The Woods Hole – Hawaii Ocean Time-series Station (WHOTS) Roger Lukas, Robert Weller and Albert Plueddemann WHOTS is a collaboration between WHOI, UH and PMEL, with cooperative NOAA and NSF funding. Through OceanSITES and JCOMM, WHOTS is part of a global network of time-series sites. sustained observations, new understanding, departures (surprises!) from either climatologies, models, or previous understandings deep T/S variability would challenge us all to think carefully about deep T/S obs The attempt to develop and maintain metadata standards through OceanSITES and JCOMM Ops is yet another thread. ERA Interim comparisons for met/flux highlights and description of salinity changes (and maybe PWP runs if you have them)

WHOTS is an element of NOAA’s Ocean Reference Stations part of the OceanSITES & JCOMM OPS international network leverages long record and context from HOT (e.g. carbon and salinity/hydrological cycle)

trends, ENSO and annual cycle resolved by HOT pCO2 Mauna Loa eddies and storms are not resolved by HOT but are resolved by WHOTS ALOHA/HOT pH Figure from PMEL ocean carbon website pCO2 water pCO2 air from PMEL ocean carbon website

WHOTS surface buoy (real-time) U, T, RH Radiation (soon in water, Laney/WHOI) Rainfall Near-surface ocean T pCO2 air and water; pH (PMEL) Need wave spectrum Mooring (delayed mode) u, T, C, S, P [0-155 m] near-bottom microcat to be added Sun-stimulated fluorescence on ocean moorings Collaborators: Dr. Robert Weller, WHOI Physical Oceanography Department Dr. Al Plueddemann, WHOI Physical Oceanography Department I received a 2009 NASA New Investigator award to begin long-term, ocean color radiometric time series on open ocean moorings. My main interest in this is to better unerstand short-term and seasonal variability in the diurnal pattern of sun-stimulated phytoplankton fluorescence. An abovewater, five-radiometer sensor suite is being integrated into the WHOTS8 mooring to be deployed at Station ALOHA off Oahu in fall 2011. This suite will record spectral water-leaving radiance as well as incident spectral irradiance, and telemeter these data to shore using an Iridium link. In addition, three underwater on the mooring will measure chlorophyl lfluorescence at three depths in the euphotic zone, to assess diurnal variability in fluorescence quenching.

T 4750 m S

Large Salinity Trends and Variations 1950 2000 WHOTS 35.5 sea surface salinity @ Koko Head SSS @ ALOHA 34.5 z fully-resolved temporal sampling HOT 25 35.4 potential density (kg m-3) 26 decadal variations long-term trend (disrupted 2009-2011) 27 1950 2000 historical hydrographic profiles within 200 km of ALOHA (note gaps) 34 HOT cruises 1988 - present

Salinity Trends on Isopycnals Freshening 24.8-26.3 σθ (180-350 m) Max S↓ @ 25.4 -0.11/decade large! The freshening signal is very robust on isopycnal surfaces, filtering out noise from internal waves Smaller signal, but correlated with O2 and nutrients The freshening signal is very robust on isopycnal surfaces, and about twice as large. Large upper pycnocline decadal variation since 2007 has disrupted mid-pycnocline trend 7

20-Year Long 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 0-100 m density ↑; 100-1000 density ↓ Stratification ↓ in upper ocean! deeper mixing  productivity 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) 8

Salinity plays an important role in stability of upper ocean on interannual and decadal time scales, with effects on mixing and productivity (Corno et al., 2007; Bidigare et al., 2009) WHOTS HOT CTD photo

Evaporation: Comparison of WHOTS with ECMWF-Interim decorrelation scale for evaporation large relative to reanalysis grid scale important biases in mean and variance of ECMWF analyzed evaporation daily averages

Precipitation: WHOTS net evaporative regime Sean Whelan (WHOI) net evaporative regime Rainfall small space-time scales Not well-observed from space Poorly represented in NWP model-reanalyses

WHOTS mixed layer salinity compared to WHOTS freshwater fluxes mixed layer depth variations contribute to mismatches between these two curves trend removed from net cumulative P-E (the freshwater needed to balance must arrive from higher latitudes directly via surface currents, or be entrained into the mixed layer at ALOHA after transport in the upper pycnocline

Integrated net heat flux into 50 m layer Clearly, cold and salty water must be transported into the surface layer at ALOHA by some combination of horizontal advection, upwelling, and vertical mixing to provide a mean balance – how much do they contribute to interannual – decadal variations?

comparison of MLD from WHOTS mooring (colored lines) with estimates from CTD profiles during HOT and WHOTS cruises

Modified Price-Weller-Pinkel mixed layer model forced with WHOTS air-sea fluxes WHOTS mooring mixed layer depth

enhanced shear  vertical mixing lateral eddy transports?? interannual variations of eddies

Summary Sustained, collaborative, multi-disciplinary science Air-sea fluxes, ocean-truthing atmospheric reanalyses, forcing and benchmarking ocean models Upper ocean climate – hydrological cycle Eddies and ecosystem dynamics Impacts as part of a global observational network Assessing ocean changes (incl. C) and enabling climate predictions Atmosphere and ocean modeling – Ocean Reference Stations Institutions and agencies must sustain infrastructure Sustained multi-institutional collaboration (WHOI, UH/SOEST, PMEL) Collaborative funding, NOAA, NSF and State of Hawaii OceanSITES data management (setting metadata standards)  WHOTS subsurface incl. V though mid-2011

Thank You! WHOTS data are available via http://uop.whoi.edu http://www.soest.hawaii.edu/WHOTS http://www.oceansites.org ftp://ftp.ifremer.fr/ifremer/oceansites/ ftp://data.ndbc.noaa.gov/data/oceansites/

Steric Height @ ALOHA Comparable to Hawaii tide gauges 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 Comparable to Hawaii tide gauges Dynamic height (0/1000 dbar) increased ~2 mm/yr, comparable to mean sea level changes in the Hawaiian Islands, and to estimates of the thermal expansion contribution to global mean sea level rise. Changes in both temperature and salinity were significant contributors, however. 1.6 mm/yr 1.6 cm/decade 25

thermosteric height trend 1962-2001 halosteric height trend 1962-2001 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 Kohl and Stammer (2008) FIG. 1. (a) Model SSH trend and (b) steric SSH trend estimated over the 40-yr period 1962–2001. A global mean trend of 0.74 mm yr1 was removed from the steric trend. Corresponding (c) thermosteric and (d) halosteric sea level change including the global mean trend of 0.92 and 0.18 mm yr1, respectively. All fields are in cm yr1. Salinity important for determining SL changes due to ocean density changes (Kohl and Stammer, 2008) 26

Salinity trends on Isopycnals water on heavier isopycnals comes from farther away (Δpsu/50 yrs) 24 σθ 25 σθ Durack and Wijffels (2010) Fig. 10 26.75 σθ 27.5 σθ Durack and Wijffels (2010) 27

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 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 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. pH trend vs depth pH This point was made in the paper 28

Subduction of ML salinity anomalies + anomalous subduction Evolution of a fresh/cold anomaly Sasaki et al. (2010) Fig. 2 Analysis of Argo float data Sasaki et al. (2010, GRL); see also Ren and Riser (2010, (Deep-Sea Research II – Suginohara memorial issue) 29

Salinity Trends on Neutral Surfaces zonally averaged salinity trends (Δpsu/1950-2008 ) 70 S 70 N Durack and Wijffels (2010) Fig. 9b Durack and Wijffels (2010) 30