Eddy-driven changes in phytoplankton community composition and biogeochemical cycling in the Sargasso Sea NASA A regional eddy-resolving carbon cycle model surrounding the Bermuda Atlantic Time-Series Study (BATS) site: analysis of remotely sensed and in situ observations NSF EDdy Dynamics, MIxing, Export, and Species composition VIMS

New Production in the Open Ocean

H 1 : Eddy-induced upwelling, in combination with diapycnal mixing in the upper ocean, introduces new nutrients into the euphotic zone. H 2 : The increase in inorganic nutrients stimulates a physiological response within the phytoplankton community. H 3 : Differing physiological responses of the various species bring about a shift in community structure. H 4 : Changes in community structure lead to increases in export from, 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. Depth

Objectively Mapped Sea Level Anomaly Real time data feed: Bob Leben, CCAR

Cyclone C1 SLA and shipboard ADCP Temp. Sal. Fluor. O 2 Sat Hydro Section: 0-250m

C1 Phytoplankton Species Composition CHORS HPLC + Letelier et al. (1993)

Cyclone C1 oxygen profiles Outside Survey 1 Inside Survey 2 Inside Survey 1 Implied remineralization: 1-3 X ANP BATS Envelope

Target Feature A4 Sea Level Anomaly Cross Section

A4 Chl Peak vs. BATS BATS: mean=.28; std=0.14; max=1.15 A4 Peak = 1.4 Shipboard cell counts: Chaetoceros spp colonies l cells per colony = ~10 5 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 # Observations

MODIS Image of A4 August 6, 2005 Chlorophyll SST

A4 Productivity vs. BATS Primary Production (mg C m -3 d -1 )

A4 Deep Oxygen Anomaly Implied remineralization = 1.6 X ANP BATS envelope

A Regional Hindcast Model Around BATS Valery Kosnyrev

BATS Retrospective Analysis Blue: Cyclones Red: Anticyclones Pink: Mode-water Eddies BATS HPLC + Letelier et al. (1993) % total 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

Upwelling calculations for A4 QSCAT Ship Vertical velocity w ave =0.27 m d -1

CycloneMode-Water Eddy Upper therm. disp.Upward MacronutrientsEnhancement Eddy-wind int.DownwellingUpwelling MixingEnhanced Revisions to the conceptual model Diatoms Picoplankton

EDDIES data document extreme variability Chl a, 14 C Productivity, O 2 Cyclones and MWEs produce phytoplankton blooms MWEs: extraordinary (relative to BATS) sustained diatom biomass MWEs favor enhanced nutrient supply enhanced mixing upwelling (wind + heating) Export flux can be inferred from O 2 anomalies in the aphotic zone C1 signal: 1-3 x ANP: “The Smoking Gun” Conclusions

WHOI LANL Dennis McGillicuddy Mat Maltrud Larry Anderson Rick Smith Scott Doney A High Resolution Model of the North Atlantic Cyclones + MWEs; τ (u a,u o ); 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 BATS: blue dots 14 C Productivity Inside A4 Core PP (mg C m -3 d -1 ) Depth (m)

BATS Retrospective Analysis Blue: Cyclones Red: Anticyclones Pink: Mode-water Eddies BATS HPLC + Letelier et al. (1993) % total Chl Sweeney et al. (2003)