International Ocean Discovery Program Expedition 360 drilled Hole U1473A at Atlantis Bank, an oceanic core complex on the Southwest Indian Ridge, with the aim of recovering representative samples of ...the lower oceanic crust. Recovered cores were primarily gabbro and olivine gabbro. These mineralogies may host serpentinization reactions that have the potential to support microbial life within the recovered rocks or at greater depths beneath Atlantis Bank. We quantified prokaryotic cells and analyzed microbial community composition for rock samples obtained from Hole U1473A and conducted nutrient addition experiments to assess if nutrient supply influences the composition of microbial communities. Microbial abundance was low (≤10
cells cm
) but positively correlated with the presence of veins in rocks within some depth ranges. Due to the heterogeneous nature of the rocks downhole (alternating stretches of relatively unaltered gabbros and more significantly altered and fractured rocks), the strength of the positive correlations between rock characteristics and microbial abundances was weaker when all depths were considered. Microbial community diversity varied at each depth analyzed. Surprisingly, addition of simple organic acids, ammonium, phosphate, or ammonium plus phosphate in nutrient addition experiments did not affect microbial diversity or methane production in nutrient addition incubation cultures over 60 weeks. The work presented here from Site U1473A, which is representative of basement rock samples at ultraslow spreading ridges and the usually inaccessible lower oceanic crust, increases our understanding of microbial life present in this rarely studied environment and provides an analog for basement below ocean world systems such as Enceladus.
The lower oceanic crust below the seafloor is one of the most poorly explored habitats on Earth. The rocks from the Southwest Indian Ridge (SWIR) are similar to rock environments on other ocean-bearing planets and moons. Studying this environment helps us increase our understanding of life in other subsurface rocky environments in our solar system that we do not yet have the capability to access. During an expedition to the SWIR, we drilled 780 m into lower oceanic crust and collected over 50 rock samples to count the number of resident microbes and determine who they are. We also selected some of these rocks for an experiment where we provided them with different nutrients to explore energy and carbon sources preferred for growth. We found that the number of resident microbes and community structure varied with depth. Additionally, added nutrients did not shape the microbial diversity in a predictable manner.
The gas exchange between water bodies and air is difficult to measure, thus the approximations of air–water gas exchange coefficient based solely on wind speed has been widely used. However, such ...approaches may not work well in river environments. In rivers, water currents may govern gas exchange. Thus, a new approximation for calculating the gas exchange coefficient (k) based on the near‐surface velocity scale (us) is suggested and compared to wind‐based estimates. Our velocity scale estimates are based on field observations during summer 2016 on the Yenisei River using an Acoustic Doppler Current Profiler, high‐frequency temperature profilers and a vessel‐mounted meteorological sensors‐suite. The results demonstrate that us‐derived gas exchange coefficients are higher than those based solely on wind speed. The results demonstrate that the wind approximation underestimates gas exchange coefficients during low‐wind conditions.
Dry mole fractions of methyl bromide (CH sub(3)Br) in marine boundary layer air and in air equilibrated with surface water were measured in the Southern Ocean. Saturation anomalies were consistently ...negative at -36 plus or minus 7%. The observed undersaturations do not support recently published predictions of highly supersaturated Antarctic waters, but instead suggest a net uptake of atmospheric CH sub(3)Br by cold, productive oceans. The observations do not appear to be supported by known chemical degradation rates and present strong evidence for an unidentified, oceanic sink mechanism such as biological breakdown. Our estimate for the global, net, oceanic sink for atmospheric methyl bromide remains negative at -21 (-11 to -32) Gg y super(-1).
Brominated very short‐lived substances (VSLSs) such as bromoform (CHBr3), dibromomethane (CH2Br2), and chlorodibromomethane (CHClBr2) are receiving increasing attention, due to their important role ...in tropospheric and lower stratospheric ozone (O3) chemistry. These brominated VSLSs were measured in air and surface water during the Gulf of Mexico and East Coast Carbon (GOMECC) cruise in the summer of 2007. Mean atmospheric mixing ratios for CHBr3, CH2Br2 and CHClBr2 for the entire cruise were 14.6 (0.7 to 138.3) ppt, 2.8 (0.5 to 13.2) ppt, and 0.5 (0.03 to 3.2) ppt, respectively; and mean sea‐surface water concentrations were 66.0 (4.4 to 1724.8) pmol L−1, 10.6 (1.9 to 153.8) pmol L−1, and 1.0 (0.1 to 17.2) pmol L−1, respectively. These compounds were supersaturated almost everywhere in the study region, except a few locations in the Florida Straits and along the east coast of Florida, where negative saturation anomalies and fluxes were observed. Mean net fluxes observed during the GOMECC cruise for CHBr3, CH2Br2, and CHClBr2 were 47.6 (−25.4 to 1056.3) nmol m−2 d−1, 9.7 (−0.5 to 112.3) nmol m−2 d−1, and 0.8 (−1.2 to 10.8) nmol m−2 d−1, respectively. The net fluxes for these polybrominated compounds from the coastally influenced waters (bottom depth ≤200 m) are significantly higher than the net fluxes observed in the open ocean (bottom depth >200 m).
