Western English Channel springs into life
5 March 2021
The annual Spring bloom marks the end of the marine winter, when there is a significant increase in phytoplankton abundance in temperate North Atlantic, sub-polar and coastal waters. The blooms are due to the increased light and temperature, as well as a good supply of nutrients created from mixing caused by weather and rainfall run-off from the land, causing a ‘population explosion’.
In late February, our Earth Observation scientists noticed increased chlorophyll concentrations in their satellite data. Chlorophyll is found in photosynthetic organisms, such as plants and phytoplankton, and when an increase is seen in satellite observations, it is often a signal of increased biological activity.
This satellite image, processed by the NERC Earth Observation Data Acquisition and Analysis Service (NEODAAS) at PML, shows the chlorophyll concentration around the UK’s South West coast on 27th February 2021, using satellite data from Copernicus’ Sentinel 3a Ocean and Land Colour Instrument (OLCI). When blooms are not occurring, the representative colours of the water in this image would be mainly blues and darker greens whereas this image clearly shows various levels of increased chlorophyll, denoted by lighter greens and greeny-yellows. Around the southwest peninsular, this is a good sign that the Spring bloom is beginning.
However, much of the higher concentrations observed (in yellow) could be sediment changing the colour of the water and activities on land affecting water properties , which demonstrates the importance of expert analysis of satellite imagery as well as input from other disciplines and functions.
The Earth Observation team reached out to the sampling team and Plankton Ecologists at PML to find out what they were seeing in situ.
The RV Plymouth Quest, PML’s main research vessel, can been seen in Plymouth Sound most days and staff onboard collect water and sediment samples at various locations, such as the L4 sampling station, for analysis back at the lab.
Back at the lab, the samples are analysed under the microscope in PML’s brand new Microscopy Lab. Analysis of these sample can used to confirm what species are present and whether the Spring bloom is beginning.
The phytoplankton community sampled from L4 on Monday 1st March shows an increase in the species diversity of diatoms, including the oval shaped, chain-forming Thalassiosira spp. and the large rectangular Odontella sinsensis. This again possibly indicates the start of the Spring bloom (photo by Claire Widdicombe, PML)
These data are then fed into the Western Channel Observatory long-term time-series, some of which dates back to 1903. Not only does this unique and internationally acclaimed time series provide a record of environmental conditions of the local marine environment but is also vital in identifying trends and changes over the long-term.
The Earth Observation Group, sampling team and Plankton Ecologists will continue to share information with each other over the coming weeks as the bloom develops, plateaus then dies off.
Increasing our understanding of how blooms develop, what biological and chemical processes are occurring and the fate of marine species as the bloom reduces, are essential in advancing research relating to marine food-webs, climate change and marine spatial planning.