Ecosystem changes after the SEEDS iron Ecosystem changes after the SEEDS iron fertilization in the western North Pacific fertilization in the western North Pacific

simulated by asimulated by aone-dimensional ecosystem modelone-dimensional ecosystem model

Naoki Yoshie1, Masahiko Fujii2, and Yasuhiro Yamanaka1

1Graduate School of Environmental Earth Science, Hokkaido Univ., Japan2School of Marine Sciences, Univ. of Maine, USA

naoki@ees.hokudai.ac.jp

Contents of today’s talkContents of today’s talk

1.1. IntroductionIntroduction of iron in the ocean of iron in the ocean [3 sheets][3 sheets]

2.2. Iron fertilization experiment in theIron fertilization experiment in thewestern North Pacific western North Pacific “SEEDS-I”“SEEDS-I” [2 sheets][2 sheets]

3.3. Ecosystem model Ecosystem model “NEMURO”“NEMURO” [3 [3 sheets]sheets]

4.4. SimulationSimulation of SEEDS-I by NEMURO of SEEDS-I by NEMURO [4 [4 sheets]sheets]

Importance of iron for Importance of iron for phytoplankton phytoplankton

Iron is anIron is an micro-nutrientmicro-nutrient and used for many biological and used for many biological and chemical processes in the cell of phytoplankton.and chemical processes in the cell of phytoplankton.

ProcessProcess CatalystCatalystPhotosynthesis & respiration: Photosynthesis & respiration: heme [cytochromeheme [cytochromec, bf6c, bf6], Fe-S ], Fe-S proteins [ferrodoxin], aconitase… proteins [ferrodoxin], aconitase…Detoxification of reactive oxygen:Detoxification of reactive oxygen: superoxide dismutasesuperoxide dismutaseNitrogen metabolism:Nitrogen metabolism: nitrate & nitrite reductasenitrate & nitrite reductase

Availability of Iron Availability of Iron controlscontrols,,1.1. productivityproductivity,,2.2. species compositionspecies composition,,3.3. trophic structuretrophic structure of planktonic communities.of planktonic communities.

Simplified iron cycle in the oceanSimplified iron cycle in the ocean

Major sources of iron in the open ocean are dust and upwelling.NE Pacific : upwelled iron < aerosol iron (from

Martin)S. Ocean : upwelled iron > aerosol iron (from de

Baar)

AerosolIron

UpwelledIron

Uptaked by PhytoplanktonDissolved

Iron

ParticulateIron

Observed iron conc. in N Pacific (Morel and Price 2003)

Dep

th (

m)

0

1000

2000

3000

4000

Climate change affects the fluxes of dust and upwelling.

Iron depletionin the surface

85E 120E

5N

What’s role of aeolian dust in marine What’s role of aeolian dust in marine ecosystem?ecosystem?

165E

55NMineral Dust Transport and Deposition (from Uematsu)

SeaWiFS: Apr. 11, 2001

MODIS: Mar. 20, 2001

Dust stream over Korea

Satellite images of duststorm (from Uno)

Aeolian dust is an important iron supplier to the marine ecosystem in the western North Pacific.

EisenEx EiFexEisenEx EiFex

SOIREESOIREE

, II, II

SOFeXSOFeX

SEEDSI &II

SERIESSEEDSI &IISEEDSI &II

SERIESSERIES

IronEx IIronEx I

CYCLOPSCYCLOPSFeEPFeEP

What is “SEEDS”?What is “SEEDS”?

Mesoscale iron fertilization experiments in the world

SEEDS (Subarctic pacific iron Experiment for Ecosystem Dynamics Study)is an iron fertilization experiment in the western North Pacific.

The general result of SEEDS-I was reported by Tsuda et al., 2003 in Science, and details were summarized in the SEEDS special issue (2005) in Prog. Oceanogr.

Courtesy of Boyd

Observed feature of SEEDS-IObserved feature of SEEDS-I(From Tsuda et al., 2003)

Time lag

The time lag between iron-fertilization and start of bloom was observed. The reason of this time lag was initially considered as the delay of diatom’s physiological response.

During observation period, a lot of particulate organic carbon (POC)was suspended in the surface water and was not exported to deeper layers.

The time lag and the fate of POC were demonstratedby ecosystem model “NEMURO for SEEDS”.

An ecosystem model “NEMURO”

NEMURO (3N-2P-3Z-3D) coupled with carbon-calcium cycle (Yamanaka et al., 2004)

A lower trophic level ecosystem model “NEMURO (North pacific Ecosystem Model Used for Regional Oceanography)” was developed by MODEL task team of PICES (North Pacific Marine Science Organization) focusing on linkage between lower and higher trophic levels. Around 30 papers were published and submitted.

NEMURO do not explicitly include iron cycles, because NEMURO originally focuses on ecosystem dynamics.

3Nut 3Det

2Phyt

3Zoo

Simulation of SEEDS-I by Simulation of SEEDS-I by NEMURONEMURO

(Yoshie (Yoshie et alet al., 2005)., 2005)

In addition to the iron cycle built into ecosystem model, we had to change in ecosystem dynamics for simulating SEEDS-I.

That is, we divided diatom into two groups: sensitive and insensitive to iron fertilization, in NEMURO.

We extended NEMURO for We extended NEMURO for SEEDSSEEDS

We extended NEMURO for We extended NEMURO for SEEDSSEEDS

We assumedcentric : low potential in low iron conc.

high potential in high iron conc.pennate: med. potential regardless of iron conc.

2 diatoms centric pennate

The iron fertilization experiment was conducted by changing P-I parameters of diatoms (e.g. Chai et al., 2002; Fujii et al., 2005)

Results of model Results of model simulationssimulations

Results of model Results of model simulationssimulations

NEMURO for SEEDS successfully reproduced observed time change including the time lag.

Time lag

Total potential averaged by two diatoms hardly changes from day 0 to 4, because contribution of centric to total biomass is negligibly small.

Why SEEDS has the time lag?Why SEEDS has the time lag?

Increasing the biomass of centric diatom takes several days.

Simulations after the observation Simulations after the observation period period

Simulations after the observation Simulations after the observation period period

Phytoplankton biomass has its peaks during the observation period. Phytoplankton biomass has its peaks during the observation period. Cumulative POC export flux increases gently, and its value at day13 (the last Cumulative POC export flux increases gently, and its value at day13 (the last day of observation) reaches only about 25 % of its total change over 48 days. day of observation) reaches only about 25 % of its total change over 48 days.

NEMURO for SEEDS demonstrates that the fixed organic NEMURO for SEEDS demonstrates that the fixed organic carbon sinks to deeper layers after the observation period.carbon sinks to deeper layers after the observation period.

25%

100%

SummarySummary

Why SEEDS had the time lag between iron-fertilization and starting bloom?BecauseBecause the time lag was caused the time lag was caused not by the delay of physiological not by the delay of physiological response of diatom (at least SEEDS-I)response of diatom (at least SEEDS-I),,but but by the delay of increment of high-potential diatomby the delay of increment of high-potential diatom..

Addition to introducing iron into simple ecosystem models, Addition to introducing iron into simple ecosystem models, intermediate complexity ecosystem model intermediate complexity ecosystem model representing ecosystem dynamicsrepresenting ecosystem dynamics is necessary to is necessary to reproduce the iron fertilization experiment.reproduce the iron fertilization experiment.

Thank you