OS31B-1256

The Effects of Freezing, Melting and Partial Ice Cover on Gas Transport in Laboratory Seawater Experiments

* Loose, B brice@ldeo.columbia.edu, Department of Earth and Environmental Sciences, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
* Loose, B brice@ldeo.columbia.edu, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
McGillis, W wrm2102@columbia.edu, Department of Earth and Environmental Engineering, Columbia University, 918 S. W. Mudd Hall Mail Code: 4711 500 West 120th Street, New York, NY 10027, United States
McGillis, W wrm2102@columbia.edu, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
Schlosser, P schlosser@ldeo.columbia.edu, Department of Earth and Environmental Engineering, Columbia University, 918 S. W. Mudd Hall Mail Code: 4711 500 West 120th Street, New York, NY 10027, United States
Schlosser, P schlosser@ldeo.columbia.edu, Department of Earth and Environmental Sciences, Columbia University, 61 Route 9W, Palisades, NY 10964, United States
Schlosser, P schlosser@ldeo.columbia.edu, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
Perovich, D Donald.K.Perovich@usace.army.mil, US Army Corps of Engineers Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, NH 03755, United States
Takahashi, T taka@ldeo.columbia.edu, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States

Sea ice physico-chemical processes affect gas dynamics, which may be relevant to polar ocean budgets of climatically-active gases. We used SF₆ and O₂ as inert gas tracers in a tank experiment to observe the transport of gases between water, ice and air during freezing/melting and partial ice cover. The results show that during ice growth, the rejection of O₂ and SF₆ was greater than the rejection of salt per unit of ambient concentration in seawater. Unconsolidated ice crystal growth produced an increase in dissolved O₂ concentration, indicating that the water-air gradient may favor gas evasion during the early stages of sea-ice formation. Measurements of the gas transfer velocity (k), using SF₆ and O₂ during conditions of partial ice cover exceed the proportionality between the fraction of open water and k determined between 0% and 100% open water conditions. At 15% open water, k equals 35% of k during ice-free conditions, indicating the importance of under-ice turbulence for gas exchange. In our experiments most of this turbulence was produced by pumps installed for circulation of the water in the tank to avoid density stratification. Varying the turbulent kinetic energy (TKE) delivered to the water by these pumps produced a correspondent variation in k. Measurements of TKE using particle velocimetry suggest that turbulence in the ice-water boundary layer dominated the convection driven by heat loss through the open water, and the magnitude of net TKE production was similar to that measured beneath drifting ice in the field.

OS31B-1257

Air-Water Surface Divergence Patterns and Their Relation to Gas Transfer

* Turney, D E dturney@bren.ucsb.edu, University of California, Santa Barbara, 1005 Bren Hall, Santa Barbara, CA 93117,
Banerjee, S banerjee@che.ccny.cuny.edu, City College of New York, 160 Convent Avenue, New York, NY 10031,

Air-water transfer of volatile chemicals is an important process for understanding the behavior of many biogeochemical environments. Recent investigations reported in the literature have suggested that fluid motions termed "surface divergence" control the transfer rate in a relatively well understood manner. Essentially these motions are upwellings and downwellings that refresh the fluid at the interface. However, spatial patterns and time-series of these fluid motions have not been analyzed thoroughly. Here we present three-dimensional spatial patterns of surface divergent motions at an air-water interface in conditions of i) flow down a straight channel and ii) wind forcing with wind waves. We analyze the validity of various surface divergence theories and make new insights into the nature of turbulent and/or wavy flow near an air-water interface. We also suggest a new approach to estimating air-water gas transfer from surface divergence observations.

http://microbreaking.chemengr.ucsb.edu

OS31B-1258

The ocean skin temperature distribution and the bulk-skin temperature difference

* Jessup, A jessup@apl.washington.edu, U. Washington, Applied Physics Laboratory, Seattle, WA 98105-6698, United States
Phadnis, K kphadnis@apl.washington.edu, U. Washington, Applied Physics Laboratory, Seattle, WA 98105-6698, United States
Atmane, M Mohamed.Atmane@snclavalin.com, U. Alberta, Dept. Civil & Env. Eng., Edmonton, AB T6G 2H1, Canada
Zappa, C zappa@ldeo.columbia.edu, Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY 10964-1000, United States
Loewen, M mrloewen@ualberta.edu, Columbia University, Lamont-Doherty Earth Observatory, Palisades, NY 10964-1000, United States
Asher, B asher@apl.washington.edu, U. Washington, Applied Physics Laboratory, Seattle, WA 98105-6698, United States

An experiment in a wind-wave flume was conducted to investigate the relationship between the bulk-skin temperature difference (deltaT) and the ocean skin temperature distribution (Tskin PDF). Skin temperature was measured with an infrared radiometer, bulk temperature was measured with a profiler, and the distribution was measured with an infrared camera. The gradient flux technique was used to measure the net heat flux, which was varied by controlling the wind speed, air-water temperature difference, and relative humidity. This data set provides a unique opportunity to compare direct measurements of deltaT to the Tskin PDF. We found that the percentile of the distribution of measured skin temperatures that corresponded to the measured sub-skin bulk temperature was in the 99.8th or higher percentile for 18 out of 21 cases and higher than the 99.9th percentile when deltaT > 0.15 K. This result shows that the bulk temperature corresponds to the maximum value in the Tskin PDF. We found that the analytical expression for fitting the distribution developed by Garbe et al. [JGR, 2004] was successfully only when the distribution was truncated at the 99.9th percentile, removing the warmest temperatures. However, because the measured bulk temperature (Tbulk) was found to correspond to these same warmest temperatures, especially when deltaT > 0.15 K, our results demonstrate that the method of Garbe et al. [2004] underestimates Tbulk and therefore deltaT. This conclusion was supported by comparing deltaT values from the GasEx01 cruise reported by Garbe et al. [2004] with deltaT from concurrent, direct measurements of Tskin and Tbulk The comparison showed that deltaT from the PDF fitting technique consistently underestimated the measured deltaT by an average factor of 5. We have shown that the skin layer is completely renewed by near-surface turbulence, which is a fundamental assumption of surface renewal theory. Paradoxically, we also have shown that a technique based on a widely-cited interpretation of surface renewal theory is inadequate. We anticipate that these mixed findings will motivate further research into alternative air-sea transfer models.

