Browsing by Subject "WIND-SPEED"

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  • Morgan, Eric J.; Lavric, Jost V.; Arevalo-Martinez, Damian L.; Bange, Hermann W.; Steinhoff, Tobias; Seifert, Thomas; Heimann, Martin (2019)
    Ground-based atmospheric observations of CO2, delta(O-2/N-2), N2O, and CH4 were used to make estimates of the air-sea fluxes of these species from the Luderitz and Walvis Bay upwelling cells in the northern Benguela region, during upwelling events. Average flux densities (+/- 1 sigma) were 0:65 +/- 0:4 mu mol m(-2) s(-1) for CO2, -5.1 +/- 2:5 mu mol m(-2) s(-1) for O-2 (as APO), 0:61 +/- 0:5 nmol m(-2) s(-1) for N2O, and 4:8 +/- 6:3 nmol m(-2)s(-1) for CH4. A comparison of our top-down (i.e., inferred from atmospheric anomalies) flux estimates with shipboard-based measurements showed that the two approaches agreed within +/- 55% on average, though the degree of agreement varied by species and was best for CO2. Since the top-down method overestimated the flux density relative to the shipboard-based approach for all species, we also present flux density estimates that have been tuned to best match the shipboard fluxes. During the study, upwelling events were sources of CO2, N2O, and CH4 to the atmosphere. N2O fluxes were fairly low, in accordance with previous work suggesting that the evasion of this gas from the Benguela is smaller than for other eastern boundary upwelling systems (EBUS). Conversely, CH4 release was quite high for the marine environment, a result that supports studies that indicated a large sedimentary source of CH4 in the Walvis Bay area. These results demonstrate the suitability of atmospheric time series for characterizing the temporal variability of upwelling events and their influence on the overall marine greenhouse gas (GHG) emissions from the northern Benguela region.
  • Heiskanen, Jouni J.; Mammarella, Ivan; Haapanala, Sami; Pumpanen, Jukka; Vesala, Timo; Macintyre, Sally; Ojala, Anne (2014)
  • Rovelli, L.; Attard, K. M.; Heppell, C. M.; Binley, A.; Trimmer, M.; Glud, R. N. (2018)
    Headwater streams are important in the carbon cycle and there is a need to better parametrize and quantify exchange of carbon-relevant gases. Thus, we characterized variability in the gas exchange coefficient (k(2)) and dissolved oxygen (O-2) gas transfer velocity (k) in two lowland headwaters of the River Avon (UK). The traditional one-station open-water method was complemented by in situ quantification of riverine sources and sinks of O-2 (i.e., groundwater inflow, photosynthesis, and respiration in both the water column and benthic compartment) enabling direct hourly estimates of k(2) at the reach-scale (similar to 150 m) without relying on the nighttime regression method. Obtained k(2) values ranged from 0.001 h(-1) to 0.600 h(-1). Average daytime k(2) were a factor two higher than values at night, likely due to diel changes in water temperature and wind. Temperature contributed up to 46% of the variability in k on an hourly scale, but clustering temperature incrementally strengthened the statistical relationship. Our analysis suggested that k variability is aligned with dominant temperature trends rather than with short-term changes. Similarly, wind correlation with k increased when clustering wind speeds in increments correspondent with dominant variations (1 m s(-1)). Time scale is thus an important consideration when resolving physical drivers of gas exchange. Mean estimates of k(600) from recent parametrizations proposed for upscaling, when applied to the settings of this study, were found to be in agreement with our independent O-2 budget assessment (within <10%), adding further support to the validity of upscaling efforts aiming at quantifying large-scale riverine gas emissions.
  • Norris, S. J.; Brooks, I. M.; Moat, B. I.; Yelland, M. J.; de Leeuw, G.; Pascal, R. W.; Brooks, B. (2013)
  • Kouznetsov, Rostislav D.; Zilitinkevich, Sergej S. (2010)