Mesoscale Eddy Variability in the Sargasso Sea and its impact on Upper Ocean Biogeochemistry
Rodney J Johnson, Nicholas Bates, Dennis J. McGillicuddy, Andreas AndersonSteve Bell, Nathan Buck, Tony Knap, Paul Lethaby, Vivienne Lochhead, Keven Neely,
Christine Pequignet, Sybille Pluvinage and Megan Roadman
1- Bermuda Bilo ….., 2 - WHOI …...
Objectives
DataBATS years 1988-2004BATS Validation #18, 19 : Survey cruises of cyclone to the east of BermudaEDDIES Transects 1 &2EDDIES Transects 3&4
Location Map of Bermuda Time-series Sites overlaid on Sea Surface Height
Sea surface height data courtesy of (http://www-ccar.colorado.edu)
r=0.49
r=0.81 r= -0.39
r= -0.35
BVAL 18(07/Jul/1997 to 13/Jul/1997)Target Feature: Cyclone 240km to ENE of BermudaSurvey Grid:A 5X5 -160km2 box with 40km station spacing 35 CTD casts (0-700m)(28 with biogeochemistry)25 XBT drops (mid -way between stations and Eddycenter) BVAL 19(22/Jul/1997 to 29/Jul/1997)Target Feature: repeat survey of BVAL18 cycloneSurvey Grid: Added a legto the south, north and line through Eddy center43 CTD casts (0-700m)(34 with biogeochemistry)29 XBT drops (mid -way between stations and Eddycenter)
(a) BVAL18 Temperature - 80m (d) BVAL19 Temperature - 80m
(b) BVAL18 Nitrate (umol/kg) - 80m (e) BVAL19 Nitrate (umol/kg) -80m
(c) BVAL18 Chlorophyll_a (ug/kg) - 40m (f) BVAL19 Chlorophyll _a (ug/kg) - 60m
1-D Model (Physical- Price et al, 1986; NO3-McGillicuddy & Robinson, 1997) results showing nitrate uptake at 80m. Model initialized with BVAL18 Eddy center conditionson 07/July. BVAL19 80m NO3 at Eddy center shown as red circle. Total estimated model uptake in the euphotic zone for the 35 day run was found to be 0.14 mol N m -2 .
EDDIES 2004 Transect Cruises
EDT1 Operations (July 2004) Target Feature : Cyclone C1Transect#1: NE-SW through EC (St.111)Transect#2: S-N through EC (St. 110) ]30 CTD Casts ( black triangles)2 Sediment Trap Deployments [1 at EC and control at NE of C1 (red dots)3 Production deployments9 Thorium pump profiles
EDT2 Operations (Aug 2004)Target Feature : Cyclone C1Main Transect :N-S through EC (St. 264)27 CTD Casts (black triangles)1 Sediment Trap Deployment at EC ( red dots)1 Production deployments at EC9 Thorium pump profiles
EDT3 Operations (July 2005)Target feature : Anticyclone A4Transects: E-W through EC(St.2317)N-S through EC(2316)43 CTD casts (blue solid circles)2 Sediment Trap deployments at EC( Array A - blue track, Array B -green track)3 Primary production deployments at EC(red asterisk)8 Thorium pump profiles8 SPMR profiles
EDT4 Operations (August 2005)Target feature : Anticyclone A4Transects:W-E through EC (St.2070)43 CTD casts (blue solid circles)2 Sediment Trap deployments at EC( Array A - blue track, Array B -green track)3 Primary production deployments( 1 at EC, 1 at Traps A and 1 at Traps B)8 Thorium pump profiles8 SPMR profiles
EDDIES 2005 Transect Cruises
Import O2 profiles from Bval 18, 9 to showpossible o2 deficit ……I.e wanting to show thateddies seem to generate O2 deficits .
More I look at the timeseries always seems to be indications
[BATS (1989-2004) min,mean,max shown as solid black lines ]
Mass C N 2004 Cyclone C1EDT1 - EC 65.3 19.3 2.7EDT1- Control 47.9 12.7 1.9EDT2 -EC 68.1 23.0 3.5EDT2- B190 Control 77.0 22.8 3.3
2005 Mode Water Eddy - A4EDT3 - EC Array A 81.2 17.2 2.6EDT3 - EC Array B 61.0 14.6 2.2EDT4 - EC Array A 68.0 12.5 2.2EDT4 - EC Array B 59.0 12.3 2.0
BATS Climatology (summer 1988-2003)Mass(150m) 107.8 39.0 mg m-2 day-1
Carbon (150m) 27.2 8.0 mg C m-2 day-1
Nitrogen (150m) 4.3 1.5 mg N m-2 day-1
2004 - C1EDT1-PP1 at Eddy Center 536EDT1-PP2 at Eddy Center 367EDT1-PP3 at high fluorescence site 307( south west of eddy center)EDT2-PP1 at Eddy Center 594
2005-Mode Water Eddy A4EDT3-PP1 at Eddy Center 200EDT3-PP2 at Eddy Center 311EDT3-PP3 at Eddy Center 307EDT4-PP1 at Eddy Center 808*EDT4-PP2 at sediment traps A 650*EDT4-PP3 at sediment traps B 605*
BATS Climatology (summer 1988-2003)
426 ± 207 mg C m-2 day-1
EDDIES IntegratedPrimary Production(0-140m)
EDDIES Sediment Trap Flux
Summary and Conclusions
3 different responses
BVAl18 Large Nutrient injection with considerable consumption over weeksConsumption consistent with simple uptake dynamics
C1 - no observed enhancement , state of decay, Large O2 anomaly. O2 remnant reduces between Edt1 and EDT2 suggest local dynamics at play. Deficit equivalent to 1.5 m N
A4 - Elevated biomass as indicated by Fluorometer and POC at EC, Obvious liftingof seasonal thermocline. Very patchy … sub 20km scale for resolution. Deep O2 minwhich seems to develop between cruises. Magnitude similar to C1 O2 Anomaly. Supports very high prodcutivity in EDT4 , yet low trap flux!! The Dichotomy !
Clear Eddies are far more complex than antciapted givene patchiness, age and laos seems MW eddies may have biggest ecological efefct yet cant identify from satellite.
BATS implictions …huge for doing assement of dynamic systems, since we never knowwhere we really are situated in the eddy with just a single point measurement. A joint vesselhigh resolution survey striggled to capture eddy center over aperiod of 2-4 weeks !