OS31B-1259

The Relationship Between Temperature and Gas Concentration Fluctuation Rates at an Air-Water Interface

* Asher, W E asher@apl.washington.edu, Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
Jessup, A T jessup@apl.washington.edu, Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
Liang, H hannah.liang@gmail.com, Applied Physics Laboratory University of Washington, 1013 NE 40th Street, Seattle, WA 98105, United States
Zappa, C J zappa@ldeo.columbia.edu, Lamont Doherty Earth Observatory Columbia University, 61 Route 9W, Palisades, NY 10964, United States

The air-sea flux, F, of a sparingly soluble nonreactive gas can be expressed as F = k_G(C_S-C_W), where k_G is the gas transfer velocity, C_S is the concentration of gas that would be expected in the water if the system were in Henry's Gas Law equilibrium, and C_W is the gas concentration in the bulk water. An analogous relationship for the net heat flux can also be written using the heat transfer velocity, k_H, and the bulk-skin temperature difference in the aqueous phase. Surface divergence theory for the air-water transfer of gas and heat predicts that k_G and k_H will scale as the square root of the surface divergence rate, r. However, because of the interaction between diffusivity and the scale depth of the surface divergences, the scale factor for heat is likely to be different from the scale factor for gases. Infrared imagery was used to measure the timescales of variations in temperature at a water surface and laser-induced fluorescence (LIF) was used to measure temporal fluctuations in aqueous-phase concentrations of carbon dioxide (CO₂) at a water surface. The rate at which these temperature and concentration fluctuations occur is then assumed to be related to r. The divergence rates derived for temperature from the IR images can be compared to the rates for gas derived from the LIF measurements to understand how r estimated from the two measurements differ. The square root of r is compared to concurrently measured k_G for helium and sulfur hexafluoride to test the assumption that r^1/2 scales with k_G. Additionally, we measured k_H using the active controlled flux technique, and those heat transfer velocities can also be used to test for a r^1/2 dependence. All measurements reported here were made in the APL-UW synthetic jet array facility.

OS31B-1260

Air-Ocean CO2 flux by the gradient method

* IWATA, T , Okayama University, 3-1-1, Tsushima-naka, Okayama, 700-8530, Japan

Micrometeorological methods are expected as crucial for the direct measurement of air-ocean exchange of carbon dioxide (CO2). Micrometeorological methods are able to observe temporally and spatially small- scaled CO2 flux. These methods will serve for the study on processes controlling air-ocean CO2 exchange. The aerodynamic gradient method is plain and simple compared with the eddy-covariance method. A fine buoy system was developed for the measurement of CO2 concentration profile in the lower atmosphere. Some observations were performed various oceans ( arctic, subarctic shelf, frontal zone, sub- arctic gyre, subtropical or tropical ) between 2006 and 2008. Vertical gradients of CO2 concentration showed ideal semi-logarithmic profile and clear dependency on pCO2. Half-hour CO2 flux calculated by the gradient method showed downward flux between -80 and 20 mmol m-2 d-1. The gas transfer velocity derived from CO2 fluxes and pCO2 showed closer fit to Liss and Merlivat (1986) or Wanninkhof (1992).

OS31B-1261

Open Ocean DMS Air/Sea Fluxes Over the Eastern South Pacific Ocean

Marandino, C A cmarandi@uci.edu, University of California, Irvine, Earth System Science Department, Irvine, CA 92697,
De Bruyn, W J debruyn@chapman.edu, Chapman University, Department of Physical Science, Orange, CA 92866,
Miller, S D smiller@albany.edu, State Univerity of New York, Center for Atmospheric Research, Albany, NY 12222,
* Saltzman, E S esaltzma@uci.edu, University of California, Irvine, Earth System Science Department, Irvine, CA 92697,

Dimethylsulfide (DMS) eddy correlation air/sea fluxes and gradients were measured aboard the R/V Knorr in January 2006 (Knorr_06). The cruise took place in the Eastern Pacific Ocean, from Manzanillo, Mexico to Punta Arenas, Chile. Atmospheric pressure chemical ionization mass spectrometry was used to measure DMS in air and in air equilibrated with surface seawater using a membrane equilibrator. Gas transfer coefficients (k_DMS) computed from the data exhibit a linear dependence on wind speed, over the wind speed range from 1 to 9 m s^-1. The k vs U relationship from this study is compared to the results of previous eddy covariance and dual tracer studies and to the NOAA/COARE gas transfer model. The Knorr_06 k values are in good agreement with those derived from earlier DMS flux studies, but differ significantly from prior CO₂ data at low wind speeds. The NOAA/COARE model tends to underpredict the wind speed-dependence of k_DMS observed on this and previous DMS-based field studies.

OS31B-1262

Satellite Estimation of Air-Sea Gas Transfer During GasEx-3 Using QuikSCAT and Jason- 1 Microwave Radars

Frew, N M nfrew@whoi.edu, Woods Hole Oceanographic Institution, MC&G Mail Stop 4, Woods Hole, MA 02543, United States
* Glover, D M dglover@whoi.edu, Woods Hole Oceanographic Institution, MC&G Mail Stop 25, Woods Hole, MA 02543, United States
Caruso, M J mcaruso@rsmas.miami.edu, Univeristiy of Miami, RSMAS 11811 SW 168th St, Miami, FL 33177, United States

We have developed a scatterometer-based algorithm for estimating air-sea gas transfer velocity (k) from QuikSCAT normalized radar backscatter (σ°) at 25 km and one day resolution. With this algorithm we were able to evaluate k during the Southern Ocean GasEx field campaign in an area bounded by 40°-60°S and 50°-30°W daily for a month prior to and a month after the field study. In this initial stage of the investigation we seek to analyze the spatial and temporal variability of k during the study and to use S.O. GasEx field measurements of k to better constrain the algorithm parameters. Our algorithm calculates k from a field-determined, quadratic function of the small-scale wave mean square slope (〈 s² 〉). The 〈 s² 〉, in turn, is calculated from an empirical function of QuikSCAT normalized radar backscatter (σ°). Our algorithm is calibrated with an altimeter-based 〈 s² 〉-σ° relationship using co-located QuikSCAT-altimeter σ°. This approach incorporates many of the wave state effects: wave-wave interactions (and perhaps wave breaking), boundary layer stability, variable fetch, and the presence or absence of surface active organic material that compromise the many wind speed based k parameterizations. Summary statistics of the evolution of k during S.O. GasEx and comparisons between field and remotely sensed data will be discussed.

http://eos.whoi.edu/~david/qstrans/gasex3.html

OS31B-1263

Direct measurements of momentum and latent heat transfer coefficients during the GasExIII 2008 field program in the Southern Ocean: Comparisons with the COARE3.0 bulk flux algorithm

* Fairall, C chris.fairall@noaa.gov, NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States
Bariteau, L ludovic.bariteau@noaa.gov, CIRES, University of Colorado, and NOAA ESRL, 325 Broadway, Boulder, CO 80305, United States
Hare, J jeff.hare@noaa.gov, CIRES, University of Colorado, and NOAA ESRL, 325 Broadway, Boulder, CO 80305, United States
Pezoa, S sergio.pezoa@noaa.gov, NOAA Earth System Research Laboratory, 325 Broadway, Boulder, CO 80305, United States
Edson, J james.edson@uconn.edu, Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States
Cifuentes-Lorenzen, A alejandro.cifuentes@huskymail.uconn.edu, Department of Marine Sciences, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States
McGillis, W wrm2102@columbia.edu, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964,
Zappa, C zappa@ldeo.columbia.edu, Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY 10964,

In 2008 a six-week research expedition aboard the NOAA Ship Ronald H. Brown was conducted with sponsorship from NASA, NOAA, and NSF. The Southern Ocean Gas Exchange Experiment departed Feb. 28 from Punta Arenas, Chile, and spent most of its time in the storm track east of the Southern tip of S. America (51 S 36 W). Scientists from dozens of universities and research institutions were on board to measure turbulence, waves, bubbles, temperature, ocean chemistry and biology, and investigate how these factors relate to the air-sea exchange of carbon dioxide and other climate-relevant gases. A consortium of researchers from NOAA/ESRL - U. Colorado, U. Connecticut, Columbia U., and U. Hawaii cooperated on comprehensive suite of instruments to make direct motion-corrected covariance and inertial-dissipation flux measurements and associated forcing variables such as near-surface bulk meteorology, surface waves and whitecap fraction. In this paper we report on analysis of the turbulent fluxes of momentum and water vapor and a comparison of the bulk transfer coefficients with the COARE algorithm (version 3.0).

