 6 percent.

The plankton of the seas are a major "sink" for the extra carbon dioxide emitted in the combustion of fossil fuels. Whether caused by currently rising global temperatures or not, the loss of natural plankton productivity in the oceans also means the loss of an important factor in removing much of the principal greenhouse gas that has caused the world's climate to warm for the past century or more.

"This research shows that ocean primary productivity is declining, and it may be the result of climate changes such as increased temperatures and decreased iron deposition into parts of the oceans," Gregg said. "This has major implications for the global carbon cycle."

Gregg teamed with Margarita E. Conkright and three other scientists from the National Oceanic and Atmospheric Administration to evaluate observations by two NASA satellites as well as shipboard plankton measurements by NOAA vessels.

MONSTER ICE CHUNK BREAKS OFF

At the same time, Stanford University scientists using two other NASA satellites and one flown by the Defense Department have observed dramatic new changes in the vast ice sheets along the west coast of Antarctica. These changes, in turn, are having a major impact on phytoplankton there.

They report that a monster chunk of the Ross Ice Shelf—an iceberg almost 20 miles wide and 124 miles long, more than twice the size of Rhode Island—has broken off the west face of the shelf and is burying a vast ocean area of phytoplankton that is the base of the food web in an area exceptionally rich in plant and animal marine life.

Antarctica

Click Here for MPEG movie of 
iceberg in motion at NASA website
818kb

Hundreds of thousands of Adelie and emperor penguins are endangered by the huge iceberg, which has been stuck against the coast ever since it broke off from the Ross Ice Shelf last year, according to Kevin R. Arrigo and Gert L. van Dijken of Stanford. Whales, seals and the millions of shrimp-like sea creatures called krill are also threatened by the loss of many square miles of phytoplankton.

Although sea surface temperatures around Western Antarctica are not warming, the loss of plankton is proving catastrophic to all the higher life forms that depend on the plant masses, Arrigo and van Dijken say.

Icebergs in Antarctica are designated by letters and numbers for aerial surveys across millions of square miles of the southern ocean, and this berg is known as C-19. "We estimate from satellite observations that C-19 in the Ross Sea has covered 90 percent of all the phytoplankton there," said Arrigo, a Stanford biological oceanographer.

WILDLIFE HABITAT THREATENED

Huge as it is, the C-19 berg is only the second-largest recorded in the Ross Sea region. An even larger one, dubbed B-15, broke off, or "calved," in 2001. Although it also blotted out a large area of floating phytoplankton on the sea surface, it only wiped out about 40 percent of the microscopic plants, Arrigo said.

Approximately 25 percent of the world's populations of emperor penguins and 30 percent of the Adelie penguins nest in colonies that are threatened by the C-19 berg, Arrigo said.

"In the waters directly impacted by C-19, there are usually about 280,000 pairs of Adelie penguins and these penguins, as well as all the other higher- level animals such as seals and whales, would all have to contend with a 90 percent loss in marine productivity," he said.

"There's no strong evidence yet that global warming has caused this portion of the ice shelf to break off, but the biologic impact is huge," Arrigo said.

Gregg's team as well as Arrigo and van Dijken have published their findings in recent issues of the journal Geophysical Research Letters.

source: http://www.sfgate.com/cgi-bin/article.cgi?file=/chronicle/archive/2003/10/06/MN31432.DTL&type=printable 6oct03

Ocean primary production and climate: Global decadal changes

Geophysical Research Letters v.30, n.16, 1809 Oct03

Watson W. Gregg
Laboratory for Hydrospheric Processes, NASA/Goddard Space Flight Center, USA

Margarita E. Conkright
Ocean Climate Laboratory, NOAA/National Oceanographic Data Center, USA

Paul Ginoux
NOAA Geophysical Fluid Dynamics Laboratory, USA

John E. O'Reilly
NOAA/National Marine Fisheries Service, USA

Nancy W. Casey
Science Systems and Applications, Inc., USA

Abstract

[1] Satellite-in situ blended ocean chlorophyll records indicate that global ocean annual primary production has declined more than 6% since the early 1980's. Nearly 70% of the global decadal decline occurred in the high latitudes. In the northern high latitudes, these reductions in primary production corresponded with increases in sea surface temperature and decreases in atmospheric iron deposition to the oceans. In the Antarctic, the reductions were accompanied by increased wind stress. Three of four low latitude basins exhibited decadal increases in annual primary production. These results indicate that ocean photosynthetic uptake of carbon may be changing as a result of climatic changes and suggest major implications for the global carbon cycle.

Received 7 January 2003; accepted 21 May 2003; published 9 August 2003.

Index Terms: 4215 Oceanography: General: Climate and interannual variability (3309); 1615 Global Change: Biogeochemical processes (4805); 1635 Global Change: Oceans (4203); 4806 Oceanography: Biological and Chemical: Carbon cycling.

doi:10.1029/2003GL016889, 2003

source: http://www.agu.org/pubs/crossref/2003/2003GL016889.shtml 6oct03

Impact of iceberg C-19 on Ross Sea primary production

Geophysical Research Letters v.30, n.16, 1836 Oct03
Kevin R. Arrigo and Gert L. van Dijken

Dept. of Geophysics, Stanford Univ.,Stanford, California, USA

Abstract

[1] For the second time in 26 months, a large iceberg (C-19) calved off the face of the Ross Ice Shelf. Rather than breaking up, as did its predecessor B-15, the iceberg C-19 remained largely intact, eventually stopping temporarily near Pennell Bank before moving out of the southwestern Ross Sea. The presence of C-19 restricted advection of sea ice out of the region, resulting in unusually high sea ice cover during the spring and summer. Consequently, phytoplankton blooms in the region were diminished dramatically and primary production was reduced by over 90%, relative to normal years. Calving events over the last two decades indicate that reduced primary productivity may be a typical consequence of large icebergs that drift through the southwestern Ross Sea during spring and summer.

Received 12 May 2003; accepted 13 June 2003; published 19 August 2003.

Index Terms: 1827 Hydrology: Glaciology (1863); 4207 Oceanography: General: Arctic and Antarctic oceanography; 4275 Oceanography: General: Remote sensing and electromagnetic processes (0689).

doi:10.1029/2003GL017721, 2003

source:  http://www.agu.org/pubs/crossref/2003/2003GL017721.shtml 6oct03