Showing papers by "Burke Hales published in 2009"

Climatological mean and decadal change in surface ocean pCO2, and net sea–air CO2 flux over the global oceans

Abstract: A climatological mean distribution for the surface water pCO2 over the global oceans in non-El Nino conditions has been constructed with spatial resolution of 4° (latitude) ×5° (longitude) for a reference year 2000 based upon about 3 million measurements of surface water pCO2 obtained from 1970 to 2007. The database used for this study is about 3 times larger than the 0.94 million used for our earlier paper [Takahashi et al., 2002. Global sea–air CO2 flux based on climatological surface ocean pCO2, and seasonal biological and temperature effects. Deep-Sea Res. II, 49, 1601–1622]. A time-trend analysis using deseasonalized surface water pCO2 data in portions of the North Atlantic, North and South Pacific and Southern Oceans (which cover about 27% of the global ocean areas) indicates that the surface water pCO2 over these oceanic areas has increased on average at a mean rate of 1.5 μatm y−1 with basin-specific rates varying between 1.2±0.5 and 2.1±0.4 μatm y−1. A global ocean database for a single reference year 2000 is assembled using this mean rate for correcting observations made in different years to the reference year. The observations made during El Nino periods in the equatorial Pacific and those made in coastal zones are excluded from the database. Seasonal changes in the surface water pCO2 and the sea-air pCO2 difference over four climatic zones in the Atlantic, Pacific, Indian and Southern Oceans are presented. Over the Southern Ocean seasonal ice zone, the seasonality is complex. Although it cannot be thoroughly documented due to the limited extent of observations, seasonal changes in pCO2 are approximated by using the data for under-ice waters during austral winter and those for the marginal ice and ice-free zones. The net air–sea CO2 flux is estimated using the sea–air pCO2 difference and the air–sea gas transfer rate that is parameterized as a function of (wind speed)2 with a scaling factor of 0.26. This is estimated by inverting the bomb 14C data using Ocean General Circulation models and the 1979–2005 NCEP-DOE AMIP-II Reanalysis (R-2) wind speed data. The equatorial Pacific (14°N–14°S) is the major source for atmospheric CO2, emitting about +0.48 Pg-C y−1, and the temperate oceans between 14° and 50° in the both hemispheres are the major sink zones with an uptake flux of −0.70 Pg-C y−1 for the northern and −1.05 Pg-C y−1 for the southern zone. The high-latitude North Atlantic, including the Nordic Seas and portion of the Arctic Sea, is the most intense CO2 sink area on the basis of per unit area, with a mean of −2.5 tons-C month−1 km−2. This is due to the combination of the low pCO2 in seawater and high gas exchange rates. In the ice-free zone of the Southern Ocean (50°–62°S), the mean annual flux is small (−0.06 Pg-C y−1) because of a cancellation of the summer uptake CO2 flux with the winter release of CO2 caused by deepwater upwelling. The annual mean for the contemporary net CO2 uptake flux over the global oceans is estimated to be −1.6±0.9 Pg-C y−1, which includes an undersampling correction to the direct estimate of −1.4±0.7 Pg-C y−1. Taking the pre-industrial steady-state ocean source of 0.4±0.2 Pg-C y−1 into account, the total ocean uptake flux including the anthropogenic CO2 is estimated to be −2.0±1.0 Pg-C y−1 in 2000.

Corrigendum to "Climatological mean and decadal change in surface ocean pCO2, and net sea-air CO2 flux over the global oceans" [Deep Sea Res. II 56 (2009) 554-577]

Abstract: Taro Takahashi a, , Stewart C. Sutherland , Rik Wanninkhof , Colm Sweeney , Richard A. Feely , David W. Chipman , Burke Hales , Gernot Friederich , Francisco Chavez , Christopher Sabine , Andrew Watson , Dorothee C.E. Bakker , Ute Schuster , Nicolas Metzl , Hisayuki Yoshikawa-Inoue , Masao Ishii , Takashi Midorikawa , Yukihiro Nojiri , Arne Körtzinger , Tobias Steinhoff , Mario Hoppema , Jon Olafsson , Thorarinn S. Arnarson , Bronte Tilbrook , Truls Johannessen , Are Olsen , Richard Bellerby , C.S. Wong , Bruno Delille , N.R. Bates , Hein J.W. de Baar u

A novel method for determination of aragonite saturation state on the continental shelf of central Oregon using multi‐parameter relationships with hydrographic data

Abstract: [1] We developed a multiple linear regression model to robustly determine aragonite saturation state (Ωarag) from observations of temperature and oxygen (R2 = 0.987, RMS error 0.053), using data collected in the Pacific Northwest region in late May 2007. The seasonal evolution of Ωarag near central Oregon was evaluated by applying the regression model to a monthly (winter)/bi-weekly (summer) water-column hydrographic time-series collected over the shelf and slope in 2007. The Ωarag predicted by the regression model was less than 1, the thermodynamic calcification/dissolution threshold, over shelf/slope bottom waters throughout the entire 2007 upwelling season (May–November), with the Ωarag = 1 horizon shoaling to 30 m by late summer. The persistence of water with Ωarag < 1 on the continental shelf has not been previously noted and could have notable ecological consequences for benthic and pelagic calcifying organisms such as mussels, oysters, abalone, echinoderms, and pteropods.

Turbulent supply of nutrients to phytoplankton at the New England shelf break front

Abstract: [1] We present observations from deployments of a microstructure turbulence instrument (the Towed Microstructure and Auxiliary Sensor Instrument) aboard a pumping profiling vehicle (the Lamont Pumping SeaSoar) towed behind a research vessel at the New England shelf break front in August 2002. From these we determined coincident fine-scale vertical eddy diffusivity and gradients of nitrate, phosphate, and silicate on several transects spanning the front. We then quantified vertical turbulent nutrient fluxes through the base of the euphotic zone (defined as the 1% light level), the base of the density transition zone, maximum nutrient gradients (the nutriclines), and the depth of maximum stratification (the pycnocline). Vertical eddy diffusivity estimates spanned a wide range from near-molecular levels at the pycnocline to values exceeding 10−3 m2 s−1 at depth and in the surface layers. Vertical nutrient fluxes were maximal at the 1% light level and decreased by 2 orders of magnitude as they moved upward through the water column to the depth of the pycnocline. Nutrient fluxes were enhanced shoreward of the front because of high mixing rates and nutrient gradients at the depth of the 1% light level. Nitrate fluxes there averaged about 6 × 10−5 mmol N m−2 s−1, sufficient to support a net community productivity of 30 mmol C m−2 d−1. Seaward of the front, these fluxes averaged about 1 × 10−5 mmol N m−2 s−1 and would support correspondingly lower productivity. A small part of the upward flux appeared to support a silicifying community of phytoplankton that consumed phosphate in proportion to nitrate at about double the canonical Redfield stoichiometry.