OS31B-1264

Influence of Waves, Whitecaps, and Turbulence on the Gas Transfer during the Southern Ocean Gas Exchange Experiment

* Zappa, C J zappa@ldeo.columbia.edu, Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
Cifuentes-Lorenzen, A alejandro.cifuentes@huskymail.uconn.edu, University of Connecticut, Avery Point, Department of Marine Sciences 1080 Shennecossett Road, Groton, CT 06340, United States
Edson, J B james.edson@uconn.edu, University of Connecticut, Avery Point, Department of Marine Sciences 1080 Shennecossett Road, Groton, CT 06340, United States
McGillis, W R wrm2102@columbia.edu, Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
Bariteau, L Ludovic.Bariteau@noaa.gov, National Oceanographic Atmospheric Administration, Physical Science Division 325 Broadway, Boulder, CO 80305, United States
Fairall, C W Chris.Fairall@noaa.gov, National Oceanographic Atmospheric Administration, Physical Science Division 325 Broadway, Boulder, CO 80305, United States

The exchange of carbon dioxide and other trace gases across the air-sea interface plays an important role in global and regional biogeochemical cycles. The gas transfer velocity (k) is thought to be controlled by near- surface turbulence at low to moderate wind speeds and by bubble-mediated processes at higher wind speeds. At low to moderate wind speeds, small-scale waves including microbreaking disrupt the diffusive boundary layer, contribute to mixing at the surface, and enhance exchange. Likewise, at higher wind speeds, large-scale wave breaking, or whitecapping, generates mixing and additionally enhances gas transfer via bubble-mediated exchange. The parameterization for k based on the direct covariance fluxes is shown to have a cubic dependence on wind speed. This result supports the hypothesis that, if bubble mediated exchange is important, the transfer velocity should increase proportionally with whitecap coverage, since whitecap coverage been shown to increase with at least a cubic dependence on wind speed. However, the very large uncertainties under high wind speed conditions limit the universality of this result and the role of breaking waves and bubble modulated transfer. Here, we present results of the combination of turbulence, deep-ocean wave statistics, whitecapping, and CO2 gas exchange measured during the Southern Ocean Gas Exchange Experiment (SO GasEx) with sustained conditions between 10-20 m s-1. Directional ocean wave spectra, significant wave height, peak wave period, and peak wave direction were obtained with a Wave and Surface Current Monitoring System (WaMoS® II). WaMoS® II also has the capability to resolve two-dimensional maps of surface elevation snapshots with the significant advantage of continuous availability of wave data in rough seas. In addition, significant wave height was measured using a laser altimeter as well as a nadir-looking microwave system. Oceanic turbulent kinetic energy dissipation rates were measured using a pulse-coherent Doppler sonar mounted at 2-m depth from a drifting surface buoy. Lastly, wave-breaking statistics and whitecapping coverage are reported using two high-resolution digital cameras from the flying bridge. We present results of process studies that investigate the various models for gas transfer that incorporate turbulence and wave- breaking statistics with the goal of developing a focused parameterization.

OS31B-1265

Optical Measurements of Bubble Injections in the Southern Ocean

* Randolph, K L kaylan.randolph@uconn.edu, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States
Dierssen, H M heidi,dierssen@uconn.edu, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States
Buonassissi, C chritopher.bounassissi@uconn.edu, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States
Freeman, S sfreeman@wetlabs2.com, WET Labs, Inc. (East Coast Branch), 165 Dean Knauss Drive, Narragansett, RI 02882, United States
Twardowski, M S mtwardo@wetlabs2.com, WET Labs, Inc. (East Coast Branch), 165 Dean Knauss Drive, Narragansett, RI 02882, United States

Bubbles, due to their size compared to wavelengths of light and refractive index relative to water, are effective at backscattering light. The magnitude of light reflected from the sea surface (remote sensing reflectance, Rrs) can be significantly enhanced due to bubble entrainment at temporal scales of minutes and the spectral nature of the light field can be shifted towards green wavelengths. Here, we use optical measurements collected during the Southern Ocean Gas Exchange Experiment (SOGasEx, March 10 through April 4, 2007) to address questions related bubble populations and light scattering. Time series measurements of particle size distribution (PSD), volume scattering function, and backscattering measured at high frequency (1-20 Hz) from the surface layer of the Atlantic Sector of the Southern Ocean will be presented. The PSD from 2-1500 ¥ìm, acquired using a LISST-100X and LISST-FLOC (Laser In-Situ Scattering and Transmissiometry, Sequoia Scientific Inc.) shows significant enhancement of particle populations in time periods on the order of minutes that are related to bubble injections. Simultaneous measurements of the full volume scattering function (MASCOT, WET Labs) are used to differentiate bubble particles using a characteristic bubble scattering feature between 60¢ª and 80¢ª. We will also present the depth-dependent relationships between the power-law slope of the PSD, backscattering and physical parameters (i.e. wind speed, whitecap coverage, and significant wave height) in order to assess the intensity of the bubble field in these waters and the potential influence on light scattering in the Southern Ocean.

OS31B-1266

Measurements of the air-sea flux of ozone from the Ronald H. Brown

* Hare, J jeff.hare@noaa.gov, Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, CIRES Campus Box 216 University of Colorado, Boulder, CO 80309, United States
Bariteau, L ludovic.bariteau@noaa.gov, Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, CIRES Campus Box 216 University of Colorado, Boulder, CO 80309, United States
Fairall, C chris.fairall@noaa.gov, NOAA Earth System Research Laboratory (ESRL), Physical Sciences Division (PSD), NOAA ESRL / PSD 325 Broadway, Boulder, CO 80305, United States
Helmig, D detlev.helmig@colorado.edu, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, INSTAAR Campus Box 450 University of Colorado, Boulder, CO 80309, United States
Ganzeveld, L laurens.ganzeveld@wur.nl, Department of Environmental Sciences, Wageningen University, Department of Environmental Sciences Earth System Science - Climate Change Wageningen University, Wageningen, 6708PB, Netherlands
Lang, K kathrin.lang@noaa.gov, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, INSTAAR Campus Box 450 University of Colorado, Boulder, CO 80309, United States
Hueber, J jhueber@colorado.edu, Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, INSTAAR Campus Box 450 University of Colorado, Boulder, CO 80309, United States

