Methyl Bromide In Preindustrial Air: Measurements From an Antarctic Ice Core

This paper presents the first ice core measurements of methyl bromide (CH3Br). Samples from a shallow Antarctic ice core (Siple Dome, West Antarctica), ranging in mean gas dates from 1671 to 1942, had a mean CH3Br mixing ratio of 5.8 ppt. These results extend the existing historical record derived from air and Antarctic firn air to about 350 years before present. Model simulations illustrate that the ice core results are consistent with estimates of the impact of anthropogenic activity ( fumigation, combustion, and biomass burning) on the atmospheric CH3Br burden, given the large current uncertainties in the modern atmospheric CH3Br budget. A preindustrial scenario assuming no fumigation, no combustion, and a 75% reduction in biomass-burning sources yields aSouthern Hemisphere mean mixing ratio of 5.8 ppt, in good agreement with the ice core results. There is a significant imbalance between the known CH3Br sources and sinks in the modern atmospheric CH3Br budget. The ice core data do not sufficiently constrain the model to determine how much of the unknown source\u27\u27 was present in the preindustrial budget. The results do indicate that most of the southern hemispheric component of this unknown source\u27\u27 is not anthropogenic

Positive priming of terrestrially derived dissolved organic matter in a freshwater microcosm system

© 2015. American Geophysical Union. All Rights Reserved. The role of priming processes in the remineralization of terrestrially derived dissolved organic carbon (TDOC) in aquatic systems has been overlooked. We provide evidence for TDOC priming using a lab-based microcosm experiment in which TDOC was primed by the addition of 13C-labeled algal dissolved organic carbon (ADOC) or a 13C-labeled disaccharide (trehalose). The rate of TDOC remineralization to carbon dioxide (CO2) occurred 4.1±0.9 and 1.5±0.3 times more rapidly with the addition of trehalose and ADOC, respectively, relative to experiments with TDOC as the sole carbon source over the course of a 301h incubation period. Results from these controlled experiments provide fundamental evidence for the occurrence of priming of TDOC by ADOC and a simple disaccharide. We suggest that priming effects on TDOC should be considered in carbon budgets for large-river deltas, estuaries, lakes, hydroelectric reservoirs, and continental shelves. Key Points Priming of organic matter exists in aquatic systems Ramifications of this work have major implications on greenhouse gas emissions First evidence for lab conditions of priming setting stage for more fieldwork

A comprehensive estimate for loss of atmospheric carbon tetrachloride (CCl4) to the ocean

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Atmospheric Chemistry and Physics 16 (2016): 10899-10910, doi:10.5194/acp-16-10899-2016.Extensive undersaturations of carbon tetrachloride (CCl4) in Pacific, Atlantic, and Southern Ocean surface waters indicate that atmospheric CCl4 is consumed in large amounts by the ocean. Observations made on 16 research cruises between 1987 and 2010, ranging in latitude from 60° N to 77° S, show that negative saturations extend over most of the surface ocean. Corrected for physical effects associated with radiative heat flux, mixing, and air injection, these anomalies were commonly on the order of −5 to −10 %, with no clear relationship to temperature, productivity, or other gross surface water characteristics other than being more negative in association with upwelling. The atmospheric flux required to sustain these undersaturations is 12.4 (9.4–15.4) Gg yr−1, a loss rate implying a partial atmospheric lifetime with respect to the oceanic loss of 183 (147–241) yr and that  ∼  18 (14–22)  % of atmospheric CCl4 is lost to the ocean. Although CCl4 hydrolyzes in seawater, published hydrolysis rates for this gas are too slow to support such large undersaturations, given our current understanding of air–sea gas exchange rates. The even larger undersaturations in intermediate depth waters associated with reduced oxygen levels, observed in this study and by other investigators, strongly suggest that CCl4 is ubiquitously consumed at mid-depth, presumably by microbiota. Although this subsurface sink creates a gradient that drives a downward flux of CCl4, the gradient alone is not sufficient to explain the observed surface undersaturations. Since known chemical losses are likewise insufficient to sustain the observed undersaturations, this suggests a possible biological sink for CCl4 in surface or near-surface waters of the ocean. The total atmospheric lifetime for CCl4, based on these results and the most recent studies of soil uptake and loss in the stratosphere is now 32 (26–43) yr.This research could not have been done without the support of our various institutions and the programs through which they support science, including funds at various times from NASA’s Upper Atmosphere Research Program, the US Department of Energy, NOAA’s Climate Program Office, the Atmospheric and Geosciences sections of the National Science Foundation, and the National Research Council of the US National Academies of Science

