1. Ocean Climate Trends Around Hawai`i Roger Lukas ± January 20, 2011 © 2011 ± HOT co-PIs and other collaborators

2. Sea level Temperature Salinity Circulation Mixing Biogeochemistry (CO 2, pH, O 2, nutrients, primary production, …) What is changing in the ocean? Density; stratification complex coupling

3. Main Focus and Summary Oceanic component of hydrological cycle is crucial in determining warming and other impacts Hydrological cycle acceleration -> much of subtropical gyre is receiving less rainfall; more rainfall midlatitudes Salinity matters! Upper ocean increase around Hawaii -> reduced stratification and enhanced mixing Enhanced CO 2 global warming can paradoxically lead to regional ocean cooling trends Impacts of salinity changes on biology?

4. A simple summary (IPCC Chapter 5) HI SL rise

5. Global mean sea level is rising, 1870 19922010

6. … but not uniformly (as Mark showed) – How much is due to ocean warming? Surface height trend dominated by ocean density changes, and those are dominated by dynamics. More recent period, surface buoyancy flux trends may be emerging. (50-year GECCO reanalysis by Kohl and Stammer, 2008) Total SSH trend 1962-2001Steric height trend 1962-2001 -8 – +8 mm/yr-9 – +9 mm/yr

7. Salinity important for determining SL changes due to ocean density changes (Kohl and Stammer, 2008) Ocean dynamics are important – subtropical gyre intensification, thermocline/halocline displacements thermosteric height trend 1962-2001 halosteric height trend 1962-2001 -13 – +13 mm/yr-8 – +8 mm/yr

8. Steric Height @ ALOHA 0/1000 dbar +1.16 cm/decade (all casts) +1.11 cm/decade (annual averages) 80/1000 dbar 1.6 cm/decade (with and without averaging) mixed layer salinity increase overcompensated warming 1.6 mm/yr 1.6 cm/decade Comparable to Hawaii tide gauges

9. A simple summary (IPCC Chapter 5) HI SL rise SL rise due to density change warmingaccelerated H 2 O cycle salinity increase – SL↓ Freshening SL↑

10. Surface Salinity subtropical gyres salty, getting saltier Durack and Wijffels (2010) S mean Freshwater flux (m 3 /yr) 1980-1993 (Josey et al., 1998) 50-year salinity trend (psu)

11. Thermohaline Trends @ ALOHA Warming over much of upper ocean (x 275-350 m!) Peak warming 150-200 m (S max ), not at surface Cooling below 700 m Salinity increasing in upper 200 m Freshening in the thermocline θ(z)S(z) 0.4 °C/decade 0.16/decade

12. Station ALOHA Lukas and Santiago-Mandujano (2008) 19502007 19882007 19882007 surface salinity 1 psu

13. Salinity Trends on Isopycnals Freshening 24.8-26.3 σ θ (180-350 m) Max S↓ @ 25.4 -0.11/decade large! Analysis of 21 annual means Analysis of 217 cruise means layer Trend with decadal cycle Trend w/o decadal cycle S max 0.041/ decade 0.039/ decade 0.011/ decade main thermocline -0.089/ decade -0.087/ decade -0.096/ decade The freshening signal is very robust on isopycnal surfaces Small signal, but correlated with O 2 and nutrients

14. Subduction of ML salinity anomalies + anomalous subduction Analysis of Argo float data Sasaki et al. (2010, GRL); see also Ren and Riser (2010, (Deep-Sea Research II – Suginohara memorial issue) Evolution of a fresh/cold anomaly

15. Salinity Trends on Neutral Surfaces Durack and Wijffels (2010) zonally averaged salinity trends (Δpsu/1950-2008 ) 70 S70 N

16. Salinity trends on Isopycnals water on heavier isopycnals comes from farther away (Δpsu/50 yrs) 24 σ θ 25 σ θ Durack and Wijffels (2010) 26.75 σ θ 27.5 σ θ

17. Large vertical excursions of isopycnals due to internal waves and eddies – Poor signal/noise Depth of isopycnals (color scale on right) over time @ ALOHA Depth   Density 25 m Z s.d. S mean

18. Isopycnal Depth Trends shoaling deepening Weakening stratification 12 m/decade deepening consistent with gyre intensification increasing stratification

19. Density and Stratification 0-100 m density ↑ 100-1000 density ↓ σ θ (z) 0.1 kg m -3 /decade

20. Density and Stratification 0-100 m density ↑ 100-1000 density ↓ Stratification ↓ in upper ocean σ θ (z)N(z)

21. Density and Stratification 0-100 m density ↑ 100-1000 density ↓ Stratification ↓ in upper ocean 200-350 m ↑ σ θ (z)N(z) dark blue – annual means light blue – cruise means Less stable more stable 0 m 200 m

22. Mixed Layer Deepening ~4 m/dec Warming ~ 0.05 °C/dec Salinity ↑ ~0.15/dec Density ↑ ~0.1 kg m -3 /dec Freeland et al. (1997) found 6 m/decade shoaling @ Station Papa Carton et al. (2008) found deepening in NPAC over 45 years

23. A Simple Summary (IPCC Chapter 5) HI acidification salinity increase warmingaccelerated H 2 O cycle SL rise SL rise due to density change

24. Updated and adapted from Dore et al. (2009, Proc Natl Acad Sci USA 106:12235 ) pH of surface ocean Acidification @ ALOHA pH trend vs depth Annual, interannual, decadal and longer term changes in surface forcing, mixing, and advection Local and remote physics are crucial, not just pCO 2, temperature and biology pH DIC This point was made in the paper Maximum not in surface layer

25. Dissolved Oxygen and Nutrients O 2 9 μmol/kg/decade Phosphate 0.06 μmol/kg/decade Remineralization of organic material along streamlines?

26. Summary warming upper ocean increasing upper ocean salinity (with decreasing[?] subducted signal below) decreasing density (ex ML)  increasing dynamic height dynamics vs thermohaline forcing? MLD increasing isopycnal depths and stratification trends show complex vertical structure Acknowledgements Funding for HOT has been provided by the National Science Foundation and the State of Hawaii. We thank the many HOT staff and ships’ crews for their dedication. Sea level rise, ocean warming and biogeochemistry are complicated by ocean dynamics, and by thermodynamic influences of salinity

27. Climate Change and Hawai`i Long recognized as important problem for Hawai`i Not widely recognized as an important problem for Hawai`i until recently

28. Moberly and Mackenzie (1985) Focused on sea level rise and warming Sound advice offered to the State on appropriate responses UH can play an important role in the research required to adapt and mitigate “Regretfully, the infrastructure for research activity at University of Hawaii has not kept pace with these or other lines of active research in the past decade. The University’s indirect costs, such as secretaries salaries and equipment repair, are the State’s responsibilities, and if met properly the University will be able to contribute beyond