Human activities have doubled the concentration of ozone in the global troposphere. Ozone is a highly reactive gas and is the third most important 'greenhouse' gas. A significant term in the global ozone atmospheric budget is the uptake by ocean surfaces, but direct observations are quite rare and uncertain. Due to our limited knowledge of the physical and chemical processes involved in the oceanic ozone destruction, climate models typically use only one singular ozone deposition value for all the world's oceans. In order to improve these models, and to have a better understanding of the deposition process into the sea, direct measurements of the air-sea flux of ozone have been made aboard the NOAA Ship Ronald H. Brown during cruises in the Gulf of Mexico (TexAQS and GOMECC) and on the Southern Ocean GasEx cruise. The ozone concentration was measured by a fast-response instrument deployed by INSTAAR, in collaboration with CIRES and NOAA ESRL/PSD researchers. This fast response sensor operates on the chemiluminescence principle and, when combined with sonic anemometer vertically velocity, is used to estimate the ozone flux over the ocean by direct eddy correlation. The preliminary results show a median value for the ozone deposition in the SOGasEx region of about 0.015 cm/s. We will present results from the various deployments of the system, but we will concentrate on the analysis from the SOGasEx cruise. Implications to the NOAA/COARE parameterization will be discussed.

http://instaar.colorado.edu/outreach/ozone-oceans/index.html

OS31B-1267

Tracking the SO-GasEx tracer patch with ADCP and high-resolution surface data

* Hebert, D hebert@gso.uri.edu, University of Rhode Island, Graduate School of Oceanography 215 South Ferry Road, Narragansett, RI 02882, United States
Hales, B bhales@coas.oregonstate.edu, Oregon State University, 104 Ocean Admin, Corvallis, OR 97331, United States
Strutton, P strutton@coas.oregonstate.edu, Oregon State University, 104 Ocean Admin, Corvallis, OR 97331, United States
Ho, D T ho@hawaii.edu, University of Hawaii, Department of Oceanography 1000 Pope ROad, Honolulu, HI 96822, United States

During the Southern Ocean Gas-exchange Experiment (SO-GasEx), we employed detailed analysis of the upper-water-column velocity data (via Acoustic Doppler Current Profiling (ADCP)) and high-resolution mapping of the hydrography of the surface waters in the patch (temperature, salinity, pCO₂, chlorophyll, dissolved oxygen, and nitrate). ADCP-based velocity profiles were used to select the locations of the two injections. Subsequently they were used to make progressive vector estimations of the patches' migration over the course of the experiment. In addition, the velocity estimates were used to calculate point- wise back trajectories during the patch surveys to correct the tracer and hydrographic property fields to provide quasi-instantaneous snapshots of the tracer-infused region. This approach provided superior realizations of the structure of the patch tracer and hydrographic distributions over those generated without correction for advection. In the first patch, this approach showed small but statistically significant and coherent within patch variability in the surface hydrographic properties. In the second patch, surface properties were far more uniform and appeared to be in near steady-state over the course of the experiment.

OS31B-1268

Air-Sea Gas Exchange Measured with 3He/SF6 during SO GasEx

* Ho, D T ho@hawaii.edu, University of Hawaii, Department of Oceanography 1000 Pope Rd, Honolulu, HI 96822, United States
Wanninkhof, R rik.wanninkhof@noaa.gov, NOAA/AOML, 4301 Rickenbacker Cswy, Miami, FL 33149, United States
Schlosser, P schlosser@ldeo.columbia.edu, Lamont-Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964, United States
Sullivan, K F Kevin.Sullivan@noaa.gov, NOAA/AOML, 4301 Rickenbacker Cswy, Miami, FL 33149, United States

Two 3He/SF6 dual gas tracer experiment were conducted during the Southern Ocean Gas Exchange Experiment (SO GasEx) to determine gas transfer velocities, k(600). During the experiment, wind speeds of up to 19.5 m/s were encountered. A total of 361 3He and 609 SF6 samples were taken at 40 CTD casts and 2 pumped stations. k(600) was calculated from the decrease in the observed 3He/SF6 ratio, assuming that dispersion is a first order process. The results are compared to those of previous 3He/SF6 dual tracer experiment in the coastal and open ocean, and with commonly used parameterizations between wind speed and gas transfer velocity.

OS31B-1269

Water Column Carbon Trends During the SO Gas Exchange Experiment

* Sabine, C L chris.sabine@noaa.gov, Ocean Climate Research Division, NOAA/PMEL, 7600 Sand Point Way NE, Seattle, wa 98115, United States
Feely, R A Richard.A.Feely@noaa.gov, Ocean Climate Research Division, NOAA/PMEL, 7600 Sand Point Way NE, Seattle, wa 98115, United States
Zappa, C zappa@ldeo.columbia.edu, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
McGillis, W mcgillis@ldeo.columbia.edu, Lamont-Doherty Earth Observatory of Columbia University, 61 Route 9W, Palisades, NY 10964, United States
DeGrandpre, M michael.degrandpre@umontana.edu, Chemistry Department, University of Montana, Missoula, MT 59812, United States
Johnson, G C gregory.c.johnson@noaa.gov, Ocean Climate Research Division, NOAA/PMEL, 7600 Sand Point Way NE, Seattle, wa 98115, United States
Jones, S M stacy.maenner@noaa.gov, Ocean Climate Research Division, NOAA/PMEL, 7600 Sand Point Way NE, Seattle, wa 98115, United States
Lebon, G geoffrey.t.lebon@noaa.gov, Ocean Climate Research Division, NOAA/PMEL, 7600 Sand Point Way NE, Seattle, wa 98115, United States

The Southern Ocean GasEx experiment was conducted aboard the NOAA ship Ronald H. Brown from 29 February to 12 April, 2008. The scientific work focused on quantifying gas transfer velocities using deliberately injected tracers, measuring CO₂ and DMS fluxes directly in the marine air boundary layer, and elucidating the physical, chemical, and biological processes controlling air-sea fluxes with measurements in the upper-ocean and marine air. The oceanic projects used shipboard and autonomous drifting instruments to conduct a Lagrangian study of the evolution of chemical and biological properties over the course of the experiment. The shipboard measurements included rosette casts to 500 m at approximately 12 hour intervals. Despite the fact that the partial pressure of CO₂ in the mixed layer waters was significantly lower than the atmosphere, the dissolved inorganic carbon concentrations were relatively stable over the period of the study. This resulted from the counteracting process of CO₂ uptake from the atmosphere and CO₂ drawdown from ongoing biological productivity. The autonomous measurements provided high resolution data to evaluate carbon variability at higher frequencies. We will compare the shipboard and autonomous measurements and evaluate the controls on the mixed layer carbon system during the SO GasEx experiment.

http://so-gasex.org/

OS31B-1270

Low Net Community Production from Oxygen/Argon Mass Balance during the Southern Ocean Gas Exchange Experiment

* Hamme, R C rhamme@uvic.ca, University of Victoria, School of Earth and Ocean Sciences, P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
Cassar, N ncassar@princeton.edu, Princeton University, Department of Geosciences, M28 Guyot Hall, Princeton, NJ 08544, United States

Mass balance techniques using oxygen/argon ratios can yield high quality estimates of net community production. By ratioing with argon, the oxygen signal is corrected for physical influences such as bubble- mediated gas exchange and temperature change. We made near-continuous observations of dissolved oxygen/argon ratios and absolute oxygen concentrations in surface seawater pumped into the ship during the Southern Ocean Gas Exchange Experiment (SO GasEx). This experiment focused on an area to the east of the southern tip of South America during March and April 2008. Oxygen was measured by optode and calibrated with Winkler titrations. Oxygen/argon ratios were measured using a quadrupole mass spectrometer with a membrane equilibrator inlet. Ratios were standardized by comparison with air values and further calibrated by discrete measurements made by high-accuracy sector mass spectrometry. Repeated Winkler measurements of oxygen concentrations in water collected from Niskin bottles and the underway system confirmed the absence of heterotrophic activity in the ship's seawater lines. Spatial surveys showed significant variability in net community production around the study area. Preliminary estimates of productivity in the ³He/SF₆ tracer patches laid down for the gas exchange experiment suggested that the first tracer patch had small but measurable rates of net community production but that the second tracer patch was characterized by net respiration or recent upwelling.

