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Physics
PAR/Irradiance
Overall, the irradiance measurements across the time series show a very similar trend. Light is absorbed most rapidly between 20 and 40m at each station. The depth of the euphotic zone ranges from 30 to 45m at the 1% light level, and 50 to 70m at the 0.1% light level. Station 34 shows a rapid decline in irradiance between 5 and 10m. This is probably the result of a sinking coccolithophore bloom. The coccolithophores of the phytoplankton can in certain conditions reflect light. This would cause a pause in the irradiance profile. This is supported by the transistometer data, which shows a layer of high disturbance at the same depth range.
Fluorescence
Peak fluorescence up to 0.132 mg m-
There was in increase in fluorescence values through depth from the surface to 20
m from 0.04 to 0.132 mg m-
Temperature
Temperature profiles were taken at each station from 1000 to 1500 UTC. Near surface
results from 0-
CDOM
The coloured dissolved organic matter concentration is consistently lowest in the
surface 10 m, at approximately 0.023-
Turbidity
Throughout the day the pattern of turbidity remains largely constant at each station
down through the water column. The surface 10-
Beam transmission
Beam transmission follows a very close relationship with turbidity; remaining lower
and more scattered in the surface water at approximately 4.5%. It then increases
below the first 15-
Physical parameters
at E1 were investigated
using CTD deployments and
ADCP data across the time period.
(Clockwise) Figure 1: Depth of the 1% and 0.1% irradiance levels against offshore stations. Figure 2: ADCP ship trace at E1 buoy showing average current velocity. Figure 3: flow magnitude profile of ship trace.
ADCP transect
The backscatter plot for the E1 time series tracked all stations continuously from 1000 UTC to 1500 UTC. From this data, high backscatter values (red and yellow) were observed at the surface and to depths of 10 m throughout the time series. This suggested a high level of plankton in the water column. Additional high backscatter levels (yellow) were seen just above 20 m depth between stations 30 and 31, and around station 33, which correlates to plankton observations on and above the Deep Chlorophyll Maximum (DCM). Unusually, there was an apparent void of plankton in and below the DCM, indicated by limited backscatter return (blue to purple) between 20 to 30 m. The backscatter was then fairly consistent between depths of 30 m and 70 m. This data was observed in real time during the time series and used to determine the depths for zooplankton trawls and seawater samples for phytoplankton analysis.
Two large peaks seen during the time series from 30 to >60 m correspond to significant
ship re-
Figure 2: CTD profiles of Turbidity and Beam Transmission from 6 E1 stations
Figure 1: CTD profiles showing temperature, salinity, fluorescence, CDOM, PAR from 6 E1 stations