Marine Atlas: Maximizing Benefits for Kiribati

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Normal conditions

El Niño conditions

Westerly Winds

Strong Trade Winds

Weaker Trade Winds

Both kinds of currents—the thermohaline ones in the deep water and the wind-driv- en one on the surface—are very important to Kiribati. On their journey, water masses transport two things around the globe and through Kiribati’s waters. Firstly, matter such as solids, dissolved substances and gases are carried by the currents, including salt, larvae (see also chapter “Travellers or homebodies”), plastics and oil (see also chapters “Plastic oceans” and “Full speed ahead”). Secondly, currents transport energy in the form of heat. Currents therefore have a significant impact on the global climate. El Niño is an example of the big impact that regional climate variability related to ocean currents has on Kiribati (see graphs and chapter “Hotter and higher”). Normally, strong trade winds blow from east to west across the Pacific Ocean around the equa- tor. As the winds push warm surface water from South America west towards Asia and Australia, cold water wells up from below in the east to take its place along the west coast of South America. This creates a tem- perature disparity across the Pacific, which also keeps the trade winds blowing. The ac- cumulation of warm water in the west heats the air, causing it to rise and create unstable weather, making the Western Pacific region warm and rainy. Cool, drier air is usually found on the eastern side of the Pacific. In an El Niño year, the trade winds weaken or break down. The warm water that is normally pushed towards the Western Pacific washes back across, piling up on the east side of the Pacific from California to Chile, causing rain and storms and increasing the risk of cyclone formation over the tropical Pacific Ocean (Climate Prediction Center, 2005).

Water Heated by the Sun

Strong Upwelling

Weak Upwelling

WarmWater

Thermocline

Deep Cold Water

120°E

140°E

160°E

180°

160°W

140°W

120°W

100°W

80°W

120°E

140°E

160°E

180°

160°W

140°W

120°W

100°W

80°W

Darwin, Australia

Kiribati

Lima, Peru

Darwin, Australia

Kiribati

Lima, Peru

The periods 1997–1998 and 2014–2016 wit- nessed some of the most extreme events on record in the region. Average annual rainfall in Kiribati is approximately 2,100 millime- tres, with just over 900 millimetres received between May and October. From July 1988 to December 1989, only 205 millimetres of rain fell, while from August 1998 to February 1999, total rainfall was 95 millimetres. How- ever, under climate models, the prevalence of drought is projected to decrease in the fu- ture (Australian Bureau of Meteorology and CSIRO, 2014). Moreover, El Niño contributes to an increase in global temperatures. In the particularly hot year of 2015, El Niño was responsible for about 10 per cent of the temperature rise. In turn, rising global and ocean temperatures may intensify El Niño (Cai et al., 2014). In Kiribati, temperatures are predicted to increase, as is the occur- rence of extreme rainfall events (Australian Bureau of Meteorology and CSIRO, 2014). In summary, sea currents driven by wind, heat and salinity influence not only Kiriba- ti’s marine biodiversity, but also its rainfall patterns and temperature on land.

5°N

SEA SURFACE CURRENTS

Direction and velocity (m/s)

5°N

0.22

0.13

0.05

0.03

Kiribati Provisional EEZ Boundary

0°

200 100

400 km

0°

5°S

170°E

175°E

180°

175°W

170°W

5°S

0°

10°S

5°S

On the other side, the Western Pacific experiences particularly dry conditions.

160°W

155°W

150°W

MAXIMIZING BENEFITS FOR KIRIBATI

SUPPORTING VALUES

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