OS31B-1271

Primary Productivity and Carbon Export During the Southern Ocean Gas Exchange (SOGasEx) Lagrangian Tracer Experiments

* Lance, V P vlance@ldeo.columbia.edu, Lamont-Doherty Earth Observatory at Columbia University, PO Box 1000, Palisades, NY 10964, United States
Strutton, P G strutton@coas.oregonstate.edu, College of Oceanic and Atmospheric Sciences, Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331-5503, United States
Marra, J F jfm7780@brooklyn.cuny.edu, Brooklyn College of the City University of New York, 2900 Bedford Avenue, Brooklyn, NY 11210, United States

Biological uptake rates of inorganic carbon were measured during two gas exchange tracer experiments in the Southern Ocean, Atlantic sector near 51°S, 38°W (SOGasEx). Primary productivity estimated from radiocarbon incubations ranged from 12 to 40 mmol C m^-2 d^-1. Time integrated primary production was estimated to be 355 and 487 mmol C m^-2 during the first experiment and second experiments respectively. New productivity (primary productivity associated with nitrate uptake) and time integrated new production, will be calculated from ¹⁵N-nitrate incubations. Over large enough temporal and spatial scales, new productivity is expected to be coupled with carbon export out of the surface, euphotic zone into the deep ocean. Particulate organic carbon distribution through the water column and over the time course of the experiments was measured in discrete samples and estimated in situ by beam transmission and will also be used to estimate the balance between carbon production and export. Primary productivity and export rates determined here will be incorporated into a carbon budget and CO₂ air- sea flux models for the SOGasEx experiments.

OS31B-1272

Depth-resolved water column spectral absorption of sunlight by phytoplankon during the Southern Ocean Gas Exchange (SOGasEx) Lagrangian tracer experiments

* Hargreaves, B R brh0@lehigh.edu, Lehigh University, Earth & Environmental Sciences 31 Williams Drive, Bethlehem, PA 18015, United States

Optical measurements made during gas exchange tracer experiments in the Southern Ocean, Atlantic sector near 51°S, 38°W from March-April 2008 (SOGasEx) were used to develop daily integrated depth- resolved PAR absorbed by phytoplankton. Particulate and phytoplankton pigment spectral absorption coefficients (a_p and a_ph), and methanol-extracted chlorophyll-a concentrations (chl-a) from discrete samples within and below the upper mixed layer (40 stations) were combined with data from optical casts where chlorophyll-a and cdom fluorescence and PAR scalar irradiance were measured (11 stations), PAR K_d was measured from a buoy free of ship shadow for 0-5m (11 stations), and Wetlabs AC-9 whole water absorption coefficients to 150m were measured (14 stations, with 3 in common with fluorescence data) to estimate depth-resolved values for both total spectral absorption and spectral PAR irradiance. By combining depth-adjusted spectral absorption of phytoplankton pigments (a_ph) with depth-adjusted PAR spectral irradiance we estimated depth-resolved daily PAR irradiance absorbed by photosynthetic pigments. These data can be compared with time-integrated primary production measurements conducted on deck where solar exposure or lamp exposure was modified to simulate a range of depths. Such a synthesis should improve our estimates of depth-integrated daily primary production, and ultimately contribute to refining estimates of carbon export rates to be incorporated into a carbon budget and CO₂ air-sea flux models for the SOGasEx experiments.

OS31B-1273

Particle Populations in the Southern Ocean During the Southern Ocean Gas Exchange Experiment

* Buonassissi, C J christopher.buonassissi@uconn.edu, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States
Dierssen, H heidi.dierssen@uconn.edu, University of Connecticut, 1080 Shennecossett Road, Groton, CT 06340, United States

The particle size distribution conveys information about the size and number of phytoplankton, non-algal particles, and potentially bubbles suspended in the water column. Here, we present measurements with the LISST-100X (Sequoia Scientific) of in-situ, non-disturbed suspended particle size distributions made during the Southern Ocean Gas Exchange experiment. Measurements were obtained in the open ocean Southern Atlantic sector of the Southern Ocean and in waters surrounding South Georgia Island. The resulting slope of the particle size distribution is estimated for particles ranging from 6-250 μm assuming a Jungian or power law distribution. Data from vertical profiles conducted within the water column will be presented. Slopes of the particle size distribution (PSD) vary from 3.31 to 3.96 within the range of theoretical values. The PSD slopes showed three statistically distinct areas corresponding to the two patch locations and the waters near South Georgia Island. In the waters surrounding South Georgia Island, the PSD slope was steeper than that in the open ocean sector indicating an increased prevalence of smaller particles. The particle volume concentrations ranged from 13 to 639 μl/L. The lowest particle volume concentrations occurred in the waters near South Georgia Island. The mixed layer showed higher particle volume concentrations for particle sizes below 50 microns compared to deeper waters. For particle sizes above 50 microns, there was no significant difference in the particle volume concentrations between the mixed layer and deeper waters. The relationship between the PSD slope and chlorophyll concentration is compared with data collected from other regions of the world's oceans. Overall, the relationship follows an inverse correlation where increasing chlorophyll concentration corresponds to a decrease in the particle size distribution slope.

OS31B-1274

Spatial and Temporal Sea Surface pCO2 and O2 Variability During the North Atlantic Deep Ocean Gas Exchange Experiment (DOGEE)

* DeGrandpre, M michael.degrandpre@umontana.edu, Department of Chemistry, University of Montana, Missoula, MT 59812, United States
Beatty, C cory.beatty@umontana.edu, Department of Chemistry, University of Montana, Missoula, MT 59812, United States
Drennan, W wdrennan@rsmas.miami.edu, Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, FL 33149, United States
Upstill-Goddard, R rob.goddard@newcastle.ac.uk, School of Marine Science and Technology, University of Newcastle upon Tyne, Newcastle, NE1 7RU, United Kingdom

We present results from in situ biogeochemical measurements performed during the UK SOLAS Deep Ocean Gas Exchange Experiment (DOGEE). Sensors for the partial pressure of CO2 (pCO2), dissolved O2 (DO), light intensity, and chl-a fluorescence were mounted on two Air Sea Interaction Spar (ASIS) buoys at 1 m and 5 m depths. The buoys were deployed on 22 June 2007 in two tracer-spiked water masses located at approximately 45N, 20W and remained in the water until 11 July 2007. One of the tracer patches contained an artificial surfactant. The buoys did not successfully follow the patches but traced a parallel trajectory approximately 30 km apart. These data are used to provide spatial context for the pCO2 observations. At both locations, sea surface pCO2 began nearly 40 uatm below atmospheric saturation but rose steadily, reaching saturation by the end of the deployment. While heating significantly increased the pCO2, air-sea uptake also appears to have played a role. Diurnal pCO2 variability was primarily controlled by heating and cooling with very little signal evident from net community metabolism. Dissolved O2 was 2-3% above saturation. We will use the pCO2-DO combination to examine if gas transfer rates can be estimated using an in-situ "dual-tracer" methodology.

