# Presentation: 306545

## 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
- 	http://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

## New Production in the

- Open Ocean

## Hypotheses

- 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 export
- from, and changes in biogeochemical cycling within, the upper ocean.

## 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
- http://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

- 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 1988-2003

- BATS: mean=.28; std=0.14; max=1.15

- 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

- # Observations

## MODIS Image of A4August 6, 2005

- 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

- BATS
- envelope

## A Regional Hindcast Model Around BATS

- Valery Kosnyrev    http://science.whoi.edu/users/mcgillic/tpd/tpd.html

## BATS Retrospective Analysis 1993-1995

- 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?

- Enhanced mixing: trapping and amplification of
-       near-inertial motions (Kunze, 1985)
- Upwelling due to eddy-wind interactions
-       (Martin and Richards, 2001)

## Martin and Richards

## Upwelling calculations for A4

## Revisions to the conceptual model

|  | Cyclone | Mode-Water Eddy |
| --- | --- | --- |
| Upper therm. disp. | Upward | Upward |
| Macronutrients | Enhancement | Enhancement |
| Eddy-wind int. | Downwelling | Upwelling |
| Mixing |  | Enhanced |

- Diatoms

- Picoplankton

## Conclusions

- 	Chl a, 14C Productivity, O2
- 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 O2 anomalies in the aphotic zone
- 	C1 signal: 1-3 x ANP: “The Smoking Gun”

## A High Resolution Model of the North Atlantic

- WHOI                            	 LANL
- Dennis McGillicuddy         Mat Maltrud
- Larry Anderson               	 Rick Smith
- Scott Doney

- 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 Productivity
- Inside A4 Core

- PP (mg C m-3 d-1)

- Depth (m)

## BATS Retrospective Analysis 1993-1995

- Blue: Cyclones      Red: Anticyclones       Pink: Mode-water Eddies

- BATS HPLC + Letelier et al. (1993)

- % total Chl

- Sweeney et al. (2003)