A comprehensive estimate for loss of atmospheric carbon tetrachloride (CCl4) to the ocean

© The Author(s), 2016. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Atmospheric Chemistry and Physics 16 (2016): 10899-10910, doi:10.5194/acp-16-10899-2016.Extensive undersaturations of carbon tetrachloride (CCl4) in Pacific, Atlantic, and Southern Ocean surface waters indicate that atmospheric CCl4 is consumed in large amounts by the ocean. Observations made on 16 research cruises between 1987 and 2010, ranging in latitude from 60° N to 77° S, show that negative saturations extend over most of the surface ocean. Corrected for physical effects associated with radiative heat flux, mixing, and air injection, these anomalies were commonly on the order of −5 to −10 %, with no clear relationship to temperature, productivity, or other gross surface water characteristics other than being more negative in association with upwelling. The atmospheric flux required to sustain these undersaturations is 12.4 (9.4–15.4) Gg yr−1, a loss rate implying a partial atmospheric lifetime with respect to the oceanic loss of 183 (147–241) yr and that  ∼  18 (14–22)  % of atmospheric CCl4 is lost to the ocean. Although CCl4 hydrolyzes in seawater, published hydrolysis rates for this gas are too slow to support such large undersaturations, given our current understanding of air–sea gas exchange rates. The even larger undersaturations in intermediate depth waters associated with reduced oxygen levels, observed in this study and by other investigators, strongly suggest that CCl4 is ubiquitously consumed at mid-depth, presumably by microbiota. Although this subsurface sink creates a gradient that drives a downward flux of CCl4, the gradient alone is not sufficient to explain the observed surface undersaturations. Since known chemical losses are likewise insufficient to sustain the observed undersaturations, this suggests a possible biological sink for CCl4 in surface or near-surface waters of the ocean. The total atmospheric lifetime for CCl4, based on these results and the most recent studies of soil uptake and loss in the stratosphere is now 32 (26–43) yr.This research could not have been done without the support of our various institutions and the programs through which they support science, including funds at various times from NASA’s Upper Atmosphere Research Program, the US Department of Energy, NOAA’s Climate Program Office, the Atmospheric and Geosciences sections of the National Science Foundation, and the National Research Council of the US National Academies of Science

Saturation anomalies of alkyl nitrates in the tropical Pacific Ocean

This paper reports the first measurements of the saturation state of low molecular weight alkyl nitrates (methyl, ethyl, isopropyl, and n-propyl nitrate) in the tropical Pacific Ocean. These compounds were supersaturated with saturation anomalies as high as 2000%. Air/sea flux estimates based on these measurements suggest that surface ocean emissions are sufficient to account for observed levels of tropospheric alkyl nitrates in this region. Model calculations suggest that atmospheric loss rates are faster than can be explained by photolysis and reaction with OH alone. The implication is that removal via transport is important, and there must be a net export of alkyl nitrates from the tropics to other regions of the atmosphere

Carbonate chemistry, nutrient concentration, and dissolved oxygen concentration for discreet water samples collected during multiple cruises between June 2017 to Sept 2018 within Galveston Bay, TX