Key Points
Bromofrom, dibromomethane, dibromochloromethane in the coastal United States
VSLSs in urbanized coastal region
An improved oceanic budget for methyl chloride Hu, Lei; Yvon-Lewis, Shari A.; Butler, James H. ...
Journal of geophysical research. Oceans,
February 2013, Volume:
118, Issue:
2
Journal Article
Peer reviewed
Open access
We present results that improve the estimates of the global net sea‐to‐air flux, global oceanic emission, global oceanic uptake, and partial atmospheric lifetime of methyl chloride (CH3Cl) with ...respect to oceanic loss. This study includes improved parameterizations for solubility and saturation anomaly‐sea surface temperature relationships for CH3Cl, along with the use of an updated gas transfer velocity from a recent study. By measuring solubilities of CH3Cl in pure water and seawater over a temperature range from 0°C to 40°C, we obtained a new solubility function with both temperature and salinity dependencies. We also developed a new parameterization of seasonal CH3Cl saturation anomaly (∆%) as a function of both sea surface temperature and wind speed using data from 10 different cruises with an extensive coverage in the global surface ocean. Using the new solubility function and the new seasonal ∆%‐(SST, wind speed) relationships, we estimated the global net sea‐to‐air flux of CH3Cl at 335 (210 to 480) Gg yr−1. For the first time, the global flux of CH3Cl was broken into a unidirectional gross emission and a unidirectional gross uptake, which were estimated at 700 (510 to 910) Gg yr−1 and −370 (−430 to −300) Gg yr−1. The partial atmospheric lifetime of CH3Cl with respect to the oceanic uptake was revised to 12 (10–15) years, resulting in a revision on the atmospheric lifetime of CH3Cl from the previous estimate of 1.0 year to 1.2 years.
Key Points
Global net sea‐to‐air fluxes of CH3Cl was estimated at 335 (210 to 480) Gg yr‐1
The atmospheric lifetime of CH3Cl becomes 1.2 years
Parameterizations on solubility and saturation anomaly of CH3Cl were improved
Equaliberty in the Dutch Caribbean is a collection of
essays that explores fundamental questions of equality and freedom
on the non-sovereign islands of the Dutch Caribbean. Drawing on
in-depth ...ethnographic research, historical and media analysis, the
study of popular culture, and autoethnographic accounts, the
various contributions challenge conventional assumptions about
political non/sovereignty. While the book recognizes the existence
of nationalist independence movements, it opens a critical space to
look at other forms of political articulation, autonomy, liberty,
and a good life. Focusing on all six different islands and through
a multitude of voices and stories, the volume engages with the
everyday projects, ordinary imaginaries, and dreams of equaliberty
alongside the work of independistas and traditional social
movements aiming for more or full self-determination. As such, it
offers a rich and powerful telling of the various ways of being in
and belonging to our contemporary postcolonial world.
Here we use a portable method to obtain high spatial resolution measurements of concentrations and calculate diffusive water-to-air fluxes of CH4 and CO2 from two Subarctic coastal regions (Kasitsna ...and Jakolof Bays) and an Arctic lake (Toolik Lake). The goals of this study are to determine distributions of these concentrations and fluxes to (1) critically evaluate the established protocols of collecting discrete water samples for these determinations, and to (2) provide a first-order extrapolation of the regional impacts of these diffusive atmospheric fluxes. Our measurements show that these environments are highly heterogeneous. Areas with the highest dissolved CH4 and CO2 concentrations were isolated, covering less than 21% of the total lake and bay areas, and significant errors can be introduced if the collection of discrete water samples does not adequately characterize these spatial distributions. A first order extrapolation of diffusive fluxes to all Arctic regions with similar characteristics as Toolik Lake suggests that these lakes are likely supplying 0.21 and 15.77 Tg of CH4 and CO2 to the atmosphere annually, respectively. Similarly, we found that the Subarctic Coastal Ocean is likely supplying 0.027 Tg of CH4 annually and is taking up roughly 524 Tg of CO2 per year. Although diffusive fluxes at Toolik Lake may not be as substantial when comparing against present seep ebullition and spring ice-out values, warming in the Arctic may result in the increase of methane discharge and methane emissions to the atmosphere. Thus further work is needed to understand this changing environment. This study suggests that high spatial resolution measurement protocols, similar to the one used here, should be incorporated into field campaigns to reduce regional uncertainty and refine global emission estimates.
