Upwelling indicator time series over eastern boundary upwelling systems from satellite sea surface temperature

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Figure 1: Global sea surface temperature from satellite data showing the California, Peru, Canary and Benguela ecosystems and upwelling (black boxed areas).

Upwelling ecosystems located on the eastern side of the Atlantic and Pacific oceans (Figure 1) are known for their high biological productivity that supports large marine populations and for their major contribution to the world marine fish catches (Pauly and Christensen, 1995, Fréon et al., 2009; Capone and Hutchins, 2013). Ocean acidification (Feely et al., 2008), algal blooms and low oxygen events over these continental shelves are tightly linked to the dynamics of the upwelling process (e.g. Pitcher et al., 2010, 2014, Lachkar et al., 2012) and these regional-scale dynamics are not well represented in existing models used to predict our future climate (Small et al., 2015, Di Lorenzo, 2015). In order to characterize the spatial and temporal variability of the four major eastern boundary upwelling systems and investigate linkages between upwelling and episodic events such as marine heat waves, a new sea surface temperature-based upwelling indices time series is being developed. Index calculations are based on the European Space Agency Sea Surface Temperature Climate Change Initiative (ESA SST CCI) analysis product that provides daily global gap-free sea surface temperature fields at a 0.05° horizontal grid resolution and covering the period 1st September 1981 to the present day. The method used to derive the upwelling indices is based on a segmentation algorithm using Gaussian mixture models, as illustrated in Figure 2. Initial results of change in the sea surface temperature due to these upwelling events and the extent over which these changes in temperature extend can be seen Figure 3.

Investigating linkages between these flows, their extent, and how they alter the marine carbonate system conditions will enable these episodic upwelling driven changes in the carbonate system to be monitored and studied from space.

Figure 2: Monthly mean sea surface temperature over the Southern region of the Canary upwelling system (left), segmentation with 3 regions (middle) and the associated distributions.


Figure 3: An example output from the upwelling indicator (°C) and upwelling extent (degrees) from 2001 to 2015 calculated from satellite sea surface temperature data in the Canary upwelling region at the latitude 30°N.

References

Pauly D. and V. Christensen (1995) Primary production required to sustain global fisheries. Nature, 374, 255–257.

Fréon, P., M. Barange, J. Arístegui (2009), Eastern boundary upwelling ecosystems : integrative and comparative approaches, Progress in Oceanography, 83 (1), 1–14.

Capone, D. G., Hutchins, D. A., (2013) Microbial biogeochemistry of coastal upwelling in a changing ocean, Nature Geoscience, 6, pages 711–717.

Feely, R. A., Sabine, C. L., Hernandez-Ayon, J. M., Ianson, D., & Hales, B. (2008). Evidence for upwelling of corrosive “acidified” water onto the continental shelf. Science, 320(5882), 1490-1492.

Pitcher, G.C., Figueiras, F.G., Hickey, B.M., Moita, M.T., (2010) The physical oceanography of upwelling systems and the development of harmful algal blooms. Progress in Oceanography. doi:10.1016/j.pocean.2010.02.002.

Lachkar, Z., & Gruber, N. (2012). Exploring the future evolution of multiple stressors in eastern boundary upwelling systems. OCB News, 5(2), 5-9.

Small, R. J., E. Curchitser, K. Hedstrom, B. G. Kauffman, and W. G. Large, 2015: The Benguela upwelling system: Quantifying the sensitivity to resolution and coastal wind representation in a global climate model. Journal of Climate, 28, 9409-9432, doi:10.1175/JCLI-D-15-0192.1.

Di Lorenzo, E. (2015). Climate science: The future of coastal ocean upwelling. Nature, 518(7539), 310.