eddy-driven changes in phytoplankton community composition and biogeochemical cycling in the...
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Eddy-driven changes in phytoplankton Eddy-driven changes in phytoplankton community composition and community composition and
biogeochemical cycling in the Sargasso Seabiogeochemical cycling in the Sargasso Sea
NASAA regional eddy-resolving carbon cycle model surrounding the Bermuda Atlantic Time-Series Study (BATS) site: analysis of remotely sensed and in situ observationshttp://science.whoi.edu/users/mcgillic/tpd/anim.html
NSF EDdy Dynamics, MIxing, Export, and Species composition
http://science.whoi.edu/users/mcgillic/eddies/Eddies_Project.html
VIMS
2222 OOCHOHCO
tonPhytoplank
4443 SiOH , PO , NO
Nutrients
Fish) nZooplankto(
0I
0I 1%
New Production in theNew Production in theOpen OceanOpen Ocean
12yrm N mol 0.8-0.5
H1: Eddy-induced upwelling, in combination with diapycnal mixing in the upper ocean, introduces new nutrients into the euphotic zone.
H2: The increase in inorganic nutrients stimulates a physiological response within the phytoplankton community.
H3: Differing physiological responses of the various species bring about a shift in community structure.
H4: Changes in community structure lead to increases in exportfrom, and changes in biogeochemical cycling within, the upper ocean.
Hypotheses
Three types of eddies in the Sargasso Sea
Conceptual model:Cyclones and Mode-Water Eddies will cause plankton blooms
as they form and intensify.
Dep
th
Objectively Mapped Sea Level AnomalyObjectively Mapped Sea Level Anomaly
Real time data feed: Bob Leben, CCARhttp://www-ccar.colorado.edu/realtime/nwatlanticreal-time_ssh).
Cyclone C1
SLA and shipboard ADCP
Temp.
Sal.
Fluor.
O2
Sat
Hydro Section: 0-250m
C1 Phytoplankton
Species Composition
CHORS HPLC + Letelier et al. (1993)
Cyclone C1 oxygen profiles
OutsideSurvey 1
Inside Survey 2
InsideSurvey 1
Implied remineralization: 1-3 X ANP
BATS Envelope
Target Feature A4
Sea Level Anomaly
Cross Section
A4 Chl Peak vs. BATS 1988-2003
BATS: mean=.28; std=0.14; max=1.15
4( ( ) ) ( ( ) ) 8A BATSMax Chl z Max Chl z
A4 Peak = 1.4
Shipboard cell counts: Chaetoceros spp. 8000 colonies l-1 15 cells per colony = ~105 cells l-1
Typical diatom conc: 1-10 cells l-1
A4 enhancement: 4-5 orders of magnitude above background
CHORS HPLC: diatoms>60%total Chl a
μg Chl a l-1
# O
bser
vati
ons
MODIS Image of A4August 6, 2005
Chlorophyll SST
A4 Productivity vs. BATS 1988-2003
Primary Production (mg C m-3 d-1)
A4 Deep Oxygen Anomaly
Implied remineralization = 1.6 X ANP
BATSenvelope
A Regional Hindcast Model Around BATSA Regional Hindcast Model Around BATS
Valery Kosnyrev http://science.whoi.edu/users/mcgillic/tpd/tpd.html
BATS Retrospective Analysis 1993-1995BATS Retrospective Analysis 1993-1995
Blue: Cyclones Red: Anticyclones Pink: Mode-water Eddies
BATS HPLC + Letelier et al. (1993)
% to
tal
Chl
Sweeney et al. (2003)
Why are Mode-water eddies so productive?
1. Enhanced mixing: trapping and amplification of near-inertial motions (Kunze, 1985)
2. Upwelling due to eddy-wind interactions (Martin and Richards, 2001)
Martin and Richards
oaoa
aa uuuuK
21
yxf
w xyE
1
Upwelling calculations for A4
QSCAT Ship
Vertical velocitywave=0.27 m d-1
Cyclone Mode-Water Eddy
Upper therm. disp. Upward Upward
Macronutrients Enhancement Enhancement
Eddy-wind int. Downwelling Upwelling
Mixing Enhanced
Revisions to the conceptual model
DiatomsPicoplankton
EDDIES data document extreme variabilityChl a, 14C Productivity, O2
Cyclones and MWEs produce phytoplankton blooms
MWEs: extraordinary (relative to BATS) sustained diatom biomass
MWEs favor enhanced nutrient supplyenhanced mixingupwelling (wind + heating)
Export flux can be inferred from O2 anomalies in the aphotic zoneC1 signal: 1-3 x ANP: “The Smoking Gun”
Conclusions
WHOI LANLDennis McGillicuddy Mat MaltrudLarry Anderson Rick SmithScott Doney
A High Resolution Model of the North AtlanticA High Resolution Model of the North Atlantic
Cyclones + MWEs; τ (ua,uo); diatoms + picoplankton
End
ADCP Shear: C5, A4, C3 (OC415)
Cyclone C1 oxygen profiles
Outside, Survey 1
Inside, Survey 2
Inside,Survey 1
Implied remineralization: 1-3 X ANP
A4 Productivity vs. BATS 1988-2003
BATS: blue dots 14C ProductivityInside A4 Core
PP (mg C m-3 d-1)
Dep
th (
m)
BATS Retrospective Analysis 1993-1995BATS Retrospective Analysis 1993-1995
Blue: Cyclones Red: Anticyclones Pink: Mode-water Eddies
BATS HPLC + Letelier et al. (1993)
% to
tal
Chl
Sweeney et al. (2003)