Subtropical Ocean Ecosystem. North Pacific Climate Variations

Transcription

1 Subtropical Ocean Ecosystem Structure Changes Forced by North Pacific Climate Variations Bob Bidigare Hawaii Institute tute of Marine Biology ogy University of Hawaii at Manoa

2 Acknowledgements HOT Personnel Dave Karl (UH) Roger Lukas (UH) Stephanie Christensen (UH) Cecelia Hannides (UH) Matthew Church (UH) Ricardo Letelier (OSU) Mike Landry (SIO) Yi Chao (JPL) Fei Chai (UM) NSF & NASA

3 Outline Background -Open-oceanic food web structure - Net export production External Forcing Mechanisms Operating in the Pacific - Anthropogenic forcing - Ocean climate variability Regime Shifts Materials & Methods - Field measurements - ROMS model - Ecosystem model Results & Discussion Interpretation t ti & Synthesis Conclusions & Future Directions

4 Open-Oceanic Food Web

5 Open-Oceanic Food Web Phytoplankton Pelagophyte ( Zooplankton Copepod (wikipedia.org) Prymnesiophyte ( g Diatom (astrographics.com) Cyanobacteria (hermes.mbl.edu) Euphausiid (wikipedia.org) Amphipod (wikipedia.org) Zooplankton tow (ad.brim.ac.cn )

6 Net Export Production N 2 fixation NO 3 - PON (Sediment Traps) Sigman&Hain_NatureEdu

7 Anthropogenic Forcing Influence of humankind on oceanic processes Examples - Fossil fuel burning (electricity production) -Over-fishing (human nutrition) - Iron enrichment (CO 2 sequestration) Anthropogenic impacts can result in climate change

8 Ocean Climate Variability El Niño - Southern Oscillation (ENSO): = 2-7 years (Rasmussen & Carpenter, 1982)

9 Ocean Climate Variability Pacific Decadal Oscillation (PDO): = ~15-25 years (Minobe, 1999) Warm Phase Cool Phase

10 Operational definition Regime Shifts For practical purposes, it is probably useful to accept as a regime shift, changes in marine system function that are relatively abrupt, persistent, occurring at large spatial scales, observed at different trophic levels and related to climate forcing. de Young et al. (2004)

11 Historical context Regime Shifts.there are probably bl a great number of possible regimes and abrupt discontinuities connecting them, flip-flops from one regime to another; multifarious regimes involving biology or climate, or oceanography, or migrations, temperature, or weather, or combinations of these, etc. Sardines, for example, are either here or not here. Isaacs (1976)

12 Regime Shifts Correlated with the PDO during Chavez et al. (2003)

13 Regime Shifts Characteristics - The time-scale for change between states is much shorter than the time within alternate states - The differences should include more than a few components of the ecosystem and cover more than one trophic level and more than a single species - The forcing mechanism for the shift is external to the biological ecosystem and is typically y triggered by changes in the physical environment de Young et al. (2004)

14 Regime Shifts Causal mechanisms - Change in food web structure caused by temporal variations in the availability of growth-limiting nutrients (bottom-up control) Increasing P new Steady-state food web interactions at a given system nutrient content (N T ) Thingstad (1998)

15 Regime Shifts Causal mechanisms - Removal of the keystone species (top-down control) (e.g., over-fishing) Control Removal of Keystone Species Thingstad (1998)

16 Regime Shifts Questions and uncertainties - It is not clear if regime shifts represent geographical shifts or local changes in food web structure (or a combination of both) - There is no convincing evidence that changes in ocean climate (ENSO or PDO) induce bi-stable modes in marine ecosystems - It is not clear if regime shifts have an oscillatory behavior or whether they represent a punctuated change in the equilibrium of an ocean system Steele (2004) & de Young et al. (2004)

17 Regime Shifts Questions and uncertainties - Regime shifts can be difficult to detect & characterize statistically de Young et al. (2004)

