The distribution and ecology of the Gammaridea (Crustacea : Amphipoda) of the lower Chesapeake estuaries

Gammarid amphipods of three tidal rivers entering Chesapeake Bay were studied for ten months, particularly in the York River where 40 species were record during the period. Several species moved up or down the rivers with changing salinity. The more abundant species had longer breeding seasons. The number of described species from lower Chesapeake Bay is now 42 and the presence of 10 undescribed species and of several which bracket the region indicates that much remains to be learned about amphipods in the Bay. Nineteen of these have a boreal affinity and seven are limited to the Virginian subprovince. A reference to the most recent significant work on each species is given and a key is included as an appendix

Air-sea CO2 exchange in the equatorial Pacific

Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C08S02, doi:10.1029/2003JC002256.GasEx-2001, a 15-day air-sea carbon dioxide (CO2) exchange study conducted in the equatorial Pacific, used a combination of ships, buoys, and drifters equipped with ocean and atmospheric sensors to assess variability and surface mechanisms controlling air-sea CO2 fluxes. Direct covariance and profile method air-sea CO2 fluxes were measured together with the surface ocean and marine boundary layer processes. The study took place in February 2001 near 125°W, 3°S in a region of high CO2. The diurnal variation in the air-sea CO2 difference was 2.5%, driven predominantly by temperature effects on surface solubility. The wind speed was 6.0 ± 1.3 m s−1, and the atmospheric boundary layer was unstable with conditions over the range −1 < z/L < 0. Diurnal heat fluxes generated daytime surface ocean stratification and subsequent large nighttime buoyancy fluxes. The average CO2 flux from the ocean to the atmosphere was determined to be 3.9 mol m−2 yr−1, with nighttime CO2 fluxes increasing by 40% over daytime values because of a strong nighttime increase in (vertical) convective velocities. The 15 days of air-sea flux measurements taken during GasEx-2001 demonstrate some of the systematic environmental trends of the eastern equatorial Pacific Ocean. The fact that other physical processes, in addition to wind, were observed to control the rate of CO2 transfer from the ocean to the atmosphere indicates that these processes need to be taken into account in local and global biogeochemical models. These local processes can vary on regional and global scales. The GasEx-2001 results show a weak wind dependence but a strong variability in processes governed by the diurnal heating cycle. This implies that any changes in the incident radiation, including atmospheric cloud dynamics, phytoplankton biomass, and surface ocean stratification may have significant feedbacks on the amount and variability of air-sea gas exchange. This is in sharp contrast with previous field studies of air-sea gas exchange, which showed that wind was the dominating forcing function. The results suggest that gas transfer parameterizations that rely solely on wind will be insufficient for regions with low to intermediate winds and strong insolation.This work was performed with the support of the National Science Foundation Grant OCE-9986724 and the NOAA Global Carbon Cycle Program Grants NA06GP048, NA17RJ1223, and NA87RJ0445 in the Office of Global Programs

Ocean Acidification: Summary for Policymakers

Third Symposium on the Ocean in a High-CO2 Worl

Ozeanversauerung: Zusammenfassung für Entscheidungsträger

Third Symposium on the Ocean in a High-CO2 Worl

Opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes

Iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean. The mechanisms and rates of Fe supply to the ocean interior are still poorly understood and quantified. Iron isotope ratios of different Fe pools can potentially be used to trace sources and sinks of the global Fe biogeochemical cycle if these boundary fluxes have distinct signatures. Seafloor hydrothermal vents emit metal rich fluids from mid-ocean ridges into the deep ocean. Iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of Fe isotopes during plume dispersal in the deep ocean are understood. In this study we assess the behaviour of Fe isotopes in a Southern Ocean hydrothermal plume using a sampling program of Total Dissolvable Fe (TDFe), and dissolved Fe (dFe). We demonstrate that δ56Fe values of dFe (δ56dFe) within the hydrothermal plume change dramatically during early plume dispersal, ranging from −2.39 ± 0.05‰ to −0.13 ± 0.06‰ (2 SD). The isotopic composition of TDFe (δ56TDFe) was consistently heavier than dFe values, ranging from −0.31 ± 0.03‰ to 0.78 ± 0.05‰, consistent with Fe oxyhydroxide precipitation as the plume samples age. The dFe present in the hydrothermal plume includes stabilised dFe species with potential to be transported to the deep ocean. We estimate that stable dFe exported from the plume will have a δ56Fe of −0.28 ± 0.17‰. Further, we show that the proportion of authigenic iron-sulfide and iron-oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved Fe passed into the neutrally buoyant plume. We show that such controls yield variable dissolved Fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere, and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records

Contribution of ocean, fossil fuel, land biosphere, and biomass burning carbon fluxes to seasonal and interannual variability in atmospheric CO2

