Vol.9 No.4 - December 2001

1 December 2001

It is now widely accepted that the world’s climate is warming rapidly. Research into past climate changes, modern observations and computer modelling are helping scientists to determine and understand the processes, thus improving predictions about the effects of future warming. Aspects of this research, involving New Zealand’s oceans, are covered in the 10 articles in this issue.

Ocean circulation: the planet's great heat engine

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Barbara Manighetti
Giant currents in the deep ocean transport so much heat around the globe that they play a critical role in shaping the earth’s climate.
The ocean is in perpetual motion: that’s obvious to anyone who looks out over the sea. But the tides and waves that we see are just a tiny part of the movement in the ocean as a whole. Most movement comprises large-scale, unseen shifts to equal out water density differences caused by variations in temperature and salinity (saltiness) from the Poles to the Tropics.

The crystal ball: model predictions of future climate

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Brett Mullan
Melissa Bowen
Stephen Chiswell
“Coupled global climate models” currently provide our best predictions of the effects of increasing greenhouse gases on global and local climates.
The climate system has so many complex interacting components that predicting the Earth’s response to increased greenhouse gas emissions requires the use of sophisticated computer models.

Currents of change: the ocean flow in a changing world

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Lionel Carter
There is evidence that warming following the last ice age caused major shifts in the strengths and locations of ocean currents. Will this trend continue in a warming “greenhouse” world?
An oceanographer could not live in a better place. New Zealand’s long, narrow landmass straddles two of the planet’s major water masses – Subtropical and Subantarctic surface waters.

Editorial

Turning up the heat
New Zealand’s ocean in a warming world
Although seen many times, this marvellous Apollo 17 view of Africa, Antarctica and the Southern Ocean remains a symbol of the intimate link between the ocean and atmosphere. Powerful weather systems, outlined by swirls of white cloud, sweep eastward across the ocean. Winds within these systems create turbulent seas which help transfer greenhouse gases into one of the world’s major carbon stores, the ocean.

Glossary

Antarctic Circumpolar Current: the movement of shallow-to-deep Southern Ocean waters from west to east around the globe, circumnavigating Antarctica, in response to the rotation of the Earth and planetary winds. The current was first reported by James Cook in 1775.

Sea level on the move?

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Derek Goring
Rob Bell
A well-cited consequence of global warming is sea-level rise. What evidence is there that this is happening?

NIWA sea-level recorder network of sites on the open coast, well away from harbours and inlets and the effects of reclamation, siltation and dredging.

On the face of it, our title is fatuous. Sea level is always on the move, as indicated in the adjacent figure and table.

NIWA news forum

On this page

UNEP Effects Panel meeting in Wellington
The ocean in the 21st Century and beyond
Waves, sediment and ecology
Hydrodynamics of mussel farms
Coastal and Storm Hazards Workshop
UV Radiation and Its Effects: an update
NIWA Sponge Taxonomy Workshop – University of Mississippi

UNEP Effects Panel meeting in Wellington,
24 February to 4 March 2002
The next meeting of the United Nations Environment Programme (UNEP) Effects Panel will be held in Wellington from 24 February to 4 March 2002, and will be hosted by NIWA at Greta Point.

What grows up must fall down: the potential impact of climate change on plankton and carbon export

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Scott Nodder
Philip Boyd
A small but significant proportion of carbon from the atmosphere is lost when organic particles sink to the ocean floor. How might climate change affect this process?
The ocean covers 70% of the earth’s surface and stores a huge quantity of atmospheric carbon dioxide (CO2), especially at southern latitudes. As discussed in the previous article in this issue (see pages 26–27), the sea surface acts as a bottleneck for the transfer of CO2 and other gases into the ocean.

Back to the future: productivity upheaval in a warming ocean

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Helen Neil
Cores of sediment from the ocean floor hold a record of past algal blooms in the ocean. What can this tell us about previous changes to the climate?
With concern mounting over global climate change one big question is: what will be the response of the ocean environment to such change?
Some of our best clues come from information on past periods which we know were warmer than today. These periods provide a reference for identifying human-induced change. When making comparisons, scientists must take some key features into account.

The ocean surface: the greenhouse bottleneck

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Murray Smith
Craig Stevens
Kim Currie
Mike Harvey
Gas exchange at the sea surface is a vital link between the ocean and atmosphere, especially in relation to climate change. But measuring what is actually going on at the surface can be very difficult.
A crucial piece in the global warming jigsaw is the way greenhouse gases are transferred between air and sea. The oceans act as a remarkable sponge holding 50 times more carbon dioxide (CO2) than the atmosphere.

The Changing Oceans Research Team

From left to right
Lionel Carter: Educated at the Universities of Auckland and British Columbia (PhD); marine geologist at the NZ Oceano-graphic Institute (18 years) and NIWA (10 years).
Melissa Bowen: PhD from MIT/Woods Hole; research scientist for 2 years at the University of Colorado; Visiting Scientist at NIWA.
Basil Stanton: Educated at Canterbury University; 36 years as a physical oceanographer at NIWA and its predecessors.
Phil Sutton: Educated at the University of Auckland and Scripps Institute of Oceanography (PhD); a physical oceanographer at NIWA for 8 years.
Mike Harvey: PhD from

Hours to decades: the nature of variability and change

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Philip Sutton
The ocean is so variable that identifying subtle, long-term trends – like climate change – is far from straightforward.
The ocean changes on all scales of time and distance. However, some scales are more important than others, because they have large variations – or “signals” – associated with them. For instance, tides have a very clear cycle with a dominant 12.4-hour period. The annual cycle is also obvious as the ocean warms and cools once a year with the seasons. Similarly, some length scales dominate.

Is the sea around New Zealand warming?

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Basil Stanton
Long-term records of sea-surface temperatures around New Zealand show an overall warming over the last 100 years but there has been a slight cooling trend in the past decade.

We enjoy our ocean environment. But is it getting warmer? (Photo courtesy Fiji Travel)

The temperature of the ocean is an important part of the climate system because of the enormous capacity of the ocean to store heat and move heat around the globe.
The top 3 m of the ocean has the same heat capacity as the whole of the earth’s atmosphere.

New Zealand in a warming world

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Stephen Chiswell
Melissa Bowen
Brett Mullan
Most scientists agree that the Earth’s climate is warming as a result of increasing greenhouse gases. But regional climate changes make it difficult to identify the effects in different parts of the world.
At the start of the 21st Century, the world appears to be a warmer place than at any time since the Dark Ages. For the Northern Hemisphere there is evidence that the 20th Century was the warmest of any century over the past 1,000 years.