Oceanography

Technical advances over the past 50 years have allowed improved knowledge to be gained of the properties of sea water at great depths. Yet the first centimetres of the ocean remain its least well known part. They are difficult to sample and study owing to the mixing the oceanographic vessel provokes between this superficial layer and the deeper strata of water. Nevertheless, a whole ecosystem exists within this layer, carrying numerous living organisms like bacteria, zooplankton and larger animals such as flying fish, which feed and reproduce in it.

Using echo-sounding equipment to create images and maps of areas below the ocean floor, researchers have begun to unravel a new story about the Antarctic Ice Sheet.

Images of areas below the Eastern Ross Sea, next to West Antarctica, provide evidence that the subcontinent was involved in the general growth of the Antarctic Ice Sheet as it formed many millions of years ago, according to scientists at the University of California, Santa Barbara. The National Science Foundation provided funding for the project.

Changes in Antarctica, an area that contains approximately 90 percent of the world’s ice, are particularly important for understanding some implications of global warming.

Global climate change is causing Antarctic ice shelves to shrink and split apart, yielding thousands of free-drifting icebergs in the nearby Weddell Sea. According to a new study in this week’s journal Science these floating islands of ice – some as large as a dozen miles across – are having a major impact on the ecology of the ocean around them, serving as “hotspots” for ocean life, with thriving communities of seabirds above and a web of phytoplankton, krill, and fish below.

The icebergs hold trapped terrestrial material, which they release far out at sea as they melt. The researchers discovered that this process produces a “halo effect” with significantly increased phytoplankton, krill and seabirds out to a radius of more than two miles around the icebergs.

Sediment cores retrieved from the Arctic’s deep-sea floor by the Integrated Ocean Drilling Program’s Arctic Coring Expedition (ACEX) report that the Arctic Ocean changed from a landlocked body of water (a ‘lake stage’) through a poorly oxygenated ‘estuarine sea’ phase to a fully oxygenated ocean at 17.5 million years ago during the latter part of the early Miocene era.

The authors attribute the change in Arctic conditions to the evolution of the Fram Strait into a wider, deeper passageway that allowed an inflow of saline North Atlantic water into the Arctic Ocean.

Monitoring the saltiness of the ocean water could provide an early indicator of climate change. Significant increases or decreases in salt in key areas could forewarn of climate change in 10 to 20 years time. Presenting their findings at a recent European Science Foundation (ESF) conference, scientists predicted that the waters of the southern hemisphere oceans around South Africa and New Zealand are the places to watch.

Huge waves that struck Reunion Island and coastlines across Indonesia earlier this month all originated from the same storm that occurred south of Cape Town, South Africa, and were tracked across the entire Indian Ocean for some 10 000 kilometres over a nine-day period by ESA's Envisat satellite.


Picture taken on 14 May 2007 in Saint-Leu, on the French Indian Ocean island of Reunion, of a giant wave breaking on the coast. Credits: AFP

A novel analysis of water flow in the Southern Ocean surrounding the Antarctic is revealing previously hidden structures that are crucial in controlling the transport of drifting plants and animals as well as the distribution of nutrients and pollutants that affect ocean life.

Researchers at the University of New South Wales in Australia and the Universitat Paderborn in Germany discovered that barriers to currents, which can lead to swirling gyres and eddies that trap material for long periods, may escape detection with traditional analyses that concentrate on monitoring average water flow or sea surface height.

NASA satellite data have helped scientists solve a decades-old puzzle about how vast blooms of microscopic plants can form in the middle of otherwise barren mid-ocean regions. A research team led by the Woods Hole Oceanographic Institution, Woods Hole, Mass., has used the data in its work to show that episodic, swirling current systems known as eddies act to pump nutrients up from the deep ocean to fuel such blooms.

Scientists have observed the first evidence that the Southern Ocean's ability to absorb the major greenhouse gas, carbon dioxide, has weakened by about 15 per cent per decade since 1981.

In research published today in Science, an international research team – including CSIRO's Dr Ray Langenfelds – concludes that the Southern Ocean carbon dioxide sink has weakened over the past 25 years and will be less efficient in the future. Such weakening of one of the Earth's major carbon dioxide sinks will lead to higher levels of atmospheric carbon dioxide in the long-term.


The Bureau of Meteorology's Baseline Air Pollution Station at Cape Grim, north-west Tasmania. Credit: CSIRO Australia

The small ice caps of Mont Blanc and the Dôme du Goûter are not melting, or at least, not yet. This is what CNRS researchers have announced in the Journal of Geophysical Research. At very high altitudes (above 4200 meters), the accumulation of snow and ice has varied very little since the beginning of the 20th century. But if summer temperatures increase by a few degrees during the 21st century, the melt could become more marked, and could affect the "permanent" ice fields.


Figure 1 – Researchers from the Glaciology Laboratory taking an ice core sample on top of Mont Blanc, in 2005. © C. Vincent, CNRS 2007.