OS31B-1275

Spring Bloom Dynamics of the Eastern Bering Sea Shelf as Estimated from Oxygen/Argon Ratios and Triple Oxygen Isotopes

* Prokopenko, M prokopen@usc.edu, Dept.of Earth Sci.,USC, 3651 Trousedale Pkwy, Los Angeles, CA 90089, United States
Granger, J jgranger@princeton.edu, Geosciences Dept, Princeton Univ., Guyot Hall, Princeton, NJ 08544, United States
Mordy, C W Calvin.W.Mordy@noaa.gov, Genwest Sys., P.O. Box 397, Edmonds, WA 98020, United States
DiFiore, P pdifiore@princeton.edu, Geosciences Dept, Princeton Univ., Guyot Hall, Princeton, NJ 08544, United States
Cassar, N ncassar@princeton.edu, Geosciences Dept, Princeton Univ., Guyot Hall, Princeton, NJ 08544, United States
Cokelet, E Edward.D.Cokelet@noaa.gov, NOAA/PMEL, 7600 Sand Pt W. NE, Seattle, WA 98115, United States
Kachel, N B Nancy.Kachel@noaa.gov, UW/JISAO, Seattle, Seattle, WA 98020,
Kachel, D N David.Kachel@noaa.gov, NOAA/PMEL, 7600 Sand Pt W. NE, Seattle, WA 98115, United States
Sambrotto, R sambrotto@ldeo.columbia.edu, LDEO, Columbia Univ., 61 Rt. 9W, Palisades, NY 10964, United States
Moran, B moran@gso.uri.edu, URI, 70 Lower College Rd., Kingston, RI 02881, United States

The Bering Sea's position at the end of the global ocean "conveyor belt" and shoaling of nutrient rich water masses onto its broad shelf make the Eastern Bering Sea shelf one of the most productive regions of the polar oceans, with reported annual primary production rates of 150 to 500 gC*m^-2 yr^-1. Much of this production occurs during spring blooms, which follow the inception of water column stratification after the retreat of sea-ice. The fate of the bloom biomass determines the amount of the export production available to higher trophic levels in the shelf ecosystem, but due to the hydrographic variability of the ice edge regime direct measurements of productivity rates are not easily extrapolated in space and time. Hence, a more integrative approach is needed. Here we report estimates of Net Community and Gross Photosynthetic Production rates (GPP and NCP) obtained from O₂/Ar and triple oxygen isotope ratios measured as a part of the BEST (Bering Sea Ecosystem Study) project during six weeks of spring 2007. Under steady state conditions, NCP and new production should be stoichiometrically equivalent to net photosynthetic O₂ production and can be estimated from oxygen air-sea exchange fluxes. In this study, O₂/Ar ratios, used to distinguish between biological and physical components of oxygen flux, were measured continuously by a quadrupole mass spectrometer equipped with an Equilibrator Inlet (EIMS, modified from Kaiser et al., 2005). To calibrate EIMS results, discrete samples were collected from the ship's underway seawater system and from hydrocasts. Dissolved O₂ and Ar were cryogenically isolated and extracted offline and analyzed on an IRMS at the Geosciences Dept, Princeton Univ. To estimate the rates of gross photosynthetic production, oxygen triple isotope ratios of dissolved O₂ were measured on the same discrete samples. Ventilation rates (piston velocities) were calculated based on Quikscat wind speeds and the parameterization of Wanninkhof (1992). During the 12-day interval (22-23 April and 4-5 May 2007) between two repeat occupations of the same transect at 60°N, an extensive bloom developed at the edge of the retreating ice field. The biological oxygen fluxes increased from 20±60 mmol*m^-2d^-1 in April to a maximum of 1863±200 mmol*m^-2d^-1 in May. The rise in NCP rates was coincident with a shoaling of the mixed layer depth from > 30 m to ~ 8 m. Based on triple O isotope measurements, the fraction of NCP to GPP was 15 ± 20 % at the initial stages of the bloom, and increased substantially 12 days into the bloom. If we assume the bloom production increasing linearly from zero to 1863 mmolO₂*m^-2d^-1 over the initial 12 days and then decreasing to zero over the next 12 days, this event would produce 185 gC*m^-2 or about 40 % of the maximum annual total production previously estimated for the Eastern Bering Sea Shelf.

OS31B-1276

Biological Productivity from an Oxygen Mass Balance in the subarctic North Pacific

* Giesbrecht, K E karinag@uvic.ca, School of Earth and Ocean Sciences University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
Hamme, R C rhamme@uvic.ca, School of Earth and Ocean Sciences University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada

Biological productivity is an important process controlling the export of carbon into the deep ocean and thus influencing the earth's climate. An O₂ mass balance of the upper ocean can estimate this export of organic carbon if the physical processes affecting the O₂ concentrations are accounted for. This can be accomplished by measuring the dissolved O₂/Ar ratio, because their similar physical properties allow us to consider Ar an 'abiotic' O₂ analogue. Here we present a two-year data set of O₂/N₂/Ar ratio measurements collected at Station Papa and along Line P in 2007/08. Line P, situated in the subarctic North Pacific, is a series of oceanographic stations running from the southwest tip of Vancouver Island to Station Papa (50°N, 145°W), one of the oldest deep-ocean time series in existence which is located in the High-Nutrient/Low-Chlorophyll (HNLC) region of the subarctic gyre. Current cruises along Line P run three times per year, typically in February, June and August. The dissolved gas ratios are measured using a stable isotope mass spectrometer and oxygen concentrations by titration. In a simple steady state, we equate biological O₂ production to diffusive gas exchange, using the O₂/Ar ratio to normalize the physical component of the oxygen signal and calculate the net biological oxygen production. Diffusive gas exchange is calculated using a wind speed parameterization. Preliminary estimates of the net biological production in the mixed layer at Station Papa for 2007 are calculated at 30.9 and 14.0 mmol C m^-2 d^{- 1} for June and August respectively, both exhibiting mixed layer O₂/Ar supersaturations. The O₂/Ar undersaturation in the mixed layer for February 2007 suggests net respiration at that time. The wind speed parameterization of diffusive gas exchange is the major source of error for this method. We plan to refine our productivity calculation to account for vertical mixing and also by measuring rates of production using a number of different methods, so that we may determine if the values obtained converge on a result. Future investigations to obtain a better-constrained estimate of the biological carbon export in this region by measuring Nitrogen and Carbon uptake rates in the euphotic zone using dual, stable isotope tracer ¹⁵N/¹³C incubations in addition to the oxygen mass balance will be discussed.

