A current affair: the movement of ocean waters around Australia



File 20181219 27776 1jdhree.jpg?ixlib=rb 1.1
Where do the ocean waters that wash the Gold Coast come from?
Flickr/LJ Mears , CC BY-NC-SA

Charitha Pattiaratchi, University of Western Australia; Ems Wijeratne, University of Western Australia, and Roger Proctor, University of Tasmania

Many people in Australia will head to the beach this summer and that’ll most likely include a dip or a plunge into the sea. But have you ever wondered where those ocean waters come from, and what influence they may have?

Australia is surrounded by ocean currents that have a strong controlling influence on things such as climate, ecosystems, fish migrations, the transport of ocean debris and on water quality.

We did a study, published in April 2018, that helps to give us a better understanding of those ocean currents.

Surface currents around the Australian continent.
Ems Wijeratne/Charitha Pattiaratchi/Roger Proctor



Read more:
New map shows that only 13% of the oceans are still truly wild


Go with the flow: Indian Ocean

Our 15 year simulation indicates that water from the Pacific Ocean enters the Indonesian Archipelago through the Mindanao current (north) and Halmahera Sea (south).

It then enters the Indian ocean as the Indonesian Throughflow between many Indonesian Islands, with flow through the Timor Passage being the most dominant.

Most of this water flows west as the South Equatorial Current. Re-circulation of the SEC creates the Eastern Gyre that contributes to the Holloway Current. This in turn feeds the Leeuwin Current – the longest boundary current in the world (Ocean currents that flow adjacent to a coastline are called boundary currents)

The Leeuwin Current is the major boundary current along the west coast and as it moves southward. Indian Ocean water is supplied by the South Indian Counter Current increasing the Leeuwin Current transport by 60%.

The Leeuwin Current turns east at Cape Leeuwin, in Western Australia’s south-west, and continues to Tasmania as the South Australian and Zeehan Currents.

The Leeuwin Current passes the lighthouse at the Cape Leeuwin in WA.
Flickr/Cheng, CC BY-NC-ND

There is a strong seasonal variation in the strength of the boundary currents in the Indian Ocean with a progression southwards of the peak transport along the coast.

The Holloway Current peaks in April/May (coinciding with changes in the monsoon winds), the Leeuwin Current reaches a maximum along the west and south coasts in June and August.




Read more:
Climate change is slowing Atlantic currents that help keep Europe warm


Go with the flow: Pacific Ocean

In the Pacific Ocean, the northern branches of the South Equatorial Current are the main inputs initiating the Hiri Current and East Australian Current.

At around latitude 15 degrees south the currents split in two: southward to form the East Australian Current, and northward to form the Hiri Current which contributes to a clockwise gyre in the Gulf of Papua.

The East Australian Current is the dominant current in the region transporting 33 million cubic metres of water per second southward.

At around 32S, the East Australian Current separates from the coast and 60% of the water flows eastward to New Zealand as the Tasman Front. The remaining 40% flows southward as the East Australian Current extension and contributes to the Tasman Outflow.

The Tasman outflow is the major conduit of water from the Pacific to Indian Ocean and contributes to the Flinders Current, flowing westward from Tasmania and past Cape Leeuwin into the Indian Ocean.

Along the southern continental slope, the Flinders Current appears as an undercurrent beneath the Leeuwin Current and a surface current further offshore. The Flinders Current contributes to the Leeuwin Undercurrent directly as a northward flow, flowing to the north-west of Australia in water depths 300 metres to 800 metres.

Impact of the currents

Understanding ocean circulation is a fundamental tenet of physical oceanography and scientists have been charting the pathways of ocean currents since the American hydrographer Matthew Maury, one of the founders of oceanography, who first charted the Gulf Stream in 1855.

One of the first maps of circulation around Australia was by Halliday (1921) who showed the movement of “warm” and “cold” waters around Australia. Although some of the major features (such as the East Australian Current) were correctly identified, a more fine scale description is now available.

Ocean surface currents around Australia by Halliday 1921.

The unique feature of ocean currents around Australia is that along both east and west coasts they transport warmer water southwards and influence the local climate, particularly air temperature and rainfall, as well as species distribution.




Read more:
Explainer: how the Antarctic Circumpolar Current helps keep Antarctica frozen


For example, the south west of Australia is up to 5C warmer in winter and receives more than double the rainfall compared to regions located on similar latitudes along western coastlines of other continents.

Similarly many tropical species of fish are found in the southwest of Australia that hitch a ride on the ocean currents.

The Pacific Ocean is the origin of waters around Australia with a direct link to the east and an indirect link to west.

Ocean water from the Pacific Ocean flows through the Indonesian Archipelago, a region subject to high solar heating and rainfall runoff, creating lower density water. This water, augmented by water from the Indian Ocean, flows around the western and southern coasts, converging along the southern coast of Tasmania.

