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)