Abstract
The oceans’ phytoplankton that underpin the marine food chain appear to be changing in abundance due to global climate change. Here, we compare the first four years of data from a citizen science ocean transparency study, conducted by seafarers using home-made Secchi Disks and a free Smartphone application called Secchi, with contemporaneous satellite ocean colour measurements. Our results show seafarers collect useful Secchi Disk measurements of ocean transparency that could help future assessments of climate-induced changes in the phytoplankton when used to extend historical Secchi Disk data.
Highlights
The ocean’s phytoplankton accounts for approximately 50% of global net primary production [1,2] and underpins the marine food chain [3], it affects the optical and thermal sea surface properties [4,5], provides the World with oxygen [6], and plays a central role in the global carbon cycle [7]
In a study of a 100-year trend in global upper-ocean phytoplankton chlorophyll concentrations, Boyce et al [9] reported a 40% decline in global phytoplankton primary production since 1950; they proposed that water column mixing and the supply of growth-promoting nutrients to the sea surface had reduced due to warming global temperatures
Linear regression analysis after removing negative values (b = 1.64, 95% CI 1.51–1.76, p
Summary
The ocean’s phytoplankton accounts for approximately 50% of global net primary production [1,2] and underpins the marine food chain [3], it affects the optical and thermal sea surface properties [4,5], provides the World with oxygen [6], and plays a central role in the global carbon cycle [7]. In a study of a 100-year trend in global upper-ocean phytoplankton chlorophyll concentrations, Boyce et al [9] reported a 40% decline in global phytoplankton primary production since 1950; they proposed that water column mixing and the supply of growth-promoting nutrients to the sea surface had reduced due to warming global temperatures. The study [9] attracted criticism as the analysis combined two methods for measuring phytoplankton chlorophyll to achieve a 100-year global dataset [10,11]; Secchi Disk ocean transparency measurements were the dominant data in the first 50 years of the time series whereas colorimetric measurements were more popular in recent decades. Different phytoplankton abundance data indicated that phytoplankton had increased in the North Atlantic and North Pacific over the same period [12].
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