OS31B-1277

Air-Water Exchange of N₂ and O₂ from In Situ Measurements in the Subarctic and Subtropical Pacific Oceans: Oxygen Flux and Net Biological Production

* Emerson, S emerson@u.washington.edu, School of Oceanography, University of Washington P.O. Box 355351, Seattle, WA 98195,

In-situ measurements of wind speed, atmospheric pressure, surface-ocean total dissolved gas pressure and oxygen concentration are used to determine the flux of nitrogen and oxygen between the ocean and atmosphere in the subarctic and subtropical Pacific Oceans. Measurements were made hourly over a period of about one year on surface moorings at the Hawaii Ocean Time series (HOT) in 2005 and at Station P in 2007. Gas pressures in the mixed layer were determined using a gas tension device (GTD) and an oxygen sensor calibrated by Winkler O₂ titrations. The pressures of nitrogen and oxygen vary smoothly within a few percent of atmospheric saturation in the subtropical Pacific Ocean, but in the subarctic surface waters these values are punctuated by very rapid excursions caused by storms. The primary flux of oxygen in the upper ocean is between the ocean and atmosphere. We use a simple ocean mixed-layer model to determine this flux and estimate the net biological oxygen production at these sites. Assuming that the net biological oxygen and carbon production are stoichiometrically related over an annual cycle, this method provides a measure of the annual carbon export from the mixed layer, an important component of the ocean's role in the global carbon cycle. There is net biological O₂ production most of the year in the subtropical ocean; however, little evidence of net O₂ production in the wintertime in the subarctic Pacific. This contrasts with earlier ¹⁴C primary production measurements which indicate that wintertime production is about half that in summer at both locations. Annual estimates of biologically produced carbon export at these two sites will be contrasted at the presentation in the fall meeting. This research indicates that it should be possible to derive estimates of the net annual air-water oxygen fluxes caused by biological production at any location of the open ocean where there is a surface mooring. Large, abrupt atmospheric pressure changes (up to 50 millibars or about 5 percent) associated with extreme weather in the winter time in the subarctic Pacific are often followed by relatively stable conditions. In these cases the response of the pN₂ of the ocean is determined by the rate of gas exchange at the air- water interface. These observations may be a clue to a new method for determining the gas exchange rate at high latitudes using in situ gas measurements.

OS31B-1278

Noble gas constraints on gas exchange during deepwater formation

* Nicholson, D P roo2@u.washington.edu, University of Washington, School of Oceanography, Box 357940, Seattle, WA 98195, United States
Emerson, S emerson@u.washington.edu, University of Washington, School of Oceanography, Box 357940, Seattle, WA 98195, United States

Glacial/interglacial cycles in the pCO₂ of the atmosphere of ~80-90 ppm have been well recorded in the ice core record and strongly correlate with temperature and ice volume. While the relationship between pCO₂ and climate has been clearly documented, a satisfactory mechanism that explains the cycles of pCO₂ remains elusive. Simple box models of the carbon cycle have suggested that atmospheric pCO₂ is highly sensitive to forcing in the high latitude oceans such as enhanced nutrient uptake in polar regions. Indeed, the high latitude deepwater formation regions are considered the windows through which the deep ocean interior communicates with the atmosphere. Results from general circulation models (GCMs), on the other hand, suggest low latitude processes are equally important in regulating the pCO₂ of the atmosphere. A primary reason for this discrepancy is differences in how deepwater is formed between these types of models. Better constraints on the mechanisms of deepwater formation and gas exchange are needed to resolve these discrepancies. We use noble gas ratios measured in Pacific and Atlantic deepwater to constrain the size of the surface outcrop of deepwater formation and thus the degree of communication between deep ocean and atmosphere. Noble gases are excellent tracers of gas exchange processes during deepwater formation because of their inert nature and varying physical properties. When high latitude outcrop areas are small, water does not have time to fully equilibrate with the atmosphere and thus a large preformed disequilibrium is subducted. This physical disequilibrium cannot be measured directly for dissolved organic carbon, because of the complicating impacts of the biological carbon cycle. Noble gas ratios, δ^40/36Ar ratio in particular, record this disequilibrium. We use deepwater measurements of δ^40/36Ar with precision at the 0.01 ‰ level to evaluate appropriate size of deepwater formation areas in models.

OS31B-1279

Anomalously Low pCO2 Measured in the San Francisco Estuary

* Fuller, J R jfull@sfsu.edu, Romberg Tiburon Center/SFSU, 3150 Paradise Drive, Tiburon, CA 94920, United States
Wilkerson, F fwilkers@sfsu.edu, Romberg Tiburon Center/SFSU, 3150 Paradise Drive, Tiburon, CA 94920, United States
Parker, A E aeparker@sfsu.edu, Romberg Tiburon Center/SFSU, 3150 Paradise Drive, Tiburon, CA 94920, United States
Marchi, A amarchi@sfsu.edu, Romberg Tiburon Center/SFSU, 3150 Paradise Drive, Tiburon, CA 94920, United States

Estuaries have been identified as potential net sources of CO₂ to the atmosphere. Bacterial respiration of organic matter entering the estuary leads to supersaturated levels of pCO₂. The southern embayment of the San Francisco Estuary (SFE) is no exception due in part to wastewater treatment practices. Persistently high levels of pCO₂ between 600 and 1000 μatm have been reported for this embayment by the U.S. Geological Survey over the period 1976-1980 and more recently (2007-2008) by the authors. However, both studies also found notable exceptions to the high pCO₂ levels during the spring phytoplankton bloom. An average level of 375 μatm, slightly above the contemporary atmospheric level, was observed during an April 1980 transect. Our recent measurements over the same transect have observed an even greater drawdown of pCO₂ to as low as 175 μatm. In addition the pCO₂ drawdown persisted from early March 2008 until the end of May. These anomalously low levels correspond directly with an algal bloom as evidenced by high concentrations of chlorophyll a and supersaturated dissolved oxygen. To our knowledge these are the lowest levels reported for the SFE and they indicate that portions of the estuary are a sink for atmospheric CO₂ during bloom conditions. The hydrology of the southern embayment is dominated at times by the input of wastewater which is often treated to the advanced secondary level with inorganic nitrate as the product. This possibly contributes to a healthy estuarine algal population that helps to maintain current pCO₂ levels in the SFE to those of 30 years ago despite significant urban growth around the estuary over that period. These findings have major implications both to estuarine management and to estimates of the estuarine component in global air-sea CO₂ exchange

OS31B-1280

Micrometeorological Measurement of Fetch- and Atmospheric Stability-Dependent Air- Water Exchange of Legacy Semivolatile Organic Contaminants in Lake Superior

* Perlinger, J A jperl@mtu.edu, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, United States
Tobias, D E detobias@mtu.edu, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, United States
Rowe, M D mdrowe@mtu.edu, Michigan Technological University, 1400 Townsend Dr., Houghton, MI 49931, United States

