The document summarizes results from the STRATIPHYT-I cruise which studied the coupling of turbulence and plankton distributions in the Northeast Atlantic. The cruise measured high resolution temperature and salinity profiles using a microstructure profiler to determine vertical mixing coefficients. In parallel, measurements of phytoplankton and nutrients were taken in the top 100m. The objective was to better understand how changes in vertical stratification from climate change may impact phytoplankton communities through effects on turbulent mixing and nutrient fluxes.

1. COUPLING OF TURBULENCE AND PLANKTON DISTRIBUTIONS IN THE NORTHEAST ATLANTIC!
First results from the STRATIPHYT-I cruise!
Elena Jurado, Henk A. Dijkstra, Hans van der Woerd, Corina Brussaard
1: Institute for Marine and Atmospheric Research (IMAU), UU Utrecht University, The Netherlands. 2: Institute for Environmental studies (IVM),
1!
VU University Amsterdam, The Netherlands. 3: Dept. Biological Oceanography, NIOZ, The Netherlands.
e.juradocojo@uu.nl
INTRODUCTION and Objective STRATIPHYT-I cruise MICROSTRUCTURE PROFILER: SCAMP
(July-August 2009) 148 profiles Temperature-Salinity-Depth in 15 stations
-! Predicted stratification increase in the Northeast Atlantic Ocean due to Climate Salinity [psu]
Change (IPCC-AR4). solid circle: SCAMP + CTD 35 35.4 35.8 36.2 36.6 37
0
What is the impact of the changes of the vertical Iceland! open circle: CTD
stratification on the phytoplankton communities?
depth [m]
20
40 SCAMP (Free-falling Self-
Contained Autonomous
-! Turbulent mixing affects the vertical nutrient fluxes. Also it may alter 60
Microstructure Profiler )
phytoplankton contact rate, sinking speeds, light availability. 80
-! Detailed coupling of turbulence, stratification, nutrient transport and 100
phytoplankton distribution is not well understood. Lack of comprehensive 0
studies in the ocean.
depth [m]
20
-! Small-scale turbulence, within the dissipation range, is needed to understand 40
links between turbulent mixing and phytoplankton. It requires devices with very 60
high space-time resolution.
80
** STRATIPHYT-I cruise: parallel measurements of high resolution temperature 100
and salinity profiles + phytoplankton and nutrients in the first 100m of the NE 0
Atlantic Ocean. Atlantic !
Ocean! 20
depth [m]
40
Objective: Determine the vertical mixing coefficient KT during the cruise, with the Gran Canaria! 60
aim to further relate to phytoplankton and nutrient distributions.
80
2!
100
6 10 14 18 22 26
Temperature [degC]
Bathymetry [m]
METHOD ASSUMPTIONS: TURBULENT PARAMETERS:
148 SCAMP high •! Sharpening/Smoothing •! SCAMP falls at a Parameter Units Main formula used
resolution profiles of: constant velocity and free
•! Brick-Wall Filtering N, Buoyancy frequency rad/s
•! Temperature of tension
•! Conductivity •! Trimming according to depth and to
•! Isotropic turbulence kB, Batchelor wavenumber cyc/m fitting to
•! Pressure velocity of SCAMP refs: 1,2,3
•! Local closure approach S: Spectrum of temperature gradient fluctuations
•! 1m binning
•! Gradient of temperature !", Temperature variance dissipation rate degC2/s refs: 1,3
•! Rejection of bin if bad fitting to
fluctuations follow
Batchelor Spectrum1 rad4m2/s3 ref: 4
Batchelor Spectrum #, Turbulent dissipation rate
•! Steady state of turbulent
KT, Vertical eddy diffusivity of heat m2/s ref: 5
4!
kinetic energy
3!
K$, Vertical eddy diffusivity of density m2/s ref: 6
VERTICAL MIXING COEFFICIENT (KT) PHYTOPLANKTON / NUTRIENTS
!! Deep Chlorophyl Maximum (DCM) measured
35N 36N 38N 40N 42N 44N 45N 49N 54N 56N 59N 61N 62N 63N 35N 36N 38N 40N 42N 44N 45N 49N 54N 56N 59N 61N 62N 63N 35N 36N 38N 40N 42N 44N 45N 49N 54N 56N 59N 61N 62N 63N during the cruise with a standard CTD
DCM
log(N2) [rad2 s-2]
log(KT) [m2 s-1]
log(#) [m2 s-1]
!! Concentration of NOx, measured during the cruise
NOx [µmol L-1]
in grey: instablity in grey: bad Batchelor fitting in grey: bad Batchelor fitting
12 m/s
wind
2 m/s
Mixed Layer !!Maximum of phytoplankton and nutrient
!! Pioneering measures of the vertical mixing coefficient on a latitudinal concentrations go upward with increasing
transect. latitude.
log(KT) [m2 s-1]
Below thermocline !! At some locations, relatively large values of the vertical mixing coefficient !!Also, mixing below the Mixed Layer increases
which may be relevant for phytoplankton distributions. with latitude.
!! Depth profiles of KT: surface intensified (10-3-10-1 m2 s-1), thermocline
Thermocline weakened (10-6-10-5 m2 s-1), below thermocline weakly intensified !! Sub-mixed layer mixing seems to have
(10-5-10-3 m2 s-1). an important effect on the DCM and the
!! Raised mixing below the Mixed Layer towards higher latitudes. No nutrients distribution.
significant trend in the Mixed Layer, coupled to weather conditions.
References Acknowledgements
1.!Ruddick et al. (2000). J. Atm. Ocean. Tech. 17(11):1541-1555; 2. Batchelor (1959). J. Fluid. Mech. 5: 113-133; 3. Dillon and Caldwell (1980). J. Geophys. Res. 85: 1910-1916; 4. Oackey (1982). J. PELAGIA cruise.
Phys. Ocean. 12: 256-271; 5. Osborn and Cox (1972). Geophys. Astrophys. Fluid Dyn. 3(1):321-345; 6. Osborn (1980). J. Phys. Ocean. 10(1): 83-89; 7. MORE DETAILS in, Cruise report STRATIPHYT-1. This work is supported by NWO-ZKO through the STRATIPHYT project.
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