Ocean-scale modelling of

Calanus finmarchicus

Douglas Speirs

Acknowledgments: Bill Gurney (Strathclyde)

Mike Heath (FRS Aberdeen)

Simon Wood (Glasgow University)

SOC, PML, SAHFOS, US-GLOBEC

Calanus finmarchicus – a marine copepod

2 mm

• Up to 90% of copepod biomass throughout the sub-arctic North Atlantic.

• Important prey species for fish in both shelf and ocean ecosystems.

• Extensive database from field surveys and laboratory experiments.

The life-cycle of Calanus finmarchicus

• Omnivorous, but feeds mainly on phytoplankton.

• x1000 difference in body weight between eggs and adults.

• Stage duration strongly dependent on temperature

• Naupliar survival strongly dependent on food.

• Reproduction & growth in upper layers (<200m).

• Overwinters in a resting state at depths of 500-2000m.

Coupling Life-Cycle to Physical Oceanography

NORTH ATLANTIC OCEAN SHELF SEAS

Overwintering at depth

Export to shelf seas

Growth and reproductionin the upper ocean

In the ocean, Calanus switchesbetween surface and deepcirculation regimes during eachannual cycle.

Each spring, the shelf seas arere-colonised with Calanus fromthe ocean.

Calanus abundance and Circulation

The modelling challenge

The Challenge• Physiologically and spatially explicit demographic model

• Ocean-basin scale – advection plus diffusion

• Hypothesis tests require wide parameter exploration

• Need exceptional computational efficiency

The Solution• Focus on Calanus (physical and biotic environment as given)

• Separate computation of physical and biological components

• Discrete-time approach ( 104 speed-up relative to Lagrangian ensemble)

A Calanus-focussed model

The Biological Model

• Development rate a function of temperature and food

• Diapause entry from end C5

• Fixed fraction of each generation enter diapause

• Diapause exit photoperiod cued

• Surface mortality increases with biomass and temperature

Yearly Population Cycle

Continuous Plankton Recorder Surveys

Test Data – Time Series & CPR

Water column integrated abundance of overwintering C4 and C5 C. finmarchicus

-60 -50 -40 -30 -20 -10 0 10

Longitude

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70L

atit

ud

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0 10000 20000 30000 40000 50000

C alanus finm arch icus ( m - 2 , 0 - 3 0 0 0 m )C5

Time Series Test

Gulf of Maine

OWS Mike

surfaceC5-C6

diapauseC5

Diapauser Survey Test

CPR Test

Jan./Feb.

May/Jun.

Jul./Aug.

observed predicted

August Sea Temperature at 20m

The Impact of Transport

Domain Connectivity

Year 1

Year 3

Year 6

Travels of the Great Salinity Anomaly

Conclusions

•Ocean-scale population model feasible•Numerical efficiency is key

•Fractional diapause entry

•Diapause entry late in C5

•Photoperiod-cued diapause exit

•Temperature-dependent mortality

•Limited impact of transport

•High domain connectivity

Washout of a non-developing population from Gulf of Maine

Boundary effects on C5-C6 seasonal cycle

Gulf of Maine Export

Invasion of Gulf of Maine

Future Prospects

•

• Tests on independent data sets (UK-GLOBEC Irminger Sea data)

• Automated parameter optimization

• Hindcasting of decadal trends

• Nested models for shelf regions

• Coupled target species - ecosystem models

Calanus abundance map compiled from data supplied by SAHFOS toNERCMarine Productivity project GR2/2749 and the EU-TASC project

1958-1999 average surface abundance of C. finmarchicus (stage C5 and CVI)

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-6 -4 -2 0 2 4 6NAO index

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1996-onwards

Annual Mean Temperature & Food

Overwintering depths in various regions...

-3500

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Dep

th (m

)

LS MAR IrB IcB RB NEI FSC ENS NT

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Longitude

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C alanus finm arch icus ( m - 2 , 0 - 3 0 0 0 m )

C5

Calanus abundance map compiled from data supplied by SAHFOS toNERCMarine Productivity project GR2/2749 and the EU-TASC project

Geographical focus of Marine Productivity and other Calanus-centric programmes during the 1990’s..

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050100150200250300350400450500550600

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Multi-nationalprogrammes:EU-ICOSEU-TASC

National programmes:UK, Norway, Germany, Denmark, Iceland, Canada, USA

NERC MarineProductivity

C5’s & phytoplankton carbon at OWSM

•Diapause occurs at end of C5 stage

•Fixed fraction of each generation