•High resolution measurements revealed strong spatial heterogeneities in CH4 and CO2 fluxes.•Highest dissolved CH4 and CO2 values were isolated covering <12% of the total study area.•Substantial errors in regional extrapolations can be incurred if non-uniformity of fluxes is ignored.
Measurements of methyl bromide (CH3Br) and methyl chloride (CH3Cl) were made during the Gulf of Mexico and the East Coast Carbon (GOMECC) cruise in the summer of 2007. This was the first large-scale ...study of CH3Br and CH3Cl in the coastal ocean. The mean atmospheric mixing ratios were 10.1 ppt for CH3Br and 517 ppt for CH3Cl. Surface seawater concentrations ranged from 0.8 pM to 5.0 pM for CH3Br and from 61.5 pM to 179 pM for CH3Cl. Biological processes contribute to the elevated seawater concentrations of CH3Br, while a combination of biological processes and terrestrial sources may contribute to elevated seawater concentrations of CH3Cl. Vertical distributions show highest concentrations of CH3Br and CH3Cl in the subsurface seawater below the mixed layer due to high degradation rates near the surface. Good correlation of the production rates between CH3Br and CH3Cl suggests they have some common sources in the coastal ocean. After excluding the open ocean points, annual coastal emissions in the studied region were 0.01-0.06 Gg yr-1 for CH3Br and 0.3-1.6 Gg yr-1 for CH3Cl. By simple extrapolation, the global coastal emissions were estimated at 0.5-3.6 Gg yr−1 for CH3Br and 19-98 Gg yr-1 for CH3Cl. Including the coastal ocean emissions of CH3Br and CH3Cl will increase the estimate of global oceanic emissions by 1%0-9% and 1%-8%, respectively.
Brominated very short-lived substances (BrVSLS), such as bromoform, are important trace gases for stratospheric ozone chemistry. These naturally derived trace gases are formed via ...bromoperoxidase-mediated halogenation of dissolved organic matter (DOM) in seawater. Information on DOM type in relation to the observed BrVSLS concentrations in seawater, however, is scarce. We examined the sensitivity of BrVSLS production in relation to the presence of specific DOM moieties. A total of 28 model DOM compounds in artificial seawater were treated with vanadium bromoperoxidase (V-BrPO). Our results show a clear dependence of BrVSLS production on DOM type. In general, molecules that comprise a large fraction of the bulk DOM pool did not noticeably affect BrVSLS production. Only specific cell metabolites and humic acid appeared to significantly enhance BrVSLS production. Amino acids and lignin phenols suppressed enzyme-mediated BrVSLS production and may instead have formed halogenated nonvolatile molecules. Dibromomethane production was not observed in any experiments, suggesting it is not produced by the same pathway as the other BrVSLS. Our results suggest that regional differences in DOM composition may explain the observed BrVSLS concentration variability in the global ocean. Ultimately, BrVSLS production and concentrations are likely affected by DOM composition, reactivity, and cycling in the ocean.
Recent work has shown the presence of anomalous dissolved organic matter (DOM), with high optical yields, in deep waters 15 months after the Deepwater Horizon (DWH) oil spill in the Gulf of Mexico ...(GOM). Here, we continue to use the fluorescence excitation–emission matrix (EEM) technique coupled with parallel factor analysis (PARAFAC) modeling, measurements of bulk organic carbon, dissolved inorganic carbon (DIC), oil indices, and other optical properties to examine the chemical evolution and transformation of oil components derived from the DWH in the water column of the GOM. Seawater samples were collected from the GOM during July 2012, 2 years after the oil spill. This study shows that, while dissolved organic carbon (DOC) values have decreased since just after the DWH spill, they remain higher at some stations than typical deep-water values for the GOM. Moreover, we continue to observe fluorescent DOM components in deep waters, similar to those of degraded oil observed in lab and field experiments, which suggest that oil-related fluorescence signatures, as part of the DOM pool, have persisted for 2 years in the deep waters. This supports the notion that some oil-derived chromophoric dissolved organic matter (CDOM) components could still be identified in deep waters after 2 years of degradation, which is further supported by the lower DIC and partial pressure of carbon dioxide (pCO2) associated with greater amounts of these oil-derived components in deep waters, assuming microbial activity on DOM in the current water masses is only the controlling factor of DIC and pCO2 concentrations.
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