01.02.2012: Analysis of biochemical observations against observations of the horizontal velocity field for HOE-DYLAN 5 and 9

HOE-DYLAN 9

See all figures for HD 9 [PDF].

• There is a daily cycle in Chl in the upper 100 m. Not sure if this is real.
• Chl max is larger during the first half of the cruise in HD 5 and 9.
• Oxygen: Sudden disappearance of oxygen maximum with possibly a corresponding oxygen increase below the normal depths of the oxygen maximum. There is also some variability at depth that appears to be accounted for by horizontal advection (as seen in the salinity data). For HD 9, the salinity anomaly nearly mirrors the oxygen anomaly.
• During HD 9, two different water masses were sampled, seen in the different background salinity value between the first and second half of the cruise.
• How can we explain the downward propagation of salinity anomalies with time?
• Most importantly, no sign of different response of the ecosystem (Chl and oxygen) to the two different water masses.
• Wind appears normal trades during HD5 and 9.
• Description of the horizontal velocity field: - background inertial/diurnal variability (to check) - one inertial event is interesting during HD 9 as it started from the surface and propagated below the surface mixed layer; once again, no sign of any perturbation in the ecosystem. - semi-diurnal tides stronger during the second half of the cruise for both HD5 and 9: Link to the decrease in Chl max (note that the reverse was true for HD 7, although the change in Chl max was I think weaker than the change observed during HD 5 and 9)? - Vertical velocity shear tends to be larger during the second half of HD 9 (and it seems to be contributed by at least the inertial/diurnal band and the high-frequency band)
• Changes in stratification reflects the change in water mass being sampled.

HOE-DYLAN 5

See all figures for HD 5 [PDF].

On top of what has already been said in the previous section:

• Changes in isopycnal depth of the Chl max (not seen in HD 9)
• Decrease in oxygen maximum around day 5 likely to be associated with horizontal advection
• Vertical shear larger during the first half of the cruise (and it is also contributed by at least the inertial/diurnal band and the high-frequency band).

Questions/Things to do

1. Use HOT data to see if there is a link between the amplitude of the Chl max and the amplitude of the semi-diurnal tides. If yes, why.
2. Was the inertial activity background? (see Eric 1996’s paper and Pinkel 2008’s paper).
3. Are optical data correlated with changes in Chl max? There may be a tendency but not a strong correlation
4. Look at backscatter (a measure of zooplankton and larger creatures): Any correlation to changes in Chl?
5. Re-read papers about the horizontal patchiness of plankton. Do some address the patchiness at scales lower than the submesoscale (which is to be the scale at which there is a high portion of the DCM variability)?

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Plots related to the horizontal velocity have been done with SADCP_analysis_1.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/HOE_DYLAN/analysis/SADCP/ on the main disk. Plots of stratification have been done with stratification_analysis_1.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/HOE_DYLAN/analysis/stratification/ on the main disk. Plots of biochemical quantities and salinity have been done with chlorophyll_analysis_1.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/HOE_DYLAN/analysis/chlorophyll/ on the main disk. Plots of wind have been done with wind_analysis_1.m in RESEARCH/PROJECTS/MARINE_BIOLOGY/SUBMESOSCALE_PROCESSES/HOE_DYLAN/analysis/met/ on the main disk.