17th Oct, 2017

ex-hurricane Ophelia

Thanks for that excellent post Claire – it is likely that the large waves were imported from the area of maximum winds when the storm was to the south of Ireland earlier in the day.  The height of the waves was far in excess of the strength of the winds we experienced yesterday (barely a gale).

17th Oct, 2017

ex hurricane OPHELIA

The E1 data buoy recorded the arrival and magnitude of the ex hurricane OPHELIA yesterday. A short, sharp drop in pressure was accompanied by a short, sharp rise in temperature and followed by high winds and huge waves – the maximum wave height measured was in excess of 11m. It will be interesting to see if we find any unusual plankton in next week’s samples.

Left: Phytoplankton abundance – chlorophyll-a concentration estimated using satellite ocean colour. Right: Enhanced ocean colour map, where green/brown indicates phytoplankton-rich water.

VIIRS satellite data shows the usual Autumn bloom further out west between the Lizard and Brittany, but also a more defined patch up to 5 mg Chl m-3 between the Lizard and Plymouth.

Net samples at Station L4 have been dominated by phytoplankton such as diatoms (C. wailesii, Guinardia spp., Pseudo-nitzschia spp, Ceratulina pelagica), dinoflagellates (Ceratium spp) and coccolithophores (Coccolithus pelagicus). Interestingly, we’ve also found Ceratium candelabrum which is relatively rare at L4 and is more commonly associated with warm, high salinity oceanic waters. Likely blown in from the shelf with the recent storms.

Left: Coscinodiscus spp. Right: Ceratium candelabrum

 

The annual bloom of Phaeocystis is well underway with concentrations 4 times higher at E1 (ca. 200 cells per mL recorded by Glen Tarran using flow cytometry) than at L4 (ca. 500 cells per mL) with both sites showing even distribution throughout the water column. A diverse mix of diatoms still thrive at both sites with the colony-forming species Chaeotoceros socialis dominating. This is not unexpected expected as C. socialis often co-occurs with Phaeoctistis blooms in the western English Channel.
PhD student Rachel Coppock also noted from the coarse net tows a distinct lack of Calanus at L4, while E1 was absolutely teeming with mature Calanus.

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.

oxy_fluor_turb

 

nitrate_cdom

 

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:

http://www.westernchannelobservatory.org.uk/buoys.php

For the latest conditions

 

 

nitrate_cdom

oxy_fluor_turb

 

 

 

 

 

 

 

temp_sal

 

 

 

 

 

 

 

 

 

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:

http://westernchannelobservatory.org.uk/webcams.php

 

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