Author Posting. © American Geophysical Union, 2008. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 113 (2008): G01010, doi:10.1029/2007JG000408.Seasonal and interannual variability in atmospheric carbon dioxide (CO2) concentrations was simulated using fluxes from fossil fuel, ocean and terrestrial biogeochemical models, and a tracer transport model with time-varying winds. The atmospheric CO2 variability resulting from these surface fluxes was compared to observations from 89 GLOBALVIEW monitoring stations. At northern hemisphere stations, the model simulations captured most of the observed seasonal cycle in atmospheric CO2, with the land tracer accounting for the majority of the signal. The ocean tracer was 3–6 months out of phase with the observed cycle at these stations and had a seasonal amplitude only ∼10% on average of observed. Model and observed interannual CO2 growth anomalies were only moderately well correlated in the northern hemisphere (R ∼ 0.4–0.8), and more poorly correlated in the southern hemisphere (R < 0.6). Land dominated the interannual variability (IAV) in the northern hemisphere, and biomass burning in particular accounted for much of the strong positive CO2 growth anomaly observed during the 1997–1998 El Niño event. The signals in atmospheric CO2 from the terrestrial biosphere extended throughout the southern hemisphere, but oceanic fluxes also exerted a strong influence there, accounting for roughly half of the IAV at many extratropical stations. However, the modeled ocean tracer was generally uncorrelated with observations in either hemisphere from 1979–2004, except during the weak El Niño/post-Pinatubo period of the early 1990s. During that time, model results suggested that the ocean may have accounted for 20–25% of the observed slowdown in the atmospheric CO2 growth rate.We acknowledge the support of NASA grant NNG05GG30G and NSF grant ATM0628472

The state of the Martian climate

60°N was +2.0°C, relative to the 1981–2010 average value (Fig. 5.1). This marks a new high for the record. The average annual surface air temperature (SAT) anomaly for 2016 for land stations north of starting in 1900, and is a significant increase over the previous highest value of +1.2°C, which was observed in 2007, 2011, and 2015. Average global annual temperatures also showed record values in 2015 and 2016. Currently, the Arctic is warming at more than twice the rate of lower latitudes

Triosephosphate Isomerase Gene Characterization and Potential Zoonotic Transmission of Giardia duodenalis

To address the source of infection in humans and public health importance of Giardia duodenalis parasites from animals, nucleotide sequences of the triosephosphate isomerase (TPI) gene were generated for 37 human isolates, 15 dog isolates, 8 muskrat isolates, 7 isolates each from cattle and beavers, and 1 isolate each from a rat and a rabbit. Distinct genotypes were found in humans, cattle, beavers, dogs, muskrats, and rats. TPI and small subunit ribosomal RNA (SSU rRNA) gene sequences of G. microti from muskrats were also generated and analyzed. Phylogenetic analysis on the TPI sequences confirmed the formation of distinct groups. Nevertheless, a major group (assemblage B) contained most of the human and muskrat isolates, all beaver isolates, and the rabbit isolate. These data confirm that G. duodenalis from certain animals can potentially infect humans and should be useful in the detection, differentiation, and taxonomy of Giardia spp

Preservation of iron(II) by carbon-rich matrices in a hydrothermal plume

Hydrothermal venting associated with mid-ocean ridge volcanism is globally widespread. This venting is responsible for a dissolved iron flux to the ocean that is approximately equal to that associated with continental riverine runoff. For hydrothermal fluxes, it has long been assumed that most of the iron entering the oceans is precipitated in inorganic forms. However, the possibility of globally significant fluxes of iron escaping these mass precipitation events and entering open-ocean cycles is now being debated, and two recent studies suggest that dissolved organic ligands might influence the fate of hydrothermally vented metals. Here we present spectromicroscopic measurements of iron and carbon in hydrothermal plume particles at the East Pacific Rise mid-ocean ridge. We show that organic carbon-rich matrices, containing evenly dispersed iron(II)-rich materials, are pervasive in hydrothermal plume particles. The absence of discrete iron(II) particles suggests that the carbon and iron associate through sorption or complexation. We suggest that these carbon matrices stabilize iron(II) released from hydrothermal vents in the region, preventing its oxidation and/or precipitation as insoluble minerals. Our findings have implications for deep-sea biogeochemical cycling of iron, a widely recognized limiting nutrient in the oceans

Trends in the sources and sinks of carbon dioxide

Efforts to control climate change require the stabilization of atmospheric CO2 concentrations. This can only be achieved through a drastic reduction of global CO2 emissions. Yet fossil fuel emissions increased by 29% between 2000 and 2008, in conjunction with increased contributions from emerging economies, from the production and international trade of goods and services, and from the use of coal as a fuel source. In contrast, emissions from land-use changes were nearly constant. Between 1959 and 2008, 43% of each year's CO2 emissions remained in the atmosphere on average; the rest was absorbed by carbon sinks on land and in the oceans. In the past 50 years, the fraction of CO2 emissions that remains in the atmosphere each year has likely increased, from about 40% to 45%, and models suggest that this trend was caused by a decrease in the uptake of CO2 by the carbon sinks in response to climate change and variability. Changes in the CO2 sinks are highly uncertain, but they could have a significant influence on future atmospheric CO2 levels. It is therefore crucial to reduce the uncertainties