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

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)

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

visual aliasing due to inadequate resolution of brick wall structure

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)

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

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

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)

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

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

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

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

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

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

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)

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

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

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

Thermohaline Trends @ ALOHA θ(z) S(z) Warming over much of upper ocean (x 275-350 m!) Peak warming 150-200 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 100-300 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 300-650 dbar peaks at ~0.17K/decade, comparable to the surface layer warming. A freshening trend of about -0.02/decade also occurred between 600-800 m. From 700-1300 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)

Density and Stratification σθ(z) N(z) 0-100 m density ↑ 100-1000 density ↓ Stratification ↓ in upper ocean 200-350 m ↑ 0 m Less stable 0.65 r^2 for annual means @ 80 m; Decadal amplitude ~ 0.8 cph @ 80 m dark blue – annual means light blue – cruise means more stable 200 m

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

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

pCO2 of surface ocean and overlying atmosphere

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

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

P-stimulation of N2-supported blooms Dave Karl NASA

Sources and sinks of DIC – balancing budgets Keeling et al. 2004, Global Biogeochem Cycles 18, GB4006, doi:10.1029/2004GB002227

Resources http://aloha.manoa.hawaii.edu http://www.soest.hawaii.edu/HOT_WOCE/ http://hahana.soest.hawaii.edu/hot/hot_jgofs.html http://www.soest.hawaii.edu/whots/ http://aco-ssds.soest.hawaii.edu/ACO http://www.whoi.edu/virtual/oceansites/index.html 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. 2010. Oceanic ecosystem time-series programs: Ten lessons learned. Oceanography 23(3):104–125, doi:10.5670/oceanog.2010.27.

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

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

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

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

Alford et al. (2011)