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. Changes are also likely to occur to the intensity of La Nina, El Nina/La Nina, the Interdecadal Pacific Oscillation (IPO), and local currents around New Zealand, with concurrent impacts on ecology and bird habitats.
One of the key, large scale currents relevant to New Zealand is the AMOC:
“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
- Marine heat waves, which occur as a result of increasing temperatures lead to phenological changes. Sessile species such as kelp forests already are dying, taking with them the biodiversity that they support. Tropical and invasive species already are replacing them (2019 summary article. Links to research papers are at the bottom of this page).
- Altered weather patterns: see here for the impacts.
- 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 the Northern Hemisphere cryosphere directly contributes to the way in which AMOC functions, and in turn the way global weather behaves. Rapid reduction of greenhouse gasses (GHG) is required to reduce the speed of this melt.
Seabird population trends 1950-2010