Tasman Sea high- and low- chlorophyll events, their links to marine heat waves, cool spells, and global teleconnections

ABSTRACT

Previous work has suggested that marine heat waves (MHW) and cool spells (MCS) in the Tasman Sea are responses to a stalling of an eastward propagating austral wavenumber-4 atmospheric pressure wave. We investigate extrema in sea surface chlorophyll (SSC), defining high- and low-chlorophyll events (HCE and LCE) analogous to MHW and MCS, but using Tasman-Sea averaged SSC anomalies. From 2002 to 2020, there were 13 HCE and 10 LCE, with no indication of changes in frequency, duration, or intensity of events. HCE tend to occur when Tasman-Sea averaged sea surface temperature is anomalously cool, and LCE tend to occur when Tasman-Sea averaged surface temperature is anomalously warm, however, there is no direct relationship between temperature and chlorophyll extrema. Canonical HCE/LCE formed from the 2002 to 2020 events suggest that HCE/LCE are also driven by the austral wavenumber-4 atmospheric wave. HCE occur during periods of low wind stress after a period of increased wind stress, whereas LCE may be a result of strong vertical mixing that mixes surface phytoplankton downwards. The implications of this work are that changes in Tasman Sea primary production in a future ocean will depend on any changes in the wavenumber-4 atmospheric wave.

KEYWORDS:

• Tasman Sea
• marine heat waves
• high chlorophyll events
• low chlorophyll events
• wavenumber 4 atmospheric wave
• net primary production

Acknowledgements

The Moderate Resolution Imaging Spectroradiometer (MODIS) mapped 8-day 9-km composite sea surface chlorophyll data were downloaded from NASA’s Ocean Color website (https://oceandata.sci.gsfc.nasa.gov/directaccess/MODIS-Aqua/Mapped/8-Day/9km/chlor_a). Daily Optimum Interpolation Sea Surface Temperature (OISST) data were downloaded from (https://www.ncdc.noaa.gov/oisst). The National Centers for Environmental Prediction (NCEP) daily reanalyses of atmospheric pressure and wind stress were obtained from http://www.esrl.noaa.gov/psd/data/gridded/data.ncep.reanalysis.surfaceflux.html. We thank these organisations for freely providing these data. The author thanks the reviewers for their comprehensive reviews.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the New Zealand Ministry of Business, Innovation and Employment through grant MBIE C01X1703 to NIWA’s Atmosphere, Climate and Hazards, and Coasts and Oceans programmes.