So next time you head for a dip in the coastal waters around Australian, spare a thought for where that water has come from and where it may be going next.The Conversation

Time for a plunge in the water at Bondi Beach, NSW.
Flickr/Roderick Eime, CC BY-ND

Charitha Pattiaratchi, Professor of Coastal Oceanography, University of Western Australia; Ems Wijeratne, Assistant Professor, UWA Oceans Institute, University of Western Australia, and Roger Proctor, Director, Australian Ocean Data Network, University of Tasmania

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Advertisements

We’re in the era of overtourism but there is a more sustainable way forward



File 20190115 152980 uuwf5.jpg?ixlib=rb 1.1
Many European holiday destinations now struggle with overcrowding and pollution.
from http://www.shutterstock.com, CC BY-ND

Regina Scheyvens, Massey University

If you live in a tourist destination, you might dread the holiday invasion. Likewise, disgruntled tourists complain about crowded and polluted beaches, national parks or attractions.

Graffiti in Oviedo, northern Spain, following a spate of attacks on tourism facilities in Barcelona.
EPA/ALBERTO MORANTE, CC BY-ND

Overtourism is now a serious issue in many parts of the world. A good visitor experience may not be a finite resource in the same way as oil, but many popular destinations in Europe are reaching what could be termed “peak tourism”.

Concerns have been raised from Amsterdam to Dubrovnik about noise pollution, crowded parks, pressure on public facilities and rising rents. And in what is depicted as a “global battle” between travellers and locals, anti-tourism street marches have occurred in Barcelona and Venice.




Read more:
Anti-tourism attacks in Spain: who is behind them and what do they want?


Unsustainable tourism growth

Tucked away in a seemingly idyllic spot in the South Pacific, New Zealand is not immune to such concerns, which is why Massey University is hosting the world’s first research conference on tourism and the sustainable development goals this month.

Between 2013 and 2018, international tourist arrivals in New Zealand grew by 1.2 million to a total of 3.8 million. During the 12 months to March last year, tourists spent almost $40 billion, and the industry now provides one in every 12 jobs.

Economists see this growth as very positive for the country’s development, but many New Zealanders are ambivalent: 39% have expressed concern over the negative impacts of the growth in international visitors. The pressure on some destinations is particularly intense. For example, the 20,000 permanent residents of the summer and winter playground of Queenstown play host to around three million visitors a year.

Tourists digging holes in the vulcanic sand of a hot water beach in New Zealand.
from http://www.shutterstock.com, CC BY-ND



Read more:
Rethinking tourism and its contribution to conservation in New Zealand


Meanwhile local government bodies lament the pressure on public infrastructure and demands for waste disposal from freedom campers. Contractors at four Central Otago freedom camping sites have struggled to clear 16 tonnes of rubbish accumulated over the last two months.

A test case for concerns about the promise versus the pitfalls of tourism is the case of cruise tourism in Akaroa Harbour. The battle line lies between some business owners whose livelihoods depend on cruise tourists and local residents who feel their beautiful harbour and quaint town are marred by air and noise pollution and congestion associated with hundreds of tourists dropping in on their town with each cruise.




Read more:
Why Australia might be at risk of ‘overtourism’


In Australia, the Guinness World Record-certified whitest sand beach in the world – Hyams Beach – has turned away thousands of potential visitors during the Christmas and New Year period. There are only 110 permanent residents and 400 parking spaces, but up to 5000 tourists wanting to visit the beach each day during summer.

These experiences reflect the pressures and tensions tourism brings to many parts of the world, and the need for better ways of regulating tourist activity and capturing the gains from tourism.

A more sustainable way forward

It is clear that most people do not wish to see an end to tourism. But they do want the industry to be far more sustainable. While the term “sustainable tourism” has long been criticised for its lack of clout – and the way it can be seen as merely “sustaining tourism”, there is a way forward. We can look to the United Nations’ 17 sustainable development goals (SDGs), ratified in 2015 by 193 countries and set to guide global development through to 2030.

The SDGs require governments, civil society and business interests to play their parts in creating a more sustainable world. Furthermore, they are multi-faceted, considering social, economic and environmental aspects of sustainability.




Read more:
‘Sustainable tourism’ is not working – here’s how we can change that


The SDGs can help to guide the tourism industry to make more sustainable choices. For example, a strategy by hotels, cruise ships and restaurants to buy as much fresh produce from local farmers as possible would shorten the supply chain and save food miles (thus contributing to SDG 13 on combating climate change). It would also enhance local development (SDG 1 on eliminating poverty).

Tourist resorts in the Pacific could tackle the sexual harrassment from guests that many resort employees experience to show they care about SDG 8 on “decent work for all” and SDG 5 on “empowering all women and girls”.

Tourism trades in luxury products and indulgent experiences, and as such it places a heavy burden on the natural environment and results in waste management issues. SDG 12 on sustainable production and consumption can encourage companies to offer tourists more sustainable products and to reduce wastage of energy, fresh water and food.

Efforts to capture the benefits of tourism while preventing overtourism should pay careful attention to the SDGs.The Conversation

Regina Scheyvens, Professor of Development Studies, Massey University

This article is republished from The Conversation under a Creative Commons license. Read the original article.