Coastal waters including the Laurentian Great Lakes are particularly susceptible to local, regional, and long- range transport and deposition of semivolatile organic contaminants (SOCs) as gases and/or associated with particles. Recently-marketed SOCs can be expected to undergo net deposition in surface waters, whereas legacy SOCs such as polychlorinated biphenyls (PCBs) are likely to be at equilibrium with respect to air-water exchange, or, if atmospheric concentrations decrease through, e.g., policy implementation, to undergo net gas emission. SOC air-water exchange flux is usually estimated using the two-film model. This model describes molecular diffusion through the air and water films adjacent to the air-water interface. Air-water exchange flux is estimated as the product of SOC fugacity, typically based on on-shore gaseous concentration measurements, and a transfer coefficient, the latter which is estimated from SOC properties and environmental conditions. The transfer coefficient formulation commonly applied neglects resistance to exchange in the internal boundary layer under atmospherically stable conditions, and the use of on-shore gaseous concentration neglects fetch-dependent equilibration, both of which will tend to cause overestimation of flux magnitude. Thus, for legacy chemicals or in any highly contaminated surface water, the rate at which the water is cleansed through gas emission tends to be over-predicted using this approach. Micrometeorological measurement of air-water exchange rates of legacy SOCs was carried out on ships during four transect experiments during off-shore flow in Lake Superior using novel multicapillary collection devices and thermal extraction technology to measure parts-per-quadrillion SOC levels. Employing sensible heat in the modified Bowen ratio, fluxes at three over-water stations along the transects were measured, along with up-wind, onshore gaseous concentration and aqueous concentration. The atmosphere was unstable for one of the four trajectories and stable for the other three trajectories. Two of three transects carried out under stable conditions are complicated because, as revealed by back-trajectory analysis, different air masses were sampled at each station, and, for one of these transects, the air masses spent significant portions of time over land. Analyses of legacy pesticide concentrations carried out to date suggest that under stable and unstable conditions, fluxes were out of the lake. We present and compare micrometeorological measurements and two-film estimates of fluxes of legacy pesticides and PCBs.

http://www.cee.mtu.edu/~jperl/

OS31B-1281

Application of an Internal Boundary Layer Transport Exchange Model to Gas Transfer of Semivolatile Organic Contaminants in Lake Superior

* Rowe, M D mdrowe@mtu.edu, Michigan Technological University, 1400 Townsend Dr, Houghton, MI 49931, United States
Perlinger, J A jperl@mtu.edu, Michigan Technological University, 1400 Townsend Dr, Houghton, MI 49931, United States
Fairall, C W Chris.Fairall@noaa.gov, NOAA Earth System Research Laboratory, Physical Science Division, Boulder, CO 80301, United States

A two-dimensional Lagrangian internal boundary layer transport exchange (IBLTE) model was developed that is capable of predicting the modification of temperature, humidity, and trace gas concentrations and fluxes as a function of fetch in offshore flow. This model was specifically designed to complement over-water flux measurement campaigns in several ways: design and improvement of experimental methods, selection of sampling times and locations, and interpretation of results. The IBLTE model incorporates the NOAA COARE bulk flux algorithm and gas transfer model to calculate turbulence scaling parameters and gas transfer velocity, respectively. The internal boundary layer growth rate was calibrated using a large data set of air temperature and humidity modification over Lake Ontario collected during International Field Year for the Great Lakes, 1973. Current methods to estimate air-water exchange of SOCs in the Great Lakes have rarely been verified with over-water measurements. Given temporal and spatial variability of these fluxes and complexity of flux measurements, simultaneous development and improvement of models and measurement methods helps to reveal shortcomings of each approach. The IBLTE model is applied to micrometeorological SOC flux measurements performed along a transect experiment in Lake Superior in July, 2006. Measurements were collected at three over-water stations at 16, 28, and 59 km fetch under off-shore flow conditions. Measured and modeled temperature and humidity modification and vertical temperature gradients were compared for validation of the modeled vertical transport. Modification of concentration, temperature, and flux with fetch resulted from fetch-dependent equilibration, growth of the IBL, and variation of the lake surface temperature during the transect experiment. Modeled hexachlorobenzene fluxes were greater in magnitude than measured fluxes at the 16 and 28 km stations but nearly equal at the 59 km station. Both model and measurements indicated vertical gradients in HCB concentration were smaller in magnitude at the first two stations than at the third station. Measured fluxes are sensitive to uncertainty in HCB concentration measurements when the vertical gradient is small. The IBLTE model is a useful tool that allowed consideration of the entire experimental data set and enabled hypothesis-testing regarding the sources of discrepancies between model and measurement.

OS31B-1282

Direct Numerical Simulation of Scalar Transport in Free-Surface Turbulence With Applications to Air-Sea Gas Transfer

* Kermani, A kermani@jhu.edu, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218,
Shen, L Lian.Shen@jhu.edu, Johns Hopkins University, 3400 N. Charles Street, Baltimore, MD 21218,

We perform direct numerical simulation of scalar transport in free-surface turbulence to study gas and heat transfer across the air-sea interface. Based on our simulation result and theoretical analysis, we obtain a mathematical basis for using surface temperature to find residence time of surface elements in experimental methods such as controlled flux technique. We have developed a highly accurate Eulerian-Lagrangian method to quantify surface element residence time, based on which distribution of surface age can be obtained. It is concluded that surface renewal statistics can be best described by a lognormal distribution. Interfacial transfer happens mainly at short residence times. Danckwerts' exponential distribution is modified to provide a more accurate description of surface age, which agrees well with the result we obtain from direct numerical simulation. The results obtained in this study may be used as a basis for model development for air-sea gas and heat transfer.

OS31B-1283

Tuning a Physically-Based Model of the air-sea gas Transfer Velocity

* Jeffery, C D cdj200@noc.soton.ac.uk, National Oceanography Centre, University of Southampton, Waterfront Campus, European Way,, Southampton, SO14 3ZH, United Kingdom
Robinson, I S isr@noc.soton.ac.uk, National Oceanography Centre, University of Southampton, Waterfront Campus, European Way,, Southampton, SO14 3ZH, United Kingdom
Woolf, D K David.Woolf@thurso.uhi.ac.uk, Environmental Research Institute, North Highland College, UHI Millennium Institute, Castle Street,, Thurso, KW14 7JD, United Kingdom

Gas transfer velocities are estimated for one year using a 1-d upper-ocean model and a modified NOAA- COARE transfer velocity parameterization. Tuning parameters are evaluated with the aim of bringing the parameterization in line with current estimates based on simple wind-speed dependent models, derived from bomb-radiocarbon inventories and deliberate tracer release experiments. This is an important step toward more reliable estimates of air-sea gas transfer. We suggest that A=1.3 and B=1.0, for the sub-layer scaling parameter and bubble mediated exchange respectively, are suitable for calculating the global average CO₂ transfer velocity k. Using these parameters and a simple polynomial approximation we estimate a global annual average k of 16.4±4.7 cm hr^-1 when using global mean winds of 6.89 m s^-1 from the NCEP/NCAR Reanalysis 1 1954--2000. Given the non-specific nature of the parameterization, global k for DMS and CH₄ (11.9 and 18.0 cm hr^-1 respectively) is also estimated, highlighting the importance of continued development of physically-based models.

Authors (2008), Title, Eos Trans. AGU, 89(53), Fall Meet. Suppl., Abstract xxxxx-xx