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Douglas Speirs

Jo King:. Mechanisms relating the ocean-scale distribution of Calanus finmarchicus to environmental heterogeneity. Douglas Speirs. Acknowledgments: Bill Gurney (Strathclyde) Mike Heath (FRS Aberdeen)

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Douglas Speirs

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  1. Jo King: Mechanisms relating the ocean-scale distribution of Calanus finmarchicus to environmental heterogeneity Douglas Speirs Acknowledgments: Bill Gurney (Strathclyde) Mike Heath (FRS Aberdeen) Simon Wood (Glasgow University) SOC, PML, SAHFOS

  2. Why Calanus finmarchicus ? • Widespread & Abundant • Links to Fish Stocks • Extensively studied 2 mm

  3. Continuous Plankton Recorder Surveys

  4. Calanus abundance and Circulation

  5. 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.

  6. Coupling Life-Cycle to Physical Oceanography

  7. 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)

  8. A Calanus-focussed model

  9. Representing Physical Transport Update at regularly spaced times: Ti Class abundance just before update Class abundance just after update Transfer matrix element from y to x for period to Ti. Determine by particle tracking in flow fields from GCM plus random (diffusive) component.

  10. The Biological Model • Uniform ‘physiological age’ for each group of stages • Development rate a function of temp. and food • Diapause entry from start of C5 stage – cued by low food

  11. Updating the Biological Model Update all classes in given group at given location at times {Ux,i} such that according to where Survival of individual in q at x over increment up to u

  12. Updating the system state For each cell, in turn: • Collect all un-processedupdates from the adult, surface developer and diapauser groups • Form the union of the subsets of each sequence which fall before the next transport update • Process the new sequence in time order, updating all classes in that group at that location at each operation. Do next transport update, Output state variables. Produces model realisations in good agreement with PDE and Lagrangian ensemble solutions, but MUCH faster.

  13. Prototype - Environment Winter (day 42) Spring (day 133) Summer (day 217) Autumn (day 308) Flow (HAMSOM) Temp. (HAMSOM) Food (SeaWiFS)

  14. Prototype – diapause control hypotheses

  15. N.E. Atlantic - test data • Overall plausibility test • Continuous Plankton Recorder surveys (SAHFOS) • Winter surveys of resting stages Ocean Weathership M Westmann Islands Saltenfjorden Murchison Faroe shelf Foinaven Stonehaven

  16. Hypothesis Testing - OWS Mike Surface Copepodites Diapausers H1 H1 H3 H3 Newly surfaced overwinterers Sharp drop at awakening No diapausers in spring

  17. Plausibility test – Diapausers Winter (day 28) Spring (day 154) Summer (day 224) Autumn (day 336) H1: H3:

  18. Plausibility test – Surface Copepodites Winter (day 28) Spring (day 154) Summer (day 224) Autumn (day 336) H1: H3:

  19. Prototype - Conclusions • Spatially and physiologically resolved model on an ocean • basin scale can be made fast enough for wide-ranging • parameter exploration • Current data on C. finmarchicus abundance in the N.E. • Atlantic is best fitted by a model which assumes diapause is • initiated by low food conditions. • Models which assume diapause duration is determined by • development are invariably falsified • Awakening must be conditioned on a highly spatially • correlated cue – such as photoperiod.

  20. Test Data – Time Series & CPR

  21. Prototype Model - Time Series Test Gulf of Maine OWS Mike surface C5-C6 diapause C5

  22. Prototype Model – CPR Test observed predicted observed Jan./Feb. May/Jun. Jul./Aug.

  23. C5’s & phytoplankton carbon at OWSM • Diapause occurs at end of C5 stage • Fixed fraction of each generation

  24. Annual Mean Temperature & Food => temperature-dependent background mortality Labrador Sea is cold

  25. Revised Model - Time Series Test Gulf of Maine OWS Mike surface C5-C6 diapause C5

  26. Revised Model – CPR Test observed predicted Jan./Feb. May/Jun. Jul./Aug.

  27. Yearly Population Cycle

  28. The Impact of Transport

  29. Domain Connectivity Year 1 Year 3 Year 6

  30. Conclusions Matching Calanus demography => • Fractional diapause entry • Diapause entry late in C5 • Photoperiod-cued diapause exit • Temperature-dependent mortality • Limited impact of transport • High domain connectivity Fitted model => • Ocean-scale population model feasible • Numerical efficiency is key

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