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nut_phyto 






Phytoplankton Chlorophyll and Nutrient Studies

  on Georges Bank

David W. Townsend, Keska Kemper, Maura A. Thomas, 

   Annette L. Brickley and Abigail M. Deitz 




PROJECT OVERVIEW:


The project began in the winter of 1997 as part of the U.S.  GLOBEC Georges Bank Program.
The purpose of our component of that multi-institutional study is to
investigate the idea that the growth and production of zooplankton
and fish on Georges Bank are limited by the amount of nutrients
(especially nitrogen) that is brought onto the Bank from the
nutrient-rich, deeper waters around the Bank's edges (cf.  Townsend
and Pettigrew, 1997).  



The sampling period was chosen to bracket the winter-to-spring
transition, which is coincident with the Georges Bank GLOBEC broad
scale cruises conducted in 1997, 1998 and 1999.  The cruise dates
were:



1997*January 13 - 20 (R/V Albatross) 
    *February 11 - 22 (R/V Oceanus) 
    *March 16 - 29 (R/V Oceanus) 
    *April 20 - May 3 (R/V Oceanus) 
    *May 19 - 30 (R/V Oceanus) 
    *June 18 - 28 (R/V Albatross)

1998*February 7 -17 (R/V Oceanus)
    *March15 - 26 (R/V Oceanus)
    *April  16 - 26 (R/V Oceanus)
    *May 10 - 20 (R/V Albatross)
    *June 17 - 25 (R/V Albatross)   

1999*January 11 - 24 (R/V Albatross)
    *February 11 - 23 (R/V Oceanus)
    *March 10 - 23 (R/V Endeavor)
    *April 16 - 28 (R/V Oceanus)
    *May 19 - 27 (R/V Albatross)
    *June 14 - 24 (R/V Albatross)





Water samples were collected on all cruises for the analysis of
phytoplankton biomass (chlorophyll a and phaeophytin).  In addition,
dissolved inorganic nutrient concentrations (NO3+NO2, SiO4, PO4 and
NH4) were determined for four of the six Broadscale cruises in 1997,
five of six in 1998, and all six in 1999.  Water collections were made
at various depths at all of the regular hydrographic stations (1-40 or
Sta 41 after 1997) using Niskin bottles mounted on the rosette
sampler.  Additional surface water samples were collected at positions
between the regular stations (numbered >41; refer to 
Station Location Map for example).  Note that because data files
are in some cases ordered by station number, time does not necessarily
increase monotonically throughout a given data file.  Detection limits
for ammonia vary for each month of analysis; for details contact Maura
Thomas (mthomas@maine.edu) or David Townsend (davidt@maine.edu).




Phytoplankton chlorophyll a and phaeopigments were determined
fluorometrically (Parsons et al., 1984).  The extracted chlorophyll
measurements involved collecting 100ml from all bottle samples taken
at depths shallower than 60m, filtering through GF/F filters, and
extracting in 90% acetone in a freezer for at least 12 hours.  The
samples were analyzed at sea using a Turner Model 10 fluorometer.



Water samples for DIN were filtered through 0.45 Millipore cellulose
acetate membrane filters and then frozen immediately in 20ml
acid-washed polyethylene scintillation vials by first placing the
vials in a seawater-ice bath for approximately 10 minutes.  Samples
were analyzed in the lab following the cruise using a Technicon II
4-Channel Auto-Analyzer.



In addition to dissolved inorganic nutrients and chlorophyll, in
1999 we are also analyzing samples for particulate organic carbon
and nitrogen, dissolved organic nitrogen, and particulate and
dissolved organic phosphorus.



Results from the vertical profiles taken at each station can be
viewed as contour plots (using Surfer Software, Golden Colorado) for
1997,
1998
  and 
1999.
  Plotted variables include Temperature and
Salinity for the hydrographic data, Chlorophyll a for the pigment
analyses and Nitrate plus Nitrite, Silicate, Ammonium and Phosphate
for the inorganic nutrient analyses.  The hydrographic data were
contoured only for the surface(2m).  The pigment and inorganic
nutrient concentrations were contoured for the surface(2m), 20meter
and 60 meter depths.




FIELD NAMES:






Field Name Description Units 


chl_a  chlorophyll a pigment, in  
   milligrams per meter cubed (mg/m3) or 
  	micrograms per liter (µg/l)  
	


day Day  n/a  


depth Sample depth  meters  


flvolt fluorometer voltage measurement  Volts  


lat Latitude  Decimal degrees  


lon Longitude  Decimal degrees  


month Month  n/a  


NH4  Ammonium  µM (micromolar) or µg-at NH3-N/l   


NO3_NO2  Nitrate and Nitrite 
	 µM (micromolar) or µg-at NO3-N and NO2-N/l  


phaeo total phaeopigment 
    milligrams per meter cubed (mg/m3) 
   or micrograms per liter (µg/l)   


PO4 Orthophosphate  µM (micromolar) or µg-at PO4-P/l  


press Pressure  Decibars  


sal Salinity  practical salinity units  


Si(OH)4 Orthosilicic Acid  µM (micromolar) or µg-at Si(OH)4-Si/l  


station_std Standard station number  n/a  


temp Temperature  Degrees Centigrade  


time Time (local)  n/a  


yrday_local Year day, local time  Decimal number  








REFERENCES:


Parsons, T.R., Y.  Maita and C.M.  Lalli.  1984.  A Manual of
Chemical and Biological Methods for Seawater Analysis.  Pergamon,
Oxford.  173pp.




Townsend, D.W.  and N.R.  Pettigrew.  1997.  Nutrient limitation of
secondary production on Georges Bank.  J.  Plankton Res.  19:
221-235.