18 Evidence for a Recent Regime Shift in the Pacific Ocean Peterson & Schwing (2003)

19 Question: Is there evidence for a regime shift in the subtropical Pacific during the late 1990 s?

20 Hawaii Ocean Time-series Program Monthly measurements of physical, biological and biogeochemical parameters at Station ALOHA (23.75 N N, 158 W) during 1988-present

21 Regional Ocean Model System (ROMS) Pacific Ocean 60 N 40 S, 50-km resolution, 20 layers & NCEP forcing odeled Mo

22 Mixed Layer T reinforces S anomaly Decreased stability

23 ROMS Simulation: SSS anomaly (OBSERVED-red, ROMS-blue) Station ALOHA

24 rapid onset from strong negative anomalies penetration to m decay of event

25 Stratification weakened, deeper penetration of winter mixing

26 Food Web Model Imbedded in ROMS

27 Modeled pco 2 & Air-Sea CO 2 Flux at Station ALOHA pco -1 2 rate of increase: 2.6 atm y 2.5 atm y -1, Keeling et al. (2004)

28 Station ALOHA: ENSO anomaly (black) PDO anomaly (grey) North Pacific Index T-S relationships Modeled d nitrate t flux Phytoplankton biomass Bidigare et al. (2009)

29 Microalgae biomass Cyanobacteria biomass Measured ZP biomass Modeled ZP biomass Measured PN flux Bidigare et al. (2009)

30 Evidence for a Recent Regime Shift in the Pacific Ocean ENSO anom maly ( o C) During the 2 ENSO & the PDO were PDO index 0-2 both in a positive mode (warm phase): A trigger ENSO index PDO index PDO ENSO for shift in ecosystem structure and function Year

31 Summary of Regime Shifts Detected for Atmospheric, Physical, Chemical & Biological i l Variables During Bidigare et al. (2009)

32 Proposed mechanism for secular changes in plankton community structure & particle export in the subtropical North Pacific Bidigare et al. (2009)

33 Supporting Evidence for the Rapid Assimilation of Nitrate Following a Mixing Event at Station ALOHA Johnson et al. (2010)

34 Supporting Evidence for Enhanced Net Community Production Following a Mixing Event at Station ALOHA Riser & Johnson (2008)

35 Nolan et al. (2008)

36 ~5 Sta. ALOHA Nolan et al. (2008)

37 Project Columbia: ROMS 12.5-km Computer at NASA Advanced Supercomputing Facility: Ranked #2 Supercomputer in the world 20 interconnected SGI Altix 512-processor systems a total of 10,240 Intel Itanium 2 processors Pacific basin-scale ROMS: (1520x1088x30) 12.5-km horizontal resolutions & 30 vertical layers 50-year ( ) integration Yi Chao (JPL)

38 Project Columbia: ROMS Yi Chao (JPL)

39 Conclusions Plankton biomass and biogeochemical fluxes are not in steady-state at Station ALOHA The carrying capacity of the North Pacific Subtropical Ocean has increased during These findings underscore the importance of nitrate flux and plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time-scales Need for high-frequency measurements coupled with high-resolution 3-D circulation/food web models

40 Conclusions Plankton biomass and biogeochemical fluxes are not in steady-state state at Station ALOHA The carrying capacity of the North Pacific Subtropical Ocean has increased during These findings underscore the importance of nitrate flux and plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time-scales Need for high-frequency measurements coupled with high-resolution 3-D circulation/food web models

41 Conclusions Plankton biomass and biogeochemical fluxes are not in steady-state state at Station ALOHA The carrying capacity of the North Pacific Subtropical Ocean has increased during These findings underscore the importance of nitrate flux and plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time-scales Need for high-frequency measurements coupled with high-resolution 3-D circulation/food web models

42 Conclusions Plankton biomass and biogeochemical fluxes are not in steady-state state at Station ALOHA The carrying capacity of the North Pacific Subtropical Ocean has increased during These findings underscore the importance of nitrate flux and plankton community structure, as modulated by climate forcing, in regulating particle export over interannual and decadal time-scales Need for high-frequency measurements coupled with high-resolution 3-D circulation/food web models