Dataset: Galveston Bay Carbonate ChemistryThese data include carbonate chemistry, nutrient concentration, and dissolved oxygen concentration for discreet water samples collected within Galveston Bay, TX. Eight single day cruises were conducted quarterly aboard the R/V Lithos or R/V Trident from June 2017 through September 2018. In addition, discreet water samples were collected at sites 10 - 60 km outside the mouth of the bay and up to 15m deep to characterize incoming seawater to the bay. These samples were collected on three cruises (WTX1 - R/V Manta, WTX3 - R/V Manta, WTX4 - R/V Pelican) in June, August, and November 2017. Discreet water samples were collected for total alkalinity and dissolved inorganic carbon, dissolved oxygen, and dissolved nutrients. CTD profiles were collected at each sampling site. Stochastic coastal acidification events in response to high volume rainfall and runoff that often accompanies tropical cyclone events has the potential to represent a significant threat to valuable calcifying reef ecosystems. Understanding acidification response and recovery to such events is critical to improving conservation and protection of coastal ecosystems, like oyster and coral reefs, particularly as climate change continues and tropical cyclone rainfall intensity increases. These data assess the impact of the rainfall and runoff from Hurricane Harvey on the acidification levels in Galveston Bay, TX. Samples were collected and analyzed primarily by Tacey Hicks, with assistance from other students in Dr. Katie Shamberger ’s research group, at Texas A&M University. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/881549NSF Division of Ocean Sciences (NSF OCE) OCE-1800913, NSF Division of Ocean Sciences (NSF OCE) OCE-176038

Biological degradation of methyl chloride in coastal seawater

Methyl chloride (CH3Cl) is the most abundant halocarbon in the atmosphere, and constitutes a significant fraction of the total atmospheric halogen burden. Chemical reactions of CH3Cl in seawater are slow, and it has been believed that the oceans are not an important sink for this compound. However, direct measurements of CH3Cl degradation rates in coastal seawater (Bedford Basin, Nova Scotia), using a stable isotope incubation technique, indicate rapid loss attributed to microbial activity. A series of weekly measurements from March 2000 to May 2001 yielded degradation rates ranging from 0–30% d−1, with an annual mean of 7.4% d−1. If biological uptake of CH3Cl occurs throughout the oceans at similar rates, the mean partial atmospheric lifetime of CH3Cl with respect to oceanic removal could be a few years, rather than several decades as previously thought. This rapid removal would make the oceans a major sink for CH3Cl and lower the overall atmospheric lifetime of CH3Cl from the current estimate of 1.3 to about 1.0 years. Measurements of the degradation rate of CH3Cl in open ocean waters are needed in order to quantify the oceanic uptake rate

Carbonate chemistry, nutrient concentration, and dissolved oxygen concentration for discreet water samples collected during multiple cruises between June 2017 to Sept 2018 within Galveston Bay, TX

Dataset: Galveston Bay Carbonate ChemistryThese data include carbonate chemistry, nutrient concentration, and dissolved oxygen concentration for discreet water samples collected within Galveston Bay, TX. Eight single day cruises were conducted quarterly aboard the R/V Lithos or R/V Trident from June 2017 through September 2018. In addition, discreet water samples were collected at sites 10 - 60 km outside the mouth of the bay and up to 15m deep to characterize incoming seawater to the bay. These samples were collected on three cruises (WTX1 - R/V Manta, WTX3 - R/V Manta, WTX4 - R/V Pelican) in June, August, and November 2017. Discreet water samples were collected for total alkalinity and dissolved inorganic carbon, dissolved oxygen, and dissolved nutrients. CTD profiles were collected at each sampling site. Stochastic coastal acidification events in response to high volume rainfall and runoff that often accompanies tropical cyclone events has the potential to represent a significant threat to valuable calcifying reef ecosystems. Understanding acidification response and recovery to such events is critical to improving conservation and protection of coastal ecosystems, like oyster and coral reefs, particularly as climate change continues and tropical cyclone rainfall intensity increases. These data assess the impact of the rainfall and runoff from Hurricane Harvey on the acidification levels in Galveston Bay, TX. Samples were collected and analyzed primarily by Tacey Hicks, with assistance from other students in Dr. Katie Shamberger ’s research group, at Texas A&M University. For a complete list of measurements, refer to the full dataset description in the supplemental file 'Dataset_description.pdf'. The most current version of this dataset is available at: https://www.bco-dmo.org/dataset/881549NSF Division of Ocean Sciences (NSF OCE) OCE-1800913, NSF Division of Ocean Sciences (NSF OCE) OCE-176038

On the outflow of Weddell Sea Deep Water over the South Scotia Ridge: observations from a high-resolution hydrographic survey

Póster presentado en 2010 AGU Fall Meeting, celebrado del 13 al 17 de diciembre de 2010 en San Francisco, Calif. (Estados Unidos)Peer Reviewe