Changes to oceanic currents
Braided River Status
Several braided river bird species depend on coastal and marine ecosystems, especially as a food source in winter. Changes to oceanic currents, including the Atlantic meridional overturning circulation (AMOC) which helps drive the flow of cool waters past New Zealand, may alter water temperatures and vertical dispersal of nutrients through the water column, with concurrent impacts on ecology and bird habitats.
“The Atlantic meridional overturning circulation has declined in strength by 15% since the mid-20th century to a new record low.”
–Caeser et al (2018) Nature vol. 556
Why is it a problem for braided river birds?
- Higher temperatures
- any change in the way currents flow around New Zealand, particularly a slowdown of the AMOC, will change the oceanic ecology, resulting in less food supply for those bird species that depend in part on oceanic ecosystems
- possible phenological changes?
- Contribution to rising sea levels
- higher sea temperatures (thermosteric changes) causes water to expand in volume, increasing sea levels. This is occurring globally as part of a suite of changes due to rising temperatures. The effects can be amplified regionally and locally due to changing oceanic currents delivering warmer than usual water to an area. It can also be amplified or dampened due to El Nina/La Nina and IPO. See here for the effect of rising sea levels
Sea surface temperatures November 2017: both graphics from @BenNollWeather (NIWA)
- Ice melt from Greenland and Northern Hemisphere directly contribute to the way in which AMOC functions. Rapid reduction of greenhouse gasses (GHG) is required to reduce the speed of this melt.
Seabird population trends 1950-2010
- Hoegh-Guldberg & Bruno (2010) The Impact of Climate Change on the World’s Marine Ecosystems; Science Vol. 328, Issue 5985, pp. 1523 -1528 doi 10.1126/science.1189930
- Caeser et al (2018) Observed fingerprint of a weakening Atlantic Ocean overturning circulation; Nature volume 556, pp191–196 doi 0.1038/s41586-018-0006-5
- Thornalley et al (2018) Anomalously weak Labrador Sea convection and Atlantic overturning during the past 150 years; Nature volume 556, pp227–230 doi:10.1038/s41586-018-0007-4
- Constable et al (2014) Climate change and Southern Ocean ecosystems I: how changes in physical habitats directly affect marine biota. Global Change Biology Oct;20(10) pp3004-25. doi: 10.1111/gcb.12623.