1. The Hawaii Ocean Time-series and Science at Station ALOHA
Roger Lukas
GES 100 9/22/11

2. Understanding Signals versus “Noise” (and Instrument/Methods Errors)
What is a time-series?
Exploration/discovery in time in a consistent way!
green and orange symbols show different methods
expeditions
trend analysis highly uncertain
Understanding Signals versus “Noise” (and Instrument/Methods Errors)

3. Why do we need time series?
Expeditionary measurements explore the ocean and map distributions of stuff
affected by time in unknown ways (aliasing)
difficult to study processes and trends (rates of change)
Aliasing

4. visual aliasing due to inadequate resolution of brick wall structure

5. The Ocean Sampling Problem
Observational platforms
processes
Large range of time and space scales! Want to study climate, have to capture eddies
Tommy Dickey (UCSB)

6. Objectives of HOT
Observe and understand ocean physics and climate variations
Observe and understand biogeochemistry and ecosystem variations and their relation to climate

7. What is HOT? ~ monthly cruises since 1988
NSF, State of Hawaii, NOAA, etc funding
Show HOT video intro

8. Why Station ALOHA? North Pacific subtropical gyre
Representative of the subtropical gyre
Deep ocean (~4800 m)
Far enough from direct island influences
Close enough to Honolulu (one day roundtrip)

9. What (and how) do we measure?
Shipboard lowering, water collection, drifting arrays, moorings

10. What (and how) do we measure?
Moorings – show WHOTS deployment/recovery video
ACO deployment and seafloor video
Real-time data
audio!
video …
Gliders give us spatial perspective
Shipboard Acoustic Doppler Current Profiler

11. What (and how) do we measure?
ACO deployment and seafloor video
Real-time data
audio!
video …

12. ALOHA Kauai Deep Maui Deep HAW-4 cable Makaha cable station
Oahu Seamounts
Kaena Pt.
Kahe Pt.
HAW-4 cable
Makaha cable station

13. ALOHA Kauai Deep Maui Deep HAW-4 cable Makaha cable station
Oahu Seamounts
Kaena Pt.
Kahe Pt.
HAW-4 cable
Makaha cable station

14. ALOHA Kauai Deep cold overflow events Maui Deep Oahu Seamounts
Kaena Pt.
Kahe Pt.
cold overflow events

16. What have we learned? Variations and change are the rule in the ocean
Ocean climate is changing
Ocean and atmospheric physics drive ecosystem
Ecosystem is much more complex than imagined 20 years ago
1-dimensional (depth-time) models are not adequate; advection is important (hmmm, currents)

17. What is changing in the ocean?
Sea level
Temperature
Salinity
Circulation
Mixing
Biogeochemistry (CO2, pH, O2, nutrients, primary production, …)
Density; stratification
complex coupling

18. Physics and Climate Distinct trends over 20+ years
ENSO –> decadal large-scale wind and rainfall variations result in complex ocean changes
Salinity effects on stability (resistance to mixing)
Eddies are frequent
Internal tides – ALOHA is hot spot
Abyssal circulation – cold events and turbulence

19. Station ALOHA Lukas and Santiago-Mandujano (2008)
surface salinity
1 psu
1988
2007
1950
2007
Station ALOHA Lukas and Santiago-Mandujano (2008)
1988
2007

20. Thermohaline Trends @ ALOHA
θ(z)
S(z)
Warming over much of upper ocean (x m!)
Peak warming m (Smax), not at surface
Cooling below 700 m
Salinity increasing in upper 200 m
Freshening in the thermocline
0.16/decade
0.4 °C/decade
Density decreased in the upper 1000 m, except in the upper 100 m where the warming trend (~0.16K/decade) was more than offset by increasing salinity. The largest density decreases were in the m range. The maximum warming was at 180 m (~0.4K/decade), with a peak cooling around 250 m. The density decrease near 250 m is due to a freshening trend of -0.06/decade. This freshening is clearly due to advection (see later isopycnal analysis). The broad warming between dbar peaks at ~0.17K/decade, comparable to the surface layer warming. A freshening trend of about -0.02/decade also occurred between m. From m, temperature decreased over the observational period. Deep and abyssal trends in temperature and salinity are also revealed in the HOT record. Below 1500 m potential temperature, salinity and potential density all increased.
Note that the fraction of variance (r2) explained by the regression is highly significant upper 200 m, but remains significant below. (DoF ~ 217 – 8)

21. Density and Stratification
σθ(z)
N(z)
0-100 m density ↑
density ↓
Stratification ↓ in upper ocean
m ↑
0 m
Less stable
0.65 r^2 for annual 80 m; Decadal amplitude ~ m
dark blue – annual means light blue – cruise means
more stable
200 m

22. Low N:P of entrained nutrients
Mean Nitracline Depth
Updated and adapted from Dore et al. 2008, Prog Oceanogr 76:2

23. Biogeochemistry ENSO – decadal productivity and other ecosystem
regime shifts – N2 to P limitation
importance of events (e.g. eddies) to long-term upper-ocean nutrients and productivity

24. pCO2 of surface ocean and overlying atmosphere

25. Acidification @ ALOHA DIC Maximum not in surface layer
Updated and adapted from Dore et al. (2009, Proc Natl Acad Sci USA 106:12235 )
Maximum not in surface layer
DIC
pH of surface ocean
In addition to understanding physical climate variations in the North Pacific Ocean, we need to understand how biogeochemical variations are affected by physics. We can understand the acidification of the mixed layer as a result of being nearly in equilibrium with increased atmospheric CO2, although entrainment of less alkaline waters is important on some time scales. However, subsurface pH trends cannot be understood so easily. While confidence intervals are large, there is apparent vertical structure in these trends, and some reasons to believe that they are real.
Annual, interannual, decadal and longer term changes in surface forcing, mixing, and advection
Local and remote physics are crucial, not just pCO2, temperature and biology
pH trend vs depth pH
This point was made in the paper

26. Anomalies of pH and mixed layer depth
Updated and adapted from Dore et al. 2009, Proc Natl Acad Sci USA 106:12235

27. P-stimulation of N2-supported blooms
Dave Karl
NASA

28. Sources and sinks of DIC – balancing budgets
Keeling et al. 2004, Global Biogeochem Cycles 18, GB4006, doi: /2004GB002227

35. Resources http://aloha.manoa.hawaii.edu
Karl, D.M., J.E. Dore, R. Lukas, A.F. Michaels, N.R. Bates, and A. Knap, 2001: Building the Long-Term Picture: The U.S. JGOFS Time-Series Programs. Oceanography 14(4):6-17
Karl, D.M Oceanic ecosystem time-series programs: Ten lessons learned. Oceanography 23(3):104–125, doi: /oceanog

37. Kauai Deep
Maui Deep
ALOHA
Oahu Seamounts
Kaena Pt.
Kahe Pt.

43. pH of surface ocean
Updated and adapted from Dore et al. 2009, Proc Natl Acad Sci USA 106:12235

44. Acidification by carbonic acid
Adapted from Dore et al. 2009, Proc Natl Acad Sci USA 106:12235

46. Dissolved Oxygen and Nutrients
O2 9 μmol/kg/decade
Phosphate 0.06 μmol/kg/decade
Remineralization of organic material along streamlines?

47. Alford et al. (2011)