There seems to be a distinct difference now between the bloom reported on nearly 2 weeks ago (see post from 7 April) and now, in that the level of nitrate is dropping away rapidly.  Although the instrument (Satlantic SUNA) has not had a post field calibration applied, the values have dropped some 3 – 4 uM in the past two days, indicative of phytoplankton consumption of the nutrients.  The levels of chlorophyll at 06:00 this morning were >4 mg/m3; the issues of high-light quenching of the fluorescence close to the surface is a known problem, especially on clear sunny days between mid-morning and early evening.  For the latest from the L4 buoy data check out the figures below.





The CTD data is also clearly showing surface stratification with Tuesday’s profile (18 April) showing a top mixed layer extending down to 20m which is 0.5 degC warmer than the water beneath.

Given the sunny and calm conditions today, it is hardly surprising that the phytoplankton are responding.  The latest from the L4 buoy is showing ~3 mg/m3 of chlorophyll, and the waters appear to be green (although looks can be deceiving depending on what angle you are looking at with respect to the sun).  See:

For the latest conditions






















During Friday (31 March) and Saturday (01 April) there was relatively intense rainfall (~5mm/hr).  This has had the effect of increasing the river Tamar flow rate, and elevating the level of turbidity, nitrate and reducing the salinity.  The tidal cycle can clearly be seen interacting with this with a periodicity of ~12 hours.

14th Mar, 2017

L4 buoy relaunched

The L4 buoy, which has been in-shore since October for routine winter maintenance, has now been relaunched.  Special thanks to James, Oban, John and the boat crew for making this happen, and particularly ahead of the imminent dredge disposal which will be occurring some 3 nM to the NW of L4.  We shall be closely monitoring the turbidity levels, which should be at or below 1NTU under background conditions (as they are today).  New for 2017 is the re-introduction of the Satlantic SUNA nitrate sensor, which previously we have had little success with.  However, early indications are good with values at L4 being close to what is expected (~10uM) ahead of the spring bloom.

The latest temperature and salinity data for L4 and E1 are now available as easy to view plots.  The above shows the series for 2016 (asterisks) compared with the average (solid line: period 1903 – present) and standard deviation (dashed line).  As for 2015 the winter and autumn were markedly warm with a cooler spring period.  This is reflected throughout the water column.

The salinity at E1 was on average about 0.1 PSU above the long-term average, possibly indicative of a dry year and / or greater influence of open Atlantic water pushing in from the west.

Following more than a year of downtime the Penlee Point webcam is now back and live (about an hour behind time).  Check out:


The following from Andrea McEvoy:

100 zooplankton samples were taken and analysed which represents 50 time points for the year.

January 2016 saw the appearance of many mystery fibres at L4. Pennie and Maddie also sampled them at various points around the Sound and in the Plym. I think Alice (Pennie’s student) traced them down to be linen.

Unusual entoproct larvae appeared in Dec 2015 and throughout Jan/Feb 2016. They are tiny sessile solitary or colonial organisms. They are not well studied. They have been seen at L4 and at Milbay Marina before but have not been formally recorded in the database before.

Bolinopsis(Ctenophore) appeared in June, this was a new record for the L4 database as was Proboscidactyla stellate(Hydrozoa).

Bolinopsis probably wasn’t noted before because it is very fragile and breaks up easily during sampling.

I received the following from Gerald Boalch and thought it would be good to post on the blog. I was under the mistaken impression that the “L” in “L4” was named after the Lumby sampler, and assumed this was a scientist from the MBA (which may still be correct). Intrigued – read on …

The hydrographic stations were first set up in 1910 when ICES set up a programme of sampling stations around Europe on a regular basis. Each nation had a set of stations to sample every quarter and the ones set for MBA were labelled E for England, Scottish ones were labelled S and so on. The first set of E stations were E1,E2 and E3, these were in a line from Plymouth to Ushant. If you look at the ICES reports for the 1910 period onwards you will see the details, otherwise the reports in the JMBA by Armstrong Butler and Boalch from 1964 onwards give details of the stations as we used to work these three. There were other E stations heading up from Ushant towards the Irish Sea. The L stations were Local stations worked by the MBA on the way to E1, I think they were L 1 to L6. They had no connection with Lumby. We used to use the Lumby sampler for surface samples at most stations. When we were doing the Western Channel surveys we worked a three watch system right through the 24 hours and the system was that 10 minutes before arriving at the station the bridge would send a crew member to put out the Lumby and that crew member would then find the scientist on watch ant tell him the Lumby was out and we would be on station in 10 minutes so that the scientist could get ready to do what ever sampling was required. The Lumby also had the advantage that a surface sample could be taken even if the captain said it was not safe to stop the ship and work a station.

Thought it would be worth a follow-up showing how much the temperature varies at L4 during the day (at the moment).  Unsurprisingly there is a very strong diurnal cycle at the moment with typical temperature differences (measured at around 1.5 m) being around 1 degC.  The most extreme difference was on 25 July where the temperature varied around 3.5 degC.  This was a combination of strong solar insolation (near perfect solar trace from the SPN1), little in the way of wind (< 2 m/s) and warm air temperatures (22 degC).  The data from the buoy are reported every hour, and shows the real value of having near-continuous data being streamed back from L4.


Last 11 days temperature measured at L4 buoy



Temperature and PAR – last 7 days: L4 buoy


Windspeed and direction – last 7 days: L4 buoy

28th Jul, 2014

E1 and L4 temperatures

There has been quite a bit of attention in the media recently about the warm sea temperatures around the coast. Below see the plots for L4 and E1, updated with the most recent data. It shows that there is much more variability at L4 due to the strong effects of the tides. At E1 the temperatures are close to the maximum ever recorded (1908, 1976 and 1983 seem to be ahead at the moment).  To view the images properly you will need to click on them … asterisks represent the measurements made this year.

L4 temperature series (1988 – 2014)












E1 temperature series – surface and 50 m (1903 – 2014)