L4 flow cytometry data

These plots show data generated using flow cytometry. Samples for flow cytometry have been collected at the WCO since 2007. The data can be downloaded from the Pangaea website as files for each year from 2007 – 2011 and from the BODC website from 2012. Once you are into either site, type "Tarran L4" into the search box to find out how to access the data. Flow cytometry involves using a laser-based machine to count particles and measure light that they scatter as well as fluoresce. A copy of the protocols can be downloaded here. Different groups of particles have different light scattering and fluorescence properties. This makes it possible for us to distinguish different groups of algae (phytoplankton) in live samples of seawater from L4 because the chlorophyll inside them fluoresces red when the laser beam shines on them. We can also count different groups of bacteria and tiny single celled zooplankton (heterotrophic nanoflagellates) by staining the same seawater samples with a dye that attaches to the DNA in the cells and fluoresces green when the laser beam shines on them. These measurements are taken every week by collecting seawater samples from 4 depths at station L4, bringing them back to the laboratory and then analysing them on the flow cytometer. We then have measurements of the plankton abundance as cells per millilitre of seawater through the water column which we use to see how their abundance changes with time as shown in the example plots below.

During 2022, Synechococcus sp., cryptophyte and Phaeocystis sp. abundances were similar to long-term averages. Coccolithophores and LNA bacteria were above average abundance, whilst picoeukaryote and nanoeukaryote algae, along with heterotrophic flagellates were, perhaps below their long-term averages. The stand out period for the year was the 3 weeks from 21 June - 11 July when there were 3 instances where coccolithophore abundance was at or above 1000 cells per mL at Station L4 (A). There was no such increase in abundance at Station E1, 26 km further offshore. There were similar increases in coccolithophore abundance at Station L4 in 2020 and 2018 at exactly the same time of year (B). Bacteria with relatively low nucleic acid content (LNA bacteria) saw their highest recorded abundance at L4 since the time series began in 2007 with an abundance over 3 million per mL (C). The closest abundance to 2022 was back in 2016 when 1.86 million cells per mL were recorded. Bacteria with relatively high nucleic acid were also different than previous years in that their abundance appeared to be much more variable throughout the year (D).